Background: The distribution and colocalization of nitric oxide synthase and NADPH-diaphorase have been investigated quite extensively in the mammalian gut; however, no such study has been undertaken in the avian gut. In the present report, we have therefore studied the distribution and coexpression of nitric oxide synthase (NOS), NADPH-diaphorase, and vasoactive intestinal polypeptide (VIP) in enteric neurons of the newly hatched chicken gut.
Methods: Immunohistochemical methods were used to detect NOS immunoreactivity (NOS-IR) and VIP immunoreactivity (VIP-IR). NADPH-diaphorase activity was detected using a histochemical technique.
Results: Neurons expressing NADPH-diaphorase activity, NOS-IR, and VIP-IR were detected in both the myenteric and submucous plexus of all regions of the gastrointestinal tract examined. All NADPH-diaphorase positive neurons were also NOS-IR and all NOS-IR neurons were NADPH-diaphorase positive, in both plexuses, indicating that NADPH-diaphorase can be used as a marker for NOS containing neurons in the chicken gut. The majority of VIP-IR neurons also expressed NADPH-diaphorase activity. Only few neurons that expressed NADPH-diaphorase activity did not express VIP-IR. The proportion of VIP immunopositive neurons that were NADPH-diaphorase negative increased anally and these neurons were more prominent in the submucous than the myenteric plexus ganglia. NADPH-diaphorase positive, NOS-IR, and VIP-IR nerve fibres were detected in the circular muscle, but very few, if any, were present in the longitudinal muscle. VIP-IR, but not NOS-IR or NADPH-diaphorase activity, was detected in mucosal fibres, in contrast to the situation in the mammalian gut.
Conclusions: These results indicate that in birds, as in mammals, nitric oxide may play a role in the neural control of the gut musculature, but that it is unlikely to be involved in the nervous control of mucosal activity.