Barbaresi P, Guandalini P, Manzoni T
Institute of Human Physiology, University of Ancona, Italy.
J Comp Neurol. 1995 Sep 18;360(2):319-30. doi: 10.1002/cne.903600209.
The present light and electron microscopic experiments were carried out on the first somatic sensory area (SI) of cats to determine the laminar distribution of axon terminals from the ipsilateral second somatic sensory area (SII) and to identify the types of synapses between these terminals and the neuronal elements of SI. Phaseolus vulgaris-leucoagglutinin (PHA-L) was iontophoretically injected into multiple sites and at different cortical depths of the forepaw representation zone of SII. Fixed brain blocks containing the injected SII and ipsilateral SI were cut into slices and processed immunocytochemically to stain PHA-L-filled fibers and terminals. Light microscopic examination of SI revealed patches of anterograde labeling in the forepaw representation zone, concentrated mainly in supragranular layers. In these layers, thin immunolabeled fibers branched extensively and formed a dense plexus that was more prominent in layers II and I. Conversely, the infragranular layers contained fragments of vertically oriented thick fibers that rarely emitted axon collaterals. PHA-L-labeled axons had numerous swellings along their course, interpreted as boutons en passant, and stalked boutons. Of 19,661 labeled terminals (17,833 beads and 1,828 stalked boutons), 84.74% were observed in supragranular layers, with the highest concentration in layer II (33.15%) and lower in layers I (26.27%) and III (25.30%). The proportion of terminals was lower in layers IV (6.49%) and V (5.45%) and lowest in layer VI (3.32%). These counts also showed that boutons en passant were the majority (90.70%) and stalked boutons, the minority (9.30%). The ratio of these two types of presynaptic specializations was similar (9:1) in all six layers. Electron microscopic examination of the labeled regions of SI showed that both axon swellings and stalked boutons formed synapses of the asymmetric type with SI neuronal elements. The majority (85.37%) of a sample of 130 labeled terminals synapsed on SI neurons in layers I-III. The identified postsynaptic profiles were dendritic spines (61.11%) or medium-sized and small dendrites (38.89%). These results are discussed in relation to those of a companion study on the laminar pattern of the projection from SI to SII of cats (P. Barbaresi, A. Minelli, and T. Manzoni, 1994, J. Comp. Neurol. 343:582-596). Based on the anatomical organization of these reciprocal connections, there seems to be no clear hierarchicalal relationship between SI and SII in cats.
本研究采用光镜和电镜技术，对猫的第一躯体感觉区（SI）进行实验，以确定来自同侧第二躯体感觉区（SII）的轴突终末的层状分布，并识别这些终末与SI神经元成分之间的突触类型。将菜豆白细胞凝集素（PHA-L）离子导入SII前爪代表区的多个部位和不同皮质深度。将含有注射了PHA-L的SII和同侧SI的固定脑块切成薄片，并进行免疫细胞化学处理，以标记充满PHA-L的纤维和终末。对SI进行光镜检查发现，前爪代表区有顺行标记斑，主要集中在颗粒上层。在这些层中，细的免疫标记纤维广泛分支，形成一个密集的神经丛，在II层和I层更为明显。相反，颗粒下层含有垂直排列的粗纤维片段，很少发出轴突侧支。PHA-L标记的轴突在其行程中有许多膨体，被解释为旁触体，还有有柄突触小体。在19661个标记终末（17833个珠状终末和1828个有柄突触小体）中，84.74%见于颗粒上层，其中II层浓度最高（33.15%），I层（26.27%）和III层（25.30%）较低。IV层（6.49%）和V层（5.45%）的终末比例较低，VI层最低（3.32%）。这些计数还表明，旁触体占多数（90.70%），有柄突触小体占少数（9.30%）。这两种突触前特化类型的比例在所有六层中相似（9:1）。对SI标记区域的电镜检查表明，轴突膨体和有柄突触小体均与SI神经元成分形成不对称型突触。在130个标记终末样本中，大多数（85.37%）与I-III层的SI神经元形成突触。已识别的突触后形态为树突棘（61.11%）或中小型树突（38.89%）。结合一项关于猫从SI到SII投射的层状模式的相关研究结果（P. Barbaresi、A. Minelli和T. Manzoni，1994年，《比较神经学杂志》343:582-596）对这些结果进行了讨论。基于这些相互连接的解剖结构，猫的SI和SII之间似乎没有明显的层级关系。
