Neurobiology of stress in the cerebellar circuitry

摘要 儿童时期的社会隔离（SI）增加了对神经精神疾病（包括焦虑）的易感性 精神障碍抑郁症和认知障碍对这些疾病的有限治疗突出了 确定新的治疗靶点的重要性。最近的证据强调了小脑的作用 早期生活压力的影响例如，新生儿小脑含有最高水平的糖皮质激素受体 (GR)在整个大脑中，这表明小脑富含分子机制，用于处理 应激反应小脑广泛地连接到对心理敏感的大脑网络， 应力然而，SI应激是否以及如何调节小脑中的基因表达，从而导致小脑 功能障碍和适应不良行为仍然难以捉摸。为了解决知识差距，我们分离了实验性的 小鼠单独圈养在笼子里。他们表现出的行为变化让人联想到高度焦虑，抑郁， 社交记忆丧失此外，我们发现SI损害浦肯野细胞（PC）的内在兴奋性， 小脑皮质的输出神经元小脑基因表达对应激刺激有高度反应 例如啮齿类动物体内皮质酮（一种应激激素）的升高。这些发现为我们的核心假设提供了依据 SI通过特异性地影响PC的内在兴奋性来损害小脑输出活动; PC兴奋性通过小脑-皮质网络纠正SI引起的行为缺陷。为了验证这个假设， 我们提出了一个多学科的方法，有三个具体目标：（1）确定减少的分子基础 PC固有兴奋性（SI）。我们将采用两种全基因组RNA测序技术， 无偏见的看法转录签名和表观遗传修饰的SI以及鉴定SI响应 PC中的离子通道，例如，Kv1.5。GR的PC特异性敲除将揭示GR依赖的基因组 由SI重新编程。(2)定义PC活性在SI全身反应中的意义。利用病毒基因 转移，我们将获得精确的时空控制的PC兴奋性，以测试的必要性和充分性， 小脑活动介导对SI的全系统反应。(3)详细说明小脑皮层通道 SI的潜在适应不良行为我们的努力将集中在解剖神经回路， 小脑到下游的亚/皮层区域及其对SI行为表型的贡献。 这项工作的完成将促进我们对分子、细胞和电路机制的理解 支持小脑在应激反应中的非传统作用，结果将最终 帮助开发新的治疗策略，以改善心理健康。

ABSTRACT Social isolation (SI) during childhood increases the susceptibility to neuropsychiatric disorders, including anxiety disorders, depression, and cognitive impairments. Limited treatment for these disorders highlights the importance of identifying new therapeutic targets. Recent evidence has underscored the role of the cerebellum in early-life stress. For example, the neonatal cerebellum contains the highest level of glucocorticoid receptor (GR) in the entire brain, indicating that the cerebellum is enriched in the molecular machinery for processing the stress response. The cerebellum is extensively connected to brain networks that are sensitive to psychological stress. However, whether and how SI stress regulates gene expression in the cerebellum to result in cerebellar dysfunction and maladaptive behaviors remain elusive. To address the knowledge gap, we isolated experimental mice in singly housed cages. They displayed behavioral changes reminiscent of high anxiety, depression, and social memory loss. Moreover, we found that SI impaired intrinsic excitability of Purkinje cells (PCs), the sole output neurons in the cerebellar cortex. And cerebellar gene expression was highly responsive to stress stimuli such as an elevation of corticosterone, a stress hormone, in rodents. These findings fuel our central hypothesis that SI impairs the cerebellar output activity by specifically affecting the intrinsic excitability of PCs; and restoring PC excitability rectifies SI-caused behavioral deficits via the cerebello-cortical networks. To test the hypothesis, we propose a multidisciplinary approach with three specific aims: (1) Determine the molecular basis of reduced PC intrinsic excitability by SI. We will employ two genome-wide RNA sequencing techniques to obtain an unbiased view of transcriptional signatures and epigenetic modifications of SI as well as to identify SI-responsive ion channels in PCs, e.g., Kv1.5. PC-specific knockout of GR will uncover the GR-dependent genomic reprogramming by SI. (2) Define the significance of PC activity in systemic response to SI. Using viral gene transfer, we will gain precise spatiotemporal control of PC excitability to test the necessity and sufficiency of cerebellar activity in mediating the system-wide response to SI. (3) Specify the cerebellum-cortex gateways underlying maladaptive behaviors of SI. Our efforts will be focused on dissecting the neural circuits that connect the cerebellum to the downstream sub/cortical areas and their contributions to the behavioral phenotypes of SI. Completion of this work will advance our understanding of the molecular, cellular and circuitry mechanisms underpinning the non-conventional role of the cerebellum in the stress response, and the results will ultimately help develop novel therapeutic strategies to improve mental health.