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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 183 (1998), S. 121-133 
    ISSN: 1432-1351
    Keywords: Key words Antenna ; CNS ; Glomerulus ; Insect ; Olfaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Stimulation of the antenna of the male moth, Manduca sexta, with a key component of the female's sex pheromone and a mimic of the second key component evokes responses in projection neurons in the sexually dimorphic macroglomerular complex of the antennal lobe. Using intracellular recording and staining techniques, we studied the antennal receptive fields of 149 such projection neurons. An antennal flagellum was stimulated in six regions along its proximo-distal axis with one or both of the pheromone-related compounds while activity was recorded in projection neurons. These neurons fell mainly into two groups, based on their responses to the two-component blend: neurons with broad receptive fields that were excited when any region of the flagellum was stimulated, and neurons selectively excited by stimulation of the proximal region of the flagellum. Projection neurons that were depolarized by stimulation of one antennal region were not inhibited by stimulation of other regions, suggesting absence of antennotopic center-surround organization. In most projection neurons, the receptive field was determined by afferent input evoked by only one of the two components. Different receptive-field properties of projection neurons may be related to the roles of these neurons in sensory control of the various phases of pheromone-modulated behavior of male moths.
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  • 2
    ISSN: 1432-1351
    Keywords: Inhibition ; Local interneurons ; Manduca sexta ; Olfaction ; Synaptic interactions ; Antennal lobe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Intracellular recordings were made from the major neurites of local interneurons in the moth antennal lobe. Antennal nerve stimulation evoked 3 patterns of postsynaptic activity: (i) a short-latency compound excitatory postsynaptic potential that, based on electrical stimulation of the antennal nerve and stimulation of the antenna with odors, represents a monosynaptic input from olfactory afferent axons (71 out of 86 neurons), (ii) a delayed activation of firing in response to both electrical- and odor-driven input (11 neurons), and (iii) a delayed membrane hyperpolarization in response to antennal nerve input (4 neurons). Simultaneous intracellular recordings from a local interneuron with short-latency responses and a projection (output) neuron revealed unidirectional synaptic interactions between these two cell types. In 20% of the 30 pairs studied, spontaneous and current-induced spiking activity in a local interneuron correlated with hyperpolarization and suppression of firing in a projection neuron. No evidence for recurrent or feedback inhibition of projection neurons was found. Furthermore, suppression of firing in an inhibitory local interneuron led to an increase in firing in the normally quiescent projection neuron, suggesting that a disinhibitory pathway may mediate excitation in projection neurons. This is the first direct evidence of an inhibitory role for local interneurons in olfactory information processing in insects. Through different types of multisynaptic interactions with projection neurons, local interneurons help to generate and shape the output from olfactory glomeruli in the antennal lobe.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 177 (1995), S. 545-557 
    ISSN: 1432-1351
    Keywords: Interneuron ; Odor coding ; Olfaction ; Pheromone ; Tobacco budworm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The chemical and temporal features of the sex-pheromone emitted by Heliothis virescens females are encoded by a diverse array of output pathways from the male-specific macroglomerular complex (MGC) in the antennal lobe. Most output neurons (29 out of 32) were activated by antennal stimulation with the principal component of the sex-pheromone blend of this species, (Z)-11-hexadecenal. Six neurons were excited solely by this component, 8 neurons also responded to the second essential blend component, (Z)-9-tetradecenal, and 14 neurons displayed equivalent responses to the two. Many neurons also effectively encoded the onset and duration of the stimulus. In one additional neuron, a prolonged excitatory response (synergism) was evoked only by the blend of the two components, indicating that some MGC neurons function as ‘blend detectors’. In contrast to the situation in Helicoverpa zea, none of the MGC neurons in H. virescens responded selectively to (Z)-9-tetradecenal, suggesting that these two noctuid species employ different neural strategies to encode information about their respective pheromone blends. Three MGC-output neurons responded selectively to (Z)-11-hexadecenyl acetate, an odorant released by some sympatric species that disrupts normal upwind flight to pheromones. Thus, changes in the attractant and deterrent chemical signals, as well as the physical features of these odor plumes, are encoded in the MGC across a diverse parallel array of output pathways to the protocerebrum.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 178 (1996), S. 5-19 
    ISSN: 1432-1351
    Keywords: Olfaction ; Insect ; Pheromone ; Olfactory glomeruli ; Chemical communication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 178 (1996), S. 21-31 
    ISSN: 1432-1351
    Keywords: 5-Hydroxytryptamine ; Serotonin ; Neuromodulation ; Antennal lobe ; Cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The modulatory actions of 5-hydroxy-tryptamine (5HT or serotonin) on a morphologically identifiable class of neurons dissociated from antennal lobes of Manduca sexta at stages 9–15 of the 18 stages of metamorphic adult development were examined in vitro with whole-cell patch-clamp recording techniques. Action potentials could be elicited from approximately 20% of the cells. These cells were used to examine effects of 5HT (5 × 10−6 to 5 × 10−4 M) on cell excitability and action-potential waveform. 5HT increased the number of spikes elicited by a constant depolarizing current pulse and reduced the latency of responses. 5HT also led to broadening of action potentials in these neurons and increased cell input resistance. Modulation of potassium channels by 5HT is likely to contribute to these responses. 5HT causes reversible reduction of at least 3 distinct potassium currents, one of which is described for the first time in this study. Because effects of 5HT on antennal-lobe neurons in culture mimic those observed in situ in the brain of the adult moth, in vitro analysis should contribute to elucidation of the cellular mechanisms that underlie the modulatory effects of 5HT on central olfactory neurons in the moth.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 182 (1998), S. 703-714 
    ISSN: 1432-1351
    Keywords: Key words Glomerulus ; Evoked potential ; Olfaction ; Oscillation ; Pheromone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Using intra- and extracellular recording methods, we studied the activity of pheromone-responsive projection neurons in the antennal lobe of the moth Manduca sexta. Intracellularly recorded responses of neurons to antennal stimulation with the pheromone blend characteristically included both inhibitory and excitatory stages of various strengths. To observe the activity of larger groups of neurons, we recorded responses extracellularly in the macroglomerular complex of the antennal lobe. The macroglomerular complex is part of a specialized olfactory subsystem and the site of first-order central processing of sex-pheromonal information. Odors such as the pheromone blend and host-plant (tobacco) volatiles gave rise to evoked potentials that were reproducible upon repeated antennal stimulation. Evoked potentials showed overriding high-frequency oscillations when the antenna was stimulated with the pheromone blend or with either one of the two key pheromone components. The frequency of the oscillations was in the range of 30–50 Hz. Amplitude and frequency of the oscillations varied during the response to pheromonal stimulation. Recording intracellular and extracellular activity simultaneously revealed phase-locking of action potentials to potential oscillations. The results suggest that the activity of neurons of the macroglomerular complex was temporally synchronized, potentially to strengthen the pheromone signal and to improve olfactory perception.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 167 (1990), S. 309-320 
    ISSN: 1432-1351
    Keywords: Chemosensory integration ; Olfaction ; Brain ; Larva ; Caterpillar ; Manduca sexta ; Lepidoptera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The physiology and morphology of olfactory interneurons in the brain of larval Manduca sexta were studied using intracellular recording and staining techniques. Antennal olfactory receptors were stimulated with volatile substances from plants and with pure odorants. Neurons responding to the stimuli were investigated further to reveal their response specificities, dose-response characteristics, and morphology. 2. We found no evidence of specific ‘labeled-lines’ among the odor-responsive interneurons, as none responded exclusively to one plant odor or pure odorant; most olfactory interneurons were broadly tuned in their response spectra. This finding is consistent with an ‘across-fiber’ pattern of odor coding. 3. Mechanosensory and olfactory information are integrated at early stages of central processing, appearing in the responses of some local interneurons restricted to the primary olfactory nucleus in the brain, the larval antennal center (LAC). 4. The responses of LAC projection neurons and higher-order protocerebral interneurons to a given odor were more consistent than the responses of LAC local interneurons. 5. The LAC appears to be functionally subdivided, as both local and projection neurons had arborizations in specific parts of the LAC, but none had dendrites throughout the LAC. 6. The mushroom bodies and the lateral protocerebrum contain neurons that respond to olfactory stimulation.
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  • 8
    ISSN: 1432-0878
    Keywords: Serotonin ; Immunocytochemistry ; Insect nervous system ; Protocerebrum ; Suboesophageal ganglion ; Manduca sexta (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Serotonin-immunoreactive neurons in the median protocerebrum and suboesophageal ganglion of the sphinx moth Manduca sexta were individually reconstructed. Serotonin immunoreactivity was detected in 19–20 bilaterally symmetrical pairs of interneurons in the midbrain and 10 pairs in the suboesophageal ganglion. These neurons were also immunoreactive with antisera against DOPA decarboxylase. All major neuropil regions except the protocerebral bridge are innervated by these neurons. In addition, efferent cells are serotonin-immunoreactive in the frontal ganglion (5 neurons) and the suboesophageal ganglion (2 pairs of neurons). The latter cells probably give rise to an extensive network of immunoreactive terminals on the surface of the suboesophageal ganglion and suboesophageal nerves. Most of the serotonin-immunoreactive neurons show a gradient in the intensity of immunoreactive staining, suggesting low levels of serotonin in cell bodies and dendritic arbors and highest concentrations in axonal terminals. Serotonin-immunoreactive cells often occur in pairs with similar morphological features. With one exception, all serotonin-immunoreactive neurons have bilateral projections with at least some arborizations in identical neuropil areas in both hemispheres. The morphology of several neurons suggests that they are part of neuronal feedback circuits. The similarity in the arborization patterns of serotonin-immunoreactive neurons raises the possibility that their outgrowing neurites experienced similar forces during embryonic development. The morphological similarities further suggest that serotonin-immunoreactive interneurons in the midbrain and suboesophageal ganglion share physiological characteristics.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 254 (1988), S. 255-281 
    ISSN: 1432-0878
    Keywords: Insect nervous system ; Antennal lobe ; Olfactory system ; Protocerebrum ; Antennal interneurons ; Manduca sexta (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the moth Manduca sexta, the number and morphology of neuronal connections between the antennal lobes and the protocerebrum were examined. Cobalt injections revealed eight morphological types of neurons with somata adjacent to the AL neuropil that project in the inner, middle, and outer antenno-cerebral tracts to the protocerebrum. Neurons innervating the macroglomerular complex and many neurons with fibers in the inner antennocerebral tract have uniglomerular antennal-lobe arborizations. Most neurons in the middle and outer antenno-cerebral tracts, on the other hand, seem to innervate more than one glomerulus. Protocerebral areas receiving direct input from the antennal lobe include the calyces of the mushroom bodies, and circumscribed areas termed “olfactory foci” in the lateral horn of the protocerebrum and several other regions, especially areas in close proximity to the mushroom bodies. Fibers in the inner antenno-cerebral tract that innervate the male-specific macroglomerular complex have arborizations in the protocerebrum that are distinct from the projections of sexually non-specific neurons. Protocerebral neurons projecting into the antennal lobe are much less numerous than antennal-lobe output cells. Most of these protocerebral fibers enter the antennal lobe in small fiber tracts that are different from those described above. In the protocerebrum, these centrifugal cells arborize in olfactory foci and also in the inferior median protocerebrum and the lateral accessory lobes. The morphological diversity of connections between the antennal lobes and the protocerebrum, described here for the first time on a single-cell level, suggests a much greater physiological complexity of the olfactory system than has been assumed so far.
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  • 10
    ISSN: 1432-0878
    Keywords: Neuropeptides ; FMRFamide ; Immunocytochemistry ; Insect nervous system ; Manduca sexta (Insecta)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Using an antiserum against the tetrapeptide FMRFamide, we have studied the distribution of FMRFamide-like substances in the brain and suboesophageal ganglion of the sphinx mothManduca sexta. More than 2000 neurons per hemisphere exhibit FMRFamide-like immunoreactivity. Most of these cells reside within the optic lobe. Particular types of FMRFamide-immunoreactive neurons can be identified. Among these are neurosecretory cells, putatively centrifugal neurons of the optic lobe, local interneurons of the antennal lobe, mushroom-body Kenyon cells, and small-field neurons of the central complex. In the suboesophageal ganglion, groups of ventral midline neurons exhibit FMRFamide-like immunoreactivity. Some of these cells have axons in the maxillary nerves and apparently give rise to FMRFamide-immunoreactive terminals in the sheath of the suboesophageal ganglion and the maxillary nerves. In local interneurons of the antennal lobe and a particular group of protocerebral neurons, FMRFamide-like immunoreactivity is colocalized with GABA-like immunoreactivity. This suggests that FMRFamide-like peptides may be cotransmitters of these putatively GABAergic interneurons. All FMRFamide-immunoreactive neurons are, furthermore, immunoreactive with an antiserum against bovine pancreatic polypeptide, and the vast majority is also immunoreactive with an antibody against the molluscan small cardioactive peptide SCPB. Therefore, it is possible that more than one peptide is localized within many FMRFamide-immunoreactive neurons. The results suggest that FMRFamide-related peptides are widespread within the nervous system ofM. sexta and might function as neurohormones and neurotransmitters in a variety of neuronal cell types.
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