Development of glutamate-induced intracellular Ca2+ rise in the embryonic chick retina

Neurotransmitters affect neuronal development by regulating intracellular Ca2+ concentrations. We studied spatiotemporal pattern of the development of glutamate-induced intracellular Ca2+ rise in the embryonic chick retina, where developmental changes in mitotic activity, cell death, and synapse formation have been well established. Glutamate was bath-applied to the central part of the retina dissected at embryonic day 3 (E3) to E13, and changes in intracellular Ca2+ concentration were measured with Fura-2 fluorescence. The Ca2+ rise to glutamate first appeared at E6, reached a maximum at E9-10, and then declined before the appearance of synaptic structures (E12). Ca2+ rises to kainate (KA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) appeared earlier and were larger in amplitude than those to N-methyl-D-aspartic acid. The KA/AMPA receptor of the E9 chick retina was permeable for Ca2+, suggesting the functional expression of Ca2+-permeable KA/AMPA receptors at the stage of retinal cell death. The Ca2+ rise to glutamate and KA occurred intensely at the inner plexiform layer, the inner part of inner nuclear layer, and the ganglion cell layer, where the cell death occurs. The Ca2+ rise to high K+, in contrast, occurred intensely at the nerve fiber layer and the ganglion cell layer, developing continuously from E3 until E11. Our study shows that the Ca2+ rise to glutamate develops with the decline of the mitotic activity of the retinal cells and is transiently enhanced during the period of cell death in the embryonic chick retina.