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Functional analysis of neural circuits involved in the dynamics of olfactory memories in Drosophila melanogaster
Séverine Trannoy, doctorante - Ph.D student Crédits : ESPCI ParisTech
Pairing one odor with sugar, to starved flies, induces appetitive olfactory memory. 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), the olfactory memory center. We proposed a new model of the dynamic of appetitive memory phases in whch 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. Indeed, blocking the neurotransmission of these neurons during the consolidation phase leads to an 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 process.