Overtraining reduces morphine abolition of classically conditioned responses.

MAUK, M. D., T. G. CASTELLANO, 1. A. RIDEOUT, 1. MADDEN, IV, 1. D. BARCHAS AND R. F. THOMPSON. Overtraining reduces morphine abolirion of clossically conditioned responses. PHYSIOL BEHAV 3q3) 49W95, 1983.-We have previously reponed that intravenous injection of morphine produces selective abolition of recently learned, aversively motivated classically conditioned responses. We now report that morphine administered to overtrained animals produces considerably less effect on conditioned responding than in animals recently trained. This effect cannot he accounted for by factors related to consolidation. Results are discussed in relation to a two process model of aversive learning.