Von Frey Filament Test Research Articles

A Viable Animal Model of Neuroarthropathic Changes in Wild-Type Rodents

Category:Diabetes, Hindfoot, Midfoot/ForefootIntroduction/Purpose:Neuroarthropathy is a progressively debilitating disease commonly affecting the lower extremity, which can lead to profound bone and joint destruction, limb deformity, and even amputation. While there are several causes, long- standing neuropathy is the most common. This leads to loss of protective sensation to the foot, which combined with repetitive micro-trauma as a result of physical activity can lead to bone and joint destruction of the lower extremity as well as major deformity. Currently there are no animal models of this disease process. The purpose of this study was to develop a novel rodent model of neuroarthropathy through the induction of the underlying neuropathic state combined with a treadmill running protocol that closely resembles local micro-trauma seen in humans.Methods:Following IAUCUC approval, 8 diet-induced obesity (DIO) C57BL/6 mice were obtained along with 6 non-obese C57BL/6 control mice. DIO mice were fed a high-fat diet (60% fat by kcal) ad libitum starting at the age of 6 weeks. Control mice were administered a standard low-fat diet (10% fat by kcal) ad libitum from birth. Starting at 14 weeks-old, all mice underwent a controlled, high-intensity cardiovascular training protocol using a rodent treadmill four times per week at 30 minute intervals. This was carried out for seven weeks including a one-week acclimation period. Speed, distance and time were held constant between groups. Weekly hind-paw sensory assessments were performed including von Frey filament and hotplate testing. Anteroposterior and mediolateral X-Rays were obtained at the beginning and conclusion of the study and radiographic analysis was performed bilaterally for all specimens. Lastly, histopathologic analysis was performed to assess musculoskeletal destructive changes to the hind-paw.Results:Baseline hotplate testing revealed that obese and non-obese mice did not differ in thermal response latency (p=0.53), however following the seven-week running protocol, obese mice demonstrated increased thermal response latency compared to controls (p=0.006). Von Frey filament testing in obese mice depicted significantly reduced hind-paw withdrawal reflexes compared to controls, both prior-to and following treadmill running (p<0.001). Comparison of initial and final radiographs for obese (figures 1.A and 1.B) and non-obese mice (figures 1.D and 1.E) showed an average increase in talo-first metatarsal angle of 7.66 degrees (p=0.007) and 0.66 degrees (p=0.75) respectively. The difference in change between groups was also significant (p<0.05). Preliminary histopathological analysis revealed significant abnormal bone remodeling in obese mice following treadmill running (figure 1.C) compared to controls.Conclusion:Obese, neuropathic animals, when challenged with a controlled exercise regimen designed to induce micro-trauma develop reliable sensory, radiographic, and histopathologic parameters reminiscent of neuroarthropathy in humans. Conversely, non-obese control animals, treated with the same exercise regimen, do not develop these neurodegenerative and musculoskeletal changes. Perhaps wild-type obese mice can be further characterized as a viable model for the development of idiopathic neuroarthropathy.

Anterior insular cortex mediates hyperalgesia induced by chronic pancreatitis in rats

Central sensitization plays a pivotal role in the maintenance of chronic pain induced by chronic pancreatitis (CP), but cortical modulation of painful CP remains elusive. This study was designed to examine the role of anterior insular cortex (aIC) in the pathogenesis of hyperalgesia in a rat model of CP. CP was induced by intraductal administration of trinitrobenzene sulfonic acid (TNBS). Abdomen hyperalgesia and anxiety were assessed by von Frey filament and open field tests, respectively. Two weeks after surgery, the activation of aIC was indicated by FOS immunohistochemical staining and electrophysiological recordings. Expressions of VGluT1, NMDAR subunit NR2B and AMPAR subunit GluR1 were analyzed by immunoblottings. The regulatory roles of aIC in hyperalgesia and pain-related anxiety were detected via pharmacological approach and chemogenetics in CP rats. Our results showed that TNBS treatment resulted in long-term hyperalgesia and anxiety-like behavior in rats. CP rats exhibited increased FOS expression and potentiated excitatory synaptic transmission within aIC. CP rats also showed up-regulated expression of VGluT1, and increased membrane trafficking and phosphorylation of NR2B and GluR1 within aIC. Blocking excitatory synaptic transmission significantly attenuated abdomen mechanical hyperalgesia. Specifically inhibiting the excitability of insular pyramidal cells reduced both abdomen hyperalgesia and pain-related anxiety. In conclusion, our findings emphasize a key role for aIC in hyperalgesia and anxiety of painful CP, providing a novel insight into cortical modulation of painful CP and shedding light on aIC as a potential target for neuromodulation interventions in the treatment of CP.

The Safety and Analgesic Effect of Datura Flos Pharmacopuncture in Sprague-Dawley Rats

Background: The aim of this study was to investigate the safety and analgesic effects of Datura Flos pharmacopuncture (DFP). Methods: The analgesic effects of DFP were assessed using mechanical (hot plate), chemical (formalin test), and thermal (von Frey filament test) pain tests. Forty male Sprague Dawley rats were assigned randomly into DFP (75 mg/kg, 150 mg/kg), lidocaine 0.5%, or normal saline group for treatment on Kl3. Gross pathology, histopathology, biochemistry and hematology were performed. Results: In the hot plate test, DFP at a high dose (HDDFP; 150 mg/kg) produced a significant analgesic effect, at 10 and 20-minutes post injection (p < 0.01). Low dose DFP (LDDFP; 75 mg/kg) also showed an analgesic effect at 10 minutes post injection (p < 0.01). In the formalin test, HDDFP produced an analgesic effect, for 0-10 and 10-20 minutes (p < 0.01) post treatment, whereas LDDFP showed analgesic effects between 10-20 minutes (p < 0.05). In the von Frey filament test, DF-H produced an analgesic effect, 10 (p < 0.01) and 20 minutes post treatment (p < 0.05). LDDFP showed analgesic effect at 10 minutes (p < 0.05). In the acupuncture response test, HDDFP produced an analgesic effect at 10 minutes post treatment (p < 0.05). DF-H did not cause any anatomical changes to the liver or kidney and there were no abnormalities in biochemistry or hematology. Conclusion: DF-H was not toxic and provided short term analgesia, suggesting it may be useful in the management of pain. ©2019 Korean Acupuncture & Moxibustion Medicine Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Effects of imidazoline I2 receptor agonists on reserpine-induced hyperalgesia and depressive-like behavior in rats.

Pharmacotherapies for fibromyalgia treatment are lacking. This study examined the antinociceptive and antidepressant-like effects of imidazoline I2 receptor (I2R) agonists in a reserpine-induced model of fibromyalgia in rats. Rats were treated for 3 days with vehicle or reserpine. The von Frey filament test was used to assess the antinociceptive effects of I2 receptor agonists, and the forced swim test was used to assess the antidepressant-like effects of these drugs. 2-BFI (3.2-10 mg/kg, intraperitoneally), phenyzoline (17.8-56 mg/kg, intraperitoneally), and CR4056 (3.2-10 mg/kg, intraperitoneally) all dose-dependently produced significant antinociceptive effects, which were attenuated by the I2R antagonist idazoxan. Only CR4056 significantly reduced the immobility time in the forced swim test in both vehicle-treated and reserpine-treated rats. These data suggest that I2R agonists may be useful to treat fibromyalgia-related pain and comorbid depression.

Analgesic Effect of Toll-like Receptor 4 Antagonistic Peptide 2 on Mechanical Allodynia Induced with Spinal Nerve Ligation in Rats.

Neuroinflammation is one of the key mechanisms of neuropathic pain, which is primarily mediated by the Toll-like receptor 4 (TLR4) signaling pathways in microglia. Therefore, TLR4 may be a reasonable target for treatment of neuropathic pain. Here, we examined the analgesic effect of TLR4 antagonistic peptide 2 (TAP2) on neuropathic pain induced by spinal nerve ligation in rats. When lipopolysaccharide (LPS)-stimulated BV2 microglia cells were treated with TAP2 (10 µM), the mRNA levels of proinflammatory mediators, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, cyclooxygenase (COX)-2, and inducible nitric oxide synthase (iNOS), were markedly decreased by 54–83% as determined by quantitative PCR (qPCR) analysis. Furthermore, when TAP2 (25 nmol in 20 µL PBS) was intrathecally administered to the spinal nerve ligation-induced rats on day 3 after surgery, the mechanical allodynia was markedly decreased for approximately 2 weeks in von Frey filament tests, with a reduction in microglial activation. On immunohistochemical and qPCR analyses, both the level of reactive oxygen species and the gene expression of the proinflammatory mediators, such as TNF-α, IL-1β, IL-6, COX-2, and iNOS, were significantly decreased in the ipsilateral spinal dorsal horn. Finally, the analgesic effect of TAP2 was reproduced in rats with monoiodoacetate-induced osteoarthritic pain. The findings of the present study suggest that TAP2 efficiently mitigates neuropathic pain behavior by suppressing microglial activation, followed by downregulation of neuropathic pain-related factors, such as reactive oxygen species and proinflammatory molecules. Therefore, it may be useful as a new analgesic for treatment of neuropathic pain.

The Impact of Riluzole on Neurobehavioral Outcomes in Preclinical Models of Traumatic and Nontraumatic Spinal Cord Injury: Results From a Systematic Review of the Literature.

Study Design:Systematic review.Objective:To evaluate the impact of riluzole on neurobehavioral outcomes in preclinical models of nontraumatic and traumatic spinal cord injury (SCI).Methods:An extensive search of the literature was conducted in Medline, EMBASE, and Medline in Process. Studies were included if they evaluated the impact of riluzole on neurobehavioral outcomes in preclinical models of nontraumatic and traumatic SCI. Extensive data were extracted from relevant studies, including sample characteristics, injury model, outcomes assessed, timing of evaluation, and main results. The SYRCLE checklist was used to assess various sources of bias.Results:The search yielded a total of 3180 unique citations. A total of 16 studies were deemed relevant and were summarized in this review. Sample sizes ranged from 14 to 90, and injury models included traumatic SCI (n = 9), degenerative cervical myelopathy (n = 2), and spinal cord-ischemia (n = 5). The most commonly assessed outcome measures were BBB (Basso, Beattie, Besnahan) locomotor score and von Frey filament testing. In general, rats treated with riluzole exhibited significantly higher BBB locomotor scores than controls. Furthermore, riluzole significantly increased withdrawal thresholds to innocuous stimuli and tail flick latency following application of radiant heat stimuli. Finally, rats treated with riluzole achieved superior results on many components of gait assessment.Conclusion:In preclinical models of traumatic and nontraumatic SCI, riluzole significantly improves locomotor scores, gait function, and neuropathic pain. This review provides the background information necessary to interpret the results of clinical trials on the impact of riluzole in traumatic and nontraumatic SCI.

Activation of spinal Extacellular Signal‐Regulated Kinases and c‐jun N‐terminal kinase signaling pathways contributes to morphine‐induced acute and chronic hyperalgesia in mice

This study investigated the activation of mitogen-activated protein kinases in the spinal dorsal horn to explore the mechanisms underlying morphine-induced acute and chronic hyperalgesia in mice. Male adult mice were given a single subcutaneous injection (SC) of morphine (1 μg/kg) or twice-daily administration of morphine (10 mg/kg/day) for 8 days. Thermal hyperalgesia and mechanical allodynia were assessed using the radiant heat and von Frey filament test. Levels of phospho (p)-extracellular signal-regulated kinases (p-ERK), p-c-Jun N-terminal kinase (p-JNK), p-p38, p-PKCγ, N-methyl-d-aspartate receptor (NMDAr), and c-Fos protein in the spinal dorsal horn were examined by Western blot assays. A single ultra-low dose or repeated administration of morphine induced hyperalgesia in mice and caused a significant increase in the levels of p-ERK and p-JNK, but not p-p38, in the spinal dorsal horn. The level of c-Fos protein was significantly elevated following administration of morphine. The protein levels of p-PKCγ and NMDAr subunits (NR2B and NR2A) were also altered. Pretreatment with the NMDAr antagonist MK-801 or the protein kinase C (PKC) inhibitor calphostin C (CC) suppressed the morphine-induced increase in p-ERK, p-JNK, and c-Fos. Administration of MK-801 and CC also relieved morphine-induced hyperalgesia. These findings suggest that activation of the spinal ERK and JNK signaling pathways contribute to morphine-induced acute and chronic hyperalgesia in mice.

Role of cannabinoid receptor 1 and the peroxisome proliferator-activated receptor α in mediating anti-nociceptive effects of synthetic cannabinoids and a cannabinoid-like compound.

Osteoarthritis (OA) is characterized by cartilage degeneration, subchondral sclerosis, and pain. Cannabinoids have well-established anti-nociceptive properties in animal models of chronic pain. The aim of this study is to evaluate the anti-nociceptive effects of synthetic cannabinoids (WIN-55,212 and HU210) and the cannabinoid-like compound palmitoylethanolamide (PEA) in rat models of OA and to assess the role of cannabinoid receptor 1 (CB1) and the peroxisome proliferator-activated receptor α (PPARα) in mediating these effects. Intra-articular injection of monosodium iodoacetate (MIA) in the knee joint was used as a model of osteoarthritis. The von Frey filament test and weight-bearing difference were used to assess the anti-nociceptive effects of WIN-55,212, HU210, and PEA on MIA-induced OA in rats. Open-field locomotor activity system was used confirm the analgesic effects of those compounds. HU210, WIN55, 212, and PEA in a dose-dependent manner restored the paw withdrawal threshold (PWT) and the weight-bearing difference induced by MIA injection. SR141716A (a CB1 antagonist) significantly reversed the anti-nociceptive effects of all the administered drugs in terms of PWT. However, in terms of weight-bearing difference, SR141716A significantly reduced the anti-nociceptive effect of HU210 but not PEA or WIN55, 212. GW6471 (a PPARα antagonist) significantly reversed the anti-nociceptive effects of PEA but not those of HU210 or WIN55, 212. HU210, WIN55, 212 and PEA significantly restored the MIA-induced reduction in locomotor activity. In conclusions, both CB1 and PPARα receptors are involved in mediating pain in osteoarthritis. Therefore, targeting these receptors may be of great clinical value.

Opposing roles of Sigma‐1 and Sigma‐2 receptors in heavy alcohol drinking and associated mechanical allodynia in mice

Alcohol Use Disorder (AUD) is a serious and complex neuropsychiatric disorder characterized by excessive alcohol intake, inability to control consumption, and the emergence of a negative emotional state in the absence of alcohol. While the role of the Sigma‐1 receptor (Sig‐1R) in animal models of AUD has been demonstrated, the role of Sigma‐2 receptor/Transmembrane Protein 97 (Sig‐2R/TMEM97), which has recently been cloned, is still unclear. Using an intermittent access, 2‐bottle choice paradigm, the effects of the Sig‐2R/TMEM97 modulator JVW‐1034 (0–30 mg/kg, i.p.) on ethanol drinking in male C57Bl/6J mice were assessed. Sucrose intake was used to control for non‐specific effects of the drug on an alternate reinforcer in a separate study, and locomotor intake was also assessed. In addition, using an automated von Frey filament test, the effects of JVW‐1034 on mechanical sensitivity in alcohol drinking mice was tested during withdrawal. The effects of the Sig‐2R modulator were compared to those of BD‐1063 (0–30 mg/kg, i.p.), a preferential Sig‐1R antagonist. Results showed that JVW‐1034 reduced alcohol intake and preference in this model, without affecting water intake. Sucrose intake was not affected by the drug, suggesting selectivity of the effect for alcohol. JVW‐1034 also blocked the mechanical allodynia induced by chronic alcohol drinking without affecting sensitivity in control mice. Lastly, JVW‐1034 did not affect locomotor activity in either group. BD‐1063 had a very similar profile. These data suggest that Sig‐1R and Sig‐2R play opposite roles in the regulation of alcohol drinking and associated allodynia and hyperalgesia, and lay the foundation for more extensive studies examining the involvement of the Sig‐2R/TMEM97 system in AUD.Support or Funding InformationR01‐AA024439This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Investigation the molecular structure of novel graphene hybrid scaffold in nerve regeneration

In this study, a novel hybrid scaffold made of transition metal was prepared on the base of graphene. After characterization of the synthetic Mo0.25Co1.257W0.25S3 hybridized with graphene oxide (MCWS/GO) using XRD, EDX, and FESEM, the cytotoxicity and the cell apoptosis of the composite were assumed using MTT and Annexin V/PI flow-cytometry methods, respectively. To treat spinal cord and sciatic nerve injuries, ethidium bromide induced damages was used in rats by T-10 to T-12 laminectomy and sciatic nerve stimulation. The spinal subarachnoid space was perfused with normal saline in control groups in comparison with using MoWCoS Graphene-based scaffold over the spinal cord and sciatic injuries which was diffused slowly. The regeneration of nerve tissues in the experiment was tested before and after using MCWS/GO by pathology, physiology and RT-qPCR of nerve growth factor (NGF), neurotrophin-3 (NT3), brain-derived neurotrophic factor (BDNF) and p75 NTR tests. The results from the MTT and flow cytometry tests revealed that MCWS/GO did not have high toxicity and that the number of necrotic cells was low. There was a significant up-regulation in BDNF, NT3, and NGF genes expression in experimental groups while the p75 NTR was inversely down-regulated by using MCWS/GO. However, MCWS/GO actively regenerated nerve damages as revealed by Basso, Beattie, and Bresnahan (BBB) and von Frey filament tests. Recovery of behavioral reflexes appeared 2–5 weeks after MCWS/GO transplantation. The results showed that the inorganic scaffold represents a new class of Nanomaterial which can work in nerve regeneration. Our findings provide an impetus for further investigation of this kind of compound as a novel therapy for neural injuries which are considered as a beneficial source for the neurodegenerative diseases.

β-Caryophyllene, a Natural Sesquiterpene, Attenuates Neuropathic Pain and Depressive-Like Behavior in Experimental Diabetic Mice.

Neuropathic pain (NP) is associated with chronic hyperglycemia and emotional disorders such as depression in diabetic patients, complicating the course of treatment. Drugs currently used to treat NP have undesirable side effects, so research on other natural sources has been required. β-caryophyllene (BCP), a natural sesquiterpene found in some food condiments and considered an agonist to cannabinoid receptor type 2, could have potential therapeutic effects to treat conditions such as NP and emotional disorders. For this reason, we assessed whether BCP modulates nociception, anxiety, and depressive-like behavior in streptozotocin (STZ)-induced experimental diabetic BALB/c female mice. BCP was orally chronic administrated (10 mg/kg/60 μL). Pain developed with STZ was evaluated with von Frey filament test, SMALGO®, and hot plate test. Anxiety and depression-like behavior were assessed by marbles test, forced swim test, and tail suspension test. BCP significantly reduced glycemia in experimental diabetic mice. The pain was also mitigated by BCP administration. Depression-like behavior assessed with tail suspension test was attenuated with orally chronic BCP administration. Substance P and cytokines such as interleukin-1β (IL-1β), tumor necrosis factor α (TNF-α), and interleukin-6 (IL-6) were also attenuated with BCP administration. NP was positively correlated with substance P and IL-6 and IL-1β release. Our data using an orally chronic BCP administration in the STZ challenged mice to suggest that glycemia, diabetes-related NP, and depressive-like behavior could be prevented/reduced by dietary BCP.

Poly(lactic-co-glycolic acid) microparticles in fibrin glue for local, sustained delivery of bupivacaine

To control postoperative pain, a bolus solution of anesthetic drugs is often injected locally, which, however, is limited by short-term drug efficacy and low bioavailability. To resolve this, we propose a composite formulation of bupivacaine-loaded poly(lactic-co-glycolic acid) microparticles (BPC-MPs) and fibrin glue. We prepared the BPC-MPs using the emulsion method and formulated them with fibrin glue to produce FG_BPC-MPs. We performed in vitro drug release experiments for 35 days with the formulations in pH 7.4 phosphate buffered saline (PBS) at 37 ℃. To evaluate in vivo pain-relief efficacy, the pain-induced animals via L5-spinal nerve ligation were treated with FG_BPC-MPs, as well as the control formulations, and the paw withdrawal latency was evaluated with the von Frey filament test. The FG_BPC-MPs exhibited a sustained drug release with a reduced initial burst for up to 35 days. When tested in vivo, a dramatic increase in paw withdrawal threshold was observed during the entire 10-day testing period, suggesting that the pain-relief efficacy was improved and prolonged compared with that for the other control formulations. The FG_BPC-MPs loaded with bupivacaine can be a promising formulation for the treatment of local, persistent pain after surgery.

Transcranial direct current stimulation (tDCS) and trigeminal pain: A preclinical study.

Our objective was to evaluate the Transcranial direct current stimulation (tDCS) effect on facial allodynia induced by chronic constriction of the infraorbital nerve (CCI-ION) and on the brainstem levels of TNF-α, NGF, IL-10, and serum LDH in rats. Rats were exposed to the CCI-ION model. Facial allodynia was assessed by von Frey filaments test at baseline, 3, 7, 10, and 14days postsurgery and 24hr and 7days after the bimodal tDCS sessions for 20min/day/8days. Chronic constriction of the infraorbital nerve induced a significant decrease in the mechanical threshold 14days after surgery. This effect was reversed by tDCS treatment, with the mechanical threshold returning to basal levels at 24hr after the end of the treatment and it persisted for 7days after the end of the treatment. tDCS also decreased LDH serum levels compared to those in the control group. There was an interaction between pain and treatment with respect to brainstem levels of NGF, TNF-α, and IL-10. Chronic constriction of the infraorbital nerve model was effective in establishing trigeminal neuropathic pain on 14days after surgery, and tDCS reduced allodynia and LDH serum levels and promoted alterations in NGF, TNF-α, and IL-10 brainstem levels. Thus, we suggest that tDCS may be a potential therapy in the trigeminal pain treatment.

Ginsenoside Rf relieves mechanical hypersensitivity, depression-like behavior, and inflammatory reactions in chronic constriction injury rats.

The aim of this study was to investigate whether ginsenoside Rf can effectively relieve pain hypersensitivity in a neuropathic pain rat model. Neuropathic pain was induced in rats by chronic constriction injury (CCI) to the right sciatic nerve. Ginsenoside Rf was administered intraperitoneally after CCI surgery. The von Frey filament test and forced swimming test were performed to examine pain hypersensitivity and depression-like behavior in rats. Western blot was used to measure the levels of inflammatory cytokines in the dorsal root ganglion (DRG) and the spinal cord. Pretreatment of ginsenoside Rf for 7days did not affect the onset of mechanical allodynia in CCI rats; however, a single dose of ginsenoside Rf 1day after surgery attenuated established mechanical allodynia in CCI rats. Additionally, chronic treatment of ginsenoside Rf 1week before and 2weeks after CCI surgery diminished mechanical allodynia and depression-like behavior without affecting spontaneous locomotor activity in CCI rats. Furthermore, in CCI rats, chronic ginsenoside Rf treatment partially reversed the upregulation of proinflammatory cytokines in the spinal cord and/or the DRG but elevated IL-10, an anti-inflammatory factor, in the DRG. Ginsenoside Rf alleviated neuropathic pain and its associated depression and restored the balance between proinflammatory and anti-inflammatory cytokines. Our results suggest that ginsenoside Rf may be a potential therapy for nerve injury-induced neuropathic pain.

Losartan treatment attenuates the development of neuropathic thermal hyperalgesia induced by peripheral nerve injury in rats

AimsNeuroinflammatory changes in the central nervous system are widely involved in the initiation and maintenance of neuropathic pain after peripheral nerve injury. The present study investigated how losartan treatment may affect the development of neuropathic pain and neuroinflammation. Main methodsThe effect of losartan treatment on the development of peripheral neuropathy was studied in L5 spinal nerve ligation (SNL) model in rats with systemic (100 mg/kg) or intrathecal (10 μl/ 20 μM solution) application of losartan. Electronic von Frey filament and plantar test were used to determine pain thresholds to mechanical and thermal stimulations. At the 7th post-operative day, CD68-positive cells in DRG and dorsal roots were quantified by immunohistochemistry and western blot analyses were used to compare the expression levels of neuroinflammatory markers in lumbar spinal cord (SC). Key findingsOur data confirmed the presence of SNL-evoked heat hyperalgesia and mechanical allodynia. Losartan application blocked the SNL-induced hypersensitivity to thermal stimuli but failed to prevent mechanical allodynia. No significant difference between systemic and i.t. administration of losartan was observed. Immunohistochemistry confirmed the presence of infiltrated macrophages in the ipsilateral DRG that was significantly attenuated with the losartan treatment. Western blot SC tissue analysis revealed that systemic treatment with losartan prevented SNL-induced upregulation of CCR2, TNFα, TNFR1, and OX42 while its effect on CCL2 and AT1R expression was not significant. SignificanceOur results show that losartan treatment attenuates neuroinflammation and neuropathic pain after SNL. These effects of losartan represent an interesting direction for the development of novel treatments of peripheral neuropathy.

Alleviation of mechanical stress-induced allodynia by improving blood flow in chronic constriction injury mice

Reduced blood flow in the skin is observed in patients with neuropathic pain and in animal models. The aim of the present study was to elucidate the relationship between reduced skin blood flow and neuropathic pain in mice with a chronic constriction injury (CCI). Noradrenaline-induced contraction was enhanced in isolated plantar arteries ipsilateral to the CCI surgery compared to the contralateral arteries. Ten μM hydralazine, a peripheral vasodilator, at improved the enhanced contractile response in the ipsilateral arteries. The plantar blood flow in vivo was lower on the ipsilateral side of the CCI mice than on the contralateral side, and a 50% paw withdrawal threshold, as measured using the von Frey filament test, was lower on the former than on the latter side. An intraperitoneal injection (i.p.) of hydralazine (1 mg/kg) or phentolamine (5 mg/kg) improved blood flow in the skin and hyperalgesia in the ipsilateral plantar. In adrenalectomized CCI mice, plantar blood flow in the skin on the ipsilateral side was increased compared to in sham-operated mice, which was accompanied by alleviation of hyperalgesia. Moreover, the enhanced contractile response to noradrenaline was also observed in the ipsilateral plantar arteries isolated from the adrenalectomized CCI mice. Either hydralazine (1 mg/kg, i.p.) or an adrenalectomy barely affected mean arterial pressure in the CCI mice, whereas phentolamine (5 mg/kg, i.p.) lowered it. These results suggest that reduced blood flow in the skin contributes to neuropathic pain and that improving that blood flow with peripheral vasodilators, such as hydralazine, can alleviate it.

Subcutaneous botulinum toxin type A injections for provoked vestibulodynia: a randomized placebo-controlled trial and exploratory subanalysis.

Previous studies using botulinum toxin type A (BT) to treat provoked vestibulodynia (PVD) reported conflicting findings, possibly attributable to singular injections or low doses. We assessed PVD treatment effectiveness with high-dose single injections of BT (50 or 100 units) versus placebo, and then repeat BT 100 U injections over 6months. This was a randomized, double-blind, three-arm, placebo-controlled study with 33 PVD patients. BT 50 U (arm A), 100 U (arm B) or saline (arm C) were injected subcutaneously into the dorsal vulvar vestibulum and pain was assessed after 3months. The investigation proceeded as an unblinded exploratory analysis, in which symptomatic patients received a BT 100 U injection. Symptomatic patients in arm C received a second BT 100 U injection at the 6-month visit. Symptoms were measured at 3-month cycles using: (1) cotton swab-provoked visual analogue scale (VAS), (2) von Frey filaments, and (3) Marinoff dyspareunia scale. The three groups were comparable in terms of demographics and baseline clinical characteristics. Three months after the initial injection, no significant differences in pain were observed among the study arms, yet significant improvements occurred within all groups using the von Frey filaments test. Results from the exploratory analyses showed repeat injections of 100 U BT over 6months led to significant pain reduction (VAS and von Frey filaments). Fifty-eight percent (7/12) of patients assessable after repeat injections were symptom-free or had ≥ 2 VAS reduction. Adverse events were minor and no serious adverse events occurred during the RCT or exploratory analysis. PVD symptoms after one subcutaneous injection of BT (50 or 100 units) did not significantly differ compared to placebo, yet all three study arms experienced a reduction in pain 3months after a single injection. Exploratory analyses indicated that repeat high-dose BT injections may significantly reduce pain over 6months. This trial was registered with the Swiss Medical Agency (reference number: 2007DR2102) in 2007.

Muscle Fiber Type Changes in Lumbrical Muscles at Early Stages of Chronic Nerve Compression.

Chronic nerve compression (CNC) neuropathy is a common disease in the clinic and provokes paraesthesia, or numbness at early stage. The changes in muscle fiber composition and motor nerve terminal morphology in distal muscles were studied in this study. A well-established CNC model was used to assess the changes in the muscles. Behaviors were measured by von Frey filament test. The myosin heavy chain isoforms and neuromuscular junctions (NMJs) were stained by immunofluorescence to show the muscle fiber types composition and motor nerve terminals morphologic changes in the flexor digitorum longus (FDL) and lumbrical muscle. The fiber cross-sectional areas of different muscle fiber types were measured. The small-fiber degeneration of cutaneous nerve fibers was examined by detecting the protein gene product 9.5 (PGP9.5) with immunofluorescence. At 2nd month after compression, the proportion of type I and type II B fibers was markedly decreased, and that of type II A fibers was increased in the lumbrical muscle. There was no significant change in composition of muscle fiber types in FDL and NMJ morphology of FDL and lumbrical muscles. Intra-epidermal nerve fibre density (IENFD) declined at 2nd month after the compression. Our study reveals the morphological changes of the FDL and lumbrical muscle at an early stage of CNC. These findings may be helpful to understand muscle damage and pathophysiological development of the nerve compression, and provide new evidence for early treatment of CNC.

Involvement of NMDA receptors in the development of mirror image pain

Damage on one side of the body evoked pain bilaterally on both the injured and uninjured sides. The abnormal phenomenon called mirror image pain, is generally observed in many clinical pain syndromes and in various animal pain models. However, its mechanism is not fully understood. In the present study, we investigated the mechanism of mirror image pain in the complete Freund's adjuvant (CFA)-induced inflammatory pain model measuring the revealed mechanical allodynia by von Frey filament test. After CFA injection, the paw withdrawal threshold to mechanical stimuli was significantly decreased not only in the ipsilateral paw (CFA injected paw) but also in the contralateral paw (CFA non-injected paw). The decrease in mechanical threshold of the contralateral paw, which is called mirror image pain, had delayed onset as compared to the ipsilateral mechanical allodynia. NMDA receptor antagonist treated after CFA injection did not attenuate bilaterally allodynia, however, pretreatment with NMDA receptor antagonist was significantly attenuated the development of mirror image pain, without affecting the ipsilateral mechanical allodynia. These results suggest that the mechanism of mirror image pain via NMDA receptor activation was different from ipsilateral mechanical allodynia.

Tropomyosin Receptor Kinase B Receptor Activation in the Locus Coeruleus Restores Impairment of Endogenous Analgesia at a Late Stage Following Nerve Injury in Rats

A rat model of neuropathic pain at 6 weeks after spinal nerve ligation (SNL6w) exhibits both mechanical hypersensitivity and impaired noxious stimuli-induced analgesia (NSIA). Repeated treatment with antidepressants can produce antihypersensitivity and restore NSIA. To examine the involvement of a brain-derived neurotrophic factor-mediated mechanism, a tropomyosin receptor kinase B (TrkB) agonist, 7,8-dihydroxyflavone (DHF), was administered to SNL6w rats (5 mg/kg/d for 5 days). Mechanical hypersensitivity was evaluated using the von Frey filament test and paw pressure test. NSIA was examined by measuring the change in the hind paw withdrawal threshold 30 minutes after painful stimulation induced by capsaicin injection into the fore paw. Changes in the concentrations of glutamate and GABA in the locus coeruleus area were measured by in vivo microdialysis. DHF treatment did not affect mechanical hypersensitivity, although it restored NSIA by reducing GABA release in response to the fore paw capsaicin injection. DHF treatment did not alter the baseline concentration of glutamate or GABA. These findings suggest that DHF treatment restored the stimuli–response activity of the locus coeruleus without affecting the tonic activity of the locus coeruleus. The brain-derived neurotrophic factor–TkB signaling is also involved in the NSIA-restoring effect of amitriptyline. PerspectiveThis article demonstrates that repeated treatment with TrkB agonist, DHF, restored endogenous analgesia. Repeated amitriptyline treatment showed similar effect via TrkB-mediated mechanisms, and the effect may be independent from the effect of antihypersensitivity. This effect of TrkB activation is promising for patients with chronic pain with impaired descending inhibition.