Fig. 6. Effect of N G-monomethyl-L-arginine acetate (L-NMMA) on basal and N -methyl-D-aspartate (NMDA)-induced spinal release of NO2−/NO3−. Dialysates were collected as 10-min fractions. NMDA (1.0 mM) was perfused into the lumbar intrathecal space through a dialysis probe for 10 min ( solid bar ). L-NMMA (10 mM) was perfused into lumbar intrathecal space for 90 min ( open bar ). Thirty minutes after starting administration of L-NMMA, NMDA was coperfused with L-NMMA for 10 min. Basal levels were determined by averaging three consecutive samples immediately before infusion of L-NMMA. Data are presented as mean ± SD (n = 8) of percentage values of basal levels. * P < 0.01, ** P < 0.001 vs. basal levels.