Abstract
We have investigated certain aspects of the mechanism of synaptic transmission in a sympathetic ganglion by recording the action potentials in the inferior cardiac nerve of the cat while stimulating the preganglionic fibers to the stellate. This preparation has proved admirable for such a study because the long postganglionic nerve makes possible a careful investigation of the properties of the fibers whose response is used as a measure of the activity of the ganglion.
The form of the action potential in the non-medullated fibers of the inferior cardiac nerve has been determined by recording the impulses in the nerve during direct excitation. It differs from that of medullated nerve in 2 respects which are important to this investigation. Because the conduction velocity is much less (0.4 to 1.1 meters per second) there is a marked spread of the spike potential due to temporal dispersion of impulses in the several fibers. This temporal dispersion and the large positive and negative after potentials which are found in these non-medullated nerves may combine to give the potential wave a complicated form of several crests and troughs. In this we confirm Bishop. 1 Because of these considerations it is necessary to be cautious in the use of the post ganglionic response as an index of repetitive firing from the ganglion or in the use of the ganglion potentials described by Eccles 2 , 3 as a key to ganglionic processes.
The question as to whether each preganglionic volley sets up a single postganglionic volley or whether an independent rhythm is developed in the synapses of the ganglion has long been debated. 4 , 5 , 6 We have reopened the problem with the following experiments. The preganglionic nerves have been stimulated with single and repeated shocks and the potentials in the postganglionic nerves recorded. Provided the frequency of stimulation does not exceed about 40 per second we find that each volley of impulses in the preganglionic fibers sets up only a single volley of impulses in the postganglionic nerve.
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