Comparison of electroretinogram responses from WT, GCAP2+, GCAPs−/− and GCAPs−/−GCAP2+ mice that were either raised in constant darkness or in 12

h:12 h dark:light standard cyclic light. Left panel, superimposed representative responses of WT (red), GCAPs−/− (blue) and GCAPs−/−GCAP2+ (black) mice at p40 that were reared in constant darkness, in the scotopic and photopic range. The a-wave amplitude is severely reduced in GCAPs−/−GCAP2+ mice (black trace) compared to wildtype and GCAPs−/− traces in the scotopic range. This difference is absent in the photopic range, since the transgene is only expressed in rods. Central panel, superimposed representative responses of the same phenotypes, but raised in 12h:12h dark:light standard cyclic light and dark-adapted previous to the experiment. ERG responses from GCAPs−/−GCAP2+ mice were similar to GCAPs−/− and wildtype responses. Right panel, superimposed traces of cyclic light reared wildtype and GCAP2+ mice at p40. There were no statistically significant differences in the a-wave and b-wave amplitudes of these responses, whether the mice were raised in constant darkness or in 12h:12h dark:light standard cyclic light (cyclic reared mice results shown).