, Volume 15, Issue 5, pp 645-655

Electron microscopy of glutamate decarboxylase (GAD) immunoreactivity in the inner plexiform layer of the rhesus monkey retina

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With indirect immunofluorescence, glutamate decarboxylase (GAD), the GABA synthesizing enzyme, was localized to cell bodies in the inner half of the inner nuclear layer and a few in the outer tier of the ganglion cell layer in the rhesus monkey retina. In the inner plexiform layer there were three strongly GAD-immunoreactive laminae separated by two less immunoreactive laminae. Electron microscopy demonstrated that the GAD was contained in amacrine cells and these GAD-immunoreactive amacrines were primarily pre- and postsynaptic to biopolar cell axon terminals. The GAD-containing processes possessed small synaptic vesicles and formed synapses that could be characterized as symmetrical. Large, dense-cored vesicles were often found in the cell bodies and synaptic processes of the GAD-immunoreactive amacrine cells. As the vast majority of the synaptic input and output of the GAD-containing amacrine cells was to and from bipolar cells and the strongest GAD-immunoreactivity correlated with the endings of bipolar cells that connect with a single cone, the functional effects of GABA in the primate retina are likely to be found in the responses of single cone pathways in the inner plexiform layer.