Effects of morphine on myenteric plexus neurones

Abstract

Intracellular recordings were made from neurones in the isolated myenteric plexus of the guinea-pig ileum. Approximately 50% of neurones responded to bath application of normorphine (10 nM−1 μM) with an immediate hyperpolarization. The hyperpolarization was usually associated with a fall in membrane resistance. The effect reversed on washing out the normorphine and was prevented by the addition of the opiate receptor antagonist naloxone (50–100 nM). It is suggested that the membrane hyperpolarization may be the basis for the inhibitory effects of morphine on neurone firing rates which have been reported both in the myenteric plexus and the central nervous system.