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Susan E. Shore - One of the best experts on this subject based on the ideXlab platform.
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audiotactile interactions in the mouse Cochlear Nucleus
2021Co-Authors: Josephine Ansorge, Susan E. Shore, Patrik KriegerAbstract:Multisensory integration of auditory and tactile information occurs already at the level of the Cochlear Nucleus. Rodents use their whiskers for tactile perception to guide them in their exploration of the world. As nocturnal animals with relatively poor vision, audiotactile interactions are of great importance for this species. Here, the influence of whisker deflections on sound-evoked spiking in the Cochlear Nucleus was investigated in vivo in anesthetized mice. Multichannel, silicon-probe electrophysiological recordings were obtained from both the dorsal and ventral Cochlear Nucleus. Whisker deflections evoked an increased spiking activity in fusiform cells of the dorsal Cochlear Nucleus and t-stellate cells in ventral Cochlear Nucleus, whereas bushy cells in the ventral Cochlear Nucleus showed a more variable response. The response to broadband noise stimulation increased in fusiform cells and primary-like bushy cells when the sound stimulation was preceded (~ 20 ms) by whisker stimulation. Multi-sensory integration of auditory and whisker input can thus occur already in this early brainstem Nucleus, emphasizing the importance of early integration of auditory and somatosensory information.
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multisensory activation of ventral Cochlear Nucleus d stellate cells modulates dorsal Cochlear Nucleus principal cell spatial coding
2018Co-Authors: Susan E. ShoreAbstract:Key points Dorsal Cochlear Nucleus fusiform cells receive spectrally relevant auditory input for sound localization. Fusiform cells integrate auditory with other multisensory inputs. Here we elucidate how somatosensory and vestibular stimulation modify the fusiform cell spatial code through activation of an inhibitory interneuron: the ventral Cochlear Nucleus D-stellate cell. These results suggests that multisensory cues interact early in an ascending sensory pathway to serve an essential function. Abstract In the Cochlear Nucleus (CN), the first central site for coding sound location, numerous multisensory projections and their modulatory effects have been reported. However, multisensory influences on sound location processing in the CN remain unknown. The principal output neurons of the dorsal CN, fusiform cells, encode spatial information through frequency-selective responses to direction-dependent spectral features. Here, single-unit recordings from the guinea pig CN revealed transient alterations by somatosensory and vestibular stimulation in fusiform cell spatial coding. Changes in fusiform cell spectral sensitivity correlated with multisensory modulation of ventral CN D-stellate cell responses, which provide direct, wideband inhibition to fusiform cells. These results suggest that multisensory inputs contribute to spatial coding in DCN fusiform cells via an inhibitory interneuron, the D-stellate cell. This early multisensory integration circuit likely confers important consequences on perceptual organization downstream.
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altered vesicular glutamate transporter distributions in the mouse Cochlear Nucleus following Cochlear insult
2016Co-Authors: Amarins N Heeringa, Susan E. Shore, Roxana A Stefanescu, Yehoash RaphaelAbstract:Vesicular glutamate transporters 1 and 2 (VGLUT1 and VGLUT2) have distinct distributions in the Cochlear Nucleus that correspond to sources of the labeled terminals. VGLUT1 is mainly associated with terminals of auditory nerve fibers, whereas VGLUT2 is mainly associated with glutamatergic terminals deriving from other sources that project to the Cochlear Nucleus (CN), including somatosensory and vestibular terminals. Previous studies in guinea pig have shown that Cochlear damage results in a decrease of VGLUT1-labeled puncta and an increase in VGLUT2-labeled puncta. This indicates cross-modal compensation that is of potential importance in somatic tinnitus. To examine whether this effect is consistent across species and to provide a background for future studies, using transgenesis, the current study examines VGLUT expression profiles upon Cochlear insult by intraCochlear kanamycin injections in the mouse. IntraCochlear kanamycin injections abolished ipsilateral ABR responses in all animals and reduced ipsilateral spiral ganglion neuron densities in animals that were sacrificed after four weeks, but not in animals that were sacrificed after three weeks. In all unilaterally deafened animals, VGLUT1 density was decreased in CN regions that receive auditory nerve fiber terminals, i.e., in the deep layer of the dorsal Cochlear Nucleus (DCN), in the interstitial region where the auditory nerve enters the CN, and in the magnocellular region of the antero- and posteroventral CN. In contrast, density of VGLUT2 expression was upregulated in the fusiform cell layer of the DCN and in the granule cell lamina, which are known to receive somatosensory and vestibular terminals. These results show that a Cochlear insult induces cross-modal compensation in the Cochlear Nucleus of the mouse, confirming previous findings in guinea pig, and that these changes are not dependent on the occurrence of spiral ganglion neuron degeneration.
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Increased Synchrony and Bursting of Dorsal Cochlear Nucleus Fusiform Cells Correlate with Tinnitus.
2016Co-Authors: David T. Martel, Susan E. ShoreAbstract:Tinnitus, the perception of phantom sounds, is thought to arise from increased neural synchrony, which facilitates perceptual binding and creates salient sensory features in the absence of physical stimuli. In the auditory cortex, increased spontaneous cross-unit synchrony and single-unit bursting are de facto physiological correlates of tinnitus. However, it is unknown whether neurons in the dorsal Cochlear Nucleus (DCN), the putative tinnitus-induction site, exhibit increased synchrony. Using a temporary-threshold shift model and gap-prepulse inhibition of the acoustic startle to assess tinnitus, we recorded spontaneous activity from fusiform cells, the principle neurons of the DCN, in normal hearing, tinnitus, and non-tinnitus guinea pigs. Synchrony and bursting, as well as spontaneous firing rate (SFR), correlated with behavioral evidence of tinnitus, and increased synchrony and bursting were associated with SFR elevation. The presence of increased synchrony and bursting in DCN fusiform cells suggests that a neural code for phantom sounds emerges in this brainstem location and likely contributes to the formation of the tinnitus percept. SIGNIFICANCE STATEMENT Tinnitus, a phantom auditory percept, is encoded by pathological changes in the neural synchrony code of perceptual processing. Increased cross-unit synchrony and bursting have been linked to tinnitus in several higher auditory stations but not in fusiform cells of the dorsal Cochlear Nucleus (DCN), key brainstem neurons in tinnitus generation. Here, we demonstrate increased synchrony and bursting of fusiform cell spontaneous firing, which correlate with frequency-specific behavioral measures of tinnitus. Thus, the neural representation of tinnitus emerges early in auditory processing and likely drives its pathophysiology in higher structures.
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transcutaneous induction of stimulus timing dependent plasticity in dorsal Cochlear Nucleus
2015Co-Authors: David T. Martel, Susan E. ShoreAbstract:The Cochlear Nucleus (CN) is the first site of multisensory integration in the ascending auditory pathway. The principal output neurons of the dorsal Cochlear Nucleus (DCN), fusiform cells, receive somatosensory information relayed by the CN granule cells from the trigeminal and dorsal column pathways. Integration of somatosensory and auditory inputs results in long-term enhancement or suppression in a stimulus-timing-dependent manner. Here, we demonstrate that stimulus-timing-dependent plasticity (STDP) can be induced in DCN fusiform cells using paired auditory and transcutaneous electrical stimulation of the face and neck to activate trigeminal and dorsal column pathways to the CN, respectively. Long-lasting changes in fusiform cell firing rates persisted for up to 2 h after this bimodal stimulation, and followed Hebbian or anti-Hebbian rules, depending on tone duration, but not somatosensory stimulation location: 50 ms paired tones evoked predominantly Hebbian, while 10 ms paired tones evoked predominantly anti-Hebbian plasticity. The tone-duration-dependent STDP was strongly correlated with first inter-spike intervals, implicating intrinsic cellular properties as determinants of STDP. This study demonstrates that transcutaneous stimulation with precise auditory-somatosensory timing parameters can non-invasively induce fusiform cell long-term modulation, which could be harnessed in the future to moderate tinnitus-related hyperactivity in DCN.
Paul B. Manis - One of the best experts on this subject based on the ideXlab platform.
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classification of neurons in the adult mouse Cochlear Nucleus linear discriminant analysis
2019Co-Authors: Paul B. Manis, Michael R Kasten, Ruili XieAbstract:The Cochlear Nucleus (CN) transforms the spike trains of spiral ganglion cells into a set of sensory representations that are essential for auditory discriminations and perception. These transformations require the coordinated activity of different classes of neurons that are embryologically derived from distinct sets of precursors. Decades of investigation have shown that the neurons of the CN are differentiated by their morphology, neurotransmitter receptors, ion channel expression and intrinsic excitability. In the present study we have used linear discriminant analysis (LDA) to perform an unbiased analysis of measures of the responses of CN neurons to current injections to objectively categorize cells on the basis of both morphology and physiology. Recordings were made from cells in brain slices from CBA/CaJ mice and a transgenic mouse line, NF107, crossed against the Ai32 line. For each cell, responses to current injections were analyzed for spike rate, spike shape, input resistance, resting membrane potential, membrane time constant, hyperpolarization-activated sag and time constant. Cells were filled with dye for morphological classification, and visually classified according to published accounts. The different morphological classes of cells were separated with the LDA. Ventral Cochlear Nucleus (VCN) bushy cells, planar multipolar (T-stellate) cells, and radiate multipolar (D-stellate) cells were in separate clusters and separate from all of the neurons from the dorsal Cochlear Nucleus (DCN). Within the DCN, the pyramidal cells and tuberculoventral cells were largely separated from a distinct cluster of cartwheel cells. principal axes, whereas VCN cells were in 3 clouds approximately orthogonal to this plane. VCN neurons from the two mouse strains overlapped but were slightly separated, indicating either a strain dependence or differences in slice preparation methods. We conclude that Cochlear Nucleus neurons can be objectively distinguished based on their intrinsic electrical properties, but such distinctions are still best aided by morphological identification.
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classification of neurons in the adult mouse Cochlear Nucleus linear discriminant analysis
2019Co-Authors: Paul B. Manis, Michael R Kasten, Ruili XieAbstract:Abstract The Cochlear Nucleus (CN) transforms the spike trains of spiral ganglion cells into a new set of sensory representations that are essential for auditory discriminations and perception. These transformations require the coordinated activity of different classes of neurons that are embryologically derived from distinct sets of precursors. Decades of investigation have shown that the neurons of the CN are differentiated by their ion channel expression and intrinsic excitability. In the present study we have used linear discriminant analysis (LDA) to perform an unbiased analysis of measures of the responses of CN neurons to current injections to mathematically separate cells on the basis of both morphology and physiology. Recordings were made from cells in brain slices from CBA mice and a transgenic mouse line, NF107, crossed against the Ai32 line. For each cell, responses to current injections were analyzed for spike rate, spike shape (action potential height, afterhyperpolarization depth, first spike half-width), input resistance, resting membrane potential, membrane time constant, hyperpolarization-activated sag and time constant. Cells were filled with dye for morphological classification, and visually classified according to published accounts. The different morphological classes of cells were separated with the LDA. Ventral Cochlear Nucleus (VCN) bushy cells, planar multipolar (T-stellate) cells, and radiate multipolar (D-stellate) cells were in separate clusters, and were also separated from all of the neurons from the dorsal Cochlear Nucleus (DCN). Within the DCN, the pyramidal cells and tuberculoventral cells were largely separated from a distinct clusters of cartwheel cells. DCN cells fell largely within a plane in the first 3 principal axes, whereas VCN cells were in 3 clouds approximately orthogonal to this plane. VCN neurons from the two mouse strains were slightly separated, indicating either a strain dependence or the differences in slice preparation methods. We conclude that Cochlear Nucleus neurons can be objectively distinguished based on their intrinsic electrical properties, but that such distinctions are still best aided by morphological identification.
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A map of functional synaptic connectivity in the mouse anteroventral Cochlear Nucleus.
2014Co-Authors: Luke Campagnola, Paul B. ManisAbstract:The Cochlear nuclei are the first central processors of auditory information and provide inputs to all the major brainstem and midbrain auditory nuclei. Although the local circuits within the Cochlear nuclei are understood at a cellular level, the spatial patterns of connectivity and the connection strengths in these circuits have been less well characterized. We have applied a novel, quantitative approach to mapping local circuits projecting to cells in the mouse anteroventral Cochlear Nucleus (AVCN) using laser-scanning photostimulation and glutamate uncaging. The amplitude and kinetics of individual evoked synaptic events were measured to reveal the patterns and strengths of synaptic connections. We found that the two major excitatory projection cell classes, the bushy and T-stellate cells, receive a spatially broad inhibition from D-stellate cells in the AVCN, and a spatially confined inhibition from the tuberculoventral cells of the dorsal Cochlear Nucleus. Furthermore, T-stellate cells integrate D-stellate inhibition from an area that spans twice the frequency range of that integrated by bushy cells. A subset of both bushy and T-stellate cells receives inhibition from an unidentified cell population at the dorsal–medial boundary of the AVCN. A smaller subset of cells receives local excitation from within the AVCN. Our results show that inhibitory circuits can have target-specific patterns of spatial convergence, synaptic strength, and receptor kinetics, resulting in different spectral and temporal processing capabilities.
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the roles potassium currents play in regulating the electrical activity of ventral Cochlear Nucleus neurons
2003Co-Authors: Jason S Rothman, Paul B. ManisAbstract:Using kinetic data from three different K+ currents in acutely isolated neurons, a single electrical compartment representing the soma of a ventral Cochlear Nucleus (VCN) neuron was created. The K+...
David K Ryugo - One of the best experts on this subject based on the ideXlab platform.
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Tonotopic Organization of Vertical Cells in the Dorsal Cochlear Nucleus of the CBA/J Mouse
2020Co-Authors: Michael A Muniak, David K RyugoAbstract:ABSTRACT The systematic and topographic representation of frequency is a first principle of organization throughout the auditory system. The dorsal Cochlear Nucleus (DCN) receives direct tonotopic projections from the auditory nerve (AN) as well as secondary and descending projections from other sources
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tonotopic organization of vertical cells in the dorsal Cochlear Nucleus of the cba j mouse
2014Co-Authors: Michael A Muniak, David K RyugoAbstract:The systematic and topographic representation of frequency is a first principle of organization throughout the auditory system. The dorsal Cochlear Nucleus (DCN) receives direct tonotopic projections from the auditory nerve (AN) as well as secondary and descending projections from other sources. Among the recipients of AN input in the DCN are vertical cells (also called tuberculoventral cells), glycinergic interneurons thought to provide on- or near-best-frequency feed-forward inhibition to principal cells in the DCN and various cells in the anteroventral Cochlear Nucleus (AVCN). Differing lines of physiological and anatomical evidence suggest that vertical cells and their projections are organized with respect to frequency, but this has not been conclusively demonstrated in the intact mammalian brain. To address this issue, we retrogradely labeled vertical cells via physiologically targeted injections in the AVCN of the CBA/J mouse. Results from multiple cases were merged with a normalized 3D template of the Cochlear Nucleus (Muniak et al. [2013] J. Comp. Neurol. 521:1510–1532) to demonstrate quantitatively that the arrangement of vertical cells is tonotopic and aligned to the innervation pattern of the AN. These results suggest that vertical cells are well positioned for providing immediate, frequency-specific inhibition onto cells of the DCN and AVCN to facilitate spectral processing. J. Comp. Neurol. 522:937–949, 2014. © 2013 Wiley Periodicals, Inc.
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projections of the second cervical dorsal root ganglion to the Cochlear Nucleus in rats
2006Co-Authors: Xiping Zhan, Tan Pongstaporn, David K RyugoAbstract:Physiological, anatomical, and clinical data have demonstrated interactions between somatosensory and auditory brainstem structures. Spinal nerve projections influence auditory responses, although the nature of the pathway(s) is not known. To address this issue, we injected biotinylated dextran amine into the Cochlear Nucleus or dorsal root ganglion (DRG) at the second cervical segment (C2). Cochlear Nucleus injections retrogradely labeled small ganglion cells in C2 DRG. C2 DRG injections produced anterograde labeling in the external cuneate Nucleus, cuneate Nucleus, Nucleus X, central cervical Nucleus, dorsal horn of upper cervical spinal segments, and Cochlear Nucleus. The terminal field in the Cochlear Nucleus was concentrated in the subpeduncular corner and lamina of the granule cell domain, where endings of various size and shapes appeared. Examination under an electron microscope revealed that the C2 DRG terminals contained numerous round synaptic vesicles and formed asymmetric synapses, implying depolarizing influences on the target cell. Labeled endings synapsed with the stalk of the primary dendrite of unipolar brush cells, distal dendrites of presumptive granule cells, and endings containing pleomorphic synaptic vesicles. These primary somatosensory projections contribute to circuits that are hypothesized to mediate integrative functions of hearing.
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axonal pathways to the lateral superior olive labeled with biotinylated dextran amine injections in the dorsal Cochlear Nucleus of rats
2003Co-Authors: John R Doucet, David K RyugoAbstract:The lateral superior olive (LSO) contains cells that are sensitive to intensity differences between the two ears, a feature used by the brain to localize sounds in space. This report describes a source of input to the LSO that complements bushy cell projections from the ventral Cochlear Nucleus (VCN). Injections of biotinylated dextran amine (BDA) into the dorsal Cochlear Nucleus (DCN) of the rat label axons and swellings in several brainstem structures, including the ipsilateral LSO. Labeling in the ipsilateral LSO was confined to a thin band that extended throughout the length of the structure such that it resembled an LSO isofrequency lamina. The source of this labeled pathway was not obvious, because DCN neurons do not project to the LSO, and VCN bushy cells were not filled by these injections. Filled neurons in several brainstem structures emerged as possible sources. Three observations suggest that most of the axonal labeling in the LSO derives from a single source. First, the number of labeled VCN planar multipolar cells and the amount of labeling in the LSO were consistent and robust across animals. In contrast, the number of labeled cells in most other structures was small and highly variable. Second, the locations of planar cells and filled axons in the LSO were related topographically to the position of the DCN injection site. Third, labeled terminal arborizations in the LSO arose from collaterals of axons in the trapezoid body (output tract of planar cells). We infer that planar multipolar cells, in addition to bushy cells, are a source of ascending input from the Cochlear Nucleus to the LSO.
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projections of the pontine nuclei to the Cochlear Nucleus in rats
2001Co-Authors: Matthias Ohlrogge, John R Doucet, David K RyugoAbstract:In the Cochlear Nucleus, there is a magnocellular core of neurons whose axons form the ascending auditory pathways. Surrounding this core is a thin shell of microneurons called the granule cell domain (GCD). The GCD receives auditory and nonauditory inputs and projects in turn to the dorsal Cochlear Nucleus, thus appearing to serve as a central locus for integrating polysensory information and descending feedback. Nevertheless, the source of many of these inputs and the nature of the synaptic connections are relatively unknown. We used the retrograde tracer Fast Blue to demonstrate that a major projection arises from the contralateral pontine nuclei (PN) to the GCD. The projecting cells are more densely located in the ventral and rostral parts of the PN. They also are clustered into a lateral and a medial group. Injections of anterograde tracers into the PN labeled mossy fibers in the contralateral GCD. The terminals are confined to those parts of the GCD immediately surrounding the ventral Cochlear Nucleus. There is no PN projection to the dorsal Cochlear Nucleus. These endings have the form of bouton and mossy fiber endings as revealed by light and electron microscopy. The PN represent a key station between the cerebral and cerebellar cortices, so the pontoCochlear Nucleus projection emerges as a significant source of highly processed information that is introduced into the early stages of the auditory pathway. The cerebropontocerebellar pathway may impart coordination and timing cues to the motor system. In an analogous way, perhaps the cerebropontoCochlear Nucleus projection endows the auditory system with a timing mechanism for extracting temporal information. J. Comp. Neurol. 436:
Donata Oertel - One of the best experts on this subject based on the ideXlab platform.
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Microcircuits of the Dorsal Cochlear Nucleus
2018Co-Authors: Laurence O Trussell, Donata OertelAbstract:The dorsal Cochlear Nucleus (DCN) integrates excitatory input from auditory and nonauditory sources. Auditory signals are conveyed to the deep layer by the auditory nerve and by excitatory interneurons in the ventral Cochlear Nucleus (VCN). Signals from diverse auditory, somatosensory, proprioceptive, and vestibular sources arrive through mossy fibers in the molecular layer. Thus the DCN is a multisensory integrator. Auditory and mossy inputs are processed through separate microcircuits and are then integrated and conveyed to the inferior colliculus by fusiform cells. Signals arriving from the auditory nerve and VCN in the DCN deep layer are refined by inhibitory neurons that give the acoustic responses of the principal cells a striking nonlinearity as a function of sound intensity and inhibitory sidebands in the spectral domain. Mossy inputs are preprocessed by local circuits in a granule cell region and further refined in the molecular layer. Unlike the auditory signals in the deep layer, signals in the molecular layer exhibit diverse forms of long-term synaptic plasticity. The function of the DCN is not fully understood. The sensitivity of the DCN to spectral notches suggests a role in sound localization using monoaural cues. Input associated with pinna muscles and the trigeminal nerve suggests that the DCN relates head orientation to incoming sounds. The anatomical and physiological similarity of the DCN to structures in electric fish that sensitize the fish to novel signals in the environment has led to the idea that the DCN cancels self-generated and expected features of sounds.
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the magnitudes of hyperpolarization activated and low voltage activated potassium currents co vary in neurons of the ventral Cochlear Nucleus
2011Co-Authors: Xiaojie Cao, Donata OertelAbstract:In the ventral Cochlear Nucleus (VCN), neurons have hyperpolarization-activated conductances, which in some cells are enormous, that contribute to the ability of neurons to convey acoustic informat...
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Bidirectional synaptic plasticity in the cerebellum-like mammalian dorsal Cochlear Nucleus.
2002Co-Authors: Kiyohiro Fujino, Donata OertelAbstract:The dorsal Cochlear Nucleus integrates acoustic with multimodal sensory inputs from widespread areas of the brain. Multimodal inputs are brought to spiny dendrites of fusiform and cartwheel cells in the molecular layer by parallel fibers through synapses that are subject to long-term potentiation and long-term depression. Acoustic cues are brought to smooth dendrites of fusiform cells in the deep layer by auditory nerve fibers through synapses that do not show plasticity. Plasticity requires Ca(2+)-induced Ca(2+) release; its sensitivity to antagonists of N-methyl-d-aspartate and metabotropic glutamate receptors differs in fusiform and cartwheel cells.
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octopus cells of the mammalian ventral Cochlear Nucleus sense the rate of depolarization
2002Co-Authors: Michael J Ferragamo, Donata OertelAbstract:Whole cell patch recordings in slices show that the probability of firing of action potentials in octopus cells of the ventral Cochlear Nucleus depends on the dynamic properties of depolarization. ...
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physiological identification of the targets of cartwheel cells in the dorsal Cochlear Nucleus
1997Co-Authors: Nace L Golding, Donata OertelAbstract:Golding, Nace L. and Donata Oertel. Physiological identification of the targets of cartwheel cells in the dorsal Cochlear Nucleus. J. Neurophysiol. 78: 248–260, 1997. The integrative contribution o...
Keith N Darrow - One of the best experts on this subject based on the ideXlab platform.
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direct visualization of the murine dorsal Cochlear Nucleus for optogenetic stimulation of the auditory pathway
2015Co-Authors: Elliott D Kozin, Keith N Darrow, Ariel E Hight, Ashton E Lehmann, Alyson B Kaplan, Christian M BrownAbstract:Investigation into the use of virus-mediated gene transfer to arrest or reverse hearing loss has largely been relegated to the peripheral auditory system. Few studies have examined gene transfer to the central auditory system. The dorsal Cochlear Nucleus (DCN) of the brainstem, which contains second order neurons of the auditory pathway, is a potential site for gene transfer. In this protocol, a technique for direct and maximal exposure of the murine DCN via a posterior fossa approach is demonstrated. This approach allows for either acute or survival surgery. Following direct visualization of the DCN, a host of experiments are possible, including injection of opsins into the Cochlear Nucleus and subsequent stimulation by an optical fiber coupled to a blue light laser. Other neurophysiology experiments, such as electrical stimulation and neural injector tracings are also feasible. The level of visualization and the duration of stimulation achievable make this approach applicable to a wide range of experiments.
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commissural axons of the mouse Cochlear Nucleus
2013Co-Authors: Christian M Brown, Marie Drottar, Thane E Benson, Keith N DarrowAbstract:The axons of commissural neurons that project from one Cochlear Nucleus to the other were studied after labeling with anterograde tracer. Injections were made into the dorsal subdivision of the Cochlear Nucleus in order to restrict labeling only to the group of commissural neurons that gave off collaterals to, or were located in, this subdivision. The number of labeled commissural axons in each injection was correlated with the number of labeled radiate multipolar neurons, suggesting radiate neurons as the predominant origin of the axons. The radiate commissural axons are thick and myelinated, and they exit the dorsal acoustic stria of the injected Cochlear Nucleus to cross the brainstem in the dorsal half, near the crossing position of the olivoCochlear bundle. They enter the opposite Cochlear Nucleus via the dorsal and ventral acoustic stria and at its medial border. Reconstructions of single axons demonstrate that terminations are mostly in the core and typically within a single subdivision of the Cochlear Nucleus. Extents of termination range from narrow to broad along both the dorsoventral (i.e., tonotopic) and the rostrocaudal dimensions. In the electron microscope, labeled swellings form synapses that are symmetric (in that there is little postsynaptic density), a characteristic of inhibitory synapses. Our labeled axons do not appear to include excitatory commissural axons that end in edge regions of the Nucleus. Radiate commissural axons could mediate the broadband inhibition observed in responses to contralateral sound, and they may balance input from the two ears with a quick time course.
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planar multipolar cells in the Cochlear Nucleus project to medial olivoCochlear neurons in mouse
2012Co-Authors: Christian M Brown, Thane E Benson, Keith N DarrowAbstract:Medial olivoCochlear (MOC) neurons originate in the superior olivary complex and project to the cochlea, where they act to reduce the effects of noise masking and protect the cochlea from damage. MOC neurons respond to sound via a reflex pathway; however, in this pathway the Cochlear Nucleus cell type that provides input to MOC neurons is not known. We investigated whether multipolar cells of the ventral Cochlear Nucleus have projections to MOC neurons by labeling them with injections into the dorsal Cochlear Nucleus. The projections of one type of labeled multipolar cell, planar neurons, were traced into the ventral Nucleus of the trapezoid body, where they were observed terminating on MOC neurons (labeled in some cases by a second Cochlear injection of FluoroGold). These terminations formed what appear to be excitatory synapses, i.e., containing small, round vesicles and prominent postsynaptic densities. These data suggest that Cochlear Nucleus planar multipolar neurons drive the MOC neuron's response to sound.
