Effect of naloxone on a quickly learned conditioned suppression in rats following cessation of chronic haloperidol treatment.

Rats showed marked suppression of motor activity when placed in the cage where they were previously shocked. When 14 days of consecutive administration of haloperidol was terminated, the conditioned suppression was significantly reduced. Such an effect of chronic haloperidol treatment was antagonized by pretreatment with naloxone. Thus, it is possible that the opiate-like system is involved in a part of the reduction of conditioned suppression.