For antibody staining, cryosections were prepared and stained as described previously [63]. Primary antibodies used were a polyclonal anti-blue opsin raised in rabbit (1:300; Chemicon International, Temecula, California, United States; AB5407) and a mouse monoclonal anti-rhodopsin (1:200; rho4D2). Secondary antibodies used were Cy2- or Cy3-conjugated goat anti-rabbit and anti-mouse (1:500; Jackson Immunologicals, West Grove, Pennsylvania, United States). Following antibody staining, 4′-DAPI was applied to stain nuclei (Sigma), and the sections were coverslipped and mounted in Gel/Mount (Biomeda, Foster City, California, United States).