The Role of ASICs in Migraine Pathophysiology

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DESCRIPTION (provided by applicant): Migraine headache was once thought to be predominately of vascular origin but it is now increasingly appreciated that its genesis and progression also involves maladaptive changes in the nervous system. Migraine represents the most common neurological disorder affecting up to 33% of women and 13% of men at some point in their lives. Despite its widespread prevalence, the pathophysiology that leads to migraine headache is still poorly understood and pharmacological treatment is only effective in about 50% of migraine sufferers. Developing new treatments with greater efficacy than those currently available is limited, in part, by a lack of new therapeutic targets. Thus, the identification of new targets that contribute to the pathophysiology of migraine headache is of critical importance for more effective migraine therapies. Prior preclinical work has found that trigeminal pain-sensing neurons (nociceptors) innervating the cranial meninges (i.e. the dura mater) are sensitive to substances released from mast cells. Mast cells can be activated following stress and increased estrogen levels, both of which are associated with migraines in humans. However, the cellular mechanisms by which mast-cell induced signaling is initiated are unknown. The hypothesis of this proposal is that decreased extracellular pH within the dura following mast-cell degranulation leads to activation of dural afferents via the opening of acid-sensing ion channels (ASICs). Recent studies in the laboratory have found that identified dural afferents respond to small drops in pH with currents generated by ASICs. Following exposure to mast cell mediators, these small pH drops lead to firing of action potentials. Preliminary studies also show that direct application of decreased pH solutions to the dura mater of awake animals elicit behaviors thought to be relevant to migraine pain. The proposed studies will explore ASIC-mediated dural afferent excitability and migraine-related pain behaviors in response to drops in pH by addressing the following questions. Are ASIC currents and pH-induced excitability of dural afferents increased by mast cell mediators and do these factors lead to enhanced afferent activity following small drops in pH? Does activation of ASIC channels on neuronal endings within the dura produce signs of afferent signaling and which ASIC proteins are expressed on dural afferent endings? Do mast-cell mediators increase the migraine-related behavior induced by activation of ASICs within the dura? The goal of this proposal is to determine the role of ASICs on sensory endings within the dura and how these channels might contribute to afferent signaling and migraine headache. If ASICs are found to play an important role in migraine pathophysiology, this finding would identify new targets for the pharmacological treatment of migraine and could lead to new therapies with increased efficacy over those currently available. Developing drugs targeting ASICs may ultimately provide relief to the large numbers of migraine patients that are not being adequately treated by currently available therapies.