Distribution of nitric oxide synthase and vasoactive intestinal polypeptide immunoreactivity in the sphincter of Oddi and duodenum of the possum

Abstract

The nitrergic innervation of the sphincter of Oddi (SO) and duodenum in the Australian brush-tailed possum and the possible association of this innervation with the neuropeptide vasoactive intestinal polypeptide (VIP) were investigated by using immunohistochemical localisation of nitric oxide synthase (NOS) and VIP, together with the general neuronal marker, protein gene product 9.5 (PGP9.5). Whole-mount preparations of the duodenum and attached SO without the mucosa, submucosa and circular muscle (n=12) were double- and triple-labelled. The density of myenteric nerve cell bodies of the SO in the more distal region (duodenal end) was significantly higher than that in the more proximal region. In the SO, approximately 50% of all cells were NOS-immunoreactive (IR), with 27% of the NOS-IR cells being VIP-IR. Within the duodenal myenteric plexus, NOS immunoreactivity was present in about 25% of all neurons, with 27% of these NOS-IR neurons also being VIP-IR, a similar proportion to that in the SO. Varicose nerve fibres with NOS and VIP immunoreactivity were present within the myenteric and submucous plexuses of the SO and duodenum, and in the circular and longitudinal muscle layers. The NOS-positive cells within both the SO and duodenum were unipolar, displaying a typical Dogiel type I morphology. The myenteric plexuses of the SO and duodenum were in direct continuity, with many interconnecting nerve trunks, some of which showed NOS and VIP immunoreactivity. Thus, the possum possesses an extensive NOS innervation of the SO and duodenum, with a significantly higher proportion of NOS-IR neurons within the SO, a subset of which contains VIP.

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).…”

Exogenous Adenosine Triphosphate and Adenosine Stimulate Proximal Sphincter of Oddi Motility Via Neural Mechanisms in the Anesthetized Australian Possum

“…Our data also demonstrate that ATP activates a nitrergic pathway, which may involve interneurons or nitrergic motor neurons. Immunohistochemical studies have shown that NOS containing nerves are abundant in the SO [28,29]. Studies in guinea pig, pig, and human SO have suggested that nitric oxide is released tonically to inhibit contractile activity [30,31], therefore ATP may be involved in maintaining the tonic release of nitric oxide in the SO.…”

Effects of bioactive agents on biliary motor function

“…Previous studies demonstrated a relaxatory motor effect of NO on SO motor activity and the presence of NOS-IR inhibitory neurons. The study by Simula et al [33] demonstrates that the density of NOS-IR neurons is greater in the distal half of the SO myenteric plexus. Another interesting observation is that approximately 50% of all SO myenteric neurons were NOS-IR, consistent with a significant inhibitory drive to the SO.…”