Neural Mechanisms of Itch

瘙痒的神经基础知之甚少，尽管它作为皮肤感觉的主要性质和作为许多神经和其他疾病的临床症状的重要性。在我们之前的资助期间，我们发现瘙痒是由伤害性初级神经元和伤害性脊髓丘脑束（STT）神经元的亚群介导的，一些对组胺有反应，另一些对通过我们鉴定的新型半胱氨酸蛋白酶引起组胺非依赖性瘙痒的母牛骨针有反应。我们设计了一种精确的方法，通过使用浸泡在内源性半胱氨酸蛋白酶、组胺或辣椒素中的化学惰性（热灭活）针状物来引发过敏性和伤害性化学诱发感觉（感觉迟钝）。我们建议继续我们的结合，心理物理和神经生理学研究痒需要三个不同的项目，每个项目使用不同的实验方法的综合努力。项目1将从精神病学的角度测量由含有组胺、辣椒素或内源性半胱氨酸蛋白酶的热灭活的牛骨针引起的瘙痒、伤害性感觉和感觉迟钝。将检查机械、热或化学刺激在增强或抑制瘙痒中的作用以及阻断有髓鞘神经纤维中的传导的作用，以揭示控制瘙痒的潜在神经机制。项目2将电生理记录猴外周神经纤维对项目1中使用的相同刺激的反应，以确定具有有髓轴突与无髓轴突的伤害感受神经元对瘙痒和伤害感受感觉以及对瘙痒的增强和抑制的单独贡献。项目3将电生理记录STT和丘脑神经元对项目1和2中使用的相同刺激的反应。此外，离子导入应用GABA抑制剂吗啡和阻断超节段区下行通路对STT神经元反应的影响将揭示瘙痒、伤害性感受和痛性感觉迟钝的增强和抑制的脊髓机制。一个提供行政、仪器、统计和信息学的核心将便利收集、分析和评价从每个项目获得的数据。通过增加我们对编码和调节瘙痒和伤害性感觉的外周和中枢神经机制的理解，我们的联合研究将为缓解瘙痒和疼痛的新疗法提供新的靶点。

The neural basis of Itch is poorly understood despite its importance as a primary quality of cutaneous sensation and as a clinical symptom of many neurological and other disorders. During our previous funding period we discovered that itch is mediated by subpopulations of nociceptive primary neurons and nociceptive spinothalamic tract (STT) neurons, some responsive to histamine, and others to the spicules of cowhage that evoked a histamine independent itch via a novel cysteine protease that we identified. We devised a precise method of eliciting pruritic and nociceptive chemically evoked sensations (dysesthesias) by using chemically inert (heat inactivated) spicules soaked in an endogenous cysteine protease, histamine, or capsaicin. We propose to continue our combined, psychophysical and neurophysiological study of itch requiring the integrated efforts of three different projects each using a different experimental approach. Project 1 will measure psychophysically the itch, nociceptive sensations and dysesthesias evoked by heat-inactivated cowhage spicules containing histamine, capsaicin or an endogenous cysteine protease. The effects of mechanical, thermal or chemical stimuli in enhancing or suppressing itch and the effects of blocking conduction in myelinated nerve fibers will be examined to reveal underlying neural mechanisms controlling itch. Project 2 will electrophysiologically record the responses, to the same stimuli used in project 1, of peripheral nerve fibers in monkey to determine the separate contributions of nociceptive neurons with myelinated vs. non-myelinated axons to itch and nociceptive sensations and to the enhancement and inhibition of itch. Project 3 will electrophysiologically record the responses of STT- and thalamic neurons to the same stimuli used in projects 1 & 2. In addition, the effects of iontophoretic application of morphine, a GABA inhibitor, and the blocking of descending pathways from suprasegmental areas on STT neuronal responses will reveal spinal mechanisms of the enhancement and inhibition of itch, nociception and pruritic dysesthesias. A core providing administration, instrumentation, statistics and informatics will facilitate the collection, analysis and evaluation of the data obtained from each project. By increasing our understanding of the peripheral and central neural mechanisms that code and modulate itch and nociceptive sensations, our combined studies will provide new targets for novel therapies to relieve itch and pain.