Distinct cone and rod functional responses in Nrl+/b2, Nrlb2/b2, and Nrl−/− mice. A, Representative electroretinogram traces for Nrlb2/b2 and Nrl−/− mice at ∼8 weeks of age. Top and middle rows, Photopic cone responses to stimuli with wavelengths of 520 and 360 nm that optimally activate mouse M and S opsins, respectively. Bottom row, Scotopic rod responses. Enhanced M and S cone responses were detected in Nrlb2/b2 mice, but only enhanced S cone responses in Nrl−/− mice. Families of traces are shown for light intensities of 0.5, 1.26, 2, 3.16, and 7.94 cd · s/m2 at 520 nm and 0.0001, 0.00032, 0.001, 0.0032 and 0.0316 cd · s/m2 at 360 nm for cones and 1 × 10−6, × 10−5, × 10−4, × 10−3, and × 10−2 cd · s/m2 for rods. B, Intensity–response curves of average ERG responses for groups of 4–6 mice (means ± SEM). Cone (top and middle rows) and rod (bottom row) ERG responses to varying stimulus intensities were determined for +/+, Nrl+/b2, and Nrlb2/b2 mice and, separately, for +/+, Nrl+/−, and Nrl−/− mice. Nrlb2/b2 and Nrl−/− mice were each compared with their own +/+ and heterozygous groups on comparable genetic backgrounds.