Localization of sympathetic postganglionic neurons innervating the femoral-saphenous vein in cats

Abstract

Physiological and histochemical studies have suggested that the limb veins are innervated by sympathetic adrenergic fibers. In the present experiment, horseradish peroxidase (HRP) was used as a retrograde tracer to identify and localize the sympathetic postganglionic neurons that innervate the femoral-saphenous vein in cats. In anesthetized cats, HRP was applied perivascularly on a femoral and a saphenous vein segment (4–8 mm in length for each segment) to allow uptake into the nerve endings. The sympathetic chains on both sides were dissected after the animal was sacrificed and fixed 60 h following the HRP application. Histological examination on serial section was done to count the HRP-labeled neurons in each sympathetic ganglion from L 1 to S 1. In 10 cats, the total number of HRP neurons amounted to 8569. Most neurons arose from L 3 (47%) and then L 4 (31%). The number of neurons became progressively decreasing towards both ends of the sympathetic chain. Few neurons (less than 2% of the total) were discovered in the contralateral sympathetic ganglia. In each ganglion, the distribution of HRP neurons appeared to be scattering. Our findings provide anatomical evidence to support that the femoral-saphenous vein of the cat was innervated by the sympathetic efferent fibers. The main origins of these neurons are the third and fourth lumbar sympathetic ganglia.