II54 



HANDBOOK OF PHVSIOLOGY 



NEUROPH'lSIOLOGV II 



FIG. 13. Vasodilator responses 

 in skinned hind leg of a dog. A: 

 Responses after intra-arterial in- 

 jection of acetylcholine; /) saline 

 control, increase of flow 10 per 

 cent; 2) 0.002 /iig, 150 per cent; 

 5) 0.02 iig, 170 per cent; 4) 0.2 

 fig, 270 per cent; 5) 2 /ig, 300 

 per cent. B: Responses to hypo- 

 thalamic stimulation for 15 sec. 

 /) 0.5 V. intensity, increase of flow 

 5 percent; 2) 0.75 v., 80 per cent; 

 3) i.o v., 120 per cent; 4) 1.5 v., 

 190 per cent; 5) 2.0 v., 240 per 

 cent; 6) 2.5 v., 280 per cent. C- 

 Responses after o. i mg per kg 

 atropine: /) stimulation with 1.5 

 v., increase of flow 10 per cent; 2) 

 0.02 ;ig acetylcholine, 25 per 

 cent. [From Eliasson el al. (76).] 



etOOO PttC«Sul*C t*Oi 



BLOOD FLO* SKrwHEO ', 

 HieNT HINO LIMB 



SI«N«L 



TiHK fto sec 



Cerebral Cortex 



Eliasson et al. (76) presented evidence showing that 

 the sympathetic vasodilator outflow has a cortical 

 representation. Vasodilator responses were observed 

 on electrical stimulation of the motor cortex of the 

 dog in an area between the cruciate sulcus and the 

 sulcus considered to be homologous to the fissure of 

 Rolando. Eliasson et al. also observed a few sub- 

 cortical vasodilator points indicating the existence 

 of a corticohypothalamic pathway. The available 

 histologic data do not allow any definite conclusions 

 regarding the anatomical course of these vasodilator 

 neurons. However, the latter seem to pass from the 

 cortex within the internal capsule to structures in the 

 anterior part of the hypothalamus. 



Physiologic Signijicance of Sympathetic 

 Vasodilator Nerves 



It is somewhat remarkaiile that notwithstanding our 

 fairly wide knowledge of the cerebral representation 

 of the sympathetic vasodilator outflow, we know vir- 

 tually nothing about its functional significance. In 

 my own opinion the contributions recently made by 

 Swedish investigators lend considerable weight to the 

 view that the sympathetic vasodilator outflow is 

 limited to the skeletal muscles, at all events in the 

 dog and cat. This at least applies to that sympathetic 

 vasodilator outflow the intracerebral representation 

 of which has been studied by these investigators. 



The vasodilatation in skeletal muscle observed by 

 Green & HofT (107) and Lund (157) on stimulation 

 of the sigmoid gyrus in cats or areas 4 and 6 in mon- 



kevs was attributed by them to diminution of vaso- 

 constrictor tone. However, in the absence of decisive 

 evidence, one might ascribe it equally well to activa- 

 tion of the vasodilator system. 



The fact that the sympathetic vasodilator outflow 

 has cortical, hypothalamic and mesencephalic relay 

 stations suggests that it in some way takes part in the 

 integrative control of the muscle blood flow. It is 

 generally considered that the response pattern charac- 

 terizing emotional reactions such as fear, anger, anx- 

 iety, sexual excitement and other situations requir- 

 ing sudden mobilization of the organism's resources 

 is in some way dependent on the integrative action of 

 the hypothalamus. The increase in the cardiac output 

 that attends muscular work is distributed, by means of 

 shifts of tone in the peripheral vessels, chiefly to the 

 muscles. Activation of the sympathetic vasodilator 

 outflow by hypothalamic stimulation gives rise to a 

 redistribution of blood that is characteristic of emer- 

 gency reactions. This system can produce vasodila- 

 tation in the muscles and simultaneously \asocon- 

 striction in the skin and viscera. Further, there is 

 activation of the adrenals, with selective liberation 

 of epinephrine. The amounts thus liberated do not 

 suffice to produce vasomotor reactions in the muscles 

 and skin, but they arc sufticient to increase the met- 

 aijolic processes in the muscles, heart and other 

 organs. One is tempted to assume, therefore, that 

 the sympathetic vasodilator nerves are activated in 

 circumstances which require optimal conditions for 

 muscular effort. 



The question arises whether or not the sympathetic 

 vasodilator nerves mav be involved in the control of 



