N-ACETYLASPARTYLGLUTAMATE IMMUNOREACTIVITY IN HUMAN RETINA

The acidic dipeptide N-acetylaspartylglutamate (NAAG), which satisfies many of the criteria fora neurotransmitter, was identified immunohist ochemically within two human retinae. We observed NAAG immunoreactivit y in retinal ganglion cells, their dendrites in the inner plexiform la yer, and their axons in the optic nerve fiber layer. The vast majority of ganglion cells were stained, including displaced ganglion cells, g anglion cells of different sizes, and those whose dendrites arborized in the inner and outer sublaminae of the inner plexiform layer, that i s, presumed On- and Off- cells. The sizes of labeled and unlabeled cel ls in the ganglion cell layer,as measured in counterstained material, suggest that the unlabeled cells consist primarily or only of displace d amacrine cells. We also saw immunoreactivity in small cells along th e inner margin of the inner nuclear layer, presumably amacrine cells, and in small cells with little cytoplasm in the inner plexiform and ga nglion cell layers, presumably displaced amacrine cells. These results are consistent with a role for NAAG in the transmission of visual inf ormation from the retina to the rest of the brain. Further, they are s imilar to those reported previously in rat, cat and monkey, thus demon strating the relevance of previous studies to humans.