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理解中枢神经系统中峰值放电模式和激素/递质释放之间关系的优秀模型。神经分泌神经元采用爆发模式，在神经末梢促进最有效的刺激-分泌耦合。抗利尿激素神经元的阶段性破裂活动是这种模式的典型，并且相对独特的是，它可以在体外研究，因为它主要是由固有的膜特性引起的。这一提议的总体假设是，相位破裂本身可以通过对一个主要电流的理解来解释，它由Ca++调制，并通过kappa阿片受体由dynorphin自动调节。具体目的是：目的1)确定离子种类，潜在电导变化，以及DAP （IDAP）基础电流对Ca++的依赖。实验上，我们将测试几个预测从一个强大的计算模型模拟相活动发展在过去的资助期间。我们预测，爆发下的平台电位是由Ca++依赖性抑制K+泄漏电流产生的，因此该电流在升高的[Ca++]i中达到电压依赖性。目的2)确定kappa阿片受体对VP神经元的自调节抑制机制。我们预测，在抗利尿激素神经元爆发时局部释放的肌啡能将K+泄漏电流的Ca++敏感性向右移动，提高其阈值，并终止爆发。目的3)确定自调节在体外相爆裂表达变异性中的作用。我们预测，相爆裂与dynorphin调节DAP和爆裂长度的能力有关，互补地，相爆裂活性的缺陷是由于自我调节的缺陷。一个推论是，相爆裂可能与树枝状乔木存在的程度有关。

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.