METABOLISM IN CHANGED CEREBRAL ACTIVITY 



39 



in structural components of the brain such as proteins, Hpids and 

 nucleic acids. Of these, lipids have received the major attention 

 both as constituting some 20% of the fresh weight of the adult 

 brain and for the suggested role of certain of them in the formation 

 of the myelin sheath. 



The stage of development corresponding to the period during 

 which myelin is being formed and deposited most rapidly is 

 marked by a major increase in both quantity and concentration 

 of the phospholipids. Data, derived from several sources, for 

 different species, are presented in Fig. 7. Although expressed in 

 terms varying according to the authors, the major increases in 

 quantity clearly take place within a relatively short period in the 

 physiological time scale of each particular species. Certain lipids 

 increase in quantity more markedly than others, and include the 

 major "myelin lipids", cerebrosides, cholesterol and sphingo- 

 myelin. Measurement of changes in the quantities of sphingo- 

 myelin (Fig. 8) have shown that the increase is extremely rapid, 

 occupying the period between 12-16 days after birth in the rat, and 



Months in utero (Human) 



36 40 44 48 52 56 60 64 68 

 Days in utero (Guinea pig) 



Fig. 7. The increase in the total phospholipids of brain during 



early growth and development. Data from Flexner and Flexner 



(1950), and Brante (1949). O ^ guinea pig; • = human. 



