| Objective:Persistent pain is usually observed in teeth or other intraoral structures following tooth-pulp infection.Although neuroplastic changes in the central nervous system and/or sensitization of afferents in the peripheral nervous system are thought to be involved in the pain following tooth-pulp infection,the mechanisms underlying pain following tooth-pulp infection are not fully understood.Chemokine(C-X3-C motif)Ligand 1(CX3CL1)is the only member of CX3C-chemokine subfamily,while chemokine(C-X3-C motif)receptor 1(CX3CR1)is the sole receptor of CX3CL1.It was reported that the interaction between CX3CL1 and CX3CR1 migrated leukocyte to inflamed tissues by mediating cellular chemotaxis and adhesion.While,previous study indicated that CX3CL1 and CX3CR1 in nervous system also played an important role in the inflammatory pain process.Furthermore,CX3CL1-CX3CR1 was demonstrated to mediate neuron-glia interaction via regulating the release of certain inflammatory mediators that can sensitize nociceptors.In the present study,Complete Freund’s Adjuvant(CFA)was used to induce molar tooth-pulp infection in rats.The expression of CX3CL1 and CX3CR1 in trigeminal ganglion(TG),tooth-pulp tissue and periapical tissues were detected by immunohistochemical and immunofluorescent staining.Furthermore,this study was aimed to focus on the potential mechanisms of neuro-immune system that involved in tooth-pulp infection via CX3CL1-CX3CR1 interaction.Materials and Methods:A rat animal-model with molar tooth-pulp infection was induced by performing CFA on Sprague-Dawley rats.The pulp cavities of the mandibular right first molars were exposed,and CFA was applied into the exposed tooth pulps.Naive rats served as control group underwent no treatment.Rats were perfused with paraformaldehyde phosphate buffer,then TGs and mandibles contained molars were removed bilaterally.Serial frozen sections were prepared for further study.Immunofluorescenct staining or immunohistochemistry were used to demonstrate the dynamic expression of CX3CL1 and CX3CR1 in TGs,periapical and tooth-pulp tissues.The pathological development of tooth-pulp infection were observed by hematoxylin and eosin(HE)staining.Results:1.HE staining indicated that the necrotic tissues scattered around the exposed point of crown pulp at 24 hours post CFA-administration.Irregular arrangements and vacuolar degeneration of the odontoblastic layer were observed in coronal pulp.Alveolar osteomylitis was induced by CFA as the dense mass of inflammatory cells in the periapical tissues were observed.At 6 weeks post CFA-administration,periapical granuloma was found in infected alveolar bone.2.Immunohistochemistry of CX3CL1 showed obvious CX3CL1-positive cells scattered in the coronal pulp,radicular pulp and inflammatory periapical tissues in the CFA group,but CX3CL 1-positive cells were rare in control group.Statistical analyses showed that CX3CL1-positive cells increased significantly at 24 hours post CFA-administration.It reached to the peak at 1 week,then decreased to normal level at 6 weeks post CFA-administration.3.A number of CX3CR1-positive cells were detected by immunohistochemistry in inflammatory periapical tissues in the CFA group but rare in control group.Statistical analyses showed that the CX3CR1-positive cells increased significantly form 24 hours post CFA-administration and peaked at 1 week,and keep higher till 6 weeks compared to control.4.Immunofluorescence staining indicated that CX3CL1-positive satellite glial cells(SGCs)presented typical morphology of circle and surrounded the neurons in TG.Statistical analyses showed that the percentage of CX3CL 1-positive SGCs increased significantly at 72 hours and peaked at 2 weeks,then decreased to normal level at 6 weeks post CFA-administration.CX3CR1 signals appeared in trigeminal neurons.Statistical analyses showed,after CFA-administration,CX3CR1-positive neurons increased significantly at 24 hours and 72 hours post CFA-administration compared to control group.Conclusion:1.CX3CL1 and CX3CR1 participated in the local inflammation reaction during the development of tooth-pulp infection.2.The trigeminal nervous system may contribute to tooth-pulp infection by activating CX3CL1-CX3CR1 pathway in TG.3.CX3CL1 and CX3CR1 may mediate the interaction of neuron-SGC induced by tooth-pulp infection. |
