Anatomical characterization of retinal ganglion cells that project to the nucleus of the basal optic root in the turtle (Pseudemys scripta elegans).

There is little detailed information about retinal ganglion cells which project to specific central targets in the brain. The present study examined retinal ganglion cells projecting to the nucleus of the basal optic root, a major accessory retinal target in the turtle. These ganglion cells were first selectively labeled using retrograde transport of rhodamine injected stereotaxically into the nucleus of the basal optic root. The number and distribution of the retrogradely labeled cells in the retina was then determined. Some of these retrogradely labeled cells were then injected intracellularly with Lucifer Yellow, photoconverted using diaminobenzidine, and drawn in detail using a camera lucida attachment. There were approximately 1500 ganglion cells in each retina which projected to the nucleus of the basal optic root, of which 20% had cell bodies displaced to the inner nuclear layer. More than 50% of the total population was concentrated in the visual streak region. All ganglion cells projecting to the nucleus of the basal optic root, both normal and displaced, had monostratified dendritic arborizations in stratum 1 of the inner plexiform layer. About 41% of these ganglion cells had elongated dendritic arborizations with distinct orientations, which may suggest a correlation of morphology and function. There were similarities in the overall appearance, and in the type and stratification of the dendritic arborizations of all ganglion cells projecting to the nucleus of the basal optic root. These anatomical similarities are consistent with the previously demonstrated similarities in physiology and may reflect a common role for these ganglion cells in visual processing.