Bourgeois J P, Rakic P
Département des Biotechnologies, Institut Pasteur, Paris, France.
J Neurosci. 1993 Jul;13(7):2801-20. doi: 10.1523/JNEUROSCI.13-07-02801.1993.
The kinetics of synaptogenesis in the primary visual cortex (Brodmann's area 17) were analyzed by electron microscopy in 33 rhesus monkeys, ranging in age from the 50th embryonic day (E50) to 20 years. A series of overlapping electron micrographs (vertical probes) were examined at each age on sections of the upper bank of the calcarine fissure. Synaptic contacts were first observed in the E50 specimen in the subplate and marginal zone (prospective layer I). In the cortical plate itself, synapses appear between E65 and E89 starting in the prospective layer VI. By E112, after all cortical neurons have assumed their laminar positions, synapses situated predominantly on dendritic shafts were present at a low density throughout the full thickness of the cortical plate. Thereafter, synapses accumulate more rapidly on dendritic spines and by E144 an equal number of contacts are found on both spines and shafts. The density of synapses continues to increase exponentially in all layers and reaches the mean maximum density of about 90 synapses per 100 microns 3 of neuropil by the third postnatal month. During the next 2 postnatal years the density of synaptic contacts decreases only slightly to a mean of 80/100 microns 3 of neuropil. Around the time of puberty, however, synaptic density decreases more rapidly to reach the adult level of about 40-50/100 microns 3 of neuropil. The 40% decrease in the density of synaptic contacts occurring between 2.7 and 5 years represents a loss of about 5000 synapses per second in the primary visual cortex of the two hemispheres, due primarily to the loss of asymmetric synapses situated on dendritic spines. The transient phase of high density of synaptic contacts located on dendrospines is shorter in thalamo-recipient layer IV than in either supra- or intragranular layers and is completed within the first postnatal year. It ends earlier in sublayer IVC than in layers IVAB and II-III, for example, reflecting biochemical and functional maturation of the different visual subsystems.
通过电子显微镜对33只恒河猴初级视皮层（布罗德曼17区）的突触发生动力学进行了分析，这些恒河猴的年龄从胚胎第50天（E50）到20岁不等。在每个年龄段，对距状裂上缘切片进行一系列重叠电子显微镜图像（垂直探针）检查。在E50标本的亚板层和边缘区（预期的I层）首次观察到突触接触。在皮质板本身，突触在E65和E89之间开始出现，起始于预期的VI层。到E112时，所有皮质神经元都已占据其层状位置，主要位于树突干上的突触以低密度存在于整个皮质板的全层。此后，突触在树突棘上积累得更快，到E144时，在棘和干上发现的突触数量相等。突触密度在所有层中继续呈指数增加，到出生后第三个月达到平均最大密度，约为每100立方微米神经毡90个突触。在接下来的2个出生后年份中，突触接触密度仅略有下降，降至每100立方微米神经毡80个突触的平均值。然而，在青春期前后，突触密度下降得更快，达到约40 - 50/100立方微米神经毡的成人水平。在2.7至5岁之间发生的突触接触密度40%的下降，意味着两个半球的初级视皮层中每秒约有5000个突触丧失，这主要是由于位于树突棘上的不对称突触的丧失。丘脑接受层IV中位于树突棘上的突触高密度的短暂阶段比颗粒上层或颗粒内层高，并且在出生后第一年内完成。例如，它在IVC亚层比IVAB层和II - III层结束得更早，这反映了不同视觉子系统的生化和功能成熟。
