Assessment Of Mechanical Allodynia Research Articles

Assessment of mechanical allodynia in healthy teeth adjacent and contralateral to endodontically diseased teeth: a clinical study.

The present study investigated the prevalence of mechanical allodynia (MA) in healthy teeth adjacent and contralateral to endodontically diseased teeth. This cross-sectional study included 114 patients with symptomatic irreversible pulpitis and apical periodontitis in permanent mandibular first molars who possessed healthy teeth adjacent and contralateral to the endodontically diseased tooth. The mechanical sensitivity of the teeth was determined by percussion testing. The presence or absence of pain on percussion in the teeth adjacent and contralateral to the endodontically diseased tooth and the tooth distal to the contralateral symmetrical tooth was recorded according to coding criteria. The prevalence of MA was computed as a percentage, and binary logistic regression analysis was done. The Fisher exact test and Mann-Whitney U test were used for binary and ordinal data. Age and sex did not influence the prevalence of MA. An increased prevalence of MA was found in patients with higher levels of spontaneous pain (p < 0.001). The prevalence of allodynia was 57% in teeth adjacent to endodontically diseased teeth and 10.5% in teeth contralateral to endodontically diseased teeth. In addition, on the ipsilateral side, there were more painful sensations distal to the diseased tooth than mesially. Despite being disease-free, teeth adjacent and contralateral to endodontically diseased teeth exhibited pain on percussion. There was a direct association between the severity of the patient's pain and the presence of MA.

Electroacupuncture promotes macrophage/microglial M2 polarization and suppresses inflammatory pain through AMPK.

Inflammatory pain, the most prevalent disease globally, remains challenging to manage. Electroacupuncture emerges as an effective therapy, yet its underlying mechanisms are not fully understood. This study investigates whether adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK)-regulated silent information regulator 1 (SIRT1) contributes to electroacupuncture's antinociceptive effects by modulating macrophage/microglial polarization in the spinal dorsal horn of a mouse model of inflammatory pain. In this study, mice, introduced to inflammatory pain through subcutaneous injections of complete freund's adjuvant (CFA) in the plantar area, underwent electroacupuncture therapy every alternate day for 30-min sessions. The assessment of mechanical allodynia and thermal hyperalgesia in these subjects was carried out using paw withdrawal frequency and paw withdrawal latency measurements, respectively. Western blot analysis measured levels of AMPK, phosphorylation-adenosine 5'-monophosphate (AMP)-activated protein kinase, SIRT1, inducible nitric oxide synthase, cluster of differentiation 86, arginase 1, and interleukin 10. In contrast to the group treated solely with CFA, the cohort receiving both CFA and electroacupuncture demonstrated notable decreases in both thermal hyperalgesia and mechanical allodynia. This was accompanied by a marked enhancement in AMPK phosphorylation levels. AMPK knockdown reversed electroacupuncture's analgesic effects and reduced M2 macrophage/microglial polarization enhancement. Additionally, AMPK knockdown significantly weakened electroacupuncture-induced SIRT1 upregulation, and EX-527 injection attenuated electroacupuncture's facilitation of M2 macrophage/microglial polarization without affecting AMPK phosphorylation levels. Furthermore, combining electroacupuncture with SRT1720 enhanced the analgesic effect of SRT1720. Our findings suggest that AMPK regulation of SIRT1 plays a critical role in electroacupuncture's antinociceptive effect through the promotion of M2 macrophage/microglial polarization.

Gait analysis as a robust pain behavioural endpoint in the chronic phase of the monoiodoacetate-induced knee joint pain in the rat.

The monoiodoacetate-induced rat model of osteoarthritis knee pain is widely used. However, there are between-study differences in the pain behavioural endpoints assessed and in the dose of intraarticular monoiodoacetate administered. This study evaluated the robustness of gait analysis as a pain behavioural endpoint in the chronic phase of this model, in comparison with mechanical hyperalgesia in the injected (ipsilateral) joint and development of mechanical allodynia in the ipsilateral hind paws. Groups of Sprague-Dawley rats received a single intraarticular injection of monoiodoacetate at 0.5, 1, 2 or 3 mg or vehicle (saline) into the left (ipsilateral) knee joint. An additional group of rats were not injected (naïve group). The pain behavioural methods used were gait analysis, measurement of pressure algometry thresholds in the ipsilateral knee joints, and assessment of mechanical allodynia in the ipsilateral hind paws using von Frey filaments. These pain behavioural endpoints were assessed premonoiodoacetate injection and for up to 42-days postmonoiodoacetate injection in a blinded manner. Body weights were also assessed as a measure of general health. Good general health was maintained as all rats gained weight at a similar rate for the 42-day study period. In the chronic phase of the model (days 9-42), intraarticular monoiodoacetate at 3 mg evoked robust alterations in multiple gait parameters as well as persistent mechanical allodynia in the ipsilateral hind paws. For the chronic phase of the monoiodoacetate-induced rat model of osteoarthritis knee pain, gait analysis, such as mechanical allodynia in the ipsilateral hind paws, is a robust pain behavioural measure.

Increased Expression of Thymic Stromal Lymphopoietin in Chronic Constriction Injury of Rat Nerve.

Thymic stromal lymphopoietin (TSLP) is a well-known cytokine for T helper 2 inflammatory responses. A nerve injury activates the neuroinflammation cascade and neuron–glia interaction in dorsal root ganglions (DRG)s, leading to neuropathic pain. Therefore, this study was to investigate the role of TSLP after nerve injury. Male Sprague-Dawley rats were divided as an experimental group with chronic constriction injury (CCI) to the sciatic nerve and a control group. The mechanical pain threshold response was determined by calibration forceps. After assessment of mechanical allodynia, the ipsilateral spinal cord, DRG, sciatic nerve and skin were harvested. Immunofluorescence staining was performed to identify cell types with various markers. Western blot analyses were performed to evaluate protein expressions. Mechanical allodynia developed after CCI and persisted for the next 14 days. Astrocyte reactions occurred and continued until day 14, too. After CCI, DRG and the sciatic nerve also had significantly increased expressions of TSLP/TSLP-R/STAT5. The TSLPR was localized to sensory neuronal endings innervating the skin. This study is the first to demonstrate that the TSLP complex and the STAT5 pathway in nerve are potential therapeutic targets because of their roles in pain regulation after nerve injury.

MiR-34a is differentially expressed in dorsal root ganglia in a rat model of chronic neuropathic pain

IntroductionRecent evidence shows that numerous microRNAs (miRNAs) regulate pain-related genes in chronic pain. The aim of the present study was to further explore the regulation of miRNAs and their effect on the expression of pain-associated target genes in experimental neuropathic pain. MethodsMale Wistar rats underwent chronic constriction injury (CCI) of the sciatic nerve or Sham procedure. After assessment of mechanical allodynia, the ipsilateral dorsal root ganglia (DRG) were harvested. MiRNA expression levels were analysed with Agilent microRNA microarrays and real time quantitative PCR. An interaction between miRNAs and pain-relevant genes was confirmed by luciferase assays. Western Blot analysis and ELISA were performed to evaluate protein expression, respectively. ResultsMechanical allodynia developed within 6 days after CCI. MiRNA-arrays revealed the differential expression of 49 miRNAs after 4 h, of 3 miRNAs after 1 d, of 26 miRNAs after 6 d and of 28 miRNAs after 12 d in the CCI group versus Sham. Time-dependent down regulation of miR-34a was verified by qPCR. Bioinformatic prediction revealed an interaction with several pain-relevant targets including voltage-gated sodium channel β2 subunit (SCN2B) and vesicle-associated membrane protein 2 (VAMP-2), both of which were subsequently confirmed by luciferase assay. VAMP-2 expression was statistically significantly increased 12 d after CCI. A non-significant upregulation of SCN2B in the DRG after CCI was confirmed by ELISA. DiscussionPeripheral mononeuropathic pain in rats was associated with distinct alterations of miRNA expression in the ipsilateral DRG. Notably, miR-34a was time-dependently down regulated. We validated SCN2B and VAMP-2 as new targets of miR-34a. While SCN2B expression was only marginally altered, VAMP-2 expression was increased. The present study underlines that the induction and maintenance of neuropathic pain is accompanied by expression changes of miRNAs in the peripheral nervous system, adding several previously unreported miRNAs, including miR-34a.

Tolerance to WIN55,212-2 is delayed in desensitization-resistant S426A/S430A mice

Tolerance to cannabinoid agonists can develop through desensitization of the cannabinoid receptor 1 (CB1) following prolonged administration. Desensitization results from phosphorylation of CB1 by a G protein-coupled receptor kinase (GRK), and subsequent association of the receptor with arrestin. Mice expressing a mutant form of CB1, in which the serine residues at two putative phosphorylation sites necessary for desensitization have been replaced by non-phosphorylatable alanines (S426A/S430A), display reduced tolerance to Δ9-tetrahydrocannabinol (Δ9-THC). Tolerance to the antinociceptive effects of WIN55,212-2 was delayed in S426A/S430A mutants using the tail-flick and formalin tests. However, tolerance to the antinociceptive effects of once daily CP55,940 injections was not significantly delayed in S426A/S430A mutant mice using either of these tests. Interestingly, the dose response curve shifts for the hypothermic and antinociceptive effects of CP55,940 that were induced by chronic treatment with this agonist in wild-type mice were blocked in S426A/S430A mutant mice. Assessment of mechanical allodynia in mice exhibiting chronic cisplatin-evoked neuropathic pain found that tolerance to the anti-allodynic effects WIN55,212-2 but not CP55,940 was delayed in S426A/S430A mice compared to wild-type littermates. Despite these deficits in tolerance, S426A/S430A mutant mice eventually developed tolerance to both WIN55,212-2 and CP55,940 for all pain assays that were examined, suggesting that other mechanisms likely contribute to tolerance for these cannabinoid agonists. These findings suggest that GRK- and βarrestin2-mediated desensitization of CB1 may strongly contribute to the rate of tolerance to the antinociceptive effects of WIN55,212-2, and raises the possibility of agonist-specific mechanisms of cannabinoid tolerance.

Pro-resolving mediator maresin 1 ameliorates pain hypersensitivity in a rat spinal nerve ligation model of neuropathic pain.

BackgroundPro-resolving mediators (PRMs) are considered as emerging analgesics for chronic pain. Maresin 1 (MaR1) is a newly identified member of PRMs, and recent studies implicate its potential role in some pain conditions. As the function of MaR1 in neuropathic pain remains unclear, we investigated the effects of MaR1 on pain hypersensitivity and the underlying mechanism using a rat spinal nerve ligation (SNL) model of neuropathic pain.Materials and methodsMaR1 (100 ng/10 μL) or commensurable artificial cerebrospinal fluid was delivered via intrathecal catheter from days 3 to 5 post-SNL followed by assessment of mechanical allodynia and thermal hyperalgesia. Ipsilateral L4–L5 spinal cord tissue was collected on day 7 post-SNL and assessed by Western blotting, enzyme-linked immunosorbent assay or immunohistochemistry.ResultsIntrathecal MaR1 significantly attenuated mechanical allodynia and thermal hyperalgesia from day 5 to day 7 post-SNL, which was associated with decreased spinal levels of glial markers, GFAP and IBA1. It was also found that intrathecal MaR1 downregulated phosphorylation levels of NF-κB p65 and its nuclear translocation, as well as decreased protein levels of pro-inflammatory cytokines, TNF-α, IL-1β and IL-6. Further, MaR1 treatment restored PSD95 and synapsin II levels, suggesting that MarR1 also protected synaptic integrity.ConclusionOur results indicate that MaR1 ameliorates the SNL-induced neuropathic pain by regulating glial activities and pro-inflammatory cytokines release. The present study offers insight into the potential of MaR1 as a novel intervention to ameliorate neuropathic pain.

Assessment of Mechanical Allodynia in Rats Using the Electronic Von Frey Test

Assessment of Mechanical Allodynia in Rats Using the Electronic Von Frey Test

Glycine transporter GlyT1, but not GlyT2, is expressed in rat dorsal root ganglion—Possible implications for neuropathic pain

Glycinergic inhibitory neurotransmission plays a pivotal role in the development of neuropathic pain. The glycine concentration in the synaptic cleft is controlled by the glycine transporters GlyT1 and GlyT2. GlyT1 is expressed throughout the central nervous system, while GlyT2 is exclusively located in glycinergic neurons. Aim of the present study was to investigate whether GlyTs are also expressed in the peripheral sensory nervous system and whether their expression is modulated in experimental neuropathic pain.Neuropathic pain was induced in male Wistar rats by Chronic Constriction Injury (CCI) and verified by assessment of mechanical allodynia (von Frey method). Expression patterns of GlyTs and the glycine binding subunit NR1 of the N-methyl-d-aspartate (NMDA) receptor in the spinal cord and dorsal root ganglia (DRG) were analyzed by Western blot analysis, PCR and immunohistochemistry.While both GlyT1 and GlyT2 were detected in the spinal cord, only GlyT1, but not GlyT2, was detected in DRG. Immunofluorescence revealed a strictly neuronal localization of GlyT1 and a co-localization of GlyT1 and NR1 in DRG. Compared to sham procedure, spinal cord and DRG expression of GlyT1 was not altered and NR1 was unchanged in DRG 12 days after CCI.GlyT1, but not GlyT2, is expressed in the peripheral sensory nervous system. The co-expression of GlyT1 and NMDA receptors in DRG suggests that GlyT1 regulates glycine concentration at the glycine binding site of the NMDA receptor. Differential regulation of GlyT1 expression in the spinal cord or DRG, however, does not seem to be associated with the development of neuropathic pain.

Comparison of manual and automated filaments for evaluation of neuropathic pain behavior in rats

IntroductionThe most commonly used Von Frey filaments are productive in evaluating behavioral responses of neuropathic pain in preclinical and clinical research. To reduce the potential experimenter bias, automated instruments are being developed for behavioral assessment. In preclinical research, neuropathic pain models of nerve injury with varied etiology like partial sciatic nerve ligation (PNL), chronic constricted injury (CCI) and spinal nerve ligation (SNL) are employed to screen the analgesic drugs to treat symptoms like allodynia and hyperalgesia. The current study was aimed to validate and compare conventionally used Von Frey monofilaments and automated dynamic plantar aesthesiometer using three different pain models. MethodsPNL, CCI and SNL rats were used to compare and validate the assessment of neuropathic pain using Von Frey monofilaments and automated dynamic plantar aesthesiometer. ResultsMechanical allodynia was assessed at various time points to mimic drug testing conditions in neuropathic pain models and anticipated to observe reliable and reproducible paw withdrawal threshold measurements across these models. Consistent paw withdrawal thresholds were observed in all the three models of neuropathic pain with Von Frey monofilaments, whereas variable paw withdrawal thresholds were noticed in PNL and CCI models but not in SNL model with dynamic plantar aesthesiometer. DiscussionManually used Von Frey filaments can be used in assessment of mechanical allodynia in all the three models, whereas dynamic plantar aesthesiometer is suitable for assessing mechanical allodynia in SNL but not in PNL and CCI models. The reason for variable paw withdrawal thresholds during assessment of mechanical allodynia in PNL and CCI models with dynamic plantar aesthesiometer may be due to the paw deformity and change in foot posture.

The CatWalk method: Assessment of mechanical allodynia in experimental chronic pain

The CatWalk gait analysis system has recently been suggested as a rapid and objective alternative method over the von Frey test to assess mechanical allodynia in chronic neuropathic pain models. Our results demonstrate that no correlation exists between the development of mechanical allodynia and changes in CatWalk-gait parameters in a chronic inflammatory pain model. Hence, the use of the CatWalk in assessment of experimental chronic pain is discussed.

Weight bearing of the limb as a confounding factor in assessment of mechanical allodynia in the rat

Effect of weight bearing of the hindlimbs on the assessment of mechanically-induced hindlimb withdrawal threshold was determined in intact rats and in rats with various pathophysiological conditions causing allodynia or hyperalgesia. Hindlimb withdrawal was elicited by applying a series of calibrated monofilaments to the plantar or the dorsal surface of the paw. During testing the rat was either in a restraint tube with hindlimbs hanging semi-extended without weight bearing or it was standing on a metal grid (bearing its own weight). In intact rats, the withdrawal thresholds were significantly lower when the stimulus site was the dorsal hairy skin rather than the plantar glabrous skin. Also, thresholds were significantly lower when the hindlimbs were not bearing weight. Following carrageenan-induced unilateral inflammation of the plantar paw or a tibial nerve cut there was a marked threshold decrease to test stimuli applied to plantar or dorsal paw, respectively, ipsilateral to the pathological condition in standing rats. However, when the hindlimbs were not weight bearing the unilateral threshold decrease was markedly attenuated (carrageenan-treated rats) or completely abolished (tibial cut). In contrast, in rats with a unilateral spinal nerve ligation the threshold decrease ipsilateral to the nerve lesion was highly significant independent of the weight bearing of the hindlimbs. The results indicate that weight bearing of hindlimbs is an important confounding factor in the assessment of tactile allodynia in rats.