the role of gai/o and gb protein gene expression in chronic morphine induced tolerance to analgesia in rat lumbar spinal cord

introduction: deficiency in mu opioid receptor signaling pathway is partially responsible for morphine tolerance. this deficiency may be due to uncoupling of opioid receptors and related g proteins, which in turn, it may be caused by their structural changes such as phosphorylation or by decreasing their abundance. in this study, we tried to investigate the effect of chronic administration of morphine on gi/o and g protein gene expression in rat lumbar spinal cord. material and methods: daily injections of morphine 20 mg/kg for 4 days were used to introduce morphine tolerance in nmri male rats. in 5th day, the animals were decapitated and their lumbar spinal cord were extracted and stored in-70úc. after rna extraction using rnx+ solution, cdna was synthesized using oligo-dt primer and m-mulv reverse transcriptase.parts of cdna related to b-actin, gi/o and g protein were amplified by pcr (semi-quantitative pcr) using specific primers. electro phoresis of the samples was performed on 1.5% agarose gel and the ratio of band density of gi/o and g to b-actin were calculated and compared with control group. results: chronic morphine administration did not change gi/o gene expression but increased g gene expression (p< 0.05). conclusion: it is concluded that parts of morphine tolerance is due to the over expression of g gene.these results are supported with several reports concerning adenylyl cyclase activation by g proteins