Enhancement of Activity of Nerves by X-rays

Journal/Book: Reprinted from SCIENCE June 7 1957 Vol. 125 No. 3258 pages 1140-1141.. 1957;

Abstract: Department of Biology University of Notre Dame Notre Dame Indiana No report of the response of excised mammalian nerves during x-irradiation has heretofore been published (1) . Recordings made at the and of irradiation or at considerable periods after irradiation fail to show the dynamic changes that take place during irradiation which are reported in this paper (2). Nerves transferred from irradiation chambers to recording chambers have failed to give the highly reproducible values that are necessary in quantitative work of this type. The paired ventral caudal nerves of the rat were chosen because they possess a uniform fiber spectrum (3) and therefore exhibit sharp compact spike potentials. They are long nerves with a minimum of branching well adapted to studies an conduction velocity. Their activity is not highly dependent an temperature. Each nerve was irradiated an platinum electrodes in a specially constructed. sealed chamber which was affixed to the x-ray tube. A fine spray of oxygenated Ringer-Locke's solution was capable of keeping the nerve in excellent condition for periods well over 24 hours with adequate rovision to keep the electrodes from shorting out. The Stock of solution which served as the source of the fine spray was itself not irradiated. X-irradiation was carried out at 280 kv (peak) and 20 ma at a dose rate of 6 kr/min. Electrophysiological apparatus was employed to procure records of the response of the nerve to square-wave stimulation during irradiation. Single supramaximal stimuli were applied only at the time a recording was made. Simultaneous recordings from two pairs of electrodes one near the proximal end of the nerve the other near the distal end of the nerve separated by 50 mm were displayed an the face of a cathoderay tube. Photographie records of the responses of the nerves were made from these tracings; they were later projected an a screen for exact determination of values. The amplitude of spike potential and the conduction velocity were established for control nerves and for nerves under irradiation. Irradiation was begun only after a period of stabilization during which the output of the nerve was shown to be constant for a period of time exceeding that of the period of irradiation. Figure 1 shows the result of x-irradiation an the spike amplitude and conduction velocity of a typical nerve. An almost immediate response to x-irradiation is obvious in Fig. 1 bot it was not anticipated that the effect would be to enhance the activity of the nerve. There was an initial small increase in conduction velocity followed by a steady decrease which was quite independent of the increase in spike amplitude. The increase in spike amplitude which has now been recorded in more than 50 Gases has been as great as 60 percent with a mean of 25.6 percent; in only 6 percent of the Gases did the nerve fail to show an increase in spike amplitude as a result of irradiation. Conduction velocity an the other hand has shown an average increase of only 5.8 percent with 20 percent of the nerves failing to show an increase. In one sense the conduction velocity was more sensitive to x-rays than the spike amplitude for it began to decrease long before the spike amplitude began to decrease; in another sense it was less sensitive for the response was less and at expiration of the nerve when spike amplitude was essentially zero conduction velocity was still approximately 50 percent of the original velocity. ... ___MH

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