Funded by the Department of Veterans Affairs MERIT award 2 I01 RX000379-05.

All animal procedures and protocols were approved by the Minneapolis Veterans Affairs Health Care System (VAHCS) Institutional Animal Care and Use Committee and conformed to the &#34;Guide for the Care and use of Laboratory Animals&#34; (The National Academic Press, USA)12.
1. Choice of animals
NOTE: C57Bl6 mice are used for all three arthritis models.
<ol>
	<li>Use either male or female mice, but note that the response to arthritis pain may vary depending on gender and the pathogenesis of the model being tested.</li>
	<li>Select mice that have reached sexual maturity, are no longer rapidly growing and are not old enough to have developed spontaneous arthritis that could confound pain measurements. 
	NOTE: Twelve weeks is an ideal age for pain measurement in the models described but this depends on the study design. Age at initiation of arthritis depends on the duration of time the model takes to develop. Acute inflammatory arthritis (carrageenan model) requires 3 h to develop, therefore animals are 12 weeks of age at the time of induction. Chronic inflammatory arthritis (CFA model) requires 3 weeks to develop, therefore animals are 9 weeks old at the time of induction. Chronic degenerative arthritis (collagenase model) requires 4 weeks to develop, therefore animals are 8 weeks at the time of induction. A more chronic model of degenerative arthritis can be used by inducing arthritis at 6 weeks of age. This allows 6 weeks of development of joint damage. However, chronic degenerative arthritis in mice does not produce significant evoked pain.</li>
	<li>Obtain animals from a national commercial breeder source.</li>
	<li>House animals in groups of up to 8 animals in standard polycarbonate cages with ad libitum rodent diet and water.</li>
	<li>Maintain environmental conditions at 72 &#176;C &#177; 1 &#176;C and 33% &#177; 1% humidity with 12 h light/dark cycles.</li>
</ol>
2. Intra-articular injections into the knee
<ol>
	<li>Create a 30 G 2.5 mm sterile by covering the length of a 0.5 inch needle with a sheath made of polyethylene tubing with an inside diameter of 0.38 mm and outside diameter of 1.09 mm, leaving only 2.5 mm of the needle protruding. This prevents inserting the needle too deeply and exiting the joint posteriorly.</li>
	<li>Choose a single knee to inject, shave it using any commercially available electric facial hair trimmer, and sterilize with providone-iodine scrub.</li>
	<li>Anesthetize the mouse with 3% isoflurane in 100% O2 at 1 L/min for 3 min &#177; 1 min. Maintain anesthesia using a nosecone during the procedure. Confirm anesthesia depth by toe pinch. Take care to monitor respiratory status and minimize anesthesia exposure to maintain adequate respirations.</li>
	<li>Enter the joint at the midline through the patellar tendon just inferior to the lower edge of the patella using the sterile sheathed needle once the mouse is fully anesthetized. This anterior midline approach maximizes accuracy for entering the joint and injecting the substance of interest.</li>
	<li>Use the same approach for injecting both arthritis-inducing substances and analgesic substances. Sham controls are produced by inserting the needle as above but without injecting any substance.</li>
</ol>
3. Production of arthritis
<ol>
	<li>Anesthetize animal as in step 2.3 above.</li>
	<li>Weigh the appropriate amounts (see below) of carrageenan, Complete Freund&#39;s Adjuvant and Type IV Collagenase and dilute to the appropriate concentration with normal saline in a laminar flow hood for safety and sterility.</li>
	<li>Inject 10 &#181;l of 2.5% carrageenan diluted in 0.9% sterile saline into the knee as above using a Hamilton syringe to produce acute inflammatory arthritis. Arthritis peaks 3 h after injection.</li>
	<li>Inject, 30 &#181;L (30 &#181;g) of Complete Freund&#39;s Adjuvant (CFA) into the knee to produce chronic inflammatory arthritis. There is an initial acute inflammatory phase that peaks at 1 week then a chronic phase that peaks at 3 weeks following injection.</li>
	<li>Inject 10 &#181;L containing 10 IU Type IV Collagenase to produce chronic degenerative arthritis. Arthritis pain peaks 4 weeks after injection.</li>
</ol>
4. Measurement of evoked joint pain
<ol>
	<li>Always examine the normal comparator knee first to minimize the cross-over pain response (windup) from the painful knee13.&#160;</li>
	<li>Train the examiner to apply consistent and firm pressure of 700 gf/cm2 = 10 psi using a Palpometer level 4; the device will emit 4 beeps when this level of pressure is applied. This amount of pressure will consistently elicit a greater pain response from an arthritic joint than from a normal joint. 
	NOTE: The device is calibrated at the factory to elicit 4 beeps when the appropriate level of pressure is applied. Use the device for training only; do not use on the animals but when examining the animals, apply the amount of pressure learned through the training.</li>
	<li>Restrain the mouse tightly enough to prevent casual movement by holding the scruff of the neck with the index finger and thumb and using the 4th and 5th fingers to restrain the tail. The mouse should be able to make discrete, brief movements with effort and when stimulated, but should not be able to move freely or continuously.</li>
	<li>Administer repeated firm (Palpometer level 4) palpations concurrently to the lateral and medial sides of each knee at approximately the joint line with the thumb and index finger of the free hand once per second for one minute while restraining the mouse. Do not use the Palpometer for the mouse examination; it is used only for training.</li>
	<li>Have a second observer count the number of times the animal vocalizes and fights to escape the restraint during this one-minute time-period. The sum of fights and vocalizations is the Evoked Pain Score.</li>
	<li>Always us the same examiner throughout the study and confirm the examiner and observer are blinded as to experimental condition.</li>
</ol>
5. Measurement of spontaneous joint pain.
NOTE: The Advanced Dynamic Weight Bearing (ADWB) device calculates the percent of total time the animal spends on each limb and the percent of total weight borne on each limb.
<ol>
	<li>Fill a plastic beaker with 2 L of water. Place the foam pad and medium density fiberboard that are included with the equipment along with the filled beaker on a laboratory scale and record the combined weight.</li>
	<li>Open the ADWB program and select Mice sensor type.</li>
	<li>Calibrate the system prior to each experiment:
	<ol>
		<li>Select Full calibration under the Calibration menus. Enter 0.00 as a Tare value and the weight of the foam pad, medium density fiberboard, plastic beaker, and water as the Calibration weight, then select Next.</li>
		<li>Select Tare before placing anything on the sensor. Before selecting Gain preview, cover the sensor pad with the provided foam pad, medium density fiberboard, and plastic beaker filled with 2 liters of water, in that order. Select Gain preview once the calibration weight is on the sensor.</li>
		<li>Adjust the calibration weight so it is evenly distributed across the individual sensors and when the value of the Calibration indicator is above 95, select Gain definition. This process produces a normalized mean for the individual sensors and confirms the integrity of the individual sensors. Finally, select Next.</li>
		<li>Save the calibration file into the calibration folder.</li>
	</ol>
	</li>
	<li>Select New and where provided enter the Project name and the Animal name for the first mouse to be tested.</li>
	<li>Select Browse and open the calibration file that was created for the project. Select Next, ensure Enable video capture is selected, and select OK.</li>
	<li>Weigh the animal, select Capture, and record the weight in the software. Select OK.</li>
	<li>Do not acclimate mice to the chamber before the collection of data because this device measures spontaneous behavior.</li>
	<li>Place mouse in the chamber for a period of 5 min of testing. When the animal is in the chamber select Launch. The software will record the animal&#39;s activity during this time, capture a video and synchronize with the sensor data, and automatically partition this video into analyzable and non-analyzable segments. 
	NOTE: The software considers segments analyzable when at least one stable zone is detected. A stable zone is created when sensors detect &#8805;2 g on one sensor with a minimum of one adjacent sensor detecting &#8805;1 g and when the weight distribution of a zone is stable for more than 0.38 s.</li>
	<li>Before the first analysis in a series select Easy scoring and Independent paws setting. 
	NOTE: Easy scoring allows iteration validation of segments where the stable zone does not change based on the validation of the first stable zone of that segment. Independent paws setting provides the observer with access to the keyboard shortcuts that allow individual identification of each paw. The observer assigns zones that meet minimal criteria as right hind, left hind, right fore, left fore, both forepaws, other body part, or ignore zone by using the keyboard shortcuts while holding the cursor over the segment per the video and scaled map of activated sensors.</li>
	<li>Select &#62;&#62; to move to the first analyzable segment. If a stable zone does not have the correct paw identified then hold the cursor over that zone and press the shortcut (right hind, s; left hind, a; right fore, w; left fore, q; both forepaws, e; other section of the body, z, ignore zone, x) that corresponds with the correct body part. 
	NOTE: A minimum of 1.5 min of analyzable time is required to meet analysis thresholds. Analyzed segments are added and averaged automatically for output per paw(s) by the software.</li>
	<li>The ADWB software then automatically calculates the percentage of analyzed time spent and percentage of body weight (g) placed on each of the four limb options. Export these values into a new spreadsheet by selecting Results, Export, selecting Yes to the prompt question asking if only the first five summary lines should be exported, and selecting the location of the output.</li>
	<li>Euthanize animals by CO2 inhalation followed by thoracotomy at the end of the study period.</li>
	<li>For each additional animal in the same group, select New and enter a unique animal name but do not change the project name. Select Next, ensure Enable video capture is selected, and select OK. Follow steps 5.5 to 5.12 as for the first animal.</li>
</ol>

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T., Kuner, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studying+ongoing+and+spontaneous+pain+in+rodents+-+challenges+and+opportunities.">Studying ongoing and spontaneous pain in rodents - challenges and opportunities.</a> European Journal of Neuroscience. 39, 1881-1890 (2014).</li><li>National Research Council. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Guide for the Care and Use of Laboratory Animals. , (2011).</li><li>Kuner, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Central+mechanisms+of+pathological+pain.">Central mechanisms of pathological pain.</a> Nature Medicine. 16, 1258-1266 (2010).</li><li>Banik, R., Woo, Y., Park, S., Brennan, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strain+and+Sex+Influence+on+Pain+Sensitivity+after+Plantar+Incision+in+the+Mouse.">Strain and Sex Influence on Pain Sensitivity after Plantar Incision in the Mouse.</a> Anesthesiology. 105, 1246-1252 (2006).</li><li>Mogil, J. 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The authors have nothing to disclose.

Measurement of joint pain in preclinical models of inflammatory arthritis and degenerative joint disease is an increasingly valuable tool to evaluate new treatments for arthritis pain and for restoring joint function9,10. Measuring pain behaviors in mice with chronic degenerative joint disease is challenging. As quadrupeds, they can offload a painful limb to any combination of the other three limbs or the tail. Decreased function in one limb may not be displayed as obviously as it is in bipedal humans. As prey animals, mice have a survival benefit to minimize pain behaviors.
This report demonstrates that joint pain from different pathologic mechanisms can be measured in mice with simple and relatively inexpensive methods. Inflammatory joint pain causes bigger changes in weight bearing time and distribution and therefore may be a more sensitive model for the detection of analgesia. However, other models of joint pain will be important when evaluating new potential analgesics since mechanisms of pain initiation and maintenance are likely different with different pathology. We found differences in offloading patterns between males and females and among different models of arthritis pain.
It is important to recognize that there can be strain as well as gender differences in pain behavior in mice14,15,16. It is also known that there are distinct strain differences in pain thresholds. We found that in C57/Bl6 mice, females demonstrated significantly more spontaneous pain behaviors (increased weight and time on forelimbs) than male mice with chronic degenerative joint pain (Figure 2 and Figure 3). We did not determine the estrus phase for these female mice, so we cannot say whether this had any effect on our results, but others have determined that estrus phase did not explain observed sex differences in C57/Bl6 mice17.
Evoked pain behavior is sensitive to all types of joint pain tested and has good reproducibility. It is crucial that the examiner is trained to deliver consistent, standardized palpation pressure and use consistent restraint methods that allows the range of pain behavior to detect both pain and analgesia. It is important to always examine the normal knee first to minimize the pain response in the normal knee due to a crossover effect and maximize the difference in pain response between the normal and painful knee. Using a second observer to tally the pain responses that make up the EPS is necessary so that the examiner focuses on consistent palpation and so that vocalizations and fights are consistently tallied. It may be necessary to practice the restraint method in particular to ensure the animal can react to pain adequately but does not react too easily so as to dilute the pain response. An advantage of the EPS measurement is that it is analogous to measuring joint tenderness in human patients.
We feel these methods are superior to existing methods in that they directly measure pain coming from the knee joints of mice, they can be used in different models of monoarthritis pain, they include both spontaneous and evoked pain responses, and are relatively inexpensive but reliable and reproducible. As therapies are developed to more effectively treat arthritis, these methods will be useful for confirming whether treatments are actually effective for the most disabling outcome of arthritis, pain.
Our methods have some limitations. Primarily, the EPS measure is limited by the requirement for a single examiner and observer and the need for very consistent technique. The evoked pain measures are more automated and are not as subject to inter-observer differences. Further refinement of the EPS measure might include automated methods for counting vocalizations in response to palpation, such as using an ultrasonic bat detector to count vocalizations. This method would need to be compared to our current method to confirm sensitivity and specificity before it could be widely implemented.
In summary, we describe two different pain behavior measures for quantifying joint pain in mice. Gender and strain differences must be considered before choosing an experimental model. Measures of evoked pain require careful training and consistent implementation by the examiner. Both spontaneous and evoked pain behaviors are recommended to evaluate pain severity and functional limitation and should be utilized to fully evaluate the effects of new potential analgesics.

Pain is the main cause of disability from arthritis1,2. Currently available analgesics are often ineffective, toxic, and potentially contribute to the nation-wide narcotic problem3. Surgery is not always an option for end-stage arthritis, particularly in the elderly, who may have multiple co-morbidities. Intra-articular steroids and viscosupplementation may be effective in early disease but typically lose their effectiveness in late stage disease4. There is a great unmet need for effective analgesics for arthritis pain that cannot be addressed with currently available treatments.
Pre-clinical models are useful for understanding the mechanism of action of pain therapies and for predicting limiting toxicities, but pain measurement in animals is challenging5. Pain measures can be direct and spontaneous (static or dynamic weight bearing, foot posture, gait analysis, spontaneous movement and mechanical or thermal sensitivity) or indirect/evoked (hind limb withdrawal test, knee compression force, or brain imaging)6. For mild forms of monoarthritis, gait analysis is insensitive and lacks consistency7. Static weight bearing is useful for measuring pain in rat hindlimbs but can be difficult in mice. Mechanical sensitivity measures such as the von Frey test indirectly detect sensitization of the foot pad in the setting of knee arthritis, but do not directly measure knee pain and are cumbersome to perform. Knee compression force as measured with the P.A.M. (Pressure Application Measurement) device can be used in rats, but the large device is difficult to use in mice without producing negative behaviors that do not necessarily reflect pain8.
We have developed methods for measuring spontaneous and evoked pain in three different models of murine arthritis that are sensitive and reproducible for measuring pain severity and the analgesic effects of intra-articular therapies9,10. We can also correlate pain relief with other histologic markers of pain and screen investigational drugs that would not be possible in humans. We can evaluate synergism of modestly effective analgesics to identify more effective combination therapies. By utilizing proven methods for both evoked and spontaneous pain, we avoid the pitfall of failing to identify pain that is reflected in one type of pain behavior but not the other and more closely mirror pain measurement in humans11. By limiting pain evaluation to two methodologies, we minimize stress on the animals, which can affect pain behavior, and maximize productivity of the laboratory.

<table border="0" cellpadding="0" cellspacing="0" style="width:821px;" width="820">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:183px;">Advanced Dynamic Weightbearing Device</td>
			<td style="width:221px;">Bioseb In Vivo Research Instruments, Vitrolles, France</td>
			<td style="width:203px;">Model: BIO-DWB-M - For mice</td>
			<td style="width:215px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:183px;">C57/Bl6 mice (male and female)</td>
			<td style="width:221px;">Jackson Labs, Bar Harbor ME</td>
			<td style="width:203px;">Stock No:&#160;000664&#160;|&#160;Black 6</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:183px;">Carrageenan</td>
			<td style="width:221px;">Sigma-Aldrich, St. Louis, MO, USA</td>
			<td style="width:203px;">22049-5G-F</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:183px;">Complete Freund&#39;s Adjuvant</td>
			<td style="width:221px;">Sigma-Aldrich, St. Louis, MO, USA</td>
			<td style="width:203px;">F5881</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:183px;">Palpometer</td>
			<td style="width:221px;">Palpometer Systems, Inc. Victoria, B.C</td>
			<td style="width:203px;">Not available - no longer in business</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:183px;">Type IV Collagenase</td>
			<td style="width:221px;">Worthington Biomedical Corp, Lakeville, NJ</td>
			<td style="width:203px;">LS004210</td>
			<td></td>
		</tr>
	</tbody>
</table>

spontaneous and evoked measures of pain in murine models of monoarticular knee pain

Pain is the main cause of disability from arthritis. There is currently an unmet need for adequate treatments for arthritis pain. Pre-clinical models are necessary and useful for studying the mechanisms of pain and for evaluating efficacy of arthritis therapies. Measuring pain in animal models of arthritis is challenging. We have developed methods for measuring evoked and spontaneous pain in three models of murine arthritis. We quantitate the evoked pain responses of mice subjected to firm palpation of a painful knee. We also evaluate spontaneous pain by the proportion of weight and the amount of time placed on each of their 4 limbs after induction of arthritis pain in one knee. Joint pain in these mouse models produces a significant increase in evoked pain responses and an alteration in weight bearing. Since mice are quadrupeds, they offload the painful limb to the contralateral limb, to the forelimbs, or some combination. These methods are simple, require minimal equipment, and are reproducible and sensitive for detecting pain. They are useful for studying both disease-modifying arthritis treatments and analgesics in mice.

Acute and chronic inflammatory and chronic degenerative joint pain was produced by IA injection into the left knee of C57BL/6J male and female mice prior to pain assessment using the protocol outlined above. Joint pain was measured as evoked pain scores (EPS) and spontaneous pain behaviors measured with an advanced dynamic weight bearing (ADWB) device. For the purposes of this report, individual comparisons were made using Student&#39;s t tests. For experiments where analgesic doses are being compared, ANOVA may be a more appropriate statistical comparison.
EPS (the sum of tallied fights plus vocalizations) increased with all three types of joint pain (Figure 1). ADWB measures of percent weight bearing on the left hind limb compared to na&#239;ve mice were reduced in acute and chronic inflammatory joint pain. Females but not males with chronic degenerative joint pain (COL) showed similar reductions in ADWB measures (Figure 2A). Males with acute inflammatory joint pain transferred more weight to the forelimbs than na&#239;ve animals. Weight bearing on forelimbs increased in female mice compared to na&#239;ve but not in males with chronic degenerative joint pain (COL) (Figure 2B). ADWB measures of percent time on the affected left hind limb decreased compared to na&#239;ve in mice with acute and chronic inflammatory joint pain, but this was not statistically significant. These animals did spend significantly less time on the left hind limb than on the right hind limb. In both males and females with chronic degenerative joint pain, there was no difference in time spent on the left hind limbs compared to na&#239;ve. Females with chronic degenerative joint pain spent more time on the nonarthritic right hind limb compared to naive (Figure 3A). Mice with acute inflammatory joint pain and females with chronic degenerative joint pain spent significantly more time on the forelimbs than na&#239;ve animals (Figure 3B).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59024/59024fig1.jpg" /> 
Figure 1. Evoked pain scores for left (blue column) and right (red column) hind limbs. Right hind limbs served as internal controls and did not undergo any IA injections. Measurements were taken in the following conditions: uninjected na&#239;ve (male and female), acute inflammatory carrageenan-induced arthritis (CAR), chronic inflammatory Complete Freund&#39;s Adjuvant-induced arthritis (CFA) and chronic noninflammatory Collagenase-induced arthritis (COL - male and female). In na&#239;ve animals the EPS of the left hind knee was not statistically different from the right in males and only minimally different in females (**P = 0.038) likely due to some increased pain response in the knee examined second (the left) due to crossover pain response. In all arthritic groups the arthritic left knee EPS was significantly greater than the nonarthritic contralateral right knee. When comparing the EPS of the left knee of arthritis groups to na&#239;ve animals, all arthritis groups had significantly greater EPS scores in the arthritic left knee compared to na&#239;ve left knees. This was true in both males and females. *P &#60; 0.05 compared to male na&#239;ve, #P &#60; 0.05 compared to female na&#239;ve. All error bars are SEM in all figures. <a href="https://www.jove.com/files/ftp_upload/59024/59024fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59024/59024fig2.jpg" /> 
Figure 2: Spontaneous pain behavior measured by percent body weight borne on limbs. (A) Spontaneous pain behavior measured by total percent body weight on the left (blue column) and right (red column) hind limbs. In both male and female na&#239;ve animals, there was no significant difference between percent weight borne on the left and right hind limbs. Male mice with CAR and CFA induced joint pain and females with COL induced joint pain bore significantly less weight on the left hind limb compared to the naive. *P &#60; 0.05 compared to male na&#239;ve, #P &#60; 0.05 compared to female na&#239;ve. (B) Spontaneous pain behavior measured by total percent body weight placed on the forelimbs. In males with CAR induced acute joint pain and females with COL induced chronic joint pain, there was a significant increase in the amount of weight borne on the forelimbs. This was not seen in males with CFA or COL induced joint pain. Na&#239;ve females tended to bear more weight on the forelimbs than na&#239;ve males (P = 0.02). Additional weight may be borne by other body parts such as the tail or rump. These were usually minimal and did not contribute significantly to the understanding of the pain response and are therefore not shown. *P &#60; 0.05 compared to male na&#239;ve, #P &#60; 0.05 compared to female na&#239;ve and to male 4 week COL in forelimb weightbearing. <a href="https://www.jove.com/files/ftp_upload/59024/59024fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59024/59024fig3.jpg" /> 
Figure 3:&#160;Spontaneous pain behavior measured by percent time spent on limbs. (A) Spontaneous pain behavior measured by total percent time spent on the left (blue column) and right (red column) hind limbs. There was no significant difference between right and left hind limbs in male and female na&#239;ve mice with respect to time spent on the limb. Male mice with CAR and CFA induced arthritis appeared to spend less time weightbearing with the arthritic left hind limb compared to na&#239;ve, but this was not statistically significant and likely due to increased variability in this measure in these mice. There was a significant difference in these animals comparing right to left as the right hind limb spent more total time weightbearing than the left. In females with COL induced arthritis, the right hind limb was weightbearing a greater proportion of time than in na&#239;ve females. *P &#60; 0.05 comparing right to left, #P &#60; 0.05 compared to female na&#239;ve and to male 4 week COL in time spent on forelimbs. (B) Spontaneous pain behavior measured by total amount of time spent on the forelimbs. In males with CAR induced arthritis and females with COL induced arthritis the mice spent significantly more time weightbearing on the fore limbs than did the na&#239;ve animals. Female na&#239;ve mice spent more time on the forelimbs than male na&#239;ve animals. *P &#60; 0.05 compared to male na&#239;ve, #P &#60; 0.05 compared to female na&#239;ve. <a href="https://www.jove.com/files/ftp_upload/59024/59024fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Spontaneous and Evoked Measures of Pain in Murine Models of Monoarticular Knee Pain at JoVE.com

Spontaneous and Evoked Measures of Pain in Murine Models of Monoarticular Knee Pain

We have developed an evoked measure of arthritis pain and coupled it with a standardized method for measuring spontaneous pain in different murine models of chemically induced arthritis. These measures are sensitive and reproducible for different types of joint pain.

Pain is the main cause of disability from arthritis. There is currently an unmet need for adequate treatments for arthritis pain. Pre-clinical models are ...

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8.3K Views.  University of Minnesota. We have developed an evoked measure of arthritis pain and coupled it with a standardized method for measuring spontaneous pain in different murine models of chemically induced arthritis. These measures are sensitive and reproducible for different types of joint pain.

Video: Spontaneous and Evoked Measures of Pain in Murine Models of Monoarticular Knee Pain

Assessment of Cardiac Function and Energetics in Isolated Mouse Hearts Using 31P NMR Spectroscopy

Bioengineered mouse models have become powerful research tools in determining causal relationships between molecular alterations and models of cardiovascular disease. Although molecular biology is necessary in identifying key changes in the signaling pathway, it is not a surrogate for functional significance. While physiology can provide answers to the question of function, combining physiology with biochemical assessment of metabolites in the intact, beating heart allows for a complete picture of cardiac function and energetics. For years, our laboratory has utilized isolated heart perfusions combined with nuclear magnetic resonance (NMR) spectroscopy to accomplish this task. Left ventricular function is assessed by Langendorff-mode isolated heart perfusions while cardiac energetics is measured by performing 31P magnetic resonance spectroscopy of the perfused hearts. With these techniques, indices of cardiac function in combination with levels of phosphocreatine and ATP can be measured simultaneously in beating hearts. Furthermore, these parameters can be monitored while physiologic or pathologic stressors are instituted. For example, ischemia/reperfusion or high workload challenge protocols can be adopted. The use of aortic banding or other models of cardiac pathology are apt as well. Regardless of the variants within the protocol, the functional and energetic significance of molecular modifications of transgenic mouse models can be adequately described, leading to new insights into the associated enzymatic and metabolic pathways. Therefore, 31P NMR spectroscopy in the isolated perfused heart is a valuable research technique in animal models of cardiovascular disease.

Assessment of Cardiac Function and Energetics in Isolated Mouse Hearts Using 31P NMR Spectroscopy

Langendorff-mode isolated heart perfusion, in conjunction with 31P NMR spectroscopy, combines the fields of biochemistry and physiology into one experiment. The protocol allows for the dynamic measurement of high energy phosphate content and turnover in the heart while concurrently monitoring physiologic function. When performed correctly, this is a valuable technique in the assessment of cardiac energetics.

Bioengineered mouse models have become powerful research tools in determining causal relationships between molecular alterations and models of ...

Chronic Constriction of the Sciatic Nerve and Pain Hypersensitivity Testing in Rats

Chronic neuropathic pain, resulting from damage to the central or peripheral nervous system, is a prevalent and debilitating condition, affecting 7-18% of the population1,2. Symptoms include spontaneous (tingling, burning, electric-shock like) pain, dysaesthesia, paraesthesia, allodynia (pain resulting from normally non-painful stimuli) and hyperalgesia (an increased response to painful stimuli). The sensory symptoms are co-morbid with behavioural disabilities, such as insomnia and depression. To study chronic neuropathic pain several animal models mimicking peripheral nerve injury have been developed, one of the most widely used is Bennett and Xie's (1988) unilateral sciatic nerve chronic constriction injury (CCI)3 (Figure 1). Here we present a method for performing CCI and testing pain hypersensitivity.
CCI is performed under anaesthesia, with the sciatic nerve on one side exposed by making a skin incision, and cutting through the connective tissue between the gluteus superficialis and biceps femoris muscles. Four chromic gut ligatures are tied loosely around the sciatic nerve at 1 mm intervals, to just occlude but not arrest epineural blood flow. The wound is closed with sutures in the muscle and staples in the skin. The animal is then allowed to recover from surgery for 24 hrs before pain hypersensitivity testing begins.
For behavioural testing, rats are placed into the testing apparatus and are allowed to habituate to the testing procedure. The area tested is the mid-plantar surface of the hindpaw (Figure 2), which falls within the sciatic nerve distribution. Mechanical withdrawal threshold is assessed by mechanically stimulating both injured and uninjured hindpaws using an electronic dynamic plantar von Frey aesthesiometer or manual von Frey hairs4. The mechanical withdrawal threshold is the maximum pressure exerted (in grams) that triggers paw withdrawal. For measurement of thermal withdrawal latency, first described by Hargreaves et al (1988), the hindpaw is exposed to a beam of radiant heat through a transparent glass surface using a plantar analgesia meter5,6. The withdrawal latency to the heat stimulus is recorded as the time for paw withdrawal in both injured and uninjured hindpaws. Following CCI, mechanical withdrawal threshold, as well as thermal withdrawal latency in the injured paw are both significantly reduced, compared to baseline measurements and the uninjured paw (Figure 3). The CCI model of peripheral nerve injury combined with pain hypersensitivity testing provides a model system to investigate the effectiveness of potential therapeutic agents to modify chronic neuropathic pain. In our laboratory, we utilise CCI alongside thermal and mechanical sensitivity of the hindpaws to investigate the role of neuro-immune interactions in the pathogenesis and treatment of neuropathic pain.

Due to the simplicity of surgery and the robust behavioural outcome, chronic constriction of the sciatic nerve is one of the pre-eminent animal models of neuropathic pain. Within 24 hrs following surgery, pain hypersensitivity is established and can be quantitatively measured using a von Frey aesthesiometer (mechanical test) and plantar analgesia meter (thermal test).

Chronic neuropathic pain, resulting from damage to the central or peripheral nervous system, is a prevalent and debilitating condition, affecting 7-18% of ...

Urinary Bladder Distention Evoked Visceromotor Responses as a Model for Bladder Pain in Mice

Approximately 3-8 million people in the United States suffer from interstitial cystitis/bladder pain syndrome (IC/BPS), a debilitating condition characterized by increased urgency and frequency of urination, as well as nocturia and general pelvic pain, especially upon bladder filling or voiding. Despite years of research, the cause of IC/BPS remains elusive and treatment strategies are unable to provide complete relief to patients. In order to study nervous system contributions to the condition, many animal models have been developed to mimic the pain and symptoms associated with IC/BPS. One such murine model is urinary bladder distension (UBD). In this model, compressed air of a specific pressure is delivered to the bladder of a lightly anesthetized animal over a set period of time. Throughout the procedure, wires in the superior oblique abdominal muscles record electrical activity from the muscle. This activity is known as the visceromotor response (VMR) and is a reliable and reproducible measure of nociception. Here, we describe the steps necessary to perform this technique in mice including surgical manipulations, physiological recording, and data analysis. With the use of this model, the coordination between primary sensory neurons, spinal cord secondary afferents, and higher central nervous system areas involved in bladder pain can be unraveled. This basic science knowledge can then be clinically translated to treat patients suffering from IC/BPS.

Approximately 3-8 million people in the United States suffer from interstitial cystitis/bladder pain syndrome (IC/BPS), a debilitating condition characterized in part by pelvic pain. In order to study nervous system contributions to the condition, a physiological model of urinary bladder pain is used in mice and rats.

Approximately 3-8 million people in the United States suffer from interstitial cystitis/bladder pain syndrome (IC/BPS), a debilitating condition ...

The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice

Neuropathic pain arises as a consequence of a lesion or a disease affecting the somatosensory system. This syndrome results from maladaptive changes in injured sensory neurons and along the entire nociceptive pathway within the central nervous system. It is usually chronic and challenging to treat. In order to study neuropathic pain and its treatments, different models have been developed in rodents. These models derive from known etiologies, thus reproducing peripheral nerve injuries, central injuries, and metabolic-, infectious- or chemotherapy-related neuropathies. Murine models of peripheral nerve injury often target the sciatic nerve which is easy to access and allows nociceptive tests on the hind paw. These models rely on a compression and/or a section. Here, the detailed surgery procedure for the &#34;cuff model&#34; of neuropathic pain in mice is described. In this model, a cuff of PE-20 polyethylene tubing of standardized length (2 mm) is unilaterally implanted around the main branch of the sciatic nerve. It induces a long-lasting mechanical allodynia, i.e., a nociceptive response to a normally non-nociceptive stimulus that can be evaluated by using von Frey filaments. Besides the detailed surgery and testing procedures, the interest of this model for the study of neuropathic pain mechanism, for the study of neuropathic pain sensory and anxiodepressive aspects, and for the study of neuropathic pain treatments are also discussed.

Neuropathic pain is a consequence of a lesion or disease affecting the somatosensory system. The &#8220;cuff model&#8221; of neuropathic pain in mice consists of the implantation of a polyethylene cuff around the main branch of the sciatic nerve. Mechanical allodynia is tested using von Frey filaments.

Neuropathic pain arises as a consequence of a lesion or a disease affecting the somatosensory system. This syndrome results from maladaptive changes in ...

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.

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.

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

Chronic Constriction Injury of the Rat's Infraorbital Nerve (IoN-CCI) to Study Trigeminal Neuropathic Pain

Animal models are important tools to study the pathophysiology and pharmacology of neuropathic pain. This manuscript describes the surgical and behavioral procedures to study trigeminal neuropathic pain in rats. To meet the specificity of trigeminal neuropathic pain syndromes, the infraorbital nerve (IoN) is subjected to a chronic constriction injury (CCI) by loosely ligating the nerve. An intra-orbital approach is presented here to expose and ligate the IoN in the orbital cavity. After IoN ligation, rats exhibit changes in spontaneous behavior and in response to von Frey hair stimulation that are indicative of persistent pain and mechanical allodynia. Two phases can be defined in the development of the behavioral changes. During the first week following IoN-CCI (phase 1), rats show an increased and asymmetric face grooming activity, i.e., with face wash strokes primarily directed to the nerve-injured IoN territory. A distinction is made between face grooming behavior that is part of a more general body grooming behavior, which remains largely unaffected by IoN-CCI, and face grooming that is neither preceded nor followed by body grooming, which is significantly increased after IoN-CCI. During this period, responsiveness to mechanical stimulation of the IoN territory is reduced. This hyporesponsiveness is abruptly replaced by an extreme hyperresponsiveness whereby even very weak stimulus intensities provoke nocifensive behavior (phase 2). The phenomenological similarities between these behavioral alterations and reported signs of facial pain (i.e., responses to noxious stimulation of the face) suggest the presence of dysesthesia/paresthesia and mechanical allodynia in the ligated IoN territory.

Chronic Constriction Injury of the Rat's Infraorbital Nerve IoN-CCI to Study Trigeminal Neuropathic Pain

This manuscript describes a rodent model to study trigeminal neuropathic pain. The methods described include surgical procedures to perform a chronic constriction injury of the rat&#8217;s infraorbital nerve and the post-surgical behavioral tests to measure the changes in spontaneous and evoked behavior that are indicative of persistent pain and allodynia.

Animal models are important tools to study the pathophysiology and pharmacology of neuropathic pain. This manuscript describes the surgical and behavioral ...

The Monoiodoacetate Model of Osteoarthritis Pain in the Mouse

A major symptom of patients with osteoarthritis (OA) is pain that&#160;is triggered by peripheral as well as central changes within the pain pathways. The current treatments for OA pain such as NSAIDS or opiates are neither sufficiently effective nor devoid of detrimental side effects. Animal models of OA are being developed to improve our understanding of OA-related pain mechanisms and define novel pharmacological targets for therapy. Currently available models of OA in rodents include surgical and chemical interventions into one knee joint. The monoiodoacetate (MIA) model has become a standard for modelling joint disruption in OA in both rats and mice. The model, which is easier to perform in the rat, involves injection of MIA into a knee joint that induces rapid pain-like responses in the ipsilateral limb, the level of which can be controlled by injection of different doses. Intra-articular injection of MIA disrupts chondrocyte glycolysis by inhibiting glyceraldehyde-3-phosphatase dehydrogenase and results in chondrocyte death, neovascularization, subchondral bone necrosis and collapse, as well as inflammation. The morphological changes of the articular cartilage and bone disruption are reflective of some aspects of patient pathology. Along with joint damage, MIA injection induces referred mechanical sensitivity in the ipsilateral hind paw and weight bearing deficits that are measurable and quantifiable. These behavioral changes resemble some of the symptoms reported by the patient population, thereby validating the MIA injection in the knee as a useful and relevant pre-clinical model of OA pain.
The aim of this article is to describe the methodology of intra-articular injections of MIA and the behavioral recordings of the associated development of hypersensitivity with a mind to highlight the necessary steps to give consistent and reliable recordings.

Osteoarthritis (OA), or degenerative joint disease, is a debilitating condition associated with pain that remains only partially controlled by available analgesics. Animal models are being developed to improve our understanding of OA-related pain mechanisms. Here we describe the methodology for the monoiodoacetate model of OA pain in the mouse.

A major symptom of patients with osteoarthritis (OA) is pain that&#160;is triggered by peripheral as well as central changes within the pain pathways. The ...

Subcutaneous Trigeminal Nerve Field Stimulation for Refractory Facial Pain

Chronic or neuropathic trigeminal facial pain can be challenging to treat. Neurosurgical procedures should be applied when conservative treatment fails. Neuromodulation techniques for chronic facial pain include deep brain stimulation and motor cortex stimulation, which are complex to perform. Subcutaneous nerve field stimulation is certified for chronic back pain and is the least invasive form of neuromodulation. We applied this technique to treat chronic and neuropathic trigeminal pain as an individual therapy concept. First, trial stimulation is performed. Subcutaneous leads are placed in the painful trigeminal dermatome under local anesthesia. The leads are connected to an external neurostimulator that applies constant stimulation. Patients undergo a 12 day outpatient trial to assess the effect of the stimulation. Electrodes are removed after the trial. If the patient reports pain reduction of at least 50% in intensity and/or attack frequency, a reduction in medication or increase in quality of life, permanent implantation is scheduled. New electrodes are implanted under general anesthesia and are subcutaneously tunneled to an infraclavicular internal pulse generator. Patients are able to turn stimulation on and off and to increase or decrease the stimulation amplitude as needed.
This technique represents a minimal invasive alternative to other more invasive means of neuromodulation for trigeminal pain such as motor cortex stimulation or deep brain stimulation.

Treating chronic or neuropathic facial pain can be challenging when medical or standard treatment fails. Subcutaneous nerve field stimulation is the least invasive form of neuromodulation and is used for chronic back pain. We applied this technology to treat chronic and neuropathic trigeminal facial pain.

Chronic or neuropathic trigeminal facial pain can be challenging to treat. Neurosurgical procedures should be applied when conservative treatment fails. ...

Reproducible Motor Deficit Following Aortic Occlusion in a Rat Model Of Spinal Cord Ischemia

Spinal cord ischemia is a fatal complication following thoracoabdominal aortic aneurysm surgery. Researchers can investigate the strategies for preventing and treating this complication using experimental models of spinal cord ischemia. The model described here demonstrates varying degrees of paraplegia that relate to the length of occlusion following thoracic aortic occlusion in a rat spinal cord ischemia model.
A 2-Fr. balloon-tipped catheter was advanced through the femoral artery into the descending thoracic aorta until the catheter tip was placed at the left subclavian artery in anesthetized male Sprague-Dawley rats. Spinal cord ischemia was induced by inflating the catheter balloon. After a set period of occlusion (9, 10, or 11 min), the balloon was deflated. Neurologic assessment was performed using the motor deficit index at 24 h after surgery, and the spinal cord was harvested for histopathological examination.
Rats that underwent 9 min of aortic occlusion showed mild and reversible motor impairment in the hind limb. Rats subjected to 10 min of aortic occlusion presented with moderate but reversible motor impairment. Rats subjected to 11 min of aortic occlusion displayed complete and persistent paralysis. The motor neurons in the spinal cord sections were more preserved in rats subjected to shorter duration of aortic occlusion.
Researchers can achieve a reproducible hind limb motor deficit following thoracic aortic occlusion using this spinal cord ischemia model.

This study demonstrates the technique to make a minimally invasive and easily reproducible model of spinal cord ischemia in rats. Various degrees of hind limb motor deficit can be produced by controlling the aortic occlusion time.

Spinal cord ischemia is a fatal complication following thoracoabdominal aortic aneurysm surgery. Researchers can investigate the strategies for preventing ...

A Quantitative Sensory Testing Paradigm to Obtain Measures of Pain Processing in Patients Undergoing Breast Cancer Surgery

Chronic pain following surgery, persistent postsurgical pain, is an important highly prevalent condition contributing to significant symptom burden and lower quality of life. Persistent postsurgical pain is relatively refractory to treatment hence generating a high need for preventive strategies and treatments. Therefore, the identification of patients at risk of developing persistent pain is an area of active ongoing research. Recently it was demonstrated that peri-operative disruptions in central pain processing may be able to predict persistent postsurgical pain at long term follow-up in breast cancer patients. The aim of the current report is to present a short protocol to obtain pain thresholds to different stimuli at multiple sites and a measure of endogenous analgesia in breast cancer patients. We have used this method successfully in a clinical context and detail some representative results from a clinical study.

Persistent postsurgical pain may be related to changes in pain processing. By assessing pain in response to standardized stimuli, changes in pain processing can be elucidated. We present methods to obtain pain thresholds to different stimuli and a measure of endogenous analgesia in patients undergoing breast cancer surgery.

Chronic pain following surgery, persistent postsurgical pain, is an important highly prevalent condition contributing to significant symptom burden and ...

Spontaneous and Evoked Measures of Pain in Murine Models of Monoarticular Knee Pain

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Assessment of Cardiac Function and Energetics in Isolated Mouse Hearts Using ³¹P NMR Spectroscopy

Chronic Constriction of the Sciatic Nerve and Pain Hypersensitivity Testing in Rats

Urinary Bladder Distention Evoked Visceromotor Responses as a Model for Bladder Pain in Mice

The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice

In vitro Functional Characterization of Mouse Colorectal Afferent Endings

Chronic Constriction Injury of the Rat's Infraorbital Nerve (IoN-CCI) to Study Trigeminal Neuropathic Pain

The Monoiodoacetate Model of Osteoarthritis Pain in the Mouse

Subcutaneous Trigeminal Nerve Field Stimulation for Refractory Facial Pain

Reproducible Motor Deficit Following Aortic Occlusion in a Rat Model Of Spinal Cord Ischemia

A Quantitative Sensory Testing Paradigm to Obtain Measures of Pain Processing in Patients Undergoing Breast Cancer Surgery