The PPL1 cluster contains five distinct DAN types with stereotyped innervation zones within the MB lobes, the neuropil housing the axon fibers of MB intrinsic neurons (Mao and Davis, 2009). DAN output has been shown to be necessary for the acquisition

of aversive olfactory memories (Schwaerzel et al., 2003), and artificial stimulation of the PPL1 DANs in the presence of an odor is sufficient to form aversive olfactory memory (Claridge-Chang et al., 2009). These studies provide evidence that the PPL1 DANs convey the unconditioned stimulus (US) to the MBs, where it converges with the olfactory conditioned stimulus (CS) for the acquisition of aversive olfactory memories. Two distinct dopamine receptors, dDA1 and DAMB, are highly expressed within the MB intrinsic neurons and are coupled to the cAMP signaling pathway, and thus are likely mediators of dopaminergic effects on olfactory memory (Sugamori

et al., 1995, Han et al., 1996 and Kim Erlotinib mouse et al., 2003). Indeed, the dDA1 receptor is required for both aversive and appetitive olfactory memory formation in adult flies (Kim et al., 2007). While the DAMB receptor mutant was reported to produce aversive olfactory memory defects in larvae (Selcho et al., 2009), these results were confounded by odor preference defects and leave the role of DAMB in adult olfactory learning and memory largely unknown. Here we utilize bidirectional modulation of DAN activity Ixazomib with temporal precision, in vivo

functional imaging of DAN activity, and dopamine receptor mutant analysis to address the role that dopamine plays in memory. Our results indicate that dopamine has a dual role in both the acquisition of olfactory memories and the forgetting of these memories. We used the GAL4 > UAS system (Brand and Perrimon, 1993) to acutely modulate the activity of Drosophila’s DANs during the period of memory retention after olfactory classical conditioning. Oxygenase Our initial studies employed a tyrosine-hydroxylase (TH) gal4 line (TH-gal4) to drive UAS-transgene expression in the DANs in the fly brain ( Mao and Davis, 2009 and Friggi-Grelin et al., 2003). We drove expression of a UAS-shits1 transgene encoding a temperature-sensitive Dynamin protein that blocks synaptic output at restrictive temperatures ( Kitamoto, 2001) or a UAS-trpA1 transgene encoding a temperature-sensitive cation channel to stimulate DANs at elevated temperatures ( Hamada et al., 2008). Both of these transgenes provide for normal neuronal function below 25°C but modulate activity at temperatures above 29°C. Thus, these two tools allow for the control of neuronal activity in a bidirectional way. Remarkably, we discovered that blocking synaptic output from DANs with UAS-shits1 for 40 min or more after learning significantly enhanced memory measured at 3 hr ( Figure 1A), whereas there was no significant increase in memory with control +/UAS-shits1 flies.