Name: whisker-signaled eyeblink classical conditioning in head-fixed mice
Uploaded: 2016-03-30T14:00:00
Description: Watch this Scientific Journal Video about Whisker-signaled Eyeblink Classical Conditioning in Head-fixed Mice at JoVE.com

This work was funded by the Department of Defense (W81XWH-13-01-0243) and the National Institutes of Health (R37 AG008796). We thank Alan Baker in Northwestern University&#39;s machine shop for building the head-fixed cylinder apparatus. We thank Dr. Shoai Hattori for his guidance in MATLAB and Solidworks. We thank Dr. John Power for the LabView software that controlled the experiment.

All procedures involving mice were performed in accordance with protocols approved by Northwestern University&#39;s Institutional Animal Care and Use Committee based on guidelines issued by the National Institute of Health.
1. The Cylinder (Figure 2A)
<ol>
	<li>Construct the cylinder as described by Chettih et al. and Heiney et al. from a long foam cylinder14-15. Cut a 10 cm length of cylinder and drill a hole through the center to fit the axle, a metal rod 12.7 ...

<ol>
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F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptive+timing+of+motor+output+in+the+mouse:+the+role+of+movement+oscillations+in+eyelid+conditioning.">Adaptive timing of motor output in the mouse: the role of movement oscillations in eyelid conditioning.</a> Front in Integ Neurosci. 5 (72), (2011).</li><li>Heiney, S. A., Wohl, M. P., Chettih, S. N., Ruffolo, L. I., Medina, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cerebellar-Dependent+Expression+of+Motor+Learning+during+Eyeblink+Conditioning+in+Head-Fixed+Mice.">Cerebellar-Dependent Expression of Motor Learning during Eyeblink Conditioning in Head-Fixed Mice.</a> J Neurosci. 34 (45), 14845-14853 (2014).</li><li>Siegel, J. 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=Trace+Eyeblink+Conditioning+in+Mice+is+Dependent+upon+the+Dorsal+Medial+Prefrontal+Cortex,+Cerebellum,+and+Amygdala:+Behavioral+Characterization+and+Functional+Circuity.">Trace Eyeblink Conditioning in Mice is Dependent upon the Dorsal Medial Prefrontal Cortex, Cerebellum, and Amygdala: Behavioral Characterization and Functional Circuity.</a> eNeuro. , (2015).</li><li>Galvez, R., Weiss, C., Cua, S., Disterhoft, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+method+for+precisely+timed+stimulation+of+mouse+whiskers+in+a+freely+moving+preparation:+application+for+delivery+of+the+conditioned+stimulus+in+trace+eyeblink+conditioning.">A novel method for precisely timed stimulation of mouse whiskers in a freely moving preparation: application for delivery of the conditioned stimulus in trace eyeblink conditioning.</a> J Neurosci Meth. 177 (2), 434-439 (2009).</li><li>Gruart, A., S&#225;nchez-Campusano, R., Fern&#225;ndez-Guiz&#225;n, A., Delgado-Garc&#236;a, J. 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F., Weiss, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trace+eyeblink+conditioning+is+hippocampally+dependent+in+mice.">Trace eyeblink conditioning is hippocampally dependent in mice.</a> Hippocampus. 14 (1), 58-65 (2004).</li><li>Joachimsthaler, B., Brugger, D., Skodras, A., Schwarz, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spine+loss+in+primary+somatosensory+cortex+during+trace+eyeblink+conditioning.">Spine loss in primary somatosensory cortex during trace eyeblink conditioning.</a> J Neurosci. 35 (9), 3772-3781 (2015).</li><li>Boele, H. 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Classical eyeblink conditioning is a form of associative learning that is a useful tool for understanding the neural substrates underlying learning and memory. Previous methods employed for eyeblink conditioning in rodents such as mice involved a chamber that allowed for the animal to move about freely. A head-fixed preparation for eyeblink conditioning in mice, using the apparatus described by Chettih et al. and Heiney et al. and most recently utilized in light-evoked trace eyeblink conditioning in Sie...

Eyeblink conditioning is a form of Pavlovian conditioning and a model system for investigating the neural mechanisms of associative learning and memory. It has been investigated in various species, including humans, rabbits, cats, rats, and mice. The paradigm involves the presentation of two paired stimuli: a neutral conditioned stimulus (CS; e.g., a tone, a flash of light, or whisker stimulation), and a salient unconditioned stimulus (US; e.g., an air puff to the eye, or periorbital shock). The US elicits an unconditioned, reflexive eyeblink response (i.e., UR). Eventually, after several presentations of the paired CS-US, the subject learns to associate the CS with the US. This learning manifests itself in the form of a conditioned response (CR), an eyeblink elicited by the CS alone that precedes the presentation of the US.
Eyeblink conditioning in the trace form includes a stimulus-free interval of a few hundred milliseconds that separates the CS and the US (Figure 1). Trace conditioning is a form of declarative learning since it requires awareness of the stimulus contingencies1. The temporal gap requires the animal to keep a neural &#39;trace&#39; of the CS in forebrain regions such as the hippocampus in order for the US and the CS to become associated1-6. Along with the forebrain regions, trace conditioning is also dependent on the cerebellum7.
Eyeblink conditioning is, therefore, a useful paradigm for the investigation of the multiple facets of memory, including acquisition, consolidation, and retrieval. During eyeblink conditioning, a control group of animals is presented with unpaired stimuli in random order to test for pseudoconditioning or sensitized responses to the CS that may be caused by US presentation alone rather than a learned CS-US association.
A commonly used apparatus for the investigation of eyeblink conditioning in rodents is a chamber in which the rodents are allowed to move about freely during the training process8-10. With this type of apparatus, a tether is normally attached to a headpiece that is affixed to the rodent&#39;s skull. The tether allows for the delivery of the US (and sometimes the CS) and for transmitting the animal&#39;s response to those stimuli (i.e., the eyeblink response)10. The tether itself may be modified based on the type of stimuli delivered and how the eyeblink response is recorded.
The reason for using &#34;freely-moving&#34; tethered mice for eyeblink conditioning is that mice struggle against restraint. Though other species may be more amenable to restraint, the major advantage of using mice in eyeblink conditioning experiments is that the majority of available genetically modified mutant strains are mouse strains. In addition to struggling, complete restraint of mice results in acute distress. A head-fixed mouse preparation that minimizes stress would increase the physiological information that can be obtained during eyeblink conditioning. For example, this system would allow imaging of cortical neurons with 2-photon microscopy11.
Head-fixed preparations have been used in previous experiments for optical imaging of the cortex through removable cranial implants, in vivo electrophysiological recordings of the rodent brain with tetrode arrays, two-photon calcium imaging, and also as a platform for eyeblink conditioning in mice11-16.
In the head-fixed system, reliable stimulation and recordings are ensured without complete restraint of the mouse (Figure 2). A headpiece like the one used in the freely moving system is affixed to the mouse&#39;s skull. During training, the headpiece is affixed to a connector that is attached to bars over a cylindrical treadmill in order to stabilize the rodent&#39;s head (Figure 2A). The cylindrical treadmill allows the mouse to rest comfortably, but if the mouse so wishes, also allows it to run or to walk. With the use of this system, mice can be trained with a whisker vibration as the CS and a mild periorbital electrical shock as the US (Figure 1). The US is delivered through wires surgically placed underneath the skin lateral to the eye. The CS is delivered via a comb that is attached to a 2-layer rectangular bending actuator (Figure 2B). The comb and bending actuator are then attached to a magnetic base that is moved to the proper position during training and is adjusted for optimal delivery for each individual animal. The comb is positioned to straddle the selected whiskers. During delivery of the CS, a signal is sent to the bending actuator that displaces the comb and leads to vibration of the whiskers17.
Other stimuli such as a tone or a flash of light have been used as effective conditioned stimuli in mice in the past16,18,19. The reason whisker stimulation is chosen for the CS in this experimental paradigm is the dependence of murine animals on their vibrissae for somatosensory information input during exploration. Whisker stimulation has been shown to be a reliable and effective CS20. Furthermore, given the well-established and organized cortical substrate of the vibrissae system (i.e., the barrel cortex), whisker stimulation as the CS provides an elegant tool for mapping cortical changes and plasticity associated with learning eyeblink conditioning20,21. A head-fixed system allows for the precise stimulation of selected whiskers to compare responses between stimulated neurons and neurons receiving inputs from non-stimulated whiskers. Finally, many strains of mice exhibit age-related hearing loss as relatively young adults22, and eyelid closure during the conditioned blink alters a visual CS (although a visual CS does ameliorate issues with startle responses16). Whisker stimulation is not affected by either of these complications.
Presented here are unique and important modifications upon other head-fixed preparations for eyeblink conditioning, including methods for CS and US delivery, and the acquisition of the eyeblink response. The reliability of this apparatus and the training paradigm in eyeblink conditioning is demonstrated by learning curves from conditioned mice and a relatively flat learning curve from pseudoconditioned control animals (Figure 7A).

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			<td height="21" style="height:21px;width:436px;">Exervo TeraNova Foam Roller 36&#34; x 6&#34;&#160;</td>
			<td style="width:357px;">Amazon</td>
			<td style="width:181px;">B002ONUM0E</td>
			<td style="width:377px;">For cylinder</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:436px;">Plexiglas</td>
			<td style="width:357px;"></td>
			<td></td>
			<td>Custom-made; 1 cm thick</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:436px;">Metal Rods (12.7mm diameter)</td>
			<td style="width:357px;"></td>
			<td></td>
			<td>Custom-made</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:436px;">4-40 machine screw (.25 in long)</td>
			<td style="width:357px;">Amazon Supply</td>
			<td>&#160;B00F33Q8QO</td>
			<td>For cylinder</td>
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		<tr height="22">
			<td height="22" style="height:22px;width:436px;">Classic Design Hair Comb</td>
			<td style="width:357px;">Conair</td>
			<td style="width:181px;">93505WG-320</td>
			<td>For whisker stimulation</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">2-Layer Rectangular Bending Actuator</td>
			<td style="width:357px;">Piezo Systems</td>
			<td>T220-A4-303X&#160;</td>
			<td>For whisker stimulation</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Solder and Flux Kit</td>
			<td style="width:357px;">Piezo Systems</td>
			<td>MSF-003-NI</td>
			<td>For whisker stimulation</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Magnetic Base</td>
			<td style="width:357px;">Thor Labs</td>
			<td style="width:181px;">MB175</td>
			<td>For whisker stimulation</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Threaded rod for magnetic base</td>
			<td style="width:357px;"></td>
			<td style="width:181px;"></td>
			<td>Custom-made</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:436px;">Strips based on 221 series nylon strip connectors from Electronic Connector Corp.</td>
			<td style="width:357px;"></td>
			<td style="width:181px;"></td>
			<td>Custom-made, based on Weiss and Disterhoft, 2008</td>
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		<tr height="20">
			<td height="20" style="height:20px;width:436px;">TO-220 Style Transistor</td>
			<td style="width:357px;">Amazon Supply</td>
			<td>B0002ZPZYO&#160;</td>
			<td>For connector; for the wings</td>
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			<td height="20" style="height:20px;width:436px;">Relia-Tac Sockets</td>
			<td style="width:357px;">Electronic Connector Corp.</td>
			<td style="width:181px;">220-S02</td>
			<td>For connector</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Relia-Tac Pins</td>
			<td style="width:357px;">Electronic Connector Corp.</td>
			<td style="width:181px;">220-P02</td>
			<td>For headpiece</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">0-80 stainless steel machine screw (1 in. long)</td>
			<td>Amazon Supply</td>
			<td>B000FN68EE</td>
			<td>Locking Screw</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">0-80 stainless steel machine screw hex nut (5/32 in. thick)</td>
			<td>Amazon Supply</td>
			<td>B000N2TK7Y</td>
			<td>Locking Screw Head</td>
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			<td height="20" style="height:20px;width:436px;">Loctite Super Glue-Liquid</td>
			<td>Loctite</td>
			<td>1365896</td>
			<td>Cyanoacrylic glue; for the locking screw</td>
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		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Quick Setting Epoxy</td>
			<td style="width:357px;">Ace Hardware</td>
			<td>18613</td>
			<td>For connector and whisker stimulation system</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Ethernet Cable Wires</td>
			<td style="width:357px;"></td>
			<td></td>
			<td>Ethernet cable can be taken apart to use the individual wires for the connector</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:436px;">Polyimide coated stainless steel wires (2 in. long, .005 in. diameter)</td>
			<td style="width:357px;">PlasticsOne</td>
			<td>005sw/2.0 37365 S-S&#160;</td>
			<td>For headpiece, EMG and shock wires</td>
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		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Stainless steel uncoated wire (.005 in. diameter)</td>
			<td style="width:357px;">AM Systems</td>
			<td>792800</td>
			<td>For headpiece, ground wires</td>
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			<td height="20" style="height:20px;width:436px;">Tenma Variable Autotransformer</td>
			<td style="width:357px;">Tenma</td>
			<td>72-110</td>
			<td>For the whisker stimulation; rheostat to adjust current to the bending actuator</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Amplifier</td>
			<td style="width:357px;">A-M Systems</td>
			<td>1700</td>
			<td>Amplifier for filtering and amplifying EMG signals</td>
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			<td height="20" style="height:20px;width:436px;">WPI A385R stimulus isolator</td>
			<td style="width:357px;">World Precision Instruments</td>
			<td>31405</td>
			<td>For the electrical shock</td>
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		<tr height="18">
			<td height="18" style="height:18px;width:436px;">Isothesia (Isoflurane)</td>
			<td style="width:357px;">Henry Schein: Animal Health</td>
			<td style="width:181px;">50031</td>
			<td>For surgery; anesthesia</td>
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		<tr height="18">
			<td height="18" style="height:18px;width:436px;">Buprenex Injectable CIII</td>
			<td style="width:357px;">Reckett Benckiser Pharmaceuticals Inc</td>
			<td style="width:181px;">NDC 12496-0757-1</td>
			<td>For surgery; analgesic</td>
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			<td style="width:181px;">NDC 17478-062-35</td>
			<td>Artificial tear ointment to prevent dry eyes while under anesthesia</td>
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			<td style="width:357px;">PDI</td>
			<td>NDC 10819-3883-1</td>
			<td>For surgery; antiseptic</td>
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			<td>May be purchased from any standard pharmacy</td>
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			<td>4-7.</td>
			<td>For surgery</td>
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			<td height="20" style="height:20px;width:436px;">Stainless steel surgical scalpel blades</td>
			<td style="width:357px;">Integra Miltex</td>
			<td style="width:181px;">4-310 or 4-315</td>
			<td>For surgery; number 10 or 15 scalpel blade</td>
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			<td height="20" style="height:20px;width:436px;">3% Hydrogen Peroxide</td>
			<td style="width:357px;"></td>
			<td style="width:181px;"></td>
			<td>May be purchased from any standard pharmacy</td>
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			<td style="width:357px;">Roboz</td>
			<td style="width:181px;">RS-5459</td>
			<td>For surgery, to hold back skin</td>
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			<td style="width:357px;">Amazon Supply</td>
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			<td>For surgery, to wrap ground wire around</td>
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			<td height="20" style="height:20px;width:436px;">Professional Rotary Tool</td>
			<td style="width:357px;">Walnut Hollow</td>
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			<td>Hand drill for surgery, to drill holes in skull</td>
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			<td height="20" style="height:20px;width:436px;">Inverted Cone Burr</td>
			<td style="width:357px;">Roboz</td>
			<td>RS-6282C-34</td>
			<td>Inverted cone burr size 34; for surgery, to drill holes in skull</td>
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			<td height="20" style="height:20px;width:436px;">Engraving Cutter Drill Bit</td>
			<td style="width:357px;">Dremel</td>
			<td>106</td>
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			<td height="20" style="height:20px;width:436px;">C&#38;B Metabond-Quick! Cement System &#34;B&#34; Quick Base</td>
			<td style="width:357px;">Parkell</td>
			<td style="width:181px;">S398</td>
			<td>For surgery; adhesive luting cement system; important to prevent headpiece avulsion</td>
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			<td height="20" style="height:20px;width:436px;">C&#38;B Metabond-Quick! Cement System Clear L-Powder</td>
			<td style="width:357px;">Parkell</td>
			<td style="width:181px;">S399</td>
			<td>For surgery; adhesive luting cement system; important to prevent headpiece avulsion</td>
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			<td height="40" style="height:40px;width:436px;">C&#38;B Metabond-Quick! Cement System &#34;C&#34; Universal TBB Catalyst 0.7 ml</td>
			<td style="width:357px;">Parkell</td>
			<td style="width:181px;">S371</td>
			<td>For surgery; adhesive luting cement system; important to prevent headpiece avulsion</td>
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			<td height="40" style="height:40px;width:436px;">C&#38;B Metabond-Quick! Cement System Ceramic Mixing Dish with temperature strip</td>
			<td style="width:357px;">Parkell</td>
			<td style="width:181px;">S387</td>
			<td>For surgery; adhesive luting cement system; important to prevent headpiece avulsion</td>
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		<tr height="25">
			<td height="25" style="height:25px;width:436px;">Swiss Tweezers, style #5</td>
			<td style="width:357px;">World Precision Instruments</td>
			<td style="width:181px;">504506</td>
			<td>For surgery</td>
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		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Puritan Cotton-Tipped Applicators</td>
			<td style="width:357px;">VWR International</td>
			<td>10806-005&#160;</td>
			<td>For surgery</td>
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		<tr height="20">
			<td height="20" style="height:20px;width:436px;">Dental Caulk Grip Cement Kit</td>
			<td style="width:357px;">Dentsply</td>
			<td>675570</td>
			<td>For surgery; dental cement</td>
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	</tbody>
</table>

whisker-signaled eyeblink classical conditioning in head-fixed mice

Eyeblink conditioning is a common paradigm for investigating the neural mechanisms underlying learning and memory. To better utilize the extensive repertoire of scientific techniques available to study learning and memory at the cellular level, it is ideal to have a stable cranial platform. Because mice do not readily tolerate restraint, they are usually trained while moving about freely in a chamber. Conditioned stimulus (CS) and unconditioned stimulus (US) information are delivered and eyeblink responses recorded via a tether connected to the mouse's head. In the head-fixed apparatus presented here, mice are allowed to run as they desire while their heads are secured to facilitate experimentation. Reliable conditioning of the eyeblink response is obtained with this training apparatus, which allows for the delivery of whisker stimulation as the CS, a periorbital electrical shock as the US, and analysis of electromyographic (EMG) activity from the eyelid to detect blink responses.

8-10 week old male C57Bl6/J mice were trained on trace eyeblink conditioning on the head-fixed cylindrical treadmill apparatus. 8 mice were trained with paired CS-US presentations (conditioned group) and 9 mice were trained with unpaired CS and US presentations (pseudoconditioned group).
Example EMG recordings of a conditioned response from a conditioned mouse are shown in Figures 3 and 4. EMG r...

Watch this Scientific Journal Video about Whisker-signaled Eyeblink Classical Conditioning in Head-fixed Mice at JoVE.com

Whisker-signaled Eyeblink Classical Conditioning in Head-fixed Mice

The preparation presented here for whisker-signaled eyeblink conditioning in head-fixed mice precisely stimulates specific whiskers while allowing mice to ambulate on a cylindrical treadmill. A whisker stimulation conditioned stimulus (CS) paired with a periorbital shock unconditioned stimulus (US) results in reliable associative learning on this apparatus.

Eyeblink conditioning is a common paradigm for investigating the neural mechanisms underlying learning and memory. To better utilize the extensive ...

The overall goal of this protocol is to use genetic advances in mice, and our understanding of the whisker system, to investigate the neurobiological basis of eyeblink conditioning, a translatable paradigm for studying learning and memory. This method can help answer mechanistic questions in learning and memory by using calcium imaging and electrophysiology in genetically manipulated mice while stimulating specific whiskers during conditioning. The main advantage of this technique is the ability to secure the heads of mice while minimizing stress, by allowing the mice to ambulate at their own pace on a cylindrical treadmill.The implications of this technique extend toward potential treatments for memory impairments, including those associated with normal aging and Alzheimer's disease. Preparation of the cylinder and the whisker stimulation system are each covered in the text protocol. This section covers preparation of the headpiece.The headpiece strip is a 3D printed seven hole strip modeled from the Amphenol 221 series nylon strip that is no longer manufactured commercially. From the 3D printed piece, tap the first hole in the strip for 0-80 by one inch machine screw and leave one hole empty after the first hole. Next, using a vice, put five gold-plated pins in the remaining five holes.Push the pins through the narrower holes in the plastic. Next, using a thermal stripper, strip a half centimeter of polyimide coating. Then, solder the stripped end to one of the pins where the pin has an opening.Cut the soldered wire to between six and seven millimeters and strip about two millimeters of the wire. Now, repeat this process to attach four wires in total to the five pins. The first two wires will record eyelid EMG responses while the second two will deliver electrical stimulation to the periorbital region.To the fifth pin, solder an uninsulated five centimeter stainless steel wire to serve as an electrical ground. After making all the connections, check each of them with a multimeter to ensure their electrical continuity. Begin with a fully anesthetized animal, confirmed by a toe pinch.Inject a dose of buprenorphine hydrochloride as an analgesic. Then apply a small amount of ophthalmic ointment to the corneas and shave the top of the animal's head. Next, secure the animal's head to a stereotaxic frame and disinfect the scalp with three alternating scrubs of povidone iodine and alcohol.With a number 10 or 15 scalpel blade, make an incision along the midline of the scalp, exposing the skull from the front of the eyes to past the interparietal bone. Retract the flaps of the skin with six microclips, exposing as much of the skull as possible, including the sides and back. Next, use the scalpel to scrape the periostium off the skull.Then clean the top of the skull with 3%hydrogen peroxide three times. Once the skull has dried, drill two holes with a size 34 inverted cone bur, being careful not to damage the brain. Place one hole in front of bregma, and place the other hole in front of lambda, left of the midline when conditioning the right eye, or vice versa.These holes should be drilled carefully to fit the screws, and great effort should be made to not damage the brain. Into the holes, place screws for the electrical connections. Each full turn will lower the screw 0.28 millimeters, so two full turns is sufficient.Next, create several small divits on the skull in order to increase the surface area for the cement. From the completed headpiece, wind the ground wire in a figure eight configuration around the two screws. Leave some slack in the ground wire so the headpiece can be positioned properly.Now, apply cold luting cement. Coat the skull and the screws liberally and allow the cement to dry. Once the cement is dried, position the headpiece vertically, with the pins standing up above the skull.Secure the headpiece with a holder attached to an arm from the frame. The holder must have five gold-plated sockets to accept the pins of the headpiece. Position the two EMG wires on the muscularis orbicularis oculi above the eye socket.Then, position the two stimulating wires. Put the stripped ends under the skin two to four millimeters directly caudal to the eye. Do not let their ends touch each other.If the wires are so long that they could scratch the eye of the animal, trim them back or bend them back. Some bare wire must remain exposed. Now, cement the base of the wires to the skull with a little more luting cement and allow it to dry.Use about half the volume previously used. To proceed, remove the microclips and reposition the skin. Allow the skin to settle naturally to prevent tension on the skin that would distort the eyelid inhibiting blinking and thus ruin the experiment.Once the skin is settled, remove the headpiece holder and seal the exposed area with dental cement. Avoid dripping cement on the eyes, or the pins of the headpiece. Then use a cotton swab dampened with dental cement solvent to smooth and manipulate partially cured cement as needed.Once the cement has dried completely, remove the animal from the stereotaxic frame and allow it to recover on a warm surface before returning it to its home cage. Start habituating mice after they have had at least five days of recovery time. To secure the mouse, briefly restrain it by the tail to pinch it behind the shoulders.Then lift the mouse from under the abdomen and torso. Next, attach a connector to the headpiece and turn the locking screw. Then, place the mouse gently on the cylinder and hold it still while using two screws to fasten the connector to the bars above the cylinder.Then release the mouse. In the first two sessions, let the mouse habituate to the cylinder for the same length of time as a conditioning session. During the habituation, record the spontaneous blink rate.Also, pre-expose the mice to the whisker vibration stimulator without applying electrical stimulation. With the piezo system close to the conditioned side, slip the teeth of the comb over individual whiskers. Select the same whiskers for every session.Then proceed with classical conditioning training as presented in the text. Eight to ten week old male C57 Black 6J mice were trained with trace eyeblink conditioning in the headfixed cylindrical treadmill. EMG recordings of each trial were taken.The EMGs were rectified and integrated with a 10 millisecond time constant, then averaged across all the trials. The evolution of conditioned repsonses over 10 training sessions shows that gradually the response got larger in amplitude and the response latency became shorter. This evolution is not seen in the responses from the psuedoconditioned mice, where the stimuli are presented in random order.The evolution of well timed, and thus well learned, conditioned responses can also be seen in the histograms of the time to the peak of the response following CS onset. After watching this video, you should have a good understanding of how to prepare the headpiece, surgically implant the headpiece on a mouse, and place the mouse on the cylindrical treadmill, for headfixed eyeblink conditioning. Your mice should exhibit a good learning curve across days as they acquire the conditioning.Once mastered, this technique can be done in one hour if it is performed properly. While attempting this procedure, it's important to remember to remain vigilant in observing any distress from the animals. Appropriate steps should be taken in order to minimize stress to the animals.

Research

JoVE Journal

Behavior

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