The b-wave of the cone ERG increases in amplitude and speed during the first few minutes of adaptation to a rod-suppressing background light. Earlier studies implicate rod pathway input to the cone pathway in these changes.
The timing and amplitude of the cone b-wave and isolated oscillatory potentials (OP) during the first 10 minutes of light adaptation in wild-type (WT) mice and two mutant lines without functional rods was examined: rhodopsin knockout ( Rho −/− ), lacking rod outer segments, and NRL knockout ( Nrl −/− ), in which rods are replaced by S-cones. Expression of the immediate-early gene c-fos, which is increased in the inner retina by light-induced activity, was evaluated by immunohistochemistry in dark- and light-adapted retinas.
WT b-wave and OP amplitudes increased, and implicit times decreased during light adaptation. Subtracting OP did not alter b-wave changes. Rho −/− b-wave and OP amplitudes did not increase during adaptation. B-wave timing and amplitude and the timing of the major OP at 1 minute of adaptation were equivalent to WT at 10 minutes. The light-adapted ERG b-wave in Nrl −/− mice, which originates in both the rod and cone pathways, changed in absolute amplitude and timing similar to WT. C-fos expression was present in the inner retinas of dark-adapted Rho −/− but not WT or Nrl −/− mice.