METABOLISM IN CHANGED CEREBRAL ACTIVITY 37 



hand, the fraction containing hexose phosphates and diphospho- 

 pyridine nucleotide, when calculated on the same basis, was found 

 to decrease by half during this period, a decrease which is also 

 calculable from the data of Mandel et al. (1953). 



Patterns of change in the acid-soluble phosphates in the brain 

 of the developing chick embryo are similar, though individual 

 differences have been noted. In the chick the relative physiological 

 stages occur rapidly; from 0-10 days incubation, stage I; 12-19 

 days, stage II ; 19-26 days, stage III and the beginnings of stage IV. 

 From the 10th-19th days of incubation Mandel et al. (1947) found 

 that the quantities of phosphocreatine increased from 0-15 /xmoles/ 

 gwetwt. at 10 days, to 1-8 /xmoles/g wet wt. on the 19th day. 

 Quantities of pyrophosphate (presumably from adenosine triphos- 

 phate) decreased from 3'OjLtmoles/g wet wt. on the 10th day. 

 Szepsenwol and Partridge (1952) found no such change until the 

 18th-20th day of incubation when the quantities of phospho- 

 creatine increased rapidly from 0-6 /xmoles/g wet ^vt. to 1-2 

 /xmoles/g wet wt. on the 22nd-23rd day. Increase in phospho- 

 creatine was accompanied by a decrease in adenosine triphosphate. 

 Reasons for these differences are not readily apparent. In the chick 

 embryo the period between 10-19 days incubation corresponds to 

 the period of active myelination and the development of a fairly 

 well defined electrocorticogram (Garcia- Aust, 1954). As noted, 

 above, in both the rat and guinea pig, this period in development 

 is accompanied by an increase in the total quantities of phospho- 

 creatine and adenosine triphosphate in the brain. The coincidence 

 of the two processes suggests that during the period of increasing 

 functional organization there is also an increase in the systems 

 involved in the synthesis of the energy-rich phosphates. 



There is no good reason why such an increase in synthetic 

 activity need be reflected in an increased quantity/unit of mass of a 

 phosphate such as phosphocreatine, though this clearly takes place 

 in the chick brain. Indeed it seehis more likely, as Flexner and 

 Flexner (1950) consider, that during thib period the rate of 

 turnover of the phosphorus in such compounds is greatly increased. 

 In so far as the respiratory activity increases, with which phos- 

 phorylation is linked, this view has much to support it, though 

 critical data are lacking. 



Increase in rates of synthesis while concentrations remain 

 relatively constant, implies a simultaneous increase in systems 



