Chromatic Bipolar Cell Pathways in the Mouse Retina

Abstract

Like most mammals, mice feature dichromatic color vision based on short (S) and middle (M) wavelength-sensitive cone types. It is thought that mammals share a retinal circuit that in dichromats compares S-and M-cone output to generate blue/green opponent signals, with bipolar cells (BCs) providing separate chromatic channels. Although S-cone-selective ON-BCs (type 9 in mouse) have been anatomically identified, little is known about their counterparts, the M-cone-selective OFF-BCs. Here, we characterized cone connectivity and light responses of selected mouse BC types using immunohistochemistry and electrophysiology. Our anatomical data indicate that four (types 2, 3a/b, and 4) of the five mouse OFF-BCs indiscriminately contact both cone types, whereas type 1 BCs avoid S-cones. Light responses showed that the chromatic tuning of the BCs strongly depended on their position along the dorsoventral axis because of the coexpression gradient of M-and S-opsin found in mice. In dorsal retina, where coexpression is low, most type 2 cells were green biased, with a fraction of cells (Ϸ14%) displaying strongly blue-biased responses, likely reflecting S-cone input. Type 1 cells were also green biased but did not comprise blue-biased "outliers," consistent with type 1 BCs avoiding S-cones. We therefore suggest that type 1 represents the green OFF pathway in mouse. In addition, we confirmed that type 9 BCs display blue-ON responses. In ventral retina, all BC types studied here displayed similar blue-biased responses, suggesting that color vision is hampered in ventral retina. In conclusion, our data support an antagonistically organized blue/green circuit as the common basis for mammalian dichromatic color vision.

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

“…Thus, the center response of the DB1 bipolar cell is expected to comprise a luminance signal without spectral bias. Interestingly, the putative homologs in mouse (Type 1, Ghosh et al, 2004) and ground squirrel (cb1 or former b7, appear to follow the more general pattern in that they avoid blue cones and selectively contact L/M-cones (Li and DeVries, 2006;Breuninger et al, 2011). Although we did observe rare examples of DB1 contacts with rod photoreceptors, such contacts were only seen at ≈0.03% of rod photoreceptors and were not made by all DB1 cells.…”

“…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, 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.…”

Light-Driven Calcium Signals in Mouse Cone Photoreceptors

“…We used a custom-built two-photon (2P) microscope (Denk et al, 1990) as described earlier (Euler et al, 2009;Breuninger et al, 2011). In brief, the system was equipped with a mode-locked Ti/sapphire laser (MaiTai-HP DeepSee; Newport Spectra-Physics) tuned to ϳ860 nm, two detection channels for fluorescence imaging of eCFP [483 band pass (BP) 32; AHF] and citrine (535 BP 50; AHF) and a 20ϫ water-immersion objective (XLUMPlanFL 20ϫ water-immersion, 0.95 NA; Olympus).…”

“…A custom-built dichromatic light stimulator (Breuninger et al, 2011) was mounted below the recording chamber and consisted of two bandpass-filtered (UV: 360 BP 12; green: 578 BP 10; AHF) LEDs. Their light was combined by a beam-splitter (400 DCLP; AHF) focused by an achromatic air condenser lens (0.8 NA, HDIC; Zeiss) and projected through the glass bottom of the recording chamber.…”

Imaging Ca²⁺ Dynamics in Cone Photoreceptor Axon Terminals of the Mouse Retina

“…Note: Any upright two-photon microscope that fulfils the following minimal requirements can be used: It has to be equipped with (a) a pulsed laser tuneable to ~860 nm, (b) a minimum of two simultaneously acquired fluorescence channels, (c) filters for eCFP and citrine fluorescence, (d) a light stimulator (for possible designs, see 24,26 ), and (e) software that allows recording time-lapsed image sequences at a frame rate sufficient to resolve the Ca 2+ signals of interest.…”