Caffeine-induced stimulus control.

Six rats were trained to discriminate the effects of caffeine (60 mg/kg, pretreatment time: 1 hour) and saline in a two-lever choice task using a fixed ratio 10 schedule of water reinforcement. Stimulus control was assumed to be present when 80% or more of the first ten responses were appropriate for the treatment condition on each of five consecutive days. The mean number of sessions prior to the onset of criterion performance was 22 (SE = 3; range = 11--32). In trained subjects, doses of caffeine of 30, 10, and 3 mg/kg were followed by a progressively smaller proportion of responses on the caffeine-appropriate lever. Stimulus control by caffeine began to diminish about four hours after administration and was completely absent after 24 hours. The caffeine cue generalized partially to d-amphetamine and completely to aminophylline. Neither pizotyline nor spiperone antagonized stimulus control induced by caffeine.