Simultaneous measurement of nitrite and nitrate levels as indices of nitric oxide release in the cerebellum of conscious rats

We examined the modulation of nitric oxide production in vivo by measuring levels of nitrite (NO₂/^-) and nitrate (NO₃/^-) in the dialysate of the cerebellum in conscious rats, by using an in vivo brain microdialysis technique. The levels of both NO₂/^- and NO₃/^- were decreased by the intraperitoneal injection of N(G)-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase, whereas N(G)-nitro-D-arginine methyl ester 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-arginine methyl ester. Direct infusion of L-glutamate, N-methyl-D-aspartate, or KCl into the cerebellum through a dialysis probe resulted in an increase in NO₂/^- and/or NO₃/^- levels. The effects of N-methyl-D-aspartate and KCl were dependent on extracellular calcium. Furthermore, the stimulatory effects of L-glutamate and N-methyl-D-aspartate were inhibited by N(G)-nitro-L- arginine methyl ester and (±)-3-(2-carboxypiperazin-4-yl) propyl-1- phosphonic acid (CPP), an N-methyl-D-aspartate receptor antagonist. These results suggest that NO₂/^- and NO₃/^- levels may be related to nitric oxide production in vivo.