EFFECTS OF CENTRAL DEPRESSANTS ON THE CORTICAL AUDITORY RESPONSES EVOKED BY REPETITIVE CLICK STIMULI IN THE CAT

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Abstract
The repetitive click responses in the auditory cortex were recorded by a series of click stimulation at different frequencies from 1 to 20/sec in the encephale isole preparations of the cat, and the effects of central depressants such as pentobarbital sodium, chloralose, urethane, ethyl alcohol and chlorpromazine on the responses were studied. The repetitive click responses in unanesthetized animal were classified into following three groups the evoked potentials observed within 0. 5 seconds after the on- set of stimulation (the early potentials), marked decrease in amplitude of the evoked potentials for about 1 second followed with the early potentials (the initial inhibition), and the repetitive evoked potentials succeeding to the initial inhibition. The repetitive click responses in the third group were gradually decreased in amplitude at the stimulation frequency above 8/sec (the late depression). Pentobarbital sodium and chloralose increased amplitude and number of the early potentials at the small doses and decreased the amplitude at the large doses. On the other hand, urethane, ethyl alcohol and chlorpromazine depressed the amplitude of the early potentials progressively with increase of the doses. All the depressants used prolonged the initial inhibition phase and the manifestation of the rhythmic after-discharges in the small doses. However, the large doses of pentobarbital sodium and chloralose resulted in marked decrease in amplitude of the succeeding evoked potentials and obscured the initial inhibition. Urethane, ethyl alcohol and chlorpromazine in the large doses prolonged apparently the initial inhibition phase. The small doses of pentobarbital sodium decreased the stimulation threshold of the recruiting response, while other depressants used increased it even in the small doses.