Schedule-induced chlordiazepoxide intake: differential effect of cocaine and ethanol histories

Groups of rats were given differential histories of drinking either water, cocaine (0.15 mg/ml), or ethanol (2.5%) solutions under fixed-time (FT) 1-min schedule-induced polydipsia conditions in daily, 3-hr sessions. The session solution for all groups was then changed to chlordiazepoxide (0.25 mg/ml), and after daily session intakes had stabilized, FT values of 3 and 5 min were probed for single sessions. Probe-session chlordiazepoxide intakes were greater for the Ethanol History Group than for Cocaine History and Water History Groups. Previous research showed that probe conditions elevated intakes for agents with abuse potential (cocaine, ethanol, midazolam), but not for those lacking such potential (water, chlordiazepoxide, flurazepam). The present study demonstrated that a history of ethanol overindulgence yielded elevated probe intakes for chlordiazepoxide, while a history of cocaine or water overindulgence did not. This is consistent with animal and human evidence indicating that a history of either alcohol or sedative abuse increases the probability that benzodiazepines will function as reinforcers and/or be abused.