Yohimbine-induced stimulus control in the rat.

Rats were first trained in a 2-lever operant test chamber using a fixed ratio 10 schedule of water reinforcement. Discrimination training was then begun. In sessions following the injection (i.p.) of yohimbine . HC1 (3 mg/kg), responses on 1 of the 2 levers were reinforced. In sessions following the injection of saline, responses on the remaining lever were reinforced. The distribution of responses between the 2 levers prior to reinforcement provided an index of discrimination. The criterion for stimulus control was set at 80% correct responses in each of five consecutive sessions. In a group of six rats, criterion performance was begun after a mean of 33 sessions. Cross tests were conducted in yohimbine-trained subjects with d-amphetamine, harmaline, and LSD. Each test drug yielded intermediate results, i.e., response distribution was significantly different from both the yohimbine and the saline training conditions. No significant antagonism of yohimbine-induced stimulus control was achieved with BC-105, phentolamine, or butaclamol, purported antagonists at serotonergic, alpha-adrenergic, and dopaminergic receptor sites, respectively.