Induction of aversive learning through thermogenetic activation of Kenyon cell ensembles in Drosophila

Abstract

Drosophila represents a model organism to analyze neuronal mechanisms underlying learning and memory. Kenyon cells of the Drosophila mushroom body are required for associative odor learning and memory retrieval. But is the mushroom body sufficient to acquire and retrieve an associative memory? To answer this question we have conceived an experimental approach to bypass olfactory sensory input and to thermogenetically activate sparse and random ensembles of Kenyon cells directly. We found that if the artifical activation of Kenyon cell ensembles coincides with a salient, aversive stimulus learning was induced. The animals adjusted their behavior in a subsequent test situation and actively avoided reactivation of these Kenyon cells. Our results show that Kenyon cell activity in coincidence with a salient aversive stimulus can suffice to form an associative memory. Memory retrieval is characterized by a closed feedback loop between a behavioral action and the reactivation of sparse ensembles of Kenyon cells.

Stochastic and Arbitrarily Generated Input Patterns to the Mushroom Bodies Can Serve as Conditioned Stimuli in Drosophila

“…Fly stocks were raised on standard cornmeal-agar medium at 18 • C, 60% relative humidity, and under a 12 h light-dark cycle. Flies were generated as described by Vasmer et al (2014). A Hsp70-FLP insertion on the X-chromosome (provided by G. Struhl) was combined with the GH146-Gal4 (Stocker et al, 1997) insertion on the second chromosome to generate a strain homozygous for both P-element inserts.…”

“…A Hsp70-FLP insertion on the X-chromosome (provided by G. Struhl) was combined with the GH146-Gal4 (Stocker et al, 1997) insertion on the second chromosome to generate a strain homozygous for both P-element inserts. These flies were crossed with a strain carrying the UAS-FRT-CD2(Stop)-FRT-mCherry-dTRPA1 (Vasmer et al, 2014;Pooryasin and Fiala, 2015) construct with the insertion balanced over CyO. Female F1 offspring younger than 2 days were anesthetized using CO 2 and transferred to a fresh food vial.…”

“…Flies were trained as described by Vasmer et al (2014), schematically illustrated in Figure 1C. Female flies aged 4-6 days FIGURE 1 | mCherry-dTRPA1 expression in random subsets of olfactory projection neurons (OPNs).…”

“…They are arbitrary in the sense that no genetically determined pattern of Kenyon cell activity or circuit diagram carries any behaviorally relevant information about the odor or any other stimulus. In a previous study, we showed that artificially and stochastically activated groups of Kenyon cells, in coincidence with a punishing electric shock, can be learned as aversive cue without direct sensory input (Vasmer et al, 2014). By modifying their behavior, trained animals avoided reactivation of those Kenyon cell ensembles whose activities were associated with the punishment.…”

SIFamide Translates Hunger Signals into Appetitive and Feeding Behavior in Drosophila

“…The dense innervation of the AL and the SOG, which receive olfactory and gustatory input, respectively, suggest that SIFamide might modulate chemosensory processing. Therefore, we monitored the flies' behavior evoked by chemosensory stimulation while SIFamidergic neurons were thermogenetically activated using the temperature-sensitive cation channel, dTRPA1 (Hamada et al, 2008;Vasmer et al, 2014). At 18 C, starved flies approached a source of the food-related odorant, ethyl acetate (EA), across different concentrations ( Figure 1C), whereas satiated flies behaved indifferently toward this odorant ( Figure 1D).…”