Response of a Sympathetic Ganglion to High Frequency Stimulation. ∗

Abstract

If a preganglionic mammalian nerve is stimulated at a low frequency, each volley of impulses initiates a fairly well synchronized discharge in the postganglionic nerve. 1 When the rate of stimulation is increased to 30 or 40 per second there is a progressive decrease in the height of the postganglionic spike potential. This apparent failure in the capacity of the ganglion to transmit impulses at a high frequency is a property of the synapse which must be taken into consideration in the formulation of any theory which attempts to explain the mechanism of synaptic transmission.

All of our experiments were performed on cats in a room maintained at close to body temperature. The pregaglionic fibers in the third or fourth thoracic root were stimulated by means of a thyra-tron stimulator and the impulse discharge from the stellate ganglion was recorded in the inferior cardiac nerve.

The effect which we are considering can be demonstrated by stimulating the preganglionic nerve at a frequency of about 60 per second. The successive postganglionic spike potentials rapidly decrease in height and after a variable number of stimuli they can no longer be detected at ordinary amplifications. There is no such rapid failure at these frequencies of the spike potential in either the pre- or postganglionic nerves when they are stimulated directly. This suggests that the ganglion blocks the transmission of impulses at high frequencies.

Two observations argue against such a conclusion. In the first place we have found that stimulation of the preganglionic fibers at frequencies as high as 120 per second produces cardiac acceleration throughout long periods of stimulation. In the second place, the electrical record of postganglionic activity during such stimulation frequently shows a negative displacement of the base line which continues until the end of the stimulus. It would appear therefore that there is continued activity in the postganglionic fibers despite the absence of the usual spike potential.