Bioelectric Activity of Mammalian Nerves during X-Irradiation

Abstract

The effect of x rays on certain bioelectric responses, in vitro, of the ventral caudal nerves of the rat was investigated. Electroric stimulation was used to determine the amplitude of the action potential and the conduction velocity of the propagated impulse, as well as the sensitivity of the nerve to stimulation. These vaInes were determined before and during exposure to x rays. Considerable increases in spike amplitude were noted very soon after the beginning of x irradiation, with lesser increases for sensitivity and for conduction velocity. Each factor investigated reached its maximum and declined at a time quite independent of the time at which the other factors reached their maxima. This indicated independence of controlling mechanisms. The action of x rays was not synergistic in that the x ray beam could be cut off and the nerve would continue to respond for some time in its enhanced condition. The response, in fact, would continue to rise if it was in the rising phase when the x ray beam was cut off, and continue to fall if it was in the falling phase; the rise or fall proceeded at slower ratss when the x ray beam was cut off. The risemore » did not continue indefinitaly but reached a certain peak, after which the activity declined and ultimately fell to a level at which no response could be elicited. Stimulation at 50/sec and 100/sec caused a decline in the activity of the nerve. Once thls decline was compensated for, the effect of x irradiation was evident: Stimulation at higher frequencies reduced considerably the enhancement of spike amplitude attributable to x rays, showed a somewhat lesser effect on enhancement of sensitivity, and showed no effect on enhancement of conduction velocity. Nerves under stimulation and x irradiation failed to respend as long as nerves under x irradiation alone. (auth)« less