Morphology of dopaminergic amacrine cells in the mouse retina: Independence from homotypic interactions

Abstract

To determine the role of homotypic interactions between neighboring dopaminergic amacrine (DA) cells upon dendritic morphogenesis, the morphology of single cells was examined relative to the positioning of all neighboring homotypic cells. For each labeled cell, the dendritic field was reconstructed, its Voronoi domain calculated, and the two were related. The dendritic fields of DA cells were observed to be large, sparse and highly irregular. Dendrites readily overlapped those of neighboring cells, showing no evidence for dendritic tiling nor inter-digitation consistent with homotypic repulsion or avoidance. Furthermore, a direct comparison of dendritic field area to the Voronoi domain area of the same cell showed no evidence for dendritic growth being constrained or biased by the local distribution of homotypic neighbors in wild-type retinas. A comparison of the processes of adjacent filled cells confirmed their immediate proximity to one another within the inner plexiform layer, indicating that they do not engage in mutual avoidance by coursing at different depths. Together, these results suggest that the morphogenesis of DA cells is independent of homotypic interactions. However, in the absence of the pro-apoptotic Bax gene, which yields a four-fold increase in DA cell number, a small but significant reduction in dendritic field size was obtained, though not so great as would be predicted by the increase in density. The present results are considered in light of recent studies on the role of cell adhesion molecules expressed by developing DA cells.

Astrocyte structural reactivity and plasticity in models of retinal detachment

“…Dye-filling is a more accurate and complete method for the study of individual cells, but it is labor-intensive, making it difficult to obtain data for a large population of cells (see supplemental figures 1, 2). The organization of cellular domains within biological systems is a common phenomenon (Bushong et al, 2004; Honda, 1983; Reese and Keeley, 2014; Senft and Woolsey, 1991) and the domain of dendritic arbors is commonly used to classify neuronal sub-types in the retina (Amthor and Oyster, 1995; Keeley and Reese, 2010; Wässle et al, 1981). Unlike retinal neurons, astrocyte morphology varies greatly with few easily observable patterns across the retina, thus it has proven difficult to determine if there is heterogeneity in the population that may be responsible for defining domains of different astrocytic types.…”

“…in 4% buffered paraformaldehyde) were carried out as described elsewhere (Keeley and Reese, 2010). After preparing the wholemounts as above, retinas were stained with the nuclear stain Hoechst 33342 (Invitrogen; Carlsbad, CA) diluted 1:1000 in PBS for 1 hour, rinsed with PBS, then transferred to a fixed stage Nikon Eclipse E600 epifluorescence microscope (Nikon Instruments Inc., Melville, NY).…”

Independent Genomic Control of Neuronal Number across Retinal Cell Types

“…Such developmental plasticity enables two populations of synaptically-connected neurons, the numbers of which vary widely and largely independent of one another, to conserve a fundamental design feature: a uniform dendritic coverage by the post-synaptic cell to sample the entirety of the population of their afferents. Curiously, this plasticity would appear to be the rule in the OPL (Lee et al, 2011; Reese et al, 2005), whereas within the inner plexiform layer, there are multiple exceptions to it (Farajian et al, 2004; Keeley and Reese, 2010a; Lin et al, 2004). …”

Self-avoidance and Tiling: Mechanisms of Dendrite and Axon Spacing

“…Dscam mutations lead to aberrant bundling of neurites (both within and between cells) and uneven spacing of cell bodies of bNOS and dopaminergic amacrine cells (Fuerst et al 2008). Because the processes from neighboring dopaminergic amacrine cells show extensive overlap and make only minor adjustments in field size when present in excess numbers, repulsive signaling is probably not critical for their normal spacing (Keeley and Reese 2009). Dscam may therefore ensure selfavoidance by counterbalancing the action of other adhesion systems that would otherwise lead to the fasciculation of processes (Fuerst et al 2008;).…”