Development of responses to excitatory and inhibitory amino acids in spiking cells during retinal regeneration in the adult newt.

Responsiveness to amino acids in solitary spiking cells dissociated from regenerating newt retinae at different stages were studied by whole-cell patch-clamp methods in comparison with that in the normal retina. Cells from regenerating retinae of 1-2 cell thickness ("early" stage) lacked the receptors for kainate (KA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), N-methyl-D-aspartate (NMDA), gamma-aminobutyric acid (GABA), and glycine. AMPA/KA, NMDA, GABAA, and glycine receptors, each of which were electrophysiologically and pharmacologically similar to those in the normal retina, appeared in spiking cells before regenerating retina had segregated into two synaptic layers. During subsequent regeneration stage, the time course of appearance of amino acid receptors seems to be different between excitatory and inhibitory ones. Cells which responded to GABA and glycine gradually increased in number to normal levels, and the current amplitude induced by these amino acids also increased monotonically. The number of cells responding to the excitatory amino acids appeared to be maximal at a period of synaptic segregation. During subsequent regeneration, however, cells responded to AMPA and NMDA decreased in number and returned to the number of cells in the normal retina, while cells which responded to KA were maintained at the same number as those in the normal retina. The amplitudes of the current induced by excitatory amino acids also became maximal at a period of synaptic segregation. During subsequent regeneration, AMPA- and KA-induced currents declined to the normal level, while NMDA-induced currents were maintained.