The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform

Stephen M. Highstein - One of the best experts on this subject based on the ideXlab platform.

  • Characteristics of regenerating Horizontal Semicircular Canal afferent and efferent fibers in the toadfish, Opsanus tau.
    The Journal of comparative neurology, 1999
    Co-Authors: Allen F. Mensinger, Stephen M. Highstein
    Abstract:

    The Horizontal Semicircular Canal nerve of the toadfish, Opsanus tau, was transected and allowed to regenerate. The time course, morphometrics, and projection patterns of regenerating afferent and efferent vestibular fibers were determined. Nerve transections were performed both pre- and postganglionically, and regeneration was assessed in afferent and efferent fibers by bulk labeling the peripheral axons of the Horizontal Semicircular Canal nerve with biocytin after nerve regrowth. Afferent fibers regrew through the transection site within 14 days and projected to all vestibular nuclei within 3 weeks. Bouton and branch number, axon length, surface area, volume, fiber diameter, and internodal distance were quantified for afferent fibers from eight sites within the vestibular nuclei, and axon number and soma size was quantified for the efferent fibers. Extensive regeneration was seen within 5 weeks of transection in all nuclei, and most morphometric parameters approached or exceeded control levels within 10 weeks. Regeneration appeared to recapitulate morphogenesis with an initial overproduction of boutons and branch points followed by elimination of presumably superfluous structures. Internodal distance remained significantly shorter in regenerating afferent axons than in control fish throughout the 15-week observation period. Efferent fibers also were observed to regenerate. Efferent axon number, diameter, and soma size were indistinguishable from those in controls from 3 weeks posttransection through week 15. Electrophysiological recordings from the Horizontal Canal nerve during mechanical stimuli of the Canal confirmed that the regenerated axons transmitted normal signals. The return of normal equilibrium and behavior coincided with the projection of afferent fibers into the central vestibular nuclei, indicating that functional connections had been reestablished.

  • Examination of the cupula and stereocilia of the Horizontal Semicircular Canal in the toadfish Opsanus tau
    The Journal of comparative neurology, 1998
    Co-Authors: Robert B. Silver, Anthony P. Reeves, Antionette Steinacker, Stephen M. Highstein
    Abstract:

    We imaged the Horizontal Semicircular Canal (HSCC) crista and cupula of toadfish, Opsanus tau, by using a) confocal light microscopy of isolated vital HSCC; b) serial sections of fixed, trichrome-stained HSCC; and c) scanning electron microscopy of fixed HSCCs. HSCC were dissections which included an ampulla and an attached Canal tube (long and slender Canal portion), and, in some cases, a small portion of the utricular wall. Cupulae were seen as multipartite mucus connective tissue shells rising from the crista and extending toward the ampullary roof. They were composed of several refractile bands traversing the cupulae perpendicular to longitudinal fibers extending from the cupular base to its apex. Alcian green–stained cupulae showed an asymmetric alcianphilic, dark, X-shaped structure, indicating that the pillar is rich in mucin and carbohydrate, an interpretation supported by images of trichrome-stained sections. The cupular antrum is devoid of prominent refractile fibers. No tubes or channels were observed in the cupula or antrum of vital preparations. Cupular shell fibers cover the surface of the crista, are roughly parallel, and are associated with a translucent material having a refractive index greater than the surrounding endolymph. Stereocilia were thin, 100-μm-long structures, with little longitudinal curvature, which end with no end bulb. No strands extend from stereocilia to the roof or other portions of the cupular antrum. Gross movements of stereocilia were not seen in mechanically quiescent preparations. Within the cupular antrum, stereocilia were parallel to connective tissue fibers, all embedded in an isotropic gel. This fiber-reinforced gel and cupular matrix are sensitive to N-acetlyneuraminidase and β-N-acetyl glucosaminidase, and minimally sensitive to β-N-acetyl hexosaminidase. Connective tissue fibers may serve to stiffen the gel, whose matrix would restrict lateral motion of embedded fibers and stereocilia thereby providing mechanical support for stereocilia. J. Comp. Neurol. 402:48–61, 1998. © 1998 Wiley-Liss, Inc.

  • differential central projections of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish opsanus tau
    The Journal of Comparative Neurology, 1997
    Co-Authors: Allen F. Mensinger, R Boyle, John P Carey, Stephen M. Highstein
    Abstract:

    Anatomical and neurophysiological studies were undertaken to examine the central projection pattern of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish,Opsanus tau. The variations in individual response characteristics of vestibular nerve afferents to rotational stimulus provided a means of typing the afferents into descriptive classes; the afferents fell into a broad continuum across the spectrum from low-gain, velocity-sensitive to high-gain, acceleration-sensitive responses (Boyle and Highstein [1990b] J. Neurosci. 10:1557‐1569; Boyle and Highstein [1990a] J. Neurosci. 10:1570‐1582). In the present study, each afferent was typed as a low-gain, high-gain, or acceleration fiber during rotational or mechanical stimulation (Rabbitt et al. [1995] J. Neurophysiol. 73:2237‐2260) and was then intracellularly injected with biocytin. The axons were reconstructed, and the morphology, synaptic boutons, and projection pattern of each axon were determined. The results indicated that the three descriptive classes of vestibular nerve afferents have unique as well as overlapping central projection patterns and destinations in the vestibular nuclei, with intranuclear parcellation in the anterior octavus, magnocellularis, tangentialis, posterior octavus, and descending octavus nuclei. In general, increased sensitivity and faster response dynamics were correlated with both a more extensive central projection and a progressive increase in morphological complexity. Lowgain, velocity-sensitive fibers were the simplest morphologically, with the fewest number of branches (n 517) and shortest length (4,282 µm), and projections were confined to the middle portions of the vestibular nuclei. High-gain, velocity-sensitive fibers were morphologically more diverse than low-gain fibers, with a greater number of branches (n 5 26), longer length (6,059 µm), 29% greater volume, and a more widespread projection pattern with projections to both the anterior and the middle portions of the vestibular nuclei. Acceleration fibers were morphologically distinct from low- and high-gain fibers, with more elaborate branching (n 5 41), greatest overall length (17,370 µm) and volume (16% greater than high gains), and displayed the most extensive central projection pattern, innervating all vestibular nuclei except tangentialis. Thus, there are anatomically demonstrable differential central projections of Canal afferents with different response dynamics within the vestibular complex of the fish. J. Comp. Neurol. 384:71‐85, 1997. r 1997 Wiley-Liss, Inc. Indexing terms: teleost; synaptic bouton; vestibular nuclei

  • Sensory transduction of head velocity and acceleration in the toadfish Horizontal Semicircular Canal.
    Journal of neurophysiology, 1994
    Co-Authors: Richard D. Rabbitt, R Boyle, Stephen M. Highstein
    Abstract:

    1. Sinusoidal mechanical indentation of the long-and-slender limb of the Horizontal Semicircular Canal and/or utricle was used to produce adequate stimulation of the labyrinth. Indentation of the Canal increased, while indentation of the utricle decreased the afferent discharge rate. This follows because indentation of the Canal and utricle produce oppositely directed mechanical stimuli as defined by endolymph flow, transcupular pressure, and cupular deflection. Simultaneous in-phase indentations of both the Canal and utricle, with amplitudes adjusted to produce equal (but opposite) magnitudes of afferent response modulation, generate destructive interaction that minimizes the afferent modulation, whereas sinusoidal indentation 180 degrees out-of-phase generates constructive interaction that maximizes the afferent modulation. This observation correlates directly with analysis of the labyrinthine elasto-hydrodynamics which predicts that balanced in-phase indentations minimize macromechanical endolymph flow through the ampullary cross section and maximize the dilatational pressure within the ampulla acting equally on both sides of the cupula and across the labyrinthine wall. 2. Two groups of afferents are identified according to their response to balanced sinusoidal indentation of the Canal limb and the utricle. In one group there is complete destructive interaction and the afferent response can be effectively nulled by adjusting the relative amplitude and phase of the two stimuli. In the second group a residual afferent response remains that cannot be nulled. The residual is described in the model as unit-specific sensitivity to dilatational pressure acting equally on both sides of the cupula.

R Boyle - One of the best experts on this subject based on the ideXlab platform.

  • differential central projections of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish opsanus tau
    The Journal of Comparative Neurology, 1997
    Co-Authors: Allen F. Mensinger, R Boyle, John P Carey, Stephen M. Highstein
    Abstract:

    Anatomical and neurophysiological studies were undertaken to examine the central projection pattern of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish,Opsanus tau. The variations in individual response characteristics of vestibular nerve afferents to rotational stimulus provided a means of typing the afferents into descriptive classes; the afferents fell into a broad continuum across the spectrum from low-gain, velocity-sensitive to high-gain, acceleration-sensitive responses (Boyle and Highstein [1990b] J. Neurosci. 10:1557‐1569; Boyle and Highstein [1990a] J. Neurosci. 10:1570‐1582). In the present study, each afferent was typed as a low-gain, high-gain, or acceleration fiber during rotational or mechanical stimulation (Rabbitt et al. [1995] J. Neurophysiol. 73:2237‐2260) and was then intracellularly injected with biocytin. The axons were reconstructed, and the morphology, synaptic boutons, and projection pattern of each axon were determined. The results indicated that the three descriptive classes of vestibular nerve afferents have unique as well as overlapping central projection patterns and destinations in the vestibular nuclei, with intranuclear parcellation in the anterior octavus, magnocellularis, tangentialis, posterior octavus, and descending octavus nuclei. In general, increased sensitivity and faster response dynamics were correlated with both a more extensive central projection and a progressive increase in morphological complexity. Lowgain, velocity-sensitive fibers were the simplest morphologically, with the fewest number of branches (n 517) and shortest length (4,282 µm), and projections were confined to the middle portions of the vestibular nuclei. High-gain, velocity-sensitive fibers were morphologically more diverse than low-gain fibers, with a greater number of branches (n 5 26), longer length (6,059 µm), 29% greater volume, and a more widespread projection pattern with projections to both the anterior and the middle portions of the vestibular nuclei. Acceleration fibers were morphologically distinct from low- and high-gain fibers, with more elaborate branching (n 5 41), greatest overall length (17,370 µm) and volume (16% greater than high gains), and displayed the most extensive central projection pattern, innervating all vestibular nuclei except tangentialis. Thus, there are anatomically demonstrable differential central projections of Canal afferents with different response dynamics within the vestibular complex of the fish. J. Comp. Neurol. 384:71‐85, 1997. r 1997 Wiley-Liss, Inc. Indexing terms: teleost; synaptic bouton; vestibular nuclei

  • Sensory transduction of head velocity and acceleration in the toadfish Horizontal Semicircular Canal.
    Journal of neurophysiology, 1994
    Co-Authors: Richard D. Rabbitt, R Boyle, Stephen M. Highstein
    Abstract:

    1. Sinusoidal mechanical indentation of the long-and-slender limb of the Horizontal Semicircular Canal and/or utricle was used to produce adequate stimulation of the labyrinth. Indentation of the Canal increased, while indentation of the utricle decreased the afferent discharge rate. This follows because indentation of the Canal and utricle produce oppositely directed mechanical stimuli as defined by endolymph flow, transcupular pressure, and cupular deflection. Simultaneous in-phase indentations of both the Canal and utricle, with amplitudes adjusted to produce equal (but opposite) magnitudes of afferent response modulation, generate destructive interaction that minimizes the afferent modulation, whereas sinusoidal indentation 180 degrees out-of-phase generates constructive interaction that maximizes the afferent modulation. This observation correlates directly with analysis of the labyrinthine elasto-hydrodynamics which predicts that balanced in-phase indentations minimize macromechanical endolymph flow through the ampullary cross section and maximize the dilatational pressure within the ampulla acting equally on both sides of the cupula and across the labyrinthine wall. 2. Two groups of afferents are identified according to their response to balanced sinusoidal indentation of the Canal limb and the utricle. In one group there is complete destructive interaction and the afferent response can be effectively nulled by adjusting the relative amplitude and phase of the two stimuli. In the second group a residual afferent response remains that cannot be nulled. The residual is described in the model as unit-specific sensitivity to dilatational pressure acting equally on both sides of the cupula.

  • Morphological correlates of response dynamics and efferent stimulation in Horizontal Semicircular Canal afferents of the toadfish, Opsanus tau.
    Journal of neurophysiology, 1991
    Co-Authors: R Boyle, John P Carey, Sm Highstein
    Abstract:

    1. We used the intraaxonal labeling technique to study correlations between the terminal dendritic morphology of Horizontal Semicircular Canal primary afferents and their response dynamics to sinusoidal head rotation and combined electrical stimulation of central efferent vestibular neurons. Thirty-eight Canal afferents were identified by their sensitivity and phase of response to rotation between 0.1 and 1.0 Hz (+/- 10 degrees/s) and were subsequently labeled with horseradish peroxidase or biocytin. The afferent's dendritic field and synaptic specializations in the neuroepithelium of the crista were examined under light microscopy. 2. Rate and regularity of background discharge of the afferent were not correlated with its axon diameter or relative location of its dendritic field in the crista. 3. Response sensitivity of the afferent to rotation was correlated both with the relative location of its dendritic field in the crista and with the number of terminal endings it possesses. Afferents having low sensitivities, slow dynamics, and few terminal endings supply the peripheral portions of the crista; afferents with higher sensitivities, faster dynamics, and greater number of terminal endings supply the more central portions. It is suggested that the differences in sensitivity among the afferents reflect principally the variations in both the cupular dynamics along the crista and the number of possible hair cell contact sites in the neuroepithelium. 4. Response phase of the afferent was correlated only with the extent of its dendritic processes along the transverse axis of the crista. Afferents having transversely oriented dendritic fields had less phase lags relative to acceleration than did those having a more longitudinally oriented dendritic field. 5. Efferent stimulation produced a change in both the afferent's discharge rate and its response sensitivity to rotation. Afferents discharge rate and its response sensitivity to rotation. Afferents having a centrally located dendritic field and acceleration afferents, defined by their response to rotation, were the most affected by efferent stimulation. These results suggest that efferent innervation is either directed toward, or most efficacious in, the central regions of the crista and that it may select specific hair cell-afferent complexes.

Allen F. Mensinger - One of the best experts on this subject based on the ideXlab platform.

  • Characteristics of regenerating Horizontal Semicircular Canal afferent and efferent fibers in the toadfish, Opsanus tau.
    The Journal of comparative neurology, 1999
    Co-Authors: Allen F. Mensinger, Stephen M. Highstein
    Abstract:

    The Horizontal Semicircular Canal nerve of the toadfish, Opsanus tau, was transected and allowed to regenerate. The time course, morphometrics, and projection patterns of regenerating afferent and efferent vestibular fibers were determined. Nerve transections were performed both pre- and postganglionically, and regeneration was assessed in afferent and efferent fibers by bulk labeling the peripheral axons of the Horizontal Semicircular Canal nerve with biocytin after nerve regrowth. Afferent fibers regrew through the transection site within 14 days and projected to all vestibular nuclei within 3 weeks. Bouton and branch number, axon length, surface area, volume, fiber diameter, and internodal distance were quantified for afferent fibers from eight sites within the vestibular nuclei, and axon number and soma size was quantified for the efferent fibers. Extensive regeneration was seen within 5 weeks of transection in all nuclei, and most morphometric parameters approached or exceeded control levels within 10 weeks. Regeneration appeared to recapitulate morphogenesis with an initial overproduction of boutons and branch points followed by elimination of presumably superfluous structures. Internodal distance remained significantly shorter in regenerating afferent axons than in control fish throughout the 15-week observation period. Efferent fibers also were observed to regenerate. Efferent axon number, diameter, and soma size were indistinguishable from those in controls from 3 weeks posttransection through week 15. Electrophysiological recordings from the Horizontal Canal nerve during mechanical stimuli of the Canal confirmed that the regenerated axons transmitted normal signals. The return of normal equilibrium and behavior coincided with the projection of afferent fibers into the central vestibular nuclei, indicating that functional connections had been reestablished.

  • differential central projections of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish opsanus tau
    The Journal of Comparative Neurology, 1997
    Co-Authors: Allen F. Mensinger, R Boyle, John P Carey, Stephen M. Highstein
    Abstract:

    Anatomical and neurophysiological studies were undertaken to examine the central projection pattern of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish,Opsanus tau. The variations in individual response characteristics of vestibular nerve afferents to rotational stimulus provided a means of typing the afferents into descriptive classes; the afferents fell into a broad continuum across the spectrum from low-gain, velocity-sensitive to high-gain, acceleration-sensitive responses (Boyle and Highstein [1990b] J. Neurosci. 10:1557‐1569; Boyle and Highstein [1990a] J. Neurosci. 10:1570‐1582). In the present study, each afferent was typed as a low-gain, high-gain, or acceleration fiber during rotational or mechanical stimulation (Rabbitt et al. [1995] J. Neurophysiol. 73:2237‐2260) and was then intracellularly injected with biocytin. The axons were reconstructed, and the morphology, synaptic boutons, and projection pattern of each axon were determined. The results indicated that the three descriptive classes of vestibular nerve afferents have unique as well as overlapping central projection patterns and destinations in the vestibular nuclei, with intranuclear parcellation in the anterior octavus, magnocellularis, tangentialis, posterior octavus, and descending octavus nuclei. In general, increased sensitivity and faster response dynamics were correlated with both a more extensive central projection and a progressive increase in morphological complexity. Lowgain, velocity-sensitive fibers were the simplest morphologically, with the fewest number of branches (n 517) and shortest length (4,282 µm), and projections were confined to the middle portions of the vestibular nuclei. High-gain, velocity-sensitive fibers were morphologically more diverse than low-gain fibers, with a greater number of branches (n 5 26), longer length (6,059 µm), 29% greater volume, and a more widespread projection pattern with projections to both the anterior and the middle portions of the vestibular nuclei. Acceleration fibers were morphologically distinct from low- and high-gain fibers, with more elaborate branching (n 5 41), greatest overall length (17,370 µm) and volume (16% greater than high gains), and displayed the most extensive central projection pattern, innervating all vestibular nuclei except tangentialis. Thus, there are anatomically demonstrable differential central projections of Canal afferents with different response dynamics within the vestibular complex of the fish. J. Comp. Neurol. 384:71‐85, 1997. r 1997 Wiley-Liss, Inc. Indexing terms: teleost; synaptic bouton; vestibular nuclei

John P Carey - One of the best experts on this subject based on the ideXlab platform.

  • differential central projections of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish opsanus tau
    The Journal of Comparative Neurology, 1997
    Co-Authors: Allen F. Mensinger, R Boyle, John P Carey, Stephen M. Highstein
    Abstract:

    Anatomical and neurophysiological studies were undertaken to examine the central projection pattern of physiologically characterized Horizontal Semicircular Canal vestibular nerve afferents in the toadfish,Opsanus tau. The variations in individual response characteristics of vestibular nerve afferents to rotational stimulus provided a means of typing the afferents into descriptive classes; the afferents fell into a broad continuum across the spectrum from low-gain, velocity-sensitive to high-gain, acceleration-sensitive responses (Boyle and Highstein [1990b] J. Neurosci. 10:1557‐1569; Boyle and Highstein [1990a] J. Neurosci. 10:1570‐1582). In the present study, each afferent was typed as a low-gain, high-gain, or acceleration fiber during rotational or mechanical stimulation (Rabbitt et al. [1995] J. Neurophysiol. 73:2237‐2260) and was then intracellularly injected with biocytin. The axons were reconstructed, and the morphology, synaptic boutons, and projection pattern of each axon were determined. The results indicated that the three descriptive classes of vestibular nerve afferents have unique as well as overlapping central projection patterns and destinations in the vestibular nuclei, with intranuclear parcellation in the anterior octavus, magnocellularis, tangentialis, posterior octavus, and descending octavus nuclei. In general, increased sensitivity and faster response dynamics were correlated with both a more extensive central projection and a progressive increase in morphological complexity. Lowgain, velocity-sensitive fibers were the simplest morphologically, with the fewest number of branches (n 517) and shortest length (4,282 µm), and projections were confined to the middle portions of the vestibular nuclei. High-gain, velocity-sensitive fibers were morphologically more diverse than low-gain fibers, with a greater number of branches (n 5 26), longer length (6,059 µm), 29% greater volume, and a more widespread projection pattern with projections to both the anterior and the middle portions of the vestibular nuclei. Acceleration fibers were morphologically distinct from low- and high-gain fibers, with more elaborate branching (n 5 41), greatest overall length (17,370 µm) and volume (16% greater than high gains), and displayed the most extensive central projection pattern, innervating all vestibular nuclei except tangentialis. Thus, there are anatomically demonstrable differential central projections of Canal afferents with different response dynamics within the vestibular complex of the fish. J. Comp. Neurol. 384:71‐85, 1997. r 1997 Wiley-Liss, Inc. Indexing terms: teleost; synaptic bouton; vestibular nuclei

  • Morphological correlates of response dynamics and efferent stimulation in Horizontal Semicircular Canal afferents of the toadfish, Opsanus tau.
    Journal of neurophysiology, 1991
    Co-Authors: R Boyle, John P Carey, Sm Highstein
    Abstract:

    1. We used the intraaxonal labeling technique to study correlations between the terminal dendritic morphology of Horizontal Semicircular Canal primary afferents and their response dynamics to sinusoidal head rotation and combined electrical stimulation of central efferent vestibular neurons. Thirty-eight Canal afferents were identified by their sensitivity and phase of response to rotation between 0.1 and 1.0 Hz (+/- 10 degrees/s) and were subsequently labeled with horseradish peroxidase or biocytin. The afferent's dendritic field and synaptic specializations in the neuroepithelium of the crista were examined under light microscopy. 2. Rate and regularity of background discharge of the afferent were not correlated with its axon diameter or relative location of its dendritic field in the crista. 3. Response sensitivity of the afferent to rotation was correlated both with the relative location of its dendritic field in the crista and with the number of terminal endings it possesses. Afferents having low sensitivities, slow dynamics, and few terminal endings supply the peripheral portions of the crista; afferents with higher sensitivities, faster dynamics, and greater number of terminal endings supply the more central portions. It is suggested that the differences in sensitivity among the afferents reflect principally the variations in both the cupular dynamics along the crista and the number of possible hair cell contact sites in the neuroepithelium. 4. Response phase of the afferent was correlated only with the extent of its dendritic processes along the transverse axis of the crista. Afferents having transversely oriented dendritic fields had less phase lags relative to acceleration than did those having a more longitudinally oriented dendritic field. 5. Efferent stimulation produced a change in both the afferent's discharge rate and its response sensitivity to rotation. Afferents discharge rate and its response sensitivity to rotation. Afferents having a centrally located dendritic field and acceleration afferents, defined by their response to rotation, were the most affected by efferent stimulation. These results suggest that efferent innervation is either directed toward, or most efficacious in, the central regions of the crista and that it may select specific hair cell-afferent complexes.

Y. Uchino - One of the best experts on this subject based on the ideXlab platform.

  • comparison of spinal projection of the vestibular neurons receiving inputs from Horizontal Semicircular Canal and otolith in cats
    Equilibrium Research, 2005
    Co-Authors: Naoharu Kitajima, Akemi Sugita, Izumi Koizuka, Y. Uchino
    Abstract:

    We studied the properties of Horizontal Semicircular Canal (HC) nerve-activated vestibulospinal neurons, which include vestibulo-spinal (VS) and vestibulo-oculo-spinal (VOS) neurons. Axonal pathways, projection levels, and locations of HC nerveactivated vestibulospinal neurons were studied. The HC nerve was selectively stimulated. HC nerve-activated vestibulospinal neurons were mainly located in the ventral portion of the medial and lateral vestibular nuclei, and the middle portion of the descending nucleus. The majority of HC nerve-activated VS and VOS neurons sent descending axons through the medial vestibulospinal tract (MVST); the remaining neurons sent descending axons through the ipsilateral (i-) lateral vestibulospinal tract (LVST). Most neurons that had descending projections through the i-MVST were VS neurons, while most that had descending projections through the contralateral MVST were VOS neurons. All neurons with descending projections through the i-LVST were VS neurons. Almost all the HC nerve-activated vestibulospinal neurons were activated antidromically only from the cervical segment. No neurons were activated from the L3 segment. On the other hand, 14% of the utricular and 7% of the saccular nerve-activated vestibulospinal neurons were activated from the lumbar segment. The projection of HC nerveactivated vestibulospinal neurons to regions below the thoracic spinal cord appears to be minor, which is in marked contrast with the projection of otolith-activated neurons. It is likely that the majority of HC nerve-activated vestibulospinal neurons terminate in the cervical cord and have strong connections with neck motoneurons.

  • Convergence of the Horizontal Semicircular Canal and otolith afferents on cat single vestibular neurons
    Experimental Brain Research, 2001
    Co-Authors: Mohammad Zakir, H Sato, H Meng, Y. Uchino
    Abstract:

    We studied the convergence of two afferent pairs of single vestibular neurons by selective stimulation of the Horizontal Semicircular Canal (HC) and saccular (SAC) nerves, and the HC and utricular (UT) nerves in decerebrate cats. All recorded neurons were classified as vestibulospinal (VS), vestibulo-oculospinal (VOS) or vestibulo-ocular (VO), by antidromic stimulation from the oculomotor/trochlear nuclei and the spinal cord: neurons that could not be activated from any test sites were classified as vestibular (V) neurons. Of a total of 125 neurons activated by stimulation of the HC/SAC nerves, 21(17%) received convergent inputs. Twelve of 21 neurons received monosynaptic excitatory inputs from both nerves. About half (9/21, 43%) of the convergent neurons were classified as VS neurons, the majority of which descended through the ipsilateral lateral vestibulospinal tract (i-LVST). The HC/SAC convergent neurons were located in the rostral part of the descending, the medial and the caudal-ventral part of the lateral vestibular nucleus. In 80 neurons studied by stimulation of the HC/UT nerves, both inputs converged in 12 (15%) neurons, more than half of which were VS neurons. Eight of 12 convergent neurons received excitatory inputs followed by inhibition from both the HC and UT nerves. A few convergent neurons (3/12) projected to the oculomotor/trochlear nucleus. Half of the convergent and non-convergent VS neurons descended to the spinal cord through the i-LVST, and the only one VOS convergent neuron via the medial vestibulospinal tract. Most of the convergent neurons were located in the lateral, the rostral part of the descending and medial vestibular nucleus. The percentages of HC/SAC and HC/UT convergence were half those of the posterior Semicircular Canal (PC), PC/SAC (33%) and PC/UT (33%) convergence, respectively. The convergent neurons receiving the HC and otolith inputs may contribute at least partly to the vestibulocollic reflex.