Circadian behavior circuits, Alzheimer’s pathology, chemogenetic output and input

阿尔茨海默病（AD）和相关痴呆与昼夜节律的进行性破坏有关。阿尔茨海默病及相关痴呆患者昼夜节律功能障碍的一个特殊特征是“日落综合征”，这是一种鲜为人知的临床现象，其特征是在傍晚时分躁动、攻击性和谵妄。日落的神经生物学尚不清楚，但其症状的时间周期性表明，主生物钟、下丘脑视交叉上核（SCN）或SCN调节特定节律的途径可能受到干扰。内在光敏性视网膜神经节细胞（RGCs）表达光色素黑视素，通过视网膜下丘脑束（RHT）投射到SCN，并在每日的光暗循环中引导其活动。Clifford Saper博士的实验室已经证明，睡眠-觉醒和运动活动（LMA）节律是由SCN通过其主要的突触后靶点室旁下区（SPZ）到下丘脑背内侧（DMH）的一条通路来调节的。最近，我在萨珀博士实验室的博士后工作发现，雄性小鼠的攻击倾向也遵循由gaba能SPZ神经元调节的日常节奏。这项工作进一步证明，这些SPZGABA神经元接受来自SCN的功能输入，以相位依赖的方式活跃，并投射到驱动攻击行为的下丘脑腹内侧（VMH）神经元，共同表明中央昼夜节律钟在24小时内控制攻击倾向的新途径。重要的是，我发现破坏SCN􀀂SPZ􀀂VMH通路导致在早期休息阶段（夜间小鼠的光照期）攻击性增加，这在时间上类似于经历日落的患者表现出增加的躁动和攻击性。这表明，该回路中某些结构的功能可能在阿尔茨海默病和相关痴呆中受到损害，并且该途径可能是治疗显示日落患者的昼夜节律功能障碍和攻击的有希望的治疗靶点。我开始通过检查TAPP小鼠（也称为appsw - tau）的昼夜节律来验证这一假设，TAPP小鼠会产生淀粉样蛋白斑块和tau神经原纤维缠结（两者都是AD神经病理学的标志）。我发现这些小鼠在已知发生ad相关神经病理后不久，就表现出早期静息期攻击性增加和活动期LMA减弱。在本提案中，我试图通过检查这些小鼠的脑组织中SCN， SPZ及其输出目标VMH和DMH中的a- β和tau来扩展这项工作。据推测，与日落相关的昼夜节律功能障碍可能是ad相关的干扰对昼夜节律系统提供输入的区域造成的，例如血清素能和胆碱能通路，我也将研究ad相关的神经病理学在这些区域。我还将评估所有这些途径中的细胞损失，以及视网膜中的细胞损失（特别是投射并携带SCN的rgc）。最后，我试图确定操纵SPZ和RGC活动（使用化学发生激活）对TAPP小鼠攻击性增加和昼夜睡眠-觉醒节律减弱的影响，以及对AD神经病理模式的影响。虽然日落是一个重要的临床问题，但很少有研究关注昼夜节律系统如何影响躁动和攻击，而且几乎没有研究这些回路如何受到AD的影响。研究这些神经回路，并确定对其神经元活动的操纵是否可以改善小鼠AD相关的行为障碍，可能会指出一种最终的治疗方法，可以极大地提高AD患者及其照顾者的生活质量。

Alzheimer’s disease (AD) and related dementias are associated with progressive disruption of circadian rhythms. One particular feature of circadian dysfunction in patients with AD and related dementias is “sundowning syndrome”, a poorly understood clinical phenomenon characterized by agitation, aggression, and delirium during the early evening hours. The neurobiology of sundowning remains unknown, however the temporal periodicity of it symptoms suggests a possible disturbance in the master circadian clock, the suprachiasmatic nucleus (SCN) of the hypothalamus, or in the pathways by which the SCN modulates particular rhythms. Intrinsically photosensitive retinal ganglion cells (RGCs), that express the photopigment melanopsin, project to the SCN via the retinohypothalamic tract (RHT) and entrain its activity the daily lightdark cycle. Dr. Clifford Saper’s lab has shown that sleep-wake and locomotor activity (LMA) rhythms are regulated by the SCN via a pathway through its major postsynaptic target, the subparaventricular zone (SPZ), to the dorsomedial hypothalamus (DMH). More recently, my work postdoctoral work in Dr. Saper’s lab revealed that aggression propensity in male mice also follows a daily rhythm that is regulated by GABAergic SPZ neurons. This work further demonstrated that these SPZGABA neurons receive functional input from the SCN, are active in a phase-dependent manner, and project to neurons within the ventromedial hypothalamus (VMH) that drive attack behavior, altogether suggesting a novel pathway by which the central circadian clock gates aggression propensity across the 24h day. Importantly, I found that disrupting the SCN􀀂SPZ􀀂VMH pathway led to increased aggression during the early resting phase (the light period for nocturnal mice), which is temporally analogous to when patients who experience sundowning display increased agitation and aggression. This suggests that the function of certain structures within this circuit may be compromised in AD and related dementias, and that this pathway may be a promising therapeutic target for treating circadian dysfunction and aggression in patients who display sundowning. I began testing this hypothesis by examining circadian rhythms in TAPP mice (also known as APPSwe-Tau), which develop amyloid-beta (a-beta) plaques and tau neurofibrillary tangles (both hallmarks of AD neuropathology). I found that these mice exhibit increased early resting period aggression and blunted active period LMA at ages shortly after they are known to develop AD-related neuropathology. In this proposal, I seek to expand on this work by examining brain tissue from these mice for a-beta and tau in the SCN, the SPZ, and their output targets the VMH and the DMH. It has been hypothesized that circadian dysfunction associated with sundowning may instead result from AD-related disturbances to areas that provide input to the circadian system, such as serotoninergic and cholinergic pathways, and I will also examine AD-related neuropathology in such areas. I will also assess cell loss in all of these pathways, as well as in the retina (specifically RGCs that project to and entrain the SCN). Finally, I seek to determine the effects of manipulating SPZ and RGC activity (using chemogenetic activation) on increased aggression and blunted circadian sleep-wake rhythms in TAPP mice, and on the patterns of AD neuropathology. While sundowning is an important clinical problem, there has been little work focused on how the circadian system effects agitation and aggression, and almost none on how such circuits are affected by AD. Interrogating such circuits, and determining whether manipulation of their neuronal activity can ameliorate AD-related behavioral disturbances in mice, may point to an eventual therapy that could greatly improve quality of life for AD patients and their caregivers.