DISTRIBUTION OF PHOSPHATE-ACTIVATED GLUTAMINASE-LIKE IMMUNOREACTIVITYIN THE RETINA OF RODENTS

The distribution of phosphate-activated glutaminase-like immunoreactiv ity was examined in the retinas of rodents. Intense glutaminase immuno reactivity was observed in many neuronal perikarya in the ganglion cel l layer and inner nuclear layer including those of ganglion, bipolar a nd amacrine cells and possibly horizontal cells. Almost all bipolar ce lls containing protein kinase C were immunoreactive for glutaminase, s uggesting that the majority of glutaminase immunoreactive bipolar cell s were of the ON type. Intense glutaminase immunoreactivity was also f ound in the neuropil of the inner and outer plexiform layers and aroun d the outer limiting membrane. Weak to moderate immunoreactivity was s een in the outer nuclear layer and photoreceptor inner and outer segme nts. Under electron microscopy, glutaminase immunoreactivity was seen in bipolar cell axons and amacrine cell processes in the inner plexifo rm layer. In the outer plexiform layer, immunoreactivity was found in the Muller 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 glutamin ase has additional roles in Muller cells. A population of amacrine cel ls and horizontal cells showed immunoreactivity to glutaminase.