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...

A Novel Method for Enhanced Analysis of Insect Taste Neuron Activity

<ol>
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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Candidate+taste+receptors+in+Drosophila.">Candidate taste receptors in Drosophila.</a> Science. 287 (5459), 1830-1834 (2000).</li><li>Koh, T. 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=The+Drosophila+IR20a+clade+of+ionotropic+receptors+are+candidate+taste+and+pheromone+receptors.">The Drosophila IR20a clade of ionotropic receptors are candidate taste and pheromone receptors.</a> Neuron. 83 (4), 850-865 (2014).</li><li>S&#225;nchez-Alca&#241;iz, J. 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=An+expression+atlas+of+variant+ionotropic+glutamate+receptors+identifies+a+molecular+basis+of+carbonation+sensing.">An expression atlas of variant ionotropic glutamate receptors identifies a molecular basis of carbonation sensing.</a> Nat Commun. 9 (1), 4252 (2018).</li><li>Dweck, H. K. M., Carlson, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diverse+mechanisms+of+taste+coding+in+Drosophila.">Diverse mechanisms of taste coding in Drosophila.</a> Sci Adv. 9 (46), (2023).</li><li>Chyb, S., Dahanukar, A., Wickens, A., Carlson, J. 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+Gr5a+encodes+a+taste+receptor+tuned+to+trehalose.">Drosophila Gr5a encodes a taste receptor tuned to trehalose.</a> Proc Natl Acad Sci U S A. 100, 14526-14530 (2003).</li><li>Dahanukar, A., Lei, Y. T., Kwon, J. Y., Carlson, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two+Gr+genes+underlie+sugar+reception+in+Drosophila.">Two Gr genes underlie sugar reception in Drosophila.</a> Neuron. 56 (3), 503-516 (2007).</li><li>Delventhal, R., Carlson, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bitter+taste+receptors+confer+diverse+functions+to+neurons.">Bitter taste receptors confer diverse functions to neurons.</a> Elife. 5, e11181 (2016).</li><li>Dweck, H. K. M., Talross, G. J. S., Luo, Y., Ebrahim, S. A. M., Carlson, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ir56b+is+an+atypical+ionotropic+receptor+that+underlies+appetitive+salt+response+in+Drosophila.">Ir56b is an atypical ionotropic receptor that underlies appetitive salt response in Drosophila.</a> Curr Biol. 32 (8), 1776-1787 (2022).</li><li>Hiroi, M., Marion-Poll, F., Tanimura, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differentiated+response+to+sugars+among+labellar+chemosensilla+in+Drosophila.">Differentiated response to sugars among labellar chemosensilla in Drosophila.</a> Zoolog Sci. 19 (9), 1009-1018 (2002).</li><li>Jeong, Y. T., 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=An+odorant-binding+protein+required+for+suppression+of+sweet+taste+by+bitter+chemicals.">An odorant-binding protein required for suppression of sweet taste by bitter chemicals.</a> Neuron. 79 (4), 725-737 (2013).</li><li>Jiao, Y., Moon, S. J., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Drosophila+gustatory+receptor+required+for+the+responses+to+sucrose,+glucose,+and+maltose+identified+by+mRNA+tagging.">A Drosophila gustatory receptor required for the responses to sucrose, glucose, and maltose identified by mRNA tagging.</a> Proc Natl Acad Sci U S A. 104 (35), 14110-14115 (2007).</li><li>Jiao, Y., Moon, S. J., Wang, X., Ren, Q., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gr64f+is+required+in+combination+with+other+gustatory+receptors+for+sugar+detection+in+Drosophila.">Gr64f is required in combination with other gustatory receptors for sugar detection in Drosophila.</a> Curr Biol. 18 (22), 1797-1801 (2008).</li><li>Kim, S. H., 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=Drosophila+TRPA1+channel+mediates+chemical+avoidance+in+gustatory+receptor+neurons.">Drosophila TRPA1 channel mediates chemical avoidance in gustatory receptor neurons.</a> Proc Natl Acad Sci U S A. 107 (18), 8440-8445 (2010).</li><li>Lacaille, F., 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=An+inhibitory+sex+pheromone+tastes+bitter+for+Drosophila+males.">An inhibitory sex pheromone tastes bitter for Drosophila males.</a> PLoS One. 2 (7), e661 (2007).</li><li>Lee, Y., 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=Gustatory+receptors+required+for+avoiding+the+insecticide+L-canavanine.">Gustatory receptors required for avoiding the insecticide L-canavanine.</a> J Neurosci. 32 (4), 1429-1435 (2012).</li><li>Lee, Y., Kim, S. H., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Avoiding+DEET+through+insect+gustatory+receptors.">Avoiding DEET through insect gustatory receptors.</a> Neuron. 67 (4), 555-561 (2010).</li><li>Lee, Y., Moon, S. J., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+gustatory+receptors+required+for+the+caffeine+response+in+Drosophila.">Multiple gustatory receptors required for the caffeine response in Drosophila.</a> Proc Natl Acad Sci U S A. 106 (11), 4495-4500 (2009).</li><li>Lee, Y., Moon, S. 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J., Lee, Y., Jiao, Y., Montell, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Drosophila+gustatory+receptor+essential+for+aversive+taste+and+inhibiting+male-to-male+courtship.">A Drosophila gustatory receptor essential for aversive taste and inhibiting male-to-male courtship.</a> Current Biology. 19, 1623-1627 (2009).</li><li>Rimal, S., 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=Mechanism+of+acetic+acid+gustatory+repulsion+in+Drosophila.">Mechanism of acetic acid gustatory repulsion in Drosophila.</a> Cell Rep. 26 (6), 1432-1442 (2019).</li><li>Shim, J., 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=The+full+repertoire+of+Drosophila+gustatory+receptors+for+detecting+an+aversive+compound.">The full repertoire of Drosophila gustatory receptors for detecting an aversive compound.</a> Nat Commun. 6, 8867 (2015).</li><li>Xiao, S., Baik, L. S., Shang, X., Carlson, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Meeting+a+threat+of+the+Anthropocene:+Taste+avoidance+of+metal+ions+by+Drosophila.">Meeting a threat of the Anthropocene: Taste avoidance of metal ions by Drosophila.</a> Proc Natl Acad Sci U S A. 119 (25), e2204238119 (2022).</li><li>Zhang, Y. V., Ni, J., Montell, 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+molecular+basis+for+attractive+salt-taste+coding+in+Drosophila.">The molecular basis for attractive salt-taste coding in Drosophila.</a> Science. 340 (6138), 1334-1338 (2013).</li><li>Delventhal, R., Kiely, A., Carlson, J. 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(84), e51355 (2014).</li><li>Marella, S., 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=Imaging+taste+responses+in+the+fly+brain+reveals+a+functional+map+of+taste+category+and+behavior.">Imaging taste responses in the fly brain reveals a functional map of taste category and behavior.</a> Neuron. 49 (2), 285-295 (2006).</li><li>Thorne, N., Amrein, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atypical+expression+of+Drosophila+gustatory+receptor+genes+in+sensory+and+central+neurons.">Atypical expression of Drosophila gustatory receptor genes in sensory and central neurons.</a> J Comp Neurol. 506 (4), 548-568 (2008).</li><li>Wang, Z., Singhvi, A., Kong, 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=Taste+representations+in+the+Drosophila+brain.">Taste representations in the Drosophila brain.</a> Cell. 117 (7), 981-991 (2004).</li></ol>

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 border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Microscope</td>
			<td>Olympus</td>
			<td>BX51WI</td>
			<td>equipped with a 50X objective (LMPLFLN 50X, Olympus) and 10X eyepieces.&#160;</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&#228;rzh&#228;user Micromanipulators</td>
			<td>Micromanipulator PM 10 Piezo Micromanipulator</td>
			<td></td>
		</tr>
		<tr>
			<td>manual Micromanipulators</td>
			<td>M&#228;rzh&#228;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&#160; 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&#160;</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&#8482; 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>
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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.

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

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

Our lab investigates how animals detect and respond to odors, taste, and some pheromone. We've made significant strides in understanding the molecular basis of chemoreception. We've made several advances in the field, including the discovery of the first insect odor receptors, the discovery of the first insect taste receptors, and the elucidation of basic principles of the logic of odor and taste coding.This technique allows the measurement of test neuron activity before, during, and after the stimulus. Thus, it allows extensive analysis of OFF responses that occur after a taste stimulus. It also allows the measurement of taste neuron activity to the river of volatile compounds.The classical technique for taste electrophysiology was unable to measure taste responses to hydrophobic compounds such as long-chain pheromones that have very low solubility in water. However, with the help of this technique, we can overcome this limitation by separating the recording electrode from the glass stimulus capillary. Our research explores the functioning of the chemosensory systems in animals, focusing on their role in feeding and mating choices.We're currently examining non-coding RNAs and micro peptides in fruit flies'olfactory systems, and how mosquitoes and tsetse flies use these systems to find human hosts.

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

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.

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

Preparing the Recording Electrodes and Drosophila for Analyzing Responses of Taste Neurons

Base Recording from Taste Sensilla of Drosophila for Analyzing Responses of Taste Neurons

708 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.   

A Novel Method for Enhanced Analysis of Insect Taste Neuron Activity

Summary