Abstract
Purpose :
Amacrine cells, the most diverse cell class in the retina, shape the light response properties of retinal ganglion cells (RGCs). Yet the functions of the many amacrine cell types are little understood, especially in the primate retina. Here, we characterize the functional properties of several novel macaque polyaxonal amacrine cell (PAC) types, including their gap junction coupling to RGCs, receptive field (RF) properties, and responses to naturalistic scenes.
Methods :
512-electrode recordings were performed from the peripheral macaque retina ex vivo. Cells were identified as PAC or RGC based on their electrical images (average spatiotemporal voltage pattern of their spikes): PACs have multiple axons and slower spike propagation, while RGCs have one axon heading towards the optic disc. To summarize the spatiotemporal and chromatic properties of each cell, the spike-triggered average was calculated from responses to spatiotemporal noise. Cells were clustered into types based on these properties. Cross-correlations of spike trains were used to assess electrical coupling.
Results :
In most recordings, the well-known A1 PAC type was identified based on its spatial and temporal properties. In some recordings, multiple novel PAC types were identified. Most had larger RFs than A1 cells, with more spatial structure and irregular outlines. Several PAC types had a spatially segregated mixture of ON and OFF subregions in their RFs. One type displayed ON sensitivity in the center with several radiating OFF branches. Most PAC types exhibited larger RF coverage than A1s. At least one PAC type (in addition to the A1) appeared to form an electrically coupled network. One ON PAC type was apparently coupled to ON parasol RGCs, with some cells exhibiting weak bidirectional coupling and others strong unidirectional coupling RGC->PAC. These cells are the likely substrate of a coupled network that performs distant lateral inhibition previously identified indirectly in ON parasol cell recordings. Finally, distinct PAC types with similar RFs had distinct patterns of response to naturalistic movies.
Conclusions :
Multiple novel PAC types in the primate retina were identified, with unusual and diverse functional properties. Cross-correlation of spike trains revealed electrical connectivity within some PAC types and between specific PAC and RGC types. Early results suggest distinct roles of different PAC types in natural image signaling.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.