Central command blunts the baroreflex bradycardia to aortic nerve stimulation at the onset of voluntary static exercise in cats

Abstract

Komine, Hidehiko, Kanji Matsukawa, Hirotsugu Tsuchimochi, and Jun Murata. Central command blunts the baroreflex bradycardia to aortic nerve stimulation at the onset of voluntary static exercise in cats. Am J Physiol Heart Circ Physiol 285: H516-H526, 2003. First published May 1, 2003 10.1152/ajpheart.00013.2003.-To examine whether the central characteristics of the aortic baroreflex alter from moment to moment during static exercise, we identified the dynamic changes in the sizes of the bradycardia and depressor response evoked by stimulation of the aortic depressor nerve (ADN). Three conscious cats were trained to voluntarily extend the right forelimb and press a bar for 31 Ϯ 1 s with a peak force of 337 Ϯ 22 g while maintaining a sitting posture. The ADN stimulation-induced bradycardia was attenuated at the initial period of exercise (up to 8 s from the exercise onset) to 62 Ϯ 5% of the preexercise bradycardia and remained blunted until the end of exercise. The most blunted bradycardia was observed immediately before or when the forelimb was extended before force development. The baroreflex-induced bradycardia was suppressed again at cessation of exercise when the forelimb was retracted and recovered within a few seconds. In contrast, static exercise did not affect the ADN stimulation-induced depressor response. The ADN stimulation-induced bradycardia was also blunted at the beginning of naturally occurring body movement such as spontaneous postural change or grooming behavior. Thus it is likely that the central characteristics of the aortic baroreflex dynamically change from moment to moment during voluntary static exercise and during natural body movement and that particularly a central inhibition of the cardiac component of the aortic baroreflex is induced by central command at the onset of static exercise, whereas the central property of the vasomotor component of the baroreflex is preserved.aortic depressor nerve; aortic baroreceptors; baroreflex sensitivity; baroreflex depressor response; central modulation of the arterial baroreflex ARTERIAL BLOOD PRESSURE (AP) is sensed by arterial baroreceptors in the carotid sinus and aortic arch regions, whose activities transmit the beat-to-beat changes in AP to the central nervous system and evoke the baroreflex responses of autonomic efferent nerve activities to the heart and blood vessels. For example, if AP increases during resting, arterial baroreceptors are stimulated in proportion to the rise in AP, which elicits reflex bradycardia and depressor response and thereby restores AP to the control level. However, it is well known that heart rate (HR) and AP increase simultaneously during static or dynamic exercise in humans and conscious animals, indicating that arterial baroreflex function is modulated by exercise.The effect of exercise on the arterial baroreflexes has been extensively studied in humans and animals. When baroreflex sensitivity was assessed as a ratio of the change in R-R interval or HR in response to an alteration in AP, it was reduced during d...

Gadolinium does not blunt the cardiovascular responses at the onset of voluntary static exercise in cats: a predominant role of central command

“…The cats were operantly conditioned to perform static exercise as previously described in detail (5,9,22,24,26). They were trained to sit quietly in a transparent plastic box (width 35 ϫ height 40 ϫ depth 50 cm) with a small window (width 5 ϫ height 7 cm), extend a forelimb through the window, and press a bar for 10 -40 s while maintaining a sitting posture.…”

“…Matsukawa and colleagues (22,26,34) have recently provided clear evidence that central command acts upon the arterial baroreflex circuit within the brainstem and modulates its central property at the start of static exercise. The baroreflex bradycardia elicited by aortic nerve stimulation was blunted immediately before static exercise in conscious cats, even in the absence of muscular exertion, and at the onset of spontaneous muscle contraction in decerebrate cats; in contrast, the depressor response to aortic nerve stimulation was not affected by static exercise (22,34). It is likely that central command inhibits selectively the cardiac component of the arterial baroreflex at the onset of exercise, which, in turn, induces an abrupt increase in HR.…”

Orexin neuron-mediated skeletal muscle vasodilation and shift of baroreflex during defense response in mice

“…However, two other important features of the defense response have not yet been analyzed. Those are skeletal muscle vasodilation and attenuation of reflex bradycardia or resetting of the baroreflex (11,23,29,35,38).The aim of this study was to examine whether orexin also contributes to redistribution of blood flow and suppression of reflex bradycardia during the defense response using ORX/ ATX-Tg mice. We used ORX/ATX-Tg mice in the present experiment so that we might gain some insight into the physiological significance of the other neuropeptides or modulatory factors contained in the orexinergic neuron by comparing present data with our previous data using ORX-KO mice (22).…”

“…However, two other important features of the defense response have not yet been analyzed. Those are skeletal muscle vasodilation and attenuation of reflex bradycardia or resetting of the baroreflex (11,23,29,35,38).…”

Central command blunts sensitivity of arterial baroreceptor-heart rate reflex at onset of voluntary static exercise

“…However, it has remained unknown whether such modulation of arterial baroreflex function can be applied over the whole period of exercise, especially at the beginning of exercise. It is conceivable that the functional characteristics of the arterial baroreflex dynamically alter from moment to moment during exercise.Recently, we evaluated the effect of voluntary static exercise on the dynamic characteristics of arterial baroreflex function, using stimulation of the aortic depressor nerve (ADN) given at various times during exercise in conscious intact or unanesthetized decerebrate cats (12,26). The sizes of the baroreflex bradycardia and depressor response to ADN stimulation reflected the central characteristics of the cardiac and vasomotor components of the aortic baroreflex, respectively.…”