Matthew N. Levy

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  • M N Levy
  • 1997
The principal functions of the heart are regulated by the sympathetic and parasympathetic divisions of the autonomic nervous system. In general, the sympathetic nerves to the heart are facilitatory, whereas the parasympathetic (vagus) nerves are inhibitory. The kinetics of the two autonomic divisions differ substantially. The vagal effects develop very(More)
We determined the effects of the timing of repetitive bursts of vagal stimulation on the positive chronotropic responses of the heart to trains of cardiac sympathetic nerve stimulation in open-chest anesthetized dogs. Trains of sympathetic stimulation alone, at frequencies of 2 and 4 Hz, decreased the cardiac cycle length by 176 +/- 19 msec (mean +/- SE)(More)
In the heart and in the blood vessel walls, complex adrenergic-cholinergic interactions occur both prejunctionally, at the level of the autonomic nerve terminals, and postjunctionally, at the level of the responding cells themselves. The principal prejunctional interaction appears to be an inhibition of the release of norepinephrine from adrenergic nerve(More)
We developed a mathematical model of the underlying cellular mechanisms responsible for the changes in sinus cycle length (SCL) elicited by vagal stimulation in intact animals. The model incorporated a stimulation-mediated depletion of the releasable pool of acetylcholine (ACh) in the nerve endings, the in vitro reaction kinetics of acetylcholinesterase,(More)
BACKGROUND In animals, parasympathetic nerve fibers that innervate the sinoatrial node can be selectively stimulated to increase atrial cycle length. These nerve fibers course through an epicardial fat pad at the margin of the right superior pulmonary vein, the superior vena cava, and the right atrium. We hypothesized that similar nerves exist and can be(More)
Vagus nerve activity can change heart rate substantially within one cardiac cycle, and the chronotropic effects decay almost completely within one cardiac cycle after cessation of vagal activity. The ability of the vagus nerves to regulate heart rate beat by beat can be explained in large part by the speed at which the neural signal is transduced to a(More)
ATP transiently increases the intracellular Ca2+ concentration in cardiac myocyte suspensions. Pretreatment with norepinephrine (NE) greatly potentiates the ATP response. We performed experiments on adult rat myocyte suspensions loaded with fura-2 to investigate the mechanism of NE potentiation. We found that forskolin (an activator of adenylate cyclase),(More)
In the isolated, blood-perfused, canine right atrium, stimulation of the intramural autonomic nerves evoked negative chronotropic and inotropic responses. The responses were not maintained at a constant level during tonic neural stimulation, but they tended to drift back toward their control levels. These time-dependent changes in the cardiac responses were(More)
We applied trains of stimuli to the vagosympathetic trunks of anesthetized dogs and studied the time courses of the resultant chronotropic and inotropic responses. These responses were maximum soon after the onset of the test stimulus train but then declined over the next 1-5 min despite continued stimulation. The fade ratio was defined as the magnitude of(More)