Crossover in baroreflex pathways controlling renal sympathetic nerve activity.

Experiments were performed to investigate the physiologic significance of the crossover of baroreceptor afferent input to the contralateral nucleus tractus solitarius (NTS) in terms of reflex control of renal sympathetic nerve activity and to determine the physiologic significance of neuronal crossover which may occur beyond the NTS. Experiments were done in 14 alpha-chloralose anesthetized rabbits. Baroreflex control of left renal nerve activity was determined from responses to phenylephrine-induced increases and nitroglycerin-induced decreases in arterial pressure. Under control conditions, the mean regression slope for changes in renal nerve activity (imp/sec/mmHg change in arterial pressure) was -2.2 +/- 0.5. After unilateral NTS lesion (n = 14) the gain of the reflex was -2.4 +/- 0.4 imp/sec/mmHg. Denervation of baroreceptors ipsilateral to the NTS lesion (n = 6) did not alter the regression slope (-2.7 +/- 0.5 imp/sec/mmHg), but interruption of the contralateral carotid and aortic baroreceptor afferent fibers (n = 8) markedly reduced the slope of the linear regression relationship from -2.4 +/- 0.3 to -1.1 +/- 0.3 imp/sec/mmHg. We interpret these data to suggest that baroreceptor afferent input exerts its major reflex influence via the ipsilateral NTS and that there is modest influence exerted by fibers which cross over to the contralateral side. In addition, since we recorded from the left renal nerves and alternated the side of the NTS lesion, we interpret our findings regarding a lesion in only one NTS to suggest that there is crossover in the baroreflex pathway beyond the NTS which permits the NTS on one side to exert an influence on the renal nerves on the contralateral side similar to that seen when the NTSs on both sides are intact.