CENTRAL NERVOUS REGULATION OF BODY TEMPERATURE 



'175 



to such procedures as local thermal stimulation in the 

 brain demonstrates and localizes structures with spe- 

 cific thermal sensitivity ('central thermodetectors') but 

 does not give information about the unitary responses 

 of the detectors. An effector response to local electrical 

 stimulation in the brain may theoretically be elicited 

 by excitation of either afferent, integrative or efferent 

 neurons in the thermoregulatory system. 



In the study of chronic brain lesions, careful 

 histological control of the position of the lesions at 

 necropsy is all-important and the possibility of 

 bleeding, infection or interference with blood supply 

 extending the destruction to other parts of the brain 

 must also be kept in mind. In chronic experiments it 

 is usually more difficult to measure exactly the index 

 of response than in acute experiments; well-standard- 

 ized tests have to be used (98). The general condition 

 of the chronic animal with marked inanition (51) or 

 infection may also severely influence the reactivity 

 of the effector index studied; intactness of some 

 aspect of temperature regulation may therefore be 

 more significant than its impairment in chronic 

 destruction experiments. The chronic studies give 

 information about coordinated temperature regula- 

 tion in the unanesthetized animal which is indispens- 

 able and cannot be gained from acute studies. 



Chronic Implantation Techniques 



A method of implantation of multiple needle 

 electrodes into the brain for acute and chronic 

 experiments has been worked out by Hess (106), as 

 exemplified in figure i. It is thus possible to study the 

 effect of electrical or thermal stimulation, or of 

 electrocoagulation, in long-term experiments on un- 

 anesthetized animals. Other types of electrodes or 

 thermodes may be placed chronically near to the 

 brain surface by ordinar\' neurosurgical procedures. 



Indirect Thermal Stimulation of Brain 



The brain may Ije warmed or cooled \ia its blood 

 circulation, or by changing the temperature either of 

 the whole body or preferably of the carotid arterial 

 blood stream. Such a temperature change affects 

 vascular receptive structures (29, 196, 198), and 

 surface thermoceptors, in the whole body or only in 

 the head, as well as large parts of the brain. The 

 portion of the brain which is supplied by the carotid 

 arteries varies in extent in different animals. 



Temperature Measurements 



It is an important and well-known fact that both 

 the absolute level and temporal changes of tempera- 

 ture may show large regional variations in the body 

 (19). This is likely to be especially true in the anesthe- 

 tized animal subjected to extensive operative measures 

 unless special precautions are taken. 



The rectal temperature alone may be an insuffi- 

 cient measure of central body temperature (146) or 

 of brain temperature. Like all local temperatures it 

 is influenced by local rates of metabolism and blood 

 flow as well as by level of central body temperature 

 (89, 90). The oral temperature is usually a belter 

 index of brain teinperature than is the rectal one. The 

 brain temperature may, however, be measured di- 

 rectly botii in acute (35a, 187, 203) and chronic (71, 

 132a, 135, 180) experiments. 



HYPOTHALAMIC THERMOCEPTIVE STRUCTURES 



Existence and Localization 



The existence of thermorecepti\e structures in the 

 brain was suggested by Kahn in 1904 (122) : warming 

 of the carotid blood evokes signs of cutaneous vaso- 

 dilatation, sweating and polypnea in the rabbit, cat 

 and dog. Such structures were shown in 191 2 to be 

 localized deep in the brain near the corpus striatum 

 by Barbour (8) since circulation of water at 42 °C 

 through a thermode, the tip of which was placed near 

 the receptive structure in the rabbit brain, was found 

 to produce vasodilatation in the ears, while cooling 

 to 33°C produced vasoconstriction. The effect of local 

 brain warming was repeatedly confirmed (94, 97, 

 148, 163, 164), but the exact localization of the re- 

 sponsive region long remained unknown. 



A few earlier and many later reports had indicated 

 the hypothalamus to be essential for an intact tem- 

 perature regulation, or even necessary for any tem- 

 perature regulation at all. It was definitely shown in 

 1938 by Magoun and co-workers (141 ) in the cat, and 

 later confirmed in the monkey (26), that thermocep- 

 tive structures exist in the brain and that they are 

 localized cxclusi\ely to the supraoptic and preoptic 

 parts of the hypothalamus. In these experiments 

 localized diathermic warming producing a moderate 

 temperature increase of the anterior hypothalamus, 

 but of no other regions in the brain, evoked a typical 

 heat loss response with polypnea or panting and also 

 sweating in the anesthetized cat (figs. 2, 3). 



