| Abstract: | The physiological role of the sympathetic nerves in the maintenance of cerebral blood flow autoregulation (CBFA) is not established. Seven macaque monkeys implanted with Doppler flow meters on both internal carotid arteries were unilaterally sympathectomized by removal of the superior cervical ganglion. This preparation allowed for comparison of blood flows through innervated (intact) and denervated (sympathectomized) cerebral beds, with each animal serving as its own control. CBF was monitored while the animal breathed room air and upon acute exposure to 9 and 12% CO₂, following exsanguination and during metaraminol infusion. Phencyclidine was used to anesthetize the animals during the experiments. The extent of sympathetic denervation was assessed by the fluorescence histochemical technique of Falck and Hillarp. Both innervated and denervated sides exhibited CBFA, but during the breathing of room air, flow was 34% greater on the denervated side, in the arterial blood pressure range of 60-140 mm Hg. Nine and 12% CO₂ elicited vasodilation, but there were no differences in right and left flows. These results support the hypothesis that the sympathetic nerves establish a basal vascular tone and thereby determine the initial setting from which CFBA takes place but are not responsible for CBFA itself. The vasodilatory effect of the CO₂ levels tested are not affected by the presence of sympathetic nerves. |
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