Interplexiform cells in macaque monkey retina

The presence of interplexiform cells in primate retina has been disputed, with the dopaminergic interplexiform cell in the New World monkey being the most fully understood. We have examined interplexiform cells in the Old World monkey using immunocytochemistry with the peroxidase-antiperoxidase method of visualization. In several species of macaque retina, two types of interplexiform cells are found. One stains with antisera to tyrosine hydroxylase, a biosynthetic enzyme for dopamine, and the other stains with antisera to gamma aminobutyric acid (GABA). The cell bodies of these two populations of interplexiform cells are located among the amacrine cells in the inner nuclear layer, and they send processes into both the inner and outer plexiform layers. GABA-positive interplexiform processes to the outer plexiform layer arise from the cell body while tyrosine hydroxylase-positive interplexiform processes most often originate from the heavily tyrosine hydroxylase-stained sublamina one of the inner plexiform layer. Cell-body diameter measurements and morphology suggest that these are different neuronal populations.