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AimTo determine whether Porphyromonas gingivalis lipopolysaccharide (LPS) can directly activate trigeminal neurons, to identify which receptors are involved and to establish whether activation leads to secretion of the neuropeptide calcitonin gene‐related peptide (CGRP) and/or the translocation of NF‐κB.MethodologyMouse trigeminal ganglion (TG) cells were cultured in vitro for 2 days. The effect of P. gingivalis LPS (20 μg mL−1) on calcium signalling was assessed (by calcium imaging using Cal‐520 AM) in comparison with the transient receptor potential channel A1 (TRPA1) agonist cinnamaldehyde (CA; 100 μmol L−1), the TRP channel V1 (TRPV1) agonist capsaicin (CAP; 1 μmol L−1) and high potassium (60 mmol L−1 KCl). TG cultures were pre‐treated with either 1 μmol L−1 CLI‐095 to block Toll‐like receptor 4 (TLR4) signalling or with 3 μmol L−1 HC‐030031 to block TRPA1 signalling. CGRP release was determined using ELISA, and nuclear translocation of NF‐κB was investigated using immunocytochemistry. Data were analysed by one‐way analysis of variance, followed by Bonferroni’s post hoc test as appropriate.ResultsPorphyromonas gingivalis LPS directly exerted a rapid excitatory response on sensory neurons and non‐neuronal cells (P < 0.001 to P < 0.05). The effects on neurons appear to be mediated via TLR4‐ and TRPA1‐dependent pathways. The responses were accompanied by an increased release of CGRP (P < 0.001) and by NF‐κB nuclear translocation (P < 0.01).ConclusionsPorphyromonas gingivalis LPS directly activated trigeminal sensory neurons (via TLR4 and TRPA1 receptors) and non‐neuronal cells, resulting in CGRP release and NF‐κB nuclear translocation. This indicates that P. gingivalis can directly influence activity in trigeminal sensory neurons and this may contribute to acute and chronic inflammatory pain.

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Increased proteinase-activated receptor-2 (PAR2) expression is observed in various diseases related to inflammation. However, the expression of PAR2 in odontoblasts in response to dental caries has not been investigated. Therefore, to explore the functions of odontoblasts during the progression of carious infection, we measured PAR2 and NF-κB expression using immunofluorescence techniques in the odontoblast layer and pulpocytes in the sub-odontoblast region of 44 teeth extracted from children undergoing dental treatment (eight sound samples, 13 early carious samples, 16 advanced carious samples, and eight exposed pulp samples). PAR2 and NF-κB were expressed at moderate levels in sound teeth with non-carious pulp, and the expression levels changed as caries progressed. PAR2 was significantly upregulated in the odontoblast layer during early-stage and advanced-stage caries, and reduced below healthy levels in teeth with exposed pulp. NF-κB was significantly upregulated in early-stage caries and significantly downregulated in advanced-stage and late-stage caries. Moreover, in the sub-odontoblast region, NF-κB expression increased with the progression of caries. Overall, this study suggests PAR2 may represent a crucial cell signalling receptor in the dentine-pulp complex during dental inflammation, and that NF-κB may be one of the key pathways that regulate inflammatory immune responses in the dental pulp.