We thank Dr. J-L. Galzi (UMR7242 CNRS; Illkirch, France) for his support. 
This work was supported by the CNRS, INSERM, Universit&#233; de Strasbourg, Alsace BioValley and by grants from Conectus, Agence National de la Recherche (ANR 08 EBIO 014.02) Conseil R&#233;gional d&#8217;Alsace (Pharmadol), Communaut&#233; Urbaine de Strasbourg (Pharmadol), ICFRC (Pharmadol), OSEO (Pharmadol), Direction G&#233;n&#233;rale des Entreprises (Pharmadol).

All experiments were carried out in strict accordance with the European guidelines for the care of laboratory animals (European Communities Council Directive 86/609/ECC) and the ethical guidelines for investigation of experimental pain in conscious animals13. Male C57BL6/N Tac mice (10 weeks, 25 - 30 g) were housed in an institutional animal facility with a care staff in charge of operating the facility in compliance with environmental standards. Animals were housed in groups (maximum five mice per cage) under a 12 hr / 12 hr light / dark cycle at a constant temperature (21 &#177; 1 &#176;C) with free access to food and water. All experiments were performed at the same period of the day (10:00 am to 4:00 pm) using a cohort of 16 mice. Specific materials and equipment are indicated in the Materials table.
A five-step procedure to monitor morphine induced-hyperalgesia and tolerance
The protocol is divided into five sequential steps (A-E) over a duration of 15 days Figure 1.
1. Mice Handling (Step A; d-7 to d-5)
<ol>
	<li>Handle mice and habituate them to freely enter into the restrainer. This preliminary step reduces stress - thus minimizing any confusion with stress-induced analgesia - and allows the animals to be accustomed to the investigator, handling and manipulation into the mouse restrainer. Each mouse is gently handled for 5 min every day.</li>
</ol>
2. Basal Nociceptive Response (Step B; d-4 to d-1)
<ol>
	<li>Measure tail withdrawal latencies using the Tail Immersion Test (TIT):
	<ol>
		<li>Set the thermostat to 48 &#176;C.</li>
		<li>Gently introduce the mouse into the restrainer. Dip the protruding 2/3 end of its tail into the water bath and start the chronometer.</li>
		<li>Stop the chronometer as soon as the mouse withdraws its tail from the hot water and record the latency time (in sec). In the absence of any nociceptive reaction, a 25 sec cut-off is used to prevent tissue damage.</li>
		<li>Replace the mouse in its cage and test the next one until the end of the series.</li>
		<li>Repeat the nociceptive response measurements two more times, taking measurements from the animals in the same order. The nociceptive response latency (sec) for each mouse is determined as the mean value for three successive determinations.</li>
	</ol>
	</li>
	<li>Measure mechanical responses using the Tail Pressure Test (TPT)
	<ol>
		<li>Gently introduce the mouse into the restrainer and position its tail under the conic tip of the analgesimeter.</li>
		<li>Press the foot-switch to apply uniformly increasing pressure onto the proximal part of the tail until the first nociceptive reaction (struggling, squeaking) occurs. At the moment the animal reacts, record the current force (in grams) that elicits the nociceptive response. In the absence of any reaction, a 600 g cut-off value is used to avoid tissue damage.</li>
		<li>Repeat this measure on the median and distal parts of the tail of the same mouse. An interval of at least 30 sec is observed between measures on a given mouse to avoid adaptation or stress bias. Replace the mouse in its cage and test the next animal until the end of the series (i.e. all mice are tested). The nociceptive value (grams) for each mouse is taken as the mean value for three measurements (i.e. proximal, median and distal parts of the tail of each animal).</li>
	</ol>
	</li>
	<li>Repeat nociceptive testing (all the procedures outlined under step 2) on subsequent days, d-3 to d-1.</li>
</ol>
3. Measurement of Morphine Analgesia (Step C; d0)
<ol>
	<li>Define the best combination of animals that allows the selection of two groups (n=8 per group) of mice with stable and comparable average nociceptive values, whichever nociceptive modality (TIT or TPT) is considered. This value will be taken as the basal nociceptive response of reference for future &#8216;Saline&#8217; and &#8216;Morphine&#8217; groups.</li>
	<li>Measure the body weight of each animal.</li>
	<li>Prepare a morphine solution (0.5 mg morphine per ml) in sterile physiological saline (NaCl 0.9%) for subcutaneous administration (5 mg morphine per kg of animal&#8217;s body weight).</li>
	<li>Measure the nociceptive response latency (taken as time point 0) for each mouse of both &#8216;Saline&#8217; and &#8216;Morphine&#8217; groups in the TIT (all steps under 2.1 above). Then measure nociception in the TPT (all steps under 2.2 above).</li>
	<li>Inject subcutaneously morphine (typically 0.25 ml of a 0.5 mg/ml morphine solution per 25 g mouse weight) and saline (0.25 ml per 25 g mouse weight) to the &#8216;morphine&#8217; and &#8216;saline&#8217; groups, respectively.</li>
	<li>Measure nociceptive values on the TIT and TPT (all procedures outlined above under steps 2.1 and 2.2, respectively) over a time-course (at 30 min interval) to assess morphine (5 mg/kg)-induced analgesia:
	<ol>
		<li>After 30 min post-injection, measure the nociceptive response (single determination) for each mouse of the &#8216;Saline&#8217; and &#8216;Morphine&#8217; groups, using the TIT then the TPT.</li>
		<li>Then measure nociceptive response values (TIT and TPT) in all mice at time points (in hr): 1-1.5-2-2.5-3 and 3.5 post-injection.</li>
	</ol>
	</li>
</ol>
4. Chronic Morphine Treatment - Morphine-induced Hyperalgesia (Step D; d1 to d6)
<ol>
	<li>On Day: d1
	<ol>
		<li>Measure nociceptive response values on the TIT and TPT as described above (steps 2.1 and 2.2). Carefully annotate withdrawal latencies and pressure limits for each animal.</li>
		<li>Prepare a fresh morphine solution as detailed in step 3.2.</li>
		<li>Inject subcutaneously morphine (5 mg/kg b.w.) to the entire &#8216;Morphine&#8217; group and physiological saline (0.25 ml per 25 g mouse weight) to the &#8216;Saline&#8217; group. Let the animals rest until the next day.</li>
	</ol>
	</li>
	<li>On Days: d2, d3, d4, d5 and d6 repeat the operations described under Section 4.1</li>
</ol>
5. Evidence for Analgesic Tolerance (Step E; d7)
<ol>
	<li>Evaluate morphine-induced analgesia according to the time-course paradigm already detailed in Section 3.</li>
</ol>
6. Data Acquisition and Statistical Analyses
<ol>
	<li>Assessment of Basal Nociceptive Response Values (Step B)
	<ol>
		<li>Calculate for each day (over the d-4 to d-1 period) the mean &#177; SEM values (n=8) for basal nociceptive responses as afforded from TIT and TPT within the &#8216;Saline&#8217; and &#8216;Morphine&#8217; groups.</li>
		<li>Plot mean basal nociceptive values as a function of time (day) for both groups Figure 2.</li>
	</ol>
	</li>
	<li>Analysis of Morphine Analgesia Time-course at Days d0 (Step C) and d7 (Step E)
	<ol>
		<li>Calculate, at each time point after morphine injection, the mean &#177; SEM values (n=8) for nociceptive responses as afforded from TIT (in sec) and TPT (in g) in each group.</li>
		<li>Plot mean nociceptive response values as a function of time for the &#8216;Saline&#8217; and &#8216;Morphine&#8217; groups at day 0 Figure 3 and day 7 Figure 5.</li>
	</ol>
	</li>
	<li>Development of Morphine-induced Hyperalgesia (Step D)
	<ol>
		<li>Calculate for each day (over the d0-d7 treatment period) the mean &#177; SEM values (n=8) for basal nociceptive response values as afforded from TIT and TPT within the &#8216;Saline-treated&#8217; and &#8216;Morphine-treated&#8217; groups.</li>
		<li>Plot mean basal nociceptive response values as a function of time (day) for the &#8216;Saline-treated&#8217; and &#8216;Morphine-treated&#8217; groups Figure 4.</li>
	</ol>
	</li>
	<li>Evidence for Analgesic Tolerance (Steps C and E)
	<ol>
		<li>Determine from the morphine time-course experiment performed at d0 Figure 3 the time value (or time range) required for morphine to induce a maximal analgesic response.</li>
		<li>Take this value (usually 30 min) as the reference time to estimate at d7 Figure 5 the nociception baseline value (saline-treated group) and the actual analgesic response (morphine-treated group) to acute morphine.</li>
		<li>Nociceptive values taken at time point 30 min from morphine time-course experiments performed at d0 and d7 for the saline-treated and morphine-treated groups, are presented as histograms Figure 6.</li>
		<li>Statistics: Analyze data using one-way repeated measures ANOVA. The factors of variation were treatment (between subjects) and time (within subject). To check differences separately in each group, repeated measures ANOVA was performed. Comparisons between two groups were performed using unpaired t-test or paired t-test when appropriate.</li>
	</ol>
	</li>
	<li>The Level of Significance is Set at P&#60;0.05. All Statistical Analyses are Carried out using the STATview Software.</li>
</ol>

The authors declare that they have no competing financial interests.

Critical Steps
Choice of the animal model for nociception measurements
Variability in nociceptive and analgesic sensitivity among mice strains has been examined (reviews&#160;14-16)&#160;reviews using various pain models differing in their etiology (nociceptive, inflammatory, neuropathic), modality (thermal, chemical, mechanical), duration (acute, tonic, chronic) and site of administration (cutaneous, subcutaneous, visceral). When compared to other strains, C57BL/6J (&#8220;J&#8221; for Jackson Laboratory) mice became a popular animal model for pain studies as they exhibit a high basal nociceptive sensitivity17,18 and a moderate analgesic response to opiates14,19. Following chronic morphine treatment, they also develop significant analgesic tolerance20,21, hyperalgesia21,22 and dependence20,23.
Here, experiments were performed on C57BL/6N Tac mice (&#8220;N&#8221; for National Institute of Health and &#8220;Tac&#8217; for Taconics farm) which belong to a separate branch of the B6 lineage. Although C57BL/6 mice have been long considered as interchangeable, recent studies pointed to significant behavioral differences among C57BL/6J and C57BL/6N strains24. In particular, the lower sensitivity of the three C57BL/6N substrains (including the Tac one) to acute thermal pain may be regarded as an advantage for testing this phenotype.
Male mice were selected as the vast majority of pain studies, using mice as the animal model, are performed on juvenile males25. In our hands, they provided robust and reproducible data when examined from the analgesia or hyperalgesia points of view. Occasionally, we noticed a tendency for C57BL/6N females to provide more variable responses, both in the TIT and TPT tests. Although this observation may reflect natural variations linked to the hormonal status of females, overall mechanisms underlying sex differences in pain and analgesia still remain a matter of controversy. Some aspects of this hot debate will be briefly presented in the next &#8216;Limitations of the technique&#8217; section.
Animal habituation
Mice were first allowed to get accustomed to the animal facility during one week. Similar to any other behavioral study, testing was performed following a 3 day-acclimatization period (Figure 1, step A). As nociceptive tests are sensitive to stress, first measures may give longer latencies than subsequent ones, especially in non-habituated mice26,27. The habituation step allows also the obtention of more stable nociceptive response values within the same day and between days Figures 2 and&#160;4. To reduce circadian effects on nociceptive and analgesic sensitivity28,29, all testings were conducted between 10:00 am and 4:00 pm.
Selection of nociceptive tests
Nociceptive tests use either thermal, mechanical, chemical or electrical stimuli (review&#160;26,27,30. Their choice is critical as different nociceptive modalities may be processed through different nociceptors and fibers18,31,32.
We selected the tail immersion test (TIT)33, a modified version of the classical tail flick test developed by D&#8217;amour and Smith34, and the tail pressure test (TPT), adapted from Randall and Selitto35, as examples of thermal and mechanical modalities to study morphine-induced analgesia, hyperalgesia and tolerance in mice. Both tests have been widely used in rats. A cut off time was systematically defined to avoid or limit the risk of tissue damage.
Morphine-induced analgesia, hyperalgesia and tolerance
Morphine, the prototypical mu-opiate agonist, was selected here as it is a potent analgesic and OIH-inducer, both in humans and mice1,2,36. Morphine analgesic potency is known to vary with mice strains, routes of administration and nociceptive modalities. In C57BL/6 mice, reliable analgesia is usually obtained following subcutaneous injections of morphine in the 1-20 mg/kg dose range14,21. Accordingly, we chose to study acute analgesia following a single administration (s.c.) of morphine at 5 mg/kg, close to its ED50 value (7-20 mg/kg) assessed from thermal nociception19,21.
Repeated morphine administration is often accompanied with analgesic tolerance (evidenced either from a rightward shift of the dose-response curve or from a decrease in analgesic response amplitude or duration) and hyperalgesia (an exacerbated sensitivity to painful stimuli evidenced from a decrease in basal nociceptive value). Both adverse phenomena depend on rodent strains, on the nature of the opiate compound which is selected and its dosage, on treatment duration and on nociceptive modalities21. For example, experimental paradigms to study tolerance and hyperalgesia consist in daily administration of high and constant (20 to 40 mg/kg per day)22 or of escalating (up to 50 or even 200 mg/kg)20,21 morphine doses. Accordingly, we promoted the development of hyperalgesia and tolerance in C57BL/6 mice through daily morphine administration (5 mg/kg; s.c.) over a 8-day period. This moderate morphine dose was preferred over higher ones to better mimic clinic usage.
Set up of TIT operational window
A possible pitfall in TIT might be related to the role of the tail in the thermoregulation of rodents26,37. As ambient temperature is a key factor in nociceptive response variations, it should be kept constant (here at 21 &#176;C) throughout experiments38. Heat intensity is usually set up to detect a nociceptive response within 5 to 10 sec27. Indeed, greater latencies may increase the risk for monitoring animal movements unrelated to the nociceptive stimulus, whereas shorter ones may reduce the differential power of the test. We performed TIT measurements at a fixed temperature of 48 &#176;C. Tail withdrawal latencies were close to 9 sec (basal nociceptive value) and varied from 4 sec (hyperalgesia) to 25 sec (maximal analgesia; cut off). In addition to practical reasons, measurements of nociceptive response values at a fixed temperature may a priori involve the same repertoire of nociceptors and circuits, thereby facilitating data interpretation.
Possible Modifications 
Optimization of the TIT operational window for analgesia and OIH measurements
When focusing on an analgesic response, low baseline values (higher heat intensity) may favor the detection of a delay in the response. In turn, to address the consequence of a painful stimulus or the development of OIH, higher baseline values (lower heat intensity; here 48 &#176;C) may facilitate the detection of faster responses Figure 4.
Although we found morphine at 5 mg/kg a convenient dose to induce a robust analgesic response Figure 3&#160;and to promote (upon repeated administration) significant hyperalgesia Figure 4, its dosage may be adapted as mentioned before (Critical step : Morphine-induced analgesia, hyperalgesia and tolerance). For example, lower doses may be used to reduce analgesia amplitude (thereby avoiding cut-off limitations) whereas higher doses may be chosen to accelerate hyperalgesia onset and increase its amplitude.
Overall, optimization of the &#8216;nociceptive window&#8217; should be adapted to the genetic background of mice under study and take into account the possibility for the involvement of distinct arrays of nociceptors and circuits.
Alternative opiate agonists (fentanyl, remifentanyl)
Although most clinically used opiates target the mu-opioid receptor as agonists, they differ considerably with respect to their pharmacological properties both in vitro and in vivo. For example, remifentanyl and fentanyl, in marked contrast with morphine, behave as full agonists and promote internalization of mu-opioid receptors39. Opiate analgesics such as morphine and fentanyl have half-lives in the range of hours40, while remifentanyl has an ultra-short half life of several minutes41. In humans, best evidence for OIH is from patients who received opiates during surgery, including short-acting compounds such as remifentanyl2,42. Thus, fentanyl and remifentanyl may be valuable tools too to study the development of hyperalgesia and tolerance in mice, under TIT and TPT paradigms.
Alternative modes of induction of OIH (chronic vs acute administration)
OIH is seen in humans and animal models as a consequence of opiate administration, whether at very low or extremely high dosages1,2. We report here on OIH development following chronic treatment of mice with moderate doses of morphine. Several days of treatment of C57BL/6N mice were necessary to evidence a clear and reproducible hyperalgesic state Figure 4. Daily morphine injections could be adequately replaced with implanted morphine pellets : upon their removal, both thermal hyperalgesia and mechanical allodynia have been already reported in mice43. Infusion of opiates through a micro-osmotic pump is another possibility44. In rodents, long-lasting hyperalgesia is also achievable following acute administration of fentanyl using a protocol mimicking the use of this mu-opioid agonist in human surgery36,45,46.
Limitations of the Technique
Animal species and models for pain
Comparative studies of numerous mouse strains provided evidence for great variations in nociceptive responses to painful stimuli17,31,47 and in OIH levels following 4-days morphine treatment22. Whether mechanisms underlying pain processing and modulation in animal models (mice and rats) are relevant for chronic pain patients remains a fundamental and opened question. Thus, much caution should be paid to the interpretation of animal data and to their predictive validity for humans16.
Sex differences in pain and analgesia
Most preclinical studies on animal models for pain have been conducted on male rodents16,25,48. Despite this selection bias, the emerging view was to consider males as better responders to opiate analgesics49,50, less prone to develop opioid-induced hyperalgesia 51,52 and more tolerant to morphine analgesia53 than their female counterparts (review&#160;54). However, sex differences with regard to nociception and analgesic drugs efficacy do not resume in such &#8216;a one size fits all&#8217; paradigm. Indeed, a wealth of data now indicates that numerous variables may influence the magnitude and direction of sex differences such as opioid drug efficacy and selectivity, nociceptive assay, genetic background, age, gonado-hormonal status or social interaction48,54. In humans, clinical pain is more prevalent in women but whether this fact reflects actual sex differences remains a matter of debate48,55,56. For example, global analysis of fifty clinical trials indicated no significant differences in analgesic properties between genders whereas meta-analyses performed on patients-controlled subjects pointed to a significantly greater opioid efficacy in women57.The latter observation, which markedly contrasts with what has been found in rodents, again raises several questions regarding the origin for such divergences16,48,55,57. Altogether, sex differences in analgesia do exist and merit further focus on underlying mechanisms and clinical implications.
About nociceptive tests
The tail withdrawal test is a spinal reflex but it may be subject to supraspinal influences58. TIT is relatively easy to perform on rats but requires more expertise in mice. A potential difficulty is to maintain the mouse in a correct posture without inducing unwanted stress. The proposed protocol may be adjusted according to cohort size. 16 animals (8 control and 8 treated) are easily managed as far as measurement of their basal nociceptive response values (using TIT first, then TPT for the whole series of mice) is under concern. Monitoring analgesia time courses requires the establishment of a precise time schedule and the evaluation of the maximal number of animals that may be tested (TIT first, then TPT) within the imparted time interval (here 30 min). The whole cohort of animals may thus be divided into subgroups to allow the experimenter to respect kinetic limitations.
Significance of the Technique with respect to Existing / Alternative Methods 
OIH in rats versus mouse
Rats have been extensively used to study opioid analgesia, hyperalgesia and tolerance, following acute or chronic opiate administration46,59-61. Indeed, for several practical reasons, they may be considered superior to mice as an animal model for pain experiments16,61. However, until recently, the generation of genetically modified rats was not a straightforward procedure. As numerous genetically modified mouse strains are already available, our model offers the opportunity to study the contribution of numerous individual genes in OIH and tolerance development in mice.
TIT and TPT versus other nociceptive tests
TIT is a variant of the tail flick test, the most obvious difference being the area of stimulation. In contrast with radiant heat, immersion of the tail into hot water leads to a quick and uniform increase in its temperature. Compared to other forms of thermal nociception testing (hot-plate or Hargreaves tests), TIT provides fairly reproducible results both across and within subjects.
TPT is a very popular test for the study of mechanical nociception26,27,35 which probably involves distinct nociceptive fibers and molecular transducers then TIT32. It provides quick and reliable measurements59 but requires some expertise from the experimenter and large animal cohorts. As an alternative to the analgesimeter used in the present study, other procedures or apparatus relying on strain gauges do exist (review&#160;27). TPT is best suited for studying mechanical hyperalgesia whereas von Frey filaments are usually taken to evaluate mechanical allodynia (review&#160;27).
Future Applications or Directions after Mastering this Technique
The experimental OIH/tolerance model we present here may be similarly adapted to genetically modified mice in order to evaluate the role of individual genes in the modulation of pain. It also provides a model system to investigate the effectiveness of potential therapeutic agents to relieve chronic pain.

Opioid-induced hyperalgesia (OIH) and analgesic tolerance limit the clinical efficacy of opiates in animals and humans1-3. The involvement of pro-inflammatory4,5 or of pro-nociceptive (anti-opioid)6,7 systems are currently explored hypotheses. The elucidation of the mechanisms underlying OIH and tolerance necessitates a combination of in vivo and in vitro approaches, using appropriate animal models, experimental protocols and molecular tools.
Behavioral pharmacology is the dominant paradigm to monitor and quantify analgesic and hyperalgesic states in laboratory animals (rats, mice). The application of a noxious stimulus (thermal, mechanical or chemical) to a convenient body part (hindpaw, tail) of the animal leads to a nocifensive withdrawal that can be easily scored.
We propose here a methodological approach for inducing, recording and quantifying OIH and tolerance in wild-type mice, using the tail-immersion and tail pressure tests. The procedure allows an easy, sensitive and reproducible determination of thermal and mechanical nociceptive response values in mice. As demonstrated in the video protocol, C57BL/6 mice experience significant hyperalgesia following chronic morphine administration and maintain this for several days. Both thermal and mechanical nociceptive values are significantly reduced, compared to baseline measurements on na&#239;ve animals. Moreover, our experimental set-up allows to monitor, in addition to the development of OIH, the decline of the analgesic response to morphine (tolerance). Presented data support the view that hyperalgesia and tolerance may involve common cellular and molecular mechanisms8,9, although this is disputed in the literature1,10-12. Finally, this protocol may be similarly adapted to genetically modified mice in order to evaluate the role of individual genes in the modulation of pain. It also provides a model system to evaluate the effectiveness of potential therapeutic agents to improve opiate analgesic effects.

<table><tbody><tr><td>C57BL/6N Tac mice</td><td>Taconic, Ry, Denmark</td><td>C57BL/6N Tac B6-M</td><td>Male mice (25-30 g)</td></tr><tr><td>Morphine hydrochloride</td><td>Francopia, Paris, France</td><td>CAS no. 52-26-6</td><td>Delivered with special authorization</td></tr><tr><td>Syringes (Terumo)</td><td>Dutscher, Brumath, France</td><td>050000</td><td>Polypropylene, sterile, volume: 1 ml</td></tr><tr><td>Needles (Terumo)</td><td>Dutscher, Brumath, France</td><td>050101</td><td>26 G &amp;frac12; (Terumo reference : NN2613RO1)</td></tr><tr><td>Mouse restrainer</td><td>Home-made</td><td></td><td>Two metallic grids (5 x 11 cm) assembled with adhesive tape and staples</td></tr><tr><td>Thermostated water bath GR150</td><td>Grant Instruments, Cambridge, UK</td><td>GP 0540003</td><td></td></tr><tr><td>Analgesimeter</td><td>Panlab, Barcelona, Spain</td><td>LE 7306</td><td></td></tr><tr><td>Kaleidagraph software</td><td>Synergy software, Reading, PA, USA</td><td>Kaleidagraph 4.03&amp;nbsp;</td><td>Scientific graphing</td></tr><tr><td>STATview software</td><td></td><td></td><td>Free download, statistics</td></tr></tbody></table>

assessment of morphine-induced hyperalgesia and analgesic tolerance in mice using thermal and mechanical nociceptive modalities

Opioid-induced hyperalgesia and tolerance severely impact the clinical efficacy of opiates as pain relievers in animals and humans. The molecular mechanisms underlying both phenomena are not well understood and their elucidation should benefit from the study of animal models and from the design of appropriate experimental protocols. 
We describe here a methodological approach for inducing, recording and quantifying morphine-induced hyperalgesia as well as for evidencing analgesic tolerance, using the tail-immersion and tail pressure tests in wild-type mice. As shown in the video, the protocol is divided into five sequential steps. Handling and habituation phases allow a safe determination of the basal nociceptive response of the animals. Chronic morphine administration induces significant hyperalgesia as shown by an increase in both thermal and mechanical sensitivity, whereas the comparison of analgesia time-courses after acute or repeated morphine treatment clearly indicates the development of tolerance manifested by a decline in analgesic response amplitude. This protocol may be similarly adapted to genetically modified mice in order to evaluate the role of individual genes in the modulation of nociception and morphine analgesia. It also provides a model system to investigate the effectiveness of potential therapeutic agents to improve opiate analgesic efficacy.

Assessment of Basal Nociceptive Values of Na&#239;ve Mice (Step B)
TIT and TPT were sequentially applied to the whole cohort of mice (n=16), providing mean nociceptive response values. Best combination of animals allowed an a posteriori definition of two groups (n=8) of mice, referred to as Saline and Morphine, which display similar and stable basal nociceptive values Figure 2. The equivalence of both groups is valid whatever the nociceptive test (TIT: Figure 2A; TPT : Figure 2B) that was selected.
Time-course for Morphine Analgesia at Day 0 (Step C)
Morphine analgesia was evaluated following a single injection (s.c.) of morphine (5 mg/kg) in na&#239;ve mice using both TIT Figure 3A and TPT Figure 3B. In both tests, statistical analyses with one way repeated measures ANOVA reveal that there is a significant interaction between treatment and time for TIT (F(7, 98) = 72, p&#60;0.001) and TPT (F(7, 98) = 31, p&#60;0.001). TIT and TPT data analyses using repeated measures ANOVA indicate that there is no effect of saline injection (F(7, 49) = 0.49, p&#62;0.05) and F(7, 49) = 1.85, p&#62;0.05 respectively for TIT and TPT tests), whereas morphine injection induces a strong analgesia in mice (F (7, 49) = 92.46, p&#60;0.001) and F(7, 49) =34.37, p&#60;0.001 respectively for TIT and TPT tests). The maximal analgesic effect of morphine was reached after 30 min in TIT and after 60 min in TPT as compared to saline-injected controls (p&#60;0.001, unpaired t-test).
Repeated Morphine Administrations Induces Hyperalgesia in Mice (Step D)
Basal nociceptive values were measured every day before saline or morphine administration (see protocol). As shown in Figure 4, once daily morphine administrations over a 6 days treatment period induced a significant and progressive lowering of thermal (F(7, 56) = 11.6, p&#60;0.001, repeated measures ANOVA; Figure 4A) and mechanical (F(7,56) = 15,55, p&#60;0.001, repeated measures ANOVA; Figure 4B) basal nociceptive values. Hyperalgesia developed rapidly as it started to be significant at day 1 in TIT (p&#60;0.01, unpaired t-test, compared to saline-injected controls) and at day 2 in TPT (p&#60;0.05, unpaired t-test, compared to saline-injected controls).
Time-course for Morphine Analgesia at Day 7, after Chronic Morphine Treatment (Step E)
On day 7, mice that received daily morphine or saline injections over a 7-day period (d0 to d6) were examined in TIT Figure 5A and TPT Figure 5B first for their basal nociceptive values and then for their analgesic response to acute morphine (5 mg/kg, sc.). In agreement with the development of hyperalgesia shown in Figure 4, the basal nociceptive value (time 0) of mice that were chronically treated with morphine was significantly lower than that of saline-injected control mice (p&#60;0.001, unpaired t-test). Following acute morphine, the nociceptive response of the chronic morphine-treated group significantly increased, but only slightly exceeded the basal nociceptive value of saline-injected control mice measured at 30 min in TIT and TPT (p&#60;0.01 and p&#60;0.05, unpaired t-test, respectively) and at 60 min in TIT (p&#60;0.05; unpaired t-test). From 2 hr after morphine treatment until the end of experiment, nociceptive responses returned to lower values than those of control mice (p&#60;0.001, unpaired t-test).
Comparison of Maximum Analgesic Responses of Mice to Morphine before (Day 0) and after Chronic Morphine Treatment (Day 7).
Nociceptive threshold values presented in Figure 6 are from TIT (A) and TPT (B) performed 30 min after saline or morphine injection as illustrated in Figures 3 (day 0) and 5 (day 7). A strong decrease in morphine analgesia was observed in mice after chronic morphine treatment for 7 days in comparison with their initial analgesia response at day 0 in both nociceptive tests (p&#60;0.001 paired t-test). These data demonstrate that tolerance did develop in pain hypersensitive animals.
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51264/51264fig1highres.jpg" width="500" /> 
Figure 1. A five-step procedure to monitor morphine induced-hyperalgesia and tolerance. The protocol is divided into five sequential steps (A-E) over a total duration of 15 days.
<img alt="Figure 2" fo:content-width="5in" src="/files/ftp_upload/51264/51264fig2highres.jpg" width="500" /> 
Figure 2. Definition of the basal nociceptive response values (Step B; d-4 to d-1). The tail immersion (TIT) (A) and tail pressure (TPT) (B) tests are applied to the whole series of animals in order to evaluate their basal nociceptive values. Thereafter, two groups of mice (n=8), referred to as &#8216;Saline&#8217; and &#8216;Morphine&#8217; groups, are defined so that they exhibit stable and comparable average nociceptive values, whatever the nociceptive modality that is considered.
<img alt="Figure 3" fo:content-width="5in" src="/files/ftp_upload/51264/51264fig3highres.jpg" width="500" /> 
Figure 3. Time-course for morphine analgesia at day 0 (Step C) in TIT (A) and TPT (B). The basal nociceptive response value of mice was determined every 30 min after single morphine (5 mg/kg, sc.) or saline injections. Data are expressed as means &#177; SEM, n=8 mice per group.*P &#60; 0.05, **P &#60; 0.01, ***P &#60; 0.001, unpaired t-test as compared to control group.
<img alt="Figure 4" fo:content-width="5in" src="/files/ftp_upload/51264/51264fig4highres.jpg" width="500" /> 
Figure 4. Development of hyperalgesia following repeated morphine administration (Step D; d1 to d6). The basal nociceptive value of mice was determined by TIT (A) and TPT (B) once daily before morphine (5 mg/kg, sc.) or saline administration. Data are expressed as mean values &#177; SEM, n=8 mice per group. *P &#60; 0.05, **P &#60; 0.01, ***P &#60; 0.001 by unpaired t-test as compared with the saline-treated control group.
<img alt="Figure 5" fo:content-width="5in" src="/files/ftp_upload/51264/51264fig5highres.jpg" width="500" /> 
Figure 5. Time-course for morphine analgesia in chronic-morphine treated mice at day 7 (Step E) in TIT (A) and TPT (B). Mice that were chronically treated with morphine (black dots) or saline (white triangles) from day 0 to day 6, received on day 7 a single injection of morphine (5 mg/kg, sc.) or saline, respectively. The nociceptive response of mice was determined every 30 min after morphine or saline injection. Data are expressed as means &#177; SEM, n=8 mice per group. *P &#60; 0.05, **P &#60; 0.01 by unpaired t-test as compared with the saline-treated control group. Error bars that do not exceed symbols size are hidden.
<img alt="Figure 6" fo:content-width="5in" src="/files/ftp_upload/51264/51264fig6highres.jpg" width="500" /> 
Figure 6. Comparison of maximum analgesic responses of mice to morphine (5 mg/kg, sc.) before (day 0) and after chronic morphine treatment (day 7). Values reported here are from experiments shown in Figure 3 and Figure 5. Nociceptive values were measured using TIT (A) and TPT (B) 30 min after morphine or saline injection. Data are expressed as means &#177; SEM, n=8 mice per group. ***P &#60; 0.001 by paired t-test.

Watch this Scientific Journal Video about Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities at JoVE.com

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities

We describe a protocol to examine the development of opioid-induced hyperalgesia and tolerance in mice. Based on the measurement of thermal and mechanical nociceptive responses of na&#239;ve and morphine-treated animals, it allows to quantify the increase in pain sensitivity (hyperalgesia) and decrease in analgesia (tolerance) associated with chronic opiate administration.

Opioid-induced hyperalgesia and tolerance severely impact the clinical efficacy of opiates as pain relievers in animals and humans. The molecular ...

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Drugs for Pain Management: Opioid Analgesics and General Anesthetics

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33.2K 조회수.  Université de Strasbourg. We describe a protocol to examine the development of opioid-induced hyperalgesia and tolerance in mice. Based on the measurement of thermal and mechanical nociceptive responses of naïve and morphine-treated animals, it allows to quantify the increase in pain sensitivity (hyperalgesia) and decrease in analgesia (tolerance) associated with chronic opiate administration.

비디오: Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities

Use of the Operant Orofacial Pain Assessment Device (OPAD) to Measure Changes in Nociceptive Behavior

We present an operant system for the detection of pain in awake, conscious rodents. The Orofacial Pain Assessment Device (OPAD) assesses pain behaviors in a more clinically relevant way by not relying on reflex-based measures of nociception. Food fasted, hairless (or shaved) rodents are placed into a Plexiglas chamber which has two Peltier-based thermodes that can be programmed to any temperature between 7 &deg;C and 60 &deg;C. The rodent is trained to make contact with these in order to access a reward bottle. During a session, a number of behavioral pain outcomes are automatically recorded and saved. These measures include the number of reward bottle activations (licks) and facial contact stimuli (face contacts), but custom measures like the lick/face ratio (total number of licks per session/total number of contacts) can also be created. The stimulus temperature can be set to a single temperature or multiple temperatures within a session. The OPAD is a high-throughput, easy to use operant assay which will lead to better translation of pain research in the future as it includes cortical input instead of relying on spinal reflex-based nociceptive assays.

Use of the Operant Orofacial Pain Assessment Device OPAD to Measure Changes in Nociceptive Behavior

We present a user-friendly, high-throughput operant system for the evaluation of pain behaviors in awake, conscious rodents. The Orofacial Pain Assessment Device (OPAD) can assess pain through a reward/conflict paradigm thus providing a more humane way of testing. This protocol will yield more clinically relevant and translational data from rodents.

통각 행동의 변화를 측정하는 조작 적 구강 안면 통증 평가 장치 (OPAD)의 사용

We present an operant  system for the detection of pain in awake, conscious rodents. The Orofacial  Pain Assessment Device (OPAD) assesses pain behaviors ...

연구

행동분석학

Determining heat and mechanical pain threshold in inflamed skin of human subjects

In a previous article in the Journal of Visualized Experiments we have demonstrated skin microdialysis techniques for the collection of tissue-specific nociceptive and inflammatory biochemicals in humans. In this article we will show pain-testing paradigms that are often used in tandem with microdialysis procedures. Combining pain tests with microdialysis provides the critical link between behavioral and biochemical data that allows identifying key biochemicals responsible for generating and propagating pain.
Two models of evoking pain in inflamed skin of human study participants are shown. The first model evokes pain with aid of heat stimuli. Heat evoked pain as described here is predominantly mediated by small, non-myelinated peripheral nociceptive nerve fibers (C-fibers). The second model evokes pain via punctuated pressure stimuli. Punctuated pressure evoked pain is predominantly mediated by small, myelinated peripheral nociceptive nerve fibers (A-delta fibers). The two models are mechanistically distinct and independently examine nociceptive processing by the two major peripheral nerve fiber populations involved in pain signaling.
Heat pain is evoked with aid of the TSA II, a commercially available thermo-sensory analyzer (Medoc Advanced Medical Systems, Durham, NC). Stimulus configuration and delivery is handled with aid of specific software. Thermodes vary in size and shape but in principle consist of a metal plate that can be heated or cooled at various rates and for different periods of time. Algorithms assessing heat-evoked pain are manifold. In the experiments shown here, study participants are asked to indicate at what point they start experiencing pain while the thermode in contact with skin is heated at a predetermined rate starting at a temperature that does not evoke pain. The thermode temperature at which a subject starts experiencing pain constitutes the heat pain threshold.
Mechanical pain is evoked with punctuated probes. Such probes are commercially available from several manufacturers (von Frey hairs). However, the accuracy of von Frey hairs has been criticized and many investigators use custom made punctuated pressure probes. In the experiments shown here eight custom-made punctuated probes of different weights are applied in consecutive order, a procedure called up-down algorithm, to identify perceptional deflection points, i.e., a change from feeling no pain to feeling pain or vice versa. The average weight causing a perceptional deflection constitutes the mechanical pain threshold.

Algorithms assessing heat and mechanical pain thresholds in experimentally inflamed skin of human study subjects are shown. The two pain testing paradigms independently examine nociceptive processing by the two major peripheral nerve fiber populations transmitting pain, i.e., non-myelinated C fibers and small myelinated A-delta fibers.

열과 인간 주제에 염증이 피부에 기계적 통증 임계값 결정

In a previous article in the Journal of Visualized Experiments we have demonstrated skin microdialysis techniques for the collection of tissue-specific ...

생물학

Rapid Determination of the Thermal Nociceptive Threshold in Diabetic Rats

Painful diabetic neuropathy (PDN) is characterized by hyperalgesia i.e., increased sensitivity to noxious stimulus, and allodynia i.e., hypersensitivity to normally innocuous stimuli1. Hyperalgesia and allodynia have been studied in many different rodent models of diabetes mellitus2. However, as stated by B&ouml;lcskei et al, determination of "pain" in animal models is challenging due to its subjective nature3. Moreover, the traditional methods used to determine behavioral responses to noxious thermal stimuli usually lack reproducibility and pharmacological sensitivity3. For instance, by using the hot-plate method of Ankier4, flinch, withdrawal and/or licking of either hind- and/or fore-paws is quantified as reflex latencies at constant high thermal stimuli (52-55 &deg;C). However, animals that are hyperalgesic to thermal stimulus do not reproducibly show differences in reflex latencies using those supra-threshold temperatures3,5. As the recently described method of B&ouml;lcskei et al.6, the procedures described here allows for the rapid, sensitive and reproducible determination of thermal nociceptive thresholds (TNTs) in mice and rats. The method uses slowly increasing thermal stimulus applied mostly to the skin of mouse/rat plantar surface. The method is particularly sensitive to study anti-nociception during hyperalgesic states such as PDN. The procedures described bellow are based on the ones published in detail by Alm&aacute;si et al 5 and B&ouml;lcskei et al 3. The procedures described here have been approved the Laboratory Animal Care and Use Committee (LACUC), Wright State University.

Here, we describe a rapid reliable and simple procedure to determine the lowest temperature at which rats or mice show nocifensive behavior, i.e. the thermal nociceptive threshold (TNT). This method applies a slowly increasing thermal stimulus allowing precise and reproducible estimation of TNTs with minimum, if any, stress to the animals.

당뇨병 쥐의 열전달 Nociceptive 본부 신속한 결정

Painful diabetic neuropathy (PDN) is characterized by hyperalgesia i.e., increased sensitivity to noxious stimulus, and allodynia i.e., hypersensitivity ...

신경과학

Back Mechanical Sensitivity Assessment in the Rat for Mechanistic Investigation of Chronic Back Pain

Low back pain is the leading cause of disability worldwide, with dramatic personal, economic, and social consequences. To develop novel therapeutics, animal models are needed to examine the mechanisms and effectiveness of novel therapies from a translational perspective. Several rodent models of back pain are used in current investigations. Surprisingly, however, no standardized behavioral test was validated to assess mechanical sensitivity in back pain models. This is critical to confirm that animals with presumed back pain present local hypersensitivity to nociceptive stimuli, and to monitor sensitivity during interventions designed to relieve back pain. The objective of this study is to lay down a simple and accessible test to assess mechanical sensitivity in the back of rats. A test cage was fabricated specifically for this method; length x width x height: 50 x 20 x 7 cm, having a stainless-steel mesh on the top. This test cage allows the application of mechanical stimuli to the back. To perform the test, the back of the animal is shaved in the region of interest, and the test area is marked to repeat the test on different days, as needed. The mechanical threshold is determined with Von Frey filaments applied to the paraspinal muscles, utilizing the up-down method described previously. The positive responses include (1) muscle twitching, (2) arching (back extension), (3) rotation of the neck (4) scratching or licking the back, and (5) escaping. This behavioral test (Back Mechanical Sensitivity (BMS) test) is useful for mechanistic research with rodent models of back pain for the development of therapeutic interventions for the prevention and management of back pain.

To develop novel therapeutic interventions for the prevention and management of back pain, animal models are required to examine the mechanisms and effectiveness of these therapies from a translational perspective. The present protocol describes the BMS test, a standardized method to assess back mechanical sensitivity in the rat.

만성 요통의 기계론적 조사를 위한 쥐의 등 기계적 민감도 평가

Low back pain is the leading cause of disability worldwide, with dramatic personal, economic, and social consequences. To develop novel therapeutics, ...

Assessment of Nerve Injury-Induced Mechanical Hypersensitivity in Rats Using an Orofacial Operant Pain Assay

Pain has sensory and affective components. Unlike traditional, reflex-based pain assays, operant pain assays can produce more clinically relevant results by addressing the cognitive and motivational aspects of pain in rodents. This paper presents a protocol for assessing mechanical hypersensitivity following chronic constriction injury of the infraorbital nerves (CCI-ION) in rats using an orofacial operant pain system. Before CCI-ION surgery, rats were trained in an orofacial pain assessment device (OPAD) to drink sweetened condensed milk while making facial contact with the metal spiked bars and lick-tube.
In this assay, rats can choose between receiving milk as a positive reinforcer or escaping an aversive mechanical stimulus that is produced by a vertical row of small pyramid-shaped spikes on each side of the reward access hole. Following 2 weeks of training in the OPAD and before the CCI-ION surgery, baseline mechanical sensitivity data were recorded for 5 days for each rat during a 10 min testing session. During a session, the operant system automatically records the number of reward bottle activations (licks) and facial contacts, contact duration, and latency to the first lick, among other measures.
Following baseline measurements, rats underwent either CCI-ION or sham surgery. In this protocol, mechanical hypersensitivity was quantified by measuring the number of licks, latency to the first lick, the number of contacts, and the ratio of licks to facial contacts (L/F). The data showed that CCI-ION resulted in a significant decrease in the number of licks and the L/F ratio and an increase in the latency to the first lick, indicating mechanical hypersensitivity. These data support the use of operant-based pain assays to assess mechanical pain sensitivity in preclinical pain research.

This protocol describes the assessment of mechanical hypersensitivity in a rat model of neuropathic orofacial pain using an operant-based orofacial pain assessment device.

구강 안면 조작 통증 분석을 사용한 쥐의 신경 손상 유발 기계적 과민증 평가

Pain has sensory and affective components. Unlike traditional, reflex-based pain assays, operant pain assays can produce more clinically relevant results ...

A Simple and Inexpensive Method for Determining Cold Sensitivity and Adaptation in Mice

Cold hypersensitivity is a serious clinical problem, affecting a broad subset of patients and causing significant decreases in quality of life. The cold plantar assay allows the objective and inexpensive assessment of cold sensitivity in mice, and can quantify both analgesia and hypersensitivity. Mice are acclimated on a glass plate, and a compressed dry ice pellet is held against the glass surface underneath the hindpaw. The latency to withdrawal from the cooling glass is used as a measure of cold sensitivity.
Cold sensation is also important for survival in regions with seasonal temperature shifts, and in order to maintain sensitivity animals must be able to adjust their thermal response thresholds to match the ambient temperature. The Cold Plantar Assay (CPA) also allows the study of adaptation to changes in ambient temperature by testing the cold sensitivity of mice at temperatures ranging from 30 &#176;C to 5 &#176;C. Mice are acclimated as described above, but the glass plate is cooled to the desired starting temperature using aluminum boxes (or aluminum foil packets) filled with hot water, wet ice, or dry ice. The temperature of the plate is measured at the center using a filament T-type thermocouple probe. Once the plate has reached the desired starting temperature, the animals are tested as described above.
This assay allows testing of mice at temperatures ranging from innocuous to noxious. The CPA yields unambiguous and consistent behavioral responses in uninjured mice and can be used to quantify both hypersensitivity and analgesia. This protocol describes how to use the CPA to measure cold hypersensitivity, analgesia, and adaptation in mice.

The Cold Plantar Assay (CPA) measures cold responsiveness between 30 &#176;C and 5 &#176;C, and can also measure cold adaptation. This protocol describes how to use the CPA to measure cold hypersensitivity, analgesia, and adaptation in mice.

마우스에 콜드 민감도 및 적응을 결정하기위한 간단하고 저렴한 방법

Cold hypersensitivity is a serious clinical problem, affecting a broad subset of patients and causing significant decreases in quality of life.  The cold ...

Development of Recombinant Proteins to Treat Chronic Pain

Chronic pain is difficult to treat and new approaches to resolve persistent pain are urgently needed. Anti-inflammatory cytokines are promising candidates for treating debilitating pain conditions due to their capacity to regulate aberrant neuro-immune interactions. However, physiologically they work in a network of various cytokines, and therefore their therapeutic effect may not be optimal when used as stand-alone drugs. To overcome this limitation, we developed a fusion protein of the anti-inflammatory cytokines IL4 and IL10. Here, we describe the methods for production and quality control of IL4-10 recombinant fusion protein and we test the effectiveness of the IL4-10 fusion protein to resolve pain in a mouse model of persistent inflammatory pain.

In this paper we provide details for the methods of production and quality control of an IL4-10 recombinant fusion protein. We also show how to test the effectiveness of this protein to resolve pain in a mouse model of inflammatory pain.

만성 통증 치료에 재조합 단백질의 개발

Chronic pain is difficult to treat and new approaches to resolve persistent pain are urgently needed. Anti-inflammatory cytokines are promising candidates ...

의학

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.

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.

Murine 모델 Monoarticular 무릎 통증의 통증의 자연과 갖는 측정

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 ...

Mechanical Conflict-Avoidance Assay to Measure Pain Behavior in Mice

Pain comprises of both sensory (nociceptive) and affective (unpleasant) dimensions. In preclinical models, pain has traditionally been assessed using reflexive tests that allow inferences regarding pain's nociceptive component but provide little information about the affective or motivational component of pain. Developing tests that capture these components of pain are therefore translationally important. Hence, researchers need to use non-reflexive behavioral assays to study pain perception at that level. Mechanical conflict-avoidance (MCA) is an established voluntary non-reflexive behavior assay, for studying motivational responses to a noxious mechanical stimulus in a 3 chamber paradigm. A change in a mouse's location preference, when faced with competing noxious stimuli, is used to infer the perceived unpleasantness of bright light versus tactile stimulation of the paws. This protocol outlines a modified version of the MCA assay which pain researchers can use to understand affective-motivational responses in a variety of mouse pain models. Though not specifically described here, our example MCA data use the intraplantar complete Freund's adjuvant (CFA), spared nerve injury (SNI), and a fracture/casting model as pain models to illustrate the MCA procedure.

The mechanical conflict-avoidance assay is used as a non-reflexive readout of pain sensitivity in mice which can be used to better understand affective-motivational responses in a variety of mouse pain models.

마우스의 통증 행동을 측정하기위한 기계적 충돌 회피 분석

Pain comprises of both sensory (nociceptive) and affective (unpleasant) dimensions. In preclinical models, pain has traditionally been assessed using ...

Partial Sciatic Nerve Ligation: A Mouse Model of Chronic Neuropathic Pain to Study the Antinociceptive Effect of Novel Therapies

Management of chronic pain remains challenging to this day, and current treatments are associated with adverse effects, including tolerance and addiction. Chronic neuropathic pain results from lesions or diseases in the somatosensory system. To investigate potential therapies with reduced side effects, animal pain models are the gold standard in preclinical studies. Therefore, well-characterized and well-described models are crucial for the development and validation of innovative therapies. 
Partial ligation of the sciatic nerve (pSNL) is a procedure that induces chronic neuropathic pain in mice, characterized by mechanical and thermal hypersensitivity, ongoing pain, and changes in limb temperature, making this model a great fit to study neuropathic pain preclinically. pSNL is an advantageous model to study neuropathic pain as it reproduces many symptoms observed in humans with neuropathic pain. Furthermore, the surgical procedure is relatively fast and straightforward to perform. Unilateral pSNL of one limb allows for comparison between the ipsilateral and contralateral paws, as well as evaluation of central sensitization. 
To induce chronic neuropathic hypersensitivity, a 9-0 non-absorbable nylon thread is used to ligate the dorsal third of the sciatic nerve. This article describes the surgical procedure and characterizes the development of chronic neuropathic pain through multiple commonly used behavioral tests. As a plethora of innovative therapies are now being investigated to treat chronic pain, this article provides crucial concepts for standardization and an accurate description of surgeries required to induce neuropathic pain.

Partial sciatic nerve ligation induces long-lasting chronic neuropathic pain, characterized by exaggerated responses to thermal and mechanical stimuli. This mouse model of neuropathic pain is commonly used to study innovative therapies for pain management. This article describes in detail the surgical procedure to improve standardization and reproducibility.

부분 좌골 신경 결찰: 새로운 치료법의 항통각수용 효과를 연구하기 위한 만성 신경병성 통증의 마우스 모델

Management of chronic pain remains challenging to this day, and current treatments are associated with adverse effects, including tolerance and addiction. ...