Effects and mechanisms of cannabidiol in attenuating orofacial inflammatory pain and ameliorating pain-related affective deficits.

Abstract

BACKGROUND/OBJECTIVES: Orofacial inflammatory pain remains a significant clinical challenge due to the lack of effective therapeutic agents that specifically target its complex pathophysiology. Conventional analgesics often provide inadequate relief and fail to address the profound negative affective states that frequently accompany chronic pain, further diminishing patients' quality of life. This study evaluated the therapeutic potential of cannabidiol (CBD) in mitigating sensory and affective dimensions of inflammatory pain and elucidated its underlying mechanisms. METHODS: Acute orofacial inflammatory pain was induced via subcutaneous formalin injection into the upper lip of mice. Chronic inflammatory pain and associated negative affect were modeled using intraplantar injection of complete Freund's adjuvant (CFA). A comprehensive behavioral battery-including von Frey filament testing, open field test, elevated plus maze, forced swim test, tail suspension test, sucrose preference test, and Y-maze-was employed to assess nociception and affective states. Mechanistic studies involved RT-qPCR, ELISA, LC-MS/MS, immunofluorescence and in vivo fiber photometry was employed to examine inflammatory, oxidative, endocannabinoid, and serotonergic pathways. RESULTS: Local administration of CBD significantly suppressed formalin-induced acute orofacial pain, specifically attenuating Phase II inflammatory sensitization. At the peripheral level, CBD downregulated FAAH and PGE2, reduced levels of pro-inflammatory cytokines (IL-1β, TNF-α) and oxidative stress markers, and increased levels of endocannabinoids in the blood-effects mediated primarily through CB2 receptor activation. Central actions of CBD were evidenced by reduced neuronal activation (c-Fos) in the spinal trigeminal nucleus caudalis (Sp5C) and anterior cingulate cortex, as well as increased anandamide (AEA) in the Sp5C and periaqueductal gray, which were mediated through CB1 receptor signaling. In the CFA-induced chronic pain model, systemic CBD administration not only alleviated mechanical allodynia but also markedly ameliorated anxiety- and depression-like behaviors and restored cognitive performance. Fiber photometry further revealed that CBD normalized deficits in serotonin transient activity in the central amygdala. CONCLUSIONS: CBD exerts robust multi-dimensional therapeutic effects across sensory, affective, and cognitive domains in inflammatory pain models. The findings underscore the translational potential of CBD as a novel therapeutic strategy for comprehensive management of orofacial pain and pain-related debilitating emotional comorbidities.