Abstract
Purpose :
Amacrine cells (ACs) are a diverse class of inhibitory interneurons that provide feedforward, feedback, lateral, and crossover inhibition in the IPL to shape the visual signals sent to RGCs. The great diversity of ACs has been a major obstacle to access individual cell types for systematic studies. The development of genetic tools that allow for cell type-specific targeting and manipulation would be an important step towards the characterization of AC types. In this study, we aim to use new mouse intersectional genetic tools to morphologically and functionally dissect amacrine cell circuits.
Methods :
We first used a Cre/tTA intersectional strategy that relies on two orthogonal binary systems, Cre/loxP and tTA/TRE, to discover new AC types and to target them with increased specificity. We then performed functional analysis. Specifically, we characterized their light response properties by imaging Ca2+ responses at the sites of neurotransmitter release, and then identified their post-synaptic RGCs with intersectional ChR2 activation. Finally, we developed a chemogenetic mouse line to inactivate the ACs and examine their functional roles in different circuits.
Results :
By creating VGAT-iCreER;CaMK2a-tTA intersectional strategy combined with temporally controlled Cre induction, we discovered a narrow-field AC subtype (named CK2-AC1) in the mouse retina and achieved single AC type labeling. CK2-AC1 responded strongly to local motion but not to global motion. Optogenetic stimulation showed that CK2-AC1 provided glycinergic inputs to HD2-RGC, but not to UHD-RGC. Chemogentic inactivation demonstrated that CK2-AC1 provided suppression to HD2-RGC during local stimulation, but not during global stimulation. Meanwhile, we discovered that HD2-RGC received inhibition from TH2-AC during global stimulation, but not during local motion. Therefore, CK2-AC1 and TH2-AC mediate two parallel inhibitory pathways to control object motion sensitivity (OMS) of HD2-RGC.
Conclusions :
This study introduced a workflow based on Cre/tTA intersectional strategies for systematically analyzing AC types and examining their circuit roles in visual processing. Using this workflow, we discovered a new AC type and revealed its functional roles in the OMS circuits. We conclude that CK2-AC1, together with TH2-AC, control the OMS signals that HD2-RGC sends to the brain.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.