NEURO- MUSCULAR ORGANIZATION OF SHIVERING 
a weak corneal reflex. At much lighter anesthetic levels noxious 
stimuli tended to inhibit shivering but such inhibition was followed 
by rebound facilitation (Fig. 14), 
DISCUSSION 
These observations must be considered in terms of neural 
mechanisms which serve to activate, inhibit, and regulate the rhythm 
of shivering. 
Activating Considerations 
Magoun et al. (193 8), Strom (1950), Von Euler (1950), Hemingway 
et al.(1954), andAnderssonetal.(1956)have localized a primary in- 
hibitory region at the junction of the ante ro-lateral hypothalamus 
and the lateral pre-optic region. A primary shivering activating sys- 
tem has been shown by Stuart, Hemingway, and Kawamura (1960) to 
exist in the dorso-medial portion ofthe posterior hypothalamus. The 
results here reported suggest that: 
First: The shivering activating region may have a stronger re- 
sistance to barbiturate anesthesia than the shivering inhibitory 
region. Shivering, once initiated during light anesthesia, continues 
as the rectal temperature rises above 38 C. 
Second; The excitability of the activating region is possibly 
affected by blood hormone levels particularly the thyrotropic 
hormone or thyroid hormone levels because in winter the thyroid 
function is active and it is somewhat depressed i» the hot summer 
season. This is suggested by the fact that it is difficult to induce 
shivering in anesthetized cats in the summer even though the blood 
and skin temperatures are low. 
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