INACTIVATION OF SENSITIZATION IN SENSORY NEURONS

众所周知，前列腺素(PGs)等炎性物质会使感觉神经元对随后的刺激敏感，导致一种称为痛觉过敏的高度敏感性状况。目前我们认为炎性PGS通过激活cAMP转导通路增强感觉神经元的敏感性和兴奋性。然而，对于控制敏感性增强的强度或持续时间的调节机制和转导级联反应，导致炎症反应和痛觉过敏的神经源性方面，人们知之甚少。建议的研究试图建立钙/一氧化氮/cGMP通路导致感觉神经元增强的兴奋性或敏感化失活的生理机制。这一假设认为，cGMP通过激活cGMP依赖的蛋白激酶(PKG)并可能调节其他细胞内介质，改变各种膜电流的性质或状态，从而逆转cAMP/PKA通路所产生的增强的神经元兴奋性。这项建议中概述的研究将以培养的大鼠背根神经节细胞作为模型系统。这些神经元的电生理特性将用膜片钳技术进行检测。这使得可以测量整个细胞或单个离子通道产生的膜电流。结合膜片钳记录，将测量细胞内钙、cAMP和cGMP浓度的变化，并将其与所观察到的神经元兴奋性的变化相关联。这项建议的具体目的是：1)使用荧光钙指示剂来量化细胞内钙浓度的变化，从而直接确定钙对致敏失活所涉及的信号通路的激活的贡献；2)建立对不同转导级联的基本了解，并确定失活通路是针对刺激的性质还是更广泛的细胞设计的一部分；3)确定引起致敏失活的特定细胞内介质及其作用机制。这将为确定由失活的介体(S)调节的特定靶蛋白提供初步步骤。最终，如果我们能够建立调节兴奋性上下调节的调节机制，就有可能设计有选择地调节改变的途径的疗法，从而抑制与慢性炎症性疾病相关的持续性疼痛和高度敏感性，如类风湿性关节炎。

Inflammatory agents such as the prostaglandins (PGs) are known to sensitize sensory neurons to subsequent stimulation, resulting in a condition of heightened sensitivity known as hyperalgesia. At present we that inflammatory PGS enhance the sensitivity and excitability of sensory neurons through activation of the cAMP transduction cascade. However, very little is known regarding the regulatory mechanisms and transduction cascades controlling the intensity or duration of the enhanced sensitivity that results in neurogenic aspects of the inflammatory response and hyperalgesia. The proposed studies seek to establish the physiological mechanisms whereby the calcium,/nitric oxide/cGMP pathways lead to inactivation of the enhanced excitability or sensitization of sensory neurons. The hypothesis of this proposal is that cGMP, through activation of cGMP- dependent protein kinase (PKG) and its possible modulation of other intracellular mediators, alters the properties or state of various membrane currents to reverse the enhanced neuronal excitability produced by the cAMP/PKA pathway. The studies outlined in this proposal will use rat dorsal root ganglion cells grown in culture as a model system. The electrophysiological properties of these neurons will be examined with the patch-clamp technique. This allow measurement of membrane currents arising from the whole cell or single-ion channels. In conjunction with patch-clamp recordings, changes in the concentration of intracellular calcium, cAMP, and cGMP will be measured and correlated to the observed alterations in neuronal excitability. The specific aims of this proposal are: 1) To quantify the changes in intracellular calcium concentration using fluorescent calcium indicators and thus determine directly the contributions of calcium to the activation of signaling pathways involved in the inactivation of sensitization; 2) To establish a fundamental understanding of the different transduction cascades and to determine whether the inactivating pathways are specific to the nature of the stimulus or part of a more generalized cellular design; 3) To determine the specific intracellular mediators and their mechanisms of action that give rise to the inactivation of sensitization. This will provide an initial step in determining the specific target proteins that are modulated by the mediator(s) of inactivation. Ultimately, if we can establish the regulatory mechanism modulating the up and down regulation of excitability, it will be possible to design therapies that selectively modulate the altered pathway and thus curb the persistent pain and heightened sensitivity associated with chronic inflammatory conditions, such as rheumatoid arthritis.