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HANDBOOK OF PHYSIOLOGY' 



NEUROPHYSIOLOGY 11 



FIG. 5. Slow 'temperature potential' 

 from the anterior hypothalamus. Cat is 

 under urethane anesthesia. One calomel 

 capillary electrode is inserted by the 

 Horsley-Clarke technique into the hypo- 

 thalamus, a slow potential (upper curve) 

 was recorded against another electrode 

 elsewhere in the brain. Hypothalamic 

 temperature (tower curve) is recorded by 

 a thermojunction. Brain is warmed by 

 conductive heating of the intact carotid 

 arteries. [From von Euler (203).] 



a fact suggesting an analogy between central chemo- 

 ceptive and thermoceptive structures (206). The 

 structure of the medullary chemodetectors is as 

 unknown as is that of the hypothalamic thermodetec- 

 tors. This absence of histologically defined receptors 

 is hardly more surprising for central receptive mecha- 

 nisms than for peripheral receptors, such as those for 

 pain. 



It should be remembered that temperature changes 

 influence all excitable tissues to a greater or lesser 

 extent (28). Diff"erent types of peripheral nerve fibers 

 show different thermosensiti\'ity (137, 202). Local 

 heating of mammalian C-fibers up to 41 °C or more 

 depolarizes them and generates impulses, while 

 cooling A-fibers has a similar effect. The central 

 thermodetectors, however, seem to be more sensitive 

 to temperature changes than are C-fibers. 



CENTR.AL INTEGRATIVE STRUCTURES 



Effects of Stimulation 



In 1884 and 1885 basal parts of the forebrain had 

 already been suggested to influence temperature 

 regulation by Ott (155, 156), and .\ronsohn & Sachs 

 (5) observed that mechanical punctiu'e into the region 

 of the corpus striatum in the rabbit is followed l)v a 

 transient rise of body temperature ('heat puncture' 

 or Wdrmestich) with signs of increased metaijolism. 

 This observation is difficult to interpret in terms of 

 normal physiology. The puncture probably produced 

 an irritative lesion (120) near to (211) but not de- 

 stroying those hypothalamic structures which later 

 have been shown to contain a coordinating mecha- 

 nism for the regulation of body temperature. 



Electrical stimulation within the hypothalamus can 

 evoke a multitude of responses. The skeletal muscular 

 system (108, iii) may show increased or decreased 



tone either generally or in localized muscle groups. 

 In the circulatory system (36) there may result in- 

 creased sympathetic vasoconstrictor activity, either 

 generally with resultant large increases of arterial 

 blood pressure or in localized regions such as the 

 skin; or alternatively decreased vasoconstrictor ac- 

 tivity in the skin; or increased sympathetic vasodila- 

 tor activity to skeletal muscle. Increased or decreased 

 sympathetic accelerator activits- to the heart may also 

 appear, and increased activity of the adrenal medullae 

 with augmented secretion of either epinephrine or 

 norepinephrine (67). The respiratory ssstem may 

 show increased or decreased activity, e.g. apnea, 

 hyperpnea, polypnea or panting (4, 109). 



It is evident therefore that the main thermoregula- 

 tory effector systems can be inffuenced by hypotha- 

 lamic stimulation. Such information does not define 

 the quantitative role of the hypothalamic structures 

 in normal temperature regulation, however. On the 

 other hand, localized electrical stimulation in the 

 anterior hypothalamus of an unanesthetized animal 

 can evoke not only isolated effector responses but also 

 a coordinated response of the main heat-lo.ss mecha- 

 nisms, i.e. panting, cutaneous vasodilatation and 

 inhibition of shivering (figs. 6, 7), as demonstrated h\ 

 .■\ndersson rt al. (4). Such a coordinated response has 

 not been obtained from other cerebral regions, corti- 

 cal or subcortical. The response is probably not de- 

 pendent on cortical integration because chronic 

 decortication does not markedly influence either a 

 normally coordinated temperature regulation in the 

 unanesthetized animal, or the individual eflTector 

 responses to hypothalamic, electrical or thermal 

 stimulation. The anterior hypothalamus therefore 

 seems to be the location of a main coordinative 

 mechanism which promotes heat loss, a conclusion 

 which can also be drawn from results of chronic 

 ablation experiments (see below). 



