BIOCHEMICAL CHANGES IN NEONATAL BRAIN 



103 



cellular nitrogen (and DNA), namely rats less than 1 week of age, have not 

 yet been studied. 



Proportions of centrifugally isolated nuclei, mitochondria, and microsomes 

 for cortices and brain stems of various age groups (with and without prior 

 x-irradiation) are presented in Table I. Mitochondria in the cortex ap- 

 peared to increase per unit cellular volume with increasing age (and devel- 

 opment). The only consistent changes following irradiation appeared to be 

 decreases in wet volumes of mitochondria in some of the younger (8- to 

 9-day) and older (28- to 30 day rats). However, since electron microscope 

 examination of brain mitochondrial fractions obtained by the technique of 

 Schneider and Hogeboom (1950) reveal the presence of materials other 

 than mitochondria, the present results can only be regarded as tentative. 



Gas chromatograms of fatty acids from nuclei and mitochondria in 



TABLE I 



Wet V'olu.mes of Intracellvlar Components of Cortex and 

 Brain Stem, with and withott Irradiation 



*MI per inl4 of starting tissue. In some ccises the sum of the wet volumes of the intracellular com- 

 ponents exceeds that of the starting tissue. This phenomenon is due to uncontrolled hydration of the 

 solids and inefficient packing in the volumeti ic tubes. 



