Our results thus suggest that a postsynaptic cell determines the molecular composition of presynaptic terminals onto it. Even though we used the PV IN mouse line to improve specificity compared to wild-type IN recordings (Figure 1), we unexpectedly found

two PV IN types instead of one. The axonal projection pattern of type 2 PV INs—which was confined to L5—indicated that these were classical BCs. The ascending selleck inhibitor axonal arborization of the type 1 PV INs, however, has to our knowledge not been described previously in any detail (compare Kapfer et al., 2007; Kätzel et al., 2011; Thomson et al., 2002). We investigated the possibility that these were Chandelier cells (Woodruff et al., 2009) by looking for putative synaptic contacts on the axon hillocks of PCs, which were reciprocally connected with type 1 PV INs. However, putative contacts from type 1 as well as from type 2 PV INs onto PCs were perisomatically located on dendrites (Figure S6). We next

asked whether type 1 and type 2 PV INs were of different ages, but this was not the case (postnatal day [P] 13.6 ± 0.9 versus 13.5 ± 1.5, p = 0.96). Indeed, type 1 and 2 PV INs were occasionally found in the same acute slice. Finally, we immunostained GFP-positive INs for PV expression. In mature animals, PV immunolabeling and GFP fluorescence unsurprisingly colocalized well (as shown before, see Chattopadhyaya et al., 2004), but at P14, a subset of GFP-positive INs did not stain for PV (Figure S7), raising mafosfamide the possibility that young click here type 1 PV INs are immature and have not yet developed PV expression. We also compared PV INs

to the wild-type INs recorded in Figures 1 and 2. We found that, morphologically (Figure S2) as well as electrophysiologically (Table S1), type 2 PV INs and wild-type INs were indistinguishable. In summary, we classify type 2 PV INs and wild-type INs as BCs and SOM INs as MCs. Cross-layer innervating type 1 PV INs, however, require further investigation to be fully classified, as their somato-dendritic target in L2/3 is presently unknown. Therefore, we do not further explore the role of this cell type here. Our results indicate that PC-PC and PC-MC, but not PC-BC, connections possess preNMDARs. We also investigated the effect of AP5 on reciprocating BC-PC connections but found AP5 had no effect (data not shown), suggesting the absence of functional preNMDARs here. Based on these findings—which are summarized schematically in Figure 8A—we constructed a simple phenomenological computer model of the local circuit that incorporated measured synaptic dynamics in control and preNMDAR blockade conditions. We used this model to investigate the role of preNMDARs in the local neocortical circuit.