104 SCHJEIDE, YAMAZAKI, CLEMENTE, RAGAN AND SIMONS 



cerebral cortices of rats aged 8-9 days to 30 days appear in Fig. 7. The 

 most prominent fatty acids in these cross sections include palmitic, stearic, 

 oleic, arachadonic, and linoleic, in that order. Experience with fatty acids 

 from the developing livers of chicken embryos has shown that, as the cell 

 matures, the percentage of palmitic acid in the nucleus decreases and the 

 percentage of oleic acid increases markedly (Schjeide, 1960). X-irradiation 

 retards the adjustment of these fatty acid ratios, and it may that this is a 

 reflection of inhibition of differentiation in the nucleus. Re-enforcing this 

 finding is the observation that the fatty acid profiles of mitochondria from 

 irradiated chicken embryos contain an increased percentage of oleic acid. 



Although the nuclear fatty acids of neonatal rat brains failed to show 

 changes as dramatic as those observed in the embryonic livers, there was 

 generally a decrease in the ratio of palmitic acid to stearic acid and oleic 

 acid in nuclei as a function of increasing age (Fig. 8). In cortices of all 

 stages the decrease of this ratio was retarded by a dose of 750 r (Fig. 8). 

 The decrjease in ratio was also retarded in nuclei of irradiated brain stems 

 (Fig. 8). Significantly, control fatty acid ratios of the nuclei in brain stems 

 (the more mature portion of the brain at this early age) were those assumed 

 to be more characteristic of adult-type nuclei (Fig. 8). 



Linoleic acid in brain lipids decreased with age, reflecting the develop- 

 ment of the "blood brain barrier." Irradiation did not appear to have any 

 consistent effect on the percentage of linoleic acid in the brain lipids. 



Discussion 



Although the foregoing represents a purely introductory survey of bio- 

 chemical effects of radiation on maturing brain, three points of interest 

 stand out at this early stage. 



First, per unit dry weight of cortex and cerebellum, the total lipid, total 

 phospholipid, and total nitrogen appear relatively unchanged by exposure 

 of the heads of rats to 750 r of x-irradiation. Thus, in these respects, the irra- 

 diated neonatal cortex and cerebellum can be considered essentially as 

 miniatures of their control counterparts, difTering primarily in having fewer 

 total cells per organ and having these cells poorly arranged in the greater 

 structural context. A similar situation appears to exist in the deformed skele- 

 tons of rat embryos irradiated between 12 and 16 days of gestation (Russell, 

 1954). As far as is known, calcification mechanisms of the structurally-poor 

 skeletons are unimpaired by the radiations that initiated the deformity; i.e., 

 the enzymes involved in calcification appear to be present in sufficient quan- 

 tity in irradiated bone. 



Contrasting with the lack of biochemical effects of radiations hereto ob- 

 served on cerebellum and cerebral cortex is the inhibition of lipid synthesis 



