The Eta ganglion cell type of cat retina.

We define a morphologic type of ganglion cell in cat retina by using intracellular staining in vitro. The eta cell has a small soma, slender axon, and delicate, highly branched dendritic arbor. Dendritic fields are intermediate in size among cat ganglion cells, with diameters typically two to three times those of beta cells. Fields increase in size as a function of distance from the area centralis, ranging in diameter from 90 microm to 200 microm centrally to a maximum of 600 microm in the periphery. This increase is unusually radially symmetric. By contrast with other cat ganglion cell types, eta cells do not have markedly smaller dendritic fields within the visual streak than above or below it nor much smaller fields nasally than temporally. Dendrites ramify broadly throughout sublamina a (OFF sublayer) of the inner plexiform layer. They arborize most densely in S2, where they costratify with dendrites of OFF alpha cells. There is apparently no matching ON variety of eta cell. Experiments combining retrograde labeling with intracellular staining indicate that eta cells project to the superior colliculus and to two components of the dorsal lateral geniculate nucleus (the C laminae and medial interlaminar nucleus). Eta cells apparently project contralaterally from the nasal retina and ipsilaterally from the temporal retina. The morphology and projection patterns of the eta cell suggest that its physiologic counterpart is a type of sluggish or W-cell with an OFF center, an ON surround, and possibly a transient light response.