Altered Midbrain GABAergic Circuitry Drives Greater Cocaine Self-administration

项目摘要。 可卡因在很大程度上是被滥用最广泛的精神刺激剂，它仍然是主要的公众 美国的健康问题。可卡因的使用量正在缓慢下降，但近年来可卡因的使用量有所回升。 可卡因滥用伴随着与可卡因有关的住院和死亡人数急剧增加。这些事实 强调需要有效的药物来治疗可卡因使用障碍(CUD)，因为目前没有FDA- 批准的治疗CUD的药物治疗。我们令人兴奋的初步结果突出了一种新的分子 可作为目标以减轻或防止吸食和寻找可卡因的底物。具体地说，我们展示了 可卡因暴露改变KCC2的表达，KCC2是一种定义中脑氯离子梯度的K-氯-共转运体 GABA神经元。重要的是，这种可卡因诱导的神经适应与脑内神经回路的改变有关 促进和提高可卡因进一步摄入的中脑GABA神经元。这些发现支持这项工作 一种假说认为，最初服用可卡因改变了中脑GABA能回路，并增加了 随着时间的推移，可卡因的消费量会增加。因此，KCC2是治疗CUD的潜在靶点。 KCC2主要在中枢神经系统中表达，并适用于治疗操作 在人类身上。KCC2作为治疗靶点非常有吸引力，因为它通常具有极高的结构性活性。 因此，当正常受试者接受KCC2激活剂治疗时，KCC2活性已经很高，以至于 进一步增加其活性的尝试不会产生有害的副作用。在正常生理状态下 条件下，KCC2维持超极化、抑制所需的低神经元内氯离子浓度 GABA能电流。我们的初步结果表明，可卡因呈剂量依赖性地下调KCC2功能 在中脑GABA神经元中，从而改变了中脑GABA能回路。作为这些电路的结果 变化，KCC2的下调导致可卡因自我给药增加。也就是说，可卡因本身就是通过 下调KCC2，使重度可卡因自我管理永久化。我们的初步结果表明，如果我们 阻止KCC2下调或纠正KCC2功能，我们就减少了可卡因的自我给药。 这项提议的总体目标是描述中脑GABA能回路的功能状态 以及KCC2功能在可卡因自我给药、灭绝和恢复过程中的处置 寻找可卡因(目标1和2)。在成瘾周期的每个阶段，我们将确定 中脑GABA能回路作为可卡因摄取或寻求的因果贡献者。最后，我们将应用两个 机制不同的药物疗法以增强KCC2功能以减少可卡因的自我给药和 戒毒期间的可卡因寻觅行为(Aim3)。这些与翻译相关的研究将测试潜在的 促进KCC2功能的治疗药物缓解由KCC2引起的可卡因自我给药增强 可卡因本身。建议将KCC2作为缓解慢性阻塞性肺疾病的新的治疗靶点的研究是及时的，高度的 重要的、适当地针对过渡到大量使用可卡因的因素。

Project Summary. Cocaine is the most widely abused psychostimulant by a wide margin, and it remains a major public health problem in the US. Cocaine use was slowly declining, but in recent years there has been a resurgence in cocaine abuse accompanied by a sharp increase in cocaine-related hospitalizations and deaths. These facts highlight the need for effective medications for cocaine use disorder (CUD) because there are presently no FDA- approved pharmacologic treatments for CUD. Our exciting preliminary results highlight a novel molecular substrate that could be targeted to attenuate or prevent cocaine taking and seeking. Specifically, we show that cocaine exposure alters the expression of KCC2, a K+-Cl- cotransporter that defines the Cl- gradient in midbrain GABA neurons. Importantly, this cocaine-induced neuroadaptation is associated with circuitry changes in midbrain GABA neurons that promote and elevate further cocaine taking. These findings support the working hypothesis that initial cocaine taking alters midbrain GABAergic circuitry and increases the vulnerability for increased cocaine consumption over time. Thus, KCC2 represents a potential therapeutic target to treat CUD. KCC2 is expressed primarily in the central nervous system, and it is amenable to therapeutic manipulation in humans. KCC2 is highly attractive as a therapeutic target because it is usually constitutively highly active. Therefore, when normal subjects are treated with KCC2 activators, KCC2 activity is already high, such that attempts to increase its activity further do not produce deleterious side effects. Under normal physiological conditions, KCC2 maintains a low intra-neuronal Cl- concentration required for hyperpolarizing, inhibitory GABAergic currents. Our preliminary results indicate that cocaine dose-dependently downregulates KCC2 function in midbrain GABA neurons, thereby altering midbrain GABAergic circuitry. As a consequence of these circuitry changes, downregulation of KCC2 leads to increased cocaine self-administration. That is, cocaine use itself, by downregulating KCC2, perpetuates heavy cocaine self-administration. Our preliminary results indicate that if we prevent KCC2 downregulation or correct KCC2 function, then we decrease cocaine self-administration. The overall goal of this proposal is to characterize the functional state of the midbrain GABAergic circuitry and the disposition of KCC2 function during cocaine self-administration, extinction, and the reinstatement of cocaine seeking (Aims1 & 2). At each phase of the addiction cycle, we will determine the functional state of the midbrain GABAergic circuitry as a causal contributor to cocaine taking or seeking. Finally, we will apply two mechanistically different pharmacotherapies to boost KCC2 function to decrease cocaine self-administration and cocaine-seeking behavior during abstinence (Aim3). These translationally-relevant studies will test potential therapeutic drugs acting to boost KCC2 function to mitigate enhanced cocaine self-administration induced by cocaine itself. The proposed studies of KCC2 as a novel therapeutic target to mitigate CUD are timely, highly significant, and appropriately aimed at the factors underlying the transition to heavy cocaine use.