Fig. 2
NMDAR-dependent LTP at LPP-GC synapses is induced by a single bout of high frequency stimulation (HFS) at subthreshold level. A Schematic diagram illustrating the recording configuration for synaptic stimulation and whole cell recording of mature GC. Lateral perforant pathway (LPP) in outer molecular layer (OML) was electrically stimulated by a bout of HFS (10 stimuli at 100 Hz). Scale bar is 100 μm. B HFSL is defined as low intensity HFS that induce subthreshold response. HFSL-evoked subthreshold responses of RS- (black) and BS-GCs (red) (left), and their cumulative EPSP amplitudes (right). C Time courses of normalized EPSP amplitude before and after HFSL (same as in B). Each point represents averaged value for adjacent 3 EPSP amplitudes (30 s binned). Black dashed line denotes baseline EPSP. Inset, Representative traces for average of 30 EPSP traces before (a) and 26–30 min (b) after HFSL (This holds for inset traces in all subsequent figures except in Fig. 2F and Fig. 7C). D LTP magnitudes before and after HFSL. There was no significant difference between RS and BS (RS/BS, n = 12/13). E Left, Representative traces for EPSP summation in control (black) and after application of APV (brown, 50 μM). Right, Mean values for EPSP area in RS [3.0 ± 0.3 mV s (Con) vs. 1.3 ± 0.2 mV s (APV), n = 5, *p < 0.05] and in BS [2.9 ± 0.3 mV s (Con) vs. 1.9 ± 0.1 mV s (APV), n = 5, *p < 0.05]. Note that the APV effect on subthreshold EPSP summation was examined at synapses which have already underwent LTPsub. F Time course of normalized EPSP before and after HFSL in the presence of APV in both GCs. EPSP amplitude was not potentiated (RS, 1.7 ± 6.0%, n = 3, light brown; BS, − 2.5 ± 4.5%, n = 4, brown). Inset, EPSPs averaged over 1 to 5 min before (a) and after (b) HFSL. Shades and error bars, S.E.M. *p < 0.05. n.s., not significant (p > 0.05)