Onset and offset of the diazepam stimulus complex.

Rats were trained to discriminate 3.0 mg/kg diazepam from saline in a two lever operant procedure. The time from injection to test session was 30 minutes. The diazepam discrimination consisted of initial responses on the lever paired with saline, but after training shifted to the lever paired with diazepam (onset). When tested with saline immediately after injection, animals responded consistently on the saline lever throughout the test. A shift from the drug lever to the saline lever at a later time point was also observed (offset). In addition, it was not possible to establish a peripheral diazepam drug stimulus complex. The results show that diazepam exerts discriminative control from 10 to 210 minutes after intraperitoneal injections, confirming a central action of the diazepam drug stimulus complex. The method might be useful in experimentation on drug control of lever selection.