62 METABOLISM IN CHANGED CEREBRAL ACTIVITY 



phosphate rose. The animals were frozen in hquid air immediately 

 after or upon the point of death and it was considered that the 

 changes observed could not be ascribed to the normal depletion 

 occurring after death. No such effects were observed in rats which 

 had been conditioned to tumbling in the drum. Further studies of 

 this type have been carried out principally by Russian workers. 

 Rats are conditioned to expect an electric shock to the paws when a 

 light is switched on, and are able to escape by jumping out of a hole 

 in the cage. In conditioned animals, switching on the light 

 produces signs of fear, squealing, etc., together with the escape 

 reaction. On jumping through the hole the animals fall into liquid 

 air and are frozen. It was found that the conditioned reflex 

 resulted in a decrease in levels of adenosine triphosphate (Sytinsky, 

 1956; Vladimirova, 1956). Curiously, little change was found in 

 the levels of phosphocreatine. Similar changes were noted in 

 unconditioned animals stimulated by electroshock. The increase 

 in inorganic phosphate was found to exceed that derived from the 

 loss of adenosine triphosphate, suggesting that phosphate deriva- 

 tives other than adenosine triphosphate were involved in the 

 response. Similar changes, including a decrease in phospho- 

 creatine, were found in rats excited by persistent teasing (Shapot, 

 1957). Rats, injected with phenamine to enhance reflexes, were 

 teased with straws for an hour, during which they showed signs of 

 anger. In such a state cerebral adenosine triphosphate was de- 

 creased by half while adenosine diphosphate increased. Levels of 

 phosphocreatine fell by 30%. The changes were similar to those 

 found in animals convulsed by the injection of camphor. The 

 Russian workers generally attach considerable importance to the 

 ratio ATP/ADP. Shapot (1957) considers it to be more indicative 

 of the functional state of the brain than absolute quantities of 

 either, since, in part, the rates of cerebral metabolism are condi- 

 tioned by the levels of phosphate acceptors such as adenosine 

 diphosphate (see p. 110). Excitation induced by intermittent 

 electric shocks applied to the skin was found to increase the specific 

 radioactivity of the hexose phosphates relative to that of adenosine 

 triphosphate (Vladimirov and Rubel, 1957). Interpretation of this 

 type of result is complicated by the probable changes occurring in 

 adenosine triphosphate which is used as a standard of reference 

 (see p. 46). The possibility of excitation affecting the metabolism 

 of other phosphates has been examined with respect to the phos- 



