The mushroom bodies (MBs) are known to be the most prominent olfactory memory center in Drosophila. The MB Kenyon cells 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 high order brain center affects naïve behaviors such as olfaction and gustation. 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. We show that salt avoidance is enhanced upon optogenetic activation of the Kenyon cells. This effect was also observed after ablation of pPAM DANs with simultaneous optogenetic activation of the KCs. We were able to phenocopy this effect by optogenetic activation of TH-Gal4 positive dopaminergic neurons, however not after artificial activation of single DANs of the DL1 cluster. In contrast, larvae showed no salt avoidance 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 coherent 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.

With the focus on dopaminergic neurons, I conducted two experiments with two different driver lines to see how the naive gustatory behavior in Drosophila larvae is affected.

The first cross I tested was R58E02-Gal4 x UAS-ChR2-XXL, which gave me the following results:

As seen in the figures, there was no effect under blue light.

For the second experiment I crossed TH-Gal4 x UAS-ChR2-XXL with these results:

With this experiment, there was an effect on gustatory behavior as there is a clear significant difference between the experimental group and the control group.

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