HISTOCHEMISTRY OF NITRIC-OXIDE SYNTHASE IN THE NERVOUS-SYSTEM

Nitric oxide synthase, which generates the physiological messenger mol ecule nitric oxide, and its associated NADPH diaphorase (NADPHd) activ ity are distributed throughout selective neuronal populations of the c entral and peripheral nervous system. Considerable evidence has been a ccumulated to indicate that NADPHd activity labels cells lacking neuro nal nitric oxide synthase, i.e., the specificity of the reaction has t o be considered for the reliable detection of the enzyme in neuronal b ut also non-neuronal tissue. In the present review, critical aspects o f nitric oxide synthase visualization in neurones, using its NADPHd ac tivity, are discussed. Furthermore, the organization of the central an d peripheral nitric oxide synthase-containing neuronal systems is desc ribed. Nitric oxide synthase is present in local cortical and striatal neurones, hypothalamic magnocellular neurones, mesopontine cholinergi c neurones, cerebellar intemeurones, preganglionic sympathetic and par asympathetic neurones, neurones in parasympathetic autonomic and enter ic ganglia and primary viscero-afferent neurones. Finally, injury-rela ted alterations in nitric oxide synthase activity are briefly outlined . In this respect, the histochemistry of nitric oxide synthase may rep resent a valuable marker for neurochemical, if not structural, alterat ions observed in neural diseases, regeneration and transplantation.