A hypothesis for generation of central command signal during exercise

 

Kanji Matsukawa

Department of Physiology, Graduate School of Health Sciences, Hiroshima University

1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan

 

We can feel that a heartbeat is influenced by central command from higher brain centers in association with emotions and voluntary activities including exercise.  In daily life, a positive relationship between arterial pressure (AP) and heart rate (HR) is usually obtained, suggesting that central command, but not the arterial baroreflexes, determines the level of HR.  However, cardiac autonomic outflow in a conscious condition has been little understood due to technical difficulty of direct recording, especially cardiac vagal nerve activity (CVNA).  Furthermore, the neural networks for generating central command remain little known, because it is difficult to accomplish a comprehensive study with voluntary exercise.  First, I would like to summarize the response in cardiac sympathetic nerve activity (CSNA) during voluntary exercise in conscious cats and the responses in CVNA and CSNA during spontaneous fictive exercise in paralyzed decerebrate cats.   CSNA increased prior to or at the onset of voluntary exercise in conscious cats.  Such abrupt increase in CSNA was also observed during spontaneous fictive exercise, whereas a decrease in CVNA was never obtained.  Central command, therefore, contributes to exercise tachycardia via sympathetic activation but not vagal withdrawal as opposed to the traditional concept.  In addition, the fact that the rapid sympathetic response occurred during fictive exercise in decerebrate cats suggests that the brainstem, but not the cerebral cortex, may play an essential role in generating central command.  In the later part of my talk, I would like to argue a hypothesis for generation of central command in the brainstem.  Since the positive AP-HR relationship in daily life was lost or weakened in idiopathetic Parkinson’s patients, we hypothesized that the midbrain dopaminergic system [substantia nigra (SN) or ventral tegmentum area (VTA)] may play a role in generating central command.  Indeed, the cardiovascular response at the onset of voluntary exercise in Parkinson’s patients was blunted as compared to normal subjects.  Chemical or electrical stimulation of VTA but not SN increased renal sympathetic outflow, HR, and AP in anesthetized cats and rats.  Taken together, we propose the hypothesis that VTA may be involved in generation of central command during exercise.

 

Key words: Central command, Cardiac sympathetic and parasympathetic outflows, Voluntary exercise