Effect of Pregnancy on TMJ Nociception in Rats

OBJECTIVE: Does TMJ nociception, as measured by a behavioral assay, differ during pregnancy, potentially due to the effect of sex steroids? METHODS: Thirty — two Sprague Dawlcy rats were randomly allocated to either mid— (EH 11) or late— (EH 17) pregnancy groups. The animals within each group were further allocated to a saline or CFA treatment. At EH 11 or EH 17, the animals were injected bilaterally into TMJ with either saline (15 μL.) or 1 μg/μL CFA (15 μL). Nociception was measured with a feeding assay (pellet recording) and analyzed by comparing in-tra—meal rates using a distance—based permutation method. RESULTS: CFA injection resulted in the animals eating longer in both the mid — pregnant and late—pregnant groups. Plasma estradiol was higher in the late — pregnant group versus the mid — pregnant group. Importantly, the CFA injected late—pregnant group ate for a shorter amount of time (i. e., shorter meal rate) than the CFA injected rats at mid — pregnancy. CONCLUSION: The reduced nociceptive response (shorter meal rate) in the CFA injected late — pregnant group may be due to greater estradiol versus the CFA injected mid — pregnancy rats. Thus, one potential reason why women report fewer TMJ symptoms during pregnancy is the higher level of circulating estradiol.