Females Have Greater Nociceptive Responses from Ligature of Masseter Tendon

Objectives: Previous evidence from our lab indicated that females have a higher level of nociception as a result of temporomandibular joint (TMJ) inflammation.  Inflammation in this study was induced by injecting complete Freund’s adjuvant into the TMJ.  In contrast, another study in our lab demonstrated that proestrus levels of estrogen may reduce the nociceptive response.  Could the gender effect be a result of alteration in only the inflammatory pathways?  To address this question we tested the gender differences in a non-inflammatory orofacial pain model.

Methods: Two ligatures were placed around the tendon attachment of the anterior superficial portion of the masseter muscle.  The ligatures were placed 3 mm from each other along the tendon.  The tendon on both sides of the head were ligated. Animals were placed in feeding units and a correlate of orofacial nociception (meal duration) was measured from one day before the ligatures were placed to 18 days following ligature surgery.  Twenty days following ligature surgery the response to Von Frey filament pressure was determined.  The response to the filaments was measured for another two weeks.

Results: Meal duration was significantly effected (p<0.001) by ligature of the tendon for 18 days following surgery, when analyzing the ligature effect on days 8 through 14 there was also a significant effect (p<0.05).  Males were significantly less (p<0.05) responsive (shorter meal duration) than females through day 10 post surgery.  Filament testing showed that ligation significantly increased the nociceptive response (p<0.001) and that males were less responsive than the females (p<0.05).

Conclusion: These findings demonstrate that meal duration can detect oral-facial nociception using this ligature model and secondly show there are gender differences in the rats’ responses to the non-inflammatory nociception created.  Support provided by the Baylor Oral Health Foundation.