Study On Distribution,Quantity And Gene Expression Of Mechanoreceptors In Ligaments And Tendons Of Knee Joint In Rabbits

Objective: To observe morphology,quantity,distribution and to detect gene expression of mechanoreceptors in the anterior cruciate ligament(ACL),posterior cruciate ligament(PCL),medial collateral ligament(MCL),lateral collateral ligament(LCL),patellar tendon(Pa T)and popliteal tendon(Po T)of the knee joint in adult male rabbits.Methods: Twelve 6-month-old New Zealand male rabbits were randomly divided into two groups with 6 rabbits in each group.In one group,the complete ACL,PCL,MCL,LCL,Pa T and Po T of bilateral knee joints were collected to prepare continuous frozen sections with a thickness of 10 μm.These sections underwent H&E staining,S100 B and NF-160 double-label immunofluorescence staining in order to observe the morphology,distribution and quantity of mechanoreceptors in the five ligaments and Po T using optical microscope,laser confocal microscope and computer image analysis system,respectively.In another group,the complete ACL,PCL,MCL,LCL,Pa T and Po T of bilateral knee joints were used to extract total RNA in order to determine S100 B,CGRP and NEFM gene expression.Results: 1.A total of 5 kinds of mechanoreceptors were observed in ACL,PCL,MCL,LCL,Pa T and Po T including Ruffini corpuscles,Pacinian corpuscles,Golgi-tendon bodies,atypical mechanoreceptors and free nerve endings by H&E immuneofluorescence staining.The free nerve endings were distributed in the whole ligament,other mechanoreceptors were mainly distributed in the attachment points of ligaments with the femur and tibia.2.In different ligaments,the kind and quantity of mechanoreceptors were also different.The total amount of mechanoreceptors was significantly lower in MCL,LCL,Pa T and Po T as compared with ACL and PCL(P <0.001),but there was no significant statistical difference between ACL and PCL(P >0.05).All examined mechanoreceptors were present in ACL,PCL and LCL.However,no Pacinian corpuscles and Golgi-tendon bodies were found in MCL and Po T as well as Pacinian corpuscles were not observed in Pa T.3.q RT-PCR indicated that NEFM,S100 B and CGRP gene expressions were the highest in ACL among all ligaments,NEFM and S100 B levels were significantly higher in ACL than in other ligaments(P< 0.05),but there was no significant difference in CGRP level between ACL and other ligaments except LCL(P > 0.05).Conclusion: The quantity,type and gene expression of mechanoreceptors are different among ACL,PCL,MCL,LCL,Pa T and Po T.There are all five kinds of mechanoreceptors in ACL,PCL and LCL.The quantity of mechanoreceptors is the highest in ACL followed by PCL.Thus,the quantity and distribution of mechanoreceptors may be related to ligament’s function.