The Changes Of N/OFQ Expression In Rats Brain With Chronic Pain Occlusal Interference Moels

Objective:To build up the chronic unilateral occlusal disorders models in rats,immunohistochemical staining was employed to detect changes of N/OFQ expression in rats brain with occlusal interference-induced masticatory muscle hyperalgesia,so as to investigate potential central mechanism of the masticatory muscle hyperalgesia caused by occlusal interference preliminarily.Method: In the experiment,24 SD rats aged 8 weeks were selected,among which 18 rats were applied for experimental group modeling.An orthodontic rubber band(3 M U n i t e k,1/8 #)was inserted between the first and two molars on the left side of the upper jaw,the second and the third molars were used as anchorage,the first molar was pushed into the middle,so that an occlusal state of cusp-fossa misfit in the upper and lower first molars was gradually formed.Check daily to ensure that the applied rubber band did not fall off until the end of the experiment.The remaining six rats in the control group were anesthetized and mouths were forced open for about 5min but restorations were not applied.Then were raised in the same environment.On the 5th,10 th and21st days after the establishment of the model,6 rats in each experimental groupsand 6 rats on the 6th days of the control group were selected randomly and respectively,measured the changeable of masticatory muscle hyperalgesia.Subsequently,the rats were anesthetized and perfusion-fixed.Then,rats brain tissues slices were prepared.Immunohistochemical staining was used to detect the expression of N/OFQ in the nuclei of rat midbrain,thereby to investigate the relationship between the changes of the expression of orphanin FQ and masticatory muscle hyperalgesia in rats.Results:The pain thresihold in the control group was 208.9±13,meanwhile,there were 117.8±11,73.3±10,198.7±6 on the 5th day,10 th day and 21 st day in the experimental group.Semi-quantitative immunohistochemica analysis showed that the average optical density of OFQ was 0.184±0.007 in the control group at 21 st day;meanwhile,corresponding expressions were 0.253±0.008,0.326±0.010 and 0.203±0.004 on the 5th day,10 th day and 21 st day in the experimental group,respectively.The difference between any of the two groups was statistically significant(P<0.01).The expression of orphanin FQ in the model group was significantly higher than that in the control group,the expression was highest at 10 th days in the experimental group,and the expression on the 21 st day was lower than that on the 5th day and the 10 th day.Conclusions:.The pain of masticatory muscles in the occlusal interference model can promote the expression of orphanin FQ in the brain of rats.Furthermore,the degree of masticatory muscle hyperalgesia was positively correlated with the expression of orphanin FQ in rats brain.