A barbiturate-like effect of adrenocorticotropic hormone on the partial reinforcement acquisition and extinction effects.

Abstract

Abstract Rats were trained to run in a straight alley for a food reward, either with reward on every trial (continuous reinforcement, CR) or with reward on a random 50 per cent of trials (partial reinforcement, PR), and then extinguished. Control animals, injected with gel, showed the usual partial reinforcement acquisition effect (increased running speed in PR animals relative to CR animals at the end of training) and partial reinforcement extinction effect (increased resistance to extinction in PR animals), but both these effects were absent in rats injected daily during acquisition with 8 I.U. adrenocorticotrophic hormone (ACTH); the drugged PR animals and the drugged CR animals behaving like undrugged CR controls. Neither 2 nor 4 I.U. ACTH daily during acquisition had these effects, though both doses increased acquisition running speed. The results obtained with 8 I.U. ACTH closely resembled those previously obtained with amylobarbitone.