Cocaine disrupts both behavioural inhibition and conditional discrimination in rats.

RATIONALE: Stimulant addicts exhibit increased behavioural disinhibition under the influence of the drug. In laboratory animals, however, the effects of amphetamine on behavioural disinhibition are equivocal, and the effects of cocaine have not been investigated.
OBJECTIVES: The current set of experiments was designed to test the effects of cocaine on behavioural disinhibition and to assess whether the possible impairments are due to deficits in conditional discrimination or attention.
METHODS: Separate groups of rats were trained to respond in an asymmetrically reinforced Go/No-go task, a Conditional discrimination task or a Vigilance task. Upon reaching criterion performance, animals were treated with cocaine (0-20 mg/kg) immediately prior to testing.
RESULTS: Cocaine (15 mg/kg) increased No-go interval responses, indicating an increase in behavioural disinhibition. Conditional discrimination was also impaired by cocaine (15 and 20 mg/kg); animals made more incorrect trials per completed trial. Cocaine-treated animals also made more premature responses in this task, indicating increased behavioural disinhibition independent of a conditional discrimination deficit. Finally, cocaine (0-20 mg/kg) had no effect on vigilance.
CONCLUSIONS: Administration of moderate to high doses of cocaine increases behavioural disinhibition, and this increase may be independent of an impairment in conditional discrimination.