This project was sponsored by National Natural Science Foundation of China (81873365 and 81603676), Zhejiang Provincial Natural Science Funds for Distinguished Young Scholars (LR17H270001) and research funds from Zhejiang Chinese Medical University (Q2019J01, 2018ZY37, 2018ZY19).

The animal protocols were approved by Zhejiang Chinese Medical University Animal Ethics Committee.
1. Animals
<ol>
	<li>Obtain male Sprague-Dawley (SD) rats (280&#8211;320 g, 8-10 weeks of age) from Shanghai Laboratory Animal Center. House the animals in Zhejiang Chinese Medical University Laboratory Animal Center. Note that the breeding conditions should include 12 h/ 2h light/dark cycles and keep temperature constant at 24 &#176;C. Provide water and food ad libitum. Note that a total of 48 rats are used in this study. One note, in this model, we need to observe the pain response during the whole process. If pain medication is applied, then we cannot successfully establish the pain model. After the experiments, the rats are sacrificed.</li>
</ol>
2. CPIP model establishment
<ol>
	<li>Anesthetize all rats (including sham and CPIP model groups) with sodium phenobarbital (50 mg/kg, intraperitoneal injection [i.p.]). Maintain anesthesia with up to 20 mg/kg/h phenobarbital [i.p.], if necessary. Check the reflexes of each animal by pinching its hind paw or tail tip using forceps. Make sure that the rats are not responsive before model establishment. Place vet ointment on eyes to avoid dryness during the procedure. Place the anesthetized rats on a heated pad maintained at 37 &#176;C for the following procedure.</li>
	<li>Ischemia and reperfusion of the hind paw
	<ol>
		<li>Lubricate the right hind paw and ankle with glycerol once the rat is anesthetized.</li>
		<li>Slide a Nitrile 70 Durometer O-ring with a 7/32&#34; (5.5 mm) internal diameter into the larger side of a 1.5 mL Eppendorf tube (with the snap-cap cut off before use). Carefully insert the hind paw into the hollow Eppendorf tube until reaching the bottom.</li>
		<li>Gradually slide the O-ring from the tube to the right hind limb near the ankle joint and place for 3 h. Apply the same treatment to a sham group of rats, except that a broken O-ring, which is cut off and should not induce ischemia, should be placed around the ankle.</li>
		<li>Cut off the O-ring 3 h after the ischemia step. Carefully watch the rat until it recovers enough consciousness to maintain sternal recumbency. Note that the rat that received anesthesia should not be placed back to the company of other rats until it fully recovered.</li>
	</ol>
	</li>
</ol>
3. Nocifensive behavioral tests
<ol>
	<li>Place the rat in a transparent Plexiglas chamber that is sitting on a mesh floor. Habituate the rat for 0.5 h before any behavioral testing.</li>
	<li>Mechanical allodynia
	<ol>
		<li>Use von Frey filaments (0.4, 0.6, 1.0, 2.0, 4.0, 6.0, 8.0, 15.0, and 26.0 g filaments) for the test. Begin the test from the middle filament (4.0 g). Vertically apply the filaments to the middle plantar surface of the hind paw. Slightly apply suitable force to bend the filament for up to 5 s. A sudden retraction of the hind paw in response to the stimuli is considered a nocifensive behavior. Conduct the mechanical allodynia test on days -3, -2, -1, and every other day until day 13.</li>
		<li>Apply the up-down testing method to test the threshold. Apply the Dixon method for calculating 50% paw withdrawal threshold (PWT)13,14,15.</li>
	</ol>
	</li>
	<li>Thermal hyperalgesia
	<ol>
		<li>Use Hargreaves&#39; method to examine thermal hyperalgesia. Directly aim the light beam emitted from a bulb (50 W) to the hind paw to measure the paw withdrawal latency (PWL). Set 20 s as the cut-off threshold to avoid excessive injury from the heating.</li>
		<li>Repeat each test 3x in 5 min intervals for each hind paw. Take the average of these three tests as the PWL of each rat16. Conduct the thermal hyperalgesia test on days -3, -2, -1, and every other day until day 13.</li>
	</ol>
	</li>
	<li>Capsaicin-induced acute nocifensive behavior
	<ol>
		<li>Prepare capsaicin stock solution (200 mM) using dimethyl sulfoxide (DMSO) and further dilute to 1:1000 in sterile phosphate-buffered saline (PBS) for hind paw injection. The final DMSO concentration in PBS is 0.1% (vehicle contains 0.1% DMSO in PBS only). Inject capsaicin or vehicle into the hind paw (intraplantar injection) at a volume of 50 &#956;L using a 30 G needle attached to 1 mL syringe.</li>
		<li>Record the nocifensive behavior (i.e., licking, biting, or flinching of the injected paw) using a video camera for 10 min right after the injection and quantified thereafter as previously described17,18,19.</li>
	</ol>
	</li>
	<li>Hind paw edema evaluation: Evaluate the hind paw edema by measuring the increase in paw diameter. Measure with a digital caliper and calculate the difference between the basal value and the test value observed at different time points. Assess the changes in paw thickness at 15 min, 24 h, 48 h, and 72 h after model establishment.</li>
</ol>

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The authors declare no conflicts of interest in this work.

This protocol describes the detailed methods for establishing a rat CPIP model by applying ischemia/reperfusion to hind limbs of the rats. It involves the evaluation of hind limb appearance, edema, mechanical/thermal hypersensitivities, and acute nocifensive behaviors in response to capsaicin injection.
Limb ischemia/reperfusion is a common factor contributing to CRPS-I in human patients12. This protocol describes how to establish the rat CPIP model, which is a commonly used animal model to recapitulate human CRPS-I6. Ischemia was induced in the rat&#39;s hind limb with a tight O-ring applied to the ankle for 3 h under anesthesia. The O-ring was removed, and reperfusion occurred. After the model establishment, the CPIP model rat developed early hyperemia and edema in the hind limb. The model also displays neuropathic pain behaviors, including persistent mechanical/thermal hypersensitivities. These symptoms all mimic the typical characteristics of human CRPS-I 21.
CRPS patients exhibit obvious increased responses to capsaicin-induced pain in the affected limbs20. However, it remains unclear whether CPIP model animals exhibit similar responses. Thus, in this study, nocifensive behaviors of CPIP rats were examined in response to intraplantar capsaicin injection into the ipsilateral hind paw. It was found that CPIP model rats showed significantly higher nocifensive responses to capsaicin injection compared to sham rats. To our knowledge, this is the first report of this phenomenon in CPIP model rats.
In a previous study, TRPV1 channel expression was shown to be upregulated in ipsilateral hind paw tissues and DRG neurons that innervated the hind paw12. Furthermore, it has been found that spinal glial cells are activated in CPIP model rats, resulting in central pain sensitization and facilitation of pain perception and transmission9,12. Therefore, peripheral and central pain sensitization may both be involved in the increased nocifensive behaviors in response to capsaicin injection in CPIP model rats. Future studies are needed to test whether capsaicin injection results in enhanced responses in contralateral hind paws of CPIP model rats, as well. In the tests performed here, we did not observe autotomy in the CPIP model rats. This contrasts with rats that have undergone sciatic sectioning, who usually develop autotomy in addition to chronic pain hypersensitivities22,23. In addition, no referred pain response has been reported in CRPS-I patients or CPIP mode animals.
One of the critical steps in the model is to maintain anesthesia throughout the procedure. In this study, the anesthesia was initiated by intraperitoneal injection of sodium phenobarbital (50 mg/kg). This dosage is frequently used in many studies involving rat anesthesia, including studies with CPIP rat model establishment9,12,24. Besides, anesthesia should be maintained via 20 mg/kg/h (i.p.) sodium phenobarbital when necessary to guarantee successful implement of the procedure12,24.
In the initial CPIP model established by Coderre et al., the O-ring was actually slid off from the outside of a 3 cm3 syringe (cut in half) when the hind paw was placed into the barrel of the syringe as far as possible25. Here, in our study, we made minor modifications to this method. We used a 1.5 mL Eppendorf tube (with the snap-cap cut off beforehand) instead of the syringe, since this material was more accessible and fit just well with the diameter of the rat&#39;s hind paw. The O-ring can be easily placed on the ankle part of the rats in this modified method without injuries to allow for model establishment.
At present, the CPIP rat model was exclusively established in male rats based upon previous studies, including our present study25. However, it should be noted that the incidence of CRPS-I is more frequent in female than in male patients according to epidemiological analysis26,27. This is further supported by the findings that female animals exhibited more pain responses than male animals when CPIP was established28. Therefore, it will be necessary to establish the CPIP model in both male and female animals in the future. This will be important for studying the translational significance of this model.
In conclusion, described here are methods for establishing a rat CPIP model. This CPIP rat model recapitulates many clinical characters of human CRPS-I, and its properties may render it a suitable animal model to study CRPS-I.

Complex regional pain syndrome (CRPS) reprents complex and chronic pain symptoms resulting from fractures, trauma, surgery, ischemia or nerve injury1,2,3. CRPS is classified into 2 subcategories: CRPS type-I and type-II (CRPS-I and CRPS-II)4. Epidemiological studies revealed that the prevalence of CRPS was approximately 1:20005. CRPS-I, which shows no obvious nerve damage, can result in chronic pain and dramatically affects the life quality of the patients. Current available treatments show inadequate therapeutic effects. Therefore, CRPS-I still remains an important and challenging clinical problem that needs to be addressed.
Establishing a preclinical animal model mimicking CRPS-I is crucial for exploring the mechanisms underlying CRPS-I. In order to address this issue, Coderre et al. designed a rat model by applying prolonged ischemia and reperfusion to the hind limb to recapitulate CRPS-I6. It is known that ischemia/reperfusion injury is among one of the major causes of CRPS-I7. The rat CPIP model exhibits many CRPS-I-like symptoms, which include hind limb edema and hyperemia in the early stage after model establishment, followed with persistent thermal and mechanical hypersensitivities6. With the aid from this model, it is proposed that central pain sensitization, peripheral TRPA1 channel activation and reactive oxygen species generation, etc. contribute to CRPS-I8,9,10. We recently successfully established the CPIP rat model and performed RNA-sequencing of the dorsal root ganglia (DRGs) that innervate the affected hind paw11. We discovered some potential mechanisms that are possibly involved in mediating the pain hypersensitivities of CRPS-I11. We further identified transient receptor potential vanilloid 1 (TRPV1) channel in DRG neurons as an important contributor to the mechanical and thermal hypersensitivities of CRPS-I12.
In this study, we described the detailed procedures involved in the establishment of the rat model of CPIP. We further evaluated the rat CPIP model by measuring the mechanical and thermal hypersensitivities as well as its responsiveness to acute capsaicin challenge. We propose that the rat CPIP model can be a reliable animal model for further investigation of the mechanisms involved in CRPS-I.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1.5 ml Eppendorf tube</td>
			<td>Eppendorf</td>
			<td>22431021</td>
			<td></td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>Sigma-Aldrich</td>
			<td>D1435</td>
			<td></td>
		</tr>
		<tr>
			<td>Capsaicin</td>
			<td>APEXBIO</td>
			<td>A3278</td>
			<td></td>
		</tr>
		<tr>
			<td>Digital caliper</td>
			<td>Meinaite</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>O-ring</td>
			<td>O-Rings West</td>
			<td>Nitrile 70 Durometer</td>
			<td>7/32 in. 
			internal diameter</td>
		</tr>
		<tr>
			<td>Plantar Test Apparatus</td>
			<td>UGO Basile, Italy</td>
			<td>37370</td>
			<td></td>
		</tr>
		<tr>
			<td>von Frey filaments</td>
			<td>UGO Basile, Italy</td>
			<td>NC12775</td>
			<td></td>
		</tr>
	</tbody>
</table>

chronic post-ischemia pain model for complex regional pain syndrome type-i in rats

Complex regional pain syndrome type-I (CRPS-I) is a neurological disease that causes severe pain among patients and remains an unresolved medical condition. However, the underlying mechanisms of CRPS-I have yet to be revealed. It is known that ischemia/reperfusion is one of the leading factors that causes CRPS-I. By means of prolonged ischemia and reperfusion of the hind limb, the rat chronic post-ischemia pain (CPIP) model has been established to mimic CRPS-I. The CPIP model has become a well-recognized animal model for studying the mechanisms of CRPS-I. This protocol describes the detailed procedures involved in the establishment of the rat model of CPIP, including anesthesia, followed by ischemia/reperfusion of the hind limb. Characteristics of the rat CPIP model are further evaluated by measuring the mechanical and thermal hypersensitivities of the hind limb as well as the nocifensive responses to acute capsaicin injection. The rat CPIP model exhibits several CRPS-I-like manifestations, including hind limb edema and hyperemia in the early stage after establishment, persistent thermal and mechanical hypersensitivities, and increased nocifensive responses to acute capsaicin injection. These characteristics render it a suitable animal model for further investigation of the mechanisms involved in CRPS-I.

After placing the O-ring on the ankle, the ipsilateral hind paw skin showed cyanosis, an indication of tissue hypoxia (Figure 1A). After cutting the O-ring, the ipsilateral hind paw began to fill with blood and showed robust swelling, which demonstrated an intense sign of hyperemia (Figure 1A). The paw swelling gradually diminished and returned to normal 48 h after the ischemic/reperfusion procedure (two-way ANOVA with Sidak post-hoc test, Figure 1B). All of these signs are consistent with previous studies6,12.
Then, mechanical allodynia was measured using a von Frey hair test. The ipsilateral hind paw of the CPIP group exhibited obvious mechanical allodynia 1 day after model establishment compared to the sham group. The mechanical allodynia of the ipsilateral hind paw persisted until 13 days of the observation timeframe (two-way ANOVA with Sidak post-hoc test, Figure 1C). The contralateral hind paw of the CPIP group also displayed mechanical hyperalgesia similar to the ipsilateral hind paw, lasting for 13 days (two-way ANOVA with Sidak post-hoc test, Figure 1D).
Thermal hyperalgesia was then measured using a Hargreaves&#39; test. Bilateral hind paws of CPIP rats exhibited significantly reduced withdrawal latency in response to noxious thermal stimuli, a sign of thermal hyperalgesia, compared to the sham group rats (two-way ANOVA with Sidak post hoc test, Figure 1E,F). This observation is consistent with previous studies11,12. The thermal hyperalgesia of the ipsilateral hind paw persisted until the end of the observation timeframe, whereas the thermal hyperalgesia of the contralateral hind paw lasted for 7 days (two-way ANOVA with Sidak post-hoc test, Figure 1E,F). The above results suggest that CPIP rats develop robust and persistent mechanical and thermal hypersensitivities, consistent with previous observations11,12.
CRPS patients exhibited an obvious increased response to capsaicin-induced pain in affected areas20. It was then examined whether the CPIP rat model can recapitulate this phenomenon. Nocifensive behavior in CPIP rats was observed in response to intraplantar capsaicin (a TRPV1 agonist) injection into the ipsilateral hind paw. First, the nocifensive responses of the rats when a vehicle was injected were tested. The sham group showed a slight nocifensive response to vehicle injection, whereas the CPIP group showed a significantly higher response compared to the sham group (one-way ANOVA with Sidak post-hoc test, Figure 2). Furthermore, capsaicin injection resulted in robust nocifensive response in the sham group (Figure 2). More importantly, CPIP rats showed significantly higher responses to capsaicin injection than the sham group (Figure 2). These data suggest that CPIP rats exhibited enhanced nocifensive responses to capsaicin, a phenomenon mimicking human patients with CRPS-I.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60562/60562fig1b.jpg" /> 
Figure 1: The CPIP rat model showed thermal and mechanical pain hypersensitivities in bilateral hind limbs. (A) Typical images taken during different time points (during ischemia, 10 min after reperfusion, and 7 days later). (B) Ipsilateral hind paw thickness measurements of both CPIP and sham groups. (C,D) 50% paw withdraw threshold (50% PWT, index of mechanical hyperalgesia) of ipsilateral (C) and contralateral (D) hind paws of rats. (E,F) Paw withdrawal latency (PWL, index of thermal hyperalgesia) of ipsilateral (E) and contralateral (F) hind paws of rats (n = 8 rats per group, **p &#60; 0.01). Results are expressed as mean &#177; SEM (two-way ANOVA followed by Sidak post-hoc test). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60562/60562fig1alarge.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/60562/60562fig2b.jpg" /> 
Figure 2: CPIP rats exhibited more nocifensive behaviors compared to sham rats in response to intraplantar capsaicin injection into ipsilateral hind paws. The cumulated time the rats spent licking, biting, or flinching the hind paws was calculated over 10 min after vehicle (0.1% DMSO in PBS, intraplantar) or capsaicin (10 nmol in 50 &#956;L volume, intraplantar) injection (n = 8 rats per group, **p &#60; 0.01). Results are expressed as mean &#177; SEM (one-way ANOVA followed by Sidak post-hoc test). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60562/60562fig2alarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Chronic Post-Ischemia Pain Model for Complex Regional Pain Syndrome Type-I in Rats at JoVE.com

Chronic Post-Ischemia Pain Model for Complex Regional Pain Syndrome Type-I in Rats

Provided here is a protocol that details steps to establish an animal model of chronic post-ischemia pain (CPIP). This is a well-recognized model mimicking human complex regional pain syndrome type-I. Mechanical and thermal hypersensitivities are further evaluated, as well as capsaicin-induced nocifensive behaviors observed in the CPIP rat model.

Complex regional pain syndrome type-I (CRPS-I) is a neurological disease that causes severe pain among patients and remains an unresolved medical ...

chronic-post-ischemia-pain-model-for-complex-regional-pain-syndrome

Nanyang Technological University

Research

JoVE Journal

Behavior

7.5K Views.  Key Laboratory of Acupuncture and Neurology of Zhejiang Province. Provided here is a protocol that details steps to establish an animal model of chronic post-ischemia pain (CPIP). This is a well-recognized model mimicking human complex regional pain syndrome type-I. Mechanical and thermal hypersensitivities are further evaluated, as well as capsaicin-induced nocifensive behaviors observed in the CPIP rat model.

Video: Chronic Post-Ischemia Pain Model for Complex Regional Pain Syndrome Type-I in Rats

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.

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

Determining Pain Detection and Tolerance Thresholds Using an Integrated, Multi-Modal Pain Task Battery

Human pain models are useful in the assessing the analgesic effect of drugs, providing information about a drug&#39;s pharmacology and identify potentially suitable therapeutic populations. The need to use a comprehensive battery of pain models is highlighted by studies whereby only a single pain model, thought to relate to the clinical situation, demonstrates lack of efficacy. No single experimental model can mimic the complex nature of clinical pain. The integrated, multi-modal pain task&#160;battery presented here encompasses the electrical stimulation task, pressure stimulation task, cold pressor task, the UVB inflammatory model which includes a thermal task and a paradigm for inhibitory conditioned pain modulation. These human pain models have been tested for predicative validity and reliability both in their own right and in combination, and can be used repeatedly, quickly, in short succession, with minimum burden for the subject and with a modest quantity of equipment. This allows a drug to be fully characterized and profiled for analgesic effect which is especially useful for drugs with a novel or untested mechanism of action.

Human pain models are valuable tools used to assess the analgesic potential of novel compounds and predict their clinical efficacy, especially when used in an integrated manner. Although implementation of these models is complex, with proper execution, the pain models described in this protocol can provide predictive and reliable results.

Human pain models are useful in the assessing the analgesic effect of drugs, providing information about a drug&#39;s pharmacology and identify ...

A Protocol of Manual Tests to Measure Sensation and Pain in Humans

Numerous qualitative and quantitative techniques can be used to test sensory nerves and pain in both research and clinical settings. The current study demonstrates a quantitative sensory testing protocol using techniques to measure tactile sensation and pain threshold for pressure and heat using portable and easily accessed equipment. These techniques and equipment are ideal for new laboratories and clinics where cost is a concern or a limiting factor. We demonstrate measurement techniques for the following: cutaneous mechanical sensitivity on the arms and legs (von-Frey filaments), radiant and contact heat sensitivity (with both threshold and qualitative assessments using the Visual Analog Scale (VAS)), and mechanical pressure sensitivity (algometer, with both threshold and the VAS). The techniques and equipment described and demonstrated here can be easily purchased, stored, and transported by most clinics and research laboratories around the world. A limitation of this approach is a lack of automation or computer control. Thus, these processes can be more labor intensive in terms of personnel training and data recording than the more sophisticated equipment. We provide a set of reliability data for the demonstrated techniques. From our description, a new laboratory should be able to set up and run these tests and to develop their own internal reliability data.

The goal of this procedure is to demonstrate a battery of quantitative techniques for sensory and pain measurement in humans. The equipment and techniques described are commonly found in pain clinics or are easy to obtain.

Numerous qualitative and quantitative techniques can be used to test sensory nerves and pain in both research and clinical settings. The current study ...

Psychophysically-anchored, Robust Thresholding in Studying Pain-related Lateralization of Oscillatory Prestimulus Activity

In perceptual studies, it is often important to objectively assess the equality of delivered stimulation across participants or to quantify the intra-individual sensation magnitude that is evoked by stimulation over multiple trials. This requires a robust mapping of stimulus magnitude to perceived intensity and is commonly achieved by psychophysical estimation methods such as the staircase procedure. Newer, more efficient procedures like the QUEST algorithm fit a psychophysical function to the data in real time while at the same time maximizing the efficiency of data collection. A robust estimate of the threshold intensity between painful and nonpainful perceptions can then be used to reduce the influence of variations in sensory input in subsequent analyses of oscillatory brain activity. By stimulating at a constant threshold intensity determined by an adaptive estimation procedure, the variance in the ratings can be directly attributed to perceptual processes. Oscillatory activity can then be contrasted between &#34;pain&#34; and &#34;no-pain&#34; trials directly, yielding activity that closely relates to perceptual classification processes in nociception.

Psychophysical methods such as the QUEST estimation procedure can efficiently yield robust estimates of the stimulation intensity at which nonpainful sensations transition into painful sensations. By stimulating repeatedly at the threshold intensity, the variability in rating responses can directly be attributed to perceptual classifications in subsequent analyses.

In perceptual studies, it is often important to objectively assess the equality of delivered stimulation across participants or to quantify the ...

Treating Low Back Pain in Failed Back Surgery Patients with Multicolumn-lead Spinal Cord Stimulation

Failed back surgery syndrome (FBSS) refers to persistent, chronic pain following spinal surgery. Spinal cord stimulation with dorsal epidural leads can be used to treat back and leg pain in FBSS patients. This paper presents a detailed protocol for using spinal cord stimulation with surgical leads in FBSS patients. In our department, with the patient under general anesthesia, we place the lead in the epidural space by means of a small laminectomy at the 10th thoracic level. Placement of the lead is followed by a 1 month trial period with an externalized lead. If pain relief is greater than 50% at the end of this 1 month stimulation trial (required by Belgian reimbursement criteria), an internal pulse generator is then placed under the skin and connected to the lead in a second surgical procedure. We have demonstrated that using this technique in rigorously selected FBSS patients can significantly improve back pain, leg pain, patient activity, and quality of life for a sustained period of time.

This paper presents a method that uses spinal cord stimulation with a multicolumn lead to treat neuropathic low back pain in failed back surgery patients.

Failed back surgery syndrome (FBSS) refers to persistent, chronic pain following spinal surgery. Spinal cord stimulation with dorsal epidural leads can be ...

Simultaneous Recordings of Cortical Local Field Potentials and Electrocorticograms in Response to Nociceptive Laser Stimuli from Freely Moving Rats

Electrocortical responses, elicited by laser heat pulses that selectively activate nociceptive free nerve endings, are widely used in many animal and human studies to investigate the cortical processing of nociceptive information. These laser-evoked brain potentials (LEPs) consist of several transient responses that are time-locked to the onset of laser stimuli. However, the functional properties of the LEP responses are still largely unknown, due to the lack of a sampling technique that can simultaneously record neural activities at the surface of the cortex (i.e., electrocorticogram [ECoG] and scalp electroencephalogram [scalp EEG]) and inside the brain (i.e., local field potential [LFP]). To address this issue, we present here an animal protocol using freely moving rats. This protocol is composed of three main procedures: (1) animal preparation and surgical procedures, (2) a simultaneous recording of ECoG and LFP in response to nociceptive laser stimuli, and (3) data analysis and feature extraction. Specifically, with the help of a 3D-printed protective shell, both ECoG and LFP electrodes implanted on the rat&#39;s skull were securely held together. During data collection, laser pulses were delivered on the rat&#39;s forepaws through gaps in the bottom of the chamber when the animal was in spontaneous stillness. Ongoing white noise was played to avoid the activation of the auditory system by the laser-generated ultrasounds. As a consequence, only nociceptive responses were selectively recorded. Using the standard analytical procedures (e.g., band-pass filtering, epoch extraction, and baseline correction) to extract stimulus-related brain responses, we obtained results showing that LEPs with a high signal-to-noise ratio were simultaneously recorded from ECoG and LFP electrodes. This methodology makes the simultaneous recording of ECoG and LFP activities possible, which provides a bridge of electrocortical signals at the mesoscopic and macroscopic levels, thereby facilitating the investigation of nociceptive information processing in the brain.

We developed a technique that simultaneously records both electrocorticography and local field potentials in response to nociceptive laser stimuli from freely moving rats. This technique helps establish a direct relationship of electrocortical signals at the mesoscopic and macroscopic levels, which facilitates the investigation of nociceptive information processing in the brain.

Electrocortical responses, elicited by laser heat pulses that selectively activate nociceptive free nerve endings, are widely used in many animal and ...

Multi-Modal Signals for Analyzing Pain Responses to Thermal and Electrical Stimuli

The assessment of pain relies mostly on methods that require a person to communicate. However, for people with cognitive and verbal impairments, existing methods are not sufficient as they lack reliability and validity. To approach this problem, recent research focuses on an objective pain assessment facilitated by parameters of responses derived from physiology, and video and audio signals. To develop reliable automated pain recognition systems, efforts have been made in creating multimodal databases in order to analyze pain and detect valid pain patterns. While the results are promising, they only focus on discriminating pain or pain intensities versus no pain. In order to advance this, research should also consider the quality and duration of pain as they provide additional valuable information for more advanced pain management. To complement existing databases and the analysis of pain regarding quality and length, this paper proposes a psychophysiological experiment to elicit, measure, and collect valid pain reactions. Participants are subjected to painful stimuli that differ in intensity (low, medium, and high), duration (5 s / 1 min), and modality (heat / electric pain) while audio, video (e.g., facial expressions, body gestures, facial skin temperature), and physiological signals (e.g., electrocardiogram [ECG], skin conductance level [SCL], facial electromyography [EMG], and EMG of M. trapezius) are being recorded. The study consists of a calibration phase to determine a subject&#8217;s individual pain range (from low to intolerable pain) and a stimulation phase in which pain stimuli, depending on the calibrated range, are applied. The obtained data may allow refining, improving, and evaluating automated recognition systems in terms of an objective pain assessment. For further development of such systems and to investigate pain reactions in more detail, additional pain modalities such as pressure, chemical, or cold pain should be included in future studies. Recorded data of this study will be released as the &#8220;X-ITE Pain Database&#8221;.

This article focuses on the experimental elicitation of pain through heat (thermal) and electrical stimulation while recording physiological, visual, and paralinguistic responses. It aims at collecting valid multimodal data for analyzing pain based on its intensity, quality, and duration.&#160;

The assessment of pain relies mostly on methods that require a person to communicate. However, for people with cognitive and verbal impairments, existing ...

Investigating Pain-Related Avoidance Behavior using a Robotic Arm-Reaching Paradigm

Avoidance behavior is a key contributor to the transition from acute pain to chronic pain disability. Yet, there has been a lack of ecologically valid paradigms to experimentally investigate pain-related avoidance. To fill this gap, we developed a paradigm (the robotic arm-reaching paradigm) to investigate the mechanisms underlying the development of pain-related avoidance behavior. Existing avoidance paradigms (mostly in the context of anxiety research) have often operationalized avoidance as an experimenter-instructed, low-cost response, superimposed on stimuli associated with threat during a Pavlovian fear conditioning procedure. In contrast, the current method offers increased ecological validity in terms of instrumental learning (acquisition) of avoidance, and by adding a cost to the avoidance response. In the paradigm, participants perform arm-reaching movements from a starting point to a target using a robotic arm, and freely choose between three different movement trajectories to do so. The movement trajectories differ in probability of being paired with a painful electrocutaneous stimulus, and in required effort in terms of deviation and resistance. Specifically, the painful stimulus can be (partly) avoided at the cost of performing movements requiring increased effort. Avoidance behavior is operationalized as the maximal deviation from the shortest trajectory on each trial. In addition to explaining how the new paradigm can help understand the acquisition of avoidance, we describe adaptations of the robotic arm-reaching paradigm for (1) examining the spread of avoidance to other stimuli (generalization), (2) modeling clinical treatment in the lab (extinction of avoidance using response prevention), as well as (3) modeling relapse, and return of avoidance following extinction (spontaneous recovery). Given the increased ecological validity, and numerous possibilities for extensions and/or adaptations, the robotic arm-reaching paradigm offers a promising tool to facilitate the investigation of avoidance behavior and to further our understanding of its underlying processes.

Avoidance is central to chronic pain disability, yet adequate paradigms for examining pain-related avoidance are lacking. Therefore, we developed a paradigm that allows investigating how pain-related avoidance behavior is learned (acquisition), spreads to other stimuli (generalization), can be mitigated (extinction), and how it may subsequently re-emerge (spontaneous recovery).

Avoidance behavior is a key contributor to the transition from acute pain to chronic pain disability. Yet, there has been a lack of ecologically valid ...

A Complex Diving-For-Food Task to Investigate Social Organization and Interactions in Rats

For many species, where status is a vital motivator that can affect health, social hierarchies influence behavior. Social hierarchies that include dominant-submissive relationships are common in both animal and human societies. These relationships can be affected by interactions with others and with their environment, making them difficult to analyze in a controlled study. Rather than a simple dominance hierarchy, this formation has a complicated presentation that allows rats to avoid aggression. Status can be stagnant or mutable, and results in complex societal stratifications. Here we describe a complex diving-for-food task to investigate rodent social hierarchy and behavioral interactions. This animal model may allow us to assess the relationship between a wide range of mental illnesses and social organization, as well as to study the effectiveness of therapy on social dysfunction.

This protocol describes a method of examining social hierarchy in a rat model. Rats perform a complex diving-for-food task in which they form a distinct hierarchy according to their willingness to dive underwater and swim to obtain a food pellet. This method is used to understand decision making and social relationships among highly social animals in small groups.

For many species, where status is a vital motivator that can affect health, social hierarchies influence behavior. Social hierarchies that include ...

Animal Models of Depression - Chronic Despair Model (CDM)

Major depressive disorder is one of the most prevalent forms of mental illnesses and causes tremendous individual suffering and socioeconomic burden. Despite its importance, current pharmacological treatment is limited, and novel treatment options are urgently needed. One key factor in the search for potential new drugs is evaluating their anti-depressive potency in appropriate animal models. The classical Porsolt forced swim test was used for this purpose for decades to induce and assess a depressive-like state. It consists of two short periods of forced swimming: the first to induce a depressed state and the second on the following day to evaluate the antidepressant effect of the agent given in between the two swim sessions. This model might be suitable as a screening tool for potential antidepressive agents but ignores the delayed onset of action of many antidepressants. The CDM was recently established and represented a modification of the classical test with notable differences. Mice are forced to swim for 5 consecutive days, following the idea that in humans, depression is induced by chronic rather than by acute stress. In a resting period of several days (1-3 weeks), animals develop sustained behavioral despair. The standard read-out method is the measurement of immobility time in an additional delayed swim session, but several alternative methods are proposed to get a broader view of the mood status of the animal. Multiple analysis tools can be used targeting behavioral, molecular, and electrophysiological changes. The depressed phenotype is stable for at least 4 weeks, providing a time window for rapid but also subchronic antidepressant treatment strategies. Furthermore, alterations in the development of a depressive-like state can be addressed using this approach. CDM, therefore, represents a useful tool to better understand depression and to develop novel treatment interventions.

Animal Models of Depression - Chronic Despair Model CDM

The chronic despair mouse model (CDM) of depression consists of repetitive forced swim sessions and another delayed swim phase as a read-out. It represents a suitable model for induction of a chronic depressive-like state stable for at least 4 weeks, amendable to evaluate subchronic and acute treatment interventions.

Major depressive disorder is one of the most prevalent forms of mental illnesses and causes tremendous individual suffering and socioeconomic burden. ...