Cognitive judgment bias in the psychostimulant-induced model of mania in rats

RATIONALE: Animal models of mania lack genuine cognitive parameters. The present gold standard of mania models, amphetamine-induced hyperlocomotion, is rather unspecific and does not necessarily target its cardinal symptoms. Therefore, alternative behavioral markers that are sensitive to stimulants are required. OBJECTIVES: In the present study, by combining the psychostimulant-induced model of mania in rodents with the recently developed ambiguous-cue interpretation (ACI) tests, we investigated the effects of chronic administration of d-amphetamine and cocaine on the cognitive judgment bias of rats. METHODS: To accomplish this goal, in two separate experiments, previously trained animals received chronic, daily injections of either d-amphetamine (2 mg/kg) or cocaine (10 mg/kg) for 2 weeks and were subsequently tested with the ACI procedure. RESULTS: Chronic treatment with both psychostimulants did not make rats more “optimistic.” CONCLUSIONS: The results are discussed in terms of behavioral and pharmacological actions of the tested compounds and their implications for modeling mania in animals.