Neurons of the Rostral Ventrolateral Medulla Contribute to Obesity-Induced Hypertension in Rats

Abstract
Activation of the sympathetic nervous system contributes to the pathogenesis of obesity-induced hypertension. The present study sought to determine whether sympathetic regulatory neurons of the rostral ventrolateral medulla contribute to the elevated blood pressure in obese rats. Male Sprague–Dawley rats (350 to 425 g) were placed on a moderately high-fat diet (32% kcal as fat) or a low-fat (LF) diet (10.6% kcal as fat). After 13 weeks, rats fed the moderately high-fat diet segregated into obesity-prone (OP) and obesity-resistant (OR) groups based on their body weight (OP: 839±22 g; OR: 668±15 g; LF: 680±18 g; n=15 for all groups; P P A receptor agonist muscimol (200 pmol/100 nL) decreased mean arterial blood pressure to similar levels across the groups (OP: 49±1 mm Hg; OR: 50±2 mm Hg; LF: 49±1 mm Hg), but the magnitude of this decrease was significantly greater in the OP versus the OR and LF rats (OP: −58±2 mm Hg; OR: −49±1 mm Hg; LF: −48±3 mm Hg; P 50 in response to phenylephrine and norepinephrine was similar across the groups. The present findings suggest that the elevated sympathetic nerve activity and arterial blood pressure in obese rats depends on the tonic activity of rostral ventrolateral medulla sympathetic neurons.