NO-synthase: what can research on invertebrates add to what is already known?

The present study attempts to review presently known data regarding the distribution of nitric oxide (NO) synthase and the function of NO in invertebrate species. NO is synthesized from L-arginine by the enzyme NO-synthase, and activates guanylate cyclase which in turn leads to an increase in levels of cGMP in target cells. Major contributions to the knowledge of NO as a messenger molecule in invertebrates have been made by NADPH-diaphorase histochemistry and biochemical assays. These techniques suggest the presence of a L-arginine/NO pathway in a variety of tissues, thus implicating multiple roles for NO in invertebrates.