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Kumiko Percival, Paul Martin, Ulrike Grunert; Analysis of retinal ganglion cells projecting to the koniocellular superficial (K1) layer of the lateral geniculate nucleus in marmoset monkey. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3408. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal projections to the K3 layer of the koniocellular (KC) division of the dorsal lateral geniculate nucleus (LGN) have been shown to represent a distinct pathway dominated by small bistratified and large sparse ganglion cells (Szmajda et al., 2008). Here, we show evidence for further segregation of pathways within the KC layers.
Ganglion cells were retrogradely labeled from tracer injections into the LGN of anaesthetised marmosets (Callithrix jacchus). In two animals two injections were made (targeted at K3 and K1), in one animal one injection was made (targeted at the magnocellular layers and K1) Retrogradely labeled cells were photofilled (Dacey et al., 2003) to reveal their dendritic morphology. Morphological characteristics of ganglion cells (dendritic field diameter, branch density and stratification level within the inner plexiform layer) were quantified.
We have identified a group of ganglion cells that is unique to injections that included the K1 layer. These cells were similar in dendritic field diameter to parasol ganglion cells from comparable eccentricities. The K1 projecting ON cells (n = 7) stratified at similar regions as ON parasol cells, whereas the K1 projecting OFF cells (n = 2) stratified closer to the amacrine layer in comparison to OFF parasol cells. The K1 layer projecting cells differed from parasol cells in that they exhibited more densely branching dendritic trees and numerous spine-like protrusion. At eccentricities > 2.5mm the dendritic branch density of K1 projecting cells (435.6mm dendritic length per mm2 SD 66.9mm, n = 9 cells) was on average 1.5 times larger than that of parasol cells (297.8mm dendritic length per mm2 SD 52.0mm, n = 5 cells, p < 0.002, Wilcoxon rank sum test).
K1 projecting ganglion cells show morphological characteristics distinct from previously described K3 projecting cells and parasol cells. This subdivision of morphologically distinct ganglion cell types to distinct KC layers may reflect a functional segregation of pathways within the KC layers.
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