The anti-nociceptive effect of reserpine and haloperidol mediated by the nigro-striatal system: antagonism by naloxone.

Reserpine (10 mg/kg) and haloperidol (2 mg/kg) injected intraperitoneally increased the reaction time of the tail-flick response in intact but not in pre-nigrally decerebrate or spinal rats. The antinociceptive effect of both drugs was antagonized by intraperitoneal injections of dopa (100 mg/kg), apomorphine (2 mg/kg) or naloxone (1 mg/kg) as well as by bilateral micro-injections into the caudate nuclei of apomorphine (100 microgram and 20 microgram) and naloxone (10 microgram). It is concluded that the nigrostriatal feedback system is involved in the anti-nociceptive effect of reserpine and haloperidol.