Submitted on December 18, 2008
Revised on March 23, 2009
Accepted on March 23, 2009
Electrophysiological Properties of Dural Afferents in the Absence and Presence of Inflammatory Mediators
Andrea M. Harriott1 and Michael S Gold2*
1 University of Maryland, Baltimore
2 University of Pittsburgh
* To whom correspondence should be addressed. E-mail: msg22{at}pitt.edu.
Migraine is a debilitating condition characterized by recurrent severe head pain. Although mechanisms underlying a migraine attack remain controversial, one proposal is that inflammatory mediator (IM) induced activation and sensitization of dural afferents contributes to the initiation of migraine pain. We and others have shown that the electrophysiological properties of afferents, both in the absence and presence of IM, vary as a function of target of innervation. These differences may account for unique aspects of pain syndromes associated with specific body regions. Therefore, the purpose of the present study was to test the hypothesis that the electrophysiological properties of dural afferents differ from those innervating the temporalis muscle (TM), a structure in close proximity to the dura but that is not associated with pain syndromes at all similar to migraine. Acutely dissociated retrograde labeled primary afferents innervating the dura and TM were examined with whole cell current clamp recordings. Passive and active electrophysiological properties were determined before and after the application of IM: (µM) prostaglandin E2 (1), bradykinin (10), histamine (1). In the absence of IM, there were significant differences between the two populations, particularly with respect to the response to suprathreshold stimulation where dural afferents were more excitable than TM afferents. Importantly, while both populations of afferents were sensitized by IM, the pattern of passive and active electrophysiological changes associated with IM-induced sensitization of these two populations of afferents suggested that there were both similarities and marked differences between the two with respect to underlying mechanisms of sensitization. If the differences between dural and TM afferents are due to a differential pattern of ion channel expression rather than differences in the relative density/biophysical properties of the same ion channels, it may be possible to selectively treat migraine pain by targeting the distinct mechanisms underlying IM-induced sensitization of dural afferents.
