Biomedical subjects

N Dieringer

Publications and source records attributed to N Dieringer.

At least 19 recordsLinked to original sources

PubMed1995

Spinal plasticity after hemilabyrinthectomy and its relation to postural recovery in the frog.

1. Brachial dorsal root-evoked ventral root responses were studied in the isolated brain/spinal cord preparation of frogs. One group of frogs (n = 20) had survived a hemilabyrinthectomy (HL) between 7 and 70 days. In another group of frogs (n = 30), a nerve branch to an individual labyrinthine organ was sectioned uni- or bilaterally 15 days before the recording session. In a third group of frogs (n = 5), a weight had been mounted eccentrically on the head for 15 days. A fourth group of intact frogs (n = 8) served as a control. 2. In chronic HL frogs (> or = 60 days postoperatively) the amplitudes of short- and long-latency ventral root potentials recorded on the operated side were consistently increased with respect to control values in response to all converging inputs tested. On the intact side most of these potentials were consistently increased as well, except for crossed long-latency responses after stimulation of the dorsal root on the operated side. 3. Practically identical responses were recorded in these preparations before and after the disconnection of the spinal cord from the brain stem at the level of the obex. Before this disconnection, ventral root potentials were recorded in response to electric stimulation of either one of the VIIIth nerves on the intact or on the operated side. Ventral root potentials recorded on the operated but not on the intact side were slightly increased in chronic HL frogs. 4. The time course of these changes was studied at intervals between 7 and 70 days after the lesion. The amplitudes of short-latency dorsal root-evoked ventral root potentials were increased relatively early (7-15 days) or relatively late (> or = 30 days) after HL. Ventral root potentials evoked by stimulation of either one of the N.VIII were significantly reduced in amplitude seven days after HL but normalized again or increased above control values after longer survival periods. These differences in the time courses suggest the presence of multiple, not singular mechanisms for intraspinal changes. 5. Changes in dorsal root-evoked ventral root potentials similar to those after HL were seen 15 days after a selective unilateral section of the utricular, but not after a unilateral section of the horizontal canal or saccular nerve branch. Therefore these changes were initiated either by asymmetric utricular afferent inputs or by asymmetric proprioceptive inputs resulting from lesion-induced postural deficits. 6. These two possibilities were investigated in two different sets of experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

'Vestibular compensation': neural plasticity and its relations to functional recovery after labyrinthine lesions in frogs and other vertebrates.

Removal of the labyrinthine organs on one side is followed by a number of severe postural and dynamic reflex deficits. Some of these deficits, in particular the posture of head and body, are normalized again over a period that varies strongly between species. Other, more persistent motor deficits are substituted, e.g. by the saccadic system. This partial normalization of the function is accompanied by changes in response properties of the central vestibular neurons on the operated side. Available evidence suggests the occurrence of reactive synaptogenesis in cat and frog. In the latter species the synaptic efficacy of commissural vestibular connections increases and the metabolic activity of central vestibular neurons on the operated side recovers post-operatively. The onset of both changes, however, is delayed by about 30 days, which is too late to be causally related with the initial, rapid period of postural recovery in frog and cat. In frogs additional, early (7-15 days p.o.) and late (45-60 p.o.) synaptic changes were detected in the branchial spinal cord. These multiple changes survive the isolation of the spinal cord and must be propriospinal in origin. Selective lesions of individual vestibular nerve branches indicate that inactivation of utricular inputs is a sufficient and necessary condition to provoke postural deficits and early spinal changes similar to those after hemilabyrinthectomy. Therefore, a close correlation between spinal plasticity and postural recovery is indicated. In essence, the elimination of vestibular afferent inputs results in a series of behavioral distortions that are partially normalized by a multitude of synaptic mechanisms at distributed anatomical sites over different periods of time.

Animals↗

PubMed1994

Size-related colocalization of glycine and glutamate immunoreactivity in frog and rat vestibular afferents.

Presence and distribution of glutamate, glycine, GABA and beta-alanine in VIIIth nerves of frogs and rats were investigated with postembedding immunocytochemical methods on serial semithin sections. In Scarpa's ganglion of the frog, all cell bodies were glutamate immunoreactive. About 17% of the cells per section were also glycine immunoreactive, but none were GABA or beta-alanine immunoreactive. The mean diameter of glycine-positive cell bodies (26.7 +/- 6.9 microns; N = 130) was significantly (P < 0.0001) larger than that of glycine-negative cell bodies (15.7 +/- 5.4 microns; N = 272). The intensity of glutamate immunostaining decreased with cell diameter, whereas the intensity of glycine immunostaining increased with cell diameter. As a result, the staining intensities for glutamate and glycine in a given cell were negatively correlated. Glycine immunoreactivity was also present in a size-related manner in distal and proximal afferent fibers. The majority of thin fibers (< 4 microns) was glycine negative, whereas most of the thick fibers (> 10 microns) were glycine positive. Glycine-positive fibers were observed in the sensory epithelial of all end organs in the inner ear. The saccular macula and its nerve, however, contained only few glycine immunoreactive structures. In Scarpa's ganglion of the rat, all cells were immunoreactive for glutamate, about 12% for colocalized glycine, and none for GABA or beta-alanine. Glycine-positive cell bodies were significantly (P < 0.0001) larger (32.2 +/- 5.2 microns; N = 82) than glycine-negative cell bodies (25.1 +/- 5.3 microns; N = 274). Cell bodies in the spiral ganglion were only glutamate immunoreactive, whereas staining for glutamate, glycine, and GABA was dense in the ventral cochlear nucleus. These results demonstrate that thicker vestibular afferent fibers represent a particular subpopulation that differs from the majority of thinner afferents due to their glycine immunoreactivity.

Alanine↗

PubMed1994

Abducens nerve responses of the frog during horizontal linear acceleration: data and model.

Abducens nerve responses of frogs were evoked by sinusoidal oscillations on a horizontal linear sled. The depth of modulation of these responses and their phases depended on the orientation of the head with respect to the direction of linear acceleration. Longitudinal acceleration evoked abducens responses that consisted of two discharge maxima per stimulus cycle. At consecutively more oblique head orientations, one of these two discharge maxima increased and the other decreased. Transverse accelerations evoked abducens responses that consisted of only one discharge maximum per stimulus cycle. Removal of the labyrinthine organs on one side abolished these responses in the contralateral abducens nerve but did not affect the responses in the ipsilateral abducens nerve. The latter result indicates that the responses in each abducens nerve originate from hair cells on the contralateral utricle. The experimentally determined modulation and phase values and their dependence on the orientation angle of the acceleration vector were used to characterize a functional cluster of hair cells located medially with respect to the striola in a fan-like sector on the utricle ('lateral rectus fan'). Parameters of this fan were used to develop a model that satisfactorily simulates the recorded abducens responses. This model predicts a majority of afferents with excitatory and a few afferents with inhibitory contributions to the abducens nerve responses. The phasic response components of about 90% of these afferents are larger than their tonic response components.

Abducens Nerve↗

PubMed1994

Morphological and electrophysiological consequences of unilateral pre- versus postganglionic vestibular lesions in the frog.

The combined removal of the labyrinthine sense organs and of the ganglion of Scarpa on one side (postganglionic section) resulted in a degeneration of afferent fibres in the eighth nerve of the frog (Rana temporaria) within 2-4 days. If the eighth nerve was sectioned more peripherally (preganglionic section) and its distal part was removed together with the labyrinthine organs degeneration of afferent fibres was absent or restricted to very few fibres. Electrical stimulation of vestibular afferents in vitro evoked monosynaptic field potentials in the ipsilateral and via commissural fibres di- and polysynaptic field potentials in the contralateral vestibular nuclei. Afferent-evoked field potentials recorded on the intact side of chronic frogs (> or = 60 days) with a pre- or postganglionic lesion and afferent-evoked field potentials recorded on the operated side of chronic frogs with a preganglionic lesion had amplitudes that were very similar to those recorded in control frogs. Commissurally evoked field potentials recorded on the operated side of chronic frogs with pre- or postganglionic lesions were significantly increased (by about 90%) with respect to control amplitudes. In both groups the time-course of this increase was very similar, started between 15 and 30 days and saturated for survival periods longer than 60 days. Unilateral inactivation of vestibular afferents, but not degeneration, is the likely common denominator of the central process leading to the reported neural changes. A reactive supersensitivity of central vestibular neurons on the operated side for glutamate as a possible mechanism is unlikely, since converging afferent and commissural inputs are both glutamatergic and only one of them, the commissural input, was potentiated. Comparison of the time-courses of neural changes in the vestibular nuclei and postural recovery in the same individuals excludes a causal relation between both phenomena.

Animals↗

PubMed1994

Unilateral ablation of the frontal eye field of the rat affects the beating field of ocular nystagmus.

Spontaneous saccadic orientation and compensatory eye movements in response to optokinetic and vestibular velocity steps were studied in head-restrained, pigmented rats before and 1-2 weeks after unilateral ablation of the frontal eye field (FEF). One group of rats (n = 5) received a deep lesion and another group of rats (n = 4) received a superficial lesion of the left FEF. Postoperative response parameters such as the duration of slow buildup of eye velocity, the steady state velocity gain, the duration of optokinetic afternystagmus and of per- and postrotatory vestibular nystagmus were similar in the two groups of rats and did not differ from preoperative values measured in the same individuals. Superimposed upon these velocity components of nystagmus was a transient orienting response that expressed itself by a shift of the beating field of nystagmus in quick phase direction (gaze shift). The amplitudes of this gaze shift in quick phase direction were asymmetric in rats with a deep FEF lesion. Gaze shift amplitudes toward the side of the lesion were significantly enhanced and gaze shift amplitudes toward the intact side were significantly reduced. Similar asymmetries were observed in the distribution of spontaneous orienting movements of these rats in the light. Spontaneous saccadic eye movements of the same animals in darkness, however, were symmetric in amplitude to either side. These deficits suggest a partial sensory hemineglect after a deep unilateral lesion of the FEF and an involvement of this structure in the selective attention for targets in visual space. Thus the FEF orients the gaze at rest by means of saccades toward points of interest and during simulated circular locomotion by means of a shift of the beating field of nystagmus toward the visual sector that will be approached next.

Animals↗

PubMed1994

Plasticity in vestibular and spinal circuits after hemilabyrinthectomy in the frog.

Removal of the labyrinthine organs on one side results in static and dynamic disturbances. Some functional recovery is seen in frogs over time. Electrophysiological studies of the isolated brainstem and/or spinal cord of hemilabyrinthectomized frogs demonstrate changes in vestibular and spinal circuits. Comparison of the time courses of these changes with the known time course of postural recovery excludes changes in the vestibular nuclei as an explanation for the initial postural recovery process. Selective labyrinthine lesion suggest a causal link between utricular lesion, postural deficit, spinal plasticity and postural normalization.

Animals↗

PubMed1993

Evidence for separate eye and head position command signals in unrestrained rats.

Compensatory horizontal eye-head movements of unrestrained rats were recorded with search coils in a magnetic field in response to combined optokinetic plus vestibular sinusoidal oscillations (0.05-1 Hz). The velocity contribution of compensatory slow head movements for image stabilization was relatively small (about 30%). The beating field of ocular nystagmus shifted during each half cycle in quick phase direction. These changes in eye position were counterbalanced by concomitant changes in head position. As a result, the orientation of gaze position was kept straight ahead with respect to the body length axis. These results imply independent and task-specific recruitment orders for the ocular and neck motor system.

Animals↗

PubMed1993

GABA- and glycine-like immunoreactivities in the cerebellum of the frog.

Immunocytochemistry was performed on consecutive semi-thin sections of frog cerebellum with antibodies raised against GABA and glycine. Somata of Purkinje cells and stellate cells were immunoreactive for GABA but not for glycine. In the granular layer some neurons were immunoreactive for GABA, fewer for glycine and even fewer for both GABA and glycine. Most of the GABA-positive neurons appear to be Golgi cells. Most of the glycine-positive neurons appear to be displaced cerebellar nucleus neurons. Compared with mammals true basket cells are missing, stellate cells are fewer in number and colocalization of GABA and glycine in Golgi neurons is encountered about ten times less often in the frog than in the rat.

Animals↗

PubMed1993

Electrophysiological and pharmacological characterization of vestibular inputs to identified frog abducens motoneurons and internuclear neurons in vitro.

Synaptic vestibular inputs of antidromically identified motoneurons and internuclear neurons in the abducens nucleus were studied electrophysiologically and pharmacologically in the isolated brain of grass frogs (Rana temporaria). The prevailing response pattern of abducens motoneurons (AbMOT) following stimulation of the VIIIth nerve was crossed disynaptic excitation and uncrossed disynaptic inhibition. A few AbMOT (five of 46), however, exhibited uncrossed excitation instead of inhibition. Abducens internuclear neurons (AbINT), identified by antidromic activation following stimulation of the contralateral medial longitudinal fascicle, exhibited disynaptic response patterns to stimulation of the VIIIth nerve that were very similar in latency and rise time to those of AbMOT except for the absence of uncrossed disynaptic inhibition. Bath application of strychnine (50 microM), a glycine antagonist, blocked the uncrossed inhibitory vestibular input to AbMOT and AbINT completely and reversibly, whereas picrotoxin (100 microM), a GABA (gamma-aminobutyric acid) antagonist, had no detectable effect on these disynaptic potentials. These results suggest glycine as the transmitter of inhibitory vestibular projections onto AbMOT and AbINT. The pharmacology of the excitatory vestibular input of these neurons was studied by electrical stimulation of the vestibular nuclear complex. Crossed monosynaptic excitatory inputs in AbMOT and AbINT were blocked completely by CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) (10 microM), an antagonist of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors, indicating glutamatergic excitation. Comparison of these results with those in the cat suggests the presence of a basic horizontal vestibulo-ocular reflex that is very similarly organized, and corroborates the hypothesis that major behavioural differences in the performance of compensatory eye movements between species result from the properties of supplementary networks and not from differences in a common 'three-neuron' vestibulo-ocular arc.

Abducens Nerve↗

PubMed1993

The role of compensatory eye and head movements in the rat for image stabilization and gaze orientation.

Compensatory horizontal eye movements of head restrained rats were compared with compensatory horizontal eye-head movements of partially restrained rats (head movements limited to the horizontal plane). Responses were evoked by constant velocity optokinetic and vestibular stimuli (10-60 degrees/s) and recorded with search coils in a rotating magnetic field. Velocity and position components of eye and head responses were analysed. The velocity gains of optokinetic and vestibular responses of partially restrained and of head restrained rats were similarly high (between 0.8 and 1.0). Eye movements in partially restrained rats also contributed most (about 80%) to the velocity components of the responses. At stimulus velocities above 10 degrees/s, the "beating field" of the evoked optokinetic and vestibular nystagmus was shifted transiently in the direction of ocular quick phases. The amplitude of this shift of the line of sight was about 3-10 degrees in head restrained and about 20-30 degrees in partially head restrained rats. Most of this large, transient gaze shift (about 80%) was accomplished by head movements. We interpret this gaze shift as an orienting response, and conclude that the recruitment of the ocular and the neck motor systems can be independent and task specific: head movements are primarily used to orient eye, ear and nose towards a sector of particular relevance, whereas eye movements provide the higher frequency dynamics for image stabilization and vergence movements.

Animals↗

PubMed1993

Spinal compensation for postural deficits after hemilabyrinthectomy?

Removal of the labyrinthine organs on one side results in static and dynamic disturbances. Some functional recovery occurs over time and is paralleled in frogs by an increase in the efficacy of central vestibular pathways. Here, we report concomitant increases in dorsal root evoked ventral root responses in the brachial spinal cord and compare the time courses of neural changes in the brain stem and in the spinal cord with the progress of postural recovery in frogs. From this comparison we conclude that postural deficits are compensated by a spinal substitution process on the operated side.

Animals↗

PubMed1992

Chemical identification and morphological characterization of the inferior olive in the frog.

Tritiated D-aspartate was injected into the cerebellar cortex of grassfrogs, Rana temporaria. Retrograde labeling was observed in a cell column of the contralateral caudal medulla, but not in other areas known to give rise to cerebellar mossy fibers. The aspartate-positive neurons are therefore considered to represent the origin of cerebellar climbing fibers in the inferior olive, as reported earlier for rat and turtle by other investigators. Contrary to earlier reports we found no extraolivary climbing fibers in the VIIIth nerve and in Scarpa's ganglion. Our results support the view that the climbing fiber system of vertebrates is anatomically, physiologically and chemically very distinct and phylogenetically very conservative.

Animals↗

PubMed1992

Differences in optokinetic and vestibular ocular reflex performance in teleosts and their relationship to different life styles.

Horizontal eye movements in response to vestibular and optokinetic stimulation were investigated in 20 species of marine and fresh water teleosts. Most species performed spontaneous saccadic eye movements in light and in darkness. Successive saccades occurred either at irregular intervals and in different directions (few species), or in bursts of smaller saccades in one direction followed by saccades in the opposite direction (majority of species). Thus, in the latter group the lines of sight shifted cyclically from one side to the other about every 10-15 s. Eye movement responses in goldfish and toadfish were prototypical for two major functional groups. Optokinetic and vestibular nystagmus in the goldfish were much more regular and attained significantly higher gains than in the oyster toadfish. Optokinetic afternystagmus (OKAN) and per-/postrotatory nystagmus lasted about 10-12 s in the goldfish, but only 2-3 s in the oyster toadfish. Bilateral labyrinthectomy in goldfish resulted in optokinetic gains and OKAN durations that were very close to those of intact toadfish. These results indicate the presence (in goldfish) and the absence (in toadfish) of a functioning velocity storage network, respectively. Other non-ostariophysan teleosts failed to show a 'goldfish-like' response pattern as well. Ostariophysan species differed in their reflex performance as well. A 'goldfish-like' response pattern was observed in five of the seven cypriniform species and in two of the four characiform species but not in the four siluriform species. Positively correlated, combined response properties suggest that some species are better equipped for gaze stabilization at higher velocities than other species. These behavioral differences may parallel different specializations in locomotor pattern and mode of life. Absence of a functioning velocity storage network in bottom-dwelling teleosts (as in Amphibia) may be related to the sporadic, slow locomotion of these species and the resulting small requirements for continuous gaze stabilization during self-motion at higher velocities.

Animals↗

PubMed1991

Internuclear neurons in the ocular motor system of frogs.

Medial and lateral rectus motoneurons of frogs were localized after retrograde labeling with horseradish peroxidase (HRP) injected in the medial rectus muscle or applied on the cut end of the abducens nerve. Coordinates of these cell columns were used as target areas for the injection of small amounts of HRP (20-60 nl) and [3H]leucine (25-40 nl) and as search areas for retrogradely and anterogradely labeled internuclear neurons (INT) in in vivo and in vitro experiments. HRP injection in the medial rectus subdivision of the oculomotor nucleus (n = 6) resulted in retrograde labeling of cell bodies in the contralateral principal abducens nucleus. On the average about 16 cells per animal were found. Somatic diameters were about 13.5 +/- 2.8 microns (n = 32). The number and the size of these abducens internuclear neurons (AbINT) are smaller than those of lateral rectus motoneurons (n = 75; diameter: 19 +/- 3.2 microns). A crossed projection of AbINT to medial rectus motoneurons in the contralateral oculomotor nucleus is further supported by autoradiographic results. Following injection of [3H]leucine into the abducens nucleus, a high density of silver grains was visible within the contralateral oculomotor nucleus, mainly in the caudal part of the oculomotor nucleus, where medial rectus motoneurons are located. Injection of [3H]leucine in vivo (n = 4) and in vitro (n = 3) resulted in a similar high density of silver grains within the contralateral oculomotor nucleus, but the background level of silver grains was significantly higher after in vitro (264 +/- 38/2,500 microns2) than after in vivo injections (195 +/- 17/2,500 microns2). HRP injection in the principal abducens nucleus (n = 9) resulted in retrograde labeling of cell bodies in the medial rectus subdivisions of the bilateral oculomotor nuclei. Ipsilateral projections predominated, with about 10 (+/- 8) labeled cells over contralateral projections (about 3 +/- 2). Average diameters of these oculomotor internuclear neurons (OcINT) were again smaller (10.8 +/- 2 microns; n = 18) than those of medial rectus motoneurons (14.4 +/- 3 microns; n = 52). In addition, retrogradely labeled cells were consistently encountered in the bilateral vestibular nuclei, the cerebellar nuclei, the dorsal brainstem caudal to the abducens nuclei, and ipsilaterally in the pretectum. Most of the vestibular neurons were located in the rostral part of the vestibular nuclear complex. These neurons might constitute part of the three-neuronal arc of the vestibulo-ocular reflex in the frog. Labeled cells in the pretectum were restricted to the ipsilateral posterior thalamic nucleus (P).(ABSTRACT TRUNCATED AT 400 WORDS)

Abducens Nerve↗

PubMed1991

Adaptation and habituation of the vestibulo-ocular reflex in intact and inferior olive-lesioned rats.

The gain of the vestibulo-ocular reflex (VOR) of intact pigmented rats was adaptively modified by training protocols that created a visual-vestibular conflict. For training, head restrained animals were oscillated on a turntable in front of an optokinetic pattern projected onto a cylindrical wall. The optokinetic pattern either moved the same amplitude with the animal ("in-phase": 0.05 Hz +/- 20 degrees/s) or opposite in direction ("out-of-phase": turntable and pattern 0.05 Hz +/- 10 degrees/s each). VOR responses were tested in darkness before and after each 8 min training period for a duration of 40 min. During "out-of-phase" training the gain of compensatory eye movements measured in light was close to 2 from the beginning on and the VOR tested in darkness increased in gain progressively from 0.48 (+/- 0.12) to 0.9 (+/- 0.3; P less than 0.05) in 5 out of 7 rats. Two rats did not adapt their VOR gain. Phase values decreased slightly by about 10 degrees. During "in-phase" stimulation compensatory eye movements were almost completely suppressed (gain close to 0) from the beginning on and the VOR tested in darkness decreased gradually in gain from 0.62 (+/- 0.17) to 0.13 (+/- 0.1; P less than 0.001) in all 6 trained rats. Phase values decreased in parallel from 151 degrees to 119 degrees (P less than 0.01). The effectiveness of the "in-phase" training paradigm in the absence of compensatory eye movements indicates that retinal image slip is the relevant signal for adaptation. In seven rats with histologically verified almost complete inferior olive (IO) lesions (chemically induced at least 45 days prior to training), "out-of-phase" and "in-phase" stimulation evoked compensatory eye movements with gains comparable to those in intact rats. VOR parameters measured in darkness were altered with respect to those of control rats. Gain differed extremely between individuals and phase lag re acceleration was in all IO-lesioned rats larger than in intact rats. The time constant of the VOR in response to table velocity steps was significantly longer (17 s +/- 4) than in intact rats (11 s +/- 3). Training did not alter the gain of the VOR in 5 out of 7 IO-lesioned rats. One rat increased its gain during "out-of-phase" training in the first, but not during a second training session (and not during "in-phase" training) and another rat decreased its gain during "in-phase" training (but not during "out-of-phase" training).(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗

PubMed1991

Spatial organization of linear vestibuloocular reflexes of the rat: responses during horizontal and vertical linear acceleration.

1. The spatial properties of linear vestibuloocular reflexes (LVOR) were studied in pigmented rats in response to sinusoidal linear acceleration on a sled. The orientation of the animal on the sled was altered in 15 degrees steps over the range of 360 degrees. Horizontal, vertical, and torsional components of eye movements were recorded with the magnetic field search coil technique in complete darkness. Conjugacy of the two eyes was studied in the horizontal movement plane. 2. Acceleration along the optic axis of one eye (approximately 50 degrees lateral) induced maximal vertical responses in the ipsilateral eye and, at the same time, maximal torsional responses in the contralateral eye. These vertical and torsional responses of the LVOR coincide with those obtained when the respective coplanar vertical semicircular canals are stimulated. Such a congruence suggests a common reference frame for LVOR and angular vestibuloocular reflexes (AVOR), with the result that direct combination of signals indicating apparent and real head tilt is facilitated. 3. Transformations of vertical and torsional responses into head coordinates (pitch and roll) show that these movements are compensatory in direction for any combination of apparent head tilt in pitch and roll planes. 4. Gain (rotation of the eye/apparent rotation of the gravity direction) was approximately 0.3 at 0.1 Hz and decreased to approximately 0.1 at 1.0 Hz. Vertical responses tended to have a larger gain than torsional responses. Phase lag relative to peak acceleration increased from about -9 degrees to about -47 degrees over the same frequency range. 5. Vertical linear acceleration evoked only vertical eye movements at a frequency of 1.0 Hz. 6. Horizontal responses of both eyes were symmetric or asymmetric in amplitude and in-phase (conjugate) or out-of-phase (disconjugate) with respect to each other, depending on the direction of linear acceleration. Translation in the transverse direction evoked conjugate compensatory horizontal responses. Forward-backward translation evoked movements of both eyes that were symmetric in amplitude, but 180 degrees out-of-phase. Translation along diagonal axes evoked almost no horizontal responses in the eye facing in the direction of linear motion but maximal horizontal responses in the eye facing away from the direction of linear motion. These disconjugate movements resulted in a modulation of the vergence angle of the eyes. 7. Disconjugate horizontal responses in darkness are best explained by the assumption that part of the visual consequences of a translational head displacement (i.e., change of viewing distance in light) is taken into account centrally.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

The cervico-ocular reflex in intact and chronically labyrinthectomized frogs.

Eye movements in response to horizontal oscillation of the body against the stationary head (cervico-ocular reflex) were measured with search coils in the frequency range between 0.02 and 1.0 Hz in intact and chronica bilaterally labyrinthectomized frogs. The evoked eye movements were compensatory in direction but only about 1-2% of the amplitude of the stimulus (+/- 5-20 degrees). In chronic bilaterally labyrinthectomized frogs (n = 5) very similar response characteristics were measured. The very small amplitudes of these responses in controls and in frogs with removed labyrinthine organs render this reflex functionally irrelevant for both gaze stabilization and recovery from dynamic vestibular deficits after a loss of labyrinthine function.

Animals↗