ONE-TRIAL TOLERANCE TO THE EFFECTS OF CHLORDIAZEPOXIDE ON THE ELEVATED PLUS-MAZE MAY BE DUE TO LOCOMOTOR HABITUATION, NOT REPEATED DRUG EXPOSURE

The phenomenon of ''one-trial tolerance'' to the effects of chlordiaze poxide hydrochloride (CDP) in the elevated plus maze was re-examined. Unlike previous experiments, pre-exposure to the maze resulted in habi tuation and a consequential reduction in time spent on the open arms. The habituation effect was measured by recording the actual distance t ravelled by the rats in the maze and this was found to be significantl y reduced by pre-exposure. Pre-exposure to the maze in the presence of CDP resulted in a reduced response to its ''anxiolytic-like'' effects (increasing time on the open arms compared to vehicle control rats). However, although the time spent on the open arms was reduced by pre-e xposure, CDP significantly increased the time spent on the open arms b y rats pre-exposed under a non-drugged state. These results suggest th at rats do not become tolerant to the effects of CDP, but rather the r educed response to CDP after pre-exposure is due to habituation of exp loratory behaviour.