HIBERNATION IN MAMMALS— LYMAN and CHATFIELD 109 



denied the blood supply to the liver by evisceration and ligation, the blood sugar 

 drops to hypoglycemic levels by the time the rostral portion of the animal has 

 reached Z7° , thus demonstrating the importance of the liver as a source of glycogen 

 (fig. 21). 



Glycogen in the heart muscle, which is high in hijjernating animals, is still higher 

 in animals denied food before hibernating. Macleod and Prendergast"'' reported a 

 similar situation in the case of rats when the glycogen stores in the rest of the body 

 were abnormally low. As in skeletal muscle, heart muscle glycogen declines during 

 arousal. It is well established that glycogen of muscle is used directly as a source of 

 energy^^" and the loss of glycogen in skeletal and heart muscle during arousal must 

 indicate utilization by the muscles themselves. The extra store of glycogen in the 

 heart of the hibernator re-emphasizes the importance of the heart in the process of 

 arousal, for in the early stages of arousal the heart is capable of increasing its work 

 load without depending on any exogenous source for energy (fig. 21).'^^^ 



Electrical activity in the central nervous system. According to Rohmer, 

 ct al,^^ as the European ground squirrel woke from hibernation there was a pro- 

 gressive increase in the frequency of the waves in the electroencephalogram, while 

 the amplitude (except for the "accident complexe") gradually increased up to a 

 central temperature of 18°-21° C. and then diminished. Chatfield et a/./' recorded 

 the electrocorticogram of the hamster during arousal and correlated it with the tem- 

 perature of the cerebral cortex. Because of the steep temperature gradient between 

 cranial and caudal parts of the body during arousal, head temperatures provide a 

 much more valid comparison than body temperatures in such an experiment. It was 

 found that no electrical activity could be detected until the cortical temperature had 

 reached 19° to 21° C. At this temperature, slow, low voltage activity appeared, which 

 was replaced at higher temperatures by spontaneous burst activity and, when the 

 cortical temperature was about 29° C, by very fast frequency, low voltage dis- 

 charges characteristic of an awake animal ffig. 8). Local strychninization of the 

 cortex did not produce convulsive activity until the temperature had reached levels 

 at which spontaneous activity would normally have' appeared. Though the cortex 

 appeared quiescent early in arousal, peripheral movement could still be elicited at 

 temperatures as low as 12° C. by electrical stimulation of motor areas. Merzbacher^^^ 

 had previously reported that the cerebral cortex of torpid noctule bats was elec- 

 trically excitable, but had given no temperatures. Chatfield, et al.,^'^ were able to 

 record a complex cortical response from stimulation of the sciatic nerve when the 

 cortical temperature of chilled anaesthetized hamsters was as low as 9° C. (fig. 22). 

 It was concluded that the brain stem reticular activating system was least resistant 



I tt C. Kayser. M. L. Rietsch and M. A. Lucot (Arch. d. Sci. Physiologiques 8: 155. 1954") 

 report a higher R.Q. in waking hamsters than in waking ground squirrels, and associate this with 

 the extremely obese condition of the latter before entering hibernation, resuhing in a greater use 

 of fat during the waking process. They report a higher R.Q. in the ground squirrel toward the end 

 of the hibernating season when the animal is extremely thin and consider that this indicates a use 

 of protein. However, the interpretation of the source of energy by the measurement of respira- 

 tory quotient alone appears to us to be somewhat tenuous when the respiratory quotient is 

 above 0.7. C. L. Dodgen and F. R. Blood (Am. J. Physiol. i"9.- 631. 1954) report a higher 

 respiratory quotient in waking bats than during hibernation, and attribute this to the utilization 

 of carbohydrate and/or protein as well as fat. From earher observations (Federation Proc. 12: 

 34, 1953) of a very low supply of glycogen in the livers of hibernating bats, they emphasize that 

 fat must play an important role. 



