Pearce Amy R, Marotte Lauren R
Developmental Neurobiology and Endocrinology Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 0200, Australia.
J Comp Neurol. 2003 Jun 23;461(2):205-16. doi: 10.1002/cne.10681.
The time course of development and laminar distribution of thalamocortical synapses in the visual cortex of the marsupial mammal the wallaby (Macropus eugenii) has been studied by electron microscopy from the time of afferent ingrowth to the appearance of layer 4, the main target for thalamic axons. Axons were labeled from the thalamus by a fluorescent carbocyanine dye in fixed tissue or by transneuronal transport of horseradish peroxidase conjugated to wheat germ agglutinin from the eye. Thalamic axons first reached the cortex 2 weeks after birth and grew into the developing cortical plate without a waiting period in the subplate. The first thalamocortical synapses were detected 2 weeks later solely throughout the loosely packed zone of the cortical plate, where layer 6 cells previously have been shown to reside. As the thickness of the cortex increased with age, thalamocortical synapses were increasingly prevalent in the loosely packed zone of the cortical plate. With the appearance of layer 4, thalamocortical synapses were found there as well as in the marginal zone and layer 6. There was no evidence for an early population of thalamocortical synapses in the subplate. The first synapses made by thalamic axons were in a region containing layer 6 cells, one of their normal targets in the mature cortex.
通过电子显微镜，从传入神经长入到第4层（丘脑轴突的主要靶区）出现的这段时间，对有袋类哺乳动物沙袋鼠（尤金袋鼠，Macropus eugenii）视觉皮层中丘脑皮质突触的发育时间进程和层状分布进行了研究。在固定组织中，用荧光碳氰染料标记丘脑轴突，或通过与麦胚凝集素偶联的辣根过氧化物酶的跨神经元运输，从眼睛标记丘脑轴突。丘脑轴突在出生后2周首次到达皮层，并长入发育中的皮质板，而不在亚板中等待。2周后，仅在皮质板疏松堆积区检测到第一批丘脑皮质突触，此前已证明第6层细胞位于该区域。随着皮层厚度随年龄增加，丘脑皮质突触在皮质板疏松堆积区越来越普遍。随着第4层的出现，在那里以及边缘区和第6层都发现了丘脑皮质突触。没有证据表明亚板中早期存在丘脑皮质突触。丘脑轴突形成的第一批突触位于含有第6层细胞的区域，这是它们在成熟皮层中的正常靶区之一。
