Abstract
If volleys of impulses enter a sympathetic ganglion at frequencies not exceeding 15 or 20 per second, each impulse arriving at a given synapse causes the discharge of not more than one impulse from the corresponding ganglion cell. 1 Thus no repetitive discharge has been observed, and there is evidence that this is also true in certain cases of synaptic transmission in the central nervous system. To account for this it has been assumed that there is a rapid decay of the excitatory state developed by the presynaptic impulses. The neurohumoral hypothesis takes cognizance of this fact by assuming that the acetylcholine is rapidly hydrolyzed.
We have recently discovered conditions in which the statements made in the preceding paragraph do not correctly describe the course of the excitation at the synapses. For we have observed a long-lasting discharge of impulses from ganglion cells, following a brief period of preganglionic stimulation at a frequency of 40 or more per second.
All of the nerves leading to and from the stellate ganglion of the cat were sectioned. The preganglionic trunk was then stimulated while recording the impulses in the postganglionic inferior cardiac nerve.
At the lower frequencies each preganglionic volley initiates a single volley of impulses in the postganglionic nerve. If the frequency of stimulation be 40 or more per second the synchronized discharge of impulses does not continue throughout the course of a period of stimulation but soon becomes random due to the asynchronous activity of the several ganglion cells. 2 When the stimulation of the preganglionic nerve is stopped the discharge from the ganglion does not cease but the random discharge from many cells continues for some time thereafter.
Get full access to this article
View all access options for this article.