Cutaneous Mechanoreceptor Feedback from the Hand and Foot Can Modulate Muscle Sympathetic Nerve Activity

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.

Keywords: afferent feedback; autonomic nervous system; cutaneous; microneurography; muscle sympathetic neural activity; vibration.

Figure 1

Diagram of the vibration pads on the palm of hand (A) and foot sole (B). Two 7.5 cm by 7.5 cm pads were secured to each location with elastic straps, and positioned to maximize skin contact. Pads produced a mechanical vibration of 150 Hz, 220 μm peak-to-peak amplitude.

Figure 2

Representative 60 s integrated muscle sympathetic nerve activity (MSNA) tracings from one participant during the end of baseline and beginning of vibration in the hand and foot. The dashed line indicates the onset of vibration.

Figure 3

Muscle sympathetic nerve activity (MSNA) burst frequency (A), burst incidence (B), and normalized mean burst amplitude (C) and area (D) during 2 min of baseline rest and hand vibration.

Figure 4

Muscle sympathetic nerve activity (MSNA) burst frequency (A), burst incidence (B), and normalized mean burst amplitude (C) and area (D) during 2 min baseline rest and foot sole vibration.

Figure 5

Muscle sympathetic nerve activity (MSNA) burst frequency (A), burst incidence (B), and normalized mean burst amplitude (C) and area (D) during 2 min of baseline rest and the onset (10 s) of hand vibration.

Figure 6

Muscle sympathetic nerve activity (MSNA) burst frequency (A), burst incidence (B), and normalized mean burst amplitude (C) and area (D) during 2 min of baseline rest and the onset (10 s) of foot sole vibration.