Hypothalamic Neuronal Plasticity in Chronic Stress

描述(由申请人提供)：慢性压力可导致情绪、生理和行为反应的长期或永久性变化，从而增加身体和精神障碍的风险。应激反应主要由下丘脑室旁核(PVN)控制，PVN含有功能各异的神经元群，参与调节下丘脑-垂体-肾上腺皮质(HPA)轴和自主神经系统。刺激表达促肾上腺皮质激素释放激素(CRH)的小细胞神经元，在基础和应激条件下都会增加垂体促肾上腺皮质激素(ACTH)的释放和随后的皮质酮(CORT)分泌。虽然自主神经前神经元和神经内分泌神经元的活性增加有利于急性应激时的短期存活，但在慢性应激时这些神经元的持续兴奋可导致严重的代谢、免疫和心理功能障碍。然而，慢性应激引起下丘脑室旁核神经元过度活动的潜在机制尚不清楚。慢性不可预测的轻度应激(CUMS)大鼠模型提供了一个很好的类比，可以很好地模拟人类慢性和低级别应激源导致的抑郁。在这个项目中，我们将使用CUMS大鼠模型来验证这一中心假设，即慢性应激通过上调NKCC1和PVN中EGABA的去极化位移来减少GABA能抑制，并有助于增强应激反应。我们最近发展了一种新的方法，通过在体内用CRH启动子驱动的GFP标记表达CRH的神经元来识别大鼠CRH表达的神经元。我们建议追求以下四个特定目标：(1)确定慢性应激时阳离子-氯转运体表达水平的变化；(2)确定NKCC1在慢性应激下PVN CRH表达神经元的EGABA去极化位移和兴奋性增加中的作用；(3)确定增加的谷氨酸能输入对慢性应激中PVN中NKCC1上调的贡献；以及(4)确定NKCC1在PVN中上调在慢性应激反应中的作用。GABA翻转电位的去极化移动和NKCC1在PVN中的上调在慢性应激中的重要性尚未被认识到。我们的项目有望产生新的信息，这些信息将显著促进我们对慢性应激所涉及的分子机制的理解。这一新信息可以为治疗慢性应激条件下过度应激反应提供重要的理论依据。此外，这些发现可能会导致开发新的疗法来预防和治疗抑郁症等精神疾病。

DESCRIPTION (provided by applicant): Chronic stress can result in long-term or permanent changes in the emotional, physiological, and behavioral responses that lead to increased risk for physical and psychiatric disorders. Stress responses are controlled importantly by the paraventricular nucleus (PVN) of the hypothalamus, which contains functionally distinct neuronal populations involved in the regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis and autonomic nervous system. Stimulation of corticotrophin-releasing hormone (CRH)-expressing parvocellular neurons increases pituitary adrenocorticotropic hormone (ACTH) release and subsequent corticosterone (CORT) secretion under both basal and stressed conditions. Although increased activity of both preautonomic neurons and neuroendocrine neurons are beneficial for short-term survival during acute stress, persistent excitation of these neurons during chronic stress can result in serious metabolic, immune and psychological dysfunction. However, the underlying mechanisms causing hyperactivity of PVN neurons in chronic stress remain unclear. The chronic unpredictable mild stress (CUMS) rat model provides a good analogy to the precipitation of depression by chronic and low-grade stressors in humans. In this project, we will use the CUMS rat model to test the central hypothesis that chronic stress diminishes GABAergic inhibition and contributes to enhanced stress responses through upregulation of NKCC1 and the depolarizing shift of EGABA in the PVN in chronic stress. We have recently developed a novel method to identify rat CRH-expressing neurons by tagging the CRH- expressing neurons with GFP driven by CRH promoter in vivo. We propose to pursue the following four specific aims: (1) determine changes in the cation-chloride cotransporter expression levels in chronic stress; (2) determine the role of NKCC1 in the depolarizing shift of EGABA and increased excitability of the PVN CRH-expressing neurons in chronic stress; (3) determine the contribution of increased glutamatergic inputs to the NKCC1 upregulation in the PVN in chronic stress; and (4) determine the role of NKCC1 upregulation in the PVN in exaggerated stress response in chronic stress. The importance of the depolarizing shift of GABA reversal potential and upregulation of NKCC1 in the PVN in chronic stress has not been recognized previously. Our project is expected to generate novel information that will significantly advance our understanding of the molecular mechanisms involved in the chronic stress. This new information could provide an important rationale for the treatment of exaggerated stress response during chronic stress conditions. Also, these findings may lead to the development of novel therapies to prevent and treat psychiatric diseases such as depression.