Effects of aerobic exercise on learning, memory, and hippocampal neuromorphology in mice with Alzheimer’s disease

doi:10.12307/2022.673

Abstract

Abstract: BACKGROUND: Exercise helps prevent and retard cognitive decline related to Alzheimer’s disease, dementia, and age. However, whether exercise prevents cognitive decline in patients with Alzheimer’s disease is related to the neuromorphological changes of the hippocampus is still unclear.
OBJECTIVE: To investigate the effects of long-term aerobic exercise on learning and memory ability and neuromorphology of the hippocampus in mice with Alzheimer’s disease and its neuromechanism on Alzheimer’s disease.
METHODS: Twelve wild-type mice aged 3 months were divided into two groups (n=6 per group): a wild exercise group and a wild control group. Mice in the wild exercise group were given an exercise intervention for 5 months, and mice in the wild control group had no intervention. Twelve APP/PS1 double transgenic mice with Alzheimer’s disease were divided into two groups (n=6 per group): a model exercise group and a model control group. Mice in the model exercise group were given an exercise intervention for 5 months, and mice in the model control group had no intervention. After the exercise intervention, the memory ability of mice was tested through the eight-arm maze test. Neuromorphological changes of the hippocampus in mice were observed using Nissl staining under transmission electron microscope.
RESULTS AND CONCLUSION: The results of the eight-arm maze test showed that the memory ability of mice in the wild exercise group was better than that in the wild control group and the model exercise group (P < 0.05), and the memory ability of mice in the model exercise group and the wild control group was better than that in the model control group (P < 0.05). The results of Nissl staining showed that the Nissl bodies with clear nuclei and nucleoli were clearly visible in the hippocampal dentate gyrus, CA3 and CA1 areas of mice in the wild exercise group and the wild control group. In the mice with Alzheimer’s disease, the Nissl bodies in the hippocampus, especially in the dentate gyrus and CA3 areas, were fuzzy, and the nuclei and nucleoli were difficult to distinguish. In particular, in the model control group, the structure of nerve cells was relatively fuzzy, some neurons were seriously damaged, nerve cells arranged loosely with large spacing interval. Under the transmission electron microscopy, the number of synapses in the hippocampal dentate gyrus was decreased in the model control group compared with the wild control group. Some synaptic clefts, presynaptic membrane, and postsynaptic membrane were blurred, and there were fewer vesicles in the presynaptic membrane. The density of postsynaptic dense zone was lower. Compared with the model control group, the number of synapses in the hippocampal dentate gyrus was increased in the model exercise group. The distribution of synaptic vesicles in the presynaptic membrane was dense and uniform, and the density of postsynaptic dense zone was increased. To conclude, exercise can improve the structure of hippocampal nerve cells in Alzheimer’s disease mice to a certain extent, which may be one of the neuromechanisms by which exercise improves the learning and memory ability of Alzheimer’s disease mice.

Key words: aerobic exercise, Alzheimer’s disease, hippocampus, neuromorphological structure, learning and memory, cognition, synapse, neuromechanism

CLC Number:

Zhang Yeting, Fu Yan, Li Xue, Wei Cuilan, Li Chuikun, Yuan Qiongjia. Effects of aerobic exercise on learning, memory, and hippocampal neuromorphology in mice with Alzheimer’s disease[J]. Chinese Journal of Tissue Engineering Research, 2023, 27(20): 3188-3194.

Figures/Tables 6

整体而言，阿尔茨海默症小鼠相较于野生型小鼠重复进入各臂的次数较多，吃完所有食物用时较长。通过两因素被试间方差分析工作记忆错误次数，干预方式的主效应显著[F(1，20)=7.143，P=0.028，ηP2=0.472]，基因型的主效应显著[F(1，20)=3.681，P=0.003，ηP2=0.696]；干预方式与基因型的交互作用不显著[F(1，20)=2.571，P=0.147，ηP2=0.243]。表明干预方式与基因型作为主效应均可以显著影响小鼠工作记忆错误次数，但是它们的交互作用并不显著。野生运动组小鼠的工作记忆错误次数显著低于野生对照组，模型运动组小鼠的工作记忆错误次数显著低于模型对照组(P=0.047，P=0.016)；模型对照组小鼠的工作记忆错误次数显著高于模型运动组，模型运动组小鼠的工作记忆错误次数显著高于野生运动组(P=0.003，P=0.009)。通过两因素被试间方差分析工作记忆错误率，干预方式的主效应显著[F(1，20)=10.146，P=0.013，ηP2=0.559]，基因型的主效应显著[F(1，20)=48.78，P < 0.005，ηP2=0.859]，干预方式与基因型的交互作用不显著[F(1，20)=1.936，P=0.202，ηP2=0.195]。表明干预方式与基因型作为主效应均可以显著影响小鼠工作记忆错误率，但是它们的交互作用并不显著。野生运动组小鼠的工作记忆错误次率显著低于野生对照组，模型运动组小鼠的工作记忆错误次率显著低于模型对照组(P=0.024，P=0.012)；模型对照组小鼠的工作记忆错误率显著高于野生对照组，模型运动组小鼠的工作记忆错误率显著高于野生运动组(P < 0.005，P=0.004)。通过两因素被试间方差分析参考记忆错误次数，干预方式的主效应显著[F(1，20)=11.130，P=0.010，ηP2=0.582]，基因型的主效应不显著[F(1，20)=2.783，P=0.134，ηP2=0.696]，干预方式与基因型的交互作用不显著[F(1，20)=1.565，P=0.246，ηP2=0.164]。表明干预方式对小鼠参考记忆错误次数的改变并不受基因型的影响，且基因型并未对小鼠的参考记忆错误次数产生显著影响。野生运动组小鼠的参考记忆错误次数显著低于野生对照组，模型运动组小鼠的参考记忆错误次数显著低于模型对照组(P=0.017，P=0.012)；模型对照组小鼠的参考记忆错误次数显著高于野生对照组，模型运动组小鼠的参考记忆错误次数与野生运动组相比无明显差异(P=0.022，P=0.148)。通过两因素被试间方差分析参考记忆错误率，干预方式的主效应显著[F(1，20)=17.027，P=0.003，ηP2=0.68]，基因型的主效应显著[F(1，20)=22.851，P=0.001，ηP2=0.741]，干预方式与基因型的交互作用不显著[F(1，20)=2.169，P=0.179，ηP2=0.213]。表明干预方式与基因型作为主效应均可以显著影响小鼠参考记忆错误率，但是它们的交互作用并不显著。野生运动组小鼠的参考记忆错误率与野生对照组相比无明显差异，模型运动组小鼠的参考记忆错误率显著低于模型对照组(P=0.097，P=0.004) ；模型对照组小鼠的参考记忆错误率显著高于野生对照组，模型运动组小鼠的参考记忆错误率与野生运动组相比无明显差异(P=0.002，P=0.238)。 2.3 各组小鼠海马神经形态见图2。"

电镜下可观察到，野生型小鼠海马齿状回区的锥体细胞层中神经细胞排列较为整齐，细胞膜完整且较为清楚，细胞质中的细胞器如线粒体、粗面内质网、核糖体、高尔基复合体等较为丰富，甚至可以区分出溶酶体；细胞核呈现形状较为规则的圆形且比较大，核膜光滑完整，核仁清晰可见。阿尔茨海默症小鼠海马齿状回区神经锥体细胞的细胞核核膜有一定程度的皱缩、内陷及溶解断裂现象，细胞质中的细胞器如线粒体、内质网、高尔基复合体等的数量较野生型小鼠明显减少，其中有的线粒体出现了肿胀与空泡等现象，甚至有的线粒体的嵴出现溶解消失的情况，内质网出现了轻度扩张及液泡化的现象，高尔基的囊泡也有扩张现象发生；细胞核核膜出现皱缩及内陷呈锯齿样，而染色质则有固缩边聚现象。虽然模型对照组及模型运动组小鼠海马齿状回区神经细胞细胞核核膜都出现了一定程度的皱缩、内陷、溶解断裂现象，但是模型运动组小鼠的线粒体形态明显优于模型对照组小鼠。以上这些变化表明，APP/PS1双转基因小鼠的海马齿状回区神经细胞出现了受损及退化现象，而运动对这种受损及退化过程可能具有一定的预防作用。电镜下还可观察到，野生对照组与野生运动组小鼠海马齿状回区分子层的神经突触大多结构完整清晰，位于突触前的囊泡分布也较为密集均匀，在突触后膜处能够观察到浓密的电子致密物聚集，电子致密物的密度高；与野生对照组相比，模型对照组突触的分布较为稀疏，而部分突触前后膜及突触间隙较为模糊，突触前膜内的囊泡分布较少，电子致密物的密度较低；模型运动组突触前膜内的囊泡相较于模型对照组分布较为密集均匀，电子致密物密度有所增高。通过两因素被试间方差分析小鼠海马齿状回区突触的数量，干预方式的主效应显著[F(1，20)= 11.745，P=0.003，ηP2=0.37]，基因型的主效应显著[F(1，20)=16.632，P=0.001，ηP2=0.454]，干预方式与基因型的交互作用不显著[F(1，20)=0.016，P=0.900，ηP2=0.001]。表明干预方式与基因型作为主效应均可以显著影响海马齿状回区突触的数量，但是它们的交互作用并不显著。野生运动组的突触数量显著高于野生对照组，模型运动组的突触数量显著高于模型对照组(P=0.03，P=0.021)；模型对照组的突触数量显著低于野生对照组，模型运动组的突触数量显著低于野生运动组(P=0.002，P=0.048)。通过两因素被试间方差分析小鼠海马齿状回区电子致密物厚度，干预方式的主效应不显著[F(1，20)=2.347，P=0.141，ηP2=0.105]，基因型的主效应不显著[F(1，20)=3.95，P=0.061，ηP2=0.165]，干预方式与基因型的交互作用不显著[F(1，20)=0.505，P=0.486，ηP2=0.025]。表明干预方式与基因型作为主效应均不能显著影响海马齿状回区电子致密物厚度，且它们的交互作用并不显著。通过两因素被试间方差分析小鼠海马齿状回区突触间隙距离，干预方式的主效应不显著[F(1，20)=0.19，P=0.668，ηP2=0.009]，基因型的主效应不显著[F(1，20)=0.084，P=0.775，ηP2=0.004]，干预方式与基因型的交互作用不显著[F(1，20)=0.224，P=0.641，ηP2=0.011]。表明干预方式与基因型作为主效应均不能显著影响海马齿状回区突触间隙距离，且它们的交互作用并不显著。以上数据表明，长期有氧运动无论是对野生型小鼠，还是对APP/PS1转基因阿尔茨海默症小鼠而言，都可以显著增加其海马突触的数量。但是对其突触电子致密物厚度及突触间隙距离没有显著影响。中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程 "

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