The MicroRNA Expression Profile Changes Of Spinal Cord In Chronic Morphine Tolerant Rat

Obsjective:To investigate the microRNA (miRNA, miR) expression profile changes in the spinal cord of chronic morphine tolerant rats, and initially discuss the putative role that miRNAs may play during the process of choronic morphine tolerance.Methods:A total of12Sprague-Dawly (SD) rats weighting280-320g were randomly divided into two groups after intrathecal catheterization following the modified Yaksh method:the morphine tolerant group (MT, n=6) and the normal saline group(NS, n=6). The MT group rats were given l0μg morphine intrathecally twice a day during6consecutive days to establish a chronic morphine tolerant model; in contrast, the NS group rats was administrated20μL normal saline (NS) as the same way. On day7, the sacral enlargements of the rats were removed, and the total RNA of3rats of each group were extracted for miRNA expression profile array analysis using LNA technology of Exiqon Company, and the rest of3rats of each group were used for qRT-PCR test to validate the results of miRNAs changes between the two groups. Results:1. The thermal pain threshold of MT group was increased significantly compared with the NS group after morphine injection on day1(P<0.05); the analgesic effect of morphine weakened after consecutive injection, but the thermal pain threshold of MT group was still higher than that of the NS group on day3and day5(P<0.05); no obviously antinociceptive effect of morphine was observed on day7, and there was no statistically significant difference between the two groups (P>0.05).2. Based on the microRNA expression profile array, there are2miRNAs up regulated and8miRNAs down regulated in the MT group rats, compared with the NS group.3. The changes of miRNAs verified by qRT-PCR test accord with that of the miRNA microarray analysis.Conclusions:1. The chronic morphine antinociceptive tolerance occurs after6days of intrathecal morphine injection in rats.2. There are miRNA changes in the spinal cord of morphine tolenrant rats in contrast with the normal saline group rats, of which2miRNAs are up regulated and8miRNAs down regulated.