A light microscopic and electron microscopic study of the superficial layers of the superior colliculus of the tree shrew (Tupaia glis)

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Abstract
Histochemical, Golgi, and electron microscopic methods were used to study the superficial layers of the superior colliculus of the tree shrew. Following horseradish peroxidase injections in the dorsal lateral geniculate nucleus (LGd) and the pulvinar (Pul), retrogradely labeled somata were found in the upper two‐thirds and the lower third of the stratum griseum superficiale (SGS), respectively, as has been described by Albano et al. ('79). In tissue prepared with Golgi methods, somata, similar in location and shape to those projecting to the LGd, had narrow, vertically oriented dendritic arbors, which were confined to the upper two‐thirds of the SGS. Cells located in the lower third of the SGS had larger somata, similar to those projecting to the Pul, and wider dendritic arbors, which were confined to the lower two‐thirds of the SGS. Electron microscopic comparison of the number of degenerating terminals following enucleation and striate cortex lesion indicated that within the SGS terminals from the retina overwhelmingly outnumbered those from the cortex. In both types of material, degenerating terminals were observed throughout the SGS. However, the majority of the degenerating optic terminals were located in the upper SGS, whereas most of the degenerating striate terminals were found in the lower SGS. Thus, cells that project to the LGd and those that project to the Pul differ not only with respect to location, size, and dendritic morphology, but also with respect to the proportion of retinal and striate afferents which terminate in the region of their dendritic trees.