Vitamins in neuropathy: pathophysiological and therapeutic roles.

PURPOSE OF REVIEW: Vitamin deficiency is a risk factor in the development of peripheral neuropathy, which leads to complex and severe diseases. This review provides an update overview of the literature on the roles of vitamins in peripheral neuropathy, highlighting their pathophysiological and therapeutic roles. RECENT FINDINGS: The importance and clinical manifestations and implications of the vitamins and vitamin deficiencies are further demonstrated in peripheral neuropathy and the associated diseases. Vitamin deficiency is common in various severe and complex diseases such as diabetes, chemotherapy, acute nutritional axonal neuropathy, dermatitis, complex regional pain syndrome, postherpetic neuralgia, carpal tunnel syndrome, and so forth and some rare clinical case reports. There is evidence that deficiencies of almost all vitamins are associated with diabetic neuropathy. Vitamin supplementation may serve as an effective therapeutic strategy. SUMMARY: The vitamins play critical roles in maintaining physiological functions, and vitamin deficiencies cause peripheral neuropathy with various severe and complex diseases. The therapeutic benefits of vitamins and further understanding of the mechanisms for vitamin treatment effects should be emphasized and highlighted. More clinical trials are needed to establish optimal treatment strategies for vitamins in the various neuropathies. A large range of people/patients screening for vitamin deficiencies may be considered in order to provide early diagnosis and timely medical assistance.

Gut microbiota depletion by antibiotics ameliorates somatic neuropathic pain induced by nerve injury, chemotherapy, and diabetes in mice.

BACKGROUND: Gut microbiota has been found involved in neuronal functions and neurological disorders. Whether and how gut microbiota impacts chronic somatic pain disorders remain elusive. METHODS: Neuropathic pain was produced by different forms of injury or diseases, the chronic constriction injury (CCI) of the sciatic nerves, oxaliplatin (OXA) chemotherapy, and streptozocin (STZ)-induced diabetes in mice. Continuous feeding of antibiotics (ABX) cocktail was used to cause major depletion of the gut microbiota. Fecal microbiota, biochemical changes in the spinal cord and dorsal root ganglion (DRG), and the behaviorally expressed painful syndromes were assessed. RESULTS: Under condition of gut microbiota depletion, CCI, OXA, or STZ treatment-induced thermal hyperalgesia or mechanical allodynia were prevented or completely suppressed. Gut microbiota depletion also prevented CCI or STZ treatment-induced glial cell activation in the spinal cord and inhibited cytokine production in DRG in OXA model. Interestingly, STZ treatment failed to induce the diabetic high blood glucose and painful hypersensitivity in animals with the gut microbiota depletion. ABX feeding starting simultaneously with CCI, OXA, or STZ treatment resulted in instant analgesia in all the animals. ABX feeding starting after establishment of the neuropathic pain in CCI- and STZ-, but not OXA-treated animals produced significant alleviation of the thermal hyeralgesia or mechanical allodynia. Transplantation of fecal bacteria from SPF mice to ABX-treated mice partially restored the gut microbiota and fully rescued the behaviorally expressed neuropathic pain, of which, Akkermansia, Bacteroides, and Desulfovibrionaceae phylus may play a key role. CONCLUSION: This study demonstrates distinct roles of gut microbiota in the pathogenesis of chronic painful conditions with nerve injury, chemotherapy and diabetic neuropathy and supports the clinical significance of fecal bacteria transplantation.

B vitamins as a treatment for diabetic pain and neuropathy.

WHAT IS KNOWN AND OBJECTIVE: B vitamin therapy is a common treatment for diabetic pain and neuropathy, yet its use remains controversial in patients lacking B vitamin deficiencies. The aim of this review was to summarize the current evidence for the efficacy of B vitamin therapy in diabetic patients with neuropathy. COMMENT: We screened the English literature for clinical studies evaluating B vitamins as a therapy for pain and neuropathy in diabetic patients. We selected 43 relevant studies for qualitative analysis based on our selection criteria. Our survey of the literature revealed substantive heterogeneity with respect to efficacies of reported outcomes, as well as study design. Most beneficial outcomes were reported against baseline measures, with few positive comparisons against placebo. This highlights the need for larger, placebo-controlled studies. WHAT IS NEW AND CONCLUSION: B vitamins should be considered a plausible therapy for diabetic neuropathy, but its overall efficacy remains uncertain and requires further study.

Inhibition of YAP/TAZ Activity in Spinal Cord Suppresses Neuropathic Pain.

UNLABELLED: Neuropathic pain, often caused by nerve injury, is a major clinical challenge. Mechanisms that underlie neuropathic pain remain elusive and effective medications are limited. Numerous investigations of pain mechanisms have focused on alterations and phenotypic switches of the nociceptive transmitters and modulators, as well as on their receptors and downstream signaling pathways that have already exerted roles in the pain processes of mature nervous systems. We have demonstrated recently that nerve injury may elicit neuronal alterations that recapitulate events occurring during development. Signaling of the representative activated molecule Wnt thus becomes a trigger for the development of neuropathic pain and is a potential therapeutic target. We report that the transcriptional regulators YAP and TAZ, which orchestrate Wnt response via incorporation in the ß-catenin destruction complex, are key in the pathogenesis of neuropathic pain and may serve as an "ON-OFF" switch for neuropathic pain status in rats. Peripheral nerve injury causes rapid-onset and long-lasting nuclear accumulation of YAP/TAZ/ß-catenin in the spinal dorsal horn. Spinal inhibition or knock-down of either YAP or TAZ suppresses mechanical allodynia induced by nerve injury or the pain initiators lysophosphatidic acid and Wnt3a. Promoting the nuclear accumulation of YAP/TAZ leads to mechanical hypersensitivity in naive animals. Further, we discovered a new small molecule, dCTB, which targets YAP/TAZ/ß-catenin and can greatly suppress neuropathic pain and the associated neurochemical alterations. Our study reveals that YAP and TAZ are core mechanisms underlying the pathogenesis of neuropathic pain and are targets in the screening for potent analgesics for the treatment of neuropathic pain. SIGNIFICANCE STATEMENT: Mechanisms that underlie neuropathic pain remain elusive. We have demonstrated recently that nerve injury can activate Wnt signaling, which becomes a trigger for the development of neuropathic pain. We report that the transcriptional regulators YAP and TAZ, which orchestrate Wnt response via incorporation in the ß-catenin destruction complex, are key in the pathogenesis of neuropathic pain and may serve as an "ON-OFF" switch for neuropathic pain status. Further, we discovered a new small molecule, dCTB, which targets YAP/TAZ/ß-catenin and can greatly suppress neuropathic pain. Our study reveals that YAP and TAZ are core mechanisms underlying the pathogenesis of neuropathic pain and are targets in the screening of potent analgesics for the treatment of neuropathic pain.

B Vitamins Potentiate Acute Morphine Antinociception and Attenuate the Development of Tolerance to Chronic Morphine in Mice.

OBJECTIVES: Opiate analgesics are the most effective treatments for severe pain, but their clinical utility is often hampered by the development of analgesic tolerance. There are striking similarities between morphine actions and neuropathic pain. We have demonstrated that B vitamins can attenuate neuropathic pain after peripheral nerve injury, sensory neuron inflammation/compression, and transient spinal cord ischemia. Given this similarity, the present study investigated whether B vitamins might be able to modify the antinociceptive effect of morphine as well as morphine tolerance in mice. METHODS: Cell signaling was assayed by Western blot and immunohistochemistry. Antinociception was assessed in ICR mice using the tail flick. The effects of B vitamins on acute morphine-induced antinociception and chronic morphine tolerance were studied. RESULTS: 1) Co-administration of B vitamins with morphine potentiates acute morphine antinociception. 2) B vitamins attenuate the development of antinociceptive tolerance to chronic morphine administration and inhibit morphine-induced p-NR1, p-PKC in the spinal cord. 3) Morphine induces microglial activation, as evidenced by increased p38 MAPK phosphorylation, IBA1, and IL-1ß in the spinal cord, and these changes are inhibited by B vitamins. 4) Treatment of B vitamins alone shows no notable effects on pain threshold and activity of microglia invivo. CONCLUSIONS: B vitamins potentiate acute morphine antinociception and attenuate chronic morphine tolerance.

Radiotherapy Suppresses Bone Cancer Pain through Inhibiting Activation of cAMP Signaling in Rat Dorsal Root Ganglion and Spinal Cord.

Radiotherapy is one of the major clinical approaches for treatment of bone cancer pain. Activation of cAMP-PKA signaling pathway plays important roles in bone cancer pain. Here, we examined the effects of radiotherapy on bone cancer pain and accompanying abnormal activation of cAMP-PKA signaling. Female Sprague-Dawley rats were used and received tumor cell implantation (TCI) in rat tibia (TCI cancer pain model). Some of the rats that previously received TCI treatment were treated with X-ray radiation (radiotherapy). Thermal hyperalgesia and mechanical allodynia were measured and used for evaluating level of pain caused by TCI treatment. PKA mRNA expression in dorsal root ganglion (DRG) was detected by RT-PCR. Concentrations of cAMP, IL-1ß, and TNF-α as well as PKA activity in DRG and the spinal cord were measured by ELISA. The results showed that radiotherapy significantly suppressed TCI-induced thermal hyperalgesia and mechanical allodynia. The level of PKA mRNA in DRG, cAMP concentration and PKA activity in DRG and in the spinal cord, and concentrations of IL-1ß and TNF-α in the spinal cord were significantly reduced by radiotherapy. In addition, radiotherapy also reduced TCI-induced bone loss. These findings suggest that radiotherapy may suppress bone cancer pain through inhibition of activation of cAMP-PKA signaling pathway in DRG and the spinal cord.

Attenuation Effect of Spinal Manipulation on Neuropathic and Postoperative Pain Through Activating Endogenous Anti-Inflammatory Cytokine Interleukin 10 in Rat Spinal Cord.

OBJECTIVES: The purpose of this study was to investigate roles of the anti-inflammatory cytokine interleukin (IL) 10 and the proinflammatory cytokines IL-1ß and tumor necrosis factor α (TNF-α) in spinal manipulation-induced analgesic effects of neuropathic and postoperative pain. METHODS: Neuropathic and postoperative pain were mimicked by chronic compression of dorsal root ganglion (DRG) (CCD) and decompression (de-CCD) in adult, male, Sprague-Dawley rats. Behavioral pain after CCD and de-CCD was determined by the increased thermal and mechanical hypersensitivity of the affected hindpaw. Hematoxylin and eosin staining, whole-cell patch clamp electrophysiological recordings, immunohistochemistry, and enzyme-linked immunosorbent assay were used to examine the neural inflammation, neural excitability, and expression of c-Fos and PKC as well as levels of IL-1ß, TNF-α, and IL-10 in blood plasma, DRG, or the spinal cord. We used the activator adjusting instrument, a chiropractic spinal manipulative therapy tool, to deliver force to the spinous processes of L5 and L6. RESULTS: After CCD and de-CCD treatments, the animals exhibited behavioral and neurochemical signs of neuropathic pain manifested as mechanical allodynia and thermal hyperalgesia, DRG inflammation, DRG neuron hyperexcitability, induction of c-Fos, and the increased expression of PKCγ in the spinal cord as well as increased level of IL-1ß and TNF-α in DRG and the spinal cord. Repetitive Activator-assisted spinal manipulative therapy significantly reduced simulated neuropathic and postoperative pain, inhibited or reversed the neurochemical alterations, and increased the anti-inflammatory IL-10 in the spinal cord. CONCLUSION: These findings show that spinal manipulation may activate the endogenous anti-inflammatory cytokine IL-10 in the spinal cord and thus has the potential to alleviate neuropathic and postoperative pain.

A Traditional Chinese Medicine Xiao-Ai-Tong Suppresses Pain through Modulation of Cytokines and Prevents Adverse Reactions of Morphine Treatment in Bone Cancer Pain Patients.

Treating cancer pain continues to possess a major challenge. Here, we report that a traditional Chinese medicine Xiao-Ai-Tong (XAT) can effectively suppress pain and adverse reactions following morphine treatment in patients with bone cancer pain. Visual Analogue Scale (VAS) and Quality of Life Questionnaire (EORTC QLQ-C30) were used for patient's self-evaluation of pain intensity and evaluating changes of adverse reactions including constipation, nausea, fatigue, and anorexia, respectively, before and after treatment prescriptions. The clinical trials showed that repetitive oral administration of XAT (200 mL, bid, for 7 consecutive days) alone greatly reduced cancer pain. Repetitive treatment with a combination of XAT and morphine (20 mg and 30 mg, resp.) produced significant synergistic analgesic effects. Meanwhile, XAT greatly reduced the adverse reactions associated with cancer and/or morphine treatment. In addition, XAT treatment significantly reduced the proinflammatory cytokines interleukin-1ß and tumor necrosis factor-α and increased the endogenous anti-inflammatory cytokine interleukin-10 in blood. These findings demonstrate that XAT can effectively reduce bone cancer pain probably mediated by the cytokine mechanisms, facilitate analgesic effect of morphine, and prevent or reduce the associated adverse reactions, supporting a use of XAT, alone or with morphine, in treating bone cancer pain in clinic.

Activation of the cAMP-PKA signaling pathway in rat dorsal root ganglion and spinal cord contributes toward induction and maintenance of bone cancer pain.

The objective of this study was to explore the role of cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) signaling in the development of bone cancer pain in rats. Female Sprague-Dawley rats (N=48) were divided randomly into four groups: sham (n=8), tumor cell implantation (TCI) (n=16), TCI+saline (n=8), and TCI+PKA inhibitor (n=16). Bone cancer-induced pain behaviors - thermal hyperalgesia and mechanical allodynia - were tested at postoperative days -3, -1, 1, 3, 5, 7, 10, and 14. A PKA inhibitor, Rp-cAMPS (1 mmol/l/20 µl), was injected intrathecally on postoperative days 3, 4, and 5 (early phase) or 7, 8, and 9 postoperative days (late phase). The expression of PKA mRNA in dorsal root ganglia (DRG) was detected by reverse transcription-PCR. The concentration of cAMP and activity of PKA in DRG and spinal cord were measured by enzyme-linked immunosorbent assay. TCI treatment induced significant pain behaviors, manifested as thermal hyperalgesia and mechanical allodynia. Spinal administration of the PKA inhibitor Rp-cAMPS during the early phase and late phase significantly delayed or reversed, respectively, TCI-induced thermal hyperalgesia and mechanical allodynia. TCI treatment also led to obvious tumor growth and bone destruction. The level of PKA mRNA in the DRG, as well as the concentration of cAMP and the activity of PKA, in both the DRG and spinal cord were significantly increased after TCI treatment (P<0.01). We conclude that the inhibition of the cAMP-PKA signaling pathway may reduce bone cancer pain.

Establishment of a rat model of type II diabetic neuropathic pain.

OBJECTIVE: To establish a rat model of type II diabetic neuropathic pain. METHODS: Sixty Sprague Dawley rats were randomly divided into two groups: group A (N = 10) was fed a normal diet, and group B (N = 50) was fed a high-fat and high-sugar diet. After 8 weeks, the body weight of all rats was recorded, and rats in both groups had their fasting plasma glucose, insulin concentration, and insulin sensitivity index measured and calculated. Subsequently, the rats in group B were randomly divided into three subgroups that were each given different doses of streptozotocin (STZ) by a single intraperitoneal injection (subgroup B1 received 30 mg/kg, subgroup B2 received 35 mg/kg, and subgroup B3 40 mg/kg). Two weeks after the STZ injection, the four groups of rats had their insulin sensitivity index, mechanical withdrawal threshold, and thermal withdrawal latency assessed, allowing us to establish a rat model of type II diabetic neuropathic pain and to determine the optimum dose of STZ. Four weeks after STZ injection (2 weeks after the model was established), the pain threshold was measured in the rats in group A and the group treated with the most effective STZ dose. We also measured the expression of phosphorylated extracellular signal-regulated kinase (p-ERK), phosphorylated cyclic AMP response element-binding protein (p-CREB), and phosphorylated N-methyl d-aspartate receptor subtype B (p-NR2B) in the dorsal root ganglion (DRG) and spinal cord dorsal horn regions, which are closely related to neuropathic pain, and also recorded the TTX-R sodium currents in the acutely isolated DRG neurons. RESULTS: After 8 weeks of a high-fat, high-sugar diet, the body weight of the rats in group B was significantly increased. Although the fasting blood glucose levels did not change significantly, the fasting insulin levels were slightly elevated, and the insulin sensitivity index was significantly reduced. Two weeks after STZ injection, the blood glucose levels of the rats in subgroup B1 were elevated but did not remain so for a prolonged period. In contrast, the rats in subgroup B3 had elevated blood glucose that was accompanied by a high mortality rate, while the blood glucose levels of the rats in subgroup B2 were moderately elevated and relatively stable. In addition, the pain threshold was significantly decreased (P < 0.05), and the mortality was low in this group. Because of this, the dose of STZ that was used in group B2 was considered the most effective dose of STZ for induction of diabetes. Four weeks after STZ injection, the pain threshold in the rats of group B2 was still significantly decreased, and the expression of p-ERK, p-CREB, and p-NR2B in the dorsal root ganglion (DRG) and spinal cord dorsal horn was significantly increased. The tetrodotoxin-resistant sodium current density in DRG neurons was also significantly elevated (P < 0.05). CONCLUSIONS: A rat model of type II diabetic neuropathic pain can be established by feeding rats a high-fat, high-sugar diet for 8 weeks, in combination with intraperitoneal injection of 35 mg/kg STZ. This model can be stably maintained for at least 2 weeks.

Diabetic Neuropathic Pain: Directions for Exploring Treatments.

Diabetic neuropathic pain (DNP) is one of the common and severe late-stage complications of diabetes mellitus, which could greatly influence the patients' quality of life. Patients with DNP often experience spontaneous pain and evoked pain such as mechanical allodynia and thermal hyperalgesia, meaning that their physical and psychological health are severely impaired. Unfortunately, the mechanisms of DNP remain highly elusive, so substantial breakthrough in effective DNP targeted treatments is still clinically challenging. This article will hence summarise the main mechanisms currently known to underlie DNP pathogenesis, along with describing some of the current and potential treatment methods against diabetic neuropathic pain.

Neurobiological basis of emergence from anesthesia.

The suppression of consciousness by anesthetics and the emergence of the brain from anesthesia are complex and elusive processes. Anesthetics may exert their inhibitory effects by binding to specific protein targets or through membrane-mediated targets, disrupting neural activity and the integrity and function of neural circuits responsible for signal transmission and conscious perception/subjective experience. Emergence from anesthesia was generally thought to depend on the elimination of the anesthetic from the body. Recently, studies have suggested that emergence from anesthesia is a dynamic and active process that can be partially controlled and is independent of the specific molecular targets of anesthetics. This article summarizes the fundamentals of anesthetics' actions in the brain and the mechanisms of emergence from anesthesia that have been recently revealed in animal studies.

Blocking proteinase-activated receptor 2 signaling relieves pain, suppresses nerve sprouting, improves tissue repair, and enhances analgesic effect of B vitamins in rats with Achilles tendon injury.

ABSTRACT: Tendon injury produces intractable pain and disability in movement, but the medications for analgesia and restoring functional integrity of tendon are still limited. In this study, we report that proteinase-activated receptor 2 (PAR2) activation in dorsal root ganglion (DRG) neurons contributes to chronic pain and tendon histopathological changes produced by Achilles tendon partial transection injury (TTI). Tendon partial transection injury increases the expression of PAR2 protein in both somata of DRG neurons and their peripheral terminals within the injured Achilles tendon. Activation of PAR2 promotes the primary sensory neuron plasticity by activating downstream cAMP-PKA pathway, phosphorylation of PKC, CaMKII, and CREB. Blocking PAR2 signaling by PAR2 small-interference RNA or antagonistic peptide PIP delays the onset of TTI-induced pain, reverses the ongoing pain, as well as inhibits sensory nerve sprouting, and promotes structural remodeling of the injured tendon. Vitamin B complex (VBC), containing thiamine (B1), pyridoxine (B6), and cyanocobalamin (B12), is effective to ameliorate TTI-induced pain, inhibit ectopic nerve sprouting, and accelerate tendon repair, through suppressing PAR2 activation. These findings reveal a critical role of PAR2 signaling in the development of chronic pain and histopathological alterations of injured tendon following Achilles tendon injury. This study suggests that the pharmaceuticals targeting PAR2, such as VBC, may be an effective approach for the treatment of tendon injury-induced pain and promoting tendon repair.

Reduced conduction failure of the main axon of polymodal nociceptive C-fibres contributes to painful diabetic neuropathy in rats.

Painful diabetic neuropathy is a common complication of diabetes mellitus and can affect many aspects of life and severely limit patients' daily functions. Signals of painful diabetic neuropathy are believed to originate in the peripheral nervous system. However, its peripheral mechanism of hyperalgesia has remained elusive. Numerous studies have accumulated that polymodal nociceptive C-fibres play a crucial role in the generation and conduction of pain signals and sensitization of which following injury or inflammation leads to marked hyperalgesia. Traditionally, the number of nociceptive primary afferent firings is believed to be determined at the free nerve endings, while the extended main axon of unmyelinated C-fibres only involves the reliable and faithful propagation of firing series to the central terminals. We challenged this classic view by showing that conduction of action potential can fail to occur in response to repetitive activity when they travel down the main axon of polymodal nociceptive C-fibres. Quantitative analysis of conduction failure revealed that the degree of conduction failure displays a frequency-dependent manner. Local administration of low threshold, rapidly activating potassium current blocker, α-dendrotoxin (0.5 nM) and persistent sodium current blocker, low doses of tetrodotoxin (<100 nM) on the main axon of C-fibres can reciprocally regulate the degree of conduction failure, confirming that conduction failure did occur along the main axon of polymodal nociceptive C-fibres. Following streptozotocin-induced diabetes, a subset of polymodal nociceptive C-fibres exhibited high-firing-frequency to suprathreshold mechanical stimulation, which account for about one-third of the whole population of polymodal nociceptive C-fibres tested. These high-firing-frequency polymodal nociceptive C-fibres in rats with diabetes displayed a marked reduction of conduction failure. Delivery of low concentrations of tetrodotoxin and Nav1.8 selective blocker, A-803467 on the main axon of C-fibres was found to markedly enhance the conduction failure in a dose-dependent manner in diabetic rats. Upregulated expression of sodium channel subunits Nav1.7 and Nav1.8 in both small dorsal root ganglion neurons and peripheral C-fibres as well as enhanced transient and persistent sodium current and increased excitability in small dorsal root ganglion neurons from diabetic rats might underlie the reduced conduction failure in the diabetic high-firing-frequency polymodal nociceptive C-fibres. This study shed new light on the functional capability in the pain signals processing for the main axon of polymodal nociceptive C-fibres and revealed a novel mechanism underlying diabetic hyperalgesia.

Characterization of Inflammatory Signals in BV-2 Microglia in Response to Wnt3a.

Activation of microglia is one of the pathological bases of neuroinflammation, which involves various diseases of the central nervous system. Inhibiting the inflammatory activation of microglia is a therapeutic approach to neuroinflammation. In this study, we report that activation of the Wnt/ß-catenin signaling pathway in a model of neuroinflammation in Lipopolysaccharide (LPS)/IFN-γ-stimulated BV-2 cells can result in inhibition of production of nitric oxide (NO), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). Activation of the Wnt/ß-catenin signaling pathway also results in inhibition of the phosphorylation of nuclear factor-κB (NF-κB) and extracellular signal-regulated kinase (ERK) in the LPS/IFN-γ-stimulated BV-2 cells. These findings indicate that activation of the Wnt/ß-catenin signaling pathway can inhibit neuroinflammation through downregulating the pro-inflammatory cytokines including iNOS, TNF-α, and IL-6, and suppress NF-κB/ERK-related signaling pathways. In conclusion, this study indicates that the Wnt/ß-catenin signaling activation may play an important role in neuroprotection in certain neuroinflammatory diseases.

Lactobacillus rhamnosus GG and butyrate supplementation in rats with bone cancer reduces mechanical allodynia and increases expression of µ-opioid receptor in the spinal cord.

Introduction: Chronic cancer pain is one of the most unbearable symptoms for the patients with advanced cancer. The treatment of cancer pain continues to possess a major challenge. Here, we report that adjusting gut microbiota via probiotics can reduce bone cancer pain (BCP) in rats. Methods: The model of BCP was produced by tumor cell implantation (TCI) to the tibia in rats. Continuous feeding of Lactobacillus rhamnosus GG (LGG) was used to modulate the gut microbiota. Mechanical allodynia, bone destruction, fecal microbiota, and neurochemical changes in the primary dorsal root ganglion (DRG) and the spinal dorsal horn (DH) were assessed. Results: LGG supplementation (109 CFU/rat/day) delayed the production of BCP for 3-4 days and significantly alleviated mechanical allodynia within the first 2 weeks after TCI. TCI-induced proinflammatory cytokines TNF-α and IL-ß in the DH, and TCI-induced bone destruction in the tibia were both significantly reduced following LGG supplementation examined on day 8 after TCI. Meanwhile, we found that LGG supplementation, in addition to inhibiting TCI-induced pain, resulted in a significantly increased expression of the µ-opioid receptor (MOR) in the DH, but not in the DRG. LGG supplementation significantly potentiated the analgesic effect of morphine. Furthermore, LGG supplementation led to an increase in butyrate levels in the feces and serum and a decrease in histone deacetylase 2 (HDAC2) expression in the DH. Feeding TCI-rats with sodium butyrate solution alone, at a dose of 100 mg/kg, resulted in decreased pain, as well as decreased HDAC2 expression and increased MOR expression in the DH. The increased expression of MOR and decreased HDAC2 were also observed in neuro-2a cells when we treated the cells with serum from TCI rats with supplementation of LGG or sodium butyrate. Discussion: This study provides evidence that reshaping the gut microbiota with probiotics LGG can delay the onset of cancer pain. The butyrate-HDAC2-MOR pathway may be the underlying mechanism for the analgesic effect of LGG. These findings shed light on an effective, safe, and non-invasive approach for cancer pain control and support the clinical implication of probiotics supplementation for patients with BCP.

Emergence of consciousness from anesthesia through ubiquitin degradation of KCC2 in the ventral posteromedial nucleus of the thalamus.

The emergence of consciousness from anesthesia, once assumed to be a passive process, is now considered as an active and controllable process. In the present study, we show in mice that, when the brain is forced into a minimum responsive state by diverse anesthetics, a rapid downregulation of K+/Cl- cotransporter 2 (KCC2) in the ventral posteromedial nucleus (VPM) serves as a common mechanism by which the brain regains consciousness. Ubiquitin-proteasomal degradation is responsible for KCC2 downregulation, which is driven by ubiquitin ligase Fbxl4. Phosphorylation of KCC2 at Thr1007 promotes interaction between KCC2 and Fbxl4. KCC2 downregulation leads to γ-aminobutyric acid type A receptor-mediated disinhibition, enabling accelerated recovery of VPM neuron excitability and emergence of consciousness from anesthetic inhibition. This pathway to recovery is an active process and occurs independent of anesthetic choice. The present study demonstrates that ubiquitin degradation of KCC2 in the VPM is an important intermediate step en route to emergence of consciousness from anesthesia.

Activation of cGMP-PKG signaling pathway contributes to neuronal hyperexcitability and hyperalgesia after in vivo prolonged compression or in vitro acute dissociation of dorsal root ganglion in rats.

Injury or inflammation affecting sensory neurons in the dorsal root ganglia (DRG) causes hyperexcitability of DRG neurons that can lead to spinal central sensitization and neuropathic pain. Recent studies have indicated that, following chronic compression of DRG (CCD) or acute dissociation of DRG (ADD) treatment, both hyperexcitability of neurons in intact DRG and behaviorally expressed hyperalgesia are maintained by activity in cGMP-PKG signaling pathway. Here, we provide evidence supporting the idea that CCD or ADD treatment activates cGMP-PKA signaling pathway in the DRG neurons. The results showed that CCD or ADD results in increase of levels of cGMP concentration and expression of PKG-I mRNA, as well as PKG-I protein in DRG. CCD or ADD treated-DRG neurons become hyperexcitable and exhibit increased responsiveness to the activators of cGMP-PKG pathway, 8-Br-cGMP and Sp-cGMP. Hyperexcitability of the injured neurons is inhibited by cGMP-PKG pathway inhibitors, ODQ and Rp-8-pCPT-cGMPS. In vivo delivery of Rp-8-pCPT-cGMPS into the compressed ganglion within the intervertebral foramen suppresses CCD-induced thermal hyperalgesia. These findings indicate that the in vivo CCD or in vitro ADD treatment can activate the cGMP-PKG signaling pathway, and that continuing activation of cGMP-PKG pathway is required to maintain DRG neuronal hyperexcitability and/or hyperalgesia after these two dissimilar forms of injury-related stress.