Anti-allodynic and anti-hyperalgesic activity of (±)-licarin A in neuropathic rats via NO-cyclic-GMP-ATP-sensitive K+ channel pathway.

The study aimed to examine the effect of intraperitoneal and intrathecal (±)-licarin A in neuropathic pain induced by L5 and L6 spinal nerve ligation (SNL) in male Wistar rats and the possible involvement of the NO-cGMP-ATP-sensitive K+ channel pathway. Neuropathic pain signs (allodynia and hyperalgesia) were evaluated on postoperative Day 14 using von Frey filaments. Single intraperitoneal (0.01, 0.1, 1, and 10 mg/kg) and intrathecal (0.01, 0.1, 1, and 10 µg/rat) administration of (±)-licarin A improved allodynia and hyperalgesia. The (±)-licarin A-induced anti-allodynic and anti-hyperalgesic activity was prevented by the intrathecal injection of  l-NAME (100 µg/rat; nonselective nitric oxide synthase inhibitor), ODQ (10 µg/rat; guanylate cyclase inhibitor), and glibenclamide (50 µg/rat; adenosine triphosphate (ATP)-sensitive K+ channel blocker). The data suggest that (±)-licarin A exerts its anti-allodynic and anti-hyperalgesic activity by activating the NO-cGMP-ATP-sensitive K+ channel pathway.

Pramipexole inhibits formalin-induce acute and long-lasting mechanical hypersensitivity via NF-kB pathway in rats.

Pain is one of the most frequent causes for patients to seek medical care. It interferes with daily functioning and affects the quality of life of the patient. There is a clear need to investigate nonopioid or non-nonsteroidal anti-inflammatory drug alternatives for the treatment of pain. In this study, we determined the effect of acute pre- and posttreatment with pramipexole (PPX), a dopamine D2/D3 selective agonist, on formalin 1%-induced acute and long-lasting nociceptive behavior sensitivity in rats. Moreover, we sought to investigate whether the antiallodynic and antihyperalgesic effect induced by PPX was mediated through the nuclear factor-κB (NF-kB) signaling pathway. Moreover, acute systemic pretreatment with PPX (1 and 3 mg/kg, ip) suppressed the formalin-induced nociceptive behavior during both phases of the formalin test and the development of formalin-induced secondary mechanical allodynia and hyperalgesia in both paws. Acute systemic posttreatment with PPX (3 mg/kg, ip) reverted the formalin-induced long-lasting secondary mechanical allodynia and hyperalgesia. Furthermore, PPX inhibits the protein expression of NF-κB-p65 and the levels of tumor necrosis factor-α and interleukin-1ß in the spinal cord of animals with secondary mechanical allodynia and hyperalgesia induced by formalin. These data suggest that PPX has a potential role in producing anti-inflammatory activity. Moreover, the antiallodynic and antihyperalgesic effects induced by PPX can be mediated through the NF-kB signaling pathway.

Synthesis and Biological Activities of Dehydrodiisoeugenol: A Review.

Dehydrodiisoeugenol (DHIE) is a neolignan found in more than 17 plant species, including herbs, fruit, and root. DHIE was, for the first time, isolated from Myristica fragrans bark in 1973. Since then, many methodologies have been used for the obtention of DHIE, including classical chemistry synthesis using metal catalysts and biocatalytic synthesis; employing horseradish peroxidase; peroxidase from Cocos nucifera; laccase; culture cells of plants; and microorganisms. Increasing evidence has indicated that DHIE has a wide range of biological activities: anti-inflammatory, anti-oxidant, anti-cancerogenic, and anti-microbial properties. However, evidence in vivo and in human beings is still lacking to support the usefulness potential of DHIE as a therapeutic agent. This study's review was created by searching for relevant DHIE material on websites such as Google Scholar, PubMed, SciFinder, Scholar, Science Direct, and others. This reviews the current state of knowledge regarding the different synthetical routes and biological applications of DHIE.

Participation of angiotensin-(1-7) in exercise-induced analgesia in rats with neuropathic pain.

Exercise reduces neuropathic pain in animals and humans. Recent studies indicate that training exercise favors the synthesis and action of angiotensin-(1-7) (Ang-(1-7)), a vasoactive peptide of the renin-angiotensin system (RAS), in various tissues. Interestingly, Ang-(1-7) also relieves neuropathic pain; however, it remains to be elucidated whether exercise mitigates this type of pain through Ang-(1-7). In this study, we investigated the role of Ang-(1-7) in exercise-induced analgesia in a neuropathic pain model. Male Wistar rats were ligated of lumbar spinal nerves (L5 and L6) or sham-operated. Then, they were subjected to acute (2-h) or chronic (4-week) exercise protocols. Tactile allodynia was evaluated before and after each exercise intervention. Microosmotic pumps were implanted subcutaneously for the release of Ang-(1-7) or A779 (selective Mas receptor (MasR; Ang-(1-7) receptor) antagonist). Plasma levels of Ang II and Ang-(1-7) were quantified by HPLC. Spinal nerve ligation (SNL) produced tactile allodynia. Both acute and chronic exercise reversed this neuropathic behavior. A779 treatment prevented the antiallodynic effect induced by each exercise protocol. SNL increased the plasma Ang II/Ang-(1-7) ratio; however, exercise did not modify it. Acute treatment with Ang-(1-7) via MasR mimicked exercise-mediated antinociception. Collectively, these results suggest that activation of the Ang-(1-7)/MasR axis of the RAS represents a potential novel mechanism by which exercise attenuates neuropathic pain in rats.

Lactoferrin and Its Potential Impact for the Relief of Pain: A Preclinical Approach.

Pain is one of the most disabling symptoms of several clinical conditions. Neurobiologically, it is classified as nociceptive, inflammatory, neuropathic and dysfunctional. Opioids and nonsteroidal anti-inflammatory drugs (NSAIDs) are conventionally prescribed for the treatment of pain. Long-term administration of opioids results in the loss of analgesic efficacy, leading to increased dosage, tolerance, and addiction as the main drawbacks of their use, while the adverse effects of NSAIDs include gastric ulcer formation, intestinal bleeding, acute kidney injury, and hepatotoxicity. Lactoferrin is an iron-binding, anti-inflammatory glycoprotein that displays analgesic activities associated, in part, by interacting with the low-density lipoprotein receptor-related protein (LRP), which may result in the regulation of the DAMP-TRAF6-NFκB, NO-cGMP-ATP K+-sensitive channel and opioid receptor signaling pathways. This review summarizes and discusses for the first time the analgesic effects of lactoferrin and its presumable mechanisms based on pre-clinical trials. Given its anti-nociceptive and anti-inflammatory properties, lactoferrin may be used as an adjunct to enhance the efficacy and to decrease the tolerogenic effects of canonical therapeutic drugs prescribed for pain treatment.

Stereoselective Synthesis and Antiallodynic Activity of 3-Hydroxylated Paroxetines.

The design, stereoselective synthesis and in vivo antiallodynic activity of four novel paroxetine analogs, named 3-hydroxy paroxetines (3HPXs), is reported herein. Among the novel synthesized compounds, three showed an antiallodynic effect, while (R,R)-3HPX was found to be 2.5 times more bioactive than (-)-paroxetine itself in neuropathic rats. Consequently, the current investigation not only discloses a novel promising analgesic drug, but also reveals that functionalization at the C3 position of paroxetine could be as effective as the common functionalization at either C4 or within the sesamol group.

Synergistic antiallodynic and antihyperalgesic interaction between L-DOPA and celecoxib in parkinsonian rats is mediated by NO-cGMP-ATP-sensitive K+ channel.

Pain is a usual and troublesome non-motor symptom of Parkinson's disease, with a prevalence of 29-82%. Therefore, it's vital to find pharmacological treatments for managing PD-associated pain symptoms, to improve patients' quality of life. For this reason, we tested the possible synergy between L-DOPA and celecoxib in decreasing allodynia and hyperalgesia induced by unilateral lesioning with 6-OHDA into the SNpc in rats. We also tested whether the antiallodynic and antihyperalgesic effect induced by combination of L-DOPA and celecoxib is mediated by the NO-cGMP-ATP-sensitive K+ channel pathway. Tactile allodynia and mechanical hyperalgesia were evaluated using von Frey filament. Isobolographic analyses were employed to define the nature of the drug interaction using a fixed dose ratio (0.5: 0.5). We found that acute and sub-acute (10-day) treatment with a single dose of L-DOPA (3-25 mg/kg, i. p.) or celecoxib (2.5-20 mg/kg, i. p.) induced a dose-dependent antiallodynic and antihyperalgesic effect in parkinsonian rats. Isobolographic analysis revealed that the ED50 values obtained by L-DOPA + celecoxib combination was significantly less than calculated additive values, indicating that co-administration of L-DOPA with celecoxib produces synergistic interactions in its antiallodynic and antihyperalgesic effect in animals with nigrostriatal lesions. Moreover, the antiallodynic and antihyperalgesic effects induced by L-DOPA + celecoxib combination were blocked by intrathecal pre-treatment with L-NAME, ODQ, and glibenclamide. Taken together, the data suggest that L-DOPA + celecoxib combination produces an antiallodynic and antihyperalgesic synergistic interaction at the systemic level, and these effects are mediated, at the central level, through activation of the NO-cGMP-ATP-sensitive K+ channel pathway.

Anti-allodynic effect induced by curcumin in neuropathic rat is mediated through the NO-cyclic-GMP-ATP sensitive K+ channels pathway.

BACKGROUND: Recent studies pointed up that curcumin produces an anti-nociceptive effect in inflammatory and neuropathic pain. However, the possible mechanisms of action that underline the anti-allodynic effect induced by curcumin are not yet established. The purpose of this study was to determine the possible anti-allodynic effect of curcumin in rats with L5-L6 spinal nerve ligation (SNL). Furthermore, we study the possible participation of the NO-cyclic GMP-ATP-sensitive K+ channels pathway in the anti-allodynic effect induced by curcumin. METHODS: Tactile allodynia was measured using von Frey filaments by the up-down method in female Wistar rats subjected to SNL model of neuropathic pain. RESULTS: Intrathecal and oral administration of curcumin prevented, in a dose-dependent fashion, SNL-induced tactile allodynia. The anti-allodynic effect induced by curcumin was prevented by the intrathecal administration of L-NAME (100 µg/rat, a non-selective nitric oxide synthase inhibitor), ODQ (10 µg/rat, an inhibitor of guanylate-cyclase), and glibenclamide (50 µg/rat, channel blocker of ATP-sensitive K+ channels). CONCLUSIONS: These data suggest that the anti-allodynic effect induced by curcumin is mediated, at least in part, by the NO-cyclic GMP-ATP-sensitive K+ channels pathway in the SNL model of neuropathic pain in rats.

Unilateral lesion of the nigroestriatal pathway with 6-OHDA induced allodynia and hyperalgesia reverted by pramipexol in rats.

Pain is the non-motor symptom with the highest prevalence in patients with Parkinson's Disease (PD) affecting 40-85%. This study aimed to investigate the development of tactile allodynia and mechanical hyperalgesia after the nigrostriatal dopaminergic lesion induced by the unilateral 6-hydroxydopamine (6-OHDA) injection at different doses in the substantia nigra pars compacta (SNpc). Moreover, we studied the possible antiallodynic and antihyperalgesic effect with the acute and the subacute treatment of the pramipexole (PPX) in rats. First, dopaminergic lesion was realized by the unilateral injection of 6-OHDA (6, 10 and 16 µg/µl) into the SNpc. To know the establishment of motor deficits, we measure several turns and forelimb-use asymmetry by rotational behavior and cylinder, respectively. On the other hand, to investigate allodynia and hyperalgesia induced by 6-OHDA, we used the von Frey filaments. Moreover, antiallodynic and antihyperalgesic effect induced by PPX (0.03, 0.3 and 3 mg/kg, s.c.) was examined on acute and subacute conditions. We found that major dopaminergic lesion with 16 µg/µl of 6-OHDA caused the highest allodynia and hyperalgesia effects in both paws, as well as the major motor deficits. In addition, the treatment with PPX at 0.3 mg/kg reverts the allodynia and the hyperalgesia induced by 6-OHDA. In conclusion, the dopaminergic lesion into SNpc induce allodynia and hyperalgesia in both paws; interestingly the treatment with PPX can be suggested as an analgesic drug for patients with PD.

Antiallodynic effect induced by [6]-gingerol in neuropathic rats is mediated by activation of the serotoninergic system and the nitric oxide-cyclic guanosine monophosphate-adenosine triphosphate-sensitive K+ channel pathway.

The present study evaluated the possible antiallodynic effect induced by [6]-gingerol in rats with L5-L6 spinal nerve ligation (SNL). Moreover, we determined the possible mechanism underlying the antiallodynic effect induced by [6]-gingerol in neuropathic rats. The animals underwent L5-L6 SNL for the purpose of developing tactile allodynia. Tactile allodynia was measured with von Frey filaments. Intrathecal administration of [6]-gingerol reversed SNL-induced tactile allodynia. The [6]-gingerol-induced antiallodynic effect was prevented by the intrathecal administration of methiothepin (30 µg per rat; nonselective 5-hydroxytryptamine [5-HT] antagonist), WAY-100635 (6 µg per rat; selective 5-HT1A receptor antagonist), SB-224289 (5 µg per rat; selective 5-HT1B receptor antagonist), BRL-15572 (4 µg per rat; selective 5-HT1D receptor antagonist), and SB-659551 (6 µg per rat; selective 5-HT5A receptor antagonist), but naloxone (50 µg per rat; nonselective opioid receptor antagonist) did not prevent the [6]-gingerol-induced antiallodynic effect. Moreover, intrathecal administration of Nω-nitro-l-arginine methyl ester (100 µg per rat; nonselective nitric oxide [NO] synthase inhibitor), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 µg per rat; inhibitor of guanylate cyclase), and glibenclamide (50 µg per rat; channel blocker of adenosine triphosphate [ATP]-sensitive K+ channels) prevented the [6]-gingerol-induced antiallodynic effect. These data suggest that the antiallodynic effect induced by [6]-gingerol is mediated by the serotoninergic system involving the activation of 5-HT1A/1B/1D/5A receptors, as well as the NO-cyclic guanosine monophosphate-ATP-sensitive K+ channel pathway but not by the opioidergic system.

Antinociceptive effect of (-)-epicatechin in inflammatory and neuropathic pain in rats.

The aim of this study was to investigate the antinociceptive potential of (-)-epicatechin and the possible mechanisms of action involved in its antinociceptive effect. The carrageenan and formalin tests were used as inflammatory pain models. A plethysmometer was used to measure inflammation and L5/L6 spinal nerve ligation as a neuropathic pain model. Oral (-)-epicatechin reduced carrageenan-induced inflammation and nociception by about 59 and 73%, respectively, and reduced formalin- induced and nerve injury-induced nociception by about 86 and 43%, respectively. (-)-Epicatechin-induced antinociception in the formalin test was prevented by the intraperitoneal administration of antagonists: methiothepin (5-HT1/5 receptor), WAY-100635 (5-HT1A receptor), SB-224289 (5-HT1B receptor), BRL-15572 (5-HT1D receptor), SB-699551 (5-HT5A receptor), naloxone (opioid receptor), CTAP (µ opioid receptor), nor-binaltorphimine (κ opioid receptor), and 7-benzylidenenaltrexone (δ1 opioid receptor). The effect of (-)-epicatechin was also prevented by the intraperitoneal administration of L-NAME [nitric oxide (NO) synthase inhibitor], 7-nitroindazole (neuronal NO synthase inhibitor), ODQ (guanylyl cyclase inhibitor), glibenclamide (ATP-sensitive K channel blocker), 4-aminopyridine (voltage-dependent K channel blocker), and iberiotoxin (large-conductance Ca-activated K channel blocker), but not by amiloride (acid sensing ion channel blocker). The data suggest that (-)-epicatechin exerts its antinociceptive effects by activation of the NO-cyclic GMP-K channels pathway, 5-HT1A/1B/1D/5A serotonergic receptors, and µ/κ/δ opioid receptors.

Synergistic Interaction of a Gabapentin- Mangiferin Combination in Formalin-Induced Secondary Mechanical Allodynia and Hyperalgesia in Rats Is Mediated by Activation of NO-Cyclic GMP-ATP-Sensitive K+ Channel Pathway.

Preclinical Research Gabapentin is an anticonvulsant used to treat neuropathic pain. Mangiferin is an antioxidant that has antinociceptive and antiallodynic effects in inflammatory and neuropathic pain models. The purpose of this study was to determine the interaction between mangiferin and gabapentin in the development and maintenance of formalin-induced secondary allodynia and hyperalgesia in rats. Gabapentin, mangiferin, or their fixed-dose ratio combination were administrated peripherally. Isobolographic analyses was used to define the nature of the interaction of antiallodynic and/or antihyperalgesic effects of the two compounds. Theoretical ED50 values for the combination were 74.31 µg/paw and 95.20 µg/paw for pre- and post-treatment, respectively. These values were higher than the experimental ED50 values, 29.45 µg/paw and 37.73 µg/paw respectively, indicating a synergistic interaction in formalin-induced secondary allodynia and hyperalgesia. The antiallodynic and antihyperalgesic effect induced by the gabapentin/mangiferin combination was blocked by administration of L-NAME, the soluble guanylyl cyclase inhibitor, ODQ and glibenclamide. These data suggest that the gabapentin- mangiferin combination produces a synergistic interaction at the peripheral level. Moreover, the antiallodynic and hyperalgesic effect induced by the combination is mediated via the activation of an NO-cyclic GMP-ATP-sensitive K+ channel pathway. Drug Dev Res 78 : 390-402, 2017. © 2017 Wiley Periodicals, Inc.

Anti-allodynic effect of mangiferin in neuropathic rats: Involvement of nitric oxide-cyclic GMP-ATP sensitive K+ channels pathway and serotoninergic system.

The neurobiology of neuropathic pain is caused by injury in the central or peripheral nervous system. Recent evidence points out that mangiferin shows anti-nociceptive effect in inflammatory pain. However, its role in inflammatory and neuropathic pain and the possible mechanisms of action are not yet established. The purpose of this study was to determine the possible anti-allodynic effect of mangiferin in rats with spinal nerve ligation (SNL). Furthermore, we sought to investigate the possible mechanisms of action that contribute to these effects. Mechanical allodynia to stimulation with the von Frey filaments was measured by the up and down method. Intrathecal administration of mangiferin prevented, in a dose-dependent fashion, SNL-induced mechanical allodynia. Mangiferin-induced anti-allodynia was prevented by the intrathecal administration of L-NAME (100µg/rat, non-selective nitric oxide synthase inhibitor), ODQ (10µg/rat, inhibitor of guanylate-cyclase) and glibenclamide (50µg/rat, channel blocker of ATP-sensitive K+ channels). Moreover, methiothepin (30µg/rat, non-selective 5-HT receptor antagonist), WAY-100635 (6µg/rat, selective 5-HT1A receptor antagonist), SB-224289 (5µg/rat, selective 5-HT1B receptor antagonist), BRL-15572 (4µg/rat, selective 5-HT1D receptor antagonist) and SB-659551 (6µg/rat, selective 5-HT5A receptor antagonist), but not naloxone (50µg/rat, non-selective opioid receptor antagonist), were able to prevent mangiferin-induced anti-allodynic effect. These data suggest that the anti-allodynic effect induced by mangiferin is mediated at least in part by the serotoninergic system, involving the activation of 5-HT1A/1B/1D/5A receptors, as well as the nitric oxide-cyclic GMP-ATP-sensitive K+ channels pathway, but not by the opioidergic system, in the SNL model of neuropathic pain in rats.

The potential role of serotonergic mechanisms in the spinal oxytocin-induced antinociception.

The role of oxytocin (OXT) in pain modulation has been suggested. Indeed, hypothalamic paraventricular nuclei (PVN) electrical stimuli reduce the nociceptive neuronal activity (i.e., neuronal discharge associated with activation of Aδ- and C-fibers) of the spinal dorsal horn wide dynamic range (WDR) cells and nociceptive behavior. Furthermore, raphe magnus nuclei lesion reduces the PVN-induced antinociception, suggesting a functional interaction between the OXT and the serotoninergic system. The present study investigated in Wistar rats the potential role of spinal serotonergic mechanisms in the OXT- and PVN-induced antinociception. In long-term secondary mechanical allodynia and hyperalgesia induced by formalin or extracellular unitary recordings of the WDR cells we evaluated the role of 5-hydroxytryptamine (5-HT) effect on the OXT-induced antinociception. All drugs were given intrathecally (i.t.). OXT (1×10-5-1×10-4nmol) or 5-HT (1×10-3-1×10-1nmol) prevented the formalin-induced sensitization, an effect mimicked by PVN stimulation. Moreover, administration of OXT (1×10-5nmol) plus 5-HT (1×10-3nmol) at ineffective doses, produced antinociception. This effect was antagonized by: (i) d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH29]OVT (oxytocin receptor antagonist; 2×10-2nmol); or (ii) methiothepin (a non-specific 5-HT1/2/5/6/7 receptor antagonist; 80nmol). Similar results were obtained with PVN stimulation plus 5-HT (5×10-5nmol). In WDR cell recordings, the PVN-induced antinociception was enhanced by i.t. 5-HT and partly blocked when the spinal cord was pre-treated with methiothepin (80nmol). Taken together, these results suggest that serotonergic mechanisms at the spinal cord level are partly involved in the OXT-induced antinociception.

Discovery of 2-(3,4-dichlorophenoxy)-N-(2-morpholin-4-ylethyl)acetamide: A selective σ1 receptor ligand with antinociceptive effect.

Compound 2-(3,4-dichlorophenoxy)-N-(2-morpholin-4-ylethyl)acetamide (1) was designed, prepared and the in vitro binding evaluation against σ1 and σ2 receptors was measured. Compound 1 showed high σ1 receptor affinity (Ki=42 nM) and it was 36-times more selective for σ1 than σ2 receptor. Also, it was performed a molecular docking of compound 1 into the ligand binding pocket homology model of σ1 receptor, showing a salt bridge between the ionized morpholine ring and Asp126, as well as important short contacts with residues Tyr120, His154 and Trp164. Ligand efficiency indexes and predicted toxicity analysis revealed an excellent intrinsic quality of 1. The antinociceptive effect of compound 1 was determined using the formalin test. The ipsilateral local peripheral (10-300 µg/paw) and intrathecal (100 µg/rat) administration of 1 produced a reduction in formalin-induced nociception. The in vivo results indicated that 1 may be effective in treating inflammatory pain.

Role of spinal 5-HT2 receptors subtypes in formalin-induced long-lasting hypersensitivity.

BACKGROUND: The purpose of this study was to determine the role of spinal 5-HT2A, 5-HT2B and 5-HT2C receptors in the development and maintenance of formalin-induced long-lasting secondary allodynia and hyperalgesia in rats, as well as their expression in the dorsal root ganglia (DRG) during this process. METHODS: 0.5-1% formalin was used to produce long-lasting secondary allodynia and hyperalgesia in rats. Western blot was used to determine 5-HT2 receptors expression in DRG. RESULTS: Formalin (0.5-1%) injection produced long-lasting (1-12 days) secondary allodynia and hyperalgesia in both ipsilateral and contralateral hind paws. Intrathecal pre-treatment or post-treatment with the 5-HT2 receptor agonist, DOI (1-10nmol), increased 0.5% formalin-induced secondary allodynia and hyperalgesia in both paws. In contrast, intrathecal pre-treatment with the selective 5-HT2A (ketanserin 1-100nmol), 5-HT2B (RS 127445 1-100nmol) or 5-HT2C (RS 102221 1-100nmol) receptor antagonists prevented and reversed, respectively, 1% formalin-induced secondary allodynia and hyperalgesia in both paws. Likewise, the pronociceptive effect of DOI (10nmol) was blocked by ketanserin, RS 127445 or RS 102221 (0.01nmol). 5-HT2A/2B/2C receptors were expressed in DRG of naïve rats. Formalin injection (1%) increased bilaterally 5-HT2A/2B receptors expression in DRG. In contrast, formalin injection decreased 5-HT2C receptors expression bilaterally in DRG. CONCLUSION: Data suggest that spinal 5-HT2A/2B/2C receptors have pronociceptive effects and participate in the development and maintenance of formalin-induced long-lasting hypersensitivity. These receptors are expressed in DRG and their expression is modulated by formalin.

Inhibition of peripheral anion exchanger 3 decreases formalin-induced pain.

We determined the role of chloride-bicarbonate anion exchanger 3 in formalin-induced acute and chronic rat nociception. Formalin (1%) produced acute (first phase) and tonic (second phase) nociceptive behaviors (flinching and licking/lifting) followed by long-lasting evoked secondary mechanical allodynia and hyperalgesia in both paws. Local peripheral pre-treatment with the chloride-bicarbonate anion exchanger inhibitors 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid and 4-acetamido-4'-isothiocyanato-2,2'-stilbenedisulfonic acid prevented formalin-induced nociception mainly during phase 2. These drugs also prevented in a dose-dependent fashion long-lasting evoked secondary mechanical allodynia and hyperalgesia in both paws. Furthermore, post-treatment (on day 1 or 6) with 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid reversed established hypersensitivity. Anion exchanger 3 was expressed in dorsal root ganglion neurons and it co-localized with neuronal nuclei protein (NeuN), substance P and purinergic P2X3 receptors. Furthermore, Western blot analysis revealed a band of about 85 kDa indicative of anion exchanger 3 protein expression in dorsal root ganglia of naïve rats, which was enhanced at 1 and 6 days after 1% formalin injection. On the other hand, this rise failed to occur during 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid exposure. These results suggest that anion exchanger 3 is present in dorsal root ganglia and participates in the development and maintenance of short and long-lasting formalin-induced nociception.

Mechanisms underlying the antinociceptive effect of mangiferin in the formalin test.

The purpose of this study was to investigate the possible antinociceptive effect of mangiferin, a glucosylxanthone present in Mangifera indica L., in inflammatory pain. Furthermore, we sought to investigate the possible mechanisms action that contributes to these effects. The ipsilateral local peripheral (1-30 µg/paw), intrathecal (1-30 µg/rat) and oral (1-30 mg/kg) administration of mangiferin produced a dose-dependent reduction in formalin-induced nociception. The antinociceptive effect of this drug was similar to that induced by diclofenac after oral and local peripheral administration. Furthermore, mangiferin was also able to reduce 0.1% capsaicin- and serotonin-induced nociceptive behavior. The local peripheral antinociceptive effect of mangiferin in the formalin test was blocked by naloxone (50 µg/paw), naltrindole (1 µg/paw), 5-guanidinonaltrindole (5-GNTI, 1 µg/paw), N(G)-L-nitro-arginine methyl ester (L-NAME, 100 µg/paw), 1H-(1,2,4)-oxadiazolo [4,2-a]quinoxalin-1-one (ODQ, 50 µg/paw) and glibenclamide (50 µg/paw), but not by methiothepin (30 µg/paw). These results suggest that the antinociceptive effects induced by mangiferin are mediated by the peripheral opioidergic system involving the activation of δ, κ, and probably µ, receptors, but not serotonergic receptors. Data also suggests that mangiferin activates the NO-cyclic GMP-ATP-sensitive K(+) channels pathway in order to produce its local peripheral antinociceptive effect in the formalin test. Mangiferin may prove to be effective in treating inflammatory pain in humans.

Role of 5-HT1B/1D receptors in the reduction of formalin-induced nociception and secondary allodynia/hyperalgesia produced by antimigraine drugs in rats.

AIMS: The present study analyzed the potential antinociceptive effect of the antimigraine drugs sumatriptan, dihydroergotamine or methysergide in rats submitted to the formalin test. Moreover, by using selective antagonists, the role of 5-HT1B/1D serotonergic receptors was investigated in the antinociception induced by these antimigraine drugs. MAIN METHODS: The formalin test was used to assess the nociceptive activity. Overt pain-like behavior (flinching, 1h) and evoked nociception (long-lasting secondary mechanical allodynia and hyperalgesia, 6 days) were determined in the same rat. KEY FINDINGS: Ipsilateral, but not contralateral, pre-treatment (in µg/paw) with sumatriptan (10-300), methysergide (1-30) or dihydroergotamine (1-30) significantly prevented flinching behavior (at 1h) as well as secondary allodynia and hyperalgesia (at day 6) induced by formalin. Interestingly, the antinociceptive (flinching), antiallodynic and antihyperalgesic effects of sumatriptan were completely prevented by peripheral pre-treatment with selective antagonists at the 5-HT1B (SB 224289; 100) or 5-HT1D (BRL 15572; 100) receptors. In contrast, the acute antinociceptive effects of methysergide and dihydroergotamine were partially prevented by SB 224289 and BRL 15572. The antiallodynic and antihyperalgesic effects of both drugs were completely prevented by BRL 15572 and partially prevented by SB 224289. Given alone, SB 224289 or BRL 15572 did not modify per se the long-lasting secondary allodynia and hyperalgesia. SIGNIFICANCE: The above findings suggest that: (i) the antimigraine drugs sumatriptan, methysergide and dihydroergotamine reduce the acute and chronic nociception induced by formalin; and (ii) this antinociceptive effect results from activation of peripheral 5-HT1B/1D serotonergic receptors.

Role of the spinal Na+/H+ exchanger in formalin-induced nociception.

This study assessed the role of the Na(+)/H(+) exchanger (NHE) in the formalin-induced nociception as well as the expression of the NHE isoform 1 (NHE1) in the rat spinal cord by using immunohistochemistry. Rats received a 50µl injection of diluted formalin (0.5%). Nociceptive behavior was quantified as the number of flinches of the injected paw. Intrathecal administration of the partially selective NHE1 inhibitors DMA, EIPA (0.3-30µM/rat) and the selective NHE1 inhibitor zoniporide (0.03-3µM/rat) significantly increased formalin-induced flinching behavior in a dose-dependent manner during both phases of the test. Immunohistochemical analysis of the rat lumbar spinal cord showed that NHE1 was mainly expressed in the lamina I of the dorsal horn of the spinal cord. Double immunofluorescence staining showed co-localization of NHE1 with the peptide-rich sensory nerve fiber markers, substance P and calcitonin gene-related peptide, but not with markers of neuronal cell bodies (NeuN), microglia (OX-42) or astroglia (GFAP). Collectively, these pharmacological and anatomical results suggest that spinal NHE1 plays a role in formalin-induced nociception acting as a protective protein extruding H(+).