Behavioral effects of acute and chronic imipramine in the elevated T-maze model of anxiety.

The elevated T-maze is an animal model of anxiety, consisting of three elevated arms: one enclosed and two open. Inhibitory avoidance of the open arms-representing learned fear-has been related to generalized anxiety and the unconditioned escape from one of the open arms to panic. In the present study, we investigated the effects of acute and chronic (21 days) administration of imipramine (5, 10, and 15 mg/kg; IP) in male Wistar rats that have been previously exposed for 30 min to one of the open arms of the T-maze, 24 h before the test. The results show that this preexposure shortens the first escape latency, without changing open-arm avoidance. Under these experimental conditions, chronic imipramine exerted anxiolytic-like effects in the two elevated T-maze tasks; impaired the acquisition of inhibitory avoidance and prolonged escape latency from the open arms. Acute imipramine enhanced both avoidance and escape latencies. Both acute and chronic imipramine decreased locomotor activity measured in a square arena. The obtained results are compatible with the view that inhibitory avoidance and one-way escape in the elevated T-maze reflect different types of fear/anxiety, that may be related to generalized anxiety and panic disorder, respectively.