Hyperactivity induced in rats by long-term isolation: further studies on a new animal model for the detection of antidepressants.

Male rats isolated at the time of calcification of the incisors show after 10 months of social deprivation a marked and sustained increase in locomotor activity together with other behavioural changes. The ages of separation as well as the prolonged isolation period appear to be critical with regard to the stability of the behavioural syndrome and to the sensitivity of the rats to different pharmacological treatments. The locomotor activity of solitary housed rats is selectively blocked after acute treatment with several antidepressants which are inactive according to the traditional laboratory procedures for detecting the activity of this class of drugs. Handling of the isolated animals for 30 consecutive days produces, on the other hand, a permanent attenuation of the hyperactivity syndrome. It is suggested that the present animal model may be of value for the detection of antidepressants and for elucidating the role of an important social variable in the production of neurochemical changes associated to depressive disorders.