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BACKGROUND: Previous studies have shown that heat shock protein 70 (HSP70) has neuroprotective effects by decreasing phosphorylation of Tau protein, thereby reducing the expression of Tau protein and proper aggregation.OBJECTIVE: To observe and verify expressional changes of HSP70 and Tau in retinal ganglion cells following stretch injury to the right optic nerve in rats, and to determine the effect of heat stress pretreatment on HSP70 and Tau protein expressions.DESIGN, TIME AND SETTING: A randomized, controlled, animal experiment was performed at the Laboratory of Neurology Research institute of the First Affiliated Hospital of Chongqing Medical University from March to June 2006.MATERIALS: instant SABC immunohistochemistry kit, as well as mouse anti-HSP70 and rabbit anti-Tau polyclonal antibodies, were purchased from Wuhan Boster Bioengineering Limited, China.METHODS: A total of 57 male, Wistar rats were randomly assigned to 4 groups: control (n=3);150-180 g stretch force was induced in the right optic nerves in stretch-only group (n=18) to establish optic nerve stretch injury model; heat stress was applied to 18 animals in heat-stress treatment group; 18 rats in the heat-stress pretreatment plus stretch group were subjected to identical stretch injury as stretch-only group after 24-hour heat-stress pretreatment. According to sacrifice time, the groups were assigned to 6 subgroups at different time points of 4, 8, and 16 hours,and 1,3, and 5 days, with 3 rats in each subgroup. No treatment was performed in the control group except anesthesia.MAIN OUTCOME MEASURES: Morphological changes of optic nerves and retinal ganglion cells following stretch injury were observed by light microscopy following hematoxylin-eosin staining.HSP70 and Tau protein expression levels were observed in retinal ganglial cells from each group using immunohistochemistry.RESULTS: (1) Compared with the control group, morphological axonal and retinal ganglial cell changes, as well as a decreased number of retinal ganglial cells, were identified in the stretch-only group (P<0.01). Pathological damage in optical nerve and retinal ganglial cells were not remarkable in the heat-stress pretreatment plus stretch group, with no statistical difference in the number of retinal ganglial cells compared with the control group (P>0.05). (2) Compared with the control group,significantly increased HSP70 expression in retinal ganglial cells occurred in the stretch-only,heat-stress treatment, and heat-stress pretreatment plus stretch groups (P<0.05 or P<0.01). The peak of HSP70 expression was earlier in the heat-stress pretreatment plus stretch group compared with the stretch-only and heat-stress treatment groups, and was expressed over a longer period of time compared with the heat-stress treatment group. Compared with the control group, Tau expression in the retinal ganglial cells rapidly increased 4-16 hours following stretch injury in the stretch-only group (P<0.05 or P<0.01), and obviously decreased in the heat-stress pretreatment plus stretch group (P<0.05 or P<0.01).CONCLUSION: Tau expression increased following stretch injury, with an earlier expression peak than HSP70, which indicated that stretch injury-induced HSP70 expression was not strong or quick enough to sufficiently protect the nerve. A much more enhanced HSP70 expression, with an earlier peak and longer expression period, was observed in rats subjected to stretch injury following heat stress, which demonstrated that HSP70 exhibited neuroprotective functions by reducing abnormal aggregation of Tau.