Inhibitory Effects of Palmatine on P2X7 Receptor Expression in Trigeminal Ganglion and Facial Pain in Trigeminal Neuralgia Rats

Abstract

Trigeminal Neuralgia (TN) refers to recurrent severe paroxysmal pain in the distribution area of the trigeminal nerve, which seriously affects the quality of life of patients. This research applied the chronic constriction injury of the infraorbital nerve (CCI—ION) approach to induce an animal model of TN in rats. The mechanical pain threshold of each group of rats was determined postoperatively; the expression of P2X7 receptor in trigeminal ganglion (TG) was assessed by qRT-PCR, immunofluorescence and Western blot; and the changes of the proinflammatory cytokines IL-1β and TNF-α in serum of rats were detected by ELISA. The results showed that the administration of palmatine in the TN rats could reduce the mechanical pain threshold, significantly decrease the expression of P2X7 receptor in TG, and lower the serum concentrations of IL-1β and TNF-α, compared to the sham group. In addition, the phosphorylation level of p38 in TG of TN rats was significantly decreased after treatment with palmatine. Likewise, inhibition of P2X7 expression by shRNA treatment could effectively counteract the adversary changes of pain sensitivity, IL-1β and TNF-α production, and p38 phosphorylation in TN rats. Our data suggest that palmatine may alleviate mechanical facial pain in TN rats possibly by reducing the expression of P2X7 receptor in TG of TN rats, which may be attributable to inhibiting p38 phosphorylation and reducing the release of IL-1β and TNF-α.

Ligand-gated ion channel P2X7 regulates hypoxia-induced factor-1α mediated pain induced by dental pulpitis in the medullary dorsal horn

“…The P2X7 receptor has drawn much attention because of its special role in driving inflammatory processes and pathological pain in nervous system diseases ( Takenouchi et al, 2010 ; Yang et al, 2015 ; Cheffer et al, 2018 ; Yin et al, 2021 ). Notably, studies have shown that upregulation of P2X7 contributes to microglial activation ( He et al, 2012 ; Zhou et al, 2019 ; Yin et al, 2021 ).…”

Single-cell RNA sequencing reveals distinct transcriptional features of the purinergic signaling in mouse trigeminal ganglion

“…Purinergic receptor activation up-regulates intracellular Ca 2+ concentration via P2XR-mediated extracellular Ca 2+ influx and P2YR-/P1R-mediated Ca 2+ release from the calcium stores ( North, 2002 ; Abbracchio et al, 2006 ; Antonioli et al, 2013 ). Purinergic receptors expressed in the TG can be greatly up-regulated following orofacial inflammation and/or nerve injury, contributing to the initiation and maintenance of orofacial allodynia and hyperalgesia ( Shinoda et al, 2005 , 2007 ; Katagiri et al, 2012 ; Ito et al, 2013 ; Yin et al, 2021 ). P2rx3 , the gene that encodes P2 × 3Rs, was mainly expressed in neurons, and was virtually absent in other cell types.…”

“…Among immune cell subpopulations, P2rx7 was expressed not only in macrophages but also in MLCs and monocytes. There is evidence that P2 × 7R in the TG or STN is involved in orofacial pain ( Currò et al, 2020 ; Yin et al, 2021 ). However, given the cell type-specific expression patterns of P2XRs, there may be differences in mechanisms by which P2XR subtypes promote orofacial pain.…”

Olfactory Ensheathing Cells Alleviate Facial Pain in Rats with Trigeminal Neuralgia by Inhibiting the Expression of P2X7 Receptor

“…The facial skin, muscles, and connective tissue of each rat were carefully separated, and the infraorbital nerve was exposed. Ligation was performed with 0–4 absorbable sutures at an interval of 1–2 mm [ 22 , 24 , 27 , 28 ]. The ligation degree was 1/4th the diameter of the nerve without affecting normal blood supply to the nerve.…”

“…Then, TG sections (10 µm) were prepared on a freezing microtome and placed on immunosorbent slides. The sections were washed, three times, with PBS buffer, sealed with 5% BSA at 37 °C for 30 min, and incubated overnight with rabbit anti-rat P2X7 antibody (1:8000, Alomone Labs, Jerusalem, Israel) and mouse anti-rat GFAP antibody (1:1000, Boster) in a wet box at 4 °C [ 28 , 30 ]. After 12 h, the slide was removed and washed, 3 times, with PBS buffer, then, the tissue sections were incubated in CY-3 goat anti-rabbit antibody (1:200, Boster, Wuhan, China) and FITC goat anti-mouse antibody (1:200, Boster) in a dark environment at room temperature for 1 h. Next, the sections were washed again, 3 times, with PBS buffer and sealed with anti-fluorescence quenching sealing tablets containing DAPI dye (Solarbio, Beijing, China).…”