Measures of anxiety and stress in the rat following chronic treatment with yohimbine.

Yohimbine (2.5 and 5 mg/kg) was investigated in two animal tests of anxiety and on baseline corticosterone plasma concentrations, following both acute and chronic administration. Acute treatment with yohimbine produced the following effects: a reduction in the percentage of total arm entries made onto the open arms and in the percentage of time spent on the open arms of an elevated plus-maze (indicating anxiogenic properties), an increase in baseline plasma corticosterone concentrations, and a reduction in locomotor activity (recorded in the social interaction test). No significant effects were observed on anxiety levels as measured by the social interaction test. Following chronic treatment, we saw no evidence for sensitization to the effects of yohimbine.