CENTRAL NERVOUS REGULATION OF BODV TEMPERATURE 



.83 



RESPIBftTlON 



BLOOD 

 PRESSURE 



INSP 

 MM HG. 

 120 



BLOOD FLOW 



V CEPHALIC* OX 



STIMULATION 



TIME I MIN. 



RESPIRATORY FREQUENCY 





FIG. 12. Effect of diathermic 

 and conductive heating of the 

 anterior hypothalamus on cutane- 

 ous blood flow and respiratory 

 rate. Cat is under urethane anes- 

 thesia. Experimental technique 

 is the same as in fig. 4. Respira- 

 tory depth is measured by a 

 perithoracic pneumograph. /, 2, 

 8, g and to signal diathermic 

 heating; j, conductive heating. 

 [From Strom (187).] 



first in the face and ears, then in forehmbs or hands, 

 and then in hind Hmbs or feet (7). Cutaneous blood 

 flow is ciianged by variations of sympathetic vaso- 

 constrictor tone (69); no unequivocal evidence for 

 the existence in the .skin of specific \asodilator fibers 

 (sympathetic or dorsal root antidromic) has been 

 put forward (70). 



Local thermal stimulation of the anterior hypo- 

 thalamus evokes cutaneous va.sodilatation (as shown 

 in figs. 4, 13, 14, 15) which appears within a few 

 seconds of a steady warming and reaches an early 

 maximum, then again diminishes or disappears. If 

 the warming is more intense, the \'asodilatation can 

 be .seen to remain to some extent during continued 

 heating. This result can be expressed as a dynamic 

 (transient) and a static (steadv) response to a sudden 

 and steady stimulus; in qualitative terms it resembles 

 the afferent firing response from a surface thermo- 

 receptor to a sudden leinperature change. The vaso- 



dilator response also becomes apparent as a rise in 

 skin teinperature, with a certain time lag due to the 

 heat capacity of the skin. The vasodilatation appears 

 in the same sequence and with the saine spatial gradi- 

 ent in the different areas of the body as during heat 

 stress of the intact body. Unilateral hypothalainic 

 warming gives a bilaterally similar response. 



In the intact animal, the heat-regulatory responses 

 of cutaneous blood flow are accompanied by con- 

 verse changes in blood flow in deeper organs, such 

 as the skeletal muscles (16) and viscera (80, 81, 174). 

 Such a redistribution of blood flow between surface 

 layers and deeper layers has obvious significance for 

 arterial pressure homeostasis. It might theoretically 

 be evoked either as a coordinated hypothalamic re- 

 sponse or as a secondary effect of baroceptive reflex 

 mechanisms. Local hypothalamic warming has given 

 discrepant results relative to muscular or intestinal 

 blood flow, some workers finding changes (182, 183), 



