Acetylcholine antirelease effect of morphine and its modification by calcium

The effects of morphine (10 mg/kg) and calcium (10 mg/kg) were studied on the neocortical release of acetylcholine (ACh) in ketamine-anesthetized rats. Morphine decreased ACh release as measured by the dorsal leech muscle as well as by an enzymatic assay. Calcium was ineffective alone but antagonized the action of morphine. This study supports the hypothesis that the ACh antirelease action of narcotics is mediated through an interaction with calcium.