Rats with chronic post-ischemia pain exhibit an analgesic sensitivity profile similar to human patients with complex regional pain syndrome--type I

Involvement of nuclear factor κB and descending pain pathways in the anti-hyperalgesic effect of β-citronellol, a food ingredient, complexed in β-cyclodextrin in a model of complex regional pain syndrome - Type 1

Complex regional pain syndrome type 1 (CRPS-1) is a painful syndrome without effective treatment. In order to explore possible new treatments, we used an animal model of CRPS-1 to examine the effects of β-Citronellol (βCT), a monoterpene found in a variety of plants that has been shown to have analgesic effects. We aimed to assess its effects alone, and complexed with β-cyclodextrin (βCD), which has been previously used to enhance the effects of a number of medicines. The βCT-βCD was characterized physiochemically using high performance liquid chromatography (HPLC) and differential scanning calorimetry (DSC) and shown to have 80% efficiency. In the animal model, Swiss mice were treated with βCT, βCT-βCD, vehicle, pregabalin or sham and evaluated for hyperalgesia and motor coordination. Inflammatory mediators were measured by Western blot or ELISA and the descending pain pathway by immunofluorescence. βCT was shown to have an anti-hyperalgesic effect (without affecting motor coordination) that reduced inflammatory mediators and activated the descending pain pathway, and these effects were increased with complexation in βCD. Our results showed βCT-βCD to be a promising treatment for CRPS-1.

Manual Therapy Reduces Pain Behavior and Oxidative Stress in a Murine Model of Complex Regional Pain Syndrome Type I

Complex regional pain syndrome type I (CRPS-I) is a chronic painful condition. We investigated whether manual therapy (MT), in a chronic post-ischemia pain (CPIP) model, is capable of reducing pain behavior and oxidative stress. Male Swiss mice were subjected to ischemia-reperfusion (IR) to mimic CRPS-I. Animals received ankle joint mobilization 48h after the IR procedure, and response to mechanical stimuli was evaluated. For biochemical analyses, mitochondrial function as well as oxidative stress thiobarbituric acid reactive substances (TBARS), protein carbonyls, antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) levels were determined. IR induced mechanical hyperalgesia which was subsequently reduced by acute MT treatment. The concentrations of oxidative stress parameters were increased following IR with MT treatment preventing these increases in malondialdehyde (MDA) and carbonyls protein. IR diminished the levels of SOD and CAT activity and MT treatment prevented this decrease in CAT but not in SOD activity. IR also diminished mitochondrial complex activity, and MT treatment was ineffective in preventing this decrease. In conclusion, repeated sessions of MT resulted in antihyperalgesic effects mediated, at least partially, through the prevention of an increase of MDA and protein carbonyls levels and an improvement in the antioxidant defense system.

Nociceptive mechanisms involved in the acute and chronic phases of a complex regional pain syndrome type 1 model in mice

Complex regional pain syndrome I (CRPS-I) is a chronic painful pathology still undertreated. CTK 01512-2 is a recombinant version of the spider peptide Phα1β, and it functions as a voltage-gated calcium channel blocker and a transient receptor potential ankyrin 1 (TRPA1) antagonist with antinociceptive effect in different pain models. Here, we investigate the mechanisms involved in the acute and chronic nociceptive phases of a model of CPRS-I in mice and assess the antinociceptive effect of CTK 01512-2 using this model. Adult male and female mice C57BL/6 (20-30 g) were used to determine mechanical (von Frey test) or cold (acetone test) allodynia induction. Inflammatory parameters (serum and tibial nerve lactate levels, hind paw temperature and edema, or tissue cell infiltration) were evaluated after chronic post-ischemia pain (CPIP, a model of CPRS-I) induction. Anti-inflammatory and anti-neuropathic drugs or CTK 01512-2 were tested. First, we detected that CPIP-induced mechanical and cold allodynia in male and female mice in a similar way. In the acute phase (1 day after CPIP), an increase in inflammatory parameters were observed, as well as the anti-allodynic effect of anti-inflammatory compounds. In the chronic phase (17 days after CPIP), mice exhibited mechanical and cold allodynia, and anti-neuropathic drugs induced antinociception, while no inflammatory alterations were found. CTK 01512-2 reversed the CPIP allodynic effect in both nociceptive phases. Thus, this CPRS-I model can be used to understand the mechanisms involved in CPRS-I induced pain and inflammation. Besides, we observed that CTK 01512-2 has a valuable antinociceptive effect in this pain model.

MiR-187-3p mimic alleviates ischemia-reperfusion-induced pain hypersensitivity through inhibiting spinal P2X7R and subsequent mature IL-1β release in mice

BACKGROUND

Ischemia-reperfusion (IR)-induced pain hypersensitivity shares features of neuroinflammation and neuropathic pain, accompanied by overproduction of interleukin (IL)-1β. Multiple microRNAs (miRs) are dysregulated during IR; among these miRs, miR-187-3p was recently reported to drive IL-1β release in retinal disease by activating members of the purinergic receptor family. However, the roles of miR-187-3p in the spinal cord are unclear. Thus, we investigated whether miR-187-3p is involved in the pathogenesis of IR-induced pain hypersensitivity by regulating the P2X7R signal and subsequent IL-1β release.

METHODS

A mouse model was established by 5-min occlusion of the aortic arch. Pain hypersensitivity was assessed by the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). MiR-187-3p, P2X7R, cleaved caspase-1 and mature IL-1β expression levels were measured by RT-PCR and Western blotting. The in vivo roles of miR-187-3p, P2X7R and IL-1β were explored by intrathecal treatment with synthetic miRs, selective agonists and antagonists in separate experiments. Double immunofluorescence staining was performed to delineate the cellular distribution of P2X7R and IL-1β.

RESULTS

IR-induced progressively decreased PWT and PWL values were closely related to decreases in miR-187-3p and increases in P2X7R expression levels over time. The functional miR-187-3p/P2X7R pair was preliminarily predicted by a bioinformatic database and confirmed in vivo by quantitative analysis, as mimic-187 greatly increased miR-187-3p but decreased P2X7R expression levels, whereas inhibitor-187 reversed these changes. In contrast, downregulating P2X7R by mimic-187 or A-438079 treatment comparably increased PWT and PWL values in IR-injured mice, while upregulating P2X7R by inhibitor-187 or BzATP treatment decreased PWT and PWL values in sham-operated mice. Moreover, P2X7R and IL-1β immunoreactivities in each group were changed in the same patterns. This finding was further supported by results showing that downregulating IL-1β by A-438079 and IL-1β-neutralizing antibody similarly decreased P2X7R, cleaved caspase-1 and mature IL-1β expression levels, whereas BzATP treatment increased these levels. Expectedly, mimic-187 treatment preserved PWT and PWL values, with decreased cleaved caspase-1 and mature IL-1β expression levels, whereas inhibitor-187 reversed these effects.

CONCLUSIONS

The spinal miR-187-3p/P2X7R pair functioned in a mouse IR model. Increasing miR-187-3p protected against pain hypersensitivity and mature IL-1β overproduction, partially through inhibiting P2X7R activation.

Anti-allodynic Effect of Mangiferin in Rats With Chronic Post-ischemia Pain: A Model of Complex Regional Pain Syndrome Type I

The present study reproduces chronic post-ischemia pain (CPIP), a model of complex regional pain syndrome type I (CRPS-I), in rats to examine the possible transient and long-term anti-allodynic effect of mangiferin (MG); as well as its potential beneficial interactions with some standard analgesic drugs and sympathetic-mediated vasoconstriction and vasodilator agents during the earlier stage of the pathology. A single dose of MG (50 and 100 mg/kg, p.o.) decreased mechanical allodynia 72 h post-ischemia-reperfusion (I/R). MG 100 mg/kg, i.p. (pre- vs. post-drug) increased von Frey thresholds in a yohimbine and naloxone-sensitive manner. Sub-effective doses of morphine, amitriptyline, prazosin, clonidine and a NO donor, SIN-1, in the presence of MG were found to be significantly anti-allodynic. A long-term anti-allodynic effect at 7 and 13 days post-I/R after repeated oral doses of MG (50 and 100 mg/kg) was also observed. Further, MG decreased spinal and muscle interleukin-1β concentration and restored muscle redox status. These results indicate that MG has a transient and long-term anti-allodynic effect in CPIP rats that appears to be at least partially attributable to the opioid and α2 adrenergic receptors. Additionally, its anti-inflammatory and antioxidant mechanisms could also be implicated in this effect. The association of MG with sub-effective doses of these drugs enhances the anti-allodynic effect; however, an isobolographic analysis should be performed to define a functional interaction between them. These findings suggest the possible clinical use of MG in the treatment of CRPS-I in both early sympathetically maintained pain and long-term sympathetically independent pain.

The Rodent Tibia Fracture Model: A Critical Review and Comparison With the Complex Regional Pain Syndrome Literature

Distal limb fracture is the most common cause of complex regional pain syndrome (CRPS), thus the rodent tibia fracture model (TFM) was developed to study CRPS pathogenesis. This comprehensive review summarizes the published TFM research and compares these experimental results with the CRPS literature. The TFM generated spontaneous and evoked pain behaviors, inflammatory symptoms (edema, warmth), and trophic changes (skin thickening, osteoporosis) resembling symptoms in early CRPS. Neuropeptides, inflammatory cytokines, and nerve growth factor (NGF) have been linked to pain behaviors, inflammation, and trophic changes in the TFM model and proliferating keratinocytes were identified as the primary source of cutaneous cytokines and NGF. Tibia fracture also activated spinal glia and upregulated spinal neuropeptide, cytokine, and NGF expression, and in the brain it changed dendritic architecture. B cell-expressed immunoglobulin M antibodies also contributed to pain behavior, indicating a role for adaptive immunity. These results modeled many findings in early CRPS, but significant differences were also noted.

PERSPECTIVE

Multiple neuroimmune signaling mechanisms contribute to the pain, inflammation, and trophic changes observed in the injured limb of the rodent TFM. This model replicates many of the symptoms, signs, and pathophysiology of early CRPS, but most post-fracture changes resolve within 5 months and may not contribute to perpetuating chronic CRPS.

Effects of Different Parameters of Continuous Training and High-Intensity Interval Training in the Chronic Phase of a Mouse Model of Complex Regional Pain Syndrome Type I

This study evaluated the effects of continuous and interval running on a treadmill on mechanical hyperalgesia in an animal model of chronic postischemia pain and analyzed the mechanism of action of this effect. Different groups of male Swiss mice with chronic postischemia pain, induced by 3 hours of paw ischemia followed by reperfusion, ran on the treadmill in different protocols-the speed (10, 13, 16, or 19 m/min), duration (15, 30, or 60 minutes), weekly frequency (3 or 5 times), weekly increase in continuous and interval running speed-were tested. Mechanical hyperalgesia was evaluated by von Frey filament 7, 14, and 21 days after paw ischemia followed by reperfusion. On day 11 after paw ischemia followed by reperfusion and after 5 days of continuous and interval running, concentrations of cytokines, oxidative stress parameters, and extracellular signal-regulated kinase 1/2 and AKT 1/2/3 expression in the spinal cord were measured. The results showed that continuous running has an antihyperalgesic effect that depends on intensity and volume. Interval running has a longer-lasting antihyperalgesic effect than continuous running. The antihyperalgesic effect depends on intensity and volume in continuous running, and increasing speed maintains the antihyperalgesic effect in both protocols. In the spinal cord, both runs decreased tumor necrosis factor-α and interleukin-6 levels and increased interleukin-10. Both running protocols reduced oxidative damage in the spinal cord. Only interval running had lower concentrations of phosphorylated extracellular signal-regulated kinase 1/2 in the spinal cord. Interval running presented a great antihyperalgesic potential with more promising results than continuous running, which may be owing to the fact that the interval running can activate different mechanisms from those activated by continuous running. PERSPECTIVE: A minimum of .5-hour sessions of moderate to high intensity ≥3 times a week are essential parameters for continuous and interval running-induced analgesia. However, interval running was shown to be more effective than continuous running and can be an important adjuvant treatment to chronic pain.

Pregabalin Treatment of a Patient With Complex Regional Pain Syndrome

BACKGROUND

Complex regional pain syndrome (CRPS) is a painful and disabling neurovascular condition. There is no consensus on the etiopathogenesis or the treatment. We present a patient with CRPS type 1 accompanied by a psychiatric disorder to discuss the relationship between CRPS and psychiatric disease and to emphasize the response of this case to treatment with pregabalin.

PATIENT DESCRIPTION

A 15-year-old girl presented with swelling, severe pain, edema, hyperesthesia, allodynia, and sweating changes in the left arm and was diagnosed as CRPS type 1. The presence of disturbed family relations was revealed on psychiatric examination, and a diagnosis of major depression was made. Her symptoms did not respond to selective serotonin reuptake inhibitors and noradrenergic and specific serotonergic antidepressives, gabapentin, or stellate ganglion blockage, but the patient's pain resolved with pregabalin. Symptom-oriented measures and psychiatric support enabled ongoing treatment. A social services evaluation led to her being placed in the care of social services to protect her from the chaotic and traumatic family life.

CONCLUSION

Detailed psycological and psychiatric evaluation is recommended in individuals with CRPS because psychiatric support and improvement of associated psychosocial concerns in addition to pregabalin seems to facilitate treatments in some patients.

The bifunctional μ opioid agonist/antioxidant [Dmt(1)]DALDA is a superior analgesic in an animal model of complex regional pain syndrome-type i

Reactive oxygen species (ROS) play an important role in the development of complex regional pain syndrome-Type I (CRPS-I), as also demonstrated with the chronic post ischemia pain (CPIP) animal model of CRPS-I. We show that morphine and the antioxidant N-acetylcysteine (NAC) act synergistically to reduce mechanical allodynia in CPIP rats. The tetrapeptide amide [Dmt(1)]DALDA (H-Dmt-d-Arg-Phe-Lys-NH2) is a potent and selective μ opioid receptor (MOR) agonist with favorable pharmacokinetic properties and with antioxidant activity due to its N-terminal Dmt (2',6'-dimethyltyrosine) residue. In the CPIP model, [Dmt(1)]DALDA was 15-fold more potent than morphine in reversing mechanical allodynia and 4.5-fold more potent as analgesic in the heat algesia test. The results indicate that bifunctional compounds with MOR agonist/antioxidant activity have therapeutic potential for the treatment of CRPS-I.

Neurogenic neuroinflammation in fibromyalgia and complex regional pain syndrome

Although fibromyalgia and complex regional pain syndrome (CRPS) have distinct clinical phenotypes, they do share many other features. Pain, allodynia and dysaesthesia occur in each condition and seem to exist on a similar spectrum. Fibromyalgia and CRPS can both be triggered by specific traumatic events, although fibromyalgia is most commonly associated with psychological trauma and CRPS is most often associated with physical trauma, which is frequently deemed routine or minor by the patient. Fibromyalgia and CRPS also seem to share many pathophysiological mechanisms, among which the most important are those involving central effects. Nonetheless, peripheral effects, such as neurogenic neuroinflammation, are also important contributors to the clinical features of each of these disorders. This Review highlights the differing degrees to which neurogenic neuroinflammation might contribute to the multifactorial pathogenesis of both fibromyalgia and CRPS, and discusses the evidence suggesting that this mechanism is an important link between the two disorders, and could offer novel therapeutic targets.

Paroxetine alleviates rat limb post-ischemia induced allodynia through GRK2 upregulation in superior cervical ganglia

Long-lasting neuroplastic changes induced by transient decrease in G protein-coupled receptor kinase 2 (GRK2) in nociceptors enhances and prolongs inflammatory hyperalgesia. Here, we investigated the effects of paroxetine (a selective serotonin reuptake inhibitor and GRK2 inhibitor) on GRK2 expression in superior cervical ganglion (SCG) in a rat model of complex regional pain syndrome type I (CRPS-I). After ischemia-reperfusion (I/R) injury, the ipsilateral 50% paw withdrawal thresholds (PWTs) to mechanical stimuli and the expression levels of GRK2 protein and mRNA in the ipsilateral SCGs all decreased significantly; the ipsilateral cold allodynia scores increased significantly. No significant differences were found in the contralateral side except GRK2 mRNA reduced significantly at day 2-day 9 after I/R injury, but still higher than those in ipsilateral SCGs. After paroxetine administration, the ipsilateral 50% PWTs at day 2, 7, 14, and 21 were significantly higher than those in control group; The GRK2 protein and mRNA levels in ipsilateral SCGs were also significantly up-regulated after day1; The ipsilateral cold allodynia scores were significantly reduced after day7. No significant differences were found in the contralateral 50% PWTs, cold allodynia scores, and GRK2 protein level except GRK2 mRNA levels increased significantly at day1-day7 after paroxetine administration. Therefore, a transient decrease of GRK2 expression in SCG neurons might be involved in the development and maintenance of allodynia in CRPS-I and paroxetine might alleviate this allodynia through GRK2 protein upregulation in SCGs.

Dexmedetomidine alleviates rat post-ischemia induced allodynia through GRK2 upregulation in superior cervical ganglia

A transient decrease in G protein-coupled receptor kinase 2 (GRK2) in nociceptors can produce long-lasting neuroplastic changes in nociceptor function, eventually enhancing and prolonging inflammatory hyperalgesia. Here, we investigated the effects of selective α2-adrenoceptor agonist dexmedetomidine (DMED) on GRK2 expression in superior cervical ganglion (SCG) in a rat model of complex regional pain syndrome type I (CRPS-I). The ipsilateral 50% paw withdrawal thresholds (PWTs) to mechanical stimuli decreased significantly starting from 24 h after ischemia-reperfusion (I/R) injury, and lasted for over 3 weeks; the ipsilateral cold allodynia scores, GRK2 protein and mRNA levels in SCGs all increased significantly. No significant differences were found in the contralateral side except GRK2 mRNA reduced significantly after 48 h I/R injury, but still higher than those in the ipsilateral side. Following daily injection of 10 μg/kg of DMED for a maximum of 7 days, the ipsilateral PWTs on days 1, 2, 7, 14, and 21 after DMED administration were significantly higher than those in control group; the GRK2 protein and mRNA expressions in the ipsilateral SCGs were also significantly upregulated; the ipsilateral cold allodynia scores were significantly reduced. No significant differences were found in the contralateral 50%PWTs, cold allodynia scores, and GRK2 protein level except GRK2 mRNA levels increased significantly on days 1 to 7 after DMED administration. Therefore, a transient decrease of GRK2 expression in SCG neurons might be involved in the development and maintenance of allodynia in CRPS-I and DMED might alleviate this allodynia through GRK2 upregulation in SCG neurons.

Topical combinations to treat microvascular dysfunction of chronic postischemia pain

BACKGROUND

Growing evidence indicates that patients with complex regional pain syndrome (CRPS) exhibit tissue abnormalities caused by microvascular dysfunction in the blood vessels of skin, muscle, and nerve. We tested whether topical combinations aimed at improving microvascular function would relieve allodynia in an animal model of CRPS. We hypothesized that topical administration of either α2-adrenergic (α2A) receptor agonists or nitric oxide (NO) donors given to increase arterial blood flow, combined with either phosphatidic acid (PA) or phosphodiesterase (PDE) inhibitors to increase capillary blood flow, would effectively reduce allodynia and signs of microvascular dysfunction in the animal model of chronic pain.

METHODS

Mechanical allodynia was induced in the hindpaws of rats with chronic postischemia pain (CPIP). Allodynia was assessed before and after topical application of vehicle, single drugs or combinations of an α2A receptor agonist (apraclonidine) or an NO donor (linsidomine), with PA or PDE inhibitors (lisofylline, pentoxifylline). A topical combination of apraclonidine + lisofylline was also evaluated for its effects on a measure of microvascular function (postocclusive reactive hyperemia) and tissue oxidative capacity (formazan production by tetrazolium reduction) in CPIP rats.

RESULTS

Each of the single topical drugs produced significant dose-dependent antiallodynic effects compared with vehicle in CPIP rats (N = 30), and the antiallodynic dose-response curves of either PA or PDE inhibitors were shifted 5- to 10-fold to the left when combined with nonanalgesic doses of α2A receptor agonists or NO donors (N = 28). The potent antiallodynic effects of ipsilateral treatment with combinations of α2A receptor agonists or NO donors with PA or PDE inhibitors were not reproduced by the same treatment of the contralateral hindpaw (N = 28). Topical combinations produced antiallodynic effects lasting up to 6 hours (N = 15) and were significantly enhanced by low-dose systemic pregabalin in early, but not late, CPIP rats (N = 18). An antiallodynic topical combination of apraclonidine + lisofylline was also found to effectively relieve depressed postocclusive reactive hyperemia in CPIP rats (N = 61) and to increase formazan production in postischemic tissues (skin and muscle) (N = 56).

CONCLUSIONS

The present results support the hypothesis that allodynia in an animal model of CRPS is effectively relieved by topical combinations of α2A receptor agonists or NO donors with PA or PDE inhibitors. This suggests that topical treatments aimed at improving microvascular function by increasing both arterial and capillary blood flow produce effective analgesia for CRPS.

Topical combinations aimed at treating microvascular dysfunction reduce allodynia in rat models of CRPS-I and neuropathic pain

Growing evidence indicates that various chronic pain syndromes exhibit tissue abnormalities caused by microvasculature dysfunction in the blood vessels of skin, muscle, or nerve. We tested whether topical combinations aimed at improving microvascular function would relieve allodynia in animal models of complex regional pain syndrome type I (CRPS-I) and neuropathic pain. We hypothesized that topical administration of either α(2)-adrenergic (α(2)A) receptor agonists or nitric oxide (NO) donors combined with either phosphodiesterase (PDE) or phosphatidic acid (PA) inhibitors would effectively reduce allodynia in these animal models of chronic pain. Single topical agents produced significant dose-dependent antiallodynic effects in rats with chronic postischemia pain, and the antiallodynic dose-response curves of PDE and PA inhibitors were shifted 2.5- to 10-fold leftward when combined with nonanalgesic doses of α(2)A receptor agonists or NO donors. Topical combinations also produced significant antiallodynic effects in rats with sciatic nerve injury, painful diabetic neuropathy, and chemotherapy-induced painful neuropathy. These effects were shown to be produced by a local action, lasted up to 6 hours after acute treatment, and did not produce tolerance over 15 days of chronic daily dosing. The present results support the hypothesis that allodynia in animal models of CRPS-I and neuropathic pain is effectively relieved by topical combinations of α(2)A or NO donors with PDE or PA inhibitors. This suggests that topical treatments aimed at improving microvascular function may reduce allodynia in patients with CRPS-I and neuropathic pain.

PERSPECTIVE

This article presents the synergistic antiallodynic effects of combinations of α(2)A or NO donors with PDE or PA inhibitors in animal models of CRPS-I and neuropathic pain. The data suggest that effective clinical treatment of chronic neuropathic pain may be achieved by therapies that alleviate microvascular dysfunction in affected areas.

Oleaginous extract from the fruits Pterodon pubescens Benth induces antinociception in animal models of acute and chronic pain

ETHNOPHARMACOLOGICAL RELEVANCE

Pterodon pubescens Benth is a medicinal plant commonly used for therapeutic purposes in folk medicine for rheumatic diseases' treatment. In the present work we analyzed the chemical composition of the oleaginous extract of P. pubescens Benth (OEPp) and extended the antinociceptive effect of OEPp evaluating its role on animal models of acute and chronic pain.

MATERIALS AND METHODS

The antinociceptive and antiedematogenic effects of OEPp (3-100mg/kg, i.g.) were evaluated in the formalin test; mechanical allodynia in the postoperative pain and complex regional pain syndrome type-I (CRPS-I) animal models; and thermal hyperalgesia was induced by plantar incision. Finally, we performed a phytochemical analysis of OEPp.

RESULTS

The chemical composition of OEPp was analyzed by mass spectrometry (GC/MS) and eight sesquiterpene compounds were identified, i.e. three major sesquiterpene (E-cariofilene, γ-muurolene, biciclogermacrene), and nine vouacapane diterpenes, four of which showed in major concentration (6α-acetoxyvouacapane, 6α,7β-dimetoxivouacapan-17-ene, 6α-acetoxy,7β-hidroxyvouacapane, 6α,7β-diacetoxycouacapane). Furthermore, the results of the present study demonstrate, for the first time, that the OEPp reduced mechanical allodynia in the postoperative pain and CRPS-I animal models. OEPp also increased the paw withdrawal latency in hot- and cold-plate tests in the postoperative pain model. In addition, the present work confirms and extends previous data from literature showing that systemic administration of OEPp caused significant inhibition against both phases of pain response to formalin intraplantar injection and edema formation.

CONCLUSIONS

Together, present and previous findings show that OEPp given intra-gastrically caused significant inhibition against both phases of formalin intraplantar injection and effectively inhibited mechanical and thermal hyperalgesia in the postoperative pain and CRPS-I animal models.

Role of peripheral endothelin receptors in an animal model of complex regional pain syndrome type 1 (CRPS-I)

Chronic post-ischemic pain (CPIP) is an animal model of CRPS-I developed using a 3-h ischemia-reperfusion injury of the rodent hind paw. The contribution of local endothelin to nociception has been evaluated in CPIP mice by measuring sustained nociceptive behaviors (SNBs) following intraplantar injection of endothelin-1 or -2 (ET-1, ET-2). The effects of local BQ-123 (ETA-R antagonist), BQ-788 (ETB-R antagonist), IRL-1620 (ETB-R agonist) and naloxone (opioid antagonist) were assessed on ET-induced SNBs and/or mechanical and cold allodynia in CPIP mice. ETA-R and ETB-R expression was assessed using immunohistochemistry and Western blot analysis. Compared to shams, CPIP mice exhibited hypersensitivity to local ET-1 and ET-2. BQ-123 reduced ET-1- and ET-2-induced SNBs in both sham and CPIP animals, but not mechanical or cold allodynia. BQ-788 enhanced ET-1- and ET-2-induced SNBs in both sham and CPIP mice, and cold allodynia in CPIP mice. IRL-1620 displayed a non-opioid anti-nociceptive effect on ET-1- and ET-2-induced SNBs and mechanical allodynia in CPIP mice. The distribution of ETA-R and ETB-R was similar in plantar skin of sham and CPIP mice, but both receptors were over-expressed in plantar muscles of CPIP mice. This study shows that ETA-R and ETB-R have differing roles in nociception for sham and CPIP mice. CPIP mice exhibit more local endothelin-induced SNBs, develop a novel local ETB-R agonist-induced (non-opioid) analgesia, and exhibit over-expression of both receptors in plantar muscles, but not skin. The effectiveness of local ETB-R agonists as anti-allodynic treatments in CPIP mice holds promise for novel therapies in CRPS-I patients.

Role of NFkappaB in an animal model of complex regional pain syndrome-type I (CRPS-I)

NFkappaB is involved in several pathogenic mechanisms that are believed to underlie the complex regional pain syndrome (CRPS), including ischemia, inflammation and sensitization. Chronic postischemia pain (CPIP) has been developed as an animal model that mimics the symptoms of CRPS-I. The possible involvement of NFkappaB in CRPS-I was studied using CPIP rats. Under sodium pentobarbital anesthesia, a tourniquet was placed around the rat left ankle joint, producing 3 hours of ischemia, followed by rapid reperfusion (IR injury). NFkappaB was measured in nuclear extracts of muscle and spinal cord tissue using ELISA. Moreover, the anti-allodynic (mechanical and cold) effect was tested for systemic, intrathecal, or intraplantar treatment with the NFkappaB inhibitor pyrrolidine dithiocarbamate (PDTC). At 2 and 48 hours after IR injury, NFkappaB was elevated in muscle and spinal cord of CPIP rats compared to shams. At 7 days, NFkappaB levels were normalized in muscle, but still elevated in spinal cord tissue. Systemic PDTC treatment relieved mechanical and cold allodynia in a dose-dependent manner, lasting for at least 3 hours. Intrathecal-but not intraplantar-administration also relieved mechanical allodynia. The results suggest that muscle and spinal NFkappaB plays a role in the pathogenesis of CPIP and potentially of human CRPS.

PERSPECTIVE

Using the CPIP model, we demonstrate that NFkappaB is involved in the development of allodynia after a physical injury (ischemia and reperfusion) without direct nerve trauma. Since CPIP animals exhibit many features of human CRPS-I, this observation indicates a potential role for NFkappaB in human CRPS.

Regulation of peripheral blood flow in complex regional pain syndrome: clinical implication for symptomatic relief and pain management

BACKGROUND

During the chronic stage of Complex Regional Pain Syndrome (CRPS), impaired microcirculation is related to increased vasoconstriction, tissue hypoxia, and metabolic tissue acidosis in the affected limb. Several mechanisms may be responsible for the ischemia and pain in chronic cold CPRS.

DISCUSSION

The diminished blood flow may be caused by either sympathetic dysfunction, hypersensitivity to circulating catecholamines, or endothelial dysfunction. The pain may be of neuropathic, inflammatory, nociceptive, or functional nature, or of mixed origin.

SUMMARY

The origin of the pain should be the basis of the symptomatic therapy. Since the difference in temperature between both hands fluctuates over time in cold CRPS, when in doubt, the clinician should prioritize the patient's report of a persistent cold extremity over clinical tests that show no difference. Future research should focus on developing easily applied methods for clinical use to differentiate between central and peripheral blood flow regulation disorders in individual patients.