[H-3] L-N-G-NITROARGININE BINDING AFTER TRANSIENT FOCAL ISCHEMIA AND NMDA-INDUCED EXCITOTOXICITY IN TYPE-I AND TYPE-III NITRIC-OXIDE SYNTHASE NULL MICE

We investigated the density and distribution of nitric oxide synthase (NOS) binding by quantitative autoradiography using [H-3]L-N-G-nitroar ginine ([H-3]L-NNA) after transient focal ischemia or intrastriatal in jection of N-methyl-D-aspartate (NMDA) in wild-type (SV-129 and C57bla ck/6) and type I (neuronal) and type III (endothelial) NOS-deficient m ice. The middle cerebral artery (MCA) was occluded by an intraluminal filament for 3 h followed by 10 min to 7 days of reperfusion. Specific [H-3]L-NNA binding, observed in the wild-type and type III mutant mou se at baseline, increased by 50-250% in the MCA territory during ische mia and the first 3 h of reperfusion. The density of binding sites (B- max), but not the dissociation constant (K-d), increased significantly during the ischemic period as did type I NOS mRNA as detected by quan titative reverse transcription polymerase chain reaction. [H-3]L-NNA b inding after intrastriatal NMDA injection also increased by 20-230%. I n the type I NOS-deficient mouse, [H-3]L-NNA binding was low and only a very small increase was observed after ischemia or excitotoxicity. U nder conditions of this study, [3H]L-NNA did not bind to type II NOS a s there was no difference in the distribution or density of [H-3]L-NNA binding in the rat spleen obtained after lipopolysaccharide treatment despite induction of NOS type II catalytic activity. Our data suggest that an ischemic/excitotoxic insult up-regulates type I NOS gene expr ession and [H-3]L-NNA binding and that this up-regulation may play a p ivotal role in the pathogenesis of ischemic/excitotoxic diseases.