Additive Expression of Consolidated Memory through Drosophila Mushroom Body Subsets.

Associative olfactory memory in Drosophila has two components called labile anesthesia-sensitive memory and consolidated anesthesia-resistant memory (ARM). Mushroom body (MB) is a brain region critical for the olfactory memory and comprised of 2000 neurons that can be classified into αß, α'ß', and γ neurons. Previously we demonstrated that two parallel pathways mediated ARM consolidation: the serotonergic dorsal paired medial (DPM)-αß neurons and the octopaminergic anterior paired lateral (APL)-α'ß' neurons. This finding prompted us to ask how this composite ARM is retrieved. Here, we showed that blocking the output of αß neurons and that of α'ß' neurons each impaired ARM retrieval, and blocking both simultaneously had an additive effect. Knockdown of radish and octß2R in αß and α'ß' neurons, respectively, impaired ARM. A combinatorial assay of radish mutant background rsh1 and neurotransmission blockade confirmed that ARM retrieved from α'ß' neuron output is independent of radish. We identified MBON-ß2ß'2a and MBON-ß'2mp as the MB output neurons downstream of αß and α'ß' neurons, respectively, whose glutamatergic transmissions also additively contribute to ARM retrieval. Finally, we showed that α'ß' neurons could be functionally subdivided into α'ß'm neurons required for ARM retrieval, and α'ß'ap neurons required for ARM consolidation. Our work demonstrated that two parallel neural pathways mediating ARM consolidation in Drosophila MB additively contribute to ARM expression during retrieval.

Parallel circuits control temperature preference in Drosophila during ageing.

The detection of environmental temperature and regulation of body temperature are integral determinants of behaviour for all animals. These functions become less efficient in aged animals, particularly during exposure to cold environments, yet the cellular and molecular mechanisms are not well understood. Here, we identify an age-related change in the temperature preference of adult fruit flies that results from a shift in the relative contributions of two parallel mushroom body (MB) circuits­the ß'- and ß-systems. The ß'-circuit primarily controls cold avoidance through dopamine signalling in young flies, whereas the ß-circuit increasingly contributes to cold avoidance as adult flies age. Elevating dopamine levels in ß'-afferent neurons of aged flies restores cold sensitivity, suggesting that the alteration of cold avoidance behaviour with ageing is functionally reversible. These results provide a framework for investigating how molecules and individual neural circuits modulate homeostatic alterations during the course of senescence.

Anatomical characterization of thermosensory AC neurons in the adult Drosophila brain.

Temperature preference is vital for the survival of all animals. A small set of warm-activated anterior cell (AC) neurons acting as an internal thermosensor in the Drosophila brain is critical for optimal temperature selection ( Hamada et al., 2008 , Nature, 454, 217-220). Here, the authors analyze the circuit components of the AC neurons by characterization of its spatial distribution, dendrite-axon polarity, and the putative type of neurontransmitter released. The results show that the AC neurons are serotonergic, do not have any dendrites, and send axons bilaterally to the superior dorsofrontal protocerebrum (SDFP). Searching the FlyCircuit database for neurons with serotonin receptor and dendrites in the SDFP, the authors found a dorsal-anterior-lateral (DAL) neuron as a candidate postsynaptic partner of the AC neurons. In conclusion, by morphological analysis of the AC neurons, the authors show a general strategy for predicting brain circuits orchestrating thermosensory behaviors.