HIGH ENERGY IRRADIATION: BIOELECTRIC EFFECTS 287 



Discussion 



The present findings indicate that irradiation of frog nerve with 30 krad 

 or less of high energy alpha particles or deuterons was below the minimal 

 dose required to evoke an early impaimient of neural activity. Such a result 

 is in general agreement with other obsenations found in the literature. 

 Schmitz and Schaefer (1933) reported no functional damage to frog sciatic 

 ner\e when exposed to 10 kr or x-rays. For rat sciatic nerve, no apparent 

 effect on neural conduction after exposure to 10 kr of x-rays has been ob- 

 served (Janzen and Warren, 1942). Similarly, Rothenberg (1950) adminis- 

 tered 50 kr to squid's stellar axon and reported that when the preparation 

 was electrically stimulated, good action potentials were present. From the 

 data offered in this paper, it is reasonable to report that 30 krad of 910 Mev 

 alpha particles represents a threshold dose for the destruction of bioelectrical 

 activity of the amphibian nerve. An explanation on the molecular level 

 which w'ould account for what determines the functional resistivity of nerve 

 to ionizing radiation is not found in the literature. 



For a prompt inhibition of bioelectric activity of frog sciatic nerve, about 

 300 krad of alpha particles or deuterons was required. Using a frog muscle- 

 nerve preparation, Audiat (1932) and Audiat et al., (1934) observed that 

 administering 300 kr of x-rays caused a loss of neural excitability. Gerstner 

 (1955; Gerstner et al., 1956) stated that the sciatic nerve of bullfrog {Rana 

 catesheiana) suffered a conduction block when exposed to about 300 kr of 

 high intensity x-radiation. The neural alterations of mammalian nerve 

 during x-irradiation have been investigated by Bachofer (1957) and Bachofer 

 and Gartereaux (1960a, b), and they established that approximately 500 kr 

 will extinguish the amplitude of the spike potential of the ventral caudal 

 nerve of the rat. Extirpation of axonal activity of the median and lateral 

 single giant nerve fibers of the earthwomi {Lumhricus terrestris) was shown 

 to occur after 246 and 306 kr of x-rays (Bachofer and Gautereaux, 1959). 

 The neural mechanisms affected by these massive doses of irradiation have 

 not been established. 



The sodium influx into squid giant axon immediately after x-irradiation 

 has been reported by Rothenberg (1950) using Na-*. After 125 kr, sodium 

 influx was increased markedly. On exposure to 50 kr, the rise in sodium 

 permeability was smaller, but significant. The Na^^ experiments on frog 

 nerves (described in this report) after alpha particle irradiation are in 

 harmony with the view that irradiation increases sodium ion permeability. 

 However, the alpha particle dose must be near 150 krad to express a sodium 

 permeability increase. 



Experiments have revealed that the relative biologic effectiveness (RBE) 

 of alpha particles is twice that of deuterons in inhibiting neural activity. It 



