Ethological analysis of rodent behaviour: elucidation of the behavioural effects of psychotropic drugs

P.J. Mitchell and P.H. Redfern

Department of Pharmacy & Pharmacology, University of Bath, Bath, UK

A wide diversity of animal models has been used to examine psychotropic drug activity. In recent years antidepressant drug research has focused on the search for new therapies with a rapid onset of action. It follows that, to be relevant, animal models must have the ability to measure the time course of drug-induced changes in behaviour. Highly sophisticated animal models have been developed which yield a positive behavioural response to prolonged, chronic, drug treatment.

Two 'ethologically-relevant' animal models, the resident-intruder and social hierarchy paradigms, have been especially useful in elucidating the behavioural effects of antidepressant drugs. In the resident-intruder paradigm, male Wistar resident rats are housed in isolation for a minimum of 3 days before being exposed to an unfamiliar conspecific intruder. During the ensuing social encounter, control resident rats exhibit a wide range of non-social, social and conflict-related (i.e. agonistic) behaviours which are quantified during subsequent ethological analysis. In the social hierarchy model male Wistar rats are housed in triads. All group members are routinely involved in intense levels of social and agonistic behaviour at the onset of the dark phase of the light:dark cycle. Ethological analysis of such behaviour (where the 'winner' and 'loser' of each social encounter is identified) reveals the relative social position of each group member (the most successful group member during these encounters indicates the dominant animal).

Together these models of rodent social and agonistic behaviour have demonstrated that chronic treatment with antidepressant drugs (irrespective of their acute pharmacological activity) increases rodent aggressive behaviour which, in turn, results in increased hierarchical status in closed social groups. Furthermore, the increased rodent aggression is most likely a behavioural manifestation of increased assertive behaviour and arguably reflects similar changes in human behaviour (including the externalization of emotions) expressed during the recovery from depressive illness.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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