I I 74 HANDBOOK OF PHYSIOLOGY ^ NEUROPHYSIOLOGY 11 



FIG. I. Lefl: Stereotaxic instrument, modified Horslcy-Clarke type, with a cat head fastened in 

 a horizontal plane through the external auditory canals and lower orbital bone margins. One bi- 

 polar and one unipolar needle electrode are inserted into the brain from above in a known direction 

 to a known depth. (From B. Uvnas.) Right: Sagittal section of a goat skull, showing three pairs of 

 electrode tips located in the region where the hypothalamus would be situated in the intact animal, 

 slightly above the optic chiasma {Ch. opt.) and hypophysis (Hyp.), illustrating Hess" technique for 

 chronic implantation of electrodes. The electrode holder is fastened by screws to the skull ; electrodes 

 are inserted through drilled holes. (From B. Andersson.) 



fore warm receptors. Tlie difference in function 

 between cold and warm receptors is thus only quan- 

 titative. They are discussed at length ijy Zotterman 

 in Chapter XVIII. 



The anterior hypothalamus contains a temperature 

 receptive region, but the structure of the sensitive 

 elements is not known. For this reason it is preferable 

 to refer to them as 'thermodetectors' rather than as 

 'thermoreceptors." 



Nervous integration of the signals from .surface 

 thermoreceptors seems to occur at all levels of the 

 central nervous system. The integrative structures are 

 proljablv, and their ner\ous effector systems certainly, 

 involved in other homeostatic and coordinating mecha- 

 nisms, such as the regulation of arterial pressure, 

 water balance and skeletal muscular actis'ity. Differ- 

 ent functions which are served throunh common 

 integrative structures will condition each otiier, either 

 inhibiting or facilitating; a certain temperature recep- 

 tive input may therefore result in a \ariable effector 

 output (71 ). The effector systems and reactions 

 available for this purpose include pulmonary ventila- 

 tion, cutaneous blood flow, sweating, salivation (20), 

 piloerection, skeletal muscular activity (21), water 

 mo\ements and change of body position. 



EXPERIMENTAL METHODS 



Information on central nervous regulation of body 

 temperature can be gained by different experimental 

 approaches. Some of these will be evaluated critically 

 here. 



Stncotaxic Techniques for Acute and Chronic Experiments 



The stereotaxic instrument, originally devised by 

 Horsley & Clarke (113) and later modified (166), 

 allows the exactly guided (116) introduction of 

 needle electrodes from above through the brain into 

 its deeper portions, e.g. the hypothalamus (illustrated 

 bv fig. I ). The electrode tip can usually be directed 

 to within i or 2 mm of a calculated position in the 

 In pothalamus. By this technique circumscribed nerv- 

 ous structures can be stimulated electrically, ther- 

 mally or by injection. Their electrical activity may 

 also be recorded, or they can be destroyed by electro- 

 coagulation to study in chronic experiments the 

 resulting impairment of temperature regulation. 



The result of local stimulation is largely judged by 

 the responses of the thennoregnlatory effector systems 

 as an index; this is a limitation. An effector response 



