Gradients of protein kinase C substrate phosphorylation in primate visual system peak in visual memory storage areas

Two protein kinase C (PKC) substrates of 50 and 81 kDa display topographical gradients in 32P-incorporation along the occipitotemporal visual processing pathway in rhesus monkey cerebral cortex. The 50 kDa protein appears to be homologous to protein F1 from rat (47 kDa) on the basis of isoelectric point, two-dimensional phosphopeptide maps, and kinase specificity, while the 81 kDa protein is probably the same as a previously described PKC substrate. The phosphorylation of protein F1 and 81 kDa was significantly higher in temporal regions of the occipitotemporal pathway, which have been implicated in the storage of visual representations, than in occipital regions, which appear to be less important for visual memory functions. These results suggest that the PKC phosphorylation system, which has been related previously to changes in neural plasticity, plays a progressively greater role in later stages of visual processing, and that this role may involve the storage of visual information in inferotemporal cortical areas.