Histochemical studies of the adrenergic innervation of canine cerebral arteries

The glyoxylic acid method was used to examine the adrenergic innervation of the major cerebral arteries of the circle of Willis in dogs. Fluorescent nerve fibers were observed in whole-mount preparations of the part of the internal carotid artery lying in the cavernosus sinus, the anterior, middle and posterior cerebral arteries, the posterior communicating artery and the basilar artery. Adrenergic nerve fibers were most abundant in the proximal portions of the anterior, middle and posterior cerebral arteries as well as in the posterior communicating artery. The distal smaller arteries were less densely innervated than larger ones. The basilar artery contained a moderate number of fluorescent fibers while the internal carotid artery lying in the cavernosus sinus had a very sparse innervation. The peak wavelengths of the excitation and emission spectra of the fluorescence were analyzed by means of a microepifluorescence spectrophotometer and were about 415 and 465 nm, respectively. These values suggest that the fluorescent fibers are adrenergic ones containing norepinephrine.