Signaling balance and opioid dependence

阿片类药物是缓解严重疼痛的基本药物，目前还没有替代药物。 术后及其他严重指征。然而，长期使用阿片类药物会导致许多副作用， 以及物质使用障碍(SUD)的巨大风险。SUD或“成瘾”的诊断依据是行为 广泛表现为失控或“强迫性”吸毒和决策障碍的特征 或“认知灵活性”，即使在几个月到几年的禁欲之后也是如此。然而，大多数临床前研究 毒品滥用的研究重点是吸毒和寻求奖励的模式，而不是 行为灵活性是人类肥皂水的基础。此外，对SUD机制的临床前研究已经被 仅限于比较已服药或未服药的动物。这使得人们很难将阿片类药物- 在生物学和行为上引起的改变，仅仅是由于那些实际背后的人接触毒品而发生的 流行性出血热的病理学我们已经开发了一种独特的工具来绕过阿片类药物滥用的这一重大混乱 研究。具体地说，我们已经开发出一种表达修饰的u阿片受体的敲入小鼠。 (MOR)具有改变的信令属性。当被其内源性配体、内啡肽和 脑啡肽通过G蛋白信号来控制神经元的活动。在G蛋白被激活后 内源性配体，大多数G蛋白偶联受体(GPCR)，包括MOR，然后迅速招募抑制素 这会抑制G蛋白信号，促进受体内吞作用，并促进MOR的快速循环。这 机制，从而仔细地滴定G蛋白信号，其精确度和时间进程非常适合响应 到以脉动方式释放的发射器。相比之下，吗啡激活的MORS及其所有的 衍生物有效地结合了G蛋白信号，但不能很好地结合阻滞剂。在gpcr的当前白话中 在药理学上，吗啡被称为一种“有偏见的”激动剂，它优先向G蛋白传递信号，而不是抑制素 内啡肽是一种“平衡”的激动剂，既能利用G蛋白，又能利用阻滞剂。RMOR受体是 被设计成在被吗啡激活时有效地结合G蛋白和arrestin而不改变 响应内源递质的信号传递。重要的是，在我们之前广泛的工作中，我们发现 RMOR小鼠不会对吗啡产生耐受性或依赖性，也不会过渡到强迫药物 在野生型(WT)小鼠的条件下寻找SUD模型。最近，我们发现虽然 吗啡导致WT小鼠认知灵活性的长期变化，这种影响在RMOR小鼠中也不存在。 在这里，我们将使用WT和RMOR小鼠来精确定位肥皂泡背后的分子和突触机制。 所有小鼠都接受药物治疗，但只有WT表现出病理性吗啡反应的范式。我们建议任何 吗啡引起的两种基因类型的变化可能反映了对药物暴露的反应，而 仅限于WT小鼠的变化可能有助于肥皂泡的病理。

Opioid drugs are essential medications for the relief of serious pain, with no substitutes currently available for postsurgical and other severe indications. Long term use of opioids, however, leads to numerous side effects, and to substantial risk of substance use disorder (SUD). SUD or “addiction” is diagnosed based on behavioral characteristics that manifest broadly as loss of control or “compulsive” drug seeking and impaired decision making or “cognitive flexibility” even after months to years of abstinence. However, the majority of preclinical research of drug abuse focuses on models of drug-taking and reward-seeking rather than on the long-lasting changes in behavioral flexibility that underlie human SUDs. In addition, preclinical studies of SUD mechanism have been limited to comparing animals that have or have not taken drug. This has made it difficult to dissociate opioid- induced changes in biology and behavior that occur merely due to drug exposure from those that actually underlie the pathology of a SUD. We have developed a unique tool to circumvent this significant confound in opioid abuse research. Specifically, we have developed a knock-in mouse that expresses a modified mu opioid receptor (MOR) with altered signaling properties. The MOR when activated by its endogenous ligands, endorphins and enkephalins, engages G protein signaling to control neuronal activity. Following G protein activation by endogenous ligand, most G protein coupled receptors (GPCR), including the MOR, then rapidly recruit arrestins that silence the G protein signal and promote receptor endocytosis and, for the MOR, rapid recycling. This mechanism thereby carefully titrates G protein signal with a precision and time course ideally suited to respond to transmitters that are released in a pulsatile manner. In contrast, MORs activated by morphine and all its derivates effectively engage G protein signaling but poorly engage arrestins. In the current vernacular of GPCR pharmacology, morphine is termed a “biased” agonist, signaling preferentially to G protein over arrestins while endorphins are “balanced” agonists, engaging both G proteins and arrestins. The RMOR receptor was engineered to effectively engage both G protein and arrestin when activated by morphine without altering signaling in response to endogenous transmitters. Importantly, in our extensive previous work, we have found that RMOR mice do not develop tolerance or dependence to morphine nor do they transition to compulsive drug seeking in a model of SUD under conditions where wild type (WT) mice do. More recently, we have found while morphine causes long-lasting changes in cognitive flexibility in WT mice, this effect is also absent in RMOR mice. Here we will use WT and RMOR mice to pinpoint molecular and synaptic mechanisms that underlie SUDs in a paradigm where all mice receive drug but only WT show pathologic morphine responses. We propose that any morphine-induced changes that occur in both genotypes is likely to reflect a response to drug exposure, whereas changes confined to WT mice likely contribute to the pathology of SUDs.