Micronized palmitoylethanolamide reduces joint pain and glial cell activation

Objective and design: Temporomandibular disorder (TMD) is a common painful condition in the temporomandibular joint (TMJ). Joint inflammation is believed to be a chief cause of pain in patients with TMD, through the release of pro-inflammatory cytokines that induce peripheral sensitization of nerve terminals followed by microglial stimulation. Materials and subject: TMJ was induced in rats with the injection of complete Freund’s adjuvant (CFA) emulsion into the left TMJ capsule. Treatment: The present study would assess the effects of micronized palmitoylethanolamide (m-PEA) on glial activation and trigeminal hypersensitivity. Methods: Ten mg/kg m-PEA or corresponding vehicle was administered 1 h after CFA and mechanical allodynia and edema were evaluated at 24 and 72 h after CFA injection. Results: CFA-injected animals showed TMJ edema and ipsilateral mechanical allodynia accompanied by a robust growth in GFAP protein-positive satellite glial cells and activation of resident macrophages in the TG. Moreover, m-PEA administration significantly reduced the degree of TMJ damage and pain, macrophage activation in TG and up-regulation of Iba1. Conclusions: The results confirm that m-PEA could represent a novel approach for monitoring pain during trigeminal nerve sensitization.