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N Dieringer

Publications and source records attributed to N Dieringer.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1988

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

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

2-Amino-5-phosphonovalerate↗
PubMed1987

The role of compensatory eye and head movements for gaze stabilization in the unrestrained frog.

Compensatory eye, head and gaze movements of unrestrained frogs were recorded simultaneously in response to table movements in the light. Passive displacement was compensated with a gain between 0.55 and 0.85, depending on stimulus amplitude. At small stimulus amplitudes gaze was stabilized exclusively by compensatory eye movements. At larger stimulus amplitudes compensatory head movements contributed up to 80% gaze stabilization. The contribution of compensatory eye movements became increasingly more restricted to those brief transient periods, at which head velocity changed only slowly in response to a change in stimulus direction or velocity. The wave forms of both eye and head movements exhibited characteristic and complementary distortions. Their combination, the gaze wave form compensated almost exactly in phase for the imposed passive displacement in space. Head saccades of small amplitude were rather well compensated by fast eye movements in the opposite direction, with the result that the combined gaze movement was smooth. The occurrence of these compensatory fast eye movements depended neither upon the function of the labyrinthine organs nor upon retinal image slip.

Animals↗
PubMed1987

A precise and inexpensive magnetic field search coil system for measuring eye and head movements in small laboratory animals.

The design of a magnetic field search coil system based on the phase detection principle is described. The system was developed to record eye and head movements of small, unrestrained laboratory animals. It is compact, linear over 360 degrees, has a high resolution and allows the use of minute, commercially available search coils. Potential pitfalls and critical factors in the use of the system are discussed and original movement records are presented.

Animals↗
PubMed1986

Evidence for an alteration in brainstem cholinergic pathways following unilateral labyrinthectomy in the frog.

Following VIIIth nerve stimulation, field potentials recorded in the contralateral vestibular nuclei of isolated medullae are larger in amplitude and more sensitive to atropine in chronically hemilabyrinthectomized frogs than those of controls. The atropine-sensitive component occurs at a latency which precludes involvement of the monosynaptic commissural projection between second order vestibular neurons. Therefore, in addition to this commissural projection, the contributions of more indirect pathways have to be considered in an attempt to understand the neuronal basis of behavioral improvement following vestibular lesions.

Animals↗
PubMed1986

Partial restitution of lesion-induced deficits in the horizontal vestibulo-ocular reflex performance measured from the bilateral abducens motor output in frogs.

The responses of the bilateral abducens nerves to small table velocity steps in the dark were measured in four groups of animals: One group was intact prior to recording (controls), one group was hemi-labyrinthectomized the day before the recordings (acute HL), the horizontal canal nerve was sectioned the day before the recordings (acute HCN) in another and the last group was hemi-labyrinthectomized between 60 and 90 days prior to recording (chronic HL). In controls (N = 6) the slopes of the change in discharge rate to increasingly larger velocity steps increased maximally with about 200 imp/s per 1 degree/s and decreased maximally with about -60 imp/s per 1 degree/s. This difference is explained by low resting rates and by recruitment of spontaneously inactive vestibular afferent, central vestibular and abducens neurons. Results obtained from acute HL (N = 4) and acute HCN (N = 4) animals were practically identical. In neither case was a spontaneous nystagmic activity pattern observed. Results differed from those obtained in controls due to an asymmetric reduction in responsiveness. Comparison of the slopes of the evoked increases and decreases in discharge rates of abducens nerves to increasingly larger velocity steps with those in controls show that normal abducens responses are predominantly controlled by crossed excitation and by uncrossed inhibition. Disinhibition and disfacilitation play minor roles. In chronic HL animals (N = 6) that had posturally recovered to a similar degree, responses evoked by steps towards the intact side at larger velocity steps were slightly reduced with respect to those in acute HL or HCN animals. Responses evoked by steps towards the lesioned side differed between individuals. They were either similar to those in controls (N = 1), to those in acute animals (N = 2) or lay between these two extremes (N = 3). The improvement in response to velocity steps towards the lesioned side in 4 of 6 animals is explained by an increase in activity released by disinhibition. This inhibition in turn is controlled by horizontal canal-dependent input from the intact side. Plugging of this canal abolished all direction-specific responses in this plane in the dark, suggesting that the partial restitution of function of horizontal reflex performance depends exclusively on signals derived from receptors of this canal.

Abducens Nerve↗
PubMed1986

Extraocular proprioceptive signals affect ocular motor activity neither directly nor parametrically in the presence of optokinetic or vestibular stimulation in the frog.

Direct and parametric effects of stretch receptors in the extraocular muscles on abducens nerve activity were investigated in the unanesthetized immobilized frog. Horizontal passive rotations of one eye in the physiological range (+/- 5 degrees) did not elicit responses in the activity of abducens nerve on either side; however, larger rotations or pull of one eye evoked long latency direction-unspecific responses simultaneously in both nerves. When the animal was stimulated vestibulary in the horizontal plane with sinusoidal or constant acceleration, abducens activity was not altered in correlation to passive eye movements in the physiological range. Similarly, the activity of either nerve evoked by simultaneous or preceding optokinetic stimulation of one eye with constant pattern velocity was not modified by passive rotation of the contralateral eye.

Abducens Nerve↗
PubMed1986

[Comparative neurobiology of the organization of gaze-stabilizing reflex systems in vertebrates].

During locomotion gaze is stabilized against passive head movements by compensatory eye movements. The efficacy and the neuronal organization of optokinetic and vestibular reflexes of different vertebrate species is compared. Besides many similarities between species a number of differences can be found as well. Increase in the efficacy of compensatory reflexes is not correlated with an increase in the efficacy of basic neuronal circuits but with the appearance of functionally new connections and of new network properties. This increasingly higher complexity allows to maintain gaze stability at increasingly higher speeds of locomotion or to suppress these reflexes during visual pursuit of a moving object.

Animals↗
PubMed1984

Increased projection of ascending dorsal root fibers to vestibular nuclei after hemilabyrinthectomy in the frog.

The projections from brachial, ascending dorsal root fibers were studied autoradiographically in controls and chronically (four months) hemilabyrinthectomized frogs. Comparison showed that projections into the partially denervated vestibular nuclear complex of chronically hemilabyrinthectomized animals were far more dense than in control animals. In the cerebellar granular layer, no obvious difference in the extent of dorsal root projections was observed between both groups of animals. Cerebellar areas such as the auricular lobe and the dorsal rim, which normally receive many terminals from vestibular but not from dorsal root afferents, were not invaded by dorsal root fibers in chronically hemilabyrinthectomized frogs.

Afferent Pathways↗
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↗
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↗
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↗
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↗