Neurite outgrowth in adult goldfish retinas. Retinal explants were cultured for 5 d. A, No addition, control retina. B, No addition, primed retina (underwent optic nerve transection 5–7 d previously). C, Purpurin (1μg/ml) added to the control retina. D, Retinol (1μm) added to the control retina. E, Purpurin (1 μg/ml) with retinol (1 μm) added to the control retina. F, Retinoic acid (1 μm) added to the control retina. G, Purpurin with retinol and disulphiram (10 μm) added to the control retina. H, Disulphiram (10μm) added to the control retina. Scale bar, 200 μm.