Abstract
Purpose :
Rods expressing R9AP95 transgene have accelerated photoresponse recovery kinetics and higher visual temporal constrast sensitivity in mesopic lights compared to control mice. We used ex vivo transretinal ERG recordings to test the hypothesis that the faster kinetics in R9AP95 rods increased the magnitude and bandwidth of the frequency responses compared to WT rods.
Methods :
Transretinal flicker ERGs were recorded from WT (n = 4-5 retinas) and R9AP95 (n= 4-5 retinas) mice. Retinas were perfused with Ames medium supplemented with DL-AP4 (50 μM), CNQX (20 μM) and BaCl2 (100 μM) to isolate the photoreceptor response. In some experiments CsCl (5mM) was added to block the hyperpolarization-activated responses in rods. Photoresponses to sinusoidal flicker of 75% contrast at 0.75 - 28 Hz were recorded at retinal irradiance levels ranging from 10 - 3200 R*/rod/s. The fundamental magnitude of flicker response was determined using an FFT. Statistical analysis used: 2 Way-ANOVA, p = 0.05.
Results :
The frequency responses of WT and R9AP95 rods exhibited different adaptation properties to increasing background illumination levels. At dim illumination levels (10 R*/rod/s), the frequency response functions of both had a low-pass shape (bandwidth = ~2 Hz) with maximal responses of 26±2 and 16±2 μVs (Mean±SD), respectively, at the lowest frequency (0.75 Hz). The WT responses scaled in proportion to the illumination levels (10 - 80 R*/rod/sec), while the R9AP95 responses had an extended bandwidth (3 Hz) and shifted peak (1.5 Hz). At intermediate levels (200 - 800 R*/rod/s), WT rods had an extended bandwidth (3.5 Hz) and a slight band-pass shape with shifted peak of 1.5 Hz. At these levels, R9AP95 responses were larger, had a shifted peak (3 Hz) and increased bandwidth (5 Hz). Above 800 R*/rod/s, the WT responses decreased with illumination at low frequencies (0.75 - 3 Hz), adopting a more band-pass shape. These changes reversed with application of CsCl, consistent with a contribution from hyperpolarization-activated conductances. For all responses, high frequency asymptotes ranged from -2.0 to -2.7 log units/decade.
Conclusions :
Transgenic acceleration of rod phototransduction inactivation kinetics in R9AP95 rods increases the tuning and bandwidth of its responses at lower illumination levels compared to control and increases the magnitude of the their contrast response in mesopic lights.
This is a 2020 ARVO Annual Meeting abstract.