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Jeffery A Winer - One of the best experts on this subject based on the ideXlab platform.

  • projections of auditory cortex to the Medial Geniculate Body of the cat
    The Journal of Comparative Neurology, 2001
    Co-Authors: Jeffery A Winer, James J Diehl, David T Larue
    Abstract:

    The corticofugal projection from 12 auditory cortical fields onto the Medial Geniculate Body was investigated in adult cats by using wheat germ agglutinin conjugated to horseradish peroxidase or biotinylated dextran amines. The chief goals were to determine the degree of divergence from single cortical fields, the pattern of convergence from several fields onto a single nucleus, the extent of reciprocal relations between corticothalamic and thalamocortical connections, and to contrast and compare the patterns of auditory corticoGeniculate projections with corticofugal input to the inferior colliculus. The main findings were that (1) single areas showed a wide range of divergence, projecting to as few as 5, and to as many as 15, thalamic nuclei; (2) most nuclei received projections from approximately five cortical areas, whereas others were the target of as few as three areas; (3) there was global corticothalamicthalamocortical reciprocity in every experiment, and there were also significant instances of nonreciprocal projections, with the corticothalamic input often more extensive; (4) the corticothalamic projection was far stronger and more divergent than the corticocollicular projection from the same areas, suggesting that the thalamus and the inferior colliculus receive differential degrees of corticofugal control; (5) cochleotopically organized areas had fewer corticothalamic projections than fields in which tonotopy was not a primary feature; and (6) all corticothalamic projections were topographic, focal, and clustered, indicating that areas with limited cochleotopic organization still have some internal spatial arrangement. The areas with the most divergent corticothalamic projections were polysensory regions in the posterior ectosylvian gyrus. The projection patterns were indistinguishable for the two tracers. These findings suggest that every auditory thalamic nucleus is under some degree of descending control. Many of the projections preserve the relations between cochleotopically organized thalamic and auditory areas, and suggest topographic relations between nontonotopic areas and nuclei. The collective size of the corticothalamic system suggests that both lemniscal and extralemniscal auditory thalamic nuclei receive significant corticofugal input.

  • gabaergic organization of the cat Medial Geniculate Body
    The Journal of Comparative Neurology, 1999
    Co-Authors: Camillan L Huang, David T Larue, Jeffery A Winer
    Abstract:

    A study of neurons and processes (puncta) immunolabeled by antibodies to ! -aminobutyric acid (GABA) or glutamic acid decarboxylase was undertaken in the Medial Geniculate Body of the adult cat. The proportion and types of GABAergic cells were determined with high resolution methods, including postembbedding immunocytochemistry on semithin plastic sections. A second goal was to draw parallels and differences between the auditory thalamus and other thalamic nuclei. Finally, the types of GABAergic puncta and their concentration in the three major subdivisions of the Medial Geniculate Body were analyzed. The results were that (1) each division had many GABAergic neurons, averaging approximately 26% of the neuronal population; (2) the ventral division had the highest proportion of these cells (33%), the Medial division the fewest (18%), and the dorsal division was intermediate (26%); (3) there was a gradient in the proportion of GABAergic neurons, i.e., the ventral and Medial division values increased caudorostrally, whereas the value in the dorsal division declined; (4) the predominant GABAergic cell type in each division was a small neuron with a soma approximately 10‐12 µm in diameter; (5) a small population of much larger GABAergic neurons was present mainly in the dorsal division; (6) in addition to the fine, granular puncta in each division, a type of giant GABAergic puncta was found only in the dorsal division nuclei. The results obtained with the two antibodies were essentially identical. These findings suggest a structural basis for qualitative differences in the distribution of GABAergic processing within the Medial Geniculate complex. The GABAergic arrangement in the ventral division was stereotyped, with only one type of putative GABAergic interneuron, and the puncta were correspondingly homogeneous. In contrast, the dorsal division had two types of GABAergic neurons, and the giant GABAergic puncta represent a new substrate for inhibitory interactions. The Medial division also had more than one type of GABAergic neuron and a slightly lower concentration of puncta. These qualitative and quantitative distinctions suggest a morphologic basis for possible differences in inhibitory processing among Medial

  • two systems of giant axon terminals in the cat Medial Geniculate Body convergence of cortical and gabaergic inputs
    The Journal of Comparative Neurology, 1999
    Co-Authors: Jeffery A Winer, David T Larue, Camillan L Huang
    Abstract:

    The thalamus plays a critical role in processing sensory information that involves interactions between extrinsic connections and intrinsic circuitry. Little is known regarding how these different systems might interact. We found an unexpected nuclear convergence of two types of giant axon terminals, each of which must have independent origins, in the dorsal division of the cat Medial Geniculate Body. The first class of giant terminal was labeled after injections of biotinylated dextran amines (BDA) in seven auditory cortical areas.Asecond type was found in sections immunostained for ! -aminobutyric acid (GABA); these endings had the same nuclear distribution, and they were numerous. The origin of this GABAergic terminal is unknown. The giant corticothalamic terminals were presumably those described in prior accounts using different tracers (Rouiller and de Ribaupierre [1990] Neurosci. Lett. 208:29‐ 35; Ojima [1994] Cerebral Cortex 6:646‐663), but with BDA they are labeled more fully. Clusters of such endings were often linked, and hundreds may occur in a single section. Their boutons formed a substantial proportion of the corticothalamic population. Other types of corticoGeniculate axon terminals were also labeled, including two kinds that are much smaller and that match closely the classical descriptions of corticothalamic axons. The giant GABAergic endings were found in all dorsal division nuclei and in thalamic visual nuclei such as the lateral posterior nucleus. Like the giant cortical endings, the giant GABAergic terminals often encircled large, pale, immunonegative profiles that may be dendritic. This implies a close spatial, and perhaps a close functional, relationship between the populations of giant axon terminals. Insofar as physiological studies found that pharmacological inactivation of rat somatic sensory cortex suppresses peripheral information transmission through the posterior thalamus, corticofugal input may be essential for normal processing (Diamond et al. [1992] J. Comp. Neurol. 319:66‐84). Our findings suggest that the giant corticothalamic endings could play an important role in descending control. Perhaps they are counterbalanced by a GABAergic system and affect thalamic oscillations implicated in shifts in vigilance and attention. J. Comp. Neurol. 413:181‐197, 1999. ! 1999 Wiley-Liss, Inc.

  • neural architecture of the rat Medial Geniculate Body
    Hearing Research, 1999
    Co-Authors: Jeffery A Winer, Jack B Kelly, David T Larue
    Abstract:

    The rat Medial Geniculate Body was subdivided using Nissl preparations to establish nuclear boundaries, with Golgi-Cox impregnations to identify projection and local circuit neurons, and in fiber stained material to delineate the fiber tracts and their distribution. Three divisions were recognized (ventral, dorsal and Medial): the first two had subdivisions. The ventral division had lateral and Medial parts. The main cell type had bushy tufted dendrites which, with the afferent axons, formed fibrodendritic laminae oriented from dorso-lateral to ventro-Medial; such laminae were not as regular Medially, in the ovoid nucleus. The dorsal division contained several nuclei (dorsal superficial, dorsal, deep dorsal, supraGeniculate, and ventrolateral) and neurons with radiating or bushy dendrites; the nuclear subdivisions differed in the concentration of one cell type or another, and in packing density. A laminar organization was present only in the dorsal superficial nucleus. Medial division neurons were heterogeneous in size and shape, ranging from tiny cells to magnocellular neurons; the various cell types intermingled. so that no further subdivision could be made. This parcellation scheme was consistent with, and supported by, the findings from plastic embedded or fiber stained material. There were very few small neurons with locally ramifying axons and which could perform an intrinsic role like that of Golgi type II cells. Their rarity was consistent with the small number of such profiles in plastic embedded or Nissl material and the few GABAergic Medial Geniculate Body neurons seen in prior immunocytochemical work. While similar neuronal types and nuclear subdivisions are recognized in the rat and cat, there may be major interspecific differences with regard to interneuronal organization in the auditory thalamus whose functional correlates are unknown.

  • origins of Medial Geniculate Body projections to physiologically defined zones of rat primary auditory cortex
    Hearing Research, 1999
    Co-Authors: Jeffery A Winer, David T Larue, Sharon L Sally, Jack B Kelly
    Abstract:

    Abstract Medial Geniculate Body neurons projecting to physiologically identified subregions of rat primary auditory cortex (area 41, Te1) were labeled with horseradish peroxidase in adult rats. The goals were to determine the type(s) of projection neuron and the spatial arrangement of these cells with respect to thalamic subdivisions. Maps of best frequency were made with single neuron or unit cluster extracellular recording at depths of 500–800 μm, which correspond to layers III–IV in Nissl preparations. Tracer injections were made in different cortical isofrequency regions (2, 11, 22, or 38 kHz, respectively). Labeled neurons were plotted on representative sections upon which the architectonic subdivisions were drawn independently. Most of the cells of origin lay in the ventral division in every experiment. Injections at low frequencies labeled bands of neurons laterally in the ventral division; progressively more rostral deposits at higher frequencies labeled bands or clusters more Medially in the ventral division, and through most of its caudo-rostral extent. Medial division labeling was variable. Labeled cells were always in the lateral half of the nucleus and were often scattered. There were few labeled cells in the dorsal division. Seven types of thalamocortical neuron were identified: ventral division cells had a tufted branching pattern, while Medial division neurons have heterogeneous shapes and sizes and were larger. Dorsal division neurons had a radiate branching pattern. The size range of labeled neurons spanned that of Nissl stained neuronal somata. Area 41 may receive two types of thalamic projection: ventral division input is strongly convergent, highly topographic, spatially focal, and restricted to one type of neuron only, while the Medial division projection is more divergent, coarsely topographical, involves multiple cortical areas, and has several varieties of projection neuron. Despite species differences in local circuitry, many facets of thalamocortical organization are conserved in phylogeny.

David T Larue - One of the best experts on this subject based on the ideXlab platform.

  • projections of auditory cortex to the Medial Geniculate Body of the cat
    The Journal of Comparative Neurology, 2001
    Co-Authors: Jeffery A Winer, James J Diehl, David T Larue
    Abstract:

    The corticofugal projection from 12 auditory cortical fields onto the Medial Geniculate Body was investigated in adult cats by using wheat germ agglutinin conjugated to horseradish peroxidase or biotinylated dextran amines. The chief goals were to determine the degree of divergence from single cortical fields, the pattern of convergence from several fields onto a single nucleus, the extent of reciprocal relations between corticothalamic and thalamocortical connections, and to contrast and compare the patterns of auditory corticoGeniculate projections with corticofugal input to the inferior colliculus. The main findings were that (1) single areas showed a wide range of divergence, projecting to as few as 5, and to as many as 15, thalamic nuclei; (2) most nuclei received projections from approximately five cortical areas, whereas others were the target of as few as three areas; (3) there was global corticothalamicthalamocortical reciprocity in every experiment, and there were also significant instances of nonreciprocal projections, with the corticothalamic input often more extensive; (4) the corticothalamic projection was far stronger and more divergent than the corticocollicular projection from the same areas, suggesting that the thalamus and the inferior colliculus receive differential degrees of corticofugal control; (5) cochleotopically organized areas had fewer corticothalamic projections than fields in which tonotopy was not a primary feature; and (6) all corticothalamic projections were topographic, focal, and clustered, indicating that areas with limited cochleotopic organization still have some internal spatial arrangement. The areas with the most divergent corticothalamic projections were polysensory regions in the posterior ectosylvian gyrus. The projection patterns were indistinguishable for the two tracers. These findings suggest that every auditory thalamic nucleus is under some degree of descending control. Many of the projections preserve the relations between cochleotopically organized thalamic and auditory areas, and suggest topographic relations between nontonotopic areas and nuclei. The collective size of the corticothalamic system suggests that both lemniscal and extralemniscal auditory thalamic nuclei receive significant corticofugal input.

  • gabaergic organization of the cat Medial Geniculate Body
    The Journal of Comparative Neurology, 1999
    Co-Authors: Camillan L Huang, David T Larue, Jeffery A Winer
    Abstract:

    A study of neurons and processes (puncta) immunolabeled by antibodies to ! -aminobutyric acid (GABA) or glutamic acid decarboxylase was undertaken in the Medial Geniculate Body of the adult cat. The proportion and types of GABAergic cells were determined with high resolution methods, including postembbedding immunocytochemistry on semithin plastic sections. A second goal was to draw parallels and differences between the auditory thalamus and other thalamic nuclei. Finally, the types of GABAergic puncta and their concentration in the three major subdivisions of the Medial Geniculate Body were analyzed. The results were that (1) each division had many GABAergic neurons, averaging approximately 26% of the neuronal population; (2) the ventral division had the highest proportion of these cells (33%), the Medial division the fewest (18%), and the dorsal division was intermediate (26%); (3) there was a gradient in the proportion of GABAergic neurons, i.e., the ventral and Medial division values increased caudorostrally, whereas the value in the dorsal division declined; (4) the predominant GABAergic cell type in each division was a small neuron with a soma approximately 10‐12 µm in diameter; (5) a small population of much larger GABAergic neurons was present mainly in the dorsal division; (6) in addition to the fine, granular puncta in each division, a type of giant GABAergic puncta was found only in the dorsal division nuclei. The results obtained with the two antibodies were essentially identical. These findings suggest a structural basis for qualitative differences in the distribution of GABAergic processing within the Medial Geniculate complex. The GABAergic arrangement in the ventral division was stereotyped, with only one type of putative GABAergic interneuron, and the puncta were correspondingly homogeneous. In contrast, the dorsal division had two types of GABAergic neurons, and the giant GABAergic puncta represent a new substrate for inhibitory interactions. The Medial division also had more than one type of GABAergic neuron and a slightly lower concentration of puncta. These qualitative and quantitative distinctions suggest a morphologic basis for possible differences in inhibitory processing among Medial

  • two systems of giant axon terminals in the cat Medial Geniculate Body convergence of cortical and gabaergic inputs
    The Journal of Comparative Neurology, 1999
    Co-Authors: Jeffery A Winer, David T Larue, Camillan L Huang
    Abstract:

    The thalamus plays a critical role in processing sensory information that involves interactions between extrinsic connections and intrinsic circuitry. Little is known regarding how these different systems might interact. We found an unexpected nuclear convergence of two types of giant axon terminals, each of which must have independent origins, in the dorsal division of the cat Medial Geniculate Body. The first class of giant terminal was labeled after injections of biotinylated dextran amines (BDA) in seven auditory cortical areas.Asecond type was found in sections immunostained for ! -aminobutyric acid (GABA); these endings had the same nuclear distribution, and they were numerous. The origin of this GABAergic terminal is unknown. The giant corticothalamic terminals were presumably those described in prior accounts using different tracers (Rouiller and de Ribaupierre [1990] Neurosci. Lett. 208:29‐ 35; Ojima [1994] Cerebral Cortex 6:646‐663), but with BDA they are labeled more fully. Clusters of such endings were often linked, and hundreds may occur in a single section. Their boutons formed a substantial proportion of the corticothalamic population. Other types of corticoGeniculate axon terminals were also labeled, including two kinds that are much smaller and that match closely the classical descriptions of corticothalamic axons. The giant GABAergic endings were found in all dorsal division nuclei and in thalamic visual nuclei such as the lateral posterior nucleus. Like the giant cortical endings, the giant GABAergic terminals often encircled large, pale, immunonegative profiles that may be dendritic. This implies a close spatial, and perhaps a close functional, relationship between the populations of giant axon terminals. Insofar as physiological studies found that pharmacological inactivation of rat somatic sensory cortex suppresses peripheral information transmission through the posterior thalamus, corticofugal input may be essential for normal processing (Diamond et al. [1992] J. Comp. Neurol. 319:66‐84). Our findings suggest that the giant corticothalamic endings could play an important role in descending control. Perhaps they are counterbalanced by a GABAergic system and affect thalamic oscillations implicated in shifts in vigilance and attention. J. Comp. Neurol. 413:181‐197, 1999. ! 1999 Wiley-Liss, Inc.

  • neural architecture of the rat Medial Geniculate Body
    Hearing Research, 1999
    Co-Authors: Jeffery A Winer, Jack B Kelly, David T Larue
    Abstract:

    The rat Medial Geniculate Body was subdivided using Nissl preparations to establish nuclear boundaries, with Golgi-Cox impregnations to identify projection and local circuit neurons, and in fiber stained material to delineate the fiber tracts and their distribution. Three divisions were recognized (ventral, dorsal and Medial): the first two had subdivisions. The ventral division had lateral and Medial parts. The main cell type had bushy tufted dendrites which, with the afferent axons, formed fibrodendritic laminae oriented from dorso-lateral to ventro-Medial; such laminae were not as regular Medially, in the ovoid nucleus. The dorsal division contained several nuclei (dorsal superficial, dorsal, deep dorsal, supraGeniculate, and ventrolateral) and neurons with radiating or bushy dendrites; the nuclear subdivisions differed in the concentration of one cell type or another, and in packing density. A laminar organization was present only in the dorsal superficial nucleus. Medial division neurons were heterogeneous in size and shape, ranging from tiny cells to magnocellular neurons; the various cell types intermingled. so that no further subdivision could be made. This parcellation scheme was consistent with, and supported by, the findings from plastic embedded or fiber stained material. There were very few small neurons with locally ramifying axons and which could perform an intrinsic role like that of Golgi type II cells. Their rarity was consistent with the small number of such profiles in plastic embedded or Nissl material and the few GABAergic Medial Geniculate Body neurons seen in prior immunocytochemical work. While similar neuronal types and nuclear subdivisions are recognized in the rat and cat, there may be major interspecific differences with regard to interneuronal organization in the auditory thalamus whose functional correlates are unknown.

  • origins of Medial Geniculate Body projections to physiologically defined zones of rat primary auditory cortex
    Hearing Research, 1999
    Co-Authors: Jeffery A Winer, David T Larue, Sharon L Sally, Jack B Kelly
    Abstract:

    Abstract Medial Geniculate Body neurons projecting to physiologically identified subregions of rat primary auditory cortex (area 41, Te1) were labeled with horseradish peroxidase in adult rats. The goals were to determine the type(s) of projection neuron and the spatial arrangement of these cells with respect to thalamic subdivisions. Maps of best frequency were made with single neuron or unit cluster extracellular recording at depths of 500–800 μm, which correspond to layers III–IV in Nissl preparations. Tracer injections were made in different cortical isofrequency regions (2, 11, 22, or 38 kHz, respectively). Labeled neurons were plotted on representative sections upon which the architectonic subdivisions were drawn independently. Most of the cells of origin lay in the ventral division in every experiment. Injections at low frequencies labeled bands of neurons laterally in the ventral division; progressively more rostral deposits at higher frequencies labeled bands or clusters more Medially in the ventral division, and through most of its caudo-rostral extent. Medial division labeling was variable. Labeled cells were always in the lateral half of the nucleus and were often scattered. There were few labeled cells in the dorsal division. Seven types of thalamocortical neuron were identified: ventral division cells had a tufted branching pattern, while Medial division neurons have heterogeneous shapes and sizes and were larger. Dorsal division neurons had a radiate branching pattern. The size range of labeled neurons spanned that of Nissl stained neuronal somata. Area 41 may receive two types of thalamic projection: ventral division input is strongly convergent, highly topographic, spatially focal, and restricted to one type of neuron only, while the Medial division projection is more divergent, coarsely topographical, involves multiple cortical areas, and has several varieties of projection neuron. Despite species differences in local circuitry, many facets of thalamocortical organization are conserved in phylogeny.

Jeffrey J Wenstrup - One of the best experts on this subject based on the ideXlab platform.

  • inputs to combination sensitive neurons in the Medial Geniculate Body of the mustached bat the missing fundamental
    The Journal of Neuroscience, 1995
    Co-Authors: Jeffrey J Wenstrup, Carol D Grose
    Abstract:

    This study examined projections to combination-sensitive neurons in the Medial Geniculate Body of the mustached bat. These specialized neurons respond to the combination of two temporally and spectrally distinct components of the bat's sonar pulse and echo, encoding target information. Combination-sensitive neurons respond to the bat's sonar fundamental, between 24-31 kHz, in conjunction with a higher harmonic signal. They are thought to be formed in the Medial Geniculate Body (MGB) by convergent input from inferior colliculus representations of 24-31 kHz and higher frequencies. This study used anterograde and retrograde tract-tracing methods in conjunction with physiological recording to test this MGB convergence hypothesis. In anterograde tracing experiments, multiple deposits of two different tracers were placed in the central nucleus of the inferior colliculus (ICC), one tracer in the 24-31 kHz region and another in an ICC representation responding to a higher sonar harmonic. We found only limited overlap in the MGB labeling patterns of the two tracers, and little in many areas where combination-sensitive neurons are common. In retrograde tracing experiments, a single deposit of tracer was placed at a combination-sensitive recording site in the MGB. With the deposit mostly limited to combination-sensitive MGB areas, labeling in 24-31 kHz representations of the ICC was absent or minor. These results suggest that many combination-sensitive neurons in the MGB do not receive 24-31 kHz ICC input. The strongest inputs to combination-sensitive MGB regions originate in high-frequency representations of the ICC and combination-sensitive regions of auditory cortex. Additional projections arrive from the thalamic reticular nucleus, external nucleus of the inferior colliculus, and pericollicular tegmentum. Each projection may contribute to the 24-31 kHz sensitivity of combination-sensitive neurons in the Medial Geniculate Body.

  • projections of physiologically defined subdivisions of the inferior colliculus in the mustacbed bat targets in the Medial Geniculate Body and extrathalamic nuclei
    The Journal of Comparative Neurology, 1994
    Co-Authors: Jeffrey J Wenstrup, David T Larue, Jeffery A Winer
    Abstract:

    This study examined the output of the central nucleus of the inferior colliculus to the Medial Geniculate Body and other parts of the nervous system in the mustached bat (Pteronotus parnellii). Small deposits of anterograde tracers (horseradish peroxidase, [3H]leucine, Phaseolus vulgaris leucoagglutinin, wheat germ agglutinin conjugated to horseradish peroxidase, or biocytin) were made at physiologically defined sites in the central nucleus representing major components of the bat's echolocation signal. The topography, frequency specificity, and axonal morphology of these outputs were studied. The Medial Geniculate Body was a major target of inferior collicular neurons, with three distinct input patterns. The projection to the ventral division was tonotopically organized, but had a relatively sparse contribution from neurons representing frequency modulated components of the biosonar pulse. The second input was to the rostral Medial Geniculate Body, in which projections from inferior collicular neurons representing constant frequency sonar components were separated from those representing frequency modulated components. A third input was to the supraGeniculate nucleus, which received strong, topographically arranged projections. Inputs to the dorsal nucleus and Medial division were also observed. Extrathalamic regions receiving input included the pontine gray, external nucleus of the inferior colliculus, pericollicular tegmentum, nucleus of the brachium of the inferior colliculus, and pretectum. These central nucleus projections differed in organization and the structure of axon terminals, suggesting different physiological influences on their target nuclei. These results demonstrate that the central nucleus has divergent projections to various sensory and premotor nuclei, besides its well-established projection to the Medial Geniculate Body. © 1994 Wiley-Liss, Inc.

  • the neurons of the Medial Geniculate Body in the mustached bat pteronotus parnellii
    The Journal of Comparative Neurology, 1994
    Co-Authors: Jeffery A Winer, Jeffrey J Wenstrup
    Abstract:

    The neurons in the Medial Geniculate Body were studied in Golgi preparations from adult mustached bats (Pteronotus parnellii). Their somatic and dendritic configurations were compared with those of cells in other, nonecholocating mammals. A second goal was to use the thalamic nuclear subdivisions derived from Golgi material to integrate the findings in parallel studies of cytoarchitecture, immunocytochemistry, and tectothalamic connections. Three primary divisions are defined. The ventral division is large and has a stereotyped neuronal organization. Medium-sized perikarya (about 10 μm in diameter) represent tufted neurons; the fibrodendritic plexus forms laminae in the lateral part along which midbrain axons terminate. A smaller, possibly intrinsic, neuron with thin, sparse dendrites is rarely impregnated. Neurons in the larger, Medial part, which represents frequencies of 60 kHz and higher, have more spherical dendritic fields; their branching pattern remains tufted, and the laminar organization was less evident. The dorsal division is about equal in size, and it has many nuclei and a corresponding neuronal diversity. These neurons are medium-sized except in the supraGeniculate nucleus, where many cells are larger. Four dorsal division nuclei are recognized. Each has neurons with radiate or weakly tufted dendritic arbors. Superficial dorsal nucleus neurons are oriented from Medial to lateral, imparting a slightly laminated appearance to the neuropil. A few smaller, stellate neurons with modest dendritic domains are present. SupraGeniculate nucleus neurons have radiating dendritic fields that project spherically; they have fewer branches than dorsal nucleus neurons. The posterior limitans nucleus is dorsoMedial to the supraGeniculate nucleus; it has small neurons with long, sparsely branched dendrites. The rostral pole nucleus, included in the dorsal division on cytoarchitectonic grounds, had too few neurons impregnated to reveal its neuronal architecture. The Medial division, the smallest of the main parts, is one nucleus with at least six types of cells, including the magnocellular, bushy tufted, disc-shaped, medium-sized multipolar, elongated, and small stellate neurons. There is no laminar arrangement. Many of the neurons resemble those in rodent, marsupial, carnivore, and primate auditory thalamic nuclei. Despite such morphological correspondences, functional differences, such as the evolution of combination sensitivity, suggest that structurally comparable auditory thalamic neurons may subserve diverse physiological representations. © 1994 Wiley-Liss, Inc.

Philip H Smith - One of the best experts on this subject based on the ideXlab platform.

  • unique combination of anatomy and physiology in cells of the rat paralaminar thalamic nuclei adjacent to the Medial Geniculate Body
    The Journal of Comparative Neurology, 2006
    Co-Authors: Philip H Smith, Edward L Bartlett, Anna Kowalkowski
    Abstract:

    The Medial Geniculate Body (MGB) has three major subdivisions - ventral (MGV), dorsal (MGD) and Medial (MGM). MGM is linked with paralaminar nuclei that are situated Medial and ventral to MGV/MGD. Paralaminar nuclei have unique inputs and outputs when compared with MGV and MGD and have been linked to circuitry underlying some important functional roles. We recorded intracellularly from cells in the paralaminar nuclei in vitro. We found that they possess an unusual combination of anatomical and physiological features when compared to those reported for “standard” thalamic neurons seen in the MGV/MGD and elsewhere in the thalamus. Compared to MGV/MGD neurons, anatomically, 1) paralaminar cell dendrites can be long, branch sparingly and encompass a much larger area. 2) their dendrites may be smooth but can have well defined spines and 3) their axons can have collaterals that branch locally within the same or nearby paralaminar nuclei. When compared to MGV/MGD neurons physiologically 1) their spikes are larger in amplitude and can be shorter in duration and 2) can have dual afterhyperpolarizations with fast and slow components and 3) they can have a reduction or complete absence of the low threshold, voltage-sensitive calcium conductance that reduces or eliminates the voltage-dependent burst response. We also recorded from cells in the parafascicular nucleus, a nucleus of the posterior intralaminar nuclear group, because they have unusual anatomical features that are similar to some of our paralaminar cells. Like the labeled paralaminar cells, parafascicular cells had physiological features distinguishing them from typical thalamic neurons.

  • effects of paired pulse and repetitive stimulation on neurons in the rat Medial Geniculate Body
    Neuroscience, 2002
    Co-Authors: Edward L Bartlett, Philip H Smith
    Abstract:

    Abstract Many behaviorally relevant sounds, including language, are composed of brief, rapid, repetitive acoustic features. Recent studies suggest that abnormalities in producing and understanding spoken language are correlated with abnormal neural responsiveness to such auditory stimuli at higher auditory levels [Tallal et al., Science 271 (1996) 81–84; Wright et al., Nature 387 (1997) 176–178; Nagarajan et al., Proc. Natl. Acad. Sci. USA 96 (1999) 6483–6488] and with abnormal anatomical features in the auditory thalamus [Galaburda et al., Proc. Natl. Acad. Sci. USA 91 (1994) 8010–8013]. To begin to understand potential mechanisms for normal and abnormal transfer of sensory information to the cortex, we recorded the intracellular responses of Medial Geniculate Body thalamocortical neurons in a rat brain slice preparation. Inferior colliculus or corticothalamic axons were excited by pairs or trains of electrical stimuli. Neurons receiving only excitatory collicular input had tufted dendritic morphology and displayed strong paired-pulse depression of their large, short-latency excitatory postsynaptic potentials. In contrast, Geniculate neurons receiving excitatory and inhibitory collicular inputs could have stellate or tufted morphology and displayed much weaker depression or even paired-pulse facilitation of their smaller, longer-latency excitatory postsynaptic potentials. Depression was not blocked by ionotropic glutamate, GABA A or GABA B receptor antagonists. Facilitation was unaffected by GABA A receptor antagonists but was diminished by N -methyl- D -aspartate (NMDA) receptor blockade. Similar stimulation of the corticothalamic input always elicited paired-pulse facilitation. The NMDA-independent facilitation of the second cortical excitatory postsynaptic potential lasted longer and was more pronounced than that seen for the excitatory collicular inputs. Paired-pulse stimulation of isolated collicular inhibitory postsynaptic potentials generated little change in the second GABA A potential amplitude measured from the resting potential, but the GABA B amplitude was sensitive to the interstimulus interval. Train stimuli applied to collicular or cortical inputs generated intra-train responses that were often predicted by their paired-pulse behavior. Long-lasting responses following train stimulation of the collicular inputs were uncommon. In contrast, corticothalamic inputs often generated long-lasting depolarizing responses that were dependent on activation of a metabotropic glutamate receptor. Our results demonstrate that during repetitive afferent firing there are input-specific mechanisms controlling synaptic strength and membrane potential over short and long time scales. Furthermore, they suggest that there may be two classes of excitatory collicular input to Medial Geniculate neurons and a single class of small-terminal corticothalamic inputs, each of which has distinct features.

  • comparison of the fine structure of cortical and collicular terminals in the rat Medial Geniculate Body
    Neuroscience, 2000
    Co-Authors: Edward L Bartlett, J M Stark, R W Guillery, Philip H Smith
    Abstract:

    Neurons throughout the rat Medial Geniculate Body, including the dorsal and ventral divisions, display a variety of responses to auditory stimuli. To investigate possible structural determinants of this variability, measurements of axon terminal profile area and postsynaptic dendrite diameter were made on inferior colliculus and corticothalamic terminal profiles in the Medial Geniculate Body identified by anterograde tracer labeling following injections into the inferior colliculus or cortex. Over 90% of the synapses observed were axodendritic, with few axosomatic synapses. Small ( 1.0 microm(2)) collicular profiles were found throughout the Medial Geniculate, but were smaller on average in the dorsal division (0.49+/-0.49 microm(2)) than in the ventral division (0.70+/-0.64 microm(2)). Almost all corticothalamic profiles were small and ended on small-caliber dendrites (0.57+/-0.25 microm diameter) throughout the Medial Geniculate. A few very large (>2.0 microm(2)) corticothalamic profiles were found in the dorsal division and in the marginal zone of the Medial Geniculate. GABA immunostaining demonstrated the presence of GABAergic profiles arising from cells in the inferior colliculus. These profiles were compared with GABAergic profiles not labeled with anterograde tracer, which were presumed to be unlabeled inferior colliculus profiles or thalamic reticular nucleus profiles. The distributions of dendritic diameters postsynaptic to collicular, cortical and unlabeled GABAergic profiles were compared with dendritic diameters of intracellularly labeled Medial Geniculate neurons from rat brain slices. Our results demonstrate a corticothalamic projection to Medial Geniculate Body that is similar to other sensory corticothalamic projections. However, the heterogeneous distributions of excitatory inferior collicular terminal sizes and postsynaptic dendritic diameters, along with the presence of a GABAergic inferior collicular projection to dendrites in the Medial Geniculate Body, suggest a colliculoGeniculate projection that is more complex than the ascending projections to other sensory thalamic nuclei. These findings may be useful in understanding some of the differences in the response characteristics of Medial Geniculate neurons in vivo.

  • anatomic intrinsic and synaptic properties of dorsal and ventral division neurons in rat Medial Geniculate Body
    Journal of Neurophysiology, 1999
    Co-Authors: Edward L Bartlett, Philip H Smith
    Abstract:

    Anatomic, intrinsic, and synaptic properties of dorsal and ventral division neurons in rat Medial Geniculate Body. Presently little is known about what basic synaptic and cellular mechanisms are em...

  • a monosynaptic gabaergic input from the inferior colliculus to the Medial Geniculate Body in rat
    The Journal of Neuroscience, 1997
    Co-Authors: Daniel Peruzzi, Philip H Smith, Edward L Bartlett, Douglas L. Oliver
    Abstract:

    The goal was to investigate possible monosynaptic GABAergic projections from the inferior colliculus (IC) to thalamocortical neurons of the Medial Geniculate Body (MGB) in the rat. Although there is little evidence for such a projection in other sensory thalamic nuclei, a GABAergic, ascending auditory projection was reported recently in the cat. In the present study, immunohistochemical and tract-tracing methods were used to identify neurons in the IC that contain GABA and project to the MGB. GABA-positive projection neurons were most numerous in the central nucleus and less so in the dorsal and lateral cortex. They were rare in the lateral tegmental system and brachium of the IC. The dorsal nucleus of the lateral lemniscus also contained GABA-positive projection neurons. In brain slices, stimulation of the brachium produced monosynaptic inhibitory postsynaptic potentials in morphologically identified thalamocortical relay neurons. The inhibitory potentials cannot originate locally, because they persisted when ionotropic glutamatergic transmission was blocked. Typically, brachium stimulation elicited a GABAA-mediated inhibitory potential followed by an excitatory potential and a longer latency GABAB-mediated inhibitory potential. We conclude that the GABA-containing neurons of the IC make short-latency, monosynaptic inputs to the thalamocortical projection neurons in the MGB. Such inputs may distinguish the main auditory pathway from indirect or tegmental auditory pathways as well as from other sensory systems. Monosynaptic inhibitory inputs to the Medial Geniculate may be important for the regulation of firing patterns in thalamocortical neurons.

Lin Chen - One of the best experts on this subject based on the ideXlab platform.

  • characterization of rebound depolarization in neurons of the rat Medial Geniculate Body in vitro
    Neuroscience Bulletin, 2016
    Co-Authors: Xin Xing Wang, Yan Jin, Hui Sun, Jinsheng Zhang, Ming Wang, Lin Chen
    Abstract:

    Rebound depolarization (RD) is a response to the offset from hyperpolarization of the neuronal membrane potential and is an important mechanism for the synaptic processing of inhibitory signals. In the present study, we characterized RD in neurons of the rat Medial Geniculate Body (MGB), a nucleus of the auditory thalamus, using whole-cell patch-clamp and brain slices. RD was proportional in strength to the duration and magnitude of the hyperpolarization; was effectively blocked by Ni(2+) or Mibefradil; and was depressed when the resting membrane potential was hyperpolarized by blocking hyperpolarization-activated cyclic nucleotide-gated (HCN) channels with ZD7288 or by activating G-protein-gated inwardly-rectifying K(+) (GIRK) channels with baclofen. Our results demonstrated that RD in MGB neurons, which is carried by T-type Ca(2+) channels, is critically regulated by HCN channels and likely by GIRK channels.

  • Sodium salicylate potentiates the GABAB-GIRK pathway to suppress rebound depolarization in neurons of the rat's Medial Geniculate Body
    Hearing research, 2015
    Co-Authors: Xin Xing Wang, Yan Jin, Jinsheng Zhang, Ming Wang, Bin Luo, Jing Wu Sun, Lin Chen
    Abstract:

    Rebound depolarization (RD) is a voltage response to the offset from pre-hyperpolarization of neuronal membrane potential, which manifests a particular form of the postsynaptic membrane potential response to inhibitory presynaptic inputs. We previously demonstrated that sodium salicylate (NaSal), a tinnitus inducer, can drastically suppress the RD in neurons of rat Medial Geniculate Body (MGB) (Su et al, 2012; PLoS ONE 7, e46969). The purpose of the present study was to investigate the underlying cellular mechanism by using whole-cell patch-clamp recordings in rat MGB slices. NaSal (1.4 mM) had no effects on the current mediated by T-type Ca(2+) channels, indicating that it does not target these channels to suppress the RD. Instead, NaSal was shown to hyperpolarize the resting membrane potential to suppress the RD. NaSal had no effects on the current mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, indicating that it does not target these channels to hyperpolarize the resting membrane potential. NaSal induced an outward leak current that could be abolished by CGP55845, a GABAB receptor blocker, or respectively by Ba(2+) and Tertiapin-Q, blockers for G-protein-gated inwardly rectifying potassium (GIRK) channels, indicating that NaSal potentiates the GABAB-GIRK pathway to hyperpolarize the resting membrane potential. Our study demonstrates that NaSal targets GABAB receptors to alter functional behaviors of MGB neurons, which may be implicated in NaSal-induced tinnitus.

  • altered neuronal intrinsic properties and reduced synaptic transmission of the rat s Medial Geniculate Body in salicylate induced tinnitus
    PLOS ONE, 2012
    Co-Authors: Bin Luo, Yan Jin, Edward Lobarinas, Richard Salvi, Lin Chen
    Abstract:

    Sodium salicylate (NaSal), an aspirin metabolite, can cause tinnitus in animals and human subjects. To explore neural mechanisms underlying salicylate-induced tinnitus, we examined effects of NaSal on neural activities of the Medial Geniculate Body (MGB), an auditory thalamic nucleus that provides the primary and immediate inputs to the auditory cortex, by using the whole-cell patch-clamp recording technique in MGB slices. Rats treated with NaSal (350 mg/kg) showed tinnitus-like behavior as revealed by the gap prepulse inhibition of acoustic startle (GPIAS) paradigm. NaSal (1.4 mM) decreased the membrane input resistance, hyperpolarized the resting membrane potential, suppressed current-evoked firing, changed the action potential, and depressed rebound depolarization in MGB neurons. NaSal also reduced the excitatory and inhibitory postsynaptic response in the MGB evoked by stimulating the brachium of the inferior colliculus. Our results demonstrate that NaSal alters neuronal intrinsic properties and reduces the synaptic transmission of the MGB, which may cause abnormal thalamic outputs to the auditory cortex and contribute to NaSal-induced tinnitus.

  • activation of presynaptic gabab receptors modulates gabaergic and glutamatergic inputs to the Medial Geniculate Body
    Hearing Research, 2011
    Co-Authors: Bin Luo, Haitao Wang, Lin Chen
    Abstract:

    The Medial Geniculate Body (MGB) receives ascending inputs from the inferior colliculus and descending inputs from the auditory cortex. In the present study, we intended to determine whether activation of presynaptic GABA(B) receptors modulates GABAergic and glutamatergic inputs to the MGB with whole-cell patch-clamp recordings in brain slices of the rat. To evoke a synaptic response, we electrically stimulated the ascending and descending inputs to MGB neurons with bipolar electrodes placed on the brachium of the inferior colliculus and the superior thalamic radiation. To isolate presynaptic mechanisms, we blocked the effects of postsynaptic GABA(B) receptors by filling recording electrodes with the internal solution containing cesium and QX-314. The activation of presynaptic GABA(B) receptors by exogenous agonist was shown to modulate synaptic inputs to the MGB as demonstrated by that (1) baclofen, a GABA(B) receptor agonist, reversibly suppressed both inhibitory postsynaptic currents (IPSCs) and excitatory postsynaptic currents (EPSCs) and this suppressive effect could be blocked by CGP35348, a GABA(B) receptor antagonist, (2) baclofen significantly increased the ratio of IPSCs or EPSCs elicited by paired-pulse stimulation, and (3) baclofen depressed EPSCs and IPSCs in response to repetitive stimulation. The activation of presynaptic GABA(B) receptors by endogenously released GABA was shown to modulate the synaptic transmission as demonstrated by that CGP55845, another GABA(B) receptor antagonist, increased the ratio of IPSCs to paired-pulse stimulation in young (P8-10) rats, although not in juvenile (P15-18) rats. Our study provides electrophysiological evidence for the presence of functional presynaptic GABA(B) receptors in the MGB and suggests an age-dependent role of these receptors in the synaptic transmission in this central auditory region.