SIMULTANEOUS MEASUREMENT OF NITRITE AND NITRATE LEVELS AS INDEXES OF NITRIC-OXIDE RELEASE IN THE CEREBELLUM OF CONSCIOUS RATS

We examined the modulation of nitric oxide production in vivo by measu ring levels of nitrite (NO2-) and nitrate (NO3-) in the dialysate of t he cerebellum in conscious rats, by using an in vivo brain microdialys is technique. The levels of both NO2- and NO3- were decreased by the i ntraperitoneal injection of N-G-nitro-L-arginine methyl ester, an inhi bitor of nitric oxide synthase, whereas N-G-nitro-D-arginine methyl es ter had no effect. L-Arginine by itself increased NO2- and NO3- levels and diminished the reduction of their levels caused by N-G-nitro-L-ar ginine methyl ester. Direct infusion of L-glutamate, N-methyl-D-aspart ate, or KCl into the cerebellum through a dialysis probe resulted in a n increase in NO2- and/or NO3- levels. The effects of N-methyl-D-aspar tate and KCl were dependent on extracellular calcium. Furthermore, the stimulatory effects of L-glutamate and N-methyl-D-aspartate were inhi bited by N-G-nitro-L-arginine methyl ester and (+/-)-3-(carboxypiperaz in-4-yl) propyl-1-phosphonic acid (CPP), an N-methyl-D-aspartate recep tor antagonist. These results suggest that NO2- and NO3- levels may be related to nitric oxide production in vivo.