INITIATION, MAINTENANCE AND EXTINCTION OF COCAINE SELF-ADMINISTRATIONWITH AND WITHOUT CONDITIONED REWARD

Relapse prevention in abstinent cocaine addicts remains a major focus of drug addiction therapy. We used a rat model of cocaine addiction th at focused on cocaine seeking behavior elicited interoceptively and by conditioned stimuli. Each of 18 rats could self-administer a maximum of 20 intravenous cocaine injections (1.5 mg/kg) per session per day. To prevent initiation of responding by cocaine itself priming injectio ns were never administered. Although cocaine was available beginning e very session the rats displayed a self-imposed period of abstinence fo llowed by a period of rapid consumption. The abstinence period was var iable among rats but consistent for individual rats. In experiment 1 w e studied the contribution of a CS+ (stimulus light and lever retracti on) to the motivation to initiate and maintain a cocaine self-administ ration episode. We compared the number of responses the rats emitted t o receive the first and subsequent injections of the day between a gro up responding on a fixed-ratio (FR) schedule (n=6) and a group respond ing on a second-order (SO) schedule (n=5) of reinforcement. For all ra ts the number of responses per injection was raised daily until a rat failed to consume more than four injections. The SO group was able to emit approximately four times as many responses as the FR group to obt ain their first and subsequent injections. In experiment 2 (n=7) respo nses during extinction were counted with and without the CS+. Respondi ng was greater in the presence of the CS+ than in its absence. The pre sent model demonstrates that the motivation to self-administer cocaine is variable and greatly enhanced by conditioned stimuli.