VENLAFAXINE EXHIBITS PRECLINICAL ANTIDEPRESSANT ACTIVITY IN THE RESIDENT-INTRUDER SOCIAL-INTERACTION PARADIGM

Venlafaxine, a novel 2-phenyl-2-(1-hydroxycycloalkyl) ethylamine, is a potent inhibitor of 5-hydroxytryptamine and noradrenaline reuptake and exhibits a profile of activity in pre-clinical in vitro biochemical studies predictive of antidepressant activity. The studies described here examined the effects of acute and chronic treatment with venlafaxine on the behaviour of resident rats confronted with an unfamiliar, non-treated, intruder conspecific. Ethological analysis of the social encounters revealed that acute, subcutaneous, treatment with venlafaxine, 20-180 mumol kg-1, induced a selective, dose-related, reduction in aggressive behaviour (ID50 = 24.87 mumol kg-1) concomitant with increased flight behaviour. In contrast, chronic treatment with venlafaxine, 20 mumol kg-1 day-1, via subcutaneously-implanted osmotic mini-pumps, induced a marked elevation in aggressive behaviour concomitant with reduced flight behaviour. These diametrically opposite effects of acute and chronic venlafaxine treatment on the agonistic behaviour of resident rats are consistent with the behavioural effects of similar treatment regimes previously identified for a range of antidepressant drugs that differ widely in their acute pharmacology. These data strongly support the potential antidepressant activity of venlafaxine and are consistent with the results of recent clinical trials which demonstrate that venlafaxine exhibits significant antidepressant activity.