<p><b>A–C:</b> Immunocytochemical triple staining of Calbindin (red), PKCα (green), and VGluT1 (blue) on P28 old wild-type (A), ΔEx14–17 (B), I756T (C) outer retinae shows sprouting of ON-bipolar cell dendrites as well as horizontal cell processes into the ONL of both <i>Cacna1f</i> mutants. The VGluT1 labeling shows the existence of presynaptic contacts with the sprouting elements. <b>D:</b> Comparison of the severity of horizontal cell sprouting in the wild-type, ΔEx14–17, I756T mutant outer retina at P6, P14, P28, two months, and eight months. Asterisks indicate the onset of noticeable sprouting in the <i>Cacna1f</i> mutants. In the I756T mutant retina, noticeable horizontal cell sprouting started earlier (P14) than in the ΔEx14–17 mutant retina (P28), but declined at eight months, when sprouting still continued in the ΔEx14–17 mutant retina. ONL, outer nuclear layer; OPL, outer plexiform layer. Scale bar in A for A–C<b>:</b> 10 µm; in D: 20 µm.</p
