EFFECTS OF RADIATION ON CNS AND ON BEHAVIOR 637 



et al. (1959) ha\'e shown that specific cerebral structures of rats are differ- 

 entially affected by radiation on successive days after conception. He sug- 

 gested that it should be possible to relate behavioral measures to specific 

 malformations of cerebral cortical structure. 



The behavior studies on the effects of irradiation early in life give data in 

 keeping with the known radiosensitivity of the developing nervous system. 

 Levinson (1952) fetally x-irradiated rats with 300-600 r on the 11th, 13th, 

 15th, 17th, and 19th postconception days. When the animals were 50 days 

 old, they were tested on a Lashley Type III maze. Deficits were found to be 

 directly related to the radiation dose and to be most severe for groups irradi- 

 ated on the 13th day. Tait ct al. ( 1952) irradiated rats during the final week 

 of pregnancy using 30, 90, 180, and 360 r. The offspring of the animals re- 

 ceiving 90 r or more were significantly poorer maze learners than control 

 animals. 



Subsequently, Levinson and Zeigler (1959) subjected rats 2, 4, 6, 8, 14, 

 18, and 24 days of age to doses of 0, 150, 250, and 350 r. Beginning at 45 

 days of age, they measured learning performance on a Lashley Type III 

 maze and on the Hebb-Williams closed-field test. The 350 r group was essen- 

 tially an LD/50/30 group and so was combined with the 250 r group for 

 analysis of variance. No learning deficits appeared in the surviving infants 

 irradiated at 18 or 24 days, but there were significant differences in all other 

 groups, with maximum deficits in the 2 day and 4 day groups. The severity 

 of the learning deficits increased as a negatively accelerated function of dose 

 level. Furchtgott (1951) had previously irradiated rats at 3 weeks of age 

 and obtained similar negative results. 



Recently Furchtgott et al. (1958) in part replicated and extended Levin- 

 son's (1952) and Furchtgott's (1951) studies by giving rats 100, 200, and 

 300 r on days 14, 16, or 18 of the gestation period, or neonatally, and testing 

 their perfoiTnance at 45-50 days of age on the Lashley Type III maze. Few 

 300 r subjects of any age, or 14 day irradiated subjects at any dose level, met 

 the criterion of two out of three errorless trials in less than 20 sec each. 

 Degree of learning deficit was clearly a function of dose level and age at 

 irradiation. Maximum deficit resulted from irradiation at 14 days after con- 

 ception, in accord with Hicks' anatomic timetable and with Levinson's prior 

 findings. At postconception day 14, a 100 r dose was effective in producing 

 significant deficit, and on day 18, a 200 r dose. Only neonatal subjects 

 receiving 300 r showed learning deficit. 



Although the number of experiments is small and the range of learning 

 tests limited, the obtained data are highly significant and consistent and in 

 excellent agreement with known radiation-anatomic correlations. There can 

 be little question but that fetal and neonatal irradiation at dose levels below 



