LESIONS IN ROSTRAL VENTROMEDIAL OR ROSTRAL VENTROLATERAL MEDULLA BLOCK NEUROGENIC HYPERTENSION

Neurogenic hypertension results from the removal of inhibitory baroreceptor afferent input to vasomotor systems in the central nervous system. We sought to determine whether the bilateral destruction of neurons in the rostral ventrolateral or rostral ventromedial medulla, made using microinjections of N-methyl-D-aspartic acid (30 nmol in 200 nL), would block the acute increase in arterial pressure after sinoaortic deafferentation in pentobarbital-anesthetized rats. Bilateral lesions of the rostral ventrolateral or rostral ventromedial medulla decreased mean arterial pressure (107+/-4 to 78+/-5 and 115+/-3 to 94+/-3 mm Hg, respectively). In rostral ventrolateral or rostral ventromedial medulla lesioned rats, sinoaortic deafferentation failed to increase arterial pressure. Sham lesions or lesions placed rostral to the rostral ventrolateral or rostral ventromedial medulla did not significantly lower arterial pressure. Subsequent sinoaortic deafferentation significantly increased mean arterial pressure (109+/-3 to 145+/-4 and 109+/-5 to 141+/-3 mm Hg, respectively). In eight rats we used an infusion of angiotensin II to return arterial pressure to control levels after lesion of the rostral ventrolateral (n=4) or rostral ventromedial (n=4) medulla. In these animals, sinoaortic deafferentation failed to increase arterial pressure. We conclude that neurons in the rostral ventrolateral and rostral ventromedial medulla are involved in the normal maintenance of arterial pressure and the development of hypertension after sinoaortic deafferentation in pentobarbital-anesthetized rats.