Ethanol Behavioral Responses in Drosophila.

Drosophila melanogaster is a powerful genetic model for investigating the mechanisms underlying ethanol-induced behaviors, metabolism, and preference. Ethanol-induced locomotor activity is especially useful for understanding the mechanisms by which ethanol acutely affects the brain and behavior. Ethanol-induced locomotor activity is characterized by hyperlocomotion and subsequent sedation with increased exposure duration or concentration. Locomotor activity is an efficient, easy, robust, and reproducible behavioral screening tool for identifying underlying genes and neuronal circuits as well as investigating genetic and molecular pathways. We introduce a detailed protocol for performing experiments investigating how volatilized ethanol affects locomotor activity using the fly Group Activity Monitor (flyGrAM). We introduce installation, implementation, data collection, and subsequent data-analysis methods for investigating how volatilized stimuli affect activity. We also introduce a procedure for how to optogenetically probe neuronal activity to identify the neural mechanisms underlying locomotor activity.

Methods for Exploring the Circuit Basis of Ethanol-Induced Changes in Drosophila Group Locomotor Activity.

Locomotion is a behavioral readout that can be used to understand responses to specific stimuli or perturbations. The fly Group Activity Monitor (flyGrAM) provides a high-throughput and high-content readout of the acute stimulatory and sedative effects of ethanol. The flyGrAM system is adaptable and seamlessly introduces thermogenetic or optogenetic stimulation to dissect neural circuits underlying behavior and tests responses to other volatilized stimuli (humidified air, odorants, anesthetics, vaporized drugs of abuse, etc.). The automated quantification and readout of activity provide users with a real-time representation of the group activity within each chamber throughout the experiment, helping users to quickly determine proper ethanol doses and duration, run behavioral screens, and plan follow-up experiments.

Circuits that encode and guide alcohol-associated preference.

A powerful feature of adaptive memory is its inherent flexibility. Alcohol and other addictive substances can remold neural circuits important for memory to reduce this flexibility. However, the mechanism through which pertinent circuits are selected and shaped remains unclear. We show that circuits required for alcohol-associated preference shift from population level dopaminergic activation to select dopamine neurons that predict behavioral choice in Drosophila melanogaster. During memory expression, subsets of dopamine neurons directly and indirectly modulate the activity of interconnected glutamatergic and cholinergic mushroom body output neurons (MBON). Transsynaptic tracing of neurons important for memory expression revealed a convergent center of memory consolidation within the mushroom body (MB) implicated in arousal, and a structure outside the MB implicated in integration of naïve and learned responses. These findings provide a circuit framework through which dopamine neuronal activation shifts from reward delivery to cue onset, and provide insight into the maladaptive nature of memory.

Cue-Induced Ethanol Seeking in Drosophila melanogaster Is Dose-Dependent.

Alcohol use disorder generates devastating social, medical and economic burdens, making it a major global health issue. The persistent nature of memories associated with intoxication experiences often induces cravings and triggers relapse in recovering individuals. Despite recent advances, the neural and molecular mechanisms underlying these memories are complex and not well understood. This makes finding effective pharmacological targets challenging. The investigation of persistent alcohol-associated memories in the fruit fly, Drosophila melanogaster, presents a unique opportunity to gain a comprehensive understanding of the memories for ethanol reward at the level of genes, molecules, neurons and circuits. Here we characterize the dose-dependent nature of ethanol on the expression of memory for an intoxication experience. We report that the concentration of ethanol, number of ethanol exposures, length of ethanol exposures, and timing between ethanol exposures are critical in determining whether ethanol is perceived as aversive or appetitive, and in how long the memory for the intoxicating properties of ethanol last. Our study highlights that fruit flies display both acute and persistent memories for ethanol-conditioned odor cues, and that a combination of parameters that determine the intoxication state of the fly influence the seemingly complex retention and expression of memories associated with intoxication. Our thorough behavioral characterization provides the opportunity to interrogate the biological underpinnings of these observed preference differences in future studies.