Social stress in mice has been used for modelling mood disorders in humans. This study was performed in order to analyze the putative effect of housing conditions, the effect of imipramine hydrochloride IH and electro-convulsive stimuli (ECT) on low ranked mice. Groups of Balb C mice were housed in groups of nine and three subjects. Subjects were identified according to their behavioural categories (dominant, intermediate and subordinate). Aggressive submissive patterns were determined in two housing conditions, nine vs. three subjects. Emotional behaviour was determined in both housing conditions; exploratory activity, forced swimming and defensive shock test behaviour were studied. In a second experiment, Imipramine hydrochloride (IH) was administered intraperitoneally (IP) for five days (10, 20 and 30 mg/kg) to the subordinate animal in independent groups. The animals were injected 24 hrs before the experimental session. Aggression, submissive posture, affiliation, individual recognition, and fear were recorded. In a third experiment, subordinate subjects were stimulated for 5 or 10 sessions with electro convulsive stimuli (ECS). Nine subject groups showed a low ratio of aggressive/submissive posture, while the highest levels of this behaviour were observed in the three animal groups. Dominant subjects showed increased exploratory activity in the open field model, while subordinate animals showed low activity. In the forced swimming paradigm, high immobility time was observed in dominants, while low immobility was seen in the subordinate animals. Defensive burying behaviour was lower in subordinate compared with dominant animals. IH administration reduced submissive posture, avoidance and fear behaviour, while increasing social behaviours. ECS elicited an effect similar to IH, except for the increase in avoidance. A partial rearrangement of the mice’s social organization elicited by IH treatment and ECS was observed. The results are analysed in terms of the suitability of social stress related to housing as a method to induce depression-like behaviours. Thus, social stress in mice could be proposed as a putative model for the analysis of the neurobiology of depression.
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