Effect of acute and repeated cocaine exposure on response matching capabilities of Sprague-Dawley rats responding for sucrose on concurrent schedules of reinforcement.

Cocaine exposure impairs the ability to match responding when rewarded and non-rewarded response options are reversed. However, it is unclear whether the impairment can also be observed when two rewarded responses differing in delay or magnitude of reward are reversed. Therefore, we tested the effect of acute (Experiment 1) and repeated (Experiment 2) cocaine on response matching between options dynamically varying in reinforcement schedule. Male Sprague-Dawley rats responded on concurrent fixed ratio 25 (FR25) and variable ratio 15 (VR15) schedules for sucrose. On tests, a progressive ratio (PR) schedule replaced the VR15, creating a within-session dynamic reversal point. In Experiment 1, acute cocaine (0, 1, 3 or 15mg/kg IP) did not alter response matching. In Experiment 2, rats chronically exposed to cocaine (30mg/kg/dayx5days, IP) were tested after a 10-day withdrawal period on three sets of FR25/PR matching tasks with varying rates of PR escalation. Cocaine pre-exposure significantly increased perseverative matching errors, although repeated testing compensated the impairment. These results suggest that prior exposure to cocaine can produce perseverative behavior even when animals are required to match two well-learned and rewarded response options. The implications for addictive behaviors are discussed. Copyright 2010 Elsevier Inc. All rights reserved.