Conditional control by midazolam and amphetamine in a rapid appetitive discrimination procedure.

The present two experiments examined conditional control by midazolam and amphetamine cues in an appetitive discrimination procedure. In each of two experiments, male Wistar rats were subjected to a small number of two types of training sessions in a conditioning box. During one type of session, a stimulus was consistently followed by food in a magazine, whereas during the other type of session, this very same stimulus was followed by nothing. Groups of rats were injected with either midazolam (0.1 mg/kg, s.c.) or amphetamine (0.5 mg/kg, s.c.), prior to each food-reinforced session, and with saline prior to each food non-reinforced session. Other groups received the reverse treatment. Subsequent non-reinforced test session showed that, in both experiments, only the rats that had been food reinforced in a drug state displayed shorter magazine-response latencies in their previously reinforced than in their previously non-reinforced state, both prior to and during the stimulus. This finding was interpreted as reflecting the joint operation of unconditioned and conditioned drug effects, with the latter being based on occasion setting by the drug cues that was induced by the relatively short discrimination training procedure. The present results parallel those of previous aversive drug-discrimination experiments adopting a similar short discrimination procedure.