Spreading of sudomotor axon reflexes in human skin.
BACKGROUND
Acetylcholine (ACh) activates both sudomotor fibers and primary afferent nociceptors. This leads to sudomotor and vasodilator axon reflexes, which can be diminished, for example, in neuropathies. In some neuropathies, however, there is increased axon reflex sweating, a response pattern that has never been observed for vasodilator flares.


OBJECTIVE
To compare both types of axon reflexes and to elucidate possible differences.


METHODS
In healthy young male subjects, sweat response and flare reaction in response to ACh were quantified. Constant-current iontophoresis (300 mC) of ACh was performed on the lateral lower legs. The sudomotor axon reflex was visualized with iodine starch staining, and the sweat response was quantified with capacitance hygrometry (quantitative sudomotor axon reflex test [QSART]). The vasodilator flare was visualized and quantified by laser Doppler imaging. All measurements were performed during and for 10 minutes after finishing the iontophoresis.


RESULTS
The sudomotor axon reflex area increased from 30.6 cm2 at the end of the iontophoresis to 39.2 cm2 (p < 0.001) 10 minutes later, while QSART response had already decreased. Flare size and flare intensity remained nearly constant during the observation period.


CONCLUSIONS
Despite fast cleavage of acetylcholine by cholinesterases, sudomotor axon reflexes spread in the skin, indicating a possible peripheral amplification of sweating.
Schlereth
Tanja
T
Department of Neurology, Johannes Gutenberg University, Mainz, Germany. schleret@uni-mainz.de
Brosda
Nadine
N
Birklein
Frank
F
D000109:Acetylcholine / Q000378:metabolism; D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D001808:Blood Vessels / Q000294:innervation / Q000502:physiology; D004525:Efferent Pathways / Q000502:physiology; D006801:Humans; D008297:Male; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D009619:Nociceptors / Q000502:physiology; D010525:Peripheral Nerves / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000502:physiology; D012867:Skin / Q000098:blood supply / Q000294:innervation*; D013545:Sweat Glands / Q000294:innervation* / Q000502:physiology*; D013546:Sweating / Q000502:physiology*; D017779:Sympathetic Fibers, Postganglionic / Q000502:physiology*; D014664:Vasodilation / Q000502:physiology; D014666:Vasomotor System / Q000502:physiology*
D000109:Acetylcholine