Cocaine-Induced Oscillation Is Conditionable

We have recently shown that under some circumstances, sensitization produced by a stimulant such as cocaine (COC) can give way, with successive drug administrations, to alternating attenuations and reinstatements of the effect, an outcome that we have termed oscillation. Because sensitization to COC can be conditioned, we inquired whether COC-induced oscillation also was conditionable. The end point used was shock-induced hypoalgesia (paw withdrawal from a hot plate), as we have previously shown that oscillation follows initial sensitization of this measure with one to five pretreatments of 12 mg/kg (IP) of COC spaced at 1-week intervals, with the last COC injection occurring 30 min prior to the footshock. Experiment 1 indicated that a conditioned stimulus (CS)—a distinctive environment—which repeatedly had been paired with COC, would substitute for the last COC injection in sustaining the oscillatory effect. Experiment 2 showed that a previously established CS successfully substituted for all COC injections in first inducing sensitization that was then followed by oscillation. These findings strongly suggest that COC-induced oscillation shares with COC-induced sensitization, the property that both can be conditioned.