猫初级听皮层γ-氨基丁酸能神经元和星形胶质细胞年龄相关变化

AGE-RELATED CHANGES OF GABAergic NEURONS AND ASTROCYTES IN CAT PRIMARY AUDITORY CORTEX

目的探讨青年猫和老年猫初级听皮层(AI)的年龄相关变化及可能产生的生理作用。方法Nissl染色示两组猫初级听皮层的分层结构并进行细胞计数;免疫组织化学染色示两组猫γ-氨基丁酸(GABA)能神经元和星形胶质细胞的形态、密度及分布。结果与青年猫相比,老年猫的初级听皮层细胞平均密度无显著的年龄相关变化,GABA_IR细胞的密度显著下降(尤其是Ⅱ、Ⅲ、Ⅳ层),阳性胞体较小,阳性反应明显减弱;老年猫的GFAP_IR细胞密度显著增大,阳性胞体膨大,突起稠密粗大,阳性反应明显增强,其中的Ⅰ层和白质尤为明显。结论GABA能神经元显著的年龄相关性改变可能为老年性听觉功能衰退的神经机制在皮层水平提供了直接的形态学证据;而星形胶质细胞活动增强可能是导致GABA能神经元及GABA递质含量减少的重要原因之一。

Objective A morphometric study was carried out on GABAergic neurons and astrocytes in primary auditory cortex of 4 young cats （1-3 years old, 20-2.5 kg） and 4 old cats （10-13-year-old, 3-3.5 kg）, in order to explore the age-related changes and the probably physical effects underlying these changes. Methods The same regions of the primary auditory cortex （AI） were comparatively studied. Nissl staining and immunohistochemical methods were applied to explore the differences of GABAergic neurons and astrocytes （specifically labeled by GFAP as a mark as antibody） in the primary auditory cortex （AI） between young and old cats. Serial cross-sections from two age groups were stained with Nissl for layer structure observation and demonstration of neurons; Adjacent sections were stained with anti-GABA immunohistochemistry for localizing and characterizing GABAergic and with anti-GFAP for astrocytes in AI. Results The diameter, density and number of GABAergic neurons in AI of old cats declined significantly compared with the counterpart in young cats, especially in layers Ⅱ , Ⅲ of AI; but the change in GFAP-IR cells was reversed： old cats showed clearly larger number and stronger staining of GFAP-IR cells than that in young cats. The GFAP-IR cell bodies and dendrites swelled obviously in old cats, especially in layer Ⅰ of AI and in white matter. Conclusion The result presented a direct morphological evidence for weakness of GABAergic intracortical inhibition, which is considered to be a possible mechanism for age-related acoustic function decline. The enhanced function of astrocytes may play an important role in decreasing the GABA content in AI of the old individuals.