The appearance and maturation of excitatory and inhibitory neurotransmitter sensitivity during retinal regeneration of the adult newt.

Using living slice preparations from newt retinas at different stages of regeneration, we examined the time course of appearance and maturation of neurotransmitter-induced currents with whole-cell patch-clamp methods. Neurons from which currents were recorded were identified by Lucifer Yellow fills. All progenitor cells examined at the regenerating retinas did not express any voltage-gated Na+ currents and responsiveness to excitatory amino acid analogues (AMPA and NMDA) and inhibitory amino acids (GABA and glycine). Voltage-gated Na+ currents were first detected in premature ganglion cells with round cell body located at the most proximal level of the 'intermediate-II' regenerating retina. AMPA- GABA- and glycine-induced currents were simultaneously observed in many premature ganglion cells expressing Na+ channels, but not all, suggesting that the onset of the Na+ channels is slightly earlier than that of excitatory and inhibitory amino acid receptors in regeneration. NMDA-evoked currents were first observed in the 'intermediate-III' regenerating retina just before the synaptogenesis. Pharmacological properties and reversal potential values of the excitatory and inhibitory amino acid responses did not change substantially between regenerating ganglion cells and mature ganglion cells, while rectification properties of current-voltage relations for AMPA and NMDA responses were somewhat different between them.