BIOCHEMICAL CHANGES IN NEONATAL BRAIN 107 



older rats. Such an eflfect is seen in cells of the embryonic chicken liver 

 (Schjeide, 1960) and is thought to be indirect because of the time required 

 (3 days) for the fall in population. It remains to be determined whether the 

 decrease in mitochondria observed in the neonatal rat cortex is consistent 

 and due to direct effects, to damage to a controlling mechanism in the 

 nucleus, or to elicitation of toxic blood-borne factors. 



A third interesting result which may be a harbinger of better things to 

 come with respect to elucidation of radiation effects on cell organelles, is 

 the inhibition of change in fatty acid ratios of nuclei in all irradiated rats. 



The changes in nuclear fatty acid ratios that occur normally as a function 

 of age have tentatively been interpreted as reflecting an advance in the ma- 

 turity of these organelles. Thus, one of the interpretations for the inhibition 

 of these shifts in ratios following irradiation is that maturation (or diflFeren- 

 tiation) of the nucleus has been retarded due to injury by oxidizing radicals. 

 However, in a heterogenous tissue, such as brain, changes in organelle fatty 

 acid ratios may merely reflect changes in the proportions of resident cells. 

 The importance of good histology as an adjunct to biochemical studies in 

 these tissues is thus emphasized. 



In most animals receiving irradiatic^n to the head only, there was a de- 

 crease in total body weight and the weights of such organs as liver, spleen, 

 kidney and heart. Although the changes in weights of the various brain 

 components did not appear to correlate closely with the weight changes of 

 the above organs, the influence of irradiation on the pituitary (and hence a 

 probable change in output of certain hormones) is a possible factor in- 

 fluencing the observed results. However, a personal communication from Dr. 

 Van Dyke, of the University of California at Berkeley, indicated that growth 

 hoiTnone administered to irradiated neonatal rats has no effect in delaying 

 the onset — or modifying the intensity — of neurological aberrations. 



Summary 



All three major divisions of the brain (brain stem, cortex, and cere- 

 bellum) were inhibited in growth following irradiation (750 r) to the head 

 at 2 days of age. Growth of brain stem was not retarded until about the 16th 

 day, and due to a relatively slow rate of growth in the control animals, the 

 difference in dry weight of this part of the brain at 4 weeks postirradiation 

 was not great. In corte.x. the inhibition of growth was also first discernible 

 at about 16 days, but due to a relatively fast rate of increase in the control 

 animals, the differential between control and irradiated cortices at 4 weeks 

 was very significant. Cerebellum was most profoundly affected by x-irradia- 

 tion, the decrease in size being quite apparent early in the 2nd week follow- 

 ing exp)csure. 



