Characterization of genetically labeled catecholamine neurons in the mouse retina.

Mouse neurons were labeled transgenically with red fluorescent protein (RFP) driven by the tyrosine hydroxylase (TH) promoter and observed in living retinas and brain slices. Two types of retinal amacrine cells expressed TH::RFP. One type had large cell bodies, processes that ramified in S1 of the inner plaxiform layer (IPL) and were TH immunoreactive, identifying them as dopaminergic neurons. A second type had smaller somas, ramified in S3 and lacked TH. Dopaminergic cells had large dendritic fields and exceptionally long axon-like processes, whereas type 2 cells were more compact. Neither cell type exhibited tracer coupling. Thus, murine retinal dopaminergic neurons exhibit functional anatomy similar to their primate counterparts and TH::RFP mice are useful for in situ characterization of catecholaminergic neurons.