Bipolar cell diversity in the primate retina: Morphologic and immunocytochemical analysis of a New World monkey, the marmoset Callithrix jacchus

The aim of this study was to identify the bipolar cell types in the retina of a New World monkey, the common marmoset, and compare them with those fou nd in the Old World macaque monkey. Retinal whole-mounts, sections, or both , were stained by using DiI labeling and immunohistochemical methods. Semit hin sections were analyzed by using quantitative methods. We show that the same morphologic types of bipolar cell as described for the Old World macaq ue monkey by Boycott and Wassle (Boycott and Wassle [1991] Eur. J. Neurosci . 3:1069-1088) are present in marmoset retina: two types of midget bipolar cells, six type of diffuse bipolar cells, a blue cone bipolar cell, and one type of rod bipolar cell. The pattern of staining with different immunohis tochemical markers ("fingerprint") of each bipolar cell type in marmoset wa s also the same as described for macaque, with one exception: the flat midg et bipolar cell (FMB) class is labeled by antibodies to recoverin in macaqu e but is labeled by antibodies to CD15 in marmoset. The labeled FMB cells i n marmoset make contact with multiple cone photoreceptors throughout most o f the extrafoveal retina. The spatial density of bipolar cells in marmoset is shown to be sufficient to support one-to-one connectivity of midget bipo lar and ganglion cells in the fovea and to allow for parallel pathways to g anglion cells throughout the retina. Quantitative differences in the morpho logy and receptor connectivity between marmoset and macaque can be related to differences in cone and rod photoreceptor density between the species. W e conclude that bipolar cell diversity is a preserved feature of the primat e retina. (C) 2001 Wiley-Liss, Inc.