Ventral Cord Neurons Research Articles

Regulation of ectodermal and excretory function by the C. elegans POU homeobox gene ceh-6.

Caenorhabditis elegans has three POU homeobox genes, unc-86, ceh-6 and ceh-18. ceh-6 is the ortholog of vertebrate Brn1, Brn2, SCIP/Oct6 and Brn4 and fly Cf1a/drifter/ventral veinless. Comparison of C. elegans and C. briggsae CEH-6 shows that it is highly conserved. C. elegans has only three POU homeobox genes, while Drosophila has five that fall into four families. Immunofluorescent detection of the CEH-6 protein reveals that it is expressed in particular head and ventral cord neurons, as well as in rectal epithelial cells, and in the excretory cell, which is required for osmoregulation. A deletion of the ceh-6 locus causes 80% embryonic lethality. During morphogenesis, embryos extrude cells in the rectal region of the tail or rupture, indicative of a defect in the rectal epithelial cells that express ceh-6. Those embryos that hatch are sick and develop vacuoles, a phenotype similar to that caused by laser ablation of the excretory cell. A GFP reporter construct expressed in the excretory cell reveals inappropriate canal structures in the ceh-6 null mutant. Members of the POU-III family are expressed in tissues involved in osmoregulation and secretion in a number of species. We propose that one evolutionary conserved function of the POU-III transcription factor class could be the regulation of genes that mediate secretion/osmoregulation.

Regulation of body length and male tail ray pattern formation of Caenorhabditis elegans by a member of TGF-β family

We have identified a new member of the TGF-beta superfamily, CET-1, from Caenorhabditis elegans, which is expressed in the ventral nerve cord and other neurons. cet-1 null mutants have shortened bodies and male tail abnormal phenotype resembling sma mutants, suggesting cet-1, sma-2, sma-3 and sma-4 share a common pathway. Overexpression experiments demonstrated that cet-1 function requires wild-type sma genes. Interestingly, CET-1 appears to affect body length in a dose-dependent manner. Heterozygotes for cet-1 displayed body lengths ranging between null mutant and wild type, and overexpression of CET-1 in wild-type worms elongated body length close to lon mutants. In male sensory ray patterning, lack of cet-1 function results in ray fusions. Epistasis analysis revealed that mab-21 lies downstream and is negatively regulated by the cet-1/sma pathway in the male tail. Our results show that cet-1 controls diverse biological processes during C. elegans development probably through different target genes.

TheCaenorhabditis elegansGeneunc-25Encodes Glutamic Acid Decarboxylase and Is Required for Synaptic Transmission But Not Synaptic Development

The neurotransmitter GABA has been proposed to play a role during nervous system development. We show that the Caenorhabditis elegans gene unc-25 encodes glutamic acid decarboxylase (GAD), the GABA biosynthetic enzyme. unc-25 is expressed specifically in GABAergic neurons. Null mutations in unc-25 eliminate the UNC-25 protein or alter amino acids conserved in all known GADs, result in a complete lack of GABA, and cause defects in all GABA-mediated behaviors. In unc-25 mutants the GABAergic neurons have normal axonal trajectories and synaptic connectivity, and the size and shape of synaptic vesicles are normal. The number of synaptic vesicles at GABAergic neuromuscular junctions is slightly increased. Cholinergic ventral nerve cord neurons, which innervate the same muscles as GABAergic ventral cord neurons, have normal morphology, connectivity, and synaptic vesicles. We conclude that GAD activity and GABA are not necessary for the development or maintenance of neuromuscular junctions in C. elegans.

Control of Neural Development and Function in a Thermoregulatory Network by the LIM Homeobox Genelin-11

We show here that the lin-11 LIM homeobox gene is expressed in nine classes of head, ventral cord, and tail neurons and functions at a late step in the development of a subset of these neurons. In a lin-11 null mutant, all lin-11-expressing neurons are generated. Several of these neurons, however, exhibit neuroanatomical as well as functional defects. In the lateral head ganglion, lin-11 functions in a neural network that regulates thermosensory behavior. It is expressed in the AIZ interneuron that processes high temperature input and is required for the function of AIZ in the thermoregulatory neural network. Another LIM homeobox gene, ttx-3, functions in the antagonistic thermoregulatory interneuron AIY (). Thus, distinct LIM genes specify the functions of functionally related antagonistic interneurons within a neural network dedicated for thermoregulatory processes. Both ttx-3 and lin-11 expression are maintained throughout adulthood, suggesting that these LIM homeobox genes play a role in the functional maintenance of this neural circuit. We propose that particular LIM homeobox genes specify the distinct features of functionally related neurons that generate patterned behaviors.

The auditory-vibratory sensory system ofPolysarcus denticauda (Phaneropterinae, Tettigoniidae): III. Physiology of the ventral cord neurons ascending to the head ganglia

In Polysarcus denticauda, a phaneropterine bushcricket with extremely thick uncovered tympana and an aberrant morphology of the cristae acusticae of the complex tibial organs, the electrophysiology of the auditory-vibratory ventral cord neurons ascending to the brain was investigated. Although the receptor organs in this species have some extraordinary response properties, the central auditory-vibratory neurons could be basically classified into the same functional types of S-, V-, and VS- neurons previously described for other bushcricket species. However, in some details the responses of most of the S- and VS- neurons are different. The S-neurons are generally more tonic and the VS-neurons give smaller responses to airborne sound stimulation than do the neurons belonging to the same functional types in most other bushcricket species. Adult males of P. denticauda use an extremely complicated and variable proclamation song for intraspecific acoustic communication. The song, which is often broadcast for a long time, can be divided into three phases on the basis of its time-amplitude structure. The syllable sequence exhibits some constant and other highly variable parameters. The basic, repeated element of the proclamation song is a pair of syllables; both syllables in the pair differ in duration and amplitude as well as in repetition rate between the three phases. When P. denticauda was stimulated with the conspecific male song, the responses of most S-neurons were found to copy the time patterns relatively well. Some of the V- and VS-neurons also responded relatively well to the syllables when vibrational signals were presented simultaneously. However, under these conditions the time structure was not copied, as it was by the S-neurons. In comparative investigations, the responses of central neurons of Decticus albifrons and Tettigonia viridissima, two species with more simply constructed songs having either low or high repetition rates, reflect the parameters of the song of P. denticauda less well than do the central neurons of P. denticauda. Therefore, some physiological adaptations to this complex male proclamation song seem to be inherent in the reactions of these central neurons in P. denticauda. J. Exp. Zool. 279:9–28, 1997.© 1997 Wiley-Liss, Inc.

The Embryonic Central Nervous System Lineages ofDrosophila melanogaster: I. Neuroblast Lineages Derived from the Ventral Half of the Neuroectoderm

Central nervous system development inDrosophilastarts with the delamination from the neuroectoderm of about 30 neuroblasts (NBs) per hemisegment. Understanding the mechanisms leading to the specification of the individual NBs and their progeny requires the identification of their lineages. Here we describe 17 embryonic NB lineages derived from the ventral half of the neuroectoderm and we assign these lineages to identified medial and intermediate NBs. The lineages are composed of interneurons (NB 1-2, NB 2-1, MP2, NB 4-1, NB 5-1, NB 5-3, NB 6-1, NB 6-2, and NB 7-2), interneurons and motoneurons (NB 3-1, NB 3-2, NB 4-2, NB 5-2, NB 7-1, and NB 7-3), or interneurons, motoneurons, and glial cells (NB 1-1 and NB 2-2). NB 1-1, NB 2-2, and NB 3-1 form segment-specific lineages. Neuroectodermal progenitors forming NB 2-1, NB 5-1, and NB 7-3 divide while still in the ectoderm to give rise to an additional epidermoblast. Expression of segmentation genes is not lineal in the clones of NB 1-2 and NB 7-3 (engrailed), NB 1-1, NB 4-2, and NB 7-1 (even-skipped), and NB 7-1 (gooseberry-proximal). The timing of delamination for individual NBs as well as the number of their progeny is not strictly invariant. The 17 NBs produce about 200 neurons and only three glial cells, corresponding to about 70% of the estimated total number of neurons and 10% of the glial cells per thoracic and abdominal hemisegment. Previously identified neural cell types were linked to particular lineages and we introduce a systematic terminology for the ventral nerve cord neurons. The wild-type clones provide a foundation for the analysis of mutants, expression patterns, and experimental manipulations.

Partial reversal of aluminium-induced neurofibrillary degeneration by desferrioxamine in adult male rabbits.

Desferrioxamine, a chelating agent with a high affinity for aluminium, has been reported to slow the clinical progression of dementia associated with Alzheimer's disease [4]. We report here the effects of desferrioxamine treatment on aluminium-induced neurofibrillary degeneration in rabbits. Adult male New Zealand white rabbits received a single injection of aluminium-maltolate into the lateral cerebral ventricle. Three days later, one group of rabbits was treated with intramuscular injections of desferrioxamine twice daily; a second group received saline instead of desferrioxamine. Both groups were sacrificed 4 or 5 days following initiation of desferrioxamine or saline treatment. Minimal neurofibrillary degeneration was found in two of six desferrioxamine-treated rabbits, while all six rabbits treated with saline showed extensive neurofibrillary degeneration, particularly in the ventral horn of the lower spinal cord. Quantitation of the neurofibrillary degeneration in ventral horn neurons of lumbar cord revealed 30% to be affected in saline-treated animals compared to zero-affected neurons following desferrioxamine treatment. When sacrificed just 3 days after aluminium treatment, 50% of the rabbits already revealed neurofibrillary degeneration, corresponding to the time-point when desferrioxamine treatment was begun in the above animals; on quantitation, 7.5% of ventral lumbar cord neurons were involved. These findings indicate a partial reversal of aluminium-induced neurodegeneration by desferrioxamine. Delaying desferrioxamine treatment to 6 days after aluminium administration prevented any reversal of the aluminium effect; all animals had abundant neurofibrillary degeneration as well as a striking basophilic spicular deposit of calcium and argyrophilic material in the leptomeninges, lateral ventricles and brain parenchyma adjacent to these areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuronal firing patterns of organotypic rat spinal cord cultures in normal and in ACTH/alpha-MSH(4-10) analog (BIM 22015)-supplemented medium.

The spontaneous and evoked electrical patterns of spinal cord explants from 13- to 14-day old rat fetuses grown from 2 to 8 weeks in vitro were compared when fed either with a standard or with an adrenocorticotropic hormone/alpha-melanocyte stimulating hormone (4-10) analog (BIM 22015)-supplemented medium. Standard and BIM 22015-treated cultures developed similar patterns of extracellularly recorded activity which consisted of mostly phasic but also tonic discharges. The standard cultures when treated by BIM 22015 in acute experiments (100 micrograms/ml) showed a decrease in their frequency of discharges which fired in a regular tonic pattern. These effects were neither age- nor dose-dependent but were increased in Ca2+ free medium. The ventral cord neurons chronically fed with BIM 22015 showed a strongly bursting pattern resembling strychnine-induced synchronized bursts. Both these effects, inhibitory (acute) and excitatory (chronic), of the BIM upon spinal cord cultured ventral horn neurons are discussed as possible calcium-dependent phenomena.

Regeneration of the foreleg tibia and tarsi of Ephippiger ephippiger (Orthoptera: Tettigoniidae)

AbstractThe regenerative power of Ephippiger ephippiger (Tettigoniidae) after the experimental removal at hatching of both tibia and tarsi of the foreleg was investigated. The lost leg parts were successively regenerated with increasing degrees of morphological differentiation. This process has an effect on the postembryonic development because, subsequently, the first larval stage is prolonged. In adults, the regenerated limb is one‐quarter of the length of normal tibia and tarsi together, but it often has the gross morphology of a normal leg. The pattern of innervation and the distribution of receptor is completely changed, and the complex tibial organ is not reformed. The tympanic nerve is missing, and the axons of the regenerated receptor cells form new nerves that join the leg nerve.Physiological recordings of acoustic‐vibratory, ventral nerve cord neurons revealed the possibility of excitatory input from the contralateral, intact acoustic receptors. However, the magnitude of the response is not fully restored. Behavioral experiments showed that the operated animals are not able to compensate for the unilateral deprivation of sensory input and fail in localization of the conspecific song.

Responses to pure tone stimuli and model songs of ventral cord neurones of Corixa punctata Ill. (Heteroptera: Corixidae)

The hearing organs of Corixa punctata males were stimulated with pure tones and model songs. Carrier frequencies of the stimuli ranged from 1 to 3 kHz, thus covering the peak frequencies of the conspecific song spectra. The spike responses of ventral cord neurones were recorded extracellularly. Four different neurone types were found on the right (R) side of the prothoracic ganglion and were characterized as follows: (1) Threshold curves of the 1.2−2.4 1 R neurones showed a double peak of best frequency sensitivity (Fig. 1). According to stimulus carrier frequency their response saturated or reached a maximum between 10 and 25 dB above threshold (Fig. 2A). Neurones copied different stimulus durations in a phasic-tonic way (Fig. 3A). Time structure of a model song, simulating the conspecific sound emission, was faithfully copied in the frequency range between 1.6 and 2.8 kHz (Fig. 3E). Neurone's responses habituated at the repetition rate of pulse trains typical for the conspecific song; the degree of habituation was determined by the carrier frequency and sound intensity of the pulses (Fig. 6). (2) Threshold curves of the 1.6−2.4 2 R neurones showed two peaks of best sensitivity but were 7–14 dB less sensitive than the 1.6−2.4 1 R neurones (Fig. 1). They responded only with an “on”-burst of spikes irrespective of stimulus carrier frequency and stimulus duration; the response magnitude was mainly determined by stimulus intensity (Figs 2B, 3B, 4A and B). Because of fast habituation they responded only to the first pulse train in a sequence with natural repetition rate (Fig. 3F). (3) Neurones of the 2.4 1 R type responded best at frequencies between 2.0 and 2.8 kHz (Fig. 1). Their intensity/response curves were bell shaped (Fig. 2C). Prolonged responses were typical for stimuli shorter than 20 ms (Fig. 3C). Pure tone stimuli of longer duration or high pulse repetition rates, as they occur in the natural songs, inhibited responses in these neurones (Figs 3C, 4C and D, 5). A pulse locked response pattern was well expressed only to the first two pulses in a pulse train (Fig. 3G). Carrier frequency and sound intensity determined the degree of response habituation to the natural repetition rate of pulse trains (Fig. 6). (4) Neurones of the 1.0 1 R type did not exhibit special tuning to the song spectra of Corixa. They responded best to acoustic stimuli with carrier frequencies below 1.6 kHz (Fig. 1). At higher frequencies they were about 20 dB less sensitive than the three other neurones. Pure tone stimuli were copied in a phasic-tonic way (Fig. 3D).

The processing of directional vibratory signals in the ventral nerve cord ofLocusta migratoria

The ability of ventral cord neurons to code the direction of a vibration source was tested.

The role of two-tone suppression in song coding by ventral cord neurones in the cricketTeleogryllus oceanicus (Le Guillou)

1. The calling, courtship and aggression songs ofT. oceanicus have distinctive temporal patterns but their spectral compositions are very similar: the carrier frequency occurs around 4.5 kHz and harmonics occur which extend above background noise level up to at least 40 kHz (Fig. 1). 2. Units were recorded in the cervical connectives which responded to sound frequencies over the range from 1 kHz to at least 40 kHz. The sensitivities of some of the high frequency units were comparable to, or exceeded, the sensitivities of the units responding to the carrier frequencies of the species songs (Fig. 2). 3. At the level of the neck connectives, units responding to the range from 10 kHz to 40 kHz could be divided, on the basis of their prothoracic morphology and physiology, into Through Neurones and Ascending Neurones. All the recorded neurones showed two-tone suppression effects but they varied in their degree of susceptibility to suppression. Frequencies in the range 4–5 kHz were most effective in producing suppression of the responses to high frequency tones (Figs. 5, 6). 4. The two identified Ascending Neurone types had similar morphologies in the prothoracic ganglion (Fig. 3). ANA showed tonic responses to pure tones in the frequency range from 10 kHz to 40 kHz. Below 10 kHz high intensity inhibition of the response occurred and the latency increased from about 15 ms for an 18 kHz tone pulse, to about 55 ms for a 4.5 kHz tone (Fig. 4). ANB responded with 1–3 spikes to stimuli in the frequency range from 7 kHz to 40 kHz. The response latency to an 18 kHz tone pulse was about 15 ms. No responses were obtained to 50 ms stimuli in the range from 2 kHz to 7 kHz (Fig. 6). However, considerable rebound activity was produced in response to 4.5 kHz stimuli of 200 ms or more; the latency of the rebound to 200 ms stimuli was about 400 ms (Fig. 6C). 5. ANA neurones responded to the syllables of the natural songs (Fig. 7), clearly coding the temporal patterns of the three songs. Cutting the contralateral leg nerve resulted in no detectable change in the neurone's response pattern. ANB neurones responded only during the intervals between chirps and during pauses within chirps. A long period of bursting activity occurred at the end of each song sequence (i.e. 3 chirps). This rebound activity may be the result of extreme inhibition caused by the CF of the songs (Fig. 7). 6. Synthesised natural songs (Fig. 1 E) with the correct temporal parameters but filled with 4.5 kHz alone, 18 kHz alone or a combination of 18 kHz and 4.5 kHz, were produced to investigate the role of two-tone suppression phenomena in song coding. The responses of both ANA and ANB (Fig. 8) showed the interaction of excitatory and inhibitory inputs to these units during the coding of the species songs. 7. Two-tone inhibition effects are advanced as the basic mechanism for the accurate coding of temporal characteristics in the songs ofT. oceanicus. Two different strategies for the recognition of species song types in crickets are advanced.

Processing of vibratory and acoustic signals by ventral cord neurones in the cricket Gryllus campestris

The responses of single vibratory receptors and ascending ventral cord interneurones were studied extracellularly in Gryllus campestris L. The physiology of the vibration receptors resembled those found in tettigoniids and locusts. The frequency responses of the subgenual receptors provide two possible cues for central frequency discrimination: differences in mean tuning between groups of receptors in the different leg pairs and a range of receptors tuned to different frequencies within one subgenual organ. Most of the ascending vibratory interneurones were highly sensitive in either the low or high frequency range. Broadbanded neurones were less sensitive. The characteristic sensitivity peaks of these units are due mainly to receptor inputs from a particular leg pair, although most central neurones receive inputs from all 6 legs. Only one neurone type, TN1 received excitatory inputs from both auditory and vibratory receptors; its responses were greatly enhanced by the simultaneous presentation of both stimulus modes. The responses to sound stimuli of AN2, on the other hand, were inhibited by vibration. No other auditory interneurones investigated were influenced by inputs from vibration receptors. Central processing of vibratory information in the cricket is compared with that of tettigoniids and locusts.

Extracts of skeletal muscle increase neurite outgrowth and cholinergic activity of fetal rat spinal motor neurons.

A soluble extract of rat skeletal muscle increased neurite outgrowth and cholinergic activity of dissociated ventral spinal neurons in culture. The effects were concentration-dependent, saturable, and labile in the presence of heat or trypsin. The morphological enhancement was produced only by skeletal muscle extract and decreased with developmental age, whereas the cholinergic enhancement was produced by extracts of cerebral cortex and cardiac and skeletal muscle and did not change with age. These changes were specific for ventral cord neurons, but no species specificity was observed with respect to the muscle source or the neuronal target.

Non-linear analysis of the transmission of signals in the auditory system of the migratory locust Locusta migratorta

Investigations on the auditory system of the migratory locust using the system theory (i.e. the white-noise method) to determine the transfer characteristics of single auditory neurons are presented for the first time. The transfer characteristics of receptor cells and ascending ventral-cord neurons are evaluated with respect to a special test signal ("modulation signal"). The test signal determines the temporal course of the actual sound pressure of the stimulus. The use of the white-noise method has the advantage of applying only one particular test signal instead of a very large number of stimuli with varying amplitude and duration. The computational burden is within a reasonable range. The receptor cells in general show a good linear and quadratic coupling between the test signal and their responses whereas the ascending ventral-cord neurons normally do not. The responses of the receptors in contrast to the central auditory neurons depend only on the difference between the actual threshold and the sound-pressure level of the stimulus and not on the carrier frequency of the stimulus signal.

The auditory system in larvae of the migratory locust

ABSTRACT. The course and projection areas of the tympanal receptor fibres in the thoracic ventral cord were revealed by iontophoresis in the last three larval instars. There were no significant differences between the arrangement in larvae and that in adults. The threshold curves of the auditory organ of the last three instars were measured by recording summed potentials in the tympanal nerve. In the frequency range tested (1–20 kHz), larvae and adults differed only in sensitivity. More detailed information was obtained by single‐cell recordings from receptor neurones in the tympanal nerve of last instar larvae. No differences could be shown between the threshold curves, or the suprathreshold activity, of low frequency receptors of last instars and adults. However, the high frequency receptors of the last instars are far less sensitive in the frequency range above 12 kHz. This seems to depend on the different mechanical properties of the tympanum in larvae. The response patterns of some typical ventralcord neurones (G‐, K‐, B‐type) were identified by extracellular single‐cell recordings in last instar larvae. Convergence of auditory and vibratory inputs onto the G‐neurone and the B‐neurone (as is known to exist in the adult) was found in larvae in the final and penultimate instars to be causing similar response patterns.

Neurophysiology of the vibration sense in locusts and bushcrickets: The responses of ventral-cord neurones

In the locustid Locusta migratoria and the tettigoniids Decticus verrucivorus and Tettigonia cantans, comparative aspects of physiological properties of vibratory/auditory ventral-cord neurones were studied by single cell recordings. These neurones all receive inputs from both vibratory and auditory receptors. Nevertheless, they can be classified into “V neurones” responding preferentially to vibration stimuli, “VS neurones” responding to vibration and airborne sound, and “S neurones” responding preferentially to airborne sound. In every group, there are several types with different physiological properties, normally represented by one neurone on each body side. In Locusta and in the tettigoniid species, the same physiological types of vibratory/auditory neurones were found, although there are differences in the synaptic connectivity of the vibration receptors of the different legs. In Locusta, the middle leg receptors have the strongest influence on the generation of suprathreshold responses of the central neurones, whereas in the tettigoniids the receptors of the ipsilateral fore leg are the most influential. Two of the V neurones receive inputs mainly from campaniform sensilla and other low-frequency vibration receptors, the other V and VS neurones are mainly influenced by the subgenual receptors. Central information processing results in preferential responses to different frequency/intensity ranges in different neurones. Most VS neurone types show the same response characteristics (e.g. time pattern of response, habituation) either to vibration or to airborne-sound stimuli. Simultaneous presentation of both stimuli leads to qualitative changes in the response characteristics. Therefore, the co-processing of auditory and vibratory signals seems to be very important in the acoustic behaviour of grasshoppers.

The responses of ventral cord neurons of Decticus verrucivorus (L) to sound and vibration stimuli

The real time analysis of the song of D. verrucivorus recorded in the sun and shade shows that changes occur predominantly in the time parameters and not in the frequency content. Single unit recordings in the ventral nerve cord of D. verrucivorus show that all the acoustic units respond to both sound and vibration. However, on the basis of their response characteristics they may be classified as vibration (V), vibration and sound (VS) and sound (S) neurons. The responses of some of the units depend upon the degree of habituation. Single parameter processing was not observed; the characteristic frequencies of these units range across the whole of the frequency band investigated, and distinct intensity response fields were observed. Some of the V neurons were more sensitive than the receptors, and some units responded well to the species song when both sound and vibration were presented simultaneously. The source of the vibratory input is shown to be predominantly from the ipsilateral foreleg. Many of the units run together in an ‘acoustic bundle’; some run through fibres, passing from the posterior thoracic ganglia to the cervical connectives. In many cases the primary fibres projecting to these central units can be predicted from their response characteristics. An hypothesis of the mechanisms underlying conspecific song recognition at the ventral cord level is presented.

The coding of airborne-sound and vibration signals in bimodal ventral-cord neurons of the grasshopperTettigonia cantans

In grasshoppers, the auditory and vibrational senses converge on the same ventral-cord neurons. All neurons in the ventral cord that discharge impulses in response to either airborne-sound or vibration stimuli also receive synaptic inputs from the other sensory system. The latter elicit either subthreshold excitation or inhibition. The coding of the conspecific song in the responses of most ventral-cord neurons ofTettigonia cantans is considerably improved when the stimulus consists not of simulated natural sounds alone, but of such sounds together with either maintained vibration or vibration matched to the temporal structure of the song. Stridulating tettigoniids produce both airborne and substrate-conducted sound. Thus the perception of airborne sound and vibration, and their simultaneous processing in individual ventral-cord neurons, may be of fundamental importance — not only in localizing a nearby sound source, but also in facilitating the recognition of conspecific signals.

The auditory pathway in the ventral cord of the migratory locust (Locusta migratoria): Response transmission in the axons

Auditory neurons ascending to the supraesophageal ganglion from the ventral cord of the migratory locust,Locusta migratoria, were examined for alterations in the spike response during conduction in the axons. In each experiment the responses of a given neuron were recorded, with glass microcapillaries, in succession at different stations in the central nervous system. The responses were evaluated and compared by computer analysis. 1. The impulses in the auditory ventral-cord neurons pass unchanged along the main axon trunk, from the mesothoracic ganglion to the supraesophageal ganglion. Neither temporal pattern nor magnitude (impulses/stimulus) of the response is altered. 2. The responses of neurons of a given type are the same on the left and right sides of an animal. 3. The head ganglia exert no influence upon the response or its conduction in the G, B and C neurons. 4. At the points where the axons branch, various time-dependent “filtering processes” can appear, which cause the activity conducted in the side branches to differ from that in the axon trunk.