Zecevic N, Bourgeois J P, Rakic P
Section of Neuroanatomy, Yale University School of Medicine, New Haven, CT 06510.
Brain Res Dev Brain Res. 1989 Nov 1;50(1):11-32. doi: 10.1016/0165-3806(89)90124-7.
The density and proportion of synaptic contacts in the primate motor cortex (Brodmann area 4) were determined in 21 rhesus monkeys ranging in age from embryonic day 41 (E41) to 20 years. Two to 4 vertical electron microscopic probes, each consisting of 150-250 overlapping micrographs traversing the thickness of the cortex, were prepared for each specimen. Synapses were categorized according to their morphology (symmetrical or asymmetrical), cellular location (on spines, shafts or soma), number, and ratio of laminar distribution. The density of synapses was expressed per unit area and volume of neuropil (excluding neuronal and glia cell bodies, myelin sheath, blood vessels and extracellular space). The first synapse in the area of the emerging motor cortex were observed at E53 in the marginal zone (prospective layer I) and in the transient subplate zone situated beneath the developing cortical plate. Around midgestation (E89) synapses were observed over the entire width of the cortical plate, and their density was about 5/100 microns 3 of neuropil. During the last two months of gestation synaptic density increased 8-fold across all layers to reach about 40/100 microns 3 at the time of birth (E165). Synaptic production continued postnatally and by the end of the second postnatal month attained a level of 60/100 microns 3 neuropil which is two times higher than in the adults. This level decreased at a slow rate until sexual maturity (3 years of age) and then more rapidly to the adult level which is characterized by relative stability of about 30/100 microns 3. The decline in synaptic density after the peak in infancy occurs predominantly at the expense of asymmetric synapses situated on dendritic spines; the population of symmetric synapses on dendritic shafts remains relatively constant. The development of synaptic connections in the motor cortex of non-human primates involves initial overproduction followed by selective elimination and structural alterations.
在21只年龄从胚胎第41天（E41）到20岁的恒河猴中，测定了灵长类运动皮层（布罗德曼第4区）突触接触的密度和比例。为每个标本制备了2至4个垂直电子显微镜探针，每个探针由150 - 250张穿过皮层厚度的重叠显微照片组成。根据突触的形态（对称或不对称）、细胞位置（在棘突、轴突或胞体上）、数量以及层状分布比例进行分类。突触密度以每单位面积和神经毡体积（不包括神经元和胶质细胞体、髓鞘、血管和细胞外空间）来表示。在E53时，在边缘区（预期的第I层）和位于发育中的皮质板下方的短暂的亚板区观察到了新兴运动皮层区域的第一个突触。在妊娠中期左右（E89），在整个皮质板宽度上都观察到了突触，其密度约为每100立方微米神经毡5个。在妊娠的最后两个月，所有层的突触密度增加了8倍，在出生时（E165）达到约每100立方微米40个。突触生成在出生后仍在继续，到出生后第二个月末达到每100立方微米神经毡60个的水平，这比成年时高出两倍。这个水平以缓慢的速度下降，直到性成熟（3岁），然后更快地下降到成年水平，其特征是相对稳定在约每100立方微米30个。婴儿期峰值后突触密度的下降主要是以位于树突棘上的不对称突触为代价；树突轴突上的对称突触数量保持相对恒定。非人灵长类运动皮层中突触连接的发育涉及最初的过度生成，随后是选择性消除和结构改变。
