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>
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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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6.8K vistas.  Shanghai Jiaotong University School of Medicine. 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....