262 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



DR REFLEX 



VR REFLEX 



INCOMING SPIKE 

 EVOKING RESPONSE 



20 30 



TEMPERATURE CO 



Fig. 2. — The effect of cooling the spinal cord on reflex response : Changes in magnitudes of 

 responses in terms of amplitude and duratitm of potentials. 



tetanus. Afferent stimulation will touch off the rhythmic firiiig l)ut it will appear 

 spontaneously even in a de-afferented cord (Koizumi, 1955). This observation of 

 repetitive firing and actual tetanus in hypothermia is in line with the work men- 

 tioned by Dr. McQueen to the effect that hypothermia may aggravate epilepsy and 

 certain types of neural seizures. 



In conclusion I would like to reinforce my suggestion that the phase of hyper- 

 reactivity which occurs before uniform depression sets in shoitld not be left out of 

 our considerations. Hyperactivity of centers may explain some peripheral phe- 

 nomena. The relative timing of these phases in various brain and cord centers as 

 an animal is cooled is not yet known. The origin of reported atttonomic activity, 

 metabolic changes, neuroendocrine discharges, the awakening from hibernation, etc. 

 should be considered with hyperresponsive spill-over, as well as specific response 

 pathways, in mind. The origin of shivering is not understood but explanation might 

 come from a study of the effects of cold on the higher centers of the nervous sys- 

 tem and hyperresponsiveness may be involved. As in the heart, temperature gradi- 

 ents are important because if gradients are sufficiently great an electrotonic current 

 flow is established which will actually excite ((iranit, 1955). Matters such as this 

 have been discussed extensively in the netu"ophysiological literature but they are 

 also relevant to behavior of heart cells and the origin of fibrillation. 



REFERENCES 



1. Brooks, C. McC, and Koizumi, K. : Origin of dorsal root reflex, J. Neurophvsiol. l'^:6\, 

 1956. 



