Patterns of reinnervation of denervated cerebral arteries by sympathetic nerve fibers after unilateral ganglionectomy in rats.

In order to clarify the manner in which previously denervated cerebral arteries become reinnervated after unilateral excision of the superior cervical ganglion (SCG), we observed directly the reinnervating sympathetic nerve fibers originating in the contralateral SCG by using anterograde labeling with wheat germ aggulutinin-horseradish peroxidase in rats. The nerve fibers sprouted from the nerve fibers in the contralateral anterior cerebral artery and reinnervated the arterial wall of the anterior cerebral artery of the denervated side as early as one week after ganglionectomy. In addition to this sprouting route, three other reinnervating nerve fiber routes were observed in the circle of Willis of the denervated side two weeks after ganglionectomy: the proximal portion of the internal carotid artery, the route passing between bilateral ethmodial arteries, and the posterior communicating artery. Eight weeks after ganglionectomy, these reinnervating nerve fibers formed a fairly dense plexus in a circular pattern in the circle of Willis. However, the reinnervation could not be observed in the arterial branches derived from the circle of Willis (middle cerebral artery and posterior cerebral artery) even 16 weeks after ganglionectomy. The present results clearly demonstrated the time course, distribution pattern and limitation of the reinnervation from the contralateral SCG following unilateral ganglionectomy. The fact that reinnervation could be observed only in the main cerebral arteries of the circle of Willis, in which the nerve plexus appeared to have a circular pattern, suggests a difference between the qualities of sympathetic innervation controlling the cerebral circulation in these arteries and the other arterial branches related to these differences in reinnervation capacity.