Psychotropic drugs and Sidman avoidance in rats: IRT distribution changes.

The effects of d-amphetamine, caffeine, chlorpromazine, diazepam and and pentobarbital on Sidman avoidance responding (R-S interval, 30 sec; S-S interval, 3 sec) in rats, especially on the interresponse time (IRT) distribution, were studied. d-Amphetamine and caffeine increased the total number of responses. Short IRTs were increased, while longer ones were decreased. Chlorpromazine, diazepam and pentobarbital all increased the number of shocks delivered. After chlorpromazine, no marked change was observed in the total number of responses. However, response bursts and escape reponses increased, while IRTs between 3 and 30 sec decreased. After diazepam and pentobarbital, the burst response scarcely increased, and the IRTs in the 3-15 sec range decreased, while the IRTs longer than 33 sec increased. These changes were more marked after diazepam than after pentobarbital. Total number of responses was decreased by both drugs. The present results suggest that in utilizing the Sidman avoidance procedure for psychotropic drug assessment, changes in the IRT distribution give a more precise profile of the drug than is afforded by the total number of responses and shocks delivered.