Towards an understanding of the function of the intrinsic cardiac ganglia
David C. Randall
Department of Physiology, University of Kentucky College of Medicine, Lexington, KY 40536-0298, USA
Prior to the 1950s, the ability of the heart to respond to challenges was perceived primarily in terms of the intrinsic properties of the myocardium, but two captivating studies published at about mid-century inaugurated a re-examination of this issue. The finding that the diameter of the canine heart decreased during exercise relative to rest (Rushmer et al. 1959) was contrary to the then current understanding of Starling's Law and, shortly thereafter, the importance of the extrinsic (i.e. autonomic neural) control of cardiac function became more apparent. A second signal observation was Alexander's description of the 'pressor' and 'depressor' regions of the brainstem (see Gebber, 1990). Our knowledge of the central nervous control of autonomic function has expanded dramatically since that time, but, until recently, little attention had been directed to the role of the neurons residing at the heart itself. In fact, it is still not widely appreciated that these 'intrinsic cardiac ganglia' include neuronal types (e.g. sensory and interneurons) other than classic parasympathetic neurites so that the potential exists for intracardiac reflex control of the heart's function. The article by Thompson et al. (2000) in this issue of TheJournal of Physiology takes a key step in testing the reality of the concept of such a 'heart brain' (Randall et al. 1996).
