Figure 4. Effect of GLU-receptor inhibitors on agonist-stimulated cGMP production in cultured neurons. The effect of the GLU-receptor antagonists ketamine (A), MK-801 (B), and CNQX (C) on cGMP production was determined in neuronal cultures stimulated by GLU and the GLU analogs NMDA, KAIN, and QUIS. Data represent the mean plus/minus SEM for n = 5–18 experiments, each performed in triplicate. *P < 0.05 antagonist versus control without antagonist for each agonist, by ANOVA and Bonferroni post boc correction.