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At least 595 records · Page 33Linked to original sources
PubMed1992

Response of pontomedullary reticulospinal neurons to vestibular stimuli in vertical planes. Role in vertical vestibulospinal reflexes of the decerebrate cat.

1. To investigate the neural substrate of vestibulospinal reflexes in decerebrate cats, we studied the responses of pontomedullary reticulospinal neurons to natural stimulation of the labyrinth in vertical planes. Our principal aim was to determine whether reticulospinal neurons that terminate in, or are likely to give off collaterals to, the upper cervical segments had properties similar to those of the vestibulocollic reflex (VCR). 2. Antidromic stimulation was used to determine whether the neurons projected to the neck, lower cervical, thoracic, or lumbar levels. Dynamics of the responses of spontaneously firing neurons were studied with sinusoidal stimuli delivered at 0.05-1 Hz and aligned to the plane of body rotation, that produced maximal modulation of the neuron (response vector orientation). Each neuron was assigned a vestibular input classification of otolith, vertical canal, otolith + canal, or spatial-temporal convergence (STC). 3. We found, in agreement with previous studies, that the largest fraction of pontomedullary reticulospinal neurons projected to the lumbar cord, and that only a small number ended in the neck segments. Neurons projecting to all levels of the spinal cord had similar responses to labyrinth stimulation. 4. Reticulospinal neurons that received only vertical canal inputs were rare (1 of 67 units). Most reticulospinal neurons (48%) received predominant otolith inputs, 18% received otolith + canal input, and only 9% had STC behavior. These data are in sharp contrast to the results of our previous studies of vestibulospinal neurons. A considerable portion of vestibulospinal neurons receives vertical canal input (38%), fewer receive predominantly otolith input (22%), whereas the proportion that have otolith + canal input or STC behavior is similar to our present reticulospinal data. 5. The response vector orientations of our reticulospinal neurons, particularly those with canal inputs (canal, otolith + canal, STC) were predominantly in the roll quadrants. There was no evidence of convergence of inputs from like canals across the midline (e.g., right anterior + left anterior). 6. Two characteristics of the VCR, STC behavior and bilateral input from symmetric vertical canals (in some muscles), cannot be accounted for by the reticulospinal neurons that we studied. Because these characteristics are also not seen in vestibulocollic neurons, they are likely to be the result of the appropriate convergence of vestibular signals in the spinal cord. 7. Pontomedullary reticulospinal neurons seem particularly well suited to play a role in gravity-dependent postural reflexes of neck and limbs.

Acoustic Stimulation↗
PubMed1992

Spinal commissural neurons mediating vestibular input to neck motoneurons in the cat upper cervical spinal cord.

Spinal commissural neurons (CNs) activated di- or trisynaptically by stimulation of ipsilateral vestibular afferents were stained with intraaxonal injection of horseradish peroxidase in the cat upper cervical spinal cord. Stem axons of CNs in lamina VIII or VII, after crossing the midline, had ascending and/or descending main branches that gave off multiple axon collaterals to laminae IX and VIII over a few cervical segments. Terminal boutons appeared to make contact with proximal dendrites and somata of retrogradely-labelled neck motoneurons. Therefore, these CNs were regarded as mediating vestibular afferent input to contralateral neck motoneurons trisynaptically at the shortest.

Animals↗
PubMed1997

The coding of head orientations in neurons of bilateral vestibular nuclei of cats after unilateral labyrinthectomy: response to off-vertical axis rotation.

In decerebrate cats that had been acutely hemilabyrinthectomized (HL), the extracellular activities of vestibular nuclear neurons on the lesioned and labyrinth-intact sides were studied during constant-velocity off-vertical axis rotations (OVAR) in the clockwise (CW) and counterclockwise (CCW) directions (at 10 degrees tilt). Over the range of 1.75-15 degrees/s, two types of neuronal responses were identified on both sides. Some neurons showed symmetric and velocity-stable bidirectional response sensitivity (delta defined as the CW gain over the CCW gain) while other neurons exhibited asymmetric and velocity-variable delta. The mathematically derived gain tuning ratios of these two groups of neurons were within the range of one-dimensional and two-dimensional neurons respectively. The best response orientations in one-dimensional neurons and the orientations of the maximum response vector, S(max), in two-dimensional neurons were found to point in all directions on the horizontal plane. On the labyrinth-intact side, both the one-dimensional and two-dimensional neurons showed asymmetry in the neuron numbers and/or the response gains between the two roll quadrants as well as between the two pitch quadrants. In addition, both the neuron number and gain were significantly higher for neurons in the head-down/ipsilateral-side-down half-circle than those in the head-up/contralateral-side-down half-circle. None of the aforementioned asymmetries was observed on the lesioned side. That a comparable pattern of distribution was observed in the one-dimensional and two-dimensional neurons suggests that these neurons maintain a common spatial reference frame in encoding head orientational signals arising from the ipsilateral and contralateral otoliths. Furthermore, a predominance of two-dimensional neurons that exhibited a greater gain with CW rotations was observed on both sides of HL cats. Of the response dynamics observed amongst neurons on the two sides of HL cats, no difference was found with regard to the response gain and the pattern of response lead. However, a difference in response lag was observed between neurons on the two sides of HL cats. These suggest that there is a segregation of otolithic signals to reach the ipsilateral and contralateral vestibular nuclei. Taken together, the present study demonstrates that one-dimensional and two-dimensional neuronal responses could be elicited with inputs arising solely from the ipsilateral or contralateral otoliths. The observed orientational tuning and the CW-CCW asymmetry to bidirectional rotation may provide the essential directional coding of head orientations. Further, the imbalance of spatial/dynamic response patterns between the bilateral vestibular nuclei following the restriction of otolith inputs by HL implies that converging otolithic inputs from the bilateral labyrinths are essential for producing the neuronal responses in control animals. The results are also discussed in terms of the possible contribution of the various neural asymmetries between neuronal subpopulations in the bilateral vestibular nuclei to the behavioral symptoms accompanying acute HL.

Animals↗
PubMed1997

Role of pre-inspiratory neurons in vestibular and laryngeal reflexes and in swallowing and vomiting.

Fifteen pre-inspiratory (Pre-I) neurons were extracellularly recorded in the pre-Bötzinger complex and their involvements in vestibular (VN) and superior laryngeal (SLN) nerve reflexes and in fictive swallowing and vomiting were tested in decerebrated and artificially ventilated cats. Both type I (1 of 9) and type II (1 of 6) pre-I neurons could project to the contralateral ventral respiratory group region. Pre-I neurons changed their firing during VN and SLN respiratory reflexes and fictive swallowing and vomiting; different response properties were observed among individual pre-I neurons. These results suggest that pre-I neurons are a population of heterogeneous and multi-functional propriobulbar neurons.

Animals↗
PubMed1996

The effects of ginkgolide B (BN52021) on guinea pig vestibular nucleus neurons in vitro: importance of controlling for effects of dimethylsulphoxide (DMSO) vehicles.

The present study investigated the effects of the platelet-activating factor (PAF) receptor antagonist, ginkgolide B, on guinea pig medial vestibular nucleus (MVN) neurons in vitro and addressed the potential problem of using dimethylsulphoxide (DMSO) as a solvent. Using DMSO as a solvent, 10(-10), 10(-8) and 10(-4) M ginkgolide B had no effect on extracellularly recorded MVN neurons in brainstem slices in vitro. Using 10(-6) M ginkgolide B, 50% (5/10) of MVN neurons exhibited a decrease in firing rate and 10% (1/10) of neurons responded with an increase in firing rate. While attempting to control for possible DMSO vehicle effects, 40% (4/10) of MVN neurons displayed a decrease in firing rate when ginkgolide B (10(-6) M) was presented before the DMSO control solution. When the DMSO vehicle was presented first, only 10% (1/10) responded similarly. In some cases the DMSO vehicle alone also produced a decrease in MVN neuron firing rate. These results emphasise the importance of using adequate DMSO control conditions in ginkgolide research.

Animals↗
PubMed1976

[Postnatal maturation of vestibular nuclei in the cat: histological study by the Golgi-Cox method (author's transl)].

Postnatal maturation of vestibular nuclei in the cat was studied from both the qualitative and quantitative points of view, following impregnation of the sections by the Golgi-Cox method. Three principal data arise from our results. (1) The different vestibular neurones undergo significant growth during the first two weeks of extra-uterine life: during this time, the progressive disappearance of dendritic growth cones and filopodia, an increase in area and volume of the perikarya as well as that of dendritic fields are remarkable; the smallest neurones completing their maturation before the largest. (2) Average sized neurones of the superior vestibular nucleus show a significant increase in the number of dendritic spines between birth and the age of 3 days. (3) On the 12th day, a decrease in the number of dendritic spines is noted. This decrease is accompagnied by a modification in spine density along the dendrites.

Animals↗
PubMed1981

Physiological and anatomical characteristics of primary vestibular afferent neurons in the bullfrog.

Intracellular recordings were made in the VIIIth nerve of the bullfrog (Rana catesbiana) to measure the membrane characteristics and obtain records of spontaneous and evoked spike activity of primary semicircular canal afferents. Physiological stimulation of the canals was achieved by rotating the preparation on a servomotor driven turntable with the animals' head centered in the rotational axis. The responses of each neuron to sinusoidal rotations at frequencies of 0.05Hz, 0.5Hz and for impulsive accelerations of 400 deg/sec2 were obtained. Membrane characteristics measured included the cell resting and action potential amplitude, and spike-activation threshold for applied currents. Physiologically characterized neurons were injected with horseradish peroxidase by applying pneumatic pressure and/or iontophoretic currents to the micropipettes containing 5% HRP in 1 M KCI. Following survival times of 12--48 h, the VIIIth nerve and attached vestibular end organ was removed for histochemical processing using a diaminobenzidine procedure to visualize the HRP reaction product. Light microscopy was used to discern the anatomical features of the neurons and to trace their peripheral dendritic trajectories from the ganglion to their termination(s) in the crista. Our studies have revealed that the bullfrog's primary vestibular afferents are characterized by a broad range of soma and axon diameters which correspond to an equally broad range of spontaneous and evoked activity characteristics. The largest neurons had more irregular spontaneous firing rates and consistently exhibited the greatest gain and smallest phase shifts with respect to head acceleration. These neurons consistently terminated at or near the central region of the crista. On the other hand, the smallest neurons were characterized by having the most regular spontaneous discharge patterns, the lowest gains, and greatest phase shifts with respect to head acceleration. Our findings are thus consistent with the view that the anatomical features of the primary vestibular neurons are important in determining the neuron's physiological characteristics. In terms of response dynamics our observations indicate that the receptors in the frog's crista ampullaris are heterogeneous and differentially sensitive to a wide range of stimulus frequencies.

Afferent Pathways↗
PubMed1994

Response of commissural and other upper cervical ventral horn neurons to vestibular stimuli in vertical planes.

1. To study their contribution to the vestibulocollic reflex, we have studied, in decerebrate paralyzed cats, the effect of sinusoidal vestibular stimulation in multiple vertical planes on the spontaneous activity of neurons in the C3 ventral horn. Antidromic microstimulation was used to identify 17/42 neurons as commissural; 10 of these were confirmed to have a projection to the contralateral ventral horn. 2. Dynamics of the responses of spontaneously firing neurons were studied with 0.05-1 Hz sinusoidal stimuli delivered near the plane of rotation that produced maximal modulation of neuron activity (response vector orientation). On the basis of their responses, we classified 38 neurons as receiving otolith, semicircular canal, or otolith + canal input. All three response types were found among commissure and nonantidromic neurons. 3. Two-thirds of neuron response vector orientations pointed contralaterally. They were either near the anterior or posterior canal planes or in the roll quadrant. In the case of neurons with input from canals, the latter indicates convergence from the vertical canals on the same side. There were almost no vectors in the pitch quadrants. The distribution of response vector orientations resembles that seen in the vestibular nuclei and pontomedullary reticular formation, suggesting that commissural neurons may not make a new contribution to spatial processing in the vertical vestibulocollic reflex. 4. It is presumed that commissural neurons are premotor. If so, some have the properties to be in the pathway between the contralateral utricle and neck motoneurons. More generally, their actions could modify the effectiveness of vestibulospinal and reticulospinal fibers that have similar spatial properties and make synapses with neck motoneurons.

4-Aminopyridine↗
PubMed2002

Vestibular convergence patterns in vestibular nuclei neurons of alert primates.

Sensory signal convergence is a fundamental and important aspect of brain function. Such convergence may often involve complex multidimensional interactions as those proposed for the processing of otolith and semicircular canal (SCC) information for the detection of translational head movements and the effective discrimination from physically congruent gravity signals. In the present study, we have examined the responses of primate rostral vestibular nuclei (VN) neurons that do not exhibit any eye movement-related activity using 0.5-Hz translational and three-dimensional (3D) rotational motion. Three distinct neural populations were identified. Approximately one-fourth of the cells exclusively encoded rotational movements (canal-only neurons) and were unresponsive to translation. The canal-only central neurons encoded head rotation in SCC coordinates, exhibited little orthogonal canal convergence, and were characterized with significantly higher sensitivities to rotation as compared to primary SCC afferents. Another fourth of the neurons modulated their firing rates during translation (otolith-only cells). During rotations, these neurons only responded when the axis of rotation was earth-horizontal and the head was changing orientation relative to gravity. The remaining one-half of VN neurons were sensitive to both rotations and translations (otolith + canal neurons). Unlike primary otolith afferents, however, central neurons often exhibited significant spatiotemporal (noncosine) tuning properties and a wide variety of response dynamics to translation. To characterize the pattern of SCC inputs to otolith + canal neurons, their rotational maximum sensitivity vectors were computed using exclusively responses during earth-vertical axis rotations (EVA). Maximum sensitivity vectors were distributed throughout the 3D space, suggesting strong convergence from multiple SCCs. These neurons were also tested with earth-horizontal axis rotations (EHA), which would activate both vertical canals and otolith organs. However, the recorded responses could not be predicted from a linear combination of EVA rotational and translational responses. In contrast, one-third of the neurons responded similarly during EVA and EHA rotations, although a significant response modulation was present during translation. Thus this subpopulation of otolith + canal cells, which included neurons with either high- or low-pass dynamics to translation, appear to selectively ignore the component of otolith-selective activation that is due to changes in the orientation of the head relative to gravity. Thus contrary to primary otolith afferents and otolith-only central neurons that respond equivalently to tilts relative to gravity and translational movements, approximately one-third of the otolith + canal cells seem to encode a true estimate of the translational component of the imposed passive head and body movement.

Animals↗
PubMed1984

Floccular influence on excitatory relay neurones of vestibular reflexes of anterior semicircular canal origin in the cat.

Floccular influence on excitatory vestibular reflex arcs of anterior semicircular canal origin was examined in the anaesthetized cat. Stimulation of the anterior semicircular canal nerve (ACN) evoked disynaptic excitatory postsynaptic potentials (EPSPs) in all sampled inferior oblique (IO), superior rectus (SR), and biventor cervicis (BIV) muscle motoneurones of the contralateral side. Conditioning stimulus to the flocculus depressed the amplitude of the EPSPs in both IO and SR motoneurones by 50% on the average but not in any BIV motoneurones. The excitatory vestibulo-ocular neurones identified by orthodromic and antidromic responses to stimulation of the ACN and the contralateral IO motoneurone pool, respectively, were classified as VOC (vestibulo-ocular neurones with axons descending to the cervical segment) or VO (vestibulo-ocular proper) neurones on the basis of whether or not they responded antidromically to stimulation of the spinal cord in the C1 segment. All of the VO neurones in the superior vestibular nucleus (n = 19) were inhibited from the flocculus while the activities of three-fourths of the VO neurones (36/48) in the other vestibular nuclei were not suppressed by floccular stimulation. In contrast, none of VOC neurones (n = 49) received floccular inhibition. Besides inhibition, floccular stimulation induced the antidromic or orthodromic responses in some VO and VOC neurones.

Animals↗
PubMed1998

Involvement of round and oval windows in the vestibular response to pressure changes in the middle ear of guinea pigs.

Changes in ambient pressure can elicit the vertigo and bodily disequilibrium known clinically as alternobaric vertigo. Our previous studies showed that changes in middle ear pressure altered the activity of the primary vestibular neuron, and the finding suggests that the pressure-induced vestibular response causes alternobaric vertigo. To investigate the roles played by the round window (RW) and the oval window (OW) in the vestibular response induced by pressure, we measured the change in perilymphatic pressure and the firing rates of primary vestibular neurons after the application of positive or negative pressure to the middle ear. We found an increase in the pressure-induced vestibular response in the group with a closed OW, and a decrease in the group with a closed RW. Measurements showed that the amplitude of the change in perilymphatic pressure in the group with a closed OW did not differ from that in the control group, whereas the amplitude of the perilymphatic pressure change in the group with a closed RW was significantly reduced. A discrepancy between the number of neurons responding and the amplitude of the perilymphatic pressure change in the closed OW group suggests that the vestibular response induced by the change in middle ear pressure was not related solely to the magnitude of the pressure change in the inner ear, but also involved the oval and round windows.

Animals↗
PubMed1995

The effects of long-term, low-dose diazepam treatment on the guinea pig righting reflex and medial vestibular nucleus neuronal activity.

Guinea pigs received a 2 mg/kg IP injection of diazepam, or an equivalent volume of vehicle, daily for 28-60 days. To determine whether tolerance developed to the ataxic effects of diazepam on the righting reflex, daily righting reflex latency (RRL) measurements were made before and 20, 30, and 40 min following the diazepam or vehicle injection for 28 days. Analyses of the RRLs for individual animals indicated that a significant decrease in RRL over time (indicating tolerance) occurred in only one out of nine animals receiving diazepam and in none of the vehicle animals. Medial vestibular nucleus (MVN) neurons in brain stem slices from animals receiving chronic diazepam treatment had a significantly higher average firing rate than those from vehicle controls. These results suggest that: a) long-term treatment with single 2 mg/kg daily IP injections of diazepam does not result in tolerance to diazepam's ataxic effects on the righting reflex in the majority of animals; b) this form of diazepam treatment may, nonetheless, induce a hyperactivity of brain stem MVN neurons that may be consistent with the occurrence of a withdrawal syndrome.

Animals↗
PubMed1997

Transneuronal down regulation of vestibulo-ocular neurons following vestibular ablation.

Unilateral ablation of vestibular input causes lasting morphological changes bilaterally in superior vestibulo-ocular neurons (SVON). The present study was performed to see if these changes in SVON are more pronounced after bilateral vestibular neurectomy. Twenty-three SVON from both vestibular nuclei of 2 cats sacrificed 8 weeks after bilateral ablation were examined utilizing morphometric ultrastructural techniques. There was a significantly greater somal atrophy, loss of synaptic profiles, rough endoplasmic reticulum and polyribosomes compared to unilateral neurectomy. These changes indicate a down regulation that is proportional to the level of deafferentation and may account for functional deficits seen in the vestibulo-ocular reflex after peripheral ablation.

Animals↗
PubMed1984

Experimental vestibular pharmacology: a minireview with special reference to neuroactive substances and antivertigo drugs.

Neurotransmitters and neuromodulators involved in the function of vestibular nuclei were reviewed with special reference to drugs used for treatment of motion sickness and vertigo. Biochemical, histochemical and electrophysiological studies have demonstrated that acetylcholine is a transmitter candidate from the afferent vestibular nerve to the lateral vestibular nucleus (LVN), because acetylcholine satisfies most criteria for a chemical transmitter in the central nervous system. It is unlikely, however, that monoamines such as noradrenaline, dopamine and serotonin are transmitters in the vestibular neurons, since cell bodies and nerve terminals containing the monoamines have not been detected yet in the vestibular nuclei. Although histamine and H1-receptor blockers inhibit neuron activities in the vestibular nuclei, it is unclear at present whether histaminergic system is directly related to the function of vestibular neurons. It has been established that GABA is an inhibitory transmitter from the cerebellar Purkinje cells to the LVN neurons. Diazepam is considered to enhance the GABA effect on the LVN, thereby modifying the vestibular neuronal firing. Enkephalin-containing cell bodies and nerve terminals are found in the medial vestibular nucleus, and a few substance P-containing neurons have been observed in the vestibular nuclei. However, the functional role of these peptides on the vestibular system remains to be determined. Unlike histamine H1-receptor blockers, vasodilators such as cinnarizine, ifenprodil and adenosine triphosphate, which are effective in treatment of vertigo, produce an enhancement of responsiveness of neuron activities in the vestibular nuclei, probably as a result of an increase in blood flow in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1988

Lesion-induced vestibular plasticity in the frog: are N-methyl-D-aspartate receptors involved?

The synaptic excitation of central vestibular neurons in the isolated superfused brainstem of chronic hemilabyrinthectomized (HL) frogs and of controls was studied electrophysiologically and pharmacologically. Central vestibular neurons were excited either through vestibular afferent fibers or through the vestibular commissural pathway by means of electrical stimulation of the ipsilateral or the contralateral VIIIth nerve. In chronic HL frogs, commissural field potential amplitudes were on the average larger than those of intact frogs and the shape parameters of intracellularly recorded commissural EPSPs of chronic animals were on the average shifted towards those of vestibular afferent EPSPs. In control frogs, vestibular afferent EPSPs were generated independently from N-methyl-D-aspartate (NMDA) receptors, whereas commissural EPSPs exhibited a delayed NMDA receptor mediated component. Commissural EPSPs of HL frogs exhibited a NMDA receptor mediated component as well. The size of this EPSP component was larger when the time to peak of the EPSP was longer. EPSPs with similar rise times exhibited NMDA mediated components of similar size, irrespective of whether they originated from chronic animals or controls. The tendency of these EPSPs towards shorter rise times in chronic animals was paralleled by a similar decrease of the relative size of their NMDA receptor mediated component. It is concluded that the increased synaptic efficacy of commissural fibers observed in chronic HL frogs does not result from an increased NMDA receptor component.

2-Amino-5-phosphonovalerate↗