Regional distribution of binding sites for the nitric oxide synthase inhibitor L-[3H]nitroarginine in rat brain.

The regional distribution of NG-nitro-L-[(3)H]arginine (L-[(3)H]NOARG) binding to different regions of rat brain was studied by quantitative autoradiography. These studies revealed highest density of binding sites in cerebellum, anterior olfactory nucleus, islands of Calleja and substantia nigra with appreciable binding site densities in inferior colliculus, superior colliculus, olfactory tubercle and dorsal tegmental nucleus. The regional distribution of L-[(3)H]NOARG binding, is in good agreement with the distribution of nitric oxide synthase studied previously by NADPH-diaphorase staining and immunohistochemistry using antibodies against neuronal nitric oxide synthase. The kinetics of L-[(3)H]NOARG binding to the cytosolic preparations of cerebral cortex, cerebellum, hippocampus and striatum was studied using an in vitro binding technique. Specific L-[(3)H]NOARG binding was of nanomolar affinity, saturable, and best fit to a single-site model in all four brain regions. These studies support the potential use of L-[(3)H]NOARG binding as a tool for further elucidation of the regional distribution and functional properties of NOS in the central nervous system.