No abstract

Rod bipolar cells in the macaque monkey retina were labeled by three antibodies: an antibody against the alpha- and beta-subspecies of protein kinase C (PKC), a polyclonal antiserum against the L7 protein from mouse cerebellum, and a monoclonal antibody against rabbit olfactory bulb (MAb 115A 10). The MAb 115A10 antibody also labeled some cone bipolar and some amacrine cells. The antibody against PKC was used to study the synaptic connectivity of rod bipolar cells. Reconstructions of 28 rod spherules showed that usually two and up to four rod bipolar processes invaginate each rod spherule. Six rod bipolar axons in the inner plexiform layer were reconstructed; they all showed the same pattern of connectivity. Synaptic output at rod bipolar dyads usually was onto two amacrine cell profiles: one that resembled the All amacrine cell and another that frequently made a reciprocal synapse. Rod bipolar cells did not contact ganglion cells. Synaptic input to rod bipolar cells came from reciprocal amacrine cells at dyads and other amacrine cells. In these respects, the rod pathway in the monkey is very similar to that described in cat and rabbit. The density of rod bipolar cells was determined and compared with the density of rods. There is a maximum of 15,000-20,000 rod bipolar cells/mm2 at 1-3 mm eccentricity, close to where rod density is maximum. Rod density is 10 times higher than rod bipolar cell density within 2 mm of the fovea, and 30 times higher at 15 mm eccentricity. This change in relative density is compensated by an increase in the number of rods contacted by individual rod bipolar cells (seen in Golgi-stained whole-mount retina) so that the number of rod bipolar terminal boutons in each rod photoreceptor remains relatively constant with changing eccentricity. We estimate that each rod bipolar cell is contacted by about 20 rods at 2-4 mm eccentricity and about 60 rods at 6-7 mm eccentricity.

To understand the transmission of sensory signals in visual pathways we studied the morphology and central projection of ganglion cell populations in marmoset monkeys. Retinal ganglion cells were labeled by photofilling following injections of retrograde tracer in the lateral geniculate nucleus (LGN), or by intracellular injection with neurobiotin. Ganglion cell morphology was analyzed using hierarchical cluster analysis. In addition to midget and parasol ganglion cells, this method distinguished three main clusters of wide-field cells that correspond to small bistratified, sparse, and broad thorny cells identified previously. The small bistratified and sparse cells occupy neighboring positions on the hierarchical (linkage distance) tree. These cell types are presumed to carry signals originating in short-wavelength sensitive (S or "blue") cones in the retina. The linkage distance from these putative S-cone pathway ganglion cells to other wide-field cells is similar to the linkage distance from midget cells to parasol cells, suggesting that S-cone cells form a distinct functional subgroup of ganglion cells. Small bistratified cells and large sparse cells were the most commonly labeled wide-field cells following LGN injections in koniocellular layer K3. This is consistent with physiological evidence that the role of this layer includes transmission of S-cone signals to the visual cortex. Other wide-field cell types were also labeled following injections including K3, and other koniocellular LGN layers; these cell types may correspond to "non-blue koniocellular" receptive fields recorded in physiological studies.