28 BRIZZEE, JACOBS, KHARETCHKO AND SHARP 



Materials and Methods 



Three groups of rats of the Sprague-Dawley strain were exposed in utero 

 to fractionated doses of total body x-irradiation. 



Two of the groups received 12.5 and 25 r per day at the rate of 60 r per 

 minute on gestation days 10 through 17 giving total doses of 100 and 

 200 r, respectively. A third group (Brizzee et al., 1961) received a total 

 dose of 300 r given at 60 r per day on gestation days 10 through 14. These 

 animals and a series of control animals treated in the same manner as the 

 above groups, except for the exjx)sure to radiation, were grouped according 

 to age at 1,5, 10, and 20 days with from 4 to 6 animals per group and the 

 sexes equally divided. The tissues were fixed and stained as reported previ- 

 ously (Brizzee and Jacobs, 1959; Brizzee et al., 1961) and subjected to 

 quantitative histologic analysis. The parameters studied were neuron packing 

 density, neuron nuclear, cytoplasmic, and soma volume, nucleocytoplasmic 

 ratio, gray cell coefficient, glial packing density, and the glia/neuron index 

 in area 2 (Krieg, 1946). In addition, total brain weight was determined and 

 cortical thickness measured in areas 2, 4, 41, and 17 (Krieg, 1946). All of 

 the volumetric, density, and thickness determinations were confined to the 

 submolecular layers only. Methods employed in the quantitative histologic 

 determinations have been described in earlier publications (Brizzee and 

 Jacobs, 1959; Brizzee r^ ai, 1961). 



In the behavioral studies, 9 pregnant rats were divided into three equal 

 groups: a full-body group, a half-body group in which the lower half of the 

 dam was shielded by lead, and a control group which received no irradiation. 

 Irradiation took place each day from the 10th through the 17th days of 

 gestation. Each irradiated animal received 40 r per day for a total of 320 r 

 (60 r per min). For the half-body group, a shield made of blocks of lead 

 2 X 4X 8 in. was constructed so that only the thorax, neck, and head were 

 exposed to radiation. 



To assess the duration of the effects of x-irradiation on locomotor coordi- 

 nation, the three groups of rats were divided into three subgroups to be 

 tested at different ages. Group one was tested at age 40 days, group two at 

 age 90 days, and group three at age 140 days. The test of locomotor coordi- 

 nation required the rats to traverse a bridge made of two parallel rods. 



At 115 days of age the rats in the 90- to 140-day groups were given 2 

 trials in a simple L-shaped water maze. The next day all the rats were run 

 in a 14-unit multiple-T water maze patterned after the Stone design (Heron, 

 1930; Sharp, in press). 



At age 50 days 6 rats from each group were sacrificed, and their cerebral 

 cortexes studied in the same manner as in the first three groups. 



In plotting the values of the various parameters in Figs. 1-6 the vertical 



