Meal pattern changes associated with temporomandibular joint inflammation/pain in rats; analgesic effects

Establishing a valid animal model to study temporomandibular joint (TMJ) pain has proven extremely difficult. Using complete Freund's adjuvant (CFA) to induce TMJ inflammation, we recently showed that meal pattern analysis could be used as a noninvasive biological marker to study TMJ pain in an animal model. The purpose of this study was to further validate our animal model by determining whether aspects of CFA-induced TMJ inflammation/pain are reversed with ibuprofen (IBU) treatment. In the first trial, 48 male rats were used and in the second trial, 32 female ovariectomized rats, given 17beta-estradiol replacement, were used. The rats were assigned to one of four groups: control (CON-CON); control+IBU (CON+IBU); CFA-CON; and CFA+IBU. In the male trial, CFA injection (P<.01) caused TMJ swelling and chromodacryorrhea (CFA-CON); IBU eliminated these changes in the CFA+IBU group. Meal pattern analysis showed the pertinent CFA-induced change and the IBU effect was that meal duration was increased in the CFA-CON group (P<.01), but normal in the CFA+IBU-treated group on the first, but not second, day postinjection. In the female trial, CFA increased TMJ swelling, but did not cause significant chromodacryorrhea (CFA-CON); IBU eliminated swelling in the CFA+IBU group. Meal duration was increased (P<.01) in the CFA-CON group, but was normal in the CFA+IBU-treated group on both the first and second days postinjection. In both trials, interleukin-1beta (IL-1beta) levels were increased similarly in CFA-CON and CFA+IBU groups (P<.01). This study shows that CFA-induced TMJ inflammation/pain can cause changes in meal patterns (i.e., meal duration), which may be used as a behavioral marker for TMJ inflammation/pain.