The Effects Of Running Exercise On The Hippocampus In APP/PS1 Transgenic AD Mice

PART ONE THE EFFECTS OF EXERCISE ON THE SPATIAL LEARNING AND MEMORY ABILITIES IN DIFFERENT STAGES OF APP/PS1 TRANSGENIC AD MICEObjective: To study the effects of running exercise on the spatial learning and memory abilities of the APP/PS1 tansgenic AD mice in early stage and in late stage, respectively, in order to provide theoretical bases for the further studies on the neurobiological bases underlying the effects of exercise on Alzheimer′s disease(AD).Methods: Twenty 6-month-old male APP/PS1 mice and twenty 12-month-old male APP/PS1 mice were respectively randomly assigned to control group(AD control) or running group(AD runner). The wild-type mice with same ages were regarded as normal control group(Wild-type). All mice were housed in groups of 5 mice. The AD runner mice were placed on a treadmill to run for 20 min per day, 5 days per week, for a period of 4 months. All the mice from other groups were housed in sedentary conditions. During the first weeks, the running speed of 5 m/min was gradually increased to 10 m/min. After that, the running speed was maintained at 10 m/min. For the first 7 days of treatment, 12-month-old male APP/PS1 mice were injected with 50 mg/kg 5-bromodeoxyuridine(Brd U) once a day. The spatial learning and memory abilities were assessed using the Morris water maze.Results: 1. There were significant differences in the escape latency time among the 10-month-old Wild-type mice, AD control mice and AD runner mice(p = 0.007). The escape latency time of the 10-month-old AD control mice was significantly longer than that of the Wild-type mice with same ages(p = 0.004). The escape latency time of the 10-month-old AD runner mice was significantly shorter than that of the AD control mice with same ages(p = 0.009). In the removed platform task, there were significant differences in the time spending in the target quadrant among the 10-month-old Wild-type mice, AD control mice and AD runner mice(p = 0.000). The time spending in the target quadrant of the 10-month-old AD control mice was significantly less than that of the Wild-type mice with same ages(p = 0.000). The time spending in the target quadrant of the 10-month-old AD runner mice was significantly more than that of the AD control mice with same ages(p = 0.006). There were significant differences in the times of platform location crosses among the 10-month-old Wild-type mice, AD control mice and AD runner mice(p = 0.003). The times of platform location crosses of the 10-month-old AD control mice were less than those of the AD runner mice with same ages(p = 0.001). There were no significant differences in the times of platform location crosses between the 10-month-old AD control mice and Wild-type mice(p = 0.12). 2. There were significant differences in the escape latency time among the 16-month-old Wild-type mice, AD control mice and AD runner mice(p = 0.000). The escape latency time of the 16-month-old AD control mice was significantly longer than that of the Wild-type mice with same ages(p = 0.000). The escape latency time of the 16-month-old AD runner mice was significantly shorter than that of the AD control mice with same ages(p = 0.002). In the removed platform task, there were significant differences in the time spending in the target quadrant among the 16-month-old Wild-type mice, AD control mice and AD runner mice(p = 0.004). The time spending in the target quadrant of the 16-month-old AD control mice was significantly less than that of the Wild-type mice with same ages(p = 0.004). The time spending in the target quadrant of the 16-month-old AD runner mice was significantly more than that of the AD control mice with same ages(p = 0.005). There were significant differences in the times of platform location crosses among the 16-month-old Wild-type mice, AD control mice and AD runner mice(p = 0.006). The times of platform location crosses of the 16-month-old AD control mice were more than those of the Wild-type mice with same ages(p = 0.002). There were no significant differences in the times of platform location crosses between the 16-month-old AD control mice and AD runner mice(p = 0.050).Conclusions: Regular and moderate intensity running exercise could not only delay the progress of the spatial learning and memory ability decline in the early stage of AD mice, but also improve the spatial learning and memory dysfuctions in the late stage of AD mice. These results suggested that regular and moderate intensity running exercise might be used as the potential means for the provention and treatment of AD.PART TWO THE EFFECTS OF EXERCISE ON THE HIPPOCAMPUS AND THE MYELINATED FIBERS OF THE HIPPOCAMPUS IN THE EARLYSTAGE OF APP/PS1 TRANSGENIC AD MICEObjective: To study the effects of running exercise on the hippocampus and the myelinated fibers of the hippocampus in the early stage of APP/PS1 transgenic AD mice in order to explore the morphological bases for the effects of running exercise on the spatial learning and memory abilities of transgenic AD mice and provide the theoretical bases for searching the behavior means and drugs to early infervene AD.Methods: After a four-month period of running exercise from 6-month-old to 10-month-old, six mice from each group were randomly selected. After anesthesia and infusion, one side of cerebral hemisphere was randomly selected from each brain. After being dehydrated, the hemispheres were embedded in opti-mum cutting temperature compound(O.C.T) and then cut coronally at 40 μm equidistant intervals with cryoultramicrotome, from the rostral end to caudal end of mouse hemisphere. All sections containing hippocampus were sampled with systermatic random fashion according to stereological sampling principles and 7 series of tissue sections were obtained. One series of tissue sections randomly selected from seven series per animal were used to estimate the hippocampal volume and the volume of hippocampal sub-regions. The other series of tissue sections were used to analyze amyloid plaques and the myelin sheaths in the hippocampal formation. The other side of cerebral hemisphere was cut into successive equidistant cerebral slices. Three or four tissue blocks were randomly sampled from the CA1 field and DG field, respectively. The volume of the CA1 field and the volume of the DG field, the total length and total volume of the myelinated fibers and total volume of the myelin sheaths in the CA1 field, and the total length and total volume of the myelinated fibers and total volume of the myelin sheaths in the DG field were estimated with the stereological methods.Results: 1. The hippocampal volume, the volume of the CA1 field and the volume of the DG field in the 10-month-old AD control mice were significantly decreased than those in the Wild-type mice with same ages(p = 0.000,p = 0.026 and p = 0.000). The hippocampal volume, the volume of the CA1 field and the volume of the DG field of the 10-month-old AD runner mice were significantly bigger than those of the AD control mice with same ages(p = 0.000,p = 0.010 and p = 0.006). 2. We could not observe any amyloid plaques in the hippocampus of the 10-month-old Wild-type mice. However, there were a few amyloid plaques in the hippocampus of the 10-month-old AD control mice and AD runner mice. The amyloid plaques in the hippocampus of the 10-month-old AD runner mice were less than those of the AD control mice with same ages. 3. There were more cross sections of myelin sheaths in the hippocampus of the 10-month-old Wild-type mice than those of the AD control mice and AD runner mice with same ages. In additon, there were more cross sections of myelin sheaths in the hippocampus of the 10-month-old AD runner mice than those of the AD control mice with ages. 4. There was no significant difference in the length of the myelinated fibers of the CA1 field between the 10-month-old Wild-type mice and AD control mice(p = 0.949). The volume of myelinated fibers and the volume of myelin sheaths in the CA1 field of the 10-month-old AD control mice were significantly smaller than those of the Wild-type mice with same ages(p = 0.033 and p = 0.018). There were no significant differences in the length and volume of the myelinated fibers in the CA1 field between the 10-month-old AD runner mice and AD control mice(p = 0.070 and p = 0.063). The volume of the myelin sheaths in the CA1 field of the 10-month-old AD runner mice was significantly larger than that of the AD control mice with same ages(p = 0.018). 5. There was no significant difference in the length of the myelinated fibers in the DG field between the 10-month-old Wild-type mice and AD control mice(p = 0.482). The volume of the myelinated fibers and the volume of the myelin sheaths in the DG field of the 10-month-old AD control mice were significantly smaller than those of the Wild-type mice with same ages(p = 0.037 and p = 0.007). The length and volume of the myelinated fibers and the volume of the myelin sheaths in the DG field of the 10-month-old AD runner mice were significantly more than those of the AD control mice with same ages(p = 0.013, p = 0.018 and p = 0.006).Conclusions: 1. There were significant decreases of the hippocampal volume, the volume of the CA1 field and the volume of the DG field in the 10-month-old APP/PS1 mice. Regular and moderate intensity running exercise could delay the atrophy of the hippocampus and sub-regions in the early stage of APP/PS1 mice. 2. There were a few amyloid plaques in the hippocampus of the 10-month-old APP/PS1 mice. Regular and moderate intensity running exercise could reduce the amyloid plaques in the hippocampus in the early stage of APP/PS1 mice. 3. There were marked demyelinations of the myelinated fibers in the CA1 field of APP/PS1 mice at 10 months age, and regular and moderate intensity running exercise could reduce the marked demyelinations of the myelinated fibers in the CA1 field in the early stage of APP/PS1 mice. 4. There were marked demyelinations of the myelinated fibers in the DG field of APP/PS1 mice at 10 months age, and regular and moderate intensity running exercise could protect the myelin sheaths of the DG field from breaking down in the early stage of APP/PS1 mice.PART THREE THE EFFECTS OF EXERCISE ON THE HIPPOCAMPUS AND THE NEURONS OF THE HIPPOCAMPUS IN THE LATE STAGE OF APP/PS1 TRANSGENIC AD MICEObjective: To study the effects of running exercise on the hippocampus and the neurons and neurogenesis of the hippocampus in the late stage of APP/PS1 transgenic AD mice in order to explore the neurobiological bases for the effects of running exercise on the spatial learning and memory abilities of transgenic AD mice and provide the structural bases for searching the behavior means and drugs to delay the progress and treat late AD.Methods: After a four-month period of running exercise from 12-month-old to 16-month-old, six mice from each group were randomly selected. After anesthesia and infusion, one side of cerebral hemispheres was randomly selected from each brain. After being dehydrated, the hemispheres were embedded in O.C.T and then cut coronally at 50 μm equidistant intervals with cryoultramicrotome, from the rostral end to caudal end of mouse hemisphere. All sections containing hippocampus were sampled with systermatic random fashion according to stereological sampling principles and 6 series of tissue sections were obtained. One series of tissue sections randomly selected from six series per animal were used to estimate the hippocampal volume and the volume of the hippocampal sub-regions. One series of tissue sections were used to analyze amyloid plaques in the hippocampus. One series of tissue sections were used to estimate the total number of the neurons in the hippocampus using Nissl’s staining and stereological methods. One series of tissue sections were used to estimate the total number of the newborn cells in the hippocampus using immunohistochemistry technique and stereological methods. The other tissue sections were used to analyze newborn neurons in the hippocampus using double-labelling immunofluorescence and laser scanning confocal microscope. Results: 1. There were no significant differences in the hippocampal volume, the volume of the CA1 field and the volume of the DG field among the 16-month-old Wild-type mice, AD control mice and AD runner mice. 2. We could not observe any amyloid plaques in the hippocampus of the 16-month-old Wild-type mice. However, there were a lot of amyloid plaques in the hippocampus of the 16-month-old AD control mice and AD runner mice. The amyloid plaques in the hippocampus of the 16-month-old AD runner mice were less than those of the AD control mice with same ages. 3. The total number of the neurons in the hippocampus, the number of the neurons in the CA1 field and the number of the neurons in the DG field of the 16-month-old AD control mice were significantly decreased than those of the Wild-type mice with same ages(p = 0.003, p = 0.020 and p = 0.010). The 16-month-old AD runner mice had more neurons in the hippocampus and in the DG field than AD control mice with same ages(p = 0.005 and p = 0.013). But there was no significant difference in the number of the neurons in the CA1 field between AD runner mice and AD control mice(p = 0.200). 4. The total number of the Brdu+ cells in the hippocampus and the number of the Brdu+ cells in the DG field of the 16-month-old AD control mice were significantly decreased than those of the Wild-type mice with same ages(p = 0.027 and p = 0.004). But there was no significant difference in the number of the Brdu+ cells in the CA1 field between AD control mice and Wild-type mice(p = 0.198). The 16-month-old AD runner mice had more Brdu+ cells in the hippocampus and the DG field than AD control mice with same ages(p = 0.040 and p = 0.004). But there was no significant difference in the number of the Brdu+ cells in the CA1 field between AD runner mice and AD control mice(p = 0.078). 5. Few new neurons were observed in the CA1 field of the 16-month-old Wild-type mice and AD runner mice, but none of new neurons was observed in the CA1 field in AD control mice with same ages. Many new neurons were observed in the DG field of the Wild-type mice, AD control mice and AD runner mice, but the least new neurons were observed in the DG of AD control mice.Conclusions: 1. Regular and moderate intensity running exercise could not change the atrophy of the hippocampus and the sub-regions of the hippocampus in the late stage of APP/PS1 mice. 2. There were a few amyloid plaques in the hippocampus of the 10-month-old APP/PS1 mice. Regular and moderate intensity running exercise could reduce the amyloid plaques in the hippocampus in the early stage of APP/PS1 mice. 3. There were marked loss of the neurons in the field CA1 and DG of APP/PS1 mice at 16 months age, and regular and moderate intensity running exercise could repress the loss of the neurons within the DG field in the late stage of APP/PS1 mice. 4. There were the deficits of the neurogenesis and the survival of the new neurons in the hippocampus of aged APP/PS1 mice. Running exercise was able to induce the neurogenesis and promote the survival of newborn neurons in the hippocampus of aged APP/PS1 mice.