The integrity of the social hierarchy in mice following administration of psychotropic drugs.

1 Mice in small groups develop a despotic type of social hierarchy, a feature of which is to resist alteration through the medium of psychotropic drugs. This makes a rapid pharmacologically induced change in the social hierarchy impossible. 2 Patrolling the territory and a certain level of social interaction are both critical factors in maintaining the phenomenon of inertia in the social hierarchy. Psychotropic drugs (diazepam, droperidol and mescaline) altered both these factors to a varying degree and also displayed a differing ability to maintain the inertia of the social hierarchy. 3 A drug-induced alteration in the level of aggression in a subordinate mouse in a group of three does not cause an alteration in its social position. 4 Chronic administration of diazepam, droperidol or mescaline, all of which alter the level of aggression in different ways, can result in an inversion of the social hierarchy where a competitive rival is present in the group of mice. The rate of inversion of the social hierarchy depends on the type of pre-existing social hierarchy. 5 It is suggested that the ability of psychotropic drugs to maintain the inertia of the hierarchy be used as an index of their effect upon certain types of species-specific behaviour; in particular aggression.