I I 76 HANDBOOK OF PHYSIOLOGY — NEUROPHYSIOLOGY II 



350 



20& 



150 



100 



50 



\l ^ 



d. b C 



Fio. 2. Effect of diathermic heating of the anterior hypo- 

 thalamus on respiratory rate. Cat is under urethane anesthesia. 

 Heating is through two parallel electrodes with bare tips in- 

 serted by the Horsley-Clarkc technique from above into the 

 hypothalamus; electrode tip locations a-d are shown on lower 

 part (schematic drawing of transverse section through a cat 

 brain). Heating responses from locations a-d on respiratory 

 rate are shown on upper part (breaths per minute on ordinates) ; 

 heavy line indicates panting. AC, anterior commissure ; C, caudate 

 nucleus; CC, corpus callosum; GP, globus pallidas; IC, internal 

 capsule; LV, lateral ventricle; OC. optic chiasma; S, septum; 

 and jF, third ventricle. [From Magoun ct al. ( 141 ).l 



FIG. 3. .Schematic outline of the region reactive to local heat- 

 ing, projected on a paramedian sagittal section through a cat 

 brain CG, central grey matter, F, fornix;//, habenula,///", hab- 

 inulopeduncular tract; HI', hypothalamus; IN, infundibulum; 

 .\l, mammillary body; OC.V, oculomotor nerve; OT/J, olfactory 

 tubercle; PC, posterior commissure; SC, superior colliculus; 

 .S.M, stria meduUaris, TH, thalamus; otherwise as in fig. 2. 

 [From Magoun et al. 1141).! 



The iherinosen.siti\itv ol the liypothalamus has been 

 additionally confirmed in several other reports (63, 

 68, loi, 187, 189), extended to other animals, and 

 obtained in chronic animals without anesthesia (loi, 

 190). Warming of the hypothalamic thermodetectors 

 in addition to polypnea and sweating also produces 

 cutaneous \'asodilatation (fig. 4). Inhibition of shiv- 

 ering also occurs if shivering is initially present, other- 

 wise other signs of decreased skeletal muscular activity 

 are evident. The result of hypotlialamic wanning is 

 therefore a coordinated response of body temperature 

 regulation, with activation of heat-loss mechanisms 

 and suppression ot the main heat-production mecha- 

 nism. 



If central nervous thermodetectors are to register 

 central body temperature (e.g. the temperature of 

 arterial blood in the aorta), they should be trans- 

 fused bv so rapid a blood flow that local heat produc- 

 tion would not significantly influence the temperature 

 around the thermodetectors. It therefore seems signifi- 

 cant that the anterior hypothalamus has an 

 abundance of capillaries, much more so than regions 

 such as the posterior hypothalamus (65). The close 

 proximitv of the hypotiialamus to the arterial circle 



