title: Central command does not suppress baroreflex control of cardiac sympathetic nerve activity at the onset of spontaneous motor activity in the decerebrate cat.
abstract: Our laboratory has reported that central command blunts the sensitivity of the aortic baroreceptor-heart rate (HR) reflex at the onset of voluntary static exercise in animals. We have examined whether baroreflex control of cardiac sympathetic nerve activity (CSNA) and/or cardiovagal baroreflex sensitivity are altered at the onset of spontaneously occurring motor behavior, which was monitored with tibial nerve activity in paralyzed, decerebrate cats. CSNA exhibited a peak increase (126 ± 17%) immediately after exercise onset, followed by increases in HR and mean arterial pressure (MAP). With development of the pressor response, CSNA and HR decreased near baseline, although spontaneous motor activity was not terminated. Atropine methyl nitrate (0.1-0.2 mg/kg iv) with little central influence delayed the initial increase in HR but did not alter the response magnitudes of HR and CSNA, while atropine augmented the pressor response. The baroreflex-induced decreases in CSNA and HR elicited by brief occlusion of the abdominal aorta were challenged at the onset of spontaneous motor activity. Spontaneous motor activity blunted the baroreflex reduction in HR by aortic occlusion but did not alter the baroreflex inhibition of CSNA. Similarly, atropine abolished the baroreflex reduction in HR but did not influence the baroreflex inhibition of CSNA. Thus it is likely that central command increases CSNA and decreases cardiac vagal outflow at the onset of spontaneous motor activity while preserving baroreflex control of CSNA. Accordingly, central command must attenuate cardiovagal baroreflex sensitivity against an excess rise in MAP as estimated from the effect of muscarinic blockade.
authors.affiliation: Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan matsuk@hiroshima-u.ac.jp.
authors.forename: Kanji
authors.initials: K
authors.lastname: Matsukawa
authors.affiliation: Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Ishii
authors.affiliation: Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Asahara
authors.affiliation: Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Idesako
mesh_terms: D000818:Animals; D017704:Baroreflex; D001683:Biological Clocks; D001794:Blood Pressure; D002415:Cats; D063226:Central Pattern Generators; D003655:Decerebrate State / Q000503:physiopathology*; D025461:Feedback, Physiological; D006339:Heart Rate; D009068:Movement; D013564:Sympathetic Nervous System / Q000503:physiopathology*
keywords: arterial baroreflex sensitivity; baroreflex bradycardia; cardiac vagal (parasympathetic) nerve activity; exercise; renal sympathetic nerve activity