Changes Of Mu Opioid Receptor In Brain Regions Of Morphine Dependent Rats

Our study was to observe the changes in rat brainregions of binding and gene expression of mu opioid receptor afterchronic morphine.MateriaIs and methods: Adult male Sprague-Dawley rats wereadministered with morphine by intraperitoneal injection with doseadded according to an escalating schedule. Four regions ofhypo-thylamus. hippocamp. striatum and frontal contex were removedto experience the radio-ligand binding and reversetranscription-polymerase chain reaction (RT-PCR) study. In thebinding study we used ~3[H]DAGO as the radio-ligand, Which bind mureceptor with a high affinity, thus the changes of the binding represent theregulations of mu receptor. To experience RT-PCR study, a primerspecific to mu opioid receptor was used and the β -actin was used ascontrol gene.Result: After naloxone administraion, the morphine group ratsresulted in a remarked abstinence syndrome. The behavior score ofprecepitated abstinence syndrome were different from that of the controlrats (16.5±2.4 vs 3. 5 ±0.6, P<0.05 ). That means the mode of addictionon morphine have been developed. In the morphine addiction rats, thebinding of~3[H]DAGO decreased significantly(p<0.05) and the expressionof mu opioid receptor tmRNA was significanly inhibited in the studiedbrain regions except the frontal contex.Conclusion: The levels of both binding and mRNA of mu opioidreceptor decreased sighficantly after chronic morphine. That maybe oneof the cause of morphine addiction.