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
, 5th International Conference on Methods and Techniques
in Behavioral Research, 30 August - 2 September 2005, Wageningen, The
Netherlands.
© 2005 Noldus
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