The CRF(1) receptor antagonist DMP696 produces anxiolytic effects and inhibits the stress-induced hypothalamic-pituitary-adrenal axis activation without sedation or ataxia in rats.

Rationale: CRF(1) antagonists may be effective in the treatment of anxiety disorders while having fewer side effects compared with classical benzodiazepines.

Objectives: The effects of a small molecule selective CRF(1) antagonist DMP696 on anxiety-like behaviors and stress-induced increases in corticosterone in rats exposed to a novel environment and on locomotor activity and motor coordination were determined in rats. These effects of DMP696 were compared with those produced by the classical benzodiazepine chlordiazepoxide (CDP).

Methods: DMP696 or CDP were administered PO, 60 minutes before behavioral testing in rats. Their effects on latency to exit a dark chamber and stress-induced increase in corticosterone in the Defensive Withdrawal test (an animal model of anxiety), locomotor activity, and rotorod performance (measure of ataxia) were determined.

Results: DMP696 significantly reduced exit latency and reversed the stress-induced increase in corticosterone in the Defensive Withdrawal test at doses of 3.0-10 mg/kg and higher. In contrast, CDP significantly decreased exit latency at 10 and 30 mg/kg, but not at 100 mg/kg, due to concurrent non-specific side effects. Unlike DMP696, CDP had no effect on the stress-induced increase in corticosterone at lower doses, but resulted in a significant increase at higher doses. DMP696 did not reduce locomotor activity or impair motor coordination at doses up to 30-fold higher than doses effective in the Defensive Withdrawal model. In contrast, CDP produced significant sedation and ataxia at the same doses that were effective in reducing exit latency.

Conclusions: These data suggest that the CRF(1) antagonist DMP696 might retain the therapeutic benefits of classical benzodiazepines but have fewer motoric side effects.