Pain Inhibition Research Articles

Infusion of aerial parts of Salvia chudaei Batt. & Trab. from Algeria: Chemical, toxicological and bioactivities characterization

Ethnopharmacological relevanceSalvia chudaei Batt. & Trab. from Algeria is traditionally used to relieve several dysfunctions, including inflammatory and pain-related situations. Aim of the studyThis work aimed to confirm scientifically the referred properties. For that, the phenolic composition and antioxidant activity were evaluated as well as acute toxicity, anti-inflammatory and analgesic effects of different doses of the infusion of S. chudaei aerial parts. Materials and methodsInfusion of aerial parts of S. chudaei was prepared and screened for phenolic composition by generalized methods TPC and TFC then by LC-DAD-ESI/MSn. DPPH and FRAP were used to evaluate antioxidant activity. Using mice, acute toxicity, anti-inflammatory by carrageenan-induced paw edema, and analgesic by acetic acid-induced writhing and formalin-induced pain activities were tested. ResultsThe infusion showed 2018 mg GAE/100g DW of phenolics and 1956 mg ECE/100g DW of flavonoids. Phenolic profile by LC-DAD-ESI/MSn revealed the presence of ten compounds: syringic acid hexoside derivative, kaempferol-O-diglucuronide, kaempferol-O-deoxyhexoside-hexoside, kaempferol-O-glucuronide, apigenin-O-diglucuronide, caffeic acid, 4-O-caffeoylquinic acid, eriodictyol-O-glucuronide, rosmarinic acid hexoside, and rosmarinic acid. This acid was the major compound representing 54% of the total content of the identified compounds and an absolute content of 18 mg/g of extract. Additionally, the infusion exhibited a good antioxidant activity (DPPH: 81 μmol TE/g DW, FRAP: 438 μmol FSE/g DW). By oral administration to mice, the infusion showed a significant (p<0.05) dose-dependent reduction of carrageenan-induced inflammation and inhibition of formalin-induced pain (late and early phase) and acetic acid-induced writhing compared with the control. On the other hand, infusion up to 8 g/kg b.w. showed no signs of toxicity or mortality. ConclusionThis study reveals, for the first time, that the infusion of the aerial parts of S. chudaei is not toxic in a single dose and has remarkable antioxidant, anti-inflammatory, and analgesic activities, supporting the use of this species in folk medicine.

Suppression of Pain in the Late Phase of Chronic Trigeminal Neuropathic Pain Failed to Rescue the Decision-Making Deficits in Rats.

Trigeminal neuropathic pain (TNP) led to vital cognitive functional deficits such as impaired decision-making abilities in a rat gambling task. Chronic TNP caused hypomyelination in the anterior cingulate cortex (ACC) associated with decreased synchronization between ACC spikes and basal lateral amygdala (BLA) theta oscillations. The aim of this study was to investigate the effect of pain suppression on cognitive impairment in the early or late phases of TNP. Blocking afferent signals with a tetrodotoxin (TTX)-ELVAX implanted immediately following nerve lesion suppressed the allodynia and rescued decision-making deficits. In contrast, the TTX used at a later phase could not suppress the allodynia nor rescue decision-making deficits. Intra-ACC administration of riluzole reduced the ACC neural sensitization but failed to restore ACC-BLA spike-field phase synchrony during the late stages of chronic neuropathic pain. Riluzole suppressed allodynia but failed to rescue the decision-making deficits during the late phase of TNP, suggesting that early pain relief is important for recovering from pain-related cognitive impairments. The functional disturbances in ACC neural circuitry may be relevant causes for the deficits in decision making in the chronic TNP state.

How effective is an evidence-based exercise intervention in individuals with patellofemoral pain?

ObjectivesGuidelines for a comprehensive rehabilitation programme for patellofemoral pain (PFP) have been developed by international experts. The aim of this study was to analyse the effect of such a rehabilitative exercise programme on pain, function, kinesiophobia, running biomechanics, quadriceps strength and quadriceps muscle inhibition in individuals with PFP. DesignObservational study. SettingClinical environment. ParticipantsTwenty-seven participants with PFP. Main outcome measuresSymptoms [numeric pain rating scale (NPRS)and the pain subscale of the Knee Injury and Osteoarthritis Outcome Score (KOOS)], function measured by using the KUJALA scale and KOOS, kinesiophobia measured by using the Tampa scale, three-dimensional biomechanical running data, quadriceps isometric, concentric and eccentric strength and arthrogenic muscle inhibition (AMI) were acquired before and after the six-week exercise programme. ResultsAlthough pain did not significantly improve all patients were pain-free after the six-week exercise programme (NPRS: p = 0.074). Function, kinesiophobia and quadriceps AMI improved significantly after the six-week exercise programme (KUJALA: p = 0.001, KOOS: p = 0.0001, Tampa: p = 0.017, AMI: p = 0.018). Running biomechanics during stance phase did not change after the exercise intervention. Quadriceps strength was not different after the six-week exercise programme (isometric: p = 0.992, concentric: p = 0.075, eccentric: p = 0.351). ConclusionThe results of this study demonstrate that the current exercise recommendations can improve function and kinesiophobia and reduce pain and AMI in individuals with PFP. There is a need for reconsideration of the current exercise guidelines in stronger individuals with PFP.

Elucidating the structure and functions of Resolvin D6 isomers on nerve regeneration with a distinctive trigeminal transcriptome.

Innervation sustains cornea integrity. Pigment epithelium‐derived factor (PEDF) plus docosahexaenoic acid (DHA) regenerated damaged nerves by stimulating the synthesis of a new stereoisomer of Resolvin D6 (RvD6si). Here, we resolved the structure of this lipid isolated from mouse tears after injured corneas were treated with PEDF + DHA. RvD6si synthesis was inhibited by fluvoxamine, a cytochrome P450 inhibitor, but not by 15‐ or 5‐LOX inhibitors, suggesting that the 4‐ and 17‐hydroxy of DHA have an R R‐ or S R‐configuration. The two compounds were chemically synthesized. Using chiral phase HPLC, four peaks of RvD6si1‐4 from tears were resolved. The R R‐RvD6 standard eluted as a single peak with RvD61 while pure S R‐RvD6 eluted with RvD63. The addition of these pure mediators prompted a trigeminal ganglion transcriptome response in injured corneas and showed that R R‐RvD6 was the more potent, increasing cornea sensitivity and nerve regeneration. R R‐RvD6 stimulates Rictor and hepatocyte growth factor (hgf) genes specifically as upstream regulators and a gene network involved in axon growth and suppression of neuropathic pain, indicating a novel function of this lipid mediator to maintain cornea integrity and homeostasis after injury.

Dexamethasone-loaded thermo-sensitive hydrogel attenuates osteoarthritis by protecting cartilage and providing effective pain relief.

BackgroundWe utilized the destabilization of medial meniscus (DMM)-induced mice to illustrate the osteoarthritis (OA) suppressing and pain-relieving effects of a novel prolonged-release intra-articular (IA)-dexamethasone-loaded thermo-sensitive hydrogel (DLTH).MethodsThe effects of temperature and pH on DLTH formation and in vitro DLTH release profile were assessed. C57BL/6J mice were randomly divided into three groups: Ctrl group, Model group and DLTH group. The DLTH group received joint injections of 10 µL DLTH (1 mg/kg) into the right knee once a week from week 2 to week 11. We performed micro-computed tomography (Micro-CT) and histological analyses of safranin O-fast green, hematoxylin and eosin, and tartrate-resistant acid phosphatase in knee joints. We also carried out immunohistochemical (IHC) staining for matrix metalloproteinase-9 (MMP-9), MMP-13, and a disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS-5) in cartilage and Ki-67 in synovia. Pain behavioral testing was carried out in all mice. The serum content of prostaglandin E2 (PGE2) and real-time polymerase chain reaction (PCR) of inflammatory cytokines and pain-related factors in dorsal root ganglia (DRGs) were evaluated.ResultsIt took 20 minutes to form DLTH at pH 7.0 and 37 °C. The cumulative release profiles of dexamethasone (Dex) from DLTH at 37 °C revealed a rapid release in the first 24 h and a sustained slow release for 7 days. In vivo study illustrated that DLTH attenuated OA bone destruction and ameliorated synovitis and progression of OA in DMM-induced mice. The chondroprotective effects of DLTH were mediated by decreased expressions of MMP-9, MMP-13, and ADAMTS-5. The results showed that IA-DLTH exerted pain-relieving effects in OA mice. Upregulation of nociceptive response time (NRT) and downregulations of serum PGE2, inflammatory factors, and pain-related mediators in DRGs of mice in the DLTH group were recorded.ConclusionsData presented in this study elucidated that DLTH exhibited a long and lasting Dex release and it is a potential sustainable drug delivery system (DDS) to treat OA locally. IA-DLTH injection exerted chondroprotective and pain-relieving effects in DMM-induced arthritis. The involvement of MMP-9, MMP-13, ADAMTS-5, and inflammatory and pain-related factors, may account for the suppression of OA progression and pain.

Pharmacokinetic, acute toxicity, and pharmacodynamic studies of semen strychni total alkaloid microcapsules

Purpose: To investigate the safety and effectiveness of semen strychni total alkaloid microcapsules (SSTAM), compared with semen strychni total alkaloids (SSTA).&#x0D; Methods: Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was employed to assess pharmacokinetics of brucine and strychnine in rats. Acute toxicity was investigated in pre-test and formal experiments in mice. The pharmacodynamics of SSTAM and SSTA were evaluated by their analgesic and anti-inflammatory activities.&#x0D; Results: With respect to brucine, the half-life of SSTA group (1.6 mg/kg), low-dose SSTAM group (6 mg/kg) and high-dose SSTAM group (10 mg/kg) was 5.723, 9.321 and 9.025 h, respectively. With respect to strychnine, the half-life of SSTA group, low-dose SSTAM group and high-dose SSTAM group was 4.065, 8.819 and 8.654 h, respectively. The LD50 values of SSTAM group and SSTA group were 236.59 and 30.27 mg/kg, respectively. The pain inhibition rates of SSTAM groups (25 and 50 mg/kg) were higher than that of SSTA group (p &lt; 0.05) while the pain threshold values of the SSTAM groups (25 and 50 mg/kg) were higher than that of blank control (p &lt; 0.01) and SSTA groups (p &lt; 0.01) at 60 min and 120 min. The inhibition rates of the SSTAM groups (25 and 50 mg/kg) were higher than that of SSTA group based on ear swelling and cotton ball granulation tests. Compared with blank control and SSTA groups, the absorbance values of SSTAM groups (25 and 50 mg/kg) were lower (p &lt; 0.01).&#x0D; Conclusion: SSTAM increases the dosage of administration but reducea the toxicity of the alkaloids in rats, and is thus a potentially safe and effective drug delivery system.

The neurodynamic treatment induces biological changes in sensory and motor neurons in vitro

Nerves are subjected to tensile forces in various paradigms such as injury and regeneration, joint movement, and rehabilitation treatments, as in the case of neurodynamic treatment (NDT). The NDT induces selective uniaxial repeated tension on the nerve and was described to be an effective treatment to reduce pain in patients. Nevertheless, the biological mechanisms activated by the NDT promoting the healing processes of the nerve are yet still unknown. Moreover, a dose–response analysis to define a standard protocol of treatment is unavailable. In this study, we aimed to define in vitro whether NDT protocols could induce selective biological effects on sensory and motor neurons, also investigating the possible involved molecular mechanisms taking a role behind this change. The obtained results demonstrate that NDT induced significant dose-dependent changes promoting cell differentiation, neurite outgrowth, and neuron survival, especially in nociceptive neurons. Notably, NDT significantly upregulated PIEZO1 gene expression. A gene that is coding for an ion channel that is expressed both in murine and human sensory neurons and is related to mechanical stimuli transduction and pain suppression. Other genes involved in mechanical allodynia related to neuroinflammation were not modified by NDT. The results of the present study contribute to increase the knowledge behind the biological mechanisms activated in response to NDT and to understand its efficacy in improving nerve regenerational physiological processes and pain reduction.

Computational and Pharmacological Studies on the Antioxidant, Thrombolytic, Anti-Inflammatory, and Analgesic Activity of Molineria capitulata.

Molineria capitulata is an ornamental plant that has traditionally been used to treat several chronic diseases. The present study was designed to examine the antioxidant, cytotoxic, thrombolytic, anti-inflammatory, and analgesic activities of a methanolic extract of M. capitulata leaves (MEMC) using both experimental and computational models. Previously established protocols were used to perform qualitative and quantitative phytochemical screening in MEMC. A computational study, including molecular docking and ADME/T analyses, was performed. The quantitative phytochemical analysis revealed the total phenolic and flavonoid contents as 148.67 and 24 mg/g, respectively. Antioxidant activity was assessed by examining the reducing power of MEMC, resulting in absorbance of 1.87 at 400 µg/mL, demonstrating a strong reduction capacity. The extract exhibited significant protection against blood clotting and showed the highest protein denaturation inhibition at 500 µg/mL. In both the acetic acid-induced writhing and formalin-induced paw-licking models, MEMC resulted in significant potential pain inhibition in mice. In the computational analysis, 4-hydroxybenzaldehyde, orcinol glucoside, curcapital, crassifogenin C, and 2,6-dimethoxy-benzoic acid displayed a strong predictive binding affinity against the respective receptors. These findings indicated that M. capitulata possesses significant pharmacological activities to an extent supported by computational studies.

Inhibition of inflammatory pain and cough by a novel charged sodium channel blocker

Many pain-triggering nociceptor neurons express TRPV1 or TRPA1, cation-selective channels with large pores that enable permeation of QX-314, a cationic analogue of lidocaine. Co-application of QX-314 with TRPV1 or TRPA1 activators can silence nociceptors. In this study, we describe BW-031, a novel more potent cationic sodium channel inhibitor, and test whether its application alone can inhibit pain associated with tissue inflammation and whether this strategy can also inhibit cough. We tested the ability of BW-031 to inhibit pain in three models of tissue inflammation:- inflammation in rat paws produced by complete Freund's adjuvant or by surgical incision and a mouse ultraviolet (UV) burn model. We tested the ability of BW-031 to inhibit cough induced by inhalation of dilute citric acid in guinea pigs. BW-031 inhibited Nav 1.7 and Nav 1.1 channels with approximately sixfold greater potency than QX-314 when introduced inside cells. BW-031 inhibited inflammatory pain in all three models tested, producing more effective and longer-lasting inhibition of pain than QX-314 in the mouse UV burn model. BW-031 was effective in reducing cough counts by 78%-90% when applied intratracheally under isoflurane anaesthesia or by aerosol inhalation in guinea pigs with airway inflammation produced by ovalbumin sensitization. BW-031 is a novel cationic sodium channel inhibitor that can be applied locally as a single agent to inhibit inflammatory pain. BW-031 can also effectively inhibit cough in a guinea pig model of citric acid-induced cough, suggesting a new clinical approach to treating cough.

Studying human nociceptors: from fundamentals to clinic.

Chronic pain affects one in five of the general population and is the third most important cause of disability-adjusted life-years globally. Unfortunately, treatment remains inadequate due to poor efficacy and tolerability. There has been a failure in translating promising preclinical drug targets into clinic use. This reflects challenges across the whole drug development pathway, from preclinical models to trial design. Nociceptors remain an attractive therapeutic target: their sensitization makes an important contribution to many chronic pain states, they are located outside the blood–brain barrier, and they are relatively specific. The past decade has seen significant advances in the techniques available to study human nociceptors, including: the use of corneal confocal microscopy and biopsy samples to observe nociceptor morphology, the culture of human nociceptors (either from surgical or post-mortem tissue or using human induced pluripotent stem cell derived nociceptors), the application of high throughput technologies such as transcriptomics, the in vitro and in vivo electrophysiological characterization through microneurography, and the correlation with pain percepts provided by quantitative sensory testing. Genome editing in human induced pluripotent stem cell-derived nociceptors enables the interrogation of the causal role of genes in the regulation of nociceptor function. Both human and rodent nociceptors are more heterogeneous at a molecular level than previously appreciated, and while we find that there are broad similarities between human and rodent nociceptors there are also important differences involving ion channel function, expression, and cellular excitability. These technological advances have emphasized the maladaptive plastic changes occurring in human nociceptors following injury that contribute to chronic pain. Studying human nociceptors has revealed new therapeutic targets for the suppression of chronic pain and enhanced repair. Cellular models of human nociceptors have enabled the screening of small molecule and gene therapy approaches on nociceptor function, and in some cases have enabled correlation with clinical outcomes. Undoubtedly, challenges remain. Many of these techniques are difficult to implement at scale, current induced pluripotent stem cell differentiation protocols do not generate the full diversity of nociceptor populations, and we still have a relatively poor understanding of inter-individual variation in nociceptors due to factors such as age, sex, or ethnicity. We hope our ability to directly investigate human nociceptors will not only aid our understanding of the fundamental neurobiology underlying acute and chronic pain but also help bridge the translational gap.

Pain processing in older adults with dementia-related cognitive impairment is associated with frontal neurodegeneration

Experimental pain research has shown that pain processing seems to be heightened in dementia. It is unclear which neuropathological changes underlie these alterations. This study examined whether differences in pressure pain sensitivity and endogenous pain inhibition (conditioned pain modulation (CPM)) between individuals with a dementia-related cognitive impairment (N=23) and healthy controls (N=35) are linked to dementia-related neurodegeneration. Pain was assessed via self-report ratings and by analyzing the facial expression of pain using the Facial Action Coding System. We found that cognitively impaired individuals show decreased CPM inhibition as assessed by facial responses compared to healthy controls, which was mediated by decreased gray matter volume in the medial orbitofrontal and anterior cingulate cortex in the patient group. This study confirms previous findings of intensified pain processing in dementia when pain is assessed using non-verbal responses. Our findings suggest that a loss of pain inhibitory functioning caused by structural changes in prefrontal areas might be one of the underlying mechanisms responsible for amplified pain responses in individuals with a dementia-related cognitive impairment.

Reduction in Pain Inhibitory Modulation and Cognitive-Behavioral Changes in Patients With Chronic Low Back Pain: A Case-Control Study

BackgroundRecent studies indicate that the assessment of conditioned pain modulation (CPM) responses and emotional factors can provide important information regarding chronification mechanisms, choices for more efficient therapeutic strategies, and clinical variables supporting a therapeutic prognosis. AimsTo investigate the impact of nonspecific chronic low back pain (NSCLBP) on CPM and psychosocial factors in individuals with NSCLBP compared with healthy controls. DesignCase-control study. MethodsEighteen patients with NSCLBP and 18 healthy controls were recruited for this study. Pain intensity and affective-emotional aspects of pain, functional disability, kinesiophobia, depression, anxiety, and catastrophizing pain were obtained using a questionnaire. A CPM protocol was established to assess the functioning of the descending inhibitory system, with a cold pressor test as a conditioning stimulus and pressure pain threshold as a test stimulus. The maximal isometric strength of the trunk extensors also was evaluated. ResultsHealthy participants demonstrated a greater CPM response than those with NSCLBP. Patients with NSCLBP exhibited significantly lower pressure pain threshold than healthy subjects. Moreover, patients with NSCLBP presented with a considerable exacerbation of cognitive-behavioral changes. NSCLBP patients showed diminished maximal isometric strength of the trunk extensor compared to healthy subjects. ConclusionsThe endogenous pain inhibition system is reduced in patients with NSCLBP, with significant cognitive-behavioral changes indicated by high levels of anxiety and moderate pain intensity. SettingClinical School of Physical Therapy of the Federal University of Delta of Parnaíba, Piauí - Brazil. Participants/Subjects36 subjects with and without NSCLBP.

Comparative study on the pharmacodynamic difference of oral administration of Xiaojin Pills accompanied with Chinese Baijiu and water

Ethnopharmacological relevanceXiaojin Pills is a classic prescription for the treatment of mammary glands hyperplasia with a history of nearly 300 years, and is also the first choice of Chinese patent medicine for the clinical treatment of mammary glands hyperplasia in contemporary traditional Chinese medicine clinic. Clinical and animal studies have shown that Xiaojin Pills has the effects of anti-mammary glands hyperplasia, promoting blood circulation, anti-inflammation and analgesia. However, its initial administration method was “taking orally after soaked with Chinese Baijiu”, the modern method was changed to “taking orally with water” in recent 20 years. Whether there is any difference in the efficacy of the two administration methods is still unknown. Aim of the studyTo reveal the difference in efficacy and metabolic mechanism of anti-mammary gland hyperplasia between the oral administration of Xiaojin Pills accompanied with Chinese Baijiu (XJP&B) and water (XJP&W). Materials and methodsCOX-2 inhibition rate test and anti-platelet aggregation activity test were used to investigate the efficacy difference between the 40 vol% Chinese Baijiu and water extracts of Xiaojin Pills on anti-inflammatory and blood-activating in vitro. Kunming male mice (20 ± 5 g) and SD female rats (200–220 g) were orally treated with XJP&B and XJP&W, respectively. Then the difference in anti-inflammatory and analgesic effects between XJP&B and XJP&W were evaluated via xylene-induced ear swelling test, formaldehyde-induced pain test, and acetic acid-induced writhing test in mice. Determination of nipple diameter, pathological examination of mammary gland tissue, determination of serum E2, P and FSH content and hemorheological parameters of rats with mammary gland hyperplasia were performed to explore the efficacy difference in anti-mammary gland hyperplasia between XJP&B and XJP&W. Metabolomics was used to study the difference of anti-mammary gland hyperplasia mechanism between XJP&B and XJP&W. ResultsThe results showed that the effect of XJP&B was superior to that of XJP&W in anti-platelet aggregation, inhibition of inflammation and pain, and anti-mammary gland hyperplasia. Interestingly, the advantages were more significant under low-dose condition. In addition, the mechanism of the two combinations against mammary gland hyperplasia was indeed different. Their common metabolic pathways include tryptophan metabolism and alanine, aspartic acid and glutamic acid metabolism. However, Chinese Baijiu and XJP&B also have additional regulatory effects on linoleic acid metabolic pathway. ConclusionIn brief, this research demonstrated that the efficacy of XJP&B was better than that of XJP&W in activating the blood, anti-inflammation, analgesia and anti-mammary gland hyperplasia, which means that XJP&B has synergistic and superior effects. The special dose-effect relationship under the condition of XJP&B was also found, laying the foundation for clinical treatment to reduce the dosage and shorten the medication cycle, which is beneficial to reduce the economic burden of patients.

A Comparison of 1000Hz to 30Hz Spinal Cord Stimulation Strategies in Patients with Unilateral Neuropathic Leg Pain Due to Failed Back Surgery Syndrome: A Multicenter, Randomized, Double-Blinded, Crossover Clinical Study (HALO).

IntroductionMulticenter, randomized, double-blinded crossover study. The Netherlands (ClinicalTrials.gov NCT02112474). We hypothesized that the pain suppressive effects of 1000 Hz and 30 Hz spinal cord stimulation (SCS) strategies are equally effective in patients with chronic, neuropathic, unilateral leg pain after back surgery.MethodsThirty-two patients (18–70 years, minimum leg pain 50 mm on 100 mm visual analog scale (VAS), minimal back pain) were randomized (1:1) to start 1000 Hz or 30 Hz neurostimulation for 9 days. After a 5-day washout, they crossed over, for another 9 days. Primary outcome was pain suppression (mean of VAS scores 4×/day) during the crossover period. The main investigators were blinded to strategy allocation, patients were blinded to the outcome, a blinded assessor analyzed the primary outcome.ResultsThe primary outcome was analyzed in 26 patients. There was no period effect (delta 4 mm, p = 0.42, 95% CI [− 5, 13]), allowing direct intrapatient comparison of the treatment effect (delta 1 mm, p = 0.92, 95% CI [− 13, 14]). Ninety-two percent of patients in both periods experienced greater than 34% pain suppression (minimal clinically important difference, MCID). Secondary outcomes (22 patients): pain suppression and improved quality of life were sustained at 12 months; both were statistically significant and clinically relevant. Fifty percent of patients had greater than 80% pain suppression (p < 0.001).At study termination, all events were resolved; no unanticipated events were reported. Medtronic provided a grant for additional study costs.ConclusionWe conclude that our hypothesis regarding the effect of 1000 Hz and 30 Hz stimulation strategies on pain suppression was confirmed. Both stimulation strategies led to a large, sustainable, clinically relevant pain suppression and improvement in quality of life.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40122-021-00268-7.

Gate Mechanism and Parameter Analysis of Anodal-First Waveforms for Improving Selectivity of C-Fiber Nerves.

PurposeFew investigations have been conducted on the selective stimulation of small-radius unmyelinated C nerves (C), which are critical to both the recovery of damaged nerves and pain suppression. The purpose of this study is to understand how an anodal pulse in an anodal-first stimulation could improve C-selectivity over myelinated nociceptive Aδ nerves (Aδ) and to further clarify the landscape of the solution space.Materials and MethodsAn adapted Hodgkin–Huxley (HH) model and the McIntyre–Richardson–Grill (MRG) model were used for modeling C and Aδ, respectively, to analyze the underlying ion dynamics and the influence of relevant stimulation waveforms, including monopolar, polarity-symmetric, and asymmetric pulses.ResultsThe results showed that polarity asymmetric waveforms with preceding anodal stimulations benefit C-selectivity the most, underlain by the decrease in the potassium ion current of C.ConclusionThe optimal parameters for C-selectivity have been identified in the low-frequency band, remarkably benefiting the design of selective stimulation waveforms for the recovery of damaged nerves and pain management.

The inhibitory effect of conditioned pain modulation on temporal summation in low-back pain patients.

The literature on conditioned pain modulation (CPM) is inconclusive in relation to low-back pain and it is unclear how CPM affects temporal summation as a proxy of central pain integration. The aim of this study was to examine whether the CPM effect would be different on pain induced by temporal summation than single stimuli in a group of low back pain patients. A total of 149 low-back pain patients were included. CPM was examined using single, repeated and temporal summation (repeated-single difference) of mechanical pressure pain as test stimuli at an individualized, fixed supra-pain-threshold force, before and after 2min of cold pressor test (0-2 degrees Celsius). Participants werecategorized as CPM responders or non-responders according to three different criteria: simple (any pain inhibition), strict (pain inhibition of more than 10VAS) and reversed (pain inhibition or facilitation of less than 10VAS). Clinical data on back pain was collected for correlation and descriptive purposes. Significant modulation was observed for all three test stimuli. Effects sizes were comparable in relative terms, but repeated pressure pain modulation was greater in absolute terms. No correlations to clinical data were observed, for any measure. The current data suggests that repeated pressure pain may be better suited as the CPM test stimuli, than single pressure pain and temporal summation of pressure pain, as the CPM effect in absolute terms was greater. Employing temporal summation as the test stimulus in a CPM paradigm may be more sensitive than a single test stimulus.

The T-type calcium channel antagonist, Z944, reduces spinal excitability and pain hypersensitivity.

Background and PurposeT‐type voltage‐gated calcium channels are an emerging therapeutic target for neurological disorders including epilepsy and pain. Inhibition of T‐type channels reduces the excitability of peripheral nociceptive sensory neurons and reverses pain hypersensitivity in male rodent pain models. However, administration of peripherally restricted T‐type antagonists failed to show efficacy in multiple clinical and preclinical pain trials, suggesting that inhibition of peripheral T‐type channels alone may be insufficient for pain relief.Experimental ApproachWe utilized the selective and CNS‐penetrant T‐type channel antagonist, Z944, in electrophysiological, calcium imaging and behavioural paradigms to determine its effect on lamina I neuron excitability and inflammatory pain behaviours.Key ResultsVoltage‐clamp recordings from lamina I spinal neurons of adult rats revealed that approximately 80% of neurons possess a low threshold T‐type current, which was blocked by Z944. Due to this highly prevalent T‐type current, Z944 potently blocked action‐potential evoked somatic and dendritic calcium transients in lamina I neurons. Moreover, application of Z944 to spinal cord slices attenuated action potential firing rates in over half of laminae I/II neurons. Finally, we found that intraperitoneal injection of Z944 (1–10 mg·kg−1) dose‐dependently reversed mechanical allodynia in the complete Freund's adjuvant model of persistent inflammatory pain, with a similar magnitude and time course of analgesic effects between male and female rats.Conclusion and ImplicationsT‐type calcium channels critically shape the excitability of lamina I pain processing neurons and inhibition of these channels by the clinical stage antagonist Z944 potently reverses pain hypersensitivity across sexes.

Medullary Kappa-Opioid Receptor Neurons Inhibit Pain and Itch Through a Descending Circuit

In perilous and stressful situations, the ability to suppress pain can be critical for survival. The rostral ventromedial medulla (RVM) contains neurons that robustly inhibit pain processing in the spinal cord through a top-down modulatory pathway. Although much is known about the role of the RVM in the inhibition of pain, the precise identities and mechanisms of pain-inhibitory neurons in the RVM have never been identified. We now expose a cellular circuit that inhibits pain and itch in mice. Through a combination of molecular, tracing, and behavioral approaches, we found that RVM neurons containing the kappa-opioid receptor (KOR) inhibit itch and pain. With chemogenetic inhibition, we uncovered that these neurons are required for stress-induced analgesia. Using intersectional chemogenetic and pharmacological approaches, we determined that RVM KOR neurons inhibit pain and itch through a descending circuit. Lastly, we identified a dynorphinergic pathway arising from the PAG that modulates nociception within the RVM. These discoveries highlight a distinct population of RVM neurons capable of broadly and robustly inhibiting itch and pain.

Temporal summation of mechanical pain prospectively predicts movement-evoked pain severity in adults with chronic low back pain

BackgroundBiopsychosocial factors above and beyond pathoanatomical changes likely contribute to the severity of chronic low back pain. A pro-nociceptive endogenous pain modulatory balance (↓inhibition and ↑facilitation) may be an important contributor to chronic low back pain severity and physical function; however, additional research is needed to address this possibility. The objective of this study was to determine whether quantitative sensory tests of endogenous pain inhibition and facilitation prospectively predict movement-evoked pain and cLBP severity self-reported on a validated questionnaire.MethodsOne hundred thirty-four individuals with chronic low back pain were enrolled in this two-session study. During the first study session, temporal summation of mechanical pain and conditioned pain modulation were assessed at the lumbar spine to determine endogenous pain facilitation and inhibition, respectively. One week later, participants returned for a second study session whereby they reported their pain severity and pain interference using the Brief Pain Inventory-Short Form. Movement-evoked pain and physical function capacity were assessed upon completion of the balance, walking, and transition from sit to stand tests of the Short Physical Performance Battery.ResultsTemporal summation of mechanical pain, but not conditioned pain modulation, significantly and prospectively predicted greater movement-evoked pain and poorer physical function on the Short Physical Performance Battery. Neither temporal summation nor conditioned pain modulation were significantly related to self-reported pain severity or pain interference on the Brief Pain Inventory-Short Form.ConclusionsFindings suggest that a pro-nociceptive pain modulatory balance characterized by enhanced pain facilitation may be an important driver of movement-evoked pain severity and poor physical function in individuals with chronic low back pain.

Synthesis of Novel Esters of Mefenamic Acid with Pronounced Anti-nociceptive Effects and a Proposed Activity on GABA, Opioid and Glutamate Receptors

BackgroundMefenamic acid (MFA), a commonly prescribed non-steroidal anti-inflammatory drug (NSAID), possesses a greater risk of dose-related central nervous system (CNS) toxicity than other NSAIDs. In this study, α-tocopherol and α-tocopherol acetate were selected as prodrug moieties for MFA in an attempt to reduce the CNS toxicity and enhance the therapeutic efficacy. Methodα-tocopherol monoester of MFA (TMMA) and α-tocopherol di-ester of MFA (TDMA) were synthesized by esterification reaction and were subjected to various in vivo characterizations. ResultsMasking of the carboxylate group of MFA with the proposed pro-moieties significantly (p<0.05) delayed the onset of tonic-clonic seizure in mice. Besides, the intraperitoneal administration of TMMA and TDMA in mice produced significantly (p<0.05) stronger anti-inflammatory effects in the carrageenan-induced paw edema test and greater anti-nociceptive effect in the acetic acid-induced writhing test than MFA at an equimolar dose of 20 mg/kg. Treatment with TMMA and TDMA caused a significant (p<0.05) inhibition of pain at 1st and 2nd phases of formalin-induced licking test in mice, whereas treatment with MFA inhibited the 2nd phase only. Pretreatment with naloxone and flumazenil significantly (p<0.05) reversed the anti-nociceptive effect of MFA, TMMA and TDMA in the acetic acid-induced writhing test. In addition, treatment with TMMA and TDMA caused significantly (p<0.05) a higher inhibition of pain in the glutamate-induced licking response in mice than MFA. ConclusionMasking the carboxylate moiety of MFA by α-tocopherol and α-tocopherol acetate has a great potential for reducing CNS toxicity, enhancing the therapeutic efficacy and altering the mode of anti-nociceptive action.