Effects of drug-state change on discrimination performance.

A single dose of d-amphetamine (0.25, 0.50, or 1.00 mg/kg), administered in 5 successive sessions, did not seriously impede the discrimination performance of male Holtzman rats under cued reinforcement conditions. A 2.00 mg/kg dose, however, produced a total cessation of operant behavior. In 2 post-drug (saline) sessions, groups previously treated with 0.50 or 1.00 mg/kg demonstrated an initial decrement and subsequent recovery in performance. A second experiment demonstrated that rats administered either saline or 0.50 mg/kg d-amphetamine for 5 successive sessions showed a decrement and subsequent recovery in performance when switched to the opposite treatment condition for the next 2 sessions. These data may be explained in terms of a change in drug state.