title: Biphasic effects of tonic stimulation of muscle nociceptors on skin sympathetic nerve activity in human subjects.
abstract: Skin sympathetic nerve activity (SSNA) controls skin blood flow and sweat release, and acute noxious stimulation of skin has been shown to cause a decrease in SSNA in the anaesthetised or spinal cat. In awake human subjects, acute muscle pain causes a transient rise in SSNA, but the impact of long-lasting (tonic) stimulation of muscle nociceptors on skin sympathetic outflow, blood flow and sweat release is unknown. We tested the hypothesis that tonic stimulation of muscle nociceptors causes a sustained increase in sympathetic outflow to the skin. SSNA was recorded from the common peroneal nerve of 10 awake human subjects. Tonic muscle pain was induced by infusing hypertonic saline (7 %) into the tibialis anterior muscle over ~40 min, titrated to achieve a constant level of muscle pain. SSNA initially increased following the onset of the infusion, reaching a peak of 164 % of baseline within 5 min, but then showed a prolonged and sustained decrease, reaching a nadir of 77 % in 20 min. Conversely, skin blood flow (and vascular conductance) initially decreased, followed by a progressive increase; there were no consistent changes in sweat release. In 9 of 10 subjects, SSNA and skin blood flow were inversely related. We conclude that sympathetic outflow to the skin exhibits a biphasic response to long-lasting stimulation of muscle nociceptors: an initial increase presumably related to the 'arousal' or 'alerting' component of pain, characterised by increased SSNA and decreased skin blood flow, followed by a prolonged decrease in SSNA and increased skin blood flow. The latter may be a purposeful response that contributes to wound healing.
authors: School of Medicine, University of Western Sydney, Locked Bag 1797, Penrith, Sydney, NSW 2751, Australia.
authors: Samuel C
authors: SC
authors: Hall
authors: Azharuddin
authors: A
authors: Fazalbhoy
authors: Ingvars
authors: I
authors: Birznieks
authors: Vaughan G
authors: VG
authors: Macefield
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007273:Injections, Intramuscular / Q000009:adverse effects; D008297:Male; D059352:Musculoskeletal Pain / Q000139:chemically induced / Q000503:physiopathology*; D009619:Nociceptors / Q000502:physiology*; D010147:Pain Measurement; D010543:Peroneal Nerve / Q000503:physiopathology*; D012119:Respiration; D012462:Saline Solution, Hypertonic / Q000009:adverse effects; D012867:Skin / Q000098:blood supply* / Q000294:innervation*; D013997:Time Factors; D055815:Young Adult
chemical_list: D012462:Saline Solution, Hypertonic