Dose effects of various concentrations of glycine on LTP A: At the concentration of 1μM glycine the initial potentiation induced by TBS does not last 1 h, thus indicating that at such low concentration is enough to prevent LTP (n = 10 cells, 10 slices, 5 animals). At 10μM glycine not only prevents all potentiation but also slightly decreases conductances recorded at the soma (n = 10 cells, 10 slices, 5 animals), although this reduction is not significant. At 100μM glycine blocks LTP and induces a significant depression up to 1 h post-TBS (n = 12 cells, 12 slices, 6 animals). B-E: Excitatory (black) and inhibitory (grey) conductances were found to be equally affected by TBS application, regardless of the treatment, confirming that the E-I balance is unaltered by glycine and LTP. *p<0.05, **p<0.01, ***p<0.001 compared to pre-TBS.