Persistent Pain and Mu Opioid Actions in Locus Coeruleus

描述（由申请人提供）： 蓝斑（LC）是唤醒、记忆、自主神经功能和压力整合的纽带。它也是阿片类药物调节急性伤害性感受的重要部位。相对而言，很少有人知道LC在持续性疼痛过程中的功能，或者持续性疼痛状态如何改变LC神经元的反应。初步数据表明，DAMGO，一种选择性μ阿片受体（莫尔）激动剂，在具有持续炎症的大鼠的LC中的功效大大降低，所述持续炎症是通过在后爪中注射完全弗氏佐剂（CFA）产生的。我们假设持续性疼痛状态可能诱导（1）LC中内源性阿片肽的持续释放，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，可能降低激动剂疗效或导致受体下调。将阿片样物质受体拮抗剂显微注射到CFA或盐水处理的大鼠的LC中，以确定它们是否产生或加剧热痛觉过敏，这表明内源性阿片样物质激动剂的释放增加。将通过RIA和ELISA测定盐水和CFA处理的大鼠的LC中这些肽的水平。放射性配体结合研究将确定来自盐水和CFA处理的大鼠的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蛋白酪氨酸磷酸酶和激酶的抑制如何改变DAMGO在盐水和CFA处理的大鼠中的作用。这些研究将为持续性疼痛状态如何改变阿片类镇痛药的作用以及在持续性疼痛条件下发生的适应性变化提供新的见解。它们还可能为内源性阿片耐受性和依赖性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.