Transmission Of Neuropathic Pain Research Articles

Gallic Acid Alleviates Neuropathic Pain Behaviors in Rats by Inhibiting P2X7 Receptor-Mediated NF-κB/STAT3 Signaling Pathway.

Neuropathic pain is a complex disease with high incidence. Adenosine triphosphate (ATP) and its activated P2X7 receptor are involved in the signal transmission of neuropathic pain. Gallic acid (3,4,5-trihydroxybenzoic acid) is a traditional Chinese medicine obtained from natural plants that exhibit anti-inflammatory, analgesic, and antitumor effects. However, the underlying mechanism for gallic acid in analgesia remains unknown. This study aims to reveal how gallic acid alleviates neuropathic pain behaviors in a rat model with chronic constriction injury (CCI). Real-time PCR, western blotting, double-label immunofluorescence, molecular docking, and whole-cell patch clamp technology were used to explore the therapeutic action of gallic acid on neuropathic pain. The results showed that after CCI rats were treated with gallic acid for 1 week, the mechanical withdrawal threshold and thermal withdrawal latency were increased, accompanied by inhibition of the upregulated expression of P2X7 and TNF-α at both mRNA and protein levels, and reduced NF-κB and phosphorylated-STAT3 in the dorsal root ganglia. At the same time, gallic acid significantly decreased the coexpression of P2X7 and glial fibrillary acidic protein in the dorsal root ganglia. In addition, gallic acid could suppress ATP-activated current in human embryonic kidney 293 (HEK293) cells transfected with the plasmid expressing P2X7 but had no effect on ATP activation current of P2X7-mutant plasmid (with the point mutation sequence of the key site where gallic acid binds to the P2X7 receptor). Therefore, our work suggests that gallic acid may alleviate neuropathic pain in CCI rats by inhibiting the P2X7 receptor and subsequent activation of the TNF-α/STAT3 signaling pathway.

The Inhibition by Guanfu Base A of Neuropathic Pain Mediated by P2Y12 Receptor in Dorsal Root Ganglia.

Activation of satellite glial cells (SGCs) in the dorsal root ganglia (DRG) is involved in mechanical and thermal hyperalgesia. The upregulated P2Y12 receptor expressed in SGCs of the DRG participates in the nociceptive transmission of neuropathic pain. Guanfu base A (GFA) has been reported to exhibit antiarrhythmic and anti-inflammatory effects. In this study, we explored the effects of GFA on P2Y12 receptor-mediated mechanical and thermal hyperalgesia in chronic constriction injury (CCI) rats. Sprague-Dawley rats were randomly divided into sham operation group (Sham), CCI operation group (CCI), CCI rats treated with guanfu base A group (CCI + GFA) and control rats treated with GFA group (Ctrl + GFA). Mechanical withdrawal threshold and thermal withdrawal latency were measured. P2Y12 expression in L4-L6 dorsal root ganglion (DRG) was detected by quantitative real-time PCR and Western blot. After CCI treatment, mechanical and thermal hyperalgesia and the expression values of P2Y12 receptor mRNA and protein in DRG were increased. Dual-labeling immunofluorescence showed that the coexpression of P2Y12 receptor and glial fibrillary acidic protein (GFAP) in the DRG of CCI rats was increased compared to sham rats. GFA relieved mechanical and thermal hyperalgesia in the CCI rats, decreased the expression of P2Y12 mRNA and protein and phosphorylation of p38 MAPK in the DRG, and increased the ADP-downregulated cAMP concentrations in HEK293 cells transfected with P2Y12 plasmid. After CCI rats were treated with GFA, the coexpression of P2Y12 receptor and GFAP in the DRG was significantly decreased compared to the untreated CCI group. Thus, downregulating the P2Y12 receptor relieved mechanical and thermal hyperalgesia in the CCI rats.

NGF and BDNF expression in mouse DRG after spared nerve injury

Neuropathic pain is initiated by a primary lesion in the peripheral nervous system and spoils quality of life. Neurotrophins play important roles in the development and transmission of neuropathic pain. There are conflicting reports that the dorsal root ganglion (DRG) in an injured nerve contribute to neuropathic pain, whereas several studies have highlighted the important contribution of the DRG in a non-injured nerve. Clarifying the role of neurotrophins in neuropathic pain is problematic because we cannot distinguish injured and intact neurons in most peripheral nerve injury models. In the present study, to elicit neuropathic pain, we used the spared nerve injury (SNI) model, in which injured DRG neurons are distinguishable from intact ones, and mechanical allodynia develops in the intact sural nerve skin territory. We examined nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) expression in the DRGs of SNI model mice. NGF and BDNF levels increased in the injured L3 DRG, while NGF decreased in the intact L5 DRG. These data offer a new point of view on the role of these neurotrophins in neuropathic pain induced by peripheral nerve injury.

Effects of nanoparticle-encapsulated curcumin on HIV-gp120-associated neuropathic pain induced by the P2X3 receptor in dorsal root ganglia.

HIV-1 envelope glycoprotein (Glycoprotein 120, gp120) can directly stimulate primary sensory afferent neurons and cause chronic neuropathic pain. The P2X3 receptor in the dorsal root ganglia (DRG) is associated with the transmission of neuropathic pain. Curcumin isolated from the herb Curcuma rhizome has anti-inflammatory and anti-tumor effects. The water solubility, targeting and bioavailability of curcumin can be improved by nanoparticle encapsulation. In this study, we sought to explore the effects of nanoparticle-encapsulated curcumin (nano curcumin) on HIV-gp120-induced neuropathic pain mediated by the P2X3 receptor in DRG neurons. The results showed that mechanical and thermal hyperalgesia in rats treated with gp120 were increased compared to those in the control group. The expression levels of P2X3 mRNA and protein in rats treated with gp120 were higher than those in the control group. Nano curcumin treatment decreased mechanical hyperalgesia and thermal hyperalgesia and upregulated the expression levels of P2X3 mRNA and protein in rats treated with gp120. Nano curcumin treatment also reduced the ERK1/2 phosphorylation levels in gp120-treated rat DRG. In addition, P2X3 agonist α,β-methylene ATP (α,β-meATP)-induced currents in DRG neurons cultured with gp120 significantly decreased after co-treatment with nano curcumin. Therefore, nano curcumin treatment may inhibit P2X3 activation, decrease the sensitizing DRG primary afferents and relieve mechanical hyperalgesia and thermal hyperalgesia in gp120-treated rats.

P2Y12 shRNA treatment relieved HIV gp120-induced neuropathic pain in rats

Human immunodeficiency virus (HIV) envelope glycoprotein (glycoprotein 120, gp120) can induce chronic neuropathic pain by directly stimulating primary sensory afferent neurons. Activation of satellite glial cells (SGCs) in dorsal root ganglia (DRG) plays an important role in the transmission of neuropathic pain. The P2Y12 receptor is expressed in SGCs of DRG. In this study, we investigated the role of the P2Y12 receptor in HIV gp120-induced neuropathic pain. The results showed that peripheral nerve exposure to HIV gp120 increased mechanical and thermal hyperalgesia in gp120-treated model rats. The gp120 treatment increased the expression of P2Y12 mRNA and protein in DRG SGCs. Treatment with P2Y12 short hairpin RNA (shRNA) in DRG SGCs decreased the upregulated expression of P2Y12 mRNA and protein in DRG SGCs as well as relieved mechanical and thermal hyperalgesia in gp120-treated rats. Reduction of P2Y12 receptor decreased co-expression of P2Y12 and glial fibrillary acidic protein (GFAP), expression of GFAP, interleukin (IL)-1β, tumor necrosis factor (TNF)-receptor 1 (TNF-R1), and phosphorylation of Akt (p-Akt) proteins in DRG of gp120-treated rats. Upregulation of GFAP is a marker of SGC activation. Therefore, P2Y12 shRNA treatment decreased HIV gp120-induced mechanical and thermal hyperalgesia in gp120-treated rats.

A317491 relieved HIV gp120-associated neuropathic pain involved in P2X3 receptor in dorsal root ganglia.

Glycoprotein 120 (gp120) is an HIV envelope glycoprotein. Gp120 can directly stimulate the primary sensory afferent neurons and cause hyperalgesia. The P2X3 receptor in dorsal root ganglia (DRG) is involved in the transmission of pain. In this study, we aimed to explore the role of the P2X3 receptor in gp120-induced neuropathic pain. Our data showed that mechanical and thermal hyperalgesia in rats treated with gp120 were increased compared to those in the control group. The expression levels of the P2X3 mRNA and protein in rats treated with gp120 were higher than those in the control group. The P2X3 antagonist A317491 decreased mechanical hyperalgesia and thermal hyperalgesia and the up-regulated expression levels of P2X3 mRNA and protein in rats treated with gp120. A317491 decreased ERK1/2 phosphorylation levels in the gp120-treated rat DRG. In addition, P2X3 agonist α,β-methylene ATP (α,β-meATP)-activated currents in DRG neurons cultured with gp120 were higher than those in control neurons. The inhibitory effect of A317491 on α,βme-ATP-induced currents in DRG neurons from the gp120-treated neurons was larger than that for control neurons. Molecular docking data showed that A317491 may be acted in the gp120 protein to inhibit the gp120 initiated the P2X3 activation, decrease the sensitizing DRG primary afferents and reduce the signal transmission of neuropathic pain in gp120-treated rats. Therefore, the inhibition of the P2X3 receptor in rat DRG neurons relieved gp120-induced mechanical hyperalgesia.

Estrogen affects neuropathic pain through upregulating N-methyl-D-aspartate acid receptor 1 expression in the dorsal root ganglion of rats.

Estrogen affects the generation and transmission of neuropathic pain, but the specific regulatory mechanism is still unclear. Activation of the N-methyl-D-aspartate acid receptor 1 (NMDAR1) plays an important role in the production and maintenance of hyperalgesia and allodynia. The present study was conducted to determine whether a relationship exists between estrogen and NMDAR1 in peripheral nerve pain. A chronic sciatic nerve constriction injury model of chronic neuropathic pain was established in rats. These rats were then subcutaneously injected with 17β-estradiol, the NMDAR1 antagonist D(-)-2-amino-5-phosphonopentanoic acid (AP-5), or both once daily for 15 days. Compared with injured drug naïve rats, rats with chronic sciatic nerve injury that were administered estradiol showed a lower paw withdrawal mechanical threshold and a shorter paw withdrawal thermal latency, indicating increased sensitivity to mechanical and thermal pain. Estrogen administration was also associated with increased expression of NMDAR1 immunoreactivity (as assessed by immunohistochemistry) and protein (as determined by western blot assay) in spinal dorsal root ganglia. This 17β-estradiol-induced increase in NMDAR1 expression was blocked by co-administration with AP-5, whereas AP-5 alone did not affect NMDAR1 expression. These results suggest that 17β-estradiol administration significantly reduced mechanical and thermal pain thresholds in rats with chronic constriction of the sciatic nerve, and that the mechanism for this increased sensitivity may be related to the upregulation of NMDAR1 expression in dorsal root ganglia.

Ryk receptors on unmyelinated nerve fibers mediate excitatory synaptic transmission and CCL2 release during neuropathic pain induced by peripheral nerve injury.

BackgroundNeuropathic pain is a major pathology of the central nervous system associated with neuroinflammation. Ryk (receptor-like tyrosine kinase) receptors act as repulsive axon-guidance molecules during development of central nervous system and neural injury. Increasing evidence suggests the potential involvement of Wnt/Ryk (wingless and Int) signaling in the pathogenesis of neuropathic pain. However, its underlying mechanism remains unknown.ResultsThe expression and location of Ryk receptor as well as its ligand Wnt1 were detected by qPCR, Western blot, and immunohistochemistry. We found that Ryk, a specific Wnt receptor, was expressed in IB4+ (Isolectin B4) and CGRP+ (calcitonin gene-related peptide) dorsal root ganglia neurons and their ascending unmyelinated fibers in the dorsal horn of the spinal cord. Ryk was upregulated after spinal nerve ligation surgery. Wnt1 was also increased in activated astrocytes in the dorsal horn after spinal nerve ligation. The presynaptic mechanism of Ryk in regulation of neuropathic pain was determined by electrophysiology in spinal slice. Spinal nerve ligation model was established, and the therapeutic potential of inhibiting Ryk receptor was determined. Spine-specific blocking of the Wnt/Ryk receptor signaling attenuated the spinal nerve ligation-induced mechanical allodynia but not thermal hyperalgesia. Further, it also blocked Ca2+-dependent signals including CaMKII and PKCγ, subsequent release of CCL2 (CCR-like protein) in the dorsal horn. An in vitro study showed that inactivating Ryk receptors with anti-Ryk antibodies or lentiviral Ryk shRNA led to the inactivation of Wnt1 for excitatory synaptic transmission in spinal slices and subsequent decrease in CCL2 expression in the dorsal root ganglia neurons.ConclusionThese studies demonstrate the existence of critical crosstalk between astrocytes and unmyelinated fibers, which indicate the presynaptic mechanism of Ryk in cytokine transmission of neuropathic pain and the therapeutic potential for Wnt/Ryk signaling pathway in the treatment of neuropathic pain.

The protective effect of resveratrol in the transmission of neuropathic pain mediated by the P2X7 receptor in the dorsal root ganglia

The P2X7 receptor mediates afferent nerve activation and is related to chronic neuropathic pain. Resveratrol (RES) has also been reported to exhibit anti-inflammatory effects. In this study, we investigated the neuroprotective effect of RES on the transmission of neuropathic pain mediated by the P2X7 receptor. The P2X7 mRNA and protein expression levels in L4-L5 dorsal root ganglia (DRG)s of the chronic constriction injury (CCI) group were significantly higher than those observed in the Ctrl + NS, Sham + RES and Sham groups. RES increased the threshold of thermal and mechanical hypersensitivity in rats with chronic neuropathic pain. The P2X7 mRNA and protein expression levels in the CCI + RES group were decreased compared with those in the CCI group. Our results showed that RES inhibited the upregulated co-expression of P2X7 and glial fibrillary acidic protein (GFAP, a marker of satellite glial cells) in satellite glial cells of DRG in the CCI group. The results demonstrated that the expression of GFAP was increased in the CCI group and that RES inhibited the upregulated expression of GFAP in the rats in the CCI group. In addition, the phosphorylation levels of p38 and extracellular regulated protein kinases (ERK)1/2 in the CCI group were markedly higher than those observed in the Ctrl + NS, Sham + RES and Sham groups, whereas the phosphorylation levels of p38 and ERK1/2 in CCI + RES group were markedly lower than those observed in the CCI group. RES inhibited BzATP-activated currents in DRG non-neurons in the CCI rats. Our data provide evidence that RES may suppress the transmission of neuropathic pain mediated by the P2X7 receptor in the satellite glial cells of dorsal root ganglia.

Effects of intermedin on dorsal root ganglia in the transmission of neuropathic pain in chronic constriction injury rats.

Neuropathic pain is a common and severely disabling state that affects millions of people worldwide. The P2X3 receptor plays a crucial role in facilitating pain transmission. Intermedin (IMD), which is also known as adrenomedullin 2 (AMD2) is a newly discovered hormone that is a member of the calcitonin/calcitonin gene-related peptide family. The present research investigates the effects of IMD on pain transmission in neuropathic pain states as mediated by P2X3 receptors in dorsal root ganglia (DRG). Chronic constriction injury (CCI) rats were used as the neuropathic pain model. Adult male Sprague-Dawley rats were randomly assigned to five groups as follows: blank control group (Control), sham operation group (Sham), CCI rats treated with saline group (CCI+NS), CCI rats treated with IMD1-53 group (CCI+IMD1-53 ), and CCI rats treated with IMD inhibitor IMD14-47 group (CCI+IMD14-47 ). The mechanical withdrawal threshold (MWT) was tested by the von Frey method, and the thermal withdrawal latency (TWL) was tested via automatic thermal stimulus instruments. Changes in the expression of P2X3 receptors and IMD in CCI rat L4/L5 DRG were detected using immunohistochemistry, reverse transcription-polymerase chain reaction, and Western blotting. After treatment with intrathecal injection (i.t.), mechanical and thermal hyperalgesia in the CCI+IMD1-53 group was maintained, but MWT and TWL in the CCI+IMD14-47 groups increased. The expression levels of P2X3 receptors and IMD in L4/L5 DRG in the CCI+NS and CCI+IMD1-53 groups were significantly increased compared with those in the Control group or the Sham group. After application of IMD14-47 in CCI rats, there was a decrease in the expression levels of P2X3 receptors and IMD in L4/L5 DRG. The phosphorylation of p38 and ERK1/2 in L4/L5 DRG in the CCI+NS group and the CCI+IMD1-53 group was stronger than that in the Control group or the Sham group; however, the phosphorylation of p38 and ERK1/2 in the CCI+IMD14-47 group was much lower than that in the CCI+NS group or the CCI+IMD1-53 group. Our findings indicate that IMD might increase the sensitization effects of IMD on P2X3 receptors to alleviate chronic neuropathic pain injury. The IMD agonist IMD1-53 might enhance nociceptive responses mediated by P2X3 receptors in neuropathic pain, and the IMD inhibitor IMD14-47 could inhibit the sensitization of the P2X3 receptor in chronic neuropathic pain injury.

Case Report: Neuropathic pain in a patient with congenital insensitivity to pain.

We report a unique case of a woman with Channelopathy-associated Insensitivity to Pain (CIP) Syndrome, who developed features of neuropathic pain after sustaining pelvic fractures and an epidural hematoma that impinged on the right fifth lumbar (L5) nerve root. Her pelvic injuries were sustained during painless labor, which culminated in a Cesarean section. She had been diagnosed with CIP as child, which was later confirmed when she was found to have null mutations of the SCN9Agene that encodes the voltage-gated sodium channel Nav1.7. She now complains of troubling continuous buzzing in both legs and a vice-like squeezing in the pelvis on walking. Quantitative sensory testing showed that sensory thresholds to mechanical stimulation of the dorsum of both feet had increased more than 10-fold on both sides compared with tests performed before her pregnancy. These findings fulfill the diagnostic criteria for neuropathic pain. Notably, she mostly only experiences the negative symptoms (such as numbness and tingling, but also electric shocks), and she has not reported sharp or burning sensations, although the value of verbal descriptors is somewhat limited in a person who has never felt pain before. However, her case strongly suggests that at least some of the symptoms of neuropathic pain can persist despite the absence of the Nav1.7 channel. Pain is a subjective experience and this case sheds light on the transmission of neuropathic pain in humans that cannot be learned from knockout mice.

Electroacupuncture and A-317491 depress the transmission of pain on primary afferent mediated by the P2X3 receptor in rats with chronic neuropathic pain states.

P2X is a family of ligand-gated ion channels that act through adenosine ATP. The P2X3 receptor plays a key role in the transmission of neuropathic pain at peripheral and spinal sites. Electroacupuncture (EA) has been used to treat neuropathic pain effectively. To determine the role of EA in neuropathic pain mediated through the P2X3 receptor in dorsal root ganglion neurons and the spinal cord, a chronic constriction injury (CCI) model was used. Sprague-Dawley rats were divided into four groups: sham CCI, CCI, CCI plus contralateral EA, and CCI plus ipsilateral EA. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were recorded. Furthermore, the expression of the P2X3 receptor was evaluated through Western blotting and immunofluorescence. The effects of EA and A-317491 were investigated through the whole-cell patch-clamp method and intrathecal administration. Our results show that the MWT and TWL of EA groups were higher than those in the CCI group, whereas the expression of the P2X3 receptor was lower than that in the CCI group. However, no significant difference was detected between the two EA groups. EA depressed the currents created by ATP and the upregulation of the P2X3 receptor in CCI rats. Additionally, EA was more potent in reducing mechanical allodynia and thermal hyperalgesia when combined with A-317491 through intrathecal administration. These results show that both contralateral and ipsilateral EA might inhibit the primary afferent transmission of neuropathic pain induced through the P2X3 receptor. In addition, EA and A-317491 might have an additive effect in inhibiting the transmission of pain mediated by the P2X3 receptor.

Case Report: Neuropathic pain in a patient with congenital insensitivity to pain

We report a unique case of a woman with Channelopathy-associated Insensitivity to Pain (CIP) Syndrome, who developed features of neuropathic pain after sustaining pelvic fractures and an epidural hematoma that impinged on the right fifth lumbar (L5) nerve root. Her pelvic injuries were sustained during painless labor, which culminated in a Cesarean section. She had been diagnosed with CIP as child, which was later confirmed when she was found to have a null mutation of the SCN9a gene that encodes the voltage-gated sodium channel Nav1.7. She now complains of troubling continuous buzzing in both legs and a vice-like squeezing in the pelvis on walking. Quantitative sensory testing showed that sensory thresholds to mechanical stimulation of the dorsum of both feet had increased more than 10-fold on both sides compared with tests performed before her pregnancy. These findings fulfill the diagnostic criteria for neuropathic pain. Notably, she only experiences the negative symptoms (such as numbness and tingling) and she has not reported sharp, burning or electric shock sensations, although the value of verbal descriptors is somewhat limited in a person who has never felt pain before. However, her case strongly suggests that at least some of the symptoms of neuropathic pain can persist despite the absence of the Nav1.7 channel. Pain is a subjective experience and this case sheds light on the transmission of neuropathic pain in humans that cannot be learned from knockout mice.

Pineal gland and neuropathic pain

The pineal gland is a small neuroendocrine organ involved primarily in the circadian rhythm by the secretion of melatonin [1]. In addition, the pain modulatory properties of melatonin are generally recognized but its involvement in neuropathic pain regulation is not fully understood. In fact, it is known that the activation of the endogenous melatonin system in the spinal cord can reduce the generation, development and maintenance of central sensitization [2]. Moreover, melatonin showed an analgesic effect, in fact several works in animals [2] and in humans [3] underline its ability to inhibit hyperalgesia. In particular, intracerebroventricular and intraperitoneal melatonin, with its higher doses, produces a blockade of thermal hyperalgesia in mice with partial tight ligation of the sciatic nerve. The aim of our work is to characterize the morphological changes in peripheral structures, such as plantar skin and dorsal root ganglia (DRG) of rats in a neuropathic pain model (chronic constriction injury) after a single melatonin treatment monitoring the behaviour and the changes in NO-system using immunohistochemical techniques. The behavioural results show an increase of withdrawal latency during plantar test already after 30 min from melatonin administration. The immunohistochemical results suggest that melatonin plays a crucial role in keratinocytes-mediated neuropathic pain transmission through the modulation of nitroxidergic system, which could have also a protective role at this site. In addition, at DRG level the NO-system is maintained at low level. These results suggest that melatonin administration or modulation of pineal gland activity may have clinical utility in neuropathic pain therapy in the future.

Effects of anti-rVEGF on the expression of VEGF receptor-2 and P2X2/3 receptors of the spinal dorsal horn in neuropathic pain rats

Neuropathic pain is caused by the peripheral or central nervous system structure damage or dysfunction. VEGF is involved in nociception and inflammation. VEGF may target VEGF receptor-2 (VEGFR-2) on the surface of neurons. P2X(2/3) receptors play a crucial role in facilitating pain transmission at the spinal sites. Chronic constriction injury (CCI) rats were used as neuropathic pain model. Sprague-Dawley male rats were randomly divided into sham group, anti-recombinant VEGF antibody group with phosphate-buffer saline (anti-rVEGF+PBS group), CCI rats treated with phosphate-buffer saline group (CCI+PBS group) and CCI rats treated with anti-recombinant VEGF antibody group (CCI+anti-rVEGF group). The expressions of VEGFR-2, P2X(2) and P2X(3) protein in spinal dorsal horn (SDH) were detected by immunohistochemistry, double-label immunofluorescence and western blotting. The protein levels of VEGFR-2, P2X(2) and P2X(3) in L4/5 SDH of CCI+PBS group were higher than those in sham group. VEGFR-2 and P2X(2) or P2X(3) receptors were co-expressed in the cytoplasm and surface membranes of SDH. Anti-rVEGF treatment in CCI rats reduced the expression of VEGFR-2 and P2X(2/3) receptors in L4/5 SDH compared with those in CCI+PBS group. Therefore, VEGF may activate VEGFR-2 to participate the process of neuropathic pain. Anti-rVEGF treatment in CCI rats reduced the expression of VEGFR-2 and inhibited the transmission of neuropathic pain in L4/5 SDH via decreasing the expression of P2X(2/3). There is a cross-potentiation between VEGFR-2 and P2X(2/3) receptors in neuropathic pain state.

Role of Neurotrophins in Neuropathic Pain

Neurotrophins (NTs) belong to a family of structurally and functionally related proteins, they are the subsets of neurotrophic factors. Neurotrophins are responsible for diverse actions in the developing peripheral and central nervous systems. They are important regulators of neuronal function, affecting neuronal survival and growth. They are able to regulate cell death and survival in development as well as in pathophysiologic states. NTs and their receptors are expressed in areas of the brain that undergo plasticity, indicating that they are able to modulate synaptic plasticity.Recently, neurotrophins have been shown to play significant roles in the development and transmission of neuropathic pain. Neuropathic pain is initiated by a primary lesion or dysfunction in the nervous system. It has a huge impact on the quality of life. It is debilitating and often has an associated degree of depression that contributes to decreasing human well being. Neuropathic pain ranks at the first place for sanitary costs.Neuropathic pain treatment is extremely difficult. Several molecular pathways are involved, making it a very complex disease. Excitatory or inhibitory pathways controlling neuropathic pain development show altered gene expression, caused by peripheral nerve injury. At present there are no valid treatments over time and neuropathic pain can be classified as an incurable disease.Nowadays, pain research is directing towards new molecular methods. By targeting neurotrophin molecules it may be possible to provide better pain control than currently available.

Effect of emodin on neuropathic pain transmission mediated by P2X 2/3 receptor of primary sensory neurons

Neuropathic pain is the most difficult type of pain to cure. The P2X 2/3 receptors play a crucial role in facilitating the transmission of pain at neuropathic pain states. Emodin is a natural anthraquinone in rhubarb. The present research investigated the effects of emodin on the pain transmission in neuropathic pain states that was mediated by P2X 2/3 receptor in primary sensory neurons. Chronic constriction injury (CCI) model was used as neuropathic pain model. Emodin was dissolved in 0.5% sodium carboxymethyl cellulose (CMC) as vehicle. Sprague–Dawley male rats had been randomly divided into Sham + vehicle group, CCI + emodin group, and CCI + vehicle group. Mechanical withdrawal threshold and thermal withdrawal latency were measured. P2X 2/3 expression in L4/L5 dorsal root ganglion (DRG) was detected by immunohistochemistry, in situ hybridization (ISH) and RT-PCR. The mechanical withdrawal threshold and thermal withdrawal latency in CCI + vehicle group were lower than those in Sham + vehicle group and CCI + emodin group ( p < 0.05), while P2X 2 and P2X 3 receptor expression of L4/L5 DRG in CCI + vehicle group was higher than those in the other two groups ( p < 0.05). The co-local staining of P2X 2 and P2X 3 in the DRG of CCI group appeared to be more intense than that in the DRG of the other two groups with double-label fluorescence immunohistochemistry. The results showed that the application of emodin alleviated the hyperalgesia of CCI rats and significantly decreased the P2X 2/3 expression of L4/L5 DRG in CCI + emodin group compared with that in CCI + vehicle group ( p < 0.05). The data of ISH and RT-PCR in P2X 2 and P2X 3 mRNA expression suggest that the pharmacologic mechanism of emodin is involved in the nucleic acid level. The results showed that emodin can inhibit the transmission of neuropathic pain mediated by P2X 2/3 receptor of primary sensory neurons to alleviate chronic neuropathic pain.

Intrathecal Administration of AS1928370, a Transient Receptor Potential Vanilloid 1 Antagonist, Attenuates Mechanical Allodynia in a Mouse Model of Neuropathic Pain

Transient receptor potential vanilloid 1 (TRPV1) is primarily expressed in central and peripheral terminals of non-myelinated primary afferent neurons. We previously showed that AS1928370, a novel TRPV1 antagonist that can prevent ligand-induced activation but not proton-induced activation, ameliorates neuropathic pain in rats without hyperthermic effect. In this study, we investigated its analgesic profile in mice. AS1928370 showed good oral bioavailability and high penetration into the brain and spinal cord in mice. The mean plasma-to-brain and plasma-to-spinal cord ratios were 4.3 and 3.5, respectively. Pretreatment with AS1928370 significantly suppressed both capsaicin-induced acute pain and withdrawal response in hot plate test at 10-30 mg/kg per os (p.o.). At lower oral doses (0.3-1.0 mg/kg), AS1928370 improved mechanical allodynia in mice undergoing spinal nerve ligation. Intrathecal administration of AS1928370 (30 µg/body) also significantly suppressed mechanical allodynia. In addition, AS1928370 showed no effect on locomotor activity up to 30 mg/kg p.o. These results suggest that spinal TRPV1 has an important role in the transmission of neuropathic pain and that the central nervous system (CNS) penetrant TRPV1 receptor antagonist AS1928370 is a promising candidate for treating neuropathic pain.

VEGF and its receptor-2 involved in neuropathic pain transmission mediated by P2X 2/3 receptor of primary sensory neurons

The pathogenesis of neuropathic pain is complex. P2X 2/3 receptor plays a crucial role in nociception transduction of chronic pain. VEGF inhibitors are effective for pain relief. The present study investigated the effects of VEGF and VEGF receptor-2 (VEGFR2) on the pain transmission in neuropathic pain states that mediated by P2X 2/3 receptor in primary sensory neurons. Chronic constriction injury (CCI) model was used as neuropathic pain model. Sprague–Dawley rats had been randomly divided into sham group, CCI group and CCI rats treated with anti-rVEGF antibody group. Mechanical withdrawal threshold and thermal withdrawal latency were measured. Expressions of VEGF, VEGFR2 and P2X 2/3 in L4–6 dorsal root ganglia (DRG) were detected by immunohistochemistry, RT-PCR and western blot analysis. The mechanical withdrawal threshold and thermal withdrawal latency in CCI group were lower than those in sham group and CCI rats treated with anti-rVEGF antibody group ( p < 0.05), while VEGF, VEGFR2 and P2X 2/3 receptors’ expressions of L4–6 DRG in CCI group were higher than those in the other two groups ( p < 0.05). The expressions of VEGF, VEGFR2 and P2X 2/3 in L4–6 DRG of CCI rats treated with anti-rVEGF antibody group were decreased compared with those in CCI group ( p < 0.05). The results show that VEGF and VEGFR2 are involved in the pathogenesis of neuropathic pain and VEGF primarily potentiates pain responses mediated by P2X 2/3 receptor on DRG neurons. Anti-rVEGF treatment in CCI rats may alleviate chronic neuropathic pain by decreasing the expressions of VEGFR2 and P2X 2/3 receptors on DRG neurons to inhibit the transmission of neuropathic pain signaling.

P.1.c.046 The involvement of opioidergic receptors in the local peripheral anti-hyperalgesic effect of levetiracetam

The role of voltage-gated sodium channels in the transmission of neuropathic pain is well recognized. For instance, genetic evidence recently indicate that the human Nav1.7 sodium channel subtype plays a crucial role in the ability to perceive pain sensation and may represent an important target for analgesic/anti-hyperalgesic drugs. In this study a newly synthesized tocainide congener, named NeP1, was tested in vitro on recombinant hNav1.4 and hNav1.7 channels using patch-clamp technique and, in vivo, in two rat models of persistent neuropathic pain obtained either by chronic constriction injury of the sciatic nerve or by oxaliplatin treatment. NeP1 efficiently blocked hNav1.4 and hNav1.7 channels in a dose- and use-dependent manner, being by far more potent than tocainide. Importantly, the new compound displayed a remarkable use-dependent effect, which likely resulted from a very high affinity for inactivated compared to closed channels. In both models of neuropathic pain, NeP1 was greatly more potent than tocainide in reverting the reduction of pain threshold in vivo. In oxaliplatin-treated rats, NeP1 even produced greater and more durable anti-hyperalgesia than the reference drug tramadol. In addition, in vivo and in vitro studies suggest a better toxicological and pharmacokinetic profile for NeP1 compared to tocainide. Overall, these results indicate NeP1 as a new promising lead compound for further development in the treatment of chronic pain of neuropathic origin.