In summary, our data demonstrate a key role for glutamatergic synaptic transmission during CNS circuit refinement in mediating the exclusion of axons from inappropriate target regions. However, contrary to Carfilzomib mouse what current models of activity-dependent development

would predict, our data also demonstrate that RGC populations with markedly reduced synaptic activity can still consolidate and maintain normal amounts of target territory, even in the presence of more active competitors. These findings advance our understanding of the mechanisms that establish developing CNS circuits by helping to clarify the direct contributions of glutamatergic synaptic transmission to axon refinement. The ET33 Sert-Cre line was generated by GENSAT (Gong et al.,

2007) and obtained from Mutant Mouse Regional Resource Centers (http://www.mmrrc.org/strains/17260/017260.html). The lox-STOP-lox-mGFP-IRES-NLS-LacZ-pA reporter (Hippenmeyer et al., 2005) was a gift selleck chemicals from J.L. Rubenstein (University of California, San Francisco) and lox-STOP-lox-lacZ (Soriano, 1999) and lox-STOP-lox-tdTomato (Ai9; Madisen et al., 2010) were obtained from The Jackson Laboratory. Homozygous floxed VGLUT2 mice were previously described (Hnasko et al., 2010). All mouse lines were congenic on the C57BL/6 background except for the mGFP mice, which were on a mixed 129SV/J and C57BL/6 background. Eyes were removed and fixed in 4% PFA for 8 hr at 4°C. Retinal whole mounts were prepared by extracting the retina from razoxane the eye. Retinal sections were prepared by hemisecting fixed eyes, crypoprotecting the sections in 30% sucrose, freezing them, and cryosectioning them at 12 μm. LGN histology: brains

were fixed overnight in 4% PFA at 4°C, cryoprotected in 30% sucrose, and sectioned in the coronal plane at 40 μm. X-gal staining: retinas were washed in buffer (0.0015 M MgCl2, 0.01% deoxycholate, and 0.02% NP40 in phosphate buffer) three times for 15 min, placed in stain (2.45 mM X-gal in dimethylformamide, 5.0 mM potassium ferrocyanide, and 5.0 mM potassium ferricyanide in wash buffer) for 2 hr at 37°C, and washed again three times for 15 min. Visualization of mGFP reporter was performed as described (Huberman et al., 2008b). Imaging the tdTomato reporter did not require immunostaining. Retinas were harvested from P3 mice, digested with papain (16.5 U/ml; Worthington), dissociated, and plated on glass coverslips (coated with 10 mg/ml poly-D-lysine and 2 mg/ml laminin) at 25,000 cells/well in a 24-well plate. Cells were incubated in defined media (Meyer-Franke et al., 1995). At DIV 2, cultured retinal cells were fixed in 4% paraformaldehyde, rinsed in PBS, and blocked for 30 min in a 1:1 mix of goat serum and antibody buffer (150 mM NaCl, 50 mM Tris base, 1% L-lysine, and 0.4% azide). Cells were incubated in guinea pig anti-VGLUT2 polyclonal antibody (1:1500, Millipore) overnight at 4°C and then rinsed in PBS three times for 10 min.