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

Abstract

Electroacupuncture (EA) is an efficacious treatment for alleviating visceral pain, but the underlining mechanisms are not fully understood. This study investigated the role of medullary subnucleus reticularis dorsalis (SRD) neurons in the effects of EA on visceral pain. We recorded the discharges of SRD neurons extracellularly by glass micropipettes on anesthetized rats. The responses characteristics of SRD neurons to different intensities of EA (0.5, 1, 2, 4, 6, and 8 mA, 0.5 ms, and 2 Hz) on acupoints “Zusanli” (ST 36) and “Shangjuxu” (ST 37) before and during noxious colorectal distension (CRD) were analyzed. Our results indicated that SRD neurons responded to either a noxious EA stimulation ranging from 2 to 8 mA or to noxious CRD at 30 and 60 mmHg by increasing their discharge frequency at an intensity-dependent manner. However, during the stimulation of both CRD and EA, the increasing discharges of SRD neurons induced by CRD were significantly inhibited by 2–8 mA of EA. Furthermore, SRD neurons can encode the strength of EA, where a positive correlation between current intensity and the magnitude of neuronal responses to EA was observed within 2–6 mA. Yet, the responses of SRD neurons to EA stimulation reached a plateau when EA exceeded 6 mA. In addition, 0.5–1 mA of EA had no effect on CRD-induced nociceptive responses of SRD neurons. In conclusion, EA produced an inhibiting effect on visceral nociception in an intensity-dependent manner, which probably is due to the somatovisceral interaction at SRD neurons.

Electroacupuncture-Induced Muscular Inflammatory Pain Relief Was Associated With Activation of Low-Threshold Mechanoreceptor Neurons and Inhibition of Wide Dynamic Range Neurons in Spinal Dorsal Horn

“…In fact, many human and animal studies have shown that EA with different intensities activated different types of peripheral afferent fibers and produce different extents of analgesia ( Xu et al, 2003 ; Zhu et al, 2004 ; Xin et al, 2016 ). Some studies have shown that EA with high-intensity stimulation is more effective than low-intensity stimulation of EA ( Barlas et al, 2006 ; Yu et al, 2018 ; Lv Z. T. et al, 2019 ). Conversely, some contrary conclusions have also been reported in animal studies ( Lee et al, 2005 ; Ceccherelli et al, 2008 ), which implies the necessity to explore the appropriate intensity of EA in the treatment of diseases.…”

The efficacy and neural mechanism of acupuncture therapy in the treatment of visceral hypersensitivity in irritable bowel syndrome

“…Based on these results, ACC mediated the modulatory effect of EA on abdominal pain in IBS rats, and this effect was influenced by the distribution of acupoints. In addition, the role of medullary subnucleus reticularis dorsalis-ACC loop in reducing visceral hypersensitivity has also been suggested ( Yu et al, 2018 ).…”

“…Furthermore, additional studies have shown that ginger moxibustion, characterized by fluctuating temperature, and mild moxibustion techniques effectively induce acupoint sensitization, achieving better treatment outcomes than laser moxibustion, which involves stable temperature application ( Sun et al, 2021 ). Two additional studies documented noteworthy suppression of visceral hypersensitivity resulting from neuronal activity within the subnucleus reticularis dorsalis and wide dynamic range regions, employing EA at intensities ranging from 2 to 6 mA ( Yu et al, 2018 ; Yu et al, 2019 ). These pieces of evidence indicate that in the investigation of the neural mechanisms underlying the relief of VH, there is a relatively concentrated focus on the selection of acupoints.…”

Mechanisms of acupuncture–electroacupuncture on inflammatory pain

“…17 Moreover, high-frequency EA stimulation is more effective than low-frequency stimulation. 18,19 Acupuncture also follows that (e.g. 120–180 rotations per minute).…”