2.13 Data and statistical analysis
The data and statistical analysis comply with the recommendations of theBritish Journal of Pharmacology on experimental design and analysis in pharmacology (Curtis et al., 2018). Data are presented as the mean ± standard errors of the mean (SEM). All data were subjected to a test of normality (Shapiro-Wilk or Kolmogorov-Smirnov), and either parametric or nonparametric analysis was conducted accordingly. Immunohistochemical and naïve behavioral data were compared across genotypes with Welch’s t-test. The time course of drug and pain model effects was assessed by repeated-measures two-way ANOVA, followed by Bonferroni’s multiple comparisons post hoc test. For immunoblot quantification, the amount of MOP protein was normalized to the mean of the WT control value, and the control value was set as 1. All statistical analyses were performed with GraphPad Prism 8.0 software (Graph Pad Inc., San Diego, CA). All tests were two-tailed and  the criterion of statistical significance was a probability less than 5%.