The Effect Of 2,5-hexanedione On The Neurofilament And Neurogenesis Of Adult Rat Hippocampus

Adult neurogenesis occurs throughout life,two major areas in the brain are well known to be neurogenic in the adulthood:the subventricular zone of the lateral ventricles and the subgranular zone in the hippocampal dentate gyrus.Neurogenesis of adult brain plays a critical role in the regulating brain function under both physiological and pathological conditions, especially for the hippocampus-related adult neurogenesis. The hippocampal neurogenesis has play important roles in the learning and memory, and also in regulating emotion and mood. Adult neurogenesis is a dynamic process, including the proliferation of neural progenitor cells, the fate determination of neural progenitor cells progenies, the differentiation, morphogenesis and maturation of adult-born neurons, and the eventual integration into the neural networks. Furthermore, each of these processes is subject to regulation by numerous intrinsic and extrinsic factors. Because n-hexane is a lipid compoundand used in lots of industrial fields, chronic exposure of n-hexane can lead to accumulation and toxicity of it.2,5-hexanedione is the major neurotoxic metabolite of n-hexane.Some studies have shown that 2,5-hexanedione decreased the numbers of newly generated cells in the hippocampal dentate gyrus in the mouse and induced early spatial memory deficit in the rats.Chronic exposure to 2,5-hexanedione causes central and peripheral motor neuronal axon atrophy which is related to the nerofilaments. Lots of experiments have showed that chronic exposure to n-hexane reduces the neurofilaments of cortex,spinal cord,sciatic nerve,and tibial nerve. But there is no report on the effects of 2,5-hexanedione on the self-renew and the differentiation of the neural progenitor cells as well as on the expression of hippocampal neurofilament.Objective:(1)The expression of NF-L in cortex、hippocampus in 2,5-hexanedione exposure rats.(2)The effect of 2,5-hexanedione on the hippocampus-related adult neurogenesis in 2,5-hexanedione exposure rats.Methods:Experimental animals were randomly divided into three groups: control group,middle-dose group, and high- dose group.Experimental rats were treated with2,5-hexanedione by intraperitoneal injection(i.p.) at a dosage of 200 or 400mg/kg/day for continuous 5 weeks(five times per week). The body weight was measured weekly to adjust the dosage. During the experiment, rats accessed to drinking water and food freely. All animal experimental procedures were carried out in accordance with the Animal Guideline of Dalian Medical University. After five-week of 2,5-hexanedione administration,brains were sliced for immunofluorescence detection,newborn hippocampal cells of each group were counted, and the percentages of the newborn Sox2+,SRY(sex-determining region Y)-box 2,cells as well as newborn neurons were counted. Hippocampus and cortex were dissected for Western blot analysis to detect the expression of NF-L.Results :1.Western blot results demonstrated that the expressions of NF-L in the cortex and hippocampus were different. Compared with the control group, the level of NF-L in the cortex, the middle-dose group decreased significantly(1.00 vs.0.72±0.06,p<0.01)and the high-dose group also decreased significantly(1.00 vs.0.47±0.06,p<0.01).Moreover, the expression of NF-L in the high-dose group was further reduced than that in the middle-dose group(0.47±0.06 vs.0.72±0.06,p<0.01).In the hippocampus,there was no significant differences between the middle-dose group and the control group for the NF-L levels(0.88±0.09 vs.1.00,p>0.05),while in the high-dose group, the expression of NF-L was significantly reduced as compared with that of the middle-dose group(0.55±0.06 vs.0.88±0.09,p<0.01)and was significantly reduced as compared with the control group(0.55±0.06 vs.1.00,p<0.01).2.Immunofluorescence showed that there was no significant differences between the middle doses group and the control group for the numbers of newborn cells in SGZ/GCL(14±1.00 vs.8±0.92%,p<0.01), however,the percentage of newborn neurons in the high-dose group was significantly decreased as compared with that of control(27±0.82 vs.16±1.80%,p<0.01),and the percentage of the newborn Sox2+ cells increased significantly in the high-dose group as compared with that in the control group(54±2.80 vs.70±1.97%,p<0.01).Conclusion:Exposure to 2,5-hexanedione reduced the expression levels of NF-L in the cortex and hippocampus of high-dose group, decreased the number of newborn cells and the percentage of newborn neurons in the high-dose group, however, increased the percentage of the newborn Sox2+ cells in the high-dose group.