HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 287/3/H1312    most recent 00163.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Li, J. Search for Related Content PubMed PubMed Citation Articles by Li, J.

Central integration of muscle reflex and arterial baroreflex in midbrain periaqueductal gray: roles of GABA and NO

Division of Cardiology, Department of Medicine, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033; andInternal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas 75235

Submitted 17 February 2004 ; accepted in final form 9 April 2004

It has been suggested that the midbrain periaqueductal gray (PAG) is a neural integrating site for the interaction between the muscle pressor reflex and the arterial baroreceptor reflex. The underlying mechanisms are poorly understood. The purpose of this study was to examine the roles of GABA and nitric oxide (NO) in modulating the PAG integration of both reflexes. To activate muscle afferents, static contraction of the triceps surae muscle was evoked by electrical stimulation of the L₇ and S₁ ventral roots of 18 anesthetized cats. In the first group of experiments (n = 6), the pressor response to muscle contraction was attenuated by bilateral microinjection of muscimol (a GABA receptor agonist) into the lateral PAG [change in mean arterial pressure (MAP) = 24 ± 5 vs. 46 ± 8 mmHg in control]. Conversely, the pressor response was significantly augmented by 0.1 mM bicuculline, a GABA_A receptor antagonist (MAP = 65 ± 10 mmHg). In addition, the effect of GABA_A receptor blockade on the reflex response was significantly blunted after sinoaortic denervation and vagotomy (n = 4). In the second group of experiments (n = 8), the pressor response to contraction was significantly attenuated by microinjection of L-arginine into the lateral PAG (MAP = 26 ± 4 mmHg after L-arginine injection vs. 45 ± 7 mmHg in control). The effect of NO attenuation was antagonized by bicuculline and was reduced after denervation. These data demonstrate that GABA and NO within the PAG modulate the pressor response to muscle contraction and that NO attenuation of the muscle pressor reflex is mediated via arterial baroreflex-engaged GABA increase. The results suggest that the PAG plays an important role in modulating cardiovascular responses when muscle afferents are activated.

blood pressure; exercise pressor reflex

This article has been cited by other articles:

				I. H. Zucker Novel Mechanisms of Sympathetic Regulation in Chronic Heart Failure Hypertension, December 1, 2006; 48(6): 1005 - 1011. [Full Text] [PDF]

				S. C. Tjen-A-Looi, P. Li, and J. C. Longhurst Midbrain vlPAG inhibits rVLM cardiovascular sympathoexcitatory responses during electroacupuncture Am J Physiol Heart Circ Physiol, June 1, 2006; 290(6): H2543 - H2553. [Abstract] [Full Text] [PDF]