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Biomedical subjects

J H Ryu

Publications and source records attributed to J H Ryu.

At least 127 records · Page 7Linked to original sources
PubMed1981

Nonlinear characteristics of single neurons in the vestibular nuclei.

The characteristics of response of 99 vestibular nuclei neurons were investigated in the cat anesthetized with pentobarbital sodium. All neurons responded to stimulation of the horizontal semicircular canals (HSCC) with prolonged 2, 4, 6, or 8 degrees/second2 angular acceleration. Neural response was recorded utilizing the single-neuron recording technique. The vestibular neurons responded nonlinearly to stimulation of the HSCC. Specifically (1) the time required to reach the maximum response level decreased nonlinearly with an increase in stimulus magnitude (SM); (2) the maximum response level increased nonlinearly with the increase in SM: (3) the neural response to excitatory stimulus was not the mirror image of that to an inhibitory stimulus. Several existing mathematical models were simulated by utilization of the IBM Continuous System Modeling Program, account for the nonlinear response of the vestibular nuclei neurons. The nonlinearities observed in the responses may be due to (1) nonlinear behavior of the end organ, (2) the influence of the CNS including the vestibular efferent system, or (3) the inherent neural properties of the vestibular nuclei.

Acceleration↗
PubMed1980

Responses to step and repeated impulse accelerations in second order vestibular neurons of the cat.

The characteristics of response of 98 vestibular nuclei neurons were investigated in the barbiturate anesthetized cat. All type I and type II neurons (tonic and kinetic) responded to stimulation of the horizontal canals with step and impulse accelerations. Seventy-seven (79 per cent) neurons of all types demonstrated adaptation, while the remaining 21 (21 per cent) neurons showed either reverse adaptation or no adaptation. When the interval between impulses with impulse accelerations reached a critical minimum, the averaged response was remarkably like the response to step acceleration, including the rate of adaptation. A previously undescribed response decline to repetitive impulse acceleration was seen, which, while sharing some characteristics with habituation, appears to be more closely related to adaptation. Furthermore, the data suggest that adaptation seen at the vestibular nuclear level is more likely a central phenomenon rather than a peripheral one.

Acceleration↗
PubMed1976

Central vestibular compensation. Effect of the bilateral labyrinthectomy on neural activity in the medial vestibular nucleus.

An attempt was made to reconstruct the central events that occurred in the various stages of vestibular compensation after a bilateral labyrinthectomy in the cat. Bilateral labyrinthectomized cats showed no nystagmus, but had unsteady head movements and wide gaits. Neural activity in both sides of the medial vestibular nuclei (MVN) was depressed during the critical stage of compensation; however, the neural activity was full and normal during the acute and compensated stage. The experimental results suggest that removing crossed inhibitory influence and reducing the cerebellar inhibitory influence by bilateral labyrinthectomy enhances the process of recovering neural activity in the vestibular nuclei during central compensation, and that the contralateral vestibular end organ is not a source of the driving force responsible for regeneration of electrical activity in the deafferented MVN after a unilateral labyrinthectomy.

Animals↗
PubMedDate not supplied

Second-order neural responses after contralateral vestibular nerve sectioning.

The characteristics of the response to an 8 degrees/sec2 acceleration of 41 neurons in the medial vestibular nucleus of the cat following vestibular nerve sectioning were compared with those of 73 control neurons at the same site. In 14 of the vestibular nerve-sectioned animals the same neuron was recorded before and after sectioning. No difference was found between the resting discharge rates, maximal response rates, and rates of adaptation of the two groups. Following contralateral vestibular nerve sectioning Type II neurons were still plentiful, suggesting many receive ipsilateral labyrinthine innervation.

Action Potentials↗
PubMedDate not supplied

Effects of ketamine on the adaptive responses of second-order vestibular neurons of the cat.

The adaptive characteristics of 80 neurons in the vestibular nuclei of ketamine-anesthetized cats were investigated. All types I and II neurons responded to stimulation of the horizontal semicircular canals by an 8 degree/sec2 stepwise angular acceleration of 40 sec. For the purpose of this study, vestibular adaptation was defined as a decline in response at a rate of greater than -0.01 spikes/sec/sec. According to this criterion, 71 neurons (89 per cent) behaved as adapting neurons, and nine (11 per cent) showed either no adaptation or reverse adaptation. The rate of adaptation varied from neuron to neuron; the average rate was -0.312 spikes/sec/sec. The average resting discharge rate, the maximum response level, and the average adaptation rate were compared with similar neural responses in barbiturate-anesthetized cats. Although the average resting discharge rates of the two groups showed no significant difference, the average adaptation rate and the maximum response level of the ketamine-anesthetized group were significantly higher than those of the barbiturate-anesthetized group. These data suggest that the gain of the second-order neurons is higher and more actively modulated in more alert (ketamine-anesthetized) cats than in barbiturate-anesthetized cats.

Animals↗
PubMedDate not supplied

Effects of attention-requiring tasks on vestibular nystagmus.

The purpose of this investigation was to determine the influence of two types of attention-requiring tasks on vestibular nystagmus elicited by caloric stimulation: mental arithmetic and a short conversation. The subjects were divided into four groups according to stimulus paradigm and task. It was found that conversation was consistently superior to mental arithmetic in engaging the cortex and preventing response decline and even reverse caloric-induced habituation.

Adult↗