Lucifer yellow potassium salt

In retinal slices, RBC somas were identified with an upright microscope (Nikon Eclipse E600FN) equipped with an infrared GP-CAM3 Altair Astro camera, differential interference contrast (DIC) optics, and epifluorescence illumination. 0.03% Lucifer yellow potassium salt (Sigma Aldrich) or 2% biocytin (Sigma Aldrich) was added to the intracellular solution to label recorded cells. Lucifer yellow-labeled cells were visualized live during the electrophysiological recording whereas whole-mounts containing biocytin labeled cells were fixed with 4% PFA for 15 min for subsequent immunohistochemical analysis. Light-induced voltage responses were recorded in a subset of cells to confirm typical light-activated RBC responses (Euler and Masland, 2000 (link); Pang et al., 2004 (link)). The two-second long blue (500 nm) light stimulus was generated with a pE-4000 epi-fluorescence light source from CoolLED. The light intensity was reduced to 9.6 × 10⁹ photons cm⁻² s⁻¹ using ND filters, measured with a PM200 light meter (Thorlabs). In the retinal whole-mount of the rd1 retina, RBCs were exposed at the surface of the retinsa. In the rd1_Opto-mGluR6 retina, OBCs were identified via the red TruboFP635 fluorescence.

Mice were euthanized using cervical dislocation and retinas were rapidly removed. A total of 5 C57BL/6J mice and 5 FVB rd1 (p210) were used for the patch-clamp recordings. Retina slices of C57BL/6J mice and whole mounts of FVB rd1 (p210) were obtained as previously described [22 (link),31 (link),42 (link)]. The lack of photoreceptors in the FVB rd1 retina allows direct access to the OBCs in the retina whole mount, and no difference has been found in the electrophysiological properties of bipolar cells in the two preparations as previously described [31 (link)]. OBC somas were identified via Turbo FP635 fluorescence with an upright microscope (Nikon Eclipse E600FN, Tokyo, Japan) equipped with an infrared GP-CAM3 Altair Astro camera [31 (link)]. To visualize recorded cells, 0.03% Lucifer yellow potassium salt (Sigma Aldrich) was added to the intracellular solution [31 (link)].