Changes in Responses of Neurons in Spinal and Medullary Subnucleus Reticularis Dorsalis to Acupoint Stimulation in Rats with Visceral Hyperalgesia

Abstract

The purpose of this study was to explore the mechanism of acupoints sensitization phenomenon at the spinal and medulla levels. Experiments were performed on adult male Sprague-Dawley rats and visceral noxious stimuli was generated by colorectal distension (CRD). The activities of wide dynamic range (WDR) and subnucleus reticularis dorsalis (SRD) neurons were recorded. The changes of the reactions of WDR and SRD neurons to electroacupuncture (EA) on acupoints of “Zusanli-Shangjuxu” before and after CRD stimulation were observed. The results showed that visceral nociception could facilitate the response of neurons to acupoints stimulation. In spinal dorsal horn, EA-induced activation of WDR neurons further increased to 106.84 ± 17.33% (1.5 mA) (P < 0.001) and 42.27 ± 13.10% (6 mA) (P < 0.01) compared to the neuronal responses before CRD. In medulla oblongata, EA-induced activation of SRD neurons further increased to 63.28 ± 15.96% (1.5 mA) (P < 0.001) and 25.02 ± 7.47% (6 mA) (P < 0.01) compared to that before CRD. Taken together, these data suggest that the viscerosomatic convergence-facilitation effect of WDR and SRD neurons may underlie the mechanism of acupoints sensitization. But the sensitizing effect of visceral nociception on WDR neurons is stronger than that on SRD neurons.

Mast cells are important regulator of acupoint sensitization via the secretion of tryptase, 5-hydroxytryptamine, and histamine

“…It is worthwhile pointing out that the location and functional status of acupoints are considered dynamic within a certain range of time and space, varying with different physiological and pathological conditions [ 6 – 7 ]. It has also been reported that MCs not only induce a neuro-immuno response by the release of inflammatory mediators following acupuncture; they also play a crucial role in the cross-talk among the circulatory, nervous and immune networks at acupoints [ 8 – 9 ].…”

“…The dynamics of the acupoint response to disease are confined to the term “acupoint sensitization”. It refers to the dynamic transformation of an acupoint from a "silenced status" (as induced by healthy conditions) to an "activated status” (as induced by disease) [ 7 , 10 ]. Previous studies showed that acupoint sensitization markedly affects the size of an acupoint’s receptive field as well as the sensitivity and response-capacity of an acupoint to the therapeutic effects of acupuncture [ 11 – 12 ].…”

Electroacupuncture Inhibits Visceral Nociception via Somatovisceral Interaction at Subnucleus Reticularis Dorsalis Neurons in the Rat Medulla

“…The great majority of neurons within SRD did not exhibit spontaneous activity, but these neurons were activated exclusively by thermal, mechanical, and electrical noxious stimulation on any part of the body surface, thus exhibiting a “whole body” receptive field ( Villanueva et al, 1988 , 1990 ). In addition, SRD neurons also responded to noxious visceral stimulation ( Li et al, 2013 ; Yu et al, 2014 ). Similarly, the present study observed the activation responses of SRD neurons evoked by noxious pinch stimulation applied to the foot, tail and finger, and also by noxious CRD stimulation and high intensity of EA stimulation within 2–8 mA.…”

Neurobiological Mechanism of Acupuncture for Relieving Visceral Pain of Gastrointestinal Origin

“…The SDH contains abundant neurotransmitters and associated receptors, neuromodulators, and ion channels, which not only receive and transmit nociceptive information but also preliminarily process nociceptive information [ 54 , 60 , 61 ]. Research of the visceral pain model in rats has found that CRD can activate the response of wide dynamic range (WDR) SDH neurons, whereas the AP stimulation of acupoints can inhibit the neuronal response activated by visceral nociceptive afferents and thus alleviate visceral pain [ 62 ]. However, SDH neurons participate in the descending transduction pathway of visceral pain.…”