Figure 1. SMN deficiency in motoneurons impairs synapse formation and synaptic transmission. A, Representative images of a WT and SMA motoneuron (MN) immunostaining with specific antibodies against presynaptic and postsynaptic markers, synaptophysin (Syn) and PSD95, respectively. More than 95% synaptophysin-positive puncta are colocalized with postsynaptic PSD95 staining. B, Synapse number per cell is significantly decreased in SMA motoneurons than that in WT motoneurons (WT: 26.2 ± 0.9, n = 71; SMA: 21.2 ± 1.1, n = 71). p < 0.001 (unpaired t test). C, SMA motoneurons display normal survival as WT motoneurons at 12 DIV (WT: 1.7 ± 0.3%; SMA: 1.8 ± 0.4%; p = 0.75). D, Glutamatergic mEPSCs are recorded from a WT and SMA motoneuron, which can be blocked by CNQX. E, F, The frequency (E) but not amplitude (F) of mEPSC is decreased on SMA motoneurons, compared with that on WT motoneurons (frequency: WT, 0.76 ± 0.19 Hz, n = 35; SMA, 0.34 ± 0.18 Hz, n = 35; p < 0.001, unpaired t test; amplitude: WT, 9.7 ± 1.1 pA; SMA, 8.8 ± 1.3 pA; p = 0.24, unpaired t test). G, [Ca2+]i increase elicited by 100 μm glutamate. Arrow indicates application of glutamate. H, I, [Ca2+]i basal level (H) and [Ca2+]i increase with 100 μm glutamate application (I) in WT and SMA motoneurons (calcium basal level: WT, 0.66 ± 0.008, n = 75; SMA, 0.64 ± 0.009 n = 63; p = 0.24, unpaired t test). *p < 0.05. **p < 0.01. Error bars indicate SE.