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PubMed2003

Vestibular influences on CA1 neurons in the rat hippocampus: an electrophysiological study in vivo.

Vestibular information is known to be important for accurate spatial orientation and navigation. Hippocampal place cells, which appear to encode an animal's location within the environment, are also thought to play an essential role in spatial orientation. Therefore, it can be hypothesized that vestibular information may influence cornu ammonis region 1 (CA1) hippocampal neuronal activity. To explore this possibility, the effects of electrical stimulation of the medial vestibular nucleus (MVN) on the firing rates of hippocampal CA1 neurons in the urethane-anesthetized rat were investigated using extracellular single unit recordings. The firing rates of CA1 complex spike cells (n=29), which most likely correspond to place cells, consistently increased during electrical stimulation of the MVN in a current intensity dependent manner. Stimulation applied adjacent to the MVN failed to elicit a response. Overall, the firing rates of non-complex spike cells (n=22) did not show a consistent response to vestibular stimulation, although in some cells clear responses to the stimulation were observed. These findings suggest that vestibular inputs may contribute to spatial information processing in the hippocampus.

Animals↗
PubMed1985

Effect of spinal cord transection on spontaneous activity recorded from type I neurons of the medial vestibular nucleus in compensated hemilabyrinthectomized gerbils.

Spontaneous activity was recorded from type I neurons of the medial vestibular nuclei (MVN) in unanesthetized, decerebrate gerbils to determine the effect of spinal cord transection on compensation following labyrinthectomy. Immediately after labyrinthectomy there was an increase in activity of type I neurons on the intact side and an absence of activity on the injured side. Following compensation from labyrinthectomy, the distribution and activity rates approximated those of nonlabyrinthectomized animals. Spinal cord transection resulted in an increase in activity in type I MVN neurons contralateral to the labyrinthectomy in compensated animals and bilaterally in nonlabyrinthectomized animals. These results illustrate that type I neurons apparently are under an indirect inhibitory control from both the contralateral labyrinth and the spinal cord. In compensated animals spinal cord inhibition exists only on the intact side. This suggests that the symmetry in type I activity bilaterally in the compensated animal is in part the result of asymmetric spinal cord input.

Animals↗
PubMed1997

Protein kinase C in central vestibular, cerebellar, and precerebellar pathways of the rat.

The protein kinase C family of enzymes is composed of at least ten different isoforms that display a variety of distinct biochemical specificities. Many of these isoforms are highly expressed in brain, and some show regional specificity in their distribution, suggesting that they may serve specific functions. By using immunocytochemistry to localize the betaI, betaII, gamma, or delta isoforms of protein kinase C in the central vestibular system of the adult rat, we found the vestibular ganglion and its peripheral and central processes of the eighth nerve to be heavily labeled with protein kinase C betaI immunoreactivity. Labeled axons and terminals were also found in all four vestibular nuclei. Some neurons of the vestibular ganglion were weakly stained with the antibody to protein kinase C betaII, as were scattered axons in the eighth nerve, and scattered axons and terminals were found in all four vestibular nuclei among weakly labeled neurons. A few axons in the vestibular portion of the eighth nerve were labeled with protein kinase C gamma immunoreactivity, and neurons of the spinal, lateral, and superior vestibular nuclei were heavily decorated with synapses, presumably derived from Purkinje neurons, which were also strongly immunoreactive. Neurons of the medial vestibular nucleus were not as heavily innervated. With the antibody to protein kinase C delta, we found scattered, weakly immunoreactive neurons in the vestibular portion of the eighth nerve. Myelinated fiber bundles of the spinal vestibular nucleus contained moderate numbers of labeled axons, and the other vestibular nuclei were well innervated by protein kinase C delta axons and terminals. Most of these probably derive from Purkinje cells, which were labeled in longitudinal bands interspersed with bands of labeled basket cells. These data suggest that particular protein kinase C isoforms play specific roles in vestibular and cerebellar function.

Animals↗
PubMed1989

Neuronal activity in the guinea pig medial vestibular nucleus in vitro following chronic unilateral labyrinthectomy.

Unilateral labyrinthectomy (UL) causes ocular motor and postural disorders which disappear over time in a process of recovery known as vestibular compensation. Vestibular compensation is due to CNS plasticity which generates a partial recovery of resting activity in the vestibular nucleus ipsilateral to the UL, however the mechanism of this neural recovery is unknown. It has been suggested that other areas of the CNS may substitute non-vestibular sensory inputs for the missing labyrinthine input, thereby causing vestibular compensation. The present results show that resting activity can be recorded from medial vestibular nucleus (MVN) neurons in vitro, in brainstem slices from guinea pigs which have compensated for an ipsilateral UL. This result suggests that MVN neurons are capable of generating resting activity without inputs from many other CNS areas. Perfusion with high Mg2+ solution did not abolish resting activity in most cases, suggesting that part of the resting activity may be generated spontaneously by the neurons, possibly through changes in the electrical excitability of the cell membrane.

Animals↗
PubMed1995

[Cortical mechanisms of regulation of neuron activity of Deiters vestibular nucleus during vibration].

The peculiarities of the effect of vestibular, somatosensory, motor and limbic areas of brain cortex on the activity of neurons of lateral vestibular nucleus (LVN) are studied in the nembutal and chloralose anesthetized rabbits by the extracellular lead method before and after vibration exposure. It is found that the responses of neurons of Deiters's nucleus at all frequency ranges to stimulation of different areas of the cortex were predominantly of inhibitory type, being more pronounced during stimulation of the vestibular and motor areas. The facilitating corticofugal effect was noted in 20-30 % of cells and more pronounced influence was during stimulation of somatosensory and limbic areas of the cortex. During vibration there was a multidirectional effect of cortical areas on the neuronal activity of LVN. The vibration stimulus decreases an inhibitory effect and increases stimulating influence of vestibular cortex on the activity of Deiters's nucleus. The noted effect was more pronounced in neurons with low frequency of initial activity. On stimulation of other areas of the cortex an increase of inhibitory and suppression of facilitating descending effects were noted. The greatest amount of inhibited neurons was recorded during stimulation of motor cortex. The peculiarities and functional significance of the observed effects are discussed.

Animals↗
PubMed1978

The response of horizontal semicircular canal afferents to sinusoidal rotation in the cat.

Dynamic characteristics of primary vestibular afferents innervating the horizontal semicircular canal were studied in decerebrate, unanesthetized cats. Activities of individual afferent fibers were recorded intracranially by glass micropipettes. Frequency of sinusoidal rotation was varied from 0.014 Hz to 0.42 Hz, and phase and gain properties were examined. All of the fibers recorded fired spontaneously, and their firing rate ranged from 7 to 128 spikes/sec. Regularity of firing, phase lags, and gains were calculated in individual fibers. There was a tendency that the units with high spontaneous firing rates showed regular firing, larger phase lags, and lower gains that the units with low spontaneous firing rates. The transfer function of the system (firing rate of the primary afferent per angular acceleration of the head) was (formula: see text). A high frequency phase lead component was needed to account for the data obtained, indicating a slight deviation from the relationship predicted by the torsion pendulum model. The present phase properties were compared with those of vestibular nucleus neurons reported previously. It was suggested that a group of vestibular nucleus neurons transmits fairly faithfully the phase properties of primary afferents, and that another group of vestibular nucleus neurons receive additional influences from central structures, exhibiting larger phase lags than primary afferents.

Action Potentials↗
PubMed1988

Appearance and distribution of neuron-specific enolase and calbindin (CaBP 28 kDa) in the developing human inner ear.

The onset and development of neuron-specific enolase (NSE) and calbindin immunoreactivities were studied in the inner ear of human fetuses aged from 6-7 to 14 weeks of gestation. NSE occurred very early in ganglion neurons. Its appearance in vestibular sensory cells at 8 weeks coincided with the formation of the first afferent synapses, and showed an apex/base gradient in the cristae. Calbindin was found in vestibular ganglion neurons at 6-7 weeks and in the cochlear ganglion neurons at 8-9 weeks. Vestibular sensory cells and the whole ventral wall of the cochlear duct were stained from 8-9 weeks. At 14 weeks, calbindin staining occurred only in the sensory cells of the cochlear neuroepithelium. Non-neuronal secretory structures, i.e. Kölliker's organ and some cells of the transitional zone of the utricle, were also reactive. Staining appeared in Kölliker's organ with a base to apex gradient and disappeared from it with an internal to external gradient. Calbindin appeared in vestibular sensory cells later than NSE staining, synapse formation and sensory hair bundle differentiation. By contrast in the cochlea, calbindin staining appeared in the neuroepithelium before sensory cell differentiation, but remained only in the hair cells after they had differentiated and been contacted by the afferent fibers.

Antibodies↗
PubMed1992

Distribution and cerebellar projections of cholinergic and corticotropin-releasing factor-containing neurons in the caudal vestibular nuclear complex and adjacent brainstem structures.

By using immunohistochemistry combined with lesioning and retrograde neuronal labeling techniques, cholinergic neurons and corticotropin-releasing factor-immunoreactive neurons were examined for their distribution, coincidence and cerebellar projections in feline vestibular nuclear complex and adjacent brainstem structures. Cholinergic neurons as revealed here with choline acetyltransferase immunoreactivity were found massively in the abducens and hypoglossal nuclei, dorsal motor nucleus of the vagus nerve and nucleus of Roller; less numerously in the medial vestibular, prepositus hypoglossi and solitary nuclei and the caudal two-thirds of descending vestibular nucleus; and only occasionally in the intercalated and supravestibular nuclei and cell groups f, x and z. Corticotropin-releasing factor-immunoreactive neurons were found clustered in the prepositus hypoglossi nucleus and also in cell groups f and x and the rostral two-thirds of descending vestibular nucleus, less numerously in the medial vestibular, intercalated and solitary nuclei and nucleus of Roller, and only occasionally in the caudal one-third of descending vestibular nucleus, the dorsal motor nucleus of the vagus nerve, supravestibular nucleus and cell group z. The lateral and superior vestibular nuclei did not contain either type of neuron. The two types of immunopositive neurons observed in most of the brainstem nuclei differed in cell size, distribution-pattern and rostrocaudal level of occurrence. While there were many regions which exhibited both types of immunopositive neurons, perikarya colocalizing the cholinergic and peptide markers were not detected in the brainstem. Following unilateral, partial lesioning of the vestibular nuclear complex, corticotropin-releasing factor-immunoreactive mossy fiber terminals (rosettes) disappeared from the ipsilateral flocculus. However, such lesions did not produce clear-cut changes of cholinergic terminals in the vermis. Following retrograde neuronal labeling combined with immunohistochemistry, the two types of immunopositive neurons observed in most of the brainstem sites were found to project to the vermal lobules I-III, IX and X. On comparison of these immunopositive projection neurons with non-immunoreactive, retrogradely labeled neurons, the cholinergic neurons and the peptide-immunoreactive neurons were found to constitute a major part of the total vestibulocerebellar neuronal population. The results indicate chemical heterogeneity in vestibular nuclear complex and cerebellar afferents.

Afferent Pathways↗
PubMed1995

Differential effects of combined trk receptor mutations on dorsal root ganglion and inner ear sensory neurons.

We have generated double mutant mice deficient in pairs of two different Trk receptors and have analysed the effects on survival and differentiation of dorsal root ganglion (DRG), inner ear cochlear and vestibular sensory neurons. In most combinations of mutant trk alleles, the defects observed in double compared to single mutant mice were additive. However, double homozygous trkA-/-;trkB-/- DRG and trkB-/-;trkC-/- vestibular neurons showed the same degree of survival as single trkA-/- and trkB-/- mice, respectively, suggesting that those neurons required both Trk signaling pathways for survival. In situ hybridisation analysis of DRG neurons of double mutant mice revealed differential expression of excitatory neuropeptides. Whereas calcitonin-gene-related peptide expression correlated with the trkA phenotype, substance P expression was detected in all combinations of double mutant mice. In the inner ear, TrkB- and TrkC-dependent neurons were shown to at least partially depend on each other for survival, most likely indirectly due to abnormal development of their common targets. This effect was not observed in DRGs, where neurons depending on different Trk receptors generally innervate different targets.

Animals↗
PubMed2001

Resonance of spike discharge modulation in neurons of the guinea pig medial vestibular nucleus.

The modulation of action potential discharge rates is an important aspect of neuronal information processing. In these experiments, we have attempted to determine how effectively spike discharge modulation reflects changes in the membrane potential in central vestibular neurons. We have measured how their spike discharge rate was modulated by various current inputs to obtain neuronal transfer functions. Differences in the modulation of spiking rates were observed between neurons with a single, prominent after hyperpolarization (AHP, type A neurons) and cells with more complex AHPs (type B neurons). The spike discharge modulation amplitudes increased with the frequency of the current stimulus, which was quantitatively described by a neuronal model that showed a resonance peak >10 Hz. Modeling of the resonance peak required two putative potassium conductances whose properties had to be markedly dependent on the level of the membrane potential. At low frequencies (< or =0.4 Hz), the gain or magnitude functions of type A and B discharge rates were similar relative to the current input. However, resting input resistances obtained from the ratio of the membrane potential and current were lower in type B compared with type A cells, presumably due to a higher level of active potassium conductances at rest. The lower input resistance of type B neurons was compensated by a twofold greater sensitivity of their firing rate to changes in membrane potential, which suggests that synaptic inputs on their dendritic processes would be more efficacious. This increased sensitivity is also reflected in a greater ability of type B neurons to synchronize with low-amplitude sinusoidal current inputs, and in addition, their responses to steep slope ramp stimulation are enhanced over the more linear behavior of type A neurons. This behavior suggests that the type B MVNn are moderately tuned active filters that promote high-frequency responses and that type A neurons are like low-pass filters that are well suited for the resting tonic activity of the vestibular system. However, the more sensitive and phasic type B neurons contribute to both low- and high-frequency control as well as signal detection and would amplify the contribution of both irregular and regular primary afferents at high frequencies.

Action Potentials↗
PubMed2000

Relationship between vestibular primary afferents and vestibulospinal neurons in lampreys.

The distribution of vestibular primary afferents as well as their relationship with vestibulospinal and other brainstem neurons were studied in lampreys using anatomical tracers. Afferents from the anterior (aVIIIn) and the posterior (pVIIIn) branches of the vestibular nerve were located mainly in the ventral nucleus of the octavolateral area. The relationship between afferents and vestibulospinal neurons was studied by applying one fluorescent tracer to the whole vestibular nerve or one of its branches and applying another tracer to the spinal cord. Some afferents showed large, bulb-like enlargements (bulbs) and about 20 of these were found in the anterior and the intermediate octavomotor nucleus, whereas about 40 were found in the posterior octavomotor nucleus. Some of the bulbs made apparent contact with vestibulospinal neurons in the intermediate octavomotor nucleus and originated mostly from the aVIIIn, whereas bulbs in the posterior octavomotor nucleus originated from the pVIIIn. Applications of biocytin to hemisegments of rostral spinal cord labeled vestibulospinal neurons located in the ipsilateral intermediate octavomotor nucleus and the contralateral posterior octavomotor nucleus. In addition, vestibular primary afferents with bulbs in apparent contact with vestibulospinal neurons were transneuronally labeled by biocytin. They were observed in the ipsilateral aVIIIn and the contralateral pVIIIn and could be followed in the labyrinths, where they innervated the vertical and horizontal arms of the semicircular canal crests. Taken together, these results indicate that vestibular primary afferents from the aVIIIn innervate predominantly vestibulospinal neurons of the intermediate octavomotor nucleus, whereas afferents from the pVIIIn innervate vestibulospinal neurons in the posterior octavomotor nucleus. This anatomical organization suggests that afferents carrying bulbs convey dynamic information to vestibulospinal neurons, which, in turn, project to the spinal cord networks.

Afferent Pathways↗
PubMed2002

Quantitative changes in mRNA expression of glutamate receptors in the rat peripheral and central vestibular systems following hypergravity.

In order to investigate the mechanisms responsible for adaptation to altered gravity, we assessed the changes in mRNA expression of glutamate receptors in vestibular ganglion cells, medial vestibular nucleus, spinal vestibular nucleus/lateral vestibular nucleus, cerebellar flocculus, and uvula/nodulus from rats exposed to hypergravity for 2 h to 1 week using real-time quantitative RT-PCR methods. The mRNA expression of GluR2 and NR1 receptors in the uvula/nodulus and NR1 receptors in the medial vestibular nucleus increased in animals exposed to 2 h of hypergravity, and it decreased gradually to the control level. The mRNA expression of GluR2 receptors in vestibular ganglion cells decreased in animals exposed to 1 week of hypergravity. Neither the metabotropic glutamate receptor 1 nor delta2 glutamate receptor in flocculus and uvula/nodulus was affected by a hypergravity load for 2 h to 1 week. It is suggested that the animals adapted to the hypergravity by enhancing the cerebellar inhibition of the vestibular nucleus neurons through activation of the NR1 and GluR2 receptors on the Purkinje cells in uvula/nodulus especially at the early phase following hypergravity. In the later phase following hypergravity, the animals adapted to the hypergravity by reducing the neurotransmission between the vestibular hair cells and the primary vestibular neurons via down-regulation of the postsynaptic GluR2 receptors in the vestibular periphery.

Animals↗
PubMed2007

Latency of vestibular responses of pursuit neurons in the caudal frontal eye fields to whole body rotation.

The smooth pursuit system and the vestibular system interact to keep the retinal target image on the fovea by matching the eye velocity in space to target velocity during head and/or whole body movement. The caudal part of the frontal eye fields (FEF) in the fundus of the arcuate sulcus contains pursuit-related neurons and the majority of them respond to vestibular stimulation induced by whole body movement. To understand the role of FEF pursuit neurons in the interaction of vestibular and pursuit signals, we examined the latency and time course of discharge modulation to horizontal whole body rotation during different vestibular task conditions in head-stabilized monkeys. Pursuit neurons with horizontal preferred directions were selected, and they were classified either as gaze-velocity neurons or eye/head-velocity neurons based on the previous criteria. Responses of these neurons to whole body step-rotation at 20 degrees/s were examined during cancellation of the vestibulo-ocular reflex (VOR), VOR x1, and during chair steps in complete darkness without a target (VORd). The majority of pursuit neurons tested (approximately 70%) responded during VORd with latencies <80 ms. These initial responses were basically similar in the three vestibular task conditions. The shortest latency was 20 ms and the modal value was 24 ms. These responses were also similar between gaze-velocity neurons and eye/head-velocity neurons, indicating that the initial responses (<80 ms) were vestibular responses induced by semicircular canal inputs. During VOR cancellation and x1, discharge of the two groups of neurons diverged at approximately 90 ms following the onset of chair rotation, consistent with the latencies associated with smooth pursuit. The shortest latency to the onset of target motion during smooth pursuit was 80 ms and the modal value was 95 ms. The time course of discharge rate difference of the two groups of neurons between VOR cancellation and x1 was predicted by the discharge modulation associated with smooth pursuit. These results provide further support for the involvement of the caudal FEF in integration of vestibular inputs and pursuit signals.

Animals↗