Department of Pharmacology, The University of Arizona, Tucson, AZ 85724, USA.
J Neurosci Methods. 2011 Jul 15;199(1):62-8. doi: 10.1016/j.jneumeth.2011.04.036. Epub 2011 May 6.
Sustained morphine treatment has been shown to produce paradoxical pain sensitization (opioid-induced hyperalgesia) and also causes increase in spinal pain neurotransmitter, such as calcitonin gene related peptide (CGRP), concentration in experimental animals. Studies have also shown that cyclic adenosine-monophosphate (cAMP)-dependent protein kinase (PKA) plays a major role in the regulation of presynaptic neurotransmitter (such as CGRP and substance P) synthesis and release. We have previously shown that in cultured primary sensory dorsal root ganglion (DRG) neurons sustained in vitro opioid agonist treatment upregulates cAMP levels (adenylyl cyclase (AC) superactivation) and augments basal and capsaicin evoked CGRP release in a PKA dependent manner. In the present study, we investigated the in vivo role of PKA in sustained morphine-mediated pain sensitization. Our data indicate that selective knock-down of spinal PKA activity by intrathecal (i.th.) pretreatment of rats with a PKA-selective small interference RNA (siRNA) mixture significantly attenuates sustained morphine-mediated augmentation of spinal CGRP immunoreactivity, thermal hyperalgesia, mechanical allodynia and antinociceptive tolerance. The present findings indicate that sustained morphine-mediated activation of spinal cAMP/PKA-dependent signaling may play an important role in opioid induced hyperalgesia.
持续的吗啡治疗已被证明会产生矛盾的疼痛敏化（阿片类药物引起的痛觉过敏），并且还会导致脊髓疼痛递质（如降钙素基因相关肽（CGRP））的浓度增加。研究还表明，环腺苷酸-单磷酸（cAMP）依赖性蛋白激酶（PKA）在调节前突触神经递质（如 CGRP 和 P 物质）的合成和释放中起主要作用。我们之前已经表明，在培养的原代感觉背根神经节（DRG）神经元中，持续的体外阿片类激动剂治疗上调 cAMP 水平（腺苷酸环化酶（AC）超活化），并以 PKA 依赖的方式增强基础和辣椒素诱发的 CGRP 释放。在本研究中，我们研究了 PKA 在持续吗啡介导的疼痛敏化中的体内作用。我们的数据表明，通过鞘内（i.th.）预处理大鼠用 PKA 选择性小干扰 RNA（siRNA）混合物选择性敲低脊髓 PKA 活性，显著减弱了持续吗啡介导的脊髓 CGRP 免疫反应性、热痛觉过敏、机械性痛觉过敏和抗伤害性耐受的增强。本研究结果表明，持续吗啡介导的脊髓 cAMP/PKA 依赖性信号转导的激活可能在阿片类药物引起的痛觉过敏中起重要作用。
