Changes in mechanoreceptors in rabbits' anterior cruciate ligaments with age

At present, a few studies have been done on the changes in the distribution, morphology and quantity of mechanoreceptors in anterior cruciate ligament (ACL) with age. In this study, we observed the changes in mechanoreceptors of healthy rabbits' ACL with age. We found that rabbits' ACLs contained 5 kinds of mechanoreceptors including Ruffini corpuscles, Pacinian corpuscles, Golgitendon bodies, free nerve endings and atypical mechanoreceptors. In each ACL, free nerve endings were the most followed by Ruffini corpuscles, Pacinian corpuscles, Golgitendon bodies and atypical mechanoreceptors in the younger than one-old rabbits. Most of the mechanoreceptors were distributed in the synovium near the attachment points of ACL with the femur and tibia. The total quantity of mechanoreceptors were the most in the 3- and 6-month groups, but did not show a significant difference between the two group (P > 0.05). However, there were significant differences in the total quantity of mechanoreceptors between other groups (all P < 0.05). RT-PCR indicated that NEFM and S100B levels increased with age, and reached a peak in the 1-year group with significant differences as compared to other groups. NEFM and S100B levels were the second in 6-month and 2-year groups and the lowest in the 1-week group. We can conclude that in rabbits' ACLs, free nerve endings are the most common, followed by Ruffini corpuscles, Pacinian corpuscles and Golgitendon bodies. The total quantity of mechanoreceptors reaches a peak in 3 months, while NEFM and S100B reach a peak in 1 year.