Abstract
Summary The discharges of cardiac and intestinal sympathetic efferent, ear skin temperature, arterial pressure, and heart rate were simultaneously recorded in anesthetized, immobilized, and artificially ventilated rabbits. The responses to hypoxia and hypercapnia of various degrees, to asphyxia, and to thermal stimulation of the spinal cord were observed. Cardiac sympathetic activity and as indirectly determined cutaneous sympathetic activity were reduced during moderate to severe hypoxia and during hypercapnia, whereas splanchnic activity increased. In states of extreme hypoxia or asphyxia (PaO2 below 20-25 mm Hg) there was a generalized increase of cardiac and intestinal sympathetic activity. During spinal cord cooling cutaneous vasoconstriction was evoked, while cardiac and intestinal sympathetic activity decreased. During spinal cord heating the reverse response, i. e., reduction of vasoconstrictor tone in the skin and increase of cardiac and intestinal sympathetic activity, was elicited. Bilateral vagus transection did not change the patterns of regional differentiation of sympathetic efferents observed during changes of blood gas composition and central thermal stimulation. Comparison of the heart rate responses in non-vagotomized and vagotomized animals revealed that both vagal and sympathetic efferents contributed to the heart rate responses observed in the present investigation.
