Mao J, Price D D, Phillips L L, Lu J, Mayer D J
Department of Anesthesiology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298-0516, USA.
Brain Res. 1995 Apr 24;677(2):257-67. doi: 10.1016/0006-8993(95)00161-i.
Our previous studies have indicated a critical role of protein kinase C (PKC) in intracellular mechanisms of tolerance to morphine analgesia. In the present experiments, we examined (1) the cellular distribution of a PKC isoform (PKC gamma) in the spinal cord dorsal horn of rats associated with morphine tolerance by utilizing an immunocytochemical method and (2) the effects of the N-methyl-D-aspartate receptor antagonist MK-801 on tolerance-associated PKC gamma changes. In association with the development of tolerance to morphine analgesia induced by once daily intrathecal administration of 10 micrograms morphine for eight days, PKC gamma immunoreactivity was clearly increased in the spinal cord dorsal horn of these same rats. Within the spinal cord dorsal horn of morphine tolerant rats, there were significantly more PKC gamma immunostained neurons in laminae I-II than in laminae III-IV and V-VI. Such PKC gamma immunostaining was observed primarily in neuronal somata indicating a postsynaptic site of PKC gamma increases. Moreover, both the development of morphine tolerance and the increase in PKC gamma immunoreactivity were prevented by co-administration of morphine with 10 nmol MK-801 between Day 2 and Day 7 of the eight day treatment schedule. In contrast, PKC gamma immunoreactivity was not increased in rats receiving a single i.t. administration of 10 micrograms morphine on Day 8, nor did repeated treatment with 10 nmol MK-801 alone change baseline levels of PKC gamma immunoreactivity. These results provide further evidence for the involvement of PKC in NMDA receptor-mediated mechanisms of morphine tolerance.
我们之前的研究表明蛋白激酶C（PKC）在吗啡镇痛耐受性的细胞内机制中起关键作用。在本实验中，我们通过免疫细胞化学方法检测了（1）与吗啡耐受性相关的大鼠脊髓背角中PKC亚型（PKCγ）的细胞分布，以及（2）N-甲基-D-天冬氨酸受体拮抗剂MK-801对耐受性相关的PKCγ变化的影响。与通过每天鞘内注射10微克吗啡，连续八天诱导的吗啡镇痛耐受性的发展相关，这些大鼠脊髓背角中的PKCγ免疫反应性明显增加。在吗啡耐受大鼠的脊髓背角内，I-II层中PKCγ免疫染色的神经元明显多于III-IV层和V-VI层。这种PKCγ免疫染色主要在神经元胞体中观察到，表明PKCγ增加的突触后位点。此外，在八天治疗方案的第2天至第7天之间，将吗啡与10 nmol MK-801联合给药可防止吗啡耐受性的发展和PKCγ免疫反应性的增加。相比之下，在第8天接受单次鞘内注射10微克吗啡的大鼠中，PKCγ免疫反应性没有增加，单独用10 nmol MK-801重复治疗也没有改变PKCγ免疫反应性的基线水平。这些结果为PKC参与NMDA受体介导的吗啡耐受性机制提供了进一步的证据。
