Distinguishing anxiolysis and hyperactivity in an open space behavioral test.

This report describes the emotional responses of mice exposed to an unfamiliar elevated platform that is extended on two opposite sides by downward lowered steep slopes. Balb/c mice were exposed to the test for 12 min per session in 3 successive days. They received i.p. administration of diazepam (0, 0.5, 1 and 3 mg/kg) or amphetamine (0, 1, 2.5, 5 and 10 mg/kg) 30 min prior to test sessions. Separate groups of Balb/c mice were used for each dose of the drugs. Both drugs increased the number of crossings on the platform, indicating increased motor activity, and the effects were dose-dependent. Diazepam also significantly increased the number and duration of entries onto the slopes indicating an anxiolytic effect, whereas none of the saline or amphetamine-treated mice adventured onto the slopes. Amphetamine and diazepam produced an inverted U-shaped dose-response effect on different parameters of the test and demonstrate that the drug concentration which elicited a peak in mean number of entries is different from the drug concentration which elicited a peak in mean duration of entries. This study demonstrates the sensitivity and discriminatory power of an open space anxiety test for future pharmacological studies.