Fig. 13

A single presumably postganglionic neuron which is silent at normal body temperature (a) responds by graded activation in response to graded heating of the spinal cord by means of a thermode tube placed in the peridural space. Since the neuron did not respond to any other afferent stimulus it fulfilled the criteria of a vasodilatory sympathetic efferent fiber. A spontaneously active neuron, presumably a vasoconstrictor neuron (b), displays graded inhibition in response to graded spinal cord heating. Numbers above recordings indicate temperature of the water perfusing the thermode (T _p ). Lower diagrams show temperature-response relationships of vasoconstrictor neurons (c) and of putative vasodilator neurons (d) with different symbols for individual experiments. Average relationship between T _p and temperature measured in the vertebral peridural space (Tvc) is indicated at the abscissa. Note that the opposing responses of vasoconstrictor and putative vasodilator neurons to temperature increases are graded and start at non-noxious peridural space temperatures. From Gregor et al. [12]