Abstract
Purpose :
Like other mammals, the rabbit retina contains several ganglion cell types that express melanopsin and are known as intrinsically photosensitive retinal ganglion cells (ipRGCs). These include M1 cells with dendrites in sublamina a of the inner plexiform layer (IPL), M2 cells which stratify in sublamina b and M3 cells which are bistratified. It has been proposed that gap junction coupling with amacrine cells may provide a pathway via which ipRGCs can influence other retinal cells and circuits (Reifler et al., 2015). Tracer coupling has been reported in the mouse retina following dye injection of ipRGCs (Pérez de Sevilla Müller et al., 2010) but not enough detail was revealed to provide convincing evidence for a functional pathway. Here, we report the results of tracer coupling experiments in the rabbit retina.
Methods :
ipRGCs in the rabbit retina were targeted for intracellular injection by using an antibody against melanopsin. Cells were filled with 4% Neurobiotin, 0.5 – 1nA for 4-10 minutes, fixed, washed, visualized with streptavidin conjugated with Alexa 488 and examined by confocal microscopy (Zeiss 780).
Results :
M1 and M2 cells were readily distinguished by their stratification depth in the IPL. The ipRGC axons often made entertaining loops and detours after they left the soma. M1 cells were dye coupled to at least two amacrine cell types whose somas were in the inner nuclear layer, and to other M1s. M2 cells were often well coupled to displaced amacrine cells and other M2s. The displaced amacrine cells were polyaxonal types whose processes could be followed for more than 1mm. They were stratified predominantly at the same depth as M2. However, dendrites could also be located at the M1 level. This indicates the presence of an unusual bistratified axon bearing amacrine cell.
Conclusions :
In the rabbit retina ipRGCs are dye coupled to other ipRGCs, predominantly of the same type, and to amacrine cells, which provide a complex latticework of overlying dendrites. If this is repeated at the location of every ipRGC, the dense resulting network will blanket the entire retina, providing a feasible pathway for ipRGC driven signals (Reifler et al., 2015).
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.