DESCENDING PERISTALTIC REFLEX IN THE OPOSSUM ESOPHAGUS

To test the hypothesis that the distension-induced esophageal peristal tic reflex involves a polysynaptic pathway, a triple-chamber organ bat h was used to chemically isolate different regions of the opossum smoo th muscle esophagus while leaving in continuity the intramural neuromu scular apparatus. Balloon distension in the oral chamber evoked membra ne hyperpolarization in the aboral chamber, which was followed, on bal loon deflation, by depolarization, spike burst, and circular smooth mu scle contraction. This reflex was abolished by adding tetrodotoxin to any of the chambers. Addition of Ca2+-free 20 mM Mg2+ Krebs solution ( to block synaptic transmission) to the intermediate chamber did not af fect the descending peristaltic reflex. However, Ca2+-free 20 mM Mg2Krebs solution markedly attenuated the reflex when placed in either th e oral or the aboral chamber. Furthermore, the nitric oxide synthase i nhibitor N omega-nitro-L-arginine methyl ester, when placed in the abo ral chamber, abolished the reflex. Other putative neurotransmitter ant agonists were without effect when placed in any chamber. These studies suggest that the intramural neural pathway that mediates the descendi ng peristaltic reflex in the opossum esophagus is not polysynaptic, bu t rather involves long descending neurons that depend on nitric oxide as a final mediator.