Chronic constriction of the sciatic nerve and pain hypersensitivity testing in rats

Tuina alleviates neuropathic pain through regulate the activation of microglia and the secretion of inflammatory cytokine in spinal cord

OBJECTIVE

To observe the analgesic effects of Tuina on neuropathic pain (NPP) and the underlying mechanisms.

METHODS

Forty-eight Sprague-Dawley (SD) rats were assigned by random into three treatment groups: sham, chronic constriction injury (CCI), and Tuina. Each group contained sixteen rats. CCI model was generated by ligating the right sciatic nerve. Behavioral changes of CCI were assessed by the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). In addition, biochemical techniques such as immunofluorescence staining, enzyme-linked immunosorbent assay (ELISA) and Western blotting were used to profile levels of microglia activation and inflammatory factors in the spinal dorsal horn (SDH) of rats. Tuina (clockwise pressing and rubbing) was performed at Chengshan (BL57) to observe the analgesic effects on CCI rats and the underlying mechanisms.

RESULTS

Rats with CCI experienced significant reduction in the PWT and PWL of the right hind paw relative to CCI group at day 3. Tuina treatment rescued this situation significantly on days 10 and 14. Besides, Iba-1, microglia M1 receptor CD68, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) were higher in the right SDH for CCI group compared to the sham group on day 14. As expected, Tuina partially downregulated the CCI-induced overexpressed Iba-1, CD68, TNF-α, and IL-1β in the SDH of CCI model.

CONCLUSION

Tuina induces a time-dependent cumulative analgesic effect in CCI rats by inhibiting the activation of microglia and the secretion of IL-1β and TNF-α in SDH.

Peripheral direct current reduces naturally evoked nociceptive activity at the spinal cord in rodent models of pain

Objective.Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation typically inhibit pain pathways indirectly and are not suitable for all types of chronic pain. Direct current (DC) stimulation is a recently developed technology which affects small-diameter fibres more strongly than pulsatile stimulation. Since nociceptors are predominantly small-diameter Aδand C fibres, we investigated if this property could be applied to preferentially reduce nociceptive signalling.Approach.We applied a DC waveform to the sciatic nerve in rats of both sexes and recorded multi-unit spinal activity evoked at the hindpaw using various natural stimuli corresponding to different sensory modalities rather than broad-spectrum electrical stimulus. To determine if DC neuromodulation is effective across different types of chronic pain, tests were performed in models of neuropathic and inflammatory pain.Main results.We found that in both pain models tested, DC application reduced responses evoked by noxious stimuli, as well as tactile-evoked responses which we suggest may be involved in allodynia. Different spinal activity of different modalities were reduced in naïve animals compared to the pain models, indicating that physiological changes such as those mediated by disease states could play a larger role than previously thought in determining neuromodulation outcomes.Significance.Our findings support the continued development of DC neuromodulation as a method for reduction of nociceptive signalling, and suggests that it may be effective at treating a broader range of aberrant pain conditions than existing devices.

Gut Microbiota Modulation and Its Implications on Neuropathic Pain: A Comprehensive Literature Review

Neuropathic pain (NP) is a chronic pain disorder arising from somatosensory nervous system impairment. Extensive evidence supports the notion that the gut microbiota (GM) is crucial in maintaining human health by performing vital tasks. At the same time, its disruption has been linked to the emergence and advancement of an expanding range of disorders, including NP, in which GM could play a role in its pathophysiology. The crosstalk between the nervous system and GM happens through immune mediators, metabolites, and nervous structures and involves both central and peripheral nervous systems. This literature review aims to thoroughly investigate the function of modulating GM in the treatment of NP. It will achieve this by integrating existing knowledge, identifying underlying mechanisms, and evaluating the possible clinical consequences of exploiting the gut-brain axis. We will cover the main therapeutic applications of the described GM-modulators, such as probiotics, faecal microbiota transplantation, dietary supplements and emotional support, to the main kinds of NP in which any evidence, even if only pre-clinical, has been unravelled in recent years. The explored NP areas include chemotherapy-induced peripheral neuropathy, diabetic neuropathy, trauma-induced neuropathic pain, trigeminal neuralgia, postherpetic neuralgia and low back pain.

Thermal escape box: A cost-benefit evaluation paradigm for investigating thermosensation and thermal pain

Thermosensation, the ability to detect and estimate temperature, is an evolutionarily conserved process that is essential for survival. Thermosensing is impaired in various pain syndromes, resulting in thermal allodynia, the perception of an innocuous temperature as painful, or thermal hyperalgesia, an exacerbated perception of a painful thermal stimulus. Several behavioral assays exist to study thermosensation and thermal pain in rodents, however, most rely on reflexive withdrawal responses or the subjective quantification of spontaneous nocifensive behaviors. Here, we created a new apparatus, the thermal escape box, which can be attached to temperature-controlled plates and used to assess temperature-dependent effort-based decision-making. The apparatus consists of a light chamber with an opening that fits around temperature-controlled plates, and a small entryway into a dark chamber. A mouse must choose to stay in a brightly lit aversive area or traverse the plates to escape to the enclosed dark chamber. We quantified escape latencies of adult C57Bl/6 mice at different plate temperatures from video recordings and found they were significantly longer at 5 °C, 18 °C, and 52 °C, compared to 30 °C, a mouse's preferred ambient temperature. Differences in escape latencies were abolished in male Trpm8-/- mice and in male Trpv1-/- animals. Finally, we show that chronic constriction injury procedures or oxaliplatin treatement significantly increased escape latencies at cold temperatures compared to controls, the later of which was prevented by the analgesic meloxicam. This demonstrates the utility of this assay in detecting cold pain. Collectively, our study has identified a new and effective tool that uses cost-benefit valuations to study thermosensation and thermal pain.

Short-term effectiveness of transcranial direct current stimulation in the nociceptive behavior of neuropathic pain rats in development

Neuropathic pain (NP) is caused by a lesion that triggers pain chronification and central sensitization and it can develop in a different manner, dependent of age. Recent studies have demonstrated the efficacy of transcranial direct current stimulation (tDCS) for treating NP. Then, we aimed to investigate the effects of tDCS and BDNF levels in neuropathic pain rats in development, with 30 days old in the beginning of experiments. Eight-five male Wistar rats were subjected to chronic constriction injury. After establishment of NP, bimodal tDCS was applied to the rats for eight consecutive days, for 20 minutes each session. Subsequently, nociceptive behavior was assessed at baseline, 14 days after surgery, 1 day and 7 days after the end of tDCS. The rats were sacrificed 8 days after the last session of tDCS. An increase in the nociceptive threshold was observed in rats in development 1 day after the end of tDCS (short-term effect), but this effect was not maintained 7 days after the end of tDCS (long-term effect). Furthermore, brain derived neurotrophic factor (BDNF) levels were analyzed in the frontal cortex, spinal cord and serum using ELISA assays. The neuropathic pain model showed an effect of BDNF in the spinal cord of rats in development. There were no effects of BNDF levels of pain or tDCS in the frontal cortex or serum. In conclusion, tDCS is an effective technique to relieve nociceptive behavior at a short-term effect in neuropathic pain rats in development, and BDNF levels were not altered at long-term effect.

Effect of electrical and chemical (activation versus inactivation) stimulation of the infralimbic division of the medial prefrontal cortex in rats with chronic neuropathic pain

Neuropathic pain (NP) represents a complex disorder with sensory, cognitive, and emotional symptoms. The medial prefrontal cortex (mPFC) takes critical regulatory roles and may change functionally and morphologically during chronic NP. There needs to be a complete understanding of the neurophysiological and psychopharmacological bases of the NP phenomenon. This study aimed to investigate the participation of the infralimbic division (IFL) of the mPFC in chronic NP, as well as the role of the N-methyl-D-aspartic acid receptor (NMDAr) in the elaboration of chronic NP. Male Wistar rats were submitted to the von Frey and acetone tests to assess mechanical and cold allodynia after 21 days of chronic constriction injury (CCI) of the sciatic nerve or Sham-procedure ("false operated"). Electrical neurostimulation of the IFL/mPFC was performed by low-frequency stimuli (20 μA, 100 Hz) applied for 15 s by deep brain stimulation (DBS) device 21 days after CCI. Either cobalt chloride (CoCl2 at 1.0 mM/200 nL), NMDAr agonist (at 0.25, 1.0, and 2.0 nmol/200 nL) or physiological saline (200 nL) was administered into the IFL/mPFC. CoCl2 administration in the IFL cortex did not alter either mechanical or cold allodynia. DBS stimulation of the IFL cortex decreased mechanical allodynia in CCI rats. Chemical stimulation of the IFL cortex by an NMDA agonist (at 2.0 nmol) decreased mechanical allodynia. NMDA at any dose (0.25, 1.0, and 2.0 nmol) reduced the flicking/licking duration in the cold test. These findings suggest that the IFL/mPFC and the NMDAr of the neocortex are involved in attenuating chronic NP in rats.

[6]-Shogaol and [6]-Gingerol active ingredients may improve neuropathic pain by suppressing cytokine levels in an experimental model

Background/aim

Neuropathic pain (NP) is a type of chronic pain usually caused by damage to the somatosensory system. Bioactive antioxidant compounds, such as curcumin and ginger, are widely preferred in the treatment of NP. However, the ingredient-based mechanism that underlies their pain-relieving activity remains unknown. The aim of this study was to investigate the therapeutic effects of trans-[6]-Shogaol and [6]-Gingerol active ingredients of the Zingiber officinale Roscoe extract on the spinal cord and cortex in the neuroinflammatory pathway in rats with experimental sciatic nerve injury.

Materials and methods

Forty-six volatile phenolic components were identified in ginger samples using gas chromatography-mass spectrometry analysis. Thirty 3-month-old male 250-300 g Wistar Albino rats were divided into three groups as (i) sham, (ii) chronic constriction injury (CCI), and (iii) CCI+ginger. NP was induced using the CCI model. A ginger extract treatment enriched with trans-[6]-shogaol and [6]-gingerol active ingredients was administered by gavage at 200 mg/kg/day for 7 days. On the 14th day of the experiment, locomotor activity was evaluated in open field and hyperalgesia in tail flick tests.

Results

In behavioural experiments, a significant decrease was observed in the CCI group compared to the sham group, while a significant increase was observed in the CCI+ginger group compared to the CCI group (p < 0.05). In the spinal cord and cortex tissues, there was a significant increase in the TNF-α, IL-1β, and IL-18 neuroinflammation results of the CCI group compared to the sham group, while there was a significant decrease in the CCI+ginger group compared to the CCI group.

Conclusion

In this study, ginger treatment was shown to have a therapeutic effect on neuroinflammation against sciatic nerve damage.

Modulation of SK Channels via Calcium Buffering Tunes Intrinsic Excitability of Parvalbumin Interneurons in Neuropathic Pain: A Computational and Experimental Investigation

Parvalbumin-expressing interneurons (PVINs) play a crucial role within the dorsal horn of the spinal cord by preventing touch inputs from activating pain circuits. In both male and female mice, nerve injury decreases PVINs' output via mechanisms that are not fully understood. In this study, we show that PVINs from nerve-injured male mice change their firing pattern from tonic to adaptive. To examine the ionic mechanisms responsible for this decreased output, we used a reparametrized Hodgkin-Huxley type model of PVINs, which predicted (1) the firing pattern transition is because of an increased contribution of small conductance calcium-activated potassium (SK) channels, enabled by (2) impairment in intracellular calcium buffering systems. Analyzing the dynamics of the Hodgkin-Huxley type model further demonstrated that a generalized Hopf bifurcation differentiates the two types of state transitions observed in the transient firing of PVINs. Importantly, this predicted mechanism holds true when we embed the PVIN model within the neuronal circuit model of the spinal dorsal horn. To experimentally validate this hypothesized mechanism, we used pharmacological modulators of SK channels and demonstrated that (1) tonic firing PVINs from naive male mice become adaptive when exposed to an SK channel activator, and (2) adapting PVINs from nerve-injured male mice return to tonic firing on SK channel blockade. Our work provides important insights into the cellular mechanism underlying the decreased output of PVINs in the spinal dorsal horn after nerve injury and highlights potential pharmacological targets for new and effective treatment approaches to neuropathic pain.SIGNIFICANCE STATEMENT Parvalbumin-expressing interneurons (PVINs) exert crucial inhibitory control over Aβ fiber-mediated nociceptive pathways at the spinal dorsal horn. The loss of their inhibitory tone leads to neuropathic symptoms, such as mechanical allodynia, via mechanisms that are not fully understood. This study identifies the reduced intrinsic excitability of PVINs as a potential cause for their decreased inhibitory output in nerve-injured condition. Combining computational and experimental approaches, we predict a calcium-dependent mechanism that modulates PVINs' electrical activity following nerve injury: a depletion of cytosolic calcium buffer allows for the rapid accumulation of intracellular calcium through the active membranes, which in turn potentiates SK channels and impedes spike generation. Our results therefore pinpoint SK channels as potential therapeutic targets for treating neuropathic symptoms.

Outcomes of Sciatic Nerve Injury Repairs: A Systematic Review

Background

The objective of this study was to investigate the surgical repair techniques and the outcomes of sciatic nerve injuries in traumatic wounds.

Methods

A literature search was conducted using the following keywords:sciatic, nerve, repair, technique, conduit, graft, reconstruction, outcome, rehabilitation, recovery, function, surgery, and NOT anesthesia.

Results

In total, 715 studies were retrieved. After abstract review, 13 articles fit the criteria. A total of 2627 repairs were carried out, including nerve grafts (n = 953), suture (n = 482), and neurolysis (n = 1192). Six studies reported good motor outcome, and good sensory outcome was reported across 2 studies. The thigh region accounted for 81.5% of lesions. Sciatic, peroneal, and tibial nerves were all equally affected. Gunshot wounds were the most common mechanism of injury (22.6%).

Conclusions

The cumulative evidence demonstrates sciatic nerve injury repair has poor motor and sensory outcomes. This study shows there is a lack of standardized outcome measures, making comparisons very difficult. Graft lengths of <4 cm within the intermediate region yielded more successful outcomes. Further higher quality studies of nerve transfers in the lower limbs are needed to determine the optimal repair to restore sciatic nerve function.

Intravenous chloral hydrate anesthesia provides appropriate analgesia for surgical interventions in male Sprague-Dawley rats

BACKGROUND

The use of chloral hydrate as a sole maintenance anesthetic agent in rodent research has been controversial due to statements made in reference literature conflicting with results of primary research studies regarding its analgesic efficacy, and because of its associated tissue damage when administered intraperitoneally.

OBJECTIVE

Our aim was to assess the analgesic efficacy of chloral hydrate using an intravenous (i.v.) route of administration, in order to prevent the local tissue irritation or ileus that has been previously reported using intraperitoneal (i.p.) routes.

METHODS

We measured tail withdrawal latencies to a nociceptive thermal stimulus (infrared beam) in Sprague-Dawley rats-first when awake (unanesthetized), and then subsequently during i.v. chloral hydrate anesthesia. During anesthesia we also measured ongoing heart and respiration rates.

RESULTS

Withdrawal latencies during chloral hydrate anesthesia were significantly higher, and often maximal, indicating a robust analgesic effect. Importantly, both respiration and heart rate remained unchanged following exposure to the nociceptive stimulus, and were comparable to values observed under other anesthetics and during natural sleep.

CONCLUSIONS

Together with previous studies, these results demonstrate that i.v. chloral hydrate provides excellent anesthetic depth and analgesic efficacy for surgical manipulations in rats.

MiRNA-206 Affects the Recovery of Sciatic Function by Stimulating BDNF Activity through the Down-regulation of Notch3 Expression

OBJECTIVE

To investigate the effects and mechanisms of microRNA 206 (miRNA-206) on neurological recovery through Notch receptor 3 (Notch3).

METHODS

The sciatic functional index (SFI), nerve conduction velocity (NCV), tricipital muscle wet weight (TWW) and cross-sectional area of the muscular fiber, and grip strength of posterior limbs were detected by establishing a model of the sciatic nerve to evaluate the effect of sciatic nerve injury model. miRNA-206 expression in the model was detected by real-time quantitative polymerase chain reaction (qRT-PCR), to regulate the effects of miRNA-206 on the proliferation of gastrocnemius myocytes by Cell Counting Kit-8 (CCK-8).

RESULTS

SFI of the model established by immediate epineurium suture after sciatic nerve resection was in the range of -150% to -100% and TWW, the average area of gastrocnemius myocytes, the NCV, and the grasping power of the hind limbs in the model were all lower than those in the normal group. And in the model, TWW, the average area of gastrocnemius myocytes, NCV, and grip strength of posterior limbs were lower in the normal group, which verified the successful establishment of the model.

CONCLUSION

Over-expression of miRNA-206 can down-regulate Notch3 expression, and then stimulate brain-derived neurotrophic factor (BDNF) activity to promote the repair and functional recovery of sciatic nerve injury.

Neohesperidin Alleviates the Neuropathic Pain Behavior of Rats by Downregulating the P2X4 Receptor

Neuropathic pain (NP) is a type of chronic pain affecting 6-8% of human health as no effective drug exists. The purinergic 2X4 receptor (P2X4R) is involved in NP. Neohesperidin (NH) is a dihydroflavonoside compound, which has anti-inflammatory and antioxidative properties. This study aimed to investigate whether NH has an effect on P2X4R-mediated NP induced by chronic constriction injury (CCI) of the sciatic nerve in rats. In this study, the CCI rat model was established to observe the changes of pain behaviors, P2X4R, and satellite glial cells (SGCs) activation in dorsal root ganglion (DRG) after NH treatment by using RT-PCR, immunofluorescence double labeling and Western blotting. Our results showed CCI rats had mechanical and thermal hyperalgesia with an increased level of P2X4R. Furthermore, SGCs were activated as indicated by increased expression of glial fibrillary acidic protein and increased tumor necrosis factor-alpha receptor 1and interleukin-1β. In addition, phosphorylated extracellular regulated protein kinases and interferon regulatory factor 5 in CCI rats increased. After NH treatment in CCI rats, the levels of above protein decreased, and the pain reduced. Overall, NH can markedly alleviate NP by reducing P2X4R expression and SGCs activation in DRG.

Genome-wide Analysis of Histone H3 Lysine 27 Trimethylation Profiles in Sciatic Nerve of Chronic Constriction Injury Rats

The histone H3 lysine 27 trimethylation (H3K27me3) is one of the most important chromatin modifications, which is associated with injury-activated gene expression in Schwann cells (SCs). However, the alteration of genome-wide H3K27me3 enrichments in the development of neuropathic pain is still unknown. Here, we applied the chromatin immunoprecipitation sequencing (ChIP-seq) approach to identify the alteration of differential enrichments of H3K27me3 in chronic constriction injury (CCI) sciatic nerve of rats and potential molecular mechanisms underlying the development of neuropathic pain. Our results indicated that CCI increased the numbers of SCs displaying H3K27 methyltransferase enhancer of zeste homolog 2 (EZH2) and H3K27me3 in the sciatic nerve. ChIP-seq data showed that CCI significantly changed H3K27me3 enrichments on gene promoters in the sciatic nerve. Bioinformatics analyses exhibited that genes gaining H3K27me3 were mostly associated with regulation of cell proliferation, response to stress and oxidation-reduction process. Genes losing this mark were enriched in neuronal generation, and MAPK, cAMP as well as ERBB signaling pathways. Importantly, IL1A, CCL2, NOS2, S100A8, BDNF, GDNF, ERBB3 and C3 were identified as key genes in neuropathic pain. CCI led to significant upregulation of key genes in the sciatic nerve. EZH2 inhibitor reversed CCI-induced increases of H3K27me3 and key gene protein levels, which were accompanied by relieved mechanical allodynia and thermal hyperalgesia in CCI rats. These results indicate that genes with differential enrichments of H3K27me3 in SCs function in various cellular processes and pathways, and many are linked to neuropathic pain after peripheral nerve injury.

P2X7 receptor-activated microglia in cortex is critical for sleep disorder under neuropathic pain

Neuropathic pain (NP) is associated with sleep disturbances, which may substantially influence the quality of life. Clinical and animal studies demonstrated that neurotransmitter is one of the main contributors to cause sleep disturbances induced by NP. Recently, it was reported that P2X7 receptors (P2X7R) are widely expressed in microglia, which serves crucial role in neuronal activity in the pain and sleep-awake cycle. In this study, we adopted the chronic constriction injury (CCI) model to establish the progress of chronic pain and investigated whether P2X7R of microglia in cortex played a critical role in sleep disturbance induced by NP. At electroencephalogram (EEG) level, sleep disturbance was observed in mice treated with CCI as they exhibited mechanical and thermal hypersensitivity, and inhibition of P2X7R ameliorated these changes. We showed a dramatic high level of P2X7R and Iba-1 co-expression in the cortical region, and the inhibition of P2X7R also adversely affected it. Furthermore, the power of LFPs in ventral posterior nucleus (VP) and primary somatosensory cortex (S1) which changed in the CCI group was adverse after the inhibition of P2X7R. Furthermore, inhibition of P2X7R also decreased the VP-S1 coherence which increased in CCI group. Nuclear magnetic resonance demonstrated inhibition of P2X7R decreased glutamate (Glu) levels in thalamic and cortical regions which were significantly increased in the CCI mice. Our findings provide evidence that NP has a critical effect on neuronal activity linked to sleep and may built up a new target for the development of sleep disturbances under chronic pain conditions.

Neuropathy, its Profile and Experimental Nerve Injury Neuropathic Pain Models: A Review

Neuropathy is a terrible disorder that has a wide range of etiologies. Drug-induced neuropathy, which happens whenever a chemical agent damages the peripheral nerve system, has been linked here to the iatrogenic creation of some drugs. It is potentially permanent and causes sensory impairments and paresthesia that typically affects the hands, feet, and stockings; motor participation is uncommon. It might appear suddenly or over time, and the long-term outlook varies. The wide range of chronic pain conditions experienced by people has been one of the main obstacles to developing new, more effective medications for the treatment of neuropathic pain. Animal models can be used to examine various neuropathic pain etiologies and symptoms. Several models investigate the peripheral processes of neuropathic pain, whereas some even investigate the central mechanisms, such as drug induce models like vincristine, cisplatin, bortezomib, or thalidomide, etc., and surgical models like sciatic nerve chronic constriction injury (CCI), sciatic nerve ligation through spinal nerve ligation (SNL), sciatic nerve damage caused by a laser, SNI (spared nerve injury), etc. The more popular animal models relying on peripheral nerve ligatures are explained. In contrast to chronic sciatic nerve contraction, which results in behavioral symptoms of less reliable stressful neuropathies, (SNI) spared nerve injury generates behavioral irregularities that are more feasible over a longer period. This review summarizes the latest methods models as well as clinical ideas concerning this mechanism. Every strongest current information on neuropathy is discussed, along with several popular laboratory models for causing neuropathy.

Spinal HDAC6 mediates nociceptive behaviors induced by chronic constriction injury via neuronal activation and neuroinflammation

Neuropathic pain (NP) is often accompanied by psychiatric comorbidities and currently lacks effective treatment. Prior research has shown that HDAC6 plays a crucial role in pain sensitization, but the specific mechanisms remain unclear. HDAC6 inhibitors have been found to alleviate mechanical allodynia caused by inflammation and peripheral nerve damage. In this study, we investigated the cellular mechanisms of HDAC6 in the development and maintenance of neuropathic pain. Our findings indicate that HDAC6 expression in the spinal cord (SC) is upregulated in a time-dependent manner following chronic constriction injury (CCI). HDAC6 is primarily expressed in neurons and microglia in the spinal cord. CCI-induced HDAC6 production was abolished by intrathecal injection of a microglia inhibitor. ACY-1215, a specific HDAC6 inhibitor, significantly reduced CCI-induced mechanical allodynia, but not thermal hyperalgesia. ACY-1215 also inhibited neuron activation and suppressed CCI-induced pyroptosis and neuroinflammatory responses. In summary, our results suggest that HDAC6 contributes to the development and maintenance of NP through neuronal activation and neuroinflammation. HDAC6 may be a promising target for treating NP.

Effects of Azadirachta indica on neuropathic pain induced by chronic constriction injury to sciatic nerve of Wistar rat

OBJECTIVE

The research was designed to assess the consequences of Azadirachta indica aqueous leaf extract (AILE) on neuropathic pain in Wister rats and the role of the ATP-dependent potassium channel (K_ATP) as an underlying mechanism.

MATERIALS AND METHODS

This experimental layout was conducted on Wistar rats (n = 120) having 150 to 200 gm of body weight. On the foundation of the experimental design, rats were divided into group I (normal saline, 5 ml/kg/body weight) and group II (sham surgery and treatment with NS), group III [chronic constriction injury (CCI) in the sciatic nerve; and treated with NS], group IV (CCI and treated with AILE 400 mg/kg body weight), Group V (CCI, pretreated with Glibenclamide 15 mg/kg followed by treated with AILE 400 mg/kg). All the treatments were given once daily for a consecutive 21 days via the oral route, except Glibenclamide. Glibenclamide was given once through the intraperitoneal route on the day of the experiment.

RESULTS

Based on the neuropathic pain evaluation test, all groups were again sub-divided into subgroup "a" (walking tract analysis), "b" (cold tail immersion test), "c" (Von Frey test), and "d" (hot plate test). AILE showed a significantly higher sciatic functional index (p < 0.05) in walking track analysis, tail flick latency (p ≤ 0.05) in the cold tail immersion test, and paw withdrawal threshold (p ≤ 0.05) in the Von Frey test compared to CCI control. In addition, a nonsignificant difference in all these above-mentioned variables between the rats with CCI plus AILE and the CCI plus AILE plus glibenclamide group indicated that the K_ATP channel was not involved in the beneficial analgesic effects of AILE.

CONCLUSIONS

The outcome of the present study indicates that AILE prevented worsening of neuropathic pain after chronic constriction injury in the sciatic nerve of Wistar rats in which the K_ATP channel was not involved.

Mesenchymal stem cell spheroids alleviate neuropathic pain by modulating chronic inflammatory response genes

Chronic neuropathic pain is caused by dysfunction of the peripheral nerves associated with the somatosensory system. Mesenchymal stem cells (MSCs) have attracted attention as promising cell therapeutics for chronic pain; however, their clinical application has been hampered by the poor in vivo survival and low therapeutic efficacy of transplanted cells. Increasing evidence suggests enhanced therapeutic efficacy of spheroids formed by three-dimensional culture of MSCs. In the present study, we established a neuropathic pain murine model by inducing a chronic constriction injury through ligation of the right sciatic nerve and measured the therapeutic effects and survival efficacy of spheroids. Monolayer-cultured and spheroids were transplanted into the gastrocnemius muscle close to the damaged sciatic nerve. Transplantation of spheroids alleviated chronic pain more potently and exhibited prolonged in vivo survival compared to monolayer-cultured cells. Moreover, spheroids significantly reduced macrophage infiltration into the injured tissues. Interestingly, the expression of mouse-origin genes associated with inflammatory responses, Ccl11/Eotaxin, interleukin 1A, tumor necrosis factor B, and tumor necrosis factor, was significantly attenuated by the administration of spheroids compared to that of monolayer. These results suggest that MSC spheroids exhibit enhanced in vivo survival after cell transplantation and reduced the host inflammatory response through the regulation of main chronic inflammatory response-related genes.

Frozen vein wrapping for chronic nerve constriction injury reduces sciatic nerve allodynia in a rat model

Background

Autologous vein wrapping (VW) is used in the treatment of recurrent chronic constriction neuropathy and traumatic peripheral nerve injury. However, use of autologous veins is limited by the inability to obtain longer veins of sufficient length for larger sites. Frozen allograft tissue has several advantages, including its availability for large grafts, avoidance of donor-site morbidity, and shorter operation time. Here, we investigated the effect of frozen vein wrapping (FVW) in Wistar rats as a model of sciatic nerve injury.

Results

The rats were grouped by treatment as (i) untreated after chronic constriction injury surgery (CCI; control group), (ii) treated with vein wrapping using freshly isolated vein (VW), and (iii) treated with vein wrapping using frozen vein (FVW). Mechanical allodynia was assessed with von Frey filaments on postoperative days (PODs) 1, 3, 5, 7, and 14. Gene expression of HO-1 was evaluated by quantitative polymerase chain reaction (qPCR). The response of heme oxygenase-1 gene, Hmox-1, expression to VW and FVW was assessed by RT-PCR. Both VW and FVW significantly increased withdrawal threshold levels compared to the untreated control group on POD 1, 3, and 5. Both VW and FVW also showed increased HO-1 expression compared to the CCI group.

Conclusions

FVW increased the withdrawal threshold similar to VW in a rat CCI model for short periods. Frozen vein wrapping using vein allograft without donor site morbidity may be an alternative therapeutic option.

Glycinergic Modulation of Pain in Behavioral Animal Models

Animal models of human pain conditions allow for detailed interrogation of known and hypothesized mechanisms of pain physiology in awake, behaving organisms. The importance of the glycinergic system for pain modulation is well known; however, manipulation of this system to treat and alleviate pain has not yet reached the sophistication required for the clinic. Here, we review the current literature on what animal behavioral studies have allowed us to elucidate about glycinergic pain modulation, and the progress toward clinical treatments so far. First, we outline the animal pain models that have been used, such as nerve injury models for neuropathic pain, chemogenic pain models for acute and inflammatory pain, and other models that mimic painful human pathologies such as diabetic neuropathy. We then discuss the genetic approaches to animal models that have identified the crucial glycinergic machinery involved in neuropathic and inflammatory pain. Specifically, two glycine receptor (GlyR) subtypes, GlyRα1(β) and GlyRα3(β), and the two glycine transporters (GlyT), GlyT1 and GlyT2. Finally, we review the different pharmacological approaches to manipulating the glycinergic system for pain management in animal models, such as partial vs. full agonism, reversibility, and multi-target approaches. We discuss the benefits and pitfalls of using animal models in drug development broadly, as well as the progress of glycinergic treatments from preclinical to clinical trials.

Neurological and Inflammatory Effects of Radio Frequency and Cryoablation in a Rat Sciatic Nerve Model of Submucosal Nerve Ablation

BACKGROUND

Minimally-invasive ablation with radio frequency (RF) and cryoablation have been widely adopted to treat conditions with aberrant neural activity such as excessive mucus production in rhinitis, but neurological and inflammatory effects on treated tissues are poorly understood.

OBJECTIVE

To gain an understanding of the physiological changes caused by nerve ablation using RF and cryoablation devices.

METHODS

Using clinical devices for rhinitis treatment that ablate nerves with access from the nasal cavity, we applied temperature-controlled RF and cryoablation to rat sciatic nerves. To model the ablation through mucosal tissue similarly to the rhinitis procedure, RF ablation and cryoablation were applied through a layer of muscle.

RESULTS

Both ablation techniques induced acute and sustained neurodegeneration visualized with histological sections at two days and one month after treatment. After both treatments, rats showed a change in muscle tone, but small increases in sensitivity measured by a von Frey test were only observed 2 days after cryoablation and one month after the RF ablation. Both treatments caused reductions in nerve conduction velocity at one month after treatment. Inflammation in treated nerves and surrounding tissues that persisted to one month.

CONCLUSIONS

The two neurolytic devices used in the clinic work similarly by axonal disintegration and which leads to disruption of electrical signals. The data suggest that these methods are effective methods of nerve ablation that could be used to treat diseases related to elevated neuron activity such as rhinitis.

Diterbutyl phthalate attenuates osteoarthritis in ACLT mice via suppressing ERK/c-fos/NFATc1 pathway, and subsequently inhibiting subchondral osteoclast fusion

Osteoarthritis (OA) is the most common arthritis with a rapidly increasing prevalence. Disease progression is irreversible, and there is no curative therapy available. During OA onset, abnormal mechanical loading leads to excessive osteoclastogenesis and bone resorption in subchondral bone, causing a rapid subchondral bone turnover, cyst formation, sclerosis, and finally, articular cartilage degeneration. Moreover, osteoclast-mediated angiogenesis and sensory innervation in subchondral bone result in abnormal vascularization and OA pain. The traditional Chinese medicine Panax notoginseng (PN; Sanqi) has long been used in treatment of bone diseases including osteoporosis, bone fracture, and OA. In this study we established two-dimensional/bone marrow mononuclear cell/cell membrane chromatography/time of flight mass spectrometry (2D/BMMC/CMC/TOFMS) technique and discovered that diterbutyl phthalate (DP) was the active constituent in PN inhibiting osteoclastogenesis. Then we explored the therapeutic effect of DP in an OA mouse model with anterior cruciate ligament transaction (ACLT). After ACLT was conducted, the mice received DP (5 mg·kg^-1·d^-1, ip) for 8 weeks. Whole knee joint tissues of the right limb were harvested at weeks 2, 4, and 8 for analysis. We showed that DP administration impeded overactivated osteoclastogenesis in subchondral bone and ameliorated articular cartilage deterioration. DP administration blunted aberrant H-type vessel formation in subchondral bone marrow and alleviated OA pain assessed in Von Frey test and thermal plantar test. In RANKL-induced RAW264.7 cells in vitro, DP (20 μM) retarded osteoclastogenesis by suppressing osteoclast fusion through inhibition of the ERK/c-fos/NFATc1 pathway. DP treatment also downregulated the expression of dendritic cell-specific transmembrane protein (DC-STAMP) and d2 isoform of the vacuolar (H+) ATPase V0 domain (Atp6v0d2) in the cells. In conclusion, we demonstrate that DP prevents OA progression by inhibiting abnormal osteoclastogenesis and associated angiogenesis and neurogenesis in subchondral bone.

Manual therapy regulates oxidative stress in aging rat lumbar intervertebral discs through the SIRT1/FOXO1 pathway

With the increasing burden of a globally aging population, low back pain has become one of the most common musculoskeletal disorders, caused mainly by intervertebral disc (IVD) degeneration. There are currently several clinical methods to alleviate back pain, but there is scarce attention paid as to whether they can improve age-related IVD degeneration. It is therefore difficult to conduct an in-depth evaluation of these methods. A large number of clinical studies have shown that manual therapy (MT), a widely used comprehensive alternative method, has effects on pain, the mechanisms of which require further study. In this study, MT was performed on aging rats for 6 months, and their behaviors were compared with those of a non-intervention group of aging and young rats. After the intervention, all rats were examined by X-ray to observe lumbar spine degeneration, and the IVD tissues were dissected for detection, including pathological staining, immunofluorescence, Western bolt, etc. This study demonstrated the possibility that MT intervention delay the lumbar IVD degeneration in aging rats, specifically improving the motor function and regulating senescence-associated β-galactosidase, p53, p21, p16, and telomerase activity to retard the senescence of cells in IVDs. Moreover, MT intervention can modify oxidative stress, increase the expression of SIRT1 and FOXO1 in IVDs and decrease ac-FOXO1 expression, suggesting that MT can reduce oxidative stress through the SIRT1/FOXO1 pathway, thereby playing a role in delaying the aging of IVDs. This study shows that drug-free, non-invasive mechanical interventions could be of major significance in improving the physical function of the elderly.

Pain and Pain Management in Sea Turtle and Herpetological Medicine: State of the Art

Simple Summary

Rescue and rehabilitative medicine of sea turtles must deal with several circumstances that would be certainly considered painful in other species (trauma, situations that require surgery); thus, it would be natural to consider the use of analgesic drugs to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. However, in these animals (as well as in reptiles in general), many obstacles stand in the way of the application of safe and effective therapeutic protocols. It has been demonstrated that, anatomically and physiologically, turtles and reptiles in general must be considered able to experience pain in its definition of an “unpleasant sensory and emotional experience”. Unfortunately, specific studies concerning sea turtles and reptiles on pain assessment, safety, and clinical efficacy of analgesic drugs currently in use (mostly opioids and non-steroidal anti-inflammatory drugs—NSAIDs) are scarce and fragmentary and suffer from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

Abstract

In sea turtle rescue and rehabilitative medicine, many of the casualties suffer from occurrences that would be considered painful in other species; therefore, the use of analgesic drugs should be ethically mandatory to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. Nonetheless, pain assessment and management are particularly challenging in reptilians and chelonians. The available scientific literature demonstrates that, anatomically, biochemically, and physiologically, the central nervous system of reptiles and chelonians is to be considered functionally comparable to that of mammals albeit less sophisticated; therefore, reptiles can experience not only nociception but also “pain” in its definition of an unpleasant sensory and emotional experience. Hence, despite the necessity of appropriate pain management plans, the available literature on pain assessment and clinical efficacy of analgesic drugs currently in use (prevalently opioids and NSAIDs) is fragmented and suffers from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

A New Potential Antidepressant: Dexmedetomidine Alleviates Neuropathic Pain-Induced Depression by Increasing Neurogenesis in the Hippocampus

INTRODUCTION

Studies have suggested dexmedetomidine (DEX) as a potential antidepressant. However, no relevant research exists on its effects and mechanisms in curing depression caused by chronic pain. Therefore, an understanding of DEX's role in depressive disorders proposes new approaches for antidepressant treatment.

METHODS

In this study, C57Bl/6 mice (n = 80) were divided into sham (n = 8) and chronic constrictive injury (CCI, n = 72) groups. The CCI group was further divided into six subgroups: CCI + normal saline (NS), CCI + DEX6.25, CCI + DEX12.5, CCI + DEX25, CCI + DEX50, and CCI + DEX100. Fourteen days after CCI, mice that did not develop a depressive phenotype were excluded through sucrose preference test (SPT), forced swimming test (FST), paw thermal withdrawal latency (PTWL), and serum corticosterone (CORT). Subsequently, mice in the sham group were administered 0.1 mL/10 g NS once daily. However, mice in the CCI subgroups were administered NS (0.1 mL/10 g), DEX (6.25 µg/kg), DEX (12.5 µg/kg), DEX (25 µg/kg), DEX (50 µg/kg), and DEX (100 µg/kg) intraperitoneally once daily for 1 week, respectively. Afterward, bromodeoxyuridine (BrdU) was injected intraperitoneally once daily as well for 3 consecutive days before sampling, following BrdU- and doublecortex (DCX)-positive cell detection in the hippocampus through immunofluorescence.

RESULTS

The success rate of the chronic pain-depression (CPD) model was 62.5%. As observed, DEX dose-dependently affected sucrose preferences during the SPT and immobility time during FST. Results also showed that 25 µg/kg DEX had the best promotion effect during increased sucrose preference and reduced immobility time. Moreover, although DEX improved PTWL and serum CORT, no improvement over the DEX 25 µg/kg treatment was observed. Compared to the sham group, the percentage of BrdU+ and DCX+ cells was also significantly lower in the CCI + NS group. Besides, DEX dose-dependently affected cell proliferation and neuronal differentiation. Additionally, the percentage of BrdU+ and DCX+ cells in the dentate gyrus (DG) region of the hippocampus was highest in the CCI + DEX25 group.

CONCLUSION

Therefore, DEX dose-dependently alleviates depression induced by chronic pain through neurogenesis promotion in the DG region of the hippocampus.

The Contribution of TSLP Activation to Hyperalgesia in Dorsal Root Ganglia Neurons of a Rat

Peripheral nerve injury involves divergent alterations within dorsal root ganglia (DRG) neurons sensitized by persistent inflammation. Thymic stromal lymphopoietin (TSLP) production is crucial in the development of chronic inflammatory responses. Herein, we investigate the changes of TSLP expression in rats’ DRG neurons between injured and uninjured sides in the same rat. Linalyl acetate (LA) was served as a TSLP inhibitor and given intraperitoneally. Rats were assigned to be group of chronic constriction injury (CCI) of the sciatic nerve and the group of CCI of the sciatic nerve administrated with LA. Over 14 days, the rats were measured for paw withdrawal thresholds. DRGs were collected to assess morphological changes via immunofluorescence study. After receiving CCI, the rats rapidly developed mechanical hyperalgesia. TSLP expression at DRG, on the ipsilateral injured side, was consistent with changes in pain behaviors. TSLP appeared in nerve fibers with both small diameters and large diameters. Additionally, TSLP was expressed mostly in transient receptor potential vanilloid-1 (TRPV1)-positive nociceptive neurons. Administration with LA can attenuate the pain behaviors and expression of TSLP in DRG neurons, and in apoptotic neurons at the injured side, but not in the contra-lateral uninjured side. Overall, these results imply that altered expressions of TSLP in nociceptive DRG neurons contributed to mechanical hyperalgesia in a CCI rat model.

Effects of cyanocobalamin and its combination with morphine on neuropathic rats and the relationship between these effects and thrombospondin-4 expression

Background

Thrombospondin-4 (TSP4) upregulates in the spinal cord following peripheral nerve injury and contributes to the development of neuropathic pain (NP). We investigated the effects of cyanocobalamin alone or in combination with morphine on pain and the relationship between these effects and spinal TSP4 expression in neuropathic rats.

Methods

NP was induced by chronic constriction injury (CCI) of the sciatic nerve. Cyanocobalamin (5 and 10 mg/kg/day) was administered 15 days before CCI and then for 4 and 14 postoperative days. Morphine (2.5 and 5 mg/kg/day) was administered only post-CCI. Combination treatment included cyanocobalamin and morphine, 10 and 5 mg/kg/day, respectively. All drugs were administered intraperitoneally. Nociceptive thresholds were detected by esthesiometer, analgesia meter, and plantar test, and TSP4 expression was assessed by western blotting and fluorescence immunohistochemistry.

Results

CCI decreased nociceptive thresholds in all tests and induced TSP4 expression on the 4th postoperative day. The decrease in nociceptive thresholds persisted except for the plantar test, and the increased TSP4 expression reversed on the 14th postoperative day. Cyanocobalamin and low-dose morphine alone did not produce any antinociceptive effects. High-dose morphine improved the decreased nociceptive thresholds in the esthesiometer when administered alone but combined with cyanocobalamin in all tests. Cyanocobalamin and morphine significantly induced TSP4 expression when administered alone in both doses for 4 or 14 days. However, this increase was less when the two drugs are combined.

Conclusions

The combination of cyanocobalamin and morphine is more effective in antinociception and partially decreased the induced TSP4 expression compared to the use of either drug alone.

Potamogeton perfoliatus L. Extract Attenuates Neuroinflammation and Neuropathic Pain in Sciatic Nerve Chronic Constriction Injury-Induced Peripheral Neuropathy in Rats

Sciatic nerve injury is often associated with neuropathic pain and neuroinflammation in the central and peripheral nervous systems. In our previous work, Potamogeton perfoliatus L. displayed anti-inflammatory, antipyretic and analgesic properties, predominantly via the inhibition of COX-2 enzyme and attenuation of oxidative stress. Herein, we extended our investigations to study the effects of the plant’s extract on pain-related behaviors, oxidative stress, apoptosis markers, GFAP, CD68 and neuro-inflammation in sciatic nerve chronic constriction injury (CCI) rat model. The levels of the pro-inflammatory marker proteins in sciatic nerve and brainstem were measured with ELISA 14 days after CCI induction. Pretreatment with the extract significantly attenuated mechanical and cold allodynia and heat hyperalgesia with better potential than the reference drug, pregabalin. In addition, CCI lead to the overexpression of prostaglandin E2 (PGE2), inducible nitric oxide synthase (iNOS), tumor necrosis alpha (TNFα), nuclear factor κB (NF-κB), cyclooxygenase-2 (COX-2), 5-lipoxygenase (5-LOX), and NADPH oxidase-1 (NOX-1) and decreased the catalase level in sciatic nerve and brainstem. The observed neuro-inflammatory changes were accompanied with glial cells activation (increased GFAP and CD68 positive cells), apoptosis (increased Bax) and structural changes in both brainstem and sciatic nerve. The studied extract attenuated the CCI-induced neuro-inflammatory changes, oxidative stress, and apoptosis while it induced the expression of Bcl-2 and catalase in a dose dependent manner. It also decreased the brainstem expression of CD68 and GFAP indicating a possible neuroprotection effect. Taking together, P. perfoliatus may be considered as a novel therapy for neuropathic pain patients after performing the required clinical trials.

Selected Thiadiazine-Thione Derivatives Attenuate Neuroinflammation in Chronic Constriction Injury Induced Neuropathy

Neuropathic pain refers to a lesion or disease of peripheral and/or central somatosensory neurons and is an important body response to actual or potential nerve damage. We investigated the therapeutic potential of two thiadiazine-thione [TDT] derivatives, 2-(5-propyl-6-thioxo-1, 3, 5-thiadiazinan-3-yl) acetic acid [TDT1] and 2-(5-propyl-2-thioxo-1, 3, 5-thiadiazinan-3-yl) acetic acid [TDT2] against CCI (chronic constriction injury)-induced neuroinflammation and neuropathic pain. Mice were used for assessment of acute toxicity of TDT derivatives and no major toxic/bizarre responses were observed. Anti-inflammatory activity was assessed using the carrageenan test, and both TDT1 and TDT2 significantly reduced carrageenan-induced inflammation. We also used rats for the induction of CCI and performed allodynia and hyperalgesia-related behavioral tests followed by biochemical and morphological analysis using RT-qPCR, immunoblotting, immunohistochemistry and immunofluorescence. Our findings revealed that CCI induced clear-cut allodynia and hyperalgesia which was reversed by TDT1 and TDT2. To determine the function of TDT1 and TDT2 in glia-mediated neuroinflammation, Iba1 mRNA and protein levels were measured in spinal cord tissue sections from various experimental groups. Interestingly, TDT1 and TDT2 substantially reduced the mRNA expression and protein level of Iba1, implying that TDT1 and TDT2 may mitigate CCI-induced astrogliosis. In silico molecular docking studies predicted that both compounds had an effective binding affinity for TNF-α and COX-2. The compounds interactions with the proteins were dominated by both hydrogen bonding and van der Waals interactions. Overall, these results suggest that TDT1 and TDT2 exert their neuroprotective and analgesic potentials by ameliorating CCI-induced allodynia, hyperalgesia, neuroinflammation and neuronal degeneration in a dose-dependent manner.

Epineural Methylene Blue Injection May Aid Localization of Digital Nerves in Dupuytren's Surgery

Background

In Dupuytren's surgery, limited fasciectomy is still the gold-standard treatment. A relatively high risk of iatrogenic nerve injury has been observed especially when the spiral cords of the Dupuytren's tissue pull digital nerves away from their normal anatomical location. Intraoperative neural marking could facilitate locating the potentially displaced nerves. Hence, surgery could be undertaken more quickly with a lower risk of iatrogenic nerve injury.

Objectives

We hypothesize that digital nerves may be stained with methylene blue (MB) in vivo providing a visual aid to distinguish them from Dupuytren's tissue. We aim to (a) test an in vivo nerve staining technique using MB in a rat sciatic nerve model and to (b) assess the safety of epineural MB injection.

Methods

Three experiments were performed: first, the effects of (a) sham surgery, (b) epineural needle insertion, and (c) 40 μL epineural saline injection were tested in the rat sciatic nerve. Second, we determined the (a) histoanatomical localization of the epineurally injected 40 µL 1 m/m% MB stock solution and (b) we tested which saline dilution (i.e., 1:40, 1:80, and 1:160) of the stock solution does provide optimal blue color upon 40 µL epineural injection. Third, the functional and morphological effect of 40 µL 1:80 diluted MB injection was compared with that of saline, injected into the contralateral sciatic nerve. The functional effects were tested by assessing the pain threshold by using a dynamic plantar esthesiometer (DPA) and by examination of the animal's gate and paw posture. Sciatic nerves were subjected to histological examination and morphometry to test structural damage.

Results

Neither epineural needle insertion nor saline injection caused any functional or morphological changes. Histological examination revealed that the MB stained the epineural compartment. Epineural injection of 40 μL 1:80 diluted MB into the sciatic nerve stained an 18.18-mm segment of the nerve distal to the puncture point. DPA revealed unchanged pain threshold values on the plantar surface of the limbs. Normal gait and foot posture suggested normal motor functions in all groups. No histological changes were seen in the stained nerves, and the nerve fiber density remained unchanged.

Conclusion

We demonstrated that in vivo nerve staining with MB is a suitable method to mark nerves without causing detectable negative effect to the stained nerve. Human trials are required to prove the efficacy of the technique in Dupuytren's disease.

Effects of Gentiopicroside on activation of NLRP3 inflammasome in acute gouty arthritis mice induced by MSU

Acute gouty arthritis is a self-limiting inflammatory disease resulting from the deposition of monosodium urate (MSU) crystals. It has been shown that Gentiopicroside (GPS) possesses anti-inflammatory and analgesic functions. The aim of this study was to parse out whether GPS has an effect on acute gouty arthritis. We established an acute gouty arthritis model by the injection of MSU into the paw, and found that GPS relieves MSU-induced mechanical, thermal hyperalgesia, and paw swelling. Furthermore, GPS down-regulated the release of pro-inflammatory cytokines in paw tissues, including IL-1β, IL-6, IL-18, and TNF-α. The results of H&E staining and MPO activity measurement showed that GPS inhibits neutrophil infiltration. And the over-expressions of NOD-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and Caspase-1 induced by MSU were inhibited by treatment with GPS. These results revealed that GPS can treat acute gouty arthritis based on anti-inflammatory and analgesic properties in vivo, which might be ascribed to the inhibition on NLRP3 inflammasome. Furthermore, we performed in vitro study to confirm the results of in vivo study. Consistently, the results proved that GPS could inhibit the activation of NLRP3 inflammasome in RAW264.7 macrophages stimulated by LPS-MSU. In conclusion, this study provides an experimental basis for the application of GPS and expands the potential value of GPS in the therapy of acute gouty arthritis.

Long-Term Sequelae of Frostbite-A Scoping Review

Frostbite is tissue damage caused by freezing temperatures and constitutes an important cause of morbidity in cold climate zones and high altitude. The direct effects of sub-zero temperatures lead to tissue freezing, electrolyte shifts and pH alterations, microvascular damage, and eventually to cell death. Upon rewarming, inflammatory reperfusion injury and thrombosis may lead to further tissue damage. Several studies and various case reports show that many patients suffer from long-term sequelae such as vasomotor disturbances (associated with susceptibility to refreezing), and neuropathic and nociceptive pain, as well as damage to skeletal structures. There are still many uncertainties regarding the pathophysiology of these sequelae. It has been shown that the transient receptor potential channel (TRP) family plays a role in cold allodynia. Botulinum Toxin type A (BTX-A) injections have been reported to be beneficial in vasomotor and neuropathic disturbances secondary to frostbite. Epidural sympathetic block has been used for short-term treatment of frostbite induced chronic pain. Furthermore, amitriptyline, gabapentinoids, and duloxetine may have some benefits. Frostbite arthritis clinically resembles regular osteoarthritis. In children there is a risk of epiphyseal cartilage damage leading to bone deformities. Despite some promising therapeutic concepts, the scarcity of data on frostbite long-term sequelae in the literature indicates the need of more in-depth studies of this pathology in all its aspects.

Chondroitin sulfate produces antinociception and neuroprotection in chronic constriction injury-induced neuropathic pain in rats by increasing anti-inflammatory molecules and reducing oxidative stress

OBJECTIVES

Damage to the peripheral and central nervous system lead to Neuropathic pain (NP) which is a widespread and devitalizing condition. chondroitin sulfate (CS), has been used in managing joint pain and osteoarthritis. In this study, the effectiveness of CS on NP induced by chronic constriction injury (CCI) is examined.

METHODS

Thirty Wistar rats were distributed at random into six groups (n = 5). Sciatic nerve ligation was carried out by encircling the nerve with four loose ligatures to induce NP. Allodynia (cold and mechanical) and heat hyperalgesia were assessed using Acetone, von Frey filament and Hot plate tests. CCI induction resulted to NP, prominent from the 3rd day after surgery. Structural architecture of sciatic nerves was evaluated via histological examination of the transverse section of the nerves.

RESULTS

Oral administration of CS (600 mg/kg and 900 mg/kg for 21 days) resulted in significant (P < 0.05) inhibition of allodynia (cold and mechanical) and thermal hyperalgesia. Lipid peroxidation, tumor necrosis factor-α (TNF-α), calcitonin gene related peptide (CGRP), C reactive protein (CRP), and oxidative stress were attenuated by CS. CS also improved interleukin (IL)-6, nitric oxide (NO), total antioxidant capacity (TAC).

CONCLUSION

These findings suggest that CS attenuates allodynia, and thermal hyperalgesia induced by CCI by downregulating TNF-α, CRP, CGRP, oxidative enzymes, and upregulating IL-6, NO, and TAC. Nociceptive behavioral studies and histological findings showed significant improvement in the CS treated groups compared to CCI rats. These findings are responsible for the beneficial effect of CS in NP.

Discovery and Optimization of Highly Potent and Selective AT2R Antagonists to Relieve Peripheral Neuropathic Pain

The angiotensin II type 2 receptor (AT2R) has attracted much attention as a potential target for the relief of neuropathic pain, which represents an area of unmet clinical need. A series of 1,2,3,4-tetrahydroisoquinolines with a benzoxazole side-chain were discovered as potent AT2R antagonists. Rational optimization resulted in compound 15, which demonstrated both excellent antagonistic activity against AT2R in vitro and analgesic efficacy in a rat chronic constriction injury model. Its favorable physicochemical properties and oral bioavailability make it a promising therapeutic candidate for neuropathic pain.

Neuroskeletal Effects of Chronic Bioelectric Nerve Stimulation in Health and Diabetes

Background/Aims

Bioelectric nerve stimulation (eStim) is an emerging clinical paradigm that can promote nerve regeneration after trauma, including within the context of diabetes. However, its ability to prevent the onset of diabetic peripheral neuropathy (DPN) has not yet been evaluated. Beyond the nerve itself, DPN has emerged as a potential contributor to sarcopenia and bone disease; thus, we hypothesized that eStim could serve as a strategy to simultaneously promote neural and musculoskeletal health in diabetes.

Methods

To address this question, an eStim paradigm pre-optimized to promote nerve regeneration was applied to the sciatic nerve, which directly innervates the tibia and lower limb, for 8 weeks in control and streptozotocin-induced type 1 diabetic (T1D) rats. Metabolic, gait, nerve and bone assessments were used to evaluate the progression of diabetes and the effect of sciatic nerve eStim on neuropathy and musculoskeletal disease, while also considering the effects of cuff placement and chronic eStim in otherwise healthy animals.

Results

Rats with T1D exhibited increased mechanical allodynia in the hindpaw, reduced muscle mass, decreased cortical and cancellous bone volume fraction (BVF), reduced cortical bone tissue mineral density (TMD), and decreased bone marrow adiposity. Type 1 diabetes also had an independent effect on gait. Placement of the cuff electrode alone resulted in altered gait patterns and unilateral reductions in tibia length, cortical BVF, and bone marrow adiposity. Alterations in gait patterns were restored by eStim and tibial lengthening was favored unilaterally; however, eStim did not prevent T1D-induced changes in muscle, bone, marrow adiposity or mechanical sensitivity. Beyond this, chronic eStim resulted in an independent, bilateral reduction in cortical TMD.

Conclusion

Overall, these results provide new insight into the pathogenesis of diabetic neuroskeletal disease and its regulation by eStim. Though eStim did not prevent neural or musculoskeletal complications in T1D, our results demonstrate that clinical applications of peripheral neuromodulation ought to consider the impact of device placement and eStim on long-term skeletal health in both healthy individuals and those with metabolic disease. This includes monitoring for compounded bone loss to prevent unintended consequences including decreased bone mineral density and increased fracture risk.

The antioxidant N-(2-mercaptopropionyl)-glycine (tiopronin) attenuates expression of neuropathic allodynia and hyperalgesia

The current pharmacotherapy of neuropathic pain is inadequate as neuropathic pain involves varied clinical manifestations with multifactorial etiology, modulated by a cascade of physical and molecular events leading to different clinical presentations of pain. There is an accumulating evidence of the involvement of oxidative stress in neuropathy, and antioxidants have shown promise in mitigating neuropathic pain syndromes. To explore the evidence supporting this beneficial proclivity of antioxidants, this study investigated the antinociceptive effectiveness of N-(2-mercaptopropionyl)glycine or tiopronin, a well-recognized aminothiol antioxidant, in a refined chronic constriction injury (CCI) rat model of neuropathic pain. Tiopronin (10, 30, and 90 mg/kg, i.p.) and pregabalin (30 mg/kg, i.p.) were administered daily after CCI surgery. The neuropathic paradigms of mechanical/cold allodynia and mechanical/heat hyperalgesia were assessed on days 3, 7, 14, and 21 post-nerve ligation. At the end of study, malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) levels were estimated in the sciatic nerve, dorsal root ganglion, and spinal cord for assessing the extent of oxidative stress. The expression of neuropathic nociception was attenuated by tiopronin which was observed as a significant attenuation of CCI-induced allodynia and hyperalgesia. Tiopronin reversed the neuronal oxidative stress by significantly reducing MDA, and increasing SOD, CAT, and GSH levels. Pregabalin also showed similar beneficial propensity on CCI-induced neuropathic aberrations. These findings suggest prospective neuropathic pain attenuating efficacy of tiopronin and further corroborated the notion that antioxidants are effective in mitigating the development and expression of neuropathic pain and underlying neuronal oxidative stress.

S100A4 in Spinal Substantia Gelatinosa from Dorsal Root Ganglia Modulates Neuropathic Pain in a Rodent Spinal Nerve Injury Model

Purpose

To detect the spatio-temporal expression of S100A4 in a spinal nerve ligation (SNL) rat model. Also to figure out which other molecules directly interact with S100A4 to explore the possible mechanisms which might be involved in neuropathic pain.

Methods

Seven-week-old male SD rats were used for the SNL model construction. Immunofluorescence and Western blotting were used to detect the spatio-temporal expression of S100A4 in the model. S100A4 was co-labeled with a number of related molecules and marker molecules that can distinguish between cell types. After intrathecal injection of S100A4 neutralizing antibody, the behavioral changes of SNL rats were recorded, and molecular changes compared. The direct interaction between S100A4 and other related molecules was verified by co-immunoprecipitation (co-IP) to explore its possible mechanism.

Results

After spinal nerve ligation, the content of S100A4 in the dorsal root ganglion (DRG) and spinal dorsal horn increased significantly. Intrathecal injection of S100A4 neutralizing antibody could effectively relieve the mechanical pain in rats. co-IP revealed a direct interaction between S100A4 and RAGE.

Conclusion

The content of S100A4 in the DRG and spinal dorsal horn of SNL rats increased, compared with that of the control group. Intrathecal injection of S100A4 neutralizing antibody could effectively relieve the mechanical pain in SNL rats. S100A4 may be involved in the production of neuropathic pain through RAGE or other ways, but the specific mechanism needs to be further studied.

Chronic nanocurcumin treatment ameliorates pain-related behavior, improves spatial memory, and reduces hippocampal levels of IL-1β and TNFα in the chronic constriction injury model of neuropathic pain

BACKGROUND

Memory deficit is a common cognitive comorbid in patients with neuropathic pain that need better treatment. Recent research revealed that nanocurcumin has an antinociceptive action and a protective effect against memory disorders, suggesting its possible effectiveness for the treatment of neuropathic pain and its comorbidity.

METHODS

Adult male albino Wistar rats (n = 32) were randomly divided into four experimental groups: CCI+ nanocurcumin, CCI + vehicle, sham + nanocurcumin, and sham + vehicle. Neuropathic pain induced by a chronic constriction injury of the sciatic nerve. Nanocurcumin or vehicle was injected intraperitoneally for 10 days. Behavioral assessment achieved to evaluate pain threshold in the von Frey test and radiant heat test, also spatial learning and memory examined by the Morris water maze (MWM) test. To explore the possible relation, IL-1β, and TNF-α levels of the hippocampus measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our data showed that CCI caused neuropathic pain-related behaviors and spatial learning and memory disorders in rats. Chronic treatment with nanocurcumin significantly increased pain threshold (P < 0.001; F = 27.63, F = 20.58), improved spatial memory (P < 0.01; F = 47.37), and decreased the hippocampal levels of IL-1β (P < 0.001; F = 33.57) and TNF-α (P < 0.01; F = 7.25) in CCI rats.

CONCLUSION

Chronic nanocurcumin can ameliorate pain-related behavior, improve spatial learning and memory deficits, and is associated with the reduction of IL-1β and TNF-α levels in the hippocampus in CCI rats. Nanocurcumin may be potentially providing a therapeutic alternative for the treatment of neuropathic pain and its memory impairment comorbidity.

A novel gabapentin analogue assuages neuropathic pain response in chronic sciatic nerve constriction model in rats

Gabapentin (GBP) is an established drug that has been used in the management of symptoms of neuropathy but it is associated with unwanted side effects such as sedation and motor incoordination. The goal of the study was to find out a drug with greater efficacy and safety for the treatment of neuropathic pain. Our previously synthesized GABA analogue (Gabapentsal, GPS) was tested (25-100 mg/kg, i.p) in chronic constriction injury (CCI) induced nociceptive model of static allodynia, dynamic allodynia, thermal hyperalgesia, mechanical hyperalgesia and cold allodynia in rats (Sprague Dawley). Open field and rotarod tests were performed to assess the impact of GPS on the motor performance of the animals. GBP (100 mg/kg, i.p) was used as a standard for comparison. GPS dose dependently reduced static (P <0.001) and dynamic allodynia (P <0.001), thermal hyperalgesia (P <0.001), mechanical hyperalgesia (P < 0.001) and cold allodynia (P < 0.001). In comparison to GBP, GPS failed to alter any significantly the motor performance of rats in both the open field and rotarod assays. These results suggest that GPS is effective in alleviating nociception in CCI neuropathic pain model but free from the side effect of motor discoordination seen in the treatment with GBP. In conclusion, GPS may prove to be a prospectively more effective and safer option in the management of neuropathic syndromes.

Effect of Intraoperative Electrical Stimulation on Recovery after Rat Sciatic Nerve Isograft Repair

Peripheral nerve injuries, associated with significant morbidity, can benefit from electrical stimulation (ES), as demonstrated in animal studies through improved axonal growth. This study combined the clinical gold standard of isograft repair in a rat model of sciatic nerve injury to evaluate the effects of intraoperative ES on functional tests and histology. Forty rats underwent a surgically induced gap injury to the right sciatic nerve and subsequent repair with an isograft. Half of these rats were randomly selected to receive 10 min of intraoperative ES. Functional testing, including response time to a heat stimulus and motor functional tests, were conducted. Histology of the sciatic nerves and gastrocnemius muscles were analyzed after 6 and 12 weeks of recovery. Rats that underwent ES treatment showed incremental improvements in motor function between weeks 2 and 12, with a significantly higher push-off response than the no-ES controls after 6 weeks. Although no differences were detected between groups in the sensory testing, significant improvements over time were noted in the ES group. Histology parameters, sciatic nerve measures, and gastrocnemius muscle weights demonstrated nerve recovery over time for both the ES and no-ES control groups. Although ES promoted improvements in motor function comparable to that in previous studies, the benefits of intraoperative ES were not detectable in other metrics of this rat model of peripheral nerve injury. Future work is needed to optimize sensory testing in the rodent injury model and compare electrical activity of collagen scaffolds to native tissue to detect differences.

Emotional and cognitive impairments in the peripheral nerve chronic constriction injury model (CCI) of neuropathic pain: A systematic review

BACKGROUND AND OBJECTIVE

Emotional and cognitive impairments are common comorbidities of chronic neuropathic pain that significantly impact the quality of life of patients. While the nociceptive components of the peripheral nerve chronic constriction injury (CCI) animal model have been extensively analyzed, data related to the development of mood and cognitive disorders, and especially its impact on female rats remains fragmented. We systematically reviewed the literature analyzing the methods used to induce and evaluate the development of emotional- and cognitive-like impairments and sex-specific differences in the CCI model.

DATABASES AND DATA TREATMENT

We searched PubMed, Google Scholar and Web of Science from inception to September 30th, 2019, and a total of 44 papers were considered eligible for inclusion. We included animal studies assessing nociception, locomotion, anxious-like, depressive-like and cognitive behaviours after the CCI induction.

RESULTS

The overall quality of the studies was considered moderate to high. Overall, the induction of CCI leads to the development of emotional impairments, namely anxiety- and depressive-like behaviours, as well as cognitive impairments. With the majority of the studies using male subjects, the lack of evidence on female animals prevents the evaluation of sex-specific differences.

CONCLUSIONS

This review supports the development of an anxiodepressive-like phenotype, associated with cognitive impairments, in CCI-induced animals. These results support the use of this animal model for the study of the mechanisms underlying these comorbidities, as well as a screening tool for the development/repurposing of drugs that tackle both the neuropathy-induced nociceptive and emotional impairments, such as tricyclic antidepressants. Importantly, our review also highlights the need for studies performed in female rodents as these are almost non-existent.

[Effects of different materials for partial sciatic nerve ligation on glial cell activation in rat models of chronic constriction injury]

OBJECTIVE

To compare the effects of different materials for partial sciatic nerve ligation on glial cell activation in the spinal cord in a rat model of chronic constriction injury (CCI).

METHODS

SD rats were randomly divided into the sham group (n=15), silk suture CCI group (n=15) and chromic catgut CCI group (n=14). The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) of the rats were detected at 3, 7, 11 and 15 days after the operation. The changes in the sciatic nerve, the activation of spinal cord glial cells and the expression of inflammatory factors were observed using Western blotting and RT-PCR.

RESULTS

At 3 to 15 days after the surgery, MWT and TWL of the rats were significantly lower in silk suture group and chromic catgut group than in the control group (P &lt; 0.05), and was significantly lower in chromic catgut group than in the silk suture group (P &lt; 0.05) at 3 days after the surgery. The results of sciatic nerve myelin staining showed that the sciatic nerve was damaged and demyelinated in both the ligation groups. The expressions of CD11b, GFAP, IL-1β and TNF-α in the two ligation groups were similar and all significantly higher than those in the control group (P &lt; 0.05). IL-6 mRNA level was significantly higher in chromic catgut group than in the silk suture group (P &lt; 0.05).

CONCLUSIONS

The CCI models established by partial sciatic nerve ligation with silk suture and chromic catgut all show glial activation, and the inflammatory response is stronger in chromic catgut group.

Curcumin Diglutaric Acid, a Prodrug of Curcumin Reduces Pain Hypersensitivity in Chronic Constriction Injury of Sciatic Nerve Induced-Neuropathy in Mice

The drug treatment for neuropathic pain remains a challenge due to poor efficacy and patient satisfaction. Curcumin has been reported to alleviate neuropathic pain, but its clinical application is hindered by its low solubility and poor oral bioavailability. Curcumin diglutaric acid (CurDG) is a curcumin prodrug with improved water solubility and in vivo antinociceptive effects. In this study, we investigated the anti-inflammatory mechanisms underlying the analgesic effect of CurDG in the chronic constriction injury (CCI)-induced neuropathy mouse model. Repeated oral administration of CurDG at a low dose equivalent to 25 mg/kg/day produced a significant analgesic effect in this model, both anti-allodynic activity and anti-hyperalgesic activity appearing at day 3 and persisting until day 14 post-CCI surgery (p < 0.001) while having no significant effect on the motor performance. Moreover, the repeated administration of CurDG diminished the increased levels of the pro-inflammatory cytokines: TNF-α and IL-6 in the sciatic nerve and the spinal cord at the lowest tested dose (equimolar to 25 mg/kg curcumin). This study provided pre-clinical evidence to substantiate the potential of pursuing the development of CurDG as an analgesic agent for the treatment of neuropathic pain.

The Circadian Hormone Melatonin Inhibits Morphine-Induced Tolerance and Inflammation via the Activation of Antioxidative Enzymes

Opioids are commonly prescribed for clinical pain management; however, dose-escalation, tolerance, dependence, and addiction limit their usability for long-term chronic pain. The associated poor sleep pattern alters the circadian neurobiology, and further compromises the pain management. Here, we aim to determine the correlation between constant light exposure and morphine tolerance and explore the potential of melatonin as an adjuvant of morphine for neuropathic pain treatment. Methods: Wistar rats were preconditioned under constant light (LL) or a regular light/dark (LD) cycle before neuropathic pain induction by chronic constriction injury. An intrathecal (i.t.) osmotic pump was used for continued drug delivery to induce morphine tolerance. Pain assessments, including the plantar test, static weight-bearing symmetry, and tail-flick latency, were used to determine the impact of the light disruption or exogenous melatonin on the morphine tolerance progression. Results: constant light exposure significantly aggravates morphine tolerance in neuropathic rats. Continued infusion of low-dose melatonin (3 μg/h) attenuated morphine tolerance in both neuropathic and naïve rats. This protective effect was independent of melatonin receptors, as shown by the neutral effect of melatonin receptors inhibitors. The transcriptional profiling demonstrated a significant enhancement of proinflammatory and pain-related receptor genes in morphine-tolerant rats. In contrast, this transcriptional pattern was abolished by melatonin coinfusion along with the upregulation of the Kcnip3 gene. Moreover, melatonin increased the antioxidative enzymes SOD2, HO-1, and GPx1 in the spinal cord of morphine-tolerant rats. Conclusion: Dysregulated circadian light exposure significantly compromises the efficacy of morphine’s antinociceptive effect, while the cotreatment with melatonin attenuates morphine tolerance/hyperalgesia development. Our results suggest the potential of melatonin as an adjuvant of morphine in clinical pain management, particularly in patients who need long-term opioid treatment.

Mechanisms Involved in Superiority of Angiotensin Receptor Blockade over ACE Inhibition in Attenuating Neuropathic Pain Induced in Rats

Although previous reports described the beneficial role of angiotensin-converting enzyme inhibitors (ACE-Is) or AT1 receptor blockers (ARBs) in attenuating neuropathic pain (NP), no study has yet explored the exact underlying mechanisms, as well as the superiority of using centrally versus peripherally acting renin-angiotensin-aldosterone system (RAAS) drugs in NP. We investigated the effects of 14 days of treatment with centrally (telmisartan and ramipril) or peripherally (losartan and enalapril) acting ARBs and ACE-Is, respectively, in attenuating peripheral NP induced by sciatic nerve chronic constriction injury (CCI) in rats. We also compared these with the effects of pregabalin, the standard treatment for NP. Behavioral changes, inflammatory markers (NFкB, TNF-α, COX-2, PGE2, and bradykinin), oxidative stress markers (NADPH oxidase and catalase), STAT3 activation, levels of phosphorylated P38-MAPK, ACE, AT1 receptor (AT1R), and AT2 receptor (AT2R), as well as histopathological features, were assessed in the brainstem and sciatic nerve. CCI resulted in clear pain-related behavior along with increased levels of inflammatory and oxidative stress markers, and STAT3 activity, as well as increased levels of phosphorylated P38-MAPK, ACE, AT1R, and AT2R, along with worsened histopathological findings in both the brainstem and sciatic nerve. ARBs improved both animal behavior and all measured parameters in CCI rats and were more effective than ACE-Is. At the tested doses, centrally acting ARBs or ACE-Is were not superior to the peripherally acting drugs of the same category. These findings suggest that ARBs (centrally or peripherally acting) are an effective treatment modality for NP.

Exploring the Promise of Flavonoids to Combat Neuropathic Pain: From Molecular Mechanisms to Therapeutic Implications

Neuropathic pain (NP) is the result of irregular processing in the central or peripheral nervous system, which is generally caused by neuronal injury. The management of NP represents a great challenge owing to its heterogeneous profile and the significant undesirable side effects of the frequently prescribed psychoactive agents, including benzodiazepines (BDZ). Currently, several established drugs including antidepressants, anticonvulsants, topical lidocaine, and opioids are used to treat NP, but they exert a wide range of adverse effects. To reduce the burden of adverse effects, we need to investigate alternative therapeutics for the management of NP. Flavonoids are the most common secondary metabolites of plants used in folkloric medicine as tranquilizers, and have been claimed to have a selective affinity to the BDZ binding site. Several studies in animal models have reported that flavonoids can reduce NP. In this paper, we emphasize the potentiality of flavonoids for the management of NP.

Discovery and development of ASK1 inhibitors

Aberrant activation of mitogen-activated protein kinases (MAPKs) like c-Jun N-terminal kinase (JNK) and p38 is an event involved in the pathophysiology of numerous human diseases. The apoptosis signal-regulating kinase 1 (ASK1) is an upstream target that gets activated only under pathological conditions and as such is a promising target for therapeutic intervention. In the first part of this review the molecular mechanisms leading to ASK1 activation and regulation will be described as well as the evidences supporting a pathogenic role for ASK1 in human disease. In the second part, an update on drug discovery efforts towards the discovery and development of ASK1-targeting therapies will be provided.

In Vitro and In Vivo Effects of Flavonoids on Peripheral Neuropathic Pain

Neuropathic pain is a common symptom and is associated with an impaired quality of life. It is caused by the lesion or disease of the somatosensory system. Neuropathic pain syndromes can be subdivided into two categories: central and peripheral neuropathic pain. The present review highlights the peripheral neuropathic models, including spared nerve injury, spinal nerve ligation, partial sciatic nerve injury, diabetes-induced neuropathy, chemotherapy-induced neuropathy, chronic constriction injury, and related conditions. The drugs which are currently used to attenuate peripheral neuropathy, such as antidepressants, anticonvulsants, baclofen, and clonidine, are associated with adverse side effects. These negative side effects necessitate the investigation of alternative therapeutics for treating neuropathic pain conditions. Flavonoids have been reported to alleviate neuropathic pain in murine models. The present review elucidates that several flavonoids attenuate different peripheral neuropathic pain conditions at behavioral, electrophysiological, biochemical and molecular biological levels in different murine models. Therefore, the flavonoids hold future promise and can be effectively used in treating or mitigating peripheral neuropathic conditions. Thus, future studies should focus on the structure-activity relationships among different categories of flavonoids and develop therapeutic products that enhance their antineuropathic effects.