Ionotropic glutamate receptors during the development of the chick retina

Glutamate is the main neurotransmitter of photoreceptors, bipolar cells, and ganglion cells of the vertebrate retina. Three main classes of ionotropic glutamate receptors comprising different subunits can be distinguished: AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxasolepropionate), KA (kainate), and NMDA (N-methyl-D-aspartate). This study was undertaken to characterize the AMPA (GluR1, GluR2/3, and GluR4), KA (GluR5/6/7), and NMDA (NR1) ionotropic glutamate receptor subunits and to determine their distribution during the development of the chick retina by Western blotting and immunohistochemistry. Western blotting analysis at 1 day after hatching indicated that the antibodies against GluR1, 2/3, 4, and 5/6/7 and NR1 recognized specifically a single band of 100-110 kDa. In turn, immunohistochemistry at P1 showed that all subunits were expressed in cells of the inner nuclear and ganglion cell layers of the chick retina, mostly amacrine and ganglion cells, and their processes in the inner plexiform layer. In addition, stained processes in the outer plexiform layer were observed with the antibodies against GluR2/3, GluR4, and GluR5/6/7. Although all subunits appeared around E5-E6 in the prospective ganglion cell layer, and later in the prospective inner nuclear layer, the distribution of cells containing these glutamate receptor subunits revealed distinct ontogenetic patterns. This multiplicity of glutamate receptors may contribute to different processes that occur in the chick retina during development.