Antidepressant drugs normalize the increased social behaviour of pairs of male rats induced by short term isolation.

In a situation in which a short-term isolated (I) and a group-housed (S) rat were placed together, the influence of various drugs on social behaviour was analysed. It was found that a single intraperitoneal injection of 7.5 mg/kg of the antidepressant drugs clomipramine, nortriptyline and mianserine normalized the increased social interactions of the isolated rat to the level of the group-housed rat, without affecting the social behaviour of that animal. This action of the drugs was not due to changes in locomotor activity. An opiate (morphine), an opiate antagonist (naloxone), a tranquilizer (diazepam), a neuroleptic (haloperidol) and a psychostimulant (amphetamine) did not preferentially influence the social behaviour of the isolated rat. Chronic treatment with the antidepressants did not reduce the increased social interactions of isolated animals. In spite of this it is clear that the increased social behaviour of short-term isolated rats was specifically affected by the antidepressant drugs. This suggests that this behavioural procedure might be useful for predicting antidepressant activity.