The Research Of The Circadian Rhythm Of Pain In Rats With Chronic Rotator Cuff Tears

Objective Nocturnal pain is the special clinical findings in patients with rotator cuff tears(RCT),and 91% of those over 65-year-old patients with RCT have nocturnal pain,which has severely influenced their sleep qualities.The objective of this study is to explore the circadian characteristics of pain and its molecular mechanism in rats with chronic RCT.Methods With 3-D printing technology,design implants made of polyetheretherketone(PEEK)and fix them by surgery at the acromion of Wistar rats(N=48)to imitate subacromial impingement syndrome.All the rats were divided into operation group(n=24)and shame operation group(n=24),and after surgery,would begin to run on the treadmill for 8 weeks.After 8 weeks,rats in the operation group(n=6)and the sham operation group(n=6)were randomly taken and sacrificed for pathological section of shoulder joint samples.In addition,rats in the operation group(n=12)and the sham operation group(n=12)were randomly selected,the frequency of pain response for 24 hours was measured with von Frey filaments,and the pain level was classified according to statistical analysis.The remaining rats in the operation group(n=6)and the sham operation group(n=6)were divided into two groups on average.One group was sacrificed for collecting samples of the infraspinatus muscle tendon at 9 a.m.to 10 a.m.,and the other group was sacrificed for collecting samples of the infraspinatus muscle tendon after 12 hours in the same day.The tissue were distinguished for doing quantitative PCR.Results Histopathological sections of rats in the operation group who were sacrificed after 8weeks of running on the treadmill revealed that the internal space of the infraspinal tendon is formed,and the rotator cuff tendon in the sham operation group had nosignificant changes.The pain in the operation group was roughly divided into three levels,showing circadian rhythms.;the q PCR results suggest that melatonin receptors1A(MTNR1A)play a role in the nocturnal pain of chronic rotator cuff tears in rats.Conclusion This study graded the degree of pain in the rotator cuff tears in rats semi-quantitatively,and proved that the pain has a circadian rhythmic change,which may be related to the MTNR1A.