, 2000). That GluN2B receptor activity is required for both the maintenance of silent synapses as well as inducing LTP and synapse maturation may initially seem contradictory. However, differences in Ca2+ influx during low-level or basal activity versus strong activity may activate different signaling pathways. Indeed, it is well established that an www.selleckchem.com/products/Temsirolimus.html LTP-inducing stimulus can convert AMPAR-silent synapses into AMPAR-signaling synapses (Durand et al., 1996, Isaac et al., 1997 and Liao et al., 1995), while, in neonatal neurons, AMPAR silencing can be induced with an LTD-like protocol (Xiao et al., 2004). Our results here suggest that low-level activation of GluN2B-containing

NMDARs suppresses AMPAR insertion into synaptic sites, possibly through an LTD-like mechanism at developing hippocampal neurons. Taken together, these observations demonstrate

a fundamental developmental role for the NMDA receptor subunit switch in tightly regulating AMPAR recruitment at multiple levels. Due to the perinatal lethality of the germline GluN2B KO, many groups have recently examined the effects of more selective GluN2B deletion. For example, dissociated cortical cultures from GluN2B KO mice showed an increase in mEPSC amplitude (Hall et al., 2007), in contrast to our findings, though frequency appeared to increase but was not reported. In addition, RNA interference (RNAi) was used to block GluN2B expression with similar effects; however, this manipulation resulted in a complete loss of all NMDAR current

until (Hall et al., 2007). LDN-193189 order This discrepancy may be related to the high excitatory drive of dissociated cultures, direct or indirect off-target effects of the GluN2B RNAi on GluN2A expression, or it may suggest that their experimental system may not be broadly generalizable to synapses developing in intact networks. Interestingly, deletion of GluN2B in the adult hippocampus had no effect on mEPSC amplitude or frequency (von Engelhardt et al., 2008), suggesting a purely developmental effect. Due to the increase in mEPSC frequency after deletion of GluN2B, we analyzed dendritic anatomy and spine density and saw no significant changes in overall dendrite branching or length in any of the conditions. Previous reports of GluN2 subunit effects on dendritic arborization have revealed subtle changes in dendritic arbor growth and patterning, but not significant changes in overall length (Espinosa et al., 2009 and Ewald et al., 2008). We did, however, observe a small significant decrease in spine density with the deletion of GluN2B. This reduction in spines after the deletion of GluN2B has been reported previously (Akashi et al., 2009, Espinosa et al., 2009 and Gambrill and Barria, 2011) and may be related to the unfettered early expression of GluN2A (Gambrill and Barria, 2011), as deletion of GluN1 does not alter spine density (Figure 7; Figure S5) (Adesnik et al., 2008).