Real-Time Measurement of Stimulated Dopamine Release in Compartments of the AdultDrosophila melanogasterMushroom Body

Abstract

<jats:title>Abstract</jats:title><jats:p><jats:italic>Drosophila melanogaster</jats:italic>, the fruit fly, is an exquisite model organism to understand neurotransmission. Dopaminergic signaling in the <jats:italic>Drosophila</jats:italic> mushroom body (MB) is involved in olfactory learning and memory, with different compartments controlling aversive learning (corner) 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<jats:sub>2</jats:sub> (chemogenetics), and CsChrimson (optogenetics). Evoked dopamine release was measured with fast-scan cyclic voltammetry in isolated adult <jats:italic>Drosophila</jats:italic> brains. Acetylcholine stimulated the largest dopamine release (0.40 μM), followed by P2X<jats:sub>2</jats:sub> (0.14 μM), and CsChrimson (0.07 μM). With the larger acetylcholine and P2X<jats:sub>2</jats:sub> stimulations, there were no regional or sex differences in dopamine release. However, with CsChrimson, dopamine release was significantly higher in the corner 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<jats:sub>m</jats:sub>, but the corner had a significantly lower V<jats:sub>max</jats:sub> (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 <jats:italic>Drosophila</jats:italic>, 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 <jats:italic>Drosophila</jats:italic>.</jats:p>

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, 2018; 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).…”

Microdosing ketamine in Drosophila does not block serotonin reuptake, but causes complex behavioral changes mediated by glutamate and serotonin receptors

“…Ultimately, this study shows that SERT inhibition is not required to achieve behavioral effects with microdoses of ketamine and that ketamine may increase feeding behavior via NMDA receptor antagonism, while locomotion behavior may be caused by 5‐HT 1A or 5‐HT 2 agonism (Kraus et al., 2019; Spies et al., 2018). Future studies in genetically altered flies, where NMDA or serotonin receptors are over‐ or under‐expressed, would help confirm these are the targets of ketamine or other SSRIs to elicit behavioral changes (Shin et al., 2020; Silva et al., 2014). Future work should also investigate real‐time changes with ketamine or SSRIs on other neurotransmitters, such as glutamate (Marvin et al., 2018; Richter et al., 2018).…”

Microdosing ketamine inDrosophiladoes not inhibit SERT like SSRIs, but causes behavioral changes mediated by glutamate and serotonin receptors

“…This study shows that SERT inhibition is not required to achieve behavioral effects with microdoses of ketamine, and that ketamine may increase feeding behavior via NMDA receptor antagonism, while locomotion behavior may be caused by ketamine acting as a 5-HT 1A or 5-HT 2 agonist (Kraus et al, 2019; Spies et al, 2018). Future studies in genetically altered flies, where NMDA or serotonin receptors are knocked-down, would help confirm these are the targets of ketamine or other SSRIs to elicit behavioral effects (Shin et al, 2020; Silva et al, 2014). Future work should also investigate the real-time changes of microdoses of ketamine or SSRIs on other neurotransmitters, such as glutamate (Marvin et al, 2018; Richter et al, 2018).…”