We thank Terry Shelley for manufacturing the fly arena and the light-tight enclosure, Liz Marr for help with fly stock maintenance, and Xiaojing Gao and Junjie Luo for help with the Matlab code used for data analysis. We thank Johan Lundstr&#246;m at the Monell Chemical Senses Center for demonstrating his odor delivery setup. This work was supported by grants from the Whitehall Foundation (CJP) and NIH NIDCD (R01DC013070, CJP).

1. Setup Assembly
<ol>
	<li>Manufacture the star-shaped arena (19.5 cm by 19.5 cm by 0.7 cm) out of polytetrafluoroethylene (PTFE) according to the provided drawing (Supplementary Materials, SupplementalSketch_StarShapedArena.pdf). The arena may be manufactured by a commercial or a custom facility.</li>
	<li>Acquire two glass plates (20.25 cm by 20.25 cm with thickness of 2 mm), and drill a hole (~0.7 cm in diameter) precisely in the center of one of the glass plates using a diamond-coated drill bit.</li>
	<li>Manufact...

<ol>
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R., Luo, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extremely+sparse+olfactory+inputs+are+sufficient+to+mediate+innate+aversion+in+Drosophila.">Extremely sparse olfactory inputs are sufficient to mediate innate aversion in Drosophila.</a> PLoS One. 10 (4), e0125986 (2015).</li><li>Ronderos, D. S., Lin, C. C., Potter, C. J., Smith, D. 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The four-field olfactometer described here is a versatile behavioral system for studying the olfactory responses of large populations of wild-type and mutant Drosophila flies. Each experiment takes ~1 hr (including setup, experimental runs, and cleaning), and 4-6 experiments can be routinely performed each day. A typical assay using 40-50 flies for 5 minutes generates approximately 450,000 tracked data points for analysis. The described configuration may also be used, with minor modifications, to monitor movemen...

The ability to adapt and respond to the external environment is critical for the survival of all animals. An animal needs to avoid dangers, seek out food and find mates, and learn from previous experiences. Sensory systems function to receive a variety of stimuli, such as visual, chemical and mechanosensory, and send these signals to the central nervous system to be interpreted and decoded. The brain then directs appropriate motor behaviors based on the perceived environment, such as foraging for food or escaping from a predator. Understanding how sensory systems detect the external world, and how the brain decodes and directs decisions, is a major challenge in neurobiology.
Drosophila melanogaster is a powerful model system for investigating how neural circuits guide behaviors. Besides being simple and inexpensive to maintain, Drosophila exhibit many diverse and complex stereotyped behaviors, yet do so with a compact nervous system of about 100,000 neurons. Powerful genetic techniques exist for manipulating the Drosophila genome, and thousands of transgenic lines have been generated that selectively and reproducibly label the same subsets of neurons10-13. These transgenic lines can be used to selectively manipulate the activity of the labeled neurons (activate or inhibit), and these manipulations can be used to investigate how neural functions guide behaviors.
Multiple behavioral assays have been developed for studying various Drosophila behaviors. Drosophila, like many animals, use their sense of smell for guiding many behavioral choices, such as finding food, finding mates, and avoiding dangers. Olfaction is therefore a good sensory system for investigating how external stimuli are detected and interpreted by an animal&#39;s nervous system to guide appropriate choices. As such, a number of assays have been developed for investigating larval and adult olfactory behaviors. Traditionally, olfactory behaviors in Drosophila were assayed by a two-choice T-maze paradigm, which can be used for assaying innate and learned olfactory behaviors3. In this assay, about 50 flies are given a choice between two tubes: one tube contains the odor in question and the other contains a control odorant (usually the odor solvent). The flies are given a set period of time to make a choice, and then the number of flies that are in the different chambers are counted. Although the T-maze is a simple assay for many experiments, there are several limitations. For example, olfactory behaviors are measured at only one time point, and different choices made before this time point are discarded. Similarly, the individual behaviors of the flies within the population are neglected. In addition, the T-maze requires manual counting of flies, which might introduce errors. Finally, since there are only two measured choices, this reduces the statistical power often required to detect subtle behavioral changes. An alternative to a two-choice T-maze is a four-quadrant (four-field) olfactometer14-18. In this assay, animals explore an arena in which each of the four corners of the arena is filled with a potential source of odorized air. The arena has a puckered star shape to maximize the formation of four experimentally defined odor quadrants. If odor is supplied in one of the corners then it is contained only in that one quadrant. The behaviors of the animals can be tracked as they enter and leave the odor quadrant, and easily compared to their behavior in the three control quadrants. The four-quadrant olfactometer assay thus records spatial and temporal behavioral response to the odor stimuli over a large experimental arena.
The four-quadrant olfactometer was first developed by Pettersson et al.15 and Vet et al.17 to investigate the olfactory behavioral responses of individual parasitic Hymenoptera. Faucher et al.18 and Semmelhack and Wang16 adapted the setup to monitor the olfactory responses of individual Drosophila. The four-quadrant olfactometer is equally sensitive to attractive and repulsive responses, allowing for a wide range of test odorants and conditions. Custom-written fly tracking software, developed by Alex Katsov19 and currently maintained by Julian Brown (detailed in Materials), introduced additional advantages to more recent implementations of the four-quadrant olfactometer14,20-23. It is now possible to assay up to 100 flies simultaneously at high spatial (27.5 pixels/cm) and temporal (30 frames per sec) resolution, which allows extracting various parameters, such as position, speed and acceleration of flies at any time point. This enables investigations into the dynamics of the flies&#39; behavioral responses to odors20. It should be noted, however, that the identity of individual flies within the population during the entire tracking period is not maintained. Instead, each fly track is recorded for as long as two fly tracks do not intersect. At which point, new tracks are assigned after the flies diverge. By incorporating other video-capturing software (detailed in Materials Table), the same configuration allows flexible tracking periods and could be used to track flies for up to 24 hr by taking images at a lower frame rate. This option was used to study egg-laying behaviors of flies and compare their body positions with ovipositional preferences14. The four-field olfactometer may also be used to study responses to multimodal (e.g. olfactory and visual) stimuli, or to combine optogenetic9 or thermogenetic21 stimulation with presentations of sensory stimuli. Furthermore, the high temporal resolution allows the extraction of trajectories for each individual fly in the ensemble data set. Therefore, the method allows investigation into olfactory-guided population behaviors and also individual social interactions. The data generated by this assay are robust and highly reproducible, allowing for the use of the four-field olfactometer for behavioral screens.
We describe here the setup assembly for a four-quadrant olfactometer. We further demonstrate its use in assaying olfactory attraction in response to apple cider vinegar and repulsion in response to highly concentrated ethyl propionate. Finally, we describe and provide example code for the analysis of the recorded fly tracking data.

<table border="0" cellpadding="0" cellspacing="0" width="1935">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Air delivery system&#160;</td>
			<td style="width:397px;"></td>
			<td style="width:244px;"></td>
			<td style="width:960px;">(Quantity needed)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Tubing and connectors</td>
			<td style="width:397px;"></td>
			<td style="width:244px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thermoplastic NPT(F) Manifolds</td>
			<td>Cole-Parmer, IL, USA</td>
			<td>R-31522-31</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hex reducing&#160; nipple (1/4MNPT-&#62;1/8MNPT)</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>5232T314</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tubing (ID:1/8)</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>5108K43</td>
			<td>50Ft</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tubing (ID:1/16)</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>52355K41</td>
			<td>100Ft</td>
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		<tr height="21">
			<td height="21" style="height:21px;">Barbed tube fittings</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>5117K71</td>
			<td>1pack</td>
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		<tr height="21">
			<td height="21" style="height:21px;">Push-to-connect tube fittings</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>5779K102</td>
			<td>4</td>
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		<tr height="21">
			<td height="21" style="height:21px;">Barbed Tube Fittings (1/4MNPT-&#62;1/8BF)</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>5463K439</td>
			<td>1 pack (10)</td>
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		<tr height="21">
			<td height="21" style="height:21px;">Barbed Tube Fittings (1/8MNPT-&#62;1/8BF)</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>5463K438</td>
			<td>2 pack (10)&#160;</td>
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			<td height="21" style="height:21px;">Barbed Tube Fittings (1/8MNPT-&#62;1/16BF)</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>5463K4</td>
			<td>2 pack (10)&#160;</td>
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		<tr height="21">
			<td height="21" style="height:21px;">Barbed Tube Fittings (1/4MNPT-&#62;1/4BF)</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>&#160; 5670K84</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hex head plug</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>48335K152</td>
			<td>1</td>
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		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Air pressure regulator, air filter and flowmeters</td>
			<td style="width:397px;"></td>
			<td style="width:244px;"></td>
			<td>(Quantity needed)</td>
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			<td height="21" style="height:21px;">Labatory gas drying unit</td>
			<td>W A HAMMOND DRIERITE CO LTD, OH, USA</td>
			<td>Model: L68-NP-303; stock #26840</td>
			<td>1</td>
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			<td height="21" style="height:21px;">Multitube frames for 150-mm flowtubes</td>
			<td>Cole-Parmer, IL, USA</td>
			<td>R03215-30</td>
			<td>1</td>
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		<tr height="21">
			<td height="21" style="height:21px;">Multitube frames for 150-mm flowtubes</td>
			<td>Cole-Parmer, IL, USA</td>
			<td>R03215-76</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">150-mm flowtubes</td>
			<td>Cole-Parmer, IL, USA</td>
			<td>R-03217-15</td>
			<td>9</td>
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		<tr height="21">
			<td height="21" style="height:21px;">Valve Cartridge</td>
			<td>Cole-Parmer, IL, USA</td>
			<td>R-03218-72</td>
			<td>9</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Precision Air regulator</td>
			<td>McMaster-Carr, IL, USA</td>
			<td style="width:244px;">6162K13</td>
			<td>1</td>
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			<td height="21" style="height:21px;width:335px;">Soleniod valves</td>
			<td>Automate Scientific, Berkeley, CA</td>
			<td style="width:244px;">02-10i</td>
			<td>4</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Solenoid valve controller</td>
			<td>ValveLink 8.2, Automate Scientific, Berkeley, CA</td>
			<td style="width:244px;">01-18</td>
			<td>1</td>
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			<td height="21" style="height:21px;width:335px;">Electronic flow meter</td>
			<td>Honeywell</td>
			<td style="width:244px;">AWM3100V</td>
			<td>1</td>
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		<tr height="21">
			<td height="21" style="height:21px;">DAQ (NI USB-6009, National Instruments) and a&#160;</td>
			<td>National Instruments</td>
			<td style="width:244px;">NI USB-6009</td>
			<td>1</td>
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			<td height="21" style="height:21px;width:335px;">Power supply</td>
			<td>Extech Instruments</td>
			<td style="width:244px;">382200</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Odor chambers</td>
			<td style="width:397px;"></td>
			<td style="width:244px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Polypropylene Wide Mouth jar 2oz; 60ml</td>
			<td style="width:397px;">Nalgene</td>
			<td style="width:244px;">562118-0002</td>
			<td>At least 5 are required per experiment, but a separate chamber is required for each dillution of each odorant. Available at Container Store, part #635114)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Glass odor chamber, 0.25 oz</td>
			<td style="width:397px;">Sunburst Bottle</td>
			<td style="width:244px;">LB4B</td>
			<td>At least 5 are required per experiment&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">&#34;In&#34; valve for odor chamber</td>
			<td style="width:397px;">Smart Products, Inc., CA, USA</td>
			<td style="width:244px;">214224PB-0011S000-4074</td>
			<td>1 of these parts is used per odor chamber but they need to be replaced frequently</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">&#34;Out&#34; valve for odor chamber</td>
			<td style="width:397px;">Smart Products, Inc., CA, USA</td>
			<td style="width:244px;">224214PB-0011S000-4074</td>
			<td>1 of these parts is used per odor chamber but they need to be replaced frequently</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">O ring</td>
			<td style="width:397px;">RT Dygert International, MN, USA</td>
			<td style="width:244px;">AS568-029 Buna-N O-R</td>
			<td>1 pack (100)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Fly arena, camera and behavior boxes</td>
			<td style="width:397px;"></td>
			<td style="width:244px;"></td>
			<td>(Quantity needed)</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:335px;">Behavior and camera box material</td>
			<td style="width:397px;">Interstate plastics, CA, USA</td>
			<td style="width:244px;">ABS black extruded (https://www.interstateplastics.com/Abs-Black-Extruded-Sheet-ABSBE~~ST.php)</td>
			<td>1803 sq inch</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Teflon for fly arena and odor chamber inserts, 3/8&#34; thick, 12&#34;x12&#34;</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>8545K27&#160;</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Glass plates, 1/8&#34; Thick, 9&#34;x 9&#34;</td>
			<td>McMaster-Carr, IL, USA</td>
			<td>8476K191&#160;</td>
			<td>2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Dual action thermoelectric controller</td>
			<td>WAtronix Inc, CA, USA</td>
			<td style="width:244px;">DA12V-K-0</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">IR LED array</td>
			<td>Advanced Illumination, Rochester, VT, USA</td>
			<td style="width:244px;">AL4554-88024, PS24-TL</td>
			<td>2 LED arrays and one power supply</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Air conditioner Unit</td>
			<td style="width:397px;">Melcor Store</td>
			<td style="width:244px;">&#160;MAA280T-12</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Imaging system</td>
			<td style="width:397px;"></td>
			<td style="width:244px;"></td>
			<td>(Quantity needed)</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Cosmicar/Pentax C21211TH (12.5mm F/1.4) C-mount Lens</td>
			<td style="width:397px;">B AND H PHOTO AND ELECTRONICS CORP, NY, USA</td>
			<td style="width:244px;">PEC21211 KP</td>
			<td>1</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;">CCXC-12P05N Interconnect Cable</td>
			<td style="width:397px;">B AND H PHOTO AND ELECTRONICS CORP, NY, USA</td>
			<td style="width:244px;">SOCCXC12P05N</td>
			<td>1</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">DC-700 Camera Adapter</td>
			<td style="width:397px;">B AND H PHOTO AND ELECTRONICS CORP, NY, USA</td>
			<td style="width:244px;">SODC700</td>
			<td>1</td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;">B+W 40,5 093 IR filter</td>
			<td style="width:397px;">B AND H PHOTO AND ELECTRONICS CORP, NY, USA</td>
			<td>65-072442</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TiFFEN 40.5mm Circular polarizer</td>
			<td style="width:397px;">Amazon</td>
			<td style="width:244px;"></td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">IR Videocamera</td>
			<td style="width:397px;">Industrial Vision Source, FL, USA</td>
			<td>Sony XC-EI50 (SY-XC-E150)</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">USB video converter</td>
			<td>The Imagingsource, NC, USA</td>
			<td style="width:244px;">DFG/USB2-It</td>
			<td>1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">iFlySpy2 (fly tracking software)</td>
			<td style="width:397px;">Julian Brown, Stanford, Calfornia: julianrbrown@gmail.com</td>
			<td style="width:244px;">iFlySpy2</td>
			<td>1</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:335px;">IC Capture 2.2 software</td>
			<td style="width:397px;">The Imagingsource, NC, USA (http://www.theimagingsource.com/en_US/products/software/iccapture/)</td>
			<td style="width:244px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Miscellaneous</td>
			<td style="width:397px;"></td>
			<td style="width:244px;"></td>
			<td>(Quantity needed)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Dremel rotary tool</td>
			<td style="width:397px;">Dremel, Racine, WI, USA</td>
			<td style="width:244px;">Dremel 8000-03&#160;</td>
			<td>1</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Diamond-coated drill bits for glass cutting</td>
			<td style="width:397px;">Available from various suppliers; MSC industrial Supply Co, Melville, NY</td>
			<td style="width:244px;">90606328</td>
			<td>1</td>
		</tr>
	</tbody>
</table>

olfactory behaviors assayed by computer tracking of drosophila in a four-quadrant olfactometer

A key challenge in neurobiology is to understand how neural circuits function to guide appropriate animal behaviors. Drosophila melanogaster is an excellent model system for such investigations due to its complex behaviors, powerful genetic techniques, and compact nervous system. Laboratory behavioral assays have long been used with Drosophila to simulate properties of the natural environment and study the neural mechanisms underlying the corresponding behaviors (e.g. phototaxis, chemotaxis, sensory learning and memory)1-3. With the recent availability of large collections of transgenic Drosophila lines that label specific neural subsets, behavioral assays have taken on a prominent role to link neurons with behaviors4-11. Versatile and reproducible paradigms, together with the underlying computational routines for data analysis, are indispensable for rapid tests of candidate fly lines with various genotypes. Particularly useful are setups that are flexible in the number of animals tested, duration of experiments and nature of presented stimuli. The assay of choice should also generate reproducible data that is easy to acquire and analyze. Here, we present a detailed description of a system and protocol for assaying behavioral responses of Drosophila flies in a large four-field arena. The setup is used here to assay responses of flies to a single olfactory stimulus; however, the same setup may be modified to test multiple olfactory, visual or optogenetic stimuli, or a combination of these. The olfactometer setup records the activity of fly populations responding to odors, and computational analytical methods are applied to quantify fly behaviors. The collected data are analyzed to get a quick read-out of an experimental run, which is essential for efficient data collection and the optimization of experimental conditions.

The four-quadrant olfactometer assay records and analyzes the walking activities of many flies over a large behavioral space. Odorants can be introduced into the air-streams that enter one, two, three, or all four quadrants. In the absence of odors, the flies will freely move between all four quadrants. This behavior is crucial to observe as it indicates that un-intentional biases have not been introduced into the assay. These biases can include light, temperature fluctuations, difference...

Watch this Scientific Journal Video about Olfactory Behaviors Assayed by Computer Tracking Of Drosophila in a Four-quadrant Olfactometer at JoVE.com

Olfactory Behaviors Assayed by Computer Tracking Of Drosophila in a Four-quadrant Olfactometer

We describe here a behavioral setup and data analysis method for assaying olfactory responses of up to 100 vinegar flies (Drosophila melanogaster). This system may be used with single or multiple olfactory stimuli, and adaptable for optogenetic activation or silencing of neuronal subsets.

Olfactory Behaviors Assayed by Computer Tracking Of Drosophila in a Four-quadrant Olfactometer

A key challenge in neurobiology is to understand how neural circuits function to guide appropriate animal behaviors. Drosophila melanogaster is an ...

The overall goal of this setup is to assay olfactory behaviors of flies in a four quadrant olfactometer using a provided automated fly tracking software script. This method can help address key questions regarding how olfactory neural systems detect the external world, and how the brain decodes and directs behavioral decisions. The main advantage of this technique is that it's versatile and robust, and allows repeat testing of olfactory responses by population of flies in a large experimental arena.For this protocol, prepare five odorant chambers that consist of a plastic outer container, glass inner container, and a custom-made PTFE lid insert. The insert is an original container lid with the central part removed, and two attached one way valves. Use four of the odorant chambers for solvent controls, and one chamber for a test odorant.Make sure each chamber is clean, and then load an odorant container with one milliliter of solvent or odorant dilution. Then, check the position of the container in the plastic chamber, and ensure that no liquid has been spilt. Secure the lid using the screwtop and an O-ring on the PTFE insert to prevent leaks.Rear the flies on standard cornmeal medium. In a standard bottle, place 30 males and 30 females, and allow eggs to be laid for five days at room temperature. From such bottles, collect newly eclosed flies.For each experimental cohort, collect 25 male and 25 female flies under brief carbon dioxide anesthesia and let the cohort age on standard fly medium for two to four days. 40 to 42 hours before the experiment, transfer the cohort to a vial with about 10 milliliters of one percent agarose gel for humidity without food. Starvation helps to increase the whole motion, and more than 90%of the flies should survive the starvation process.If more than 10%die, which can happen in a weak genotype, try using a one day starvation for all the flies in the experiment. At least five minutes in advance, switch on the temperature controller and set it to 25 degrees Celsius. Then, connect the odorant chambers to the arena via a plastic tube.Check the airflow rate in each quadrant of the arena using an electronic flow meter. Make sure that the control and odorant air streams are both running at 100 milliliters per minute. Flies are very sensitive to airflow, and it is critical that the airflow for each quadrant is verified before each experiment.Now, clean the arena and the glass plates using 70%ethanol. Wipe all the parts down two to three times, and allow them to fully air dry before proceeding. Next, clamp the glass plates to the arena.Then, transfer the flies into the arena without anesthesia. Using gravity, let them enter through the hole in one of the glass plates, and then cover the hole with a circular mesh. Now, place the fly loaded arena into the light-tight chamber.Then, connect the four control air streams to each arena corner. Close the door of the chamber and let the flies acclimatize to the new environment for 10 to 15 minutes. After the acclimation period, run a five to 10 minute control experiment in which flies are exposed to four control air streams.It is essential to now analyze the data immediately. If the flies are not evenly distributed in the arena, the arena must be reset. It is critical to test the behavior of control flies to just clean air.This will quickly verify that all background conditions are normal. Leaking light, temperature imbalance, tilted arena, or an odor contamination can all cause problems. If necessary, discard the flies and clean the arena again.If an odorant contamination is suspected, replace all the tubing. Continue repeating the control test with new cohorts until the animals show no preference for any of the four quadrants. Then, connect the test odorant chamber to the setup using a three way valve, or reconnect the tubing and run a test experiment for five to 10 minutes.For longer experimental recordings, rapidly stop and restart the tracking program every 20 minutes, or the data files will be too large. Between tests, discard the flies, clean the arena and glass plates with 70%ethanol, and replace the connector tubes. Keep the dry airflow going to continually flush the system.For efficiency, it is good to have two arenas so cleaning can be done during runs. If several experiments are wrong on the same day, take extreme care to ensure that no odor is left in the system from a previous run. This is normally not a problem with low concentrations of odorant or with CO2, but for highly concentrated stimuli, up to a 24 hour gap between experiment runs may be needed.For the data analysis, use the provided custom-made Matlab routine to convert the data into a Matlab format. Load the raw data file made in real time by the tracking software, and create a spacial mask that follows the contours of the arena. Apply the mask to the raw data to remove all the data points that fall outside of the arena, as they represent noise.Then, remove all the data points that move at less than 0.163 centimeters per second for longer than three seconds. This data is likely to be noise, or non-moving flies. Now, visualize the remaining data points by plotting all of them through the recording periods.The data can also be viewed as single trajectories. Odor boundaries can be quickly estimated based on the fly behavioral data. Then, calculate the attraction index, and make statistical tests as described in the text protocol.25 male and 25 female flies were tested in the behavioral apparatus. In response to dry air, flies explored the entire arena with no preference for any quadrant. The line shows the tracked trajectory of one fly.When apple cider vinegar was introduced into the top-left quadrant air stream, most of the flies were attracted to that odor quadrant. When a repellant odorant, 10%ethyl propionate, was introduced in the top-left quadrant, that quadrant was avoided. The attractive index of that quadrant scored 0.68.An attractive index is the most widely-used index in olfactory response measurement. A value above or below zero indicates attraction or repulsion. The script compensated for slight variations in arena position between trials.Data points that might have been noise or non-moving flies were removed. While the test can be run for any duration, it is interesting to view changes in the cohort's movements across 10 second bins to appreciate odor habituation and other phenomena. After watching this video, you should have a good understanding of how to effectively run and analyze olfactory behaviors in a four-field assay.Once mastered, each olfactory experiment can be completed in about an hour, and we routinely run four to six experiments during one day.

olfactory-behaviors-assayed-computer-tracking-drosophila-four

Research

JoVE Journal

Neuroscience

15.4K vistas.  Johns Hopkins University School of Medicine. The overall goal of this setup is to assay olfactory behaviors of flies in a four quadrant olfactometer using a provided automated fly tracking software script. This method can help address key questions regarding how olfactory neural systems detect the external world, and how the brain decodes and directs behavioral decisions. The main advantage of this technique is that it's versatile and robust, and allows repeat testing of olfactory responses by population of flies in a large experimental...