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W Precht

Publications and source records attributed to W Precht.

At least 37 records · Page 2Linked to original sources
PubMed1984

An electrophysiological study of pathways mediating optokinetic responses to the vestibular nucleus in the rat.

Intra- and extracellular responses of neurons in the pretectum (Pt), the nucleus reticularis tegmenti pontis (NRTP), the prepositus hypoglossal complex (NPH) and the vestibular nuclei (VN) were recorded during orthodromic/antidromic stimulation of their afferent/efferent fibers. In the Pt, many neurons were excited by stimulation of the contralateral optic nerve (ONc). Comparison of the latencies of evoked presynaptic action potentials and EPSPs yielded a time difference corresponding to one synaptic delay. Forty five per cent of these monosynaptically driven neurons were also excited antidromically from the ipsilateral NRTP. In the NRTP, ONc and Pt stimulations evoked disynaptic and monosynaptic EPSPs, respectively. Thirty six per cent of NRTP neurons orthodromically driven from ONc and/or ipsilateral Pt stimulation were also antidromically invaded from either the contralateral (67%) or the ipsilateral (33%) flocculus but never from both. In the NPH, both ipsilateral Pt and NRTP stimulations excited type II neurons monosynaptically. In addition, EPSPs evoked by Pt stimulation could be mediated to the NPH via a disynaptic route involving the NRTP. In the VN, type II neurons were excited by ipsilateral Pt stimulation. When comparing the latencies of action potentials and EPSPs evoked by Pt stimulation in the NPH and in VN type II neurons respectively, a short, possibly monosynaptic connection, may be postulated between the NPH and the VN. Our results suggest that vestibular neurons may be optokinetically driven from the contralateral eye both via Pt-NPH connections and Pt-NRTP-NPH paths. They also confirm the existence of a transcerebellar route from the Pt via the NRTP to the ipsior contralateral flocculi.

Animals↗
PubMed1984

Dynamics of maculo-ocular reflexes in the frog.

Compensatory torsional and vertical eye movements were recorded in the frog during sinusoidal linear acceleration along the longitudinal and transverse body axes, respectively. Stimulus frequencies ranged between 0.1 and 1.0 Hz and peak accelerations from 0.01 g to 0.1 g corresponding to body tilts ranging from 0.57 to 5.7 degrees. In addition, static compensatory eye movements were studied during fore-and-aft and lateral body tilt over ranges of +/- 10 degrees. The evoked eye movements were generally quite small (+/- 0.5 degree). Dynamic gain (rotation of the eye/apparent rotation of gravity direction) was 0.10-0.20 at 0.1 Hz and decreased to about 0.05 at 1.0 Hz. The gain of vertical eye movements was somewhat higher than that of torsional eye movements. Phase lag relative to peak accelerations increased from about 10 degrees to about 45 degrees over the same frequency range. Static compensatory eye movements evoked by nose-up and ipsilateral side-up tilt were larger in amplitude than those evoked by nose-down and ipsilateral side-down tilt. Static gain (rotation of the eye/tilt of the whole body) was about 0.10 for vertical and about 0.06 for torsional eye movements. No consistent eye movements could be evoked by vertical sinusoidal accelerations (maximal modulation amplitudes +/- 0.025 g). The results indicate that, as in other vertebrates, maculo-ocular reflexes contribute to gaze stabilization in the frog mainly during low frequency and static head and body tilts.

Animals↗
PubMed1984

Basic optokinetic-ocular reflex pathways in the frog.

Frogs (Rana temporaria) have two midbrain nuclei that receive contralateral retinal afferents, and whose neurons respond to optokinetic stimulation. The basal optic nucleus is composed of direction-selective neurons with different response types. One type is activated exclusively by upward moving optokinetic targets; another type is activated only by downward moving targets. Two other types of basal optic neurons show this vertical preference, but each is also activated by patterns moved horizontally from the nasal to temporal visual field. No activation of these cells was found with patterns moved horizontally from the temporal to nasal visual fields. Rather, cells in a discrete pretectal region have this type of sensitivity: they increase their resting rate with temporal to nasal stimulation and decrease it with nasotemporal stimulation. Oculomotor neurons (antidromically identified) have similar optokinetic sensitivities. As with basal optic neurons, these cells have exclusively upward or downward sensitivity, and some also have nasotemporal sensitivity. An additional type of oculomotor neuron and abducens motoneurons are activated by temporonasal pattern movement. In general, the extraocular motoneurons have similar velocity and pattern size preferences, as have the sensory nuclei. Investigations of the connectivity between the sensory and motor nuclei were primarily restricted to the relation between the pretectum and the abducens. A monosynaptic connection between the pretectum and the abducens is suggested by four points: (1) excitatory postsynaptic potential onset latency in antidromically identified abducens motoneurons, following optic nerve stimulation, is consistent with the interpretation of a disynaptic pathway to the abducens from the retina; (2) pretectal cells, sensitive to optokinetic stimulation, can be activated antidromically from stimulation of the abducens nucleus; (3) horseradish peroxidase injections into the pretectum result in labeling of axons, which terminate in the abducens nucleus; (4) horseradish peroxidase injections into the abducens result in labeling of cells in the pretectal region, where optokinetically sensitive cells are found. In the frog, there seem to be three-neuronal retino-ocular reflexes mediating optokinetic slow phase behavior as there are three-neuronal vestibulo-ocular reflexes that also mediate compensatory spatial behavior. It is suggested that these direct connections act to initiate ocular movements and accelerate the eye, whereas more indirect pathways may act to maintain eye position.

Afferent Pathways↗
PubMed1984

Pharmacology of the vestibular hair cell-afferent fiber synapse in the frog.

The isolated, intact, membranous labyrinth of the frog (Rana temporaria) has been investigated electrophysiologically in vitro to determine the nature of the transmitter substance at the synapse between the vestibular hair cells and afferent fibers. Spontaneous synaptic activity can be monitored with intra-axonal recordings from the afferents. Increased K+ in the bath results in an increase in frequency of presynaptic release, as indicated by an increased frequency of spontaneous synaptic potentials. Adding Mg2+ and lowering Ca2+ results in a decrease in synaptic potential frequency (often to zero) with no change in their mean amplitude, indicating pre-synaptic blockade. Extracellular recordings from individual vestibular afferents indicate that bath-applied glutamate and related acidic amino acids consistently increase the firing rates of these afferents in a dose-dependent manner with no evidence of desensitization. In the presence of presynaptic blockade (high Mg2+/low Ca2+), bath application of glutamate and its agonists results in a reversible depolarization of vestibular afferents, suggesting a postsynaptic action of these substances. 2-Amino-5-phosphonovaleric acid, kynurenic acid, and other acidic amino acid antagonists reversibly decrease the amplitudes of spontaneously occurring synaptic potentials without affecting their frequency, indicating subsynaptic blockade. These antagonists also block the postsynaptic depolarizations due to glutamate and its agonists. GABA and its agonists and antagonists have no consistent effect upon afferent activity. These findings suggest that glutamate, aspartate, or a related compound is the transmitter at this synapse. However, the antagonists used, or the receptors themselves, are not selective enough to discriminate adequately between the agonists. Therefore, which of these glutamate agonists are actually involved in synaptic transmission remains to be determined.

Afferent Pathways↗
PubMed1983

Afferent projections to the cerebellar flocculus in the pigmented rat demonstrated by retrograde transport of horseradish peroxidase.

The horseradish peroxidase (HRP) retrograde transport method was used to identify brainstem afferents to the cerebellar flocculus in the pigmented rat. Injections of the enzyme were made through recording microelectrodes, making it possible to localize the injection site by physiological criteria. Clearly, the largest number of afferents arise from the bilateral vestibular and perihypoglossal nuclei and from the contralateral dorsal cap (of Kooy) of the inferior olive. Additionally, a substantial number arise bilaterally from: (1) the nucleus reticularis tegmenti pontis (NRTP); (2) several of the cranial motor nuclei including the abducens, retrofacial and facial nuclei and the nucleus ambiguus; (3) the rostral part of the lateral reticular nucleus (subtrigeminal nucleus); (4) the raphe pontis and raphe magnus and (5) neurons intercalated among the medial longitudinal fasciculus (MLF) just rostral to the hypoglossal nucleus and another group rostral to the abducens nucleus. The basilar pontine nuclei contained a large number of lightly labeled neurons in all flocculus injections which were discretely located within the dorsolateral, lateral and medial divisions. These areas were labeled bilaterally but with a slight contralateral preponderance. Injection into the flocculus, but involving the adjacent ventral paraflocculus, produced a heavier labeling of pontine neurons with a slightly different distribution. Therefore, we tentatively conclude that the flocculus receives input from these pontine visual centers (dorsolateral, lateral and medial nuclei), perhaps through collateral projections from neurons projecting to the paraflocculus. The present study demonstrates strong similarities between the rat and other species studied (e.g., rabbit, cat, monkey) in terms of the brainstem nuclei projecting to the flocculus. Most noticeable in quantitative terms are the pathways known to mediate vestibular (vestibular and perihypoglossal nuclei) and visual (optokinetic) information (e.g., NRTP). Additionally, we can provide morphological evidence that the midline and paramedian pontine tegmentum, identified in the cat and monkey as containing saccade-related neurons, send large numbers of projections to the rat flocculus. Given these similarities, the rat may be a suitable animal model in which to study the pathways underlying visual-vestibular interaction and saccadic mechanisms in the flocculus.

Abducens Nerve↗
PubMed1983

Responses of different compartments of cat's splenius muscle to optokinetic stimulation.

The EMG in different compartments of the splenius muscle was recorded simultaneously with the horizontal electrooculogram in the alert, head restrained and head freed cat during optokinetic and vestibular stimulation. All compartments of the splenius muscle behaved qualitatively similarly. Tonic and phasic muscle activity was closely related to eye position.

Animals↗
PubMed1983

Short- and long-term modifications of vestibulo-ocular response dynamics following unilateral vestibular nerve lesions in the cat.

The dynamics of the horizontal vestibuloocular reflex (VOR) were determined in the dark prior to and at various time periods after unilateral removal of the vestibular nerve. One chronic group, consisting of cats that were operated at the age of 6 weeks or as adults, was studied 10.5 to 22 months later; an adult-operated group was measured 1-244 days postoperatively (p.o.). Between measurements cats were kept in a normal environment. In control animals the VOR gain was close to unity only up to certain stimulus velocities which varied amongst cats; thereafter a sharp drop in gain occurred probably due to saturation of central and peripheral neuronal responses. Therefore, VOR gains in lesioned animals were compared to the control responses yielding high gain. It is only at these small stimulus amplitudes that the two labyrinths maximally interact and, therefore, one would expect the largest changes. The gain was computed after correction for the ocular imbalance induced by the lesion. Immediately after the lesion a drop in gain to stimulations in both directions was noted; the reduction was larger for the VOR evoked on rotation to the lesioned side. Contrary to control animals, no partial response saturation occurred in lesioned animals but, following rotation to the lesioned side, complete saturation was noted with larger stimuli. Ocular balance was greatly improved within the first 3-4 days p.o. as indicated by the strong reduction of nystagmus. The time course of p.o. adaptive gain changes could be divided into three stages: in the initial stage (1-5 days p.o.) no improvement was visible; between p.o. days 5-10 one group of cats showed an abrupt increase in gain while it remained low in others. Response symmetry showed no consistent change in either group; the 3rd stage starting p.o. day 10 and extending throughout the observation period (22 months) is characterized by slowly developing changes reducing significantly response asymmetry. The incremental gain was higher in the young than in the adult-operated chronic cats. Compared to controls the phase plot of the VOR of lesioned animals shows a parallel shift of ca. 10 degrees towards larger lead over the frequency range tested (0.05-1.0 Hz) independent of direction of rotation or p.o. stages. All lesioned animals showed a clear failure to hold eye position in the dark even in the chronic stage; a drift with an exponentially decreasing velocity of ca. 2-4 degrees/s was typical.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1983

Responses of units in the rat cerebellar flocculus during optokinetic and vestibular stimulation.

The simple (SS) and complex spike (CS) responses of Purkinje (P-cells) and non-Purkinje (non P-cells) in the cerebellar flocculus were studied in alert pigmented rats (DA-HAN) during binocular and monocular optokinetic stimulation (OKS), vestibular stimulation and a combination of the two. Of a total of 98 P-cells whose SS discharges were activated by rotary stimulation of the horizontal canal in the dark (type I and type II P-cells), the vast majority (72%) responded to constant velocity binocular OKS that was produced by means of a horizontal shadow projector system. The remaining P-cells responded only to vestibular stimulation (19%), to OKS or to the presumed fast components of optokinetic and vestibular nystagmus (9%). The optokinetic responses of P-cells were generally bidirectional but asymmetrical, i.e., the increases in rate in one direction were larger in magnitude than decreases on opposite OKS and were synergistic with the semicircular canal input. During constant velocity OKS, the discharge of a few P-cells rose approximately exponentially, outlasted the stimulus by as much as 10-13.5s and, thus, resembled OKS responses of vestibular nucleus neurons. However, the majority exhibited a phasic-tonic response governed by a short "time constant" of from 0.5-3s. The velocity tuning curves of vestibular/OKS responding P-cells showed peak sensitivities with retinal slip velocities of 1.5-2 degrees/s. This is higher than the ca. 1 degree/s determined for other relay nuclei of the horizontal optokinetic pathway. The responses of non P-cells suggest that they originate from mossy fiber projections from vestibular, visual (optokinetic) and saccadic eye movement-related areas of the brainstem. Most of the units carried a combined vestibular and optokinetic signal. The majority showed a bidirection-selective response to OKS, and a small percentage showed unidirectional responses only. Monocular testing of P-cells revealed that most received a bidirection-selective, but asymmetrical, OKS input. Slightly more than half of these had a strongest OKS drive from the contralateral eye; the remaining units were driven most strongly by the ipsilateral eye. Unidirection-selective P-cells, driven by OKS to the ipsi- or contralateral eye, were uncommon; yet this class is common among other portions of the horizontal optokinetic system (e.g., vestibular nuclei, praepositus hypoglossi nucleus, nucleus reticularis tegmenti pontis).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1982

Miniature synaptic potentials absent from motoneurons of intact spinal cord.

Intracellular recordings were made from lumbar motoneurons of decerebrate, paralyzed frogs with minimal surgical damage to the spinal cord. Detectable spontaneous synaptic activity was absent in most motoneurons, as compared with published in vitro recordings. Lesions of the thoracic cord increased the incidence of small spontaneously occurring potentials. This suggests that spontaneous quantal release of transmitter observed in isolated preparations is a consequence of presynaptic neuronal damage.

Animals↗
PubMed1982

Miniature endplate potentials related to neuronal injury.

Intracellular recordings were made in vivo from muscle fibers of anesthetized or spinalized frogs. Characteristic 'spontaneous' miniature endplate potentials were rarely recorded in intact muscles by comparison with muscles acutely denervated in the same animals. It is concluded that little or no spontaneous quantal release of transmitter occurs in vivo, in contrast with isolated preparations. The presence effectively 'silent' endplates was confirmed by evoking quantal release with hypertonic saline.

Animals↗
PubMed1982

Compensatory head and eye movements in the frog and their contribution to stabilization of gaze.

Compensatory head movements, recorded in unrestrained frogs, were compared to compensatory eye movements recorded from animals that had their head fixed. Movements were evoked by oscillating the animal in the dark (vestibular stimulation) or in the light in front of an earth-fixed, patterned visual background (combined stimulation) or by rotating vertical black and white bars (optokinetic stimulation) around the stationary animal. Oscillations occurred in the horizontal plane at frequencies between 0.025 and 0.5 Hz. Gain and phase values of head and eye movements, relative to stimulus movements were calculated. Evoked eye movements were limited in amplitude to +/- 3-6 degrees, increasing with the size of the animal. Head movements were limited to +/- 30-40 degrees. Resetting fast-phases of both head and eyes were very rarely observed during sinusoidal stimulation and no eye movements were recorded in the absence of intended head movements. Vestibularly evoked head movements exhibited a frequency-dependent threshold that was not observed for vestibulo-ocular responses. Above threshold, the gain of evoked head responses increased and reached a frequency-dependent plateau at which the system behaved approximately linearly. Within the linear range, gain of vestibularly evoked responses increased with frequency (from 0.04 at 0.025 Hz to 0.75 at 0.5 Hz) and phase lead decreased (from about 80 degrees to 0 degrees). Vestibularly evoked eye movements similarly increased in gain from 0.05 to 0.56 and decreased in phase lead from about 56 degrees to 10 degrees over the same frequency range. Optokinetically evoked head and eye movements had their highest gains (about 0.8 and 0.5) at low constant velocities (less than or equal to 1-4 degrees/S) or frequencies (less than or equal to 0.025 Hz). At higher constant velocities or frequencies the gain dropped. The phase lag increased from close to zero (at 0.025 Hz) to about 60 degrees for the head and to about 20 degrees for the eye movements (at 0.25 Hz). These phase lags are explained by reaction times of the evoked movements of about 600 ms (head) and 200 ms (eyes). Combined stimulation evoked compensatory head movements with gain and phase values that were frequency-independent in the linear range. Head movements compensated for about 80-90% of the imposed gaze shift with a small phase lag (0-10 degrees). Evoked eye movements were found to be large enough in amplitude and fast enough in time to enable a frog to stabilize its gaze exclusively with slow phase compensatory movements for a large variety of frequency and amplitude combinations. The two motor systems controlling movements of the head and the eye are matched in such a way that the non-linearities of the evoked eye movements can compensate for the non-linearities of the evoked head movements.

Animals↗
PubMed1982

Resetting fast phases of head and eye and their linkage in the frog.

(1) Compensatory slow phase movements were evoked by optokinetic, vestibular and combined optokinetic and vestibular stimulation. Superimposed fast phases resetting the position of the head (in space) and of the eye (in head) were recorded with a magnetic field search coil in unrestrained and head fixed frogs, respectively. (2) Head fast phases recorded during optokinetic stimulation covaried in the frequency of their occurrence with slow phase head velocity. Their amplitude was large (average 18.9 +/- 8.9 degrees), maximal velocity increased with amplitude by 6.6 degrees/s/deg, and duration (average 230 +/- 33 ms) was almost independent on amplitude. (3) Ocular fast phases rarely occurred during sinusoidal stimulation and neither optokinetic after nystagmus nor postrotatory nystagmus were observed. Fast phases, evoked by constant velocity optokinetic or acceleratory stimuli, consisted of two components: a primary resetting fast phase and a smaller fast movement in the opposite direction. The primary fast phase had a small amplitude (average 2.2 +/- 1.3 degrees). In different stimulus conditions fast phase parameters were very similar. Maximal velocity increased by 6.5 degrees/s/deg. Duration (average 165 +/- 23.4 ms) was variable. (4) During ocular fast phases the vestibulo-collic and the optokinetic-collic reflexes were suppressed. The slow phase head velocity either became zero or a small head fast phase in the direction of the ocular fast phase occurred. Fast phase head movements were accompanied by an ocular fast phase or by a retraction of one or both eyes, depending on the amplitude of the head fast phase. At the end of a head fast phase eye position was always recentered.

Animals↗
PubMed1982

Optokinetic, vestibular, and optokinetic-vestibular responses in albino and pigmented rats.

Horizontal eye movements and neuronal activity in the vestibular nuclei and pretectum were recorded in albino and pigmented rats in response to optokinetic, vestibular (VS), combined visual-vestibular (VVS) sinusoidal stimulations. 1. VOR slow phase velocity in VS condition leads head velocity. This phase lead is smaller in albino than in pigmented rats. 2. Presence of vision (VVS) improves the phase angle of the VOR in both strains, especially at low frequencies. In pigmented rats the VOR is perfectly compensatory with respect to phase at all frequencies whereas in albinos the eye velocity still leads the head velocity. 3. There is no difference in the response characteristics of vestibular nuclear neurons (VN) to VS between albino and pigmented rats which could explain the difference in their VORs. 4. In the pigmented rat, there is a strong optokinetic input to VN which provokes a shift of the response peak towards peak head velocity. These visual-vestibular interactions at VN level are in agreement with the changes in the phase angle of the VOR. 5. In albino rat, there are no differences in the response characteristics of VN between VS and VVS, thus the decrease of the VOR phase lead observed in VVS compared to VS is due either to visual-vestibular interactions outside of the vestibular nuclei or to some general arousing effect of light. 6. Recording of responses of pretectal neurons to visual stimulation in albino rats has shown that they are activated in a phasic or tonic way by light on ("On cells") or off ("Off cells"). Contrary to the pigmented rat, pretreated neurons in albino exhibited no detectable direction specific optokinetic responses.

Animals↗
PubMed1980

Development of optokinetic responses in vestibular nuclear neurons in the young rat.

Responses of vestibular nuclear neurons (Vn) of the horizontal canal system to optokinetic stimulation could not be elicited before postnatal day 22. Between days 22 and 29 response magnitude gradually increased whereas response phase remained constant. At the end of the first postnatal month the sensitivity of the optokinetic responses was still much less than that measured in adult animals.

Afferent Pathways↗
PubMed1980

Afferent and efferent connections of cat omnipause neurons.

Afferent and efferent connections of behaviorally identified omnipause neurons involved in saccadic eye movements were investigated electrophysiologically in cats anesthetized with ketamine hydrochloride. Pause cells were polysynaptically excited by electrical stimulation of the optic chiasm (mean latency = 8.3 ms), the visual cortex (mean latency = 7.3 ms), and the superior colliculus (mean latency = 2.6 ms). Bilateral removal of either the visual cortex or the superior colliculus 1 week prior to the experiment abolished optic chiasm responses. Pause cells were antidromically activated by electrical stimulation of the prerubral fields (mean latency = 1.1 ms), or the pontine and medullary reticular formation (mean latency = 1.0 ms). Frequently, the same pause cell was antidromically excited by prerubral and pontine or medullary reticular stimulation indicating that its axon was branched. The spontaneous discharge of pause cells was polysynaptically suppressed by sustained galvanic polarization of either labyrinth, or by multiple shock stimulation in the reticular formation.

Animals↗