It has been widely recognized that electroacupuncture (EA) inducing the release of β-endorphin represents a crucial mechanism of EA analgesia. The ARC is a vital component of the endogenous opioid peptide system. However, the specific mechanisms how EA facilitates the release of β-endorphin within the ARC, eliciting analgesic effects are yet to be elucidated. In this study, we conducted in vivo and in vitro experiments by transcriptomics, microdialysis, photogenetics, chemical genetics, and calcium imaging, combined with transgenic animals. Firstly, we detected 2Hz EA at the Zusanli (ST36) increased the level of β-endorphin and transcriptional level of POMC. Our transcriptomics profiling demonstrated that 2Hz EA at the ST36 modulates the expression of c-Fos and Jun B in ARC brain nuclear cluster, and the transcriptional regulation of 2Hz EA mainly occur in POMC neurons by immunofluorescence staining verification. Meaning while, 2Hz EA specifically activated the cAMP-PKA-CREB signaling pathway in ARC which mediating the c-Fos and Jun B transcription, and 2Hz EA analgesia is dependent on the activation of cAMP-PKA-CREB signaling pathway in ARC. In order to investigate how the β-endorphin produced in ARC transfer to integration center PAG, transneuronal tracing technology was used to observe the 2Hz EA promoted the neural projection from ARC to PAG compared to 100Hz EA and sham mice. Inhibited PAGGABA neurons, the transfer of β-endorphin from the ARC nucleus to the PAG nucleus through the ARCPOMC-PAGGABA neural circuit. Furthermore, by manipulating the excitability of POMC neurons from ARCPOMC to PAGGABA using inhibitory chemogenetics and optogenetics, we found that this inhibition significantly reduced transfer of β-endorphin from the ARC nucleus to the PAG nucleus and the effectiveness of 2Hz EA analgesia in neurological POMC Cre mice and C57BL/6J mice, which indicates that the transfer of β-endorphin depends on the activation of POMC neurons prefect from ARCPOMC to PAGGABA.
Keywords: antinociceptive; electroacupuncture; mechanism; pain.