Name: in vitro characterization of the electrophysiological properties of colonic afferent fibers in rats
Uploaded: 2017-09-27T14:00:00
Description: Watch this Scientific Journal Video about In Vitro Characterization of the Electrophysiological Properties of Colonic Afferent Fibers in Rats at JoVE.com

This protocol was supported by research grants from the National Natural Science Foundation of China (#31171066, #81270464) and the Sino-German Science Center (GZ919).

The experimental protocol reported here has been approved by the Animal Ethical Committee of Shanghai Jiaotong University School of Medicine (# SYXK2013-0050).&#160;The dissection of the colorectum with intact ganglion and nerve trunk takes a minimum of 15 minutes for a person quite experienced in this technique. It is therefore necessary to keep the animal alive but under deep anesthesia whilst performing the dissections, to ensure viability of the tissue for subsequent electrophysiological recording.
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<ol>
	<li>Al-Chaer, E. D., Traub, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+basis+of+visceral+pain:+recent+developments.">Biological basis of visceral pain: recent developments.</a> Pain. 96 (3), 221-225 (2002).</li><li>Christianson, J. A., Traub, R. J., Davis, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differences+in+spinal+distribution+and+neurochemical+phenotype+of+colonic+afferents+in+mouse+and+rat.">Differences in spinal distribution and neurochemical phenotype of colonic afferents in mouse and rat.</a> J Comp Neurol. 494 (2), 246-259 (2006).</li><li>Wynn, G., Rong, W., Xiang, Z., Burnstock, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purinergic+mechanisms+contribute+to+mechanosensory+transduction+in+the+rat+colorectum.">Purinergic mechanisms contribute to mechanosensory transduction in the rat colorectum.</a> Gastroenterology. 125 (5), 1398-1409 (2003).</li><li>Dong, L., 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=Impairments+of+the+Primary+Afferent+Nerves+in+a+Rat+Model+of+Diabetic+Visceral+Hyposensitivity.">Impairments of the Primary Afferent Nerves in a Rat Model of Diabetic Visceral Hyposensitivity.</a> Mol Pain. 11, (2016).</li><li>Lynn, P. A., Blackshaw, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+recordings+of+afferent+fibres+with+receptive+fields+in+the+serosa,+muscle+and+mucosa+of+rat+colon.">In vitro recordings of afferent fibres with receptive fields in the serosa, muscle and mucosa of rat colon.</a> J Physiol. 518 (Pt 1), 271-282 (1999).</li><li>Page, A. 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=Different+contributions+of+ASIC+channels+1a,+2,+and+3+in+gastrointestinal+mechanosensory+function.">Different contributions of ASIC channels 1a, 2, and 3 in gastrointestinal mechanosensory function.</a> Gut. 54 (10), 1408-1415 (2005).</li><li>Hockley, J. R., 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=P2Y+Receptors+Sensitize+Mouse+and+Human+Colonic+Nociceptors.">P2Y Receptors Sensitize Mouse and Human Colonic Nociceptors.</a> J Neurosci. 36 (8), 2364-2376 (2016).</li><li>Peiris, M., 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=Human+visceral+afferent+recordings:+preliminary+report.">Human visceral afferent recordings: preliminary report.</a> Gut. 60 (2), 204-208 (2011).</li><li>Feng, B., Gebhart, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+silent+afferents+in+the+pelvic+and+splanchnic+innervations+of+the+mouse+colorectum.">Characterization of silent afferents in the pelvic and splanchnic innervations of the mouse colorectum.</a> Am J Physiol Gastrointest Liver Physiol. 300 (1), G170-G180 (2011).</li><li>Feng, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+guanylate+cyclase-C+attenuates+stretch+responses+and+sensitization+of+mouse+colorectal+afferents.">Activation of guanylate cyclase-C attenuates stretch responses and sensitization of mouse colorectal afferents.</a> J Neurosci. 33 (23), 9831-9839 (2013).</li><li>Feng, B., Gebhart, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+Functional+Characterization+of+Mouse+Colorectal+Afferent+Endings.">In vitro Functional Characterization of Mouse Colorectal Afferent Endings.</a> J Vis Exp. (95), e52310 (2015).</li><li>Nullens, 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=In+Vitro+Recording+of+Mesenteric+Afferent+Nerve+Activity+in+Mouse+Jejunal+and+Colonic+Segments.">In Vitro Recording of Mesenteric Afferent Nerve Activity in Mouse Jejunal and Colonic Segments.</a> J Vis Exp. (116), (2016).</li><li>Rong, W., Hillsley, K., Davis, J. B., Hicks, G., Winchester, W. J., Grundy, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Jejunalafferent+nerve+sensitivity+in+wild-type+and+TRPV1+knockout+mice.">Jejunalafferent nerve sensitivity in wild-type and TRPV1 knockout mice.</a> J Physiol. 560 (Pt 3), 867-881 (2004).</li><li>Brierley, S. M., 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=Differential+chemosensory+function+and+receptor+expression+of+splanchnic+and+pelvic+colonic+afferents+in+mice).">Differential chemosensory function and receptor expression of splanchnic and pelvic colonic afferents in mice).</a> J Physiol. 567 (Pt 1), 267-281 (2005).</li><li>Brierley, S. M., Jones, R. C. 3. r. d., Gebhart, G. F., Blackshaw, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Splanchnic+and+pelvic+mechanosensory+afferents+signal+different+qualities+of+colonic+stimuli+in+mice.">Splanchnic and pelvic mechanosensory afferents signal different qualities of colonic stimuli in mice.</a> Gastroenterology. 127 (1), 166-178 (2004).</li><li>La, J. H., Schwartz, E. S., Gebhart, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differences+in+the+expression+of+transient+receptor+potential+channel+V1,+transient+receptor+potential+channel+A1+and+mechanosensitive+two+pore-domain+K++channels+between+the+lumbar+splanchnic+and+pelvic+nerve+innervations+of+mouse+urinary+bladder+and+colon.">Differences in the expression of transient receptor potential channel V1, transient receptor potential channel A1 and mechanosensitive two pore-domain K+ channels between the lumbar splanchnic and pelvic nerve innervations of mouse urinary bladder and colon.</a> Neuroscience. 186, 179-187 (2001).</li><li>Wang, G., Tang, B., Traub, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+processing+of+noxious+colonic+input+by+thoracolumbar+and+lumbosacral+dorsal+horn+neurons+in+the+rat.">Differential processing of noxious colonic input by thoracolumbar and lumbosacral dorsal horn neurons in the rat.</a> J Neurophysiol. 94 (6), 3788-3794 (2005).</li></ol>

The protocol presented here is a relatively straightforward experimental method to assess the electrophysiological properties of the colonic afferents of rats. The protocol (from tissue dissection to setting up the nerve recording) usually takes about 2 h to complete. Tissue collection (step 3) and preparation of the suction electrode (step 5) are the critical steps. It is crucial to be able to locate the PG, the LSN, and the PN and to take care not to damage the ganglion and nerves during tissue dissection. The tip of t...

The gastrointestinal tract (GIT) is richly innervated with extrinsic afferent nerves that convey sensory signals from the gut to the central nervous system and that contribute to the gut-brain interaction. Altered excitability of these extrinsic afferents, as well as altered central processing of the afferent inputs, underlies visceral pain and other symptoms of GI conditions, including functional and inflammatory bowel diseases1. Sensory information from the colorectum is conveyed primarily through the thoracolumbar/hypogastric and the lumbosacral/pelvic nerves (PN)2. There has been an increased interest in studying the electrophysiological properties of these primary afferent fibers in rodent disease models. However, in vivo electrophysiological recordings of the colonic afferents in rodents is a technical challenge and requires considerable surgical skills. In addition, hemodynamic changes, tissue movement, and anesthetics may also impact nerve activity and sensitivity to test stimuli in vivo. Therefore, in recent years, an increasing number of studies have employed in vitro (ex vivo) preparations of different species, including mice, rats, guinea pigs, and humans, to examine the mechanisms of sensory transduction in colonic afferents and the altered excitability in disease conditions.3,4,5,6,7,8
Two types of ex vivo colonic preparation have primarily been reported: the &#34;flat-sheet&#34; preparation5,9,10 and the &#34;tube&#34; preparation3,4. A video protocol for the &#34;flat-sheet&#34; murine colorectum preparation has been previously published11. In this protocol, the mouse colorectum, with the PN) or lumbar splanchnic nerves (LSN) attached, is harvested and superfused in a tissue chamber. The colorectum is cut open longitudinally, and the nerve bundle is extended into a recording compartment filled with paraffin oil. Nerve activity is recorded using a monopolar platinum-iridium electrode. The protocol allows for the identification of the receptive fields of individual afferent fibers by using unbiased electrical stimulation. It localizes the application of chemical stimuli, as well as the application of different mechanical stimulation paradigms (e.g., focal mucosal probing and circumferential stretch), to the afferent nerve endings. Because the nerve must be extended to a separate chamber from the tissue chamber, it is critical to keep the attached nerve relatively long; the successful dissection of the nerves poses a challenge to those new to this methodology. More recently, Nullens et al. published a video protocol for the in vitro recording of the mesenteric afferents in murine jejunal and colonic segments12. In this &#34;tube&#34; preparation, the gut segment with the mesentery attached is kept intact, thus allowing for graded distension and the intra- and extra-luminal administration of different chemicals. Since the mesentery nerve is recorded using a suction electrode, which can be positioned close to the tissue, afferent activity can be recorded even though the mesentery nerve is relatively short. However, the mesentery nerve consists of mixed populations of vagal and spinal afferent fibers that innervate the jejunum or thoracolumbar hypogastric. Lumbosacral pelvic afferents innervate the colorectum, which cannot be discriminated in this protocol. Here, we present a detailed protocol for the electrophysiological recording of rat colonic afferents using the &#34;tube&#34; colorectum preparation with an intact PG. This method may allow for the characterization of the functional properties of lumbar splanchnic (hypogastric) and lumbosacral pelvic afferents.

<table width="889">
	<tbody>
		<tr height="40">
			<td height="40" style="width:215px;height:40px;">Sodium Pentobarbital</td>
			<td style="width:123px;">Shanghai Westang Bio-Tech</td>
			<td style="width:344px;">B558</td>
			<td style="width:208px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Capsaicin</td>
			<td>Sigma</td>
			<td>M2028</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Electrode puller</td>
			<td>MicroData Instrument Inc</td>
			<td>PMP107</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Neurolog System (Bioamplifier)</td>
			<td>Digitimer, Ltd</td>
			<td>Neurolog System</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">A/D converter</td>
			<td>Cambridge Electronic Design</td>
			<td>Micro1401</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Data processing software</td>
			<td>Cambridge Electronic Design</td>
			<td>Spike2 version 6</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Silver wire</td>
			<td>World Precision Instruments</td>
			<td>EP12</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Glass tubes</td>
			<td>World Precision Instruments</td>
			<td>1B150-4</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Electrode holder</td>
			<td>World Precision Instruments</td>
			<td>MEH3SBW</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Heating bath</td>
			<td>Grant</td>
			<td>GR150</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Dissecting microscope</td>
			<td>Leica</td>
			<td>Zoom2000</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Dissecting microscope</td>
			<td>World Precision Instruments</td>
			<td>PZMIII-BS</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Cigarette lighter</td>
			<td>any</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Surgical tools</td>
			<td>World Precision Instruments</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Insect pins</td>
			<td>home-made from 0.1 mm stainless steel wire</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Three way manipulator</td>
			<td>World Precision Instruments</td>
			<td>KITF-R</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Rats</td>
			<td>Any</td>
			<td>NA</td>
			<td>Any strain/sex can be used.</td>
		</tr>
	</tbody>
</table>

in vitro characterization of the electrophysiological properties of colonic afferent fibers in rats

Dysfunction of the colonic sensory nerves has been implicated in the pathophysiology of several common conditions, including functional and inflammatory bowel diseases and diabetes. Here, we describe a protocol for the in vitro characterization of the electrophysiological properties of colonic afferents in rats. The colorectum, with the intact pelvic ganglion (PG) attached, is removed from the rat; superfused with carbogenated Krebs solution in the recording chamber; and cannulated at the oral and anal ends to allow for distension. A fine nerve bundle emanating from the PG is identified, and the multiunit afferent nerve activity is recorded using a suction electrode. Distension of the colonic segment elicits gradual increases in multiunit discharge. A principal component analysis is conducted to differentiate the low-threshold, the high-threshold, and the wide-dynamic range afferent fibers. Chemical sensitivity of colonic afferents can be studied through the bath or intraluminal administration of test compounds. This protocol can be modified for application to other species, such as mice and guinea pigs, and to study the differences in the electrophysiological properties of thoracolumbar/hypogastric and lumbosacral/pelvic afferents of the descending colon in normal and pathological conditions.

Figure 1 is the schematic illustration of the experimental setup for the ex vivo &#34;tube&#34; colorectum preparation, with a representative recording from a nerve distal to the PG. The nerve presumably contained a mixture of pelvic and lumbar splanchnic afferents. In preparations from normal rats, the colonic afferent nerves typically have a low level of irregular spontaneous activity. Ramp distension of the colon induces a gradual increase in the ...

Watch this Scientific Journal Video about In Vitro Characterization of the Electrophysiological Properties of Colonic Afferent Fibers in Rats at JoVE.com

In Vitro Characterization of the Electrophysiological Properties of Colonic Afferent Fibers in Rats

Abnormal sensory function underlies visceral pain and other symptoms of functional and inflammatory bowel diseases. A protocol for the electrophysiological recording of the colonic afferent nerves in an ex vivo rat colorectum preparation is presented here.

In Vitro Characterization of the Electrophysiological Properties of Colonic Afferent Fibers in Rats

Dysfunction of the colonic sensory nerves has been implicated in the pathophysiology of several common conditions, including functional and inflammatory ...

The overall goal of this protocol is to demonstrate the methodology for the electrophysiological recordings of sensory nerves of the colorectum in vitro. This method can help answer key questions in vitro pen field such as the contribution of the outer peripheral efferens sensitivity to correct hyperalgesia. The main advantage of this technique is that it allows for the distinction of the colorectum in the similar way as the carotid distinction is performed in vivo, in animals or in patients.Visual demonstration of this method is critical because locating the ganglia and dissecting the nerves are relatively difficult. To begin this procedure, expose the abdominal cavity of a deeply anesthetized rat by performing a midline incision on the abdominal wall using a scalpel. Afterward, pull the mesentery and other tissues aside to expose the colorectum.Then, place the animal under the dissecting microscope. Through careful dissection, locate the left pelvic ganglion and identify the pelvic nerves and the lumbar splanchnic nerves joining it. Subsequently, cut these nerves a few millimeters away from the pelvic ganglion.Locating pelvic ganglion and dissecting nerves is the most critical and difficult step of this procedure. Next, cut the symphysis bone to expose the rectum. Remove the tissues above the colorectum and be careful to leave the pelvic ganglion intact.After sacrificing the rat by intravenous injection of an overdose of pentobarbital, transect the colon about three centimeters above the pelvic ganglion and remove the colorectum from the animal using forceps. Subsequently, transfer the colorectum to a Petri dish filled with pre-cooled Krebs solution. Remove the feces by gently flushing the colon.Next, remove the remnant urinary bladder and other tissues carefully, without compromising the pelvic ganglion. In this procedure, place the colon into a recording chamber and profuse the tissue continuously with carbogenated Krebs solution. Next, cannulate the colorectum at both the oral and anal ends, then start the intraluminal infusion of the colon with saline in the oral to anal direction, after that, locate the major pelvic ganglion under the dissecting microscope and use insect pins to expose the ganglion.With careful dissection, find a fine branch of nerve emanating from the ganglion and running towards the colon, then, cut the nerve close to the ganglion. Before the next step, turn on the heating bath and keep the Krebs solution at 34 degrees celsius. Now, inspect a pre-pulled glass pipette under the dissecting microscope.Break the tip of the electrode with a pair of forceps so that it is of a size compatible with the diameter of the nerve to be recorded. Following that, bevel the tip by placing it close to a lighter flare. New to this methodology may also find it tricky to bevel the tip of the electrode compatible with the size of the nerve.Next, place the beveled electrode in the electrode holder, then connect a 10 milliliter syringe to the side port of the holder for the application of negative or positive pressure to the electrode. After that, connect the holder to the head stage of the bio amplifier, and mount the head stage onto a manipulator. Following this, move the electrode to the tissue bath and fill the electrode with the Krebs solution by applying gentle suction until it contacts the silver wire of the holder.Next, place the electrode tip close to the cut end of the nerve and apply negative pressure to suck the nerve into the electrode. Then, apply more negative pressure, so that about one millimeter of the nerve is pulled into the electrode and forms a tight seal. Now, turn on the bio amplifier and set the filter to 300 to three thousand hertz.Monitor the signal on the oscilloscope and record the nerve signal and the intraluminal pressure signal in the spike data processing software. Next, apply ramp distention of the colon by closing the three way tap on the outlet cannula while continuously infusing intraluminally. Monitor the intraluminal pressure until it reaches 60 millimeters mercury, then open the three way tap on the draining cannula.Repeat this procedure at regular intervals of fifteen minutes and apply drugs extra or intraluminally to test the chemical sensitivity of the afferent nerves. Here is the schematic illustration of the experimental setup for the ex vivo tube colorectum preparation with a representative recording from a nerve distal to the pelvic ganglion. In the preparations from normal rats, the colonic afferent nerves typically have a low level of a regular spontaneous activity.Ramp distention of the colon induces a gradual increase in the firing rate. The mechanosensory property of each nerve is represented by plotting the intraluminal pressure afferent nerve response curve. Alternatively, recording can be made from a branch of the pelvic nerves proximal to the pelvic ganglion.The profile of the mechanosensory activity of the proximal pelvic nerves is usually similar to that seen in the nerve distal to the pelvic ganglion. Principal component analysis of the waveforms of the action potentials from the multiunit recording can be made to discriminate single unit activity. Here are the superimposed waveforms of two individual pelvic afferens.Once mastered, this technique can be done in two hours if it's performed properly. After watching this video, you should have a good understanding of the anatomy of the major pelvic ganglia and the other nerves and be able to locate the ganglia to dissect the nerves and record the afferent activity. An advantage of this protocol is that it may allow the comparison of the electrophysiological properties and the pharmacological profiles of the pelvic and the splanchnic afferent nerves.

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Neuroscience

A General Method for Evaluating Incubation of Sucrose Craving in Rats

For someone on a food-restricted diet, food craving in response to food-paired cues may serve as a key behavioral transition point between abstinence and relapse to food taking 1. Food craving conceptualized in this way is akin to drug craving in response to drug-paired cues. A rich literature has been developed around understanding the behavioral and neurobiological determinants of drug craving; we and others have been focusing recently on translating techniques from basic addiction research to better understand addiction-like behaviors related to food 2-4.
As done in previous studies of drug craving, we examine sucrose craving behavior by utilizing a rat model of relapse. In this model, rats self-administer either drug or food in sessions over several days. In a session, lever responding delivers the reward along with a tone+light stimulus. Craving behavior is then operationally defined as responding in a subsequent session where the reward is not available. Rats will reliably respond for the tone+light stimulus, likely due to its acquired conditioned reinforcing properties 5. This behavior is sometimes referred to as sucrose seeking or cue reactivity. In the present discussion we will use the term "sucrose craving" to subsume both of these constructs.
In the past decade, we have focused on how the length of time following reward self-administration influences reward craving. Interestingly, rats increase responding for the reward-paired cue over the course of several weeks of a period of forced-abstinence. This "incubation of craving" is observed in rats that have self-administered either food or drugs of abuse 4,6. This time-dependent increase in craving we have identified in the animal model may have great potential relevance to human drug and food addiction behaviors.
Here we present a protocol for assessing incubation of sucrose craving in rats. Variants of the procedure will be indicated where craving is assessed as responding for a discrete sucrose-paired cue following extinction of lever pressing within the sucrose self-administration context (Extinction without cues) or as responding for sucrose-paired cues in a general extinction context (Extinction with cues).

Responding for food or drug-paired cues increases over the course of a period of abstinence and this may relate to an increased susceptibility to relapse behaviors. Here we detail a procedure for evaluating this "incubation of craving" in rats that have self-administered sucrose.

For someone on a food-restricted diet, food craving in response to food-paired cues may serve as a key behavioral transition point between abstinence and ...

Electrophysiological Characterization of GFP-Expressing Cell Populations in the Intact Retina

Studying the physiological properties and synaptic connections of specific neurons in the intact tissue is a challenge for those cells that lack conspicuous morphological features or show a low population density. This applies particularly to retinal amacrine cells, an exceptionally multiform class of interneurons that comprise roughly 30 subtypes in mammals1. Though being a crucial part of the visual processing by shaping the retinal output2, most of these subtypes have not been studied up to now in a functional context because encountering these cells with a recording electrode is a rare event.
Recently, a multitude of transgenic mouse lines is available that express fluorescent markers like green fluorescent protein (GFP) under the control of promoters for membrane receptors or enzymes that are specific to only a subset of neurons in a given tissue3,4. These pre-labeled cells are therefore accessible to directed microelectrode targeting under microscopic control, permitting the systematic study of their physiological properties in situ. However, excitation of fluorescent markers is accompanied by the risk of phototoxicity for the living tissue. In the retina, this approach is additionally hampered by the problem that excitation light causes appropriate stimulation of the photoreceptors, thus inflicting photopigment bleaching and transferring the retinal circuits into a light-adapted condition. These drawbacks are overcome by using infrared excitation delivered by a mode-locked laser in short pulses of the femtosecond range. Two-photon excitation provides energy sufficient for fluorophore excitation and at the same time restricts the excitation to a small tissue volume minimizing the hazards of photodamage5. Also, it leaves the retina responsive to visual stimuli since infrared light (&gt;850 nm) is only poorly absorbed by photopigments6.
In this article we demonstrate the use of a transgenic mouse retina to attain electrophysiological in situ recordings from GFP-expressing cells that are visually targeted by two-photon excitation. The retina is prepared and maintained in darkness and can be subjected to optical stimuli which are projected through the condenser of the microscope (Figure 1). Patch-clamp recording of light responses can be combined with dye filling to reveal the morphology and to check for gap junction-mediated dye coupling to neighboring cells, so that the target cell can by studied on different experimental levels.

This article depicts the recording of individual cells from fluorescently tagged neuronal populations in the intact mouse retina. By using two-photon infrared excitation transgenetically labeled cells were targeted for patch-clamp recording to study their light responses, receptive field properties, and morphology.

Studying the physiological properties and synaptic connections of specific neurons in the intact tissue is a challenge for those cells that lack ...

Dual Electrophysiological Recordings of Synaptically-evoked Astroglial and Neuronal Responses in Acute Hippocampal Slices

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs through activation of their ion channels and neurotransmitter receptors, and process information in part through activity-dependent release of gliotransmitters. Furthermore, astrocytes constitute the main uptake system for glutamate, contribute to potassium spatial buffering, as well as to GABA clearance. These cells therefore constantly monitor synaptic activity, and are thereby sensitive indicators for alterations in synaptically-released glutamate, GABA and extracellular potassium levels. Additionally, alterations in astroglial uptake activity or buffering capacity can have severe effects on neuronal functions, and might be overlooked when characterizing physiopathological situations or knockout mice. Dual recording of neuronal and astroglial activities is therefore an important method to study alterations in synaptic strength associated to concomitant changes in astroglial uptake and buffering capacities. Here we describe how to prepare hippocampal slices, how to identify stratum radiatum astrocytes, and how to record simultaneously neuronal and astroglial electrophysiological responses. Furthermore, we describe how to isolate pharmacologically the synaptically-evoked astroglial currents.

The preparation of acute brain slices from isolated hippocampi, as well as the simultaneous electrophysiological recordings of astrocytes and neurons in stratum radiatum during stimulation of schaffer collaterals is described. The pharmacological isolation of astroglial potassium and glutamate transporter currents is demonstrated.

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs ...

Selective Tracing of Auditory Fibers in the Avian Embryonic Vestibulocochlear Nerve

The embryonic chick is a widely used model for the study of peripheral and central ganglion cell projections. In the auditory system, selective labeling of auditory axons within the VIIIth cranial nerve would enhance the study of central auditory circuit development. This approach is challenging because multiple sensory organs of the inner ear contribute to the VIIIth nerve 1. Moreover, markers that reliably distinguish auditory versus vestibular groups of axons within the avian VIIIth nerve have yet to be identified. Auditory and vestibular pathways cannot be distinguished functionally in early embryos, as sensory-evoked responses are not present before the circuits are formed. Centrally projecting VIIIth nerve axons have been traced in some studies, but auditory axon labeling was accompanied by labeling from other VIIIth nerve components 2,3. Here, we describe a method for anterograde tracing from the acoustic ganglion to selectively label auditory axons within the developing VIIIth nerve. First, after partial dissection of the anterior cephalic region of an 8-day chick embryo immersed in oxygenated artificial cerebrospinal fluid, the cochlear duct is identified by anatomical landmarks. Next, a fine pulled glass micropipette is positioned to inject a small amount of rhodamine dextran amine into the duct and adjacent deep region where the acoustic ganglion cells are located. Within thirty minutes following the injection, auditory axons are traced centrally into the hindbrain and can later be visualized following histologic preparation. This method provides a useful tool for developmental studies of peripheral to central auditory circuit formation.

Here we describe a microdissection technique followed by fluorescent dye injection into the acoustic ganglion of early chick embryos for selective tracing of auditory axon fibers in the nerve and hindbrain.

The embryonic chick is a widely used model for the study of peripheral and central ganglion cell projections. In the auditory system, selective labeling ...

Electrophysiological Recording in the Brain of Intact Adult Zebrafish

Previously, electrophysiological studies in adult zebrafish have been limited to slice preparations or to eye cup preparations and electrorentinogram recordings. This paper describes how an adult zebrafish can be immobilized, intubated, and used for in vivo electrophysiological experiments, allowing recording of neural activity. Immobilization of the adult requires a mechanism to deliver dissolved oxygen to the gills in lieu of buccal and opercular movement. With our technique, animals are immobilized and perfused with habitat water to fulfill this requirement. A craniotomy is performed under tricaine methanesulfonate (MS-222; tricaine) anesthesia to provide access to the brain. The primary electrode is then positioned within the craniotomy window to record extracellular brain activity. Through the use of a multitube perfusion system, a variety of pharmacological compounds can be administered to the adult fish and any alterations in the neural activity can be observed. The methodology not only allows for observations to be made regarding changes in neurological activity, but it also allows for comparisons to be made between larval and adult zebrafish. This gives researchers the ability to identify the alterations in neurological activity due to the introduction of various compounds at different life stages.

This paper describes how an adult zebrafish can be immobilized, intubated, and used for in vivo electrophysiological experiments to allow recordings and manipulation of neural activity in an intact animal.

Previously, electrophysiological studies in adult zebrafish have been limited to slice preparations or to eye cup preparations and electrorentinogram ...

An In Vitro Adult Mouse Muscle-nerve Preparation for Studying the Firing Properties of Muscle Afferents

Muscle sensory neurons innervating muscle spindles and Golgi tendon organs encode length and force changes essential to proprioception. Additional afferent fibers monitor other characteristics of the muscle environment, including metabolite buildup, temperature, and nociceptive stimuli. Overall, abnormal activation of sensory neurons can lead to movement disorders or chronic pain syndromes. We describe the isolation of the extensor digitorum longus (EDL) muscle and nerve for in vitro study of stretch-evoked afferent responses in the adult mouse. Sensory activity is recorded from the nerve with a suction electrode and individual afferents can be analyzed using spike sorting software. In vitro preparations allow for well controlled studies on sensory afferents without the potential confounds of anesthesia or altered muscle perfusion. Here we describe a protocol to identify and test the response of muscle spindle afferents to stretch. Importantly, this preparation also supports the study of other subtypes of muscle afferents, response properties following drug application and the incorporation of powerful genetic approaches and disease models in mice.

An In Vitro Adult Mouse Muscle-nerve Preparation for Studying the Firing Properties of Muscle Afferents

Muscle sensory neurons are involved in proprioceptor signaling and also report on metabolic state and injury related events. We describe an adult mouse in vitro muscle-nerve preparation for studies on stretch-activated muscle afferents.

Muscle sensory neurons innervating muscle spindles and Golgi tendon organs encode length and force changes essential to proprioception. Additional ...

In Vitro Recording of Mesenteric Afferent Nerve Activity in Mouse Jejunal and Colonic Segments

Afferent nerves not only convey information concerning normal physiology, but also signal disturbed homeostasis and pathophysiological processes of the different organ systems from the periphery towards the central nervous system. As such, the increased activity or &#39;sensitization&#39; of mesenteric afferent nerves has been allocated an important role in the pathophysiology of visceral hypersensitivity and abdominal pain syndromes.
Mesenteric afferent nerve activity can be measured in vitro in an isolated intestinal segment that is mounted in a purpose-built organ bath and from which the splanchnic nerve is isolated, allowing researchers to directly assess nerve activity adjacent to the gastrointestinal segment. Activity can be recorded at baseline in standardized conditions, during distension of the segment or following the addition of pharmacological compounds delivered intraluminally or serosally. This technique allows the researcher to easily study the effect of drugs targeting the peripheral nervous system in control specimens; besides, it provides crucial information on how neuronal activity is altered during disease. It should be noted however that measuring afferent neuronal firing activity only constitutes one relay station in the complex neuronal signaling cascade, and researchers should bear in mind not to overlook neuronal activity at other levels (e.g., dorsal root ganglia, spinal cord or central nervous system) in order to fully elucidate the complex neuronal physiology in health and disease.
Commonly used applications include the study of neuronal activity in response to the administration of lipopolysaccharide, and the study of afferent nerve activity in animal models of irritable bowel syndrome. In a more translational approach, the isolated mouse intestinal segment can be exposed to colonic supernatants from IBS patients. Furthermore, a modification of this technique has been recently shown to be applicable in human colonic specimens.

In Vitro Recording of Mesenteric Afferent Nerve Activity in Mouse Jejunal and Colonic Segments

Mesenteric afferent nerves convey information from the gastrointestinal tract towards the brain regarding normal homeostasis as well as pathophysiology. Gastrointestinal afferent nerve activity can be assessed by mounting isolated intestinal segments with attached afferent nerves into an organ bath, isolating the nerve, and assessing basal as well as stimulated activity.

Afferent nerves not only convey information concerning normal physiology, but also signal disturbed homeostasis and pathophysiological processes of the ...

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the pathophysiological basis of these diseases, it is necessary to precisely characterize in which way the processing of information is disturbed between the different neuronal parts of the circuit. Using extracellular in vivo electrophysiological recordings, it is possible to accurately delineate neuronal activity within a neuronal network. The application of this method has several advantages over alternative techniques, e.g., functional magnetic resonance imaging and calcium imaging, as it allows a unique temporal and spatial resolution and does not rely on genetically engineered organisms. However, the use of extracellular in vivo recordings is limited since it is an invasive technique that cannot be universally applied. In this article, a simple and easy to use method is presented with which it is possible to simultaneously record extracellular potentials such as local field potentials and multiunit activity at multiple sites of a network. It is detailed how a precise targeting of subcortical nuclei can be achieved using a combination of stereotactic surgery and online analysis of multi-unit recordings. Thus, it is demonstrated, how a complete network such as the hyperdirect cortico-basal ganglia loop can be studied in anesthetized animals in vivo.

Acute In Vivo Electrophysiological Recordings of Local Field Potentials and Multi-unit Activity from the Hyperdirect Pathway in Anesthetized Rats

In this study, the methodology is presented on how to perform multi-site in vivo electrophysiological recordings from the hyperdirect pathway under urethane anesthesia.

Converging evidence shows that many neuropsychiatric diseases should be understood as disorders of large-scale neuronal networks. To better understand the ...

Wireless Electrophysiological Recording of Neurons by Movable Tetrodes in Freely Swimming Fish

The neural mechanisms governing fish behavior remain mostly unknown, although fish constitute the majority of all vertebrates. The ability to record brain activity from freely moving fish would advance research on the neural basis of fish behavior considerably. Moreover, precise control of the recording location in the brain is critical to studying coordinated neural activity across regions in fish brain. Here, we present a technique that records wirelessly from the brain of freely swimming fish while controlling for the depth of the recording location. The system is based on a neural logger associated with a novel water-compatible implant that can adjust the recording location by microdrive-controlled tetrodes. The capabilities of the system are illustrated through recordings from the telencephalon of goldfish.

A novel wireless technique for recording extracellular neural signals from the brain of freely swimming goldfish is presented. The recording device is composed of two tetrodes, a microdrive, a neural data logger, and a waterproof case. All parts are custom-made except for the data logger and its connector.

The neural mechanisms governing fish behavior remain mostly unknown, although fish constitute the majority of all vertebrates. The ability to record brain ...

Optogenetic Activation of Afferent Pathways in Brain Slices and Modulation of Responses by Volatile Anesthetics

Anesthetics influence consciousness in part via their actions on thalamocortical circuits. However, the extent to which volatile anesthetics affect distinct cellular and network components of these circuits remains unclear. Ex vivo brain slices provide a means by which investigators may probe discrete components of complex networks and disentangle potential mechanisms underlying the effects of volatile anesthetics on evoked responses. To isolate potential cell type- and pathway-specific drug effects in brain slices, investigators must be able to independently activate afferent fiber pathways, identify non-overlapping populations of cells, and apply volatile anesthetics to the tissue in aqueous solution. In this protocol, methods to measure optogenetically-evoked responses to two independent afferent pathways to neocortex in ex vivo brain slices are described. Extracellular responses are recorded to assay network activity and targeted whole-cell patch clamp recordings are conducted in somatostatin- and parvalbumin-positive interneurons. Delivery of physiologically relevant concentrations of isoflurane via artificial cerebral spinal fluid to modulate cellular and network responses is described.

Ex vivo brain slices can be used to study the effects of volatile anesthetics on evoked responses to afferent inputs. Optogenetics are employed to independently activate thalamocortical and corticocortical afferents to non-primary neocortex, and synaptic and network responses are modulated with isoflurane.

Anesthetics influence consciousness in part via their actions on thalamocortical circuits. However, the extent to which volatile anesthetics affect ...