The dopaminergic amacrine cell

AbstractThe detailed morphology of the dopaminergic amacrine cell type has been characterized in the macaque monkey retina by intracellular injection of horseradish peroxidase (HRP). This cell type was recognized by its large soma in an in vitro, wholemount preparation of the retina stained with the fluorescent dye, acridine orange. HRP‐fills revealed a large, sparsely branching, spiny dendritic tree and a number of extremely thin, axon‐like processes that arose from the soma and proximal dendrites. The axon‐like processes were studded with distinct varicosities and were traced for up to 3 mm beyond the dendritic tree. The true lengths of the axon‐like processes were greater than 3 mm, however, because the HRP reaction product consistently diminished before an endpoint was reached. Both the dendrites and the axon‐like processes were narrowly stratified close to the outer border of the inner plexiform layer, although in a few cases single axon‐like processes projected into the outer nuclear and outer plexiform layers.The HRP‐filled amacrines appeared equivalent to a subpopulation of neurons that are intensely immunoreactive for tyrosine hydroxylase (TH). TH‐immunoreactive cells show