Effect of glycine and gamma-aminobutyric acid on excitability of central terminals of primary afferent fibers

The effect of microelectrophoretically injected glycine and GABA on the excitability of intraspinal terminals of group Ia muscle afferents was studied in experiments on cats anesthetized with pentobarbital. The excitability of the terminals, studied by Wall's method, was reduced by the action of glycine but increased by that of GABA. The possible role of the two amino acids in presynaptic inhibition of spinal reflexes is discussed.