Neural Mechanisms of Itch

描述（由申请人提供）：尽管瘙痒作为皮肤感觉的主要品质和许多神经和其他疾病的临床症状很重要，但对其神经基础了解甚少。在我们之前的资助期间，我们发现瘙痒是由痛觉初级神经元和痛觉脊髓丘脑束（STT）神经元亚群介导的，其中一些对组胺有反应，而另一些则通过我们发现的一种新型半胱氨酸蛋白酶对奶牛的针状体产生不依赖组胺的瘙痒。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）针状体，引发瘙痒和伤害性化学诱发感觉（感觉障碍）。我们建议继续我们的结合，心理物理和神经生理研究瘙痒需要三个不同的项目的综合努力，每个项目使用不同的实验方法。项目1将从心理物理角度测量含有组胺、辣椒素或内源性半胱氨酸蛋白酶的热灭活的奶牛针状体所引起的瘙痒、痛觉感觉和感觉障碍。机械、热或化学刺激在增强或抑制瘙痒中的作用以及阻断髓鞘神经纤维传导的作用将被检查，以揭示控制瘙痒的潜在神经机制。项目2将电生理记录猴子周围神经纤维对项目1相同刺激的反应，以确定有髓鞘轴突和无髓鞘轴突的伤害性神经元对瘙痒和伤害性感觉的不同贡献，以及对瘙痒的增强和抑制。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，通过对氨基丁酸（GABA）抑制剂吗啡的离子离子吸收以及阻断节段上区域下行通路对STT神经元反应的影响，将揭示脊髓增强和抑制瘙痒、痛觉和瘙痒性感觉障碍的机制。提供管理、仪器、统计和信息的核心将有助于收集、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。

DESCRIPTION (provided by applicant): 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. Public Health Relevance: The proposed psychophysical and neurophysiological studies of experimentally produced itch and pain will advance our understanding of how these sensations are mediated by sensory neurons in the peripheral and central nervous system. Identification of these neurons and their properties will provide targets for pharmacological therapies to relieve chronic itch and pain in humans.