The sympathetic efferent innervation of the cutaneous and muscle veins in cats. A comparative study using retrograde localization with horseradish peroxidase

Abstract

Previous studies using electrical stimulation, tension recording and fluorescence histochemical methods indicate that variations in the sympathoadrenergic innervation exist in regional veins of the limb. In the present experiment, we used horseradish peroxidase (HRP) as a retrograde tracer to localize and quantitate the sympathetic innervations to the saphenous, femoral and muscle veins in the cat. The animal was anesthetized with pentobarbital. In three groups of cats, a segment of saphenous ( n = 8) femoral ( n = 8) and muscle ( n = 10) vein was isolated. HRP was applied on the outer vein wall for 3–4 h to allow uptake into the nerve endings. The paravertebral sympathetic chain on the same side of HRP application was dissected after the animal was killed and fixed 60 h following the application of tracer. HRP-labeled neurons were counted in each sympathetic ganglion from L 1 to S 1. The average number of neurons (mean ± SE) were 913 ± 99, 732 ± 70 and 234 ± 32, respectively, for saphenous, femoral and muscle vein. There was no statistical difference between the saphenous and femoral vein ( P > 0.1). The muscle vein was far less innervated ( P < 0.001). When the surface area (mm 2) of the vein segment for HRP application was taken into account, the neurons per mm 2 were 44.1 ± 4.8 for saphenous vein, 24.6 ± 1.8 for femoral vein and 10.2 ± 1.3 for muscle vein. The neuron density was significantly different among the three groups ( P < 0.01). In a single ganglion, the distribution of HRP-neurons appeared to be scattering in pattern. Along the sympathetic chain, the most predominant sites were L 3 and L 4 for the saphenous and femoral veins, while L 4 and L 5 for the muscle vein. The number of neurons progressively decreased toward both ends. This study provides anatomical evidence to indicate that the superficial and deep limb veins of the cat are innervated by the sympathetic nerve. The richness of innervation appeared to be as follows: saphenous > femoral > muscle vein.