Morphology of wide-field bistratified and diffuse human retinal ganglion cells

To study the detailed morphology of human retinal ganglion cells, we used intracellular injection of horseradish peroxidase and Neurobiotin to label over 1,000 cells in an in vitro, wholemount preparation of the human retina. This study reports on the morphology of 119 wide-field bistratified and 42 diffuse ganglion cells. Cells were analyzed quantitatively on the basis of dendritic-field size, soma size, and the extent of dendritic branching. Bistratified cells were similar in dendritic-field diameter (mean +/- S.D. = 682 +/- 130 microm) and soma diameter (mean +/- S.D. = 18 +/- 3.3 microm) but showed a broad distribution in the extent of dendritic branching (mean +/- S.D. branch point number = 67 +/- 32; range = 15-167). Differences in the extent of branching and in dendritic morphology and the pattern of branching suggest that the human retina may contain at least three types of wide-field bistratified cells. Diffuse ganglion cells comprised a largely homogeneous group whose dendrites ramified throughout the inner plexiform layer. The diffuse cells had similar dendritic-field diameters (mean +/- S.D. = 486 +/- 113 microm), soma diameters (mean +/- S.D. = 16 +/- 2.3 microm), and branch points numbers (mean +/- s.D. = 92 +/- 32). The majority had densely branched dendritic trees and thin, very spiny dendrites with many short, fine, twig-like thorny processes. Five of the diffuse cells had much more sparsely branched dendritic trees (<50 branch points) and less spiny dendrites, suggesting that there are possibly two types of diffuse ganglion cells in human retina. Although the presence of a diversity of large bistratified and diffuse ganglion cells has been observed in a variety of mammalian retinas, little is known about the number of cell types, their physiological properties, or their central projections. Some of the human wide-field bistratified cells in the present study, however, show morphological similarities to monkey large bistratified cells that are known to project to the superior colliculus.