Two LBH589 mouse such GFP-based reporter molecules, supplied on transgenes with expression driven in specific neurons using the GAL4/UAS system, have

been used extensively. Synapto-pHluorin ( Figure 2) is a pH-sensitive GFP molecule that is localized to the synaptic vesicle. It provides an optical assay for synaptic transmission due to the change in pH environment between its vesicular localization and synaptic localization that occurs upon neurotransmitter release. G-CaMP ( Figure 2) is an EGFP fused to a calcium binding domain and designed in a way that increases in intracellular calcium lead to increased fluorescence. The experimental setup to assay the fluorescence of these molecules in the brain of a living fly is illustrated in Figure 3. The first memory trace to be discovered by optical imaging was discovered in the AL of the honeybee (Faber et al., 1999). The search for early forming memory traces in Drosophila through optical imaging also led to the AL. Yu et al. (2004) expressed the reporter molecule synapto-pHluorin in the PNs of the AL and visualized synaptic release in eight dorsal glomeruli in response to odor and shock stimuli presented to the living fly. This study used a “within animal” experimental design, in which the response properties of the neurons to odor was assessed within each individual animal before and after conditioning. The eight sets of

PNs that innervate selleck products the eight glomeruli all respond with release of neurotransmitter upon electric shock delivered to the body of the fly, whereas only four and three of the eight sets respond to the odors 3-octanol (Oct) and 4-methylcyclohexanol (Mch), respectively, in naive animals. Most interestingly, an additional set of PNs that innervate the D glomerulus becomes synaptically active in response to Oct as the conditioned odor immediately after conditioning ( Figure 4). Conditioning with Mch also recruits an additional set of PNs into the representation of the Adenylyl cyclase learned odor—the

set that innervates the VA1 glomerulus. Thus, a memory trace forms in the AL immediately after learning and is registered as the recruitment of a new set of PNs into the normal representation of the learned odor. Because only 8 of the ∼43 glomeruli were imaged in these experiments, it seems likely that other sets of PNs are also recruited into the representation of the learned odor, but this possibility has not been investigated. In addition, this memory trace is very short lived, with the responses to the CS+ falling to basal levels by 7 min after conditioning. This memory trace appears to be intrinsic to the PNs: tests for the existence of memory traces in neurons presynaptic to PNs (ORNs or INs) were negative. Thus, the increased activity of PNs in response to the CS+ after conditioning does not appear to be the consequence of a memory trace forming in upstream neurons. Wang et al.