Intracerebrally administered CRF has been demonstrated to elicit several behavioural deficits in novel and potentially stressful experimental paradigms, and to promote activity in familiar situations. This study examined the effect of CRA 1000, a novel non-peptide antagonist of CRF(1)receptors, on rat behaviour in tests of anxiolytic and antidepressant activity and novelty-oriented behaviour. CRA 1000 (1.25-10 mg/kg) had no major effect in elevated plus-maze and social interaction tests. However, CRA 1000 (5 mg/kg) significantly reduced immobility in the forced swimming test, suggesting an antidepressant-like effect. In the exploration box test, CRA 1000 (1.25 mg/kg) had an anxiolytic effect on rat exploratory behaviour both in intact rats and after lesioning of the projections of locus coeruleus by DSP-4 (50 mg/kg) treatment. A higher dose of CRA 1000 (5 mg/kg) tended to have anxiolytic-like effects in DSP-4 pretreated rats, but in intact animals this dose prevented the increase in exploration which develops with repeated exposure to initially anxiety-provoking situations. Taken together, these experiments demonstrate that CRF1 receptor blockade by CRA 1000 has antidepressant-like effects, does not have a robust anti-anxiety effect in non-stressed animals, but does have anxiolytic-like effects in more complex tasks, which can be observed also after denervation of the locus coeruleus projections. However, large doses of CRF1 receptor antagonists may reduce motivation of exploratory behaviour in familiar environments.
Copyright 2001 Harcourt Publishers Ltd.