Fine structural and autoradiographic study of the adrenergic innervation of the dog lateral saphenous vein.

Abstract

The tunica media of the dog lateral saphenous vein contains 8–12 layers of predominantly circular smooth muscle fibers. Numerous nerve profiles exhibit bright green fluorescence after formaldehyde gas treatment. These profiles occur amongst the muscle cells throughout the whole thickness of the media. Electron microscopy shows such profiles to be surrounded by Schwann cell processes enveloping axons which contain large (43%) and small (57%) dense-core vesicles. Axons are separated from muscle cells by 100–300 nm; in some cases intimate contacts, <i>≈</i>20 nm wide, were seen between an axon and a muscle cell projection. After incubation of the vein with exogenous radioactive noradrenaline, nerves showed a great accumulation of radioactive material. Extraneuronal tissues (muscle and connective tissue) exhibit a much lower grain density (<i>≈</i>15 times less), which is, however, far above background levels. The dense innervation of the vessel wall and the intimate neuromuscular relationship are considered to form the morphological basis for the speed of nerve-evoked contractile responses in this preparation, as well as for the great extent of transmitter inactivation through neuronal reuptake.