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Somatosensory System

開催日 2014/9/13
時間 14:00 - 15:00
会場 Poster / Exhibition(Event Hall B)

Cutaneous low-threshold mechanoreceptive Aδ and C afferent units may contribute to anti-nociceptive effect of touch

  • P3-156
  • 渡辺 信博 / Nobuhiro Watanabe:1 Piché Mathieu / Mathieu Piché:1 堀田 晴美 / Harumi Hotta:1 
  • 1:東京都健康長寿医療センター研究所 / Department of Autonomic Neuroscience, Tokyo Metropolitan Institute of Gerontology 

It is common experience that pain may be reduced by touching the skin near a painful site. As an underlying mechanism, the most common belief is that afferent inputs conveyed by large-diameter afferent fibers modulate spinal activity induced by small-diameter afferent fibers. However, an association between the types of skin mechanoreceptors and analgesia has not been confirmed. We have reported that touch inhibited cardiovascular responses to noxious somatic stimuli. Such effects were dependent on the surface texture of the touching objects. The aim of the present study was to identify cutaneous mechanoreceptors that inhibit somatically-induced cardiovascular responses. Unitary activity of skin afferents was recorded from the saphenous nerve using a bipolar wire electrode in anesthetized rats. Touch was applied to the inner thigh for 10 minutes using 1) a soft elastomer brush (microcone), which inhibited cardiovascular responses to noxious somatic stimulation, and 2) a soft elastomer flat disc (flat disc), which did not produce any effect. An increment of the discharge rate during touch with microcone and flat disc was compared for each unit. A difference by a factor of less than 2 was considered as no difference. A total of 38 slowly adapting units were recorded (Aβ, Aδ and C fibers; 13, 12 and 13 units, respectively). The mechanical threshold of all recorded units was less than 0.4 g (i.e., within innocuous range). Among Aβ units, an increment of discharge rate was greater during microcone touch in 3 units, greater during flat disc touch in 3 units, while 7 units showed no difference. Ten Aδ units exhibited greater increment of discharge rate during microcone touch but the other units showed no difference. A similar trend was seen in C units, where 8 units exhibited greater increment during the microcone touch while 5 units showed no difference. Mean increments of Aβ, Aδ and C units during microcone and flat disc were 0.55 Hz vs. 0.80 Hz, 0.57 Hz vs. 0.26 Hz, and 0.37 Hz vs. 0.24 Hz, respectively. The present study suggests that excitation of cutaneous low-threshold mechanoreceptive Aδ and C afferent units may contribute to anti-nociceptive effect of touch.

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