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PubMed1975

Statistical analysis and interpretation of the initial response of cochlear nucleus neurons to tone bursts.

1. Subject of investigation is the initial response of cochlear nucleus neurons and units presumed to be auditory nerve fibres to CF tone burst stimulation. 2. The initial response is characterized by computing the distribution of the latency of the first spike and of the duration of the first interval in the ensemble of responses to a large number of stimuli. 3. In many of the neurons the properties of both distributions appear to be related. The presumed auditory nerve fibres and spontaneously active cochlear nucleus neurons showing only activation responses to tonal stimuli (A type) exhibit irregularity in both response onset and intervals. Minimum latency and minimum first intervals are short. On the other hand, spontaneously active neurons with both activation and suppression in the response area (AS type) and silent neurons showing only activation (A(S) type) often show a more precisely timed onset of response and narrow interval distributions. In many neurons this leads to oscillations in the PSTH (chopping). In these neurons minimum latency and minimum first interval have higher values. The longer minimum latency cannot be attribute-d to longer pure time delays in these neurons. 4. The results are interpreted as speaking in favour of temporal integration as an important mechanism in many of the AS and A(S) neurons, particularly those in the DCN. The firing patterns of A neurons are thought to indicate virtual absence of this mechanism. 5. Using pure time delay estimates derived from cross-correlation functions, computed from the responses to stationary noise, an attempt is made to estimate the integration time in the cochlear and in the cochlear nucleus neurons.

Animals↗
PubMed1996

Pyramidal cells in primary auditory cortex project to cochlear nucleus in rat.

Recent work has demonstrated that the auditory cortex in rat sends direct projections to the auditory nuclei of the brainstem, including the cochlear nucleus and superior olive. To determine the cortical origin of the projections to cochlear nucleus, Fast Blue, a retrograde fluorescent tracer, was injected into the cochlear nucleus. Labeled cells in the forebrain were then studied with light microscopy and mapped. The projection was found to originate from large pyramidal neurons in layer V of primary auditory cortex. The projection was predominantly ipsilateral, and no labeled neurons were found in other cortical areas. These data imply that primary auditory cortex exerts influence over ascending auditory information at the earliest stages of the central auditory system.

Amidines↗
PubMed1987

Descending projections from the superior olivary complex to the cochlear nucleus of the cat.

Subdivisions of the cochlear nuclear complex give rise to a number of discrete projections to certain cell groups of the superior olivary complex and also received substantial descending projections from the periolivary nuclei. In the present study, we sought to determine by means of retrograde transport of horseradish peroxidase (HRP), and anterograde transport of radiolabeled protein, if the periolivary nuclei give rise to discrete projections to the various subdivisions of the cochlear nuclear complex. Following medium to large injections of HRP into the cochlear nucleus, irrespective of location, labeled cells were found in all periolivary nuclei bilaterally. In every case more than 40% of the labeled cells were found in the lateral nucleus of the trapezoid body on the same side and the ventral nucleus of the trapezoid body of both sides. Other periolivary nuclei contributing more than 5% of the total number of cells in individual cases were the contralateral lateral nucleus of the trapezoid body and the ipsilateral anterolateral and dorsal periolivary nuclei. Injections of tritiated leucine into periolivary nuclei gave rise to axonal labeling to the trapezoid body and the dorsal acoustic stria, usually bilaterally, and to terminal labeling that was widely distributed within the cochlear nuclear complex. In several cases with small injections, particularly in the lateral nucleus of the trapezoid body, the projections from the periolivary nuclei to the anteroventral and dorsal cochlear nuclei connected areas described as having similar best-frequency representation. The autoradiographic data corroborated the main results from the HRP experiments and provided additional information permitting these conclusions: the projections from the periolivary nuclei to the cochlear nuclear complex are organized tonotopically, at least in part; each periolivary nucleus (and perhaps individual cells), projects widely throughout the cochlear nuclear complex; the pattern of termination of projections from different periolivary nuclei to a given region of the cochlear nuclear complex are similar, as seen in autoradiograms, and the lateral and dorsal periolivary nuclei project mainly ipsilaterally, while the medial periolivary nuclei project bilaterally with a contralateral bias. The magnitude of these projections and their widespread distribution within the cochlear nuclear complex would suggest an important role for the descending projections in the normal functioning of the cochlear nucleus.

Acetylcholinesterase↗
PubMed2003

Investigation of the complex descending innervation of the dorsal cochlear nucleus in the rat: a transneuronal tract-tracing study using pseudorabies virus.

The afferent neuronal connections of the dorsal cochlear nucleus were investigated in rats by using a trans-synaptic retrograde tract-tracing method. The neurotropic viral tracer, the Bartha strain of the pseudorabies virus was stereotaxically injected into the dorsal cochlear nucleus, ipsilaterally. Neurons, which project directly or indirectly (one or multiple relays by other neurons) to the dorsal cochlear nucleus were infected and visualized by immunohistochemistry. Labeled neurons were found in each components of the auditory pathway, some of the monoaminergic cell groups in the lower brainstem, the hypothalamus and in some limbic areas.

Animals↗
PubMedDate not supplied

Pathways from auditory cortex to the cochlear nucleus in guinea pigs.

The inferior colliculus (IC) and superior olivary complex (SOC) are important sources of descending pathways to the cochlear nucleus. The IC and SOC are also targets of direct projections from the auditory cortex but it is not known if cortical axons contact the cells that project to the cochlear nucleus. Multi-labeling techniques were used to address this question in guinea pigs. A fluorescent anterograde tracer was injected into temporal cortex to label corticofugal axons. Different fluorescent tracers were injected into one or both cochlear nuclei to label olivary and collicular cells. The brain was subsequently processed for fluorescence microscopy and the IC and SOC were examined for apparent contacts between cortical axons and retrogradely labeled cells. The results suggest that cortical axons contact cochlear nucleus-projecting cells in both IC and SOC. In both regions, contacts were more numerous on the side ipsilateral to the injected cortex. In the IC, the contacted cells projected ipsilaterally or contralaterally to the CN. In the SOC, the contacted cells projected ipsilaterally, contralaterally or bilaterally to the CN. We conclude that auditory cortex is in a position to modulate descending pathways from both the IC and SOC to the cochlear nucleus.

Animals↗
PubMed2000

Metabolism of the dorsal cochlear nucleus in rat brain slices.

In vitro brain slices of the cochlear nucleus have been used for electrophysiological and pharmacological studies. More information is needed about the extent to which the slice resembles in vivo tissue, since this affects the interpretation of results obtained from slices. In this study, some chemical parameters of the dorsal cochlear nucleus (DCN) in rat brain slices were measured and compared to the in vivo state. The activities of malate dehydrogenase and lactate dehydrogenase were reduced in some DCN layers of incubated slices compared to in vivo brain tissue. The activities of choline acetyltransferase and acetylcholinesterase were increased or unchanged in DCN layers of slices. Adenosine triphosphate (ATP) concentrations for in vivo rat DCN were similar to those of cerebellar cortex. Compared with in vivo values, ATP concentrations were decreased in the DCN of brain slices, especially in the deep layer. Vibratome-cut slices had lower ATP levels than chopper-cut slices. Compared with the in vivo data, there were large losses of aspartate, glutamate, glutamine, gamma-aminobutyrate and taurine from incubated slices. These amino acid changes within the slices correlated with the patterns of release from the slices.

Acetylcholinesterase↗
PubMed1994

Neuronal circuits associated with the output of the dorsal cochlear nucleus through fusiform cells.

1. Intracellular recordings were made from 21 anatomically identified fusiform cells in the dorsal cochlear nucleus (DCN) of mice in slices. The aim of the experiments was to dissect the synaptic responses to shocks of the auditory nerve to correlate functional characteristics with the different classes of synaptic inputs. 2. When depolarized from rest (-57 +/- 5 mV) with current pulses, fusiform cells fired regular, overshooting action potentials that were followed by two undershoots. The frequency of firing increased with the strength of injected current by between 100 and 300 spikes/s/nA. The current-voltage relationship rectified between 10 and 15 mV below the resting potential. The slopes of current-voltage relationships of fusiform cells in the range between the resting potential and 10 mV hyperpolarization indicated an average input resistance of 86 +/- 37 M omega. 3. In each of the labeled fusiform cells frequent, spontaneous inhibitory postsynaptic potentials (IPSPs) were recorded singly or in bursts. Some, but not all, IPSPs were preceded by a slowly rising excitatory postsynaptic potential (EPSP). The temporal association of spontaneous EPSPs and IPSPs suggests that they are driven by a common source, possibly granule cells. 4. Shocks to the auditory nerve evoked synaptic responses consisting of early (1 to approximately 10 ms) and late (approximately 10 to 100 ms) components. 6,7-Dinitroquinoxaline-2,3-dione (DNQX) at 20 to 40 microM eliminated all detectable excitation and all late IPSPs. Late bursts of IPSPs, therefore, are mediated through a polysynaptic pathway that includes a DNQX-sensitive stage. Strong shocks to the nerve root elicited single monosynaptic IPSPs, indicating that inhibitory interneurons have processes close to the auditory nerve. Strychnine at 0.5 microM eliminated all detectable inhibition. 6. Cuts through the posteroventral cochlear nucleus (PVCN), which severed the descending branches of auditory nerve fibers, eliminated early EPSPs and IPSPs leaving late, slowly rising EPSPs and bursts of IPSPs in responses to shocks of the auditory nerve. Late, slowly rising EPSPs and bursts of IPSPs, as well as monosynaptic IPSPs, could also be evoked by stimulating the anteroventral cochlear nucleus (AVCN). 7. Focal applications of glutamate evoked excitation and inhibition from many parts of a slice, with patterns varying among cells, indicating that fusiform cells receive inputs through several groups of interneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

[Study on the methodology of potassium channel expression in Xenopus oocytes by messenger RNA from rat cochlear nucleus].

OBJECTIVE: To study the properties of voltage-dependent ion channels expressed in Xenopus oocytes by mRNA from rat cochlear nucleus and to lay a methodological foundation for studying the changes of ion channels in auditory centre with sensorineural hearing loss. METHODS: Poly (A)+ mRNAs isolated from the rat cochlear nucleus by acid guanidinum thiocyanate-phenol-chloroform (AGPC) method and Promega's new magnesphere technique were microinjected into Xenopus laevis oocytes to express functional ion channels. Voltage clamp technique was used to record the current of voltage-dependent ion channels. RESULTS: A voltage-dependent ion channel was detected from oocytes injected with rat cochlear nucleus mRNA. The maximum amplitude of the outward current was 364 +/- 42 nA (n = 16). It was identified as transient outward potassium channel. CONCLUSION: The model set up by the test may play an important role in studying the physiology, pathology and pharmacology of auditory centre.

Animals↗
PubMed1984

The neuronal types and the distribution of 5-hydroxytryptamine and enkephalin-like immunoreactive fibers in the dorsal cochlear nucleus of the North American opossum.

The opossum dorsal cochlear nucleus is divided into four layers distinguishable either on the basis of differential distribution of neuron types or by neuropil organization. We have used Nissl, Golgi and protargol stained preparations to examine these components. Four types of neurons (excluding granule cells) are seen. The principal neurons have large cell bodies arranged in a sheet defining layer II, their apical dendrites extend dorsally to form an elaborate arbor in layer I and their basal dendrites pass ventrally into layer III. Round cells are found throughout layers I and II. Their densely packed dendritic domains feature thick spine encrusted dendrites that have many recurrent branches. Giant neurons have large perikarya scattered throughout layers III and IV and long thick dendrites that radiate throughout the nucleus. Small multipolar neurons (stellate cells) are found throughout the nucleus. The more superficial ones have small perikarya whereas those found in deeper layers tend to be large. All four layers of the nucleus may be clearly differentiated in protargol stained sections. Layer I has small, thin fibers in parallel array, layer II has a mixture of fibers with an apparent random orientation, layer III has large diameter vertically oriented fibers, and layer IV has fibers of similar diameter but deposed horizontally. Immunohistochemical techniques have been used to identify specific fiber systems in the neuropil of the dorsal cochlear nucleus. Fibers containing 5-hydroxytryptamine (5-HT) immunoreactivity were prevalent in layers I, III and IV but sparse in layer II. Fibers containing enkephalin (ENK)-immunoreactivity were prevalent in layer I and II with only a few scattered fibers in the deeper layers. Isolated clusters of 5-HT and ENK immunoreactive fibers in layer II were found around principal neuron somata; similar clusters in the deep layers were located around the somata of giant neurons. The wide distribution of 5-HT immunoreactive fibers suggests they may be involved in a general regulation of activity in this nucleus; conversely the more circumscribed distribution of ENK immunoreactive fibers would suggest a restricted involvement of this fiber system with a specific feature of information processing.

Animals↗
PubMed1999

Preferential induction of fos-like immunoreactivity in granule cells of the cochlear nucleus by acoustic stimulation in behaving rats.

Neuronal activity in the cochlear nucleus was mapped in relation to acoustic stimuli that signalled a sensory-motor response, using Fos-like immunoreactivity. Rats were trained to associate an acoustic stimulus with a reward and then to discriminate between two sounds ('learning' rats; n = 18). The same stimuli carrying no behavioural significance were pseudo-randomly presented to 'control' rats (n = 4) to differentiate stimulus related- from learning related-activity. To establish a baseline, Fos-like immunoreactivity was determined in rats (n = 2) unexposed to acoustic stimulation. The number of Fos-positive cells was significantly increased in the rats exposed to sounds ('learning' and 'control') as compared to the non-stimulated animals. This stimulus related increase of Fos-like activity in the cochlear nucleus was most prominent in a subpopulation of small neurons, whose spatial distribution corresponds to that of the granule cells. There was also an increase in the number of Fos-positive neurons of larger size, but less prominent than for the small cells. Brief exposure to sounds (30 s) was sufficient to induce Fos-like activity.

Acoustic Stimulation↗
PubMed1999

Direct innervation of identified tectothalamic neurons in the inferior colliculus by axons from the cochlear nucleus.

The present study sought to identify tectothalamic neurons in the rat inferior colliculus that receive their innervation directly from the cochlear nuclei and to identify the axons that provide the innervation. A direct projection would bypass the binaural interactions of the superior olivary complex and provide the quickest route to the neocortex. Axons, primarily from the dorsal cochlear nucleus, were labeled with anterograde transport of dextran and terminated in the central nucleus of the inferior colliculus in a laminar pattern. Most labeled axons were thin and simply branched. Other axons were thicker, gnarly, less frequently observed and probably originated from the ventral cochlear nucleus. None had concentrated endbulbs or a nest of endings. Both types of axons terminated primarily in the central nucleus and layer 3 of the external cortex. This pattern suggests that the combination of these subdivisions in the rat are equivalent to the central nucleus as defined in other species. Tectothalamic neurons in the inferior colliculus in the same animals were identified by retrograde transport from the medial geniculate body and intracellular injection of Lucifer Yellow. A number of different cell types act as tectothalamic neurons and receive contacts from cochlear nucleus axons. These include flat cells (disc-shaped), less-flat cells and stellate cells. Two innervation patterns were seen: a combination of axosomatic and axodendritic contacts, and predominantly axodendritic contacts. Both patterns were seen in the central nucleus, but axosomatic contacts were seen less often in the other subdivisions. This is the first study to show direct connections between cochlear nuclear axons and identified tectothalamic neurons. The layers of axons from cochlear nuclei may provide convergent inputs to neurons in the inferior colliculus rather than the heavy inputs from single axons typical of lower auditory nuclei. Excitatory synapses made by axons from the cochlear nuclei on tectothalamic neurons may provide a substrate for rapid transmission of monaural information to the medial geniculate body.

Animals↗
PubMed1995

Somatosensory effects on neurons in dorsal cochlear nucleus.

1. Single units and evoked potentials were recorded in dorsal cochlear nucleus (DCN) in response to electrical stimulation of the somatosensory dorsal column and spinal trigeminal nuclei (together called MSN for medullary somatosensory nuclei) and for tactile somatosensory stimuli. Recordings were from paralyzed decerebrate cats. 2. DCN principal cells (type IV units) were strongly inhibited by electrical stimulation (single 50-microA bipolar pulse) in MSN or by somatosensory stimulation. Units recorded in the fusiform cell and deep layers of DCN were inhibited, suggesting that the inhibition affects both types of principal cells (i.e., both fusiform and giant cells). 3. Interneurons (type II units) that inhibit principal cells were only weakly inhibited by electrical stimulation and were never excited, demonstrating that the inhibitory effect on principal cells does not pass through the type II circuit. In the vicinity of the DCN/PVCN (posteroventral cochlear nucleus) boundary, units were encountered that were excited by electrical stimulation in MSN; some of these neurons responded to sound, and some did not. Their response properties are consistent with the hypothesis that they are deep-layer inhibitory interneurons conveying somatosensory information to the DCN. 4. Analysis of the evoked potentials produced by electrical stimulation in MSN suggests that the somatosensory inputs activate the granule cell system of the DCN molecular layer. A model based on previous work by Klee and Rall was used to show that the distribution of evoked potentials in DCN can be explained as resulting from radial currents produced in the DCN molecular and fusiform-cell layers by synchronous activation of granule cells inputs to fusiform and cartwheel cells. Current-source density analysis of the evoked potentials is consistent with this model. Thus molecular layer interneurons (cartwheel and stellate cells) are a second possible source of inhibition to principal cells. 5. With lower stimulus levels (20 microA) and pulse-pair stimuli (50- to 100-ms interstimulus interval), three components of the inhibitory response can be recognized in both fusiform cell layer and deep layer type IV units: a short-latency inhibition that begins before the start of the evoked potential; a longer-latency inhibition whose timing corresponds to the evoked potential; and an excitatory component that occurs on the rising phase of the evoked potential. The excitatory component is usually overwhelmed by the inhibitory components and could be derived from granule cell inputs; the long-latency inhibitory component could be derived from cartwheel cells or the hypothesized deep-layer inhibitory interneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Responses of ventral cochlear nucleus onset and chopper units as a function of signal bandwidth.

1. The responses of units in the ventral cochlear nucleus in anesthetized guinea pigs have been measured to best-frequency tones, noise bands geometrically centered around the unit best frequency, and noise bands asymmetrically positioned around the best frequency. 2. Each unit isolated was characterized using peristimulus time histograms (PSTHs) to best-frequency tones at 20 and 50 dB suprathreshold, frequency-intensity response areas and rate-versus-level functions in response to best-frequency tones and wideband noise. The data reported here are derived from full analyses of 5 chopper units and 17 onset units. The onsets were divided into onset-I (OnI), onset-L (OnL), and onset-C (OnC) by the criteria described by Winter and Palmer: the PSTHs of OnI units show only an onset response, OnL units respond with a single spike at onset followed by a low level of sustained activity, and OnC units have PSTHs with one to four onset peaks and low levels of sustained discharge. 3. In response to geometrically centered noise bands of constant spectral density, the discharge of chopper units and one OnI unit increased over a relatively narrow range of bandwidths, corresponding to the equivalent rectangular bandwidth calculated from their response area, and then became constant. In contrast, OnL and OnC units showed increases in discharge rate with noise bandwidth over very wide ranges of bandwidth. The growth of the discharge rate with noise bandwidth was approximately linear on double logarithmic axes and therefore could be described by a power function with an exponent of 0.37. This relation held even for noise levels near threshold. 4. When noise bands with constant spectral density (at the input to the earphone) were presented with one edge fixed at the unit's best frequency, the discharge rate of most chopper units and the one OnI unit increased over a narrow range of bandwidths and then became constant. This pattern was observed irrespective of whether the second edge of the noise was progressively increased above, or decreased below, the best frequency. For two of the chopper units, in which lateral inhibitory sidebands could be demonstrated, increasing the noise bandwidth led first to increases and then to decreases in the discharge rate as the noise energy impinged upon the sideband. The chopper units act like energy detectors with a filter corresponding to their single tone response area, but, for some units, with the addition of inhibitory sidebands. 5. For the OnL and OnC units, increasing the noise bandwidth above or below best frequency caused progressive increases in the discharge rate over wide ranges of bandwidth. These increases occurred even for low noise spectral densities. The growth in discharge rate for these onset units was well fitted at all spectral density levels by power functions: one above best frequency and one below. At levels of the noise 40 dB above the unit threshold, the point at which the discharge rate reached 90% of its maximum was, on average, about 2 octaves below best frequency and 1 octave above. For some onset units, changes in the discharge rate were seen as the noise bandwidth was varied over about 14 kHz, which is about one-third of the total frequency hearing range of the guinea pig. 6. The data for onset units is consistent with the hypothesis that onset units in the ventral cochlear nucleus achieve their precision in the temporal domain by integration of the inputs from auditory nerve fibers with a wide range of best frequencies. The range of frequency over which onset units integrate frequency matches that of the inhibitory input to dorsal cochlear nucleus neurons, suggesting a possible role as an inhibitory interneuron.

Acoustic Stimulation↗
PubMed1996

Membrane properties of complex spike firing neurons of the mouse dorsal cochlear nucleus in vitro.

Intracellular recordings were made from complex spike firing neurons of the mouse dorsal cochlear nucleus (DCN) in vitro. The whole cochlear nucleus was dissected out and maintained submerged in rapidly flowing artificial cerebrospinal fluid (CSF). Recordings were made with current clamp techniques in the presence or absence of ion channel blocking drugs tetrodotoxin (TTX, 1 microM), tetraethylammonium (TEA, 20 mM), 4-aminopyridine (4-AP, 5 mM) or verapamil (50, 100, 150, 250 microM). The cells showed both spontaneous firing and responses to injections of depolarising current consisting of a mixture of a tall single action potential and complexes of 2 to 3 smaller wider action potentials superimposed on a plateau depolarisation. The membrane properties were: resting membrane potential -68.8 +/- 8.5 mV, cell resistance 54.1 +/- 26.5 M omega, time constant 9.6 +/- 5.4 ms and capacitance 0.25 +/- 0.5 nF; the first three variables had bimodel distributions. The current/voltage (I/V) relationship at membrane below resting was non-linear. Previously published histological evidence from the mouse DCN has shown that both cartwheel cells and Purkinje-like neurons are present. Both DCN cartwheel cells and cerebellar Purkinje cells are known to fire both tall single action potentials and complexes of smaller wider action potentials. It is therefore possible that the recordings shown here were made from these neuron types. TTX (1 microM) abolished both the tall single and the complexes of smaller action potentials, suggesting that the tall single action potentials are sodium dependent and possibly that a TTX sensitive sodium channel is responsible for the plateau as is suggested for Purkinje cells in the cerebellum. Verapamil (100 microM) abolished only the complex action potentials and the plateau leaving the tall narrow action potentials intact, which is consistent with the smaller complexes being calcium dependent. Higher concentrations abolished all spiking activity. TEA and 4-AP used separately both caused marked depolarisation to around -20 mV, suggesting that there is a large potassium current active at and near resting.

4-Aminopyridine↗
PubMed2006

Cells in auditory cortex that project to the cochlear nucleus in guinea pigs.

Fluorescent retrograde tracers were used to identify the cells in auditory cortex that project directly to the cochlear nucleus (CN). Following injection of a tracer into the CN, cells were labeled bilaterally in primary auditory cortex and the dorsocaudal auditory field as well as several surrounding fields. On both sides, the cells were limited to layer V. The size of labeled cell bodies varied considerably, suggesting that different cell types may project to the CN. Cells ranging from small to medium in size were present bilaterally, whereas the largest cells were labeled only ipsilaterally. In optimal cases, the extent of dendritic labeling was sufficient to identify the morphologic class. Many cells had an apical dendrite that could be traced to a terminal tuft in layer I. Such "tufted" pyramidal cells were identified both ipsilateral and contralateral to the injected CN. The results suggest that the direct pathway from auditory cortex to the cochlear nucleus is substantial and is likely to play a role in modulating the way the cochlear nucleus processes acoustic stimuli.

Animals↗
PubMed1998

Accessing the tonotopic organization of the ventral cochlear nucleus by intranuclear microstimulation.

This study is part of a program to develop an auditory prosthesis for the profoundly deaf, based on multichannel microstimulation in the cochlear nucleus. The functionality of such a device is dependent on its ability to access the tonotopic axis of the human ventral cochlear nucleus in an orderly fashion. In these studies, we utilized the homologies between the human and feline ventral cochlear nuclei and the known tonotopic organization of the central nucleus of the inferior colliculus (IC). In anesthetized cats, stimuli were delivered to three or four locations along the dorsal-to-ventral axis of the posteroventral cochlear nucleus (PVCN), and for each stimulus location, we recorded the multiunit neuronal activity and the field potentials at 20 or more locations along the dorsolateral-ventromedial (tonotopic) axis of the IC. The current source-sink density (CSD), which delimits regions of neuronal activity, was computed from the sequence of field potentials recorded along this axis. The multiunit activity and the CSD analysis both showed that the tonotopic organization of the PVCN can be accessed in an orderly manner by intranuclear microstimulation in several regions of the PVCN, using the range of stimulus pulse amplitudes that have been shown in previous studies to be noninjurious during prolonged intranuclear microstimulation via chronically implanted microelectrodes. We discuss the applicability of these findings to the design of clinical auditory prostheses for implantation into the human cochlear nucleus.

Action Potentials↗
PubMed2002

Neural adaptation to pulsatile acoustical stimulation in the cochlear nucleus of the rat.

This study, carried out in adult Long-Evans rats, was designed to investigate the adaptive properties of the cochlear nucleus to pulsatile acoustical stimuli. To achieve this purpose, near-field evoked potentials were picked up from the ventral cochlear nucleus in awake animals. Individual auditory thresholds were measured and responses to 250 ms trains of repetitive clicks with pulse rates ranging from 100 to 2000 pulses per second were collected. The amplitude of the first negative (N(1)) component of the evoked potentials to consecutive individual pulses in the train was measured by using a subtraction method. As expected, a rapid amplitude decrement of the responses in the train was obtained and a three phase adaptation was described. The decrease of individual N(1) component amplitude was fitted for each rate of stimulation with exponential decrease equations and time constants were calculated. Such an analysis allowed us to characterize three distinct adaptive processes which were discussed. The results were comparable to those obtained in previous studies in the auditory nerve and suggest that the adaptation recorded in the ventral cochlear nucleus by using near-field evoked potentials reflects the adaptive properties of auditory nerve fibers.

Acoustic Stimulation↗