ABSTRACT: Trigeminal neuropathic pain is the most debilitating pain disorder but current treatments including opiates are not effective for it in most patients. The pain can often be triggered by a breath of cooling air blowing on the face. Mechanisms of trigeminal neuropathic pain exacerbation at cooling temperatures are not well understood, which prevents us from designing mechanistically based therapy to effectively treat this devastating pain. Our recent studies in rat models have suggested that thermally sensitive two-pore domain K+ channels (thermal K2Ps) may play a key role in trigeminal neuropathic pain exacerbation at cooling temperatures. Our central hypotheses here are: 1) Thermal K2Ps provide a brake to prevent nociceptor hyperexcitability under physiological conditions, 2) Trigeminal nerve injury causes thermal K2P down- regulation to impair the brake leading to trigeminal nociceptor hyperexcitability and neuropathic pain, and 3) Cooling temperatures further suppress thermal K2Ps to lead to trigeminal neuropathic pain exacerbation. We will test these hypotheses with the following specific aims. ?Aim 1. Elucidate the role of thermal K2Ps in controlling trigeminal nociceptor excitability and determine the effects of cooling temperatures on K2P functions. We will use immunohistochemistry to characterize thermal K2P expression in trigeminal nociceptors of normal rats. We will use our newly developed in situ patch-clamp recordings to characterize thermal K2P- mediated leak K+ currents in trigeminal nociceptors and their role in controlling trigeminal nociceptor excitability of normal rats. We will study effects of cooling temperatures on thermal K2P functions in trigeminal nociceptors of normal rats. ?Aim 2. Elucidate that trigeminal nerve injury down-regulates thermal K2P expression leading to trigeminal nociceptor hyperexcitability. We will use two established rat models of trigeminal neuropathic pain, the infraorbital nerve chronic constrictive injury (ION-CCI) and oxaliplatin-induced trigeminal neuropathy models. We will study changes of thermal K2P expression and thermal K2P-mediated leak K+ currents in trigeminal nociceptors of these models. We will use pharmacological and genetic approaches to elucidate that down-regulation of thermal K2Ps leads to trigeminal nociceptor hyperexcitability. We will determine how cooling temperatures further exacerbate hyperexcitability of trigeminal nociceptors of these rat models. ?Aim 3. Elucidate that thermal K2P down-regulation underlies trigeminal neuropathic pain, and establish thermal K2Ps as therapeutic targets for trigeminal neuropathic pain in rat models. We will use orofacial operant tests to study whether thermal K2P down-regulation leads to trigeminal neuropathic pain manifested with cold allodynia and hyperalgesia. We will use ION-CCI and oxaliplatin models to determine whether trigeminal neuropathic pain can be alleviated by pharmacological and genetic enhancements of thermal K2P functions in trigeminal afferent nerves. ? Completion of these Aims will fill the scientific gap of trigeminal nociception, elucidate a new mechanism of trigeminal neuropathic pain, and establish new therapeutic targets for this debilitating pain.
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