Morphine withdrawal in guinea-pig ileum is confined to one electrophysiologically defined class of myenteric neurone.

Intracellular microelectrodes were used to record changes in myenteric neurones underlying morphine dependence in the guinea-pig ileum. Of the two electrophysiologically defined classes of neurones (S and AH), only a proportion of S-neurones were involved in the naloxone-induced withdrawal responses. Withdrawal caused direct depolarization and discharge of action potentials in S-neurones and also resulted in synaptic activation of neurones of this class. Both fast and slow synaptically mediated depolarizations were evoked by naloxone. The experiments suggest that morphine withdrawal is expressed in quite specific neuronal circuits in the myenteric plexus.