Loss of social status: preliminary evaluation of a novel animal model of depression

Stable dominance hierarchies were determined in pairs of male Lister hooded rats, by repeated observation of agonistic behaviour at the onset of the dark phase of the light-dark cycle. No lasting alterations in dominance behaviour were caused by subjecting the dominant member of the pair either to restraint stress or to defeat by another dominant animal. However, defeat of the dominant animal by a male of the aggressive Tryon Maze Dull (TMD) strain caused a loss of dominant status in the home cage which lasted at least 7 days. Repeated weekly defeat by TMD animals decreased both home cage dominance behaviour and consumption of a palatable sucrose solution, relative to non-defeated animals; both behaviours were normalized in defeated animals by 3 weeks of treatment with the tricyclic antidepressant imipramine.