Name: the capillary feeder assay measures food intake in drosophila melanogaster
Uploaded: 2017-03-17T13:00:00
Description: Watch this Scientific Journal Video about The CApillary FEeder Assay Measures Food Intake in Drosophila melanogaster at JoVE.com

We thank the past and present members of the Scholz lab for discussion and Helga D&#246;ring for excellent technical support. We especially thank the members of the Biocenter workshop of the University of Cologne for their support and creativity. The work is supported by SFB 1340, SysMedAlc, and DAAD-Siemens.

1. The CAFE Assay
NOTE: The assay consists of three components: an experimental vial, a specific lid and micro- capillaries. A plastic box with cover is used to transport the prepared vials and to control the humidity more efficiently.
<ol>
	<li>Use a Drosophila melanogaster culture plastic vial (optional 8 cm height, 3.3 cm diameter) as a tube for the assay.</li>
	<li>Seal the vial with a manufactured Plexiglas lid containing an O-ring (Figures 1A, 1B). Load flies ...

<ol>
	<li>Krauth, C., Buser, J., Vogel, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+high+are+the+costs+of+eating+disorders+-+anorexia+nervosa+and+bulimia+nervosa+-+for+German+society.">How high are the costs of eating disorders - anorexia nervosa and bulimia nervosa - for German society.</a> Eur. J. Health Econ. 3 (4), 244-250 (2002).</li><li>Cawley, J., Meyerhoefer, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+medical+costs+of+obesity+and+instrumental+variables+approach.">The medical costs of obesity and instrumental variables approach.</a> J. Health Econ. 31, 219-230 (2012).</li><li>The costs of eating disorders: Social, health and economic impacts. Assessing the impact of eating disorders across the UK on behalf of BEAT. PwC Available from: <a target="_blank" href="https://www.beat.co.uk/assets/000/000/302/The_costs_of_eating_disorders_Final_original.pdf">https://www.beat.co.uk/assets/000/000/302/The_costs_of_eating_disorders_Final_original.pdf</a> (2015)</li><li>Lenard, N. R., Berthoud, H. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Central+and+peripheral+regulation+of+food+intake+and+physical+activity:+pathways+and+genes.">Central and peripheral regulation of food intake and physical activity: pathways and genes.</a> Obesity. 16, S11-S22 (2008).</li><li>Magni, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Feeding+behavior+in+mammals+including+humans.">Feeding behavior in mammals including humans.</a> Trends in Comp. Endocrinology and Neurobiology. 1163, 221-232 (2009).</li><li>Morton, G. J., Meek, T. H., Schwartz, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neurobiology+of+food+intake+in+health+and+disease.">Neurobiology of food intake in health and disease.</a> Nature Reviews Neuroscience. 15, 367-378 (2014).</li><li>Bharuchka, K. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+epicurean+fly:+using+Drosophila+melanogaster+to+study+metabolism.">The epicurean fly: using Drosophila melanogaster to study metabolism.</a> Pediatr. Res. 65 (2), 132-137 (2009).</li><li>Smith, W. W., Thomas, J., Liu, J., Li, T., Moran, T. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+fat+fruit+fly+to+human+obesity.">From fat fruit fly to human obesity.</a> Physiol. Behav. 136, 15-21 (2014).</li><li>Rajan, A., Perrimon, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Of+flies+and+men:+insights+on+organismal+metabolism+from+fruit+flies.">Of flies and men: insights on organismal metabolism from fruit flies.</a> BMC Biology. 11, (2013).</li><li>Ja, W. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prandiology+of+Drosophila+and+the+CAFE+assay.">Prandiology of Drosophila and the CAFE assay.</a> Proc. Natl. Acad. Sci. USA. 104 (20), 8253-8256 (2007).</li><li>Dethier, V. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Hungry Fly: A Physiological Study of the Behavior Associated with Feeding. , (1976).</li><li>Albin, S. D., Kaun, K. R., Knapp, J., Chung, P., Heberlein, U., Simpson, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+subset+of+serotonergic+neurons+evokes+hunger+in+adult+Drosophila.">A subset of serotonergic neurons evokes hunger in adult Drosophila.</a> Curr. Biol. 25, 2435-2440 (2015).</li><li>Deshpande, S. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantifying+Drosophila+food+intake:+comparative+analysis+of+current+methodology.">Quantifying Drosophila food intake: comparative analysis of current methodology.</a> Nat. Methods. 11 (5), 535-540 (2014).</li><li>Geer, B. W., Olander, R. M., Sharp, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+dietary+choline+utilization+in+adult+Drosophila+melanogaster+by+radioisotope+methods.">Quantification of dietary choline utilization in adult Drosophila melanogaster by radioisotope methods.</a> J. Insect Physiol. 16, 33-43 (1970).</li><li>Thompson, E. D., Reeder, B. A., Bruce, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+a+method+for+quantitating+food+consumption+for+mutation+assays+in+Drosophila.">Characterization of a method for quantitating food consumption for mutation assays in Drosophila.</a> Environ. Mol. Mutagen. 18, 14-21 (1991).</li><li>Wong, R., Piper, M. D., Wertheim, B., Partridge, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+food+intake+in+Drosophila.">Quantification of food intake in Drosophila.</a> PLoS One. 4 (6), e6063 (2009).</li><li>Scheiner, R., Steinbach, A., Classen, G., Strudthoff, N., Scholz, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Octopamine+indirectly+affects+proboscis+extension+response+habituation+in+Drosophila+melanogaster+by+controlling+sucrose+responsiveness.">Octopamine indirectly affects proboscis extension response habituation in Drosophila melanogaster by controlling sucrose responsiveness.</a> J. Insect Physiol. 69, 107-117 (2014).</li><li>Liu, Y., Luo, J., Carlsson, M. K., N&#228;ssel, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotonin+and+insulin-like+peptides+modulate+leucokinin-producing+neurons+that+affect+feeding+and+water+homeostasis+in+Drosophila.">Serotonin and insulin-like peptides modulate leucokinin-producing neurons that affect feeding and water homeostasis in Drosophila.</a> J. Comp. Neurol. 523, 1840-1863 (2015).</li><li>Ro, J., Harvanek, Z. M., Pletcher, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FLIC:+high-throughput,+continuous+analysis+of+feeding+behaviors+in+Drosophila.">FLIC: high-throughput, continuous analysis of feeding behaviors in Drosophila.</a> PLoS One. 9 (6), e101107 (2014).</li><li>Itskov, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Automated+monitoring+and+quantitative+analysis+of+feeding+behavior+in+Drosophila.">Automated monitoring and quantitative analysis of feeding behavior in Drosophila.</a> Nat. Commun. 5, 4560 (2014).</li><li>Qi, W., Yang, Z., Lin, Z., Park, J. Y., Suh, G. S. B., Wang, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+quantitative+feeding+assay+in+adult+Drosophila+reveals+rapid+modulation+of+food+ingestion+by+its+nutritional+value.">A quantitative feeding assay in adult Drosophila reveals rapid modulation of food ingestion by its nutritional value.</a> Mol. Brain. 8, 87 (2015).</li><li>Marx, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolism:+feeding+fruit+flies.">Metabolism: feeding fruit flies.</a> Nat. Methods. 12 (7), 609-612 (2015).</li><li>Spieth, H. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Courtship+behavior+in+Drosophila.">Courtship behavior in Drosophila.</a> Annu. Rev. Entomol. 19, 385-405 (1974).</li><li>Devineni, A. V., Heberlein, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preferential+ethanol+consumption+in+Drosophila+models+features+of+addiction.">Preferential ethanol consumption in Drosophila models features of addiction.</a> Curr. Biol. 19 (24), 2126-2132 (2009).</li><li>Lee, K. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lifespan+and+reproduction+in+Drosophila:+New+insights+from+nutritional+geometry.">Lifespan and reproduction in Drosophila: New insights from nutritional geometry.</a> Proc. Natl. Acad. Sci. USA. 105 (7), 2498-2503 (2008).</li><li>Pohl, J. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ethanol+preference+in+Drosophila+melanogaster+is+driven+by+its+caloric+value.">Ethanol preference in Drosophila melanogaster is driven by its caloric value.</a> Alcohol Clin. Exp. Res. 36 (11), 1903-1912 (2012).</li><li>Vargas, M. A., Luo, N., Yamaguchi, A., Kapahi, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+role+for+S6+kinase+and+serotonin+in+postmating+dietary+switch+and+balance+of+nutrients+in+D.+melanogaster.">A role for S6 kinase and serotonin in postmating dietary switch and balance of nutrients in D. melanogaster.</a> Curr. Biol. 20 (11), 1006-1011 (2010).</li><li>Masek, P., Scott, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Limited+taste+discrimination+in+Drosophila.">Limited taste discrimination in Drosophila.</a> Proc. Natl. Acad. Sci. 107 (33), 14833-14838 (2010).</li><li>Pool, A. H., Scott, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Feeding+regulation+in+Drosophila.">Feeding regulation in Drosophila.</a> Curr. Opin. Neurobiol. 29, 57-63 (2014).</li><li>Luo, J. N., Lushchak, O. V., Goergen, P., Williams, M. J., N&#228;ssel, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drosophila+insulin-producing+cells+are+differentially+modulated+by+serotonin+and+octopamine+receptors+and+affect+social+behavior.">Drosophila insulin-producing cells are differentially modulated by serotonin and octopamine receptors and affect social behavior.</a> Plos One. 9 (6), e99732 (2014).</li></ol>

The report describes the CAFE assay in a step-by-step fashion, focusing on the technical setup and its successful performance in the laboratory. Due to its simplicity, this assay could also be used educationally as a school experiment. The examples show that the assay allows investigation of food sensing, preference and consumption in Drosophila melanogaster over short and longer time periods (hours to days). The CAFE assay has been used widely in the field to investigate subjects including food and drug consump...

Eating is essential; however, deregulation of food intake resulting in eating disorders such as bulimia, anorexia or the general tendency to overeat imposes costs on individuals and society1,2,3. The goal of the present research is to uncover regulatory mechanisms of food intake and to provide a strategy for circumventing disorder formation. Numerous studies using mammalian model organisms have provided new insights of the circuitry and the role of signaling systems in eating disorders4,5,6. Nevertheless, our knowledge of the neuronal and molecular bases underlying these disorders remains far from complete. In recent years, the fruit fly Drosophila melanogaster has become a valuable model system for unraveling basic mechanistic insights into the regulation of metabolism7,8,9. The CApillary FEeder (CAFE) assay for Drosophila melanogaster was established in the lab of Seymour Benzer in 2007 inspired by an earlier work by Dethier in blowfly10, 11. The CAFE assay made it possible to directly measure food intake in Drosophila melanogaster. In this behavioral test system, flies feed on liquid food provided in graded glass capillaries placed inside a vial. The decline of the capillary meniscus indicates loss of food solution via evaporation and food consumption. Determining the evaporation rate by vials without flies allows the accurate quantification of food intake.
The CAFE assay is one of several behavioral paradigms used to measure feeding in Drosophila melanogaster and researchers have to choose the most appropriate one for their specific question. The decision to use a certain assay should consider the following points: the nature of the food provided; the feeding condition; the measurement of intake or uptake of nutrients and investigation food consumption or response to food.
The CAFE assay as described in this report is ideal for following food intake of a liquid food source under an upright feeding condition. Alternatively the food intake can be measured for a fly group on a colored food source in a vial or on a plate. Flies are normally killed or anesthetized after feeding and the amount of ingested dye is determined by spectrometry or visual inspection of the stained abdomen. Flies start to excrete the ingested food only 30 min after intake, therefore this approach is difficult to use for the analysis of continuous longer feeding behaviors12, 13.
In contrast flies are kept intact when absorbable dyes with radioactive tracers are used and their consumption of radioisotope is scored in a scintillation counter14, 15. Absorption of the radiolabel by the fly digestive system makes long-term food uptake measurement possible, but might lead to underestimation of consumption because of non-absorbed and excreted tracer molecules. Another approach to measure response to food in Drosophila melanogaster is the proboscis extension response (PER), which normally occurs for food intake16. This elegant method measures the initial response to a food stimulus but does not record the quantity of intake. Food intake is dynamically adjusted during feeding using several post-digestive feedback signals that are critical for the regulation of feeding17, 18. Several attempts have been made in recent years to semi-automate data collection in the PER assay19, 20. The PER is detected by an electric pad or a combination of electrodes and counted via computer. Combining the PER assay with radioisotope uptake revealed that this assay is limited by low sensitivity to detecting quantity feeding differences18. The manual feeding assay (MAFE)21, in which a fly is fed manually with a glass capillary, was recently developed to measure food uptake in a single immobilized fly. The MAFE assay eliminates the interferences of foraging and feeding initiation and has a time resolution of seconds, and initiation of PER and food consumption can be monitored independently in the assay. However, the way in which immobilization of the fly affects certain aspects of feeding behavior (e.g. locomotion, motivation) still needs to be investigated. For excellent comparative reviews of different assays for measuring food consumption in Drosophila melanogaster and to help researchers finding the most appropriate one, see reports by Deshpande and Marx 13, 22.
The CAFE assay avoids some of the disadvantages of other assays described above and combines simplicity of use with reliable measurement of food intake. Here, a detailed description of the CAFE assay is provided and we show a simple setup modification to reduce evaporation. Representative results including a two food choice assay (short and long term) and the sucrose uptake of flies is demonstrated. In the discussion we compare our described method with alternative ways to perform the CAFE assay, and highlight potential limitations.

<table border="0" cellpadding="0" cellspacing="0" width="582">
	<tbody>
		<tr height="31">
			<td height="31" style="height:31px;width:161px;">Vials (breeding)</td>
			<td style="width:117px;">Greiner Bio-One</td>
			<td style="width:123px;">960177</td>
			<td style="width:183px;">www.greinerbioone.com</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Vials (CAFE assay)</td>
			<td>Greiner Bio-One</td>
			<td>217101</td>
			<td>www.greinerbioone.com</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Lid-CAFE assay</td>
			<td>Workshop</td>
			<td>&#8211;</td>
			<td>&#8211;</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Plastic box, low wall</td>
			<td>Plastime</td>
			<td>353</td>
			<td>www.plastime.it</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Cover for the plastic box</td>
			<td>Workshop</td>
			<td>&#8211;</td>
			<td>&#8211;</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Capillaries</td>
			<td>BLAUBRAND&#160;</td>
			<td>REF 7087 07</td>
			<td>www.brand.de</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Pipette tips</td>
			<td>Greiner Bio-One</td>
			<td>771290</td>
			<td>www.greinerbioone.com</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Filter paper circles</td>
			<td>Whatman</td>
			<td>10 311 804</td>
			<td>www.sigmaaldrich.com</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">D(+)-Sucrose</td>
			<td>AppliChem</td>
			<td>57-50-1</td>
			<td>www.applichem.com</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Ethanol absolute</td>
			<td>VWR Chemicals</td>
			<td>20,821,330</td>
			<td>www.vwr.com</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Food color (red, E124)</td>
			<td>Backfun</td>
			<td>10027</td>
			<td>www.backfun.de</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Food color (blue, E133)</td>
			<td>Backfun</td>
			<td>10030</td>
			<td>www.backfun.de</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Soap solution (CVK 8)</td>
			<td>CVH</td>
			<td>103220</td>
			<td>www.cvh.de</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Digital caliper</td>
			<td>GARANT</td>
			<td>412,616</td>
			<td>www.hoffmann-group.com</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Vials (breeding)</td>
			<td></td>
			<td></td>
			<td>Height 9.8 cm, diameter 4.8 cm&#160;</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Vials (CAFE assay)</td>
			<td></td>
			<td></td>
			<td>Height 8 cm, diameter 3.3 cm</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Lid-CAFE assay</td>
			<td></td>
			<td></td>
			<td>Produced in university workshop, technical drawing supplied</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Plastic box, low wall</td>
			<td></td>
			<td></td>
			<td>A plastic grid inlay was custom-made for 8 x 10 vial positions&#160;</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Cover for the plastic box</td>
			<td></td>
			<td></td>
			<td>Dimensions (37 x29 x18 cm)</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Capillaries</td>
			<td></td>
			<td></td>
			<td>DIN ISO 7550 norm,&#160; IVD-guideline 98/79 EG, ends polished</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Pipette tips</td>
			<td></td>
			<td></td>
			<td>Pipettes for the outer circle are cut according to the lid</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Filter paper circles</td>
			<td></td>
			<td></td>
			<td>45 mm diameter works nicely if folded for the vials used</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">D(+)-Sucrose</td>
			<td></td>
			<td></td>
			<td>Not harmful</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Ethanol absolute</td>
			<td></td>
			<td></td>
			<td>Highly flammable liquid and vapor</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Food color (red, E124)</td>
			<td></td>
			<td></td>
			<td>Not stated</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Food color (blue, E133)</td>
			<td></td>
			<td></td>
			<td>Not stated</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Soap solution (CVK 8)</td>
			<td></td>
			<td></td>
			<td>Odor neutral soap</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Digital caliper</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Standard fly food</td>
			<td></td>
			<td></td>
			<td>(for 20 L)</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Agar</td>
			<td></td>
			<td></td>
			<td>160 g</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Brewer`s Yeast</td>
			<td></td>
			<td></td>
			<td>299.33 g</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Cornmeal</td>
			<td></td>
			<td></td>
			<td>1200g</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Molasses</td>
			<td></td>
			<td></td>
			<td>1.6 L</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Propionic acid</td>
			<td></td>
			<td></td>
			<td>57.3 mL</td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;">Nipagin 30%</td>
			<td></td>
			<td></td>
			<td>160 mL</td>
		</tr>
	</tbody>
</table>

the capillary feeder assay measures food intake in drosophila melanogaster

For most animals, feeding is an essential behavior for securing survival, and it influences development, locomotion, health and reproduction. Ingestion of the right type and quantity of food therefore has a major influence on quality of life. Research on feeding behavior focuses on the underlying processes that ensure actual feeding and unravels the role of factors regulating internal energy homeostasis and the neuronal bases of decision-making. The model organism Drosophila melanogaster, with its great variety of genetically traceable tools for labeling and manipulating single neurons, allows mapping of neuronal networks and identification of molecular signaling cascades involved in the regulation of food intake. This report demonstrates the CApillary FEeder assay (CAFE) and shows how to measure food intake in a group of flies for time spans ranging from hours to days. This easy-to-use assay consists of glass capillaries filled with liquid food that flies can freely access and feed on. Food consumption in the assay is accurately determined using simple measurement tools. Herein we describe step-by-step the method from setup to successful execution of the CAFE assay, and provide practical examples to analyze the food intake of a group of flies under controlled conditions. The reader is guided through possible limitations of the assay, and advantages and disadvantages of the method compared to other feeding assays in D. melanogaster are evaluated.

Flies of the w1118 genotype are used to demonstrate how the assay is performed. The w1118 mutants are commonly used to generate transgenic lines and to control the genetic background of transgenes marked with the white gene. Normally, for behavioral experiments, all transgenic lines are backcrossed for five generations to the same w1118 stock, which is used as an experimental control. We show different experiments: a com...

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The CApillary FEeder Assay Measures Food Intake in Drosophila melanogaster

The CApillary FEeder (CAFE) assay is a simple, budget-friendly, highly reliable method for investigating mechanisms underlying food intake. Used with the highly versatile genetic model organism Drosophila melanogaster, it provides a powerful means of gaining new insights into regulatory mechanisms of food intake.

The CApillary FEeder Assay Measures Food Intake in Drosophila melanogaster

For most animals, feeding is an essential behavior for securing survival, and it influences development, locomotion, health and reproduction. Ingestion of ...

The overall goal of the CApillary FEeder assay is to observe and measure liquid food intake of adult flies. This method can help to answer key questions in metabolic research such as how actual feeding behavior is initiated and how food consumption is terminated. The main advantages of this technique are that it's easy to use and highly reliable.Visual demonstration of the method is critical as several preparatory steps need to be carefully executed for consistent results. To begin the experiment, obtain a drosophila melanogaster culture plastic vial and seal it with a manufactured Plexiglass lid containing an O-ring. Use five microliter microcapillaries with one microliter marks to present the liquid food.Cut off the top of a two to 20 microliter pipette tip and insert the tip into the whole of the lid to position the capillaries in the conical openings. Insert an uncut two to 20 microliter pipette tip into the same opening to prevent flies from escaping. Load eight or 20 flies by trapping or with a blow pipe through the lid's central opening and close the hole with a sponge bung.Next, place the multiple prepared vials into a plastic box with a gridded inlay to handle them safely. To control breeding conditions, introduce 35 virgin females and 15 males for each experimental group into a plastic culture vial containing 50 milliliter fly food. Allow the flies to lay eggs for the first three days, then transfer adult flies to fresh food vials and let them lay eggs for two more days.After two days, repeat the transfer. On day seven, discard the adult flies. Next, anesthetize two to three day old adult flies using a CO2 pad and collect 100 flies sorted by sex in a 1.5 milliliter plastic tube.Measure their weight with a standard laboratory scale. Determine the wet weight of at least four independent fly groups sorted by sex and use the weight to calculate the microliter food consumption per milligram fly. For a three hour assay, use 20 flies in two filled capillaries.For a long term experiment, use a group of eight flies with a supply of four filled capillaries. Fill up to 10 capillaries simultaneously with previously prepared colored food solution. Insert the capillaries into the food solution and then tilt them to a 45 degree angle to accelerate filling.Stop when the liquid reaches the top five microliter mark of the capillary. Remove excess solution on the outside and inside of the capillary with tissue paper. Carefully remove the pipette tip that is closing one of the outer openings and insert a filled glass capillary, bottom end first.Secure the capillary by placing the pipette tip back next to the capillary. Repeat this step for all food solutions tested. Next, place the capillary ends inside all of the vials at the same level three to four centimeters from the lid.Leave some distance between the filter paper to prevent the capillary from leaking. Use a marker pen to label the upper end of the colored liquid. Label them individually using a stripe code to ensure the different capillaries can be identified.Place prepared CAFE assays into a plastic box with a gridded inlay. Use a sponge bung to apply 100 microliters of fresh water every 24 hours to keep the humidity constant inside the assay. Use four separate vials filled with 30 milliliters of double distilled H2O as humidity devices and place them next to the CAFE assays in the plastic box.Cover the plastic box to create a humidity controlled environment during the experiment. Transfer the box to a secure position in a temperature, light, and humidity controlled climate chamber for the experimental period. Before each 24 hour interval, make note of the dead flies and use the number of live flies to calculate the consumption per fly for the following period.At the end of the assay and before replacing the capillary, keep the CAFE assay in the upright position. Do not remove the lid and mark the lower meniscus of the capillary. Discard the data if the mark end is not below the initial mark.Replace the used capillaries with freshly filled capillaries for long term experiments every 24 hours. Measure the decline of the meniscus, then discard the old capillaries. Then carefully remove the capillaries from the assay and store them for data collection.Check if the liquid inside the capillary reached the lower end. If the liquid inside the capillary did not reach the lower end, discard the data. After the experiment, dismantle the setup and wash the vials, lids, and sponge bungs in a soap bath.Then dry them overnight at room temperature for further use. Repeat experiments with the same genotypes on at least three different days. Using a caliper, measure the distance between mark beginning and mark end on the capillary.Finally, discard the capillaries after the measurements. Two food choices were offered, a 1 molar sucrose solution and a 1 molar sucrose solution with 15%ethanol. Visual examination of the abdomen indicates the flies feed on both solutions.However food consumption per fly is nearly two folds greater for the solution containing ethanol. The ethanol preference was also observed in long term experiments where a group of eight flies had access to similar food sources for four days. The CApillary FEeder assay also reveals that male and female flies prefer higher sucrose concentrations over lower sucrose concentrations.And male flies consume significantly more of the high sucrose concentrations than their female counterparts. While attempting this procedure, it's important to remember to perform the assay in a controlled fashion and to repeat the experiment with the same genotypes on at least three different days. In addition, when testing mutant flies, it's important to consider whether the flies can actually perform the task required to obtain the food, such as sending the food source or climbing up and down the capillary.

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Research

JoVE Journal

Neuroscience

Single Sensillum Recordings in the Insects Drosophila melanogaster and Anopheles gambiae

The sense of smell is essential for insects to find foods, mates, predators, and oviposition sites3. Insect olfactory sensory neurons (OSNs) are enclosed in sensory hairs called sensilla, which cover the surface of olfactory organs. The surface of each sensillum is covered with tiny pores, through which odorants pass and dissolve in a fluid called sensillum lymph, which bathes the sensory dendrites of the OSNs housed in a given sensillum. The OSN dendrites express odorant receptor (OR) proteins, which in insects function as odor-gated ion channels4, 5. The interaction of odorants with ORs either increases or decreases the basal firing rate of the OSN. This neuronal activity in the form of action potentials embodies the first representation of the quality, intensity, and temporal characteristics of the odorant6, 7.
Given the easy access to these sensory hairs, it is possible to perform extracellular recordings from single OSNs by introducing a recording electrode into the sensillum lymph, while the reference electrode is placed in the lymph of the eye or body of the insect. In Drosophila, sensilla house between one and four OSNs, but each OSN typically displays a characteristic spike amplitude. Spike sorting techniques make it possible to assign spiking responses to individual OSNs. This single sensillum recording (SSR) technique monitors the difference in potential between the sensillum lymph and the reference electrode as electrical spikes that are generated by the receptor activity on OSNs1, 2, 8. Changes in the number of spikes in response to the odorant represent the cellular basis of odor coding in insects. Here, we describe the preparation method currently used in our lab to perform SSR on Drosophila melanogaster and Anopheles gambiae, and show representative traces induced by the odorants in a sensillum-specific manner.

Single Sensillum Recordings in the Insects Drosophila melanogaster and Anopheles gambiae

Electrophysiological responses of olfactory sensory neurons to odorants can be measured in insects using single sensillum recordings. In this video article we will demonstrate how to perform single sensillum recordings in the antennae of the vinegar fly (Drosophila melanogaster) and the maxillary palps of the malaria mosquito (Anopheles gambiae).

The sense of smell is essential for insects to find foods, mates, predators, and oviposition sites3. Insect olfactory sensory neurons (OSNs) are enclosed ...

Paired Nanoinjection and Electrophysiology Assay to Screen for Bioactivity of Compounds using the Drosophila melanogaster Giant Fiber System

Screening compounds for in vivo activity can be used as a first step to identify candidates that may be developed into pharmacological agents1,2. We developed a novel nanoinjection/electrophysiology assay that allows the detection of bioactive modulatory effects of compounds on the function of a neuronal circuit that mediates the escape response in Drosophila melanogaster3,4. Our in vivo assay, which uses the Drosophila Giant Fiber System (GFS, Figure 1) allows screening of different types of compounds, such as small molecules or peptides, and requires only minimal quantities to elicit an effect. In addition, the Drosophila GFS offers a large variety of potential molecular targets on neurons or muscles. The Giant Fibers (GFs) synapse electrically (Gap Junctions) as well as chemically (cholinergic) onto a Peripheral Synapsing Interneuron (PSI) and the Tergo Trochanteral Muscle neuron (TTMn)5. The PSI to DLMn (Dorsal Longitudinal Muscle neuron) connection is dependent on D&alpha;7 nicotinic acetylcholine receptors (nAChRs)6. Finally, the neuromuscular junctions (NMJ) of the TTMn and the DLMn with the jump (TTM) and flight muscles (DLM) are glutamatergic7-12. Here, we demonstrate how to inject nanoliter quantities of a compound, while obtaining electrophysiological intracellular recordings from the Giant Fiber System13 and how to monitor the effects of the compound on the function of this circuit. We show specificity of the assay with methyllycaconitine citrate (MLA), a nAChR antagonist, which disrupts the PSI to DLMn connection but not the GF to TTMn connection or the function of the NMJ at the jump or flight muscles.
Before beginning this video it is critical that you carefully watch and become familiar with the JoVE video titled "Electrophysiological Recordings from the Giant Fiber Pathway of D. melanogaster " from Augustin et al7, as the video presented here is intended as an expansion to this existing technique. Here we use the electrophysiological recordings method and focus in detail only on the addition of the paired nanoinjections and monitoring technique.

Paired Nanoinjection and Electrophysiology Assay to Screen for Bioactivity of Compounds using the Drosophila melanogaster Giant Fiber System

A rapid in vivo assay to test for neuromodulatory compounds using the Giant Fiber System (GFS) of Drosophila melanogaster is described. Nanoinjections in the head of the animal along with electrophysiological recordings of the GFS can reveal bioactivity of compounds on neurons or muscles.

Screening compounds for in vivo activity can be used as a first step to identify candidates that may be developed into pharmacological agents1,2. We ...

Labeling of Single Cells in the Central Nervous System of Drosophila melanogaster

In this article we describe how to individually label neurons in the embryonic CNS of Drosophila melanogaster by juxtacellular injection of the lipophilic fluorescent membrane marker DiI. This method allows the visualization of neuronal cell morphology in great detail. It is possible to label any cell in the CNS: cell bodies of target neurons are visualized under DIC optics or by expression of a fluorescent genetic marker such as GFP. After labeling, the DiI can be transformed into a permanent brown stain by photoconversion to allow visualization of cell morphology with transmitted light and DIC optics. Alternatively, the DiI-labeled cells can be observed directly with confocal microscopy, enabling genetically introduced fluorescent reporter proteins to be colocalised. The technique can be used in any animal, irrespective of genotype, making it possible to analyze mutant phenotypes at single cell resolution.

Labeling of Single Cells in the Central Nervous System of Drosophila melanogaster

We present a technique for labeling single neurons in the central nervous system (CNS) of Drosophila embryos, which allows the analysis of neuronal morphology by either transmitted light or confocal microscopy.

In this  article we describe how to individually label neurons in the embryonic CNS of Drosophila melanogaster by juxtacellular injection of the ...

Optogenetic Stimulation of Escape Behavior in Drosophila melanogaster

A growing number of genetically encoded tools are becoming available that allow non-invasive manipulation of the neural activity of specific neurons in Drosophila melanogaster1. Chief among these are optogenetic tools, which enable the activation or silencing of specific neurons in the intact and freely moving animal using bright light. Channelrhodopsin (ChR2) is a light-activated cation channel that, when activated by blue light, causes depolarization of neurons that express it. ChR2 has been effective for identifying neurons critical for specific behaviors, such as CO2 avoidance, proboscis extension and giant-fiber mediated startle response2-4. However, as the intense light sources used to stimulate ChR2 also stimulate photoreceptors, these optogenetic techniques have not previously been used in the visual system. Here, we combine an optogenetic approach with a mutation that impairs phototransduction to demonstrate that activation of a cluster of loom-sensitive neurons in the fly's optic lobe, Foma-1 neurons, can drive an escape behavior used to avoid collision. We used a null allele of a critical component of the phototransduction cascade, phospholipase C-&beta;, encoded by the norpA gene, to render the flies blind and also use the Gal4-UAS transcriptional activator system to drive expression of ChR2 in the Foma-1 neurons. Individual flies are placed on a small platform surrounded by blue LEDs. When the LEDs are illuminated, the flies quickly take-off into flight, in a manner similar to visually driven loom-escape behavior. We believe that this technique can be easily adapted to examine other behaviors in freely moving flies.

Optogenetic Stimulation of Escape Behavior in Drosophila melanogaster

Genetically encoded optogenetic tools enable noninvasive manipulation of specific neurons in the Drosophila brain. Such tools can identify neurons whose activation is sufficient to elicit or suppress particular behaviors. Here we present a method for activating Channelrhodopsin2 that is expressed in targeted neurons in freely walking flies.

A  growing number of genetically encoded tools are becoming available that allow non-invasive  manipulation of the neural activity of specific neurons in ...

Determination of the Spontaneous Locomotor Activity in Drosophila melanogaster

Drosophila melanogaster has been used as an excellent model organism to study environmental and genetic manipulations that affect behavior. One such behavior is spontaneous locomotor activity. Here we describe our protocol that utilizes Drosophila population monitors and a tracking system that allows continuous monitoring of the spontaneous locomotor activity of flies for several days at a time. This method is simple, reliable, and objective and can be used to examine the effects of aging, sex, changes in caloric content of food, addition of drugs, or genetic manipulations that mimic human diseases.

Determination of the Spontaneous Locomotor Activity in Drosophila melanogaster

Drosophila melanogaster are useful in studying genetic or environmental manipulations that affect behaviors such as spontaneous locomotor activity.&#160; Here we describe a protocol that utilizes monitors with infrared beams and data analysis software to quantify spontaneous locomotor activity.&#160;

Drosophila melanogaster has been used as an excellent model organism to study environmental and genetic manipulations that affect behavior. One such ...

Straightforward Assay for Quantification of Social Avoidance in Drosophila melanogaster

Drosophila melanogaster is an emerging model to study different aspects of social interactions. For example, flies avoid areas previously occupied by stressed conspecifics due to an odorant released during stress known as the Drosophila stress odorant (dSO). Through the use of the T-maze apparatus, one can quantify the avoidance of the dSO by responder flies in a very affordable and robust assay. Conditions necessary to obtain a strong performance are presented here. A stressful experience is necessary for the flies to emit dSO, as well as enough emitter flies to cause a robust avoidance response to the presence of dSO. Genetic background, but not their group size, strongly altered the avoidance of the dSO by the responder flies. Canton-S and Elwood display a higher performance in avoiding the dSO than Oregon and Samarkand strains. This behavioral assay will allow identification of mechanisms underlying this social behavior, and the assessment of the influence of genes and environmental conditions on both emission and avoidance of the dSO. Such an assay can be included in batteries of simple diagnostic tests used to identify social deficiencies of mutants or environmental conditions of interest.

Straightforward Assay for Quantification of Social Avoidance in Drosophila melanogaster

Here, we present a protocol to quantify the avoidance of stressed individuals. This paradigm is powerful yet user-friendly and can be used to assess the influence of genes and environment on one kind of social interaction in Drosophila melanogaster.

Drosophila melanogaster is an emerging model to study different aspects of social interactions. For example, flies avoid areas previously occupied by ...

Conditions Affecting Social Space in Drosophila melanogaster

The social space assay described here can be used to quantify social interactions of Drosophila melanogaster &#8212; or other small insects &#8212; in a straightforward manner. As we previously demonstrated 1, in a two-dimensional chamber, we first force the flies to form a tight group, subsequently allowing them to take their preferred distance from each other. After the flies have settled, we measure the distance to the closest neighbor (or social space), processing a static picture with free online software (ImageJ). The analysis of the distance to the closest neighbor allows researchers to determine the effects of genetic and environmental factors on social interaction, while controlling for potential confounding factors. Diverse factors such as climbing ability, time of day, sex, and number of flies, can modify social spacing of flies. We thus propose a series of experimental controls to mitigate these confounding effects. This assay can be used for at least two purposes. First, researchers can determine how their favorite environmental shift (such as isolation, temperature, stress or toxins) will impact social spacing 1,2. Second, researchers can dissect the genetic and neural underpinnings of this basic form of social behavior 1,3. Specifically, we used it as a diagnostic tool to study the role of orthologous genes thought to be involved in social behavior in other organisms, such as candidate genes for autism in humans 4.

Conditions Affecting Social Space in Drosophila melanogaster

The effect of genes and environment on social space of Drosophila melanogaster can be quantified through a powerful but straightforward analytical paradigm. We show here different factors that can affect this social space, and thus need to be taken into consideration when designing experiments in this paradigm.

The social space assay described here can be used to quantify social interactions of Drosophila melanogaster &#8212; or other small insects &#8212; in a ...

A Behavioral Assay for Mechanosensation of MARCM-based Clones in Drosophila melanogaster

Because of the structural and functional homology to the hair cells of the mammalian inner ear, the neurons that innervate the Drosophila external sense organs provide an excellent model system for the study of mechanosensation. This protocol describes a simple touch behavior in fruit flies which can be used to identify mutations that interfere with mechanosensation. The tactile stimulation of a macrochaete bristle on the thorax of flies elicits a grooming reflex from either the first or third leg. Mutations that interfere with mechanotransduction (such as NOMPC), or with other aspects of the reflex arc, can inhibit the grooming response. A traditional screen of adult behaviors would have missed mutants that have essential roles during development. Instead, this protocol combines the touch screen with mosaic analysis with a repressible cell marker (MARCM) to allow for only limited regions of homozygous mutant cells to be generated and marked by the expression of green fluorescent protein (GFP). By testing MARCM clones for abnormal behavioral responses, it is possible to screen a collection of lethal p-element mutations to search for new genes involved in mechanosensation that would have been missed by more traditional methods.

A Behavioral Assay for Mechanosensation of MARCM-based Clones in Drosophila melanogaster

In order to identify novel mutations affecting mechanosensation, we designed an assay that measures the behavioral response to tactile stimulation of fly bristles in mutant clones generated by the MARCM method. The combination of techniques allows for the identification of mechanosensitive mutations that would otherwise be lethal.

Because of the structural and functional homology to the hair cells of the mammalian inner ear, the neurons that innervate the Drosophila external sense ...

High Throughput Assay to Examine Egg-Laying Preferences of Individual Drosophila melanogaster

Recently, egg-laying preference of Drosophila has emerged as a genetically tractable model to study the neural basis of simple decision-making processes. When selecting sites to deposit their eggs, female flies are capable of ranking the relative attractiveness of their options and choosing the &#34;greater of two goods.&#34; However, most egg-laying preference assays are not practical if one wants to take a systematic genetic screening approach to search for the circuit basis underlying this simple decision-making process, as they are population-based and laborious to set up. To increase the throughput of studying of egg-laying preferences of single females, we developed custom chambers that each can simultaneously assay egg-laying preferences of up to thirty individual flies as well as a protocol that ensures each female has a high egg-laying rate (so that their preference is readily discernable and more convincing). Our approach is simple to execute and produces very consistent results. Additionally, these chambers can be equipped with different attachments to allow video recording the egg-laying animals and to deliver light for optogenetics studies. This article provides the blueprints for fabricating these chambers and the procedure for preparing the flies to be assayed in these chambers.

High Throughput Assay to Examine Egg-Laying Preferences of Individual Drosophila melanogaster

This protocol describes a high throughput assay for testing egg-laying preferences of Drosophila melanogaster at single-animal resolution. This assay provides a simple, efficient, and scalable platform to identify genes and circuit components that control a simple decision-making process.

Recently, egg-laying preference of Drosophila has emerged as a genetically tractable model to study the neural basis of simple decision-making processes. ...

A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

We describe a protocol for measuring ethanol self-administration in fruit flies (Drosophila melanogaster) as a proxy for changes in reward states. We demonstrate a simple way to tap into the fly reward system, modify experiences related to natural reward, and use voluntary ethanol consumption as a measure for changes in reward states. The approach serves as a relevant tool to study the neurons and genes that play a role in experience-mediated changes of internal state. The protocol is composed of two discrete parts: exposing the flies to rewarding and nonrewarding experiences, and assaying voluntary ethanol consumption as a measure of the motivation to obtain a drug reward. The two parts can be used independently to induce the modulation of experience as an initial step for further downstream assays or as an independent two-choice feeding assay, respectively. The protocol does not require a complicated setup and can therefore be applied in any laboratory with basic fly culture tools.

A Simple Way to Measure Alterations in Reward-seeking Behavior Using Drosophila melanogaster

We describe a protocol for inducing rewarding and nonrewarding experiences in fruit flies (Drosophila melanogaster) using voluntary ethanol consumption as a measure for changes in reward states.

We describe a protocol for measuring ethanol self-administration in fruit flies (Drosophila melanogaster) as a proxy for changes in reward states. We ...