, 2003). Importantly, memory retrieval through these modified Vorinostat cost KC-output synapses was predicted to guide either odor avoidance or approach behavior. A KC synapse-specific representation of memories of opposing valence would dictate that it is not possible to functionally separate the retrieval of aversive and appetitive memories by disrupting KC-wide processes. We therefore tested these models by systematically blocking neurotransmission from subsets of the retrieval-relevant

αβ neurons. We found that aversive and appetitive memories can be distinguished in the αβ KC population, showing that opposing odor memories do not exclusively rely on overlapping KCs. Whereas output from the αβs neurons is required for aversive and appetitive memory retrieval, the αβ core (αβc) neurons are only critical for conditioned approach behavior. Higher-resolution anatomical analysis of the innervation

of reinforcing DA neurons suggests that valence-specific asymmetry may be established during training. Furthermore, dendrites of KC-output neurons differentially innervate the MB in a similarly stratified manner. We therefore propose that aversive memories are retrieved and avoidance behavior triggered only from the αβ surface (αβs) Palbociclib manufacturer neurons, whereas appetitive memories are retrieved and approach behavior is driven by efferent neurons that integrate across the αβ ensemble. Several studies have reported the

importance of output from MB αβ neurons for the retrieval of aversive and appetitive olfactory memories (Dubnau et al., 2001, McGuire et al., 2001, Schwaerzel et al., 2003, Krashes et al., 2007, Krashes and Waddell, 2008 and Trannoy Levetiracetam et al., 2011). However, genetic labeling reveals further anatomical segregation of the ∼1,000 αβ neurons into at least αβ posterior (αβp or pioneer), αβ surface (αβs or early), and αβ core (αβc or late) subsets that are sequentially born during development (Ito et al., 1997, Lee et al., 1999 and Tanaka et al., 2008). We therefore investigated the role of these αβ subsets in memory retrieval. We first obtained, or identified, GAL4 lines with expression that was restricted to αβ subsets and verified their expression. Prior reports showed that the c739 GAL4 (McGuire et al., 2001) labels αβ neurons contributing to all three classes (Aso et al., 2009). In contrast, NP7175 expresses in αβc neurons and c708a in αβp neurons (Murthy et al., 2008, Tanaka et al., 2008 and Lin et al., 2007). Lastly, we identified the 0770 GAL4 line from the InSITE collection (Gohl et al., 2011) with strong expression in αβs neurons and weaker expression in αβp neurons. We expressed a membrane-tethered GFP (uas-mCD8::GFP) using the c739, 0770, NP7175, and c708a GAL4 drivers and localized expression within the overall MB neurons using a LexAop-rCD2::RFP transgene driven by 247-LexA::VP16 (Pitman et al., 2011).