Objective To investigate the role of adenylate crclase (AC)-cAMP system and Ca2+ system and NG-cGMP sled system and the effects
of a NOS inhibitor, NG-nitro-L-arginine (L-NNA)in the neuronal mechanisms of opioid tolerance and dependence. Methods The experiments were performed in five groups:coned group; opioid
agonist group; opioid agonist + nalonoxe group; LNNA + opioid agonist group and L-NNA + opioid agonist + nalonoxe group. The intracellular cALMP and cGMP levels were measured by 3 H-cAMP protein binding assay and s H-cGMP radioimmunoassay , respectively. NOS activity was determined by the conversion of 3 H-arginine to 3 H-citrulline. The change of < Ca2+ > i was studied by the laser scanning confocal microscopy thchnique . iNOS protein expression was detected using immunohistochemistry with monoclonal antibody of iNOS,and imaging analysis was performed. Results lung-term administration of high-selective δ-opioid receptor agonist DPDPE and precipitation of opioid withdrawal by naloxone significantly
induced increase of cAMP level and
i in NG-LNCXiNOS cells with stable expression of iNOS gene. The cytosolic iNOS activity and cGMP generation were enhanced by DPDPE dose-dependently. 10-4 mol/L L-NNA could block opioid agonist-induced AG-cAMP desensitization and activity of NO-cGMP second messenger pathway, but it could not reduce opioid induced elevation of i. Furthermore, L-NNA decreased iNOS-spectific protein expession in DPDPE-induced tolerance and naloxone-prmipited withdrawal cells. Conclusion NOS inhibitor may attenuate the development of opioid tolerance and withthawal via the negative regulation of AG-cAMP system and NG-cGMP system. It can be clinically used to prevent opiate tolerance and addiction.