Rockland K S
Department of Neurology, University of Iowa, College of Medicine, Iowa City 52242, USA.
J Comp Neurol. 1996 Apr 22;368(1):57-87. doi: 10.1002/(SICI)1096-9861(19960422)368:1<57::AID-CNE5>3.0.CO;2-J.
Corticopulvinar axons were anterogradely labeled by Phaseolus vulgaris-leucoagglutinin injections in the occipitotemporal cortex of the macaque to determine quantitative parameters of divergence and convergence, arbor size and shape, and distribution of terminal specializations. Forty individual axons were analyzed by serial section reconstruction and divided into two major groups. The majority of axons have numerous (typically 500-1,000) small, spinous endings (boutons terminaux). These axons have terminal fields that are beam-like or elongated (E, corresponding to classical type 1) and highly divergent (1.0-3.0 mm). These frequently innervate several of the traditionally designated pulvinar subdivisions; namely inferior pulvinar (PI) and the ventral part of interal pulvinar (PL); medial pulvinar (PM) and dorsal PL, and (one axon) PM, dorsal PL, and PI. Some axons, however (R or round, corresponding to classical type 2), have a small number (typically 70-160) of primarily large, beaded endings (boutons en passant), which concentrate in sharply delimited, round arbors (diameters 100-125 microns). R axons appear to be larger caliber than E axons (1.0-1.5 microns vs. 0.5-1.0 micron, respectively). These differences in phenotype are probably associated with distinct types of projection neurons. In visual areas, corticopulvinar terminations are reported to originate from pyramidal cell subpopulations in layer 5. Indirect evidence, presented here, suggests that the more numerous medium-sized neurons give rise to E axons, and the sparser giant pyramids give rise to R corticopulvinar axons. If this is correct, corticopulvinar connectivity may be involved in multiple transformations. Spatially, axons of giant neurons (with basal dendrites that collect intracortically from a disc-like area, about 1.0 mm in diameter) converge onto a small number of pulvinar neurons. Axons of medium neurons (with basal dendrites that occupy a small intracortical disc, about 0.3 mm in diameter) diverge over 1.0-3.0 mm in the pulvinar and may form many contacts. Giant neurons, although numerically few in relation to medium pyramids (1 or 2: 50?), are likely to have distinctive membrane properties (functionally equivalent to bursting neurons?). Their larger boutons and axon caliber may be associated with a faster transmission that compensates for their small numbers. In primates, the E and R duality does not characterize cortical projections to the caudate, lateral geniculate nucleus, pons, or superior colliculus and thus may be essentially linked to pulvinar-specific processes.
通过将菜豆白细胞凝集素注射到猕猴枕颞叶皮质中，对皮质丘脑轴突进行顺行标记，以确定发散和汇聚的定量参数、树突大小和形状以及终末特化的分布。通过连续切片重建分析了40条单个轴突，并将其分为两大组。大多数轴突有许多（通常为500 - 1000个）小的、有棘的终末（终末小体）。这些轴突具有束状或细长的终末场（E，对应于经典的1型），并且高度发散（1.0 - 3.0毫米）。它们经常支配几个传统上指定的丘脑亚区；即下丘（PI）和内丘腹侧部分（PL）；内侧丘（PM）和背侧PL，以及（一条轴突）PM、背侧PL和PI。然而，一些轴突（R或圆形，对应于经典的2型）有少量（通常为70 - 160个）主要是大的、串珠状的终末（旁支终末），这些终末集中在界限分明的圆形树突中（直径100 - 125微米）。R轴突的直径似乎比E轴突大（分别为1.0 - 1.5微米和0.5 - 1.0微米）。这些表型差异可能与不同类型的投射神经元有关。在视觉区域，据报道皮质丘脑终末起源于第5层中的锥体细胞亚群。这里提供的间接证据表明中等大小神经元数量较多，产生E轴突，而稀疏的巨型锥体产生R皮质丘脑轴突。如果这是正确的，则皮质丘脑连接可能参与多种转换。在空间上，巨型神经元（其基底树突从直径约为1.0毫米的盘状区域在皮质内收集信息）的轴突汇聚到少数丘脑神经元上。中等神经元（其基底树突占据直径约为0.3毫米的小皮质盘）在丘脑中发散超过1.0 - 3.0毫米，并且可能形成许多接触。巨型神经元虽然在数量上相对于中等锥体较少（1或2：50？），但可能具有独特的膜特性（在功能上等同于爆发性神经元？）。它们较大的终末和轴突直径可能与更快的传导相关，以补偿其数量较少的情况。在灵长类动物中，E和R的二元性并不表征皮质到尾状核、外侧膝状体、脑桥或上丘的投射，因此可能基本上与丘脑特异性过程相关。
