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At least 973 records · Page 54Linked to original sources
PubMed1996

Role of ventral respiratory group bulbospinal expiratory neurons in vestibular-respiratory reflexes.

1. Activation of the vestibular system produces reflex modulation of expiratory muscle activity. The purpose of the present study was to investigate the possible role of bulbospinal expiratory (E) neurons located in the caudal ventral respiratory group (VRG) in mediating vestibulo-respiratory reflexes. Experiments were carried out in decerebrated, paralyzed, and artificially ventilated cats. 2. Electrical stimulation of the vestibular nerve (VN), using short trains of current pulses, elicited bilateral reflex responses on abdominal muscle nerves (ABDNs). This response was not affected by lesions of the cochlear nuclei made by kainic acid injections. The ABDN response typically consisted of a combination of short-latency excitation and long-latency inhibition on the ipsilateral side and, in contrast, a combination of short-latency inhibition and long-latency excitation on the contralateral side. 3. Extracellular recordings were made from 43 caudal VRG bulbospinal E neurons that were activated antidromically from the contralateral upper lumbar spinal cord. More than 80% of these neurons responded to either ipsi- and/or contralateral VN stimulation. The neuronal response consisted of either a combination of excitation and inhibition or only inhibition. The majority of neurons had response patterns appropriate to contribute to the response observed on the contralateral ABDN; however, the latency of the VRG E neuron response was too long to initiate the ABDN response. 4. To further evaluate the contribution of caudal VRG E neurons to the vestibulo-abdominal reflex, ABDN responses were compared before and after sectioning the axons of caudal VRG bulbospinal E neurons where they cross the midline between the obex and first cervical spinal segment. These midsagittal lesions abolished expiratory modulation of ABDN discharge. The lesions also decreased the amplitude of the vestibular-evoked ABDN response but could not abolish the response. The postlesion amplitude was decreased on average to approximately 70% of prelesion values. 5. In conclusion, although the present results indicate that the majority of caudal VRG bulbospinal E neurons respond appropriately to contribute to the vestibulo-abdominal reflex, the reflex largely is unaffected by the removal of caudal VRG E input. The additional descending inputs that are important for mediating the reflex remain to be investigated and may include vestibulospinal and/or reticulospinal tracts.

Abdominal Muscles↗
PubMed1988

Neuronal coding of linear motion in the vestibular nuclei of the alert cat. II. Response characteristics to vertical optokinetic stimulation.

Extracellular activity from vestibular nuclei neurons and vertical eye movements were recorded in the alert cat during sinusoidal optokinetic stimulation in the vertical plane at frequencies varying from 0.0125 Hz to 0.75 Hz. Among a population of 96 vestibular units located in and around Deiters' nucleus, 73 neurons (76%) displayed a firing rate modulation which followed the input at the standard parameters of visual stimulation (0.05 Hz; 10.1 deg/s or 9.1 cm/s peak to peak velocity). Two different patterns of modulation were found. In 42 cells (57%) an increase in the firing rate was observed during motion of the visual scene in the downward direction, while 31 neurons (43%) showed the opposite behavior, with an enhanced firing rate during upward movement. The phase of the neuronal responses was close (+/- 45 degrees) to the velocity peaks (+90 degrees: downward and -90 degrees: upward) of visual scene motion for 65 among the 73 neurons. Mean values of phase was -6.1 +/- 19.5 degrees (SD) and -3.2 +/- 15.5 degrees (SD) with respect to the +90 degrees and -90 degrees velocity peaks, respectively. In the frequency range 0.0125-0.75 Hz, the phase of the neuronal responses remained almost stable, with only a slight lag which reaches -22 degrees at the 0.25 Hz visual stimulation. The firing rate modulation was found to be predominant at low frequencies (0.0125 Hz-0.25 Hz), with three distinct peaks of modulation occurring either at 0.025 Hz, 0.10 Hz or 0.25 Hz, depending on the recorded cells. Above 0.5 Hz, the cell modulation was very poorly developed or even absent. A gain attenuation was observed in all units, which was more important in cells showing a peak of modulation at 0.025 Hz as compared with the others (-20.7 dB vs -9.6 dB, respectively, in the 0.025 Hz-0.25 Hz decade). The gain of the optokinetic reflex (OKR) progressively decreased from mean values of 0.78 +/- 0.15 to 0.05 +/- 0.06 in the 0.025 Hz-0.5 Hz frequency range. A close correlation was observed between the OKR slow phase velocity and the modulation of the neuronal responses in the two cell populations with maximal modulations at 0.10 Hz or 0.25 Hz. No correlations were noticed in the third population characterized by a peak of modulation at 0.025 Hz. In all units, the phase of eye movement velocity and of neuronal responses were both related to the velocity of the visual surround motion. These correlations were also found when varying the amplitude of the visual stimulation at a fixed frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1990

Distributed parallel processing in the vertical vestibulo-ocular reflex: learning networks compared to tensor theory.

The vestibulo-ocular reflex (VOR) is capable of producing compensatory eye movements in three dimensions. It utilizes the head rotational velocity signals from the semicircular canals to control the contractions of the extraocular muscles. Since canal and muscle coordinate frames are not orthogonal and differ from one another, a sensorimotor transformation must be produced by the VOR neural network. Tensor theory has been used to construct a linear transformation that can model the three-dimensional behavior of the VOR. But tensor theory does not take the distributed, redundant nature of the VOR neural network into account. It suggests that the neurons subserving the VOR, such as vestibular nucleus neurons, should have specific sensitivity-vectors. Actual data, however, are not in accord. Data from the cat show that the sensitivity-vectors of vestibular nucleus neurons, rather than aligning with any specific vectors, are dispersed widely. As an alternative to tensor theory, we modeled the vertical VOR as a three-layered neural network programmed using the back-propagation learning algorithm. Units in mature networks had divergent sensitivity-vectors which resembled those of actual vestibular nucleus neurons in the cat. This similarity suggests that the VOR sensorimotor transformation may be represented redundantly rather than uniquely. The results demonstrate how vestibular nucleus neurons can encode the VOR sensorimotor transformation in a distributed manner.

Animals↗
PubMed1988

Different sensitivity to hypoxia in neuronal activities of lateral vestibular and spinal trigeminal nuclei.

Electrophysiologic studies were performed to examine the effects of hypoxia on neuronal activities of the lateral vestibular and spinal trigeminal nuclei using rats anesthetized with chloral hydrate. The rats inhaled a gas mixture of 5% oxygen and 95% nitrogen for 3.5 minutes to induce hypoxia, followed by room air. Under these conditions, mean PaO2 was decreased from 85 to 22 mm Hg 3 minutes after the start of the inhalation concomitant with a decrease in blood pressure from 108 to 55 mm Hg. There were no significant differences in these variables between rats used for vestibular nucleus experiments and rats used for trigeminal nucleus experiments. In the lateral vestibular nucleus, hypoxia inhibited postsynaptic components of the evoked field potential, spike generation of monosynaptic neurons on vestibular nerve stimulation, and firing induced by iontophoretic application of glutamate. In the spinal trigeminal nucleus, however, there were no alterations of the field potential or spike generation of the neurons on trigeminal nerve stimulation. These results indicate that the lateral vestibular nucleus neurons are much more sensitive to hypoxia than the spinal trigeminal nucleus neurons. The failure of transmission in the monosynaptic neurons of the lateral vestibular nucleus is suggested to be due to the inhibition of excitability of the postsynaptic membrane.

Acetylcholine↗
PubMed2003

Confinement but not microgravity alters NMDA NR1 receptor expression in rat inner ear ganglia.

Space flight produces changes in neuronal activity in the vestibular system. We studied the protein expression of the NMDA receptor subunit NR1 in the vestibular ganglia of rats exposed to microgravity for 17 days, beginning on postnatal day 8, as part of the NASA Neurolab mission. As a control, we studied the cochlear ganglia in the same way. NR1 expression in rats that had experienced microgravity (flight-FLT rats) was compared with that in two types of ground control. One control consisted of rats housed in regular cage conditions (VIV, vivarium); the other, asynchronous ground control (AGC), consisted of rats kept in cages similar to those used in flight (animal enclosure module, AEM), requiring no human care. After 8 days of flight, NR1 levels in the vestibular and cochlear neurons were similar in FLT, VIV and AGC rats. In contrast, 8 h after landing, the FLT and VIV animals showed similar, normal levels of NR1 staining, whereas the ganglia of the AGC animals displayed only very faint staining. Thus, microgravity did not modify NR1 expression in vestibular neurons. The lower levels of NR1 expression in the vestibular and cochlear neurons of AGC rats suggest an effect of confinement for 17 days in AEMs on the ground.

Animals↗
PubMed1964

VESTIBULAR NUCLEI: ACTIVITY OF SINGLE NEURONS DURING NATURAL SLEEP AND WAKEFULNESS.

The rate of spontaneous discharge of second-order vestibular neurons is higher during wakefulness than during drowsiness and synchronized sleep. The activity of units recorded from the lateral (and superior) vestibular nucleus remains unmodified or is slightly increased during desynchronized sleep, in spite of the complete disappearance of the postural tonus. Units in medial and descending vestibular nuclei show bursts of rapid discharge associated with the eye movements characteristic of desynchronized sleep.

Cats↗
PubMed2000

Distribution of frequenin in the mouse inner ear during development, comparison with other calcium-binding proteins and synaptophysin.

Frequenin is a calcium-binding protein previously implicated in the regulation of neurotransmission. We report its immunocytochemical detection in the mouse inner ear, in the adult, and during embryonic (E) and postnatal (P) development. The distribution of frequenin was compared with those of other calcium-binding proteins (calbindin, calretinin, parvalbumin) and synaptophysin. In the adult mouse inner ear, frequenin immunostaining was observed in the afferent neuronal systems (vestibular and cochlear neurons, their processes and endings) and in the vestibular and cochlear efferent nerve terminals. Frequenin colocalized with synaptophysin in well characterized presynaptic compartments, such as the vestibular and cochlear efferent endings, and in putative presynaptic compartments, such as the apical part of the vestibular calyces. Frequenin was not found in vestibular hair cells and in cochlear inner and outer hair cells. During development, frequenin immunoreactivity was first detected on E11 in the neurons of the statoacoustic ganglion. On E14, frequenin was detected in the afferent neurites innervating the vestibular sensory epithelium, along with synaptophysin. On E16, frequenin was detected in the afferent neurites below the inner hair cells in the organ of Corti. The timing of frequenin detection in vestibular and cochlear afferent neurites was consistent with their sequences of maturation, and was earlier than synaptogenesis. Thus in the inner ear, frequenin is a very early marker of differentiated and growing neurons and is present in presynaptic and postsynaptic compartments.

Aging↗
PubMed2001

Commissural effects in the otolith system.

We examined whether otolith-activated second- and third-order vestibular nucleus neurons received commissural inhibition from the contralateral otolithic macula oriented in the same geometric plane. For this purpose we performed intracellular recording in vestibular nucleus neurons after stimulation of the ipsi- and contralateral utricular and saccular nerves. More than half (41/72) of the utricular-activated second-order vestibular nucleus neurons received commissural inhibition from the contralateral utricular nerve. The remaining neurons (31/72) showed no visible response to contralateral utricular nerve stimulation. About half (17/36) of utricular-activated third-order neurons also received commissural inhibition from the contralateral utricular nerve. Approximately 10% (7/67) of saccular-activated second-order vestibular neurons received polysynaptic commissural inhibition, whereas 16% (11/67) received commissural facilitation. The majority (49/67) of saccular second-order vestibular neurons, and almost all (22/23) third-order neurons, showed no visible response to stimulation of the contralateral saccular nerve. The present findings suggest that many utricular-activated vestibular nucleus neurons receive commissural inhibition, which may provide a mechanism for increasing the sensitivity of vestibular neurons to horizontal linear acceleration and lateral tilt of the head. Commissural inhibition in the saccular system was less prominent than in the utricular system.

Animals↗
PubMed1991

The neuronal organization of horizontal semicircular canalactivated inhibitory vestibulocollic neurons in the cat.

1. The somatic location and axonal projections of inhibitory vestibular nucleus neurons activated by the horizontal semicircular canal nerve (HCN) were studied in anesthetized cats. Cats were anesthetized with ketamine hydrochloride and pentobarbital sodium. 2. Intracellular recordings were obtained from 11 neck extensor motoneurons which were identified by antidromic activation from the dosal rami (DR) in the C1 segment. Stimulation of the ipsilateral (i-) HCN and the ipsilateral abducens (AB) nucleus evoked IPSPs in the motoneurons. These IPSPs were fully or partially occluded when they were evoked simultaneously. 3. Intracellular recordings were obtained from 8 AB motoneurons. Stimulation of the i-HCN and the i-C1DR motoneuron pool evoked IPSPs in the AB motoneurons. These IPSPs were also partially occluded when they were evoked simultaneously, which implied that some HCN-activated neurons inhibit both i-AB motoneurons and ipsilateral neck motoneurons. 4. Unit activity was extracellularly recorded from 30 vestibular neurons that were activated monosynaptically by i-HCN stimulation. Their axonal projections were determined by stimulating the i-AB nucleus and the i-C1DR motoneuron pool. Eight neurons were activated by both stimuli, and were termed vestibulooculo-collic (VOC) neurons. Their axonal branching was examined by means of local stimulation in and around the i-AB nucleus and the i-C1DR motoneuron pool. Eighteen neurons were antidromically activated from the i-C1DR motoneuron pool but not from the i-AB nucleus. These were termed vestibulo-collic (VC) neurons. Four neurons were activated from the i-AB nucleus but not from the ventral funiculus in the C1 segment, and were termed vestibulo-ocular (VO) neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Abducens Nerve↗
PubMed1990

Selective labeling of sensory hair cells and neurons in auditory, vestibular, and lateral line systems by a monoclonal antibody.

This study reports that zn-1, a monoclonal antibody, labels hair cells but not supporting cells in the inner ear and the lateral line of the axolotl salamander, Ambystoma mexicanum. Zn-1 immunocytochemically labels the cytoplasm and stereocilia of mature hair cells in the sacculus, in the utriculus, and in the mechanoreceptive neuromast organs of the lateral line. Lower levels of labeling mark newly formed hair cells in the periphery of the sacculus and in regenerating neuromasts. Zn-1 also selectively labels neuronal processes and perikarya in the lateral line nerves and ganglia and the VIIIth cranial nerve and ganglion. Processes and perikarya are labeled by zn-1 in the dorsolateral medulla oblongata, at sites of termination of the afferent octaval and lateral line neurons. Western blot analysis revealed that zn-1 labels one or more proteins with molecular weights of 80 and 160 kDa. The identity of these protein bands remains to be determined. The presence of a specific epitope expressed in both hair cells and neurons, but not in supporting cells, in the vestibular and auditory epithelia of the ear and in the mechanoreceptive neuromasts of the lateral line suggests shared cytogenetic heritages. These findings are consistent with a close evolutionary relationship between otic and lateral line senses, such as that inherent to the theoretical evolutionary scheme outlined in van Bergeijk's "acousticolateralis hypothesis." The protein recognized by zn-1 is as yet unidentified, but its conservative evolution suggests that it may serve an important function in the statoacoustic and lateral line systems.

Afferent Pathways↗
PubMed1991

Responses of neurons in the rat vestibular nuclei to static tilt stimulation.

The response properties of otolith afferent neurons have been analysed in the monkey and the cat. However, knowledge about the rat's responses to static tilt is scarce. To elucidate central information processing of the otolith system, responses to static tilt were analysed in the rat vestibular nuclei neurons.

Animals↗
PubMed1981

Responses of vestibulospinal neurons to neck and macular vestibular inputs in the presence or absence of the paleocerebellum.

1. The role of the paleocerebellum in determining the responses of lateral vestibular nucleus (LVN) neurons either to independent or combined stimulation of macular vestibular and neck receptors has been investigated in decerebrate cats. Sinusoidal rotation around the longitudinal axis at 0.026 Hz, 5-10 degrees, represented the constant input parameters. Among the tested neurons, 100 and 131 units were recorded in animals with intact cerebellum and following partial cerebellectomy, respectively. The units were classified according to their anatomical location in either the rostroventral (cLVN) or dorsocaudal (ILVN) part of the LVN; units also were activated antidromically from the spinal cord. 2. The majority of units responded to stimulation of macular receptors both in preparations with intact cerebellum (75.0%) or with partial cerebellectomy (71.8%), the response being primarily in phase with the direction of animal orientation. The proportion of responding units and their response sensitivity were greater in the cLVN than ILVN in each preparation; no significant differences in mean firing rate and response sensitivity were observed between the two preparations for each subdivision of the LVN. In animals with cerebellum intact, the majority of cLVN and ILVN units were excited during side-down tilt; following partial cerebellectomy, this predominant response pattern still was present in cLVN but was reversed in ILVN. 3. About one-half of the units responded to sinusoidal stimulation of neck receptors in both preparations, the response being mainly in phase with the direction of neck orientation. In the intact cerebellum preparations, the proportion of cLVN units responding to neck rotation was greater than that of ILVN units, but no difference in response sensitivity was observed between these units. Following partial cerebellectomy, the proportion of cLVN units responsive to the neck input was reduced but that of ILVN units was not; however, the average response sensitivity was halved for both cLVN and ILVN units. In preparations with cerebellum intact, most of the cLVN units were excited during side-down neck rotation, whereas ILVN units were excited mainly by rotation in the opposite sense; following partial cerebellectomy, the majority of units were excited during side-up neck rotation, not only in ILVN but also in cLVN. 4. Units receiving a convergent input from both receptors were more numerous in cLVN (72.7%) than ILVN (41.8%) in preparations with intact cerebellum; following partial cerebellectomy, this disproportion of responsive units in the two divisions (45.3% and 44.9%, respectively) disappeared, due to a reduced number of cLVN units responding to the neck input. In both preparations, the macular input had a relatively greater influence on the cLVN whereas the neck input was more effective on the ILVN. 5...

Acceleration↗