Conditioned avoidance behavior in pretrained rats intermittently treated with addictive drugs.

Rats pretrained in a conditioned avoidance (CAR) paradigm were put on eight potentially addictive drugs in drinking water at two dose levels each. Fluid intake and body weight, monitored during the drugged (addiction) and nondrugged (withdrawal) states, showed drug/dose-dependent fluctuations in most groups. Extinction and relearning trials were spread over both drug and nondrug phases. CAR-performance generally deteriorated in the early drug phase but improved to near normalcy during the late drug and withdrawal phases in all groups except for alcohol and barbiturate-treated one. Excluding amphetamine, low-dose morphine and phenobarbital groups, substantial extinction of CAR occurred during the drug phase only; these three groups, as well as the high-dose alcohol, barbiturates and medazepam ones, showed extinction during the nondrug phase also. The rate and extent of a second-order relearning neither differed significantly between the groups nor was truly contingent upon prior extinction. These results are discussed in the light of state-dependent learning, comparing them with those from another series of rats primarily trained under the influence of these addictive drugs.