Discriminative stimulus properties of a small dose of cocaine.

This study characterized the interoceptive discriminative stimulus (IDS) produced by a small dose of cocaine. Rats were trained to use a dose of cocaine of 1.25 mg/kg vs saline as the basis for choosing one of two levers for food reinforcement on a fixed ratio 10 schedule. The discrimination was acquired over approx. 60 training sessions. d-Amphetamine generalized to cocaine with approximately equal potency (ED50's for cocaine and d-amphetamine were 0.07 and 0.06 mg/kg, respectively); 20 mg/kg cocaine and 10 mg/kg methylphenidate also generalized to the cocaine lever. Pentylenetetrazol, 20 mg/kg, did not generalize to the cocaine lever, and diazepam, 10 mg/kg, did not block the 1.25 mg/kg cocaine discrimination. These data indicate that when a small dose of cocaine is used as the basis of discrimination training, the discriminative stimulus that it produces is qualitatively and quantitatively similar to that produced by small doses of amphetamine, is still discriminated with a large dose of cocaine, and is dissimilar to the discriminative stimulus produced by pentylenetetrazol.