Acute and Chronic Effects of Opiates on Single Neurons of the

Karras, Peter J. and R. Alan North: Acute and chronic effects of opiates on single neurons of the myenteric plexus. J. Phar-macol. Exp. Ther. 21 7: 70-80, 1981. Extracellular recordings were made from single neurons in the myenteric plexus of the guinea-pig ileum in vitro. Tissue was removed from morphine-naive guinea pigs and maintained in vitro for up to 24 hr; the firing rate of the neurons was reduced by opiate agonists and unaffected by opiate antagonists. Tis-sues were also removed from animals which had been pre-treated with morphine during 3 days and placed into an in vitro solution which contained morphine. An increase in the concen-tration of morphine did not inhibit neuronal firing and naloxone caused a pronounced excitation of such cells. Cross-tolerance among different opiate agonists was apparent. In a third ex