[NADPH-diaphorase activity in digestive system of gastropod molluscs Achatina fulica and Littorina littorea].

Localization and peculiarities of NO-ergic elements were studied for he first time throughout the entire length of digestive tract of the marine gastropod mollusc Achatina fulica (Prosobranchia) and the terrestrial molusc Littorina littorea (Pulmonata) by using histochemical method of detection of NADPH-diaphorase (NADPHd). NO-ergic cells and fibers were revealed in all parts of the mollusc digestive tract beginning from pharynx. An intensive NADPHd activity was found in many intraepithelial cells of the open type and in their processes in intra- and subepithelial nerve plexuses, single subepithelial neurons, granular connective tissue cells, and numerous nerve fibers among muscle elements of he digestive tract wall as well as in nerves innervating the tract. NADPHd was also present in receptor cells of he oral area and in the central A. fulica ganglia participating in innervation of the digestive tract. The digestive tract NO-ergic system ofA. fulica has a more complex organization that that of L. littorea. In the A. fulica pharynx, stomach, and midgut, directly beneath epithelium, there is revealed a complex system of glomerular structures formed by thin NADPHd-positive nerve fibers coming from the side of epithelium. More superficially under the main groups of muscle elements, small agglomerations of NADPHd-positive neurons are seen, which could be considered as primitive, non-formed microganglia. Peculiarities of distribution and a possible functional role of NO-ergic elements in the digestive tract of molluscs are discussed as compared with other invertebrate and vertebrate animals.