The effects of chronic cocaine exposure on impulsivity in rats

Chronic exposure to cocaine increases impulsive behavior, leading to a reduced preference for a larger, delayed reinforcer over a smaller, immediate reinforcer. This study examined the development of impulsivity over multiple days of cocaine exposure and cessation of cocaine. Male Sprague-Dawley rats were trained on a discrete-trials delay-discounting task, during which they chose between a small, immediate reinforcer of one food pellet and a large reinforcer of 3 food pellets after an adjusted delay (0, 10, 20, 40, and 60 s). When stable preferences were established, rats received daily injections of deionized water or cocaine (3, 75, 15 mg/kg) 5 min before the delay-discounting task for 9 days. All groups showed an increased preference for the smaller reinforcer as delay to the larger reinforcer increased. Repeated exposure to 75 or 15 mg/kg cocaine further decreased preference for the larger reinforcer over the 9 days. When cocaine administration was discontinued, preference for the larger reinforcer returned to baseline levels in the 7.5 mg/kg group, but remained depressed in the 15 mg/kg group. These findings indicate that continuing exposure to cocaine dose-dependently decreases choice for the large reinforcer over time, and that the bias remains when cocaine is no longer administered, and that the recovery after high doses of cocaine occurs slowly. Behavioural Pharmacology 20:400-405 (C) 2009 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.