Orexinergic projections to neocortex: potential role in arousal, stress and anxiety-related disorders.

压力会加剧许多精神疾病，反复的压力会导致创伤后应激障碍、恐慌症和严重抑郁障碍等疾病的发病。哺乳动物的大脑皮层负责我们的高级认知功能，如语言、情景记忆和复杂感知。它与各种其他结构相互作用，如丘脑，一大群神经元，要么将感觉输入传递到皮质，要么通过这些神经元调节皮质-皮质相互作用。我们的大脑并不总是关注所有细节，也不总是分析细节背景。它的状态受神经内分泌因素的调节。这些都是小分子，如食欲素(下丘脑泌素)。食欲素只在下丘脑外侧的神经元中产生。食欲素系统对压力有高度的反应，并调节许多在应激相关精神疾病中改变的生理过程，包括睡眠/觉醒模式、食欲和认知。据报道，在严重的抑郁症和焦虑症中，食欲素水平的变化，以及对食欲素(食欲素1受体多态性)敏感性的遗传缺陷与焦虑症有关，特别是在患有应激相关精神疾病的可能性是男性的两倍的女性中。食欲素能神经元在整个中枢神经系统有广泛的投射靶点，包括对调节觉醒、食欲和神经内分泌功能至关重要的其他局部(下丘脑)神经元。然而，尽管投射可能参与调节大脑皮层觉醒和对压力的认知反应，但对大脑皮层环路的投射的作用还不是很清楚。因此，它们可能是药物开发的有希望的靶点，选择性地针对皮质，而不是涉及产生焦虑的皮质下机制。解决食欲素能神经元和皮质环路之间的解剖和功能连接，以及这个系统中的性别差异，将是开始设计食欲素能焦虑疗法的关键。在感觉皮层内，6b层是唯一对食欲素敏感的层。使用CTGF-/Drd1a-Cre转基因小鼠可以选择性地标记这些神经元，我们在研究这一细胞群体方面拥有非常丰富的专业知识。我们证明了下丘脑外侧增食欲素神经元和这些细胞之间有直接的联系。我们还证明，一些食欲素敏感的6b层神经元选择性地投射到参与高级认知功能的丘脑核团。因此，感觉层6b神经元可能起到食欲素门控电路的作用，通过皮质-丘脑-皮质环路放大反馈，在调节大脑状态和认知方面发挥重要作用。在我们的初步实验中，我们通过基因沉默了整个大脑皮层中选定的一组Drd1a-Cre神经元，并观察了这些Snap25 CKO小鼠的行为。当小鼠暴露在新的环境中时，这种操作不会影响昼夜节律或运动活动。然而，在三种不同的行为任务中，它导致了类似焦虑的行为的显著减少。这表明，一些Drd1a-Cre神经元可能是大脑皮层调节情绪行为的关键组成部分。我们将研究i)增食欲素神经元和它们的皮质靶点之间的功能连接，ii)CTGF-/Drd1a-Cre神经元对应激和觉醒的生理反应，以及这是如何被增食欲素调节的，以及ii)这些细胞参与焦虑和恐惧学习。这些回路的选择性操作为干预焦虑提供了独特的治疗途径，同时不影响自主功能。我们提出的实验将剖析这些回路的关键成分、细胞类型和性别差异，并将测试可用于治疗的分子机制。

Stress exacerbates many psychiatric conditions, and repeated stress contributes to the pathogenesis of disorders such as Post Traumatic Stress Disorder, Panic and Major Depressive Disorder. The mammalian cerebral cortex is responsible for our higher cognitive functions such as language, episodic memory, and complex perception. It interacts with various other structures, such as the thalamus, a large group of neurons that either relay sensory input to the cortex or mediate cortico-cortical interactions through these neurons. Our brain is not always paying attention to all details, and it does not always analyse detailed contexts. Its state is regulated by neuroendocrine factors. These are small molecules, such as orexin (hypocretin). Orexin is exclusively produced in neurons of the lateral hypothalamus. The orexin system is highly reactive to stress and regulates many physiological processes that are altered in stress-related mental illness, including sleep/wake patterns, appetite, and cognition. Changes in orexin levels have been reported in major depression and anxiety disorders, and genetic defects in the sensitivity to orexin (orexin 1 receptor polymorphism) have been associated with anxiety spectrum disorders, particularly in women who are twice as likely as men to suffer from stress-related mental illness. Orexinergic neurons have wide projection targets across the entire central nervous system, including to other local (hypothalamic) neurons that are important for modulating arousal, appetite, and neuroendocrine functions. However, the role of projections to cortical circuits remains less well understood, although they may be involved in regulating cortical arousal and the cognitive responses to stress. Thus, they could represent promising targets for drug development that selectively target cortical, but not subcortical mechanisms involved in generating anxiety. Resolving the anatomical and functional connectivity between orexinergic neurons and cortical circuits, as well as the gender differences in this system, will be critical for starting to design orexinergic treatments for anxiety. Within sensory cortex, layer 6b is the only orexin-sensitive layer. These neurons can be selectively labelled using Ctgf-/Drd1a-Cre transgenic mice, and we have very considerable expertise in studying this cell population. We demonstrated that there is a direct link between lateral hypothalamic orexin neurons and these cells. We also demonstrated that some of the orexin-sensitive layer 6b neurons selectively project to thalamic nuclei that are involved in higher cognitive functions. Sensory layer 6b neurons might therefore function as an orexin-gated circuit that amplifies feedback via cortico-thalamo-cortical loops and play an important role in regulating brain state and cognition. In our preliminary experiments we genetically silenced a selected population of Drd1a-Cre neurons across the entire cerebral cortex and observed the behaviour of these Snap25 cKO mice. This manipulation did not influence circadian rhythms or locomotor activity when mice were exposed to a novel environment. However, it led to a strong reduction in anxiety-like behaviour, as measured in three different behavioural tasks. This suggests that some of the Drd1a-Cre neurons may act as a key component in the cortex for regulating emotional behaviours. We shall examine i) functional connectivity between orexin neurons and their cortical targets, ii) physiological responses of Ctgf-/Drd1a-Cre neurons to stress and arousal, and how this is modulated by orexin, and ii) involvement of these cells in anxiety and fear learning. The selective manipulation of these circuits presents unique therapeutic avenues for the intervention against anxiety, while not influencing autonomous functions. Our proposed experiments will dissect key components, cell type and gender differences of these circuits and shall test the molecular mechanisms that could be exploited in therapy.