As for PC-PC and PC-MC connections (Figures 1, 2, and 5), the locus of NMDAR blockade in type 1 PV INs was presynaptic according to Dasatinib purchase CV and PPR analyses (Figures 6E and 6F). The heterogeneity of preNMDAR expression at excitatory inputs onto PV INs could also be explained by the possible existence of two types of presynaptic PCs, one of which possesses NMDARs at synaptic terminals and the other of which does not. We therefore looked for preNMDARs at synapses onto PV INs by recording spontaneous neurotransmission, as this approach relatively globally samples inputs

onto a recorded cell (see SOM INs above and Berretta and Jones, 1996; Brasier and Feldman, 2008; Sjöström et al., 2003). We found that the frequency of mEPSCs was reduced by AP5 in some, but not all, PV INs (Figures 6G–6L), in keeping with our results for evoked neurotransmission onto PV INs. Again, clustering segregated the data into http://www.selleckchem.com/products/Vorinostat-saha.html two distinct classes (Figure 6J). Our spontaneous release experiments are most parsimoniously explained by the existence of two types of PV INs, with type 1, but not type 2, possessing preNMDARs at its excitatory inputs. We next determined the morphological characteristics of the postsynaptic cell types investigated thus far:

PCs, MCs, and PV INs (Figure 7A). PCs had a characteristic apical dendrite with an axon that remained largely confined to L5, although with some cells it ventured up to L1 (see Markram et al., 1997). The morphology of MCs was characteristically inverted to that of PCs, with ascending axons ramifying up to L1 and with dangling dendrites (Silberberg and Markram, 2007). PV INs were reconstructed blind to electrophysiological type, and

upon unblinding of the data set, it was clear that the axonal morphologies of the two types were distinct: type 1 PV INs had an ascending axon that reached L2/3, whereas the axonal arbor of type 2 PV INs remained in L5 (Figures 7A and 7B). In fact, PV INs could be independently clustered into two classes based on the total length of all axonal arborizations in the supragranular Sclareol layers L2/3 and L1 (Figure 7C). The dendritic trees, however, did not differ (Figure 7D), suggesting that axonal, but not dendritic, branching pattern distinguishes these PV IN cell types (Ascoli et al., 2008; Markram et al., 2004). We were concerned that the layer-specific differences in axonal arborizations between postsynaptic neuronal types in Figure 7 were the result of a 2PLSM imaging bias. However, we found that the imaged regions were indistinguishable (Figure S5). We also examined Sholl diagrams (Sholl, 1953) but found them relatively poor at distinguishing the two PV IN types, whereas the extent of supragranular axonal branching consistently separated the two PV IN types well (Figure S5). Intriguingly, irrespective of whether the effect of AP5 or axonal supragranular layer branching was used to cluster PV INs, the same cells were grouped together (Figure 7E).