Friedman B, Price J L
J Comp Neurol. 1986 Apr 1;246(1):1-19. doi: 10.1002/cne.902460102.
In order to assess the role of input-target interactions in the development of olfactory cortex, the primary afferent fibers from the olfactory bulb to the superficial part of layer I of the cortex (layer Ia) were removed in developing and mature rats. After survival periods that vary from a few days to 2-6 months, changes were assessed in (1) the radial thickness of layer I, (2) the laminar distribution of intracortical associational fibers, which normally terminate in a deep part of layer I (layer Ib), and (3) the distribution of glia in layer I. The findings indicate that the lamination of fibers within layer I is not intrinsically prespecified, but gradually becomes "set" during the first month after birth. If the fibers from the olfactory bulb are removed, the dendrites of cortical cells are capable of accepting inputs from other fiber systems, depending on the maturational state of the dendrites and the ingrowing axons. Development of the abnormal inputs is associated with relatively normal dendritic growth, whereas lack of adequate input results in dendritic atrophy. Thus, after neonatal bulb ablation, the intracortical fibers occupy both superficial and deep parts of layer I, and a normal synaptic density is established throughout the layer. Layer I also develops to nearly its normal adult thickness, although the high density of glia that normally characterizes layer Ia is not apparent. With bulb ablation at progressively older ages (from postnatal day (P-) 3 to 21), the cortical associational fibers show progressively less extension into the denervated layer Ia. Layer I continues to grow, but not to the same extent as after P-1 ablations. In these experiments the glia distribution resembles the pattern present at the time of denervation. After adult olfactory bulb ablation, the long intracortical fibers extend very little into layer Ia, which undergoes pronounced shrinkage and becomes filled with a high concentration of glia. However, partial reinnervation of layer Ia is accomplished by the proliferation of a normally sparse native fiber system, which has been identified only with the Timm method. These results are interpreted as evidence that the normal development of lamination of afferent fibers to the olfactory cortex depends on axodendritic interaction during development.
为了评估输入 - 靶标相互作用在嗅觉皮层发育中的作用，在发育中和成年大鼠中去除了从嗅球到皮层I层浅部（Ia层）的初级传入纤维。在从几天到2 - 6个月不等的存活期后，评估了以下方面的变化：（1）I层的径向厚度；（2）通常终止于I层深部（Ib层）的皮质内联合纤维的层状分布；（3）I层中胶质细胞的分布。研究结果表明，I层内纤维的分层并非内在预先确定的，而是在出生后的第一个月内逐渐“固定”。如果去除来自嗅球的纤维，皮质细胞的树突能够接受来自其他纤维系统的输入，这取决于树突和向内生长的轴突的成熟状态。异常输入的发育与相对正常的树突生长相关，而缺乏足够的输入则导致树突萎缩。因此，新生期切除嗅球后，皮质内纤维占据I层的浅部和深部，并在整个层中建立了正常的突触密度。I层也发育到接近其正常的成年厚度，尽管通常表征Ia层的胶质细胞高密度并不明显。随着在逐渐增大的年龄（从出生后第（P -）3天到21天）进行嗅球切除，皮质联合纤维向去神经支配的Ia层的延伸逐渐减少。I层继续生长，但程度不如P - 1切除后。在这些实验中，胶质细胞分布类似于去神经支配时的模式。成年期切除嗅球后，长的皮质内纤维很少延伸到Ia层，Ia层经历明显收缩并充满高浓度的胶质细胞。然而，Ia层的部分重新支配是通过一个通常稀疏原生纤维系统的增殖完成的，该系统仅用Timm方法得以识别。这些结果被解释为证据，表明传入纤维到嗅觉皮层的分层正常发育依赖于发育过程中的轴突 - 树突相互作用。
