EFFECTS OF PRENATAL RADIATION UPON LEARNING 655 



cation of radiosensitivity of tissue at this time in utero, the current results 

 failed to yield evidence for learning deficit in rats given 10, 25, 50, or 100 r 

 at this critical day, while they did indicate that rats given 150 r at 8.5 days 

 were deficient in maze learning. 



These findings can imply two conclusions: (1) A rat is not as radio- 

 sensitive at 8.5 days as it is at 7.5 days, and (2) a rat is not sensitive to 

 damage at 8.5 days (damage detectable by maze learning), unless it re- 

 ceived more than 100 r. The first conclusion is based on the fact that 

 group d, the 50 r/7.5 day group, was found to be significantly inferior on 

 all measures of learning, not only to group e, the 50 r/8.5 day group, but 

 also to group f, the 100 r/8.5 day group. 



Age at Time of Testing 



Group F (100 r/8.5 days) was markedly inferior to the normal controls, 

 as was group g ( 150 r/8.5 days) . Moreover, group F was inferior in learning 

 to group g. Age at time of testing apparently accounts for this reversal of 

 expected results. The animal irradiated on the 8.5 day of gestation appar- 

 ently can receive sufficient insult to reveal learning impairment provided the 

 dose is great enough or the animal is old enough. 



Dose magnitude, per se, has been clearly shown to be a factor in producing 

 behavioral deficits in learning when there is marked radiosensitivity of 

 tissues requisite for efTective cognition. Tait et al. (1952), Levinson (1952) 

 and Furchtgott et al. (1958) have supported Hicks' (1953) findings in this 

 regard with doses of 90-600 r between the 11th and the 19th days of 

 gestation. On these days it is apparent that the damaged tissues are requisite 

 for efficient learning. But in all of these behavioral studies the rats were 

 between 45 and 120 days of age at the time of testing, an age which could 

 best be compared with 90-day-old rats of groups d (50 r/7.5 days) and 

 g (150 r/8.5 days). Their findings lend support to a further hypothesis that 

 the 7.5 day represents a period in utero of marked radiosensitivity which 

 reveals itself in behavior at a relatively early age. 



The results of the present study imply that age at time of testing is ex- 

 tremely critical for detection of tissue damage. One might postulate that any 

 dose given at any time during the gestation period could possibly have an 

 adverse effect on learning at some later period in the life of the organism. 



It is apparent that 25 r given on 2.5 days is related to observed learning 

 impairment in the 400-day-old rat. Since the reliability of differences for 

 this group is not high (.05, .02 for errors and trials, respectively) and the 

 N is small (3), perhaps this conclusion bears limited support. The reliability 

 of the results with groups C, D, and E (50 r), with significant differences 

 of magnitudes of .002 and greater, reported between each and their control 

 group, requires that serious consideration be given to the above hypothesis. 



