Strain differences in the distribution of NDP-ase labelled microglia in the normal rabbit retina

Nucleoside diphosphatase (NDP-ase) labelled microglial cells were examined in retinas of three strains of rabbit, the New Zealand White (albino), the Canberra Half-Lop, and the Dutch Belted. The distribution in the nerve fibre and inner plexiform layers was similar in all strains. However, the outer plexiform layer (OPL) of Dutch-Belted rabbits was completely covered with a population of non-overlapping NDP-ase positive microglia while the OPL of New Zealand White and Half-Lop strains contained only occasional isolated cells. In the Dutch-Belted strain the area covered by the processes of each cell was less in central than peripheral retina where the cell density was lower. In the central retina of the New Zealand White and Half-Lop strains the cells covered an area similar to that of peripheral Dutch-Belted cells, suggesting that they were at a low density and there was no hidden population of cells. This finding was confirmed by Griffonia simplicifolia lectin labelling. Therefore the data is consistent with there being a strain variation in OPL microglia. The intensity of NDP-ase label in the IPL and GCL was less in the New Zealand White and Half-Lop strains and although the intensity increased after retinal injury it never reached that of the Dutch-Belted retinas. These variations in the intensity of NDP-ase expression and the localization of microglial cells may be important in inflammation and also for CNS function.