Antagonism of MOR antinociception by systemically-administered CC12 in the mouse. Mice were tested for baseline (BL) responses, then received CC12 (base, 100 mg/kg, s.c.) or pH 4.5 saline (Sal). Fifteen min later, subjects were again tested (Post), and received MOR sulfate (3.2 mg/kg, s.c.) or saline (Sal), and were re-tested at the times shown (abscissa). Nociceptive latencies (ordinate, mean ± SEM for the number of subjects in parentheses) for each treatment group are shown. In this figure only, the cutoff latency used was 10 sec. ++ Significant (P < 0.001) CC12 by MOR by time interaction term was found by ANOVA, confirming antagonism of MOR by CC12 (see text).