Interaction of excitatory and depressant amino acids in the frog retina.

(1) Application of excitatory or depressant amino acids (concentrations from 10(-4) to 10(-2) M) could modify response patterns of the retinal ganglion cells to photic stimulus. Excitatory amino acids gave rise to spontaneous discharge while depressant amino acids inhibited spike discharge in response to test flashes. (2) Application of excitatory amino acids of more than 10(-3) M resulted in irreversible termination of spike discharges while recovery was always observed in the case of depressant amino acids even when the concentration of the applied solution was as high as 10(-2) M. No effect was observed when one exciting and one depressant amino acid were properly combined. (3) There is a mixture of four amino acids (two excitatory and two depressant) which could enhance the spike discharge in response to test flashes without giving rise to spontaneous firing. (4) It is implied that proper balance of excitatory and depressant amino acids is important in regulating the excitability of a number of neurons.