Two types of cone bipolar cells, the blue cone
bipolar cell and the diffuse bipolar cell (DB3), were labelled
immunohistochemically and investigated in the retina of
a New World monkey, the marmoset. Blue cone bipolar cells
were labelled with an antiserum against cholecystokinin.
Short-wavelength-sensitive (SWS) cones were labelled with
an antiserum against the SWS cone opsin. The DB3 cells
were labelled with antibodies to calbindin. Blue cone bipolar
cells in marmoset do not form a regular mosaic but instead
follow the random distribution of the SWS cones. Nevertheless,
the SWS cone to blue cone bipolar cell connectivity in
marmoset is very similar to that previously described for
macaque. In contrast to the blue cone bipolar cells, the
DB3 cells form a regular mosaic. The synaptic connectivity
of DB3 cells in the inner plexiform layer was analyzed.
They make output synapses onto ganglion cells and amacrine
cells, and gap junctions with each other. Our results provide
further evidence for the existence of parallel bipolar
cell pathways in the primate retina and support the view
that the retinae of Old World and New World primates have
common neuronal connectivity. The random distribution of
SWS cones and blue cone bipolar cells is an exception to
the general rule of a regular mosaic distribution of cell
populations in the retina.