NADPH-diaphorase and NOS enzymatic activities in some neurons of reptiliangut and their relationships with two neuropeptides

The distribution of neurons containing the enzymes NADPH-diaphorase (NADPH- d) and nitric oxide synthase (NOS) has been studied in the gastrointestinal tract of lizard (Podarcis s. sicula) and snake (Thamnophis sirtalis). The techniques employed were the NADPH-d/nitroblue tetrazolium histochemical me thod, and the indirect immunofluorescence applied to cryostat sections and to whole-mount preparations. The colocalization of NADPH-d with NOS, with v asoactive intestinal polypeptide (VIP) and with galanin (Gal) was also stud ied, and a Western blot analysis using an antibody directed against mammali an Gal was performed on lizard stomach extracts. NADPH-d positive nerve cel l bodies and fibres were found in the myenteric and submucous plexuses thro ughout the gastrointestinal tract of both reptiles. These nerve structures were also present in the other intramural nerve plexuses, although in small er quantities. Both in lizard and snake, the stomach revealed a positive ne rve population that was more dense than elsewhere in the gut. The populatio n of the NADPH-d-positive neurons observed in the lizard was larger than th at observed in the snake. The distribution of both populations was similar to those that have been described in the gut of several mammalian and non-m ammalian vertebrates. Both in lizard and snake, a one-to-one correspondence was noted between NOS- and NADPH-d-containing nerve cell bodies, and the n itrergic neurons containing Gal appeared to be more numerous than those con taining VIP. Western blot analysis recognised a single band with a molecula r weight (3.4 kDa) very similar to that of porcine Gal. It is hypothesised that at least some of the nitrergic neurons of the lizard and snake gut are inhibitory motor neurons innervating the circular smooth musculature. In a ddition, the colocalization of NOS and VIP in neurons enhances their inhibi tory action. The role of the neurons containing both NOS and Gal remains un known.