A new method to assess Pavlovian conditioning of psychostimulant drug effects

Abstract

Experimental studies of psychoactive drugs by pavlovian drug-conditioning methods, which originally began with investigations of drug-induced responses mediated by the autonomic nervous system, have now been expanded to include drug-induced response effects expressed as modulations of spontaneous motoric behaviors. In the latter application, however, equivalent behavioral response outcomes in post-treatment tests for conditioning can occur following a psychostimulant drug treatment either through drug interference effects on habituation processes, drug-induced stress effects and/or by pavlovian conditioning of the drug-induced motoric activation effect. Current methodologies for the study of pavlovian conditioned drug effects and/or drug sensitization cannot distinguish among these possibilities. This methodological inadequacy was addressed by a modification of the conventional paired-unpaired treatment protocol. In the new protocol, the animal is sequentially placed into two test compartments with the drug treatment administered in conjunction with placement into the second test compartment. This design permits a differentiation of a pavlovian conditioned drug responses from non-conditioned drug effects through continuous measurement of the non-drug behavioral baseline in both the drug and non-drug control treatment groups combined with multiple response measurements and post-treatment tests for conditioning at variable post-conditioning intervals. The present study details the use of the new modified pavlovian protocol with repeated cocaine (10 mg/kg) treatment. A cocaine conditioned response at 1, 7, and 21 days post-conditioning was identified and distinguished from habituation and stress effects.