Effect Of Childhood Growing Environment On Learning And Memory Of Mice

The enriched growth environment (EGE) can elevate ability of learning and memory of human and animal and repair brain injury and neural degeneration induced by some diseases, but the mechanism underlying effect of environment on the brain is not clear up to now. In present study, the effects of EGE and impoverished growth environment (IGE) on the spatial and emotional learning and memory of young mice (Mus musculus Km) were probed.All young mice of 3-week old were divided into 3 experimental groups: the control, EGE, and IGE groups. From begin of forth week, 5 mice selected from each group every week were used to inject intraperitoneally 5-bromine uracil (5-BrdU) (100 mg/Kg) once a day for 5 days. While into sixth day, animal head was cut down and the temporal cortex and hippocampus of animal brain was removed out for labeling new- bone neuron and calculating the number of neuronal apoptosis using TUNEL method for 3 weeks. At seventh week, the spatial and emotional learning and memory of mice were tested in Morris water maze and by step down test. Also, the concentration of MDA and SOD in homogenate of temporal cortex and hippocampus of brains were examined for understanding the relation between behavioral change induced by different environmentsand variation of level of oxidative stress.The experimental results were obtained as following: (1) In the young mice exposed to IGE, their quantity of movement intensity in early phase decreased and became easy to attack other animals and anger in the later phase. In the young mice exposed to EGE, they appeared more mild and friendly than before exposure. (2) Compared with those mice in control group, the latency that the mice in IGE group searched for a hidden under-water platform only prolonged markedly at third day. Also comparison of mice in EGE group, the latency that the mice in IGE group searched for a hidden under-water platform prolonged markedly at second and third days. The latency that mice in IGE group climbed on the stage were longer than those mice in control group when they were examined by step down test method. By calculating the times of mistakes made by mice in different groups, the times of happened mistakes by mice in IGE group increased more markedly than the mice in control and IGE groups at second day. (3) The SOD activity in homogenate of 10 % temporal cortex and hippocampus taken from brains of mice in EGE group were higher than those mice in control and IGE groups. On the otherwise, SOD activity in mice of IGE group was markedly lower than those mice in EGE group. By testing level of MDA in homogenate of 10 % temporal cortex and hippocampus taken out from brains of mice in different groups, we observed that the level of MDA were lower for EGE group and higher for EGE group than control group. But the level of MDA in IGE group was higher than in EGE group. (4) The newborn neurons labeled in region CA3 of hippocampus by 5-BrdU were calculated under the light microscope. The most of neurons in EGE group became positively colored ones, but there no positively colored neurons in IGE group and they basically became vacuoles. In the control group, almost no change in colored neurons was observed. The neuronal apoptosis in region CA3 of hippocampus was also examined with TUNEL method. The minority of neurons in control group, the large quantity of neurons in IGE group, and almost no neurons in EGE group were positively colored by TUNEL.These experimental results described above demonstrated that different childhood growth environments can affect the learning and memory of young mice and the mechanism underlying acting on the brains was perhaps related with oxidative stress in neurons and newborn neurons and neuronal apoptosis in temporal cortex and hippocampus of brains of young mice.