Effects of Imipramine on Anxiety, Depressive-like Behavior and Body Weight Gain in Rats Housed in Overcrowded Conditions

Long-term crowding in rats can lead to anxiety-depressive disorders. Antidepressants, including imipramine, are used in clinical and experimental settings to correct such states. The aim of this study was to test whether Imipramine has an antidepressant and/or anxiolytic effect on the behavior of rats kept in overcrowded conditions. The effect of daily (4 days before and 10 days during crowding) intraperitoneal injections of imipramine (10 mg/kg) on the behavior of male Wistar rats housed in overcrowded (16 rats per cage) and standard (4–5 rats per cage) conditions was studied in the open field, light–dark and elevated plus maze tests for anxiety, as well as in the forced swim test, after imipramine withdrawal (days 12 and 15 of overcrowding). In addition, body weight gain on days 8 and 12 of overcrowding and plasma corticosterone levels on day 16 of overcrowding were assessed in the same groups of rats. In standard housing conditions, imipramine did not alter rat behavior in all tests. Overcrowding led to the activation of behavioral responses in the light–dark and elevated plus maze tests, which was not reduced by imipramine (except for three indices), indicative of no significant corrective effect of this drug in these tests on the behavior of rats kept in overcrowded conditions. In the forced swim test, overcrowding led to increased immobility, while imipramine corrected this disorder. Body weight gain decreased after imipramine treatment in both standard and overcrowded (to a greater extent) conditions, suggesting a negative side effect of this antidepressant. Plasma corticosterone levels did not differ in rats kept in either overcrowded or standard conditions and were not altered by imipramine. Thus, imipramine had a therapeutic effect on increased immobility in overcrowded rats in the forced swim test, suggesting that the behavioral changes observed in this test in rats under overcrowded conditions are depressive-like behavioral disorders, i.e., imipramine exerted a pronounced antidepressant effect on rats in the forced swim test.