Does the central noradrenergic system play a role in agitation in Alzheimer's disease?

这项研究的背景是什么？阿尔茨海默病（AD）是痴呆症的最常见原因，随着疾病的发展，许多患有这种疾病的人会出现令人痛苦和难以治疗的行为。最令人痛苦和最具挑战性的行为之一是躁动，这是当痴呆症患者表现出情绪困扰以及过度活动、言语或身体攻击时。躁动大大降低了患者和护理人员的生活质量，经常导致住院或养老院，并与疾病快速进展和早期死亡有关。治疗躁动的唯一许可药物是一种抗精神病药物，它主要通过镇静患者起作用，可能导致危险的副作用，所以我们迫切需要更好、更安全、更有针对性的躁动治疗方法。阿尔茨海默病最早的大脑变化已被证明发生在靠近大脑底部的一个小结构，称为蓝斑（LC）。这种结构包含产生一种叫做去甲肾上腺素（NA）的化学物质（神经递质）的细胞，它在控制大脑对环境中明显或重要方面的反应方面起着重要作用。为了完成这一角色，左脑皮层连接并影响大脑中涉及控制情绪和抑制行为（反应抑制）的其他区域。有证据表明，在表现出攻击性或焦虑的年轻人以及患有AD的躁动患者中，这些大脑区域功能失调。我们知道，NA允许健康人的这些大脑区域正常发挥功能，但尚未有研究调查AD相关的LC变化（及其对NA活动的影响）是否会使AD患者更容易躁动。为了支持这一概念，有来自死后研究的一致证据表明，躁动的AD患者可能在他们的大脑中有一个更活跃的NA系统，以补偿更大的LC细胞损失。研究的目的是什么？如何进行？为了研究大脑中的na系统是否在AD患者的躁动中起作用，将要求50名AD伴躁动的参与者：进行磁共振成像（MRI）扫描，以测试更大的搅拌是否与LC功能和结构恶化有关。2. 完成行为测试，以测量他们的大脑调节情绪和抑制反应的能力，以及这是否与激动分数有关。3. 服用单剂量的心得安（一种治疗高血压的常用处方药，它也能阻断脑内NA的作用）来测试它是否能改善情绪调节和反应抑制。与AD患者相比，健康的老年人被认为具有更完整的LC-NA系统，因此50名没有认知障碍的健康志愿者（对照组）也将完成上述行为和药理学研究（2和3），以测试心得安是否影响健康老年人的情绪调节和反应抑制，以及这是否受到特质焦虑和愤怒评分的影响。潜在的影响和好处是什么？这项研究提供了一个独特的机会，进一步了解AD患者躁动背后的大脑过程，以及NA系统是否有作用。如果成功，这些发现有可能导致检测和治疗这种疾病的新方法，例如通过使用靶向NA系统的药物（如心得安）。

WHAT IS THE CONTEXT OF THIS RESEARCH?Alzheimer's disease (AD) is the most common cause of dementia, and many individuals with this condition develop distressing and difficult-to-treat behaviours as the disease progresses. One of the most distressing and challenging behaviours is agitation, which is when an individual with dementia shows emotional distress along with overactivity, verbal or physical aggression. Agitation substantially reduces quality of life for patients and caregivers, frequently precipitates admission to a hospital or nursing home and is associated with rapid disease progression and earlier death. The only licensed medication for agitation in dementia is an antipsychotic drug, which works primarily by sedating patients and can lead to dangerous side effects, so we urgently need better, safer and more targeted treatments for agitation. The earliest brain changes in AD have been shown to occur in a small structure near the base of the brain called the locus coeruleus (LC). This structure contains cells that produce a chemical substance (neurotransmitter) called noradrenaline (NA), which plays an important role in controlling how the brain responds to noticeable or important aspects of the environment. To fulfil this role, the LC is connected to and influences other regions of the brain involved in controlling emotions and suppressing actions (response inhibition). There is evidence that these brain regions are dysfunctional in young adults who show aggression or anxiety, as well as in agitated patients with AD. We know that NA allows these brain regions to perform their function properly in healthy people, but no study has yet investigated whether AD-related changes in the LC (and its effects on NA activity) make an individual with AD more likely to have agitation. In support of this concept, there is consistent evidence from post-mortem studies that agitated patients with AD may have a more overactive NA system in their brains to compensate for greater LC cell loss. WHAT WILL THE RESEARCH AIM TO ACHIEVE AND HOW WILL IT BE CONDUCTED?To investigate whether the NA-system in the brain plays a role in agitation in AD, fifty participants with AD and agitation will be asked to:1. Undergo an magnetic resonance imaging (MRI) scan to test whether greater agitation is related to worse LC function and structure. 2. Complete behavioural tests to measure their brain's ability to regulate emotion and inhibit responses, and whether this is related to agitation scores. 3. Receive a single dose of propranolol (a commonly prescribed medication for high blood pressure, which also blocks the action of NA in the brain) to test whether this improves emotion regulation and response inhibition.Healthy older adults are presumed to have a more intact LC-NA system compared to patients with AD, so fifty healthy volunteers without cognitive impairment (controls) will also complete the behaviour and pharmacology studies (2 and 3 above) to test whether propranolol influences emotion regulation and response inhibition in healthy older adults, and whether this is influenced by trait anxiety and anger scores. WHAT ARE THE POTENTIAL IMPLICATIONS AND BENEFITS?This study provides a unique opportunity to further our understanding of the brain processes underlying agitation in AD, and whether there is a role for the NA system. If successful, the findings have potential to lead to new approaches for detecting and treating this condition, for example by using medications that target the NA system (e.g. propranolol).