THE EFFECTS OF MUSCLE RELAXANTS ON THE VESTIBULAR EVOKED ACTIVITY OF THE LATERAL RECTUS MUSCLE

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Responses of extraocular muscles induced by giving repetitive stimulation to the horizontal ampullar nerve were studied from the point of view of the functional role of the neuromuscular system, using neuromuscular blocking agents (succinylcholine chloride and gallamine triethiodide).
The results of the electromyogram and the isometric mechanogram of the lateral rectus muscle in alert cats have indicated that the responses to succinylcholine are the increase of the resting tension in accordance with the increase of spontaneous small spike discharges, while the responses to gallamine are the depression or no change of the resting tension and the decrease of spike discharges. As for the effect of intravenous injection of succinylcholine or gallamine on the evoked tetanic and baseline tension, and spike discharges by repetitive vestibular stimulation, succinylcholine depressed the tetanic contractions and increased the baseline tension in accordance with the decrease or disappearance of large spikes and the increase of small spikes, while gallamine depressed both tetanic contraction and the baseline tension and abolished large spikes and small spikes.
From the results mentioned above, it was concluded that at least two fiber types (tonic and phasic) existed in the lateral rectus muscle and that the activity of these fibers caused tonic and phasic movements of nystagmus and eye deviation induced by vestibular stimulation.