Influences of the sympathetic and parasympathetic nerve transection on cardiovascular reflexes induced by volleys in the IXth nerve fibers of rat.

The effect of vagotomy and sympathectomy on cardio-acceleratory and arterial hypertensive reflexes evoked by electrical stimulation of the rat glossopharyngeal (IXth) nerve was studied in relation to changes in baseline heart rate and arterial blood pressure. Uni- and bi-lateral transection of the cervical vagal trunk brought about augmentation of baseline heart rate, accompanied by a depression in reflex tachycardia; the amount of depression being inversely related to that of an increase in baseline heart rate. The latter increased more after a right vagotomy than after a left vagotomy. No appreciable change in reflex hypertension as well as in baseline blood pressure was observed by different types of vagotomy. For unilateral sympathectomy, semilunar cordotomy caudal to the obex was performed. It was found that right semilunar cordotomy significantly depressed the magnitude of cardio-acceleratory and arterial hypertensive reflexes in association with a significant decrease in baseline heart rate, though there was a less pronounced decrease in baseline blood pressure. The result obtained by a left semilunar cordotomy was similar to that of a right semilunar cordotomy, except that the decrease in reflex tachycardia was very small and statistically insignificant. Thus, the efferent activities in vagus and sympathetic nerves were more effective on the right than on the left side, in modifying reflex tachycardia and baseline heart rate, whereas, right and left sympathetic efferent outflows were equally effective in depressing the reflex increase in blood pressure.