Effects of trapezoid body and superior olive lesions on choline acetyltransferase activity in the rat cochlear nucleus (original) (raw)
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Descending projections to the dorsal and ventral divisions of the cochlear nucleus in guinea pig
Hearing Research, 1991
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 cocblear 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 co&ear nucleus arose bilaterally in the ventral nucleus of the trapezoid body. The ipsilateral lateral nucleus of the trapexoid body also projected heavily to dorsal and ventral cc&ear nucleus. In addition, the ventral co&ear 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. Horseradish peroxidase; Ventral cochlear nucleus; Dorsal cochlear nucleus; Superior olivary nuclei; Inferior colliculus Inaction Previous studies have shown that in addition to synaptic endings from the VIIIth nerve (for reviews see Cant and Morest, 1984; Caspary, 1986), most neurons in the co&ear nucleus receive innervation from non-co&ear sources (Cant, 1981; Kane and Firm, 1977; Kane and Conlee, 1979; Abbreviations: AVCN = Anteroventral cochlear nucleus; CN = Cochlear nucleus; CPO = Caudal periolivary region; DCN = Dorsal cochlear nucleus; DMPO = Dorsomedial periolivary nucleus; DPO = Dorsal periolivary nucleus; IC = Inferior colliculus; LNTB = Lateral nucleus of the trapezoid body; LSO = Lateral superior olivary nucleus; MNTB = Medial nucleus of the trapezoid body; MS0 = Medial superior olivary nucleus; OCB = Olivocochlear bundle; PVCN = Posteroventral co&ear nucleus; SOC = Superior olivary complex; VCN = Ventral cochlear nucleus; VNTB-Ventral nucleus of the trapezoid body. The manner in which periolivary cell groups and other auditory areas project to specific cochlear nucleus neuronal targets is critical to the ability of these neurons to process complex signals and operate over a wide dynamic range. This study addresses the question of interspecies differences in the organization of olivary projections to specific regions of the cochlear nucleus. The methodology differs from other studies in the guinea pig by examining and quantifying the ret-
Effects of surgical lesions on choline acetyltransferase activity in the cat cochlea
Hearing research, 2017
Although it is well established that the choline acetyltransferase (ChAT, the enzyme for acetylcholine synthesis) in the mammalian cochlea is associated with its olivocochlear innervation, the distribution of this innervation in the cochlea varies somewhat among mammalian species. The quantitative distribution of ChAT activity in the cochlea has been reported for guinea pigs and rats. The present study reports the distribution of ChAT activity within the organ of Corti among the three turns of the cat cochlea and the effects of removing olivocochlear innervation either by a lateral cut aimed to totally transect the left olivocochlear bundle or a more medial cut additionally damaging the superior olivary complex on the same side. Similarly to results for guinea pig and rat, the distribution of ChAT activity in the cat outer hair cell region showed a decrease from base to apex, but, unlike in the guinea pig and rat, the cat inner hair cell region did not. As in the rat, little ChAT ac...
Projections from the ventral cochlear nucleus to the dorsal cochlear nucleus in rats
The Journal of Comparative Neurology, 1997
Local circuit interactions between the dorsal and ventral divisions of the cochlear nucleus are known to influence the evoked responses of the resident neurons to sound. In the present study, we examined the projections of neurons in the ventral cochlear nucleus to the dorsal cochlear nucleus by using retrograde transport of biotinylated dextran amine injected into restricted but different regions of the dorsal cochlear nucleus. In all cases, we found retrogradely labeled granule, unipolar brush, and chestnut cells in the granule cell domain, and retrogradely labeled multipolar cells in the magnocellular core of the ventral cochlear nucleus. A small number of the labeled multipolar cells were found along the margins of the ventral cochlear nucleus, usually near the boundaries of the granule cell domain. Spherical bushy, globular bushy, and octopus cells were not labeled. Retrogradely-labeled auditory nerve fibers and the majority of labeled multipolar neurons formed a narrow sheet extending across the medial-to-lateral extent of the ventral cochlear nucleus whose dorsoventral position was topographically related to the injection site. Labeled multipolar cells within the core of the ventral cochlear nucleus could be divided into at least two distinct groups. Planar neurons were most numerous, their somata found within the associated band of labeled fibers, and their dendrites oriented within this band. This arrangement mimics the organization of isofrequency contours and implies that planar neurons respond best to a narrow range of frequencies. In contrast, radiate neurons were infrequent, found scattered throughout the ventral cochlear nucleus, and had long dendrites oriented perpendicular to the isofrequency contours. This dendritic orientation suggests that radiate neurons are sensitive to a broad range of frequencies. These structural differences between planar and radiate neurons suggest that they subserve separate functions in acoustic processing.
Projections from the dorsal and ventral cochlear nuclei to the medial geniculate body
Frontiers in Neuroanatomy, 2014
Direct projections from the cochlear nucleus (CN) to the medial geniculate body (MG) mediate a high-speed transfer of acoustic information to the auditory thalamus. used anterograde tracers to label the projection from the dorsal CN (DCN) to the MG in guinea pigs. We examined this pathway with retrograde tracers. The results confirm a pathway from the DCN, originating primarily from the deep layers. Labeled cells included a few giant cells and a larger number of small cells of unknown type. Many more labeled cells were present in the ventral CN (VCN). These cells, identifiable as multipolar (stellate) or small cells, were found throughout much of the VCN. Most of the labeled cells were located contralateral to the injection site. The CN to MG pathway bypasses the inferior colliculus (IC), where most ascending auditory information is processed. hypothesized that CN-MG axons are collaterals of axons that reach the IC. We tested this hypothesis by injecting different fluorescent tracers into the MG and IC and examining the CN for double-labeled cells. After injections on the same side of the brain, double-labeled cells were found in the contralateral VCN and DCN. Most double-labeled cells were in the VCN, where they accounted for up to 37% of the cells labeled by the MG injection. We conclude that projections from the CN to the MG originate from the VCN and, less so, from the DCN. A significant proportion of the cells send a collateral projection to the IC. Presumably, the collateral projections send the same information to both the MG and the IC. The results suggest that T-stellate cells of the VCN are a major source of direct projections to the auditory thalamus. nucleus of IC; ICd, dorsal cortex of IC; IClc, lateral cortex of IC; icp, inferior cerebellar peduncle; m, molecular layer of DCN; MG, medial geniculate body; MGd, dorsal division of MG; MGm, medial division of MG; MGsg, suprageniculate division of MG; MGv, ventral division of MG; MVe, medial vestibular nucleus; NBIC, nucleus of the brachium of the IC; py, pyramid; RB, red beads; sp5, spinal trigeminal tract; SpVe, spinal vestibular nucleus; VCN, ventral cochlear nucleus Frontiers in Neuroanatomy www.frontiersin.org
Trauma-specific insults to the cochlear nucleus in the rat
Journal of Neuroscience Research, 2012
The effect of acoustic overstimulation on the neuronal number of the cochlear nucleus (CN) was investigated by using unbiased stereological methods in rats. We found that, after 9 weeks of recovery, neurons in the anteroventral cochlear nucleus (AVCN) degenerated, whereas those in the posteroventral and dorsal cochlear nuclei (PVCN and DCN) were preserved. The noise trauma induced near complete loss of the outer hair cells throughout the cochlea, and the inner hair cells were preserved only in the more apical regions. This pattern of selective loss of AVCN neurons in this study was different from trauma induced by auditory deafferentation by mechanical compression of auditory neurons. In contrast to noise trauma, mechanical compression caused loss of neurons in the PVCN and DCN. After 5 weeks of recovery from mechanical compression, there was no loss of inner or outer hair cells. These findings indicate that auditory deprivation, induced by different experimental manipulations, can have strikingly different consequences for the central auditory system. We hypothesized that AVCN neuronal death was induced by excitotoxic mechanisms via AMPAtype glutamate receptors and that excitatory neuronal circuits developed after acoustic overstimulation protected the PVCN and DCN against neuronal death. The results of the present study demonstrate that hearing loss from different etiologies will cause different patterns of neuronal degeneration in the CN. These findings are important for enhancing the performance of cochlear implants and auditory brainstem implants, because diverse types of hearing loss can selectively affect neuronal degeneration of the CN. V
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.
The Journal of Comparative Neurology, 1985
The distribution of the projection from one cochlear nucleus (CN) within each inferior colliculus (IC) was studied in adult, normal gerbils and adult gerbils subjected to unilateral ablation of the contralateral cochlea at 2 days of age. The projection was studied by using the Fink-Heimer technique for impregnating degenerating axons and their terminal processes with silver. Following an extensive, unilateral lesion of the CN, degeneration was seen in both ICs of all animals. In normal animals, degeneration was both more widespread and heavier in the contralateral than in the ipsilateral central nucleus of IC (ICC). Degeneration was most widespread in the rostra1 and lateral parts of both ICCs and in the ventral part of the contralateral ICC. Degeneration was observed in 26% of the area examined in ipsilateral ICC and in 73% of the area examined in contralateral ICC. In cochlea-ablated animals there was a much greater similarity in the area of degeneration in the ICC ipsilateral(57%) and contralateral (67%) to the CN lesion. The same regional distributions of degeneration were observed as in the normal animals except that the distribution of degeneration in the ipsilateral ICC more closely resembled the normal contralateral than the normal ipsilateral profile. We conclude that the normal distribution of projections from the CN within the ipsilateral ICC is substantially modified by neonatal ablation of the contralateral chochlea.
Journal of Histochemistry & Cytochemistry, 1981
Within the cochlear nucleus of the rat, as well as some nearby regions, quantitative histochemical mapping procedures were used to construct maps of the distributions of choline acetyltransferase and acetylcholinesterase activities. The results were in some ways consistent with results previously reported for cat, e.g., very low activities of both enzymes were found in the auditory nerve root, and also in the vestibular nerve root, except where acetylcholinesterase-positive centrifugal fibers are located, very high activities were found in the facial nerve system. In many ways, however, the results for the rat cochlear nucleus contrasted with those for the cat. Notably, choline acetyltransferase activities in some regions of the rat coch-'Supported by the National Institutes of Health through Research Grant NS 08000 and a National Institutes of Health Postdoctoral Fellowship to D.A.G.