大鼠视皮层神经元电生理和形态学特性在发育中的变化

为研究大鼠不同发育阶段视皮层神经元电的生理学与形态学特性,实验观察了神经元电生理和形态学特性的变化与年龄的同步化程度,探讨视皮层视觉依赖性突触的形成和重新分布的细胞内机制。应用脑片膜片钳全细胞记录技术和细胞内生物家标记相结合的方法,记录4—28d SD大鼠视皮层神经元的突触后电流(postsynaptic currents,PSCs)。共记录156个大鼠视皮层神经元,睁眼前与睁眼后组中无反应型细胞数量,多突触反应型细胞数量、细胞的输入阻抗有显著性差异。成功标记23例神经元,不同年龄的神经元的形态学成熟度不同。低输入阻抗神经元在形态学上属成熟型,高输入阻抗神经元属幼稚型。该结果表明,大鼠在发育过程中,视皮层神经元功能的成熟表现为在形觉刺激以及局部神经元网络的整合作用下的视觉依赖性突触的形成和重新分布。在视觉发育可塑性关键期内,视皮层神经元形态和电生理特性的变化与年龄的同步化程度大于皮层下结构。

Changes in electrophysiological and morphological properties of neurons during the development of the visual cortex in the rat

To investigate the intracellular mechanism of activity-dependent synapses formation and redistribution, we studied the electrophysiological and morphological characteristics of neurons of the developing visual cortex, and observed the level of synchronism of age and changes in the properties. Whole cell patch-clamp recordings and intracellular biocytin staining were used to record postsynaptic currents (PSCs) from neurons in the visual cortex of Sprague-Dawley rats (postnatal d 4-28). The histological processing was made. There were three types of PSCs in 156 cells: silent response, monosynaptic response and polysynaptic response, during the first developmental month. Before eyes opened the number of the neurons with the silent response (57.3%) was significantly higher than that after the eyes opened (11.9%) (P<0.001). However, the incidence of polysynaptic PSCs increased from 12.4% before eyes opened to 28.9% after eyes opened (P<0.01). During postnatal week 1, all cells were classified as immature. The immature cells had very high input resistances (R(N)>1.0 Gsigma), low amplitude (-0.87 mA) and short decay time (-0.98 ms). During postnatal week 4, all cells were mature with lower input resistance (R(N)<310 Msigma), larger amplitude (-66 mA), and longer decay time (-225 ms). From postnatal weeks 1 to 3, the cells had electrophysiological properties that were intermediate between the immature and mature types of cells. With biocytin intracellular staining, five types of neurons were obtained: pyramidal cells, satellite cells, basket cells, neuroglial cells and immature cells. On the basis of their electrophysiological and morphological characteristics, pyramidal cells were classified into three categories: immature, intermediate, and mature cell types. During postnatal week 1, cells were immature with very high input resistance. Morphologically immature cells had short simple dendritic arborizations which incompletely penetrated the layer where the cell body lies. From postnatal weeks 2 to 4, the cells were mature with low input resistance. They were morphologically more complex with dendritic arborizations which completely penetrated the whole layers of the visual cortex. From postnatal weeks 1 to 2, a third, intermediate cell type had electrophysiological properties that were intermediate between the immature and mature cell types. Three distinctive types of pyramidal cells in visual cortex only co-exist during postnatal weeks 1 to 2. Data show that activity-dependent synapes are formed and integrated into local neuronal networks with visual stimulation. In the critical period of visual development, the level of synchronism of age and changes in electrophysiological and morphological properties in the visual cortex is higher than that in the subcortex.