Modulation of the inflammatory response in the rat TMJ with increasing doses of complete Freund's adjuvant

Abstract

Objectives Acute inflammation stresses the physiological system, which must respond in order to reestablish homeostasis. The purpose of this study was to determine whether bilateral temporomandibular joint (TMJ) injections of different doses of Complete Freund's Adjuvant (CFA) produced dose-dependent changes in biologic markers of acute inflammation. The ability to establish an animal model with varying degrees of joint inflammation would allow evaluation of agents or conditions that could modulate the severity of the disease.Design The TMJs of three groups of male Sprague–Dawley rats were injected with CFA containing varying doses of Mycobacterium tuberculosis (MT). A group of non-injected and a group of saline injected rats were used as controls. Food intake, body weights, swelling and chromodacryorrhea were recorded daily. Interleukin-1β (IL-1β) and corticosterone levels were assayed and condylar cartilage thickness was measured 48h after injections.Results Twenty-four hours post-injection, bilateral TMJ swelling and chromodacryorrhea were significantly (P< 0.05) increased following 10μg of MT and further increased with elevated MT dose. In the CFA groups food intake was attenuated (P< 0.01) 24 and 48h post-injection and negatively correlated with dose at 24h. Body weight was also negatively correlated with dose. TMJ retrodiscal tissues IL-1β was increased (P< 0.05) in a dose-dependent manner. CFA increased corticosterone (P< 0.05), but this elevation was not dose dependent. Condylar cartilage thickness was decreased in a dose-dependent manner.Conclusions These data suggest that an intermediate dose of CFA can be used to effect submaximal levels of TMJ inflammation that will allow experimental modulation in future studies.