a, Representative images of retinal ganglion cells (RGCs) grown without astrocytes, or with control or A1 reactive astrocytes, immunostained with pre- and post-synaptic markers HOMER (green) and BASSOON (red). Co-localization (yellow puncta) was counted as a structural synapse. b, Total number of synapses normalized per each individual RGC, n = 50 neurons in each treatment. c, Quantitative PCR for astrocyte secreted synaptogenic factors. d, Representative traces of whole-cell patch clamp mEPSC recordings from RGCs. e, Frequency of mEPSCs was significantly decreased in presence of A1s (RGCs without astrocytes: 0.19 ± 0.05 Hz n = 12 neurons, RGCs with resting astrocytes: 2.28 ± 0.51 Hz n = 14 neurons, RGCs with A1s: 0.95 ± 0.19Hz n = 16 neurons). f, A1s significantly decreased mean amplitude of mEPSCs (RGCs without astrocytes: 21.81 ± 0.78 pA n = 12 neurons, RGCs with resting astrocytes: 23.89 ± 0.38 pA n = 14 neurons, RGCs with A1s: 22.32 ± 0.37 pA n = 16 neurons). g, RGCs cultured with A1s had significantly more small amplitude mEPSCs in cumulative probability histograms (p < 0.0001 Kolmogorov-Smirnov test, n = 12–16 neurons per condition). * p < 0.05, one-way ANOVA. Error bars indicate s.e.m. Scale bar: 10 μm.