The number of synapses formed by RGCs cultured from NP1/2 KO mice is normal. A, B, RGC cultured without astrocytes and stained for synaptotagmin 1 (red) and PSD-95 (green) from WT (A) or NP1/2 KO (B) mice. C, D, RGC cultured with astrocytes and stained for synaptotagmin (red) and PSD-95 (green) from WT (C) or NP1/2 KO (D) mice. Scale bar, 20 μm. E, F, Number of synapses per field identified by colocalization of PSD-95 and synaptotagmin 1 at 2 weeks in culture (E) or 4 weeks in culture (F). Twenty cells were quantified per condition. These values are typical of RGCs in culture (Ullian et al., 2001; Christopherson et al., 2005). All values are mean ± SEM.