Immunohistochemical identification of neurons in ganglia of the guinea pig sphincter of oddi

Abstract

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 synthetic enzymes in wholemount preparations, with and without colchicine treatment. Immunoreactivities for enkephalin-endorphin (ENK-END), substance P (SP), nitric oxide synthase, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) were demonstrated within the ganglionated plexus. Roughly half of the neurons in the sphincter of Oddi expressed immunoreactivity for both SP and ENK-END, but not for nitric oxide synthase. About 25% of the neurons expressed nitric oxide synthase immunoreactivity as well as NADPH-diaphorase activity. This contingent of neurons was made up of two subgroups: one that expressed immunoreactivity for VIP, the other for NPY. Neurons that expressed CGRP immunoreactivity were sparse in sphincter of Oddi ganglia; however, many axons immunoreactive for both CGRP and SP were present in the ganglionated plexus. The CGRP/SP fibers are probably visceral afferents that may influence ganglionic output through axon reflex circuits. These results, along with studies of the actions of these neuroactive compounds on sphincter tone, support the view that ganglia of the sphincter of Oddi are largely comprised of excitatory (SP/ENK-END-immunoreactive) and inhibitory (nitric oxide synthase/VIP- or NPY-immunoreactive) neurons, and that sphincter of Oddi tone is controlled by the regulation of the outputs of these two groups of cells.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

“…Recombinant human hemoglobin may alter the motor function of the sphincter of Oddi in vitro and in vivo by binding endogenous NO (Cullen et al, 1996). Neurons containing nNOS immunoreactivity or NADPH diaphorase were histochemically detected in the sphincter of Oddi of the human, monkey (De Giorgio et al, 1994), dog (Tanobe et al, 1995), guinea pig (Wells et al, 1995), and possum (Baker et al, 1993;Simula et al, 2001). The presence of NOS has also been demonstrated in the gall bladder and biliary pathways of the guinea pig (Grozdanovic et al, 1994), monkey, and human (De Giorgio et al, 1994;Uemura et al, 1997).…”

The distribution and chemical coding of neurons supplying the sphincter of Oddi in mammals

“…As already mentioned, SP and CGRP are expressed by many nerve terminals supplying the MDP/SO in the guinea pig (Wells et al 1995) and pig (Sand et al 1993). Large number of SP-positive nerve fibres associated with the SO have been also found in the cat (Feher et al 1995).…”

“…These CGRP and/or SP-positive fibres have been suggested by the authors to represent sensory nerve terminals of extrinsic origin. Talmage et al (1997) have performed investigations dealing with the identification of cholinergic neurons in guinea pig SO ganglia, thus complementary to those carried out by Wells et al (1995). Based on the results of these two studies it can be concluded that about 69% of the neurons within the guinea pig SO ganglia are immunoreactive for ChAT thus can be classified as cholinergic nerve cells .…”

“…Ganglia distributed between the SO muscles have been also well described and immunohistochemically characterized in the guinea pig (Cai and Gabella 1983a, Wells and Mawe 1993, Wells et al 1995, Kennedy and Mawe 1998, Mawe and Kennedy 1999. Cai and Gabella (1983a) have used histochemical methods for demonstration of adrenergic and cholinergic nerve structures to investigate the innervation of the gall bladder and biliary pathways.…”

“…Immunohistochemical and histochemical studies performed by Wells et al (1995) have revealed that neurons in guinea pig SO ganglia express immunoreactivity for several biologically active substances including substance P (SP), enkephalin and/or β-endorphin (ENK-END), neuropeptide Y (NPY), VIP, calcitonin gene-related peptide (CGRP) and NOS. NOS immunoreactivity was found in a subpopulation of neurons which also displayed nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity.…”