METABOLISM IN CHANGED CEREBRAL ACTIVITY 41 



increases during myelination are understandable. Similar explana- 

 tions may hold for the plasmalogens which have been established 

 histochemically as forming part of the myelin sheath (see Albert 

 and Lebland, 1946). However, although such increases are sugges- 

 tive it is widely recognized that equating increases in the quantities 

 of certain lipids with the process of myelination suffers both from 

 lack of information as to the nature of all the brain lipids and 

 depends on certain assumptions which are not yet proven (Uzman 

 and Rumley, 1958). These include: (a), that increase in a lipid 

 component represents myelin lipid because it appears at the same 

 time as myelin increases; (b), that the number of cells and cell 

 types in brain remains constant so that (a) is possible, and (c), that 

 the lipid components of various neuronal and glial elements remain 

 quantitatively and qualitatively constant. 



As with the acid-soluble phosphates increase in quantity implies 

 the development of systems capable of synthesis which are pre- 

 sumably balanced to some degree by systems capable of further 

 metabolism. However, it is still not clear whether the phos- 

 pholipids arise solely by synthesis in the brain or are partly supplied 

 from the blood or whether the capacity for synthesis is greater in 

 the infant than in the adult. In the latter circumstances it might 

 be expected that more phosphorus from the blood would be 

 incorporated into brain phospholipids in early life than in the 

 adult stage. In the infant rat it was found (Chaikoff et al, 1938) 

 that the percentage of a given dose of radioactive phosphate 

 incorporated into the phospholipids was markedly greater than in 

 the adult (Fig. 9). Interestingly, in both adult and infant the 

 decline of radioactivity, after the initial rapid rise, was a prolonged 

 process. More extended observations have been made by Davison 

 and Dobbing (1958). Here, radioactivity of the phosphohpids was 

 expressed as counts/whole brain, a method of calculation which 

 presumably overcomes changes in quantity of phospholipids due 

 to growth. The initial increase in radioactivity of the phospho- 

 lipids in the infant rat brain was similar to that found by Chaikoff 

 et al. (1938) though the decline in radioactivity was much slower. 

 Thus at 70 days after the injection of radioactive phosphate the 

 counts remaining in the brain were 60-70% of those present at the 

 peak of incorporation some 50 days previously. Measurements of 

 the amount ojf radioactivity incorporated in the phospholipids from 

 different areas of rat brain, 24 hr after a standard dose/kg body 



4— PMB 



