NEURO-MUSCULAR ORGANIZATION OF SHIVERING 
Third : The shivering activating region and the reticular activa- 
ting system have a close relationship since (a) strong noxious stimuli 
which stimulate the reticular activating system have a tendency to 
induce shivering even during deep anesthetic conditions, (b) the ret- 
icular activating system is possibly adrenergic (Bonvalletetal, 1954; 
Bradley, 1958; and Rothballer, 1956) and as such may be facilitated 
by epinephrine and depressed by acetylcholine. 
These results indicate that acetylcholine inhibits and epine- 
phrine facilitates shivering. Some conflict exists in the literature 
on this latter point. Cassidy, Dworkin,and Finney (1926) reported 
that shivering, abolished by insulin injection in anesthetized animals, 
was restoredby large doses of epinephrine. Hall and Goldstein (1940) 
reported that I. V. injection of 80-150 mg/kg epinephrine causes a 
transitory facilitation in anesthetized animals. Smaller doses (SO- 
SO mg/kg) produced inhibition without temporary facilitation. Un- 
published data of Stuart, George, and Hemingway suggest that shiv- 
ering is mildly facilitated in unanesthetized cats following sub- 
cutaneous injection of 40 mg/kg. The facilitation here reported 
following subcutaneous injection of 30 mg/kg into anesthetized dogs 
followed previous ACH injection. Obviously the question cannot be 
fully resolved until a more extensive study is performed on both 
anesthetized and unanesthetized shivering animals in which various 
doses of epinephrine are applied by both intravenous and subcutan- 
eous routes, uncomplicated by previous drug inhibition of shivering. 
Fourth, There is a relationship betweenthe activating region and 
inspiration during shivering that could be organized in one of three 
ways: (a) Excitatory impulses to the shivering activating region from 
pharyngeal cold receptors that are stimulated during inspiration 
(Cort and McCance, 1953); (b) Excitatory impulses ascendingto the 
activating region and/or descending to the spinal cord from pulmon- 
ary stretch or from the inspiratory center receptors, maximally 
stimulated at peak inspiration; (c) A generalized state of increased 
medullary excitability occurring during inspiration and facilitating 
descending extrapyramidal activity (Kawamura and Fujimoto, 1958). 
For example, the jaw opening reflex is facilitated during inspiration. 
However, it must be stressed that there was no clear relation- 
ship between inspiration and the increase in muscle tonus that pre- 
213 
