Morphine and CP 55940 treatment reduce nociceptive behaviors in BERK and hBERK1 mice. Mice were injected intraperitoneally with morphine or vehicle (A,C) and 0.3 mg/kg CP 55940 or vehicle (B,D), and grip force responses were recorded over the indicated time period. An increase in grip force indicates a decrease in nociception. All data are shown as mean ± SEM from 4 to 6 mice with 3 observations per mouse. Significance of differences: In panel A: *P < .05, **P < .01 versus baseline at 0 hours (immediately before treatment). In panel B: *P < .05, **P < .01 versus baseline; #P < .01 versus vehicle at the same time point. In panel C: *P < .05, **P < .01 versus baseline. In panel D: #P < .01 versus baseline; **P < .01 versus vehicle at the same time point.