Neuromodulatory mechanisms underlying vagus nerve stimulation therapy for Alzheimer's disease

摘要/摘要 阿尔茨海默病(AD)的认知缺陷与突触丢失和慢性 皮质和海马区小胶质细胞的炎性激活。促进觉醒的蓝斑(LC) 神经元密集地投射到记忆相关的联合皮质区域，在那里它们释放去甲肾上腺素。 (NE)。这种去甲肾上腺素的释放促进了神经元的突触可塑性，并促进了局部的抗炎作用。 小胶质细胞。值得注意的是，LC神经元是AD中最先退化的神经元之一。总之，这些发现导致了 阿尔茨海默病早期LC神经元丢失可能通过觉醒减少、减少而损害认知的假说 突触可塑性，以及由于吞噬小胶质细胞的炎症激活而增加的突触丢失。此外， 最近的理论认为，衰老和阿尔茨海默病中持续的外周炎症可能最终导致退变 LC神经元，通过孤束核调节迷走神经至LC的通路 一条小路。因此，慢性迷走神经刺激(VNS)已被用于治疗难治性抑郁症。 AD的危险因素。此外，慢性VNS在AD患者的初步研究中显示出了希望，导致 改善认知，延缓疾病进展。假设VNS的行为影响是 由于剩余LC神经元的激活增加，导致皮质和大脑中NE释放的增加 海马体。然而，动物研究表明，在低刺激下，迷走神经并不推动去甲肾上腺素的释放 强度。在更高的强度下，在人类中传递VNS会导致不适感觉(例如，在 喉咙和颈部)和咳嗽/心动过缓，这是由于大量电刺激迷走神经所致的非靶点效应。 这些偏离目标的效应严重阻碍了临床疗效。在这里，我们建议发展小说 通过慢性刺激迷走神经传入的特定亚群来改善VNS的策略 支配着特定的器官。我们的目标是使用小鼠模型来开发一种刺激方案 有效地促进皮质中NE的释放，使其达到足以调节觉醒、突触可塑性和 小胶质细胞被激活，但这并不会促使人们有意识地意识到刺激。首先，我们将 制定刺激特定的基因和解剖学定义的迷走神经传入的方案，以 改善去甲肾上腺素的释放和耐受性。然后，我们将在清醒的小鼠中使用3D双光子成像来询问，在 迷走神经传入刺激强度低于行为检测阈值，释放足够的NE 驱动皮质树突棘和小胶质细胞的分子信号。然后我们将使用这种刺激方法 逆转阿尔茨海默病模型中小胶质细胞的炎性激活。我们将独一无二地准备好 迅速实现这一目标，通过我们实验室的努力，包括有意识地意识到 刺激小鼠特定迷走神经传入亚型(DP1亲本赠与)，我们的初步数据 成像/刺激皮质LC轴突和成像A-β诱发的皮质小胶质细胞变化。这些 实验将为AD的认识和治疗策略提供新的研究方向。

SUMMARY/ABSTRACT Cognitive deficits in Alzheimer's disease (AD) have been associated with synapse loss and chronic inflammatory activation of microglia in cortex and hippocampus. Arousal-promoting locus coeruleus (LC) neurons densely project to memory-related regions of association cortex, where they release norepinephrine (NE). This NE release facilitates synaptic plasticity in neurons and drives anti-inflammatory effects in local microglia. Notably, LC neurons are among the first to degenerate in AD. Together, these findings have led to the hypothesis that early loss of LC neurons may impair cognition in AD via decreased arousal, decreased synaptic plasticity, and increased synapse loss due to inflammatory activation of phagocytic microglia. Further, recent theories posit that sustained peripheral inflammation in aging and AD may ultimately drive degeneration of LC neurons, via dysregulation of the pathway from the vagus nerve to LC via the nucleus of the solitary tract. Accordingly, chronic vagus nerve stimulation (VNS) has been used to treat drug-resistant depression, a risk factor for AD. Further, chronic VNS has shown promise in preliminary studies in AD patients, resulting in improved cognition and delayed disease progression. The behavioral effects of VNS are hypothesized to be due to increased activation of the remaining LC neurons and a resulting increase in NE release in cortex and hippocampus. However, animal studies show that VNS does not drive release of NE at low stimulation intensities. At higher intensities, VNS delivery in humans can result in uncomfortable sensations (e.g. in the throat and neck) and cough/bradycardia due to off-target effects of bulk electric stimulation of the vagus nerve. These off-target effects represent serious obstacles to clinical efficacy. Here, we propose to develop novel strategies for improved VNS via chronic stimulation of specific subsets of vagal nerve afferents innervating particular organs. Our goal is to use mouse models to develop a stimulation protocol that effectively drives NE release in cortex at levels sufficient to regulate arousal, synaptic plasticity, and microglial activation, but that does not drive conscious awareness of the stimulation. First, we will develop protocols for stimulation of specific genetically and anatomically defined sets of vagal afferents, to improve both release of NE and tolerability. We will then use 3D two-photon imaging in awake mice to ask if, at vagal afferent stimulation intensities below the threshold for behavioral detection, sufficient NE is released to drive molecular signaling in cortical dendritic spines and microglia. We will then use this stimulation approach to revert inflammatory activation of microglia in a model of Alzheimer's disease. We are uniquely poised to rapidly achieve this goal, by building on efforts in our lab involving studies of conscious awareness of stimulation of specific vagal afferent subtypes in mice (DP1 parent grant), our preliminary data imaging/stimulating LC axons in cortex and imaging Aβ-evoked changes in cortical microglia. These experiments will support a novel research direction to strategies for understanding and treatment of AD.