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Exaggerated sympathoexcitatory reflexes develop with changes in the rostral ventrolateral medulla in obese Zucker rats

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AJP Regulatory Integrative and Comparative Physiology

Published online on

Abstract

Obesity leads to altered autonomic reflexes that reduce stability of mean arterial pressure (MAP). Sympathoinhibitory reflexes such as baroreflexes are impaired, but reflexes that raise MAP appear to be augmented. In obese Zucker rats (OZR) sciatic nerve stimulation evokes larger increases in MAP by unknown mechanisms. We sought to determine the autonomic underpinnings of this enhanced somatic pressor reflex, and whether other sympathoexcitatory reflexes are augmented. We also determined whether their final common pathway, glutamatergic activation of the rostral ventrolateral medulla (RVLM), was enhanced in male OZR compared to lean Zucker rats (LZR). Sciatic nerve stimulation or activation of the nasopharyngeal reflex evoked larger rises in splanchnic SNA (79% and 45% larger in OZR respectively, P<0.05) and MAP in urethane-anesthetized, ventilated, paralyzed adult OZR compared to LZR. After elimination of baroreflex feedback by pharmacological prevention of changes in MAP and heart rate, these two sympathoexcitatory reflexes were still exaggerated in OZR (167% and 69% larger respectively, P<0.05). In adult OZR microinjections of glutamate, AMPA, or NMDA into the RVLM produced larger rises in SNA (~61% larger in OZR, P<0.05 for each drug) and MAP, but stimulation of axonal fibers in the upper thoracic spinal cord yielded equivalent responses in OZR and LZR. In juvenile OZR and LZR, sympathoexcitatory reflexes and physiological responses to RVLM activation were comparable. These data suggest the ability of glutamate to activate the RVLM becomes enhanced in adult OZR and may contribute to the development of exaggerated sympathoexcitatory responses independent of impaired baroreflexes.