A schedule induction probe technique for evaluating abuse potential: comparison of ethanol, nicotine and caffeine, and caffeine-midazolam interaction.

Previous research has shown that under daily 3h sessions of food schedule-induced drug solution polydipsia (on a fixed-time 1min (FT 1min) schedule, session probes at greater FT values induced comparatively more ml/pellet drinking of solutions of drugs possessing abuse potential (ethanol, cocaine, midazolam) than of vehicle or other drug solutions. The present study extended these findings to nicotine and caffeine, drugs that usually do not function as reinforcers in i.v. self-administration studies with animals, but are known to have reinforcing effects for humans. The positive effects for nicotine and caffeine did not depend upon prior overindulgence in ethanol. Results on the effects of chronic, presession s.c. doses of midazolam could not be interpreted as contributing to the abuse potential of caffeine, but had independent dipsogenic effects. The FT probe technique, as well as schedule-induced i.v. self-administration, are useful methods for discerning the abuse potential of agents which are usually not distinguished by i.v. self-administration methods.