Antinociceptive effect of topiramate in models of acute pain and diabetic neuropathy in rodents

Alcohol Use Disorder and Chronic Pain: An Overlooked Epidemic

Alcohol use disorder (AUD) and chronic pain disorders are pervasive, multifaceted medical conditions that often co-occur. However, their comorbidity is often overlooked, despite its prevalence and clinical relevance. Individuals with AUD are more likely to experience chronic pain than the general population. Conversely, individuals with chronic pain commonly alleviate their pain with alcohol, which may escalate into AUD. This narrative review discusses the intricate relationship between AUD and chronic pain. Based on the literature available, the authors present a theoretical model explaining the reciprocal relationship between AUD and chronic pain across alcohol intoxication and withdrawal. They propose that the use of alcohol for analgesia rapidly gives way to acute tolerance, triggering the need for higher levels of alcohol consumption. Attempts at abstinence lead to alcohol withdrawal syndrome and hyperalgesia, increasing the risk of relapse. Chronic neurobiological changes lead to preoccupation with pain and cravings for alcohol, further entrenching both conditions. To stimulate research in this area, the authors review methodologies to improve the assessment of pain in AUD studies, including self-report and psychophysical methods. Further, they discuss pharmacotherapies and psychotherapies that may target both conditions, potentially improving both AUD and chronic pain outcomes simultaneously. Finally, the authors emphasize the need to manage both conditions concurrently, and encourage both the scientific community and clinicians to ensure that these intertwined conditions are not overlooked given their clinical significance.

Topiramate affords neuroprotection in diabetic neuropathy model via downregulating spinal GFAP/inflammatory burden and improving neurofilament production

The current study aimed to test the neuroprotective action of topiramate in mouse peripheral diabetic neuropathy (DN) and explored some mechanisms underlying this action. Mice were assigned as vehicle group, DN group, DN + topiramate 10-mg/kg and DN + topiramate 30-mg/kg. Mice were tested for allodynia and hyperalgesia and then spinal cord and sciatic nerves specimens were examined microscopically and neurofilament heavy chain (NEFH) immunostaining was performed. Results indicated that DN mice had lower the hotplate latency time (0.46-fold of latency to licking) and lower von-Frey test pain threshold (0.6-fold of filament size) while treatment with topiramate increased these values significantly. Sciatic nerves from DN control mice showed axonal degeneration while spinal cords showed elevated GFAP (5.6-fold) and inflammatory cytokines (∼3- to 4-fold) but lower plasticity as indicated by GAP-43 (0.25-fold). Topiramate produced neuroprotection and suppressed spinal cord GFAP/inflammation but enhanced GAP-43. This study reinforces topiramate as neuroprotection and explained some mechanisms included in alleviating neuropathy.

Mechanistic efficacy assessment of selected novel methanimine derivatives against vincristine induced Neuropathy: In-vivo, Ex-vivo and In-silico correlates

Vincristine induced peripheral neuropathy (VIPN) is a serious untoward side effect suffered by cancer patients, which still lacks an adequate therapeutic approach. This study examined the alleviating potential of novel methanimine derivatives i.e. (E)-N-(4-nitrobenzylidene)-4-chloro-2-iodobenzamine (KB 9) and (E)-N-(2-methylbenzylidene)-4-chloro-2-iodobenzamine (KB 10) in VIPN. Vincristine was injected in BALB/c mice for 10 days to instigate nociceptive neuropathy. Dynamic and static allodynia, thermal (hot and cold) hyperalgesia were evaluated at 0, 5, 10 and 14 days using cotton brush, Von Frey filament application, hot plate test, acetone drop and cold water respectively. Tumour necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), lipid peroxide (LPO), glutathione-S-transferase (GST), catalase (CAT), superoxide dismutase (SOD) and reactive oxygen species (ROS) assays were performed to assess the efficacy of KB9 and KB10 against neuroinflammation and oxidative stress utilizing ELISA, immunohistochemistry and western blot analysis in brain and sciatic nerve tissues. Computational studies were executed to determine the stable binding conformation of both compounds with respect to COX-2 and NF-κB. Interestingly, both compounds substantially reduced protein expression related to neuroinflammation, oxidative stress (LPO, GST, SOD, CAT) and pain (NF-κB, COX-2, IL-1β and TNF-α). This molecular analysis suggested that the neuroprotective effect of KB9 and KB10 was mediated via regulation of inflammatory signaling pathways. Overall, this study demonstrated that KB9 and KB10 ameliorated vincristine induced neuropathy, through anti-inflammatory, anti-nociceptive and antioxidant mechanisms.

Pharmacokinetic profile of the selective 5-HT3 receptor antagonist ondansetron in the rat: an original study and a minireview of the behavioural pharmacological literature in the rat

The availability of agonists and antagonists to modulate the activity of the 5-hydroxytryptamine (5-HT) type 3 (5-HT3) receptor has renewed interest in its role as a therapeutic target. Ondansetron is a highly selective 5-HT3 receptor antagonist that is well tolerated as an anti-emetic for patients undergoing chemotherapy. Preclinical studies in rat have shown the effects of small doses of ondansetron on cognition, behavioural sensitisation, and epilepsy. However, the pharmacokinetic (PK) profile of ondansetron in rat has not been described, which limits the translational relevance of these findings. Here, we aim to determine, in the rat, the PK profile of ondansetron in the plasma and to determine associated brain levels. The plasma PK profile was determined following acute subcutaneous administration of ondansetron (0.1, 1, and 10 μg/kg). Brain levels were measured following subcutaneous administration of ondansetron at 1 μg/kg. Plasma and brain levels of ondansetron were determined using high-performance liquid chromatography – tandem mass spectrometry. Following administration of all three doses, measured ondansetron plasma levels (≈30–3000 pg/mL) were below levels achieved with doses usually administered in the clinic, with a rapid absorption phase and a short half-life (≈30–40 min). We also found that brain levels of ondansetron at 1 μg/kg were significantly lower than plasma levels, with brain to plasma ratios of 0.45 and 0.46 in the motor and pre-frontal cortices. We discuss our findings in the context of a minireview of the literature. We hope that our study will be helpful to the design of preclinical studies with therapeutic end-points.

Ellagic acid improves muscle dysfunction in cuprizone-induced demyelinated mice via mitochondrial Sirt3 regulation

Sirt3 enzyme and mitochondrial abnormality can be related to excess fatigue or muscular dysfunction in multiple sclerosis (MS).Ellagic acid (EA) has a mitochondrial protector, iron chelator, antioxidant, and axon regenerator in neurons.In this study the effect of EAon muscle dysfunction, its mitochondria, and Sirt3 enzyme incuprizone-induced model of MSwas examined. Demyelination was induced by a diet containing 0.2% w/w cuprizone (Cup) for 42 days and EA administered daily (5, 50, and 100 mg/kg P.O) either with or without cuprizone in mice. Behavioral tests were assessed, and muscle tissue markers ofoxidative stress, mitochondrial parameters, mitochondrial respiratory chain activity, the Sirt3 protein level, and Sirt3 expression were also determined. Luxol fast blue staining and the behavioral tests were performed toassess the implemented model. In Cup group an increased oxidative stress in their muscle tissues was observed. Also, muscle mitochondria exhibited mitochondria dysfunction, lowered mitochondrial respiratory chain activity, Sirt3 protein level, and Sirt3 expression.EA prevented most of these anomalous alterations. Sub-chronicEA co-treatment dose-dependently ameliorated behavioral and muscular impairment in mice that received Cup.EA can effectively protect muscle tissue against cuprizone-induced demeylination via the mitochondrial protection, oxidative stress prevention and Sirt3 overexpression.

Ameliorative potential of flavonoids of Aegle marmelos in vincristine-induced neuropathic pain and associated excitotoxicity

Introduction: The objective of the study is to elucidate the effect of Aegle marmelos bark hydroalcoholic extract (AMHE) and the role of its constituents marmelosin, umbelliferone, and Para-coumaric acid in attenuating neuropathic pain.Methodology: Peripheral neuropathy was induced by vincristine 100 μg/ml. AMHE was administered in three dose levels (100, 200 and 300 mg/kg) for 21 days. Mechanical hyperalgesia and allodynia were assessed by Randall Sellitto and electronic Von-Frey test, respectively. Functional loss and recovery of the nerve were assessed by sciatic functional index test. The nerve conduction velocity and formalin test were done to assess the peripheral and central response of the extract. Inflammatory mediators in both sciatic nerve and brain and neurotransmitters glutamate and aspartate were measured to support the data.Results and discussion: The inflammatory mediators in both sciatic nerve and brain (TNF-α, IL-1β, and IL-6) were found to be attenuated with AMHE-treated group in comparison to the group treated only with vincristine, which indicates the extract has anti-inflammatory property. AMHE treated rats were found to be active in all the behavioural tests, suggesting its activity could be mediated through a central and peripheral mechanism to attenuate the pain response. The levels of excitatory neurotransmitters were found to be reduced with AMHE treatment.Conclusion: It could be concluded that AMHE is active in attenuating the neuropathic pain caused by vincristine. The peripheral action would have mediated through lowering the inflammatory mediators as well as the excitotoxicity caused due to peripheral neuropathy and neuroinflammation.

Attenuation of vincristine-induced neuropathy by synthetic cyclohexenone-functionalized derivative in mice model

Vincristine (VCR) is a well-known anticancer drug which frequently induced painful neuropathy and impairs the quality of life of patients. The present study was designed to investigate the alleviative potential of a novel cyclohexenone derivative (CHD), i.e., ethyl 6-(4-methoxyphenyl)-2-oxo-4-phenylcyclohexe-3-enecarboxylate, against VCR-induced neuropathic pain in mice model. VCR was administered intraperitoneally for 10 days in two cycles to induce neuropathic pain. Static and dynamic mechanical allodynia was evaluated using von Frey hair filaments and cotton buds, respectively. Paw thermal hyperalgesia was determined through a hot plate analgesiometer. The tail cold immersion hyperalgesia and paw cold allodynia were determined by available standard protocols. The formalin nociception was induced via subplantar injection of formalin. The antioxidant potential was evaluated via 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity. The outcome of this study revealed that CHD (30-45 mg/kg) and gabapentin (75 mg/kg) significantly enhanced the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) in static and dynamic allodynia, respectively, and increased the PWL in thermal hyperalgesia and tail withdrawal latency (TWL) as compared to the VCR-treated group. CHD significantly augmented the paw withdrawal duration (PWD) in paw cold allodynia, while the same compound only increased the paw elevation and paw licking in the delayed phase of formalin nociception. Moreover, CHD significantly inhibited the DPPH free radical scavenging action (IC₅₀ = 56), butylated hydroxytoluene (BHT) (IC₅₀ = 39), and ascorbic acid (IC₅₀ = 2.93). In conclusion, CHD exhibited a profile of potential attenuative effect against the VCR-induced neuropathic pain which might be attributed to its possible antinociceptive and antioxidant effect.

Effects of isopulegol in acute nociception in mice: Possible involvement of muscarinic receptors, opioid system and l-arginine/NO/cGMP pathway

Previous studies have shown that isopulegol has anxiolytic, anticonvulsant, gastro-protective and antioxidant activities in rodents, but until now there are no studies showing activity of isopulegol in animal models of nociception and inflammation. The objective of this study was to evaluate the antinociceptive effect of isopulegol and to propose possible mechanisms involved in its effects observed in mice. Groups of male and female Swiss mice (20-35 g, n = 5-8) were used in this test under the authorization of Ethics Committee on Animal Experimentation (CEEA/UFPI N° 82/2014). In order to evaluate the antinociceptive activity of isopulegol, nociception was induced using formalin test, capsaicin and glutamate in hind paw licking model, followed by the investigation of the involvement of opioid mechanisms, K + ATP channels, muscarinic, L arginine-nitric oxide and cGMP. The oral administration of isopulegol showed antinociceptive effect in both phases of the formalin test at doses from 0.78 to 25 mg/kg (first phase) and 1.56-25 mg/kg (second phase) and also produced significant results before capsaicin test at doses from 1.56 to 12.5 mg/kg and glutamate test at doses from 3.12 to 6.25 mg/kg with a dose-dependent effect. The antinociception activity of isopulegol was inhibited in the presence of naloxone (2 mg / kg, ip), glibenclamide (3 mg/kg, ip), atropine (1 mg/kg, ip), l-arginine (600 mg/kg, ip) and methylene blue (20 mg/kg, ip). The results suggested that acute antinociceptive action of opioid isopulegol seems to be related to the K + ATP channels system, through the involvement of muscarinic receptors, inhibiting nitric oxide and cGMP.

Saponins of Tribulus terrestris attenuated neuropathic pain induced with vincristine through central and peripheral mechanism

The study comprises exploring the effects of saponins from Tribulus terrestris (TT) in attenuating the neuropathic pain caused by vincristine (100 μg/ml i.p.) for 10 days (in two 5 day cycles with 2 days pause). Mechanical hyperalgesia and allodynia were assessed by Randall-Sellitto and electronic von Frey tests, respectively. Chemical- induced nociception was assessed by formalin test. Neurophysiological effect of the extract was evaluated by recording sciatic functional index (SFI) on the test days (7, 10, 14, and 21) and sciatic nerve conduction velocity test (SNCV) on the last day. Inflammatory mediators (TNF-α, IL-1β, and IL-6) in both sciatic nerve and brain and brain neurotransmitters, glutamate and aspartate, were measured to support the behavioral response. The saponins of TT-treated group were found to be effective in the behavioral experiments, implying its activity both centrally and peripherally in attenuating pain. The inflammatory mediators in both sciatic nerve and brain (TNF-α, IL-1β, and IL-6) were found to be attenuated with TT saponin treatment in comparison to vincristine-treated group, indicating its anti-inflammatory property. The excitatory neurotransmitters, L-glutamic acid and L-aspartic acid, were also found to be attenuated with TT saponins, implying restoration of neuronal damage and synaptic activity caused by high amount of glutamate due to excess TNF-α in brain and reversing the nociceptive threshold lowered due to aspartate. Thus, TT(S) is peripherally and centrally active in lowering the inflammatory mediators, reversing the neuronal damage and increasing the nociceptive threshold caused due to peripheral neuropathy.

Topiramate induced peripheral neuropathy: A case report and review of literature

Drug-induced peripheral neuropathy had been rarely reported as an adverse effect of some antiepileptic drugs (AEDs) at high cumulative doses or even within the therapeutic drug doses or levels. We describe clinical and diagnostic features of a patient with peripheral neuropathy as an adverse effect of chronic topiramate (TPM) therapy. A 37-year-old woman was presented for the control of active epilepsy (2010). She was resistant to some AEDs as mono- or combined therapies (carbamazepine, sodium valproate, levetiracetam, oxcarbazepine and lamotrigine). She has the diagnosis of frontal lobe epilepsy with secondary generalization and has a brother, sister and son with active epilepsies. She became seizure free on TPM (2013-2017) but is complaining of persistent distal lower extremities paresthesia in a stocking distribution. Neurological examination revealed presence of diminished Achilles tendon reflexes, stocking hypesthesia and delayed distal latencies, reduced conduction velocities and amplitudes of action potentials of posterior tibial and sural nerves, indicating demyelinating and axonal peripheral neuropathy of the lower extremities. After exclusion of the possible causes of peripheral neuropathy, chronic TPM therapy is suggested as the most probable cause of patient’s neuropathy. This is the first case report of topiramate induced peripheral neuropathy in the literature.

Bioactive Fraction of Annona reticulata Bark (or) Ziziphus jujuba Root Bark along with Insulin Attenuates Painful Diabetic Neuropathy through Inhibiting NF-κB Inflammatory Cascade

The present study explains the neuroprotective ability of bioactive fractions of Annona reticulata bark (ARB) and Ziziphus jujuba root bark (ZJ) along with insulin against diabetic neuropathy. By using different solvents of increasing polarity ARB and ZJ were undergone for bioactive guided fractionation. The neuroprotective ability of the all the plant fractions were tested against H₂O₂ induced toxicity in SHSY5Y neuroblastoma cell lines and DRG neuronal cells. Among all the fractions tested, the methanol extract of ARB and ZJ (ARBME and ZJME) and its water fractions (ARBWF and ZJWF) exhibited significant neuroprotection against H₂O₂ induced toxicity in SHSY5Y cells and DRG neuronal cells. Further both the active fractions were tested against streptozotocin (55 mg/kg i.p.) induced diabetic neuropathy in male Wistar rats. Body weight changes, blood glucose levels and pain threshold through hot plate, tail immersion, cold plate and Randall-Sillitto methods were measured throughout the study at weekly interval. After completion of the drug treatment period, all the animals were sacrificed to measure the sciatic nerve lipid peroxidation, antioxidative enzyme levels (SOD, catalase, and GSH) and cytokine levels (IL-1β, IL-6, IL-10, TNF-α, iNOS, and NFκB) through ELISA and western blotting analysis. Results of this study explain that ARBME, ZJME, ARBWF, and ZJWF along with insulin potentially attenuate the thermal, mechanical hyperalgesia and cold allodynia in diabetic neuropathic rats, where insulin treatment alone failed to diminish the same. Reduction of sciatic nerve oxidative stress, NF-κB and iNOS mediated inflammatory cascade and normalization of abnormal cytokine release confirms the possible mechanism of action. The present study confirms the neuroprotective ability of ARB and ZJ against painful diabetic neuropathy through inhibiting oxidative stress and NF-κB inflammatory cascade.

Painful neuropathy: Mechanisms

Painful neuropathy, like the other complications of diabetes, is a growing healthcare concern. Unfortunately, current treatments are of variable efficacy and do not target underlying pathogenic mechanisms, in part because these mechanisms are not well defined. Rat and mouse models of type 1 diabetes are frequently used to study diabetic neuropathy, with rats in particular being consistently reported to show allodynia and hyperalgesia. Models of type 2 diabetes are being used with increasing frequency, but the current literature on the progression of indices of neuropathic pain is variable and relatively few therapeutics have yet been developed in these models. While evidence for spontaneous pain in rodent models is sparse, measures of evoked mechanical, thermal and chemical pain can provide insight into the pathogenesis of the condition. The stocking and glove distribution of pain tantalizingly suggests that the generator site of neuropathic pain is found within the peripheral nervous system. However, emerging evidence demonstrates that amplification in the spinal cord, via spinal disinhibition and neuroinflammation, and also in the brain, via enhanced thalamic activity or decreased cortical inhibition, likely contribute to the pathogenesis of painful diabetic neuropathy. Several potential therapeutic strategies have emerged from preclinical studies, including prophylactic treatments that intervene against underlying mechanisms of disease, treatments that prevent gains of nociceptive function, treatments that suppress enhancements of nociceptive function, and treatments that impede normal nociceptive mechanisms. Ongoing challenges include unraveling the complexity of underlying pathogenic mechanisms, addressing the potential disconnect between the perceived location of pain and the actual pain generator and amplifier sites, and finding ways to identify which mechanisms operate in specific patients to allow rational and individualized choice of targeted therapies.

Involvement of Cholinergic and Opioid System in γ-Terpinene-Mediated Antinociception

The literature shows that the monoterpenes are great candidates for the development of new drugs for the treatment of various pathological processes, including painful conditions. The gamma terpinene (γ-TPN) is a monoterpene present in plant species that have multiple pharmacological properties and has structural similarity to antinociceptive monoterpenes, such as limonene and alpha-phellandrene. The γ-TPN molecular mass was evaluated by mass spectrometry and showed a pseudomolecular ion with m/z 137.0 Da. The animals did not present any signs of acute toxicity at 2 g/kg, p.o. γ-TPN (1.562 to 50 mg/kg, p.o.) showed an antinociceptive effect in the formalin, capsaicin, and glutamate tests. γ-TPN has antinociceptive action when administered by others routes in glutamate test. To eliminate a possible sedative effect of γ-TPN, the open field and rota-rod test were conducted and the γ-TPN did not show muscle relaxant activity or central depressant effect. To investigate the mechanisms of action, the animals were pretreated with naloxone, glibenclamide, atropine, mecamylamine, or L-arginine in the glutamate test. γ-TPN antinociception was inhibited in the presence of naloxone, glibenclamide, atropine, and mecamylamine. The results suggest that the γ-TPN (p.o.) produced antinociceptive effect in models of chemical nociception through the cholinergic and opioid systems involvement.

Effect of curcumin in mice model of vincristine-induced neuropathy

CONTEXT

Curcumin exhibits a wide spectrum of biological activities which include neuroprotective, antinociceptive, anti-inflammatory, and antioxidant activity.

OBJECTIVE

The present study evaluates the effect of curcumin in vincristine-induced neuropathy in a mice model.

MATERIALS AND METHODS

Vincristine sulfate (0.1 mg/kg, i.p. for 10 consecutive days) was administered to mice to induce neuropathy. Pain behavior was assessed at different days, i.e., 0, 7, 10, and 14 d. Sciatic nerve total calcium, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH), nitric oxide (NO), and lipid peroxidation (LPO) were also estimated after the 14th day of study. Pregabalin (10 mg/kg, p.o.) and curcumin (15, 30, and 60 mg/kg, p.o.) were administered for 14 consecutive days.

RESULTS

Curcumin at 60 mg/kg significantly attenuated the vincristine-induced neuropathic pain manifestations in terms of thermal hyperalgesia (p < 0.001) and allodynia (p < 0.001); mechanical hyperalgesia (p < 0.001); functional loss (p < 0.001); and in the delayed phase of formalin test (p < 0.001). Curcumin at 30 and 60 mg/kg exhibited significant changes (p < 0.001) in antioxidant levels and in total calcium levels in vincristine-injected mice.

CONCLUSION

Curcumin at 30 and 60 mg/kg dose levels significantly attenuated vincristine-induced neuropathy which may be due to its multiple actions including antinociceptive, calcium inhibitory, and antioxidant effect.

Combination of diacerhein and antiepileptic drugs after local peripheral, and oral administration in the rat formalin test

Preclinical Research The present study was designed to evaluate the possible antinociceptive interaction between diacerhein and some antiepileptic drugs (carbamazepine, topiramate and gabapentin) on formalin-induced nociception. Diacerhein, each of the antiepileptics or a fixed dose-ratio combination of these drugs was assessed after local peripheral and oral administration in rats. lsobolographic analyses were used to define the interaction between drugs. Diacerhein, antiepileptic drugs (carbamazepine, topiramate and gabapentin) or their combinations yielded a dose-dependent antinociceptive effect when administered by both routes. Theoretical ED30 values for the combination estimated from the isobolograms were obtained as follows: diacerhein-carbamazepine (85.99 ± 7.07 μg/paw; 56.53 ± 4.56 mg/kg po), diacerhein-topiramate (197.97 ± 22.90 μg/paw; 13.06 ± 2.44 mg/kg po) and diacerhein-gabapentin (96.87 ± 17.73 μg/paw; 17.90 ± 4.70 mg/kg p.o.) for the local peripheral and oral administration routes, respectively. These values were significantly higher than the experimentally obtained ED30 values: diacerhein-carbamazepine (49.33 ± 3.37 μg/paw; 35.49 ± 7.91 mg/kg po), diacerhein-topiramate (133.00 ± 39.10 μg/paw; 8.87 ± 1.46 mg/kg po) and diacerhein-gabapentin (70.98 ± 14.73 μg/paw; 10.95 ± 3.23 mg/kg po). The combinations produced their antinociceptive effects without motor impairment in the rotarod test indicating synergistic interactions with a good side effect profile.

Standardized Aqueous Tribulus terristris (nerunjil) extract attenuates hyperalgesia in experimentally induced diabetic neuropathic pain model: role of oxidative stress and inflammatory mediators

The present study aimed to evaluate standardized aqueous Tribulus terristris (nerunjil) extract on the pain threshold response in streptozotocin (STZ)-induced diabetic neuropathic pain model in rats. After a single injection of STZ (40 mg/kg; i.p.), Wistar male rats were tested by the thermal and chemical-induced pain models. Diabetic rats exhibited significant hyperalgesia, and these rats were left untreated for the first four weeks. Thereafter, treatment was initiated and continued up to week-8. All the rats except the vehicle-treated group received insulin 5 IU/kg/day to maintain plasma glucose levels. Treatment with nerunjil (100 and 300 mg/kg; p.o.) for 4 weeks significantly attenuated the nociception in behavioural models. Nerunjil also inhibited the tumour necrosis factor-α and interleukin-1 beta levels. The effect of nerunjil (300 mg/kg) is comparable to the standard drug Pregabalin (100 mg/kg). Nerunjil increased the superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, and decreased the lipid peroxide levels in dose-dependent manner. Insulin alone-treated rats failed to attenuate hyperalgesic response. In comparison to insulin alone-treated rats, nerunjil exhibited significant increase in the pain threshold response. It could be concluded that in controlled diabetic states, nerunjil attenuated the neuropathic pain through modulation of oxidative stress and inflammatory cytokine release.

The mechanisms of antihyperalgesic effect of topiramate in a rat model of inflammatory hyperalgesia

Recent studies have shown that topiramate, a structurally novel anticonvulsant, exerts antinociceptive activity in animal models of neuropathic, acute somatic, and visceral pain. This study was aimed to examine: (i) the effects of systemically and locally peripherally administered topiramate in the rat inflammatory pain model and (ii) the potential role and site(s) of gamma-aminobutyric acid (GABA), opioid, and adrenergic receptors in topiramate's antihyperalgesia. Rats received intraplantar (i.pl.) injections of the pro-inflammatory compound carrageenan. A paw pressure test was used to determine: (i) the effect of systemic and local peripheral topiramate on carrageenan-induced hyperalgesia and (ii) the effects of systemic and local peripheral bicuculline (selective GABAA receptor antagonist), naloxone (nonselective opioid receptor antagonist), and yohimbine (selective α2-adrenergic receptor antagonist) on topiramate-induced antihyperalgesia. Systemic topiramate (40-160 mg/kg; p.o.) produced a significant dose-dependent reduction in the paw inflammatory hyperalgesia induced by carrageenan. The antihyperalgesic effect of systemic topiramate was significantly decreased by systemic bicuculline (0.5-1 mg/kg; i.p.), naloxone (2-5 mg/kg; i.p.), and yohimbine (1-3 mg/kg; i.p.). Local peripheral topiramate (0.03-0.34 mg/paw; i.pl.) also produced significant dose-dependent antihyperalgesia, which was significantly depressed by local peripheral yohimbine (0.05-0.2 mg/paw; i.pl.) but not by local peripheral bicuculline (0.15 mg/paw; i.pl.) or naloxone (0.1 mg/paw; i.pl.). The results suggest that topiramate produces systemic and local peripheral antihyperalgesia in an inflammatory pain model, which is, at least partially, mediated by central GABAA and opioid receptors and by peripheral and most probably central α2-adrenergic receptors. These findings contribute to better understanding of topiramate's action in pain states involving inflammation.

Pharmacological treatment of diabetic neuropathic pain

Neuropathic pain continues to be a difficult and challenging clinical issue to deal with effectively. Painful diabetic polyneuropathy is a complex pain condition that occurs with reasonable frequency in the population and it may be extremely difficult for clinicians to provide patients with effective analgesia. Chronic neuropathic pain may occur in approximately one of every four diabetic patients. The pain may be described as burning or a deep-seated ache with sporadic paroxysms of lancinating painful exacerbations. The pain is often constant, moderate to severe in intensity, usually primarily involves the feet and generally tends to worsen at night. Treatment may be multimodal but largely involves pharmacological approaches. Pharmacological therapeutic options include antidepressants (tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors), α2δ ligands and topical (5%) lidocaine patch. Other agents may be different antiepileptic drugs (carbamazepine, lamotrigine, topiramate), topical capsaicin, tramadol and other opioids. Progress continues with respect to understanding various mechanisms that may contribute to painful diabetic neuropathy. Agents that may hold some promise include neurotrophic factors, growth factors, immunomodulators, gene therapy and poly (adenosine diphosphate-ribose) polymerase inhibitors. It is hoped that in the future clinicians will be able to assess patient pathophysiology, which may help them to match optimal therapeutic agents to target individual patient aberrant mechanisms.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

The role of nitric oxide in the local antiallodynic and antihyperalgesic effects and expression of delta-opioid and cannabinoid-2 receptors during neuropathic pain in mice

Both delta-opioid receptor (DOPr) and cannabinoid-2 receptor (CB2R) agonists attenuate neuropathic pain, but the precise mechanism implicated in these effects is not completely elucidated. We investigated whether nitric oxide synthesized by neuronal (NOS1) or inducible (NOS2) nitric-oxide synthases could modulate DOPr and/or CB2R antiallodynic and antihyperalgesic effects through the peripheral nitric oxide-cGMP-protein kinase G (PKG) pathway activation and affect their expression during neuropathic pain. In wild-type (WT) mice at 21 days after chronic constriction of sciatic nerve, we evaluated the effects of [d-Pen(2),d-Pen(5)]-enkephalin (DPDPE); (2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone (JWH-015); and a NOS1 [N-[(4S)-4-amino-5-[(2-aminoethyl)amino]pentyl]-N'-nitroguanidine tris(trifluoroacetate) salt; NANT], NOS2 [l-N(6)-(1-iminoethyl)-lysine; l-NIL], l-guanylate cyclase [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; ODQ], or PKG [(Rp)-8-(para-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate; Rp-8-pCPT-cGMPs] inhibitor administered alone or combined. Expression of DOPr and CB2R mRNA in the spinal cord and dorsal root ganglia of naive and nerve-injured WT, NOS1-knockout (KO), and NOS2-KO mice, also was assessed. The subplantar administration of NANT, l-NIL, ODQ, or Rp-8-pCPT-cGMPs dose-dependently inhibited neuropathic pain and enhanced the local effects of DPDPE or JWH-015. Moreover, although the basal levels of DOPr and CB2R mRNA were similar between WT and NOS-KO animals, nerve injury only decreased (DOPr) or increased (CB2R) their expression in the dorsal root ganglia of WT and NOS2-KO mice, and not in NOS1-KO mice. Results suggest that inactivation of the nitric oxide-cGMP-PKG peripheral pathway triggered by NOS1 and NOS2 enhanced the peripheral actions of DOPr and CB2R agonists and that nitric oxide synthesized by NOS1 is implicated in the peripheral regulation of DOPr and CB2R gene transcription during neuropathic pain.

Towards a better understanding of the psychopharmacology of nutmeg: Activities in the mouse tetrad assay

ETHNOPHARMACOLOGICAL RELEVANCE

Nutmeg, the seeds of Myritica fragrans (family Myristicaceae), is a well known kitchen spice with a long-standing reputation as a psychoactive herb. Nutmeg at high doses is considered a cheap substitute to several drugs of abuse. Earlier reports have attributed amphetamine-like activities to nutmeg.

AIM OF THE STUDY

To characterize the neuropharmacological effects of different nutmeg extracts, administered orally and intraperitoneally, in comparison to Delta(9)-terahydrocannabinol, amphetamine, and morphine.

MATERIALS AND METHODS

Methanolic (ME), dichloromethane (DE), and hexane (HE) extracts were obtained from a chromatographically fingerprinted batch of nutmeg. Biological evaluation was conducted in sets of 6-8 mice in the tetrad assay at doses ranging from 100 to 500 and 500 to 1000 mg/kg for i.p. and oral administration, respectively.

RESULTS

While oral administration of all the nutmeg extracts at 500 mg/kg caused a significant increase in locomotor activity, the i.p. administration of DE showed significant reduction in rectal temperature along with a significant increase in tail flick latency at 300 mg/kg. A significant decrease in core body temperature was observed with HE at 100 mg/kg, while higher doses caused significant increases in hot plate latency.

CONCLUSION

Different behavioral effects were observed that varied by the type of extract as well as by the route of administration.

Diabetic painful and insensate neuropathy: pathogenesis and potential treatments

Advanced peripheral diabetic neuropathy (PDN) is associated with elevated vibration and thermal perception thresholds that progress to sensory loss and degeneration of all fiber types in peripheral nerve. A considerable proportion of diabetic patients also describe abnormal sensations such as paresthesias, allodynia, hyperalgesia, and spontaneous pain. One or several manifestations of abnormal sensation and pain are described in all the diabetic rat and mouse models studied so far (i.e., streptozotocin-diabetic rats and mice, type 1 insulinopenic BB/Wor and type 2 hyperinsulinemic diabetic BBZDR/Wor rats, Zucker diabetic fatty rats, and nonobese diabetic, Akita, leptin- and leptin-receptor-deficient, and high-fat diet-fed mice). Such manifestations are 1) thermal hyperalgesia, an equivalent of a clinical phenomenon described in early PDN; 2) thermal hypoalgesia, typically present in advanced PDN; 3) mechanical hyperalgesia, an equivalent of pain on pressure in early PDN; 4) mechanical hypoalgesia, an equivalent to the loss of sensitivity to mechanical noxious stimuli in advanced PDN; 5) tactile allodynia, a painful perception of a light touch; and 5) formalin-induced hyperalgesia. Rats with short-term diabetes develop painful neuropathy, whereas those with longer-term diabetes and diabetic mice typically display manifestations of both painful and insensate neuropathy, or insensate neuropathy only. Animal studies using pharmacological and genetic approaches revealed important roles of increased aldose reductase, protein kinase C, and poly(ADP-ribose) polymerase activities, advanced glycation end-products and their receptors, oxidative-nitrosative stress, growth factor imbalances, and C-peptide deficiency in both painful and insensate neuropathy. This review describes recent achievements in studying the pathogenesis of diabetic neuropathic pain and sensory disorders in diabetic animal models and developing potential pathogenetic treatments.