Exclusionary dendritic interactions in the retina of the goldfish

The retina of the goldfish grows throughout its life, in part, by the addition of new neurons at the margin. New ganglion cells added at the margin tend not to grow their dendritic arbors into the older, central retina. Hitchcock and Easter (J. Neurosci. 6, 1037-1050 (1986)) proposed that the dendrites of the new cells were prevented from extending centrally within the inner plexiform layer by the dendrites of the previous generations of cells. This proposal was tested by first killing existing ganglion cells with a retrogradely transported neurotoxin (propidium iodide; PI), and then observing the orientation and branching pattern of the dendrites of ganglion cells added subsequently at the margin. Dendrites were stained in retinal wholemounts by intracellular injections of Lucifer yellow. The data showed that cells added subsequent to the PI treatment grew their dendritic arbors preferentially toward central retina consistent with the hypothesis. It is concluded that interactions among adjacent ganglion cells regulates dendritic growth.