State-dependency of conditioning and extinction of an appetitive response with amphetamine and midazolam.

Rats received a single conditioning session in which unsignaled food pellets were delivered to the food magazine of a training box, followed by a single extinction session without pellet presentations. Groups of rats differed in the drug state induced prior to conditioning and extinction according to a 2 x 2 design using d-amphetamine sulphate (AMP, 0.5 mg/kg, S.C.) and midazolam (MID, 0.1 mg/kg, S.C.). Subsequently, all rats received nonreinforced test sessions under AMP and MID. The dependent measure was the frequency of magazine visits during selected portions of each session. Rats that received extinction in the same drug state as had been present during conditioning did not respond significantly more during the extinction session than rats extinguished in a different drug state. This implies that conditioning was not state dependent. However, during the AMP tests, the rats extinguished under MID responded more under AMP than under MID, whereas the rats extinguished under AMP did not respond differentially during the tests under AMP vs. MID. These results were interpreted as reflecting the joint operation of state-dependent extinction and unconditioned drug effects. As in studies manipulating external contextual stimuli, extinction proved to be more vulnerable to becoming context dependent than conditioning.