Supported by NIH award R01 DK093525 (GFG). We greatly appreciate the scientific review and grammatical editing of the manuscript by Dr. Amber Shaffer (University of Pittsburgh) and thank Michael Burcham for assistance in preparation of figures.

NOTE: This protocol was reviewed and approved by the University of Pittsburgh Institutional Animal Care and Use Committee.
1. Preparation of Modified Krebs Solution and Test Drug Aliquots
<ol>
	<li>Make 6 L of modified Krebs solution that contains (in mM): 117.9 NaCl, 4.7 KCl, 25 NaHCO3, 1.3 NaH2PO4, 1.2 MgSO4, 2.5 CaCl2, 11.1 D-glucose, 2 sodium butyrate, 20 sodium acetate, 0.004 nifedipine (to block spontaneous muscle contractions), and 0.003 indomethacin (to block synthesis of endogenous prostaglandins). Use ice-cold and warm Krebs solutions for tissue dissection and single-fiber recording, respectively.</li>
	<li>Prepare any chemical solutions (e.g., IS, capsaicin, ATP) in aliquots at desired concentrations.</li>
</ol>
2. Dissection of the Colorectum-nerve Tissue
<ol>
	<li>Anesthetize and euthanize male mice (6 - 8 weeks old, 20 - 30 g) in a CO2 chamber at a flow rate that displaces 10 - 30% of the chamber volume per minute until mice stop breathing completely as indicated by the absence of chest movement.</li>
	<li>Immediately following euthanasia, exsanguinate by cutting open the thoracic chamber, perforating the right atrium, and immersing the mouse carcass in an ample volume (~500 ml) of ice-cold Krebs (4 &#176;C) solution bubbled with carbogen (95% O2, 5% CO2).</li>
	<li>Carefully remove all viscera but the colon and pelvic organs. Transect the mouse in half across the T12 spinal segment slightly above the thoracic diaphragm and transfer the caudal half to a dissection chamber containing ice cold, bubbled Krebs solution.</li>
	<li>Under a stereomicroscope, remove the bladder and the reproductive organs by transecting at their junctions to the urethra, and remove the descending/abdominal aorta until it bifurcates into common iliac arteries. Free the PN or the LSN from their surrounding tissues by blunt dissection and follow the nerve from outside the iliac crest till its ventral entry point into the L6 and S1 vertebral column (for PN) or T13 and L1 vertebral column (for LSN).</li>
	<li>Cut the pubic symphysis and right and left acetabular joints, and remove the iliac bone. Carefully free either the PN or LSN from the attached muscle and connective tissue from close to the colorectum until where the nerve enters the vertebral column.</li>
	<li>Carefully resect the iliac bone to expose the distal colorectum. Dissect out the distal colorectum with the attached PN or LSN in continuum.</li>
	<li>Transfer the colorectum with the nerve attached to the bath compartment of the tissue chamber. Remove excessive connective tissue by further dissection, and open the colorectum longitudinally along the anti-mesenteric border.</li>
	<li>With mucosal side facing up, pin the mesenteric edge of the colorectum adjacent to the recording compartment into the silicone base of the chamber and attach the antimesenteric length of the colorectum to a rake of hooks connected to a force actuator (illustrated in Figure 1 and photographed in Figure 2A).</li>
	<li>Extend the PN or LSN into the recording compartment, which is connected to the bath compartment by a mouse hole and gate. Gently lay the nerve trunk onto a small glass mirror in the recording compartment, which provides a hydrophilic surface for the nerve to adhere to. Superfuse the bath compartment with warm (30 - 32 &#176;C), oxygenated Krebs solution and fill the recording compartment with mineral oil.</li>
</ol>
3. Single-fiber Recording and Localization of the Receptive Field
<ol>
	<li>Carefully peel back the epineurium (nerve sheath) from the PN or LSN under the stereomicroscope at high magnification (50 - 60X). Using fine forceps, tease the nerve trunk into 5 - 8 nerve bundles of ~100 &#181;m thickness.</li>
	<li>Place the platinum-iridium reference electrode in contact with the Krebs solution in the tissue chamber. Sequentially place the individual nerve bundles onto the recording electrode made of the same material.</li>
	<li>Use a soft paint brush to evoke APs from the colorectal afferents by gently stroking up and down the colorectal surface. Locate the nerve bundle(s) that innervate the colon through detectable AP (action potential) recordings. 
	NOTE: The PN and LSN also innervate the urinary bladder and other pelvic organs.</li>
	<li>Use a pair of 30 G needle tips to further split the nerve bundle into fine fascicle filaments of ~10 &#181;m thickness and place an individual filament onto the recording electrode.</li>
	<li>Place the round-tipped concentric electrode perpendicular to the mucosal surface to electrically excite afferent endings at suprathreshold stimulus intensity (10 mA magnitude, 0.5 msec duration @ 0.3 Hz), which produces a ~2 mm radius of current spread. Move the electrode systematically (~1.5 mm steps) along the length and width of the flattened colorectum to localize receptive endings.</li>
	<li>When an afferent ending is excited, adjust the electrode position to pinpoint the site of activation (receptive field, RF) that requires minimum stimulus intensity (stimulus threshold). Discard endings with a stimulus threshold &#62;3 mA19.</li>
	<li>Calculate the conduction velocity (CV) from 1) the distance between the stimulating electrode at the receptive field (RF) and the recording site and 2) the conduction delay (e.g., Figure 2B) between the stimulus artifact and the onset of the action potential. 
	CV (m/sec) = distance (mm) / conduction delay (msec).</li>
</ol>
4. Functional Classification of Mechanosensitive Colorectal Afferents
<ol>
	<li>After locating a RF by electrical stimulation, apply the following three mechanical stimuli to the RF:
	<ol>
		<li>Conduct the probing stimulus by pressing the tip of a calibrated von Frey-like nylon monofilament (0.4 and 1 g force) perpendicularly towards the RF on the flattened colorectum.</li>
		<li>Conduct the stroking stimulus by gently stroking the colorectal mucosa with a fine nylon filament strand (10 mg force) to generate a small surface shear stress at the RF.</li>
		<li>Conduct the circumferential stretch using a computer-controlled force actuator, which delivers a ramped stretch force (0 - 170 mN at 5 mN/sec) in circumferential direction along the anti-mesenteric edge of the colorectum via the rake of hooks described in step 2.8.</li>
	</ol>
	</li>
	<li>Classify afferents as serosal (respond only to blunt probing), mucosal (respond to mucosal stroking and blunt probing), muscular (respond to circumferential stretch and blunt probing) muscular/mucosal (respond to circumferential stretch, mucosal stroking and blunt probing), or MIA (not responsive to any of the three mechanical stimuli).</li>
	<li>For mesenteric afferents (only in the LSN innervation) that are difficult to activate selectively by electrical stimulation, locate their receptive endings by mechanical stroking/probing of the mesentery.</li>
	<li>For stretch-sensitive afferents (muscular and muscular-mucosal), determine the response threshold, which is defined as the force that evokes the first AP during ramped stretch.</li>
	<li>For serosal afferents, record their responses to ascending levels of punctate probing of the receptive field driven by the computer-controlled force actuator.</li>
</ol>
5. Chemical Application/Modulation of Receptive Endings
<ol>
	<li>Record a baseline response to a mechanical stimulus (i.e., response to ramped stretch, punctate probing, or mucosal stroking).</li>
	<li>Coat the bottom edge of a piece of tubing (brass or stainless steel, 10 mm high and 4 x 4 mm2 square or 4 - 5 mm diameter) with petrolatum and place it over the receptive field on the colorectum.</li>
	<li>Remove the Krebs solution inside the tubing, and expose the receptive ending for 3 - 5 min to 170 &#956;l of the solution containing the chemical(s) to be tested.</li>
	<li>Monitor the response of the afferent during chemical application (some afferents are chemosensitive).</li>
	<li>Remove the chemical solution and tubing to terminate the action of the chemical. Within 4 - 6 min, test the afferent response to the same mechanical stimulus as in the baseline response.</li>
	<li>Reapply the mechanical stimulus again after sufficient period of wash-out (&#62;15 min).</li>
</ol>
6. Recording and Discriminating AP spikes
<ol>
	<li>Digitize the electrical signals recorded from axons at 20 kHz and save the data to a computer. Monitor the signal on-line by an audio monitor.</li>
	<li>Analyze the AP spikes off-line and discriminate single units based upon principal component analysis of individual spike waveforms25. 
	NOTE: One record should contain no more than two easily discriminable active units.</li>
</ol>

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</ol>

The authors have nothing to disclose.

The in vitro colorectum-nerve preparation described here has proven to be a powerful approach to study neural encoding functions of individual colorectal afferents, which nicely complements other non-functional approaches (e.g., cellular, molecular, and histological studies) on visceral sensory neurons (see review 27 for details). Neuronal mechanisms contributing to nociception and long-term colorectal hypersensitivity have been revealed and pharmacological manipulations have been performed t...

Pain and hypersensitivity are the predominant complaints of patients suffering from functional gastrointestinal disorders, including irritable bowel syndrome (IBS), which exist in the absence of apparent pathobiological cause or tissue damage. For example, IBS patients exhibit hypersensitivity, including heightened responses to rectal balloon distension and increased sensitivity during normal bowel function, as well as hypersensitivity of somatic referral (i.e., tenderness to palpation of the abdominal area)1. Because targeting colorectal afferents has proven to be effective in alleviating pain and hypersensitivity in IBS patients (e.g., intra-rectal instillation of local anesthetics2,3; oral ingestion of the guanylate cyclase-C agonist linaclotide4-6), improved understanding of the afferent innervation of the colorectum is important.
Visceral afferents, including colorectal afferents, are capable of responding to chemical/nutrient- and thermal modalities (e.g., 7-9). However, visceral afferents responding to mechanical stimuli (i.e., mechanosensitive afferents) have been the most thoroughly studied because mechanical stimuli (e.g., luminal distension, stretch) are those that generally give rise to conscious sensations, including discomfort and pain10-16. In addition, the viscera are also innervated by mechanically insensitive afferents (MIAs), commonly termed silent or sleeping nociceptors17. Under normal physiological conditions, MIAs do not respond to mechanical stimulation or have very high response thresholds18, but can become active and acquire mechanosensitivity in pathophysiological conditions and contribute to hypersensitivity.
Using the in vitro preparation and protocol described here, we developed and employed an electrical stimulus strategy to search for receptive endings, permitting unbiased identification of both mechanosensitive and MIA endings in the colorectum19. The colorectal innervation is derived from lumbar splanchnic (LSN) and pelvic nerve (PN) pathways, and includes colorectal afferents that can be categorized into five mechanosensitive classes (serosal, mucosal, muscular, muscular-mucosal, mesenteric) and one MIA class20. Using this in vitro preparation, we found that colorectal MIAs acquired mechanosensitivity (sensitize) following brief exposure of their receptive fields to an inflammatory soup (IS), which sensitized 71% of MIAs in the PN pathway and 23% of MIAs in the LSN pathway19. We also documented long-term sensitization (up to 28 days) of MIAs in the context of long-lasting behavioral visceral hypersensitivity (i.e., in mice receiving intracolonic treatments with zymosan21 or 2,4,6-trinitrobenzenesulfonic acid (TNBS)22).
Among mechanosensitive afferents, muscular and muscular-mucosal afferents are the only classes that tonically encode circumferential stretch of the colorectum (i.e., are stretch-sensitive) and subserve the encoding of noxious colorectal distension23,24. Using a computer-controlled force actuator, we applied a standard, homogeneous, and reproducible ramped stretch in the circumferential direction of the flattened colorectal tissue and further categorized stretch-sensitive afferents as low-threshold and high-threshold23. In addition, the time course of sensitization of stretch-sensitive afferents after intracolonic zymosan21 or TNBS22 treatment corresponds to the onset, persistence, and/or recovery of behavioral visceral hypersensitivity, suggesting a role of stretch-sensitive colorectal afferents in visceral pain and hypersensitivity.

<table><tbody><tr><td>Leica MZ16 stereo microscope</td><td>Leica Microsystems Inc.</td><td></td><td></td></tr><tr><td>Leica IC D camera</td><td>Leica Microsystems Inc.</td><td></td><td></td></tr><tr><td>Amplifier</td><td>World Precision instruments, Inc.</td><td>SYS-DAM80</td><td>Low-noise differential amplifier</td></tr><tr><td>Two-compartment tissue chamber</td><td>Custom made</td><td></td><td></td></tr><tr><td>Power1401</td><td>Cambridge Electronic Design Limited</td><td>Power1401</td><td>Data acquisition, analog signal input/out</td></tr><tr><td>Spike2 v5.02</td><td>Cambridge Electronic Design Limited</td><td></td><td>Software package that works with the Power1401</td></tr><tr><td>Audio monitor</td><td>Natus</td><td>Am 8</td><td></td></tr><tr><td>Square pulse stimulator</td><td>Natus</td><td>S48</td><td>To deliver electrical stimuli</td></tr><tr><td>Photoelectric isolation unit</td><td>Natus</td><td>PSIU6</td><td>Stimulus isolation to reduce noise</td></tr><tr><td>Concentric bipolar microelectrode</td><td>FHC Inc.</td><td>CBFFG75</td><td>To deliver electrical stimuli</td></tr><tr><td>Dual-mode lever system</td><td>Aurora Scientific Inc.</td><td>Series 300C</td><td>To deliver mechanical stimuli</td></tr><tr><td>Forceps</td><td>Fine Science Tools</td><td>11252-00</td><td>Forceps with fine tips</td></tr></tbody></table>

in vitro functional characterization of mouse colorectal afferent endings

This video demonstrates in detail an in vitro single-fiber electrophysiological recording protocol using a mouse colorectum-nerve preparation. The approach allows unbiased identification and functional characterization of individual colorectal afferents. Extracellular recordings of propagated action potentials (APs) that originate from one or a few afferent (i.e., single-fiber) receptive fields (RFs) in the colorectum are made from teased nerve fiber fascicles. The colorectum is removed with either the pelvic (PN) or lumbar splanchnic (LSN) nerve attached and opened longitudinally. The tissue is placed in a recording chamber, pinned flat and perfused with oxygenated Krebs solution. Focal electrical stimulation is used to locate the colorectal afferent endings, which are further tested by three distinct mechanical stimuli (blunt probing, mucosal stroking and circumferential stretch) to functionally categorize the afferents into five mechanosensitive classes. Endings responding to none of these mechanical stimuli are categorized as mechanically-insensitive afferents (MIAs). Both mechanosensitive and MIAs can be assessed for sensitization (i.e., enhanced response, reduced threshold, and/or acquisition of mechanosensitivity) by localized exposure of RFs to chemicals (e.g., inflammatory soup (IS), capsaicin, adenosine triphosphate (ATP)). We describe the equipment and colorectum&#8211;nerve recording preparation, harvest of colorectum with attached PN or LSN, identification of RFs in the colorectum, single-fiber recording from nerve fascicles, and localized application of chemicals to the RF. In addition, challenges of the preparation and application of standardized mechanical stimulation are also discussed.

The setup is illustrated in Figure 1. It includes a custom-made tissue chamber that houses the colorectum in a silicone-lined bath compartment and the attached nerve in a contiguous mineral oil-filled compartment. The two-compartment chamber was machined from a solid block of acrylic plastic by a CNC machine; the bottom of both compartments was subsequently lined with firm silicone to allow easy pin down of the colorectal tissue. Extracellular APs from teased nerve fascicles are recorded using a low-nois...

Watch this Scientific Journal Video about In vitro Functional Characterization of Mouse Colorectal Afferent Endings at JoVE.com

In vitro Functional Characterization of Mouse Colorectal Afferent Endings

This video demonstrates a protocol for conducting single-fiber electrophysiological recordings on an in vitro mouse colorectum-nerve preparation.

In vitro Functional Characterization of Mouse Colorectal Afferent Endings

This video demonstrates in detail an in vitro single-fiber electrophysiological recording protocol using a mouse colorectum-nerve preparation. The ...

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Research

JoVE Journal

Medicine

9.5K Views.  University of Pittsburgh. This video demonstrates a protocol for conducting single-fiber electrophysiological recordings on an in vitro mouse colorectum-nerve preparation. 

Video: In vitro Functional Characterization of Mouse Colorectal Afferent Endings

Flexible Colonoscopy in Mice to Evaluate the Severity of Colitis and Colorectal Tumors Using a Validated Endoscopic Scoring System

The use of modern endoscopy for research purposes has greatly facilitated our understanding of gastrointestinal pathologies. In particular, experimental endoscopy has been highly useful for studies that require repeated assessments in a single laboratory animal, such as those evaluating mechanisms of chronic inflammatory bowel disease and the progression of colorectal cancer. However, the methods used across studies are highly variable. At least three endoscopic scoring systems have been published for murine colitis and published protocols for the assessment of colorectal tumors fail to address the presence of concomitant colonic inflammation. This study develops and validates a reproducible endoscopic scoring system that integrates evaluation of both inflammation and tumors simultaneously. This novel scoring system has three major components: 1) assessment of the extent and severity of colorectal inflammation (based on perianal findings, transparency of the wall, mucosal bleeding, and focal lesions), 2) quantitative recording of tumor lesions (grid map and bar graph), and 3) numerical sorting of clinical cases by their pathological and research relevance based on decimal units with assigned categories of observed lesions and endoscopic complications (decimal identifiers). The video and manuscript presented herein were prepared, following IACUC-approved protocols, to allow investigators to score their own experimental mice using a well-validated and highly reproducible endoscopic methodology, with the system option to differentiate distal from proximal endoscopic colitis (D-PECS).

Over the past few years, new generation endoscopes have emerged as important diagnostic research aids for evaluating murine colitis and colorectal tumors. We present herein a detailed protocol for endoscopic assessment of inflammation and colorectal tumors in mice, as well as a novel scoring system that uses decimal identifiers to document the endoscopic severity of colitis and colorectal tumors.

The use of modern endoscopy for research purposes has greatly facilitated our understanding of gastrointestinal pathologies. In particular, experimental ...

An In-vitro Preparation of Isolated Enteric Neurons and Glia from the Myenteric Plexus of the Adult Mouse

The enteric nervous system is a vast network of neurons and glia running the length of the gastrointestinal tract that functionally controls gastrointestinal motility. A procedure for the isolation and culture of a mixed population of neurons and glia from the myenteric plexus is described. The primary cultures can be maintained for over 7 days, with connections developing among the neurons and glia. The longitudinal muscle strip with the attached myenteric plexus is stripped from the underlying circular muscle of the mouse ileum or colon and subjected to enzymatic digestion. In sterile conditions, the isolated neuronal and glia population are preserved within the pellet following centrifugation and plated on coverslips. Within 24-48 hr, neurite outgrowth occurs and neurons can be identified by pan-neuronal markers. After two days in culture, isolated neurons fire action potentials as observed by patch clamp studies. Furthermore, enteric glia can also be identified by GFAP staining. A network of neurons and glia in close apposition forms within 5 - 7 days. Enteric neurons can be individually and directly studied using methods such as immunohistochemistry, electrophysiology, calcium imaging, and single-cell PCR. Furthermore, this procedure can be performed in genetically modified animals. This methodology is simple to perform and inexpensive. Overall, this protocol exposes the components of the enteric nervous system in an easily manipulated manner so that we may better discover the functionality of the ENS in normal and disease states.

An In-vitro Preparation of Isolated Enteric Neurons and Glia from the Myenteric Plexus of the Adult Mouse

We demonstrate a cell culture protocol for the direct study of neuronal and glial components of the enteric nervous system. A neuron/glia mixed culture on coverslips is prepared from the myenteric plexus of adult mouse providing the ability to examine individual neuron and glia function by electrophysiology, immunohistochemical, etc.

The enteric nervous system is a vast network of neurons and glia running the length of the gastrointestinal tract that functionally controls ...

Neuroscience

Video Imaging and Spatiotemporal Maps to Analyze Gastrointestinal Motility in Mice

The enteric nervous system (ENS) plays an important role in regulating gastrointestinal (GI) motility and can function independently of the central nervous system. Changes in ENS function are a major cause of GI symptoms and disease and may contribute to GI symptoms reported in neuropsychiatric disorders including autism. It is well established that isolated colon segments generate spontaneous, rhythmic contractions known as Colonic Migrating Motor Complexes (CMMCs). A procedure to analyze the enteric neural regulation of CMMCs in ex vivo preparations of mouse colon is described. The colon is dissected from the animal and flushed to remove fecal content prior to being cannulated in an organ bath. Data is acquired via a video camera positioned above the organ bath and converted to high-resolution spatiotemporal maps via an in-house software package. Using this technique, baseline contractile patterns and pharmacological effects on ENS function in colon segments can be compared over 3-4 hr. In addition, propagation length and speed of CMMCs can be recorded as well as changes in gut diameter and contraction frequency. This technique is useful for characterizing gastrointestinal motility patterns in transgenic mouse models (and in other species including rat and guinea pig). In this way, pharmacologically induced changes in CMMCs are recorded in wild type mice and in the Neuroligin-3R451C mouse model of autism. Furthermore, this technique can be applied to other regions of the GI tract including the duodenum, jejunum and ileum and at different developmental ages in mice.

This article describes a video imaging technique and high-resolution spatiotemporal mapping to identify changes in the neural regulation of colonic motility in adult mice. Subtle effects on gastrointestinal (GI) function can be detected using this approach in isolated tissue preparations to advance our understanding of GI disease.

The enteric nervous system (ENS) plays an important role in regulating gastrointestinal (GI) motility and can function independently of the central ...

Combined Recording of Mechanically Stimulated Afferent Output and Nerve Terminal Labelling in Mouse Hair Follicle Lanceolate Endings

A novel dissection and recording technique is described for monitoring afferent firing evoked by mechanical displacement of hairs in the mouse pinna. The technique is very cost-effective and easily undertaken with materials commonly found in most electrophysiology laboratories, or easily purchased. The dissection is simple and fast, with the mechanical displacement provided by a generic electroceramic wafer controlled by proprietary software. The same software also records and analyses the electroneurogram output. The recording of the evoked nerve activity is through a commercial differential amplifier connected to fire-polished standard glass microelectrodes. Helpful tips are given for improving the quality of the preparation, the stimulation and the recording conditions to optimize recording quality. The system is suitable for assaying the electrophysiological and optical properties of lanceolate terminals of palisade endings of hair follicles, as well as the outcomes from their pharmacological and/or genetic manipulation. An example of combining electrical recording with mechanical stimulation and labeling with a styryl pyridinium vital dye is given.

A simple and novel technique for recording afferent discharge due to mechanical stimulation of lanceolate terminals of palisade endings innervating mouse ear skin hair follicles is presented.

A novel dissection and recording technique is described for monitoring afferent firing evoked by mechanical displacement of hairs in the mouse pinna. The ...

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 ...

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.

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.

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

Advanced Imaging of Dorsal Root Ganglion Neurons for Sensory Modality Research

In Vivo Calcium Imaging of Dorsal Root Ganglia Neurons' Response to Somatic and Visceral Stimuli

A technique is described for surgically exposing the dorsal root ganglion (DRG) of the lumbar-6 in a live, anesthetized laboratory mouse, along with the protocol for in vivo calcium imaging of the exposed DRG in response to various visceral and somatic stimuli. Pirt-GCaMP6s mice or C57BL6 mice intrathecally injected with AAV viruses packaged with GCaMP6s were utilized to capture Ca2+ transients. The amplitude of these transients indicates sensitivity to specific sensory modalities. Afferent fibers originate from internal organs, with primary neuronal cell bodies in spinal or vagal ganglia. Studies on visceral nociception and acupuncture analgesia can potentially be conducted on primary sensory neurons using advanced imaging technologies like in vivo calcium imaging, allowing for the recording of neuronal activity ensembles in the intact animal during stimulation or intervention. The responses of DRG neuron ensembles to somatic and visceral stimuli applied to their corresponding receptive fields were recorded. This technique illustrates how neuronal populations react to various types of somatic and visceral stimuli. It is possible to comprehensively compare neuronal ensemble responses to different stimuli, which is a particularly valuable approach in research on visceral pain and segmental mechanisms of somatic stimulation, such as acupuncture.

The present protocol outlines in vivo calcium imaging for measuring the responses of ensembles of lumbar-6 DRG neurons to somatic and visceral stimuli. Thorough comparisons can be made among neurons responding to different stimuli. This protocol is valuable for investigating mechanisms of visceral pain and somatic stimulation, such as acupuncture.

A technique is described for surgically exposing the dorsal root ganglion (DRG) of the lumbar-6 in a live, anesthetized laboratory mouse, along with the ...

Generation of Mouse Proximal Colon Loop Model: A Surgical Procedure to Generate Proximal Colon Loop and Measure Intestinal Permeability by Detection of Fluorescent Markers in Serum Following Intraluminal Injection

Source: Boerner, K. et al. <a href="https://www.jove.com/v/62093">Functional Assessment of Intestinal Permeability and Neutrophil Transepithelial Migration in Mice using a Standardized Intestinal Loop Model.</a> J. Vis. Exp. (2021).
In this video, we describe a surgical procedure to generate mouse proximal colon loop or pcLoop segment followed by intraluminal injection of fluorescent markers into the segment to study the intestinal epithelial permeability.

Generation of Mouse Proximal Colon Loop Model: A Surgical Procedure to Generate Proximal Colon Loop and Measure Intestinal Permeability by Detection of Fluorescent Markers in Serum Following Intralumi

Source: Boerner, K. et al. Functional Assessment of Intestinal Permeability and Neutrophil Transepithelial Migration in Mice using a Standardized ...

JoVE Encyclopedia of Experiments

Biology

Rodent Models

Adult

Electrophysiological Recording from Colonic Afferent Nerves in an Ex Vivo Rat Colon

Source: Meng, Y. et al., <a href="https://app.jove.com/v/56090">In Vitro Characterization of the Electrophysiological Properties of Colonic Afferent Fibers in Rats.</a> J. Vis. Exp. (2017)
This video demonstrates a method to record the activity of colonic afferent nerves in an ex-vivo rat colon, cannulated at both ends and infused with saline to increase intraluminal pressure. As pressure increases, the nerve signal rises, indicating its stimulation.

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.
1. ...

Neurophysiology

Electrophysiology Techniques

Recording of Mesenteric Afferent Nerve Activity in an Ex Vivo Mouse Jejunum Segment

Source: Nullens, S., et al. <a href="https://app.jove.com/v/54576">In Vitro Recording of Mesenteric Afferent Nerve Activity in Mouse Jejunal and Colonic Segments.</a> J. Vis. Exp. (2016).
This video shows the process of recording electrical signals from mesenteric afferent nerves in a dissected mouse jejunal segment to study the effects of tissue pressure and movement changes on afferent nerve activity.

In vitro Functional Characterization of Mouse Colorectal Afferent Endings

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