| Objective The experiment was divided into three parts. 1. To establish rats models of heat stroke and evaluate the changes of cognitive function at different time points; 2.To observe the cytometric changes of pyramidal neurons in the hippocampal CA1 area in rats after heat stroke at different time points. To investigate the mechanisms of learning and memory impairment of rats after heat stroke. And to provide a feasible way to evaluate the severity of the damage in nervous system in rats after heat stroke and the effects of intervention measures. 3. To investigate the changes of iron contents and iron metabolic proteins in heat stroke, and to explore the possible mechanisms of cognitive impairment caused by heat stroke.Methods SD rats were divided randomly into Sham group and heat stroke group.And the heat stroke group was divided randomly into immediately group(HS0), 7‐day group(HS7) and 21‐day group(HS21). To establish experimental model of heat stroke. 1.The Morris water maze test was conducted at designated time points to compare the changes of learning and memory ability in each group. 2. To collect the brain tissues of rats at each time points and use Nissl staining to count the living pyramidal neurons in the hippocampal CA1 area. 3. Collected the brain tissues of rats at each time points. To detect the iron concentration by flame atomic absorption spectrophotometer. The relative expression levels of Fpn1 m RNA in each group were detected by real time PCR.And the relative expression levels of hepcidin and Fpn1 in each group were also detected by western blot.Results 1. The swimming speeds of rats were no significant differences between each groups in Morris water maze test(P>0.05), which showed there has not too much effect on the rats’ movement in heat stroke. During the place navigation test, the escape latency of rats in each group showed a tendency to shorten gradually, and it becomes stable from the third days. Compared with Sham group, the escape latency of HS7 group became longer at day 1‐5(P<0.05). And the mean escape latency of HS21 group were longer than Sham group at day 1‐3, but there has no significant differences,and the escape latency were prolonged at day 4‐5(P<0.05). Compared with HS7 group,the escape latency of HS21 group became short at day 1‐2 but there has no significant differences, and it was shorten at day 3‐5(P<0.05). In the space exploration experiment,compared with the Sham group, the time percentage of staying at the target quadrant and the frequency of crossing the platform in HS7 group were decreased significantly(P< 0.01). The frequency of crossing the platform in HS21 group was decreased significantly(P < 0.01) and the time percentage of staying at the target quadrant has no significant differences. Compared with the HS7 group,the time percentage of staying at the target quadrant in HS21 group was increased significantly(P < 0.01) and the frequency of crossing the platform has no significant differences. 2. Compared with the Sham group, the number of living pyramidal neurons in the hippocampal CA1 area at heat stroke group was significantly decreased(P<0.05), and the difference was also significant between the HS7 group and the HS21 group(P<0.05). 3. Compared with the Sham group, the iron content has increased in heat stroke group(P<0.05). Fpn1:Compared with Sham group, the Fpn1 protein were significantly increased in HS0, HS7 and HS21 group(P < 0.01). Compared with the HS0 group, the Fpn1 protein increased slightly in HS7 group(P < 0.05). Compared with the Sham group, the Fpn1 m RNA levels were significantly increased in HS7 and HS21 group and the difference is statistically significant(P< 0.05), and there was no significant difference in HS0 group(P > 0.05).Compared with HS0 group, the Fpn1 m RNA levels were significantly increased at HS7 and HS21 group and the difference was statistically significant(P < 0.05). Hepcidin protein: Compared with Sham group, the hepcidin protein were significantly increased in HS0, HS7 and HS21 group, the difference was statistically significant(P < 0.05). There was no significant difference among HS0, HS7 and HS21 group.Conclusions 1. Heat stroke can cause cognitive impairment in rats. It is serious in early stage, and it may improve in the later time but not completely back to normal.2. The number of pyramidal neurons at hippocampal CA1 area has decreased after heat stroke.3. Heat stroke can induce hepcidin expression in rat hippocampus, which may lead to degradation of Fpn1 and eventually lead to iron overload. And this may be one of the reasons of cognitive dysfunction caused by heat stroke. |
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