Somatostatin release from isolated ganglia of the myenteric plexus.

Somatostatin neurons of the myenteric plexus project caudad exclusively within the plexus synapsing with neurons in the same or other ganglia. Isolated ganglia offer a unique opportunity to examine peptide transmitter release from these interneurons. Ganglia were isolated from the myenteric plexus by sequential enzymatic digestion, centrifugation, and filtration. Single ganglia were harvested by suction and dispersed in polyacrylamide gel. The ganglia were placed in chambers (200 ganglia/chamber) and perfused with Krebs medium at the rate of 1 ml/min. Addition of the nicotinic agonist, dimethylphenylpiperazinium (DMPP), caused a concomitant increase in somatostatin (152%; P less than 0.001) and vasoactive intestinal peptide (VIP) (79%; P less than 0.05) release above basal level that was abolished by hexamethonium. Addition of the VIP antagonist, VIP-(10-28), (5 microM), to the perfusate augmented significantly DMPP-induced somatostatin release (440%; P less than 0.05), implying that the concomitant release of VIP attenuates somatostatin release. Addition of VIP (1 microM) to the perfusate abolished somatostatin release, confirming the ability of VIP to inhibit somatostatin release. The study shows that VIP interneurons exert a regulatory feedback control over somatostatin interneurons in the myenteric plexus.