IMMUNOHISTOCHEMICAL IDENTIFICATION OF NEURONS IN GANGLIA OF THE GUINEA-PIG SPHINCTER OF ODDI

The sphincter of Oddi is a smooth muscle sphincter that regulates the flow of bile into the duodenum. To identify potential chemical coding in sphincter of Oddi neurons, immunohistochemistry and histochemistry were employed to assay for putative neurotransmitters and related synt hetic enzymes in wholemount preparations, with and without colchicine treatment. Immunoreactivities for enkephalin-endorphin (ENK-END), subs tance P (SP), nitric oxide synthase, vasoactive intestinal peptide (VI P), neuropeptide Y (NPY), and calcitonin gene-related peptide (CORP) w ere demonstrated within the ganglionated plexus. Roughly half of the n eurons in the sphincter of Oddi expressed immunoreactivity for both SP and ENK-END, but not for nitric oxide synthase. About 25% of the neur ons expressed nitric oxide synthase immunoreactivity as well as NADPH- diaphorase activity. This contingent of neurons was made up of two sub groups: one that expressed immunoreactivity for VIP, the other for NPY . Neurons that expressed CORP immunoreactivity were sparse in sphincte r of Oddi ganglia; however, many axons immunoreactive for both CORP an d SP were present in the ganglionated plexus. The CGRP/SP fibers are p robably visceral afferents that may influence ganglionic output throug h axon reflex circuits. These results, along with studies of the actio ns of these neuroactive compounds on sphincter tone, support the view that ganglia of the sphincter of Oddi are largely comprised of excitat ory (SP/ENK-END-immunoreactive) and inhibitory (nitric oxide synthase/ VIP- or NPY-immunoreactive) neurons, and that sphincter of Oddi tone i s controlled by the regulation of the outputs of these two groups of c ells. (C) 1995 Wiley-Liss, Inc.