1 82 HANDBOOK OF PHYSIOLOGY -^ NEUROPHYSIOLOGY II 



H^iQH 



FIG. lo. Schematic drawing of sagittal section of a cat brain, 

 showing (doited area) the region found to be essential for de- 

 corticate polypneic panting. Transection A-A eliminates sham 

 rage in the chronic decorticate cat; transection B-B eliminates 

 decorticate polypneic panting. CM, mammillary body; E, 

 epiphysis; H, habenular complex; IC, inferior colliculus; OC, 

 optic chiasma; and SC, superior colliculus. [From Lilienthal & 

 Otenasek (134).] 



if panting cannot result. In these animals polypnea 

 results from body warming, but the increase in re- 

 spiratory rate may simply be secondary to the simul- 

 taneous increase of tissue metabolism. Resting oxygen 

 uptake of the whole body increases by about 1 3 per 

 cent per degree C temperature increase, Qio ranging 

 from 2.6 to 2.9 (59), respiratory rate increases simi- 

 larly, Qio being 2 to 3 (34). If the carotid 

 blood stream is heated, the carotid body chemore- 

 ceptors probaiily contriijutc slightly to the bulbar 

 polypnea (29), although chronic denervation of the 

 carotid body and sinus in the otherwise intact animal 

 does not significantly influence thermal polypnea 



(197)- 



Depending on the nature of the stimulus which 

 ultimately incites panting in the intact animal, one 

 may speak of either reflex thermal panting in re- 

 sponse to signals from surface receptors with un- 

 changed brain temperature, or central thermal 

 panting in response to signals from detectors acti- 

 vated by increased brain temperature. It is probable 

 that reflex panting is reinforced by successively de- 

 veloped cortical conditioning (93). 



FIG. i I. Two types of respiratory responses to hypothalamic 

 electrical stimulation i/f) in an anesthetized cat. Upper curve: 

 Rapid, shallow breaths (polypnea or panting) elicited from the 

 dorsolateral region. Lower curve: Moderately rapid, deep breaths 

 (hyperpnea) elicited from the dorsocaiidal region. [From Hess 

 & StoU (109,).] 



Cutaneous Blood Flow 



Changes of cutaneous blood flow produce skin 

 temperature changes of similar direction, even if the 

 two parameters are not linearly related. Cutaneous 

 blood flow is therefore an important thermoregulatory 

 effector system, influencing rate of heat loss from the 

 body. In the unanesthetized animal, the degree of 

 cutaneous vasodilatation depends on the coordinated 

 reaction to signals both from surface thermoreceptors 

 and ceiitral thermodetectors and from other mecha- 

 nisms influencing vasoconstrictor tone. Vasodilata- 

 tion is therefore not precisely correlated with any one 

 of these factors, e.g. local hvpothalaniic temperature 



(71)- 



When an intact animal is warmed, the vessels of 



particular skin areas become dilated in a definite 

 sequence, an observation indicating a regional 

 'vasomotor gradient' (115); this is related to a region- 

 ally different va.scular sensitivity to such factors as the 

 natural local hormones. Such thermoregulatory skin 

 areas include parts of the face and the hands and feet 

 in man (105), the ears and foot pads in the rabbit 

 and the dog, and foot pads in the cat. Tliey contain 

 ai:)undant arteriovenous anastomoses (50, 88). Blood 

 flow through such a skin area can be \aried within 

 a hundredfold range (41, 43). Vasodilatation occurs 



