Pain sensitivity is not affected by sino-aortic denervation in rats

Genetic hypertension in rats appears to be associated with diminished pain sensitivity. Acute stimulation of the baroreceptors has also been reported to decrease responsiveness to a noxious stimulus. In this study the effect of sino-aortic denervation on pain sensitivity, as measured by means of a hot plate and threshold electric footshock method has been investigated. Deafferentation resulted in a labile hypertension and tachycardia. However, hot plate response latency times were not significantly different in the sino-aortic denervated rats as compared to sham operated controls under subchronic conditions. When tested for pain sensitivity three weeks after surgery using both methods on one occasion only, again the responsiveness to noxious stimuli was not different between the two groups. At the end of the experiments, the efficacy of denervation was confirmed by assessing lability of blood pressure and measuring heart rate responses to pharmacological manipulation of blood pressure. It is concluded that surgical interruption of the baroreceptor nerves in rats does not alter pain sensitivity under subchronic conditions.