An experimental, NADPH-diaphorase histochemical and immunocytochemical study of Mesocestoides vogae tetrathyridia

In order to test the role of nitric oxide in flatworms, Mesocestoides vogae tetrathyridia were incubated together with L-arginine, which is the substr ate for nitric oxide synthesis, or with N-G-nitro-L-arginine, which is an i rreversible inhibitor of nitric oxide synthase. Normally, tetrathyridia att ach to each other with the aid of their suckers, forming clusters. The rate of cluster formation was followed during the incubations. L-Arginine stimu lated, and N-G-nitro-L-arginine clearly inhibited, the cluster formation. T his is the first time that an effect of nitric oxide has been observed in a flatworm. In addition, the pattern of the NADPH-diaphorase histochemical r eaction in the nervous system and the pattern of F-actin filaments in the m usculature stained with TRITC-labelled phalloidin were studied. NADPH-d sta ining occurred in the brain and the main nerve cords but also followed the muscle fibres stained with phalloidin. The pattern of the NADPH-d reaction was compared with that of 5-HT immunoreactivity. The implications of the re sults are discussed in relation to the background of data on neuronal signa l substances in M. vogae. (C) 1999 Australian Society for Parasitology. Pub lished by Elsevier Science Ltd. All rights reserved.