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PubMed1995

Responses of neurons in the central cervical nucleus of the rat to proprioceptive and vestibular inputs.

Activity of neurons in the central cervical nucleus (CCN) was recorded extracellularly in decerebrate, immobilized rats. Neurons were identified by their antidromic response to electrical stimulation of the contralateral superior cerebellar peduncle. Stimulation of the ipsilateral dorsal neck muscles (m. biventer cervicis and complexus [BCC]; m. splenius [S]) by a single electric pulse evoked a short-latency (approximately 1 ms) excitatory response in the majority of CCN neurons. The response was usually followed by a period of inhibition of the resting discharge (approximately 20 ms). Stimulation of the contralateral BCC or S usually produced only inhibition of the resting discharge (approximately 20 ms). Mechanical stretching of BCC or S resulted in activation (about 100% increased firing rate) of the ipsilateral CCN neurons, lasting for the duration of the stretch. A pronounced dynamic component, i.e. an extra-excitation at the beginning of the stretch and inhibition after termination of the stretch, was also observed. Stroking and pinching of the skin in the neck region affected the tested CCN neurons, while cutaneous stimuli at other sites of the body were inefficient. Stimulation of the vestibular receptors was performed in two ways. (i) Unilateral galvanic stimulation of the labyrinths by constant current pulses through the external acoustic meatus affected all CCN neurons tested. Contralateral stimulation with negative current was found to be most efficient; it produced excitation followed by inhibition. (ii) Natural vestibular stimulation was performed by rotating the animal in the transverse plane (roll, +/- 10 degrees) or the sagittal plane (pitch, +/- 5 degrees). Sinusoidal movements (0.5-1 Hz) or trapezoid movements were applied. Sinusoidal roll tilt evoked responses in all neurons tested, with a peak discharge during contralateral rolling or at the moment of transition from the ipsi- to contralateral position. All tested CCN neurons also responded statically to roll tilt, i.e. their tonic activity increased with up to 65%, of which the majority (80%) responded in the continuously maintained contralateral roll tilt position compared to the ipsilateral. Sinusoidal pitch tilt also affected all tested neurons, although the reaction was smaller than compared to roll. They usually responded by increasing their firing rate when moving towards the nose-down position. A static response (40-60% difference in the firing rate between the extreme pitch positions) was observed in some neurons. No tested neurons showed any clear rhythmic modulation during either spontaneous or induced, real or fictive locomotion.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1997

Co-localization of glycine and calbindin D-28k in the vestibular ganglion of the rat.

Bipolar neurons of the vestibular ganglion (VG) are biochemically heterogeneous. The calcium-binding protein calbindin D-28k (Calb) is present only in a subset of particularly large neurons, and the amino acid glycine (Gly) has been immunocytochemically detected in a group of similarly sized cells. The close correspondence in size and number of cells in these two subgroups suggests that the Calb- and Gly-positive populations may be identical. In order to test this hypothesis, we performed direct and indirect double-labeling for Calb and Gly in the VG of the rat. The results confirm the existence of a distinct subpopulation of Calb-immunoreactive neurons, consisting of the largest cells in the VG. In contrast, the vast majority of neurons in the VG display some degree of Gly immunoreactivity, which gradually decreases from intense to almost unlabeled. Direct evidence is provided that the fraction of cells most heavily labeled by Gly antibodies is not identical with the Calb-positive subpopulation. Although some correlation between soma diameter and labeling intensity exists, Gly immunoreactivity is clearly not restricted to large neurons. The findings imply that the functional mechanisms in which Gly is potentially involved may be shared by a large spectrum of primary vestibular afferents with a broad range of physiological properties.

Animals↗
PubMedDate not supplied

Convergence of central and peripheral signals on vestibular cells.

Nerve and cortical input convergence patterns, representing the fore- and hindlimb, were studied in single cells located in the lateral vestibular nucleus of the cat. Deitersian cells responded with excitation to cortical stimulation with a latency ranging from 4 to 14 msec, while responses ranged from 9 to 12 msec to radial nerve stimulation and from 14 to 18 msec to sciatic nerve stimulation. Lateral vestibular nuclear neurons responding to radial nerve stimulation also receive the main cortical input from the sensorimotor cortical area concerned with the forelimb. Neurons responding to sciatic nerve stimulation receive an equal cortical input from both fore- and hindlimb areas of the sensorimotor cortex. In a few cells different combinations of convergence of cortical and peripheral inputs were also observed.

Action Potentials↗
PubMed2004

Expression and distribution of mu opioid receptors in the inner ear of the rat.

Opioid peptides have demonstrated modulatory effects on the vestibular afferent discharge and are putative vestibular efferent neuromodulators. The distribution of their receptors in the mammalian vestibular epithelia is not known. We used reverse transcriptase-polymerase chain reaction (RT-PCR), in situ hybridization, Western blots and immunohistochemistry to study the expression of mu opioid receptor (MOR) in the Scarpa's ganglia and cristae ampullares of rats. MOR transcript was only detected in the somata of the vestibular afferent neurons. MOR-like immunoreactivity was observed in the somata of vestibular afferents and in nerve terminals in the cristae ampullares epithelia both in the center and peripheral regions. Double labeling of cristae sections with the MOR1 antibody in combination with antibodies against calretinin (a marker for vestibular afferents terminating in calices) and peripherin (a marker for afferents terminating in boutons), respectively showed that MOR1 immunoreactivity was in calyx, dimorphic and bouton vestibular afferents. MOR immunoreactivity was not detected in vestibular efferent fibers identified with choline acetyltransferase immunohistochemistry. These results indicate that MOR may mediate effects of vestibular efferents on afferents.

Animals↗
PubMed1983

Electrophysiological analysis of cerebellar corticovestibular and fastigiovestibular projections to the lateral vestibular nucleus in the cat.

In the lateral vestibular nucleus, vestibulospinal tract (VST) neurons were surveyed with microelectrodes in cats anesthetized with sodium pentobarbital. The VST neurons (n = 450) were classified by their properties; axonal courses (LVST and MVST). spinal segmental levels of their axonal termination (C1-3, C4-8, T1-13, L1-4, and L5-neurons), their orthodromic activation by the primary vestibular nerve (second-order and non-second-order vestibular neurons), and their location in the LVN. Inhibitory and excitatory effects of cerebellar stimulation on these classified VST neurons were investigated. 84% (259/308) neurons were observed to receive cerebellar corticovestibular inhibition. The rate was high, and almost the same among classified neurons; C1-3 to L5-neurons, and second-order and non-second-order neurons. However, the rate with MVST neurons (69%) was significantly lower than with LVST cells (87%). These neurons which received cerebellar inhibition were distributed in all areas even deep in the rostroventral region of the LVN, while neurons which did not receive were distributed in the ventral region of the LVN. Electrical stimulation of ipsi- and contralateral fastigial nuclei evoked monosynaptic excitation of the classified VST neurons. Rate of occurrence of crossed fastigiovestibular excitation was higher with cervical neurons (86%) than with lumbar neurons (43%), and higher with second-order neurons (78%) than with non-second-order neurons (41%). Neurons which received monosynaptic excitation from crossed fastigiovestibular fibers were distributed in the ventral region of the LVN. In total, 73% of the neurons were identified to receive either ipsi- or contralateral fastigiovestibular excitation. The results indicated that there was relative scarcity of fastigiovestibular projections in the dorsal region of the LVN. Spinovestibular and other afferents to the LVN were also investigated.

Animals↗
PubMed1979

Behavior of the oculomotor neurons discharge during sinusoidal lateral tilt in the rabbit.

The characteristics of the control exerted by macular and ampullar vestibular receptors on oculomotor neurons (OMN) have been investigated by submitting unanesthetized, encéphale isolé rabbits to sinusoidal lateral tilts of varying frequencies (0.013-0.2 Hz). The phase of the response exhibited a progressive shift towards head velocity with increasing frequencies of tilt. The sensitivity of the OMN significantly increased at frequencies above 0.025 Hz, corresponding to peak accelerations suprathreshold for canals related vestibular neurons. The convergent action of macular and ampullar vestibular receptors in the control of vertical eye movements is discussed in relation with stimulus frequency.

Animals↗
PubMed1980

Visual-vestibular convergence in the vestibular nuclei of the cat.

Responses from neurons of the vestibular nuclei were recorded in N2O-anaesthetized cats. Most neurons in the rostral parts of the nuclei responded to bimodal visual-vestibular stimulation, following a trapezoidal velocity profile. Both combinations of the two stimuli were tested: rotation of the animal with stationary visual field and rotation with overtaking visual field, i.e. the visual pattern running in the same direction as the turntable with twice the velocity. Some correlation of physiological data with results in corresponding psychophysical experiments were found. As a possible biological function of visual-vestibular convergence a phylogenetic solution for discrimination of body and outer world movement is discussed.

Animals↗
PubMed1993

Glutamate metabotropic receptor mediated depression of synaptic inputs to lamprey reticulospinal neurones.

The transmission of vestibular inputs to reticulospinal (RS) neurones of the posterior rhombencephalic nucleus (PRRN) has been shown to be depressed by the bath application of N-methyl-D-aspartate (NMDA). The aim of this study was to investigate the pharmacological mechanism involved using patch clamp recordings of reticulospinal neurones. It is demonstrated that the chemical component of vestibular inputs to the PRRN is mediated by glutamatergic synapses utilising alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors on the PRRN neurones. Monosynaptic excitatory postsynaptic currents (EPSCs) from octavomotorius relay cells to RS neurones are markedly depressed by the application of NMDA, a depression which was insensitive to competitive and non-competitive NMDA receptor antagonists. The effect of NMDA was eliminated by inactivation of G proteins. A similar depressive effect was observed following application of (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) to the superfusate. It is concluded that NMDA acts at a metabotropic receptor located most likely presynaptically to reticulospinal neurones on terminals of octavomotorius relay cells.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

Efferent innervation of vestibular receptors in the cat: a radioautographic visualization.

A tritiated amino acid tracing method was used to test the hypothesis that a unilateral group of vestibular efferent neurons of the brain stem may present different innervation patterns to the sensory vestibular epithelia of the ipsi- and contralateral labyrinths. Densitometric analysis of labeled efferent endings suggested a heterogeneity of the efferent projections issuing from a unilateral predominated in the maculae utriculi and cristae ampullares of the semicircular canals. These findings are discussed as a function of other data related to efferent vestibular control.

Animals↗
PubMed1997

The development of vestibulocochlear efferents and cochlear afferents in mice.

We have reinvestigated the embryonic development of the vestibulocochlear system in mice using anterograde and retrograde tracing techniques. Our studies reveal that rhombomeres 4 and 5 include five motor neuron populations. One of these, the abducens nucleus, will not be dealt with here. Rhombomere 4 gives rise to three of the remaining populations: the facial branchial motor neurons; the vestibular efferents; and the cochlear efferents. The migration of the facial branchial motor neurons away from the otic efferents is completed by 13.5 days post coitum (dpc). Subsequently the otic efferents separate into the vestibular and cochlear efferents, and complete their migration by 14.5 dpc. In addition to their common origin, all three populations have perikarya that migrate via translocation through secondary processes, form a continuous column upon completion of their migrations, and form axonal tracts that run in the internal facial genu. Some otic efferent axons travel with the facial branchial motor nerve from the internal facial genu and exit the brain with that nerve. These data suggest that facial branchial motor neurons and otic efferents are derived from a common precursor population and use similar cues for pathway recognition within the brain. In contrast, rhombomere 5 gives rise to the fourth population to be considered here, the superior salivatory nucleus, a visceral motor neuron group. Other differences between this group and those derived from rhombomere 4 include perikaryal migration as a result of translocation first through primary processes and only then through secondary processes, a final location lateral to the branchial motor/otic efferent column, and axonal tracts that are completely segregated from those of the facial branchial and otic efferents throughout their course inside the brain. Analysis of the peripheral distribution of the cochlear efferents and afferents show that efferents reach the spiral ganglion at 12.5 dpc when postmitotic ganglion cells are migrating away from the cochlear anlage. The efferents begin to form the intraganglionic spiral bundle by 14.5 dpc and the inner spiral bundle by 16.5 dpc in the basal turn. They have extensive collaterals among supporting cells of the greater epithelial ridge from 16.5 dpc onwards. Afferents and efferents in the basal turn of the cochlea extend through all three rows of outer hair cells by 18.5 dpc. Selective labeling of afferent fibers at 20.5 dpc (postnatal day 1) shows that although some afferents are still in early developmental stages, some type II spiral ganglion cells already extend for long distances along the outer hair cells, and some type I spiral ganglion cells end on a single inner hair cell. These data support previous evidence that in mice the early outgrowth of afferent and efferent fibers is essentially achieved by birth.

Animals↗
PubMed1994

Nitric oxide in the rat vestibular system.

Nitric oxide is known to function as a neurotransmitter in the central nervous system. It is also known to be involved in the central nervous system excitatory amino acid neurotransmission cascade. Activation of excitatory amino acid receptors causes an influx of calcium, which activates nitric oxide synthase. The resulting increase in intracellular nitric oxide activates soluble guanylate cyclase, leading to a rise in cyclic guanosine monophosphate. The excitatory amino acids glutamate and aspartate are found in the vestibular system and have been postulated to function as vestibular system neurotransmitters. Although nitric oxide has been investigated as a neurotransmitter in other tissues, no published studies have examined the role of nitric oxide in the vestibular system. Neuronal NADPH-diaphorase has been characterized as a nitric oxide synthase. This enzyme catalyzes the conversion of L-arginine to L-citrulline, producing nitric oxide during the reaction. We used a histochemical stain characterized by Hope et al. (Proc Natl Acad Sci 1991;88:2811) as specific for neuronal nitric oxide synthase to localize the enzyme in the rat vestibular system. An immunocytochemical stain was used to examine rat inner ear tissue for the presence of the enzyme's end product, L-citrulline, thereby demonstrating nitric oxide synthase activity. Staining of vestibular ganglion sections showed nitric oxide synthase presence and activity in ganglion cells and nerve fibers. These results indicate the presence of active nitric oxide synthase in these tissues and suggest modulation of vestibular neurotransmission by nitric oxide.

Amino Acid Oxidoreductases↗
PubMed1987

Vestibular effects in long C3-C5 propriospinal neurones.

The effects of stimulation of the vestibular nerve and of regions in and around the vestibular nuclei on long C3-C5 propriospinal neurones (PNs) were investigated with intracellular recording. Disynaptic excitatory postsynaptic potentials were evoked from the contralateral (co) or ipsilateral (i) vestibular nerve in many long PNs but mainly in crossed PNs from the co and in uncrossed from the i nerve. Disynaptic inhibitory postsynaptic potentials were evoked more rarely, mainly from the i vestibular nerve. Threshold mapping revealed an excitatory relay from the co nerve in the medial vestibular nucleus (MVN) and also that the excitatory MVN neurones projecting to the long PNs send collaterals to the abducens and interstitial nucleus of Cajal. Excitation from the i vestibular nerve was relayed in the lateral vestibular nucleus (LVN) and in the MVN. Also, non-second order LVN neurones project to the long PNs. Monosynaptic IPSPs were evoked from the i MVN and i LVN.

Brain Mapping↗
PubMed1993

Interaction of saccadic and vestibular mechanisms in combined eye-head gaze shifts.

Saccades are the only purely volitional eye movements available to primates. They are used extensively to acquire new or interesting targets in the visual environment. Most patients with saccadic disorders are referred to neurologists. Patients complaining of disorientation, however, are often presumed to be suffering from a vestibular disorder. Vestibular and saccadic physiology has been studied mostly in isolation of each other. We examine the interaction of saccadic burst neurons and vestibular signals to achieve accurate gaze shifts.

Animals↗
PubMed1982

Fine structure of the neurons and synapses of the vestibular ganglion of the cat.

The vestibular ganglion of 3-month-old cat was studied electron microscopically. The results revealed that the nerve cell bodies are surrounded by thin myelin sheaths which differ in some respects from typical axonal myelin. The neuronal soma displayed different cytoplasmic features and the neurons were classified into two types: light cells and dark cells. Light neurons contained individual clumps of Nissl substance distributed randomly throughout the cytoplasm, dark neurons were characterised by densely packed stacks of Nissl substance in the peripheral cytoplasm. The dark neurons of the ganglion are the only sensory neurons so far described which receive synapses.

Animals↗
PubMed1983

Neuronal organization of the vestibulospinal system in the cat.

In the lateral and descending vestibular nucleus, vestibulospinal neurons were surveyed extra- and intracellularly in cats anesthetized with sodium pentobarbital. The neurons were investigated both by their antidromic activation from the spinal cord (C1, C4, T1, L1 and L5 spinal levels) and from the oculomotor nucleus region, and by orthodromic activation from the vestibular nerve. Axonal courses of vestibulospinal neurons were determined electrophysiologically at C1 level, as medial (MVST) or lateral (LVST). By single and the same electrodes a number of neurons were recorded in wide regions of the lateral and descending vestibular nucleus from single cats. Thus, it became possible to investigate somatotopical localization systematically for the first time with microelectrode techniques. Neurons of origin of the LVST were localized in the lateral vestibular nucleus. Second-order vestibular neurons were localized in the ventral region of the lateral vestibular nucleus, and in the rostral region of the descending vestibular nucleus. Many second-order, double discharge MVST neurons were identified in the descending and lateral vestibular nucleus. Somatotopical localization were recognized, but non-second-order cervical neurons were identified in the dorsal region, although second-order lumbar neurons were identified in the ventral region of the lateral vestibular nucleus. Specific modes of vestibular activation of these vestibulospinal neurons were discussed, and the vestibulospinal systems in the cat and rabbit were discussed.

Afferent Pathways↗
PubMed1997

Expression of the AMPA-selective receptor subunits in the vestibular nuclei of the chinchilla.

The distribution of the AMPA type glutamate receptor has been investigated throughout the central nervous system; however, no detailed description of its distribution is available in the vestibular nuclei. In the present study, in situ hybridization histochemistry and immunohistochemistry were used to localize the messenger RNAs and proteins of the AMPA-selective receptor subunits GluR1, GluR2, GluR3 and GluR4 in the vestibular nuclei of the chinchilla. Immunohistochemistry with subunits specific antisera showed differential distribution of the subunits in the vestibular nuclei. GluR2/3 antiserum labeled the most neurons, suggesting that many if not all vestibular neurons receive glutamatergic input. GluR1-positive neurons were fewer than GluR2/3 immunoreactive neurons and GluR4 immunoreactivity was found in the fewest number of neurons. GluR1 and GluR4 immunoreactivity was also found in astrocyte-like structures. In situ hybridization with 35S-labeled complementary RNA probes confirmed the distribution of the AMPA receptor subunits obtained by immunohistochemistry. Quantitative analysis of the levels of hybridization showed a high degree of diversity in the levels of expression of the GluR2 subunit mRNA, with the highest levels of expression in the giant Deiter's cells of the lateral vestibular nuclei and the lowest levels in the small neurons throughout the vestibular nuclei. The subunit compositions of the AMPA receptors determine their physiological properties. Differential distribution and levels of expression of the receptor subunits in the vestibular nuclei may be related to the characteristics of information processing through the vestibular system.

Animals↗