Pre and post-synaptic pathways underlying the stress response in the adrenal medulla

摘要 “战或逃”反应指的是由一种刺激所引发的增强的生理和精神唤醒状态。 身体威胁、情绪化事件或代谢紊乱。虽然对每一个人的确切反应 应激源可能不同，但都具有交感神经系统激活一些基本特征。 肾上腺髓质嗜铬细胞是外周交感神经反应的核心效应细胞。当 它们在压力下被激活，向肾上腺静脉释放激素混合物，促进血液循环 在整个身体。这些激素调节心脏、肺和代谢功能， 有利于生存或维持内部条件时，他们受到威胁。肾上腺髓质的分泌物 依赖于来自节前内脏神经纤维的输入，其释放乙酰胆碱（ACh）和垂体 腺苷酸环化酶激活多肽（PACAP）的作用。人们仍然不太了解的是， 乙酰胆碱和PACAP如何调节激素释放以适应内脏放电频率的范围 与交感神经张力的变化有关。我们提出了三个具体目标，以填补这一空白， 了解压力反应途径。目标将检验总体假设， 突触前内脏输入由嗜铬细胞中不同的受体偶联途径翻译， 动态调节激素的分泌量。目标1建立在最近的初步数据基础上，这些数据显示， 第一次，任何突触结合蛋白（Syt）在内脏嗜铬细胞突触的作用。计划的研究， 使用原位切片电生理学，将定义在该突触处的Ca 2+感知的作用，并评估该想法 突触易化，由Syt 7调节，放大了嗜铬细胞的激素分泌， 内脏纤维以高频率放电。目标2的动机是初步数据显示， 磷脂酶C-β（PLC β）是将PACAP刺激信号转化为嗜铬细胞内Ca ~（2+）信号所必需的 引起胞吐作用的细胞。PACAP被认为是压力下嗜铬细胞分泌的基础。这 提示我们，随着内脏放电频率的增加，产生促进作用，PLC抑制了活动， 嗜铬细胞必须被“打开”以维持激素输出的增加。目标3建立在数据基础上， PACAP刺激嗜铬细胞的胞吐作用，但同时矛盾地限制了 嗜铬颗粒内包裹的肽激素。与生物源的差异释放有关 胺和激素肽，我们将表征PACAP刺激的融合孔的性质， 研究它们被限制的机制。我们希望这些研究将提供一个连贯的 分子和生理学的框架来理解突触前活动，突触后受体， 偶联的信号传导途径和胞吐作用在机制上与调节应激反应相关。

ABSTRACT The “fight-or-flight” response refers to the state of heightened physiological and mental arousal triggered by a physical threat, emotionally charged event, or metabolic disturbance. Although the precise reaction to each stressor may vary, all share some basic characteristics of sympathetic nervous system activation. Adrenomedullary chromaffin cells are core effectors of the sympathetic response in the periphery. When activated during stress, they discharge a cocktail of hormones into the suprarenal vein for circulation throughout the body. These hormones modulate cardiac, pulmonary, and metabolic functions in ways that favor survival or maintain internal conditions when they are threatened. Secretion from the adrenal medulla is dependent on input from preganglionic splanchnic fibers, which release acetylcholine (ACh) and pituitary adenylate cyclase-activating polypeptide (PACAP) onto chromaffin cells. What remains poorly understood is how ACh and PACAP tune hormone release to accommodate the range of splanchnic firing frequencies associated with variations in sympathetic tone. Three Specific Aims are proposed to fill this gap in our understanding of the stress response pathway. The Aims will test the overall hypothesis that variations in presynaptic splanchnic input are translated by different receptor-coupled pathways in chromaffin cells to dynamically regulate the amount of hormone output. Aim 1 builds on recent preliminary data that shows, for the first time, a role for any synaptotagmin (Syt) at the splanchnic-chromaffin cell synapse. Planned studies, using in situ slice electrophysiology, will define the role of Ca2+ sensing at this synapse, and evaluate the idea that synaptic facilitation, regulated by Syt7, amplifies hormone discharge from chromaffin cells when splanchnic fibers discharge at high frequencies. Aim 2 is motivated by preliminary data that shows Phospholipase C-epsilon (PLC) is required for transducing PACAP stimulation into Ca2+ signals in chromaffin cells that cause exocytosis. PACAP is thought to underlie chromaffin cell secretion during stress. This has prompted us to posit that with increased splanchnic firing frequencies that produce facilitation, PLC activity in chromaffin cells must be “turned on” to sustain increases in hormone output. Aim 3 builds on data which shows that PACAP stimulates exocytosis in chromaffin cells, but does so while paradoxically restricting the release of peptide hormones packaged within a chromaffin granule. Relevant for the differential release of biogenic amines and hormone peptides, we will characterize the properties of PACAP-stimulated fusion pores and investigate mechanisms by which they are constrained. We expect these studies will provide a coherent molecular and physiological framework for understanding how presynaptic activity, postsynaptic receptor- coupled signaling pathways, and exocytosis are mechanistically linked to regulate the stress response.