Kerins Ca

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.

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 Freunds 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.

Measuring persistent temporomandibular joint nociception in rats and two mice strains.

Temporomandibular joint (TMJ) pain has been reported to last for prolonged periods in humans. In rodents a variety of methods have been used to measure TMJ nociception, but for most of these methods the period of measurement has been minutes to a couple of hours. In addition, most measurement protocols required restraint or training of the animal. Previous studies from our laboratory demonstrated that feeding behavior, particularly meal duration, was an indicator of TMJ nociception in unrestrained and untrained male and female Sprague-Dawley rats for up to two days. In this study, we first found that injection of complete Freunds adjuvant (CFA) into the TMJ of rats significantly lengthened meal duration for 19 days and also decreased meal frequency for 42 days. Interestingly, the meal duration varied significantly from day to day within the 19 day period. TMJ interleukin-1 beta (IL-1 beta) and calcitonin gene-related peptide (CGRP) were significantly elevated in the TMJ tissues of CFA-injected animals and the level of these markers was attenuated as the meal duration decreased with time. Control animals injected with saline into the TMJ or CFA into the knee did not show a significant lengthening in meal duration but did show a decrease in meal frequency. In a second study, DBA/1LacJ mice given TMJ CFA injections showed a significantly lengthened meal duration on four of the seven days measured using end-of-the meal definition of 5 or 10 min. No other meal pattern changed significantly. Two days post-CFA injection, the DBA/1LacJ mice showed significantly elevated interleukin-6 (IL-6), but not elevated IL-1 beta. Seven days post-injection, both IL-6 and IL-1 beta were significantly elevated. No change in CGRP was detected. In this study C57Bl/6 mice also received TMJ CFA injections, but they did not show a lengthening in any meal pattern or significant increases in IL-1 beta, IL-6 or CGRP. Our data show, for the first time, that meal duration can be used to measure CFA-induced nociception in the TMJ over the course of several weeks in unrestrained rats and for up to seven days in the DBA/1LacJ mouse strain. In addition, C57Bl/6 mice are resistant to CFA-induced TMJ nociception at the same dose used in the DBA/1LacJ mice.

Capsaicin sensitive neurons role in the inflamed TMJ acute nociceptive response of female and male rats

Computerized meal pattern analysis, and more specifically meal duration, has recently been used as a non-invasive biological marker of nociception in the temporomandibular joint (TMJ). Cells responsible for the nociceptive response in the inflamed TMJ may include capsaicin (CAP) sensitive neurons. To test the role of CAP sensitive neurons in acute nociceptive responses first, male and female rats were treated neonatally with vehicle or CAP, an agent known to destroy a majority of C fibers. Second, after 56 days the rats were divided into four groups: neonatal vehicle-injected and treated with and without complete Freunds adjuvant (CFA). Treatment groups included neonatal non-CAP vehicle treated and TMJ not-injected (CON); vehicle treated and TMJ CFA injected (CFA); CAP-treated and not-injected (CAP); and CAP-treated and CFA injected (CAP+CFA). Meal patterns were analyzed for two days after injection. CFA-injection in non-CAP-treated rats lengthened meal duration on the first and second day after treatment in the males, but only on the first day in the females. CAP treatment in male and female rats prevented significant lengthening of meal duration induced by CFA. CAP treatment attenuated the CFA-induced increase in calcitonin gene-related peptide expression in the trigeminal ganglia similarly in males and females. The data suggests CAP-sensitive neurons are responsible, in part, for transmission of acute nociceptive responses associated with CFA administration and suggest gender can affect nociception in the inflamed TMJ region.