CAMP CASCADE--ROLE IN OPIATE MODULATION OF NMDA CURRENTS

容忍和依赖是两个主要的问题， 临床效用和阿片类药物，并促进其滥用。蜂窝 这两个过程的机制都没有得到很好的理解。 据报道，阿片类药物会引起 细胞内cAMP级联反应，但仍不清楚这些 生化变化影响不同脑的突触传递 如果它们在发展容忍方面发挥重要作用， 和依赖。在海马齿状回，我们最近的研究 显示μ激动剂抑制NMDA受体介导的突触电流， 颗粒细胞通过G蛋白介导的机制。本项目 建议进一步检查急性和慢性的调节作用 阿片对齿状回NMDA电流的影响，并确定cAMP的作用 传递鸦片效应的级联反应。待评估的假设是 急性阿片类药物通过抑制cAMP依赖性的 颗粒细胞中的磷酸化，而cAMP级联的上调 慢性阿片类药物可能会极大地增强NMDA电流， 促进耐受性和依赖性的发展。为了验证这一 假设，诱发和自发NMDA电流将被记录从 海马脑片齿状回颗粒细胞的全细胞记录 技术.实验将集中在以下具体目标：1） 确定的类型和位置（突触前与突触后） 抑制NMDA电流的阿片受体。2)为了研究NMDA 电流通过操纵cAMP级联来调节，如果是急性的， 阿片样物质作用通过抑制cAMP级联介导。3)（4） 评估慢性吗啡如何改变NMDA电流和 颗粒细胞中的cAMP级联反应，如果这些改变有助于 发展宽容和依赖。

Tolerance and dependence are two major problems which interfere with the clinical utility & opiate drugs and promote their abuse. The cellular mechanisms underlying either process have not been well understood. Opiates reportedly induce dramatic changes in the activity of intracellular cAMP cascade in rat brain, but it remains unclear how these biochemical changes affect synaptic transmission in different brain regions and if they play an important role in the development of tolerance and dependence. In hippocampal dentate gyrus, our recent studies have shown that mu agonists inhibit NMDA receptor-mediated synaptic currents in granule cells through a G protein-mediated mechanism. The present project proposes to further examine the modulatory effect of acute and chronic opiate on NMDA currents in the dentate, and to determine the role of cAMP cascade in transducing opiate effects. The hypothesis to be evaluated is that acute opiates suppress NMDA currents by inhibiting cAMP-dependent phosphorylation in granule cells, while the upregulation of cAMP cascade by chronic opiates may profoundly enhance NMDA currents, which in turn facilitates the development of tolerance and dependence. To test this hypothesis, evoked and spontaneous NMDA currents will be recorded from dentate granule cells in the hippocampal slice using whole-cell recording techniques. Experiments will focus on following specific aims: 1) To determine the type(s) and location (presynaptic vs. postsynaptic) of opiate receptors that inhibit NMDA currents. 2) To examine how NMDA currents are modulated by manipulation of the cAMP cascade, and if acute opioid effects are mediated by inhibiting cAMP cascade. 3) and 4) To evaluate how chronic morphine alters NMDA currents and the activity of cAMP cascade in granule cells, and if these alterations contribute to the development of tolerance and dependence.