Nakazawa M, Koh T, Kani K, Maeda T
Department of Ophthamology, Shiga University of Medical Science, Japan.
Brain Res Dev Brain Res. 1992 Mar 20;66(1):77-90. doi: 10.1016/0165-3806(92)90143-k.
The transient aggregation of serotonin (5-HT)-containing fibers in the early development of rat visual cortex was examined immunohistochemically. The aggregation of 5-HT immunoreactive (IR) fibers consisted of three stages which were classified according to the course of time and degree of space occupied. The primary aggregation appeared in the subplate and moved upward along the development of the cortex. The aggregation proceeded to the secondary stage in presumptive layer IV. The fibers extended in a column-like structure following the secondary aggregation and formed the tertiary aggregation. The upper edge of the tertiary aggregation formed a lattice-like pattern in layer I and its structure was recognized to be similar to the structure of a 'blob' which characterizes the primary visual cortex in monkey. This transient aggregation of 5-HT-IR fibers began in the subplate of the anterior visual cortex on postnatal day 2 (PND 2) and progressed towards the posterior. On PND 11, the secondary and tertiary aggregations were completed in the entire region. No further aggregation of 5-HT-IR fibers was observed on PND 15. The anterior-to-posterior axis in the aggregation process corresponds to the direction of differentiation in the layer structure of cortex. In order to investigate the relationship between the transient aggregation of 5-HT-IR fibers and the development of the visual pathway, the secondary and tertiary aggregation on PND 11 were observed after postnatal monocular or binocular enucleation. Enucleation of eye balls did not affect either the area occupied by the 5-HT-IR fibers in the secondary aggregation or the number of column structures in the tertiary aggregation. However, the contralateral and ipsilateral cortices of monocularly enucleated cases were irregularly shaped in the secondary aggregation. The distribution of 5-HT-IR fiber terminals in the binocular area (Oc1B) increased in density on the contralateral side in the monocular enucleation, while that of both sides in the binocular enucleation was of non-homogeneous density and were shaped irregularly. The above results suggest that the transient aggregation of 5-HT-IR fibers observed in the early stage of development of visual cortex is regulated primarily by the intrinsic factors, and that extrinsic factors, such as visual pathway input, affect the aggregation within the boundary of such intrinsic factors. That is, the visual pathway input and the input balance from both eyes affect the distribution density of 5-HT-IR fibers and the shape of the visual cortex, respectively.
采用免疫组织化学方法研究了大鼠视皮层早期发育过程中含5-羟色胺（5-HT）纤维的短暂聚集情况。5-HT免疫反应性（IR）纤维的聚集分为三个阶段，根据时间进程和所占空间程度进行分类。初级聚集出现在板下层，并随着皮层的发育向上移动。聚集进入推测的第IV层的次级阶段。纤维在次级聚集后呈柱状结构延伸，形成三级聚集。三级聚集的上边缘在第I层形成网格状图案，其结构被认为与猴子初级视皮层中“斑点”的结构相似。这种5-HT-IR纤维的短暂聚集在出生后第2天（PND 2）开始于视皮层前部的板下层，并向后发展。在PND 11时，次级和三级聚集在整个区域完成。在PND 15时未观察到5-HT-IR纤维的进一步聚集。聚集过程中的前后轴与皮层层结构的分化方向相对应。为了研究5-HT-IR纤维的短暂聚集与视通路发育之间的关系，在出生后单眼或双眼摘除后观察了PND 11时的次级和三级聚集情况。眼球摘除既不影响次级聚集中5-HT-IR纤维所占面积，也不影响三级聚集中柱状结构的数量。然而，单眼摘除病例的对侧和同侧皮层在次级聚集中形状不规则。单眼摘除时，双眼区域（Oc1B）中5-HT-IR纤维终末的对侧分布密度增加，而双眼摘除时两侧的密度不均匀且形状不规则。上述结果表明，视皮层发育早期观察到的5-HT-IR纤维的短暂聚集主要受内在因素调节，而外在因素，如视通路输入，在这种内在因素的边界内影响聚集。也就是说，视通路输入和双眼的输入平衡分别影响5-HT-IR纤维的分布密度和视皮层的形状。
