CENTRAL NERVOUS REGULATION OF BODY TEMPERATURE 



II9I 



FIG. 2 1 . Change in body temperature 

 (ordinates) of anesthetized rabbits after 

 2 hr. at +I9°C room temperature. 

 Similar effect of different anesthetics; 

 larger temperature fall at deeper levels 

 of anesthesia (abscissae, arbitrary units V 

 [From Thauer (194).] 



administered locally in the hypothalamus in se\eral 

 animals, especially rabbits (131 ), or intravenously pro- 

 duces a rapid fall in body temperature (186); shiver- 

 ing is suppressed and heat-loss mechanisms are set 

 into intense action, polypnea or panting occurring at 

 subnormal body and brain temperatures (140). 

 Local injections of drugs into the hypothalamus may 

 produce hypothermia or hyperthermia (15). Chlor- 

 promazine produces cutaneous vasodilatation but 

 does not significantly inhibit shivering (47). 



Fever 



Since the early observation that mechanical stim- 

 ulation of certain cerebral structures, later identified 

 as the hypothalamus, may elicit a transient rise of 

 body temperature ('heat puncture'), fever has com- 

 monly been regarded as evoked by an action of fever- 

 producing substances (pyrogens) on the hypothalamic 

 thermoregulatory structures. [These substances may 

 also produce degenerative cellular changes in the 

 hypothalamus (149).] A main theoretical reason for 

 this conclusion would be that an approximately nor- 

 mal coordination of the different thermolytic and 

 thermogenic mechanisms remains during fever (92, 

 203), although the body is balanced at a new and 

 higher temperature, the body 'thermostat' being 

 'reset' at a higher temperature, otherwise functioning 

 normally. Temperature regulation is not always co- 

 ordinated in fever, however (84). 



Hypothalamic lesions in cats have been reported 

 to diminish or eliminate the fever response to pyro- 

 gens (169). Fever may, however, be elicited experi- 

 mentally in animals with chronic hypothalamic 



destruction or in pontine or medullary (44) or even 

 spinal (192) animals, indicating that the pyrogens, 

 or rather the exogenous pyrogen plus the endogenous 

 activated factor demonstrated by Grant & Whalen 

 (87), may act at least partially on lower central 

 nervous structures. 



Hypothermia 



Interest in the effect of drastic lowering of the body 

 temperature (162, 185) has increased markedly since 

 hypothermia proved to be a useful tool in certain 

 surgical procedures, notably brain and heart opera- 

 tions. Shivering reaches a maximum at rectal tem- 

 peratures between 33° and 35°C, as do also circula- 

 tory and respiratory reflexes (91). The relative 

 influence of surface thermoreceptors and hypothalamic 

 thermodetectors for tiiermoregulatory effector re- 

 sponses at these low temperatures is not definitely 

 known, as discussed above. The influence of anes- 

 thesia is here put to practical use (130), certain com- 

 binations of anesthetics, muscular relaxants and sym- 

 patholytic agents being employed. 



.AGE AND SPECIES DIFFERENCES IN 

 TEMPER.«iTURE REGULATION 



Ontogenesis of Central Temperature Regulation 



The newborn animal does not possess fully effective 

 temperature regulation. Regulation against cooling 

 as well as warming develops rapidly, in the dog within 

 3 to 4 wk. (121). The effectiveness of human tempera- 



