Abstract
Purpose :
It is well established that in primates, the large majority of retinal ganglion cells, i.e. midget and parasol cells project to the parvo- and magnocellular layers of the dorsal lateral geniculate nucleus (LGN), respectively. In addition there are at least thirteen types of wide-field ganglion cell in macaque (Dacey, 2004) and marmoset retina (Masri et al., 2019). Brain targets of these low density (wide-field) ganglion cell types include the koniocellular layers of the LGN and the superior colliculus (SC) (Dacey, 2004; Szmajda et al., 2008). Here we identified the retinal ganglion cell types projecting to the medial subdivision of inferior pulvinar (PIm), the pretectum (PT) and the superior colliculus (SC) in marmoset.
Methods :
Retinas were obtained from three adult common marmosets, Callithrix jacchus which had received fluorescent tracer injections into the PIm (tracer coupled to A488), and superior colliculus or pretectum (tracer coupled to A594) using an MRI-guided approach (Kwan et al., 2019). Retinas were dissected and fixed in 4% paraformaldehyde in phosphate buffer. Retrogradely labelled cells were intracellularly injected with the lipophilic dyes DiI or DiO, imaged with a confocal microscope and classified according to dendritic field size, stratification and branch density.
Results :
The large majority of retrogradely labelled cells were obtained from SC injections. No double labelled cells were encountered. A total of 126 ganglion cells were classified. Retinal ganglion cells projecting to SC, PIm and PT nuclei comprise a variety of wide-field ganglion cell types including broad and narrow thorny, recursive bistratified, large sparse and large bistratified cells. Parasol cells were only found after SC injection and giant sparse (melanopsin-expressing) cells were only found after PT injection. Midget ganglion cells were never identified after SC, PT or PIm injections.
Conclusions :
The inferior pulvinar receives sparse direct input from the retina. Superior colliculus, pretectum and pulvinar receive input from independent cell populations. Retinal ganglion cells of the same type project to different brain nuclei.
This is a 2020 ARVO Annual Meeting abstract.