Developmental relationship between cholinergic amacrine cell processes and ganglion cell dendrites of the mouse...

Ganglion cells of the mammalian retina undergo structural remodeling before their dendrites are confined to functionally distinct laminas within the inner plexiform layer. It has been proposed that cholinergic amacrine cells provide laminar cues that remodel ganglion cell dendrites, because their processes stratify before those of the ganglion cells. To address this possibility, it is necessary to know whether cholinergic cells contact all or only some classes of ganglion cells during development. We, therefore, used two-photon microscopy to simultaneously reconstruct the dendritic arbors of different classes of ganglion cells and terminal processes of cholinergic cells in neonatal mouse retina. We determined that, after birth, cholinergic cells contacted only a subset of ganglion cells. Large bistratified cells (LBCs), resembling direction selective ganglion cells in other species, had dendrites that fasciculated with the cholinergic plexuses. The LBCs received numerous presynaptic cholinergic contacts shortly after birth. In contrast, large monostratified cells (LMCs), ramifying outside the cholinergic plexuses at maturity, received few, if any, cholinergic contacts even at early stages when their dendrites overlapped with the cholinergic processes. These observations suggest that cholinergic cells provide laminar cues for only subsets of ganglion cells. They also indicate that the synaptic organization between amacrine and ganglion cells may be specified early in development.