Fig. 3. Effects of D,L-2-amino-5-phosphonovaleric acid (AP-5) on N -methyl-D-aspartate (NMDA)-induced spinal release of glutamate ( left ) and NO2−/NO3−( right ). Dialysates were collected as 10-min fractions. NMDA (1.0 mM) was perfused into the lumbar intrathecal space through a dialysis probe during 0–10 min (as shown by the bar). AP-5 (10 mM) was perfused into lumbar intrathecal space for 90 min. Thirty minutes after starting administration of AP-5, NMDA was coperfused with AP-5 for 10 min. Basal levels were determined by averaging three consecutive samples immediately before infusion of AP-5. Data are presented as mean ± SD (n = 8) of percentage values of basal levels. *Statistical significance between NMDA and AP-5 plus NMDA ( P < 0.001 and 0.001, respectively) in changes of glutamate and NO2−/NO3−concentrations, respectively.