Changes of Mechanoreceptor in Anterior Cruciate Ligament with Hindlimb Suspension Rats

In this study, the effect of weightlessness on mechanoreceptors in ACL was investigated in rats with hindlimb suspension. The animals used in the present study were 20 Wistar male rats (weight：278±16 g). The animals were divided into 2 groups：the Suspension group (n=10, suspended for 4 weeks) and Control group (n=10, non-suspended for 4 weeks). ACL was stained with gold chloride. The frozen section was sliced to be approximately 45 μm in thickness using a cryostat. The tissue preparations were observed through an optical microscope. Based on the criteria proposed by Freeman and Wyke, mechanoreceptor was specified and counted. Four types of nerve endings, Pacinian corpuscle, Ruffini corpuscle, Golgi tendon organ-like receptor, and free nerve ending were observed. In the Susupension group, atypical Pacinian corpuscle, and Ruffini corpuscle were observed. The number of mechanoreceptors were significantly decreased in the Suspension group (median 10) compared with the Control group (median 17) (Mann Whitney U test; Z=-2.65, P < 0.01). It might be necessary to perform also to early rehabilitation to prevent the degeneration of mechanoreceptors and take into consideration the nerve control system in the clinical setting.