Ethosuximide reduces allodynia and hyperalgesia and potentiates morphine effects in the chronic constriction injury model of neuropathic pain

Differential effects of antiseizure medications on neurogenesis: Evidence from cells to animals

Neurogenesis, the process of generating functionally integrated neurons from neural stem and progenitor cells, is involved in brain development during embryonic stages but continues throughout life. Adult neurogenesis plays essential roles in many brain functions such as cognition, brain plasticity, and repair. Abnormalities in neurogenesis have been described in many neuropsychiatric and neurological disorders, including epilepsy. While sharing a common property of suppressing seizures, accumulating evidence has shown that some antiseizure medications (ASM) exhibit neuroprotective potential in the non-epileptic models including Parkinson's disease, Alzheimer's disease, cerebral ischemia, or traumatic brain injury. ASM are a heterogeneous group of medications with different mechanisms of actions. Therefore, it remains to be revealed whether neurogenesis is a class effect or related to them all. In this comprehensive literature study, we reviewed the literature data on the influence of ASM on the neurogenesis process during brain development and also in the adult brain under physiological or pathological conditions. Meanwhile, we discussed the underlying mechanisms associated with the neurogenic effects of ASM by linking the reported in vivo and in vitro studies. PubMed, Web of Science, and Google Scholar databases were searched until the end of February 2023. A total of 83 studies were used finally. ASM can modulate neurogenesis through the increase or decrease of proliferation, survival, and differentiation of the quiescent NSC pool. The present article indicated that the neurogenic potential of ASM depends on the administered dose, treatment period, temporal administration of the drug, and normal or disease context.

The immunomodulatory effects of ethosuximide and sodium butyrate on experimentally induced fibromyalgia: The interaction between IL-4, synaptophysin, and TGF-β1/NF-κB signaling

BACKGROUND AND AIMS

Fibromyalgia is a widespread chronic pain syndrome associated with several comorbid conditions that affect the quality of patients' life. Its pathogenesis is complex, and the treatment strategies are limited by partial efficacy and potential adverse effects. So, our aim was to investigate the possible ameliorative effects of ethosuximide and sodium butyrate on fibromyalgia and compare their effects to pregabalin.

MATERIALS AND METHODS

In a mouse model of reserpine induced fibromyalgia, the effect of ethosuximide, sodium butyrate, and pregabalin was investigated. Evaluation of mechanical allodynia, cold hypersensitivity, anxiety, cognitive impairment, and depression was performed. Also, the brain and spinal cord tissue serotonin, dopamine and glutamate in addition to the serum levels of interleukin (IL)-4 and transforming growth factor beta 1 (TGF-β1) were assayed. Moreover, the expression of nuclear factor kappa B (NF-κB) synaptophysin was immunoassayed in the hippocampal tissues.

KEY FINDINGS

Ethosuximide and sodium butyrate restored the behavioral tests to the normal values except for the antidepressant effect which was evident only with ethosuximide. Both drugs elevated the levels of the anti-inflammatory cytokines IL-4 and TGF-β1, reduced the hippocampal NF-κB, and increased synaptophysin expression with superiority of sodium butyrate. Ethosuximide reduced only spinal cord and brain glutamate while improved brain dopamine while sodium butyrate elevated spinal cord dopamine and serotonin with no effect on glutamate. Also, sodium butyrate elevated brain serotonin and reduced glutamate with no effect on brain dopamine.

SIGNIFICANCE

Each of sodium butyrate and ethosuximide would serve as a promising therapeutic modality for management of fibromyalgia and its comorbid conditions.

Stereospecific Effects of Benzimidazolonepiperidine Compounds on T-Type Ca2+ Channels and Pain

T-type calcium channels activate in response to subthreshold membrane depolarizations and represent an important source of Ca²⁺ influx near the resting membrane potential. These channels regulate neuronal excitability and have been linked to pain. For this reason, T-type calcium channels are suitable molecular targets for the development of new non-opioid analgesics. Our previous work identified an analogue of benzimidazolonepiperidine, 5bk, that preferentially inhibited Ca_V3.2 channels and reversed mechanical allodynia. In this study, we synthesized and screened a small library of 47 compounds derived from 5bk. We found several compounds that inhibited the Ca²⁺ influx in DRG neurons of all sizes. After separating the enantiomers of each active compound, we found two compounds, 3-25-R and 3-14-3-S, that potently inhibited the Ca²⁺ influx. Whole-cell patch clamp recordings from small- to medium-sized DRG neurons revealed that both compounds decreased total Ca²⁺. Application of 3-14-3-S (but not 3-25-R) blocked transiently expressed Ca_V3.1-3.3 channels with a similar IC₅₀ value. 3-14-3-S decreased T-type, but not N-type, Ca²⁺ currents in DRG neurons. Furthermore, intrathecal delivery of 3-14-3-S relieved tonic, neuropathic, and inflammatory pain in preclinical models. 3-14-3-S did not exhibit any activity against G protein-coupled opioid receptors. Preliminary docking studies also suggest that 3-14-3-S can bind to the central pore domain of T-type channels. Together, our chemical characterization and functional and behavioral data identify a novel T-type calcium channel blocker with in vivo efficacy in experimental models of tonic, neuropathic, and inflammatory pain.

Central and peripheral contributions of T-type calcium channels in pain

Chronic pain is a severely debilitating condition that reflects a long-term sensitization of signal transduction in the afferent pain pathway. Among the key players in this pathway are T-type calcium channels, in particular the Cav3.2 isoform. Because of their biophysical characteristics, these channels are ideally suited towards regulating neuronal excitability. Recent evidence suggests that T-type channels contribute to excitability of neurons all along the ascending and descending pain pathways, within primary afferent neurons, spinal dorsal horn neurons, and within pain-processing neurons in the midbrain and cortex. Here we review the contribution of T-type channels to neuronal excitability and function in each of these neuronal populations and how they are dysregulated in chronic pain conditions. Finally, we discuss their molecular pharmacology and the potential role of these channels as therapeutic targets for chronic pain.

Voltage-dependent CaV3.2 and CaV2.2 channels in nociceptive pathways

Noxious stimuli like cold, heat, pH change, tissue damage, and inflammation depolarize a membrane of peripheral endings of specialized nociceptive neurons which eventually results in the generation of an action potential. The electrical signal is carried along a long axon of nociceptive neurons from peripheral organs to soma located in dorsal root ganglions and further to the dorsal horn of the spinal cord where it is transmitted through a chemical synapse and is carried through the spinal thalamic tract into the brain. Two subtypes of voltage-activated calcium play a major role in signal transmission: a low voltage-activated Ca_V3.2 channel and a high voltage-activated Ca_V2.2 channel. The Ca_V3.2 channel contributes mainly to the signal conductance along nociceptive neurons while the principal role of the Ca_V2.2 channel is in the synaptic transmission at the dorsal horn. Both channels contribute to the signal initiation at peripheral nerve endings. This review summarizes current knowledge about the expression and distribution of these channels in a nociceptive pathway, the regulation of their expression and gating during pain pathology, and their suitability as targets for pharmacological therapy.

A modulator of the low-voltage-activated T-type calcium channel that reverses HIV glycoprotein 120-, paclitaxel-, and spinal nerve ligation-induced peripheral neuropathies

The voltage-gated calcium channels CaV3.1-3.3 constitute the T-type subfamily, whose dysfunctions are associated with epilepsy, psychiatric disorders, and chronic pain. The unique properties of low-voltage-activation, faster inactivation, and slower deactivation of these channels support their role in modulation of cellular excitability and low-threshold firing. Thus, selective T-type calcium channel antagonists are highly sought after. Here, we explored Ugi-azide multicomponent reaction products to identify compounds targeting T-type calcium channel. Of the 46 compounds tested, an analog of benzimidazolonepiperidine-5bk (1-{1-[(R)-{1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}(thiophen-3-yl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one) modulated depolarization-induced calcium influx in rat sensory neurons. Modulation of T-type calcium channels by 5bk was further confirmed in whole-cell patch clamp assays in dorsal root ganglion (DRG) neurons, where pharmacological isolation of T-type currents led to a time- and concentration-dependent regulation with a low micromolar IC50. Lack of an acute effect of 5bk argues against a direct action on T-type channels. Genetic knockdown revealed CaV3.2 to be the isoform preferentially modulated by 5bk. High voltage-gated calcium, as well as tetrodotoxin-sensitive and -resistant sodium, channels were unaffected by 5bk. 5bk inhibited spontaneous excitatory postsynaptic currents and depolarization-evoked release of calcitonin gene-related peptide from lumbar spinal cord slices. Notably, 5bk did not bind human mu, delta, or kappa opioid receptors. 5bk reversed mechanical allodynia in rat models of HIV-associated neuropathy, chemotherapy-induced peripheral neuropathy, and spinal nerve ligation-induced neuropathy, without effects on locomotion or anxiety. Thus, 5bk represents a novel T-type modulator that could be used to develop nonaddictive pain therapeutics.

Anti-osteoarthritis potential of peppermint and rosemary essential oils in a nanoemulsion form: behavioral, biochemical, and histopathological evidence

BACKGROUND

This study aimed to evaluate the effect of nanoemulsion containing peppermint and rosemary essential oils in rats with osteoarthritis (OA).

METHODS

In this experimental study, we prepared a nanoemulsion containing peppermint and rosemary essential oils by spontaneous emulsification and evaluated the nanoemulsion's dermal irritation and toxicity. Investigating the analgesic effect of the nanoemulsion, we randomly assigned 36 male rats to 6 groups: Control (saline injection into the knee), osteoarthritis (intra-articular injection of 2 mg monosodium iodoacetate), and four groups of OA treated with nanoemulsion gel, nanoemulsion solution, rosemary and peppermint essential oil gel, or diclofenac sodium. Treatments were administered topically at a dose of 1 ml daily. Using behavioral tests, we assessed pain on days 1, 4, 7, and 14 after injection. Finally, we did the histopathological and biochemical evaluation of rats' knee joints.

RESULTS

There were no irritation signs on the animals' skin after receiving the nanoemulsion and no changes in the hematological and biochemical parameters of rats' blood compared to the control group. Receiving nanoemulsion decreased the mechanical (P < 0.001) and thermal allodynia (P < 0.05), thermal hyperalgesia (P < 0.05), and ambulatory-evoked pain in comparison with the OA group. Also, the nanoemulsion receiving rats showed an increase in SOD and GPx activity and a decrease in MDA level. Histopathology of synovial tissues confirmed the results of behavioral and biochemical tests.

CONCLUSION

The nanoemulsion containing essential oils of peppermint and rosemary reduces osteoarthritis pain via increasing antioxidant capacity and improving the histopathological features of the rats' knee joint.

Physiopathological Role of Neuroactive Steroids in the Peripheral Nervous System

Peripheral neuropathy (PN) refers to many conditions involving damage to the peripheral nervous system (PNS). Usually, PN causes weakness, numbness and pain and is the result of traumatic injuries, infections, metabolic problems, inherited causes, or exposure to chemicals. Despite the high prevalence of PN, available treatments are still unsatisfactory. Neuroactive steroids (i.e., steroid hormones synthesized by peripheral glands as well as steroids directly synthesized in the nervous system) represent important physiological regulators of PNS functionality. Data obtained so far and here discussed, indeed show that in several experimental models of PN the levels of neuroactive steroids are affected by the pathology and that treatment with these molecules is able to exert protective effects on several PN features, including neuropathic pain. Of note, the observations that neuroactive steroid levels are sexually dimorphic not only in physiological status but also in PN, associated with the finding that PN show sex dimorphic manifestations, may suggest the possibility of a sex specific therapy based on neuroactive steroids.

Ethosuximide improves chronic pain-induced anxiety- and depression-like behaviors

Chronic pain is a heavy burden disease. Current treatments are generally weakly effective or associated with adverse effects. New therapeutic approaches are therefore needed. Recent studies have suggested T-type calcium channels as an attractive target for the treatment of chronic pain. In this perspective, it was decided to perform a preclinical evaluation of the efficacy of ethosuximide, a T-type channel blocker used clinically as an antiepileptic, as a novel pharmacological treatment for chronic pain. Assessment of the effect of ethosuximide was thus made in both nociception and pain-related comorbidities as anxiety and depression are frequently encountered in chronic pain patients. Our results show that such symptoms occurred in three animal models of chronic pain designed to reflect traumatic neuropathic, chemotherapy-induced neuropathic and inflammatory pain conditions. Administration of ethosuximide reduced both chronic pain and comorbidities with a marked intensity ranging from partial reduction to a complete suppression of symptoms. These results make ethosuximide, and more broadly the inhibition of T-type calcium channels, a new strategy for the management of uncontrolled chronic pain, likely to improve not only pain but also the accompanying anxiety and depression.

Betulinic acid, derived from the desert lavender Hyptis emoryi, attenuates paclitaxel-, HIV-, and nerve injury-associated peripheral sensory neuropathy via block of N- and T-type calcium channels

The Federal Pain Research Strategy recommended development of nonopioid analgesics as a top priority in its strategic plan to address the significant public health crisis and individual burden of chronic pain faced by >100 million Americans. Motivated by this challenge, a natural product extracts library was screened and identified a plant extract that targets activity of voltage-gated calcium channels. This profile is of interest as a potential treatment for neuropathic pain. The active extract derived from the desert lavender plant native to southwestern United States, when subjected to bioassay-guided fractionation, afforded 3 compounds identified as pentacyclic triterpenoids, betulinic acid (BA), oleanolic acid, and ursolic acid. Betulinic acid inhibited depolarization-evoked calcium influx in dorsal root ganglion (DRG) neurons predominantly through targeting low-voltage-gated (Cav3 or T-type) and CaV2.2 (N-type) calcium channels. Voltage-clamp electrophysiology experiments revealed a reduction of Ca, but not Na, currents in sensory neurons after BA exposure. Betulinic acid inhibited spontaneous excitatory postsynaptic currents and depolarization-evoked release of calcitonin gene-related peptide from lumbar spinal cord slices. Notably, BA did not engage human mu, delta, or kappa opioid receptors. Intrathecal administration of BA reversed mechanical allodynia in rat models of chemotherapy-induced peripheral neuropathy and HIV-associated peripheral sensory neuropathy as well as a mouse model of partial sciatic nerve ligation without effects on locomotion. The broad-spectrum biological and medicinal properties reported, including anti-HIV and anticancer activities of BA and its derivatives, position this plant-derived small molecule natural product as a potential nonopioid therapy for management of chronic pain.

T-type Calcium Channels in Health and Disease

Low Voltage-Activated (LVA) T-type calcium channels are characterized by transient current and Low Threshold Spikes (LTS) that trigger neuronal firing and oscillatory behavior. Combined with their preferential localization in dendrites and their specific "window current", T-type calcium channels are considered to be key players in signal amplification and synaptic integration. Assisted by the emerging pharmacological tools, the structural determinants of channel gating and kinetics, as well as novel physiological and pathological functions of T-type calcium channels, are being uncovered. In this review, we provide an overview of structural determinants in T-type calcium channels, their involvement in disorders and diseases, the development of novel channel modulators, as well as Structure-Activity Relationship (SAR) studies that lead to rational drug design.

Microextraction combined with microderivatization for drug monitoring and protein modification analysis from limited blood volume using mass spectrometry

In the clinic, ethosuximide is commonly used to treat generalized absence seizures but has recently been repurposed for other diseases. Because of adverse effects and drug interactions, high-throughput therapeutic drug monitoring of ethosuximide is necessary. Microextraction is a simple, effective, rapid, and low consumption of organic solvents method for sample preparation. In this study, microderivatization-increased detection (MDID)-combined microextraction was used to detect ethosuximide by mass spectrometry. Ethosuximide is a difficult to retain and ionize compound in the C18 nano-flow column and ionization interface, respectively. Hence, we developed a fast method for detecting ethosuximide in human plasma by using the MDID strategy (within 2 min). Chemical microderivatization parameters were studied and optimized to increase the sensitivity of ethosuximide detection at trace levels. The linear range for the analysis of ethosuximide in 10 μL plasma was 5-500 μg/mL with a coefficient of determination (r²) ≥ 0.995. The precision and accuracy of intraday and interday analyses of ethosuximide were below 13.0%. Furthermore, modifications of major proteins in plasma and blood cells, induced by ethosuximide, were identified. The proposed method effectively utilizes microliter samples to detect drug plasma concentrations under suitable microextraction procedures toward the eco-friendly goal of low consumption of organic solvents. Graphical abstract ᅟ.

Design and synthesis of novel anti-hyperalgesic agents based on 6-prenylnaringenin as the T-type calcium channel blockers

Since 6-prenylnaringenin (6-PNG) was recently identified as a novel T-type calcium channel blocker with the IC₅₀ value around 1 µM, a series of flavanone derivatives were designed, synthesized and subsequently evaluated for T-channel-blocking activity in HEK293 cells transfected with Ca_v3.2 T-type channels using a patch-clamp technique. As a result, several new flavanones blocked Ca_v3.2-dependent T-currents more potently than 6-PNG. In the synthesized compounds, 6-(3-ethylpent-2-enyl)-5,7-dihydroxy-2-(2-hydroxyphenyl)chroman-4-one 8j, 6-(3-ethylpent-2-enyl)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one 11b, 6-(2-cyclopentylideneethyl)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one 11d, and 6-(2-Cyclopentylethyl)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one 12c were more potent blocker than 6-PNG with the IC₅₀ value of 0.39, 0.26, 0.46, and 0.50 µM, respectively. Among the above four derivatives, the compound 8j provided the best result in the in vivo experiments; i.e. systemic administration of 8j at the minimum dose completely restored neuropathic pain induced by partial sciatic nerve ligation in mice.

Recent advances in the development of T-type calcium channel blockers for pain intervention

Cav 3.2 T-type calcium channels are important regulators of pain signals in the afferent pain pathway, and their activities are dysregulated during various chronic pain states. Therefore, it is reasonable to predict that inhibiting T-type calcium channels in dorsal root ganglion neurons and in the spinal dorsal horn can be targeted for pain relief. This is supported by early pharmacological studies with T-type channel blockers, such as ethosuximide, and by analgesic effects of siRNA depletion of Cav 3.2 channels. In the past 5 years, considerable effort has been applied towards identifying novel classes of T-type calcium channel blockers. Here, we review recent developments in the discovery of novel classes of T-type calcium channel blockers, and their analgesic effects in animal models of pain and in clinical trials.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

Efficacy and safety of a T-type calcium channel blocker in patients with neuropathic pain: A proof-of-concept, randomized, double-blind and controlled trial

BACKGROUND

T-type calcium channels have been shown to play an important role in the initiation and maintenance of neuropathic pain and represent a promising therapeutic target for new analgesic treatments. Ethosuximide (ETX), an anticonvulsant and a T-type channel blocker has shown analgesic effect in several chronic pain models but has not yet been evaluated in patients with neuropathic pain.

METHODS

This proof-of-concept, multicentre, double-blind, controlled and randomized trial compared the efficacy and safety of ETX (given as add-on therapy) to an inactive control (IC) in 114 patients with non-diabetic peripheral neuropathic pain. After a 7-day run-in period, eligible patients aged over 18 years were randomly assigned (1:1) to ETX or IC for 6 weeks. The primary outcome was the difference between groups in the pain intensity (% of change from the baseline to end of treatment) assessed in the intention-to-treat population. This study is registered with EudraCT (2013-004801-26) and ClinicalTrials.gov (NCT02100046).

RESULTS

The study was stopped during the interim analysis due to the high number of adverse events in the active treatment group. ETX failed to reduce total pain and showed a poor tolerance in comparison to IC. In the per-protocol analysis, ETX significantly reduced pain intensity by 15.6% (95% CI -25.8; -5.4) from baseline compared to IC (-7.8%, 95% CI -14.3; -1.3; p = 0.033), but this result must be interpreted with caution because of a small subgroup of patients.

CONCLUSION

Ethosuximide did not reduce the severity of neuropathic pain and induces, at the doses used, many adverse events.

SIGNIFICANCE

This article shows that ETX is not effective to treat neuropathic pain. Nevertheless, per-protocol analysis suggests a possible analgesic effect of ETX. Thus, our work adds significant knowledge to preclinical and clinical data on the benefits of T-type calcium channel inhibition for the treatment of neuropathic pain.

Vitamin D supplementation attenuates the behavioral scores of neuropathic pain in rats

Objective(s): Neuropathic pain due to lesion or dysfunction of the peripheral or central nervous system is often refractory to the conventional analgesics. Currently, there is no proven treatment to prevent or cure neuropathic pain. A recent surge of new data suggests the potential effects of vitamin D in the medical community. This study was designed to determine whether acute or chronic vitamin D administration was effective in alleviating symptoms of neuropathic pain in a rat model of neuropathic pain. Materials and Methods: Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve in the rats that resulted in thermal hyperalgesia, mechanical, and cold allodynia. Results: Acute vitamin D injections (250, 500, and 1000 unit/kg i.p.) on the 7th, 14th, and 21st postoperative days could not attenuate mechanical and cold allodynia as well as heat hyperalgesia compared to CCI group. But when vitamin D (1000 unit/kg i.p.) administration was started on the first day after surgery and given daily until the 21st day, cold allodynia and heat hyperalgesia considerably were attenuated. However, no differences in paw withdrawal thresholds were observed. Conclusion: These results indicate that chronic vitamin D administrations can attenuate the behavioral scores of neuropathic pain in rats.

Characterization of a rat model of bortezomib-induced painful neuropathy

Background and Purpose

Bortezomib (Velcade®) is a breakthrough treatment for multiple myeloma, significantly improving patient survival. However, its use is limited by painful neuropathy often resulting in dose reduction/cessation of first‐line treatment due to lack of treatment. The aim of this study was to characterize a clinically relevant rat model of bortezomib‐induced painful neuropathy, using established evoked measures and novel ethological techniques, to aid drug discovery.

Experimental Approach

Adult male Sprague–Dawley rats were injected i.p. with 0.1 and 0.2 mg·kg⁻¹ bortezomib, or its vehicle, on days 0, 3, 7 and 10. Multiple behavioural approaches were utilized: mechanical hypersensitivity, cold allodynia, heat hypersensitivity, motor co‐ordination, burrowing and voluntary wheel running. At maximal bortezomib‐induced mechanical hypersensitivity, 200 mg·kg⁻¹ ethosuximide/vehicle and 100 mg·kg⁻¹ phenyl N‐tert‐butylnitrone (PBN)/vehicle were administered i.p. in separate experiments, and mechanical hypersensitivity assessed 1, 3 and 24 h later.

Key Results

Bortezomib induced dose‐related mechanical hypersensitivity for up to 80 days. Bortezomib induced short‐term cold allodynia, but no significant change in heat hypersensitivity, motor co‐ordination, voluntary wheel running and burrowing behaviour compared to vehicle‐treated controls. Systemic PBN and ethosuximide significantly ameliorated bortezomib‐induced mechanical hypersensitivity.

Conclusions and Implications

These data characterize a reproducible rat model of clinical‐grade bortezomib‐induced neuropathy demonstrating long‐lasting pain behaviours to evoked stimuli. Inhibition by ethosuximide and PBN suggests involvement of calcium and/or ROS in bortezomib‐induced painful neuropathy. These drugs could be used as preclinical positive controls to assess novel analgesics. As ethosuximide is widely used clinically, translation to the clinic to treat bortezomib‐induced painful neuropathy may be possible.

Assessment of the effectiveness and safety of ethosuximide in the treatment of abdominal pain related to irritable bowel syndrome - IBSET: protocol of a randomised, parallel, controlled, double-blind and multicentre trial

INTRODUCTION

Irritable bowel syndrome (IBS) is characterised by the association of abdominal chronic pain with bowel habit disorders in the absence of identifiable organic disease. This is the first reason for consultation in gastroenterology, with an estimated prevalence of 10%-15% in industrialised countries. Although this is a benign gastrointestinal disease, its chronicity profoundly impacts the patient's quality of life and causes considerable health spending. Actual medical treatments are poorly efficient on IBS-related abdominal pain, making it a major public health concern. The mechanisms causing IBS symptoms are unknown. Recent studies have shown the involvement of T-type channel in abdominal pain. We aim to evaluate the therapeutic potential of ethosuximide, a T-type channel blocker, on the abdominal pain of patients presenting an IBS.

METHODS AND ANALYSIS

The IBSET trial is a randomised, controlled, parallel, double-blind and multicentre study. It is the first clinical trial evaluating the efficacy and safety of ethosuximide on abdominal pain related to IBS. Adults with IBS that report significant abdominal pain (≥4/10) at least for 3 months will be included. 290 patients will be randomly assigned to receive either ethosuximide or placebo over 12 weeks after 1 week of run-in period. The primary endpoint is the rate of responders (pain reduction ≥30% and Subject Global Assessment of Relief score ≥4). The intensity of abdominal pain will be assessed by an 11-point Numerical Rating Scale before and after 12 weeks of treatment and the score of the Subject Global Assessment of Relief scale at the end of treatment. The secondary endpoints are the safety of ethosuximide, the intensity and features of IBS and quality of life.

ETHICS AND DISSEMINATION

The study was approved by an independent medical ethics committee (CPP Sud-Est VI, Clermont-Ferrand, France). The results will be published in a peer-review journal and presented at international congresses.

TRIAL REGISTRATION NUMBER

NCT02973542; Pre-results.

Alleviation of neuropathic pain by regulating T-type calcium channels in rat anterior cingulate cortex

Background

It has been demonstrated that administration of T-type calcium channel (TCC) inhibitors could relieve the neuropathic pain by intraperitoneally or intrathecally. TCCs are not only expressed in dorsal root ganglia or dorsal horn, but also in some of the pain associated brain regions. In the present study, we sought to investigate whether modulating TCCs in the anterior cingulate cortex (ACC) could alleviate the neuropathic pain.

Results

(1) Ca_v3.2 was up regulated in rat ACC after chronic constriction injury (CCI). (2) T-type calcium current intensity was increased in CCI animal model. (3) TCC inhibitor reduced miniature excitatory postsynaptic currents frequency of ACC neurons in CCI animal model. (4) TCC inhibitor suppressed the firing rate of ACC neurons in CCI animal model. (5) Both mechanical and thermal allodynia were partially relieved by ACC microinjection with TCC inhibitor.

Conclusions

TCCs in the ACC may be contributing to the maintenance of neuropathic pain, and the neuropathic pain can be alleviated by inhibiting the neuronal activity of ACC through modulating the TCCs.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Antinociceptive effects of venlafaxine in a rat model of peripheral neuropathy: role of alpha2-adrenergic receptors

This study was designed to determine whether acute or chronic venlafaxine administration was effective in alleviating symptoms of neuropathic pain in a rat model of neuropathic pain, and whether the effect of venlafaxine involved manipulation of α2-adrenoceptors,by determining the effect of yohimbine, a α2-adrenoceptor antagonist on its actions. Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve in the rats that resulted in stimulus-evoked thermal hyperalgesia, tactile mechanical and cold allodynia. Acute venlafaxine injections (20 and 40 mg/kg i.p.) on the 7th, 14th and 21st postoperative days could not reduce tactile and cold hypersensitivity significantly compared to CCI group. But in these groups venlafaxine (40 mg/kg i.p.) blocked heat hyperalgesia. When venlafaxine (10 and 20mg/kg i.p.) administration was started on the first day after CCI and given daily until the 14th day, tactile hypersensitivity and heat hyperalgesia considerably were attenuated. But when venlafaxine (20mg/kg i.p.) treatment was initiated on the 10th day after CCI, once the model had been fully established, and given daily for 11 days, no differences in withdrawal thresholds were observed compared with CCI group however heat hyperalgesia significantly has been blocked. Also the effect of venlafaxine on heat hyperalgesia was reversed by pretreatment with yohimbine at all-time intervals. These results indicate that venlafaxine, when administered immediately after nerve injury, and for a sufficient period of time, can prevent the development and expression of neuropathic pain. Also we conclude that α2-adrenoceptors participate in the antinociceptive effects of venlafaxine.

Calcium-permeable ion channels in pain signaling

The detection and processing of painful stimuli in afferent sensory neurons is critically dependent on a wide range of different types of voltage- and ligand-gated ion channels, including sodium, calcium, and TRP channels, to name a few. The functions of these channels include the detection of mechanical and chemical insults, the generation of action potentials and regulation of neuronal firing patterns, the initiation of neurotransmitter release at dorsal horn synapses, and the ensuing activation of spinal cord neurons that project to pain centers in the brain. Long-term changes in ion channel expression and function are thought to contribute to chronic pain states. Many of the channels involved in the afferent pain pathway are permeable to calcium ions, suggesting a role in cell signaling beyond the mere generation of electrical activity. In this article, we provide a broad overview of different calcium-permeable ion channels in the afferent pain pathway and their role in pain pathophysiology.

Effect of curcumin on diabetic peripheral neuropathic pain: possible involvement of opioid system

Neuropathic pain is one of the most common complications of diabetes mellitus. As efficacy and tolerability of current therapy for neuropathic pain are not ideal, we need to develop the novel drug for better treatment. Curcumin as a natural flavonoid from Curcuma longa has considerable effects on nervous system such as, antidepressant, antinociceptive and neuroprotective effects. The present study was designed to investigate the effect of curcumin on diabetic peripheral neuropathic pain and possible involvement of opioid system. A single dose of 60mg/kg streptozotocin was injected intraperitoneally to induce diabetes in rats. STZ-induced diabetic rats were treated with curcumin (50mg/kg/day) acute and chronically. Thermal hyperalgesia and mechanical allodynia were measured on the days 0, 7, 14 and 21 after diabetes induction as behavioral scores of neuropathic pain. Chronic, but not acute, treatment with curcumin prevents the weight loss and attenuates mechanical allodynia in STZ-induced diabetic rats. Pretreatment with naloxone (1mg/kg) significantly reduced anti-allodynic effect of chronic curcumin in von Frey filament test. Our results suggest that curcumin can be considered as a new therapeutic potential for the treatment of diabetic neuropathic pain and the activation of opioid system may be involved in the antinociceptive effect of curcumin.