Chemical measurements in Drosophila

Fly Me to the Micron: Microtechnologies for Drosophila Research

Multicellular model organisms, such as Drosophila melanogaster (fruit fly), are frequently used in a myriad of biological research studies due to their biological significance and global standardization. However, traditional tools used in these studies generally require manual handling, subjective phenotyping, and bulk treatment of the organisms, resulting in laborious experimental protocols with limited accuracy. Advancements in microtechnology over the course of the last two decades have allowed researchers to develop automated, high-throughput, and multifunctional experimental tools that enable novel experimental paradigms that would not be possible otherwise. We discuss recent advances in microtechnological systems developed for small model organisms using D. melanogaster as an example. We critically analyze the state of the field by comparing the systems produced for different applications. Additionally, we suggest design guidelines, operational tips, and new research directions based on the technical and knowledge gaps in the literature. This review aims to foster interdisciplinary work by helping engineers to familiarize themselves with model organisms while presenting the most recent advances in microengineering strategies to biologists.

Neuronal identity control at the resolution of a single transcription factor isoform

The brain exhibits remarkable neuronal diversity which is critical for its functional integrity. From the sheer number of cell types emerging from extensive transcriptional, morphological, and connectome datasets, the question arises of how the brain is capable of generating so many unique identities. 'Terminal selectors' are transcription factors hypothesized to determine the final identity characteristics in post-mitotic cells. Which transcription factors function as terminal selectors and the level of control they exert over different terminal characteristics are not well defined. Here, we establish a novel role for the transcription factor broad as a terminal selector in Drosophila melanogaster. We capitalize on existing large sequencing and connectomics datasets and employ a comprehensive characterization of terminal characteristics including Perturb-seq and whole-cell electrophysiology. We find a single isoform broad-z4 serves as the switch between the identity of two visual projection neurons LPLC1 and LPLC2. Broad-z4 is natively expressed in LPLC1, and is capable of transforming the transcriptome, morphology, and functional connectivity of LPLC2 cells into LPLC1 cells when perturbed. Our comprehensive work establishes a single isoform as the smallest unit underlying an identity switch, which may serve as a conserved strategy replicated across developmental programs.

An LC-MS/MS method for simultaneous analysis of up to six monoamines from brain tissues

Monoamines are a class of neuromodulators that are crucial for a variety of brain functions, including control of mood, movement, sleep and cognition. From mammals to insects, the nervous system is enriched in monoamines such as dopamine, serotonin and melatonin, analytes which range from being highly polar to non-polar. Here we developed a method using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to quantify in a single run the amounts of six distinct monoamines in extracts from dissected Drosophila and mouse brain tissues. The measured monoamines were dopamine (DA), serotonin (also known as 5-hydroxytryptamine (5-HT)), octopamine (OA, an insect equivalent of norepinephrine), tyramine (TA), melatonin (MT) and N-acetylserotonin (NAS). The analytical range of these monoamines was between 0.25 and 5.0 ng/mL. This quantitative LC-MS/MS methodology has important use for simultaneous measurement of distinct neuroactive monoamines from precious biological specimens.

Anti-obesity effects of Erythrina abyssinica stem bark extract in flies exposed to a high fat diet

Background

An in vitro assay on Sigmoidin A from Erythrina abyssinica stem bark revealed its potency to inhibit pancreatic lipase. However, studies indicate activity of extract bioactive compounds in combination far exceed the favorable effects of each individual compound due to synergy and additive effects. In this study, we provide information on the effect of E. abyssinica stem bark extract in Drosophila melanogaster. The objective of the study was to determine the safety and effects of E. abyssinica stem bark extract on fly survival, body weight, triglycerides, sterol, total protein, and catalase activity of obese male D. melanogaster.

Methods

Obesity was induced by exposing D. melanogaster white mutant w¹¹¹⁸ to coconut food for two weeks. Groups 1–3 were fed on coconut food + fenofibrate at 25 mM, 50 mM, and 75 mM. Groups 4–6 were fed on coconut food + E. abyssinica stem bark extract at concentrations of 2.5 g/ml, 5.0 g/ml, and 7.5 g/ml. The positive control was exposed to only coconut food while the negative control was on regular food. Fly survival observations were done for 15 days, while acute and chronic effects were done at 30 min and after 48 h respectively following treatment. Body mass, negative geotaxis, reducing power of the extract, triglycerides (TG/TP), sterol, total protein levels, and catalase activity were measured after 10 days of exposure to the experimental diets.

Results

Fly survival changes were observed after 10 days and E. abyssinica stem bark extract had the strongest reducing power at 7.5 g/ml extract concentration. E. abyssinica stem bark extract reduced body mass, triglyceride levels (TG/TP), sterol levels, and modulated catalase activity at 7.5 g/ml extract concentration. Though the standard drug fenofibrate had the highest fat accumulation reduction potential, the extract at 7.5 g/ml was much safer in reducing fat accumulation in obese male D. melanogaster than other concentration used.

Conclusion

Antioxidants in E. abyssinica stem bark extract are responsible for the observed anti-obesity activity.

Study of the release of endogenous amines in Drosophila brain in vivo in response to stimuli linked to aversive olfactory conditioning

A highly challenging question in neuroscience is to understand how aminergic neural circuits contribute to the planning and execution of behaviors, including the generation of olfactory memories. In this regard, electrophysiological techniques like Local Field Potential or imaging methods have been used to answer questions relevant to cell and circuit physiology in different animal models, such as the fly Drosophila melanogaster. However, these techniques do not provide information on the neurochemical identity of the circuits of interest. Different approaches including fast scan cyclic voltammetry, allow researchers to identify and quantify in a timely fashion the release of endogenous neuroactive molecules, but have been only used in in vitro Drosophila brain preparations. Here, we report a procedure to record for the first time the release of endogenous amines -dopamine, serotonin and octopamine- in adult fly brain in vivo, by fast scan cyclic voltammetry. As a proof of principle, we carried out recordings in the calyx region of the Mushroom Bodies, the brain area mainly associated to the generation of olfactory memories in flies. By using principal component regression in normalized training sets for in vivo recordings, we detect an increase in octopamine and serotonin levels in response to electric shock and olfactory cues respectively. This new approach allows the study of dynamic changes in amine neurotransmission that underlie complex behaviors in Drosophila and shed new light on the contribution of these amines to olfactory processing in this animal model.

Impact of Sampling and Cellular Separation on Amino Acid Determinations in Drosophila Hemolymph

The fruit fly is a frequently used model system with a high degree of human disease-related genetic homology. The quantitative chemical analysis of fruit fly tissues and hemolymph uniquely brings chemical signaling and compositional information to fly experimentation. The work here explores the impact of measured chemical content of hemolymph with three aspects of sample collection and preparation. Cellular content of hemolymph was quantitated and removed to determine hemolymph composition changes for seven primary amine analytes. Hemolymph sampling methods were adapted to determine differences in primary amine composition of hemolymph collected from the head, antenna, and abdomen. Also, three types of anesthesia were employed with hemolymph collection to quantitate effects on measured amino acid content. Cell content was found to be 45.4 ± 22.1 cells/nL of hemolymph collected from both adult and larvae flies. Cell-concentrated fractions of adult, but not larvae, hemolymph were found to have higher and more variable amine content. There were amino acid content differences found between all three areas indicating a robust method to characterize chemical markers from specific regions of a fly, and these appear related to physiological activity. Methods of anesthesia have an impact on hemolymph amino acid composition related to overall physiological impact to fly including higher amino acid content variability and oxygen deprivation effects. Together, these analyses identify potential complications with Drosophila hemolymph analysis and opportunities for future studies to relate hemolymph content with model physiological activity.

Oral administration of methylphenidate blocks the effect of cocaine on uptake at the Drosophila dopamine transporter

Although our understanding of the actions of cocaine in the brain has improved, an effective drug treatment for cocaine addiction has yet to be found. Methylphenidate binds the dopamine transporter and increases extracellular dopamine levels in mammalian central nervous systems similar to cocaine, but it is thought to elicit fewer addictive and reinforcing effects owing to slower pharmacokinetics for different routes of administration between the drugs. This study utilizes the fruit fly model system to quantify the effects of oral methylphenidate on dopamine uptake during direct cocaine exposure to the fly CNS. The effect of methylphenidate on the dopamine transporter has been explored by measuring the uptake of exogenously applied dopamine. The data suggest that oral consumption of methylphenidate inhibits the Drosophila dopamine transporter and the inhibition is concentration dependent. The peak height increased to 150% of control when cocaine was used to block the dopamine transporter for untreated flies but only to 110% for methylphenidate-treated flies. Thus, the dopamine transporter is mostly inhibited for the methylphenidate-fed flies before the addition of cocaine. The same is true for the rate of the clearance of dopamine measured by amperometry. For untreated flies the rate of clearance changes 40% when the dopamine transporter is inhibited with cocaine, and for treated flies the rate changes only 10%. The results were correlated to the in vivo concentration of methylphenidate determined by CE-MS. Our data suggest that oral consumption of methylphenidate inhibits the Drosophila dopamine transporter for cocaine uptake, and the inhibition is concentration dependent.

Using In Vivo Electrochemistry to Study the Physiological Effects of Cocaine and Other Stimulants on the Drosophila melanogaster Dopamine Transporter

Dopamine neurotransmission is thought to play a critical role in addiction reinforcing mechanisms of drugs of abuse. Electrochemical techniques have been employed extensively for monitoring in vivo dopamine changes in the brains of model organisms including rats, mice, and primates. Here, we investigated the effects of several stimulants on dopamine clearance using recently developed microanalytical tools for in vivo electrochemical measurements of dopamine in the central nervous system of Drosophila melanogaster. A cylindrical carbon-fiber microelectrode was placed in the protocerebral anterior medial region of the Drosophila brain (an area dense with dopamine neurons) while a micropipette injector was positioned to exogenously apply dopamine. Background-subtracted fast-scan cyclic voltammetry was carried out to quantify changes in dopamine concentration in the adult fly brain. Clearance of exogenously applied dopamine was significantly decreased in the protocerebral anterior medial area of the wild-type fly following treatment with cocaine, amphetamine, methamphetamine, or methylphenidate. In contrast, dopamine uptake remained unchanged when identical treatments were employed in fumin mutant flies that lack functional dopamine transporters. Our in vivo results support in vitro binding affinity studies that predict these four stimulants effectively block normal Drosophila dopamine transporter function. Furthermore, we found 10 muM to be a sufficient physiological cocaine concentration to significantly alter dopamine transporter uptake in the Drosophila central nervous system. Taken together, these data indicate dopamine uptake in the Drosophila brain is decreased by psychostimulants as observed in mammals. This validates the use of Drosophila as a model system for future studies into the cellular and molecular mechanisms underlying drug addiction in humans.