Classically conditioned motor effects do not occur with cocaine in an unbiased conditioned place preferences procedure

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Abstract
Classical conditioning and behavioural sensitisation of motor activity induced with cocaine (10 mg/kg, i.p.) were examined using an unbiased two-compartment conditioned place preference (CPP) procedure. Habituation of the rats to the testing environment prior to training was varied (i.e. either the rats were habituated to the environment for three 30 min sessions or they were not) in order to examine a possible influence of latent inhibition on conditioned locomotion or behavioural sensitisation. Furthermore, rats were either trained with an explicit CS+ (cocaine-paired compartment) and CS — (vehicle-paired compartment), or else they were trained with no barrier between the compartments (effectively a single-compartment procedure with no explicit CS —) in order to examine a possible influence of stimulus change (training rats while confined to one compartment, but testing with no barrier between compartments). On a drug-free test day with free access to both compartments, rats previously exposed to cocaine in one compartment (CS+) and vehicle in the second compartment (CS —) spent more time in the CS+ compartment (conditioned place preference). However, under no circumstance was the rate of motor activity higher in the CS+ compartment than in the CS — compartment, as would be expected if cocaine-induced motor activity was classically conditioned to contextual cues. Whether or not increased activity extinguished with repeated drug-free exposures to previously drug-paired contexts depended on habituation experience. In addition, both habituation and current access to compartments (free or restricted) determined the presence of post-extinction sensitisation to a challenge dose of cocaine (7.5 mg/kg). Classical conditioning and non-associative sensitisation, independently or together, cannot account for this pattern of results.

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