Potent inhibition of non-opioid defeat analgesia in male mice by benzodiazepine antagonist Ro15-3505.

In male mice, defeat in social encounters is associated with an acute non-opioid analgesia, a reaction that may also be seen in response to the scent of a territorial conspecific. As this form of pain inhibition is blocked by diazepam and Ro15-1788, benzodiazepine receptor mediation has been proposed. To further test this hypothesis, the effects of a novel benzodiazepine receptor antagonist (Ro15-3505; 0.625-20 mg/kg) on basal nociception and defeat analgesia have been examined. Results show that, although devoid of intrinsic activity on the mouse tail-flick assay, Ro15-3505 totally blocks the analgesic consequences of defeat at doses above 1.25 mg/kg. Despite certain inconsistencies in the literature, present data provide further support for benzodiazepine receptor mediation of this ecologically-relevant form of pain inhibition.