Eye Movements of the Murine P/Q Calcium Channel Mutant Tottering, and the Impact of Aging
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Mice carrying mutations of the gene encoding the ion pore of the P/Q calcium channel (Cacna1a) are an instance in which cerebellar dysfunction may be attributable to altered electrophysiology and thus provide an opportunity to study how neuronal intrinsic properties dictate signal processing in the ocular motor system. P/Q channel mutations can engender multiple effects at the single neuron, circuit, and behavioral levels; correlating physiological and behavioral abnormalities in multiple allelic strains will ultimately facilitate determining which alterations of physiology are responsible for specific behavioral aberrations. We used videooculography to quantify ocular motor behavior in tottering mutants aged 3 mo to 2 yr and compared their performance to data previously obtained in the allelic mutant rocker and C57BL/6 controls. Tottering mutants shared numerous abnormalities with rocker, including upward deviation of the eyes at rest, increased vestibuloocular reflex (VOR) phase lead at low stimulus frequencies, reduced VOR gain at high stimulus frequencies, reduced gain of the horizontal and vertical optokinetic reflex, reduced time constants of the neural integrator, and reduced plasticity of the VOR as assessed in a cross-axis training paradigm. Unlike rocker, young tottering mutants exhibited normal peak velocities of nystagmus fast phases, arguing against a role for neuromuscular transmission defects in the attenuation of compensatory eye movements. Tottering also differed by exhibiting directional asymmetries of the gains of optokinetic reflexes. The data suggest at least four pathophysiological mechanisms (two congenital and two acquired) are required to explain the ocular motor deficits in the two Cacna1a mutant strains.Keywords:
Optokinetic reflex
Stimulus (psychology)
Vestibulo–ocular reflex
Since Blohmke and Toda described it, the fact has been known that the horizontal nystagmus of the eyes can be induced by electrical stimulation of the meso-diencephalon in rabbits. According to the method described by Lachmann et al, who did a great deal of research in this field, “the nystagmogenic area” was electrically stimulated in 26 rabbits. In addition to the electrical stimulation, they were given optokinetic and labyrinthine stimulations (1°/sec2 in 90see), simultaneously or independently.It was evaluated how the central nystagmus, which was induced by electrical stimulation to this area, interacted with the optokinetic and labyrinthine nystagmus and, furthermore, how the nystagmogenic area related to the physiological cooperation of the visual organ and the vestibular organ i.e. the so-called “optic-vestibular coordination”, in development of nystagmus. Following conclusions were obtained.1. Central nystagmus is always facillitated by optokinetic stimulation irrespective of the direction of the optokinetic stimulation.2. Central nystagmus is sometimes facillitated and sometimes inhibited by the labyrinthine stimulation depending on the direction of the stimulus. The effect is observed even if the subliminal rotation, which does not provoke nystagmus by itself, is applied.3. Central nystagmus is markedly facillitated by simultaneous aprication of the optokinetic and labyrinthine stimulations.4. The nystagmogenic area relates closely to the neural pathway of the optokinetic nystagmus. and plays an important role in the optic-vestibular coordination in development of nystagmus.
Optokinetic reflex
Stimulus (psychology)
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Congenital nystagmus has been relatively easily diagnosed by using optokinetic nystagmus test because of its characteristic reactions, such as lack of optokinetic nystagmus, so-called “inversive reactions (bilateral, unilateral, and partial)”, or ataxic reaction. These characteristic reactions have long been believed to be seen only in patients with congenital nystagmus. However, recently we experienced an ataxic pattern of optokinetic nystagmus in acquired diseases which is quite similar to the ataxic pattern of optokinetic nystagmus in congenital nystagmus.This fact has brought confusion in diagnosing congenital nystagmus, but at the same time, this might be a clue to elucidate the unknown pathophysiological mechanism of congenital nystagmus. In this paper we report 8 cases of acquired diseases which manifested ataxic reaction in optokinetic nystagmus test.
Optokinetic reflex
Confusion
Electronystagmography
Dysmetria
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Optokinetic reflex
Vestibulo–ocular reflex
Stimulus (psychology)
Electronystagmography
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The subject of investigation was the possibility of the transfer of habituation. In 20 pigeons frequency of optokinetic and postrotatoric head nystagmus was established. Then in 10 birds optokinetic habituation training and in 10 remaining pigeons rotatoric habituation training were performed. After acquisition of habituation in the first group, frequency of postrotatoric head nystagmus and in the second group frequency of optokinetic head nystagmus were defined. The transfer of optokinetic habituation to the rotatoric test was confirmed. The inverted process was not observed.
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Optokinetic reflex
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For the investigation of the effect of the otolith system on optokinetic nystagmus, the crab was examined using an optical cylinder. The results obtained were as follows: (1) Optokinetic nystagmus always occurred with the stimulation of the optical cylinder. (2) In crabs of which statocysts were removed, the nystagmus was depressed. (3) The nystagmus was not depressed by forward position but depressed by backward position. (4) The nystagmus directed to the right side was depressed by right lateral position but not depressed by left lateral position. Similar findings were observed in cases of nystagmus directed to the left side. Analyzation of the results indicated that the otolith system has a certain effect on optokinetic nystagmus.
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When a man looks around while on a revolving object, nystagmus is elicited. This type of nystagmus consists of two components, i.e. optokinetic nystagmus and labyrinthine nystagmus. Labyrinthine nystagmus is caused by the movement of endolymph in the semicircular canals and can be elicited by rotating the body in the dark room with the eyes opened (perrotatory nystagmus). Optokinetic nystagmus can be elicited by applying visual stimuli with the eyes opened.Optokinetic nystagmus may or may not be affected by additionally induced rotation nystagmus. It is also known that labyrinthine nystagmus is inhibited by gaze. In the present study electronystagmographic study was performed on the effect of concomitant perrotatory nystagmus (as induced by pendular rotation of the body) on the pattern of optokinetic nystagmus and the inhibitory effect of gaze on perrotatory nystagmus.The subjects were 20 healthy adults. In all subjects an inhibitory effect of gaze on perrotatory nystagmus was noted. The effect, however, was complete (total suppression of perrotatory nystagmus) in 39% of the cases and incomplete (the nystagmus still appeared though diminished in frequency and amplitude) in the other 61%.Optokinetic nystragmus was demonstrated in all cases. When a stimulus of pendular rotatory movements was applied to the subjects while optokinetic nystagmus was being elicited, no appreciable changes were observed in 39% of cases. In the remaining 61% of the cases, clearly noticeable changes in the slow component of the optokinetic nystagmus were observed.In the group whose perrotatory nystagmus was inhibited incompletely, the changes of the optokinetic nystagmus by the rotation was more clealy observed than in the group whose perrotatory nystagmus was inhibited completely.This finding suggests that the inhibition of labyrinthine nystagmus by gase should be taken into account when interaction between optokinetic nystagmus and labyrinthine nystagmus is studied.
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The aim of our work was the presence of the second phase nystagmus after rotatory, caloric and optokinetic irritation; estimation of this nystagmus magnitude and the clinical application of the second phase nystagmus. The investigation was performed in 30 healthy subjects and 65 cases of the peripheral and central vestibular pathology. Our results show that the second phase nystagmus appears more often after strong vestibular or visual irritation; the largeness of this reaction is bigger than the first reaction nystagmus. Only the asymmetry of the second phase nystagmus has the clinical apply. Labyrinthine disorders has the influence on the formation of the post-optokinetic reaction.
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Eye irritation
Electronystagmography
Caloric theory
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Horizontal optokinetic nystagmus (OKN), caloric nystagmus, and positional alcohol nystagmus (PAN) of the rhesus monkey (Macaca mulatto) were surveyed using electrooculography. OKN of the monkey appears to be similar in most respects to that of man although optokinetic after-nystagmus is more prominent in the monkey. of the parameters of OKN which were measured, slow phase velocity was most closely related to the optokinetic stimulus. Caloric nystagmus is easily induced in the monkey and parameters of caloric nystagmus declined exponentially on repeated testing. The first phase of positional alcohol nystagmus was present in all animals tested and the secondary phase in some. The data indicate that oculomotor findings in the monkey can probably be applied to man with few reservations.
Optokinetic reflex
Electrooculography
Stimulus (psychology)
Caloric theory
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