Conley M, Raczkowski D
Department of Psychology, Duke University, Durham, North Carolina 27706.
J Comp Neurol. 1990 Dec 8;302(2):425-36. doi: 10.1002/cne.903020218.
In this study we examined the organization of projections from the striate cortex to the dorsal lateral geniculate (GL) and pulvinar (PUL) nuclei in the prosimian Galago by using retrograde transport methods. Injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the PUL labeled two bands of cells in the striate cortex: the first consisted of large pyramidal cells in the upper half of layer V; the second consisted of small and medium-size pyramidal cells located in the deepest part of layer VI. The location of cells within layer VI coincided with a clear cytoarchitectonic sublayer, VIb, which contains fewer and paler staining cells than VIa. Injections of WGA-HRP involving all layers of the GL produced an uninterrupted band of pyramidal cells distributed throughout layer VI (a and b), including the region labeled after injections into the PUL. Thus as a first approximation, layer VI can be divided into an upper tier (VIa) that projects only to the GL and a lower tier (VIb) that projects to both the GL and PUL. Injections of WGA-HRP that were restricted to one or a few GL layers revealed a further refinement of the subdivisions within layer VI. Injections into the parvicellular and intercalated (or koniocellular) layers of the GL labeled neurons predominantly in the upper half of layer VIa, whereas injections restricted to the magnocellular layers labeled neurons in the lower half of layer VIa and in layer VIb. In order to determine whether individual neurons in layer VIb send axon collaterals to both the GL and PUL, we injected WGA-HRP into one nucleus and fluorescent rhodamine latex beads into the other. In three experiments, we found only one double-labeled cell. In sum, the results provide evidence that layer VI is divided into at least three sublayers: upper VIa, which projects to the intercalated and parvicellular GL layers; lower VIa, which projects to the magnocellular GL layers; and VIb, which sends separate projections to the magnocellular layers of the GL and to the PUL. The segregation observed is sufficiently discrete to propose the existence of multiple, descending pathways from layer VI of the striate cortex that complement those ascending from the GL and PUL.
在本研究中，我们运用逆行运输方法，研究了原猴类夜猴的纹状皮层向背外侧膝状体（GL）和丘脑枕（PUL）核的投射组织。将小麦胚凝集素结合辣根过氧化物酶（WGA-HRP）注入丘脑枕，标记了纹状皮层中的两条细胞带：第一条由位于第V层上半部分的大锥体细胞组成；第二条由位于第VI层最深部分的中小型锥体细胞组成。第VI层内细胞的位置与一个清晰的细胞构筑亚层VIb一致，该亚层比VIa含有更少且染色更浅的细胞。将WGA-HRP注入涉及外侧膝状体所有层的区域，产生了一条不间断的锥体细胞带，分布在整个第VI层（a和b），包括注入丘脑枕后标记的区域。因此，初步估计，第VI层可分为仅投射到外侧膝状体的上层（VIa）和投射到外侧膝状体及丘脑枕的下层（VIb）。将WGA-HRP注入外侧膝状体的一层或几层所进行的实验，揭示了第VI层内细分的进一步细化。注入外侧膝状体的小细胞层和中间层（或小细胞层），主要标记了第VIa层上半部分的神经元，而仅注入大细胞层则标记了第VIa层下半部分和第VIb层的神经元。为了确定第VIb层中的单个神经元是否向外侧膝状体和丘脑枕都发送轴突侧支，我们将WGA-HRP注入一个核，将荧光罗丹明乳胶珠注入另一个核。在三个实验中，我们仅发现了一个双标记细胞。总之，结果提供了证据，表明第VI层至少分为三个亚层：上层VIa，投射到中间层和小细胞层的外侧膝状体；下层VIa，投射到大细胞层的外侧膝状体；以及VIb，分别向外侧膝状体的大细胞层和丘脑枕发送投射。观察到的分离足够离散，表明存在从纹状皮层第VI层下行的多条通路，这些通路与从外侧膝状体和丘脑枕上行的通路相互补充。
