Altered Midbrain GABAergic Circuitry Drives Greater Cocaine Self-administration

项目摘要。 可卡因是最广泛滥用的精神兴奋剂，它仍然是一个主要的公众 美国的健康问题。可卡因的使用量在缓慢下降，但近年来又出现了复苏。 可卡因滥用伴随着与可卡因有关的住院和死亡急剧增加。这些事实 强调需要有效的药物治疗可卡因使用障碍（CUD），因为目前没有FDA- 已批准的CUD药物治疗。我们令人兴奋的初步结果突出了一种新的分子 可以靶向减弱或防止可卡因服用和寻求的基质。具体来说，我们表明， 可卡因暴露改变了KCC 2的表达，KCC 2是一种定义中脑Cl-梯度的K+-Cl-协同转运蛋白 GABA神经元。重要的是，这种可卡因诱导的神经适应与神经元回路的变化有关。 中脑GABA神经元，促进和提高进一步的可卡因服用。这些发现支持了工作 假设最初的可卡因服用改变了中脑GABA能回路，并增加了对 随着时间的推移，可卡因消费量增加。因此，KCC 2代表了治疗CUD的潜在治疗靶点。 KCC 2主要在中枢神经系统中表达，并且它适合于治疗操作 在人类身上。KCC 2作为治疗靶点是非常有吸引力的，因为它通常是组成性高活性的。 因此，当正常受试者用KCC 2激活剂治疗时，KCC 2活性已经很高，使得 进一步增加其活性的尝试不会产生有害的副作用。在正常生理条件下 条件下，KCC 2保持低的神经元内Cl-浓度所需的超极化，抑制 GABA能电流。我们的初步结果表明，可卡因剂量依赖性下调KCC 2功能 在中脑GABA神经元中，从而改变中脑GABA能回路。由于这些电路 在这些变化中，KCC 2的下调导致可卡因自我给药增加。也就是说，可卡因使用本身， 下调KCC 2，使大量可卡因自我给药永久化。我们的初步结果表明， 阻止KCC 2下调或纠正KCC 2功能，然后我们减少可卡因自我给药。 本提案的总体目标是描述中脑GABA能回路的功能状态 以及可卡因自我给药、消退和恢复过程中KCC 2功能的分布， 可卡因寻求（目标1和2）。在成瘾周期的每一个阶段，我们将确定 中脑GABA能回路作为服用或寻求可卡因的因果贡献者。最后，我们将应用两个 机制上不同的药物疗法，以提高KCC 2功能，减少可卡因自我给药， 戒断期间的可卡因寻求行为（Aim 3）。这些与医学相关的研究将测试 用于增强KCC 2功能以减轻由以下引起的可卡因自我给药增强的治疗药物： 可卡因本身KCC 2作为缓解CUD的新治疗靶点的拟议研究是及时的，高度 意义重大，并适当地针对过渡到大量使用可卡因的潜在因素。

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.