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B Chen, QL Cao, HM Petry; Distribution of Calcium Binding Proteins in the Central Visual System of the Tree Shrew . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2626.
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Purpose: The non-random and often complementary distribution of calcium binding proteins (CBPs) in the mammalian visual system (particularly in the primate lateral geniculate nucleus (LGN)) has prompted suggestions that these proteins may differentiate pathways involved in different visual functions. In the tree shrew dLGN, the small cell layers (3 & 6) that receive input from the retina and superior colliculus are heavily labeled by calbindin (CB) and very lightly by parvalbumin. On the other hand, medium and large cell layers 1, 2, 4 & 5 are heavily labeled by PV and only minimally labeled by CB (Diamond et al., 1993). This pattern is also reflective of cytochrome oxidase (CO) labeling in the dLGN (dark reactivity of 1, 2, 4 &5, and pale in 3&6). This study examined whether the distribution of CB and PV in visual cortex (VC) and superior colliculus (SC) maintained this pathway differentiation in the tree shrew. Methods: Brain tissues were obtained from adult tree shrews (Tupaia belangeri) perfused with 4% paraformaldehyde, frozen-sectioned at 30µ m and processed for immunocytochemistry (anti-Parvalbumin, Sigma; anti-Calbindin D-28Kd, Sigma) using standard ABC methods and standard histochemical procedures for CO reactions. Results: In the dLGN: CB and PV labeling followed the pattern previously described (see above). In superior colliculus, clear differences were seen. CB label was concentrated in large cells in the superficial gray and in fibers and fiber bundles in the stratum opticum. Also scattered cells in the deeper layers were labeled. In contrast, PV labeled cells were scattered across all layers including the stratum zonale. In visual cortex (V1) CB labeled a large number of small cells in layers II & IIIa and a higher concentration of cells in IVa&IVb. Less frequent labeling of mostly large cells (including pyramidal neurons) was seen in the remaining layers and white matter, except for layer I which contained no CB. In contrast, PV labeled widely scattered cells of similar morphology in layers II through VI and very few cells in the white matter. As has been reported, CO reactivity labeled layers IIIb, IVa, IVm, & VI. Conclusion: As is the case in the tree shrew dLGN, the calcium binding proteins CB and PV are distinctive markers in visual cortex and superior colliculus. However, these markers are not always specific to small or large cells, nor do they necessarily label cells in the same pathways that are differentiated in the dLGN. Furthermore, neither CB nor PV parallels the CO reactivity in tree shrew visual cortex..
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