Fig. 1.

Inhibition of visceral hyperalgesia by MK-801. The N-methyl-d-aspartate receptor (NMDAR) antagonist MK-801 [10 nmol, 5 μl it, 10 min before colorectal distension (CRD)] completely blocked stress-induced visceral hyperalgesia at day 11 in water avoidance (WA)-stressed rats (A) but had no effect in sham WA rats (B) (n = 7–8). EMG, electromyography. Data are means ± SE. *P < 0.05, significantly different between vehicle- and MK-801-treated rats (2-way ANOVA followed by Bonferroni posttest).