Electrophysiological effects of ultraviolet radiation on single nerve fibers

Abstract

Single, isolated, giant nerve fibers of the earthworm were exposed to ultraviolet radiation; electrophysiological responses were recorded before and during irradiation. Conduction velocity, spike amplitude, and rate of spike rise were determined from photographic records of oscillographic traces. Sensitivity to electrical stimulation, defined as the reciprocal of the voltage required for threshold response, was also determined before and during irradiation. A twofold effect of ultraviolet irradiation was observed: an enhancement of activity, rarely noted in biological systems, followed by a destruction of activity, the effect commonly noted. In response to electrical stimulation during ultraviolet irradiation, the nerve fibers showed a considerable increase in sensitivity and in spike amplitude, paralleled by an increase in rate of spike rise. Conduction velocity showed an initial small increase, due to irradiation, but declined while the other factors continued to rise. The enhancement of activity was shown to be due not to a synergistic action of ultraviolet radiation but rather to a change in the nerve fiber itself which was irreversible upon cessation of irradiation.