Expression of heat shock protein after +Gz exposure and its protective effects on +Gz-induced brain injury

Objective. To investigate the rule of intensity and duration of HSP70 expression in rat brain and its relationship with brain injury after repeated +Gz exposures. Method. SD male rats were arranged into control group, +2 Gz, +4 Gz, +6 Gz, and +10 Gz exposure groups. Rat brains were taken 6 h, 10 h, 1 d, 2 d, 4 d or 6 d after +Gz exposure for histopathologic and immunohistochemic or in situ hybridization studies. The expression of HSP70 and HSP70 mRNA or morphology of neurons were observed. Result. The intensity and duration of HSP70 expression were weak and brief at +2 Gz exposure, but was relatively extensive. There was a middling reaction of HSP70 only in hippocampal area after +10 Gz exposure. The duration, extension and intensity of HSP70 expression were wide, long and strong after +4 Gz and +6 Gz exposures. After 1 or 3-5 times exposures, the HSP70 expression reached its peak on the first day after +4 Gz exposures, and dropped obviously on the second day. However the expression of HSP70 maintained a high level after 2 d and was still higher than normal on the 6 d after 3-5 times repeated +4 Gz exposures. The distribution of HSP70 mRNA expression was as same as that of the HSP70 expression but the peak appeared much earlier (10 h) and its duration was shorter. After +10 Gz/5 min exposure, degenerated neurons were found in cortex, hippocampus and thalamus regions while the number of degenerated neurons were obviously decreased in such areas in pre-exposure groups with repeated +4 Gz/3 min for 3-5 times. Conclusion. The intensity and duration of HSP70 and HSP70 mRNA expression after +4 Gz and +6 Gz exposure were stronger and longer than +2 Gz and +10 Gz exposure. The degree of neuron damage after +10 Gz/5 min exposure in pre-exposure groups with repeated +4 Gz/3 min 3-5 times was obviously slight comparing with that of single +10 Gz exposure group.