Adrenergic and cholinergic innervation of the arteriovenous anastomosis in the rabbit's ear.

The distribution of adrenergic and cholinergic nerves in the arteriovenous anastomosis in the rabbit's ear was studied light microscopically using specific histochemical techniques for catecholamines and acetylcholinesterase. Histochemical observations was made with whole stretch preparations and cryostat or paraffin sections. Both kinds of nerves showed similar distribution, though the adrenergic innervation was denser than the cholinergic one. The intermediate segments of the anastomoses, which were characterized by a very thick wall, had the most dense innervation. The small arteries and arterial segments had a moderate innervation whereas most of the small veins and venous segments had few nerve fibers. The segmental variation in the vasomotor nerve supply clearly suggests that the intermediate segment has the most active contractility. An unusually rich innervation in the anastomosis, therefore, indicates the significance of the neurogenic mechanisms in the vasomotor control of the anastomosis.