The present article depicts the research on the effect of imipramine hydrochloride in the forced swimming, defensive burying and open field tests, in mice submitted to social stress. Male Balb C/J mice weighing 25-30 g were housed; three animals per cage for five consecutive days. The aggressive/ submissive behaviour was determined by a sample scanning method. The experiments carried out in the present study assessed data from the animal that consistently received aggressive behaviour from the other two cage mates. Repeated defeat and hostile behaviours during five consecutive days lead to social stress in mice placed in the lower social rank. The classical tricyclic antidepressant imipramine hydrochloride was administered during four consecutive days. The stressed mice received the following treatments: intraperitoneal (IP) injections of 0, 15 and 30 mg/kg. The tests were performed 24 hrs after the last injection. The forced swimming, the defensive burying and open field models were used in order to determine behavioural characteristics of stressed subjects, and the effect of repeated imipramine administration. In the swimming test, imipramine elicited a dose-dependent increasing immobility time, while the saline-injected group remained unchanged, similar to the control animal group. The imipramine-treated mice showed an increase in defensive burying at a dose of 30 mg/kg, but failed to change at a lower dose. In the open field a slow but consistent increase was observed, reaching a high number of crossings on the 11th day of treatment. Results are discussed in terms of the putative participation of social stress in the mediation of depressed-like behaviour in mice.
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