title: Development of attenuated baroreflexes in obese Zucker rats coincides with impaired activation of nucleus tractus solitarius.
abstract: Adult obese Zucker rats (OZR; >12 wk) develop elevated sympathetic nerve activity (SNA) and mean arterial pressure (MAP) with impaired baroreflexes compared with adult lean Zucker rats (LZR) and juvenile OZR (6-7 wk). In adult OZR, baroreceptor afferent nerves respond normally to changes in MAP, whereas electrical stimulation of baroreceptor afferent fibers produces smaller reductions in SNA and MAP compared with LZR. We hypothesized that impaired baroreflexes in OZR are linked to reduced activation of brain stem sites that mediate baroreflexes. In conscious adult rats, a hydralazine (HDZ)-induced reduction in MAP evoked tachycardia that was initially blunted in OZR, but equivalent to LZR within 5 min. In agreement, HDZ-induced expression of c-Fos in the rostral ventrolateral medulla (RVLM) was comparable between groups. In contrast, phenylephrine (PE)-induced rise in MAP evoked markedly attenuated bradycardia with dramatically reduced c-Fos expression in the nucleus tractus solitarius (NTS) of adult OZR compared with LZR. However, in juvenile rats, PE-induced hypertension evoked comparable bradycardia in OZR and LZR with similar or augmented c-Fos expression in NTS of the OZR. In urethane-anesthetized rats, microinjections of glutamate into NTS evoked equivalent decreases in SNA, heart rate (HR), and MAP in juvenile OZR and LZR, but attenuated decreases in SNA and MAP in adult OZR. In contrast, microinjections of glutamate into the caudal ventrolateral medulla, a target of barosensitive NTS neurons, evoked comparable decreases in SNA, HR, and MAP in adult OZR and LZR. These data suggest that OZR develop impaired glutamatergic activation of the NTS, which likely contributes to attenuated baroreflexes in adult OZR.
authors.affiliation: Department of Physiology, Medical College of Georgia, Augusta, Georgia;
authors.forename: Priscila S
authors.initials: PS
authors.lastname: Guimaraes
authors.forename: Domitila A
authors.initials: DA
authors.lastname: Huber
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Campagnole-Santos
authors.forename: Ann M
authors.initials: AM
authors.lastname: Schreihofer
mesh_terms: D000818:Animals; D062186:Arterial Pressure; D017704:Baroreflex / Q000187:drug effects; D001919:Bradycardia / Q000503:physiopathology / Q000517:prevention & control; D004195:Disease Models, Animal; D018690:Excitatory Amino Acid Agonists / Q000008:administration & dosage / Q000378:metabolism; D018698:Glutamic Acid / Q000008:administration & dosage / Q000378:metabolism; D006339:Heart Rate; D006439:Hemodynamics / Q000187:drug effects; D008297:Male; D008845:Microinjections; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011924:Rats, Zucker; D012021:Reflex, Abnormal / Q000187:drug effects; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000503:physiopathology; D013610:Tachycardia / Q000503:physiopathology; D013997:Time Factors; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D018690:Excitatory Amino Acid Agonists; D016760:Proto-Oncogene Proteins c-fos; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D018698:Glutamic Acid
keywords: autonomic; baroreflex; c-Fos; obesity; sympathetic nerve activity; ventrolateral medulla