Abstract
Oestrogen increases facial allodynia through its actions on activation of the MAPK extracellular-signal regulated kinase (ERK) in trigeminal ganglion neurons. This goal of study was to determine which oestrogen receptor is required for behavioural sensitization. Immunohistochemical studies demonstrated the presence of oestrogen receptor alpha (ERalpha) in nuclei of larger neurons and cytoplasm of smaller neurons, and the novel oestrogen receptor G-protein coupled receptor 30 (GPR30) in small diameter neurons that also contained peripherin, a marker of unmyelinated C-fibres. Specific agonists for ERalpha (PPT) and GPR30 (G-1), but not ERbeta (DPN), activated ERK in trigeminal ganglion neurons in vitro. Both G-1 and PPT treatment increased allodynia after CFA injections into the masseter of ovariectomized Sprague-Dawley rats. Treatment with oestrogen increased expression of ERalpha but not GPR30, while masseter inflammation increased GRP30 but not ERalpha. Differential modulation of these ERK-coupled receptors by oestrogen and inflammation may play a role in painful episodes of temporomandibular disorder and migraine.