Amphetamine discrimination: onset of the stimulus.

Rats were trained to discriminate 1.0 mg/kg (+)-amphetamine sulfate from saline in a two-lever operant procedure. The normal injection-to-session interval was fifteen minutes. When tested with amphetamine immediately after intraperitoneal injection, rats initially responded on the lever paired with saline in training, but quickly shifted to the lever paired with amphetamine in training. When tested with saline immediately after immediately after injection, animals responded appropriately for the saline treatment throughout the extinction test. The results show that (+)-amphetamine exerts discriminative response control within five minutes of intraperitioneal injection.