Functional maturation of mossy fiber synaptic properties is impaired in NeuroD2 null mice. (A) Representative whole cell voltage-clamp recording in an acute sagittal slice from P14 to P16 mouse while stimulating MF axons. A representative evoked synaptic current is shown at a holding potential of -70 mV, before and after perfusion with L-CCG (10 μM). (B) Evoked MF responses demonstrating strong paired-pulse facilitation and showing currents recorded at holding potentials of +50 and -70 mV. (C) Quantification of AMPA receptor (AMPAR)/NMDAR-mediated current ratios at the MF synapse, measured as the peak current at -70 mV relative to the peak current 50 ms into the response at +50 mV (WT = 6.08 ± 0.70, n = 27; knockout (KO) = 3.86 ± 0.68, n = 22). (D) Quantification of facilitation ratios measured as peak current of second response relative to first response at a holding potential of -70 mV and a 100 ms inter-stimulus interval (ISI; WT = 2.26 ± 0.21, n = 9; KO = 3.95 ± 0.60, n = 11). *P < 0.05, t-test. Error bars represent ± standard error of the mean.