Ultrastructural changes in the nerves innervating the cerebral artery after sympathectomy

Summary The ultrastructure of the innervation of the anterior cerebral artery of the rat was studied in control animals and in animals after superior cervical ganglionectomy.Fluorescence histochemistry shows a periarterial network of intensely fluorescent fibers which are divided into two groups, adventitial and periadventitial. The fluorescence begins to decrease 26 hours after, and completely disappears about 32 hours after, ganglionectomy.Fine structural changes are first observed 18 hours after ganglionectomy, when the axoplasm of degenerating axons becomes electron dense. This density gradually increases up to about 32 hours. By 32 hours most axons with disintegrating axolemmas become inclusion bodies of the Schwann cells. At this stage, synaptic vesicles can still be distinguished as less dense areas, but the membrane structures of synaptic vesicles and mitochondria are difficult to recognize. The degenerating axons are gradually absorbed and by 38 hours dense, residual bodies are observed in the Schwann cells. Generally speaking, the degeneration occurs first in the adventitial fibers and then in the periadventitial fibers. The transient appearance of small, granular vesicles is noticed in axon terminals about 18 hours after denervation, although very few small, granular vesicles are seen in control tissue or at later stages of degeneration.