Research Article Participation of 5-HT and AT 1 Receptors within the Rostral Ventrolateral Medulla in the Maintenance of Hypertension in the Goldblatt 1 Kidney-1 Clip Model Cássia T. Bergamaschi, 1 Nyam F. Silva, 2 Jose G. Pires, 3,4 Ruy R. Campos, 1 and Henrique A. Futuro Neto 2,3,5 1 Federal University of S˜ ao Paulo, School of Medicine, Rua Botucatu 862, 04023-060 S˜ ao Paulo, SP, Brazil 2 Federal University of Espirito Santo, 29042-751 Vit´ oria, ES, Brazil 3 UNIVIX Medical School, 29075-080 Vit´ oria, ES, Brazil 4 UNESC Medical School, 29703-900 Colatina, ES, Brazil 5 EMESCAM Medical School, 29045-402 Vit´ oria, ES, Brazil Correspondence should be addressed to Ruy R. Campos; ruy.camposjr@unifesp.br Received 30 April 2013; Accepted 2 December 2013; Published 21 January 2014 Academic Editor: Claudio Borghi Copyright © 2014 C´ assia T. Bergamaschi et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te hypothesis that changes in neurotransmission within the rostral ventrolateral medulla (RVLM) are important to maintain the high blood pressure (BP) was tested in Goldblatt one kidney-one clip hypertension model (1K-1C). Male Wistar rats were anesthetized (urethane 1.2 g/kg, i.v.), and the efects of bilateral microinjections into the RVLM of the following drugs were measured in 1K-1C or control groups: glutamate (0.1 mol/L, 100 nL) and its antagonist kynurenic acid (0.02 mol/L, 100 nL), the angiotensin AT 1 receptor antagonist candesartan (0.01 mol/L, 100 nL), and the nonselective 5-HT receptor antagonist methiothepin (0.06 mol/L, 100 nL). Experiments in 1K-1C rats were performed 6 weeks afer surgery. In anesthetized rats glutamate response was larger in hypertensive than in normotensive rats (H: Δ67 ± 6.5; N: Δ43 ± 3.54 mmHg). In contrast, kynurenic acid microinjection into the RVLM did not cause any change in BP in either group. Te blockade of either AT 1 or 5-HT receptors within the RVLM decreased BP only in 1K-1C rats. A largest depressor response was caused by 5-HT receptor blockade. Te data suggest that 5-HT and AT 1 receptors act tonically to drive RVLM in 1K-1C rats, and these actions within RVLM contribute to the pathogenesis of this model of hypertension. 1. Introduction Te importance of sympathetic nervous system activation in the pathogenesis of hypertension has been demonstrated, and the therapeutic value of sympathetic nervous inhibition in hypertensive patients is already evident and has been widely studied [1]. Ongoing activity of premotor rostral ventrolateral medulla (RVLM) neurons is responsible for the tonic generation of sympathetic vasomotor tone; inhibition of RVLM neurons causes a large decrease in both arterial blood pressure (BP) and sympathetic nervous system activity, while stimulation of this medullary region increases sympathetic vasomotor outfow and BP [2, 3]. Terefore, changes in the local neurotransmission within the RVLM can be a mecha- nism involved in the sympathetic activation in hypertension. Previous studies demonstrated that microinjection into the RVLM of excitatory amino acid (EAA) receptor antag- onists has no efect on basal level of BP [4]. Tis fact has been interpreted as suggesting that the ongoing RVLM activity is not dependent on EAA inputs to the RVLM. However, we showed previously that, in Goldblatt 2-kidneys, one-clip (2K1C) model, microinjection of kynurenic acid, a broad spectrum EAA receptor antagonist, into the RVLM, reduced BP to the same extent as autonomic blockade [5]. Similar results were later shown in SHR and in Dahl-salt sensitive rats [6, 7]. On basis of these results, it was proposed that tonic Hindawi Publishing Corporation International Journal of Hypertension Volume 2014, Article ID 723939, 6 pages http://dx.doi.org/10.1155/2014/723939