Abstract
Abstract: :
Purpose: Following the onset of light adaptation, the cone ERG of a normal mouse increases in amplitude and decreases in implicit time over about 10 minutes. We investigated the possible role of rod input to this process using two mutants that lack functional rods, the rhodopsin null (Rho–/–) and the NRL null (Nrl–/–) mouse. Rho–/– has rod nuclei but no outer segments; Nrl–/– has no rods at all. Methods: Full–field ERGs were recorded from three each of Nrl–/–, Rho–/– and wild type (WT) mice using a 0.6 log cd–s/m2 stimulus. Mice were dark adapted overnight, and recordings were then made immediately before the adapting light (1.6 log cd/m2) was turned on and at 1 min intervals for 10 min following its onset. Results: The dark–adapted ERG waveforms in Nrl–/– and Rho–/– mice were similar to the respective light–adapted response, as expected for "all cone retinas." During 10 min of light adaptation, the mean relative amplitude increase for WT, Nrl–/– and Rho–/– was 35 + 4%, 10+ 4%, and 2.0 + 0.5% (mean + SE), respectively. Implicit times of WT and Nrl–/– mice decreased 4.6 + 0.6 and 3.2 +0.6, respectively. The implicit time in Rho–/– mice remained constant during light adaptation. Conclusions: Previous reports showed that Rho–/– mice have non–functional rods and that rods are replaced by blue cones in Nrl–/–. Both mutants show only a small growth in the photopic b–wave amplitude during light adaptation, despite having normal or supernormal cone responses, supporting the hypothesis that a functional rod pathway is necessary to produce the increase seen in WT. The lack of change in Rho–/– implicit time during light adaptation also supports a role for the rod pathway. The large numbers of blue cones in Nrl–/– retinas may produce the decrease in b–wave implicit time seen in this mutant through rod like connections in the inner retina.
Keywords: electroretinography: non–clinical • photoreceptors • retina: distal (photoreceptors, horizontal cells, bipolar cells)