Functional Analysis of Distinct Nociceptor Populations

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DESCRIPTION (provided by applicant): Touch sensation is essential to daily life. Further, hypersensitivity to touch is a frequent problem associated with chronic neuropathic pain and persistent inflammatory pain. Despite its importance, amazingly little is known about the molecular and cellular mechanisms underlying touch sensation and whether different transduction mechanisms mediate innocuous versus painful mechanical stimuli. A promising mechanotransduction candidate is the Transient Receptor Potential Ankyrin 1 (TRPA1). Significant evidence suggests that TRPA1 contributes to mechanotransduction in somatosensory neurons and their sensitization to mechanical stimuli after tissue inflammation or nerve injury. Further, controversial evidence suggests that TRPA1 is involved in cold transduction and cold sensitization after nerve injury and inflammation. A number of important questions remain, however, about the specific functional roles of TRPA1 in mechanotransduction and cold transduction. 1) Evidence from our laboratory and others indicates that TRPA1 is expressed by non- neuronal keratinocytes, as well as sensory nerve terminals, yet the contribution of TRPA1 in either cell type to the net responses of cutaneous primary afferent neurons to mechanical force or cold temperatures is unknown. Experiments in this proposal will use two new lines of transgenic mice where TRPA1 is selectively deleted from either keratinocytes or sensory neurons to determine the contribution of TRPA1 in either cell type to behavioral and primary afferent fiber responses to mechanical and cold stimuli. 2) Whether TRPA1 in sensory neurons or keratinocytes mediates the plasma membrane response to mechanical force or cold is not clear. Experiments in this application will use an innovative, quantitative focal mechanical stimulator during whole cell patch clamp recordings to identify the contribution of TRPA1 to mechanical currents in the membrane of sensory neurons and keratinocytes. 3) Mechanical hypersensitivity is one of the most frequent, devastating symptoms associated with neuropathic and inflammatory pain. The contribution of TRPA1 to sensitization of primary afferent fibers to mechanical and cold stimuli after nerve injury or inflammation is unknown. Experiments in this proposal will determine whether TRPA1 in either sensory neurons or keratinocytes mediates the mechanical or cold sensitization that occurs in a model of neuropathic pain, and a model of persistent peripheral inflammation. In this proposal, complimentary Specific Aims using cellular, teased fiber and behavioral assays will provide a multifaceted approach to identify functional roles of TRPA1 in sensory transduction in normal tissue, and during neuropathic and inflammatory pain.