Meal pattern analysis in response to temporomandibular joint inflammation in the rat

Inflammation of the temporomandibular joint (TMJ) can alter behavioral responses such as food intake and mobilize stress hormones. The hypothesis of this study was that food intake and diurnal corticosterone analysis can be used as indicators of adjuvant-induced TMJ inflammation. Groups of rats received adjuvant or no injections at the beginning of the resting (AM) or activity (PM) phase. Forty-eight hours (early) or 6 weeks (late) after adjuvant injection, plasma corticosterone was assayed and food intake was recorded. Food intake was suppressed up to 4 days post-injection. As expected, the non-injected group showed low AM and high PM corticosterone. AM corticosterone was elevated, but PM corticosterone was attenuated in both early- and late-stage-injected rats. A computerized pair-fed experiment showed that adjuvant-induced hypophagia did not alter corticosterone levels. Meal pattern analysis revealed decreased food intake due to a decrease in the number of meals taken. Notably, meal size remained the same but meal duration increased. This model demonstrated that food intake and stress hormone analysis could be used as indicators for sequelae of adjuvant-induced TMJ inflammation.