Role of GABA Interneurons in the Rapid Antidepressant Actions of NMDA Receptor Blockade

重度抑郁症（MDD）是世界范围内最普遍和最令人衰弱的疾病之一，影响着 约占人口的17%，造成巨大的个人和经济负担。MDD的影响是 由于现有药物的局限性，包括反应率低，治疗 耐药患者和时滞（周-月）。这些数据突出了对更有效的药物的主要未满足的需求。 和更快起效的抗抑郁药。最近的研究表明，单次低剂量的氯胺酮， 谷氨酸-NMDA受体拮抗剂，产生快速的抗抑郁作用（2小时），持续长达7天， 耐药患者。这种快速的作用，通过一种与典型的单胺完全不同的机制 再摄取抑制剂，代表了过去6年来抑郁症领域最重要的进展之一。 几十年我们已经报道过氯胺酮引起内侧皮层突触连接的快速增加， 前额叶皮层（mPFC），其靶向和纠正由慢性压力引起的突触缺陷， 萧条尽管取得了这一进展，但氯胺酮的突触作用的细胞机制， 增加的谷氨酸传输尚未确定。我们假设最初的触发因素 氯胺酮的快速作用是阻断刺激GABA中间神经元紧张性放电的NMDA受体， 导致谷氨酸传递的去抑制和mPFC中突触形成的增加。可选择地， 氯胺酮可直接作用于锥体神经元。本申请描述了一个综合的多学科 方法，包括分子，生物化学，电生理学，形态学和行为学研究，以测试 这个去抑制假说。目的1将使用细胞类型特异性敲低GABA上的NMDA受体 中间神经元亚型以及mPFC中的锥体神经元。根据药理学证据， GluN 2B亚基将通过表达GluN 2B shRNA和细胞特异性Cre 重组酶转基因株系。初步结果表明，氯胺酮的快速行为作用是 阻断GABA中间神经元上的GluN 2B敲低，与去抑制假说一致。目标2将 通过表征生长抑素（SST）的NMDA/GluN 2B受体调节来扩展这些研究， 小清蛋白（PV）中间神经元亚型的膜片钳记录，以确定细胞基础， 这些中间神经元的NMDA和氯胺酮敏感性的差异。氯胺酮对抑制性脑缺血的影响 可塑性也将被确定，GABA中间神经元亚型在氯胺酮作用中的作用将被确定。 使用细胞特异性光遗传学方法测试。据报道，压力和抑郁会改变GABA 神经传递对女性的影响大于男性。AIM 3将使用报告小鼠来确定 GABA中间神经元亚型在慢性应激和卵巢类固醇的影响，包括分子， 细胞和转录反应。表征的细胞机制的基础上的行动 氯胺酮、慢性压力和卵巢类固醇将为更安全、快速起效的抗抑郁药提供新的靶点。

Major depressive disorder (MDD) is one of the most prevalent and debilitating illnesses world wide, affecting ~17 percent of the population and causing enormous personal and economic burden. The impact of MDD is underscored by the limitations of currently available medications, including low response rates, treatment resistant patients, and time-lag (weeks-months). These data highlight a major unmet need for more efficacious and faster-acting antidepressant agents. Recent studies demonstrate that a single low dose of ketamine, a glutamate-NMDA receptor antagonist, produces rapid antidepressant actions (2 hr) that last for up to 7 days in treatment resistant patients. This rapid action, by a mechanism completely different from typical monoamine reuptake inhibitors, represents one of the most significant advances in the field of depression over the past 6 decades. We have reported that ketamine causes a rapid increase of synaptic connections in the medial prefrontal cortex (mPFC), which targets and corrects the synaptic deficits caused by chronic stress and depression. Despite this progress, the cellular mechanisms underlying the synaptic actions of ketamine, and increased glutamate transmission have not been determined. We hypothesize that the initial trigger for the rapid actions of ketamine is blockade of NMDA receptors that stimulate tonic firing of GABA interneurons, resulting in disinhibition of glutamate transmission and increased synapse formation in mPFC. Alternatively, ketamine could act directly on pyramidal neurons. This application describes an integrated multidisciplinary approach, including molecular, biochemical, electrophysiological, morphological, and behavioral studies to test this disinhibition hypothesis. Aim 1 will use cell type specific knockdown of NMDA receptors on GABA interneuron subtypes as well as pyramidal neurons in the mPFC. Based on pharmacological evidence, the GluN2B subunit will be targeted using viral expression of floxed-GluN2B shRNA and cell specific Cre recombinase transgenic lines. Preliminary results indicate that the rapid behavioral actions of ketamine are blocked by GluN2B knockdown on GABA interneurons, consistent with the disinhibition hypothesis. Aim 2 will extend these studies by characterizing NMDA/GluN2B receptor regulation of somatostatin (SST) and parvalbumin (PV) interneuron subtypes by patch recordings in reporter mice to identify the cellular basis for differences in NMDA and ketamine sensitivity of these interneurons. The influence of ketamine on inhibitory plasticity will also be determined, and the role of GABA interneuron subtypes in the actions of ketamine will be tested using cell specific optogenetic approaches. Stress and depression are reported to alter GABA neurotransmission with greater effects in women than men. Aim 3 will use reporter mice to determine the role of GABA interneuron subtypes in the effects of chronic stress and ovarian steroids, including molecular, cellular, and transcriptional responses. Characterization of the cellular mechanisms that underlie the actions of ketamine, chronic stress, and ovarian steroids will provide novel targets for safer, rapid-acting antidepressants.