【作者】 王海涛；

【导师】 华田苗；

【作者基本信息】 安徽师范大学 ， 动物学， 2004， 硕士

【摘要】 随着年龄的增长，人及动物的许多视觉功能出现衰退,老年性视觉能力降低并非完全由眼的光学因素和视网膜形态、功能变化导致，不少方面可能决定于衰老引起的视觉中枢结构（如神经元丢失、树突野改变及突触密度下降等）和生理功能（如皮层内GABA能抑制作用减弱等）的改变。本文采用电生理和形态学手段对老年猫初级视皮层神经元的功能衰退进行观察并对其潜在的神经机制作了初步探讨。1.　运用在位细胞外记录方法比较研究视皮层V1区细胞的刺激选择和图形适应特性。结果发现:与青年猫相比，老年猫V1区细胞呈现出明显的方位和方向选择性的下降，并伴随着诱发反应及自发放的增加。刺激选择性的下降和诱发反应的增加表明老年猫V1区细胞对最优方位、方向和非最优方位、方向的刺激均有较好反应。由于老年猫V1区细胞自发放增加的幅度大于诱发反应的增加，导致了其信噪比的显著降低。这与在老年猴发现的结果一致，表明随年龄增加视皮层细胞出现功能衰退可能是一种普遍的现象。此外，老年猫V1区细胞的图形适应明显强于青年猫，这为皮层内抑制减弱理论即衰老过程中老年动物GABA能抑制作用的减弱可能是决定视觉功能衰退的主要机制提供了新的生理学证据。2.　运用银染及免疫组织化学ABC方法，在光学显微镜下观察、比较老年猫和青年猫初级视皮层V1区γ-氨基丁酸（GABA）能神经元和星形胶质细胞（GFAP为其特异性标志物）。结果发现，初级视皮层细胞数目无显著的年龄相关变化；与青年猫比较，老年猫的GFAP-IR细胞数目较多，阳性染色较深；老年猫的GABA-IR细胞的数目显著下降，阳性染色明显减弱。本文结果为皮层内GABA能抑制系统减弱可能是介导老年性视觉功能衰退的机制提供了直接的形态学证据，且进一步提示：GABA能神经元的丢失和（或）递质合成的减少可能是介导以上所述的功能衰退的重要因素。更多还原

【Abstract】 There have been a mass of research documents showing that many visual functions deteriorate with age both for human beings and for animals. Age-related visual function decline could not be completely attributed to optical and retinal changes. Considerable visual impairments in the old might result from morphological(such as cell loss, dendritic change and synaptic density decrease) or functional(such as weakened GABA inhibition) degeneration of visual pathways.In this article we made preliminary studies on the mechnisam underlying visual function degradation by electrophysiological and morphological methods.1. The stimulus selectivity and pattern adaptation of neurons in the primary visual cortex (area 17) of young adult and old cats was, for the first time, comparatively examined using single-neuron in vivo recording techniques. Neurons of old cats, compared with those of the young, showed a significant decrease in orientation and direction selectivity accompanied by an increase in peak response as well as increased spontaneous activity. Decreased stimulus selectivity and increased peak response indicated that more V1 neurons of aged cats can respond well to stimuli with previously optimal or non-optimal orientations and directions. The increase in peak response and spontaneous activity resulted in a significant decrease in signal-to-noise ratio for old cats. This result is well consistent with that found in senescent macaque monkeys, indicating a universal neural change with age. Further, pattern adaptation of V1 neurons in old cats was significantly stronger than that in young adult cats, which provided once more an evidence that lowered GABAergic inhibition effect in the elderly might be a chief pathway mechanism underlying a series of visual function declines during aging.2. Silver staining and immunohistochemical methods were applied to explore the difference of GABAergic neurons and astrocytes(specifically indicated by antibody of GFAP) in the primary visual cortex between young adult and old cats. No considerable neuron loss was found during senescence ;compared with those of young there was a significant increase in the number and staining density of GFAP-IR cells in old cats;but as for GABA-IR cells,it was just the opposite:immunoreactive cells of old cats were characterized by decreased number and weakened staining. The result presented a direct morphological evidence for weakness of GABAergic intracortical inhibition ,which is considered to be a possible candidate for neural basis of age-related visual function decline, and further suggested that GABAergic neuron loss and(or) decreased GABA synthesis might be responsible for above degradation.更多还原