660 BILLEY LEVINSON 



nervous system are confounded by possible maternal fetal interactions 

 (Meier, 1960), the developing neonatal nervous system (Hicks, 1954) 

 would appear to be the subject of choice for evaluating chemoprotection. 



It has been demonstrated (Levinson and Zeigler, 1959) that total body 

 irradiation of neonatal rats results in significant decrements in adult learning 

 performance directly proportional to radiation dose. Animals exposed to a 

 single dose of radiation during the early neonatal period show the greatest 

 learning deficits as measured by maze performance; those irradiated at 18 

 days or older do not differ significantly from control animals. 



The present study was designed to confirm and extend the observations 

 on behavioral effects of radiation administered during the first 6 days of 

 life and to explore the effectiveness of a radioprotective agent, AET 

 [S,-(2-aminoethyl) isothiuronium bromide hydrobromide], in preventing the 

 decrements in maze performance typical of the irradiated animal. 



Method 



Subjects were 236 offspring born to 20 Wistar-strain mothers and exposed 

 to x-radiation 2, 4, or 6 days after parturition. They were divided into a 

 r (control) group and two groups of 225 r and 275 r. These three main 

 groups were subdivided so that approximately half received radiation fol- 

 lowing saline injections and half following AET injections. The r non- 

 irradiated group was sham irradiated and contained a saline subclass, an 

 AET subclass, and also some normal subjects who received no injection. 



Table I shows the experimental design (excluding the 22 normal subjects) . 

 To complete this design, successive groups of neonates were irradiated until 

 each experimental group contained ten 45-day-old surviving animals. 



The subjects were weighed at 40 days of age and were prepared for 

 behavioral testing by being handled. The mortality data were collected 45 

 and 75 days before the maze tests. 



Irradiation 



The radiation source was a G.E. Model OX-250 industrial x-ray unit 

 with 250 kvp, 10 ma, and 0.55 mm Cu added filtration. The target- 

 specimen distance was 70 cm and the dose rate was 26 r per minute, meas- 

 ured in air by a Victoreen condenser r meter. For exposure to the beam, 

 the rat pups were placed in individual shallow lucite chambers arranged on 

 a slowly revolving turntable to ensure equivalent radiation. Each animal 

 received a single dose of total body radiation. 



The radiation levels were selected on the basis of data from an earlier 

 experiment (Levinson and Zeigler, 1959) so as to include a moderate radi- 

 ation level (275 r), a minimal level (225 r), and a control dose (0 r). 



