Accumulation of radioactive protein in mouse cerebral cortex after injection of 3H-fucose into the eye
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Tritiated fucose injected into the left eye of the mouse was incorporated into glycoprotein in the retinal ganglion cells, and then carried by axonal transport along the optic nerve to the right lateral geniculate body and superior colliculus. Incorporated label, about 10% of the level in the geniculate, subsequently appeared in the right visual cortex; however, even more was found in the retrosplenial cortex overlying the labeled colliculus. A similar picture was seen with 3H-proline as precursor. Interruption of the brachium of the right superior colliculus prevented label from reaching the colliculus; the amount of label in the retrosplenial cortex was reduced by 85% but there was no significant effect on labeling in the visual cortex. In radioautograms, the visual cortex on the side to which the injected eye projected showed an accumulation of silver grains with its peak (two to three times the average cortical level) in layer IV; the grain count profile was flat on the other side. In retrosplenial cortex overlying the labeled colliculus the grain count fell off with distance from the colliculus and a similar pattern was seen in hippocampus overlying the labeled geniculate. In all cases, the label appeared to be mostly over the neuropil rather than nerve cell bodies. These results suggest that the label in the visual cortex was localized in the endings of the geniculocortical fibers, and hence must initially have been transferred from optic nerve endings to neurons in the lateral geniculate body. Much of the label in the retrosplenial region and hippocampus, however, probably arrived by a non-neuronal route, possibly by diffusion from the superior colliculus and lateral geniculate body, respectively. Inhibition of protein synthesis by cycloheximide did not prevent the accumulation of label in the cortex, although the proportion appearing in the cortex relative to the amounts in the geniculate and colliculus was somewhat reduced. The possibility that some of the radioactivity may have been transferred in macromolecular form has therefore not been ruled out. © 1973.
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