Abstract
Purpose :
Previous work has shown that dopamine plays a role in light adaptation by modulating inhibition at various points in the mouse retina. The goal of this study was to 1) determine if inhibition elicited by optogenetic activation of inhibitory neurons in the retina can be measured on OFF bipolar and amacrine cells and 2) if dopamine D1 receptor activation has a modulatory effect on that inhibition.
Methods :
Retinas were isolated from 8-11 week old B6.Cg-Tg(Slc32al-COP4*H134R/EYFP) male and female mice and cut into 250 µm thick slices. Whole-cell voltage clamp recordings of light-evoked Channel Rhodopsin 2 (ChR2) currents were measured on Bipolar (n=4) and Amacrine cells (n=8). These mice contain ChR2 under the VGAT promoter in the inhibitory amacrine and horizontal cells. These cells were optogenetically activated by either a 5ms, 1s, or 5s full-field light stimulus with a 4x or 60x objective (λ = 470 nm). Photoreceptor inputs were pharmacologically blocked with CNQX (25 µM), APV (50 µM), ACET (1 μM), and L-AP4 (50 µM). D1 receptors were agonized with SKF-38393 (20 µM). All experiments were performed under ambient room light. The peak amplitude, decay Tau, time to first peak, and charge transfer (Q) were measured for all evoked responses and analyzed by 2-way ANOVA.
Results :
While measuring optogenetically evoked inhibition on amacrine cells, application of a D1 agonist did not significantly change normalized peak amplitude (p= 0.290), charge transfer (p=0.314), or time to first peak (p= 0.886) compared to control (n=8). Excitatory currents were also measured on amacrine cells during optogenetic light activation of ChR2 channels as well as voltage changes in current clamp configuration. Optogenetically evoked inhibition onto OFF bipolar cells (n=3) did not changed peak amplitude (p= 0.171), charge transfer (p=0.973), or decay tau (p= 0.393) after application of SKF-38393.
Conclusions :
Dopamine has been shown to play a role in modulating inhibition in the inner retina. However, dopamine D1 receptor agonist SKF-38393 does not change the ChR2 evoked inhibition measured on amacrine or OFF bipolar cells. Further research will look at the possible effects of presynaptic changes elicited by activation of D1 receptors.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.