We thank Dr. Yijun Song, and members of the Hattar Kuruvilla Zhao tri-lab of the Department of Biology, Johns Hopkins University for advice and help. Supported by NIH grants DC007395 and DC009946.

Part 1. The EOG recording setup
The recording apparatus consists of a recording electrode, reference electrode, air delivery tube, specimen stage, and dissecting microscope, all anchored on an air table within a Faraday cage. Micromanipulators are used for placement of the electrodes and the air delivery tube. A continuous air stream is bubbled through distilled water to add humidity before passing through the air delivery tube and over the specimen. A 60 mm culture dish filled with Sylgard to a depth of 6-8 mm is used as a mounting surface for the specimen. A well and a channel are hollowed out of the Sylgard in the mounting dish to provide a means to electrically connect the reference electrode to the specimen via modified Ringer's solution.
The recording electrode and the reference electrode are connected to an amplifier. Signals from the amplifier are sent to a digitizer and then to a computer. Software such as Axograph or pClamp can be used to control the stimulation protocol, to record the signal, and for subsequent analysis of the responses. An oscilloscope connected after the amplifier can be convenient for real time monitoring of the electrical potential while placing the recording electrode and during EOG recordings.
Delivery of odorant stimuli is controlled by a Picospritzer, which is connected to the same computer used for signal acquisition. The air pressure at the Picospritzer is set to 10 psi. A single air tank and regulator can be used to supply air to both the air table and the Picospritzer. A second air tank and regulator is used to provide air for the humidified air stream, as this requires a lower pressure and a large amount of airflow. Just prior to delivering an odorant stimulus, the Picospritzer output is connected to an odorant bottle. The odorant bottle is then connected to the air delivery tube.
Part 2: Preparing electrodes
The recording electrode is a chlorided silver wire in a pulled glass capillary filled with modified Ringer's solution (135 mM NaCl, 5 mM KCl, 1 mM CaCl2, 1.5 mM MgCl2, 10 mM HEPES, pH 7.4, filter sterilized). The reference electrode is a chlorided silver wire.
<ol>
 <li>Install silver wire into the electrode holder. For the recording electrode, one to two centimeters of wire should protrude from the end of the electrode holder. More wire can be left for the reference electrode.</li>
 <li>To add the AgCl coat to the silver wire, position the wire in 0.1 M NaCl and connect the electrode holder to the positive terminal of a 1.5-9 V DC power source. The negative terminal of the power source should be electrically connected to the 0.1 M NaCl solution. Allow the chloriding reaction to proceed for 10 minutes. To equalize any static charge between the recording and the reference electrode, briefly touch the electrodes together before installing them on the recording apparatus.</li>
 <li>Pull a glass capillary using a micropipette puller. The opening at the tip of the capillary should be around 5-10 microns in diameter. </li>
 <li>Use a diamond pencil to score and break off the blunt end of the capillary so it is ~2 cm longer than the silver wire. Fire-polish the cut end with the butane torch.</li>
 <li>Melt 0.5% agarose in modified Ringer's solution. Pull a small amount of molten agarose solution into the tip of the electrode using a transfer pipette. </li>
 <li>Fill the pulled capillary about 1/2 of the way with modified Ringer's solution (a syringe that has been heated and pulled to have a long thin end is useful for this purpose). Gently flick the capillary to dislodge any air bubbles. Store the filled electrode in the storage jar with a small amount of modified Ringer's solution in the bottom until they are ready to be used. Once a tissue sample is prepared and ready for recording, install a filled capillary over the recording electrode wire.</li>
</ol>
Part 3: Preparing odorant solutions
The odorants amyl acetate and heptaldehyde evoke large responses and are thus good choices as EOG stimulants.
<ol>
 <li>In microcentrifuge tubes, prepare a series of dilutions of odorant in dimethyl sulfoxide (DMSO). As a starting point for a dose-response curve, prepare 10-fold dilutions from 5 M to 5 x 10-6 M. Make fresh dilutions each day.</li>
 <li>Further dilute the odorants 50-fold in water by mixing 100 &mu;L diluted stock in DMSO with 4.9 mLs water in 2 ounce bottles with silicone stoppers. Let the solutions equilibrate in the bottles for at least 30 minutes. Note that the vapor concentration of odorants in each bottle is unknown, but will vary as a function of the concentration of odorants in the liquid phase. </li>
 <li>Insert two 18-gauge needles through the silicon stopper to provide input and output ports. The ports should be plugged when the bottle is not in use.</li>
</ol>
Part 4: Recording the EOG and analyzing data
<ol>
 <li>Sacrifice a mouse by CO2 euthanasia or anesthetic overdose followed by decapitation. Remove the skin overlying the skull and sagittally bisect the head along the midline. </li>
 <li>Mount one half of the head, medial side up, on the mounting dish. Carefully remove the septum to expose the turbinates.</li>
 <li>Place the dish with mounted tissue onto the recording stage. Align the stage so that the recording location on the turbinates is centered under the microscope.</li>
 <li>Turn on the air tank to deliver humidified air to the turbinate surface. Position the air delivery tube so that it is approximately 10 mm away from the recording location. The flow rate is ~600 mL/min. </li>
 <li>Set the amplifier to DC mode (AC amplification will induce artifacts in the EOG signal) with low-pass filter at 1 kHz, and gain at 100X. </li>
 <li>Mount recording and reference electrodes on the micromanipulators. </li>
 <li>Lower the reference electrode into the well on the mounting dish and cover with modified Ringer's solution such that it is electrically connected to the tissue.</li>
 <li>Carefully lower the recording electrode onto the surface of turbinate IIb or III. The electrode should barely touch the surface of the olfactory epithelium! When the electrode comes in contact with the epithelium (i.e. completes an electrical circuit) a straight baseline will appear in the oscilloscope. </li>
 <li>Attach an odorant bottle to the side port on the air delivery tube.</li>
 <li>On the computer, initiate a stimulation protocol. The sampling rate for data acquisition should be 2 kHz or higher. The software will trigger an odor pulse and begin recording. </li>
 <li>A typical stimulation protocol may be a 100-msec duration single pulse, paired 100-msec pulses separated by a 1-sec interval, or a 10-sec sustained pulse.</li>
 <li>Allow some time between protocols so the tissue is minimally adapted. One minute is sufficient for liquid concentrations of amyl acetate and heptaldehyde up to 10-3 M; at higher concentrations allow 5 minutes. After delivering high odor concentrations (such as at the end of a dose-response curve) residual odor may remain in the tube. Wash the air tube with 95% ethanol and dry before continuing with additional tissue samples.</li>
 <li>Axograph software provides tools for measuring key parameters of the EOG signal. Such parameters include the response amplitude, latency, time to peak, and time constants of termination. It may be desirable to digitally filter traces at 25 Hz before further analysis.</li>
</ol>
Representative Results
<img src="/files/ftp_upload/1850/1850fig1.jpg" alt="figure 1" /> Figure 1. Parameters for EOG analysis. Several parameters of the EOG are particularly useful for comparison of responses between mice, including the response amplitude, the latency (the time between when the stimulus is administered and the response begins), rise time (the time between the start of the response and the peak), time to peak (the time from the start of the stimulation to the peak of the response), and time constant of termination (&tau;, determined by fitting the decay phase of the response to a single exponential equation). For comparison of kinetic parameters such as latency, rise time, and time constant of termination, it is advisable to normalize the peak amplitude of the responses prior to analysis.
<img src="/files/ftp_upload/1850/1850fig2.jpg" alt="figure 2" /> Figure 2. Representative EOG signals under different stimulation protocols. (a) Examples of EOGs from a mouse in response to stimulation with increasing concentrations of amyl acetate. The black line at the top of the panel indicates the timing and duration of odorant stimulation. The concentrations in the legend are the concentrations of the liquid solution. (b) A dose-response relation averaged from five mice. Error bars are 95% confidence intervals. A decline in the peak amplitude is often observed at very high odor concentrations. (c) An example of an EOG in response to a paired-pulse stimulation. A single short pulse of odorant elicits adaptation lasting for several seconds. (d) An example of an EOG in response to a 10-sec sustained odorant stimulation. The EOG shows desensitization during continuous odorant presentation.

<ol>
	<li>Ottoson, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+the+electrical+activity+of+the+olfactory+epithelium.">Analysis of the electrical activity of the olfactory epithelium.</a> Acta Physiologica Scandinavica. 35, 1-83 (1956).</li><li>Scott, J. W., Scott-Johnson, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+electroolfactogram:+a+review+of+its+history+and+uses.">The electroolfactogram: a review of its history and uses.</a> Microsc Res Tech. 58, 152-160 (2002).</li><li>Brunet, L. J., Gold, G. H., Ngai, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=General+anosmia+caused+by+a+targeted+disruption+of+the+mouse+olfactory+cyclic+nucleotide-gated+cation+channel.">General anosmia caused by a targeted disruption of the mouse olfactory cyclic nucleotide-gated cation channel.</a> Neuron. 17, 681-693 (1996).</li><li>Belluscio, L., Gold, G. H., Nemes, A., Axel, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mice+deficient+in+G(olf)+are+anosmic.">Mice deficient in G(olf) are anosmic.</a> Neuron. 20, 69-81 (1998).</li><li>Zhao, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+expression+of+a+mammalian+odorant+receptor.">Functional expression of a mammalian odorant receptor.</a> Science. 279, 237-242 (1998).</li><li>Wong, S. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disruption+of+the+type+III+adenylyl+cyclase+gene+leads+to+peripheral+and+behavioral+anosmia+in+transgenic+mice.">Disruption of the type III adenylyl cyclase gene leads to peripheral and behavioral anosmia in transgenic mice.</a> Neuron. 27, 487-497 (2000).</li><li>Munger, 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=Central+role+of+the+CNGA4+channel+subunit+in+Ca2+-calmodulin-dependent+odor+adaptation.">Central role of the CNGA4 channel subunit in Ca2+-calmodulin-dependent odor adaptation.</a> Science. 294, 2172-2175 (2001).</li><li>Michalakis, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Loss+of+CNGB1+protein+leads+to+olfactory+dysfunction+and+subciliary+cyclic+nucleotide-gated+channel+trapping.">Loss of CNGB1 protein leads to olfactory dysfunction and subciliary cyclic nucleotide-gated channel trapping.</a> J Biol Chem. 281, 35156-35166 (2006).</li><li>Buiakova, O. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Olfactory+marker+protein+(OMP)+gene+deletion+causes+altered+physiological+activity+of+olfactory+sensory+neurons.">Olfactory marker protein (OMP) gene deletion causes altered physiological activity of olfactory sensory neurons.</a> Proc Natl Acad Sci U S A. 93, 9858-9863 (1996).</li><li>Nickell, W. T., Kleene, N. K., Gesteland, R. C., Kleene, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuronal+chloride+accumulation+in+olfactory+epithelium+of+mice+lacking+NKCC1.">Neuronal chloride accumulation in olfactory epithelium of mice lacking NKCC1.</a> J Neurophysiol. 95, 2003-2006 (2006).</li><li>Song, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Olfactory+CNG+channel+desensitization+by+Ca2+/CaM+via+the+B1b+subunit+affects+response+termination+but+not+sensitivity+to+recurring+stimulation.">Olfactory CNG channel desensitization by Ca2+/CaM via the B1b subunit affects response termination but not sensitivity to recurring stimulation.</a> Neuron. 58, 374-386 (2008).</li><li>Cygnar, K. D., Zhao, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphodiesterase+1C+is+dispensable+for+rapid+response+termination+of+olfactory+sensory+neurons.">Phosphodiesterase 1C is dispensable for rapid response termination of olfactory sensory neurons.</a> Nat Neurosci. 12, 454-462 (2009).</li><li>Kleene, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+electrochemical+basis+of+odor+transduction+in+vertebrate+olfactory+cilia.">The electrochemical basis of odor transduction in vertebrate olfactory cilia.</a> Chem Senses. 33, 839-859 (2008).</li><li>Chen, S., Lane, A. P., Bock, R., Leinders-Zufall, T., Zufall, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blocking+adenylyl+cyclase+inhibits+olfactory+generator+currents+induced+by+"IP(3)-odors".">Blocking adenylyl cyclase inhibits olfactory generator currents induced by "IP(3)-odors".</a> J Neurophysiol. 84, 575-5780 (2000).</li><li>Pinato, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electroolfactogram+responses+from+organotypic+cultures+of+the+olfactory+epithelium+from+postnatal+mice.">Electroolfactogram responses from organotypic cultures of the olfactory epithelium from postnatal mice.</a> Chem Senses. 33, 397-404 (2008).</li><li>Ezeh, P. I., Davis, L. M., Scott, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regional+distribution+of+rat+electroolfactogram.">Regional distribution of rat electroolfactogram.</a> J Neurophysiol. 73, 2207-2220 (1995).</li><li>Scott-Johnson, P. E., Blakley, D., Scott, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+air+flow+on+rat+electroolfactogram.">Effects of air flow on rat electroolfactogram.</a> Chem Senses. 25, 761-768 (2000).</li></ol>

Mice were handled and euthanized with methods approved by the Animal Care and Use Committees of The Johns Hopkins University.

With the setup described in this protocol, the odorant stimuli at the surface of the olfactory epithelium will be consistent between tissue preparations, allowing for comparison between wild type and mutant mice, even though the exact odorant concentration and dynamics are unknown. Several factors, particularly the recording location and the flow rate of humidified air, cause variations in the EOG. Care should be taken to record from similar positions on the same turbinate to minimize variation. This can easily be achieved by consistently recording from the same side of the head and keeping the footprint of the microscope, odor delivery tube, and micromanipulators on the air table unchanged between tissue samples. In addition, tissue samples should be immediately placed into the humidified air stream after dissection to prevent excessive drying of the tissue.
EOG recordings on mice can also be carried out with a liquid perfusion apparatus on prepared mouse turbinates7, 14, 15, or by leaving the head intact and inserting the electrode into a small hole drilled above the turbinates16, 17. Each variation of EOG recording has its own strengths: air-phase recordings on tissue preparations as described in this protocol require a minimal amount of setup and are the easiest to conduct; recordings using a liquid perfusion apparatus facilitate the use of pharmacological reagents, although the hydrophobic nature of many odorants complicates odor delivery; lastly, recordings in which the head is left intact can be used in 'artificial sniff' experiments, although electrode placement is more difficult than when the turbinates are fully exposed.

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>Air delivery tube</td>
<td>equipment</td>
<td>Custom fabricated</td>
<td>&nbsp;</td>
<td>The barrel of a 1-mL syringe with a T-fitting can be used as a substitute</td>
</tr>
<tr>
<td>Air table</td>
<td>equipment</td>
<td>Newport</td>
<td>LW3030B-OPT</td>
<td>&nbsp;</td>
<tr>
<td>Amplifier</td>
<td>equipment</td>
<td>Warner</td>
<td>DP-301</td>
<td>&nbsp;</td>
<tr>
<td>Computer and Data Acquisition Software</td>
<td>equipment</td>
<td>Axograph 4.9.2 on Apple Macintosh</td>
<td>&nbsp;</td>
<td>Updated versions of Axograph for Mac OS X and Windows are available from http://axographx.com/.</td>
</tr>
<tr>
<td>Butane torch</td>
<td>equipment</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>A cr&egrave;me br&ucirc;l&egrave;e torch works well</td>
</tr>
<tr>
<td>Digitizer</td>
<td>equipment</td>
<td>Axon Instruments</td>
<td>Digidata 1322A</td>
<td>&nbsp;</td>
<tr>
<td>Dissecting Scope</td>
<td>equipment</td>
<td>Scienscope</td>
<td>SSZ</td>
<td>&nbsp;</td>
<tr>
<td>Electrode holder</td>
<td>equipment</td>
<td>Harvard Apparatus</td>
<td>64-1021</td>
<td>&nbsp;</td>
<tr>
<td>Magnetic Holding Devices (12 mm)</td>
<td>equipment</td>
<td>World Precision Instruments</td>
<td>M10</td>
<td>&nbsp;</td>
<tr>
<td>Micromanipulators</td>
<td>equipment</td>
<td>World Precision Instruments</td>
<td>M3301R M3301L</td>
<td>&nbsp;</td>
<tr>
<td>Micropipette Puller</td>
<td>equipment</td>
<td>Sutter Instrument Co.</td>
<td>P2000</td>
<td>&nbsp;</td>
<tr>
<td>Oscilloscope</td>
<td>equipment</td>
<td>Tektronix </td>
<td>5110</td>
<td>&nbsp;</td>
<tr>
<td>Picospritzer III</td>
<td>equipment</td>
<td>Parker Instrumentation</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Silicone tubing</td>
<td>equipment</td>
<td>Nalge Nunc</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Specimen stage</td>
<td>equipment</td>
<td>Custom fabricated</td>
<td>&nbsp;</td>
<td>Any small solid object can be used to elevate the mounting dish. Immobilize the dish with modeling clay.</td>
</tr>
<tr>
<td>18 gage needles</td>
<td>material</td>
<td>Becton Dickinson</td>
<td>305195</td>
<td>&nbsp;</td>
<tr>
<td>2 oz. glass bottles</td>
<td>material</td>
<td>VWR International</td>
<td>16152-201</td>
<td>&nbsp;</td>
<tr>
<td>Glass capillaries</td>
<td>material</td>
<td>World Precision Instruments</td>
<td>TW150F-6</td>
<td>&nbsp;</td>
<tr>
<td>Silicone stoppers size 16D</td>
<td>material</td>
<td>Chemware</td>
<td>D1069809</td>
<td>&nbsp;</td>
<tr>
<td>Silver wire</td>
<td>material</td>
<td>World Precision Instruments</td>
<td>AGW1010</td>
<td>&nbsp;</td>
<tr>
<td>SylGuard 184</td>
<td>material</td>
<td>Dow Corning </td>
<td>SYLG184</td>
<td>From World Precision Instruments</td>
</tr>
<tr>
<td>Agarose</td>
<td>reagent</td>
<td>Invitrogen</td>
<td>15510-027</td>
<td>&nbsp;</td>
<tr>
<td>Amyl acetate</td>
<td>reagent</td>
<td>Aldrich</td>
<td>W504009</td>
<td>&nbsp;</td>
<tr>
<td>Calcium chloride (CaCl2)</td>
<td>reagent</td>
<td>Sigma</td>
<td>C-1016</td>
<td>&nbsp;</td>
<tr>
<td>Dimethyl sulfoxide (DMSO)</td>
<td>reagent</td>
<td>Sigma</td>
<td>D5879</td>
<td>&nbsp;</td>
<tr>
<td>HEPES</td>
<td>reagent</td>
<td>Fisher</td>
<td>BP310</td>
<td>&nbsp;</td>
<tr>
<td>Heptaldehyde</td>
<td>reagent</td>
<td>Aldrich</td>
<td>H2120</td>
<td>&nbsp;</td>
<tr>
<td>Magnesium chloride hexahydrate (MgCl2+6H2O)</td>
<td>reagent</td>
<td>Sigma</td>
<td>M9272</td>
<td>&nbsp;</td>
<tr>
<td>Sodium chloride (NaCl)</td>
<td>reagent</td>
<td>JT Baker</td>
<td>3624-05</td>
<td>&nbsp;</td>
<tr>
<td>flowmeter</td>
<td>equipment</td>
<td>Gilmont</td>
<td>GF-2260</td>
<td>&nbsp;</td>		</tbody>
		</table>
		</div>

analyzing responses of mouse olfactory sensory neurons using the air-phase electroolfactogram recording

Animals depend on olfaction for many critical behaviors, such as finding food sources, avoiding predators, and identifying conspecifics for mating and other social interactions. The electroolfactogram (EOG) recording is an informative, easy to conduct, and reliable method to assay olfactory function at the level of the olfactory epithelium. Since the 1956 description of the EOG by Ottoson in frogs1, the EOG recording has been applied in many vertebrates including salamanders, rabbits, rats, mice, and humans (reviewed by Scott and Scott-Johnson, 2002, ref. 2). The recent advances in genetic modification in mice have rekindled interest in recording the EOG for physiological characterization of olfactory function in knock-out and knock-in mice. EOG recordings have been successfully applied to demonstrate the central role of olfactory signal transduction components3-8, and more recently to characterize the contribution of certain regulatory mechanisms to OSN responses9-12.
Odorant detection occurs at the surface of the olfactory epithelium on the cilia of OSNs, where a signal transduction cascade leads to opening of ion channels, generating a current that flows into the cilia and depolarizes the membrane13. The EOG is the negative potential recorded extracellularly at the surface of the olfactory epithelium upon odorant stimulation, resulting from a summation of the potential changes caused by individual responsive OSNs in the recording field2. Comparison of the amplitude and kinetics of the EOG thus provide valuable information about how genetic modification and other experimental manipulations influence the molecular signaling underlying the OSN response to odor. 
Here we describe an air-phase EOG recording on a preparation of mouse olfactory turbinates. Briefly, after sacrificing the mouse, the olfactory turbinates are exposed by bisecting the head along the midline and removing the septum. The turbinate preparation is then placed in the recording setup, and a recording electrode is placed at the surface of the olfactory epithelium on one of the medial turbinates. A reference electrode is electrically connected to the tissue through a buffer solution. A continuous stream of humidified air is blown over the surface of the epithelium to keep it moist. The vapor of odorant solutions is puffed into the stream of humidified air to stimulate the epithelium. Responses are recorded and digitized for further analysis.

Watch this Scientific Journal Video about Analyzing Responses of Mouse Olfactory Sensory Neurons Using the Air-phase Electroolfactogram Recording at JoVE.com

Analyzing Responses of Mouse Olfactory Sensory Neurons Using the Air-phase Electroolfactogram Recording

The electroolfactogram (EOG) recording is an informative, easy-to-conduct, and reliable way of assessing olfactory function at the level of the olfactory epithelium. This protocol describes a recording setup, mouse tissue preparation, data collection, and basic data analysis.

Animals depend on olfaction for many critical behaviors, such as finding food sources, avoiding predators, and identifying conspecifics for mating and ...

analyzing-responses-mouse-olfactory-sensory-neurons-using-air-phase

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16.4K Views.  Johns Hopkins University. The electroolfactogram (EOG) recording is an informative, easy-to-conduct, and reliable way of assessing olfactory function at the level of the olfactory epithelium. This protocol describes a recording setup, mouse tissue preparation, data collection, and basic data analysis.

Video: Analyzing Responses of Mouse Olfactory Sensory Neurons Using the Air-phase Electroolfactogram Recording

Lentivirus-mediated Genetic Manipulation and Visualization of Olfactory Sensory Neurons in vivo

Development of a precise olfactory circuit relies on accurate projection of olfactory sensory neuron (OSN) axons to their synaptic 
targets in the olfactory bulb (OB). The molecular mechanisms of OSN axon growth and targeting are not well understood. Manipulating gene expression and subsequent 
visualizing of single OSN axons and their terminal arbor morphology have thus far been challenging. To study gene function at the single cell level within a specified 
time frame, we developed a lentiviral based technique to manipulate gene expression in OSNs in vivo. Lentiviral particles are delivered to OSNs by microinjection 
into the olfactory epithelium (OE). Expression cassettes are then permanently integrated into the genome of transduced OSNs. Green fluorescent protein expression 
identifies infected OSNs and outlines their entire morphology, including the axon terminal arbor. Due to the short turnaround time between microinjection and 
reporter detection, gene function studies can be focused within a very narrow period of development. With this method, we have detected GFP expression within as 
few as three days and as long as three months following injection. We have achieved both over-expression and shRNA mediated knock-down by lentiviral microinjection. 
This method provides detailed morphologies of OSN cell bodies and axons at the single cell level in vivo, and thus allows characterization of candidate gene function 
during olfactory development.

Lentivirus-mediated Genetic Manipulation and Visualization of Olfactory Sensory Neurons in vivo

We present a lentiviral technique for genetic manipulation and visualization of single olfactory sensory neuron axon and its terminal arborization in vivo.

Development of a precise olfactory circuit relies on accurate projection of olfactory sensory neuron (OSN) axons to their synaptic 
targets in the ...

Flash Photolysis of Caged Compounds in the Cilia of Olfactory Sensory  Neurons

Photolysis of caged compounds allows the production of rapid and localized increases in the concentration of various physiologically active compounds1. Caged compounds are molecules made physiologically inactive by a chemical cage that can be broken by a flash of ultraviolet light. Here, we show how to obtain patch-clamp recordings combined with photolysis of caged compounds for the study of olfactory transduction in dissociated mouse olfactory sensory neurons. The process of olfactory transduction (Figure 1) takes place in the cilia of olfactory sensory neurons, where odorant binding to receptors leads to the increase of cAMP that opens cyclic nucleotide-gated (CNG) channels2. Ca entry through CNG channels activates Ca-activated Cl channels. We show how to dissociate neurons from the mouse olfactory epithelium3 and how to activate CNG channels or Ca-activated Cl channels by photolysis of caged cAMP4 or caged Ca5. We use a flash lamp6,7 to apply ultraviolet flashes to the ciliary region to uncage cAMP or Ca while patch-clamp recordings are taken to measure the current in the whole-cell voltage-clamp configuration8-11.

Photolysis of caged compounds allows the production of rapid and localized increases in the concentration of various physiologically active compounds. Here, we show how to obtain patch-clamp recordings combined with photolysis of caged cAMP or caged Ca for the study of olfactory transduction in dissociated mouse olfactory sensory neurons.

Photolysis of caged compounds allows the production of rapid and localized increases in the concentration of various physiologically active compounds1. ...

Odorant-induced Responses Recorded from Olfactory Receptor Neurons using the Suction Pipette Technique

Animals sample the odorous environment around them through the chemosensory systems located in the nasal cavity. Chemosensory signals affect complex behaviors such as food choice, predator, conspecific and mate recognition and other socially relevant cues. Olfactory receptor neurons (ORNs) are located in the dorsal part of the nasal cavity embedded in the olfactory epithelium. These bipolar neurons send an axon to the olfactory bulb (see Fig. 1, Reisert &amp; Zhao1, originally published in the Journal of General Physiology) and extend a single dendrite to the epithelial border from where cilia radiate into the mucus that covers the olfactory epithelium. The cilia contain the signal transduction machinery that ultimately leads to excitatory current influx through the ciliary transduction channels, a cyclic nucleotide-gated (CNG) channel and a Ca2+-activated Cl- channel (Fig. 1). The ensuing depolarization triggers action potential generation at the cell body2-4.
In this video we describe the use of the "suction pipette technique" to record odorant-induced responses from ORNs. This method was originally developed to record from rod photoreceptors5 and a variant of this method can be found at jove.com modified to record from mouse cone photoreceptors6. The suction pipette technique was later adapted to also record from ORNs7,8. Briefly, following dissociation of the olfactory epithelium and cell isolation, the entire cell body of an ORN is sucked into the tip of a recording pipette. The dendrite and the cilia remain exposed to the bath solution and thus accessible to solution changes to enable e.g. odorant or pharmacological blocker application. In this configuration, no access to the intracellular environment is gained (no whole-cell voltage clamp) and the intracellular voltage remains free to vary. This allows the simultaneous recording of the slow receptor current that originates at the cilia and fast action potentials fired by the cell body9. The difference in kinetics between these two signals allows them to be separated using different filter settings. This technique can be used on any wild type or knockout mouse or to record selectively from ORNs that also express GFP to label specific subsets of ORNs, e.g. expressing a given odorant receptor or ion channel.

Olfactory receptor neurons (ORNs) convert odor signals first into a receptor current that in turn triggers action potentials that are conveyed to second order neurons in the olfactory bulb. Here we describe the suction pipette technique to record simultaneously the odorant-induced receptor current and action potentials from mouse ORNs.

Animals sample the odorous environment around them through the chemosensory systems located in the nasal cavity. Chemosensory signals affect complex ...

Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis

The freshwater leech, Hirudo medicinalis, is a versatile model organism that has been used to address scientific questions in the fields of neurophysiology, neuroethology, and developmental biology. The goal of this report is to consolidate experimental techniques from the leech system into a single article that will be of use to physiologists with expertise in other nervous system preparations, or to biology students with little or no electrophysiology experience. We demonstrate how to dissect the leech for recording intracellularly from identified neural circuits in the ganglion. Next we show how individual cells of known function can be removed from the ganglion to be cultured in a Petri dish, and how to record from those neurons in culture. Then we demonstrate how to prepare a patch of innervated skin to be used for mapping sensory or motor fields. These leech preparations are still widely used to address basic electrical properties of neural networks, behavior, synaptogenesis, and development. They are also an appropriate training module for neuroscience or physiology teaching laboratories.

Intracellular Recording, Sensory Field Mapping, and Culturing Identified Neurons in the Leech, Hirudo medicinalis

This article describes three nervous system preparations using leeches: intracellular recording from neurons in ventral ganglia, culturing neurons from ventral ganglia, and recording from a patch of innervated skin to map sensory fields.

The freshwater leech, Hirudo medicinalis, is a versatile model organism that has been used to address scientific questions in the fields of ...

Whole Mount Immunolabeling of Olfactory Receptor Neurons in the Drosophila Antenna

Odorant molecules bind to their target receptors in a precise and coordinated manner. Each receptor recognizes a specific signal and relays this information to the brain. As such, determining how olfactory information is transferred to the brain, modifying both perception and behavior, merits investigation. Interestingly, there is emerging evidence that cellular transduction and transcriptional factors are involved in the diversification of olfactory receptor neuron. Here we provide a robust whole mount immunological labeling method to assay in vivo olfactory receptor neuron organization. Using this method, we identified all olfactory receptor neurons with anti-ELAV antibody, a known pan-neural marker and Or49a-mCD8::GFP, an olfactory receptor neuron specifically expressed in Nba neuron using anti-GFP antibody.

Whole Mount Immunolabeling of Olfactory Receptor Neurons in the Drosophila Antenna

Herein we describe the process of whole mount immunostaining of Drosophila antennae, which enables us to better understand the molecular mechanisms involved in the diversification of olfactory receptor neurons (ORN)s.

Odorant molecules bind to their target receptors in a precise and coordinated manner. Each receptor recognizes a specific signal and relays this ...

Recording Light-evoked Postsynaptic Responses in Neurons in Dark-adapted, Mouse Retinal Slice Preparations Using Patch Clamp Techniques

The retina is the gateway to the visual system. To understand visual signal processing mechanisms, we investigate retinal neural network functions. Retinal neurons in the network comprise of numerous subtypes. More than 10 subtypes of bipolar cells, ganglion cells, and amacrine cells have been identified by morphological studies. Multiple subtypes of retinal neurons are thought to encode distinct features of visual signaling, such as motion and color, and form multiple neural pathways. However, the functional roles of each neuron in visual signal processing are not fully understood. The patch clamp method is useful to address this fundamental question. Here, a protocol to record light-evoked synaptic responses in mouse retinal neurons using patch clamp recordings in dark-adapted conditions is provided. The mouse eyes are dark-adapted O/N, and retinal slice preparations are dissected in a dark room using infrared illumination and viewers. Infrared light does not activate mouse photoreceptors and thus preserves their light responsiveness. Patch clamp is used to record light-evoked responses in retinal neurons. A fluorescent dye is injected during recordings to characterize neuronal morphological subtypes. This procedure enables us to determine the physiological functions of each neuron in the mouse retina.

We will demonstrate how to prepare retinal slices from the mouse eye and record light responses in retinal neurons. The entire procedure is conducted in dark-adapted conditions.

The retina is the gateway to the visual system. To understand visual signal processing mechanisms, we investigate retinal neural network functions. ...

Perforated Patch-clamp Recording of Mouse Olfactory Sensory Neurons in Intact Neuroepithelium: Functional Analysis of Neurons Expressing an Identified Odorant Receptor

Analyzing the physiological responses of olfactory sensory neurons (OSN) when stimulated with specific ligands is critical to understand the basis of olfactory-driven behaviors and their modulation. These coding properties depend heavily on the initial interaction between odor molecules and the olfactory receptor (OR) expressed in the OSNs. The identity, specificity and ligand spectrum of the expressed OR are critical. The probability to find the ligand of the OR expressed in an OSN chosen randomly within the epithelium is very low. To address this challenge, this protocol uses genetically tagged mice expressing the fluorescent protein GFP under the control of the promoter of defined ORs. OSNs are located in a tight and organized epithelium lining the nasal cavity, with neighboring cells influencing their maturation and function. Here we describe a method to isolate an intact olfactory epithelium and record through patch-clamp recordings the properties of OSNs expressing defined odorant receptors. The protocol allows one to characterize OSN membrane properties while keeping the influence of the neighboring tissue. Analysis of patch-clamp results yields&#160;a precise quantification of ligand/OR interactions, transduction pathways and pharmacology, OSNs&#39; coding properties and their modulation at the membrane level.&#160;

Analyzing the physiological properties of olfactory sensory neurons still faces technical limitations. Here we record them through perforated patch-clamp in an intact preparation of the olfactory epithelium in gene-targeted mice. This technique allows the characterization of membrane properties and responses to specific ligands of neurons expressing defined olfactory receptors.

Analyzing the physiological responses of olfactory sensory neurons (OSN) when stimulated with specific ligands is critical to understand the basis of ...

Using Single Sensillum Recording to Detect Olfactory Neuron Responses of Bed Bugs to Semiochemicals

The insect olfactory system plays an important role in detecting semiochemicals in the environment. In particular, the antennal sensilla which house single or multiple neurons inside, are considered to make the major contribution in responding to the chemical stimuli. By directly recording action potential in the olfactory sensillum after exposure to stimuli, single sensillum recording (SSR) technique provides a powerful approach for investigating the neural responses of insects to chemical stimuli. For the bed bug, which is a notorious human parasite, multiple types of olfactory sensillum have been characterized. In this study, we demonstrated neural responses of bed bug olfactory sensilla to two chemical stimuli and the dose-dependent responses to one of them using the SSR method. This approach enables researchers to conduct early screening for individual chemical stimuli on the bed bug olfactory sensilla, which would provide valuable information for the development of new bed bug attractants or repellents and benefits the bed bug control efforts.

Bed bugs rely on olfactory receptor neurons housed in their antennal olfactory sensilla to detect semiochemicals in the environment. Utilizing single sensillum recording, we demonstrate a method to evaluate bed bug response to semiochemicals and explore the coding process involved.

The insect olfactory system plays an important role in detecting semiochemicals in the environment. In particular, the antennal sensilla which house ...

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.

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.

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

Quadruple Immunostaining of the Olfactory Bulb for Visualization of Olfactory Sensory Axon Molecular Identity Codes

The mouse olfactory system is often used to study mechanisms of neural circuit formation&#12288;because of its simple anatomical structure. An Olfactory Sensory Neuron (OSN) is a bipolar cell with a single dendrite and a single unbranched axon. An OSN expresses only one Olfactory Receptor (OR) gene, OSNs expressing a given type of OR converge their axons to a few sets of invariant glomeruli in the Olfactory Bulb (OB). A remarkable feature of OSN projection is that the expressed ORs play instructive roles in axonal projection. ORs regulate the expression of multiple axon-sorting molecules and generate the combinatorial molecular code of axon-sorting molecules at the OSN axon termini. Thus, to understand the molecular mechanisms of OR-specific axon guidance mechanisms, it is vital to characterize their expression profiles at the OSN axon termini within the same glomerulus. The aim of this article was to introduce methods for collecting as many glomeruli as possible on a single OB section and for performing immunostaining using multiple antibodies. This would allow the comparison and analysis of the expression patterns of axon-sorting molecules without staining variation between OB sections.

Olfactory sensory neurons express a wide variety of axon-sorting molecules to establish proper neural circuitry. This protocol describes an immunohistochemical staining method to visualize combinatorial expressions of axon-sorting molecules at the axon termini of olfactory sensory neurons.

The mouse olfactory system is often used to study mechanisms of neural circuit formation&#12288;because of its simple anatomical structure. An Olfactory ...