Objective: To explore the aging changes regularity of the distribution, morphology and quantity of mechanoreceptors in anterior cruciate ligament (ACL) of healthy rabbit. Methods: Complete ACL longitudinal frozen section was collected from 18 New Zealand white rabbits who were sacrificed by air embolization of auricular veins. The rabbits were divided into 6 groups according to the age (1 week, 6 weeks, 3 months, 6 months, 1 year and 2 years, 3 rabbits in each group). After H E staining, S-100 and NF-160 immunofluorescence labeling, the morphology, type, and quantity of the mechanoreceptors were observed under optical microscope, laser confocal microscope and computer image analysis system. Results: There are five kinds of mechanoreceptors in rabbit ACL, namely Ruffini corpuscle, Pacinian corpuscle, Golgi tendon body, free nerve endings and atypical mechanoreceptors. A total of 339 mechanoreceptors were found in all 1 008 sections of 6 groups, including 168 Ruffini bodies, 89 Pacini bodies, 42 Golgi tendon bodies and 40 atypical mechanoreceptors. Most mechanoreceptors were distributed in synovium near tibia and femur of ACL. In terms of total number, there was significant difference among the groups (P<0.001). Comparing each two groups, the total number of mechanoreceptors at 3 and 6 months was the largest with no significant difference (P>0.05), and there was a significant difference among the other groups (P<0.05). Conclusions: Free nerve endings are the most common in ACL, followed by Ruffini body, Pacinian body and Golgi tendon body. The total number of mechanoreceptors increases with age, reaching a peak in 3 months group, similar to that of the 6 months group, and decreases significantly in the one year group and the two year group.
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