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Sex Associated Differential Expressions of the Alternatively Spliced Variants mRNA of OPRM1 in Brain Regions of C57BL/6 Mouse

Background/Aims: Opiates are potent analgesics but their clinical use is limited by sex-associated side effects, such as drug tolerance, opioid-induced hyperalgesia and withdrawal reaction. OPRM1, as the main receptor of opioids, plays an important role in the pharmacological process of opioids in rodents and human. We have previously investigated OPRM1, the μ opioid receptor gene, which have dozens of alternatively spliced variants probably correlating with opioid-induced effects in brain regions of four inbred mouse strains and demonstrated the strain-specific expressions of these splice variants. Also, within a strain, the regional expression patterns of some of the variants were similar while others were opposite. Thus, we are aiming to seek out the relationship between sex differences and these alternatively spliced variants. Methods: The present studies follow a SYBR green quantitative PCR (qPCR) which we had used before to examine the expression of OPRM1 splice variant mRNAs in selected brain regions of male and female C57BL/6 mice. Sex-associated differences in baseline latency, opioid-induced tolerance, analgesia and addiction were examined and determined by Tail-flick test, jumps and statistical analysis. Results: The mRNA levels of opioid receptor gene splice variants in male and female mice showed significant differences among the brain regions, implying region-specific alternative splicing of the OPRM1 gene, which was consistent with our previous study. More importantly, the complete mRNA expression profiles of the OPRM1 splice variants was also gender-specific, suggesting a sexual influence on OPRM1 alternative splicing. Conclusion: In brief, we put forward that the distinctions among baseline latency, opioid-induced tolerance, analgesia and physical dependence in male and female mice might correlate with sex associated differential expressions of OPRM1 gene.