ALBERT

Notes: Summary In long-term organized cultures of newborn mouse cerebellum, granule cell neurons were studied with silver impregnation and electron microscopy. In silver impregnated cultures, small neurons are defined as granule cell neurons from their size, morphology and location. There are also occasional large nerve endings with the morphology typical of mossy fiber endings. In correlative electron micrographs, granule cell neurons revealed a faithful reproduction of characteristic structures seen in vivo. The fine structural details of cerebellar glomeruli and myelinated granule cell bodies developed in vitro were also described.

Notes: Summary The relations between adrenergic and cholinergic terminals were studied in rat iris and rat heart with the electron microscope. Adrenergic terminals were identified by treating the animals with 5-hydroxydopamine, which produces dense-cored synaptic vesicles in adrenergic terminals in tissues fixed in glutaraldehyde and osmium. The specificity of this observation was verified. It was found that adrenergic and cholinergic nerve terminals often come in close contact with one another, the distance between the adjoining membranes being about 250 Å. At times, faint membrane thickenings could be observed in these places. The available pharmacological, physiological, and morphological evidence leaves little room for doubt that cholinergic terminal fibres can influence the adrenergic fibres. From mainly morphological evidence, it is also postulated that adrenergic terminals influence cholinergic ones.

Notes: Summary Ultrastructural studies have been carried out on the innervation of the interstitial gland of the mouse ovary. In addition Falck's fluorescence method was applied. 1. Fluorescence microscopy: In the ovarian stroma green fluorescent nerve fibers are frequently to be found in the surroundings of large and small vessels. Seldom small fibers invade blocks of interstitial cells; however, their final ramification is not discernible. 2. Electron microscopy: Terminal fibers of the autonomic nervous system reach the cells of the interstitial gland from all sides. They may be independent from the course of the vessels. Many axons penetrate the basal membrane and come into close contact with interstitial cells, partly by forming large swellings (boutons), which may be deeply embedded into the cytoplasm of the innervated cell. The synaptic cleft is about 200 Å wide. Specialized pre- and postsynaptic membranes have not been found. The innervated cells show no peculiarities. The possible function of the synapses is discussed.

Notes: Summary The fine structure of the nerves of the ovarian stroma of the domestic fowl is described for the first time. In the fowl, the nerves are concentrated upon blood vessels, smoth muscles and mainly, the thecal gland with the steroid-producing cells. Myelinated as well as unmyelinated nerve fibers were observed. Numerous axon terminals representing adrenergic and also presumptive cholinergic nerve fibers are regularly seen in membranous contact with steroid-producing cells. In these axon terminals microvesicles are oriented towards the steroid-producing cells indicating a specialization of the surface from axon-to-cell contact. Evidence has been presented that there is a membranous neuro-humoral contact between the peripheral autonomie nervous system and the steroid-producing cells in the ovary. The present investigation has demonstrated that there is morphologic evidence for a nervous control of steroid-producing cells. The physiological importance of this neuro-humoral contact is discussed.

Notes: Summary Pituicytes of Rana pipiens could be classified into two types, pale and dense, according to their relative densities of cytoplasm and the populations of free ribosomes and cell organelles. An intermediate type of pituicyte was also recognized. Lipid droplet such as are typical in the cytoplasm of mammalian pituicytes, are not in the cytoplasm of either types of frog pituicyte. Both types have long cytoplasmic processes which run among the nerve fibers, and some of them end at the pericapillary space. Nerve endings making synapse-like contacts with the cell bodies or the processes of the pituicyte are frequent. According to the structures and sizes of granules and vesicles in the nerve endings, these endings are classified into one of three types: 1) A, which appears to be a peptidergic neuronal ending containing dense granules 1,200–2,000 Å in diameter and small clear vesicles 300–400 Å in diameter; 2) B, which appear to be monoaminergic endings containing cored vesicles 600–1,000 Å in diameter and small clear vesicles 300–500 Å in diameter; 3) C, which appear to be cholinergic endings containing only small clear vesicles. Type C endings are relatively rare. In the synaptic area the axonal membranes appose those of the pituicytes across a gap of about 200 Å and numerous “presynaptic” vesicles are clustered or accumulated near the presynaptic membranes.

Notes: Summary Ependyma and subependymal regions of the lateral ventricles of cats (area of Nucleus caudatus and Corpus callosum) were fixed by perfusion and investigated electronmicroscopically. Intraventricular axons showing a beaded shape with smaller and thicker parts were found. The varicosities contain empty vesicles, dense core granules and mitochondria. Beside those certainly neuronal elements there exist intraventricular cell processes originating from ependymal cells and free cells. The neuronal processes make desmosome-like contacts with the ependyma. These regions of contact are surrounded by basket-like arranged microvilli. It is discussed, whether the contacts function like synapses or as receptors for a substance, which is still unknown. Contacts do not depend on the shape of ependymal cells. They exist with the ependyma of Nucleus caudatus (grey substance) as well as with the ependyma of Corpus callosum (white substance). Because of the different contents of cell-organelles one can differentiate three different sorts of processes situated inter- or intracellularly in the ependyma. Neuronal processes within the lateral ventricles are more numerous than those found within the ependymal layer.

Notes: Summary Synaptosomes (nerve-ending particles) prepared from the cerebral cortex of rats, aged 2–21 days, were examined after fixation in glutaraldehyde and osmium tetroxide, in order to study the development of the contact region between their pre- and postsynaptic components. Synaptosomes were present at all ages studied, although they increased in number and underwent morphological changes, e.g. a decrease in ribosomes and increase in synaptic vesicles, during development. The seventh postnatal day appeared to be a critical period for development, as many adult features were first observed at this time. The synaptic contact region was characterized by desmosome-like symmetrical thickenings until the fourth postnatal day, after which it became increasingly asymmetrical. The postsynaptic thickening, which had been undifferentiated until the seventh day, underwent a focalization of its material at this stage to form postsynaptic densities typical of the adult synapse. Cleft material was present at all ages, although for the first few days it was sparse and comparatively unorganized. An attempt has been made to distinguish between synaptosomes derived from axosomatic and axodendritic endings. The possible significance of the early desmosome-like thickenings is discussed, and the role of the cleft material and post-synaptic densities in the development of the synapse is analysed.

Notes: Summary The pars tuberalis of the hypophysis of Rana temporaria presents the general structural and the cytological characteristics of an endocrine gland. It is composed of elongated cells with long, branching processes ending on the external basement membrane of the pericapillary space. The pars tuberalis cells produce secretory granules which are accumulated in the pericapillary endings of the processes. Corresponding to its separate localization, the pars tuberalis of Rana temporaria has a separate vascularization of which the efferent capillaries anastomose with the capillary plexus of the median eminence. The general direction of the blood flow of the pars tuberalis is towards the capillaries of the median eminence. Also, the secretory products of the pars tuberalis pass into the blood stream of the hypophysial portal system. Several characteristics of the pars tuberalis show that its function must be different from that of the pars distalis of the hypophysis. Moreover, in contrast with the pars distalis, the activity of the pars tuberalis is not regulated by neurohumoral factors. The results show that a role of the pars tuberalis in the regulation of the activity of the pars distalis of the hypophysis is not excluded.

Notes: Summary Electron microscopic studies and three-dimensional graphic reconstructions from serial sections have shown that the large axon terminals of synaptic glomeruli in the ventrobasal nucleus of the rat are invaginated by spine-like protrusions from the astrocyte processes surrounding the glomeruli (“micro-trophospongium”). The astrocytic protrusions are similar in dimensions and internal morphology to the synapse-bearing dendritic excrescences that also invaginate the large axon terminals. Consequently astrocytic protrusions may be overlooked, or confused with dendritic excrescences sectioned at a non-synaptic level. The intimate neuronal—neuroglial relationship at such large axon terminals may reflect ion-exchange or metabolic interactions between the astrocytes and the axon terminal.

Notes: Summary The innervation of the adrenal cortex of the rat and the pig is investigated with the electron microscope. Nerve fibers containing synaptic and two types of dense-cored vesicles come into contact with endocrine cells. There are no specialized pre- and postsynaptic membranes. The synaptic cleft is about 200 Å wide. Generally the basement membrane between nerve and cell is absent. These observations are discussed on the base of more recent experimental findings. Small fibers having an average diameter of about 0.2 to 0.5 μ and containing only tubules and filaments are considered to represent parts of an afferent nervous system.

Notes: Summary The innervation of the mesenteric microvasculature was studied in fetal and neonatal rabbits with the aid of methods demonstrating fluorescence of catecholamines and cholinesterase activity as well as a silver impregnation procedure. The results showed that: (1) adrenergic nerve fibers were present, coursing independently in the mesentery by day twenty-one of gestation, and were found routinely in the adventitia of arterioles and venules by day 25 of gestation; (2) cholinesterase positive cells and fibers of the myenteric plexus were present by day 18 of gestation but cholinergic fibers were not present in the mesentery until day 26; the latter not being associated with blood vessels; and (3) nerve fibers in the mesentery thought to be sensory stained positively with the Holmes silver method on day 18 of gestation.

Notes: Summary Quantitative electron microscopic studies have been carried out on the human thymus. According to the equation L v =(2n)/F (Hennig, 1963) we have calculated that there is less than 0.204 mm nerve per 1 mm3 thymus tissue inside the blood-thymus-barrier (level of significance of 0.95). This result is compared to the degree of innervation in brown adipose tissue, which contains more than 160 mm nerve per 1 mm3 tissue. The biological significance of the paucity of neuronal elements in the thymus is undetermined.

Notes: Summary 1. The Harderian gland in rabbits, representing the type of a tubulo-alveolar gland, is located on the medial and posterior aspect of the eyeball and consists of two different parts, a small white lobe and a larger red one. The secretory cells in the tubular endpieces of both lobes are lipids containing cells. The lipid droplets can be stained with Sudan IV and Sudan black B. The luminal surface of both cell types is characterized by an alcianophilia at pH 2,5. 2. The tubules of both lobes have a single layer of columnar epithelium. The lipid vacuoles in the cells of the red lobe are large, these of the white lobe small. The multilocular cytoplasm of all cells contains many free ribosomes and high amounts of mitochondria lying very closely together. All cells exhibit numerous and large Golgi-zones but only few ergastoplasm membranes. 3. The lateral surfaces of the secretory cells are connected by elaborate junctional complexes (Zonulae occludentes, zonulae adhaerentes, desmosomes). These lateral surfaces are increased by intercellular canaliculi. 4. Before being released into the glandular lumen, the limiting membranes of adjacent lipid droplets fuse, thus forming a large lipid vacuole. Extrusion generally is characterized by the coalescence of the limiting membrane with the plasmalemma, the formation of an opening at the cell surface and the discharge of the secretory lipid material. In the course of another mechanism of extrusion, the fat vacuoles are transported to the apical part of the cell where consequently the plasmamembrane bulges into the lumen. Eventually the fat vacuole is pinched off surrounded by a thin cytoplasmic envelope. 5. Terminal fibers of the autonomic nervous system penetrate the basal membrane and can be found closely attached to the secretory or myoepithelial cells, partly by forming large swellings, which may be deeply embedded into the cytoplasm of the innervated cell. These terminal parts of the axons contain groups of synaptic and dense-cored vesicles, mitochondria and neurotubuli. Specific pre- and postsynaptic membranes have not been observed. The possible function of the harderian gland is discussed.

Notes: Summary Electron microscopic studies have been carried out on the innervation of the mammalian anterior pituitary and parathyroids. The total area of grid squares (2.25·10−2mm2) examined was 2000 per gland and species. In the pituitary pars distalis and in the parenchyma of the parathyroid gland we did not observe a single axon profile. According to the equation $$L_V = \frac{{2n}}{F}$$ proposed by Hennig (1963) we have calculated that there might be—if any—0.133 mm of nerves per 1 mm3 tissue in those two endocrine glands (level of significance 0.95). Comparing these results to the degree of innervation in brown adipose tissue containing more than 160 mm nerve per 1 mm3 tissue we can not imagine that such a small degree of innervation is of any biological importance. In the pituitary pars tuberalis two types of axon terminals have been found both inside and outside the basement membrane surrounding the epithelial complexes. One type contains “synaptic” and two populations of smaller dense-cored vesicles, the other one contains a population of larger granules which have some properties of the classical elementary granules. Further investigations have to clarify the functional significance of those nerve endings.

Notes: Summary The organization of the α-lobes of the corpora pedunculata in the brain of the cricket Acheta domesticus L. has been investigated in the light and electron microscopes. The cylindrical fibre complex is composed of branches of “mushroom-body” fibres (intrinsic fibres) and extrinsic fibres, which penetrate the α-lobe. Intrinsic fibres (IF) run through the α-lobe in the same direction, but not strictly parallel to each other or to the axis of the α-lobe. Extrinsic fibres (EF) and their fine branches are often arranged perpendicular to the axis of the α-lobe. There is some evidence that different IF zones occur in the α-lobe when passing from its periphery to its centre. The distribution of EF may reflect a structural order when passing from the base of the lobe to its top. Numerous polarized synapses connect the IF with the EF. The IF show clusters of vesicles and presynaptic figures especially in their “blebs”, which can be seen in Golgi preparations for light microscopy. Two types of EF are distinguished on the basis of their synaptic junctions: (1) postsynaptic EF (abundant) and (2) EF with pre- and postsynaptic sites (perhaps restricted to some regions of the α-lobe). Presynaptic IF converge on EF, which may transfer excitation from the α-lobe to different parts of the brain and nervous system.

Notes: Summary The abdominal ganglia of the crayfish Astacus pallipes contain numerous vertebrate-like synapses which are characterized by presynaptic vesicles, darkened pre- and post-synaptic membranes, cleft material, and post-synaptic “fuzz”. Such synapses occur throughout the ganglia but are most easily found dorsally, where the neuropile is relatively coarse. The neuropile is far from homogeneous. Regional variations in fiber size, in degree of profile tortuosity, and in kind, magnitude, and distribution of vesicular content result in conspicuous textural variations. The structural polarity of synapses between the lateral giant fibers and other neurons is consistent with known physiological polarity and, hence, validates our criteria for recognition of synapses within the ganglion.

Notes: Summary The penis retractor muscle of Helix pomatia is passed by thick nerve trunks, which probably are nerve nets. In the contracted muscle, they are folded meanderlike, in the extended they are pulled smooth. Four types of vesicles different in size and contents can be distinguished in the nerves. Varicose fibres accompany the muscle cells. Frequently the terminals are running in a groove of the muscle fibre. In certain axon types occur presynaptic accumulations of vesicles and thickenings of the terminal membrane. Terminal and muscle cell are separated by a cleft of 300 AE width. The muscle fibre membrane has no subsynaptic infoldings. Beside these axons thin, naked neurites are running through the connective tissue. They are characterized by a high content of neurotubuli. One part of the axons presumably possesses a monoaminergic transmitter. After the glutaraldehyde-dichromate-reaction they contain dense grana, whose diameters are mainly below 1000 AE. The nerve trunks fluoresce after exposure to paraformaldehyde vapour, excited with UV-light, green to green-yellow. The maximum of the excitation was determined at 413 nm and the maximum of emission at 496 respectively at 510 nm. It is concluded, that both, a catecholamine and 5-HT are responsible for the fluorescence. Extraction and paperchromatographic separation lead to the opinion, that the catecholamine is dopamine.

Notes: Summary The surface of 4 granule-containing cells, in a cluster within the rat superior cervical ganglion, was studied by a serial sampling technique for electron microscopy. The result shows that all the 4 cells receive one, or three afferent synaptic boutons from the preganglionic fibers impinging upon their somata, and a somatic efferent synapse exists at two locations on each soma of the 2 of these cells. The postsynaptic element of the efferent synapse is observed to be represented by non-vesiculated and vesiculated segments of dendrites, soma and a possible axon collateral of the adrenergic principal neuron of the ganglion. There is a remarkably constant development of the attachment plaque between the granule-containing cells themselves, representing 1.7–2.3% of surface area for each cell. The surface area exposed to the extracellular space (covered only by a basal lamina) varies from 0.1 to 2.3% of the total perikaryal surface of the 4 cells. A tendency is noted that those cells without efferent synapses possess a more extensive area exposed to extracellular space than those forming somatic efferent synapse to the postganglionic elements.

Notes: Summary Ultrastructural evidence is given of the occurrence of nervous elements in the mesoglea of Ctenophores based on the presence of the typical synapses of this phylum. In Beroids, nervous fibers from the ectodermal nerve-net cross the epithelial basal membrane and run through the mesoglea; they are devoid of any ensheathing cell. These neurites build highly differentiated synapses upon the muscles and upon peculiar cells, tentatively named mesenchymal cells. In Cydippids, nerve fibers and nerve cell-bodies have been observed in the mesoglea of the tentacles. The mesogleal core of each tentacle contains mesenchymal cells and a thick strand of neurons and neurites, forming a kind of elongated ganglion. Neurites of either the axial neurones or the epithelial nerve-net neurones form numerous radial nerve strands across the tentacular muscles. Interneural, neuro-muscular and neuro-mesenchymal junctions are very frequent in the tentacle. As far as the organization of the mesoglea is concerned, the Ctenophora thus appear closer to Turbellaria than to Cnidaria.

Notes: Summary The locus coeruleus of cat is populated by two types of neurons: medium sized ones, with plump cell bodies and relatively short dendrites; and small ones, with triangular bodies and relatively long dendrites. The former type is regarded here as typical of the centre, whereas the second type could simply represent displaced neurons from the adjacent griseum centrale. Electron microscopy failed to reveal any outstanding richness in pigment granules in kittens up to five weeks old. Very characteristic somatic appendages were found, mostly in the medium sized neurons. These somatic “spines” communicate with the perikaryon by means of a narrow neck region. A complex, multilayered, glial sheath surrounds the cells. This glial sheath is pierced by the somatic appendages, which are not surrounded by glia and make contact with axonal knobs. Typical dendritic spines appear to be absent. Axodendritic synapses are made on medium sized dendritic trunks. By and large, most of the synaptic vesicles present in the centre are of the small, clear-centered type. However, dense core vesicles extremely variegated in size and appearance were found, both in presynaptic and postsynaptic profiles. The possibility that dense core vesicles should be regarded as atypical lysosomes rich in by-products of the metabolism of catecholamines (melanine) has been considered.

Notes: Summary Lateral line organs in young salamanders of the species Ambystoma mexicanum were investigated with scanning and transmission electron microscopy. They were found to differ from the lateral line organs in adult animals (1) by being lower, having short hair cells and supporting cells, (2) by the hair cells having areas of lateral contact, (3) by the occasional presence, at the edge of the organ, of hair cells at an early developmental stage. Two types of nerve endings are seen: (1) afferent, and (2) less commonly, efferent vesiculated ones. Synaptic bodies have been seen in the cytoplasm without association to afferent synapses.

Notes: Summary Qualitative and quantitative studies were made to determine the amount of nerve fiber supplying corpora lutea (CL) of rats during the oestrous cycle and pregnancy and sow CL during days 4–6 after ovulation. Fluorescence microscopy of freeze-dried, paraformaldehyde treated (Falck-Hillarp method) rat ovaries reveals adrenergic nerve fibers which run along with vessels and form a network among interstitial gland cells. Nerve fibers do not enter the granulosa cell layer in follicles or CL. In the CL circumference both vascular and non-vascular nerves occur the latter being related to the fibromuscular layer and probably innervating smooth muscle cells. No striking differences exist between the innervation of the ovary in non-pregnant and pregnant rats. Bodian and methylene blue staining did not contribute to a more detailed knowledge of rat ovary nerve supply. Electron microscopic quantitative analysis of rat and pig CL (rat: day 18 of pregnancy; pig: day 4–6 after ovulation) revealed no axon profiles in 2.000 grid squares (one square measuring 2.25×10-2 mm2) of randomly taken CL sections. Thus it was possible to calculate an upper limit of 133 μm of nerve fibers per 1 mm3 CL tissue, in case there were any at all.

Notes: Summary The innervation of the pituitary gland of Carassius auratus was studied by light and electron microscopy under various physiological and experimental conditions to investigate whether or not neurosecretory fibres play a role in regulating pars distalis function. Two types of neurosecretory fibre (Type A and Type B) were distinguished. Prolactin, ACTH and TSH1 cells were innervated by Type B fibre terminals separated from the endocrine cells by a continuous basal lamina (“indirect contacts”). Gonadotropic, STH and TSH2 cells were innervated by Type A as well as Type B neurosecretory fibres, mostly without an intervening basal lamina (“direct contacts”). The assessment of the amount of neurosecretory granules and microvesicles in nerve terminals during the pre-spawning, spawning and postspawning seasons and following the administration of Oestradiol, Thyroxine, Thiourea and Metopiron respectively revealed convincing evidence for a participation in pars distalis control for Type A and Type B fibres innervating gonadotropic cells and STH cells and Type B fibres innervating TSH2 and ACTH cells. Immediately after spawning both nerve fibre types innervating gonadotropic cells and Type A fibres innervating STH cells showed a striking decrease in the amount of dense core vesicles. During the spawning season nerve fibres innervating somatotropic cells, TSH2 cells and ACTH cells also undergo changes suggesting that prior to spawning major changes in the endocrine system of the goldfish take place.—These results point to a dual control, by peptides and amines, of teleost pars distalis function.

Notes: Summary The proximal collaterals of the dorsal giant fibres of the earthworm were traced through serial sections from the cell bodies to the giant axons. Their structure and synaptic connections were examined. There are chemical as well as electrical synapses. Their fine structure is compared to that of other known invertebrate and vertebrate synapses. Both giant fibre systems have efferent chemical connections with thin postsynaptic arborizations which probably belong to ventral cord motoneurons. Moreover the median giant axon is connected by an electrical synapse with the giant interneurons. The lateral giant collaterals on the contrary receive many afferences through chemical synapses which were partly identified as sensory fibers from the epidermis, multisegmental axons from the main fibre bundles or giant interneurones. Other afferences probably come from unisegmental interneurones. In addition both lateral giant axons form an electrical chiasma synapse with special membrane folds.

Notes: Summary The olfactory mucosa of frog has been studied at an ultrastructural level to confirm previous light microscope observations in regard to the presence, in the sensory epithelium, of nerve fibres not belonging to the first cranial nerve proper. It has been observed that both myelinated and unmyelinated nerve fibres are present in the lamina propria and that eventually these fibres terminate inside the epithelium. Unmyelinated fibres usually contain dark core vesicles and similar content is seen in their intraepithelium terminals. Terminals containing only clear vesicles are also observed in the epithelium and they are believed to represent the terminals of the myelinated fibres. The significance of these ultrastructural findings is discussed in view of their functional meaning.

Notes: Summary The nervous system of juvenile and adult Ceriantheopsis americanus has been examined with the electron microscope. The nervous system is exclusively ectodermal, forming a plexus of fibres lying between the epithelium and the muscle layer. The plexus consists of three types of nerve fibre that vary in diameter from 0.1 to 20 μ, and a fourth type of fibre of uncertain nature. The reticulum, previously thought to be the ectodermal nervous system, is redescribed as the peduncles of epithelial supporting cells. Intraneural and neuromuscular synapses are described. About 97% of the interneural are polarized. The unpolarized synapses are a variety not previously described, consisting of a series of polarized zones, for which the name multipolarized synapse is proposed. Structurally, the interneural synapses are more complex than those previously seen in the Cnidaria. Presynaptic projections, periodic cleft densities, and a postsynaptic web are described. By contrast, the neuromuscular synapses bear no membrane specializations. On the basis of observed synaptic interactions of its components a preliminary model of the functional organization of the nervous system is proposed.

Notes: Summary The Octopus iris is composed of five different layers: A, the external epithelium; B, the chromatophore layer; C, the iridocyte layer; D, the layer of muscles and collagen strands; E, the pigment epithelium. The nerves innervating the sphincter and the chromatophore muscles are identified and their neuromuscular junction is described. The motor endings of chromatophore nerves have an additional ending in presynaptic position which probably functions as a modifier of neuromuscular transmission. The chromatophores are naked and exhibit a tubular channel system between plasmalemma and pigment container which looks similar to the T-system of muscle cells.

Notes: Summary In the tortoise Testudo graeca, the lizards Lacerta dugesi and Lacerta pityusensis, and the snake Natrix natrix, the innervation of the testicular interstitial tissue was studied by light and electron microscopy, the acetylcholinesterase (ache) technique, the Falck-Hillarp method for the detection of catecholamines, and the application of 6-hydroxydopamine. The intertubular spaces of the reptilian testes studied contain adrenergic nerve fibers the amount and distribution of which varies considerably both in various species and in various stages of the reproduction cycle. Nerve fibers do not enter the seminiferous epithelium. Fluorescence microscopy of the lizard testis reveals catecholaminergic varicosities which are mainly arranged around blood vessels, but do not show obvious connexions to Leydig cells. Ache-positive fibers are equally distributed in lizard testes surrounding each seminiferous tubule. In Natrix natrix ache-positive fibers are irregularly spread among groups of tubules, without showing a definite relation to Leydig cells either. By electron microscopy bundles of unmyelinated axons and axon terminals can be more easily detected in the testes of immature animals than in adult. Terminals of nerve fibers containing small (400–500 Å in diameter) and large (800–1400 Å) dense-cored vesicles and sometimes small clear vesicles establish contacts with Leydig cells. Three types of contact are described. 1. “Contacts” par distance at a distance of about 2000 Å and basal lamina interposed; 2. membranous contacts having a 200 Å gap only between axolemma and Leydig cell plasmalemma; 3. invaginations of terminals into Leydig cell perikarya. The latter may exhibit surface specialisations, which strongly resemble postsynaptic membrane thickenings. Experiments using 6-hydroxydopamine underline the adrenergic character of testicular nerve fibers, which can be regarded as another example of non-cholinergic, ache-positive neurons. In the testis of the immature tortoise profiles of axons occur which probably represent purinergic, ache-positive neurons.

Notes: Summary Synaptic junctions in intact rat cerebral cortex have been examined following glutaraldehyde fixation and phosphotungstic acid (PTA) staining. In the presynaptic ending the network has a hexagonal arrangement, while the dense projections are regularly placed along the presynaptic membrane. Cleft densities occupy the intracleft region. The postsynaptic thickening extends uninterrupted along the length of the junction. Qualitatively, the majority of junctions fall into the ‘discontinuous-continuous’ category, in which the internal coat of the presynaptic membrane together with its associated dense projections is discontinuous along the length of the junction, whereas the postsynaptic thickening is continuous. By contrast, a small number of junctions are ‘continuous-continuous’. In an attempt to analyze the junctions quantitatively, nine indices were measured. Histograms of the size distributions of seven of these appear to be bimodal, and from this it is concluded that two junction populations may be distinguishable on quantitative grounds. It is also shown that the distance separating dense projections at the presynaptic membrane is of the order of 10–15 nm. This surprisingly low value has consequences for current ideas on the relationship between synaptic vesicles and dense projections, and these are discussed at length.

Notes: Summary Working with glutaraldehyde fixed, PTA stained rat cerebral cortex, the authors compared the ultrastructural features of synaptosomes with those of intact synaptic junctions. In general there is close correspondence between the two, although the cleft densities and postsynaptic focal densities of synaptosomes show a greater degree of focalization than their counterparts in synaptic junctions. The dense projections have similar profiles in both preparations, but are more difficult to distinguish clearly in synaptosomes on account of the closer packing of the presynaptic network around their apices. The limiting membrane of the presynaptic terminal is usually visible in synaptosomes, but not in synaptic junctions. Comparing the preparations quantitatively reinforces the qualitative findings, and points to their overall similarity. However a number of the indices in synaptosomes are significantly smaller than the corresponding ones in synaptic junctions, and this points to the operation of a shrinkage factor during fractionation procedures. This is confined to the pre- and post-synaptic components and does not affect the intervening contact region. Histograms of the size distributions of the indices are similar to those obtained for intact synaptic junctions, the majority displaying two peaks. It is concluded that synaptosomes accurately reproduce the major ultrastructural features of synaptic junctions.

Notes: Summary Terminal axons emerging from the inner plexiform layer of the cat retina reach the wall of the arteria centralis retinae, as revealed by electron microscopy. Numerous unusually large dense core vesicles (about 1000 Å in diameter), of different electron densities, occur in the varicosities of these axons. These observations may be compatible with the idea of an innervation of the central artery of the retina which is non-autonomic, possibly intrinsic in nature.

Notes: Summary Neural elements within the parenchyma of the sebaceous gland have not been reported previously. Nerve endings have been observed only in the connective tissue surrounding the gland or in close association with the undifferentiated basal cells. In this study, electron microscopy revealed the possible presence of nerve endings (or terminal portions of neural elements) in the suprabasal level of functional sebaceous glands of pinnae of white rats. Morphologically, there are two distinct types of nerve endings. Type 1 is bordered by a membrane of relatively irregular contour and contains a single mitochondrion, various-sized vesicles, numerous microtubules, fine neurofilament-like fibrils, and occasional ribosome-like granules. Type II is also bordered by a membrane, but its contour was relatively smooth and rounded. Moreover, Type II contains many mitochondria, varying in size, density, and the arrangement of cristae. While ribosome-like granules are scattered throughout the structure in relative abundance, there are scarcely any fine neurofilament-like fibrils or microtubules. Whether these two structures are sensory or autonomic fibers could not be determined by electron microscopic examination.

Notes: Summary The rostro-caudal gradient of differentiation found in vertebrate embryos has been utilized to examine the sequence of synaptic junction development in the spinal cord of Xenopus laevis at a late embryonic stage. Uniform samples were taken at various points along the cord of a stage 27 embryo and examined in the electron microscope. The general ultrastructure of the cord demonstrated the rostro-caudal gradient of development. The sequence of synaptic junction development was like that in the cervical region (Hayes and Roberts, 1973). “Membrane-vesicle clusters” and “immature” synaptic junctions were found most caudally followed by synaptic junctions, first with cleft and subsynaptic membrane density, then with only cleft density and finally, most rostrally, with cleft, subsynaptic membrane, and subsynaptic cytoplasmic density. Mature synaptic junctions were found in increasing numbers from the mid to anterior trunk cord and could mediate alternating trunk flexions made by the embryos at this stage of development. “Membrane-vesicle clusters” were found near processes containing irregular vesicles and also near membrane outlines. These may be signs of dendritic growth. “Membrane-vesicle clusters” were also found in varicosities, facing the space around the spinal cord and in nerve fibres peripherally between the skin and myotomes. This suggests an association of early stages in synaptogenesis with axon growth. This and other possible inferences about axon and dendrite growth in relation to synaptogenesis are discussed.

Notes: Summary The innervation of the brown, red and yellow chromatophore muscle cells in Loligo vulgaris shows quantitative and qualitative differences. The nerve bundles regularly contain axons with electronlucent vesicles of about 300 Å diameter, and occasionally axons with dense core vesicles of about 600 Å diameter. The myofibrils of the contractile cortex show a staggered arrangement and are wound in a spiral with respect to the axis of the muscle cell. In the axial sarcoplasm there is additionally a bundle of thin filaments of about 70 Å thickness. The bundle is orientated in parallel with the longitudinal axis of the muscle cell. Its function may be to maintain tonic contractions.

Notes: Summary The ultrastructure of the innervation of the anterior cerebral artery of the rat was studied in control animals and in animals after superior cervical ganglionectomy. Fluorescence histochemistry shows a periarterial network of intensely fluorescent fibers which are divided into two groups, adventitial and periadventitial. The fluorescence begins to decrease 26 hours after, and completely disappears about 32 hours after, ganglionectomy. Fine structural changes are first observed 18 hours after ganglionectomy, when the axoplasm of degenerating axons becomes electron dense. This density gradually increases up to about 32 hours. By 32 hours most axons with disintegrating axolemmas become inclusion bodies of the Schwann cells. At this stage, synaptic vesicles can still be distinguished as less dense areas, but the membrane structures of synaptic vesicles and mitochondria are difficult to recognize. The degenerating axons are gradually absorbed and by 38 hours dense, residual bodies are observed in the Schwann cells. Generally speaking, the degeneration occurs first in the adventitial fibers and then in the periadventitial fibers. The transient appearance of small, granular vesicles is noticed in axon terminals about 18 hours after denervation, although very few small, granular vesicles are seen in control tissue or at later stages of degeneration.

Notes: Summary The ultrastructure of layers I and II of the motor cerebral cortex of rat brain has been studied at birth, 4, 7 and 14 days postnatal and in the adult. Compared with the adult, neonatal rat motor cortex exhibited a large extracellular space which decreases with increasing age. At all stages studied the neurons were seen to contain the organelles usually found in adult neurons. Growth cones were present in decreasing numbers up to 14 days old. Synapses were detectable at birth and there was an obvious increase in their number throughout the postnatal development. At the earliest stages studied there was a lack of specialization characteristic of the adult. Many synapses were either avesicular or relatively so and lacked the high degree of modification of adult pre- and postsynaptic membranes. By 7 days after birth many synapses existed which in all morphological respects resembled those of the adult, and by 14 days, the majority were of the adult type. These findings, particularly with reference to the postnatal development of synapses, have been discussed in relation to the known electrophysiological findings.

Notes: Summary Nerve fibers were demonstrated in the glycogen body of the avian lumbar spinal cord by using silver-impregnation and fluorescence microscopic (Falck-Hillarp) techniques. These nerve fibers originated from nuclear areas in lateral juxtaposition with the glycogen body. The fluorescence of the nuclear area was strongest near the polar regions of the glycogen body. It was suggested that the aminergic neurons of the avian lumbar spinal cord may influence the glycogen body. The avian glycogen body was compared with other storage sites of glycogen within the central nervous system.

Notes: Summary By means of electron microscopy “light” and “dark” pinealocytes can be distinguished in the guinea-pig pineal gland. Glial cells are rare. In the “light” pinealocyte. the most frequent cell type, some “vesicle-crowned rodlets” (VCR) show circumscribed thickenings. From these structures “vesicle-crowned balls” (VCB) have to be clearly distinguished. Furthermore “cylinders” occur, which, it is suggested, are precursors of VCB. “Dark” pinealocytes characterized by chromatin-rich nuclei and electron-dense cytoplasm are rare and contain fewer vesicles, VCR, VCB and “cylinders” than “light” pinealocytes. Numerous non-myelinated nerve fibres are situated within perivascular spaces, a few also in the parenchyma. Synapses between nerve fibres and pinealocytes were not observed. In the pineal gland of pregnant guinea-pigs the following changes can be observed in the second half of gestation. The “light” cells show many nuclear indentations and an increase of “active” zones, mitochondria, smooth ER, agranular vesicles, VCR, VCB, and “cylinders” respectively. The “dark” cells increase in number. After birth these changes reverse to normal within one week. Constant darkness leads to an activation of the “light” cells accompanied by an increase of the VCR and to an increase in number of the “dark” cells. Under constant illumination the “light” cells show a decrease of their organelles and a strong increase of the VCR. After 70 days the VCR also show a change in shape. Following reserpine treatment the VCR decrease in number and show signs of degeneration. It is discussed that the VCR function as pre- or postsynaptic structures and that they are involved either in transmitting impulses from nerve fibres to pinealocytes or from one pinealocyte to the other.

Notes: Summary Retinae from two- and three-day-old rats were explanted in plasma clots and grown in vitro with the flying coverslip method. After seven to seventeen days in culture, the retinal tissue was fixed with aldehydes and osmium tetroxide and embedded for examination with the electron microscope. Study of cross sections (perpendicular to the coverslip) revealed a histotypic pattern of organization, especially in the thicker regions of the explants. Layering of cells quite similar to that in the intact retina was seen to develop from the relatively primitive, explanted retinal epithelium. However, each layer contained fewer cells than its counterpart in vivo. All major neuronal cell types were distinguished by their location and cytological characteristics. Development of the saccules of sensory cell outer segments was observed to occur in vitro by an infolding of the plasma membrane. Synaptic ribbon complexes developed to the mature form in the outer plexiform layers, while conventional synapses were numerous in the inner plexiform layers. Synaptic ribbons were also seen in bipolar cell axons in the inner plexiform layers. Amacrine and ganglion cells in these regions were relatively sparse. A survey of posterior regions of noncultured three-day-old rat retinae showed no synapses of any sort; therefore the synapses in the cultures formed in vitro. The retina is recommended for studies of synaptogenesis in tissue culture, for it offers several advantages over expiants from other areas of the neuraxis, including a clear layering pattern, many identifiable cell processes with characteristic synaptic relationships between them, and a well-defined sequence of developmental events.

Notes: Summary This investigation is concerned with pineal organs of human embryos 60 to 150 days old. At every stage central nerve fibres enter the pineal organ by way of the habenular commissure, but are restricted to the pineal's proximal part. On about the 60th day of the development the sympathetic nervus conarii grows into the distal pole of the pineal organ from a dorso-caudal direction and plays the predominant part in the innervation of the pineal organ. After penetrating, it soon branches out and forms a network in the pineal tissue. Much later, not until the 5th embryonic month, sympathetic nerves appear accompanying the supplying vessels in the perivascular spaces. After a short time these nerves pierce the outer limiting basement membrane and penetrate the parenchyma. Towards the end of the 5th embryonic month the axons of the sympathetic nerves form varicosities containing clear and dense core vesicles. At this point large amounts of laminated granules appear primarily in cell processes, probably of pinealocytes. Isolated granules also occur in the varicosities of axons. The granules encountered here are most likely secretory granules.

Notes: Summary Nervous (sensory) pathways of the pineal complex were studied in Lampetra planeri. The following observations were made: (1) The pineal tract, containing more than 600 unmyelinated fibres, connects directly or indirectly to the posterior commissure. (2) Connections of the nervous region (NR) adjoining the parapinéal organ (“ganglion parapinéales” of Tretjakoff or “division of the left habenular ganglion” of Studnička) have been re-examined; our study shows that the rostral division of NR is connected to the parapineal organ by a short tract and to the left habenular ganglion (LHG) by a nervous layer (NL). The NR, NL, and LHG contain the same following elements: (1) A collection of typical neurones (which are rare in the NL) in an abundant meshwork of nerve fibres. (2) At least two main types of axons: (a) Type 1 axons, containing few granules (1,000–1,300 Å diameter). (b) Type 2 axons, containing numerous granules (900–2,500 Å diameter), and resembling neurosecretory axons. Type 2 axons are not observed in the pineal and parapinéal organs. (3) Axo-dendritic and axo-axonic(?) synapses. Our study concludes that NR and NL represent the rostral part of LHG; nevertheless, NR and NL may contain the parapinéal tract. The problem of possible incorporation of epithalamic elements (e.g., elements of the habenular ganglia) into the parapinéal and pineal organs in other animals has been considered phylogenetically.

Notes: Summary Umbilical vessels of guinea-pig fetuses were studied shortly before birth. In all umbilical cords investigated an innervation of the umbilical vessels is lacking. The intrafetal parts of the umbilical vessels on the other hand are richly innervated. A marked difference in the amount of nerve fibres and the pattern of innervation is found between artery and vein. The artery is supplied by a dense nerve plexus which spins around the media and which originates from nerve bundles within the outer adventitial layers. The comparatively scanty innervation of the vein exhibits a more coarsely meshed net pattern. The nerve bundles in the vein exhibit a close affinity to the vasa vasorum. Number and type of the close contacts between the muscle cells are different in the various sections of the umbilical vessels. Similar to the distribution of nerves they are almost absent in the vessels of the umbilical cord, numerously, however, in the intrafetal parts. Contrary to the innervation, the close contacts in the vein are developed more numerously and more broadly than in the corresponding artery.

Notes: Summary The vessels of the glomera that lie between the aorta and the pulmonary trunk, on the anterior and posterior wall of the pulmonary trunk, as well as the so-called glomus pulmonale of the cat have been injected with gelatine-india ink mixture. The paraganglia mentioned above are associated with the coronary circulation as chemoreceptors and are designated as the glomera coronaria. The investigations demonstrate a morphologic similarity with the glomus caroticum. Section of the vagus causes a degeneration of the synaptic structures on the glomus cells as well as changes in the cells themselves.

Notes: Summary The development of adrenergic nerves to the anterior eye segment was studied in human and guinea-pig embryos. Adrenergic terminals had already appeared in the earliest human embryos available (4–6 cm). They first appeared mainly in nerve trunks in the primitive chorioid, especially in the region of the developing ciliary body. Adrenergic nerves then grow into different structures of the eye as these develop, but typical terminals in contact with effector cells appeared late during the development, about the 25–30 cm stage. No adrenergic nerves were observed in the chamber angle. Corneal adrenergic nerves (also intraepithelial terminals) appeared much more frequently in embryos than in adults. No adrenergic neurons were observed in the retina. In the guinea-pig, the first adrenergic fibres were observed at about gestation day 35. The general principle of the development was very similar to that of the humans. At gestation day 45 to 50, the supply of adrenergic fibres was essentially that of the adult animal, except that the corneal adrenergic fibres were increasing until just before birth and that the adrenergic terminals of the chamber angle appeared shortly before term.

Notes: Summary The intrinsic innervation of the anterior byssal retractor muscle in Mytilus edulis L. has been demonstrated using Maillet's osmium-zinc iodide technique (ZIO). Grouped and isolated osmiophilic cells, thought to be neurons, and nerve fibers forming neuromuscular contacts and nerve endings, have been observed. When the period of fixation is not overly prolonged, glio-interstitial cells may also be distinguished.

Notes: Summary Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to study the innervation and vascular supply of crayfish skeletal muscle. Blood vessels and nerve terminals identified by TEM were often closely associated. Synaptic regions of the nerve terminals were always located under sarcolemma and contained both dense-cored and agranular synaptic vesicles. Axo-axonal synapses of several different types were observed. Blood vessels consisted of several “vessel cells” or “supporting cells” enclosing a lumen, which was connected to the exterior by fine channels between the “supporting cells”. SEM of whole freeze-dried muscles revealed two types of ramifying structure, which often ran in parallel over the muscle surface. One, identified as nerve, was more cylindrical and had a smoother surface than the other, which was identified as blood vessel. Fine nerve branches disappeared under the sarcolemma, probably near synaptic regions, but synapses could not be seen. Blood vessels also had fine terminations which merged into the sarcolemma.

Notes: Summary Light and electron microscopic observations on the ampullary organs of Polyodon spathula (Chondrostei, Osteichthyes) reveal a sensory epithelium similar to that found in the Lorenzinian ampulla, an electroreceptor found in marine Elasmobranchs. The sensory cells have a very small luminal part provided with a cilium. They are innervated by many nerve endings. Each nerve fibre apparently makes synaptic contact with several sensory cells. The synaptic structure in the sensory cell is composed of a flat sheet, the outermost part of which is surrounded by 3 or 4 annuli of densely staining material. The sheet extends into a protrusion of the sensory cell, and there is a corresponding invagination in the nerve terminal. The conclusion that these organs are electroreceptors, is supported by the finding that the fish responds to the introduction of an iron tube in the aquarium, whereas a wooden rod introduced in the same way causes no response.

Notes: Summary The ultrastructural characteristics of the neuromuscular junctions were studied in the neurogenic heart of Limulus polyphemus. Several types were encountered. The first type consisted of nerve terminals which synapsed along the borders of the myocardial fibers, embedded just under the sarcolemma. A second type of terminal was ensheathed in glial cells, synapsing on the outer sarcolemmal membrane. The third, and most prevalent type of junction consisted of terminals which synapsed with arms of granular sarcoplasm, remote from the fibrillar portion of the muscle fibers. Junctional complexes of the third type were often observed near intercalated discs and were often formed by several axons synapsing with arms of sarcoplasm from several muscle fibers. The results are discussed in relation to the previously reported electrophysiological characteristics of the neuromuscular junctions.

Notes: Summary The ultrastructure of the pars intermedia (PI) of the normal VII +/+ and hereditary nephrogenic diabetes inspidus DI Os/+ mice has been studied with particular reference to the morphology of the glandular cells and their innervation. Four types of cells were observed in both the genotypes of mice, 1) the light glandular cell, 2) the dark cell, 3) a type of cell similar to ependymal cells and 4) a small percentage of typical ACTH cells, observed mostly on the PI border of the cleft and rarely in the centre of PI. The predominant light glandular cells contain mainly two types of membrane bound granules: 1) electron dense core granules, which measure 1500–2500 Å and 2) electron lucent vesicles, which measure 3000–4000 Å in diameter. Granules of intermediate size with various density are also present in both types of mice. The electron dense core granules are predominant in DI Os/+ mice, whereas, electron lucent vesicles are predominant in the normal VII +/+ mice. Similar uniform size membrane bound electron dense granules have been observed in ACTH cells of PI and pars distalis. From earlier experimental evidences and the present observations, it is concluded that the dense core granules in PI may be synthesizing ACTH or ACTH-like substance. It is also discussed that these dense core granules may further mature and give rise to MSH in the form of electron lucent vesicles. If it is so, PI light glandular cells may have dual functions, of producing MSH and ACTH. One of the functions of ependymal-like cells, may be the transport of PI secretion. Three types of nerve endings are observed throughout the PI, making synaptic contact with the predominant cell type. The innervation is more in DI Os/+ mice than in normal mice. The classification of these nerves is according to Bargmann and co-workers 1) peptidergic neurosecretory fibers, contain mainly membrane bound dense core granules, measuring 1200 to 1800 Å, and are the classic neurosecretory granules; 2) adrenergic fibers, measuring 700–900 Å; 3) cholinergic fibers, measuring 300–400 Å. Adrenergic and cholinergic fibers are more towards the hypophysial cleft. The increased innervation, the synaptic contact, the extremely hypertrophied PI and the greater activity of its light glandular cells in the DI Os/+ mice show the PI is under the influence of the nervous system.

Notes: Summary The innervation of the salt gland of the goose, the duck and the swan was investigated by means of electron microscopy. Axonal swellings were observed in relationship to secretory cells as well as to central duct cells. The terminals contain synaptic and densecored vesicles. There are no specialized pre- and postsynaptic membranes.

Notes: Summary Morphological evidence is presented supporting the possibility of basal secretion into hypendymal capillaries of the adult rabbit subcommissural organ (SCO). The synthetic apparatus of the SCO cell is described as well as the heterogeneous granules and vesicles which are concentrated in the basal processes bordering a widened perivascular space. The origin of the electron dense granules, of which two fairly distinct subgroups are found, is discussed. A binding of secretory sacs to the lateral plasma membrane is seen. The possibility of a lateral secretion is supported by the presence of a system of extracellular channels between SCO cells which are filled with a flocculent material resembling that of the secretory sacs. Nerve perikarya which are separated from the SCO by only a few glial fibers are demonstrated. Synapses are described in nerve fascicles bordering on the hypendymal capillaries. The possibility of an innervation of the hypendymal region is discussed as well as possible nervous connections with the pineal gland.

Notes: Summary The salivary glands of the moth, Manduca sexta (Insecta: Sphingidae), are unlike most other salivary glands in that they are innervated from one source only. Vital staining of nerves with methylene-blue reveals numerous fine nerves extending to the glands from the oesophageal nerve, a part of the stomatogastric or visceral nervous system. Light and electron microscopy confirm that only the fluid-secreting cells, confined to a discrete region in these glands, are innervated. Axons with or without glial wrappings are found in intercellular spaces between fluid-secreting cells. Axons lacking a glial sheath contain, after glutaraldehyde-osmium tetroxide fixation, large granular and small agranular vesicles. In nerve endings in glands fixed with permanganate these smaller vesicles are granular, having the electron-dense cores characteristic of monoamine-containing neurons. These nerve endings with “synaptoid areas” are in close (“direct”) contact with the fluid-secreting cells.

Notes: Summary The vestibular fibres of ammocoetes of Lampetra planeri form a peculiar type of synaptic contact with the large nerve cells of the vestibular nuclei. In fact, a large expansion of the fibre is enveloped by the nerve cell cytoplasm, which makes a sort of spoon or actual channel by sealing its own plasma membrane with adhesion plaques around the fibre. In the whole area of juxtapposition between the fibre and the cell membranes, three different types of specialized contacts occur: desmosomoid junctions, which are the most numerous; zones having the characteristics of chemically active synapses on account of the presence of vesicles clustered on the presynaptic side; gap-junctions, where electrical transmission might occur. A puzzling feature is the presence of an enormous number of presynaptic vesicles located in the central part of the axoplasm of the fibre expansion.

Notes: Summary Electron microscope studies of axons, distributing singly or in small bundles in the human ventricular and atrial myocardium, indicate a few per-cent of the axon profiles to be significantly large in diameter (1.5–3.0 μ). They are characteristically packed with a profuse number of mitochondria along with large granular vesicles, glycogen rosettes, lysosomic bodies; and some of them terminate on a “specific terminal cell” (Knoche and Schmitt). These mitochondria-rich, large axons are assumed to be terminal portions of the cardiac afferents. About half of the axons encountered in the ventricle and 2/3 in the atrium are non-vesiculated, usually less than 0.5 μ. in diameter. The varicosities containing numerous vesicles are mostly 0.5–1.5 μ in diameter and are assumed to be terminal portions of the cardiac efferents. The ratio between the number of axon profiles containing small granular vesicles and that of axon profiles containing agranular vesicles without small granular vesicles is 2∶1 in the ventricular myocardium and 1∶1.7 in the atrial myocardium.

Notes: Summary The fibre anatomy of the glomeruli neuropil of the antennal lobes (sensory centres) of Locusta migratoria has been analysed by electron microscopy. The glomeruli consist of interneuronal and sensory elements of the antennal nerve, forming a complicated mesh-work of fine fibres. The great majority of nervous fibres is filled with clear synaptic vesicles, which stain with zinc-iodide-osmic-acid (Akert and Sandri, 1968), Two types of synaptic junctions are found, differing especially in shape and size of their synaptic gap. Both types show a clear morphological polarity, so that the distinction of pre- and postsynaptic fibres is possible. Inter- and intracellular paramembraneous synaptic material can be demonstrated by the bismuth iodide impregnation of Pfenninger et al. (1969) This method, showing the same effect as in vertebrate nervous systems, seems to be very adequate for the identification of synaptic structures and synaptic distribution. Normally presynaptic structures are situated in angles of nerve fibres. Although degeneration experiments were made, the synaptic interaction of the various fibre types could only partially be explained. Sensory fibres interact with intemeurons, which show pre- and postsynaptic zones. They seem to be responsible for the integration of different glomeruli. There is some evidence that sensory fibres have synaptic connections, too. Postsynaptic profiles with several synaptic contacts and free of vesicles are very rare, whereas “axo-axonic” contacts are found quite often. These glomeruli with their great number of vesicle-filled profiles differ from corpora pedunculata calyx glomeruli (see Lamparter et al. 1969).

Notes: Summary The hilus cells in the ovary of the pig have been investigated with the electron microscope. These elements are identical with Leydig cells. The hilus cells contain an abundant agranular endoplasmic reticulum, which is either organized as a tubular network or as an onion like system of closely packed flattened cisternae sometimes filling up half of a cell and often being concentrated around lipid droplets and pigment granules. The mitochondria have cristae, tubuli and sacculi and a matrix of variable electron density. The golgi cisternae are poorly developed. The cells have centrioles, and there are hints of an amitotic cell division. The cytoplasm of the hilus cells contains lipid droplets, which have a diameter up to 5 μm. The pigment granules are extremely polymorphic, nearly always surrounded by a single membrane. They possibly may be derived from lipid droplets and mitochondria. Single axons of the hilus nerve occasionally penetrate the basement membrane and come into close contact with the hilus cells. Typical synapses were not observed. The results are discussed on the background of light microscopical, biochemical and pathological findings and compared with those obtained on Leydig cells of different species. Various cell images are interpreted to represent progressive stages of maturation.

Notes: Summary By combining the Golgi and the electronmicroscope techniques it has been possible to identify accurately the system of centrifugal fibers which arborizes in the lamina of muscoid flies forming the so-called nervous bags. Each of them originates from a single fiber entering the lamina at the site in which the second order and the long visual fibers leave it. This single fiber represents the peripheral portion of a T-shaped trunk stemming from a small neuronal body located in the external region of the medulla. The central branch terminates within the first synaptic field of this visual center. After entering the lamina the centrifugal fiber ramifies profusely and its branches can be seen climbing and synapsing on the surface of the photoreceptor axon endings. The synaptic loci show characteristic synaptic ribbons located within the nervous bag fibers. This fact suggests that direction of conduction is from the medulla to the lamina. This study has also revealed that the intramedullar terminals of the centrifugal fibers establish intimate contacts with one of the two second order fiber endings.

Notes: Summary Quantitation of synapses at different postnatal ages has been undertaken in the cerebral cortex of the rat. In this study axial ratios of presynaptic bags, proportion of cortex occupied by presynaptic bags and numbers of synapses per unit volume of cortex have been estimated. Observations on synaptic vesicle packing densities have also been made. Synaptic bags become increasingly spherical up to 7 days of age and become more elongated thereafter. The proportion of cortex occupied by presynaptic bags increases rapidly up to 7 days of age and then at a decelerated rate up to maturity. The number of synapses per unit volume increases slowly over the first four days after which there is a rapid increase to 14 days, followed by a decelerated rate. The average presynaptic bag shows marked changes in volume with increasing age which indicate the probability of two stages of synaptic development. This two stage development is further reflected in the estimates on vesicle packing densities. The implications of the results are discussed in relationship to changes in functional activity of the cortex during postnatal development.

Notes: Summary Synaptosomes derived from 2–21 days postnatal rat cerebral cortex have been examined following glutaraldehyde fixation and block PTA staining, with the aim of investigating the maturation of the paramembranous densities at the contact region between the pre- and postsynaptic components. The internal coats of pre- and postsynaptic membranes first appear as undifferentiated plaque-like thickenings, which gradually develop into, or are replaced by, dense projections and postsynaptic focal densities respectively. Both sets of densities pass through an interconnected phase before starting to emerge as discrete entities at 5–7 days. The external coats of the pre- and postsynaptic membranes coalesce to form a plate-like structure which breaks down during development to form the cleft densities or transverse bars of the adult contact region. Although for the first few days of postnatal development only one type of synaptosome can be identified, from 5 days onwards two types corresponding to types A and B of adult life become recognizable. Increase in height of the dense projections has been correlated with increase in the number of synaptic vesicles per synaptosome during postnatal development, indicating that the synaptic vesicles may play a role in the formation and maturation of dense projections. The possible importance of other factors in this process is also discussed.

Notes: Summary The rabbit SA-node was outlined electrophysiologically and its adrenergic and cholinergic innervation patterns were studied with the electron microscope. Differentiation between adrenergic and cholinergic terminals was achieved by fixation of the specimens in KMnO4 which produces dense-cored synaptic vesicles in adrenergic terminals, whereas synaptic vesicles in cholinergic terminals are empty. It was found that adrenergic and cholinergic nerve terminals often come in close apposition to each other, the distance between adjoining membranes being in the order of 250 Å. At times, faint membrane thickenings could be seen in these places. The available pharmacological, physiological and morphological evidence leaves little room for doubt that cholinergic terminal fibers can influence the adrenergic ones. From mainly morphological evidence it is also postulated that adrenergic terminals influence cholinergic terminals.

Notes: Summary The median eminence and the pars nervosa of Rana esculenta have a different structure. The median eminence has 2 different zones: the outer zone situated near the pars distalis and the inner zone under the ependyme. In the outer zone there are, according to the size and the shape of the granules, 5 types of nerve terminals. 1. Endings containing spherical fine dense granules of 800 to 1000 Å in diameter; 2. Endings with spherical granules from 1000 to 1200 Å in diameter; 3. Endings with granules of irregular shape which are bigger than the former (1200 to 1600 Å); 4. Endings with spherical dense granules of about 1200 to 1800 Å in diameter; 5. A few endings containing only clear vesicles. Type 3 and type 4 endings are probably neurosecretory. The inner zone contains numerous neurosecretory fibres. They are of two types: one with big granules (1600–2400 Å), the second with smaller granules (1300–2000 Å). Non-neurosecretory fibres have also been observed. The pars nervosa contains two principal types of neurosecretory fibres: one with dense granules of 1600 to 2400 Å in diameter, the other with lighter granules of about 1300 to 2000 Å. In the external zone lining the pars intermedia, aminergic fibres with fine granules have been observed.

Notes: Summary Two neuron types are distinguished by electron microscopy in the lateral geniculate nucleus (LGN) of the monkey-a large cell (P cell) interpreted as a geniculostriate relay cell, and a small cell (I cell) interpreted as an inhibitory interneuron. The I cell, distinguished by its small size, infolded nucleus, small mitochondria, cilium and small granular bodies, forms about 10% of the total neuron population. It could not be determined whether this cell has an axon, but its dendrites, which contain aggregates of flattened vesicles, are thought to form a proportion of the “F processes”, profiles which are post-synaptic to the retinal (RLP) axons and presynaptic to the dendrites of the P cells. The small dark (RSD) axon terminals of unknown origin contact the dendrites of both cell types. After eye enucleation the P cells of the affected laminae of the LGN shrink and partially withdraw their dendrites from the neuropil. By 29 months' survival, they have only a narrow cytoplasmic rim around the nucleus. A necrotic process also occurs, affecting fine dendrites by 22 days and large profiles by 45 days, but it is not clear whether whole cells are destroyed by this process. At 45 days the I cells are commonly seen to form somatodendritic synapses. The appearance of these synapses is interpreted as the result of a withdrawal to the soma of the presynaptic dendrites. It is concluded that the I cells are probably inhibitory interneurons subject to excitation and presynaptic inhibition by the RLP and RSD axons, and a diagram is presented to demonstrate the possible significance of these connections for the transmission of information through the LGN.

Notes: Summary Electron microscopic studies of neural processes in the cerebellum, optic tectum, and cerebral hemisphere of the frog reveal a distinctive system of SER cisternae lying at intervals (commonly 1–2 μm apart) perpendicular to the long axis of axons and dendrites, interconnected by tubular, longitudinally orientated SER elements, and in direct continuity with the outer membrane of mitochondria. The transverse cisternae are fenestrated, with a single mierotubule (or rarely, two) passing through the centre of each 50–75 nm fenestration. Extensions of the SER-microtubule complex may be located parasynaptically in axon terminals and dendrites. The SER of dendritic spines also appears to be continuous with the fenestrated cisternae. Possible roles for the specialized SER (particularly of the parasynaptic extensions), such as calcium ion sequestration and ATP or monoamine oxidase transport, are discussed.

Notes: Summary The innervation of the portal vein of the white rat was examined with light-, fluorescence-, and electronmicroscopic techniques. The results are as follows: 1. Paraldehyde treated vein preparations (Falck's fluorescence method) demonstrate a predominantly longitudinally orientated external nerve plexus, being situated on the outermost muscle cells. Near the liver the nerve net is characterized by broad meshes, near the intestinal tract by narrow ones. The circular subendothelial inner plexus originates in the outer plexus of the intestinal vascular bed. 2. Nerve bundles in the fibrous adventitia were demonstrated with Gomori's Acethylcholinesterase method. In other respects, the enzyme activity was only observed in the intercellular spaces of the muscle layer. The electronmicroscopic demonstration of Acetylcholinesterase (Karnovsky's method) further showed that the enzyme activity is restricted to the muscle cell membrane. 3. The electronmicroscopic examination verified the results obtained with fluorescence microscopic techniques. a) In the proximity of the liver, only isolated nerve bundles occur on the outer muscle layer. The individual nerves are entirely surrounded by Schwann cells. Only a few of the axons in the vicinity to the muscle cell have agranular vesicles. Evaginations of the vesicular axons occur infrequently. Their distance from the muscle cell amounts to 1000–2000 Å. b) In more than one thousand thin sections, no axons were found inside the thick muscular layer. c) Subendothelial axons (inner plexus) are either partially or totally evaginated from the Schwann cells. They are densely filled with empty vesicles (350–650 Å) and contain a few dense core vesicles of 800–1600 Å in diameter. Synaptic endings were not observed. d) A dense collection of vesicle-containing axons, that were partially in their entirety and partially only from the muscle cell proximal side evaginated from the Schwann cells, were observed in the single muscle layer at the junction of the superior mesenteric and the portal vein. From these bundles, smaller bundles and individual axons pass between the muscle cells and reach the endothelium. Typical synapses were not observed. No vesiclecontaining axon was nearer than 1000 Å to the muscle cell. 4. Those axons possessing vesicles and being evaginated are considered to be vegetative conducting pathways. The excitation of the effector structures by transmitter substances is discussed in connection with the post mortem autonomic vascular contractility.

Notes: Summary 1. There is a gradual proximo-distal increase in the thickness of the muscle coat of the human ductuli efferentes, duetus epididymidis and ductus deferens. Circularly arranged smooth muscle bundles predominate in the ductuli efferentes and ductus epididymidis of the caput section. Scanty strands of longitudinally and obliquely oriented smooth muscle bundles form an additional, incomplete outer muscle layer around the ductus epididymidis of the corpus. Small smooth muscle-like cells constitute the muscle elements of the upper sections of the excretory ducts (from the ductuli efferentes to the midcauda). At the transition of the corpus and cauda epididymidis ordinary large smooth muscle cells join the small contractile cells to form—in more distal sections of the cauda—a composed, thick subepithelial muscle coat. In most distal portions of the cauda, the two-layered muscle coat of the ductus epididymidis is transformed into a three-layered coat, a pattern of construction which is retained in the vas deferens. 2. Electron microscopically, three types of contractile cells are distinguished in the human ductuli efferentes and ductus epididymidis: a) contractile cells of medium transparency containing exclusively thin myofilaments (60 Å in diameter), b) dark contractile cells containing bundles of thin myofilaments (60 Å in diameter) and single coarse filaments (140 Å in diameter), c) light contractile cells with loosely dispersed, interweaving thin and thick myofilaments. Commutual diameter changes at regular intervals are seen in individual myofilaments, giving the impression of structural periodicity not unlike that of filaments of striated muscle. Ordinary smooth muscle cells of the cauda epididymidis and vas deferens are characterized by uniformly sized, closely packed but evenly distributed thin myofilaments with numerous dense patches. 3. Fluorescence microscopy performed on formaldehyde treated freeze dried tissues reveals that the contractile cells of the ductuli efferentes in man and monkey receive a low number of single adrenergic terminal fibres penetrating the depth of the muscle coat. The adrenergic innervation of the ductus epididymidis is restricted to small peritubular nerve fascicles running contiguous to the most superficially located bundles of smooth muscle-like cells. The adrenergic ground plexus is rather wide-meshed in the proximal cauda, becomes increasingly dense in more distal cauda sections and in initial, funicular portions of the vas deferens, and reaches maximum density in abdominal parts of the ductus. Perivascular and adventitial adrenergic plexuses are well developed at arteries of the caput and corpus epididymidis in man, monkey, rabbit, guinea-pig and rat. 4. Electron microscopically, noradrenergic nerves have been identified by the presence of small granular vesicles in preterminal varicose axon dilatations. Nerve fibre swellings filled with small empty spherical vesicles have been considered to belong to “cholinergic” neurons whereas occasional varicosities equipped with some large membrane bound granules and abundant mitochondria may represent local expansions of sensory axons. 5. Neuromuscular relationships in the upper sections of excretory ducts comprise adrenergic synapses by distance (more than 1000 Å), and a few intimate, ensheated close contacts, whereas the main type of contact of nerves to ordinary smooth muscle cells in the lower duct section is by means of close but not intimate approach (500–2000 Å). 6. Adrenergic synapses in the ductus epididymidis and ductus deferens of the monkey resemble—what concerns their morphology, relationship to effectors and distribution pattern—those of man. 7. In accordance with the total number of vascular and non-vascular adrenergic nerves, visualized by fluorescence microscopy, the amount of noradrenaline varied considerably in different sections of the human male internal genital organs: The lowest amounts were estimated in the testis (0.12±0.03 μg/g). Medium to high concentrations were detected in various sections of the caput and corpus epididymidis (ductuli efferentes 0.60±0.09 μg/g; ductuli efferentes and caput 0.72±0.13 μg/g; corpus epididymidis 1.04±0.25 μg/g; proximal cauda 0.95±0.17 μg/g; distal cauda 0.97±0.19 μg/g). The highest noradrenaline content was found in the human vas deferens (prox. vas deferens 1.11±0.21 μg/g; interm. vas deferens 1.20±0.42 μg/g; distal portion 1.43±0.39 μg/g). 8. For comparison, the noradrenaline content of the testis and epididymis of the rhesus monkey, the epididymis of the rabbit and the vas deferens of the rabbit, mouse, guinea-pig and rat has been determined. 9. Adrenaline of exogenous origin was detected in the vas deferens, cauda epididymidis and plexus pampiniformis of two cases who received this catecholamine as part of the local anaesthetic drug mixture. Due to methodological reasons, the presence of small amounts of adrenaline of endogenous source in adrenergic nerves of the human and monkey internal male genital organs cannot be excluded. 10. The differences in motility behaviour of the ductus epididymidis (spontaneous, rhythmic contractions) and ductus deferens (absence of any spontaneous movements under conditions at rest) in vivo and in vitro have been correlated with the occurrence of specialized contractile cells in the upper segment (ductuli efferentes, ductus epididymidis of the caput, corpus and initial cauda) and ordinary large smooth muscle cells in the lower segment (ductus epididymidis of the distal cauda and the vas deferens) and furthermore correlated with differences in the pattern of the adrenergic innervation; the concept is advanced that progressive cytological differentiation of smooth muscle cells and the development of a dense direct adrenergic innervation suppresses autocontractility and, that the reverse condition may favour spontaneous motility of smooth muscle elements.

Notes: Summary The glandula infraorbitalis buccalis in rabbits represents the type of a tubuloacinar mucous secreting gland. The secretory product of gland cells is electron lucent. Extrusion generally is characterized by the formation of an opening at the cell surface and the discharge of the secretory material. Intercellular canaliculi are absent. Mitochondria and arrays of granular endoplasmic reticulum are more numerous than in other mucous glands of rabbits. Intercalated ducts are short and connect the tubules with intralobular ducts. Striated ducts are absent in the infraorbital gland. Nerve terminals occur in some instances between gland cells and between glandular and myoepithelial cells.

Notes: Summary 1. Three species of the genusGnathonemus (Gn. petersii, moorii andstanleyanus) as all species of the family Mormyridae possess two pairs of electric organs situated symmetrically on each side of the vertebral column between the caudal, dorsal and anal fins. Each organ is composed of a series of 70–170 electroplaques. 2. The stalks of the electroplaques contain no nerves. Unbranched motor nerve fibres innervate the end sections of the stalks by synaptic knobs inserting into cavities of the electroplasma. 3. The electroplasma membrane surrounds the stalk (also in the region where the stalk penetrates through holes in the body of the electroplaque) and the electroplaque. The membrane is deeply indented on the cranial side as well as on the caudal side of the electroplaque. Through this the surface is greatly enlarged. In the inside of the electroplaque are striated muscles. 4. The motor and sensory nerve fibres are clearly different in diameter. 5. The number of the nerve cells in the spinal ganglions is, in the electric organ, about a multiple larger than in the segments of the body muscular system situated in front of the electric organ. 6. The reconstruction of the peripheral sensory nerves of one segment (in view of electron microscopical analyses), reveals that these, with the exception of two free nerve endings in the integument and the free nerve endings in the dorsal myoseptum, mainly innervate four large tendons on the side of the electric organs. 7. The innervation of the electric organs leads to the hypothesis that the tendons, in connection with the function of the electric organs, possess sensory functions.

Notes: Summary Both conventional and ribbon synapses occur in the pineal organ of Bombina. Ribbon synapses are both axodendritic and axosomatic. Two axodendritic types can be distinguished on the basis of the number of dendrites and synaptic ribbons. Both conventional and ribbon synapses can be formed with the same dendrite. Other contacts, which cannot be classified as true synapses, are also found between sensory cells and nerve cells and likewise between sensory cells. The synaptology of the pineal organ permits a discussion of the problems of its neurocircuitry. Products of the acetylcholinesterase reaction occur mainly in the plexiform layer of the pineal organ. It is not possible to correlate the reaction products with definite cell types. The results of the acetylcholinesterase reaction in the pineal is compared with corresponding findings in other parts of the CNS and in the retina of the lateral eyes.

Notes: Summary The fine structure of the pancreatic nerves of the domestic fowl has been studied. Naked axon beadings were found in membranous contact with endocrine as well as exocrine cells. From an anatomical point of view it seems reasonable to suggest that the endocrine glands might be subjected to some influence of the autonomic nervous system.

Notes: Summary A subectodermal nerve-net is demonstrated in ten species of Ctenophores by means of either Methylene Blue vital staining or silver impregnation. There is no evidence of subendodermal nerve-net. The ectodermal nerve-net displays a characteristic polygonal pattern which is thought to result from morphogenetic events. Both bipolar and tripolar neurones occur. Three types of concentrations of nervous tissue are described: a) a high accumulation of nervous perikarya at the aboral sensory pole; b) a noticeable densification of the net along the eight meridional ciliary strands of every species, and around the lips of Beroidea; c) in the Cydippids Pleurobrachia and Hormiphora two thick strands of fibers and neurones interconnecting the aboral organ and the tentacles: the tentacular nerves. Ultrastructural evidence is given for the presence of nervous elements under and amidst ectodermal epithelial cells. Three features allow the recognition and characterization of neurites and neurones: a) numerous clear and/or granulated vesicles; b) microtubules in variable amounts; c) frequent and highly differentiated synaptic contacts. The very peculiar arrangement of the presynaptic elements is observed in all the species of Ctenophores so far studied. These synaptic contacts suggest chemical transmission in the nerve-net. On the basis of ultrastructural evidence the author refutes the nervous nature previously attributed to the ciliated cells of the meridional grooves. A parallel is drawn between nervous systems of Cnidaria and Ctenophora.

Notes: Summary Fluorescence and electron microscopy of the turtle heart indicates the presence of monoamine-containing, granulated cells in the wall of venous sinus and near the openings of the aortic trunks. These cells occur in clusters and are always in association with nerve fibers and/or ganglion cells within the turtle heart. Vesiculated axon terminals make a synaptic contact with the cytolemma of the granulated cell which in turn makes a synapse to the processes from the other granulated cell and to the cardiac nerve fibers. The close contact occurs also between the granulated cell process and the smooth muscle cell membrane in the wall of large vessels. The granulated cell has no special relationship to the blood capillaries. The significance of these results is discussed in relation to nervous control of the cardiac activity of the turtle.

Notes: Summary The formation and development of synaptic contacts between dissociated chick spinal cord neurons has been investigated. By the 6th day in vitro “immature” profiles with few vesicles were observed. By 14–18 days “mature” types with numerous vesicles were found, indistinguishable from those of newly hatched chick spinal cord. After this period degeneration occurred, and was especially marked in the post-synaptic element. Such degeneration could be postponed by the addition of small numbers of somatic muscle cells. The Kanaseki and Kadota (1969) technique was applied to the study of coated vesicles at various stages of synaptic development.

Notes: Summary The innervation of the Purkinje fibres in the atrium of the heart of the adult fowl was investigated by light microscopy, using the Champy-Maillet OsO4-ZnI2 technique and the cholinesterase reaction and by electron microscopy. After impregnation of the tissue with OsO4-ZnI2, the dark-stained nerve fibres were clearly visible on the unstained Purkinje fibres. In the upper part of the posterior wall of the right atrium, the diffuse portion of the conducting system is especially richly innervated by varicose and smooth nerve fibres. Some of these fibres are cholinesterase-positive. The terminal axons run in the space between the Purkinje fibres and the fibrocytic envelope. They are either naked or accompanied by Schwann cell processes. In addition to varicosities containing granular vesicles, there are varicosities containing agranular vesicles with oval profiles. In the “en passant” synapses, the width of the synaptic cleft between a varicosity and the Purkinje cell is about 600 Å. The innervation of the Purkinje fibres appears more like the innervation of smooth muscle than that of striated skeletal muscle. The possible role of Purkinje fibres as mechanical receptors is discussed.

Notes: Summary The pathways of axonal transport of secretions from neurosecretory cells (NSC) in the medial group (viz. A-, A1, B-, and C-type NSC) and the lateral group (L-type NSC) are described. Individual axons can be recognized in the electron microscope by the kind of neurosecretory particles they contain. In general, the secretions from the medial NSC are carried to the contralateral nervi corporis cardiaci (NCC), those from the lateral NSC to the ipsilateral NCC. Some axons from the A-type NSC, in addition, may run to ipsilateral NCC. All A-type axons have collaterals which run to the ipsilateral NCC. The medial and lateral bundles of “mixed” axons run through one paired NCC but remain separated spatially. Release of secretion from the C-type NSC can take place before the corpus cardiacum is reached. A- and A1-type NSC have additional collaterals that branch from the proximal part of the axons and penetrate deeply into the neuropile of the protocerebral lobes. Local swellings appear to be closely associated with fibers from non-neurosecretory neurons. The sites of contact are characterized by the accumulation of microvesicles (400 Å) near an electron-dense cleft of 150–200 Å width, and resemble regular chemical synapses. The microvesicles prove to be present within the neurosecretory fiber in most of the specimens studied, and within the non-neurosecretory fiber in only a few cases. It seems most likely that the collaterals in some phases convey afferent signals to the NSC which inhibit the release of an efferent neurochemical “messenger” of unknown nature into the neuropile.

Notes: Summary The nerve fibre layer and the neurocord of the Enteropneusts Saccoglossus horsti, Harrimania kupfferi and Ptychodera flava have been examined with the electron microscope. The nerve fibres vary in diameter between 0.15 to 10 μm. The majority of the fibres are of the smaller diameters. The nerve fibre layer is intraepidermal, and is divided by processes running radially from the epithelial cells to the basement membrane that separates the nerve fibre layer from the muscle cells. The cells of origin of these nerve fibres are situated mainly in the innermost layers of the epidermal cells. The nerve fibre profiles contain numerous vesicles of very varied diameter and contents, together with larger granular inclusions that are also found in the nerve cell bodies. Morphologically recognisable synapses are rare, but the majority of fibres are in intimate contact with one another. Sometimes the mass of fibres is divided into bundles by the epithelial cell processes. The majority of giant fibres are situated near to the basement membrane of the neurocord. The giant fibres also have a varied content of vesicles as well as neurofilaments and neurotubules. The central canal in Ptychodera flava and the remnants of the central canal in Saccoglossus horsti are both lined by columnar cells that bear microvilli as well as cilia with the typical 9 + 2 pattern of tubules. Scattered amongst these cells are mucus secreting cells which open into the cavity of the canal.

Notes: Summary 1. The stalk of the mushroom-bodies (Corpora pedunculata) of the cricket Acheta domesticus L. is composed of nerve fibers from different types of globuli cells. These fibers are arranged into four groups. 2. Extrinsic nerve fibers run through the pedunculus neuropil in different directions. 3. Synapses occur primarily in stalk zone III and in basic stalk parts of zone IV. Intrinsic nerve fibers of globuli cells contain synaptic vesicles, which stain with ZIO-impregnation (Akert and Sandri, 1968), and dense core vesicles. 4. Intrinsic and extrinsic nerve fibers make synaptic contacts. There is some evidence, that globuli cell fibers interact by chemical synapses too. 5. Special synaptic structures such as electron dense projections and accumulations of vesicles are situated predominantly in the angles of two neighbouring axons. The question of synaptic polarization can not always be resolved. 6. The different fiber types and their synaptic contacts are discussed with respect to the function of the corpora pedunculata. The results support the general view, that mushroom bodies represent an important brain center for association.

Notes: Summary The nerve supply to the iridic melanophores of the rat was studied with the electron microscope. The adrenergic and cholinergic terminals were identified with the aid of 5-hydroxydopamine, which produces dense-cored 400–800 Å synaptic vesicles in adrenergic axon varicosities, whereas the synaptic vesicles of cholinergic axons remain empty. It was found that both adrenergic and cholinergic terminal axons come in close apposition (200–250 Å) with the melanophores. The appositions have the same appearance as synapses in peripheral tissues. It seems likely that the murine iridic melanophores have a double innervation, although its functional significance is obscure.

Notes: Summary Octopus synaptosomes have been examined after glutaraldehyde fixation and phosphotungstic acid (PTA) staining of non-osmicated tissue. The results concentrate on the appearance of the contact region between the presynaptic component of synaptosomes and their postsynaptic processes. Membranes have a triple-layered appearance, consisting of an electronopaque internal coat, an electrontranslucent band and an electronopaque external coat. Good examples of this are found in synaptosomal, dendritic and axonal membranes. At specialized synaptic contact regions the external coats of the pre- and postsynaptic membranes coalesce to form a prominent synaptic plate, which has a width of 18 nm and is subdivided into zones of varying electronopacity. It is suggested that this plate is formed from the specialized external coat of the postsynaptic membrane and the unspecialized external coat of the presynaptic membrane. Presynaptic spicules extend from the internal coat of the presynaptic membrane. They are closely associated with elements of the presynaptic network. It is suggested that the synaptic plate is probably composed of mucopolysaccharides, while the relation of the plate to acetylcholinesterase is discussed. It is proposed that functional localization at the synapse is less precise in octopus than vertebrates.

Notes: Summary The pineal organ of Passer domesticus contains nerve cells within its parenchyma. Axons of the nerve cells run within the elongated stalk of the pineal organ to the habenular commissure. At the proximal end of the stalk, some axons become myelinated. In the stalk, the axons intermingle with pinealocyte processes containing synaptic ribbons. The synaptic ribbons are in contact with (1) vesicles with a diameter of 300 Å; (2) 300 Å diameter vesicles and 800–1,200 Å diameter dense-core granules; or (3) the dense-core granules only. Dense-core granules are also present in pinealocytes with 9+0 type cilia. These results suggest that sensory and secretory structures are present in the same pineal cell type. Furthermore, “conventional” synapses are present between receptor and nerve cells: The presynaptic fibers have the same structure as the fibers containing synaptic ribbons. The numbers of microfibrils and microtubules vary among postsynaptic fibers (dendrites), the pinealocyte processes, and the neurites. Thus it is difficult to obtain an exact count of the number of axons running to the brain. Efferent sympathetic nerve fibers enter the pineal organ associated with the connective tissue surrounding blood vessels. The fibers show granules of 300–500 Å diameter or 800–1,200 Å diameter. After nialamide injection, both types of granules contain a dense core. Microspectrographically serotonin and noradrenaline are demonstrated in the sympathetic nerve fibers. There is no evidence found in the material of this study to suggest that sympathetic nerve fibers perforate the basement membrane and enter the parenchymal cell complexes of the pineal organ. Pinealocyte processes and sympathetic nerve fibers often show a very similar ultrastructural pattern. The role of the avian pineal organ in photo-neuro-endocrine regulation is discussed.