Proanaphylactic action of morphine is mediated through a central cholinergic mechanism

Intracerebroventricular (i.c.v.) or intravenous (i.v.) administration of morphine (10 micrograms or 25 mg/kg, respectively) increased the mortality rate in experimental anaphylaxis in mice. This effect was blocked by the opiate antagonist naltrexone administered systemically (5 mg/kg) or i.c.v. (10 micrograms). Moreover, the effect of morphine was blocked by i.c.v. administration of the muscarine antagonist methyl atropine (10 micrograms). The systemic administration of 5 mg/kg methyl atropine was ineffective in blocking the action of morphine. The results suggest that the proanaphylactic effect of morphine involves activation of cholinergic mechanisms in the central nervous system.