Linderane Attenuates Complete Freund's Adjuvant-Induced Pain and Anxiety in Mice by Restoring Anterior Cingulate Cortex Microglia M2 Polarization through Activating Cannabinoid 2 Receptor.

Chronic pain is a common condition that causes negative emotions as the disease progresses. The anterior cingulate cortex (ACC) is a key region in the integration of nociceptive perception and emotional response in chronic pain. Linderane (LDR) is an active ingredient from Linderae radix , a traditional Chinese medicine with anti-inflammatory, analgesic, and antibacterial properties. In this study, the analgesic and antianxiety effects of LDR were evaluated using a complete Freund's adjuvant (CFA)-induced inflammatory pain model in C57BL/6 male mice. Mechanical and thermal pain sensitivity were measured through plantar mechanical analgesia and hot plate apparatus, and anxiety-like behavior was evaluated by open field and elevated plus maze tests. The results showed that LDR-alleviated CFA-induced pain and anxiety, reduced the release of inflammatory cytokines, and inhibited ACC microglial activation. Target prediction, molecular docking, and cellular thermal shift assay demonstrated that LDR could bind to the cannabinoid 2 receptor (CB2R), a key component of the endocannabinoid system with an important role in regulating pain and related emotions. Moreover, both the analgesic effect of LDR and its regulation of microglia polarization were reversed by a CB2R antagonist (SR144528) treatment. Therefore, our results suggested that LDR exerted analgesic effects by regulating microglial polarization in ACC via CB2R activation.