大鼠视皮层中脑源性神经营养因子及γ-氨基丁酸表达的年龄相关性变化

目的 比较不同年龄组大鼠初级视皮层中脑源性神经营养因子（BDNF）及抑制性神经递质γ-氨基丁酸（GABA）表达的年龄相关性变化，为探讨老年性视觉功能衰退的细胞分子机制提供线索。方法 Nissl染色显示视皮层分层并用于神经元计数；免疫组织化学法标记大鼠视皮层中BDNF及GABA免疫阳性神经元。光镜下观察并用Image-Pro Express 6.0分析软件进行细胞密度统计和免疫反应吸光度值测量。结果 青年、中年及老年组(每组n=6)大鼠初级视皮层各层的神经元平均密度差异不显著；但与青年组大鼠相比，中年组及老年组大鼠初级视皮层各层中BDNF及GABA免疫阳性神经元密度显著下降，BDNF及GABA免疫反应强度明显减弱；与中年组大鼠相比，老年组大鼠视皮层各层中BDNF及GABA免疫阳性神经元密度及其反应强度亦明显降低。在衰老过程中，大鼠初级视皮层各层内GABA表达的减少与BDNF表达的降低具有高度的相关性。结论 大鼠初级视皮层中BDNF和GABA的表达随着衰老出现进行性下降，衰老过程中BDNF分泌的减少可能引起脑内抑制性神经递质GABA表达下调，这可能是介导老年性视觉功能衰退的重要途径之一。

Aged-related changes of brain derived neurotrophic factor and γ-aminobutyric acid expression in the visual cortex of rat

Objective To compare the expression changes of brain-derived neurotrophic factor (BDNF) and inhibitory neurotransmitter γ-aminobutyric acid (GABA) in the primary visual cortex between different age groups of rats, and to provide clues for exploring the cellular molecular mechanisms that underlie senescence-related visual function declines.Methods Nissl staining was used for identification of visual cortical layers and cell counting. Immunohistochemical methods were employed to display the BDNF and GABA-immunopositive neurons in the primary visual cortex of rats. Sections were observed under a light microscope, and the cell density and the optical absorbance intensity of immunoreactions were measured and analyzed with Image-Pro Express 6.0 software. Results The mean density of Nissl-stained neurons in each cortical layer of V1 showed no significant difference among young(n=6) ,middle-aged(n=6) and elderly groups (n=6). Compared to the young group of rats, the average density and immunoreactive intensity of BDNF and GABA-positive neurons in each cortical layer of V1 in middle-aged and elderly groups were significantly decreased. The average density and intensity of BDNF and GABA-immunoreactive neurons in each cortical layer of V1 in the elderly group were significantly lower than those in the middle-aged group. The reduction of GABA expression in each cortical layer of V1 was highly correlated to the decrease of BDNF expression during the aging process.Conclusion The expression of BDNF and GABA in the primary visual cortex showed a progressive decline during aging process. The reduction of BDNF secretion may result in a down-regulation of GABA expression in the brain ,which may be one of the important mechanisms that mediate the visual function declines during aging.