Localization of nitric oxide synthase immunoreactive neurons in the enteric nervous system of the jejunum of the one-humped camel (Camelus dromedarius): A quantitative study

Distribution of neuronal nitric oxide synthase (nNOS) has been studied in the enteric nervous system of the camel jejunum by immunohistochemistry. Immunoreactivity to nNOS was discernible in selective groups of neurons and nerve terminals in the myenteric and submucosal plexuses. 20% of neurons within the myenteric and 8% within the submucosal plexuses stained positive for nNOS. The immunoreactive neurons occurred both in groups and as solitary neurons in both the myenteric and submucosal plexuses. Whilst most of the neurons possessed tapering ends which appeared to point towards the circular muscle layer, a few seemed to point towards the longitudinal layer of the muscularis externa. Nerve fibres immunoreactive to nNOS, some of which possessed varicosities, were detected in the myenteric plexus and within the circular and longitudinal layers. The submucosal immunoreactive neurons and nerve fibres were observed mainly in the inner plexus of Meissner. Immunoreactivity to nNOS was not observed either in the mucosa or the gut or around blood vessels. It is concluded that nitric oxide synthase, which catalyzes the synthesis of nitric oxide, is present in the enteric nervous system of the camel jejunum where nitric oxide probably functions as an inhibitory neurotransmitter.