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 145 records · Page 8Linked to original sources
PubMed2003

Morphology of physiologically characterised ventral cochlear nucleus stellate cells.

Stellate cells within the ventral cochlear nucleus (VCN) are a diverse cell group that have been classified according to their size and morphology. Some of these stellate cell types constitute major projection neurones into the brainstem and directly into the inferior colliculus, while others are implicated in more local processing. It is still not clear whether a specific physiological profile is uniquely associated with each distinct type of stellate cell. To investigate such associations, we have analysed 23 units with a battery of physiological stimuli in vivo and then examined their shape and outputs following juxtacellular labelling with biocytin. Five physiologically identified groups of cells were filled. These formed two major response classes: onset cells and chopper cells. The two classes could be separated purely on morphological grounds. The onset cells had large somata, large symmetrical dendritic trees and profuse axonal branches that were restricted to the cochlear nucleus on one (On-L) or both sides (On-C) of the brainstem. The chopper cells had smaller, asymmetric, dendritic trees, which were either planar or marginal, had smaller somata and an output axon that left via the trapezoid body. We have confirmed profuse projections into the dorsal cochlear nucleus from all onset cells, and more focal projections from some members of all three groups of chopper cells.

Acoustic Stimulation↗
PubMed1984

Muscarinic receptors in the cochlear nucleus and auditory nerve of the guinea pig.

The specific-binding properties of l-[3H]quinuclidinyl benzilate, a muscarinic acetylcholine-receptor antagonist, were investigated in synaptic and other membrane preparations of the guinea pig cochlear nucleus and auditory nerve. Binding parameters for all experiments were consistent with a single binding site with a Hill coefficient of 1.0. The binding of the ligand was specific and of high affinity, with values of KD in the range of 30-80 pM. Bmax was 0.352 +/- 0.023 pmol/mg protein for the dorsal cochlear nucleus and 0.215 +/- 0.011 pmol/mg protein for the ventral cochlear nucleus. The dorsal cochlear nucleus/ventral cochlear nucleus ratio for density of muscarinic receptors (1.6/1.0) was maintained across two different buffer systems, which varied with respect to the inclusion of proteolysis inhibitors. The results for auditory nerve indicated a level of binding much below that of the cochlear nucleus, with Bmax = 0.052 +/- 0.011 pmol/mg protein. The results of specific-binding experiments for l-[3H]quinuclidinyl benzilate support a role for acetylcholine as a neurotransmitter in the cochlear nucleus. The greater density of muscarinic receptors in the dorsal cochlear nucleus may indicate greater cholinergic activity in the dorsal relative to the ventral cochlear nucleus.

Animals↗
PubMed2006

Age-related structural and functional changes in the cochlear nucleus.

Presbycusis - age-related hearing loss - is a key communication disorder and chronic medical condition of our aged population. The cochlear nucleus is the major site of projections from the auditory portion of the inner ear. Relative to other levels of the peripheral and central auditory systems, relatively few studies have been conducted examining age-related changes in the cochlear nucleus. The neurophysiological investigations suggest declines in glycine-mediated inhibition, reflected in increased firing rates in cochlear nucleus neurons from old animals relative to young adults. Biochemical investigations of glycine inhibition in the cochlear nucleus are consistent with the functional aging declines of this inhibitory neurotransmitter system that affect complex sound processing. Anatomical reductions in neurons of the cochlear nucleus and their output pathways can occur due to aging changes in the brain, as well as due to age-dependent plasticity of the cochlear nucleus in response to the age-related loss of inputs from the cochlea, particularly from the basal, high-frequency regions. Novel preventative and curative biomedical interventions in the future aimed at alleviating the hearing loss that comes with age, will likely emanate from increasing our knowledge and understanding of its neural and molecular bases. To the extent that this sensory deficit resides in the central auditory system, including the cochlear nucleus, future neural therapies will be able to improve hearing in the elderly.

Age Factors↗
PubMed1991

Cytoarchitecture of cochlear nucleus in the chinchilla.

The morphology of the cochlear nucleus in the normal, adult chinchilla, as demonstrated by Nissl staining, was examined. The cytoarchitecture was determined from sections viewed at the light microscope level. The chinchilla cochlear nucleus was found to possess most of the features reported in other mammalian cochlear nuclei. It could easily be divided into dorsal and ventral components due to an intervening layer of granule cells, and most cell types previously reported in mammals were also found in the chinchilla cochlear nucleus. A distinct distribution pattern of cell types exists within each part.

Animals↗
PubMed1994

Morphology of the cochlear nucleus in CBA/J mice with chronic, severe sensorineural cochlear pathology induced during adulthood.

The effects of chronic cochlear impairment on morphological features of the adult cochlear nucleus (CN) were assessed in CBA/J mice in which severe sensorineural damage had been induced by exposure to intense noise. Sections from various CN subdivisions, stained for Nissl substance and fibers, were quantitatively evaluated in four groups of noise-exposed mice that differed with regard to the age at noise exposure (2, 6, or 11 months), age at the time the CN was evaluated (6, 11, or 24 months), and the duration (chronicity) of sensorineural impairment (4, 5, 13, or 18 months). Like-aged, non-exposed CBA mice were used as controls, so the effects of peripheral damage and aging could be compared. Cochlear damage produced significant changes in CN subdivisions thought to receive the heaviest input from cochlear afferents (anteroventral CN, octopus cell area, dorsal CN layer III). These changes included a reduction of neuropil volume, reductions in neuron size, and increases in neuronal packing density that were complementary to reduced volume in these subdivisions. Effects on neuron number were minimal in all subdivisions. Central changes in noise-exposed mice were absent or diminished in DCN layers I and II, which receive relatively less input from primary fibers. The age at onset and chronicity of damage had little to do with the severity of central effects of cochlear damage. The effects of cochlear damage were not additive with age-related changes seen in the old controls.

Age Factors↗
PubMed1970

Centrifugal inhibitory processes affecting neurones in the cat cochlear nucleus.

1. Stimulation of the lateral part of the olivary S-segment in the cat inhibited neurones in the ipsilateral cochlear nucleus. A smaller number of neurones located in the ventral division of the cochlear nucleus were excited.2. It is suggested that inhibition in the ipsilateral cochlear nucleus may be mediated directly by fibres making synaptic connexions on the cochlear nucleus neurones, or indirectly by inhibitory fibres acting at the cochlea.3. The direct inhibitory process at the cochlear nucleus is unaffected by strychnine, whereas the inhibitory process at the cochlea is abolished by strychnine.4. A cochlear nucleus neurone can be influenced simultaneously by excitatory and inhibitory processes.

Animals↗
PubMed2005

Projections from auditory cortex contact cells in the cochlear nucleus that project to the inferior colliculus.

Anterograde and retrograde tracing techniques were combined to determine whether auditory cortical axons contact cells in the cochlear nucleus that project to the inferior colliculus. FluoroRuby or fluorescein dextran was injected into auditory cortex to label cortical axons by anterograde transport. Different fluorescent tracers (Fast Blue, FluoroGold, FluoroRuby or fluorescein dextran) were injected into one or both inferior colliculi to label cells in the cochlear nucleus. After 12-15 days, the brain was processed for fluorescence microscopy and the cochlear nuclei were examined for apparent contacts between cortical axons and retrogradely labeled cochlear nucleus cells. The results suggest that axons from the ipsilateral or contralateral cortex contact fusiform and giant cells in the dorsal cochlear nucleus and multipolar cells in the ventral cochlear nucleus that project directly to the inferior colliculus. The contacts occur on cell bodies and dendrites. The target cells in the cochlear nucleus include cells that project ipsilaterally, contralaterally or bilaterally to the inferior colliculus. The results suggest that auditory cortex is in a position to exert direct effects on the monaural pathways that ascend from the cochlear nucleus.

Animals↗
PubMed1994

Click-evoked responses from the cochlear nucleus: a study in human.

Recordings from the vicinity of the cochlear nucleus in 9 patients undergoing microvascular decompression operations to relieve hemifacial spasm, trigeminal neuralgia, tinnitus, and disabling positional vertigo were conducted by placing a monopolar electrode in the lateral recess of the fourth ventricle (through the foramen of Luschka), the floor of which is the dorsolateral surface of the dorsal cochlear nucleus. The click-evoked potentials recorded by such an electrode display a slow negative wave with a peak latency of about 6-7 msec on which several sharp peaks are superimposed. None of the peaks in the recordings from the vicinity of the cochlear nucleus coincided with any vertex-positive peaks of the brain-stem auditory evoked potentials. In recordings from the lateral aspect of the floor of the fourth ventricle near the cochlear nucleus 1 patient showed 2 positive peaks, the earliest of which had a latency close to that of peak II and the second of which had a latency close to the negative peak between peaks III and IV of the brain-stem auditory evoked potentials. There is a distinct negative peak in the responses recorded from the midline of the floor of the fourth ventricle, the latency of which is only slightly shorter than that of peak V of the brain-stem auditory evoked potentials, supporting earlier findings that the sharp tip of peak V of the brain-stem auditory evoked potentials is generated by the termination of the lateral lemniscus in the inferior colliculus.

Acoustic Stimulation↗
PubMed1998

Ultrastructural and immunocytochemical characterization of neurons in the rat ventral cochlear nucleus projecting to the inferior colliculus.

Neurons in the rat ventral cochlear nucleus which project to the inferior colliculus were identified after retrograde labelling of the neural tracer wheat germ agglutinin conjugated to horse radish peroxidase. After tracer injection into the Inferior Colliculus, electron microscopy and immunocytochemical localization of glycine, GABA and glutamate in retrograde labelled neurons were employed. In the acoustic root area and posterior ventral cochlear nucleus, most of the body surface of the neurons projecting to the inferior colliculus was 10-30% covered by axo-somatic boutons and appeared as multipolar cells of type I. These large to medium size cells with sparse stacks of ergastoplasmic cisternae organized in Nissl bodies, were heavily labelled and were the main projecting neurons to the inferior colliculus. Most of these cells were glycine and GABA negative but variably glutamate positive, suggesting that they are excitatory neurons. This result suggests the absence of an inhibitory innervation of the inferior colliculus from these cells. A few retrograde labelled, large to giant neurons showed an irregular surface, sparse short stacks of ergastoplasmic reticulum, numerous microtubules, cell bodies 60-80% covered by synaptic boutons, and they appeared as multipolar cells of type II. These cells were less strongly retrograde labelled than multipolar type I, and were occasionally glycine positive, presumably inhibitory. This suggests that at least a small caliber collateral axon stemming from these neurons can reach the inferior colliculus. Occasional glycine positive octopus cells not labelled with the tracer were also observed. The contribution of glycinergic axons to the innervation of the inferior colliculus appears therefore to by very limited. Occasional labelled cells were represented by apparently globular bushy neurons, but the weak labelling suggests that the tracer was taken up by collateral axons reaching the inferior colliculus and not by the main axon. Globular bushy cells were consistently negative for both glycine and GABA, and variably positive for glutamate. In the anteroventral cochlear nucleus, labelled multipolar type I and II showed similar immunocytological and ultrastructural characteristics to those in the posteroventral cochlear nucleus but their dimension was smaller. Cells identified as spherical bushy neurons were never retrograde labelled.

Animals↗
PubMed2006

Contralateral inhibitory and excitatory frequency response maps in the mammalian cochlear nucleus.

There is increasing evidence that the responses of single units in the mammalian cochlear nucleus can be altered by the presentation of contralateral stimuli, although the functional significance of this binaural responsiveness is unknown. To further our understanding of this phenomenon we recorded single-unit (n = 110) response maps from the cochlear nucleus (ventral and dorsal divisions) of the anaesthetized guinea pig in response to presentation of ipsilateral and contralateral pure tones. Many neurones showed no evidence of input from the contralateral ear (n = 41) but other neurones from both ventral and dorsal cochlear nucleus showed clear evidence of contralateral inhibitory input (n = 61). Inhibitory response patterns were divided into two groups. In 36 neurones, contralateral tone-evoked inhibition was closely aligned with the ipsilateral excitatory response map (+/- 0.33 octaves) often extending to low stimulus levels. In 25 neurones, higher threshold contralateral inhibitory responses were found, mostly centred at frequencies greater than 0.33 octaves below the ipsilateral excitation. A few neurones (n = 8) exhibited responses consistent with excitatory input from the contralateral ear, which was closely aligned with the ipsilateral excitation, and were found exclusively in the dorsal cochlear nucleus. The latency of the contralateral interaction was, on average, longer than the ipsilateral latency. Interaural level difference curves are similar to other reports from the cochlear nucleus. Our results are consistent with the idea that contralateral interactions arise from a variety of direct and indirect neuronal projections.

Acoustic Stimulation↗
PubMed1991

Descending projections to the dorsal and ventral divisions of the cochlear nucleus in guinea pig.

The origins of extrinsic projections to the guinea pig dorsal and ventral cochlear nuclei were identified by examining the retrograde transport of horseradish peroxidase conjugated to wheatgerm agglutinin following its injection into each of these divisions. Major projections originated in periolivary regions of the superior olivary complex, the contralateral cochlear nucleus and the inferior colliculus. There was no contribution from the nuclei of the lateral lemniscus to these pathways. The heaviest projection from the periolivary regions to both divisions of the cochlear nucleus arose bilaterally in the ventral nucleus of the trapezoid body. The ipsilateral lateral nucleus of the trapezoid body also projected heavily to dorsal and ventral cochlear nucleus. In addition, the ventral cochlear nucleus received a substantial projection from the dorsal aspect of the ipsilateral dorsomedial periolivary nucleus. Projections originating bilaterally in the central nucleus of the inferior colliculus terminated in the deep layers of dorsal cochlear nucleus. These projections appear to be more strongly ipsilateral and specific than those reported in the cat.

Animals↗
PubMed1998

[Changes of GABA immunoreactivity in aged rat cochlear nucleus].

OBJECTIVES: To detect the changes of gama-aminobutyric acid (GABA) immunoreactivity in the aged rat cochlear nucleus and to investigate its relationship with the initiation of presbycusis. METHODS: The cochlear nucleuses of adult (2-3 months) and aged (20-36 months) Wistar rats were stained with streptavidin/peroxidase (S-P) technique. GABA-positive neurons were counted with a computer-aid image analysis system. RESULTS: Most of the GABA-immunoreactive cell bodies were found in the superficial layers of the dorsal cochlear nucleus (DCN). The number of GABA-positive neurons decreased significantly in the DCN of the aged rat cochlear nucleus (P < 0.001). CONCLUSION: The reduction of GABA positive neurons in the aged rat cochlear nucleus may be related to presbycusis.

Aging↗
PubMed1998

Muscimol suppression of the dorsal cochlear nucleus impairs frequency discrimination in rats.

The cochlear nucleus is composed of three sub-nuclei: the dorsal (DCN), anteroventral (AVCN) and posteroventral cochlear nucleus (PVCN). In addition to connections between these sub-nuclei, each nucleus receives frequency specific tonotopically organised input from the cochlea. Evidence suggests that connections from the DCN to the AVCN are inhibitory and organised tonotopically but the functional significance of this pathway has yet to be elucidated. The possible role of this pathway in frequency discrimination using a T-maze behavioural paradigm and DCN suppression was examined. Five rats were trained on a two choice frequency discrimination task. Once frequency difference limens for 10-30% performance above chance were determined, rats had cannulae implanted bilaterally over the DCN. After recovery rats were tested on the behavioural task with nothing, saline and the GABA agonist muscimol injected into the DCN via the cannulae. Muscimol alone significantly reduced the rats ability to perform the task. This performance decrease was attributed to an inability to discriminate high frequency and not low frequency tones suggesting that place and not temporal coding of sound was compromised by DCN suppression. These results are consistent with the hypothesis that inhibitory drive from the DCN to AVCN may be crucial for the fine tuning of frequency information.

Acoustic Stimulation↗
PubMed1998

Muscimol suppression of the dorsal cochlear nucleus modifies frequency tuning in rats.

The cochlear nucleus is composed of three sub-nuclei: the dorsal (DCN), anteroventral (AVCN) and posteroventral cochlear nucleus (PVCN). Intrinsic connections from the DCN to the AVCN are inhibitory and organised tonotopically. In this investigation, this pathway and its possible role in frequency tuning was examined using in vivo extracellular recordings. Extracellular recordings were made from 191 units in the AVCN, 69 of which were recorded after suppression of DCN by application of the GABA agonist Muscimol (15 ng, 0.26 mM). Tuning curves were plotted and characteristic frequency (CF) and response threshold (measured in dB SPL) were determined for each unit. Units recorded post-Muscimol showed significantly broader tuning characteristics and lower thresholds. Primary-like and transient chopper neurons contributed to this decrease in threshold suggesting that they receive 'on' CF inhibitory drive from the DCN. Sustained chopper units did not show a significant decrease in response threshold after Muscimol; however, there was a tendency for broader tuning and a significant increase in CF tone evoked maximum discharge rate and chopping frequency suggesting that the DCN may play a role in regulating the temporal firing of these units in addition to providing lateral inhibition. These results suggest that the DCN to AVCN pathway may aid in fine tuning frequency information.

Acoustic Stimulation↗
PubMed1997

GABA- and glycine-immunoreactive projections from the superior olivary complex to the cochlear nucleus in guinea pig.

Retrograde transport of horseradish peroxidase was combined with immunocytochemistry to identify the origins of potential gamma-aminobutyric acid (GABA) -ergic and glycinergic inputs to different subdivisions of the cochlear nucleus. Projection neurons in the inferior colliculus, superior olivary complex, and contralateral cochlear nucleus were examined, but only those from the superior olivary complex contained significant numbers of GABA- or glycine-immunoreactive neurons. The majority of these were in periolivary nuclei ipsilaterally, with a sizeable contribution from the contralateral ventral nucleus of the trapezoid body. Overall, 80% of olivary neurons projecting to the cochlear nucleus were immunoreactive for GABA, glycine, or both. Most glycine-immunoreactive projection neurons were located ipsilaterally, in the lateral and ventral nuclei of the trapezoid body and the dorsal periolivary nucleus. This suggests that glycine is the predominant neurotransmitter used by ipsilateral olivary projections. Most GABA-immunoreactive cells were located bilaterally in the ventral nuclei of the trapezoid body. The contralateral olivary projection was primarily GABA-immunoreactive and provided almost half the GABA-immunoreactive projections to the cochlear nucleus. This suggests that GABA is the predominant neurotransmitter used by contralateral olivary projections. The present results suggest that the superior olivary complex is the most important extrinsic source of inhibitory inputs to the cochlear nucleus. Individual periolivary nuclei differ in the strength and the transmitter content of their projections to the cochlear nucleus and may perform different roles in acoustic processing in the cochlear nucleus.

Animals↗
PubMedDate not supplied

Uptake and retrograde transport of [3H]GABA from the cochlear nucleus to the superior olive in the guinea pig.

The purpose of the present study is to determine which descending projections to the cochlear nucleus may use gamma-aminobutyric acid (GABA) as a neurotransmitter. [3H]GABA (120 microM) was injected into the cochlear nucleus of albino and pigmented guinea pigs. After survival times between 0.25 and 16 h, the brain stems were prepared for light microscopic autoradiography. After 2 h survival there was a pulse of label, which progressed through the fibres from the cochlear nucleus to the ipsilateral superior olive. After 5 h, retrogradely labelled neuronal cell bodies and fibres were located in the superior olivary complex bilaterally. In the trapezoid body, clusters of labelled cells were seen in the lateral nucleus, ipsilaterally, and in the ventral nucleus, bilaterally. Also there were labelled cells in the ipsilateral dorsal and anterolateral periolivary nucleus. Large and small cells of several types were labelled. Survival times of 10 h or more resulted in very light, diffuse labelling. Projections to the cochlear nucleus labelled by retrograde transport of horseradish peroxidase that did not take up [3H]GABA included the inferior colliculus, bilaterally, and the cochlear nucleus and periolivary nuclei (other than ventral trapezoid nucleus), contralaterally. The selective labelling of cell groups in the superior olive with the moderately low concentration of [3H]GABA used is consistent with the high-affinity uptake of [3H]GABA by synaptic endings in the cochlear nucleus and its retrograde by transport GABA-ergic neurons. This provides evidence for a descending projection system for inhibitory feedback from the superior olive to the cochlear nucleus.

Animals↗
PubMed1981

Morphology of the cochlear nucleus of the normal and reeler mutant mouse.

The morphology of the cochlear nuclei of normal and reeler mutant mice were studied in Nissl-stained sections. The cochlear nucleus in both mice is divisible into three parts: the anteroventral, posteroventral, and dorsal nuclei. Nine cell types can be recognized in the normal mouse. In the anteroventral nucleus spherical cells occupy the rostral pole. Globular cells are located caudally and extend to the interstitial region of the anteroventral nucleus. In the posteroventral nucleus multipolar cells are located rostrally and dark-staining cells occupy the caudal pole. Multipolar cells are also present in the anteroventral nucleus and in the deep region and molecular layer of the dorsal cochlear nucleus. The dorsal and lateral aspects of the ventral nuclei are covered by a granule cell layer. The dorsal nucleus consists of superficial molecular and pyramidal layers and a deep region. The deep region contains small and giant cells as well as multipolar cells. The pyramidal layer is made up of pyramidal cells, horizontal cells, and granule cells. Small cells are also present in the molecular layer and throughout the ventral nuclei. The dorsal cochlear nucleus of the reeler mutant mouse is disorganized and the molecular layer is reduced in thickness. The organization of the pyramidal layer is disrupted with granule cells superficial to pyramidal and horizontal cells. Cells which appear to be homologous to pyramidal cells are also present in the deep region of the dorsal nucleus. The total number of granule cells is reduced by an average of 42% over the whole nucleus and the reduction in granule cells is greatest in the granule cell cap covering the dorsal and lateral surface of the ventral cochlear nuclei. The cytoarchitecture of the ventral cochlear nucleus appears normal.

Animals↗