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KMID : 0363120220350030261
Korean Journal of Pain
2022 Volume.35 No. 3 p.261 ~ p.270
The ability of orexin-A to modify pain-induced cyclooxygenase-2 and brain-derived neurotrophic factor expression is associated with its ability to inhibit capsaicin-induced pulpal nociception in rats
Shahsavari Fatemeh

Abbasnejad Mehdi
Esmaeili-Mahani Saeed
Raoof Maryam
Abstract
Background: The rostral ventromedial medulla (RVM) is a critical region for the management of nociception. The RVM is also involved in learning and memory processes due to its relationship with the hippocampus. The purpose of the present study was to investigate the molecular mechanisms behind orexin-A signaling in the RVM and hippocampus¡¯s effects on capsaicin-induced pulpal nociception and cognitive impairments in rats.

Methods: Capsaicin (100 g) was applied intradentally to male Wistar rats to induce inflammatory pulpal nociception. Orexin-A and an orexin-1 receptor antagonist (SB-334867) were then microinjected into the RVM. Immunoblotting and immunofluorescence staining were used to check the levels of cyclooxygenase-2 (COX-2) and brain-derived neurotrophic factor (BDNF) in the RVM and hippocampus.

Results: Interdental capsaicin treatment resulted in nociceptive responses as well as a reduction in spatial learning and memory. Additionally, it resulted in decreased BDNF and increased COX-2 expression levels. Orexin-A administration (50 pmol/1 ¥ìL/rat) could reverse such molecular changes. SB-334867 microinjection (80 nM/1 ¥ìL/rat) suppressed orexin¡¯s effects.

Conclusions: Orexin-A signaling in the RVM and hippocampus modulates capsaicininduced pulpal nociception in male rats by increasing BDNF expression and decreasing COX-2 expression.
KEYWORD
Brain-Derived Neurotrophic Factor, Capsaicin, Cognitive Dysfunction, Cyclooxygenase 2, Facial Pain, Nociceptin, Orexins, Pulpitis, Rostral Ventromedial Medulla
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