Baroreceptor and chemoreceptor reflexes in postganglionic neurones supplying skeletal muscle and hairy skin.

Postganglionic neurons supplying skeletal muscle and hairy skin of the cat's hindlimb were investigated for their reactions to stimulation of carotid baroreceptors and chemoreceptors in chloralose-anaesthetized, immobilized and artificially ventilated animals. The baroreceptors were stimulated by the pulsatile blood pressure and by pressure increases applied to an isolated carotid sinus (carotid blind sac) leaving only one intact buffer nerve. Chemoreceptors were stimulated by systemic hypoxia and by intracarotid bolus injections of CO2-saturated saline. The cardiac rhythmicity of activity in the postganglionic neurones (evaluated from the post-R-wave histograms) and the neurone reactions to intracarotid pressure increases were fairly well correlated, with a coefficient of r = 0.84. The time course and magnitude of inhibitory responses to intracarotid pressure increases were identical in some of the cutaneous postganglionic neurones and postganglionic neurones supplying skeletal muscle. The majority of the postganglionic neurones supplying skin, however, exhibited a weaker inhibitory response and a different time course in their activity during and after the sinus pressure increases. Muscle postganglionic neurones were excited and the majority of the cutaneous postganglionic neurones were inhibited by stimulations of arterial chemoreceptors produced by systemic hypoxia and by intracarotid injection of CO2-saturated saline. Small fractions of the post-ganglionic neurones supplying skin were excited by stimulation of arterial chemoreceptors. The activity of these cutaneous postganglionic neurones showed a strong cardiac rhythmicity. It is proposed that those postganglionic neurones supplying skin which are affected by stimulation of baro- and chemoreceptors in the same manner as are the postganglionic neurones supplying skeletal muscle may innervate cutaneous resistance (nutritional) vessels. It is likewise suggested that those cutaneous postganglionic neurones inhibited by stimulation of arterial chemoreceptors and under weak control by the arterial baroreceptors may innervate cutaneous capacitance and shunt vessels.