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PubMed1979

Coding of increments and decrements in stimulus intensity in single units in the cochlear nucleus of the rat.

The response of single units in the cochlear nucleus when confronted with step increments and step decrements in stimulus intensity was studied in the rat using tones that were amplitude modulated with square waves or with pseudorandom noise. Cycle histograms of the responses to tones modulated with square waves revealed that the probability of firing increased as a result of step increments in stimulus intensity for tones at characteristic frequency (CF) and that the probability of firing decreased as a result of step decrements. When two tones were presented simultaneously, one at CF and one at the unit's best inhibitory frequency (BIF), and one or the other of the tones was modulated, the modulation of the cycle histogram of the responses was greater than when only one tone was presented. Modulation of the inhibitory tone gave rise to histograms that were mirror images of the histograms of the responses to modulation of the excitatory tone. An increase in probability of firing always occurred at a faster rate than a decrease, independent of whether the increase was brought about by increase in the intensity of the excitatory tone or by a decrease in the intensity of the inhibitory tone. The cycle histograms of the responses to square wave-modulated tones and the step response estimated from the responses to tones amplitude-modulated with pseudorandom noise showed a greater similarity when the cycle histograms depicted the case of an increase in the probability of firing than when they concerned a decrease in the probability of firing.

Animals↗
PubMed1978

Internal organization of membranes at end bulbs of Held in the anteroventral cochlear nucleus.

The end of bulb of Held in the rostral ventral cochlear nucleus of the chinchilla and guinea pig was studied with the freeze-fracture technique. The end bulb has multiple, small active zones which are uniformly distributed within the calyceal portion of this terminal. Single or small groups of active zones are surrounded by enlarged channels of extracellular space often containing processes of astrocytes. Small plasmalemmal deformations occur at these active zones. The number of these deformations is thought to be indicative of exocytotic transmitter release because they are more frequent in animals fixed in a noisy environment compared to animals fixed in a quiet environment. Thus, our study provides a basis for the quantitative study of changes in transmitter secretion at a central nervous system synapse driven by a controllable natural stimulus. The postsynaptic active zone at end bulbs resembles other excitatory synapses in the central nervous system in having an aggregate of large particles on the external membrane leaflet. This junctional aggregate of particles is coextensive with the presynaptic active zone and with the postsynaptic density seen in thin sections. Several perisynaptic aggregates of particles are deployed around each active zone on the external membrane leaflet. These irregularly-shaped aggregates occur preferentially opposite the channels of enlarged extracellular space and along the edge of the end bulb and are not components of intercellular junctions or plasmalemmal contacts with cytoplasmic organelles. Although the function of the different particle aggregates on the postsynaptic membrane is not clear, our findings provide a basis for studying the factors controlling and maintaining their structure as well as more evidence that a consistent relationship exists between types of synaptic action and structure of the postsynaptic membrane.

Acoustic Stimulation↗
PubMed1983

Synaptic organization of eighth nerve afferents to cat dorsal cochlear nucleus.

The synaptic organization of eighth nerve afferents to the dorsal cochlear nucleus (DCN) of cats was studied using extracellular field potential analyses. The eighth nerve was electrically stimulated and potentials produced in the DCN characterized using single shocks, paired shocks, repetitive stimulation, and one-dimensional current source-density (CSD) analysis. Field potentials and CSD profiles were correlated with the laminated cytoarchitecture of the DCN. At least four major temporally discrete components can be identified in field potentials evoked by a single shock to the eighth nerve. The amplitude and polarity of these events depends on the layers in which they are recorded. A brief positive-negative deflection (the P1-N1) is present in all layers but is maximal in the deeper layers 3 and 4. The N1 has a peak latency of approximately 0.8 ms in these layers. The N1 in the deep layers is followed by a large negative potential, termed the N2, with a peak latency of about 1.6 ms. In the superficial layers (1 and 2), the N1 is followed by a small positive potential (the P2) occurring nearly simultaneously with the N2, Immediately following the N2 is another negative potential that is most clearly observed in layer 2. The layer 2 negative wave is termed N3 and is also identifiable on the repolarizing phase of the N2 in layers 3 and 4. The N3 in layer 2 can be followed by a positive potential, the P4. Simultaneous with the P4 is a small negative wave ion layer 1, termed the N4. The P4-N4 complex is observed in about half the recordings. Frequency-following tests indicate that both the N1 and N2 waves can follow shock trains up to 333 Hz. The N1 remains nearly constant in amplitude up to about 300 Hz and decreases as the stimulus frequency is raised to 500 Hz. The N2 decrements more rapidly than the N1 at frequencies above about 250 Hz and is considerably reduced at 500 Hz. The N2 sometimes shows an increased amplitude (by about 20-40%) between 100 and 250 Hz. A paired-shock paradigm was used to characterize further potentials. The N1 was little affected by prior stimulation for intervals greater than 5 ms. The N2 and N3 generally showed a small facilitation for shock intervals from about 7 to 30 ms, with a return to base line at longer intervals. The N4 and P4 (when present) were profoundly depressed for intervals from 7 to about 30 ms, with recovery to control values by 50 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Bicuculline, strychnine and depressant amino acid responses in the anteroventral cochlear nucleus of the cat.

Experiments were conducted in the cat anteroventral cochlear nucleus, comparing the actions of strychnine and bicuculline on amino acid-induced depression of spontaneous and evoked firing. Strychnine reduced responses induced by glycine, taurine and beta-alanine more than GABA or muscimol-induced responses. These latter responses were sensitive to bicuculline. Responses to single and paired tone bursts were not sensitive to strychnine or bicuculline applied either iontophoretically or intravenously. The results indicate that the receptors for depressant amino acids are similar to the receptors found in the cat in other brainstem and spinal cord sites, but differ from those found in the cerebellum, thalamus and cerebral cortex. The data also indicate that these amino acids are not involved either in the response to tone bursts at characteristic frequency or in the suppression of this response by a second, higher frequency tone.

Amino Acids↗
PubMed1994

A computational model with ionic conductances for the fusiform cell of the dorsal cochlear nucleus.

A computational model of a fusiform cell of the dorsal cochlear nucleus was developed. The results of model simulations are compared with the results of in vitro experimental observations obtained by other investigators. The structure of the present model is similar to that of Hodgkin-Huxley [J. Physiol. 117, 500-544 (1952)]. The model incorporates five nonlinear voltage-dependent conductances (three potassium and two sodium types) and their associated equilibrium-potential batteries, a leakage conductance, the membrane capacitance, and a current source. Model responses were obtained under both current- and voltage-clamp conditions. When a hyper- and depolarizing current sequence was applied [Manis, J. Neurosci. 10, 2338-2351 (1990)], the cell model was able to reproduce builduplike and pauserlike discharge patterns closely resembling Manis' observations. A transient "A"-type potassium conductance in the model played a major role in generating this phenomenon. The model predicts that blocking the "A" conductance should convert a builduplike or pauserlike pattern into a sustained regular pattern. A persistent sodium conductance in the model played the main role in reproducing: Spontaneous regular discharge; a discharge after a long latency under a long small (+0.025 nA) current; and nonlinear voltage-current characteristics with positive currents. Usefulness of the model can be seen as follows: (1) Several sets of experimental observations can be integrated into a common framework; (2) possible roles of different ionic conductances postulated to be present in the cell can be inferred by observing the model behavior with the conductances intact or blocked; and (3) time courses of ionic currents and conductance values obtained from the model under current- and voltage-clamp conditions can serve as predictions to be tested in future experimental studies.

Cochlea↗
PubMed1989

Responses to parallel fiber stimulation in the guinea pig dorsal cochlear nucleus in vitro.

1. Parallel fibers of the guinea pig dorsal cochlear nucleus (DCN) were electrically stimulated at the pial surface of the nucleus in a brain-slice preparation. Extracellular field potentials produced by the parallel fibers and postsynaptic cells, and the response of single units were identified and characterized. Responses were compared with those reported for stimulation of parallel fibers in the cerebellum and to those seen with electrical stimulation of the auditory nerve. 2. Stimulation of the DCN parallel fibers generates a consistent set of extracellular field potentials. In layer 1 of the DCN, a short-latency triphasic wave (P1(1)-N1(1)-P2(1)) is followed by a slower negative wave (N2(1)). The onset phase of the N2(1) often exhibits a small positive notch (P2a1). In layer 2, an initial triphasic wave (P1(2)-N1(2)-P2(2)) is followed by a short-latency negative wave (N2(2)) and a slower positive wave (P3(2)). The N1(2) is approximately coincident with the N1(1), whereas the P3(2) is coincident with N2(1). The falling phase of the P3(2) is sometimes interrupted by a brief negative deflection (N3(2)). These field potentials are similar, but not identical to those reported for parallel fiber stimulation in the cerebellum in vivo (15). These responses differ substantially from those produced in the DCN by electrical stimulation of the auditory nerve (50). 3. Low-calcium solutions and pharmacologic manipulations were used to separate pre- and postsynaptic response components in the field potential records. When the slice is bathed in a low-calcium solution the P2a1, N2(1), N2(2), P3(2), and the brief late deflections are abolished. However, the P1(1)-N1(1)-P2(1) and P1(2)-N1(2)-P2(2) remain unaffected. A similar separation of pre- and postsynaptic components can be achieved with 100 microM adenosine or 0.5 mM kynurenic acid. It is concluded that the P1(1)-M1(1)-P2(1) wave is the compound action potential of the unmyelinated parallel fibers, whereas the longer-latency field potential components are generated postsynaptically. 4. The conduction velocity of the parallel fiber volley was measured to be 0.30 m/s at the pial surface, in a line approximately parallel to the strial axis of the nucleus. Mapping experiments reveal that the spread of the P1(1)-N1(1)-P2(1) is greatest along the strial axis, and more limited in the orthogonal direction. 5. Single units were recorded in layer 2. At a distance of 500-700 microns from the stimulating electrode, the latencies of single-unit discharges fall between 2.5 and 4 ms, at the time of the N2(2).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1992

GABAA receptor antagonist bicuculline alters response properties of posteroventral cochlear nucleus neurons.

1. The role of GABAergic inhibitory inputs onto posteroventral cochlear nucleus (PVCN) neurons in the anesthetized chinchilla was investigated through iontophoretic application of the GABAA receptor agonist muscimol and the GABAA receptor antagonist bicuculline. The majority of the neurons studied displayed phasic temporal response patterns. 2. All the neurons were sensitive to bicuculline and displayed an increase in discharge rate, which was greatest during the post-onset portion of the response. Most of the tested neurons were also sensitive to muscimol, which appeared to mimic the putative effect of endogenous GABA. 3. Bicuculline reduced the average first-spike latency and the average variability of the first-spike latency. Muscimol had the opposite effect. 4. Bicuculline did not significantly alter the threshold but rather increased discharge rate at suprathreshold intensities. 5. The width of the excitatory response area was not significantly increased by application of bicuculline. The increase in discharge rate occurred within the units' excitatory response areas. 6. The shape of the rate-intensity functions was not altered by bicuculline application. 7. We conclude that GABAergic inhibitory inputs control the post-onset discharge rate of some PVCN neurons. They may suppress tonic activity, resulting in more phasic discharge patterns.

Acoustic Stimulation↗
PubMedDate not supplied

The combined correlated audiohistogram. Incorporation of the superior ventral cochlear nucleus.

The state of the spheroid cells of the superior ventral cochlear nucleus (SVCN) must be accounted for along with that of stria vascularis, hair cells, and spiral ganglion neurons in the development of the combined correlated audiohistogram in cases of sensorineural hearing loss. For the stated evaluation, transverse sections through SVCN are marked off into ventrodorsally progressive zones corresponding to the frequency levels of the audiometric chart, and the loss of spheroid cells in each level is estimated on a percentage basis. The resultant "best fit" of pattern of cell injury with audiometric curve suggests that the anatomic frequency scale of SVCN parallels the logarithmic frequency scale of the standard audiometric chart.

Aged↗
PubMed1992

Morphology of HRP-labelled cochlear nerve axons in the dorsal cochlear nucleus of the developing hamster.

To study the development of the central terminal arbors of the cochlear nerve fibers in the dorsal cochlear nucleus, horseradish peroxidase-labelled axons in young and adult hamsters were analyzed morphometrically. Brainstem slices with whole cochlear nuclei were maintained in a slice chamber and the cochlear nerve root was injected with a mixture of wheat germ agglutinin-horseradish peroxidase, horseradish peroxidase and poly-L-ornithine. The poly-L-ornithine was added to keep the injection site small; small injections resulted in only a few axons being labelled and permitted reconstruction of individual fibers. Axons underwent an initial period of ingrowth that was completed prior to the onset of hearing (postnatal day 16). After this time the morphology and area of influence of the axons remained unchanged but the nucleus continued to increase in size. Since no additional cochlear nerve axons grow into the nucleus during this period of nuclear growth, the existing axons necessarily become more widely spaced as development proceeds. These anatomical changes may contribute to the progressive narrowing of auditory cell tuning curves.

Acoustic Stimulation↗
PubMed1994

Neural processes in the dorsal cochlear nucleus of the anaesthetised cat investigated from unit responses to electrical stimulation of the auditory nerve.

Extracellular responses of dorsal cochlear nucleus single units were recorded in response to biphasic, bipolar electrical stimulation of spiral ganglion cells and their peripheral processes using a banded electrode array in the scala tympani of the barbiturate anaesthetised cat. The DCN responses to this stimulus were the result of excitatory and suppressive (including inhibitory) processes. The excitatory responses from DCN units were usually within a range of 1.8-2.8 ms and these responses were probably the result of monosynaptic input from the auditory nerve. Latencies > 2.8 ms were most likely due to activation of di- and poly-synaptic pathways from auditory nerve fibres, except that latencies between 3.5-4.75 in hearing animals could have arisen from electrophonic mechanisms. Suppression of spontaneous activity was usually long acting, lasting > 70 ms following each pulse of the pulse train, but short acting suppression with a latency of 3.5-4.75 ms and a duration of < 10 ms was occasionally observed. These suppressive responses probably resulted from synaptic inhibitory input, but neural membrane properties may have contributed. In hearing animals, excitatory latencies within the range 1.8-5.2 ms were similar for units with different response area types or different PSTH patterns in response to acoustic CF tones or noise.

Acoustic Stimulation↗
PubMed1998

Refractory properties of auditory brain-stem responses evoked by electrical stimulation of human cochlear nucleus: evidence of neural generators.

In this study of electrically-evoked auditory brain-stem responses (EABRs) elicited by cochlear nucleus stimulation, 3 waves were identified after the initial wave that is directly initiated by the electric stimulus. Varying the rate of periodic stimulation or the interval between pairs of stimuli revealed that the shorter the latency of a wave, the faster it recovered from activation (i.e. shorter refractory period). The slow recovery of the third wave and an accompanying contribution to the second wave could be accounted for by postsynaptic generation in the two medial superior olivary nuclei (MSO); the faster recovery of another contribution to the second wave by generation in an axonal tract bending around the contralateral MSO; and the fastest recovery of the first wave by another axonal pathway having larger axons. Comparison with the relative latencies and spatial distribution of an acoustically-evoked auditory brain-stem response (AABR) indicated that the third wave corresponds to wave V, the second to wave IV (called IVb), and the first to a wave that precedes wave IV (called IVa). The anatomical interpretations for the two later waves of the EABR are consistent with most of the extant data on the neural generators of AABR waves IV and V. Thus, the present data and analysis strengthen the identification of the electrically evoked responses as EABRs and provide a firmer foundation for intra-operative EABR monitoring to assist auditory brain-stem implant placement.

Brain Stem↗
PubMed2002

Removal of Ca(2+) following depolarization-evoked cytoplasmic Ca(2+) transients in freshly dissociated pyramidal neurones of the rat dorsal cochlear nucleus.

Cytoplasmic [Ca(2+)] ([Ca(2+)](i)) was measured using Fura-2 in pyramidal neurones isolated from the rat dorsal cochlear nucleus (DCN). The kinetic properties of Ca(2+) removal following K(+) depolarization-induced Ca(2+) transients were characterized by fitting exponential functions to the decay phase. The removal after small transients (<82 nM peak [Ca(2+)](i)) had monophasic time course (time constant of 6.43 +/- 0.48 s). In the cases of higher Ca(2+) transients biphasic decay was found. The early time constant decreased (from 3.09 +/- 0.26 to 1.46 +/- 0.11 s) as the peak intracellular [Ca(2+)] increased. The value of the late time constant was 18.15 +/- 1.60 s at the smallest transients, and showed less dependence on [Ca(2+)](i). Blockers of Ca(2+) uptake into intracellular stores (thapsigargin and cyclopiazonic acid) decreased the amplitude of the Ca(2+) transients and slowed their decay. La(3+) (3 mM) applied extracellularly during the declining phase dramatically changed the time course of the Ca(2+) transients as a plateau developed and persisted until the La(3+) was present. When the other Ca(2+) removal mechanisms were available, reduction of the external [Na(+)] to inhibit the Na(+)/Ca(2+) exchange resulted in a moderate increase of the time constants. It is concluded that in the isolated pyramidal neurones of the DCN the removal of Ca(2+) depends mainly on the activity of Ca(2+) pump mechanisms.

Animals↗
PubMed2006

Neonatal deafness results in degraded topographic specificity of auditory nerve projections to the cochlear nucleus in cats.

We previously examined the early postnatal maturation of the primary afferent auditory nerve projections from the cat cochlear spiral ganglion (SG) to the cochlear nucleus (CN). In normal kittens these projections exhibit clear cochleotopic organization before birth, but quantitative data showed that their topographic specificity is less precise in perinatal kittens than in adults. Normalized for CN size, projections to the anteroventral (AVCN), posteroventral (PVCN), and dorsal (DCN) subdivisions are all significantly broader in neonates than in adults. By 6-7 postnatal days, projections are proportionate to those of adults, suggesting that significant refinement occurs during the early postnatal period. The present study examined SG projections to the CN in adult cats deafened as neonates by ototoxic drug administration. The fundamental organization of the SG-to-CN projections into frequency band laminae is clearly evident despite severe auditory deprivation from birth. However, when normalized for the smaller CN size in deafened animals, projections are disproportionately broader than in controls; AVCN, PVCN, and DCN projections are 39, 26, and 48% broader, respectively, than predicted if they were precisely proportionate to projections in normal hearing animals. These findings suggest that normal auditory experience and neural activity are essential for the early postnatal development (or subsequent maintenance) of the topographic precision of SG-to-CN projections. After early deafness, the basic cochleotopic organization of the CN is established and maintained into adulthood, but the CN is severely reduced in size and the topographic specificity of primary afferent projections that underlies frequency resolution in the normal central auditory system is significantly degraded.

Animals↗
PubMed2001

The temporal representation of the delay of iterated rippled noise in the ventral cochlear nucleus of the guinea-pig.

1. We have examined the temporal discharge patterns of single units from the ventral cochlear nucleus (VCN) of anaesthetized guinea-pigs in response to iterated rippled noise (IRN). The pitch range evoked by the stimuli was from 32 to 1000 Hz. 2. Single units were classified into four groups using existing classification schemes: primary-like (PL), onset (O), sustained chopper (CS) and transient chopper (CT). For all unit types the delay of the IRN stimuli was well represented in the all-order interspike interval histograms (ISIHs). 3. A subset of the onset units (onset-chopper, OC) showed a clear preference for some delays of the IRN in their first-order interval statistics. We describe this delay preference as 'periodicity tuning'. The delay at which the pitch estimate was at its maximum was designated its best periodicity. The range of best periodicities for OC units was 3.75-13 ms (between 77 and 267 Hz). 4. The other unit types also showed enhancement of the first-order interval statistics at the delay of the IRN. The range of best periodicities was 1.4-8.8 ms (113-714 Hz) for the CT group, 2.25-10.8 ms (93-444 Hz) for the CS group and 0.5-4.6 ms (217-2000 Hz) for the PL group. 5. The correlation between the maximum interval enhancement observed in response to the IRN stimuli and the peak in the first-order ISIH in response to white noise was 0.81 for OC units, 0.72 for CS units, 0.44 for CT units and -0.15 for PL units. 6. These results demonstrate that all unit types in the VCN can enhance the representation of the delay of IRN using first-order interspike intervals (ISIs) over a range of periodicities. CS and OC units show the greatest range of best periodicities and they are well-suited to encode the delay of IRN in their first-order ISIs for a wide range of pitches.

Action Potentials↗
PubMed1995

Level dependence of cochlear nucleus onset unit responses and facilitation by second tones or broadband noise.

1. The responses of onset units in the cochlear nucleus of the anesthetized guinea pig have been measured to single tones, two-tone complexes, and broadband noise (BBN; 20-kHz bandwidth). The onset units were subdivided into three groups, onset-I (OnI), onset-L (OnL), and onset-C (OnC), on the basis of a decision tree using their peristimulus time histogram (PSTH) shape and discharge rate in response to suprathreshold best-frequency (BF) tone bursts. 2. PSTHs were constructed from responses either to single tones at a unit's BF or to BBN as a function of level. When sufficient sustained activity could be elicited from the unit, arbitrarily defined as > 100 spikes/s, a coefficient of variation (CV) was calculated; the majority were characterized by a CV that was similar to transient chopper units (0.35 < CV < 0.5). First spike latency decreased monotonically with increasing sound level. For the majority of onset units, the first spike timing was very precise. 3. BF rate-level functions recorded from OnL and OnC units did not show any signs of discharge rate saturation at the highest sound levels we have used (100-115 dB SPL). No systematic relationship was observed between the threshold at BF and the shape of the rate-level function. BBN rate-level functions were typically characterized by higher discharge rates than in response to BF tones. However, for OnI units and a minority of other onset units, there was little difference in the shape of their rate-level functions in response to BF tones or BBN. 4. The threshold of most onset units to BBN was similar to the threshold to a BF tone that had similar overall root-mean-square (RMS) energy. The BBN threshold was, on average, 5.5 dB greater than the BF threshold. This result contrasts with that found in auditory-nerve fibers recorded in the same species, with the use of an identical sound system, where the threshold to BBN was, on average, 19.4 dB higher. The mean threshold difference between BBN and BF tones for a population of chopper units recorded in the same series of experiments was 17.7 dB. The relative thresholds to BBN and BF tones indicated that the bandwidths near the onset units' BF threshold were broader than could be estimated with the use of single tones. Ten units were characterized by bimodal response areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Intracellular injection with horseradish peroxidase of physiologically characterized stellate and bushy cells in slices of mouse anteroventral cochlear nucleus.

Nissl-stained tissue from brain slice preparations of the anteroventral cochlear nucleus of the mouse resembles tissue fixed in situ. Multipolar, spherical, globular, and granule cells can be distinguished after intracellular injection with horseradish peroxidase (HRP). Stellate cells have relatively large dendritic fields; their axons have collaterals which terminate within the cochlear nuclear complex. Bushy cells have smaller dendritic fields; where they can be seen, axons have no collaterals. Granule cells have few short dendrites; their very fine axons branch close to the cell body and could be followed only for short distances. Intracellular recordings from six stellate cells labeled by intracellular injection of HRP revealed that they have linear current-voltage relationships around the resting potential and that they respond to suprathreshold depolarization with large, regularly firing action potentials. Intracellular recordings from four bushy cells, also labeled by injection of HRP, showed that these cells have nonlinear current-voltage relationships around the resting potential and that they respond to suprathreshold depolarizations with only one or two small action potentials. The anatomical and physiological features of bushy cells reduce summing in time and space and make bushy cells well suited to preserve the firing patterns of auditory nerve inputs. The anatomical and physiological features of stellate cells, in contrast, allow summing in time and space.

Animals↗
PubMed1987

Morphometric study of the anteroventral cochlear nucleus of two mouse models of presbycusis.

The dimensions and volume of the anterior ventral cochlear nucleus (AVCN), the density and number of AVCN neurons, and the size of neuronal somata nuclei (in Nissl-stained tissue) were determined in two mouse models of age-related hearing loss: the C57BL/6J strain, which undergoes progressive chronic sensorineural hearing loss with onset during young adulthood, and the CBA/J, which demonstrates only moderate hearing loss with onset late in life. Frontal and horizontal AVCN sections, as well as cochleas, were analyzed in 4 C57 age-groups (1, 7, 12, 19+ months) and in 3 CBA groups (1, 10, 22 months). Within each strain no significant changes in AVCN dimensions or volume occur with aging. In C57 mice, packing density and cell number decrease between 1 and 7 months, but remain stable thereafter, despite chronic severe hearing impairment. CBA mice show a reduction in AVCN cell number and packing density only during the second year of life. In aging C57 mice, the size of spherical and perhaps globular cells increases, whereas the size of multipolar cells tends to decrease slightly. In CBA mice, all three AVCN cell types tend to decrease in size with aging. The early cell loss and cell size increases in C57 mice are most consistent in the dorsal (high frequency) region of the AVCN. Likewise, loss of cochlear spiral ganglion cells is most pronounced in the base of the cochlea, which provides input to this region. The data indicate that aging is associated with rather different central effects, depending on AVCN cell type, cochleotopic organization, genotype, and/or the type of peripheral hearing loss involved. The C57 and CBA AVCNs also differ in several aspects irrespective of age. The volume of AVCN and number of AVCN neurons are significantly greater in C57 mice.

Animals↗
PubMed1995

The development of glycine-like immunoreactivity in the dorsal cochlear nucleus.

Both anatomical and physiological lines of evidence suggest that inhibitory influences are active early in the development of the dorsal cochlear nucleus (DCN). Data from physiological/pharmacological studies suggest that in the adult these inhibitory influences may be mediated at least in part by the neurotransmitter glycine. Using a polyclonal antibody to examine the development of glycine in the DCN, we have observed that glycine-like immunoreactive cell bodies and punctate label are present in the DCN by the day of birth in the hamster and in the kitten at least 10 days prior to birth. In contrast to the development of immunoreactivity for glutamic acid decarboxylase (GAD) (Schweitzer et al., 1993), glycine-like immunoreactivity shows a homogeneous distribution throughout the DCN from the day of birth through adulthood. In addition, glycine immunoreactivity is present earlier than GAD-immunoreactivity and is present well before these brain structures become responsive to air-borne sounds. Thus, glycine is present in the very young animal and may mediate inhibitory effects that occur early in development.

Animals↗