Journal of the peripheral nervous system : JPNS
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J. Peripher. Nerv. Syst. · Mar 2011
Time course of acetylcholine-induced activation of sympathetic efferents matches axon reflex sweating in humans.
Action potentials from postganglionic C-fibres were recorded in healthy volunteers by microneurography in the peroneal nerve. Their responsiveness to mechanical or heat stimuli or to sympathetic reflex provocation tests was determined by transient slowing of conduction velocity following activation. Twenty units were classified as sympathetic efferent units. ⋯ No ACh-induced vasoconstriction was observed by laser Doppler scanning (n = 11) even after depletion of neuropeptides by chronic topical capsaicin treatment (n = 8). We conclude that ACh iontophoresis activates about half of the sympathetic fibres in human skin and provokes a corresponding axon reflex sweating. The absence of ACh-induced vasoconstriction even after the depletion of neuropeptides by capsaicin suggests that only sudomotor fibres, but not sympathetic vasoconstrictor fibres are activated by this stimulus.