Effects of sytemic hypoxia and hypercapnia on cutaneous and muscle vasoconstrictor neurones to the cat's hindlimb.

1. Reactions of cutaneous and muscle vasoconstrictor neurones to the hindlimb on systemic hypoxia and systemic hypercapnia were investigated in chloralose anaesthetized cats. Mainly four types of preparations were used: brain intact and decrebrate (pontomedullary) animals with and without carotid sinus (CSN) and vagal nerves (VN). 2. In brain intact animals with intact CSN and VN most cutaneous vasoconstrictor neurones were depressed and most muscle vasoconstrictor neurones were excited during systemic hypoxia and hypercapnia. The responses to hypercapnia were smaller than those to hypoxia. 3. In brain intact deafferented animals and in decerebrate animals with and without intact CSN and VN systemic hypoxia and hypercapnia induced excitation in both cutaneous and muscle vasoconstrictor neurones. The responses to hypoxia were significantly smaller in deafferented preparations when compared to those in preparations with intact CSN and VN. Furthermore in muscle vasoconstrictor neurones the size of the responses was not significantly different in decerebrate preparations from that in brain intact preparations. 4. These results indicate a distinct neuronal organization of the chemoreceptor reflexes in the vasoconstrictor systems in the brain stem. Suprapontine brain structures are most important for producing the inhibition of the cutaneous vasoconstrictor neurones during hypoxia and hypercapnia.