Effects of hypothermia on learning and memory ability and expression of fusion gene and fission gene mRNA of mitochondria in hippocampus of rats

Abstract

Objective To study the effects of hypothermia on learning and memory ability and mRNA expression of fusion gene and fission gene of mitochondria in hippocampus of rats. Methods 32 Wistar rats were randomly divided into 4 groups according to low-temperature exposure time in the test: high-exposure group(low-temperature exposure for 24 h/d), middle-exposure group(low-temperature exposure for 12 h/d), low-exposure group(low-temperature exposure for 6 h/d) and control group.The temperature of low-temperature exposure was 0-5 ℃.The total test time was 45 d. Morris water maze test was performed on each group from the fifth day before the end of the low-temperature test to the first day after the low-temperature test.After the water maze test, the mRNA expressions of mitochondrial fusion genes(Mfn1, Mfn2) and fission genes(Fis1, Drp1) in hippocampus were detected by RT-qPCR. Results Compared with the control group, the escaping latency of the high-exposure group and the middle-exposure group at the first day and the fifth day of water maze test were significantly longer than those in the control group, and the difference was statistically significant(P<0.05, P<0.01). The escaping latency of the sixth day and the number of platform crossings at the beginning of the water maze test were significantly different from those in the control group(P<0.05, P<0.01). Compared with the control group, the escaping latency of the high-exposure group and the middle-exposure group was significantly prolonged on the sixth day, and the number of the platform crossings decreased significantly.The difference was statistically significant(P<0.05, P<0.01). The high, middle and low-exposure group of mitochondrial fusion and fission genes mRNA expressions were as follows respectively: Mfn1: 4.05±0.21, 1.51±0.23, 1.17±0.83; Mfn2: 5.38±0.74, 0.84±0.53, 0.47±0.33; Fis1: 1.65±0.58, 0.49±0.42, 0.40±0.32; Drp1: 4.11±0.37, 0.99±0.82, 0.55±0.29.Compared with the control group, the mRNA expression of the fusion and the fission genes in the high-exposure group increased significantly(P<0.01). Conclusion The abnormalities of mitochondrial fusion and fission gen mRNA expression in the hippocampus may be one of the mechanisms of the decline of learning and memory functions caused by low temperature exposure. Key words: Low temperature; Learning and memory; Fusion gene; Fission gene; Mitochondrion; Hippocampus; Rat