Analgesic Effect In Neuropathic Pain Research Articles

Targeting exosomal double-stranded RNA-TLR3 signaling pathway attenuates morphine tolerance and hyperalgesia

Long-term morphine use leads to tolerance and hyperalgesia in patients with chronic pain, with neuroinflammation playing a key role, but its underlying mechanisms remain elusive. This study determines that repeated intrathecal morphine injections increase double-stranded RNA (dsRNA) production in spinal neurons, due to downregulated adenosine deaminase RNA specific 1 (ADAR1) expression. Lentivirus-induced ADAR1 elevation decreases the high levels of intracellular dsRNA and attenuates morphine tolerance and hyperalgesia. dsRNA is released into cerebrospinal fluid via exosomes (Exos) after repeated morphine injections and is taken up by microglia for TLR3-TRIF-IL-6 signaling activation. Blocking Exos release with GW4869 or inhibition of TLR3 signaling mitigates neuroinflammation, preventing the development of morphine tolerance and hyperalgesia. Intrathecal injection of TLR3 inhibitor alone shows analgesic effects in neuropathic pain, and co-administration with morphine amplifies the analgesic efficacy of morphine. These findings demonstrate that targeting dsRNA-TLR3 signaling to mitigate neuroinflammation could be a promising treatment for morphine tolerance.

Astaxanthin alleviates fibromyalgia pain and depression via NLRP3 inflammasome inhibition

Fibromyalgia is characterised by widespread chronic pain and is often accompanied by comorbidities such as sleep disorders, anxiety, and depression. Because it is often accompanied by many adverse symptoms and lack of effective treatment, it is important to search for the pathogenesis and treatment of fibromyalgia. Astaxanthin, a carotenoid pigment known for its anti-inflammatory and antioxidant properties, has demonstrated effective analgesic effects in neuropathic pain. However, its impact on fibromyalgia remains unclear. Therefore, in this study, we constructed a mouse model of fibromyalgia and investigated the effect of astaxanthin on chronic pain and associated symptoms through multiple intragastrical injections. We conducted behavioural assessments to detect pain and depression-like states in mice, recorded electroencephalograms to monitor sleep stages, examined c-Fos activation in the anterior cingulate cortex, measured activation of spinal glial cells, and assessed levels of inflammatory factors in the brain and spinal cord, including interleukin (IL)-1β, IL-6, and tumour necrosis factor- α(TNF-α).Additionally, we analysed the expression levels of IL-6, IL-10, NOD-like receptor thermal protein domain associated protein 3 (NLRP3), Apoptosis-associated speck-like protein containing CARD, and Caspase-1 proteins. The findings revealed that astaxanthin significantly ameliorated mechanical and thermal pain in mice with fibromyalgia and mitigated sleep disorders and depressive-like symptoms induced by pain. A potential mechanism underlying these effects is the anti-inflammatory action of astaxanthin, likely mediated through the inhibition of the NLRP3 inflammasome, which could be one of the pathways through which astaxanthin alleviates fibromyalgia. In conclusion, our study suggests that astaxanthin holds promise as a potential analgesic medication for managing fibromyalgia and its associated symptoms.

Folic acid relieves bone cancer pain by downregulating P2X2/3 receptors in rats

BackgroundBone cancer pain (BCP) remains a clinical challenge due to the limited and side effects of therapeutic methods. Folic acid has been known as an FDA approved dietary supplement and proved to have an analgesic effect in neuropathic pain. Here we investigate the role and mechanism of folic acid in bone cancer pain of a rat model. MethodsWalker 256 tumor cells were inoculated into the left tibia of rats to induce bone cancer pain model. Pain reflex were assessed by paw withdrawal threshold (PWT) response to Von Frey filaments and paw withdrawal latency (PWL) response to thermal stimulation. Folic acid was injected intraperitoneally to evaluate its analgesic effect in rats with bone cancer pain. Western blotting and qPCR were used to determine P2X2/3 receptor protein and mRNA levels in ipsilateral L4-6 dorsal root ganglion (DRG) and spinal dorsal horn (SDH). ResultsThe PWT and PWL of rats with bone cancer pain were obviously decreased compared to the naïve and sham rats. Interestingly, continuous folic acid treatment significantly increased the PWT and PWL of rats with bone cancer pain. P2X2 and P2X3 receptors were clearly upregulated at both mRNA and protein expression in L4-6 DRG and SDH of rats with bone cancer pain. P2X2 and P2X3 receptors were mainly localized with CGRP (calcitonin gene-related peptide) or IB4 (isolectin B4) positive neurons in L4-6 DRG of rats with bone cancer pain. Notably, continuous folic acid treatment significantly reduced the expression of P2X2 and P2X3 receptors in L4-6 DRG and SDH of rats with bone cancer pain. Finally, intrathecal injection of A317491 (a selective antagonist of P2X2/3 receptors) markedly elevated the PWT and PWL of rats with bone cancer pain. ConclusionThese results suggest that folic acid has an effective antinociceptive effect on bone cancer pain, which is mediated by downregulating P2X2/3 receptors in L4-6 DRG and SDH of rats with bone cancer pain. Folic acid may be a novel therapeutic strategy in cancer patients for pain relief.

Intrathecal administration of botulinum toxin type a antagonizes neuropathic pain by countering increased vesicular nucleotide transporter expression in the spinal cord of chronic constriction injury of the sciatic nerve rats

Botulinum toxin type A (BoNT/A) induces direct analgesic effects in neuropathic pain by inhibiting the release of substance P, calcitonin gene-related peptide (CGRP) and glutamate. Vesicular nucleotide transporter (VNUT) was responsible for the storage and release of ATP in vivo, and one of the mechanisms underlying neuropathic pain is VNUT-dependent release of extracellular ATP from dorsal horn neurons. However, the analgesic effect of BoNT/A by affecting the expression of VNUT remained largely unknown. Thus, in this study, we aimed to elucidate the antinociceptive potency and analgesic mechanism of BoNT/A in chronic constriction injury of the sciatic nerve (CCI) induced neuropathic pain. Our results showed that a single intrathecal injection of 0.1 U BoNT/A seven days after CCI surgery produced significant analgesic activity and decreased the expression of VNUT in the spinal cord of CCI rats. Similarly, BoNT/A inhibited the CCI-induced increase in ATP content in the rat spinal cord. Overexpression of VNUT in the spinal cord of CCI-induced rats markedly reversed the antinociceptive effect of BoNT/A. Furthermore, 33 U/mL BoNT/A dramatically reduced the expression of VNUT in pheochromocytoma (PC12) cells but overexpressing SNAP-25 increased VNUT expression in PC12 cells. Our current study is the first to demonstrate that BoNT/A is involved in neuropathic pain by regulating the expression of VNUT in the spinal cord in rats.

Activation of Cannabinoid Receptor 1 in GABAergic Neurons in the Rostral Anterior Insular Cortex Contributes to the Analgesia Following Common Peroneal Nerve Ligation

The rostral agranular insular cortex (RAIC) has been associated with pain modulation. Although the endogenous cannabinoid system (eCB) has been shown to regulate chronic pain, the roles of eCBs in the RAIC remain elusive under the neuropathic pain state. Neuropathic pain was induced in C57BL/6 mice by common peroneal nerve (CPN) ligation. The roles of the eCB were tested in the RAIC of ligated CPN C57BL/6J mice, glutamatergic, or GABAergic neuron cannabinoid receptor 1 (CB1R) knockdown mice with the whole-cell patch-clamp and pain behavioral methods. The E/I ratio (amplitude ratio between mEPSCs and mIPSCs) was significantly increased in layer V pyramidal neurons of the RAIC in CPN-ligated mice. Depolarization-induced suppression of inhibition but not depolarization-induced suppression of excitation in RAIC layer V pyramidal neurons were significantly increased in CPN-ligated mice. The analgesic effect of ACEA (a CB1R agonist) was alleviated along with bilateral dorsolateral funiculus lesions, with the administration of AM251 (a CB1R antagonist), and in CB1R knockdown mice in GABAergic neurons, but not glutamatergic neurons of the RAIC. Our results suggest that CB1R activation reinforces the function of the descending pain inhibitory pathway via reducing the inhibition of glutamatergic layer V neurons by GABAergic neurons in the RAIC to induce an analgesic effect in neuropathic pain.

Targeting the nitric oxide/cGMP signaling pathway to treat chronic pain.

Nitric oxide (NO)/cyclic guanosine 3',5'-monophosphate (cGMP) signaling has been shown to act as a mediator involved in pain transmission and processing. In this review, we summarize and discuss the mechanisms of the NO/cGMP signaling pathway involved in chronic pain, including neuropathic pain, bone cancer pain, inflammatory pain, and morphine tolerance. The main process in the NO/cGMP signaling pathway in cells involves NO activating soluble guanylate cyclase, which leads to subsequent production of cGMP. cGMP then activates cGMP-dependent protein kinase (PKG), resulting in the activation of multiple targets such as the opening of ATP-sensitive K+ channels. The activation of NO/cGMP signaling in the spinal cord evidently induces upregulation of downstream molecules, as well as reactive astrogliosis and microglial polarization which participate in the process of chronic pain. In dorsal root ganglion neurons, natriuretic peptide binds to particulate guanylyl cyclase, generating and further activating the cGMP/PKG pathway, and it also contributes to the development of chronic pain. Upregulation of multiple receptors is involved in activation of the NO/cGMP signaling pathway in various pain models. Notably the NO/cGMP signaling pathway induces expression of downstream effectors, exerting both algesic and analgesic effects in neuropathic pain and inflammatory pain. These findings suggest that activation of NO/cGMP signaling plays a constituent role in the development of chronic pain, and this signaling pathway with dual effects is an interesting and promising target for chronic pain therapy.

Botulinum toxin type A counteracts neuropathic pain by countering the increase of GlyT2 expression in the spinal cord of CCI rats

Botulinum toxin type A (BoNT/A) is a potent toxin, acts by cleaving synaptosome-associated-protein-25 (SNAP-25) to regulate the release of the neural transmitter and shows analgesic effect in neuropathic pain. However, the mechanisms of BoNT/A actions involved in nociceptions remain unclear. Glycine transporter 2 (GlyT2) is an isoform of glycine transporters, which plays an important role in the regulation of glycinergic neurotransmission. Inhibition of GlyTs could decrease pain sensation in neuropathic pain, the role of GlyT2 in the analgesic effect of BoNT/A has not been studied yet. In our present study, we demonstrated that the protein levels of GlyT2 and SNAP-25 were upregulated in the spinal cord after the development of chronic constriction injury (CCI)-induced neuropathic pain. Intraplantar application of BoNT/A (20 U/kg) attenuated mechanical allodynia induced by CCI and downregulated GlyT2 expression in the spinal cord. The application of BoNT/A s also decreased the expression of GlyT2 in pheochromocytoma (PC12) cells. Moreover, intrathecal application of lentivirus-mediated GlyT2 reversed the antinociceptive effect of BoNT/A in CCI rats. These findings indicate that GlyT2 contributes to the antinociceptive effect of BoNT/A and suggest a novel mechanism underlying BoNT/A’s antinociception action.

The Role of Saponins in the Treatment of Neuropathic Pain.

Neuropathic pain is a chronic pain caused by tissue injury or disease involving the somatosensory nervous system, which seriously affects the patient’s body function and quality of life. At present, most clinical medications for the treatment of neuropathic pain, including antidepressants, antiepileptic drugs, or analgesics, often have limited efficacy and non-negligible side effects. As a bioactive and therapeutic component extracted from Chinese herbal medicine, the role of the effective compounds in the prevention and treatment of neuropathic pain have gradually become a research focus to explore new analgesics. Notably, saponins have shown analgesic effects in a large number of animal models. In this review, we summarized the most updated information of saponins, related to their analgesic effects in neuropathic pain, and the recent progress on the research of therapeutic targets and the potential mechanisms. Furthermore, we put up with some perspectives on future investigation to reveal the precise role of saponins in neuropathic pain.

Dexmedetomidine alleviates hyperalgesia in arthritis rats through inhibition of the p38MAPK signaling pathway

Background Dexmedetomidine (DEX) has showed significant analgesic effects in neuropathic pain, but the underlying mechanism has remained elusive. Our present study aimed to explore the effect of DEX on hyperalgesia with the involvement of p38MAPK signaling pathway in a rat model of monoarthritis (MA). Methods MA rat model was induced by injection of Complete Freund’s Adjuvant (CFA). Pathological changes of MA rats were observed by HE staining and Safranin-O/Fast Green staining. Ankle circumference, paw withdrawal latency (PWL) and paw withdrawal threshold (PWT) were measured to judge the degree of hyperalgesia in MA rats. Immunohistochemistry and ELISA were applied to observe the degree of inflammation in rats. Western blot analysis was conducted to detect expression of p38MAPK signaling pathway-related factors. The mechanism of p38MAPK signaling pathway in MA rats was observed via treatment of Anisomycin or SB203580 combined with DEX. Results After 8 h of CFA induction, joint swelling and hyperalgesia occurred in rats. There were obvious pathological changes in the joint cavity, the joint cavity space became narrow and synovial bursa became rough. A large number of inflammatory cell infiltration was observed under microscope. After injection of DEX and SB203580, PWT and PWL were prolonged, the expression of serum inflammatory factors was decreased, and the expression of p38MAPK signaling pathway-related factors was decreased; while all the detected indexes were recovered in MA rats after treated with DEX and Anisomycin. Conclusions Our study provided evidence that DEX could alleviate hyperalgesia in arthritis rats through inhibition of the p38MAPK signaling pathway.

Mirogabalin, a novel ligand for α2δ subunit of voltage-gated calcium channels, improves cognitive impairments in repeated intramuscular acidic saline injection model rats, an experimental model of fibromyalgia

Mirogabalin is a novel potent and selective ligand for the α2δ subunit of voltage-gated calcium channels, and shows potent and sustained analgesic effects in neuropathic pain and fibromyalgia models. Fibromyalgia is often associated with multiple comorbid symptoms, such as anxiety, depression and cognitive impairment. In the present study, we investigated the effects of mirogabalin on cognitive impairments in an experimental animal model for fibromyalgia, repeated intramuscular acidic saline injection model (Sluka model) rats. Male rats received two repeated intramuscular injections of pH 4 acidic saline into their gastrocnemius muscle. After developing mechanical hypersensitivity as identified in the von Frey test, the animals received the test substance orally once daily for 13 days and were subjected to four cognitive function tests, (Y-maze, novel object recognition, Morris water maze and step-through passive avoidance). Sluka model rats showed cognitive impairments in all four tests. Oral administration of mirogabalin (3 and 10 mg/kg) improved the cognitive impairments in these rats. In conclusion, mirogabalin improved the impaired cognitive function in Sluka model rats. It may thus also alleviate cognitive impairments as well as painful symptoms in fibromyalgia patients.

Renin-angiotensin system blockade modulates both the peripheral and central components of neuropathic pain in rats: Role of calcitonin gene-related peptide, substance P and nitric oxide.

Nonetheless, renin-angiotensin-aldosterone system (RAAS) blockers attenuate neuropathic pain (NP), the exact molecular mechanisms of this effect are not completely understood. The study aimed to investigate the role of calcitonin gene-related peptide (CGRP), substance P (SP) and nitric oxide (NO), which are all involved in pain modulation, in the analgesic effect of different RAAS blockers in NP both on the peripheral and on the central levels. NP was induced by sciatic nerve chronic constriction injury (CCI, 14days) in rats, that were given either centrally (telmisartan and ramipril) or peripherally (losartan and enalapril) acting angiotensin-converting enzyme inhibitors (ACE-Is) or angiotensin receptor blockers (ARBs). Behavioural assessment was performed, and CGRP, SP and NO levels were detected in the injured sciatic nerve and the brainstem at the end of experiment. CCI rats showed increased spontaneous pain response and foot deformity along with elevated CGRP, SP and NO levels. ARBs and ACE-Is treatment improved pain behaviour and reduced SP and NO levels. However, sciatic CGRP was increased with different interventions and brainstem CGRP was only elevated in the losartan group. These findings suggest an intermediary role of CGRP, SP and NO in RAAS blockers analgesic effect in NP.

Transcription-independent expression of PKMζ in the anterior cingulate cortex contributes to chronically maintained neuropathic pain.

Protein kinase M ζ is well known for its role in maintaining memory and pain. Previously, we revealed that the activation of protein kinase M ζ in the anterior cingulate cortex plays a role in sustaining neuropathic pain. However, the mechanism by which protein kinase M ζ is expressed in the anterior cingulate cortex by peripheral nerve injury, and whether blocking of protein kinase M ζ using its inhibitor, zeta inhibitory peptide, produces analgesic effects in neuropathic pain maintained chronically after injury, have not previously been resolved. In this study, we show that protein kinase M ζ expression in the anterior cingulate cortex is enhanced by peripheral nerve injury in a transcription-independent manner. We also reveal that the inhibition of protein kinase M ζ through zeta inhibitory peptide treatment is enough to reduce mechanical allodynia responses in mice with one-month-old nerve injuries. However, the zeta inhibitory peptide treatment was only effective for a limited time.

Anti-nociceptive effect of dexmedetomidine in a rat model of monoarthritis via suppression of the TLR4/NF-κB p65 pathway.

As a therapeutic target for neuropathic pain, the anti-nociceptive effects of α 2-adrenoceptors (α2AR) have attracted attention. Dexmedetomidine (DEX), a potent and highly selective α2AR agonist, has exhibited significant analgesic effects in neuropathic pain, but the underlying mechanism has remained elusive. The present study investigated the effect of DEX on Toll-like receptor (TLR)4 and nuclear factor (NF)-κB p65 expression, as well as the production of pro-inflammatory cytokines. The rat monoarthritis (MA) model was induced by intra-articular injection of complete Freund's adjuvant (CFA) at the ankle joint. After induction of MA, the rats were intrathecally treated with normal saline or DEX (2.5 µg) for 3 consecutive days. The concentration of interleukin-1β and −6 as well as tumor necrosis factor-α was examined by ELISA. The expression levels of TLR4 and NF-κB p65 were determined by western blot analysis and immunohistochemistry. The results indicated that the pro-inflammatory cytokines TLR4 and NF-κB p65 were significantly upregulated in MA rats. DEX treatment markedly reduced mechanical and thermal hyperalgesia, suppressed MA-induced elevation of the pro-inflammatory cytokines and inhibited the TLR4/NF-κB p65 pathway, while these effects were blocked by pre-treatment with the selective α2AR antagonist BRL44408 (15 µg) at 30 min prior to CFA injection. These results suggested that DEX has an anti-nociceptive effect via suppressing the TLR4/NF-κB p65 pathway.

Inhibition of the NMDA and AMPA receptor channels by antidepressants and antipsychotics

It is known that some antidepressants and antipsychotics directly inhibit NMDA-type ionotropic glutamate receptors. In this study we systematically studied action of seven drugs (Fluoxetine, Citalopram, Desipramine, Amitriptyline, Atomoxetine, Chlorpromazine, and Clozapine) on NMDA receptors and Ca2+-permeable and -impermeable AMPA receptors in rat brain neurons by whole-cell patch-clamp technique. Except for weak effect of fluoxetine, all drugs were virtually inactive against Ca2+-impermeable AMPA receptors. Fluoxetine and desipramine significantly inhibited Ca2+-permeable AMPA receptors (IC50=43±7 and 105±12µM, respectively). Desipramine, atomoxetine and chlorpromazine inhibited NMDA receptors in clinically relevant low micromolar concentrations, while citalopram had only weak effect. All tested medicines have been clustered into two groups by their action on NMDA receptors: desipramine, amitriptyline, chlorpromazine, and atomoxetine display voltage- and magnesium-dependent open channel blocking mechanism. Action of fluoxetine and clozapine was found to be voltage- and magnesium-independent. All voltage-dependent compounds could be trapped in closed NMDA receptor channels. Possible contribution of NMDA receptor inhibition by certain antidepressants and antipsychotics to their analgesic effects in neuropathic pain is discussed.

Pharmacogenomic study of the role of the nociceptin/orphanin FQ receptor and opioid receptors in diabetic hyperalgesia

Targeting functionally independent receptors may provide synergistic analgesic effects in neuropathic pain. To examine the interdependency between different opioid receptors (µ-opioid peptide [MOP], δ-opioid peptide [DOP] and κ-opioid peptide [KOP]) and the nociceptin/orphanin FQ peptide (NOP) receptor in streptozotocin (STZ)-induced diabetic polyneuropathy, nocifensive activity was measured using a hot plate test in wild-type and NOP, MOP, DOP and KOP receptor knockout mice in response to the selective receptor agonists Ro65-6570, morphine, SNC-80 and U50488H, or vehicle. Nocifensive activity was similar in non-diabetic wild-type and knockout mice at baseline, before agonist or vehicle administration. STZ-induced diabetes significantly increased heat sensitivity in all mouse strains, but MOP, DOP and KOP receptor knockouts showed a smaller degree of hyperalgesia than wild-type mice and NOP receptor knockouts. For each agonist, a significant antihyperalgesic effect was observed in wild-type diabetic mice (all P<0.05 versus vehicle); the effect was markedly attenuated in diabetic mice lacking the cognate receptor compared with wild-type diabetic mice. Morphine was the only agonist that demonstrated near-full antihyperalgesic efficacy across all non-cognate receptor knockouts. Partial or near-complete reductions in efficacy were observed with Ro65-6570 in DOP and KOP receptor knockouts, with SNC-80 in NOP, MOP and KOP receptor knockouts, and with U50488H in NOP and DOP receptor knockouts. There was no evidence of NOP and MOP receptor interdependency in response to selective agonists for these receptors. These findings suggest that concurrent activation of NOP and MOP receptors, which showed functional independence, may yield an effective and favorable therapeutic analgesic profile.

THE ANALGESIC EFFECT OF PREGABALIN, A COMPARATIVE STUDY WITH MORPHINE

this study was designed to assess and compare the effects of pregabalin and morphine on acute thermal pain and on nerve injury associated pain (chronic neuropathic pain). Methods: 72 male albino rats were divided into two major groups: group I (acute pain group) 30 rats divided into 5 equal subgroups (1)control, (2) pregabalin 30 mg/kg, (3)morphine 0.5 mg/kg, (4) pregabalin 60 mg/kg, (5)morphine 1mg/kg, and group II(chronic pain group) 42 rats were divided into 7 equal subgroups (1)sham operated, (2)control normal, (3) control postoperative, (4) pregabalin 30mg/kg, (5) morphine 0.5 mg/kg, (6) pregabalin 60 mg/kg, (7) morphine 1mg/kg. For acute pain the reaction times, which indicate the tolerability of the animals to acute thermal pain, was measured using analgesia meter. However chronic neuropathic pain was induced in experimental animals by unilateral ligation of the sciatic nerve in the thigh. Results: The result of the present study revealed that neither 30 nor 60 mg/kg pregabalin produced any significant effects on the tolerability of rats to acute thermal pain. On the other hand, pregabalin (30 and 60 mg/kg) markedly reversed allodynia and hyperalgesia in rats subjected to sciatic nerve ligation. The effect of pregabalin 30 mg/kg was noticed after 60 minutes and persist for 90 minutes but the higher dose (60 mg/kg) produced analgesic effect all over the experiment. On the other hand morphine 0.5 and 1 mg/kg significantly increased the tolerability of normal and sciatic nerve ligated rats to thermal nociception. The analgesic effect of morphine was more significant than that of pregabalin all over the experiments. Conclusion: in contradiction to morphine, pregabalin was not effective for treatment of acute pain. Both pregabalin and morphine produced significant analgesic effect in neuropathic pain. The effect of morphine was more significant than that of pregabalin. Key words: Pregabalin, chronic neuropathic pain, morphine, sciatic nerve ligation.

Presence of multiple binding sites on α9α10 nAChR receptors alludes to stoichiometric-dependent action of the α-conotoxin, Vc1.1

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels involved in fast synaptic transmission. nAChRs are pentameric receptors formed from a combination of different or similar subunits to produce heteromeric or homomeric channels. The heteromeric, α9α10 nAChR subtype is well-known for its role in the auditory system, being expressed in cochlear hair cells. These nAChRs have also been shown to be involved in immune-modulation. Antagonists of α9α10 nAChRs, like the α-conotoxin Vc1.1, have analgesic effects in neuropathic pain. Unlike other nAChR subtypes there is no evidence that functional receptor stoichiometries of α9α10 exist. By using 2-electrode voltage clamp methods and maintaining a constant intracellular Ca2+ concentration, we observed a biphasic activation curve for ACh that is dependent on receptor stoichiometry. Vc1.1, but not the α9α10 antagonists RgIA or atropine, inhibits ACh-evoked currents in a biphasic manner. Characteristics of the ACh and Vc1.1 activation and inhibition curves can be altered by varying the ratio of α9 and α10 mRNA injected into oocytes, changing the curves from biphasic to monophasic when an excess of α10 mRNA is used. These results highlight the difference in the pharmacological profiles of at least two different α9α10 nAChR stoichiometries, possibly (α9)3(α10)2 and (α9)2(α10)3. As a result, we infer that there is an additional binding site for ACh and Vc1.1 at the α9–α9 interface on the hypothesized (α9)3(α10)2 nAChR, in addition to the α10–α9 and or α9–α10 interfaces that are common to both stoichiometries. This study provides further evidence that receptor stoichiometry contributes another layer of complexity in understanding Cys-loop receptors.

Duloxetine blocks cloned Kv4.3 potassium channels

The effects of duloxetine were examined on cloned Kv4.3 channels stably expressed in CHO cells using the whole-cell patch-clamp technique. Duloxetine decreased the peak amplitude of Kv4.3 currents with an acceleration of the decay rate of current inactivation in a concentration-dependent manner. The IC50 values required for the blocking effects of duloxetine on the peak amplitude and the integral of currents were 8.4 and 2.1μM, respectively. Duloxetine accelerated the rate of inactivation of Kv4.3 currents and thereby decreased the time-to-peak in a concentration-dependent manner. Analysis of the time dependence of the drug block produced estimates of 21.9μM−1s−1 and 165.9s−1, for the respective association (k+1) and dissociation (k−1) rate constants. The Kd value (k−1/k+1) yielded 7.5μM, which approximates the experimental IC50 value obtained from the concentration–response curve. The block of Kv4.3 by duloxetine was voltage-dependent at a membrane potential coinciding with the activation of the channels. At a more positive potential, however, the block was relieved. Duloxetine produced a hyperpolarizing shift in the voltage dependence of the steady-state inactivation of Kv4.3, and accelerated the closed-state inactivation of Kv4.3 in the subthreshold voltage range. Duloxetine induced a significant use-dependent block at frequencies of 1 and 2Hz. In the presence of duloxetine, the recovery from inactivation was slower than under control conditions. These results demonstrate that duloxetine exerts a concentration-dependent block of Kv4.3 by binding to the channels in the open and inactivated states and these actions may contribute to its analgesic effect in neuropathic pain.

Management of diabetic neuropathy by sodium valproate and glyceryl trinitrate spray: A prospective double-blind randomized placebo-controlled study

Objectives Combination of drugs with different mechanisms of action helps in achieving synergistic analgesic effect in neuropathic pain. Keeping this point in view, the effect and safety aspects of sodium valproate and GTN were assessed alone as well as in combination in this study. Design Prospective double-blind randomized placebo-controlled study. Material and method Eighty-seven type 2 diabetics with painful neuropathy were enrolled. Four were excluded: three with HbA 1c > 11 while one withdrew consent. The remaining 83 were given either sodium valproate and GTN spray (group A) or placebo drug and GTN spray (group B) or sodium valproate and placebo spray (group C) or placebo drug and placebo spray (group D). Quantitative assessment of pain was done by McGill pain questionnaire, visual analogue score (VAS) and present pain intensity (PPI) at the beginning of the study and after 3 months along with motor and sensory nerve conduction velocities measurements. Results All the three treatment groups experienced significant improvement in pain score in their drug phase of trial ( p < 0.001/ < 0.05) along with some of the electrophysiological parameters. The assessment of the magnitude of therapeutic effect of sodium valproate, GTN and their combination gave numbers needed to treat (NNT) of 7, 5 and 4, respectively. Conclusion Sodium valproate and GTN are well tolerated and provide significant improvement in pain scores as well as in electrophysiological parameters.

Emerging trends in the management of neuropathic pain

Despite significant improvements in our ability to treat neuropathic pain, we are far from the situation of being able to guarantee pain relief. The next few years promise to see the introduction of novel pharmacologic entities that show potential in the field of neuropathic pain treatment. Allied to this will be the realization that some drugs originally released for nonpain indications in fact have an analgesic effect in neuropathic pain. Our treatment armamentarium will be further enhanced by the release of currently available agents with proven efficacy but in new formulations. However, not every product of our improved knowledge will manifest as a new drug treatment for neuropathic pain. Despite evidence of efficacy, some drugs will fail to reach commercialization due to the lack of investment in their clinical development.