小鼠脑内NO/NOS-cGMP信号系统与吗啡依赖形成的机制

EVIDENCE FOR INVOLVEMENT OF NO/NOScGMPSIGNAL SYSTEM IN MORPHINE DEPENDENC

本文观察了吗啡依赖小鼠脑组织ｃＧＭＰ含量、钙依赖性及非钙依赖性ＮＯＳ活性的变化、蛋白激酶Ａ（ｐｒｏｔｅｉｎｋｉｎａｓｅＡ，ＰＫＡ）对ＮＯＳ活性的磷酸化调节以及一氧化氮合酶（ＮＯＳ）抑制剂对吗啡依赖形成的影响。结果发现：（１）小脑、纹状体、海马及大脑皮质ｃＧＭＰ含量明显下降；（２）纹状体及大脑皮质钙依赖性ＮＯＳ活性明显升高，而ＩＰ２０（ＰＫＡ抑制剂）可抑制此变化，小脑及海马钙依赖性ＮＯＳ活性及以上各脑区非钙依赖性ＮＯＳ活性无明显变化；（３）纹状体、大脑皮质中与ＮＯＳ分子量相当的１５０ｋＤ蛋白质的体外磷酸化水平低于对照，ＩＰ２０可抑制此变化；（４）ＮＯＳ抑制剂可抑制小鼠对吗啡依赖的形成；（５）纳洛酮拮抗组小鼠未见上述变化。结果表明，吗啡依赖小鼠脑组织普遍存在ｃＧＭＰ水平下降，纹状体、大脑皮质钙依赖性ＮＯＳ活性的增加可能与吗啡依赖有关，且受ＰＫＡ对其磷酸化调节。ＮＯＳ活性增加与ｃＧＭＰ含量的下降相矛盾，提示ＮＯ／ＮＯＳ在吗啡依赖中的作用可能是通过一种不同于产生ｃＧＭＰ信号的机制进行的。

The present study was undertaken to observe changes in cGMP contents, calciumdependent and noncalciumdependent NOS activities in brain regions isolated from morphinedependent mice as well as the effect of NOS inhibitor(LNMMA) on the development of this dependence. It was found that (1) cGMP contents in cerebellum, striatum, hippocampus and cerebral cortex were significantly decreased. (2) Calciumdependent NOS activity was noticeably increased in striatum and cerebral cortex, which was inhibited by PKA inhibitor. No similar changes were found in cerebellum and hippocampus. Changes of noncalciumdependent NOS activity did not occur in morphinedependent mice brain. (3) In the striatum and cerebral cortex of morphinedependent mice, the level of 150 kD protein phosphorylation in vitro was noticeably decreased, which was inhibited by IP20(PKA inhibitor). (4) NOS inhibitor injected(icv) 15 min prior to daily morphine injection could prevent the development of morphine dependence. (5) All the changes above were not observed in mice treated with naloxone 30 min prior to daily morphine injection. Our data suggest that the reduction of cGMP contents and the increase of calciumdependent NOS activity in striatum and cerebral cortex isolated from morphinedependent mice may be mediated by opioid receptors and involved in the development of morphinedependence. Why the increase of NOS activity was in association with the reduction of cGMP contents remains to be answered and it implies that the effect of NO/NOS involved in morphinedependence may be produced through other mechanisms other than those producing cGMP signal. NOS phosphorylation in some other brain regions, which may be regulated by PKA, probably contributes to the increase of NOS activity in morphinedependent mice.