The importance of a compound stimulus in conditioned drug-seeking behaviorfollowing one week of extinction from self-administered cocaine in rats

Previous studies have demonstrated that conditioned stimuli can increase re sponding on a drug-associated lever after extinction from drug self-adminis tration. The present study investigated singular stimuli (tone or light) or a compound stimulus (tone + light) for their ability to increase extinguis hed responding following chronic cocaine self-administration. Rats self-adm inistered cocaine for 2 weeks on a fixed ratio (FR1) schedule: of reinforce ment, in which lever responding resulted in varied presentation of a tone, light, or tone + light combination. The rats were then exposed to 1 week of daily extinction sessions. Presentation of the tone + light on day 8 of ex tinction in the absence of cocaine reinforcement resulted in a significant increase in responding, while either stimulus component alone was much weak er or failed to produce any changes from extinction rates of responding. In addition, changing the duration of the single elements of the compound did not affect the magnitude of increased responding to the compound. Followin g three final extinction sessions, robust lever responding for cocaine infu sions on day 12 of extinction was seen across all groups. These findings su ggest that compound stimuli may be critical to fully activate drug-seeking behavior in conditions of craving and relapse following prolonged extinctio n. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.