RADIATION AND AUDIOGENIC SEIZURES IN MICE 517 



the normal DBA 1 lc\cl. The rapid drop in susceptibility is strong evidence 

 for an en\ironmental influence of radiation on the seiziue response. In those 

 litters born and reared in Room G durins: the ensuing; 8 months, the seizure 

 frequency was sia^nificantly below the normal DBA/ 1 level, with no sex 

 difference in susceptibility. Many litters included in the last figures were 

 ofTsprinof of the same matings which had produced the hioh susceptibility 

 group earlier in the year. 



In addition to the lowered incidence of seizures, two other measures indi- 

 cate that the DBA/ 1 line had become uenetically less sound susceptible while 

 exposed to chronic low level radiation. The latency of fatal seizures was 

 sisjnificantly loniier, with many delayed seizures, and the proportion of the 

 fatal seizmes which occurred on the 1st trial declined from 96^ r to 49*"^ . We 

 conclude that while the low level radiation exerted a physiolos:ic effect in in- 

 creasing' the frequency and se\erity of seizures, the line had undergone genetic 

 change in the direction of lowered susceptibility to audiogenic seiziues. 



C57BL6. Although the chief influence of low level radiation on the 

 seizure response appears to be physiologic, there was further e\iclence of 

 genetic change in the colony during chronic exposure. C'.57BL6 mice are 

 normally almost completely resistant to sound stimulation. After the colony 

 had been maintained in Room R for 1 year, the C5BL6 mice were tested 

 systematically, and a seizure frequency of 16'"r was observed. 



To determine whether this imusual seiziu^e susceptibility had a genetic 

 basis, a selecti\e breeding experiment was undertaken. Males and females 

 which were negative on 4 trials, and had no littermates or close relatixes which 

 had convulsed, were bred together. Likewise, males and females which con- 

 vulsed were bred to each other. It is possible to save for breeding some ani- 

 mals that suffer fatal seizures by applying prompt artificial respiration. ) 

 Among the litters of the negative animals 3''r had seizmes. while 19'"r of the 

 progenies of con\'uIsers had seizvues. The incidence of seiziues did not change 

 in subsequent litters oi these selected matings after the colony was moved from 

 Room R to Room G. The increase in seizure susceptibility of the C57BL6 

 mice is attributed to mutations of "seizure"" genes under safe radiation le\els. 



Tests for Influence of Radiation on Seizure Response 



Since it was apparent that both DBA 1 and G57BL6 stocks had imder- 

 gone genetic change affecting their seizure susceptibilitv, we obtained new 

 stocks of mice from Jackson Laboratory and restored 2 crosses in which 

 there had been a dramatic increase in susceptibility while in Room R : the 

 Fi generation of DBA/1 by C57BL6 and the background of this Fi gener- 

 ation to C57BL6. 



Through the cooperation of Dr. Eric Simmons of the Argonne Cancer 



