Abstract
Purpose :
To study the Impulse response functions (IRFs) to luminance and photoreceptor-isolating stimuli in mice expressing a human L*-opsin instead of M-opsin.
Methods :
After dark adaptation over night, anesthetized animals were adapted for 2 min to the mean luminance (ML) of the following stimulus.
ERGs to temporal white noise modulation (wnERGs: containing all frequencies up to 20 Hz with equal amplitudes and random phases) were recorded. Both luminance and photoreceptor-isolating stimuli were used.
Responses were recorded at 7 mean luminances (MLs) between -0.7 and 1.2 log cd/m2 with luminance and at 4 MLs (between -0.8 and 1 log cd/m2) with rod and cone isolating stimuli.
For each stimulus condition, two recordings of 200 sweeps were performed. IRFs were calculated by a cross correlation of the recordings and the stimulus luminance or photoreceptor excitation. Amplitudes and latencies of the IRF trough and peak were measured at each ML.
Results :
Recordings measured with equal stimulus conditions displayed similar time courses, indicating that wnERGs gave reproducible results. IRFs of luminance stimulation showed an initial (a-wave-like) trough followed by a positive (b-wave-like) peak for all MLs. Trough and trough-to-peak (T-P) amplitudes increased monotonously with increasing ML. Latencies of trough and peak decreased with increasing ML up to 0.3 log cd/m2 and were constant for higher MLs. IRFs of L*-cone and S-cone isolating stimuli displayed similar time courses and dependency on ML. T-P amplitudes increased by a factor of 102 for L*-cones and by a factor of 2.5 for S-cones. Maximal S-cone-driven responses were 2.7 times smaller than maximal L*-cone-driven responses. In contrast to cone-driven responses, IRFs of rod-driven recordings decreased in amplitude with increasing ML by a factor of 1.7. In none of the recordings, oscillatory potentials were observed.
Conclusions :
wnERGs can be reliably recorded in mice with luminance stimulation and photoreceptor-isolating stimuli. Cone-driven responses grow with increasing ML, whilst rod-driven responses were larger at low ML. Luminance stimulation shows a rod-cone transition below 0.3 log cd/m2. Although the IRFs resemble flash ERGs superficially, they are fundamentally different and offer a novel procedure to study retinal physiology.
This is a 2021 ARVO Annual Meeting abstract.