ERG recordings

Ex vivo ERG recordings were performed as described previously utilizing the same 60-electrode MEA system as described above⁵⁰. An Ag/AgCl pellet reference electrode (Science Products E-201ML) was connected instead of the internal reference electrode of the MEA chamber. The AgCl reference was positioned 2–3 mm above the center of the MEA electrode field and was optically shielded from direct visual stimulation. Synaptic transmission from photoreceptors to bipolar cells was blocked with 50 µM L-AP4 (Sigma A7929 or Abcam ab120002), 10 µM NBQX (disodium salt, Tocris 1044), and 10 µM RS-CPP (Tocris 0173). Glial currents (slow PIII component) were inhibited with 100 µM BaCl₂ (Sigma 342920)⁵¹. Data were low-pass filtered (300 Hz, 4th order Butterworth filter) and downsampled to 1 kHz. Noisy electrodes were discarded and all remaining electrodes were averaged for the analysis of ex vivo ERG responses.