Itch neurons studied in vivo

描述(申请人提供)：慢性瘙痒，就像慢性疼痛一样，临床上被认为是痛苦和生活质量损失的主要原因。虽然瘙痒伴随着许多神经、皮肤科和全身疾病，但在研究潜在的外周神经机制时，它受到的关注比疼痛更少。有两种常用的方法来研究背根神经节神经元对引起人类瘙痒或动物瘙痒相关行为的化学刺激的生理特性。第一种方法是电生理学记录这些神经元对皮肤感受区施加瘙痒化学物质后所诱发的动作电位。第二种方法是使用分离的细胞体(SOMA)作为外周终末的模型来研究化学感觉转导的细胞分子机制。在对这一模型的测试中，我们将结合这两种方法，比较活体内完整、可视化、伤害性DRG神经元的胞体和感受野的反应特性。我们将使用遗传分子荧光标记来识别麻醉小鼠中一种特定类型的DRG神经元的胞体。动作电位将从胞体外记录，以响应传递到其皮肤感受场的瘙痒和痛觉刺激。然后，将激活感受野的瘙痒化学物质局部应用于胞体，并测量胞体膜兴奋性或细胞内钙离子的变化。为了进行比较，将从具有相同荧光标记的剧烈解离的SOMA中获得类似的测量结果。如果成功，这一结果将为研究外周神经元如何感知瘙痒中介化学物质的潜在细胞机制指明新的方法，这是开发专门作用于阻止人类病理性瘙痒的药物的重要先驱。

DESCRIPTION (provided by applicant): Chronic itch, like chronic pain, is clinically recognized as a major cause of suffering and loss in the quality of life. Although itch accompanies many neurological, dermatological and systemic diseases, it has received less attention than pain in studies of underlying peripheral neural mechanisms. There have been two general approaches to studying the physiological properties of dorsal root ganglion neurons that respond to chemical stimuli that evoke itch in humans or itch-associated behavior in animals. The first is to electrophysiologically record action potentials evoked in these neurons in response to a pruritic chemical applied to their cutaneous receptive fields. The second approach is to examine the cellular molecular mechanisms of chemical sensory transduction using the cell body (soma), dissociated and placed in culture, as a model of the peripheral terminal endings. In a test of this model, we will combine these two approaches and compare the response properties of the soma and the receptive field in the intact, visualized, nociceptive DRG neuron, in vivo. We will use genetic-molecular fluorescent markers to identify the soma of a particular type of DRG neuron in the anesthetized mouse. Action potentials will be recorded extracellularly from the soma in response to pruritic and algesic stimuli delivered to its cutaneous receptive field. Then pruritic chemicals that activated the receptive field will be topically applied to the soma and alterations in somal membrane excitability or intracellular calcium will be measured. Similar measurements will be obtained, for comparison, from acutely dissociated somas with the same fluorescent markers. If successful, the outcome will point to new methods of studying the underlying cellular mechanisms of how itch mediating chemicals are sensed in peripheral neurons, an important precursor to the development of drugs that will act specifically to block pathological itch in humans.