Nociceptin/orphanin FQ up‐regulates P2X₃ receptors in primary cultures of neonatal rat trigeminal ganglion neurons

Abstract

Recent evidence indicates a nociceptive role of the nociceptin/orphanin FQ-opioid receptor-like receptor (N/OFQ-ORL1) system in craniofacial pain; however, the mechanisms of such an effect remain unclear. We investigated whether the action of N/OFQ involves the modulation of P2X3 , a pain-transducing ionotropic receptor. Double-labeled immunohistochemical staining was used to determine the co-localization of ORL1 and P2X3 receptors in the trigeminal ganglia (TG) of neonatal Sprague-Dawley rats. The effect of N/OFQ (at a concentration ranging from 1 pM to 10 nM) on the expression of P2X3 receptors was detected by RT-PCR, western blotting, and immunocytochemical staining. We found that ORL1 receptors were co-localized with P2X3 receptors and that the application of N/OFQ could up-regulate, in a concentration-dependent manner, the expression of P2X3 receptor mRNA and P2X3 receptor protein in TG neurons. Immunocytochemical staining also revealed enhanced P2X3 immunoreactivity beneath the neuronal membrane and an increased percentage of P2X3 -positive neurons after treatment with N/OFQ. Those effects were completely blocked by a specific ORL1 antagonist, UFP-101. Our results suggest that the activation of ORL1 receptors by N/OFQ can potentiate P2X3 receptors in primary cultures of neonatal trigeminal neurons, which may be a mechanism for the nociceptive role of N/OFQ in the modulation of craniofacial pain. Our findings may also have implications in treating craniofacial pain.

N/OFQ modulates orofacial pain induced by tooth movement through CGRP-dependent pathways

“…This nding was consistent with our previous studies where we found that periodontal administration of N/OFQ antagonist UFP-101 was able to alleviate pain in rats and that N/OFQ could upregulate the expression of a nociceptor P2X3 (16,33). However, Borgland et al revealed that N/OFQ inhibited calcium currents of trigeminal neurons, supporting its antinociceptive role in TG (34).…”

“…Our previous studies have reported that N/OFQ participates in pain modulation at periodontium and trigeminal nucleus caudalis (16,32). Although previous ndings have demonstrated that N/OFQ and its receptor are actively expressed in neuronal cells of trigeminal ganglia and our previous study found an indirect evidence that N/OFQ could modulate the expression of a key nociceptor (P2X3) on trigeminal neurons (22,33), its pain-modulatory role at TG is still largely unknown. Our results revealed that intra-ganglionic administration of N/OFQ exacerbated pain while that of UFP-101 alleviated pain, suggesting that N/OFQ plays a pro-nociceptive role in orofacial pain induced by tooth movement.…”

N/OFQ modulates orofacial pain induced by tooth movement through CGRP-dependent pathways

“…Moreover, elevated pain level caused by PNOC overexpression lentivirus was strongly correlated with increased N/OFQ expression, strongly supporting the promotive role of N/OFQ in pain modulation. This nding was consistent with our previous studies where we found that periodontal administration of N/OFQ antagonist UFP-101 was able to alleviate pain in rats and that N/OFQ could upregulate the expression of a nociceptor P2X3 (16,35). However, Borgland et al revealed that N/OFQ inhibited calcium currents of trigeminal neurons, supporting its antinociceptive role in TG (36).…”

“…Our previous studies have reported that N/OFQ participates in pain modulation at periodontium and trigeminal nucleus caudalis (16,34). Although previous ndings have demonstrated that N/OFQ and its receptor are actively expressed in neuronal cells of trigeminal ganglia and our previous study found an indirect evidence that N/OFQ could modulate the expression of a key nociceptor (P2X3) on trigeminal neurons (22,35), its pain-modulatory role at TG is still largely unknown. Our results revealed that intra-ganglionic administration of N/OFQ exacerbated pain while that of UFP-101 alleviated pain, suggesting that N/OFQ plays a pro-nociceptive role in orofacial pain induced by tooth movement.…”

Effect of static magnetic field on pain level and expression of P2X3 receptors in the trigeminal ganglion in mice following experimental tooth movement

“…P2X3 receptors are only one of multitudinous neurotransmitter media such as Substance P, N-methyl-D-aspartate receptor, transient receptor potential vanilloid type 1 (TRPV1), calcitonin gene-related peptide (CGRP), etc. [Stanchev et al, 2009;Krimon et al, 2013;Wang et al, 2015].…”