Temporal parameters of d-amphetamine as a discriminative stimulus in the rat

Three groups of rats were trained on a two-lever operant discrimination using d-amphetamine (0.8, 1.6 or 2.4 mg/kg) and saline as cues. Reinforcement of responding on one lever was associated with the drug and reinforcement on the other lever was associated with saline. Following acquisition, behavioral control was evaluated during 10-min extinction tests at 0, 15, 30, 60, 90, 120, 180 or 240 min after injection of drug or saline. Onset of the stimulus properties of d-amphetamine occurred within 10 min and maximal effects were attained by 15-30 min post-injection. Drug effects were minimal or absent 2-4 h after administration. The time course for all doses of d-amphetamine was identical when each group was tested iwth its respective training dose. When subjects were tested with doses other than their training dose, the time course of the drug effect varied as a function of training dose, test dose and time after injection.