Optogenetic Isolation of the Amacrine Cell-OFF Bipolar Cell Synapse Shows Selective D1R Control of Glycinergic Transmission

Abstract

PurposeLight evoked inhibition of OFF cone bipolar cells (OFF BCs) is modulated both by background light levels and the action of dopamine through the dopamine D1 receptor (R). Since D1Rs are localized throughout the mouse retina, it is not known where in the light signaling pathway dopamine is modulating signals to OFF BCs. Here we tested a technique that allowed for the isolation of the amacrine cell (AC) to OFF BC circuit to determine if there are local D1R-induced changes in inhibition from presynaptic ACs onto OFF BCs. MethodsWe utilized the B6.Cg-Tg(Slc32al-COP4*H134R/EYFP) mouse line that expresses ChR2 in all the inhibitory cells in the retina. ACs expressing ChR2 were directly activated by light, while blocking photoreceptor mediated inputs. Inhibitory synaptic currents or ChR2-evoked excitatory currents were recorded using whole-cell patch clamp electrophysiology. ResultsOptogenetically activated inhibition from ACs elicited inhibitory currents that had slow kinetics similar to light-evoked inhibition, suggesting that they are using native synaptic mechanisms. We recorded optogenetically activated inputs to OFF BCs from pharmacologically isolated GABAergic and glycinergic input while photoreceptor inputs were blocked. D1R activation reduced glycinergic inputs to OFF BCs while leaving GABAergic inputs intact. ConclusionsD1R modulation of isolated optogenetic activation of AC-OFF BC synapses showed similar changes to previous experiments with light-evoked inhibition to OFF BCs. Together, this suggests optogenetic activation of ACs can be used to understand how dopamine differentially shapes inhibitory changes in the inner retina.