Localization of glutamate in the human retina during early prenatal development.

In this study we have localized glutamate (GLU) in fetal (14-25 weeks gestation, Wg) human retinas by immunohistochemistry. At 14 Wg, GLU-immunoreactivity (IR) was localized only in the central part of retina, showing a prominently labelled nerve fiber layer. A few ganglion cells and displaced amacrine cells were very weakly labelled. At 17 Wg, GLU was localized conspicuously in many ganglion cells, displaced amacrine cells, some amacrine cells and the prospective photoreceptor cell bodies in the neuroepithelial layer. With progressive development at 20 and 25 Wg, the IR for GLU was found additionally in the Muller cell end feet, some bipolar cells as well as in the horizontal cells that were aligned in a row along the outer border of the inner nuclear layer of the central retina. The photoreceptor cell bodies in the outer nuclear layer were also prominently immunopositive for GLU. The developmental distribution of GLU in the human retina tends to indicate that it plays an important role in the differentiation and maturation of retinal neurons.