The scotopic electroretinograms of
Cacna1f G305X KO mice (
Fig. 4A, middle column) showed the typical pattern of electronegative waveform coupled with subnormal a-wave amplitude (
Fig. 4C, top graph). At high flash-intensities, the a-wave was followed by a small positive notch, previously proven to be of photoreceptor origin.
20 No b-wave could be elicited at any flash-intensities (
Fig. 4C, middle graph). By contrast, results from the
iZEG:Cacna1f+;Pax6::Cre+;Cacna1fG305X mice showed a similarly deficient a-wave, but a well-delineated b-wave of normal implicit time with subnormal amplitude (
Fig. 4A, right-most waveforms; C, middle graph), with further indications of post-photoreceptor processing (inner retinal, mostly amacrine cells)
46 in the form of large-amplitude, well-defined oscillatory potentials (
Fig. 4B). The b-/a-wave ratio is another measure of post-photoreceptor processing. In the C57Bl/6J control mice, this ratio reached 1.98 [99%CI: 0.23] at high scotopic intensities where mostly cones are responding, and increased to 4.47 [99%CI: 0.68] at −0.6 log cd ∙ s ∙ m
−2, where both rods and cones contribute to the response (
Fig. 4C, Bottom). These values are compatible with the expectation of more photoreceptor to bipolar cell convergence at lower intensities.
47 The
iZEG:Cacna1f+;Cacna1fG305X group (controls) showed a very low b-/a-wave ratio, because the “b-wave” measured at a fixed implicit time of 59 ms is likely to be driven by the recovery phase of the photoreceptor component (0.13 [CI: 0.09] and 0.36 [CI: 0.18], for the cone and cone-rod intensities, respectively). The two
iZEG:Cacna1f+;Pax6::Cre+;Cacna1fG305X mice (“experimentally rescued retina”) showed positive ratio of 1.21 and 1.20 at high intensities, with indication of convergence by reaching 3.04 and 2.66, at 1.0 and −0.6 stimulus intensities, respectively. The presence of this convergence suggests some reestablishment of the photoreceptor-bipolar cell synapses.