Figure 1.

Levels measured over time of the decreased TWL and increased methylation of the MOR gene promoter in neuropathic pain mice.

Notes: (A) CCI induced temporal changes in thermal hyperalgesia. TWL of the ipsilateral (ipsi), but not contralateral (contra), side was reduced on days 1, 3, 7, and 14 after CCI (n=6–14/group). (B) The 5′-flanking region of the MOR gene contains 21 putative methyl CpG sites from −569 to +33 (with the ATG start codon designated +1). (C and D) Methylation statuses at the PP of the MOR gene were analyzed by MSP. Methylation levels of two sites (−344 and −255, located in the PP region) were markedly increased in the lumbar spinal cord at days 7 and 14 following CCI (n=6/group). Data are presented as mean ± SEM. One-way ANOVA followed by Bonferroni’s test. *p<0.05 or **p<0.01 versus before operation.

Abbreviations: MOR, mu opioid receptor; PCR, polymerase chain reaction; PP, proximal promoter; CCI, chronic constriction injury; ANOVA, analysis of variance; MSP, methylation-specific PCR; CpG, cytosine-phosphate-guanine; TWL, thermal withdrawal latency; SEM, standard error of the mean.