Development of Fetal Putative Blue Retinal Ganglion Cells of RHESUS MACAQUE

Steineke and Kirby (1994) reported that arbors of parasol ganglion cells that ramify in the middle layers of the inner plexiform layer (IPL) are transiently bistratified, becoming unistratified during late fetal periods. In this study I examined cells that ramify in the extreme inner and outer layers of the IPL, in fetal macaque, and compared their dendritic growth to cells ramifying in the middle IPL layers. Timed dated fetal monkeys were delivered by C-section, euthanized, and their retinas rapidly removed and horseradish peroxidase stained using diaminobenzidine. Dendritic arbors were measured in wholemounts with quantification of the area and depth of each portion of the arbor in the IPL. During mid-gestation ganglion cells with all or part of their arbor in the extreme inner or outer IPL (putative blue ganglion cells) formed four classes. The majority (48.9%) of putative blue cells were unistratified with their arbors ramifying either in the inner- or outer-most IPL. The second class (33.2%) had bistratified arbors with one portion in both the inner- or outer-most IPL and the other portion ramifying in the middle IPL. The third class (9.4%) were bistratified with one part of the arbor in the inner-most layer and the other portion in the outer-most layer of the IPL. Lastly, 8.4% of putative blue cells were observed to have tristratified arbors. These cells had the majority of their dendritic arbor in the middle IPL layers with small portions ramifying in the extreme inner and/or outer IPL. During late gestation the third and fourth classes, were rarely encountered. The other two classes were more prominent, especially the second class (70.8%) that may be precursors to the small field bistratified cells in the adult. Both of these later classes were analyzed and found to exhibit an outer- to inner-most maturation sequence within the IPL. In conclusion, four classes of putative blue ganglion cells undergo similar development and precision of dendritic growth as other ganglion cells, with the exception of some bistratified cells that may persist in the adult. Maturation appears to occur from outer- to inner-most within the IPL