Rockland K S, Virga A
Department of Anatomy, Boston University School of Medicine, MA 02118.
Vis Neurosci. 1990 Jan;4(1):11-28. doi: 10.1017/s095252380000273x.
The present study uses the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L), to investigate the detailed morphology of individual axons projecting from area V1 to prestriate area V2. Observations are derived from serial reconstructions of 45 axons. Axons are found to differ both in laminar distribution and in arbor size. The majority (25/45; 56%) terminate in the upper half of layer 4 and the lower part of layer 3. Terminal clusters typically measure about 200 microns in diameter (dimensions are uncorrected for shrinkage), and are either in one, two, or occasionally three patches. Patches are separated by 200-500 microns. Of these 25 axons, four also have minor collaterals to layer 5. Of the remaining 20 axons in our sample, eight have one or two terminal arbors (about 200 microns in diameter) mainly in layer 3; another eight have terminations, organized as a single field (about 350 microns in diameter), within layer 4; and four axons have much larger terminal fields (1.0-1.2 mm x 0.3 mm), in layers 3 and 4. These morphological differences might constitute a gradient or, alternately, indicate distinct subgroups within the striate efferent population. Large terminal fields are asymmetrical, with their long axis oriented in an anterior-posterior fashion toward the depth of the lunate sulcus. Axons with two terminal arbors have a similar bias. As this arrangement is approximately perpendicular to the border of V1, we suggest that striate axons may be extended preferentially along the length of the stripelike compartments in V2. These compartments are also arrayed perpendicular to the border between areas V1 and V2. Reconstruction of small groups of 2-4 convergent axons demonstrates that axons with different morphology (i.e. large or small terminal fields) can occur within the same projection focus. Terminal arbors belonging to different axons can overlap, but tend not to be superimposed exactly.
本研究使用顺行示踪剂菜豆白细胞凝集素（PHA-L）来研究从V1区投射到纹前区V2的单个轴突的详细形态。观察结果来自于对45个轴突的连续重建。发现轴突在层状分布和树突大小上均存在差异。大多数轴突（25/45；56%）终止于第4层的上半部分和第3层的下半部分。终末簇的直径通常约为200微米（尺寸未针对收缩进行校正），且终末簇要么呈一个、两个，偶尔呈三个斑块状。斑块之间相隔200 - 500微米。在这25个轴突中，有4个在第5层也有小的侧支。在我们样本中的其余20个轴突中，8个在第3层主要有一个或两个终末树突（直径约200微米）；另外8个在第4层有组织成单个区域（直径约350微米）的终末；4个轴突在第3层和第4层有大得多的终末区域（1.0 - 1.2毫米×0.3毫米）。这些形态学差异可能构成一个梯度，或者相反，表明纹状传出神经元群体内存在不同的亚组。大的终末区域是不对称的，其长轴以前后方向朝向月状沟的深度。具有两个终末树突的轴突也有类似的偏向。由于这种排列大致垂直于V1的边界，我们认为纹状轴突可能优先沿着V2中条纹状区室的长度延伸。这些区室也垂直于V1和V2区域之间的边界排列。对2 - 4个汇聚轴突的小群体进行重建表明，具有不同形态（即大或小的终末区域）的轴突可以出现在同一投射焦点内。属于不同轴突的终末树突可以重叠，但往往不会完全重叠。
