Behavioral Characterization of Individual Olfactory Memory Retrieval in Drosophila Melanogaster

Memory performance depends not only on effective learning and storage of information, but also on its efficient retrieval. In Drosophila, aversive olfactory conditioning generates qualitatively different forms of memory depending on the number and spacing of conditioning trials. However, it is not known how these differences are reflected at the retrieval level, in the behavior of individual flies during testing. We analyzed conditioned behaviors after one conditioning trial and after massed and spaced repeated trials. The single conditioning produces an early memory that was tested at 1.5 h. Tested at 24 h after training, the spaced and the massed protocols generate two different forms of consolidated memory, dependent, or independent of de novo protein-synthesis. We found clearly distinct patterns of locomotor activity in flies trained with either spaced or massed conditioning protocols. Spaced-trained flies exhibited immediate and dynamic choices between punished and unpunished odors during the test, whereas massed-trained flies made a delayed choice and showed earlier disappearance of the conditioned response. Flies trained with single and spaced trials responded to the punished odor by decreasing their resting time, but not massed-trained flies. These findings demonstrate that genetically and pharmacologically distinct forms of memory drive characteristically different forms of locomotor behavior during retrieval, and they may shed light on our previous observation that memory retrieval in massed-trained flies is socially facilitated. Social interactions would enhance exploratory activity, and then reduce the latency of their conditioned choice and delay its extinction

Conditional UAS-targeted repression in Drosophila

The Gal4–UAS enhancer trap system is useful for driving gene expression in various tissues. A new tool that extends Gal4 technology is described here. A fusion protein containing the Gal4 binding domain and the repression domain of the isolator suppressor of hairy wing was placed under the control of a heat shock-inducible promoter. The construct mediates the conditional repression of genes located downstream of a UAS sequence. The repressive effects of the chimeric protein on fasII gene expression were tested by western-blot analysis and in brain sections of adult Drosophila. Owing to the increasing number of Gal4 and UAS transgenic lines, this versatile system will facilitate the study of gene function

Parallel Processing of Appetitive Short- and Long-Term Memories In Drosophila

SummaryIt is broadly accepted that long-term memory (LTM) is formed sequentially after learning and short-term memory (STM) formation, but the nature of the relationship between early and late memory traces remains heavily debated [1–5]. To shed light on this issue, we used an olfactory appetitive conditioning in Drosophila, wherein starved flies learned to associate an odor with the presence of sugar [6]. We took advantage of the fact that both STM and LTM are generated after a unique conditioning cycle [7, 8] to demonstrate that appetitive LTM is able to form independently of STM. More specifically, we show that (1) STM retrieval involves output from γ neurons of the mushroom body (MB), i.e., the olfactory memory center [9, 10], whereas LTM retrieval involves output from αβ MB neurons; (2) STM information is not transferred from γ neurons to αβ neurons for LTM formation; and (3) the adenylyl cyclase RUT, which is thought to operate as a coincidence detector between the olfactory stimulus and the sugar stimulus [11–14], is required independently in γ neurons to form appetitive STM and in αβ neurons to form LTM. Taken together, these results demonstrate that appetitive short- and long-term memories are formed and processed in parallel

Two Independent Mushroom Body Output Circuits Retrieve the Six Discrete Components of Drosophila Aversive Memory

SummaryUnderstanding how the various memory components are encoded and how they interact to guide behavior requires knowledge of the underlying neural circuits. Currently, aversive olfactory memory in Drosophila is behaviorally subdivided into four discrete phases. Among these, short- and long-term memories rely, respectively, on the γ and α/β Kenyon cells (KCs), two distinct subsets of the ∼2,000 neurons in the mushroom body (MB). Whereas V2 efferent neurons retrieve memory from α/β KCs, the neurons that retrieve short-term memory are unknown. We identified a specific pair of MB efferent neurons, named M6, that retrieve memory from γ KCs. Moreover, our network analysis revealed that six discrete memory phases actually exist, three of which have been conflated in the past. At each time point, two distinct memory components separately recruit either V2 or M6 output pathways. Memory retrieval thus features a dramatic convergence from KCs to MB efferent neurons

Communication from Learned to Innate Olfactory Processing Centers Is Required for Memory Retrieval in Drosophila.

The behavioral response to a sensory stimulus may depend on both learned and innate neuronal representations. How these circuits interact to produce appropriate behavior is unknown. In Drosophila, the lateral horn (LH) and mushroom body (MB) are thought to mediate innate and learned olfactory behavior, respectively, although LH function has not been tested directly. Here we identify two LH cell types (PD2a1 and PD2b1) that receive input from an MB output neuron required for recall of aversive olfactory memories. These neurons are required for aversive memory retrieval and modulated by training. Connectomics data demonstrate that PD2a1 and PD2b1 neurons also receive direct input from food odor-encoding neurons. Consistent with this, PD2a1 and PD2b1 are also necessary for unlearned attraction to some odors, indicating that these neurons have a dual behavioral role. This provides a circuit mechanism by which learned and innate olfactory information can interact in identified neurons to produce appropriate behavior. VIDEO ABSTRACT.This work was supported by MRC LMB graduate studentships and Boehringer Ingelheim Fonds PhD fellowships (to M.-J.D. and A.S.B.) and a Janelia graduate research fellowship (to M.-J.D.), ERC starting (211089) and consolidator (649111) grants and core support from the MRC (MC-U105188491) (to G.S.X.E.J.), Agence Nationale de la Recherche funding of the MemoNetworks and MemoMap projects (to P.-Y.P. and T.P.) and the Labex Memolife PhD fellowship (to G.B.-G.), the Howard Hughes Medical Institute (to A.W. and G.M.R.), a Wellcome Trust collaborative award (203261/Z/16/Z to G.S.X.E.J., D.B., and G.M.R.), and a Cambridge Neuroscience-PSL collaborative grant supported by the Embassy of France in London (to G.S.X.E.J.). This work was also supported by the HHMI Janelia Visiting Scientist Program

Experimental evolution of olfactory memory in Drosophila melanogaster

In order to address the nature of genetic variation in learning performance, we investigated the response to classical olfactory conditioning in "high-learning" Drosophila melanogaster lines previously subject to selection for the ability to learn an association between the flavor of an oviposition medium and bitter taste. In a T-maze choice test, the seven high-learning lines were better at avoiding an odor previously associated with aversive mechanical shock than were five unselected "low-learning" lines originating from the same natural population. Thus, the evolved improvement in learning ability of high-learning lines generalized to another aversion learning task involving a different aversive stimulus (shock instead of bitter taste) and a different behavioral context than that used to impose selection. In this olfactory shock task, the high-learning lines showed improvements in the learning rate as well as in two forms of consolidated memory: anesthesia-resistant memory and long-term memory. Thus, genetic variation underlying the experimental evolution of learning performance in the high-learning lines affected several phases of memory formation in the course of olfactory aversive learning. However, the two forms of consolidated memory were negatively correlated among replicate high-learning lines, which is consistent with a recent hypothesis that these two forms of consolidated memory are antagonistic

Analyse fonctionnelle de circuits neuronaux impliqués dans la dynamique des mémoires olfactives chez Drosophila melanogaster

Les Drosophiles à jeûn peuvent être conditionnées dans le but d associer une odeur avec du sucre. Un cycle de conditionnement appétitif induit la formation de mémoire à court terme (MCT) et de mémoire à long terme (MLT). Ainsi, nous avons montré que les MCT et MLT sont formées indépendamment l une de l autre et impliquent des structures neuronales distinctes au sein des Corps Pédonculés (CPs), le centre de la mémoire olfactive. Nous avons proposé un nouveau modèle de la dynamique des phases de mémoire appétitive où la formation des MCT et MLT s effectue de manière parallèle. Suite à cette étude, nous avons identifié deux paires de neurones extrinsèques aux CPs impliqués dans la restitution de l information appétitive à long terme. Enfin, nous nous sommes intéressés aux mécanismes moléculaires et aux réseaux neuronaux impliqués dans la consolidation de la mémoire aversive. Chez la Drosophile, l appariement d une odeur à des chocs électriques deux formes de mémoires consolidées, la mémoire résistante à l anesthésie (MRA) et la MLT (dépendante de la synthèse protéique de novo). Nous avons montré que 3 paires de neurones dopaminergiques aux CPs jouent un rôle d interrupteur contrôlant une bascule entre la MRA et la MLT. Ainsi, bloquer ces trois paires de neurones dopaminergiques durant la période de consolidation induit une augmentation de la MRA et une inhibition de la MLT, alors qu activer ces neurones après conditionnement entraîne une inhibition de la MRA, et favorise la mise en place de la MLT. En conclusion, nous avons caractérisé fonctionnellement des ensembles neuronaux discrets jouant un rôle dans différentes étapes de l'apprentissage et de la mémorisation olfactifsWhen we present an odor associated with sugar to starved flies, they will be attracted by this odor. One cycle of conditioning induces both Short-Term Memory (STM) and Long-Term Memory (LTM). It is accepted that STM and LTM formation is a sequential process but the link between these two memories remains unknown. We adressed this question and clearly demonstrated that STM and LTM can be formed independently and that they involved different neural structures within the Mushroom Bodies (MB), a memory center. We proposed a new model of dynamic of appetitive memory phases where STM and LTM are formed in a parallel way. Then, using the genetically expressed thermosensible toxine allowing a transiently inactivation of neurotransmission, we identified one type of MB efferent neurons involved in appetitive LTM retrieval. Additionally, we were interested to the molecular mechanisms and the neuronal circuits involved in aversive consolidated memories. Pairing an odor with electric shocs induces aversive memory. In drosophila, there are two forms of consolidated memories, the Anesthesia-Resistant Memory (ARM) and LTM (dependent on de novo protein synthesis). We show that three pairs of oscillatory dopaminergic neurons play a essential role of gating between ARM and LTM formation. So, blocking the neurotransmission of these neurons during the consolidation phase leads to a increase of ARM and inhibition of LTM whereas, artificial activation of these neurons after conditioning leads to an inhibition of ARM and favors the implementation LTM. In conclusion, we characterized functionally a restricted population of neurons playing a role in various stage of learning and memory processPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF