Pavlovian conditional tolerance to haloperidol catalepsy: evidence of dynamic adaptation in the dopaminergic system.

An experiment with rats has demonstrated that Pavlovian conditioning factors determine the occurrence of tolerance to haloperidol catalepsy. Rats exhibited tolerance only in the environment previously associated with the drug. Previous research involving receptor binding techniques implicated an increase in the number of brain dopamine receptors as the mediator of neuroleptic tolerance. The present findings demonstrate that this change, by itself, cannot account for the conditional occurrence of such tolerance.