REPETITIVE DISCHARGE OF NEURONS

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Abstract
The nature and origin of 2 types of "after-discharge" were examined. The 1st occurs in sensory afferent fibers to the spinal cord. After the arrival of a single afferent volley, a repetitive antidromic discharge called the dorsal root reflex, DRR, is generated in the terminals of the active fibers and in their passive neighbors. The DRR was set off by stimulation of peripheral nerves. The initial latency and the variation of latency throughout the discharge depended on the nerve stimulated and the strength of stimulation. The pattern of the response differed markedly from that seen in the interneurons on which the fibers end. The time of arrival of the afferent impulse in an afferent fiber did not affect the pattern of DRR. The interjection of an impulse into a DRR resets the rhythm and it is concluded that the site of origin of the rhythm is within the fiber. "Spontaneous" activity of peripheral sensory endings is similarly reset by the introduction of additional impulse. The 2nd type of "after-discharge" examined was that produced by dorsal horn sensory interneurons after the arrival of a single volley from a peripheral sensory nerve. The pattern of discharge of the sensory interneurons varied among 3 types of responses: a low-frequency short discharge with great variation of latency, a high-frequency prolonged discharge, and a short abrupt discharge. The interjection of an additional impulse into the repetitive discharge of an interneuron fails to reset the rhythm and the discussion concludes that the repetitive firing is probably driven by bombardment from other neurons.