Electron Microscopic Observations on Human Intracranial Arteries

While a number of light microscopic investigations have demonstrated nerves within the walls of intracranial vessels,¹⁻³the nature and importance of this innervation remains conflicting.⁴Experiments on cats indicate the presence of vasomotor fibers,⁵but the evidence for a neurogenic constrictor effect on human cerebral vessels is meager. Ray and Wolff elicited painful sensations by stimulation of vessels at the base of the brain in man,⁶but little is known concerning the receptor mechanism in these or other blood vessels. Ultrastructural information on vessel innervation is also limited. Pease and Molinari mention but do not illustrate the fine structure of unmyelinated nerves in the adventitia of vessels from the subarachnoid space of the cat.⁷Single electron micrographs depicting a group of unmyelinated nerves in the coronary artery of a rabbit⁸and a rat⁹have been published. In view of the considerable current interest