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PubMed1976

Electrophysiological properties of nucleus reticularis tegmenti pontis cells: antidromic and synaptic activation.

Antidromically and synaptically activated spike and synaptic potentials in the nucleus reticularis tegmenti pontis (NRTP) of the cat were recorded intracellularly. The antidromic firing of the NRTP neurone is composed of IS-SD spikes with short duration and short spike-after-hyperpolarization. Membrane resistance and firing patterns were studied by applying depolarizing and hyperpolarizing current through the recording electrode. Findings indicate that the NRTP neurone has a relatively high membrane resistance and is capable of firing at a high frequency. Single shock stimulation of the interpositus (IP) and lateral nucleus (LN) of the cerebellum, brachium conjunctivum (BC), red nucleus (RN) and cerebral peduncle (CP) induced monosynaptic EPSPs in the NRTP neurones. Superior vestibular nucleus (SVN) stimulation induced monosynaptic IPSPs. Collision tests showed that (1) NRTP neurones are activated by the axons of IP and LN neurones which travel through BC, (2) these axons also send collaterals to RN, and (3) there is convergence of cerebellar, cerebral and brain stem inputs to a single NRTP neurone.

Action Potentials↗
PubMed1995

Vertical vestibular input to and projections from the caudal parts of the vestibular nuclei of the decerebrate cat.

1. To investigate the type of vestibular signals that neurons in the caudal parts of the vestibular nuclei transmit to the cerebellum and spinal cord, we studied their responses to natural vestibular stimulation in vertical planes in decerebrate cats with the caudal cerebellum removed. Most neurons were in the caudal half of the descending vestibular nucleus, the remainder at corresponding levels of the medial nucleus or the medial-descending border. 2. Dynamics of the responses of spontaneously firing neurons were studied with sinusoidal tilts delivered at 0.05-1 Hz near the plane of body rotation that produced maximal modulation of the neuron's activity (response vector orientation). For most neurons the predominant vestibular input could be identified as coming from otolith organs (46%) or vertical semicircular canals (37%). Some neurons had otolith+canal convergence (9%) and others either had such converging input or some other form of central processing (8%). 3. Gain and phase of the responses of otolith neurons were comparable with values obtained in earlier studies on Deiters' nucleus and the rostral descending nucleus. Many canal neurons had a steeper gain slope and more advanced phase than observed previously for more rostral neurons. This may be due to more irregular afferent input to many neurons or to the absence of the vestibulocerebellum. 4. Response vector orientations of canal neurons were closely bunched near the planes of the ipsilateral vertical canals. The small number of contralaterally projecting vectors showed evidence of convergence between the two contralateral vertical canals. As is the case elsewhere in the vestibular nuclei, there was no evidence of convergence from bilateral vertical canals. Response vector orientations of otolith neurons were restricted to the roll quadrants; the majority pointed ipsilaterally. 5. Antidromic stimulation with an electrode in the restiform body or with several electrodes in the dorsal half of the white matter of the upper cervical cord was used to identify neurons projecting to the cerebellum and spinal cord, respectively. A substantial number of spontaneously firing neurons projected to the cerebellum, but there were few spontaneously active vestibulospinal neurons. The properties of the vestibular input to cerebellar-projecting neurons were the same as those of the population as a whole, but the effect of tilt on vestibulospinal neurons appeared weak or absent. 6. Many neurons were inhibited by stimulation of the restiform body. We suggest that this is mainly due to stimulation of the axons of vestibulocerebellar Purkinje cells. 7. Our results demonstrate a robust vertical vestibular input to the caudal parts of the vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Canal-otolith interaction in the fastigial nucleus of the alert monkey.

To determine the contribution of the otoliths as well as the horizontal and vertical semicircular canals to the response of "vestibular only" neurons in the rostral fastigial nucleus of the alert monkey, we applied natural sinusoidal vestibular stimuli (0.6 Hz; +/-15 deg) around different axes. During the experiment the monkey sat erect in a primate chair with the head immobile. Semicircular canal responses were investigated during tilted yaw stimulation around an earth vertical axis. The tilt angle was varied by 30 deg and included the optimal plane for horizontal canal stimulation (15 deg nose down from the stereotactic plane). The otoliths and mainly the vertical canals made contributions during stimulation around an earth-fixed horizontal axis (vertical stimulation). Head orientation was also slowly altered (2-3 deg/s) over a range of 180 deg under both stimulus conditions (tilted yaw and vertical stimulation). Neuronal data for each paradigm were fitted by a least squares best-sine function. Computation of the hypothetical contributions made by all three pairs of semicircular canals and the otoliths to these responses showed that 74% of the 46 neurons investigated received an otolith input; in most instances it was combined with a canal input. Neurons most often received input from the horizontal and vertical canals as well as the otoliths. Only a minority of neurons received a purely otolith (13%), vertical canal (13%), or horizontal canal (4%) input. Conventional criteria (head position-related activity, spatiotemporal convergence, STC) failed to detect an otolith contribution in several such instances. Thus, canal-otolith convergence is the general rule at this central stage of vestibular information processing in the fastigial nucleus. The large variety of response types allows these neurons to participate in multiple tasks of vestibulospinal movement control.

Animals↗
PubMed2000

Floccular modulation of vestibuloocular pathways and cerebellum-related plasticity: An in vitro whole brain study.

The isolated whole brain (IWB) preparation of the guinea pig was used to investigate the floccular modulation of vestibular-evoked responses in abducens and oculomotor nerves and abducens nucleus; for identification of flocculus target neurons (FTNs) in the vestibular nuclei and intracellular study of some of their physiological properties; to search for possible flocculus-dependent plasticity at the FTN level by pairing of vestibular nerve and floccular stimulations; and to study the possibility of induction of long-term depression (LTD) in Purkinje cells by paired stimulation of the inferior olive and vestibular nerve. Stimulation of the flocculus had only effects on responses evoked from the ipsilateral (with respect to the stimulated flocculus) vestibular nerve. Floccular stimulation significantly inhibited the vestibular-evoked discharges in oculomotor nerves on both sides and the inhibitory field potential in the ipsilateral abducens nucleus while the excitatory responses in the contralateral abducens nerve and nucleus were free from such inhibition. Eleven second-order vestibular neurons were found to receive a short-latency monosynaptic inhibitory input from the flocculus and were thus characterized as FTNs. Monosynaptic inhibitory postsynaptic potentials from the flocculus were bicuculline sensitive, suggesting a GABA(A)-ergic transmission from Purkinje cells to FTNs. Two of recorded FTNs could be identified as vestibulospinal neurons by their antidromic activation from the cervical segments of the spinal cord. Several pairing paradigms were investigated in which stimulation of the flocculus could precede, coincide with, or follow the vestibular nerve stimulation. None of them led to long-term modification of responses in the abducens nucleus or oculomotor nerve evoked by activation of vestibular afferents. On the other hand, pairing of the inferior olive and vestibular nerve stimulation resulted in approximately a 30% reduction of excitatory postsynaptic potentials evoked in Purkinje cells by the vestibular nerve stimulation. This reduction was pairing-specific and lasted throughout the entire recording time of the neurons. Thus in the IWB preparation, we were able to induce a LTD in Purkinje cells, but we failed to detect traces of flocculus-dependent plasticity at the level of FTNs in vestibular nuclei. Although these data cannot rule out the possibility of synaptic modifications in FTNs and/or at other brain stem sites under different experimental conditions, they are in favor of the hypothesis that the LTD in the flocculus could be the essential mechanism of cellular plasticity in the vestibuloocular pathways.

Abducens Nerve↗
PubMed1997

Use of calcium-binding proteins to map inputs in vestibular nuclei of the gerbil.

We wished to determine whether calbindin and/or calretinin are appropriate markers for vestibular afferents, a population of neurons in the vestibular nuclear complex, or cerebellar Purkinje inputs. To accomplish this goal, immunocytochemical staining was observed in gerbils after lesions of the vestibular nerve central to the ganglion, the cerebellum, or both. Eleven to fourteen days after recovery, the brain was processed for immunocytochemical identification of calretinin and calbindin. After lesion of the vestibular nerve, no calretinin staining was seen in any of the vestibular nuclei except for a population of intrinsic neurons, which showed no obvious change in number or staining pattern. Calbindin staining was reduced in all nuclei except the dorsal part of the lateral vestibular nuclei. The density of staining of each marker, measured in the magnocellular medial vestibular nucleus, was significantly reduced. After the cerebellar lesion, no differences in calretinin staining were noted. However, calbindin staining was greatly reduced in all nuclei. The density of staining, measured in the caudal medial vestibular nucleus, was significantly lower. After a combined lesion of the cerebellum and vestibular nerve, the distribution and density of calretinin staining resembled that after vestibular nerve section alone, whereas calbindin staining was no longer seen. This study demonstrates that calretinin and calbindin are effective markers for the identification of vestibular afferents.

Animals↗
PubMed1997

Development of the human lateral vestibular nucleus: a morphometric evaluation.

The development of the human lateral vestibular nucleus was studied on serial sections of the brain of 8 fetuses and neonates at 12-40 weeks of gestation, an infant at 2 months of age and an adult of 63 years using a microscope with a drawing tube and an image-analysing computer system. A morphometric analysis revealed that the lateral vestibular nucleus, whose neurons were distinguished from glia after 16 weeks of gestation, divided cytoarchitectonically into the medial and the lateral subnuclei at 21 weeks of gestation onwards, and showed the moderate development in terms of the columnar length and volume, neuronal size and neuropil.

Female↗
PubMed2003

Long-lasting increases in intrinsic excitability triggered by inhibition.

Although experience-dependent changes in neural circuits are commonly assumed to be mediated by synaptic plasticity, modifications of intrinsic excitability may serve as a complementary mechanism. In whole-cell recordings from spontaneously firing vestibular nucleus neurons, brief periods of inhibitory synaptic stimulation or direct membrane hyperpolarization triggered long-lasting increases in spontaneous firing rates and firing responses to intracellular depolarization. These increases in excitability, termed firing rate potentiation, were induced by decreases in intracellular calcium and expressed as reductions in the sensitivity to the BK-type calcium-activated potassium channel blocker iberiotoxin. Firing rate potentiation is a novel form of cellular plasticity that could contribute to motor learning in the vestibulo-ocular reflex.

Animals↗
PubMed1975

Neuronal activity in the lateral vestibular necleus of the cat. IV. Postsynaptic potentials evoked by stimulation of peripheral somatic nerves.

The synaptic input to Deiters neurones evoked by stimulation of peripheral somatic nerves was measured by intracellular recordings. EPSPs with broad receptive fields and latencies which indicate polysynaptic connexions were commonly evoked from the FRA. In other cells, low threshold cutaneous afferents were effective at rather short latencies suggesting oligosynaptic connexions from fast ascending fibres. One example was found of EPSPs due to low threshold muscle afferents. IPSPs due to climging fibre activation of Purkinje cells as observed in most of the neurones were evoked by cutaneous volleys above 1.5-2.0T and muscle volleys above 5T (above 3-3.5T in case of Q). Often, IPSPs were evoked by stimulation of nerves, to the segmental level of which the the vestibulospinal neurone under investigation projected. A small proportion of cells received short latency IPSPs involving direct fast mossy fibre tracts, which were evoked from low threshold cutaneous afferents. IPSPs due to polysynaptic mossy fibre activation of Purkinje cells were evoked from the FRA bilaterally and from ipsilateral cutaneous afferents at 1.5-2.0T ("prolonged inhibition"). Prolonged excitatory/inhibitory events mediated by mossy fibre pathways may be involved in quadruped locomotion or other processes making use of a broad motor integration.

Animals↗
PubMed1991

The surface glycoprotein Thy-1 is excluded from growing axons during development: a study of the expression of Thy-1 during axogenesis in hippocampus and hindbrain.

Thy-1 is a developmentally regulated surface glycoprotein expressed on a number of tissues, including nerve where it is a major surface component of mature neurons. During neural development in the rat and mouse, expression of Thy-1 protein does not necessarily follow appearance of its mRNA, but additionally requires completion of the initial phase of axonal growth. Where there is a substantial lag phase between initial elongation and final axonal outgrowth into a terminal field (e.g. pontine projection to the cerebellum), Thy-1 protein appears at the cell body and dendrites of the neurons, but is excluded from their axons until the terminal phase of axonal growth is completed. In the more complex case of the vestibular ganglion neurons, whose axons project primarily to the vestibular nuclei in the brainstem before birth, and then 1-2 weeks later into the cerebellum, Thy-1 enters the proximal axonal regions where growth is completed, but not the distal growing ends. Thus complex controls govern the initial expression and distribution of Thy-1 so as to exclude it from growing regions of axons.

Animals↗
PubMed2003

Differential spatial organization of otolith signals in frog vestibular nuclei.

Activation maps of pre- and postsynaptic field potential components evoked by separate electrical stimulation of utricular, lagenar, and saccular nerve branches in the isolated frog hindbrain were recorded within a stereotactic outline of the vestibular nuclei. Utricular and lagenar nerve-evoked activation maps overlapped strongly in the lateral and descending vestibular nuclei, whereas lagenar amplitudes were greater in the superior vestibular nucleus. In contrast, the saccular nerve-evoked activation map coincided largely with the dorsal nucleus and the adjacent dorsal part of the lateral vestibular nucleus, corroborating a major auditory and lesser vestibular function of the frog saccule. The stereotactic position of individual second-order otolith neurons matched the distribution of the corresponding otolith nerve-evoked activation maps. Furthermore, particular types of second-order utricular and lagenar neurons were clustered with particular types of second-order canal neurons in a topology that anatomically mirrored the preferred convergence pattern of afferent otolith and canal signals in second-order vestibular neurons. Similarities in the spatial organization of functionally equivalent types of second-order otolith and canal neurons between frog and other vertebrates indicated conservation of a common topographical organization principle. However, the absence of a precise afferent sensory topography combined with the presence of spatially segregated groups of particular second-order vestibular neurons suggests that the vestibular circuitry is organized as a premotor map rather than an organotypical sensory map. Moreover, the conserved segmental location of individual vestibular neuronal phenotypes shows linkage of individual components of vestibulomotor pathways with the underlying genetically specified rhombomeric framework.

Action Potentials↗
PubMed1985

Effects of adenosine triphosphate on neuron activities in the lateral and medial vestibular nuclei.

Electrophysiological studies were carried out to elucidate the effects of adenosine triphosphate (ATP) on the vestibular nuclei of cats anesthetized with alpha-chloralose. Intravenous (i.v.) administration of ATP in doses of 0.5-2.0 mg/kg produced an enhancement of spike generation with vestibular nerve stimulation and spontaneous firing in both monosynaptic and polysynaptic neurons in the lateral vestibular nucleus (LVN) as well as in the medial vestibular nucleus (MVN). These effects of ATP, however, were not dose-dependent. In contrast, iontophoretic application of ATP up to 200 nA had only negligible effect on spike generation of mono- and polysynaptic neurons in the LVN and those in the MVN upon vestibular nerve stimulation. The results suggest that the enhancement of neuron activities in the vestibular nuclei following i.v. injection of ATP is due to the indirect effect probably resulting from an increase in blood flow in the brain, but not to a direct, excitatory effect of the drug on the neurons themselves.

Action Potentials↗
PubMed1976

Functional characterization of primary vestibular afferents in the frog.

1. In order to more accurately identify the nature of the vestibular input to central neurons, the response properties of single semicircular canal and otolith units in the frog VIIth nerve were studied in curarized preparations. 2. An equation describing the response plane was calculated for each canal on the basis of null point measurements. These results show that the ipsilateral canal planes are orthogonal within 2-5 degrees, and the pairs of right-left synergists are essentially coplanar. A head position of 10-20 degrees maxilla nose up produces optimal horizontal canal and minimal vertical canal activation with horizontal rotation. 3. The frequency response of the horizontal canal was examined in the range 0.025-0.5 Hz. Comparatively shorter phase-lags and a 10 fold greater acceleration gain in this frequency range distinguish the frog from the mammalian species studied. 4. Otolithic responses were tonic, phasic-tonic, and phasic in nature. The preponderance of the latter two groups is stressed (94%). Tonic responses were proportional to the gravitational vector change. Phasic responses were proportional to velocity during transitions in head position and phase-led displacement (30-80%) with sinusoidal acceleration in roll and pitch. 5. Efferent vestibular neurons respond to rotation in the horizontal (usually Type III) as well as vertical planes. Responses in the vertical planes result from canal and/or otolithic input to these neurons indicating that the vestibular efferent system receives extensive multi-labyrinthine convergence.

Animals↗
PubMed2005

Patient and normal three-dimensional eye-movement responses to maintained (DC) surface galvanic vestibular stimulation.

HYPOTHESIS: That disease or dysfunction of vestibular end organs in human patients will reduce or eliminate the contribution of the affected end organs to the total eye-movement response to DC surface galvanic vestibular stimulation (GVS). BACKGROUND: It was assumed that DC GVS (at current of 5 mA) stimulates all vestibular end organs, an assumption that is strongly supported by physiological evidence, including the activation of primary vestibular afferent neurons by galvanic stimulation. Previous studies also have described the oculomotor responses to vestibular activation. Stimulation of individual semicircular canals results in eye movements parallel to the plane of the stimulated canal, and stimulation of the utricular macula produces changes in ocular torsional position. It was also assumed that the total three-dimensional eye-movement response to GVS is the sum of the contributions of the oculomotor drive of all the vestibular end organs. If a particular vestibular end organ were to be diseased or dysfunctional, it was reasoned that its contribution to the GVS-induced oculomotor response would be reduced or absent and that patients thus affected would have a systematic difference in their GVS-induced oculomotor response compared with the response of normal healthy individuals. METHODS: Three-dimensional video eye-movement recording was carried out in complete darkness on normal healthy subjects and patients with various types of vestibular dysfunction, as diagnosed by independent vestibular clinical tests. The eye-movement response to long-duration bilateral and unilateral surface GVS was measured. RESULTS: The pattern of horizontal, vertical, and torsional eye velocity and eye position during GVS of patients independently diagnosed with bilateral vestibular dysfunction, unilateral vestibular dysfunction, CHARGE syndrome (semicircular canal hypoplasia), semicircular canal occlusion, or inferior vestibular neuritis differed systematically from the responses of normal healthy subjects in ways that corresponded to the expectations from the conceptual approach of the study. CONCLUSION: The study reports the first data on the differences between the normal response to GVS and those of patients with a number of clinical vestibular conditions including unilateral vestibular loss, canal block, and vestibular neuritis. The GVS-induced eye-movement patterns of patients with vestibular dysfunction are consistent with the reduction or absence of oculomotor contribution from the end organs implicated in their particular disease condition.

Adolescent↗