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PubMed2001

Peripheral patterns of terminal innervation of vestibular primary afferent neurons projecting to the vestibulocerebellum in the gerbil.

Retrograde transganglionic labeling techniques with biotinylated dextran amine (BDA) were used to examine the terminal field structure and topographical patterns of innervation within the vestibular sensory end organs of vestibular primary afferent neurons projecting to the cerebellar uvula/nodulus and flocculus lobules in the gerbil. Robust, dark labeling in the cristae ampullares suggested that the vast majority of the terminals of afferent neurons were of the dimorphic type. The majority (94% to the uvula/nodulus and 100% to the flocculus) innervates the peripheral zones of each of the three semicircular canal cristae. Comparison of the type and distribution of terminals across the canalicular sensory neuroepithelium with morphophysiological studies in chinchilla suggests that the labeled population consists predominantly of peripheral terminal fields of lower-to-intermediate gain, more regularly firing, tonic afferents. For otolith organ-related afferents, the uvula/nodulus receives strong inputs from primary otolith afferent neurons identified as dimorphic in type that predominately innervate the peristriolar zones of the utricular and saccular maculae. No direct otolith organ-related inputs to the flocculus were observed. In contrast to the canal afferents, the types and locations of labeled otolith afferent terminals suggest that they largely consist of irregularly firing, high-gain, phasic neurons.

Animals↗
PubMed1990

Effects of motor cortex and single muscle stimulation on neurons of the lateral vestibular nucleus in the rat.

The neuronal responses to stimulation of motor cortical sites and of forelimb single muscles were studied in the lateral vestibular nucleus of anaesthetized rats. Of the 228 neurons tested for response to stimulation of contralateral motor cortex, 63% responded to cortical sites controlling extensor muscles and 30% to those controlling flexors. The corresponding figures for responders to ipsilateral stimulation were 34 and 21%. Vestibulospinal units responded to cortical sites controlling extensor and flexor muscles whereas the remaining lateral vestibular nucleus neurons, very reactive to cortical sites controlling extensor muscles, responded little to contralateral and not at all to ipsilateral cortical sites controlling flexor muscles. The effects evoked by contralateral cortical sites controlling extensors varied, those induced by cortical sites controlling flexors were inhibitory in 77% of cases. The responses to ipsilateral motor cortex stimulation differed not so much by cortical sites controlling extensor or flexor muscles as by whether the neuron was in the dorsal or ventral zone of the lateral vestibular nucleus: mixed in the former, all inhibitory in the latter. Of the lateral vestibular nucleus units tested for response to stimulation of ipsilateral or contralateral forelimb distal muscles, only 11% responded. All the vestibulospinal units responsive to muscle stimulation lay in the dorsal zone of the nucleus. The remainder, dorsal or ventral, were not responsive to contralateral muscles. Single lateral vestibular nucleus cells influenced both by ipsilateral muscle and by contralateral motor cortex made up 24% of the pool, vestibulospinal and non-vestibulospinal. They fell into three groups: responsive to one or both structures but responding more strongly to combined stimulation; responsive to each of the two structures but showing a response to combined stimulation not significantly different from that evoked by the cortex alone; responsive only to combined stimulation. The lateral vestibular nucleus units included in these three groups accounted for 29% of those tested for response to extensor muscles and cortical sites controlling extensors and 15% of those tested for response to flexor muscles and cortical sites controlling flexors. Twenty-five per cent of the vestibulospinal neurons responded both to contralateral muscles and to ipsilateral motor cortex stimulation but none of the non-vestibulospinal neurons responded to both. All the responders to both were in the dorsal zone of the lateral vestibular nucleus and responded to extensor stimuli, always in the same way. These results indicate that motor cortex output exerts a major influence on lateral vestibular nucleus discharges, while the muscle afferents have a modulatory influence on the lateral vestibular nucleus responses to cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1993

The neurotransmitter of inhibitory synaptic inputs on inhibitory burst neurons (IBNs) controlling vestibular nystagmus in the cat.

In the pontine neural networks that govern vestibular nystagmus in the cat, inhibitory burst neurons (IBNs) are known to fire in bursts during the quick phase, and to suppress firing of the abducens motoneurons on the contralateral side. The present experiments were designed to identify the neurotransmitter controlling the burst firing pattern of IBNs. Inhibitory burst neuron activity was recorded extracellularly, and various chemicals were applied to the IBNs iontophoretically through multibarrel micropipettes. GABA and muscimol (a GABAA-receptor agonist) strongly suppressed IBN activity and eliminated the burst pattern. Bicuculline (a GABAA-receptor antagonist) increased the firing of IBNs and suppressed the inhibitory effect of GABA when applied simultaneously. Although baclofen (a GABAB-receptor agonist) had no inhibitory effect, it slightly shortened the duration of burst firing. Neither glycine nor serotonin, other inhibitory transmitter candidates, nor their respective antagonists, strychnine and methysergide, had any effect. Systemically administered picrotoxin prevented the GABA-induced suppression of IBNs. These results suggest that IBNs possess GABAA receptors and are controlled by higher GABA-liberating neurons and Cl- channels.

Animals↗
PubMed1977

Neuronal activity in the vestibular nuclei of the alert monkey during vestibular and optokinetic stimulation.

Recordings from neurons of the vestibular nuclei were performed in alert monkeys. Type I and type II units were identified by rotating the monkey about a vertical axis. Al neurons responded also when only the visual surround was rotated around the stationary monkey. The combination of visual and vestibular stimulation points towards non-algebraic summation characteristics for the two inputs, with each input dominating the response over a certain range.

Animals↗
PubMed1976

[Effect of vestibular, somatic and autonomic afferent impulsation on the activity of individual neurons in the nuclei of the cat vestibular complex].

Responses of single vestibular neurons were studied in cats under adequate and electric stimulation of different afferent sources (labyrinths, mixed nerves, n. vagus, n. depressor, limb movements). Different types of responses to the employed stimulation as well as evoked activity as bursts followed by depression of background firing are described. The activity of vestibular neurons is shown to depend on extralabyrinthal stimulation. The role of muscle-joint receptors is distinguished from natural stimulation of the vestibular apparatus during the head tilting. Somatotopic organization of vestibular nuclei and convergence of different afferental impulses to the neurons forming the vestibulospinal tract are discussed.

Animals↗
PubMed1983

The vestibulo-ocular reflex arc in the newborn kitten. An electrophysiologic investigation.

Field potentials and postsynaptic potentials were recorded in the vestibular and abducens nuclei and neurons following vestibular nerve stimulation in anesthetized newborn kittens (within 72 h after birth). Stimulation of the ipsilateral vestibular nerve evoked an initial P wave and an N1 field potential in the vestibular nuclei. No N2 potential was evoked. Latencies of the peak of the P wave, the onset and the peak of the N1 potential were 0.99 +/- 0.16 ms, 1.66 +/- 0.18 ms, and 2.51 +/- 0.23 ms, respectively. Ipsilateral vestibular nerve stimulation evoked monosynaptic excitatory postsynaptic potentials (EPSPs) and polysynaptic inhibitory postsynaptic potentials (IPSPs) in vestibular nuclear neurons. Stimulation of the contralateral vestibular nerve evoked polysynaptic IPSPs in vestibular nuclear neurons. In abducens motoneurons, ipsilateral vestibular nerve stimulation evoked monosynaptic EPSPs and disynaptic IPSPs; contralateral vestibular nerve stimulation produced disynaptic EPSPs. We conclude that short circuit pathways of the vestibulo-vestibular and vestibulo-ocular reflex arc are present in the kitten already at birth.

Abducens Nerve↗
PubMed1975

[Changes in the receptive field of pigeon tectum neurons subjected to vestibular and acoustic stimulation].

The changes in the receptive fields of neurons in the deep layers of the tectum opticum were studied as induced by labyrinthine and sound stimulation. Variations in the size of the receptive field, the particular direction of sensitive cells movement, duration of the reaction and amount of impulses in it were found. The results obtained and data from the literature allow one to suggest an active role of tectum opticum in the transformation of signals from the retina depending on the kind of information from other sensory systems.

Animals↗
PubMed1992

The nucleus of the optic tract. Its function in gaze stabilization and control of visual-vestibular interaction.

1. Electrical stimulation of the nucleus of the optic tract (NOT) induced nystagmus and after-nystagmus with ipsilateral slow phases. The velocity characteristics of the nystagmus were similar to those of the slow component of optokinetic nystagmus (OKN) and to optokinetic after-nystagmus (OKAN), both of which are produced by velocity storage in the vestibular system. When NOT was destroyed, these components disappeared. This indicates that velocity storage is activated from the visual system through NOT. 2. Velocity storage produces compensatory eye-in-head and head-on-body movements through the vestibular system. The association of NOT with velocity storage implies that NOT helps stabilize gaze in space during both passive motion and active locomotion in light with an angular component. It has been suggested that "vestibular-only" neurons in the vestibular nuclei play an important role in generation of velocity storage. Similarities between the rise and fall times of eye velocity during OKN and OKAN to firing rates of vestibular-only neurons suggest that these cells may receive their visual input through NOT. 3. One NOT was injected with muscimol, a GABAA agonist. Ipsilateral OKN and OKAN were lost, suggesting that GABA, which is an inhibitory transmitter in NOT, acts on projection pathways to the brain stem. A striking finding was that visual suppression and habituation of contralateral slow phases of vestibular nystagmus were also abolished after muscimol injection. The latter implies that NOT plays an important role in producing visual suppression of the VOR and habituating its time constant. 4. Habituation is lost after nodulus and uvula lesions and visual suppression after lesions of the flocculus and paraflocculus. We postulate that the disappearance of vestibular habituation and of visual suppression of vestibular responses after muscimol injections was due to dysfacilitation of the prominent NOT-inferior olive pathway, inactivating climbing fibers from the dorsal cap to nodulouvular and flocculoparafloccular Purkinje cells. The prompt loss of habituation when NOT was inactivated, and its return when the GABAergic inhibition dissipated, suggests that although VOR habituation can be relatively permanent, it must be maintained continuously by activity of the vestibulocerebellum.

Animals↗
PubMed1990

Spatial properties of second-order vestibulo-ocular relay neurons in the alert cat.

Second-order vestibular nucleus neurons which were antidromically activated from the region of the oculomotor nucleus (second-order vestibuloocular relay neurons) were studied in alert cats during whole-body rotations in many horizontal and vertical planes. Sinusoidal rotation elicited sinusoidal modulation of firing rates except during rotation in a clearly defined null plane. Response gain (spike/s/deg/s) varied as a cosine function of the orientation of the cat with respect to a horizontal rotation axis, and phases were near that of head velocity, suggesting linear summation of canal inputs. A maximum activation direction (MAD) was calculated for each cell to represent the axis of rotation in three-dimensional space for which the cell responded maximally. Second-order vestibuloocular neurons divided into 3 non-overlapping populations of MADs, indicating primary canal input from either anterior, posterior or horizontal semicircular canal (AC, PC, HC cells). 80/84 neurons received primary canal input from ipsilateral vertical canals. Of these, at least 6 received input from more than one vertical canal, suggested by MAD azimuths which were sufficiently misaligned with their primary canal. In addition, 21/80 received convergent input from a horizontal canal, with about equal number of type I and type II yaw responses. 4/84 neurons were HC cells; all of them received convergent input from at least one vertical canal. Activity of many vertical second-order vestibuloocular neurons was also related to vertical and/or horizontal eye position. All AC and PC cells that had vertical eye position sensitivity had upward and downward on-directions, respectively. A number of PC cells had MADs centered around the MAD of the superior oblique muscle, and 2/3 AC cells recorded in the superior vestibular nucleus had MADs near that of the inferior oblique. Thus, signals with spatial properties appropriate to activate oblique eye muscles are present at the second-order vestibular neuron level. In contrast, none of the second-order vestibuloocular neurons had MADs near those of the superior or inferior rectus muscles. Signals appropriate to activate these eye muscles might be produced by combining signals from ipsilateral and contralateral AC neurons (for superior rectus) or PC neurons (for inferior rectus). Alternatively, less direct pathways such as those involving third or higher order vestibular or interstitial nucleus of Cajal neurons might play a crucial role in the spatial transformations between semicircular canals and vertical rectus eye muscles.

Animals↗
PubMed1995

Apoptosis of neurons in the vestibular nuclei of adult mice results from prolonged change in the external environment.

Pharmacological manipulations which result in abnormal levels of excitatory amino acid (EAA) mediated neurotransmission can result in neuronal apoptosis. We accordingly hypothesised that manipulations of the external environment which induce prolonged EAA-mediated transmission in sensory neurons may also induce apoptosis. This hypothesis was tested by placing groups of adult mice, housed in their home cage, on a turntable which slowly rotated (0.8 rev./min). This non-invasive manipulation will have resulted in abnormal discharge patterns in the vestibular nuclei. Significantly greater levels of neuronal apoptosis were seen in the vestibular complex after rotation for 48 h compared with non-rotated controls. This finding was also predicted independently from a computational approach.

Animals↗
PubMed2006

Neuronal nitric oxide synthase immunopositive neurons in cat vestibular complex: a light and electron microscopic study.

Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. Nevertheless, there are little data about the neuronal nitric oxide synthase immunoreactivity (nNOS-ir) in the vestibular complex of a cat. In this respect, the aims of this study were to: (1) demonstrate nNOS-ir in the neurons and fibers, from all major and accessory vestibular nuclei; (2) describe their light microscopic morphology and distribution; (3) investigate and analyze the ultrastructure of the NOS I-immunopositive neurons, fibers, and synaptic boutons. For demonstration of the nNOS-ir, the peroxidase-antiperoxidase-diaminobenzidin method was applied. Immunopositive for nNOS neurons and fibers were present in all major and accessory vestibular nuclei. On the light microscope level, the immunopositive neurons were different in shape and size. According to the latter, they were divided into four groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), large type I (with diameter from 30 to 40 microm), and large type II (with diameter greater than 40 microm). On the electron microscope level, the immunoproduct was observed in neurons, dendrites, and terminal boutons. According to the ultrastructural features, the neurons were divided into three groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), and large (with diameter greater than 30 microm). At least two types of nNOS-ir synaptic boutons were easily distinguished. As a conclusion, we hope that this study will contribute to a better understanding of the functioning of the vestibular complex in cat and that some of the data presented could be extrapolated to other mammals, including human.

Animals↗
PubMed1990

Effects of 5-hydroxytryptamine on the firing rates of neurons of the lateral vestibular nucleus in the rat.

5-hydroxytryptamine (5-HT) was delivered microiontophoretically (20-80 nA) to cells of the lateral vestibular nucleus of anaesthetized rats to test its influence on the spontaneous activity of single neurons. 5-HT increased the rate of firing of 94% of the units tested. The enhancement persisted for up to 700 s after the end of the 5-HT ejection and the maximum magnitude of the excitation (10-3400%) showed a hyperbolic correlation (rho = 0.86) with background firing. In 43% of units the enhancement was preceded by a short-lasting (less than 105 s) depression of the neuronal firing rate, the magnitude of which was unrelated to the background mean firing rate. Both components of the 5-HT response were dose-dependent. Only the excitatory responses were antagonized by metergoline, methysergide and ketanserin. The putative 5-HT agonist, 5-methoxy-N,N-dimethyltryptamine, applied microiontophoretically, depressed the background firing rate and was not antagonized by methysergide. These results demonstrate that 5-HT modifies the responsiveness of vestibular neurons and suggest that at least two mechanisms and maybe two types of receptors are activated by 5-HT in this nucleus.

Action Potentials↗
PubMed1984

Responses of prepositus hypoglossi neurons to optokinetic and vestibular stimulations in the rat.

The responses of 47 nucleus prepositus hypoglossi neurons to vestibular optokinetic stimulations in the horizontal plane were recorded in immobilized, pigmented rats. During sinusoidal vestibular stimulation in the dark, type II (62%) and type I (38%) responses were recorded. In addition to the sinusoidal modulation of firing rate, units often showed fast rhythmic increases or decreases in firing (nystagmic modulation). The mean phase of the response relative acceleration measured at 0.025 and 0.2 Hz were 19 and 84 deg., respectively. Some units (25%) showed larger phase-lags. The sensitivities of unit responses at 0.025 and 0.2 Hz were 1.6 and 0.5 spikes X s-1/deg X s-2, respectively. The responses of NPH neurons to binocular optokinetic stimulation were divided in 2 classes: (i) neurons with unidirectional responses (18%) were excited by stimuli moving towards the side of recording and showed no change in firing on oppositely directed stimulation; all of them showed a type II pattern during vestibular stimulation; (ii) bidirectional responses showed an increase in one direction and a decrease in firing for stimulation in the opposite direction. In every case the optokinetic responses were synergistic with the vestibular responses, which consisted of both type I and type II units. On the basis of the directionality of their optokinetic response, the value of their time constants and the shape of their velocity tuning curves, it is suggested that unidirectional type II NPH neurons could serve as relays in the optokinetic pathways between NRTP (or PT) and vestibular neurons. Some other neurons, having time constants particularly long and different for the rising and falling of the response, probably serve other functions.

Animals↗
PubMed1983

Convergence of sensory inputs upon projection neurons of somatosensory cortex: vestibular, neck, head, and forelimb inputs.

Cortico-cortical neurons and pyramidal tract (PT) neurons of the cat cerebral cortex were tested for convergent inputs from electrically stimulated vestibular, neck, head and forelimb nerves. Neurons were recorded within forelimb and vestibular projection regions of cortical area 3a. Consideration was given to both suprathreshold and subthreshold inputs. Neither vestibular, neck nor head inputs were detected in the forelimb region of area 3a. In contrast, within the vestibular projection region of area 3a, 43% (6/14) of the cortico-cortical neurons and 63% (24/38) of the PT neurons received excitatory vestibular input. Inputs from the skin of the pinna (greater auricular nerve) were detected only for PT neurons (66%, 25/38). No inputs were detected from afferent nerves supplying the dorsal neck muscles biventer cervicis and complexus. Cortico-cortical and PT neurons receiving vestibular input also received convergent inputs originating from forelimb group I deep and low threshold cutaneous afferent fibers. Further, one half of the PT neurons with vestibular input (12/24) received input from three somatic sources: forelimb group I deep, forelimb low threshold cutaneous and greater auricular (head) nerves. The input connectivities suggest a role for these projection neurons of somatosensory cortex in the coordination of head and forelimb movements. The convergence of vestibular information with somatic input from the forelimb implies that vestibular-influenced neurons of area 3a projecting to the motor cortex or through the pyramidal tract would signal head position or movement with respect to proprioceptive feedback from the limbs.

Afferent Pathways↗
PubMedDate not supplied

[Effect of low-frequency vibration on the activity of dehydrogenase in neurones of anterior vestibular nucleus in rats].

To obtain the characteristics of the main changes in oxidative metabolism in the neurons of the nucleus vestibularis anterior (NVA) under the influence of low frequency vibration in rat brain the activities of some dehydrogenases (NADN-DH, NADPH-DH, succinate-DH, malate-DH, beta-oxybutyrate-DH, alpha-glycerolphosphate-DH, lactate-DH, glutamate-DH and 6-phosphogluconate-DH) were measured using histochemical methods. The sizes of subpopulations of neurons differing in enzyme activities were estimated.

Animals↗