Neuronal plasticity of trigeminal ganglia in mice following nerve injury

Abstract

Randi Lynds,1,2,* Chuang Lyu,3,* Gong-Wei Lyu,4 Xie-Qi Shi,1,2 Annika Rosén,5,6 Kamal Mustafa,6 Tie-Jun Sten Shi7 1Department of Dental Medicine, Karolinska Institutet, Huddinge, Sweden; 2Division of Oral and Maxillofacial Radiology, Department of Clinical Dentistry, Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway; 3State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute of Chinese Academy of Agricultural Sciences, 4Department of Neurology, The First Hospital of Harbin Medical University, Harbin, People’s Republic of China; 5Division for Oral and Maxillofacial Surgery, 6Tissue Engineering Group, Department of Clinical Dentistry, Faculty of Medicine and Dentistry, 7Department of Biomedicine, University of Bergen, Bergen, Norway *These authors contributed equally to this work Background: Nerve injury may induce neuropathic pain. In studying the mechanisms of orofacial neuropathic pain, attention has been paid to the plastic changes that occur in the trigeminal ganglia (TGs) and nucleus in response to an injury of the trigeminal nerve branches. Previous studies have explored the impact of sciatic nerve injury on dorsal root ganglia (DRGs) and it has shown dramatic changes in the expression of multiple biomarkers. In large, the changes in biomarker expression in TGs after trigeminal nerve injury are similar to that in DRGs after sciatic nerve injury. However, important differences exist. Therefore, there is a need to study the plasticity of biomarkers in TGs after nerve injury in the context of the development of neuropathic pain-like behaviors. Aim: The aim of this study was to investigate the plasticity of biomarkers associated with chronic persistent pain in TGs after trigeminal nerve injury. Materials and methods: To mimic the chronic nature of the disorder, we used an intraoral procedure to access the infraorbital nerve (ION) and induced a nerve injury in mice. Immunohistochemistry and quantification were used for revealing the expression level of each biomarker in TGs after nerve injury. Results: Two weeks after partial ION injury, immunohistochemistry results showed strongly upregulated expressions of activating transcription factor 3 and neuropeptide Y (NPY) in the ipsilateral TGs. Microglial cells were also activated after nerve injury. In regard to positive neuronal profile counting, however, no significant difference in expression was observed in galanin, substance P, calcitonin gene-related peptide, neuronal nitric oxide synthase, phosphorylated AKT, or P2X3 in ipsilateral TGs when compared to contralateral TGs. Conclusion: In this study, the expression and regulation of biomarkers in TGs have been observed in response to trigeminal nerve injury. Our results suggest that NPY and Iba1 might play crucial roles in the pathogenesis of orofacial neuropathic pain following this type of injury. Further investigations on the relevance of these changes may help to target suitable treatment possibilities for trigeminal neuralgia. Keywords: infraorbital nerve, orofacial pain, sensory neurons, neuropeptides, animal model

Keywords

• infraorbital nerve
• nerve injury
• orofacial pain
• sensory neurons