The epidermal growth factor receptor (EGFR) located in dorsal root ganglion has been found as a new target for chronic pain treatment. However, it is not clear whether the change of EGFR expression in the dorsal root ganglion contributes to neuropathic pain development. In this study, we used a chronic compression of unilateral lumbar dorsal root ganglions (CCD)-induced rat neuropathic pain model and found that CCD caused the upregulation of both phosphorylated EGFR and total EGFR expression in compressed lumbar 4/5 (L4/L5) dorsal root ganglions by western blotting and immunohistochemistry methods. Either inhibition of EGFR activation by EGFR inhibitor or knockdown of EGFR expression by EGFR small interference RNA (siRNA) relieved CCD-induced pain hypersensitivities to mechanical, thermal, and cold stimuli in rats. Moreover, EGFR knockdown reversed CCD-induced the increase of intracellular mammalian target of rapamycin (mTOR) expression as well as the activation of the satellite glial cells in the ipsilateral compressed L4/L5 dorsal root ganglions. These findings suggest that not only activated EGFR but also total EGFR contribute to CCD-induced neuropathic pain by enhancing intracellular mTOR signaling.

Knee osteoarthritis (KOA) is a highly prevalent, chronic joint disorder, and it is a typical disease which can develop chronic pain. Our previous study has proved that endocannabinoid (2-AG)-CB1R-GABA-5-HT pathway is involved in electroacupuncture (EA) mediated inhibition of chronic pain. However, it is still unclear which among the 5-HT receptor subtype is involved in EA evoked 5-HT mediated inhibition of chronic pain in the dorsal spinal cord. 5-HT_2A is a G protein-coupled receptor and it is involved in 5-HT descending pain modulation system. We found that EA treatment at frequency of 2 Hz +1 mA significantly increased the expression of 5-HT_2A receptor in the dorsal spinal cord and intrathecal injection of 5-HT_2A receptor antagonist or agonist reversed or mimicked the analgesic effect of EA in each case respectively. Intrathecal injection of a selective GABA_A receptor antagonist Bicuculline also reversed the EA effect on pain hypersensitivity. Additionally, EA treatment reversed the reduced expression of GABA_A receptor and KCC2 in the dorsal spinal cord of KOA mice. Furthermore, we demonstrated that intrathecal 5-HT_2A receptor antagonist/agonist reversed or mimicked the effect of EA up-regulate of KCC2 expression, respectively. Similarly, intrathecal injection of PLC and PKC inhibitors prevented both anti-allodynic effect and up-regulation of KCC2 expression by EA treatment. Our data suggest that EA treatment up-regulated KCC2 expression through activating 5-HT_2A-Gq-PLC-PKC pathway and enhanced the inhibitory function of GABA_A receptor, thereby inhibiting chronic pain in a mouse model of KOA.

Chemotherapeutic agents, such as paclitaxel (PTX), induce neuroplastic changes and alter gene expression in the prefrontal cortex (PFC), which may be associated with chemotherapy‐induced pain and negative emotions. Notably, DNA methylation undergoes adaptive changes in neurological disorders, emerging as a promising target for neuromodulation. In this study, systemic administration of PTX leads to a decrease in the expression of the DNA methyltransferase DNMT3a, while concurrently upregulating the expression of Gabrb1 mRNA and its encoded GABA_ARβ1 protein in the medial PFC (mPFC) of male mice. Overexpression of DNMT3a in the mPFC alleviates PTX‐induced pain hypersensitivity, and anxiety‐like behavior in these mice. Additionally, it reverses the PTX‐induced increase in inhibitory synaptic transmission in the pyramidal neurons of the mPFC. Mechanistically, the upregulation of GABA_ARβ1 in the mPFC is linked to the reduced expression of DNMT3a and DNA hypomethylation at the promoter region of the Gabrb1 gene. Furthermore, a long‐term diet rich in methyl donors alleviates PTX‐induced pain hypersensitivity and anxiety‐like behavior in mice. These findings suggest that the DNMT3a‐mediated upregulation of GABA_ARβ1 in the mPFC contributes to PTX‐induced neuropathic pain and anxiety, highlighting DNA methylation‐dependent epigenetic regulation as a potential therapeutic target for addressing chemotherapy‐induced cortical dysfunction.

Knee osteoarthritis (KOA) is a common and disabling condition characterized by attacks of pain around the joints, and it is a typical disease that develops chronic pain. Previous studies have proved that 5-HT₁, 5-HT₂, and 5-HT₃ receptors in the spinal cord are involved in electroacupuncture (EA) analgesia. The 5-HT₇ receptor plays antinociceptive role in the spinal cord. However, it is unclear whether the 5-HT₇ receptor is involved in EA analgesia. The 5-HT₇ receptor is a stimulatory G-protein (Gs)-coupled receptor that activates adenylyl cyclase (AC) to stimulate cyclic adenosine monophosphate (cAMP) formation, which in turn activates protein kinase A (PKA). In the present study, we found that EA significantly increased the tactile threshold and the expression of the 5-HT₇ receptor in the dorsal spinal cord. Intrathecal injection of 5-HT₇ receptor agonist AS-19 mimicked the analgesic effect of EA, while a selective 5-HT₇ receptor antagonist reversed this effect. Moreover, intrathecal injection of AC and PKA antagonists prior to EA intervention prevented its anti-allodynic effect. In addition, GABA_A receptor antagonist bicuculline administered (intrathecal, i.t.) prior to EA intervention blocked the EA effect on pain hypersensitivity. Our data suggest that the spinal 5-HT₇ receptor activates GABAergic neurons through the Gs–cAMP–PKA pathway and participates in EA-mediated inhibition of chronic pain in a mouse model of KOA.