Abstract
Stimulation of high threshold mechanical nociceptors on the skin can modulate efferent sympathetic outflow. Whether low threshold mechanoreceptors from glabrous skin are similarly capable of modulating autonomic outflow is unclear. Therefore, the purpose of this study was to examine the effects of cutaneous afferent feedback from the hand palm and foot sole on efferent muscle sympathetic nerve activity (MSNA). Fifteen healthy young participants (9 male; 25 ± 3 years [range: 22–29]) underwent microneurographic recording of multi-unit MSNA from the right fibular nerve during 2 min of baseline and 2 min of mechanical vibration (150 Hz, 220 μm peak-to-peak) applied to the left hand or foot. Each participant completed three trials of both hand and foot stimulation, each separated by 5 min. MSNA burst frequency decreased similarly during the 2 min of both hand (20.8 ± 8.9 vs. 19.3 ± 8.6 bursts/minute [Δ −8%], p = 0.035) and foot (21.0 ± 8.3 vs. 19.5 ± 8.3 bursts/minute [Δ −8%], p = 0.048) vibration but did not alter normalized mean burst amplitude or area (All p > 0.05). Larger reductions in burst frequency were observed during the first 10 s (onset) of both hand (20.8 ± 8.9 vs. 17.0 ± 10.4 [Δ −25%], p < 0.001) and foot (21.0 ± 8.3 vs. 18.3 ± 9.4 [Δ −16%], p = 0.035) vibration, in parallel with decreases in normalized mean burst amplitude (hand: 0.45 ± 0.06 vs. 0.36 ± 0.14% [Δ −19%], p = 0.03; foot: 0.47 ± 0.07 vs. 0.34 ± 0.19% [Δ −27%], p = 0.02) and normalized mean burst area (hand: 0.42 ± 0.05 vs. 0.32 ± 0.12% [Δ −25%], p = 0.003; foot: 0.47 ± 0.05 vs. 0.34 ± 0.16% [Δ −28%], p = 0.01). These results demonstrate that tactile feedback from the hands and feet can influence efferent sympathetic outflow to skeletal muscle.
Highlights
The skin represents a complex organ innervated by a variety of sensory neurons (Zimmerman et al, 2014)
The purpose of the present study was to examine the influence of low threshold cutaneous mechanoreceptor feedback from glabrous skin on the hand palm and foot sole on peripheral sympathetic outflow to skeletal muscle
These results provide support for a link between somatosensory afferent feedback from glabrous skin and autonomic efferent sympathetic outflow involved in cardiovascular regulation
Summary
The skin represents a complex organ innervated by a variety of sensory neurons (Zimmerman et al, 2014). Tactile feedback from the hands and feet are important for sensorimotor control (Kavounoudias et al, 1998; Zimmerman et al, 2014) and can be coupled to motoneuron activation (Fallon et al, 2005; Bent and Lowrey, 2013). Whether such afferent feedback from the skin is capable of modulating efferent autonomic outflow is unclear. Low threshold mechanoreceptor afferent feedback from glabrous skin on the feet is critical for maintaining posture and balance (Kavounoudias et al, 1998) but could serve as an afferent mechanism to trigger, for example, efferent sympathetic activation to help defend against the cardiovascular effects of orthostasis
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