Figure 6.

Analgesic responses to morphine administration in wild-type and M2 receptor mutant mice. Mice of the indicated genotypes were injected with morphine (10 mg/kg, injected s. c.), and antinociceptive responses were measured in the tail-flick test as described in Materials and Methods. Vehicle-treated (Veh) mice of the same genotype (littermates) served as controls. Data are presented as means ± SEM (n = 19 for each genotype) and are expressed as the percent MPE, where percent MPE = 100 × [(postdrug latency − baseline)/(10 − baseline)].