Peters Alan
Department of Anatomy and Neurobiology, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118-2526, USA.
Neurosci Biobehav Rev. 2002 Nov;26(7):733-41. doi: 10.1016/s0149-7634(02)00060-x.
Human and non-human primates show cognitive decline during normal aging. Originally, the decline was attributed to a loss of cortical neurons, but recent studies have shown there is no significant cortical neuronal loss with age. Neurons acquire pigment, but the only other obvious changes are in layer 1 of neocortex. Layer 1 becomes thinner as apical tufts of pyramidal cells lose branches, as well as synapses, and at the same time the glial limiting membrane thickens. How dendrites and synapses in deep layers are affected by age is uncertain, but there are decreases in the levels of some neurotransmitters and receptors. Throughout the brain myelin sheaths show signs of breakdown. This may contribute to cognitive decline because it would cause a slowing of conduction along nerve fibers, disrupting the timing in neuronal circuits. Concomitantly, the myelin-forming oligodendrocytes develop swellings along their processes and gain dense inclusions. Microglial cells and astrocytes accumulate large amounts of phagocytosed material with age, although the origins of this material are not known.
人类和非人类灵长类动物在正常衰老过程中会出现认知衰退。最初，这种衰退被归因于皮质神经元的丧失，但最近的研究表明，随着年龄增长，皮质神经元并没有显著丧失。神经元会积累色素，但唯一其他明显的变化发生在新皮质的第1层。随着锥体细胞的顶端树突失去分支以及突触，第1层会变薄，与此同时，神经胶质界膜会增厚。深层的树突和突触如何受到年龄影响尚不确定，但一些神经递质和受体的水平会下降。在整个大脑中，髓鞘显示出分解的迹象。这可能导致认知衰退，因为它会导致沿神经纤维的传导速度减慢，扰乱神经回路中的时间安排。与此同时，形成髓鞘的少突胶质细胞沿着其突起出现肿胀并形成致密包涵体。随着年龄增长，小胶质细胞和星形胶质细胞会积累大量吞噬物质，尽管这些物质的来源尚不清楚。
