Behavioral sensitization to cocaine, but not cocaine-conditioned behavior, is associated with increased dopamine occupation of its receptors in the nucleus accumbens.
Rats had repeated treatments with cocaine associated with a specific context (paired group). Evidence for classical conditioning of cocaine's motor-activity effects and context-specific behavioral sensitization to cocaine was obtained, relative to vehicle-treated (control) and pseudoconditioned (unpaired) groups. Only the paired group exhibiting context-specific behavioral sensitization had more dopamine bound to both D 1 -like and D 2 -like receptors in the nucleus accumbens than did rats in the control group receiving cocaine on the test day. No effects on receptor occupation were found in rats showing a classical conditioned response to a context previously paired with cocaine. Thus, sensitization to cocaine, but not classical conditioning of cocaine's behavioral effects, was associated with greater dopaminergic neurotransmission selectively in the nucleus accumbens.