(A) Freshly explanted retinas were treated with the LDH inhibitor, sodium oxamate, for 8 hr in explant culture medium, transferred to Krebs’-Ringer's for 30 min, and lactate was measured in the supernatant. Control (n = 5), Oxamate (n = 4). (B) Freshly explanted retinas were treated with oxamate or NaCl (control) in explant culture medium for 8 hr, followed by treatment with NaN3 or NaCl (untreated group) in Krebs’-Ringer's medium for 30 min. ATP per retina was then measured. n = 7, Control untreated; n = 8, Oxamate untreated n = 8, Control NaN3; n = 8, Oxamate NaN3. (C) Expression of Ldha and Ldhb as determined by IHC. Glutamine synthetase (GS), a Mueller glia-specific marker, colocalized with LDHB in the cell bodies (arrowheads), processes ensheathing the photoreceptors (arrows) and the outer limiting membrane (OLM, *). Scale bar, 50 μm. (D) ISH for Ldha and Ldhb. Ldha RNA displayed photoreceptor-enriched expression while Ldhb RNA was not observed in photoreceptors. Scale bar, 100 μm. (E, F) Freshly explanted retinas were treated with FX11 or DMSO for 8 hr and transferred to Krebs’-Ringer's for 30 min and secreted lactate was measured (E) n = 5, DMSO; n = 6, FX11, or they were transferred to Krebs’-Ringer's buffer with NaN3 or NaCl (untreated group) for 30 min for ATP quantitation (F). ATP per retina was measured at the end of the assay. n = 8, DMSO untreated; n = 8, FX11 untreated; n = 9, DMSO NaN3; n = 7, FX11 NaN3. (G) Freshly explanted retinae were transferred to Krebs’-Ringer's for 30 min and secreted lactate was measured. n = 8, Bl6/J; n = 8, Ldhafl/fl; n = 8, Rod-cre; n = 16, Rod-cre> Ldhafl/fl; n = 8, Rod-cre> Ldhafl/+. (H) Photoreceptor outer segment phenotype 42–45 days following in vivo electroporation of a knock-down construct (shRNA) for Ldha. CAG-mGFP was used for coelectroporation. Plasmid combinations listed on the left. Magnification of areas outlined in yellow is displayed on right with threshold-adjusted rendering to highlight inner and outer segments. Scale bar, 25 μm. (I) Quantification of inner+outer segment (IS+OS) lengths. n = 53–74 photoreceptors, 4–5 retinae. (J) Photoreceptor outer segment phenotype of dark-reared animals. Electroporated pups were transferred to dark on the day of eye opening (P11) and reared with their mothers for 3 weeks. (K) Quantification of inner+outer segment lengths of (J). n = 53–83 photoreceptors, 4–5 retinae. (L) Colored end products of redox reactions catalyzed by COX and SDH enzymes in retinal tissue. Scale bar, 200 μm. (M) IHC for SDH-A subunit in adult retina. Scale bar, 200 μm. ONL, outer nuclear layer. INL, inner nuclear layer. Data, Mean±SD. Statistics, unpaired, two-tailed t-test with Kolmogorov-Smirnov correction for panels A, E; two-way ANOVA with Tukey’s correction for panels B, F and K; one-way ANOVA with Tukey’s multiple comparison test for panels G, I.