Effect Of Aging On The Mechanoreceptors In Rabbit PCL: An Experimental Study

Object: This study is designed to study the effec in number ,morphology and distribution position ,with aging on the mechanoreceptors in rabbit PCL,by the observation in changing of mechanoreceptors of posterior cruciate ligaments in the different age classes healthy rabbits, is to provide some theoretical basis for better research on the proprioception of PCL.Methods: Fifteen New Zealand rabbits were used in this study ,they were classified into three groups: 2 months (young; n=5), 12 months (adult ;n=5)and 36 months (old; n=5) .we seclected the PCLs in all of the rabbit's left knees as observation objects ,randomly by throwing coin, to research the changes of number and morphology of mechanoreceptors ,and choosed the PCLs in all of the rabbit's right knees to sthdy distribution position of mechanoreceptors in ligaments (femoral attachments,body,tibial attachments).They were sacrificed in anesthesia. First, surgical procedures were carried on left knees of all of the rabbits. PCLs from left sides were obtained by cutting both tibial and femoral attachments. The morphology of receptors from the continuous sections of PCLs , stained by The NSE immuohistochemical staining and modified silver staining , were observed under a light microscope and analysed by the computer photograph system.The numbers of mechanoreceptors in all group were calculated out. The second, the same way , surgical procedures were carried on right knees of all of the rabbits. We obtained the whole PCLs from right knee. The PCLs were cut into three sections ;one is close proximity to the origin of the ligaments,tibial attachments; the other is close proximity to the insertions of the ligaments,femoral attachments, and the last sections is ligament body. The morphology of receptors from the continuous sections of PCLs, stained by The NSE immuohistochemical staining , were analysed by the computer photograph system. The distribution population of receptors in different section of PCLs were obtained.Results:The morphology of the two types of mechanoreceptors,Ruffini–like corpuscle and free nerve ending ,could be identified clearly in the ligament tissues under microscopic examination by way of modified silver staining. By using immunohistochemical techniques, we had found Ruffini–like corpuscles , Pacmi-like corpuscles , simple lamellar corpuscles, and morphologically unclassified sensory corpuscles ,and free nerve endings in the posterior cruciate ligament of rabbits.We did not observe any Golgi tendon organ mechanoreceptors.The simple lamellar and Pacim-likc corpuscles exhibited a similar structure, a central axon surrounded by a poorly developed, well-arranged inner core, surrounded by a subcapsular space ensheathed by a thick capsule . .The Ruffini-like corpuscles exhibited a fusiform body, surrounded by a thin capsule,its axons stained significantly by NSE. The numbers of Ruffni-like, Pacini-like and simple lamellar receptors decreased significantly in the old group compared to the young group(P<0.01)Besides, the number of Ruffni-like receptors of adult PCLs was significantly lower than that of the young group (p<0.05). No difference between adult and old groups. The total numbers of mechanoreceptors were significantly decreased with increasing age and the differences were statistically significant between young and other two groups (p<0.01). Although no measurements and statistical analyses were performed for the size of mechanoreceptors,a slight variation was observed regarding the size of the receptors between the young and other two groups. We could observe that the number of mechanoreceptors,which were distributed in ligament body,were lower significantly than the number of mechanoreceptors of tibial attachments and femoral attachments in all group. The number of mechanoreceptors ,which were distributed in femoral attachments ,were more than the number of mechanoreceptors in tibial attachments .In our study, there were no changes in the localization of the Mechanoreceptors with aging. Except free nerve endings, mechanoreceptors were very rarely detected in the deep part of the PCL and higher numbers of them had been observed in close proximity to bony insertions. Conclusion: The numbers of mechanoreceptors decreased with age in the PCL of healthy subjects ,their distribution location in the PCLs had no change with age.