Electrophysiological Correlates of Vasopressin Secretion

描述（由申请人提供）：哺乳动物神经分泌神经元是了解中枢神经系统中尖峰放电模式与激素/递质释放之间关系的极好模型。神经分泌神经元采取爆发模式，促进最有效的刺激分泌耦合在神经末梢。加压素神经元中的阶段性爆发活动是这种模式的示例，并且相对独特，因为它可以在体外研究，因为它主要是由内在膜特性引起的。这一提议的总体假设是，相位爆发本身可以在很大程度上解释的理解一个初级电流，其调制的Ca ++，其自身调节强啡肽通过κ阿片受体。具体目的是：目的1）确定离子种类、潜在电导变化和DAP（IDAP）潜在电流的Ca ++依赖性。在实验上，我们将测试几个预测从一个强大的计算模型模拟阶段性活动在过去的赠款期间。我们预测，平台电位潜在的爆发的结果从Ca ++依赖性抑制K+泄漏电流，使该电流达到电压依赖性升高[Ca ++] i。目的2）探讨κ阿片受体介导的VP神经元自身调节抑制的机制。我们预测，强啡肽，局部释放加压素神经元的爆发过程中，移动的Ca ++敏感性的K+泄漏电流的阈值，提高其阈值，并终止的爆发。目的3）在体外研究自发调节在时相爆发表达变异中的作用。我们预测，相位爆裂与强啡肽调节DAP和爆裂长度的能力相关，并且互补地，相位爆裂活动的缺陷是由于自动调节的缺陷。一个推论是，相位爆发可能与树突乔木存在的程度。 了解相位爆发的起源对于了解VP释放在生理和病理生理条件下是如何控制的至关重要。VP释放对正常的水平衡和心血管调节至关重要。

DESCRIPTION (provided by applicant): Mammalian neurosecretory neurons are excellent models for understanding the relationship between spike discharge patterns and hormone/transmitter release in the central nervous system. Neurosecretory neurons adopt a bursting pattern that promotes maximally efficient stimulus-secretion coupling at the nerve terminal. The phasic bursting activity in vasopressin neurons is exemplary of this pattern, and relatively unique in that it can be studied in vitro, as it results largely from intrinsic membrane properties. The global hypothesis of this proposal is that phasic bursting per se can be explained largely by the understanding of one primary current, its modulation by Ca++, and its auto-regulation by dynorphin through kappa opiate receptors. The Specific Aims are: Aim 1) Determine the ion species, underlying conductance change, and Ca++-dependence of the current underlying the DAP (IDAP). Experimentally, we will test several predictions from a powerful computational model simulating phasic activity developed during the past grant period. We predict that the plateau potential underlying bursts results from a Ca++ dependent inhibition of a K+ leak current, such that this current attains voltage-dependence in elevated [Ca++]i. Aim 2) Determine the mechanism of the auto-regulatory inhibition of VP neurons via kappa opiate receptors. We predict that dynorphin, released locally during a burst from vasopressin neurons, shifts the Ca++ sensitivity of a K+ leak current rightward, raising its threshold, and terminating the burst. Aim 3) Determine the role of auto-regulation in the variability of phasic bursting expression in vitro. We predict that phasic bursting is correlated with the ability of dynorphin to regulate the DAP and burst length and, complementarily, that deficits in phasic bursting activity are due to deficits in auto-regulation. A corollary is that phasic bursting may be related to the degree of dendritic arbor present. Understanding the origin of phasic bursting is critical to understanding how VP release is controlled in both physiological and pathophysiological conditions. VP release is critical to normal water balance and cardiovascular regulation.