[The relationship between changes in the temporal and frequency characteristics of parasympathetic nerve activity and...

Changes of chronotropic effect on the frog heart on stimulation of part of extracardiac pathways, were studied. On the 10/sec stimulation during 1.5 sec, cardioinhibitory effect occurred. On 0.2 sec duration of the stimulation the positive chronotropic effect was observed. The heart rate increased on the 3/sec stimulation of the undegenerating extracardiac fibers by the 21st day after bilateral vagotomy; of the frequency of the stimulation was increased to 10/sec, the negative chronotropic effect occurred, and sympathectomy and the reserpine injection had no influence on the positive chrontropic effects. Both the negative and positive chronotropic effects could be prevented by atropine. The different chrontropic effects on the heart are, probably, due to activity of but a single functional type of fibers: the parasympathetic nervous fibers.