Figure 7.

Glycine-induced synaptic potentiation in rats primarily reflects an increase in the effective pool size, but increases in the probability of release also contribute. Experiments were conducted in the presence of CTZ and Kyn to assess the mechanism of glycine-induced enhancement in rats (P11–P14), in which previous studies have suggested that increases in p contribute to glycine-induced enhancement. Glycine led to an average synaptic enhancement of 45 ± 4% (n = 6). A, Comparison of pairs of EPSCs recorded in control conditions and in the presence of glycine (the EPSCs in glycine were normalized to the amplitude of the first EPSC in control) showed that glycine decreased the PPR. Experiments with stimulus trains (40 pulses, 100 Hz) were used to determine the contributions of p and the effective RRP to glycine-induced enhancement using the cumulative EPSC method (B) and the Elmqvist and Quastel method (C). D, The effects of glycine on synaptic properties are summarized (n = 6, ±SEM). In these experiments, glycine decreased PPR in rats by 12 ± 3%. The use of trains to determine the contribution of effective RRP and p revealed that glycine produced small increases in p (p_train, 15 ± 4%; p_EQ, 17 ± 4%; n = 6) but produced larger increases in effective RRP (RRP_train, 26 ± 2%; RRP_EQ, 24 ± 3%; n = 6). Thus, in rats, glycine increases p in addition to increasing the effective pool size, but as in mice, increased neurotransmitter release is mainly attributable to an increase in the effective pool size.