Bipolar cells of the ground squirrel retina

Abstract

Parallel processing of an image projected onto the retina starts at the first synapse, the cone pedicle, and each cone feeds its light signal into a minimum of eight different bipolar cell types. Hence, the morphological classification of bipolar cells is a prerequisite for analyzing retinal circuitry. Here we applied common bipolar cell markers to the cone-dominated ground squirrel retina, studied the labeling by confocal microscopy and electron microscopy, and compared the resulting bipolar cell types with those of the mouse (rod dominated) and primate retina. Eight different cone bipolar cell types (three OFF and five ON) and one rod bipolar cell were distinguished. The major criteria for classifying the cells were their immunocytochemical identity, their dendritic branching pattern, and the shape and stratification level of their axons in the inner plexiform layer (IPL). Immunostaining with antibodies against Gγ13, a marker for ON bipolar cells, made it possible to separate OFF and ON bipolars. Recoverin-positive OFF bipolar cells partly overlapped with ON bipolar axon terminals at the ON/OFF border of the IPL. Antibodies against HCN4 labeled the S-cone selective (bb) bipolar cell. The calcium-binding protein CaB5 was expressed in two OFF and two ON cone bipolar cell types, and CD15 labeled a widefield ON cone bipolar cell comparable to the DB6 in primate.

Immunohistochemical identification and synaptic inputs to the diffuse bipolar cell type DB1 in macaque retina

“…Most of the diffuse bipolar cells in the primate retina are biased against S-cone contacts (Lee and Grünert, 2007), and, interestingly, the putative homologs of the DB1 bipolar in mouse (type-1, Ghosh et al, 2004) and ground squirrel (cb1 or former b7, Puller et al, 2011) are most likely M-cone selective (Breuninger et al, 2011; Li and DeVries, 2006). To determine the amount of S-cone input for DB1 cells, we double-labeled vertical sections and wholemounts with antibodies against SCGN and S-opsin (Fig.…”

Synaptic Elements for GABAergic Feed-Forward Signaling between HII Horizontal Cells and Blue Cone Bipolar Cells Are Enriched beneath Primate S-Cones

“…It was shown that NKCC is expressed in dendritic tips of ON bipolar cells, where it elicits an excitatory effect of GABA due to chloride accumulation [38], [40]–[42]. Furthermore, it is well-known that the blue cone bipolar cell is the major postsynaptic ON bipolar cell type of S-cones in various species including primate [54], [76], [87]–[89]. In summary, our findings suggest that there is a possibility of GABA release via HII horizontal cells beneath S-cones.…”

“…Antibodies against S-opsin were used to label the corresponding cones including their pedicles in macaque and ground squirrel [69], [75], [76]. The specificity of the antibody was tested by the manufacturer with a Western blot analysis using mouse retinal extract, revealing a single band at the predicted size of 40 kDa.…”

Specialized synaptic pathway for chromatic signals beneath S-cone photoreceptors is common to human, Old and New World primates

“…Goat polyclonal antibodies directed at the N-terminal peptide of human blue-sensitive opsin (Santa Cruz, sc-14363, dilution 1:100) used to label the corresponding cones including their pedicles in primates as well as other species [43, 44]. The specificity of the antibody was tested by the manufacturer with a Western blot analysis using mouse retinal extract, revealing a single band at the predicted size of 40 kDa.…”