Fig. 7
Postsynaptic AP bursts are not required for LTP induction at MPP-GC synapses. A Similar as in Fig. 2A, but medial perforant pathway (MPP) in medial molecular layer was electrically stimulated with a single bout of train pulses (10 stimuli at 100 Hz). Scale bar is 100 μm. B Left, Subthreshold voltage responses evoked by HFSL of MPP in RS- (black) and BS-GCs (red). Right, Cumulative EPSP amplitudes of EPSP summation. C Left, Time course of normalized EPSP before and after HFSL of MPP. Right, Change in normalized EPSP before and after HFSL (RS, 17.7 ± 8.8%, n = 5; BS, 9.5 ± 7.0%, n = 6). D Left, Representative EPSP summation in control (black) and after application of APV (50 μM, brown). Right, Cumulative EPSP amplitudes in control and APV conditions. E Left, Mean amplitude of 1st EPSP evoked by a bout of HFSL in control and APV conditions at MPP and LPP [MPP, 12.8 ± 1.7 mV (Con) vs. 13.5 ± 1.7 mV (APV), n = 6; LPP, 9.8 ± 0.9 (Con) vs. 7.3 ± 1.1 mV (APV), n = 11, *p < 0.05]. Right, Mean area of HFSL-induced EPSP summation [MPP, 2.3 ± 0.1 mV s (Con) vs. 1.8 ± 0.1 mV s (APV), n = 6, *p < 0.05; LPP, 3.0 ± 0.2 mV s (Con) vs. 1.6 ± 0.1 mV s (APV), n = 10, **p < 0.01]. Both plots show weaker contribution of NMDAR to EPSPs at MPP-GCs than LPP-GCs. F Left, Representative 3 AP bursts evoked by HFSH in RS- (black) and BS-GCs (red). Right, Initial AP frequency (Finit) of each cell type (RS, 101.2 ± 12.7 Hz, n = 11; BS, 152.1 ± 17.3 Hz, n = 7; *p < 0.05). G: Left, Time course of normalized EPSP before and after HFSH. Right, Magnitudes of early (LTP5, open triangle) and late phase (LTP30, closed triangle) LTP, showing that no significant difference in HFSH-induced LTPAP magnitude between RS- and BS-GCs. H LTP magnitudes as a function of Finit of AP bursts evoked by HFSH at MPP-GCs (r = 0.20, p = 0.47). Open symbols, data of individual cells. Closed symbols, averaged value of each group. Black line, linear regression line. r, Pearson’s correlation coefficient. I Left, Voltage responses evoked by a pairing protocol comprised of postsynaptic 3 APs at 100 Hz (upper, black) or 50 Hz (lower, gray) with HFSL of MPP. Middle, Time course of normalized EPSP amplitude before and after the pairing protocol. Right, Magnitudes of early (LTP5, open symbols) and late phase (LTP30, closed symbols). Note that no difference was found in LTPAP magnitude between pairing at 100 Hz and even at 50 Hz. Shades and error bars, S.E.M. *p < 0.05. **p < 0.01. n.s., not significant (p > 0.05)