| In many parts of the central nervous system, neuronal processes remodel during development to generate specific synaptic connections. Dendritic remodeling is one way synaptic specificity is achieved. In the immature retina, retinal ganglion cells (RGCs) have dendrites that ramify throughout the inner plexiform layer (IPL). Over time, the dendrites of RGCs become restricted to structurally and functionally distinct sublaminae within the IPL. Previous studies suggest that RGC dendritic remodeling may be guided by activity-dependent cues, such as neurotransmission from cholinergic amacrine cells. The cholinergic amacrine cell is a retinal interneuron presynaptic to the RGC, and has processes that stratify in distinct sublaminae before the dendrites of RGCs have remodeled. I examined the influence of cholinergic transmission on the dendritic development of two classes of RGCs. One RGC type, the large monostratified cell (LMC), has a single arbor that stratifies outside the cholinergic cell processes. Another RGC type, the large bistratified cell (LBC), has two arbors, each of which co-stratify with the cholinergic cell processes. LMC and LBC dendrites may therefore rely on signals from cholinergic cells to different extents. The dendritic stratification patterns of LMCs and LBCs were examined in a conditional knockout mouse for choline acetyltransferase (ChAT). In this mouse, ChAT cells with normal morphologies were present, but the spontaneous activity patterns in the immature retina were altered. Despite the changes in cholinergic-mediated activity, RGC dendrites continued to stratify normally in the ChAT KO mouse, even for the LBCs, which are postsynaptic targets of the cholinergic amacrine cell. Thus, activity dependent cues derived from cholinergic neurotransmission are unlikely to direct RGC dendritic stratification. However, cholinergic cells may still be providing developmental cues through other neurotransmitters, or via molecular mechanisms. |
