Hypothalamic monoaminergic mechanisms of aspirin-induced analgesia in monkeys

Microinjection of sodium acetylsalicylate (aspirin, 0.2-0.6 mg) into the preoptic anterior hypothalamic area, but not the dorsal raphe region or the periaqueductal central gray matter, produced a dose-related analgesia in conscious monkeys. The analgesia induced by intrahypothalamic administration of aspirin was antagonized by pretreatment of monkeys with either a serotoninergic receptor blocker (cyproheptadine) or two catecholaminergic receptor blockers (haloperidol and yohimbine). These suggest the existence of a monoaminergic pain-inhibitory mechanism in the preoptic anterior hypothalamic area activated by aspirin.