Background & Aims
Neuropathic pain, considered one of the most challenging conditions to treat, remains a complex medical issue. The mechanism of neuropathic pain in the orofacial region is still unclear, and treatment often proves difficult. Neuropathic pain is a form of chronic pain resulting from damage or dysfunction in the nervous system. Lysophosphatidic acid (LPA), a member of the lysophospholipid family, has been implicated in neuropathic pain within the spinal cord. This study aimed to elucidate the role of LPA in facial mechanical allodynia that develops after infraorbital nerve injury (IONI) in rats.
Methods
Male Sprague-Dawley rats (200g-260g) were used in this study. Under deep anesthesia, a guide cannula was set into the trigeminal ganglion in rat. One week later, left infraorbital nerve was partially ligated under deep anesthesia to make the IONI model.
The mechanical head-withdrawal threshold (MHWT) of the left whisker pad skin was measured using von Frey filaments every other day before and up to 14 days after the injury. Lysophosphatidic acid (LPA; 1 µl, 1 mM) was administered daily into the trigeminal ganglion under 2% isoflurane anesthesia from day 1 to day 7 after IONI (IONI-LPA). Other groups included naïve rats with LPA (naïve-LPA), IONI rats with saline (NS) (IONI-NS), and naïve rats with NS (naïve-NS).
We also used IONI model for inhibitor administration experiments. The lysophosphatidic acid inhibitor (Ki16425; 1 µl, 10 mM or 50 mM) or vehicle (10% DMSO) was administered into trigeminal ganglion from day 1 to day 7 after IONI, and the MHWT was measured until day 14.
Results
The mechanical head-withdrawal threshold (MHWT) in the IONI-LPA group was significantly lower than that in the naïve-NS group from day 2 to day 10 after injury. Similarly, the naïve-LPA group exhibited a significantly lower MHWT compared to the naïve-NS group from day 2 to day 10 and day 14 after injury. However, there was no significant difference between the IONI-LPA and naïve-LPA groups. In the LPA inhibitor administration experiment, the MHWT in the IONI-Ki16425 (50mM) group was significantly relieved compared to the IONI-vehicle (10% DMSO) group on days 4 and 8 after injury. There was no significant difference between the IONI-Ki16425 (10mM) group and the IONI-vehicle group.
Conclusions
This result suggests that LPA may play a role in the development of facial mechanical allodynia following infraorbital nerve injury. Further research is needed to explore the underlying mechanisms and potential interventions targeting LPA for the management of trigeminal neuropathic pain.
References
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Presenting Author
Ryoko Kurisu
Poster Authors
Topics
- Models: Oral/craniofacial