Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cochlear Nucleus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources
PubMed2003

The projection from auditory cortex to cochlear nucleus in guinea pigs: an in vivo anatomical and in vitro electrophysiological study.

Previous anatomical experiments have demonstrated the existence of a direct, bilateral projection from the auditory cortex (AC) to the cochlear nucleus (CN). However, the precise relationship between the origin of the projection in the AC and the distribution of axon terminals in the CN is not known. Moreover, the influence of this projection on CN principal cells has not been studied before. The aim of the present study was two-fold. First, to extend the anatomical data by tracing anterogradely the distribution of cortical axons in the CN by means of restricted injections of biotinylated dextran amine (BDA) in physiologically characterized sites in the AC. Second, in an in vitro isolated whole brain preparation (IWB), to assess the effect of electrical stimulation of the AC on CN principal cells from which intracellular recordings were derived. BDA injections in the tonotopically organized primary auditory cortex and dorsocaudal auditory field at high and low best frequency (BF) sites resulted in a consistent axonal labeling in the ipsilateral CN of all injected animals. In addition, fewer labeled terminals were observed in the contralateral CN, but only in the animals subjected to injections in low BF region. The axon terminal fields consisting of boutons en passant or terminaux were found in the superficial granule cell layer and, to a smaller extent, in the three CN subdivisions. No axonal labeling was seen in the CN as result of BDA injection in the secondary auditory area (dorsocaudal belt). In the IWB, the effects of ipsilateral AC stimulation were tested in a population of 52 intracellulary recorded and stained CN principal neurons, distributed in the three CN subdivisions. Stimulation of the AC evoked slow late excitatory postsynaptic potentials (EPSPs) in only two cells located in the dorsal CN. The EPSPs were induced in a giant and a pyramidal cell at latencies of 20 ms and 33 ms, respectively, suggesting involvement of polysynaptic circuits. These findings are consistent with anatomical data showing sparse projections from the AC to the CN and indicate a limited modulatory action of the AC on CN principal cells.

Animals↗
PubMed1982

Influence of neonatal cochlear removal on the development of mouse cochlear nucleus: II. Dendritic morphometry of its neurons.

Right cochleae were aspirated from 6-day-old mice to determine the influence of cochlear integrity on the dendritic development of neurons within cochlear nucleus (CN). At 45 days of age, cochlear destruction was confirmed histologically and the brains were stained by the Golgi-Cox method to permit dendritic morphometry in CN ipsilateral (deafferented) and contralateral (normal) to the neonatally lesioned cochleae. The dendritic field cross-sectional area of ventral CN bushy cells was reduced on the deafferented side, as was the total dendritic length of stellate cells throughout ventral and dorsal CN. The neonatal deafferentation had no statistically significant effect on the total dendritic length of those dorsal CN fusiform cells that developed. These dendritic changes are interpreted as lack of development due to the loss of auditory nerve afferents during a critical period of development and indicate that any congenital pathology that compromises the cochlear sensorineural structures may lead to central auditory abnormalities as well.

Animals↗
PubMed1999

[The effects of substance P antibody on tuning curve of auditory evoked potential of cochlear nucleus and inferior colliculus in guinea pigs].

OBJECTIVE: To explore the effects of substance P on the frequency analysis of sound signals in the auditory brainstem. METHODS: The electrodes were implanted into the cochlear nucleus (CN) and the inferior colliculus (IC) of guinea pigs. The auditory evoked potential in CN (CN-AEP) and IC (IC-AEP) was recorded with tone pip stimulation and tone burst forward masking techniques. The Q10 dB values of the tuning curves were compared between the CN-AEP and IC-AEP after injection of SP antibody or rabbit serum with the same dosage (used as control) into the nucleus. RESULTS: After injection of SP antibody, the Q10 dB values of the tuning curves of CN-AEP and IC-AEP had no significant changes in 1 kHz and 2 kHz probe tone groups. When probe tone frequencies were 4 kHz and 6 kHz, there was a significant difference between the two frequency groups in Q10 dB. In addition, the higher frequency slope and lower frequency slope value had corresponding changes. CONCLUSION: The results imply that SP could act as a neuromediator in the auditory afferent system and participated in the high frequency analysis in the auditory brainstem.

Acoustic Stimulation↗
PubMed2004

Separate projections from the inferior colliculus to the cochlear nucleus and thalamus in guinea pigs.

We used multiple-labeling techniques with retrograde fluorescent tracers to determine whether individual cells in the inferior colliculus project to the medial geniculate body (MG) and the cochlear nucleus (CN) in guinea pigs. Four possible projection patterns were examined: (1) to ipsilateral MG and ipsilateral CN; (2) to ipsilateral MG and contralateral CN; (3) to contralateral MG and ipsilateral CN; and, (4) to contralateral MG and contralateral CN. Following injections of different tracers into two or more sites, no inferior collicular cells were double-labeled from the two contralateral targets and only a few cells were double-labeled from each of the other pairs of targets. The double-labeled cells always totaled < 1% of the single-labeled populations. We conclude that collateral projections from the inferior colliculus to the MG and CN are virtually non-existent. Therefore, the ascending and descending projections to these targets arise from different cells. These cells could potentially receive different inputs and send different information to higher or lower centers of the auditory pathway.

Animals↗
PubMed2004

Ventral cochlear nucleus coding of voice onset time in naturally spoken syllables.

These experiments examined the coding of the voice onset time (VOT) of six naturally spoken syllables, presented at a number of intensities, by ventral cochlear nucleus (VCN) neurons in rats anesthetized with urethane. VOT is one of the cues for the identification of a stop consonant, and is defined by the interval between stop release and the first glottal pulse that marks the onset of voicing associated with a vowel. The syllables presented (/bot/, /dot/, /got/, /pot/, /tot/, /kot/) each had a different VOT, ranging between 10 and 108 ms. Extracellular recordings were made from single neurons (N=202) with a wide range of best frequencies (BFs; 0.66-10 kHz) that represented the major VCN response types - primary-like (67.8% of sample), chopper (19.8%), and onset (12.4%) neurons. The different VOTs of the syllables were accurately reflected in sharp, precisely timed, and statistically significant changes in average discharge rate in all cell types, as well as the entire VCN sample. The prominence of the response to stop release and voice onset, and the level of activity prior to the VOT, were influenced by syllable intensity and the spectrum of stop release, as well as cell BF and type. Our results suggest that the responses of VCN cells with BFs above the first formant frequency are dominated by their sensitivity to the onsets of broadband events in speech, and allows them to convey accurate information about a syllable's VOT.

Acoustic Stimulation↗
PubMed1997

Linear and nonlinear spectral integration in type IV neurons of the dorsal cochlear nucleus. II. Predicting responses with the use of nonlinear models.

Two nonlinear modeling methods were used to characterize the input/output relationships of type IV units, which are one principal cell type in the dorsal cochlear nucleus (DCN). In both cases, the goal was to derive predictive models, i.e., models that could predict the responses to other stimuli. In one method, frequency integration was estimated from response maps derived from single tones and simultaneous pairs of tones presented over a range of frequencies. This model combined linear integration of energy across frequency and nonlinear interactions of energy at different frequencies. The model was used to predict responses to noisebands with varying width and center frequency. In almost all cases, predictions using two-tone interactions were better than linear predictions based on single-tone responses only. In about half the cases, reasonable quantitative fits were achieved. The fits were best for noisebands with narrow bandwidth and low sound levels. In the second nonlinear method, the spectrotemporal receptive field (STRF) was derived from responses to broadband stimuli. The STRF could account for some qualitative features of the responses to broad noisebands and spectral notches embedded in broad noisebands. Quantitatively, however, the STRFs failed to predict the responses of type IV units even to simple broadband noise stimuli. For narrowband stimuli, the STRF failed to predict even qualitative features (such as excitatory and inhibitory frequency bands). The responses of DCN type IV units presumably result from interactions of two inhibitory sources, a strong one that is preferentially activated by narrowband stimuli and a weaker one that is preferentially activated by broadband stimuli. The results presented here suggest that the STRF measures effects related to the broadband inhibition, whereas two-tone interactions measure mostly effects related to narrowband inhibition. This explains why models based on two-tone interactions predict the responses to narrow noisebands much better then models based on STRFs. It is concluded that a minimal stimulus set for characterizing type IV units must contain both broadband and narrowband stimuli, because each stimulus class by itself activates only partially the integration mechanisms that shape the responses of type IV units. Similar conclusions are expected to hold in other parts of the auditory system: when characterizing a complex auditory unit, it is necessary to use a range of stimuli to ensure that all integration mechanisms are activated.

Acoustic Stimulation↗
PubMed1994

Enhancement of neural synchronization in the anteroventral cochlear nucleus. II. Responses in the tuning curve tail.

1. Discharges of neurons in the peripheral auditory system contain information about the temporal features of acoustic stimuli. Phase-locking of neurons in the anteroventral cochlear nucleus (AVCN) is usually reported to be less robust than in auditory nerve (AN) fibers, which provide their major input. In a companion paper we reported that some cells in AVCN of the cat show enhanced phase-locking compared with the AN when stimulated at the frequency to which they are most sensitive [characteristic frequency (CF)]. We called neurons "high-sync" when they showed vector strengths (R, a measure of phase-locking) > or = 0.9. Here we report phase-locking properties to stimuli at frequencies below CF. 2. Horseradish peroxidase-filled glass micropipettes or metal microelectrodes were inserted into the trapezoid body (TB), which is the large output tract of the AVCN. Acoustically driven fibers were classified on the basis of the shape of the poststimulus time (PST) histograms to short tone bursts at CF. We then presented low-frequency tones of increasing SPL and determined the maximum R value at 500 Hz (R500) for each fiber. Using the same experimental protocol we studied phase-locking in the ANs of two animals because maximal R values at the tuning curve tail have not been reported for AN fibers. 3. Although phase-locking in AN fibers is usually assumed to be independent of CF, we found that fibers with CF > 2 kHz tended to have higher R500 values than fibers with CF < or = 2 kHz. Moreover, R500 was > or = 0.9 in 20% (42 of 196) of the fibers studied and could be as high as 0.95. This population of fibers was defined as having "high-sync tails" and consisted almost entirely of fibers with low or medium spontaneous rate. 4. High-CF TB fibers stimulated at 500 Hz showed very high phase-locking. High-sync tails (R500 > or = 0.9) were found in 41 of 70 TB fibers. For a subset of these fibers (1/3 in total: 23 of 70) phase-locking was higher than is ever observed in the AN (R500 > or = 0.95); these fibers were defined as showing synchronization "enhancement." Virtually all fibers showing synchronization enhancement had primary-like-with-notch (PLN) PST histograms. Chopper and primary-like fibers showed high-sync tails for CFs > 3 kHz. 5. Synchronization filter functions were obtained for high-CF AN fibers by determining maximum synchronization for a range of stimuli below CF.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Marginal shell of the anteroventral cochlear nucleus: intensity coding in single units of the unanesthetized, decerebrate cat.

Single units were recorded in the marginal shell (38 units in 10 cats) and central core (62 units in 15 cats) of the anteroventral cochlear nucleus (AVCN) in unanesthetized decerebrate cats. The recording sites of the shell units were verified in reconstructed electrode tracks, and those of the core units were verified for 18 units and based on the recording depth for 44 units. There was a substantial presence of strongly driven units in the AVCN shell exhibiting non-saturating rate-level functions to pure tone, noise or both with dynamic ranges as wide as 89 dB. This finding supports a hypothesis that the AVCN shell may play a role in encoding acoustic stimulus intensity. The AVCN shell and core populations were different as follows. The shell population had more units which had wide dynamic ranges, low spontaneous rates (SRs) or were acoustically weakly or not driven than the core population. These differences were statistically significant (P < 0.001, Fisher's exact test).

Animals↗
PubMed1985

Electron microscopic features of physiologically characterized, HRP-labeled fusiform cells in the cat dorsal cochlear nucleus.

We report on the anatomy and physiology of three fusiform cells in the dorsal cochlear nucleus (DCN) of the cat. The extra- and intracellular responses of these cells to pure tones showed features typical of the cell type. Peristimulus time histograms (PSTHs) were usually of the pauser or buildup configuration with chopping behavior noted in certain instances. Intracellular records during stimulus presentations revealed sustained depolarizations for the duration of the tone followed by a prolonged after-hyperpolarization (AHP). On rare occasions, a hyperpolarization corresponding to the pause region of the PSTH was noted. Occasionally, a stimulus-induced depolarization would be maintained after stimulus offset. Rebound excitation was also observed after the AHP. Morphologically, all three cells showed the standard fusiform cell features at the light microscopic level. The cell body gave rise to apical and basal dendritic trees. The apical tree branched frequently and displayed numerous spines distally. The basal tree had fewer branches and fewer, more irregular appendages. The axon originated from the cell body and gave rise to one or more collaterals before leaving the nucleus via the dorsal acoustic stria (DAS). At the electron microscopic (EM) level, the axon collaterals may terminate on a variety of cell types in the DCN, including fusiform cells. Their vesicles are round and the terminals closely resemble many unlabeled terminals seen on the cell body and apical and basal dendrites of our labeled fusiform cells. Terminals containing round vesicles, believed to be eighth nerve terminals, were found, with one exception, only on the basal dendrites. The spine-laden, distal apical dendrites received primarily terminals containing round vesicles, presumed to originate from the unmyelinated axons of granule cells. The cell body and unmyelinated initial segment received mostly terminals containing pleomorphic and flat vesicles, which also made up a large percentage of the dendritic input. Some relevant correlations, between the distribution of synaptic terminals and the observed physiology, may be possible.

Acoustic Stimulation↗
PubMed2005

Synaptic influences of pontine nuclei on cochlear nucleus cells.

Using the in vitro isolated whole brain preparation of the guinea pig, we tested the synaptic effects induced by the stimulation of pontine nuclei (PN) in intracellularly recorded and stained principal cells of the cochlear nucleus (CN). Twenty percent of the recorded cells in all CN subdivisions responded to stimulation of either ipsilateral or contralateral PN, and 12% of the cells exhibited convergence of inputs from both sides. The responses were recorded only in stellate cells of the ventral CN and in the pyramidal cells of the dorsal CN, whereas no responses were observed in bushy, octopus, and giant cells. PN stimulation produced excitatory and inhibitory postsynaptic potentials as well as mixed responses. The heterogeneous nature and the wide latency range (3.2-18 ms) of observed responses suggest significant variability in the underlying synaptic mechanisms and the implicated pathways. We propose that PN projections to the CN, terminating mainly in the granule cell domain (GCD), together with other non-auditory and auditory inputs contribute to multimodal convergence in the GCD leading ultimately to modulatory actions on the output activity of CN principal cells.

Animals↗
PubMed1997

Model calculations of the effects of wide-band inhibitors in the dorsal cochlear nucleus.

In two previous papers [Reed and Blum, J. Acoust. Soc. Am. 97, 425-438 (1995), Blum et al., J. Acoust. Soc. Am. 98, 181-191 (1995)] a computational model for signal processing in the dorsal cochlear nucleus (DCN) was developed. In those modelling studies, stellate cells inhibited only type II cells. In this study, the effect of including wide-band inhibitory (WBI) connections from stellate cells to type IV cells, as proposed by Nelken and Young [J. Neurophysiol. 71, 2446-2462 (1994)], is examined. Inclusion of the WBI connections improves the fit to the experimental pure tone response maps for both the "standard" and "non-standard" cells examined by Spirou and Young [J. Neurophysiol. 66, 1750-1768 (1991)]. Thus, these modelling studies support the hypothesis of Nelken and Young [J. Neurophysiol. 71, 2446-2462 (1994)]. The degree of improvement is greatest for cells with prominent upper inhibitory sidebands. The qualitative features of the pure tone response map and the theoretical model allow one to deduce the probable frequency bias of the type II to type IV and stellate to type IV connections.

Acoustic Stimulation↗
PubMed1990

GABAergic inhibition upon auditory response properties of neurons in the dorsal cochlear nucleus of the rat.

It is well known that the superficial layers of the dorsal cochlear nucleus (DCN) are rich in GABAergic neurons. We investigated the effects of topical application of GABA receptor agonists and/or antagonists upon the auditory response properties of DCN neurons in rats anesthetized with alpha chloralose-urethane. Auditory stimuli consisted of 20 ms tone bursts presented in a free field. Response properties of DCN neurons were studied before and during iontophoretic application of GABA, bicuculline methiodide (BIC) and muscimol (MUS) alone and GABA with MUS or BIC through triple barrel electrodes glued to the recording microelectrode. Of 68 DCN neurons studied, 27 were sensitive to topical application of the GABA agonists or antagonist. In these neurons, BIC enhanced spontaneous activity as well as auditory responses and decreased the Q-30 quality factor values. MUS reduced auditory responses. BIC often increased the width of the turning curve but GABA and/or MUS reduced it. Without drug application, GABA sensitive neurons tended to have longer response latencies and larger tuning widths at 30 dB above threshold as well as larger Q-30 values as compared with neurons that were insensitive to GABA. These findings suggest that: 1) GABAergic neurons determine the width of the tuning curve in neurons with GABA receptors by curtailing the excitatory response area, and 2) such neurons receive tonic inhibition from intrinsic GABAergic neurons.

Acoustic Stimulation↗
PubMed1982

Influence of neonatal cochlear removal on the development of mouse cochlear nucleus: I. Number, size, and density of its neurons.

Right cochleae were aspirated from 6-day-old mice to determine the influence of cochlear integrity on the development of cochlear nucleus (CN). At 45 days of age, cochlear destruction was confirmed histologically, and the CN of unilaterally deafferented and control animals were analyzed morphometrically. The molecular, fusiform, and polymorphic layers of deafferented dorsal CN were reduced in volume, and the polymorphic layer neurons were fewer, smaller, and less dense. The octopus and multipolar cells regions in deafferented ventral CN (VCN) were smaller, and their neurons were fewer, smaller, and more densely packed. The VCN globular and small spherical cell regions were also smaller with fewer, denser, but normal-sized neurons. There were fewer VCN large spherical cells, but no change was measured in their size. The granule cell regions throughout CN were also reduced in volume. Overall, CN was reduced to 46% of its normal size and 34% of its normal neuronal numbers. These results in the mouse show that deafferentation before the onset of hearing causes more severe CN changes than those reported after adult deafferentation in other mammals and support the theory of a critical period in development when presynaptic integrity is much more important for neuronal maturation than it is for maintenance after the neuron is mature. This suggests that any congenital pathology that compromises the sensorineural structures of the cochlea may cause severe structural and functional abnormalities in the maturing central auditory nuclei.

Animals↗
PubMed1991

Distribution and origin of noradrenergic and serotonergic fibers in the cochlear nucleus and inferior colliculus of the rat.

We examined the monoaminergic innervation of the rat cochlear nucleus (CN) and the inferior colliculus (IC) by using retrograde transport of the fluorescent dye Fluoro-Gold combined with immunohistochemistry. We used antisera against the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT), and one against the transmitter serotonin (5-HT). Each substance revealed a distinct pattern of immunoreactive staining in the CN and the IC. In the CN, DBH-immunoreactive (-ir) fibers were present in all subnuclei. The molecular layer of the dorsal CN and the granular layer of the ventral CN, however, were largely devoid of DBH-ir fibers. In contrast, 5-HT-ir fibers were abundant in the molecular layer and the granular cell layer of the CN. In the dorsal CN and the postero- and anteroventral CN, however, this innervation was less dense and evenly distributed across subnuclei. In the IC, the DBH-ir fibers were slightly more numerous in layer 2 of the dorsal cortex than in other subnuclei, while the layer 1 of both the dorsal and the external cortex contained only a few fibers. In contrast, the 5-HT-ir fibers formed a dense network in both the dorsal and external cortices of the IC, while they were less abundant in the remaining subnuclei. PNMT-ir fibers were not found in any of the auditory brainstem nuclei. Following Fluoro-Gold injections into the CN or IC, retrogradely labeled DBH-ir neurons were found in the A6 noradrenergic cell group (locus coeruleus). The CN received additional projections from the A5 noradrenergic cell group, as well as sparse projections from the A4 and A7 cell groups. The serotonergic innervation of the CN and IC originated largely in the B7 serotonergic cell group (dorsal raphe nucleus). Serotonergic neurons in other groups of the raphe nuclei were only occasionally labeled. Our data indicate that both noradrenaline and serotonin may play a role in central auditory processing. Their differential distribution in the IC and CN subnuclei suggests that these transmitter systems might influence different functional circuits.

Animals↗
PubMed1994

Auditory brainstem of the ferret: long survival following cochlear removal progressively changes projections from the cochlear nucleus to the inferior colliculus.

Some effects on auditory brainstem connections of long (1-2.3 years) survival following unilateral cochlear removal in infant and adolescent ferrets were examined by making multiple injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in either the left or the right inferior colliculus (IC). Previous studies have shown that, in normal adult ferrets, about 50 times as many cochlear nucleus (CN) neurons project to the contralateral as to the ipsilateral IC. Right cochlear removal at P25 increased, within 30 days, the number of retrogradely labeled left CN neurons projecting to the left ipsilateral IC by 17% (from n = 235 to n = 275), relative to normals. In this study, longer survival (3 months to 1 year) after right cochlear removal at P25 resulted in larger increases (38-47%; n = 100) in the number of neurons labeled in the left CN after injections of WGA-HRP in the left IC. No change occurred in the number of neurons labeled in the right CN. Taken together, the results of these experiments show that the ratio of the number of labeled neurons in the left CN to that in the right CN increases progressively with survival time out to the maximum time tested (1 year). In contrast to these results, we have previously reported that right cochlear removal at P90 did not change the number of neurons projecting from the left CN to the left IC after 90 days of survival. However, in this study, very long survival (2.3 years) following right cochlear removal at P90 resulted in an increased (51%, from n = 235 to n = 355) number of left CN neurons labeled by WGA-HRP injections into the left IC, relative to normals. The increased number of labeled neurons included neurons throughout each division of the CN and all of the principal morphological types. In a separate series of experiments involving long survival (1-2 years), right cochlear removal at P25 or P40 did not significantly change the number of neurons in either CN retrogradely labeled by injections of WGA-HRP in the right IC, or the ratio between the number of neurons labeled in each CN. Long survival following cochlear removal at P25-P90 did not result in any loss of neurons in the ipsilateral CN or in any shrinkage of CN neurons further than the 10-20% seen at a shorter survival time (90 days).(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMedDate not supplied

A longitudinal study of changes in the cochlear nucleus in the CBA mouse.

The cochleas and brain stems of normal-hearing CBA/CaJ and CaH mice ranging in age from 1 to 18 months were examined by light microscopy to document normal age-related changes. At all ages examined, the cochlear morphologic structure appeared normal with no obvious loss of hair cells or spiral ganglion cells. In the cochlear nucleus, qualitative and quantitative changes were observed in the total nuclear volume, in globular cell size, and in neuronal packing density.

Aging↗
PubMed2005

Temperature affects voltage-sensitive conductances differentially in octopus cells of the mammalian cochlear nucleus.

Temperature is an important physiological variable the influence of which on macroscopic electrophysiological measurements in slices is not well documented. We show that each of three voltage-sensitive conductances of octopus cells of the mammalian ventral cochlear nucleus (VCN) is affected differently by changes in temperature. As expected, the kinetics of the currents were faster at higher than at lower temperature. Where they could be measured, time constants of activation, deactivation, and inactivation had Q10 values between 1.8 and 4.6. The magnitude of the peak conductances was differentially affected by temperature. While the peak magnitude of the high-voltage-activated K+ conductance, g(KH), was unaffected by changes in temperature, the peak of the low-voltage-activated K+ conductance, g(KL), was reduced by half when the temperature was lowered from 33 to 23 degrees C (Q10 = 2). Changing the temperature changed the kinetics and the magnitude of the hyperpolarization-activated mixed cation conductance, g(h), but the changes in magnitude were transient. The voltage sensitivity of the three conductances was unaffected by temperature. The action of temperature on these conductances is reflected in the resting potentials and in the shapes of action potentials.

Action Potentials↗
PubMed1985

Ontogeny of neural discharge patterns in the ventral cochlear nucleus of the mongolian gerbil.

Discharge patterns were recorded extracellularly from single neurons in the ventral cochlear nucleus (VCN) of Mongolian gerbils ranging in age from 10 days after birth (DAB) to adult, a period which includes the onset of responsiveness to acoustic stimulation. At 10 DAB none of the neurons encountered within the VCN responded to acoustic stimulation. At 12 DAB approximately 15% of the neurons isolated in VCN were responsive. This coincided with the earliest cochlear microphonic potentials and preceded the appearance of the cochlear compound action potential (AP) by two days. At 14 DAB, or older, the great majority of neurons isolated in VCN responded to acoustic stimulation. Most parameters of VCN neural function exhibited significant changes between 12 and 18 DAB: neural thresholds improved approximately 100 dB; mean spontaneous discharge rate increased; the high-frequency range of characteristic frequency (CF) values increased from 10.0 to 24.0 kHz; the upper limit for phase locking increased from 0.8 kHz to 3.0 kHz; dynamic range increased from 16 dB to 44 dB, and the proportion of units with well-defined initial onset peaks in their post-stimulus-time (PST) response patterns increased from 40% to 100% of units. Most of the neural parameters examined achieved adult characteristics by 18 DAB. Frequency tuning (Q10dB) matured earlier for high-CF units. The most sharply tuned neurons with high CFs (greater than 4 kHz) at 12 DAB had Q10dB values equal to those for adults. None of the neurons with low CFs (less than 4 kHz) had Q10dB values greater than 1.2 at this age. Classical 'on' PST response patterns were not seen at 12 and 14 DAB. A unique PST response type, characterized by very long latency phasic discharge, was observed only at 12 DAB. None of the VCN neurons recorded from 12 DAB subjects displayed rhythmic 'bursting' or 'pulsing' PST response patterns, as has been reported at the earliest stages of functional development in the VCN of the cat. Most units were capable of sustained discharge, even with long stimulus durations. Units with 'primary-like' PST response patterns at 12 exhibited greater variability in first spike latency and less pronounced initial rates of firing than was characteristic in adults, resulting in poorly defined onset peaks. In contrast, units with chopper PST response patterns showed well-defined onset peaks.

Animals↗