Fig. 9

Responses of sympathetic postganglionic fibers innervating the hindleg skin (left) and muscle (right) to noxious mechanical stimulation (horizontal bar) applied to the ipsilateral hindfoot skin (a) and to noxious thermal stimulation (b) applied by immersing the contralateral hindleg in a temperature controlled water bath (upper line with numbers, °C). Analyzed were spontaneously active (hence vasoconstrictor) fibers in anesthetized artificially ventilated cats under neuromuscular blockade. Nerve filament preparations contained a few active fibers. a Mechanical noxious stimulations of a skin area depress skin vasoconstrictor activity and activate muscle vasoconstrictor activity. b Graded heat stimulation applied to the skin is ineffective, as long as the pain threshold temperature (≈44 °C) is not exceeded. Stimulating heat nociceptors with further stepwise increases of temperature induce graded opposing responses of skin and muscle vasoconstrictor fibers that are equidirectional to those following mechanical noxious stimulation. From Horeyseck and Jänig [19]