52 METABOLISM IN CHANGED CEREBRAL ACTIVITY 



The resynthesis of phosphocreatine to levels higher than normal 

 during recovery from anoxia is likely to be due to hyperventilation 

 during recovery. In the dog, hyperventilation with air was found 

 to increase the levels of phosphocreatine from 2-7-2-8/xmoles/g 

 wet v^. to 3-3 /xmoles/g (Gurdjian et al., 1949), while in the rabbit 

 similar treatment increased phosphocreatine from 2-46 /xmoles/g to 

 3-0 /xmoles/g (Doring and Gerlach, 1957). 



The effects of deprivation of oxygen are paralleled to a large 

 degree by the effects of sodium cyanide. At doses of 0-4 mg/kg no 

 changes were noted in the levels of phosphocreatine but levels of 

 lactic acid increased. Higher concentrations leading to convulsive 

 electrical activity in the brain and death induced changes identical 

 with those caused by breathing nitrogen (Albaum et al.y 1946; 

 Olsen and Klein, 1947). 



The changes in hypoglycaemia and anoxia are thus both com- 

 plementary and different and may be compared as regards overall 

 change in phosphates since in each case the brain suffers the loss of 

 a factor necessar}^ for the maintenance of an energy supply. 

 However, the time scale is different, for changes in anoxia are much 

 more rapid than in hypoglycaemia and anoxia cannot be withstood 

 for so long a period. Nevertheless, the injection of glucose can 

 partially overcome the effects of anoxia (Britton and Kline, 1945) 

 as judged by survival time. Unfortunately no information exists on 

 changes in energy-rich phosphate under these conditions nor has 

 similar data been reported for the infant rat, in which the ability to 

 withstand anoxia is many times that of the adult. Nevertheless, it 

 seems clear that the maintenance of levels of energy-rich phosphate 

 in the adult brain is more dependent upon a fully maintained 

 oxygen uptake than upon the presence of excess glucose. 



The effects of combined hypoglycaemia and anoxia are seen in 

 severe cerebral ischaemia. It was noted (Stone et al., 1941) that 

 partial interruption of the blood supply to the brain resulted in 

 decreased levels of phosphocreatine and increased levels of in- 

 organic phosphate. More detailed studies of cerebral ischaemia, 

 with and without hypothermia, upon the ability of the brain to 

 maintain adequate levels of energy-rich phosphates have been 

 made by Thorn and collaborators (see also Schneider, 1957; 

 Gerlach et aL, 1958). At 37° a reduction of 50% in the blood 

 supply to the cat head results in a decrease in oxygen consumption 

 by the brain (Hirsch et al., 1955). Since a reduction in temperature 



