Abstract

The effects of cumulative intravenous doses of mephenesin, pentobarbital, caramiphen, chlorpromazine, zoxazolamine, carisoprodol and scopolamine upon the phasic and tonic components of the stretch reflex of ankle extensor muscles of decerebrate cats were quantitatively compared. The cats were decerebrated electrolytically at the intercollicularlevel 24 to 48 hours prior to assessing the actions of the agents upon the stretch reflex.

All of the compounds produced more depression of the tonic component of the stretch reflex than of the phasic component. The difference in degree of depression of the phasic and tonic reflex components was most marked with mephenesin and least with pentobarbital. The effects of caramiphen resembled those of mephenesin. Carisoprodol, zoxazolamine and chlorpromazine had relative effects upon the two components intermediate between the extremes observed with mephenesin and pentobarbital. Only limited depression of the tonic reflex with no depression of the phasic component was seen after doses of scopolamine which produce cholinergic blockade at peripheral autonomic sites.

The order of potency of the agents in producing 50% depression of the tonic reflex was: zoxazolamine, mephenesin, carisoprodol, caramiphen, pentobarbital, chlorpromazine, and scopolamine. Scopolamine was approximately twenty times as potent as zoxazolamine.

For 75% depression of the tonic component of the reflex the order of potency was: zoxazolamine, carisoprodol, mephenesin, caramiphen, scopolamine, pentobarbital and chlorpromazine. Chlorpromazine was almost sixteen times as potent as zoxazolamine.