Real-Time Measurement of Stimulated Dopamine Release in Compartments of the Adult Drosophila melanogaster Mushroom Body

Abstract

Drosophila melanogaster, the fruit fly, is an exquisite model organism to understand neurotransmission. Dopaminergic signaling in the Drosophila mushroom body (MB) is involved in olfactory learning and memory, with different compartments controlling aversive learning (heel) vs appetitive learning (medial tip). Here, the goal was to develop techniques to measure endogenous dopamine in compartments of the MB for the first time. We compared three stimulation methods: acetylcholine (natural stimulus), P2X 2 (chemogenetics), and CsChrimson (optogenetics). Evoked dopamine release was measured with fast-scan cyclic voltammetry in isolated adult Drosophila brains. Acetylcholine stimulated the largest dopamine release (0.40 μM), followed by P2X 2 (0.14 μM), and CsChrimson (0.07 μM). With the larger acetylcholine and P2X 2 stimulations, there were no regional or sex differences in dopamine release. However, with CsChrimson, dopamine release was significantly higher in the heel than the medial tip, and females had more dopamine than males. Michaelis-Menten modeling of the single-light pulse revealed no significant regional differences in K m, but the heel had a significantly lower V max (0.12 μM/s vs. 0.19 μM/s) and higher dopamine release (0.05 μM vs. 0.03 μM). Optogenetic experiments are challenging because CsChrimson is also sensitive to blue light used to activate green fluorescent protein, and thus, light exposure during brain dissection must be minimized. These experiments expand the toolkit for measuring endogenous dopamine release in Drosophila, introducing chemogenetic and optogenetic experiments for the first time. With a variety of stimulations, different experiments will help improve our understanding of neurochemical signaling in Drosophila.

Temporally and Spatially Localized PKA Activity within Learning and Memory Circuitry Regulated by Network Feedback

“…1 ) is consistent with sensory experience-dependent regulation ( Dombrovski and Condron, 2021 ). Importantly, MB sensory integration functions differ markedly between females and males ( Park et al, 2018 ; Shin et al, 2020 ), correlating with the report here of sex-dependent PKA signaling differences in females compared with males ( Fig. 1 ).…”

SSRI antidepressants differentially modulate serotonin reuptake and release in Drosophila

“…The Daws group also found serotonin reuptake did not significantly change in SERT KO mice (Bowman et al, 2020), which implies compensation by other neurotransmitter systems. Our group has adapted FSCV to measure neurotransmitter dynamics in Drosophila (Borue et al, 2009;Shin et al, 2020;Vickrey et al, 2009). Serotonin release is stimulated using optogenetics, as the UAS/Gal4 system is used to express CsChrimson with a tryptophan hydroxylase (trh-Gal4) driver that localizes it in serotonin neurons (Dunham & Venton, 2020;Privman & Venton, 2015).…”

Pain is so close to pleasure: the same dopamine neurons can mediate approach and avoidance in Drosophila

“…Hz (Shin et al, 2020). Our regimes of 20 Hz stimulation with 10 ms (T-mazes) or 50 ms (Joystick) pulse-width do not seem to fall outside the range of what has been shown to be effective either behaviorally or in triggering dopamine release.…”