We thank Zina Berman for support, Lisa Baik for comments on the manuscript, and other members of the Carlson laboratory for discussion. This work was supported NIH grant K01 DC020145 to H.K.M.D; and NIH grants R01 DC02174, R01 DC04729, and R01 DC011697 to J.R.C.

The following protocol complies with all the animal care guidelines of Yale University.
1. Flies
<ol>
	<li>Place 10-15 newly emerged flies in fresh standard culture vials at 25 &#176;C and 60% relative humidity in a 12:12 h light-dark cycle.</li>
	<li>Use flies when 3-7 days old.</li>
</ol>
2. Chemosensory stimuli
<ol>
	<li>Obtain chemosensory stimuli of the highest available purity. Store them as recommended by the vendor until use.</li>
	<li>Dissolve chemosensory stimuli and dilute to the desired concentrations in water or another desired, non-toxic solvent such as paraffin oil. Stir the prepared solutions for a minimum of 1 h in the case of dissolved solid compounds.</li>
</ol>
3. Glass stimulus capillary
<ol>
	<li>Pull a glass capillary to hold the stimulus from a borosilicate glass capillary (100 mm length, 1 mm outer diameter, 0.58 mm inner diameter) using a pipette puller instrument. Aim to achieve a tip diameter between 3 &#181;m and 10 &#181;m.</li>
	<li>Fill the glass capillary with the preferred stimulus solution using a microloader pipette tip. Take care to avoid bubbles, which can be removed by gentle tapping.</li>
	<li>If the stimulus crystallizes at the tip, clean or replace the glass stimulus capillary.</li>
</ol>
4. Reference and recording electrodes
<ol>
	<li>Use tungsten rods (127 &#181;m diameter and 76.2 mm length) for both reference and recording electrodes. Sharpen the reference and recording electrodes to approximately 1 &#181;m diameter at the tip (the shapes of these electrodes are depicted in Delventhal et al.36) by dipping them repeatedly for several seconds in either a 10% KNO3 (~1 M) solution or a 10% KOH (1.8 M) solution. 
	NOTE: This solution requires current (0.3-3 mA) to facilitate this process.</li>
</ol>
5. Preparation of the fly for base recording
<ol>
	<li>Draw a single fly from the vial into an aspirator. Withdraw the aspirator and trap the animal by placing a finger over the end.</li>
	<li>Expel the fly into a 200 &#181;L plastic pipette tip. Keeping the end of the aspirator in the pipette tip, use the end to push the fly forward, headfirst, toward the narrow end of the pipette tip.</li>
	<li>Trim the pipette tip at each end (i.e., anterior and posterior to the animal) using a razor blade.</li>
	<li>Use either clay or a small piece of cotton to push the fly forward further, until half of the head protrudes from the end of the trimmed pipette tip. Use forceps to gently push until the labellum at the front of the head is exposed.</li>
	<li>Fix the trimmed pipette tip onto a glass microscope slide using clay (Figure 1).</li>
	<li>Under the stereomicroscope, position the labellum laterally on a cover slip so that one lobe, along with its 31 taste sensilla, is exposed (Figure 1). The cover slip keeps the labellum in place.</li>
</ol>
6. Electrophysiology rig
<ol>
	<li>Select a room for the rig setup that has stable temperature and relative humidity (&#60;70%) and is isolated from sources of electrical and mechanical noise, such as refrigerators and centrifuges.</li>
	<li>Place the microscope on the center of an antivibration table.</li>
	<li>Secure a manual micromanipulator to the antivibration table (Figure 2).</li>
	<li>Attach a stainless-steel shaft that holds the tungsten reference electrode to the manual micromanipulator (Figure 2).</li>
	<li>Connect motorized manipulators-one with a holder for the recording electrode probe and a second one with a holder connected to a stainless-steel shaft for the glass stimulus capillary-to the same table using stands (Figure 2).</li>
	<li>Connect the recording electrode probe to an Intelligent Data Acquisition Controller (IDAC) system or another amplifier/digitizer system.</li>
	<li>Link this IDAC system to the computer at the workstation.</li>
	<li>Ground the manual and motorized manipulators to the same location within the rig.</li>
	<li>Install appropriate acquisition software for the IDAC system on the computer. Ensure that the digital acquisition drivers are compatible with the operating system (e.g., Windows XP-7, -8, or -10) on the computer.</li>
</ol>
7. Recording from taste sensilla
<ol>
	<li>Place the preparation slide on the microscope stage with a low magnification (e.g.,&#160;10x) objective in position. Move the stage until the labellum is in focus at the center of the field of view at both low-magnification and high-magnification (e.g., 50x) objectives.</li>
	<li>Insert the reference electrode into the eye using the low magnification objective. To insert the reference electrode, target the eye on the side of the fly opposite the side with the recording electrode, for example, if the recording electrode is approaching from the right, place the reference electrode in the left eye. Utilize a manual micromanipulator for precise insertion.</li>
	<li>Bring the tip of the glass stimulus capillary into focus at the center of the field of view of both low-magnification and high-magnification objectives using a motorized micromanipulator (Figure 3).</li>
	<li>Under low magnification, bring the recording electrode close to the labellum using a second motorized micromanipulator.</li>
	<li>Under high magnification, insert the recording electrode into the base of a taste sensillum using the motorized micromanipulator until the sound of neuronal firing activity from the audio output of the IDAC system is heard.</li>
	<li>Once a stable signal has been established, start recording the signal using the software that comes with the IDAC system (Figure 4A-D). To start recording, press the Start recording button.</li>
	<li>Bring the tip of the stimulus glass capillary to cover the tip of the taste sensillum using the motorized manipulator.</li>
	<li>To end the stimulus, remove the glass stimulus capillary from the sensillum using the motorized manipulator.</li>
	<li>Mark the start and end of the stimulation manually using a pedal. The pedal is connected to the IDAC, and its communication with the software is facilitated through the IDAC to mark the start/end of the stimulus.</li>
</ol>
8. Analysis
<ol>
	<li>Use the different functions of the software that comes with the IDAC system to sort spike populations by amplitude (when possible) and analyze response dynamics.
	<ol>
		<li>To count spikes, left click on the recording of interest, bringing up a window to select from. Choose To Spikes, initiating another window named Convert waves to spikes. Enter a name in the New field and press the OK button.</li>
		<li>Entering the name in the New field in step 8.1.1 leads to the Amplitude Histogram view. Choose the amplitude to count, then close this view. Left click to add a counter.</li>
		<li>Examine the spikes manually to confirm conclusions based on analysis with software. 
		NOTE: The software also allows the exportation of data in different formats for further analysis.</li>
	</ol>
	</li>
</ol>

A Novel Method for Enhanced Analysis of Insect Taste Neuron Activity

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The authors have no conflicts of interest to disclose.

In recordings from some types of sensilla, it can be challenging to differentiate the spikes of different neurons. For example, the sugar neurons and mechanosensory neurons of S and I sensilla produce spikes of similar amplitudes, making it difficult to distinguish them4,14. We find that the use of a very sharp tungsten recording electrode reduces the firing of the mechanosensory neuron, as does the judicious placement of the recording electrode. Insertion of the...

Insects, including drosophilid flies, are endowed with a sophisticated taste system that enables them to extract complex chemical information from their surroundings. This system allows them to discern the chemical composition of various substances, distinguishing between those that are nutritious and those that are harmful1,2.
At the core of this system are specialized structures known as taste hairs or sensilla, strategically located on various body parts. In drosophilid flies, these sensilla are located on the labellum, which is the major taste organ of the fly head1,2,3,4, as well as on the legs and wings1,2,5,6. The labellum is located at the tip of the proboscis and contains two lobes4,7,8. Each lobe is covered with 31 taste sensilla categorized as short, long, and intermediate4,7,8. These sensilla each house 2-4 taste neurons1,2,9,10. These taste neurons express members of at least four different gene families, namely the Gustatory receptor (Gr), Ionotropic receptor (Ir), Pickpocket (Ppk), and Transient receptor potential (Trp) genes1,2,11,12,13. This diversity of receptors and channels equips insects with the ability to recognize a wide array of chemical compounds, including both nonvolatile and volatile cues1,2,14.
For over 50 years, scientists have quantified the response of taste neurons and their receptors using a technique called tip recording3,4,6,8,13,15,16,17,18,19,20,21,22,23,24,25,26,27,28, 
29,30,31,32,33,34,35. However, this method has major limitations. First, neural activity can be measured only during contact with the stimulus, and not before or after contact. This limitation precludes the measurement of spontaneous spiking activity and prevents the measurement of OFF responses. Second, only tastants that are soluble in aqueous solutions can be tested.
These limitations can be overcome by a rarely used alternative electrophysiological technique called &#34;base recording.&#34; Here we describe this technique, which we have adapted from a method used by Marion-Poll and colleagues24, and show the crucial taste coding features that it can now conveniently measure14.

<table><tbody><tr><td>Microscope</td><td>Olympus</td><td>BX51WI</td><td>equipped with a 50X objective (LMPLFLN 50X, Olympus) and 10X eyepieces.&amp;nbsp;</td></tr><tr><td>Antivibration Table</td><td>TMC</td><td>63-7590E</td><td></td></tr><tr><td>motorized Micromanipulators</td><td>Harvard Apparatus and M&amp;auml;rzh&amp;auml;user Micromanipulators</td><td>Micromanipulator PM 10 Piezo Micromanipulator</td><td></td></tr><tr><td>manual Micromanipulators</td><td>M&amp;auml;rzh&amp;auml;user Micromanipulators</td><td>MM33 Micromanipulator</td><td></td></tr><tr><td>Magnetic stands</td><td>ENCO</td><td>Model #625-0930</td><td></td></tr><tr><td>Reference&amp;nbsp; and recording Electrode Holder</td><td>Ockenfels Syntech GmbH</td><td></td><td></td></tr><tr><td>Stimulus glass capillary Holder</td><td>Ockenfels Syntech GmbH</td><td></td><td></td></tr><tr><td>Universal Single Ended Probe</td><td>Ockenfels Syntech GmbH</td><td></td><td></td></tr><tr><td>4-CHANNEL USB ACQUISITION CONTROLLER , IDAC-4</td><td>Ockenfels Syntech GmbH</td><td></td><td></td></tr><tr><td>Stimulus Controllers</td><td>Ockenfels Syntech GmbH</td><td>Stimulus Controller CS 55</td><td></td></tr><tr><td>Personal Computer</td><td>Dell</td><td>Vostro</td><td>Check for compatibility with digital acquisition system and software</td></tr><tr><td>Tungsten Rod</td><td>A-M Systems</td><td>Cat#716000</td><td></td></tr><tr><td>Aluminum Foil and/or Faraday Cage</td><td></td><td></td><td>Electromagnetic noise shielding</td></tr><tr><td>Borosilicate Glass Capillaries</td><td>World Precision Instruments</td><td>1B100F-4</td><td></td></tr><tr><td>Pipette Puller</td><td>Sutter Instrument Company</td><td>Model P-97 Flaming/Brown Micropipette Puller</td><td></td></tr><tr><td>Stereomicroscope</td><td>Olympus</td><td>VMZ 1x-4x</td><td>For fly preparation</td></tr><tr><td>p200 Pipette Tips</td><td></td><td></td><td>Generic</td></tr><tr><td>Microloader tips&amp;nbsp;</td><td>Eppendorf</td><td>E5242956003</td><td></td></tr><tr><td>1 ml Syringe</td><td></td><td></td><td>Generic</td></tr><tr><td>Crocodile clips</td><td></td><td></td><td></td></tr><tr><td>Power Transformers</td><td>STACO ENERGY PRODUCTS</td><td>STACO 3PN221B</td><td>Assembled from P1000 pipette tips, flexible plastic tubing, and mesh</td></tr><tr><td>Modeling Clay</td><td></td><td></td><td>Generic</td></tr><tr><td>Forceps</td><td></td><td></td><td>Generic</td></tr><tr><td>Plastic Tubing</td><td>Saint Gobain</td><td>Tygon S3&amp;trade; E-3603</td><td></td></tr><tr><td>Standard culture vials</td><td>Archon Scientific</td><td></td><td>Narrow 1-oz polystyrene vails, each with 10 mL of glucose medium, preloaded with cellulose acetate plugs</td></tr><tr><td>Berberine chloride (BER)</td><td>Sigma-Aldrich</td><td>Cat# Y0001149</td><td></td></tr><tr><td>Denatonium benzoate (DEN)</td><td>Sigma-Aldrich</td><td>Cat# D5765</td><td></td></tr><tr><td>N,N-Diethyl-m- toluamide (DEET)</td><td>Sigma-Aldrich</td><td>Cat# 36542</td><td></td></tr></tbody></table>

base recording: a technique for analyzing responses of taste neurons in drosophila

Insects taste the external world through taste hairs, or sensilla, that have pores at their tips. When a sensillum comes into contact with a potential food source, compounds from the food source enter through the pore and activate neurons within. For over 50 years, these responses have been recorded using a technique called tip recording. However, this method has major limitations, including the inability to measure neural activity before or after stimulus contact and the requirement for tastants to be soluble in aqueous solutions. We describe here a technique that we call base recording, which overcomes these limitations. Base recording allows the measurement of taste neuron activity before, during, and after the stimulus. Thus, it allows extensive analysis of OFF responses that occur after a taste stimulus. It can be used to study hydrophobic compounds such as long-chain pheromones that have very low solubility in water. In summary, base recording offers the advantages of single-sensillum electrophysiology as a means of measuring neuronal activity - high spatial and temporal resolution, without the need for genetic tools - and overcomes key limitations of the traditional tip recording technique.

Figure 4A shows spontaneous spikes that arise from a sensillum. They fall into two classes based on amplitude, with the larger spikes deriving from the neuron that is sensitive to bitter compounds and the smaller spikes from the neuron that responds to sugars. The relationship between spike amplitude and functional specificity has been corroborated by genetic experiments4,14,37,<sup class...

Read this Scientific Article Protocol about Author Spotlight: Advances in Chemoreception at JoVE.com

Author Spotlight: Advances in Chemoreception &#8211; From Insect Odor Receptors to Non-Coding RNAs

A rarely used method of electrophysiological recording, base recording, allows analysis of features of taste coding that cannot be examined by conventional recording methods. Base recording also allows the analysis of taste responses to hydrophobic stimuli that cannot be studied using traditional electrophysiological methods.

Base Recording: A Technique for Analyzing Responses of Taste Neurons in Drosophila

Insects taste the external world through taste hairs, or sensilla, that have pores at their tips. When a sensillum comes into contact with a potential ...

base-recording-technique-for-analyzing-responses-taste-neurons

Research

JoVE Journal

Neuroscience

952 Views.  Yale University. A rarely used method of electrophysiological recording, base recording, allows analysis of features of taste coding that cannot be examined by conventional recording methods. Base recording also allows the analysis of taste responses to hydrophobic stimuli that cannot be studied using traditional electrophysiological methods. 

Video: Author Spotlight: Advances in Chemoreception – From Insect Odor Receptors to Non-Coding RNAs

Simultaneous Recording of Calcium Signals from Identified Neurons and Feeding Behavior of Drosophila melanogaster

To study neuronal networks in terms of their function in behavior, we must analyze how neurons operate when each behavioral pattern is generated. Thus, simultaneous recordings of neuronal activity and behavior are essential to correlate brain activity to behavior. For such behavioral analyses, the fruit fly, Drosophila melanogaster, allows us to incorporate genetically encoded calcium indicators such as GCaMP1, to monitor neuronal activity, and to use sophisticated genetic manipulations for optogenetic or thermogenetic techniques to specifically activate identified neurons2-5. Use of a thermogenetic technique has led us to find critical neurons for feeding behavior (Flood et al., under revision). As a main part of feeding behavior, a Drosophila adult extends its proboscis for feeding6 (proboscis extension response; PER), responding to a sweet stimulus from sensory cells on its proboscis or tarsi. Combining the protocol for PER7 with a calcium imaging technique8 using GCaMP3.01, 9, I have established an experimental system, where we can monitor activity of neurons in the feeding center &#x2013; the suboesophageal ganglion (SOG), simultaneously with behavioral observation of the proboscis. I have designed an apparatus ("Fly brain Live Imaging and Electrophysiology Stage": "FLIES") to accommodate a Drosophila adult, allowing its proboscis to freely move while its brain is exposed to the bath for Ca2+ imaging through a water immersion lens. The FLIES is also appropriate for many types of live experiments on fly brains such as electrophysiological recording or time lapse imaging of synaptic morphology. Because the results from live imaging can be directly correlated with the simultaneous PER behavior, this methodology can provide an excellent experimental system to study information processing of neuronal networks, and how this cellular activity is coupled to plastic processes and memory.

Simultaneous Recording of Calcium Signals from Identified Neurons and Feeding Behavior of Drosophila melanogaster

The fruit fly, Drosophila melanogaster, extends its proboscis for feeding, responding to a sugar stimulus from its proboscis or tarsus. I have combined observations of the proboscis extension response (PER) with a calcium imaging technique, allowing us to monitor the activity of neurons in the brain, simultaneously with behavioral observation.

To study neuronal networks in terms of their function in behavior, we must analyze how neurons operate when each behavioral pattern is generated.  Thus, ...

Combining Quantitative Food-intake Assays and Forcibly Activating Neurons to Study Appetite in Drosophila

Food consumption is under the tight control of the brain, which integrates the physiological status, palatability, and nutritional contents of the food, and issues commands to start or stop feeding. Deciphering the processes underlying the decision-making of timely and moderate feeding carries major implications in our understanding of physiological and psychological disorders related to feeding control. Simple, quantitative, and robust methods are required to measure the food ingestion of animals after experimental manipulation, such as forcibly increasing the activities of certain target neurons. Here, we introduced dye-labeling-based feeding assays to facilitate the neurogenetic study of feeding control in adult fruit flies. We review available feeding assays, and then describe our methods step-by-step from setup to analysis, which combine thermogenetic and optogenetic manipulation of neurons controlling feeding motivation with dye-labeled food intake assay. We also discuss the advantages and limitations of our methods, compared with other feeding assays, to help readers choose an appropriate assay.

Combining Quantitative Food-intake Assays and Forcibly Activating Neurons to Study Appetite in Drosophila

Quantitative food-intake assays with dyed food provide a robust and high-throughput means to evaluate feeding motivation. Combining the food consumption assay with thermogenetic and optogenetic screens is a powerful approach to investigate the neural circuits underlying appetite in adult Drosophila melanogaster.

Food consumption is under the tight control of the brain, which integrates the physiological status, palatability, and nutritional contents of the food, ...

Behavior

Electrophysiological Recording From Drosophila Labellar Taste Sensilla

The peripheral taste response of insects can be powerfully investigated with electrophysiological techniques. The method described here allows the researcher to measure gustatory responses directly and quantitatively, reflecting the sensory input that the insect nervous system receives from taste stimuli in its environment. This protocol outlines all key steps in performing this technique. The critical steps in assembling an electrophysiology rig, such as selection of necessary equipment and a suitable environment for recording, are delineated. We also describe how to prepare for recording by making appropriate reference and recording electrodes, and tastant solutions. We describe in detail the method used for preparing the insect by insertion of a glass reference electrode into the fly in order to immobilize the proboscis. We show traces of the electrical impulses fired by taste neurons in response to a sugar and a bitter compound. Aspects of the protocol are technically challenging and we include an extensive description of some common technical challenges that may be encountered, such as lack of signal or excessive noise in the system, and potential solutions. The technique has limitations, such as the inability to deliver temporally complex stimuli, observe background firing immediately prior to stimulus delivery, or use water-insoluble taste compounds conveniently. Despite these limitations, this technique (including minor variations referenced in the protocol) is a standard, broadly accepted procedure for recording Drosophila neuronal responses to taste compounds.

Electrophysiological Recording From Drosophila Labellar Taste Sensilla

This protocol describes extracellular recording of the action potential responses fired by labellar taste neurons in Drosophila.

The peripheral taste response of insects can be powerfully investigated with electrophysiological techniques. The method described here allows the ...

Measuring Physiological Responses of Drosophila Sensory Neurons to Lipid Pheromones Using Live Calcium Imaging

Unlike mammals, insects such as Drosophila have multiple taste organs. The chemosensory neurons on the legs, proboscis, wings and ovipositor of Drosophila express gustatory receptors1,2, ion channels3-6, and ionotropic receptors7 that are involved in the detection of volatile and non-volatile sensory cues. These neurons directly contact tastants such as food, noxious substances and pheromones and therefore influence many complex behaviors such as feeding, egg-laying and mating. Electrode recordings and calcium imaging have been widely used in insects to quantify the neuronal responses evoked by these tastants. However, electrophysiology requires specialized equipment and obtaining measurements from a single taste sensillum can be technically challenging depending on the cell-type, size, and position. In addition, single neuron resolution in Drosophila can be difficult to achieve since taste sensilla house more than one type of chemosensory neuron. The live calcium imaging method described here allows responses of single gustatory neurons in live flies to be measured. This method is especially suitable for imaging neuronal responses to lipid pheromones and other ligand types that have low solubility in water-based solvents.

Measuring Physiological Responses of Drosophila Sensory Neurons to Lipid Pheromones Using Live Calcium Imaging

The forelegs and proboscis of Drosophila contain a rich repertoire of gustatory sensory neurons. Here, we present a method using calcium imaging to measure physiological responses from sensory neurons in the foreleg and proboscis of live flies upon exogenous application of a gustatory pheromone.

Unlike mammals, insects such as Drosophila have multiple taste organs. The chemosensory neurons on the legs, proboscis, wings and ovipositor of Drosophila ...

Immunology and Infection

Taste Preference Assay for Adult Drosophila

Olfactory and gustatory perception of the environment is vital for animal survival. The most obvious application of these chemosenses is to be able to distinguish good food sources from potentially dangerous food sources. Gustation requires physical contact with a chemical compound which is able to signal through taste receptors that are expressed on the surface of neurons. In insects, these gustatory neurons can be located across the animal's body allowing taste to play an important role in many different behaviors. Insects typically prefer compounds containing sugars, while compounds that are considered bitter tasting are avoided. Given the basic biological importance of taste, there is intense interest in understanding the molecular mechanisms underlying this sensory modality. We describe an adult Drosophila taste assay which reflects the preference of the animals for a given tastant compound. This assay may be applied to animals of any genetic background to examine the taste preference for a desired soluble compound.

Taste Preference Assay for Adult Drosophila

Taste is an important sensory process which facilitates attraction to beneficial substances and avoidance of toxic substances. This protocol describes a simple ingestion assay for determining Drosophila gustatory preference for a given chemical compound.

Olfactory and gustatory perception of the environment is vital for animal survival.  The most obvious application of these chemosenses is to be able to ...

New Methods to Study Gustatory Coding

The sense of taste allows animals to detect chemicals in the environment, giving rise to behaviors critical for survival. When Gustatory Receptor Neurons (GRNs) detect tastant molecules, they encode information about the identity and concentration of the tastant as patterns of electrical activity that then propagate to follower neurons in the brain. These patterns constitute internal representations of the tastant, which then allow the animal to select actions and form memories. The use of relatively simple animal models has been a powerful tool to study basic principles in sensory coding. Here, we propose three new methods to study gustatory coding using the moth Manduca sexta. First, we present a dissection procedure for exposing the maxillary nerves and the subesophageal zone (SEZ), allowing recording of the activity of GRNs from their axons. Second, we describe the use of extracellular electrodes to record the activity of multiple GRNs by placing tetrode wires directly into the maxillary nerve. Third, we present a new system for delivering and monitoring, with high temporal precision, pulses of different tastants. These methods allow the characterization of neuronal responses in vivo directly from GRNs before, during and after tastants are delivered. We provide examples of voltage traces recorded from multiple GRNs, and present an example of how a spike sorting technique can be applied to the data to identify the responses of individual neurons. Finally, to validate our recording approach, we compare extracellular recordings obtained from GRNs with tetrodes to intracellular recordings obtained with sharp glass electrodes.

We present three new methods to study gustatory coding. Using a simple animal, the moth Manduca sexta (Manduca), we describe a dissection protocol, the use of extracellular tetrodes to record the activity of multiple gustatory receptor neurons, and a system for delivering and monitoring precisely timed pulses of tastants.

The sense of taste allows animals to detect chemicals in the environment, giving rise to behaviors critical for survival. When Gustatory Receptor Neurons ...

A Rapid Food-Preference Assay in Drosophila

To select food with nutritional value while avoiding the consumption of harmful agents, animals need a sophisticated and robust taste system to evaluate their food environment. The fruit fly, Drosophila melanogaster, is a genetically tractable model organism that is widely used to decipher the molecular, cellular, and neural underpinnings of food preference. To analyze fly food preference, a robust feeding method is needed. Described here is a two-choice feeding assay, which is rigorous, cost-saving, and fast. The assay is Petri-dish-based and involves the addition of two different foods supplemented with blue or red dye to the two halves of the dish. Then, ~70 prestarved, 2-4-day-old flies are placed in the dish and&#160;allowed to choose between blue and red foods in the dark for about 90 min. Examination of the abdomen of each fly is followed by the calculation of the preference index. In contrast to multiwell plates, each Petri dish takes only ~20 s to fill and saves time and effort. This feeding assay can be employed to quickly determine whether flies like or dislike a particular food.

A Rapid Food-Preference Assay in Drosophila

We present a protocol for a two-choice feeding assay for flies. This feeding assay is fast and easy to run and is suitable not only for small-scale laboratory research, but also for high-throughput behavioral screens in flies.

To select food with nutritional value while avoiding the consumption of harmful agents, animals need a sophisticated and robust taste system to evaluate ...

Behavioral Assays for Optogenetic Manipulation of Neural Circuits in Drosophila melanogaster

Optogenetics has become a fundamental technique in neuroscience, enabling precise control of neuronal activity through light stimulation. This study introduces easy-to-implement setups for applying optogenetic methods in Drosophila melanogaster. Two optogenetic tools, CsChrimson, a red-light-activated cation channel, and GtACR2, a blue-light-activated anion channel, were employed in four experimental approaches. Three of these approaches involve single-fly experiments: (1) a blue-light optogenetic thermotactic positional preference assay targeting temperature-sensitive heating cells, (2) a red-light optogenetic positional preference assay activating bitter sensing neurons, and (3) a proboscis extension response assay activating the sweet-sensing neurons. The fourth approach (4) is a fly maze setup to assess avoidance behaviors using multiple flies. The ability to manipulate neural activity temporally and spatially offers powerful insights into sensory processing and decision-making, underscoring the potential of optogenetics to advance our knowledge of neural function. These methods provide an accessible and robust framework for future research in neuroscience to enhance the understanding of specific neural pathways and their behavioral outcomes.

This paper presents methods for optogenetic manipulation in Drosophila melanogaster, utilizing CsChrimson and GtACR2 to activate and silence specific neurons. Four experiments are described to utilize optogenetics to explore thermotactic and gustatory behaviors, providing insights into the underlying neural mechanisms governing these processes.

Optogenetics has become a fundamental technique in neuroscience, enabling precise control of neuronal activity through light stimulation. This study ...

In Vivo Calcium Imaging of Taste-Induced Neural Responses in Adult Drosophila

For nearly two decades, in vivo calcium imaging has been an effective method for measuring cellular responses to taste stimuli in the fruit fly model organism, Drosophila melanogaster. A key strength of this methodology is its ability to record taste-induced neural responses in awake animals without the need for anesthesia. This approach employs binary expression systems (e.g., Gal4-UAS) to express the calcium indicator GCaMP in specific neurons of interest. This protocol describes a procedure in which flies expressing GCaMP are mounted with the labellum securely positioned, enabling fluorescence in the brain to be recorded at millisecond resolution under a confocal microscope while a solution is applied to the labellum, stimulating all labellar taste sensilla. The examples provided focus on calcium responses in primary gustatory receptor neurons of D. melanogaster. However, this approach can be adapted to record from other neurons of interest within the brain of Drosophilids or other insect species. This imaging method enables researchers to simultaneously record collective calcium responses from groups of gustatory neurons across the labellum, complementing electrophysiological tip recordings that quantify action potentials from individual neurons. The in vivo calcium imaging technique outlined here has been instrumental in uncovering molecular and cellular mechanisms of chemosensation, identifying unique temporal response patterns in primary taste neurons, investigating mechanisms of gustatory modulation, and exploring taste processing in downstream circuits.

A calcium imaging approach enables the recording of taste-induced responses in the brains of awake flies while a solution is applied to the labellum. Primary gustatory responses in Drosophila melanogaster are used as an example, but this protocol can be adapted to study downstream neurons or other species.

For nearly two decades, in vivo calcium imaging has been an effective method for measuring cellular responses to taste stimuli in the fruit fly model ...

Taste Preference Assay: A Method for Measuring Feeding Behavior in Drosophila

Source: Bantel, A. P. and Tessier, C. R. <a href="https://www.jove.com/video/54403/" target="_blank">Taste Preference Assay for Adult Drosophila</a>. J. Vis. Exp. (2016).
This video describes the taste preference assay, a behavioral method used to measure attraction or avoidance towards colored solutions that taste differently by assessing the fly&#39;s abdominal coloration after ingestion of the preferred substance. The featured protocol demonstrates the procedure used to measure flies&#39; preference towards solutions of varying sucrose concentrations.

Source: Bantel, A. P. and Tessier, C. R. Taste Preference Assay for Adult Drosophila. J. Vis. Exp. (2016).
This video describes the taste preference ...

Base Recording: A Technique for Analyzing Responses of Taste Neurons in Drosophila

Summary

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Taste Preference Assay for Adult Drosophila

New Methods to Study Gustatory Coding

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