Persistent Pain and Mu Opioid Actions in Locus Coeruleus

描述(由申请人提供)： 蓝斑(LC)是整合觉醒、记忆、自主神经功能和应激的纽带。它也是阿片类药物调节急性伤害性感觉的重要部位。对于LC在持续性疼痛过程中的功能以及持续性疼痛状态如何改变LC神经元的反应，人们知之甚少。初步数据表明，阿片受体(MOR)选择性激动剂DAMGO对足部注射完全弗氏佐剂(CFA)所致的持续性炎症大鼠LC的药效显著降低。我们假设持续的疼痛状态可能导致(1)内源性阿片肽在LC中的持续释放，导致MORS的代偿性脱敏或下调，以及(2)MORS中酪氨酸残基的磷酸化，可能降低激动剂的疗效或导致受体下调。将阿片受体拮抗剂显微注射到CFA或生理盐水处理的大鼠的LC中，以确定它们是否产生或加剧热痛敏，这表明内源性阿片激动剂的释放增加。用RIA和ELISA法测定生理盐水和CFA处理大鼠LC中这些多肽的水平。放射性配基结合研究将确定生理盐水和CFA处理的大鼠LC匀浆中MORS的Kd和Bmax。最后，LC神经元的全细胞电压钳记录将确定抑制蛋白酪氨酸磷酸酶和蛋白酪氨酸激酶如何改变DAMGO对生理盐水和CFA处理大鼠的影响。这些研究将为持续疼痛状态如何改变阿片类止痛剂的作用，以及在持续疼痛条件下发生在冈上的适应性变化提供新的见解。它们还可能为内源性阿片类药物耐受和依赖的机制提供新的见解。

DESCRIPTION (provided by applicant): The locus coeruleus (LC) serves as a nexus for the integration of arousal, memory, autonomic function and stress. It is also an important site for the modulation of acute nociception by opioids. Comparatively little is known about the function of the LC during persistent pain or how persistent pain states may alter the responses of LC neurons. Preliminary data indicate that the efficacy of DAMGO, a selective mu opioid receptor (MOR) agonist, is greatly reduced in the LC of rats with sustained inflammation produced by injection of complete Freund's adjuvant (CFA) in the hindpaw. We hypothesize that persistent pain states may induce (1) a sustained release of endogenous opioid peptides in the LC that causes a compensatory desensitization or downregulation of MORs and (2) phosphorylation of tyrosine residues in MORs that may decrease agonist efficacy or cause receptor downregulation. Opioid receptor antagonists will be microinjected in the LC of CFA- or saline-treated rats to determine whether they produce or exacerbate thermal hyperalgesia, indicative of an increased release of endogenous opioid agonist. Levels of these peptides in the LC of saline- and CFAtreated rats will be determined by RIA and ELISA. Radioligand binding studies will determine the Kd and Bmax for MORs in homogenates of LC from saline and CFA-treated rats. Finally, whole-cell voltage clamp recordings of LC neurons will determine how inhibition of protein tyrosine phosphatases and kinases alters the effects of DAMGO in saline- and CFA-treated rats. These studies will provide new insights into how persistent pain states alter the actions of opioid analgesics, as well as the adaptive changes that occur supraspinally under conditions of persistent pain. They may also provide new insights into the mechanisms that underlie endogenous opioid tolerance and dependence.