Descending projections from auditory cortex to excitatory and inhibitory cells in the nucleus of the brachium of the inferior colliculus (original) (raw)
Related papers
Descending projections from the inferior colliculus to the dorsal cochlear nucleus are excitatory
Journal of comparative neurology, 2017
Ascending projections of the dorsal cochlear nucleus (DCN) target primarily the contralateral inferior colliculus (IC). In turn, the IC sends bilateral descending projections back to the DCN. We sought to determine the nature of these descending axons in order to infer circuit mechanisms of signal processing at one of the earliest stages of the central auditory pathway. An anterograde tracer was injected in the IC of CBA/Ca mice to reveal terminal characteristics of the descending axons. Retrograde tracer deposits were made in the DCN of CBA/Ca and transgenic GAD67-EGFP mice to investigate the cells giving rise to these projections. A multiunit best frequency was determined for each injection site. Brains were processed by using standard histologic methods for visualization and examined by fluorescent, brightfield, and electron microscopy. Descending projections from the IC were inferred to be excitatory because the cell bodies of retrogradely labeled neurons did not colabel with EGFP expression in neurons of GAD67-EGFP mice. Furthermore, additional experiments yielded no glycinergic or cholinergic positive cells in the IC, and descending projections to the DCN were colabeled with antibodies against VGluT2, a glutamate transporter. Anterogradely labeled endings in the DCN formed asymmetric postsynaptic densities, a feature of excitatory neurotransmission. These descending projections to the DCN from the IC were topographic and suggest a feedback pathway that could underlie a frequency-specific enhancement of some acoustic signals and suppression of others. The involvement of this IC-DCN circuit is especially noteworthy when considering the gating of ascending signal streams for auditory processing. J. Comp. Neurol. 525:773-793, 2017. © 2016 Wiley Periodicals, Inc.
Neuroscience, 2001
AbstractÐInhibition by GABA is important for auditory processing, but any adaptations of the ionotropic type A receptors are unknown. Here we describe, using in situ hybridization, the subunit expression patterns of GABA A receptors in the rat cochlear nucleus, superior olivary complex, and dorsal and ventral nuclei of the lateral lemniscus. All neurons express the b3 and g2L subunit messenger RNAs, but use different a subunits. In the dorsal cochlear nucleus, fusiform (pyramidal) and giant cells express a1, a3, b3 and g2L. Dorsal cochlear nucleus interneurons, particularly vertical or tuberculoventral cells and cartwheel cells, express a3, b3 and g2L. In the ventral cochlear nucleus, octopus cells express a1, b3, g2L and d. Spherical cells express a1, a3, a5, b3 and g2L. In the superior olivary complex, the expression pro®le is a3, a5, b3 and g2L. Both dorsal and ventral cochlear nucleus granule cells express a1, a6, b3 and g2L; unlike their cerebellar granule cell counterparts, they do not express b2, g2S or the d subunit genes. The d subunit's absence from cochlear nucleus granule cells may mean that tonic inhibition mediated by extrasynaptic GABA A receptors is less important for this cell type. In both the dorsal and ventral nuclei of the lateral lemniscus, a1, b3 and g2L are the main subunit messenger RNAs; the ventral nucleus also expresses the d subunit.
Frontiers in Neuroanatomy, 2014
Individual subdivisions of the medial geniculate body (MG) receive a majority of their ascending inputs from 1 or 2 subdivisions of the inferior colliculus (IC). This establishes parallel pathways that provide a model for understanding auditory projections from the IC through the MG and on to auditory cortex. A striking discovery about the tectothalamic circuit was identification of a substantial GABAergic component. Whether GABAergic projections match the parallel pathway organization has not been examined. We asked whether the parallel pathway concept is reflected in guinea pig tectothalamic pathways and to what degree GABAergic cells contribute to each pathway. We deposited retrograde tracers into individual MG subdivisions (ventral, MGv; medial, MGm; dorsal, MGd; suprageniculate, MGsg) to label tectothalamic cells and used immunochemistry to identify GABAergic cells. The MGv receives most of its IC input (∼75%) from the IC central nucleus (ICc); MGd and MGsg receive most of their input (∼70%) from IC dorsal cortex (ICd); and MGm receives substantial input from both ICc (∼40%) and IC lateral cortex (∼40%). Each MG subdivision receives additional input (up to 32%) from non-dominant IC subdivisions, suggesting cross-talk between the pathways. The proportion of GABAergic cells in each pathway depended on the MG subdivision. GABAergic cells formed ∼20% of IC inputs to MGv or MGm, ∼11% of inputs to MGd, and 4% of inputs to MGsg. Thus, non-GABAergic (i.e., glutamatergic) cells are most numerous in each pathway with GABAergic cells contributing to different extents. Despite smaller numbers of GABAergic cells, their distributions across IC subdivisions mimicked the parallel pathways. Projections outside the dominant pathways suggest opportunities for excitatory and inhibitory crosstalk. The results demonstrate parallel tectothalamic pathways in guinea pigs and suggest numerous opportunities for excitatory and inhibitory interactions within and between pathways.
1995 Feliciano et al AN Direct projections from the rat primary auditory neocortex
It has generally been accepted that neocortical projections to the auditory brainstem do not extend beyond the level of the inferior colliculus. Consequently, it has been assumed that the neocortical influence on lower auditory nuclei is necessarily conveyed by the inferior colliculus. Nevertheless, severa} isolated reports suggest that ablation of the auditory neocortex results in degenerating fibers in the lateral lemniscus, superior olivary complex, and cochlear nuclei, thus challenging the previous tenet. In an attempt to verify the existence of direct neocortical projections to subcollicular auditory nudei and to determine the trajectories, topography, morphology, and possible targets of presumptive corticopontobulbar projections, the anterograde axonal tracers Phaseolus vulgaris-leukoagglutinin and biotinylated dextran were iontophoretically injected at different locations within the primary auditory neocortex of adult albino rats. Terminal anterograde labeling was consistently found: (1) ipsilaterally, in regions surrounding the nudei of the lateral lemniscus, including the nucleus sagulum, the horizontal cell group region (which separates dorsal and intennediate nuclei of the lateral lemniscus), and the rostral and medial paralemniscal regions; (2) bilaterally, in different subdivisions of the superior olivary complex, notably the ventral nucleus of the trapezoid body and the lateral superior olive, as well as a narrow and ill-defined region that overlies the dorsal aspect of the superior olivary complex; and bilaterally, in the dorsal cochlear •Corresponding author: Dr. Enrico Mugnaini, Lab. of Neuromorphology, Biobehavioral Science Graduate Degree Program, University of Connecticut, Box U-154, 3107 Horse Bam Hill Road, Storrs, CT nudeus and in the subregions of the granule cell domain that surround the ventral cochlear nudeus. The neocortical fibers directed to these subcollicular auditory centers travel in the ipsilateral cerebral pedunde, which they leave at different mesencephalic and rhombencephalic levels to follow specific routes to their targets. The nuclei of the lateral lemniscus themselves, the major nuclei of the superior olivary complex (with the exception of the lateral superior olive), and the magnocellular regions of the ventral cochlear nucleus were devoid of terminal labeling. The auditory corticosubcollicularprojections seem to innervate peripheral cell groups of the auditory pathway whose roles in sound processing have not been firmly established, but they do not seem to target the major nuclei of the lower auditory brainstem, which have more clearly defined roles in hearing. otinylated d extran THE AUDITORY CEREBRAL cortex is the final target of the ascending auditory pathways of the mammalian brain and plays a key role in the integration and processing of cognitive and affective aspects of acoustic information. The auditory neocortex is also the starting point for intrinsic, callosa! and descending (or corticofugal) projections. Although the corticofugal fibers innerva te nonauditory neural centers, including the cauda te putamen, the superior colliculus, and the pontine nuclei, their main targets are auditory diencephalic and mesencephalic structures, notably the medial geniculate body and the inferior colliculus (IC) (Andersen et al., 1980a, b;. Although medial geniculate 287
The Journal of comparative neurology, 2004
Metabotropic gamma-aminobutyric acid receptors (GABA(B)) are involved in pre- and postsynaptic inhibitory effects upon auditory neurons and have been implicated in different aspects of acoustic information processing. To understand better the mechanisms by which GABA(B) receptors mediate their inhibitory effects, we used pre-embedding immunocytochemical techniques combined with quantification of immunogold particles to reveal the precise subcellular distribution of the GABA(B1) subunit in the rat dorsal cochlear nucleus. At the light microscopic level, GABA(B1) was detected in all divisions of the cochlear complex. The most intense immunoreactivity for GABA(B1) was found in the dorsal cochlear nucleus, whereas immunoreactivity in the anteroventral and posteroventral cochlear nuclei was very low. In the dorsal cochlear nucleus, a punctate labeling was observed in the superficial (molecular and fusiform cell) layers. At the electron microscopic level, GABA(B1) was found at both post- ...
The Journal of Comparative Neurology, 2011
The ventral and dorsal medial geniculate (MGV and MGD) constitute the major auditory thalamic subdivisions providing thalamocortical inputs to layer IV and lower layer III of auditory cortex. No quantitative evaluation of this projection is available. Using biotinylated dextran amine (BDA)/biocytin injections, we describe the cortical projection patterns of MGV and MGD cells. In primary auditory cortex the bulk of MGV axon terminals are in layer IV/lower layer III with minor projections to supragranular layers and intermediate levels in infragranular layers. MGD axons project to cortical regions designated posterodorsal (PD) and ventral (VA) showing laminar terminal distributions that are quantitatively similar to the MGV-to-primary cortex terminal distribution. At the electron microscopic level MGV and MGD terminals are non-γ-aminobutyric acid (GABA)ergic with MGD terminals in PD and VA slightly but significantly larger than MGV terminals in primary cortex. MGV/MGD terminals synapse primarily onto non-GABAergic spines/dendrites. A small number synapse on GABAergic structures, contacting large dendrites or cell bodies primarily in the major thalamocortical recipient layers. For MGV projections to primary cortex or MGD projections to PD or VA, the non-GABAergic post-synaptic structures at each site were the same size regardless of whether they were in supragranular, granular, or infragranular layers. However, the population of MGD terminal-recipient structures in VA were significantly larger than the MGD terminal-recipient structures in PD or the MGV terminalrecipient structures in primary cortex. Thus, if terminal and postsynaptic structure size indicate strength of excitation then MGD to VA inputs are strongest, MGD to PD intermediate, and MGV to primary cortex the weakest. INDEXING TERMS electron microscopy; GABA; medial geniculate nucleus The rat auditory thalamus or medial geniculate body (MGB) has two major subdivisions, ventral (MGV) and dorsal (MGD), whose cells project primarily to layers III and IV of auditory cortex (LeDoux et al., 1985; Romanski and LeDoux, 1993a, b; Kimura et al., 2003). MGV is the major thalamic component of the rat lemniscal pathway, with cells receiving their primary ascending input from the central nucleus of the inferior colliculus (IC; LeDoux et al., 1985) and projecting exclusively to primary auditory cortex, primarily to deep layer III and layer IV. Primary auditory cortex has been defined as any portion of
Layer V in rat auditory cortex: projections to the inferior colliculus and contralateral cortex
Hearing research, 1988
This study compares the form and distribution within layer V of cells projecting to the inferior colliculus with that of commissural cells of origin in adult rat auditory cortex after horseradish peroxidase injections in the ipsilateral inferior colliculus or auditory cortex. The goal of this work was to determine whether every part of layer V participates equally in both projections, and if the cortical neurons in each pathway were similar. The types of neurons were defined in Golgi-Cox preparations and matched with the profiles of retrogradely labeled cells from architectonically defined cortical area 41. Inferior colliculus and commissural neurons form two populations that differ in their distribution in layer V, in somatic area, and in the form of their apical dendritic arbors. Corticocollicular neurons include the largest pyramidal cells, whose robustly filled apical dendrites ascend into layer II or farther. Commissural cells are smaller and have a more heterogeneous form. The...
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
Dissecting the circuitry of the auditory system
Trends in Neurosciences, 2003
The brainstem auditory system is a complex system composed of numerous parallel and serial pathways that converge on a common destination in the inferior colliculus (IC). The exact nature of the response transformations that occur in the IC have, however, been elusive -even though the IC has been the subject of numerous studies for more than 30 years. Recent studies have addressed this issue by recording from IC neurons before and during micro-iontophoresis of drugs that selectively block GABA A or glycine receptors (the dominant inhibitory receptors in the IC) or by reversibly inactivating a lower nucleus that provides inhibitory innervation to the IC. These studies have revealed some of the ways that signals, relayed via many different parallel routes, interact in the IC, and suggest some functional advantages that these interactions might have.