METABOLISM IN CHANGED CEREBRAL ACTIVITY 



43 



inherent in the assessment of stich situations are illustrated by data 

 given by Dawson and Richter (1950«) (see Table 6). Mice were 

 injected intraperitoneally with radioactive phosphorus, sacrificed 

 3 hr later, and the specific radioactivities (in counts/min per mg 

 phosphorus) of the brain phospholipids were determined. When 

 related to the specific radioactivity of the acid-soluble phosphorus 

 of brain, the incorporation of phosphorus into the phospholipids 

 was found to decrease with increasing age. This accords with a 

 decreased rate of lipid renewal as age increases. However, as 

 Dawson (1955) has pointed out, it is to be remembered that the 



Table 6. — The Effect of Age upon the Uptake of Radioactive 

 Phosphorus into the Lipids of Mouse Brain 



Dawson and Richter (1950<3). Mice killed 180 niin after injection of ^-P. 



brain of the young animal contains less phospholipid and acid- 

 soluble phosphorus than the adult. Since newly formed phospho- 

 lipid will be diluted with material already present the lower 

 relative specific activity in the older animals cannot be taken to 

 mean that the renewal of phospholipids proceeds more rapidly in 

 the young than in the old animal. It is also to be remembered that 

 the evidence available relates to the total phospholipids and provides 

 no information upon any differences which may occur in the 

 relative rates of incorporation of phosphate into the different lipids 

 during growth. 



Although enzymes capable of metabolizing the phospholipids 

 have been demonstrated in brain extracts (Chapter 3) the slow 

 decrease in radioactivity shown in Fig. 9 suggests that, in vivo^ 

 many of these enzymes are likely to operate at a low level of 



