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Updated: Aug 20, 2025
Author Spotlight: Utilizing Infraorbital Nerve Ligation in Mice for Investigating Trigeminal Neuropathic Pain and Treatment Strategies
Published on: March 8, 2024
Microglia activation and temporal changes in rat model of trigeminal neuralgia
Yanzhu Lu1, Jingqi Zhang1, Wenli Lai1
1State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases & Dept. of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China.
Objectives:
This study aimed to investigate whether the microglia in the spinal trigeminal nucleus caudal part (Sp5C) were activated in a rat model of trigeminal neuralgia and to explore whether the activation level of microglia is consistent with maxillofacial pain level.
Methods:
Chronic constriction injury of trigeminal nerve (CCI) was induced by partial ligation of infraorbital nerve (IoN) in rats. The behavioral change of rats observed at D1, D5, D10, D15, and D30 days post-surgery and the change of pain threshold were detected with electronic Von Frey filaments served as an evaluation index of maxillofacial pain. Weight change was measured by weighing. Ionized calcium binding adaptor molecule-1 (Iba-1) expression level of Sp5C at each time point was detected, and three microglia morphological categories were analyzed by immunohistochemical staining.
Results:
The changes of behavioral and pain threshold suggested the maxillofacial pain level first increased and then decreased post-surgery in the IoN-CCI group. Both the expressions of Iba-1 and proportion of ameboid morphology in ipsilateral Sp5C increased from D1 and reached their peaks in D10 and D5, respectively. Then, they recovered nearly to the same level with contralateral Sp5C on D30. This trend was consistent with the maxillofacial change.
Conclusions:
The model of trigeminal neuralgia in rats constructed by partial ligation of infraorbital nerve can induce the activation of microglia in Sp5C, and the activation level is consistent with maxillofacial pain, which reached its peak at around D10 post-surgery.
Insights
Microglia activation in the spinal trigeminal nucleus caudal part (Sp5C) correlates with trigeminal neuralgia pain severity in rats. This activation peaks around 10 days post-surgery, mirroring pain levels.
Area of Science:
- Neuroscience
- Immunology
- Pain Research
Background:
- Trigeminal neuralgia (TN) is a debilitating condition characterized by severe facial pain.
- Microglia, the resident immune cells of the central nervous system, play a role in neuroinflammation and pain signaling.
- The spinal trigeminal nucleus caudal part (Sp5C) is a key brainstem region involved in processing facial pain signals.
Purpose of the Study:
- To investigate microglia activation in the Sp5C in a rat model of TN.
- To determine if the level of microglia activation correlates with the severity of maxillofacial pain.
Main Methods:
- A rat model of TN was established using chronic constriction injury (CCI) of the infraorbital nerve (IoN).
- Behavioral changes and pain thresholds were assessed using electronic Von Frey filaments.
- Microglia activation in the Sp5C was evaluated by measuring ionized calcium binding adaptor molecule-1 (Iba-1) expression and analyzing microglia morphology via immunohistochemistry at various time points post-surgery.
Main Results:
- Maxillofacial pain levels in the IoN-CCI rats initially increased and subsequently decreased post-surgery.
- Iba-1 expression and the proportion of activated (ameboid) microglia in the ipsilateral Sp5C showed a significant increase, peaking around days 5-10.
- These changes in microglia activation mirrored the observed pattern of maxillofacial pain.
Conclusions:
- Partial ligation of the IoN in rats successfully models TN and induces microglia activation in the Sp5C.
- The degree of microglia activation in the Sp5C is consistent with the severity of maxillofacial pain in this TN model.
- Microglia activation in the Sp5C appears to be a key component in the development and maintenance of trigeminal neuralgia pain.
