Trophic interactions between rat thigh blood vessels and their innervation

Much less work has been done on the denervation of smooth muscle compared with the extensive studies carried out on skeletal muscle. It was thought that denervation of smooth muscle produced few alterations in its morphology or physiology, especially since many blood vessels have virtually no innervation, and therefore, they can survive without it. Simple severing or excising a section of nerve trunk is sufficient to denervate skeletal muscle, but this does not apply to smooth muscle. Therefore, denervation methods for smooth muscle have included those with widespread effects such as chemical and immunological sympathectomies, and superior cervical ganglionectomy. In this study, I have developed a a semi-permanent, localized denervation method for rat thigh vessels and have used this method to study the trophic interactions between blood vessels and their innervation. Female Wistar rats were denervated at 1-3 or 12 days of age, and examined at 30, 60, 90 and 120 days of age. The femoral nerve, which carries the vasomotor innervation to the thigh vessels, was severed in the thigh and brought inside the abdominal cavity. This method was necessary since preliminary experiments showed rapid re-innervation of the vessels if any part of the proximal root remained in the thigh. Inside the abdominal cavity, the nerve was slipped into a plastic tube and heat sealed. The tubing further inhibited re-innervation by preventing collateral sprouting from the proximal stump. Samples of the distal nerve stump, the proximal nerve stump, and from the femoral vein and saphenous artery were taken. In every animal, the contralateral side acted as a control. The distal and proximal nerve stumps showed marked evidence of degeneration. Fluorescence microscopy (specific for catecholamines) showed a significant decrease in the number of fluorescing dots around both the artery and vein. The presence of some fluorescencing dots around the denervated vessels may be from the nerves that were seen re-innervating the vessels at the time of sampling. These nerves came from aberrant areas. Arteries sampled at 90 days showed a significant decrease in the cross-sectional area of the tunica media on the denervated side. The denervated femoral vein, in situ, was seen to be grossly dilated compared to the control side. Measurements of the luminal perimeter of sections of the vein showed that the denervated vein had a luminal area up to three times that of the controls. The difference in wall thickness in the femoral vein was not significant at the p