Histological demonstration of increased vascular permeability in the dura mater of the rat

Neurogenic inflammation of the dura mater encephali has been suggested to play an important role in the pathophysiology of headaches. Although functional studies using extravasation techniques indicate an enhanced permeability of blood vessels after chemical or electrical stimulation of C-fibres supplying the dura mater, histological demonstration of leaky blood vessels is still a problem. We used the vascular labelling method combined with i.v. injection of colloidal silver solution to test the permeability increasing effect of intravenous administration of substance P, topical application of mustard oil or acidic phosphate buffer and local electrical stimulation of the exposed dura mater. Histological characteristics of increased vascular permeability were observed exclusively after mustard oil and acidic phosphate buffer. This observation may indicate different mechanisms of increased vascular permeability involving pinocytosis and formation of interendothelial gaps selectively visualized by the vascular labelling method.