Decreased anxiety-like behavior and trigeminal ganglion BDNF levels persist in rats with temporomandibular joint arthritis even after resolution of the nociceptive process

Abstract

In this study, pain- and anxiety-like behaviors, locomotor and exploratory activity, histological and biomarker parameters were evaluated following induction of a temporomandibular joint (TMJ) arthritis model in rats. Twenty-two adult male Wistar rats were assigned to receive either saline (sham group) or Complete Freund’s Adjuvant (CFA − pain group) into the right TMJ. Mechanical allodynia was assessed using the facial electronic von Frey (VF) test, while thermal hyperalgesia was assessed using the Orofacial Pain Assessment Device (OPAD) assay. Open-field and plus-maze tests were used to assess locomotor and exploratory activity and anxiety-like behaviors, respectively. BDNF, IL-1β, and IL-10 levels were analyzed by ELISA in both the ipsilateral and contralateral trigeminal ganglion (TG). The tissues adjacent to the TMJ were histologically evaluated for the inflammatory process. According to distribution, data were analyzed by GEE, independent t-test, or Mann-Whitney test. Significance was set at P < 0.05. On the ninth day following CFA injection, pain-rats presented mechanical allodynia, which persisted until the twenty-first day, a decrease in the number of OPAD licks, decreased BDNF levels in the contralateral TG, and an increase in the ipsilateral TG BDNF and IL-1β levels, with inflammatory infiltrates in the tissues adjacent to the TMJ (27 days). TMJ arthritis also resulted in a reduction of the anxiety index (AI) after 26 days. This study reveals that this model is effective for examining chronic alterations related to TMJ arthritis and for identifying new anti-inflammatory drugs for pain management.