Failure of SCH 23390 to function as a discriminative stimulus in rats

Four rats were studied in a two-lever, food-reinforced drug discrimination paradigm using the Dl dopamine antagonist SCH 23390 (0.03 mg/kg, IP, 30 minutes prior to the session) and saline as the training stimuli. After at least 100 training sessions there was no evidence of stimulus control over responding by SCH 23390 in 3 of the 4 rats, and only briefly in the fourth. On the other hand, food delivery exerted control over behavior indicating that SCH 23390 did not disrupt control of behavior by the reinforcing stimulus. An increase in training dose to 0.06 mg/kg for an additional 12 sessions did not improve discriminative accuracy although this dose reduced rate of responding to an extent that made further training using 0.06 mg/kg untenable. The results provide no evidence of stimulus control of behavior by SCH 23390 and suggest that SCH 23390 does not function as a discriminative stimulus in rats.