Coogan T A, Burkhalter A
Department of Neurosurgery, Washington University School of Medicine, St. Louis, Missouri 63110.
J Comp Neurol. 1988 Dec 8;278(2):242-52. doi: 10.1002/cne.902780207.
In these experiments we have asked whether the projection from the rat's primary visual cortex, area 17, to the extrastriate visual cortical area 18a is formed in a sequence and whether that sequence resembles the pattern of inside-out cortical neurogenesis. For this purpose fluorescent retrograde tracers were injected into area 18a at different postnatal ages (P1, P5, adult). Animals survived until 3-4 weeks of age, after migration is complete and neurons have arrived at their final laminar location. In the ipsilateral cortex, P1 injections retrogradely labeled cells in layers 5 and 6 of area 17. Labeling after P5 injections extended into more superficial layers and included the bottom of layer 2/3 and layers 4-6. After P5, more labeled cells were found at the top of layer 2/3, producing the adult laminar pattern, where the projection originates predominantly from layer 2/3. A similar sequence of laminar labeling was observed in the transcallosal connection of area 18a. This sequence of labeling, deep layers before superficial, resembles the pattern in which cortical neurons are born and indicates that axons arrive at their cortical targets in the order the cells were generated.
在这些实验中，我们探究了大鼠初级视觉皮层（17区）到纹外视觉皮层18a区的投射是否按顺序形成，以及该顺序是否类似于皮层由内向外神经发生的模式。为此，在不同的出生后年龄（出生后第1天、第5天、成年）将荧光逆行示踪剂注入18a区。动物存活至3 - 4周龄，此时迁移已完成，神经元已到达其最终的层状位置。在同侧皮层中，出生后第1天注射示踪剂逆行标记了17区第5层和第6层的细胞。出生后第5天注射后的标记延伸到更浅的层，包括第2/3层底部和第4 - 6层。出生后第5天之后，在第2/3层顶部发现了更多标记细胞，形成了成年层状模式，其中投射主要起源于第2/3层。在18a区的胼胝体连接中也观察到了类似的层状标记顺序。这种先深层后浅层的标记顺序类似于皮层神经元产生的模式，表明轴突按照细胞产生的顺序到达其皮层靶点。
