| BACKGROUND: Tendinopathy is a common and significant clinical problem characterized by activity-related pain, focal tendon tenderness and intratendinous imaging changes. To study of tendon disease risk factors, pathology, and treatment methods, select valid animal models are necessary. Through research previous literatures, different sites of tendinopathy have different animal models. The main methods for tendinopathy are mechanical overloading and intratendinous injection of chemicals, because human Achilles tendinopathy animal model has not been successfully established, we focus on a new method of using electric stimulus rats foot to force it jumping, repeatedly to make Achilles tendinopathy overuse.MATERIALS AND METHODS: This experimental use high voltage pulsed DC power as the electric stimulus, a height-adjustable Plexiglas cage, bottom covered with wire line cage, when rats placed on the cage bottom, different electrode wire contact the rats foots, there is current through the rats body, make the rats fell pain and jump up. At the first, the rats are easy to jump out of the cage, we put it back to the cage, after several times, the rats know how to avoid electric stimulus by jump out of the cage. We gradually increased height of cage wall, rats will continues to jump, once rats reached the height of limit value, then stop increase the height, this method repeatedly force the rats to jump, to make Achilles tendon produced excessive injury. every 5s the wire line on the bottom of the cage switching on for 0.3s, the cycle consistent 5 minutes and rest 1 minute, electric stimulus for 40 minutes a day. The control group (n=10) and the experimental group (n=24) kept under the same conditions, just don't treat with electric stimulus, free activity in rats cage. At the last day of the 2,4,6,8 experimental week, we random take 6 rats from the experimental group, cut the rat Achilles tendon after anesthesia, take Histopathological examination. Experiments carried out 8 weeks, 8 weeks later execute the control group rats with the experimental group.RESULTS: The rat Achilles tendon was taken HE staining, Picric acid-Sirius red staining, toluidine blue staining and detection of apoptosis by Tunel assay.HE staining show the changes: in control group, note the uniform appearance of tightly packed, well aligned collagen fibrils with interspersed tenocytes aligned parallel to the fibrils. After 2 weeks training, there are no obvious change to control group, after 4 weeks, slightly pathological tendinous tissue with initial matrix disorganization. after 6 weeks, gradually with the hypercellularity, After 8 weeks, highly degenerated tendon with disorganized collagen fibers, accompany hypervascularization and hypercellularity at the paratenon, but we don't see chondroid-like cell increased. this may be associated with modeling time is too short, while this experiment has not been found tendons with calcification or spontaneous rupture of Achilles tendon.Picric acid-Sirius red staining of the rat Achilles tendon in control group was taken in polarized light microscope, we can see amounts of red collagen typeâ… and fewer blue collagen typeâ…¢at 8 eight. But in our experiment, we found different grades of staining in control group,2th week group,4th week group,6th week group, (maybe induced by experimental errors), this make it difficult to value the effect of overuse in rat Achilles tendon, so we can ignore the result.Toluidine blue training: in control group, there are clear vision in the paratenon, without hypercellularity and hypervascularization. After 2 weeks training, there are no obvious changes. After 4 weeks, the paratenon was slightly increased cells, after 6 weeks, gradually increased vascularization. After 8 weeks, there are obvious hypercellularity and hypervascularization in paratenon. Because Toluidine blue training isn't specificity, we can't make sure that were mast cells or not.Tunel assay: in control group and the 2nd weeks training group there are no positive cells found. After 4 weeks training, there are a little brown cells can see, after 6 weeks training, it show an increased brown cells than 4 weeks training group. At the 8 weeks group, the brown cells increased and the cell nucleus become round and small. This result shows there are apoptosis tenocytes.CONCLUSION: this study using electric stimulus rats'feet force the rats jumping, after 8 weeks training, we found the histopathological changes in rat Achilles tendon which also presence in human tendinopathy, This research revealed the progressive changes of rat achilles tendon after excessive injury, that maybe contribute to the tendinopathy pathophysiology of process. This experiment can be further study of tendon disease risk factors, pathogenesis and treatment provides a suitable animal model.
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