PHARMACOLOGICAL ANALYSIS OF UNITARY DISCHARGES RECORDED FROM THE INFERIOR COLLICULUS CAUSED BY CLICK STIMULI IN CATS

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Abstract
The effects of pentobarbital sodium, chloralose, urethane, ethyl alcohol, chlorpromazine and methamphetamine on the unitary discharges of the inferior colliculus in response to click stimuli were studied in encephale isole preparations of cats by means of the silver filled micropipette electrode technique. The typical collicular unitary discharges caused by click stimuli were observed when the tip of electrode was inserted at the depth of 1.8 to 4.0 mm from the dorsal surface of inferior colliculus. The evoked unitary discharges were consisted of 2 patterns of spikes: one of which appeared overlapping on the descending crus of the positive evoked potential (the early spike group) and the other appeared for 30 to 40 msec following the former one (the late spike group). The evoked unitary discharges were relatively stable for 1 to 2 hours and were not modified by the external stimuli. The small doses of the central depressants such as pentobarbital sodium (1-2 mg/kg), chloralose (20-40 mg/kg) and urethane (100-200 mg/kg) depressed the late spike group in number and amplitude without affecting the early spike group. However, large doses of pentobarbital sodium (above 10 mg/kg), chloralose (80-100 mg/kg) and urethane (above 500 mg/kg) abolished the late spike group accompanied with marked depression of the early spike group. The small doses of ethyl alcohol and chlorpromazine hardly affected both early and late spike groups of the collicular unitary discharges. Ethyl alcohol in doses above 800 mg/kg and chlorpromazine in dose of 20 mg/kg decreased the late spike group in number and amplitude. The small dose of methamphetamine (0.1-0.2 mg/kg) increased markedly number and amplitude of the collicular evoked unitary discharges.