Cutaneous tactile allodynia associated with microvascular dysfunction in muscle
- Andre Laferrière†1, 2,
- Magali Millecamps†2, 4,
- Dimitris N Xanthos†2, 3,
- Wen Hua Xiao1, 2,
- Chiang Siau1,
- Marissa de Mos5,
- Christelle Sachot6,
- J Vaigunda Ragavendran1,
- Frank JPM Huygen7,
- Gary J Bennett1, 2, 4 and
- Terence J Coderre1, 2, 3, 8Email author
© Laferrière et al; licensee BioMed Central Ltd. 2008
Received: 29 September 2008
Accepted: 28 October 2008
Published: 28 October 2008
Cutaneous tactile allodynia, or painful hypersensitivity to mechanical stimulation of the skin, is typically associated with neuropathic pain, although also present in chronic pain patients who do not have evidence of nerve injury. We examine whether deep tissue microvascular dysfunction, a feature common in chronic non-neuropathic pain, contributes to allodynia.
Persistent cutaneous allodynia is produced in rats following a hind paw ischemia-reperfusion injury that induces microvascular dysfunction, including arterial vasospasms and capillary slow flow/no-reflow, in muscle. Microvascular dysfunction leads to persistent muscle ischemia, a reduction of intraepidermal nerve fibers, and allodynia correlated with muscle ischemia, but not with skin nerve loss. The affected hind paw muscle shows lipid peroxidation, an upregulation of nuclear factor kappa B, and enhanced pro-inflammatory cytokines, while allodynia is relieved by agents that inhibit these alterations. Allodynia is increased, along with hind paw muscle lactate, when these rats exercise, and is reduced by an acid sensing ion channel antagonist.
Our results demonstrate how microvascular dysfunction and ischemia in muscle can play a critical role in the development of cutaneous allodynia, and encourage the study of how these mechanisms contribute to chronic pain. We anticipate that focus on the pain mechanisms associated with microvascular dysfunction in muscle will provide new effective treatments for chronic pain patients with cutaneous tactile allodynia.
Cutaneous tactile allodynia (referred to henceforth as allodynia) is often found in patients with neuropathic pain, and is generally assumed to depend on the sensitization of the central nervous system in response to aberrant activity in damaged peripheral nerves . However, allodynia is also caused by other injuries, such as that produced by ultraviolet radiation, and occurs in association with migraine headache  and fibromyalgia . Allodynia is also prominent in complex regional pain syndrome (CRPS) , which can be initiated by either soft tissue (CRPS type-I) or nerve (CRPS type-II) injuries. Importantly, what both CRPS subtypes share with UV injury, migraine and fibromyalgia, besides allodynia, are significant vascular abnormalities caused by microvascular dysfunction [5–9]. Also since CNS sensitization, which is critical for allodynia, is more pronounced following deep tissue injury than after cutaneous injury , it is possible that microvascular dysfunction in muscle may induce significant allodynia. However, few investigators have assessed vascular abnormalities in the etiology of chronic pain, and none have studied whether microvascular dysfunction in muscle contributes to allodynia. To address these questions, we investigated whether an ischemia-reperfusion (IR) injury produces allodynia in rats, and whether the allodynia is associated with microvascular dysfunction in muscle, and key mechanisms that underlie it. We show that microvascular dysfunction leads to persistent muscle ischemia, a reduction of intraepidermal nerve fibers, and allodynia correlated with muscle ischemia, but not with skin nerve loss. The affected hind paw muscle shows lipid peroxidation, an upregulation of nuclear factor kappa B, and enhanced pro-inflammatory cytokines, while allodynia is relieved by agents that inhibit oxidative stress, nuclear factor kappa B and cytokine activity. Allodynia is increased, along with hind paw muscle lactate, when these rats exercise, and is reduced by an acid sensing ion channel antagonist. Allodynia is also significantly correlated with muscle lactate before and after exercise.
Results and discussion
To exclude the possibility that CPIP depends on a crush injury of afferent nerves, we examined whether allodynia was also induced after prolonged occlusion of the arteries supplying the hind paw. Mechanical paw-withdrawal thresholds were also persistently significantly reduced in rats whose hind paw blood vessels were occluded for 3 h (P = 0.011) (Fig. 1b), suggesting that allodynia was not caused by tourniquet-induced damage to underlying nerves.
If not nerve crush, it is likely that allodynia depends on IR injury and resultant microvascular dysfunction, which may include arterial vasospasms and capillary slow flow/no-reflow. Arterial vasospasms occur due to a reduction in nitric oxide-induced vasodilatation  and hyper-responsiveness of arterial smooth muscle cells to norepinephrine . To determine whether CPIP rats exhibit arterial hyper-responsiveness, we used laser Doppler flowmetry to examine norepinephrine-induced reductions in blood flow in the hind paws of CPIP rats. We found that at 2 days post-perfusion, norepinephrine-induced reductions in CPIP hind paw blood flow were significantly enhanced (P = 0.0062) (Fig. 1c).
Slow flow/no-reflow is a condition where damage to the capillary endothelial cells causes them to swell, and to become clogged with platelets and white blood cells, thus obstructing the passage of red blood cells . We used electron microscopy to assess the morphology of capillaries and endothelial cell thickness in CPIP hind paw muscles. Fig. 1d shows a normal capillary in the hind paw muscle of a sham-operated rat. In contrast, Fig. 1e shows a representative damaged capillary in CPIP hind paw muscle, with swollen endothelial cells and an occluded lumen. As shown in Fig. 1f, the endothelial cells in the hind paw muscle capillaries had significantly thicker (31.5%) cell walls in CPIP rats (P < 0.03971). These findings indicate that CPIP rats exhibit endothelial damage within hind paw muscle capillary beds.
To further characterize slow flow/no-reflow in CPIP rats, we used intra-arterial perfusion of India ink to stain patent blood vessels in the hind paw digital muscle of CPIP rats . As shown in Fig. 1g, most vessels in the muscle capillary bed of the contralateral CPIP hind paw are stained with India ink, indicating that they are patent. In contrast, many vessels in the ipsilateral CPIP hind paw are poorly stained (Fig. 1h). Quantifying this, we found that the ipsilateral CPIP hind paw had significantly fewer patent blood vessels than the contralateral hind paw up to 7 days post-reperfusion (P = 0.0002) (Fig. 1i). This indicates that CPIP rats have persistent capillary slow flow/no-reflow in their hind paw muscles.
It is possible that microvascular dysfunction in CPIP rats could induce secondary injury of the distal nerve endings, as previously reported in CRPS-I patients . Thus, we examined intraepidermal nerve fiber (IENF) density in the CPIP hind paw skin using immunocytochemical staining with antibodies to protein gene product 9.5 (PGP9.5), a pan-neuronal marker . Sham rats exhibits normal PGP9.5 skin staining with many IENFs observed in the epidermis (Fig. 4d). However, epidermal PGP9.5 staining is decreased in ipsilateral CPIP hind paw skin, indicating there is a reduction in IENFs (Fig. 4e). Quantifying PGP9.5 staining over the first week after IR injury, we found a significant reduction in IENF density in the epidermis of CPIP hind paw skin (P = 0.0133) (Fig. 4f). However, when we plotted IENF density against mechanical paw-withdrawal thresholds, we found no significant correlation between IENF density and allodynia in CPIP rats at either 2 or 7 days post-reperfusion (P > 0.05) (Fig. 4g). Also, CPIP rats did not exhibit any significant alteration of conduction velocity in the sural nerve (P > 0.05) (Fig. 4h). This is consistent with the absence of a tourniquet-evoked injury to peripheral nerve at the ankle, and similar to findings in CRPS-I patients, who by definition do not have detectable injury at the level of the peripheral nerve.
After IR injury, free radicals stimulate the production of pro-inflammatory cytokines , following upregulation of nuclear factor kappa B (NFκB) . We used ELISAs to determine the levels of pro-inflammatory cytokines and NFκB in CPIP hind paw muscle, as well as examining the effects of interleukin-1 receptor antagonist (IL-1RA), and an inhibitor of NFκB (pyrrolidine ditiocarbamate, PDTC), on CPIP allodynia 2 days post-reperfusion. The cytokines tumor necrosis factor-α (P = 0.0085) (Fig. 5d), IL-6 (P = 0.0014) (Fig. 5e) and IL-1β (P = 0.0021) (Fig. 5f), and the transcription factor NFκB (P = 0.0073) (Fig. 5g), were all significantly elevated in the CPIP hind paws early after reperfusion, and both IL-1RA (P = 0.0302) (Fig. 5h) and PDTC (P = 0.0009) (Fig. 5i) significantly elevated paw-withdrawal thresholds of CPIP rats, suggesting that NFκB and pro-inflammatory cytokines play a role in CPIP allodynia.
We describe here that allodynia after hind paw IR injury coincides with arterial hypersensitivity to norepinephrine, capillary slow flow/no-reflow and ischemia, and follows increased lipid peroxidation, NFκB, and pro-inflammatory cytokines in muscle tissue. Allodynia is also alleviated by agents that reduce these consequences of microvascular dysfunction, and is directly related to muscle tissue lactate. All these findings indicate that microvascular dysfunction and ischemia in muscle underlies persistent allodynia after IR injury. Our results are consistent with the demonstration that activity in muscle nociceptors is more potent than activity in cutaneous nociceptors in evoking central sensitization . Also, while injecting capsaicin or carrageenan into skin produces allodynia that lasts at most hours, the same injections into muscle induce prolonged central sensitization and cutaneous allodynia lasting up to several weeks [28, 29]. Here, IR injury induced alterations in skin nerves, however, unlike the persistent muscle ischemia, these changes were not correlated with allodynia. The finding that allodynia is correlated with muscle lactate (but not skin IENF loss) argues for a more critical role of muscle changes in allodynia. However, we can not dismiss the possibility that the skin IENF loss has some role in the production of allodynia.
Muscle ischemia and painful symptoms after ischemia-reperfusion injury highlight the importance of microvascular dysfunction in muscle to cutaneous tactile allodynia, or painful hypersensitivity to touch, in chronic pain. Arterial vasospasms, endothelial cell injury and capillary slow flow/no-reflow after ischemia-reperfusion injury induce persistent allodynia dependent on oxygen free-radicals, nuclear factor kappa B, pro-inflammatory cytokines and lactate in muscle. Microvascular dysfunction leads to abnormalities in cutaneous nerves, as well as persistent ischemia in muscle, and that allodynia is significantly correlated with the muscle ischemia, but not with skin nerve changes. Besides nerve cells, pathology in muscle microvasculature may be an important new target for development of therapies for chronic pain.
All methods were approved by the McGill Animal Care and Ethics committees.
IR injury was induced in anesthetized rats by placing an O-ring around the ankle (shams only anesthetized) for 3 h as described , or by clamping the all blood vessels supplying the hind paw for 3 h (sham rats-5 min) with vascular micro-forceps, followed by reperfusion. Thus, the saphenous artery and the superficial sural artery at the distal margin of gastrocnemius were clamped for 3 h (sham rats-5 min) with microvascular clamps, followed by reperfusion. The adjacent veins were not separated in order to minimize irritation-evoked spasm in the arteries, or stimulation or damage of the sural and saphenous nerves.
Animals were habituated to the testing apparatus 1 day prior to testing and re-acclimatized approximately 30 min prior to any testing. Paw-withdrawal threshold (PWTs) measures were performed as described previously . For drug trials, PWTs were examined at baseline, pre-drug, 20–30 min after administration of NAC, IL-1RA, PDTC, amiloride (Sigma, Oakville, ON), TEMPOL (Tocris, Ellisville, MO), or their saline vehicles, 2 days post-reperfusion. Rats with pre-drug von Frey thresholds below 6 g were randomly assigned into treatment groups. NAC (10, 50, and 200 mg/kg), TEMPOL (25, 100, and 250 mg/kg), PDTC (10, 30, and 100 mg/kg) and amiloride (0.5, 1.5, 5 mg/kg) were injected intraperitoneally, and IL-RA (25, 50 and 100 μg) intraplantarly. The highest doses used for systemic treatments did not result in any significant abnormalities in the rotorod test. All treatment and testing procedures were performed in a blinded manner.
For exercise, rats were placed on a 32.5 cm diameter circular platform bounded on the outside by a 25 cm high Plexiglas cylinder. A second, concentric Plexiglas cylinder delimited the interior side of a 7.5 cm-wide circular alley. The platform was coupled to a variable speed motor and was rotated at 16 rpm (16.3 m/min). Rats were placed on the platform for 20 min, and most ran 326 m in 20 min. A stationary partition hung down above the circular alley producing a barrier when animals ceased to run. A sustained contact with the barrier was counted as a stop. A rapid push on the partition against the pausing rat usually succeeded in re-establishing a sustained running pattern. At 2 days post-reperfusion, CPIP rats exhibited many running stoppages (which were recorded as a measure of exercise-induced pain); post-exercise PWTs were only recorded in 7 day CPIP rats that did not exhibit excessive running stoppages. To assess the effects of exercise on allodynia, we measured baseline PWTs in CPIP and sham-treated rats, then after 30 min rest, rats were exercised for 20 min. Immediately after exercise, each rat was returned to the von Frey test chamber for 15 min habituation, after which PWTs were again recorded. For assays of lactate, the rats were killed by pentobarbital overdose at the end of the second, post-exercise mechanical allodynia test (20 min post-exercise).
Electron microscopy (EM) & PGP9.5 immunocytochemistry (ICC)
Muscle (EM) or skin (ICC) tissue collected from day 2–7 CPIP or sham-treated rats was processed for EM and for PGP9.5 ICC as described .
Conduction velocity & Laser Doppler flowmetry
No-reflow was assessed in muscle tissue of day 2–21 CPIP or sham-treated rats by determining the number of ink-filled vessels after hind paw perfusion with India ink as described . Thus, animals were deeply anesthetized with sodium pentobarbital, the ascending vena cava was cut, and 50 ml of 0.1 M, 37°C PBS at pH 7.4, with 1000 U heparin sodium/ml was infused through a cannula placed in the descending aorta, followed by 10.0 ml of 25% (vol/vol) India ink (Pelikan No.17) and 6% gelatin in 0.1 M PBS. The flow rate, catheter gauge and syringe volume were set to produce a mean arterial pressure of 100–110 mm Hg. Plantar muscle samples were collected, fixed in 10% formalin in PBS for 48 h and cryoprotected in 25% sucrose in PBS. 100 μm-thick frozen sections were slide-mounted and digitally photographed under a dissecting microscope. The number of ink-filled vessels which crossed a length-calibrated straight line overlaid on the muscle image at right angle to the orientation of muscle fibers was counted at 2–3 locations on each muscle sample.
Mitochrondrial respiration in muscle from 2–21 day CPIP and sham-treated rats was estimated from the reduction of triphenyltetrazolium chloride in muscle slices and homogenized samples as previously described [17, 18]. Muscle samples were quickly frozen upon collection and kept at -80 C until processing. Thawed 300 μm-thick sections were incubated in 2% triphenyltetrazolium chloride (TTC; Sigma, St Louis, MO) in 0.05 M PBS for 20 min at 37°C. The sections were then cleared, slide-mounted and examined microscopically. Other samples were homogenized in 0.05 M PBS/0.25 M sucrose. Homogenates were incubated in 0.2% TTC in PBS for 60 min at 37°C in the dark. The formazan was then extracted by incubation in acetone (60 min, 37°C) and centrifugation (10 min at 1000 g). Formazan was estimated by sample absorbance (485 nm) of 200 μl of supernatant, divided by the amount of sample protein (determined by Bradford method). Malondialdehyde and lactate were assayed in muscle samples using colorimetric kits from OxisResearch F(oster City, CA) and BioAssay Systems (Hayward, CA), respectively.
Animals were sacrificed by decapitation. For the NFκB ELISA, muscle samples were thawed at 4°C and homogenized mechanically in 12.0 μl/mg tissue of RIPA buffer containing 50 mM Tris-HCl, 150 mM NaCl, 1 mM EDTA, 1% Igepal (Sigma, St. Louis, MO), 1% Sodium deoxycholate and 0.1% SDS (Ph 7.4), to which was added a 1% protease inhibitor cocktail (Sigma, St. Louis, MO). Homogenates were centrifuged at 3,000 g for 10 min and the supernatant was collected and processed for nuclear fraction extraction following the recommended procedure of a commercially produced extraction kit (Chemicon Nuclear Extraction Kit, Millipore Corp., Billerica, MA). Nuclear fractions were concentrated by centrifugal filtration using cellulose filters with a 30 kDa cut-off (Microcon YM-30, Millipore Corp., Billerica, MA). The nuclear fraction volume remaining after filtration was collected and diluted in buffer to a final volume of 100 μl. Total sample protein content was determined by the Bradford method (Sigma, St. Louis, MO). NFκB transcription factor measurements were then performed in duplicates using a commercially supplied binding assay (Cayman Chemical, Ann Arbor, MI) and a rabbit polyclonal antibody to the p50 subunit of NFκB (sc-7178, Santa Cruz Biotechnology, Santa Cruz, CA), according to the manufacturer's suggested protocol. NFκB-p50 quantities per well were normalized by dividing the p50 estimate by the total amount of protein measured in the sample.
For the cytokine ELISAs, approximately 200 mg of foot tissue was removed from the plantar surface and dissolved in 750 μl of protease inhibitor cocktail (Sigma, Oakville, ON), 100 μM Amino-n-caproic Acid, 10 μM disodium EDTA, 5 μM benzamidine HCl, and 0.2 μM AEBSF (pH 7.2). Samples were mechanically homogenized, sonicated, and centrifuged at 15,000 RPM at 4°C. The supernatant was used to measure concentrations of the proinflammatory cytokines TNFα, IL-6, and IL-1β using a two-site, rat-specific ELISA as described previously . All samples and standards were assayed in duplicate. Intra- and interassay coefficients of variability were < 7% for all assays and the detection limit for TNFα, IL-1β and IL-6 was ≤ 31.25 pg/ml.
Statistical significance was determined using one-way or mixed analysis of variance with Fisher's post hoc tests, or Pearson correlations.
acid sensing ion channel
chronic post-ischemia pain
complex regional pain syndrome
hind paw digital muscle
intraepidermal nerve fiber
interleukin-1 receptor antagonist
nuclear factor kappa B
protein gene product 9.5
paw withdrawal threshold
tumor necrosis factor alpha
We thank Giamal Luheshi for providing cytokine ELISA plates and expertise, Stephen Poole for supplying cytokine antibodies, Fernando Cervero for loan of the laser Doppler flowmeter, Miriam Sturkenboom for theoretical contributions to the NFκB studies, and Yves deKoninck and Michael Salter for comments on the manuscript. This research was supported by grants from CIHR, NSERC, FRSQ and The Louise and Alan Edwards Foundation to TJC. Further supported included an NSERC doctoral scholarship (DNX), AstraZeneca/Alan Edwards Centre for Research on Pain postdoctoral fellowships (MM and JVR), and a Dutch CRPS patient association (stichting Esperance) (MdM). GJB is a Canada Senior Research Chair.
- Gracely RH, Lynch SA, Bennett GJ: Painful neuropathy: altered central processing maintained dynamically by peripheral input. Pain 1992, 51: 175–194. 10.1016/0304-3959(92)90259-EView ArticlePubMed
- Wallace MS: Concentration-effect relationship of intravenous lidocaine on the allodynia of complex regional pain syndrome types I and II. Anesthesiology 2000, 92: 75–83. 10.1097/00000542-200001000-00017View ArticlePubMed
- Burnstein R, Yarnitsky D, Goor-Aryeh I, Ransil BJ, Bajwa ZH: An association between migraine and cutaneous allodynia. Ann Neurol 2000, 47: 614–624. Publisher Full Text 10.1002/1531-8249(200005)47:5%3C614::AID-ANA9%3E3.0.CO;2-NView Article
- Carli G, Suman AL, Biasi G, Marcolongo R: Reactivity to superficial and deep stimuli in patients with chronic musculoskeletal pain. Pain 2002, 100: 259–269. 10.1016/S0304-3959(02)00297-XView ArticlePubMed
- Wasner G, Schattschneider J, Heckmann K, Maier C, Baron R: Vascular abnormalities in reflex sympathetic dystrophy (CRPS I): mechanisms and diagnostic value. Brain 2001, 124: 587–599. 10.1093/brain/124.3.587View ArticlePubMed
- Albrecht PJ, Hines S, Eisenberg E, Pud D, Finlay DR, Connolly MK, Paré M, Davar G, Rice FL: Pathologic alterations of cutaneous innervation and vasculature in affected limbs from patients with complex regional pain syndrome. Pain 2006, 120: 244–266. 10.1016/j.pain.2005.10.035View ArticlePubMed
- Cornelius LA, Sepp N, Li LJ, Degitz K, Swerlick RA, Lawley TJ, Caughman SW: Selective upregulation of intracellular adhesion molecule (ICAM-1) by ultraviolet B in human dermal microvascular endothelial cells. J Invest Dermatol 1994, 103: 23–28. 10.1111/1523-1747.ep12388971View ArticlePubMed
- Skyhøj Olsen T: Migraine with and without aura: the same disease due to cerebral vasospasm of different intensity. A hypothesis based on CBF studies during migraine. Headache 1990, 30: 269–272. 10.1111/j.1526-4610.1990.hed3005269.xView ArticlePubMed
- Grassi W, Core P, Carlino G, Salaffi F, Cervini C: Capillary permeability in fibromyalgia. J Rheumatol 1994, 21: 1328–1331.PubMed
- Wall PD, Woolf CJ: Muscle but not cutaneous C-afferent input produces prolonged increases in the excitability of the flexion reflex in the rat. J Physiol 1984, 356: 443–458.PubMed CentralView ArticlePubMed
- Coderre TJ, Xanthos DN, Francis L, Bennett GJ: Chronic post-ischemia pain (CPIP): a novel animal model of complex regional pain syndrome-type I (CRPS-I; reflex sympathetic dystrophy) produced by prolonged hind paw ischemia and reperfusion in the rat. Pain 2004, 112: 94–105. 10.1016/j.pain.2004.08.001View ArticlePubMed
- Xanthos DN, Bennett GJ, Coderre TJ: Norepinephrine-induced nociception and vasoconstrictor hypersensitivity in rats with chronic post-ischemia pain. Pain 2008, 137: 640–651. 10.1016/j.pain.2007.10.031PubMed CentralView ArticlePubMed
- Wang WZ, Anderson G, Fleming JT, Peter FW, Franken RJ, Acland RD, Barker J: Lack of nitric oxide contributes to vasospasm during ischemia/reperfusion injury. Plast Reconstr Surg 1997, 99: 1099–1108. 10.1097/00006534-199704000-00028View ArticlePubMed
- Sapienza P, Edwards JD, Mingoli A, McGregor PE, Cavallari N, Agrawal DK: Ischemia-induced peripheral arterial vasospasm role of alpha 1- and alpha 2-adrenoceptors. J Surg Res 1996, 62: 192–196. 10.1006/jsre.1996.0194View ArticlePubMed
- Menger MD, Rücker M, Vollmar B: Capillary dysfunction in striated muscle ischemia/reperfusion: on the mechanisms of capillary "no-reflow". Shock 1997, 8: 2–7.View ArticlePubMed
- Tata DA, Anderson BJ: A new method for the investigation of capillary structure. J Neurosci Methods 2002, 113: 199–206. 10.1016/S0165-0270(01)00494-0View ArticlePubMed
- Blebea J, Kerr JC, Shumko JZ, Feinberg RN, Hobson RW 2nd: Quantitative histochemical evaluation of skeletal muscle ischemia and reperfusion injury. J Surg Res 1987, 43: 311–321. 10.1016/0022-4804(87)90087-4View ArticlePubMed
- Belkin M, Brown RD, Wright JG, LaMorte WW, Hobson RW 2nd: A new quantitative spectrophotometric assay of ischemia-reperfusion injury in skeletal muscle. Am J Surg 1988, 156: 83–86. 10.1016/S0002-9610(88)80360-XView ArticlePubMed
- Oaklander AL, Rissmiller JG, Gelman LB, Zheng L, Chang Y, Gott R: Evidence of focal small-fiber axonal degeneration in complex regional pain syndrome-I (reflex sympathetic dystrophy). Pain 2006, 120: 235–243. 10.1016/j.pain.2005.09.036View ArticlePubMed
- Rode J, Dhillon AP, Doran JF, Jackson P, Thompson RJ: PGP9.5: a new marker for vertebrate neurons and neuroendocrine cells. Brain Res 1983, 278: 224–228. 10.1016/0006-8993(83)90241-XView ArticlePubMed
- Inauen W, Suzuki M, Granger DN: Mechanisms of cellular injury: potential sources of oxygen free radicals in ischemia/reperfusion. Microcirc Endothelium Lymphatics 1989, 5: 143–155.PubMed
- Ascer E, Gennaro M, Cupo S, Mohan C: Do cytokines play a role in skeletal muscle ischemia and reperfusion? J Cardiovasc Surg (Torino) 1992, 33(5):588–592.
- Chandrasekar B, Streitman JE, Colston JT, Freeman GL: Inhibition of nuclear factor kappa B attenuates proinflammatory cytokine and inducible nitric-oxide synthase expression in postischemic myocardium. Biochim Biophys Acta 1998, 1406: 91–106.View ArticlePubMed
- Hagberg H: Intracellular pH during ischemia in skeletal muscle: relationship to membrane potential, extracellular pH, tissue lactic acid and ATP. Pflugers Arch 1985, 404: 342–347. 10.1007/BF00585346View ArticlePubMed
- Sahlin K, Harris RC, Nylind B, Hultman E: Lactate content and pH in muscle obtained after dynamic exercise. Pflugers Arch 1976, 367: 143–149. 10.1007/BF00585150View ArticlePubMed
- Veldman PH, Reynen HM, Arntz IE, Goris RJ: Signs and symptoms of reflex sympathetic dystrophy: prospective study of 829 patients. Lancet 1993, 342: 1012–1016. 10.1016/0140-6736(93)92877-VView ArticlePubMed
- Kleyman TR, Sheng S, Kosari F, Kieber-Emmons T: Mechanism of action of amiloride: a molecular prospective. Semin Nephrol 1999, 19: 524–532.PubMed
- Sluka KA: Stimulation of deep somatic tissue with capsaicin produces long-lasting mechanical allodynia and heat hypoalgesia that depends on early activation of the cAMP pathway. J Neurosci 2002, 22: 5687–5693.PubMed
- Radhakrishnan R, Moore SA, Sluka KA: Unilateral carrageenan injection into muscle or joint induces chronic bilateral hyperalgesia in rats. Pain 2003, 104: 567–577. 10.1016/S0304-3959(03)00114-3PubMed CentralView ArticlePubMed
- Immke DC, McCleskey EW: Lactate enhances the acid-sensing Na+ channel on ischemia-sensing neurons. Nature Neurosc 2001, 4: 869–870. 10.1038/nn0901-869View Article
- Sluka KA, Price MP, Breese NM, Stucky CL, Wemmie JA, Welsh MJ: Chronic hyperalgesia induced by repeated acid injections in muscle is abolished by the loss of ASIC3, but not ASIC1. Pain 2003, 106: 229–239. 10.1016/S0304-3959(03)00269-0View ArticlePubMed
- Jin HW, Flatters SJL, Xia WH, Mulhern HL, Bennett GJ: Prevention of paclitaxel-evoked painful peripheral neuropathy by acetyl-L-carnitine: Effects on axonal mitochondria, sensory nerve fiber terminal arbors, and cutaneous Langerhans cells. Exp Neurol 2008, 210: 229–237. 10.1016/j.expneurol.2007.11.030PubMed CentralView ArticlePubMed
- Lu GW, Bennett GJ, Nishikawa N, Hoffert MJ, Dubner R: Extra- and intracellular recordings from dorsal column postsynaptic spinomedullary neurons in the cat. Exp Neurol 1983, 82: 456–477. 10.1016/0014-4886(83)90417-XView ArticlePubMed
- Ashdown H, Dumont Y, Ng M, Poole S, Boksa P, Luheshi GN: The role of cytokines in mediating effects of prenatal infection on the fetus: implications for schizophrenia. Mol Psychiatry 2006, 11: 47–55. 10.1038/sj.mp.4001748View ArticlePubMed
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.