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  • 1
    ISSN: 1432-1017
    Keywords: Proteolipid apoprotein structure ; sonication ; non-denaturing detergent ; freeze-fracture electron microscopy ; infrared spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The conformation of brain proteolipid apoprotein (PLA) has been investigated using infrared spectroscopy and freeze-fracture electron microscopy. For this purpose, spectroscopic samples consisting of a mixture of liquid paraffin and wet protein have been prepared. These systems have allowed us to record the infrared spectra of PLA at neutral pH. The amide I and III regions reveal the existence of a predominantly α-helical structure, as well as the presence of minor β-strands and random coil forms. The effect of sonication and a non-denaturing detergent, (n-octyl-β-d-glucopyranoside), on the structure of the protein have also been investigated. Sonication produces an increase of the β and unordered structures at the expense of the α-helical conformation. These structural changes are enhanced in the presence of the non-ionic detergent n-octyl-β-d-glucopyranoside. Lipids protect the native protein structure from the effects of sonication. The aforementioned detergent changes the PLA conformation by increasing the α-helical content at the expense of β-sheet and random coil forms. Therefore the PLA structure seems to be similar to the structures of other proteins intrinsic to non-neural membranes. The effects investigated also suggest that PLA behaves in a conformationally flexible manner.
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  • 2
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The authors describe a new technique for isolation of specific fractions of synaptosomes, on the basis of their surface glycoproteins, by affinity chromatography using lectin-Sepharose columns.
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  • 3
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A modification of Hansson's histochemical technique was used to reveal carbonic anhydrase activity in mounted cryostat sections of rat olfactory mucosa, after glutaraldehyde fixation. A positive reaction that could be inhibited by acetazolamide was found in a population of olfactory receptor cells, whereas the supporting cells were negative. Axons of receptor cells were also positive and could be traced through the cribriform plate to the olfactory bulb.
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  • 4
    ISSN: 1573-6830
    Keywords: estradiol ; arcuate nucleus ; freeze-fracture ; coated vesticles ; coated pits ; neuronal plasticity ; exoendocytotic activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. In the rat hypothalamic arcuate nucleus, estradiol induces coordinated changes in the number of axosomatic synapses, the amount of glial ensheathing, and the ultrastructure of the membrane of neuronal somas. In the present study we used conventional electron microscopy and freeze-fracture to examine cellular mechanisms responsible for the estradiol-induced chages at the membrane level. 2. In freeze-fracture replicas taken 10–60 min and 24 hr after injection of 17β-estradiol to adult ovariectomized females, it was found that there was a rapid increase in the number of exoendocytotic images that reached a plateau by 30 min. 3. In thin sections from animals injected 24 hr earlier we demonstrated a significant increase in coated vesicles in the periphery of the neurons and coated pits in the perikaryal membranes and decreased axosomatic synapses. 4. We conclude that these morphological alterations are signaling estrogen-induced transport and/or turnover of perikaryal membrane constituents and extracellular components which may affect interneuronal and neuroglial interactions.
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  • 5
    ISSN: 1573-6830
    Keywords: GH ; sexual dimorphism ; GHRH ; somatostatin ; neonatal steroid environment ; testosterone ; secretory pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The secretory pattern of growth hormone (GH) is sexually dimorphic in the adult rat. However, this difference between the sexes does not become apparent until after the onset of puberty, suggesting that pubertal sex steroids play an important role in the manifestation of this phenomenon. 2. We have addressed the question as to whether there exists a sexual dimorphism in the hypothalamic neuropeptides that regulate GH release from the anterior pituitary,i.e., somatostatin (SS) and growth hormone-releasing hormone (GHRH). In addition, we have investigated whether the developmental changes in the GH secretory pattern are correlated with changes in these neuropeptides. The effect of testosterone treatment on SS and GHRH neurons during both the neonatal period and adulthood have also been studied. 3. We have found that the synthetic capacity, as reflected in relative messenger RNA (mRNA) levels, of both SS and GHRH neurons changes throughout development in both male and female rats. These mRNA levels are sexually dimorphic at certain times during maturation and can be modulated by changes in testosterone levels, suggesting that sex steroid modulation of these two neuropeptide systems could at least partially account for the sexual dimorphism seen in the adult GH secretory pattern. 4. The neonatal steroid environment has also been suggested to be involved in the generation of the final adult GH secretory pattern, although the mechanisms underlying this effect are even less well understood. In support of the hypothesis that the neonatal steroid environment plays an important role in organizing the GH axis, we have found that the number of GHRH neurons in the adult brain, as well as their sensitivity to adult steroids, is modulated by neotatal testosterone treatment. The number of SS neurons in the periventricular and paraventricular nuclei were not modulated by neonatal steroids; however, the synthetic capacity of these neurons does appear to be influenced by the neonatal steroid environment. 5. These studies suggest that both the neonatal and adult sex steroid environments influence the adult GH secretory pattern by modulating GHRH and SS neurons.
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  • 6
    ISSN: 1573-6830
    Keywords: estradiol ; arcuate nucleus ; gonadotropin releasing hormone ; ovarian cycle ; synaptogenesis ; synaptic plasticity ; GABA ; dopamine ; β-endorphin ; neural cell adhesion molecule ; insulin-like growth factor I
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Studies conducted on the rat arcuate nucleus, an area involved in the development and control of LH and FSH secretion, have shown the existence of hormonally regulated developmental sex differences in synaptic patterns and estrogen-induced synaptic plasticity during adult life. Several questions raised by these findings are examined in this review: 2. The mechanisms of estrogen-regulated developmental synaptogenesis. These include the role of glycocalyx glycoproteins in neuronal membranes, neural cell adhesion molecules, and insulin-like growth factor I. 3. The relationship among circulating estrogen, gonadotropin levels, and hypothalamic synaptic plasticity. Recent evidence for the role of GABAergic and dopaminergic synaptic inputs and POMC projections from the arcuate nucleus to the GnRH cells is discussed. 4. The synaptologic basis of age-related failure of positive feedback. The role of the cumulative effect of repeated preovulatory synaptic retraction and reapplication cycles on sensescent constant estrus is analyzed.
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  • 7
    ISSN: 1573-6830
    Keywords: estradiol ; progesterone ; testosterone ; neurosteroids ; pregnenolone ; dehydroepiandrosterone ; glial fibrillary acidic protein ; reactive astroglia ; synaptic plasticity ; neural cell adhesion molecule ; insulin-like growth factor I
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Recent evidence indicates that astroglia participate in the metabolism of gonadal hormones, in the synthesis of neurosteroids, and in the plastic responses of neurons to gonadal steroids. The role of astroglia on plastic responses of neural tissue to gonadal hormones and neurosteroids is examined in this review. 2. Gonadal steroids and neurosteroids promote astroglia plasticity in several areas of the central nervous system, including the hypothalamus, the striatum, and the hippocampus. 3. Gonadal steroids and neurosteroids modulate astroglia proliferation and the formation of reactive astroglia after brain injury. 4. Astroglia is a source of trophic factors that may mediate effects of gonadal steroids on neural tissue. 5. Astroglia is involved in the promotion of synaptic plastic changes by gonadal hormones. 6. The effect of gonadal hormones on astroglial plasticity is dependent on specific membrane interactions with neurons and on the expression of the embryonic highly polysialylated isoform of the neural cell adhesion molecule on neuronal membranes. 7. In conclusion, coordinated responses of neurons and astroglia appear to be involved in the modulation of neural function and response to injury by gonadal hormones and neurosteroids.
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  • 8
    Publication Date: 2019-07-13
    Description: Effects of microgravity on postural control and volume of extracellular fluids as well as stress associated with space flight may affect the function of hypothalamic neurosecretory neurons. Since environmental modifications in young animals may result in permanent alterations in neuroendocrine function, the present study was designed to determine the effect of a space flight on oxytocinergic and vasopressinergic magnocellular hypothalamic neurons of prepuberal rats. Fifteen-day-old Sprague-Dawley female rats were flown aboard the Space Shuttle Columbia (STS-90, Neurolab mission, experiment 150) for 16 days. Age-matched litters remained on the ground in cages similar to those of the flight animals. Six animals from each group were killed on the day of landing and eight animals from each group were maintained under standard vivarium conditions and killed 18 weeks after landing. Several signs of enhanced transcriptional and biosynthetic activity were observed in magnocellular supraoptic neurons of flight animals on the day of landing compared to control animals. These include increased c-Fos expression, larger nucleoli and cytoplasm, and higher volume occupied in the neuronal perikaryon by mitochondriae, endoplasmic reticulum, Golgi apparatus, lysosomes and cytoplasmic inclusions known as nematosomes. In contrast, the volume occupied by neurosecretory vesicles in the supraoptic neuronal perikarya was significantly decreased in flight rats. This decrease was associated with a significant decrease in oxytocin and vasopressin immunoreactive levels, suggestive of an increased hormonal release. Vasopressin levels, cytoplasmic volume and c-Fos expression returned to control levels by 18 weeks after landing. These reversible effects were probably associated to osmotic stimuli resulting from modifications in the volume and distribution of extracellular fluids and plasma during flight and landing. However, oxytocin levels were still reduced at 18 weeks after landing in flight animals compared to controls. This indicates that space flight during prepuberal age may induce irreversible modifications in the regulation of oxytocinergic neurons, which in turn may result in permanent endocrine and behavioral impairments.
    Keywords: Life Sciences (General)
    Type: Brain research. Developmental brain research (ISSN 0165-3806); 130; 2; 191-205
    Format: text
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