OPTOGENETIC ACTIVATION OF MUSHROOM BODY KENYON CELLS AFFECTS NAÏVE SALT AVOIDANCE IN <EM >DROSOPHILA</EM> LARVAE

The mushroom bodies (MBs) are known to be the most prominent olfactory memory center in Drosophila. The MB Kenyon cells (KCs) receive olfactory (via projection neurons, PNs) and gustatory (via dopaminergic neurons, DANs) input. The coincident detection of these stimuli elicits then the formation of associative memory. However, little is known whether and how this higher order brain center affects naïve behaviors such as olfaction and gustation separately. We use fruit fly larvae to test the innate salt avoidance in a simple choice assay. Drosophila larvae are tested for 3 minutes for their preference for 1.5M NaCl. Optogenetic activation of the KCs alone, as well as in combination with ablation of MB innervating pPAM DANs, enhanced naïve salt avoidance. We phenocopied this effect by optogenetic activation of TH-Gal4 positive dopaminergic neurons. Artificial activation of single DANs of the DL1 cluster within the TH-Gal4 positive DANs showed no effect on naïve behavior. In contrast, larvae showed no salt avoidance at all after optogenetic activation of sNPF-Gal4 positive neurons. Neuropeptidergic and dopaminergic signaling are tightly involved in modulation of the MBs. However, it is not clear whether our observations depend on the same or separate neuronal pathways. Therefore, we use simultaneous manipulations of different components of the MB, dopaminergic, and sNPF circuitries to unravel the neural mechanisms of modulation of naïve gustatory behaviors in the Drosophila larvae.