Distribution of phosphate-activated glutaminase-like immunoreactivity in the retina of rodents

The distribution of phosphate-activated glutaminase-like immunoreactivity was examined in the retinas of rodents. Intense glutaminase immunoreactivity was observed in many neuronal perikarya in the ganglion cell layer and inner nuclear layer including those of ganglion, bipolar and amacrine cells and possibly horizontal cells. Almost all bipolar cells containing protein kinase C were immunoreactive for glutaminase, suggesting that the majority of glutaminase immunoreactive bipolar cells were of the ON type. Intense glutaminase immunoreactivity was also found in the neuropil of the inner and outer plexiform layers and around the outer limiting membrane. Weak to moderate immunoreactivity was seen in the outer nuclear layer and photoreceptor inner and outer segments. Under electron microscopy, glutaminase immunoreactivity was seen in bipolar cell axons and amacrine cell processes in the inner plexiform layer. In the outer plexiform layer, immunoreactivity was found in the Müller cell processes, but not in the photoreceptor cell terminals. These results indicate that ganglion cells and ON type bipolar cells use glutaminase to produce transmitter glutamate and suggest glutaminase has additional roles in Müller cells. A population of amacrine cells and horizontal cells showed immunoreactivity to glutaminase.