Neural Mechanisms of Pain Relief by Microcone

Abstract

Autonomic nervous responses induced by noxious stimuli are one of the causes of chronic pain. Therefore, management of them is clinically important. We found in humans and animals that the gentle skin touch can suppress somato-cardiovascular reflexes induced by noxious heat stimulation. The effect is produced by a touch of microcone which has orderly arranged micro-projections. A touch of a flat disk made of the same material is ineffective. Tactile perception, metabolism of somatosensory cortices, and activity of cutaneous mechanoreceptor afferent Aβ-nerve fibers, essential for the perception of touch, do not differ between a microcone touch and flat disc touch. However, the metabolism of anterior cingulate cortex and low-threshold mechanoreceptive afferent Aδ-and C-nerve fiber activities are higher if caused by a microcone touch than by a flat disc touch. The inhibitory effect of somato-cardiovascular reflex by microcone disappears with a local(intrathecal)application of an opioid receptor blocker to the spinal cord. These results suggest that microcone-induced excitation of low-threshold mechanoreceptive Aδ and C skin afferents produces the release of endogenous opioids in the spinal cord, resulting in the inhibition of nociceptive transmission that contributes to cardiac sympathetic reflexes.