Figure 4.

Postsynaptic ephrinB3 expression increases excitatory synaptic function. A, EphrinB3 overexpression for 1 d increased mEPSC frequency (n = 26 for each group; *p < 0.01) but not their amplitude (p > 0.1). EphB2 overexpression did not affect excitatory synaptic transmission (n = 29; frequency, p > 0.5; amplitude, p > 0.09). B, Overexpression of ephrinB3 did not affect frequency or amplitude of mIPSCs (GFP, n = 25; ephrinB3, n = 22; frequency, p > 0.1; amplitude, p > 0.5). C, The PPRs of evoked responses (R2/R1) at various intervals were measured between two synaptically connected hippocampal neurons with paired whole-cell patch-clamp recording. Increasing external calcium concentration significantly reduced PPR (control, n = 14; high Ca²⁺, n = 9; *p < 0.005). Postsynaptic expression of ephrinB3 did not significantly change the PPR (n = 14; p > 0.5). Representative traces (average from 5 trials) under each recording condition are shown at the right. D, E, Direct comparison of presynaptic release properties in a triplet mode. D, The schematic on top depicts the triplet-recording mode in which two postsynaptic cells, one untransfected and the other overexpressing ephrinB3, share one presynaptic neuron. Postsynaptic ephrinB3 overexpression did not cause reduction in the PPR (n = 8 triplet pairs; p > 0.1, paired t test). E, However, a significant increase in evoked response amplitude was induced by ephrinB3 overexpression (*p < 0.05, paired t test). F, Two CFP-ephrinB3 constructs, one full-length bearing a silent mutation (ephrinB3*) and the other with a PDZ-binding domain deletion (ephrinB3*-ΔPDZ), are resistant to ephrinB3-siRNA. G, AMPA receptor-mediated mEPSC frequency was reduced by ephrinB3 knockdown (pSuper, n = 24; siRNA, n = 30; **p < 1 × 10⁻⁴). This reduction was fully rescued by coexpression of the mutant full-length ephrinB3* (n = 30; *p < 0.01), but not by coexpression of the ephrinB3*-ΔPDZ (n = 26; ^# p > 0.5). All error bars indicate SEM.