PLASMA-PROTEIN EXTRAVASATION INDUCED IN THE RAT DURA-MATER BY STIMULATION OF THE PARASYMPATHETIC SPHENOPALATINE GANGLION

It has been proposed that migraine could result from a neurogenic infl ammation of the dura mater. According to this theory, inflammation cou ld be initiated by an axon reflex of nociceptive nerve fibers, but the trigger of this axon reflex remains poorly understood. Previous works have shown that parasympathetic agonists can activate mast cells and/ or sensory C-fibers, inducing pain and inflammation. The aim of the pr esent work was to determine whether the activation of intracranial par asympathetic nerve fibers could trigger an inflammatory mechanism with in the rat dura mater. Activation of the intracranial parasympathetic system was achieved by electrical stimulation of the sphenopalatine ga nglion (SPG). The development of a neurogenic inflammation was estimat ed either by microscopic examination or by quantitative measurement of plasma protein extravasation (PPE) in the dura. To determine the resp ective roles of the parasympathetic and sensory innervations, two grou ps of rats were pretreated either with atropine or with capsaicin. Sti mulation of the SPG induced a PPE increase of about 200% in the stimul ated side on the dura mater. Extravasated material was mainly concentr ated around small blood vessels. This extravasation was significantly reduced by capsaicin pretreatment and completely abolished by atropine . Infusion of carbachol in the common carotid artery induced PPE in th e ipsilateral dura comparable to that induced by electrical stimulatio n of the SPG. This extravasation was also blocked by atropine infusion . These data indicate for the first time that the parasympathetic nerv ous system can trigger a neurogenic inflammation in the dura via musca rinic cholinergic receptors. Sensory C-fibers seem to play a role in t his phenomenon. With respect to the potential autonomic imbalance desc ribed in the etiology of various types of vascular headaches, such a m echanism could be important in inducing attacks. (C) 1997 Academic Pre ss.