Effect of subacute agomelatine treatment on painful diabetic neuropathy: involvement of catecholaminergic mechanisms

Catecholaminergic and Cholinergic Systems Mediate Beneficial Effect of Vortioxetine on Diabetes-Induced Neuropathic Pain

The therapeutic potential of vortioxetine on mechanical hyperalgesia/allodynia was investigated in rats with streptozotocin-induced diabetes, and its possible mechanism of action was elucidated in this study. The obtained findings demonstrated that subacute vortioxetine treatment (5 and 10 mg/kg for 2 weeks) increased the reduced paw-withdrawal thresholds of diabetic rats both in the Randall-Selitto and Dynamic plantar tests. Moreover, the falling latencies of animals did not change in the Rota-rod assessments. These results suggest that vortioxetine administration significantly improved diabetes-induced hyperalgesia and allodynia responses in the rats without affecting their motor coordination. The vortioxetine (5 mg/kg)-induced antihyperalgesic and antiallodynic effects were reversed by AMPT, yohimbine, ICI 118,551, sulpiride and atropine pre-treatments, suggesting the involvement of the catecholaminergic system, α₂- and β₂-adrenoceptors, D_2/3 dopaminergic receptors and cholinergic muscarinic receptors in the exhibited pharmacological activity, respectively. Moreover, the data from the immunohistochemical studies indicated that the inhibition of c-Fos overexpression in dorsal horn neurons also mediates the beneficial effect of this drug. Vortioxetine induced no difference in plasma glucose levels in diabetic rats. If clinical studies confirm these findings, the concomitant beneficial effect of vortioxetine on mood disorders and its neutral activity profile on glycemic control may make it an alternative drug for the treatment of neuropathic pain.

In Silico Drug Repurposing Framework Predicts Repaglinide, Agomelatine and Protokylol as TRPV1 Modulators with Analgesic Activity

Pain is one of the most common symptoms experienced by patients. The use of current analgesics is limited by low efficacy and important side effects. Transient receptor potential vanilloid-1 (TRPV1) is a non-selective cation channel, activated by capsaicin, heat, low pH or pro-inflammatory agents. Since TRPV1 is a potential target for the development of novel analgesics due to its distribution and function, we aimed to develop an in silico drug repositioning framework to predict potential TRPV1 ligands among approved drugs as candidates for treating various types of pain. Structures of known TRPV1 agonists and antagonists were retrieved from ChEMBL databases and three datasets were established: agonists, antagonists and inactive molecules (pIC50 or pEC50 < 5 M). Structures of candidates for repurposing were retrieved from the DrugBank database. The curated active/inactive datasets were used to build and validate ligand-based predictive models using Bemis−Murcko structural scaffolds, plain ring systems, flexophore similarities and molecular descriptors. Further, molecular docking studies were performed on both active and inactive conformations of the TRPV1 channel to predict the binding affinities of repurposing candidates. Variables obtained from calculated scaffold-based activity scores, molecular descriptors criteria and molecular docking were used to build a multi-class neural network as an integrated machine learning algorithm to predict TRPV1 antagonists and agonists. The proposed predictive model had a higher accuracy for classifying TRPV1 agonists than antagonists, the ROC AUC values being 0.980 for predicting agonists, 0.972 for antagonists and 0.952 for inactive molecules. After screening the approved drugs with the validated algorithm, repaglinide (antidiabetic) and agomelatine (antidepressant) emerged as potential TRPV1 antagonists, and protokylol (bronchodilator) as an agonist. Further studies are required to confirm the predicted activity on TRPV1 and to assess the candidates’ efficacy in alleviating pain.

The effectiveness of pregabalin with or without agomelatine in the treatment of chronic low back pain: a double-blind, placebo-controlled, randomized clinical trial

Background

Although various pharmacological and nonpharmacological treatments are available for the chronic low back pain (CLBP), there is no consensus on the best optimal treatment for this condition. This study aimed to investigate the efficacy of co-administration of pregabalin and agomelatine versus pregabalin with placebo to treat CLBP.

Methods

Forty-six CLBP patients without the surgical indication referred to the outpatient orthopedic clinic of Rasoul-e-Akram Hospital, Tehran, Iran, were randomly divided into two study groups: Group A [pregabalin (75 mg twice per day) + placebo] and Group B [pregabalin (75 mg twice per day) + agomelatine (25 mg per night)]. Patients were evaluated at weeks 0, 4, and 8. Outcome measures were the Persian versions of the Brief Pain Inventory (BPI) interference scale, Roland-Morris Disability Questionnaire (RMDQ), The Hospital Anxiety and Depression Scale (HADS), 36-Item Short Form Survey (SF-36), and General Health Questionnaire-28 (GHQ-28) were used.

Results

At weeks 4 and 8 after the intervention, all evaluated measures showed significant improvement in both study groups (P < 0.01). The mean improvement of GHQ-28 was 3.7 ± 1.22 in group A and 13.1 ± 4.71 in group B. This difference was statistically significant (P = 0.003). Other outcomes did not vary substantially between the two research groups. Agomelatine treatment was well tolerated, with no significant adverse effects seen in patients. Liver tests of all patients were routine during the study period. Major adverse effect was not seen in any patient. The prevalence of Minor side effects was not significantly different between two study groups.

Conclusion

Compared with the pregabalin and placebo, co-administration of pregabalin and agomelatine had no added effect on improving pain scores in CLBP patients. However, the patients’ general health was significantly improved after the combined administration of pregabalin and agomelatine.

Trial registration

The study protocol was registered in the Iranian Registry of Clinical Trials before starting the study (NO.IRCT20200620047852N1, Registration date: 23/06/2020).

Nicotinamide riboside alleviates cisplatin-induced peripheral neuropathy via SIRT2 activation

Background

Chemotherapy-induced peripheral neuropathy represents a major impairment to the quality of life of cancer patients and is one of the most common dose-limiting adverse effects of cancer treatment. Despite its prevalence, no effective treatment or prevention strategy exists. We have previously provided genetic evidence that the NAD⁺-dependent deacetylase, SIRT2, protects against cisplatin-induced peripheral neuronal cell death and neuropathy by enhancing nucleotide excision repair. In this study, we aimed to examine whether pharmacologic activation of SIRT2 would provide effective prevention and treatment of cisplatin-induced peripheral neuropathy (CIPN) without compromising tumor cell cytotoxic response to cisplatin.

Methods

Using von Frey and dynamic hot plate tests, we studied the use of nicotinamide riboside (NR) to prevent and treat CIPN in a mouse model. We also performed cell survival assays to investigate the effect of NAD⁺ supplementation on cisplatin toxicity in neuronal and cancer cells. Lewis lung carcinoma model was utilized to examine the effect of NR treatment on in vivo cisplatin tumor control.

Results

We show that NR, an NAD⁺ precursor and pharmacologic activator of SIRT2, effectively prevents and alleviates CIPN in mice. We present in vitro and in vivo genetic evidence to illustrate the specific dependence on SIRT2 of NR-mediated CIPN mitigation. Importantly, we demonstrate that NAD⁺ mediates SIRT2-dependent neuroprotection without inhibiting cisplatin cytotoxic activity against cancer cells. NAD⁺ may, in fact, further sensitize certain cancer cell types to cisplatin.

Conclusions

Together, our results identify SIRT2-targeted activity of NR as a potential therapy to alleviate CIPN, the debilitating and potentially permanent toxicity.

Gut Microbiome Alteration after Reboxetine Administration in Type-1 Diabetic Rats

Antidepressants are drugs commonly used in clinical settings. However, there are very limited studies on the effects of these drugs on the gut microbiota. Herein, we evaluated the effect of reboxetine (RBX), a selective norepinephrine (noradrenaline) reuptake inhibitor (NRI), on gut microbiota in both diabetic and non-diabetic rats. This is the first report of relation between reboxetine use and the gut microbiota to our knowledge. In this study, type-1 diabetes induced by using streptozotocin (STZ) and RBX was administered to diabetic rats and healthy controls for 14 days. At the end of the treatment, stool samples were collected. Following DNA extraction, amplicon libraries for the V3-V4 region were prepared and sequenced with the Illumina Miseq platform. QIIME was used for preprocessing and analysis of the data. As a result, RBX had a significant effect on gut microbiota structure and composition in diabetic and healthy rats. For example, RBX exposure had a pronounced microbial signature in both groups, with a low Firmicutes/Bacteroidetes ratio and low Lactobacillus levels. While another abundance phylum after exposure to RBX was Proteabacteria, other notable taxa in the diabetic group included Flavobacterium, Desulfovibrionaceae, Helicobacteriaceae, Campylobacterales, and Pasteurellacae when compared to the untreated group.

Agomelatine potentiates anti-nociceptive effects of morphine in a mice model for diabetic neuropathy: involvement of NMDA receptor subtype NR1 within the raphe nucleus and periaqueductal grey

OBJECTIVES

Opioid analgesics have been used for a long time in the treatment of acute and chronic pain. However, they have many side effects including tolerance development to a significant extent. Agomelatine, an atypical antidepressant, has been demonstrated to be effective in experimental studies on pain. However, the effect of agomelatine on morphine tolerance development and its mechanism of action are unknown. The antinociceptive effects of agomelatine, morphine and their combination were assessed in a mice model for painful diabetic neuropathy. The roles of glutamate ionotropic receptor N-methyl-D-aspartate (NMDA) type subunit-1 (GluN1) in raphe nucleus and periaqueductal gray (PAG) in the effect of agomelatine on neuropathic pain were also investigated in diabetic mice.

METHODS

Agomelatine (10 mg/kg), morphine (10 mg/kg) and agomelatine + morphine were administered intraperitoneally for 15 consecutive days (twice per day), and the analgesic responses were assessed at days 1, 3, 6, 9, 12 and 15 in healthy and diabetic mice. Real time polymerase chain reaction (RT-PCR) was used to determine the changes in GluN1 expression.

RESULTS

The tolerance development for morphine was evident, started at 6th day and remained thereafter, but not for agomelatine. GluN1 in raphe nucleus and PAG was upregulated in morphine treated but not in agomelatine-treated groups.

DISCUSSION

The combination of agomelatine with morphine alone causes outlasting analgesic effects of repeated treatment, which can be interpreted as attenuated tolerance. Moreover, we also pointed out for the first time the modulatory effects of agomelatine on GluN1 expression in raphe nucleus and PAG after chronic morphine treatment.

ABBREVIATIONS

Ca²⁺: Calcium; D2DR: Dopamine D2 receptor; GAPDH: Glyceraldehyde-3-phosphate dehydrogenase; GluN1: Glutamate ionotropic receptor N-methyl-D-aspartate type subunit-1; 5-HT: 5-hydroxytryptamine; i.p.: intraperitoneal injection; MPE: Maximal possible effect; MT: Melatonin; NMDA: N-methyl-D-aspartate; NMDAR1: NMDA receptors-1; PAG: Periaqueductal grey; PKCγ: Protein kinase C gamma; RT-PCR: Real time polymerase chain reaction; STZ: Streptozotocin.

SIRT2 protects peripheral neurons from cisplatin-induced injury by enhancing nucleotide excision repair

Platinum-based chemotherapy-induced peripheral neuropathy is one of the most common causes of dose reduction and discontinuation of life-saving chemotherapy in cancer treatment; it often causes permanent impairment of quality of life in cancer patients. The mechanisms that underlie this neuropathy are not defined, and effective treatment and prevention measures are not available. Here, we demonstrate that SIRT2 protected mice against cisplatin-induced peripheral neuropathy (CIPN). SIRT2 accumulated in the nuclei of dorsal root ganglion sensory neurons and prevented neuronal cell death following cisplatin treatment. Mechanistically, SIRT2, an NAD+-dependent deacetylase, protected neurons from cisplatin cytotoxicity by promoting transcription-coupled nucleotide excision repair (TC-NER) of cisplatin-induced DNA cross-links. Consistent with this mechanism, pharmacological inhibition of NER using spironolactone abolished SIRT2-mediated TC-NER activity in differentiated neuronal cells and protection of neurons from cisplatin-induced cytotoxicity and CIPN in mice. Importantly, SIRT2's protective effects were not evident in lung cancer cells in vitro or in tumors in vivo. Taken together, our results identified SIRT2's function in the NER pathway as a key underlying mechanism of preventing CIPN, warranting future investigation of SIRT2 activation-mediated neuroprotection during platinum-based cancer treatment.

Catecholaminergic and opioidergic system mediated effects of reboxetine on diabetic neuropathic pain

RATIONALE

Current data indicate that the noradrenergic system plays a critical role in neuropathic pain treatment. Notably, drugs that directly affect this system may have curative potential in neuropathy-associated pain.

OBJECTIVES

The aim of this study was to evaluate the potential therapeutic efficacy of reboxetine, a potent and selective noradrenaline reuptake inhibitor, on hyperalgesia and allodynia responses in rats with experimental diabetes. Furthermore, mechanistic studies were performed to elucidate the possible mode of actions.

METHODS

Experimental diabetes was induced by a single dose of streptozotocin. Mechanical hyperalgesia, mechanical allodynia, thermal hyperalgesia, and thermal allodynia responses in diabetic rats were evaluated by Randall-Selitto, dynamic plantar, Hargreaves, and warm plate tests, respectively.

RESULTS

Reboxetine treatment (8 and 16 mg/kg for 2 weeks) demonstrated an effect comparable to that of the reference drug, pregabalin, improving the hyperalgesic and allodynic responses secondary to diabetes mellitus. Pretreatment with phentolamine, metoprolol, SR 59230A, and atropine did not alter the abovementioned effects of reboxetine; however, the administration of α-methyl-para-tyrosine methyl ester, propranolol, ICI-118,551, SCH-23390, sulpiride, and naltrindole significantly inhibited these effects. Moreover, reboxetine did not induce a significant difference in the rat plasma glucose levels.

CONCLUSIONS

Our findings indicate that the antihyperalgesic and antiallodynic effects of reboxetine are mediated by the catecholaminergic system; β₂-adrenoceptors; D₁-, D₂/D₃-dopaminergic receptors; and δ-opioid receptors. The results suggest that this analgesic effect of reboxetine, besides its neutral profile on glycemic control, may be advantageous in the pharmacotherapy of diabetic neuropathy-induced pain.

Prevention of paclitaxel-induced neuropathy by formulation approach

Chemotherapy-induced peripheral neuropathy (CIPN) is a major adverse effect of paclitaxel. Several liposome-based products have been approved and demonstrated superior efficacy and safety profiles for other drugs. The first objective of this work was to evaluate the effect of liposome formulation of paclitaxel (L-PTX) on neurotoxicity in-vitro and in-vivo in comparison to the standard Taxol® formulation. The second aim was to investigate the effect of formulation on paclitaxel biodistribution following intravenous administration in an animal model. Free paclitaxel was toxic to cell of neuronal origin (IC50 = 18.4 μg/mL) at a lower concentration than to lung cancer cells (IC50 = 59.1 μg/mL), and L-PTX demonstrated a comparable toxicity in both cell lines (IC50 = 31.8 and 33.7 μg/mL). Administration of L-PTX at 2 mg/kg per dose for a total of 4 doses on day 0, 2, 4, and 6 to rats did not result in increased sensitivity in response to mechanical or thermal stimulation of hind paws, in comparison to Taxol® administration at the same dose level that resulted in neuropathy. Paclitaxel biodisposition was evaluated for two formulations in plasma, liver, lung, brain, spinal cord, skin and muscle of rats after single intravenous dose at 6 mg/kg. The exposure to paclitaxel in brain, spinal cord, muscle, and skin was lower in the L-PTX group compared to Taxol® group. PEGylated liposomes containing paclitaxel were successfully developed and demonstrated reduced neurotoxicity in-vitro in neuronal cells and prevented development of peripheral neuropathy in-vivo. This proof of concept study showed that formulation in nanoparticles is a promising approach for reducing (or preventing) neurotoxicity caused by cancer drugs.

Agomelatine modulates calcium signaling through protein kinase C and phospholipase C-mediated mechanisms in rat sensory neurons

Agomelatine, a novel antidepressant exerting its effects through melatonergic and serotonergic systems, implicated to be effective against pain including neuropathic pain but without any knowledge of mechanism of action. To explore the possible role of agomelatine on nociceptive transmission at the peripheral level, the effects of agomelatine on intracellular calcium ([Ca²⁺ ]_i ) signaling in peripheral neurons were investigated in cultured rat dorsal root ganglion (DRG) neurons. Using the fura-2-based calcium imaging technique, the effects of agomelatine on [Ca²⁺ ]_i and roles of the second messenger-mediated pathways were assessed. Agomelatine caused [Ca²⁺ ]_i signaling in a dose-dependent manner when tested at 10 and 100 μM concentration. Luzindole, a selective melatonin receptor antagonist, almost completely blocked the agomelatine-induced calcium signals. The agomelatine-induced calcium transients were also nearly abolished following pretreatment with the 100 ng/ml pertussis toxin, a Gi/o protein inhibitor. The stimulatory effects of agomelatine on [Ca²⁺ ]_i transients were significantly reduced by applications of phospholipase C (PLC) and protein kinase C (PKC) blockers, 10 μM U73122, and 10 μM chelerythrine chloride, respectively. The obtained results of agomelatine-induced [Ca²⁺ ]_i signals indicates that peripheral mechanisms are involved in analgesic effects of agomelatine. These mechanisms seems to involve G-protein-coupled receptor activation and PLC and PKC mediated mechanisms.

Agomelatine pretreatment prevents development of hyperglycemia and hypoinsulinemia in streptozotocin-induced diabetes in mice

The main objective of this study was to investigate potential effectiveness of agomelatine pretreatment in the prevention of diabetes itself and encephalopathy, with a focus on brain tissue oxidative stress and inflammatory processes in streptozotocin (STZ)-induced diabetic mice. Interleukine-1β (IL-1β) and TACR1 (NK1), which is a tachykinine receptor, were used for the investigation of inflammation in the brain regions including raphe nucleus, periaqueductal gyrus (PAG), amygdala, and nucleus accumbens. The effects of agomelatine on total antioxidant capacity were also evaluated. In the in vitro part of the study, the effects of agomelatine on cell viability were investigated in dorsal root ganglion (DRG) neurons. Fasting blood glucose levels were measured 72 h after STZ injection to determine the diabetic condition. Agomelatine pretreatment prevented both hyperglycemia and hypoinsulinemia in STZ-treated mice. When STZ was injected to induce diabetes in mice, neither hyperglycemia nor hypoinsulinemia was developed in agomelatine pretreated mice and 6 weeks after development of diabetes, agomelatine treatment significantly decreased levels of IL-1β mRNA in raphe nucleus and nucleus accumbens. TACR1 mRNA levels were lower in raphe nucleus, PAG, and amygdala of agomelatine-treated diabetic mice. The increase in total antioxidant capacity after agomelatine administration may responsible for its beneficial effect in the prevention of diabetes. We showed that agomelatine reversed high glucose-induced cell viability decreases in DRG neurons. Both the antihyperglycemic and antioxidant effects of agomelatine might have contributed to the DRG neuron viability improvement. In conclusion, agomelatine seems to both prevent development of diabetes and reverse the encephalopathic changes caused by diabetes.

The Effect of Agomelatine Treatment on Diabetes-Induced Cognitive Impairments in Rats: Concomitant Alterations in the Hippocampal Neuron Numbers

Researches that are related to the central nervous system complications of diabetes have indicated higher incidence of cognitive disorders in patients. Since the variety of nootropic drugs used in clinics is limited and none of them consistently improves the outcomes, new and effective drug alternatives are needed for the treatment of diabetes-induced cognitive disorders. Based on the nootropic potential of agomelatine, the promising efficacy of this drug on cognitive impairments of diabetic rats was investigated in the current study. Experimental diabetes model was induced by streptozotocin. After development of diabetes-related cognitive impairments in rats, agomelatine (40 and 80 mg/kg) was administrated orally for two weeks. Cognitive performance was assessed by Morris water-maze and passive avoidance tests. Then, the total numbers of neurons in both dentate gyrus and Cornu Ammonis (CA) 1–3 subfields of the hippocampus were estimated by the optical fractionator method. Agomelatine treatment induced notable enhancement in the learning and memory performance of diabetic rats. Moreover, it reversed the neuronal loss in the hippocampal subregions of diabetic animals. Obtained results suggest that agomelatine has a significant potential for the treatment of diabetes-induced cognitive impairments. However, therapeutic efficacy of this drug in diabetic patients suffering from cognitive dysfunctions needs to be confirmed by further clinical trials.

Antihyperalgesic Activity of Atomoxetine on Diabetes-Induced Neuropathic Pain: Contribution of Noradrenergic and Dopaminergic Systems

Atomoxetine is a selective noradrenaline reuptake inhibitor drug. Based on the knowledge that agents increasing monoamine levels in the central nervous system have therapeutic potential for neuropathic pain, it is planned to investigate the possible efficacy of atomoxetine on diabetes-induced hyperalgesia, in this study. Randall-Selitto (mechanical noxious stimuli) and Hargreaves (thermal noxious stimuli) tests were used to evaluate nociceptive perception of rats. Obtained data indicated that streptozotocin-induced diabetes causes significant decreases in the paw withdrawal threshold and paw withdrawal latency values of the animals, respectively. However, atomoxetine administered at 3 mg/kg/day for 7 and 14 days improved these diabetes-induced hyperalgesia responses. Furthermore, antihyperalgesic activity was antagonized with α-methyl-para-tyrosine methyl ester, phentolamine, propranolol, and sulpiride pre-treatments. The same effect was not reversed, however, by SCH 23390. These findings demonstrated, for the first time, that atomoxetine possesses significant antihyperalgesic activity on diabetes-induced neuropathic pain and this effect seems to be mediated by α- and β-adrenergic and D₂/D₃ dopaminergic receptors. Results of this present study seem to offer a new indication for an old drug; atomoxetine, but these preclinical data should first be confirmed with further well-designed clinical trials.

α2- and β2-Adrenoreceptor-Mediated Efficacy of the Atypical Antidepressant Agomelatine Combined With Gabapentin to Suppress Allodynia in Neuropathic Rats With Ligated Infraorbital or Sciatic Nerve

Previous data showed that neuropathic pain induced by mechanical lesion of peripheral nerves has specific characteristics and responds differently to alleviating drugs at cephalic versus extracephalic level. This is especially true for tricyclic antidepressants currently used for alleviating neuropathic pain in humans which are less effective against cephalic neuropathic pain. Whether this also applies to the antidepressant agomelatine, with its unique pharmacological properties as MT₁/MT₂ melatonin receptor agonist and 5-HT_2B/5-HT_2C serotonin receptor antagonist, has been investigated in two rat models of neuropathic pain. Acute treatments were performed 2 weeks after unilateral chronic constriction (ligation) injury to the sciatic nerve (CCI-SN) or the infraorbital nerve (CCI-ION), when maximal mechanical allodynia had developed in ipsilateral hindpaw or vibrissal pad, respectively, in Sprague–Dawley male rats. Although agomelatine (45 mg/kg i.p.) alone was inactive, co-treatment with gabapentin, at an essentially ineffective dose (50 mg/kg i.p.) on its own, produced marked anti-allodynic effects, especially in CCI-ION rats. In both CCI-SN and CCI-ION models, suppression of mechanical allodynia by ‘agomelatine + gabapentin’ could be partially mimicked by the combination of 5-HT_2C antagonist (SB 242084) + gabapentin, but not by melatonin or 5-HT_2B antagonist (RS 127445, LY 266097), alone or combined with gabapentin. In contrast, pretreatment by idazoxan, propranolol or the β₂ antagonist ICI 118551 markedly inhibited the anti-allodynic effect of ‘agomelatine + gabapentin’ in both CCI-SN and CCI-ION rats, whereas pretreatment by the MT₁/MT₂ receptor antagonist S22153 was inactive. Altogether these data indicate that ‘agomelatine + gabapentin’ is a potent anti-allodynic combination at both cephalic and extra-cephalic levels, whose action implicates α₂- and β₂-adrenoreceptor-mediated noradrenergic neurotransmission.

Opioid system mediated anti-nociceptive effect of agomelatine in mice

AIMS

This study was planned to examine the antinociceptive efficacy of agomelatine against acute mechanical, thermal, and chemical nociceptive stimuli, as well as to determine the opioid receptor subtypes mediating these effects.

MAIN METHODS

Tail-clip, hot-plate, and acetic acid-induced writhing tests were performed to evaluate anti-nociceptive effect. Besides, possible effect of agomelatine on the motor coordination of animals was assessed with a Rota-rod test.

KEY FINDINGS

Agomelatine (40mg/kg and 60mg/kg) significantly prolonged the reaction time of mice in both the tail-clip and hot-plate tests, suggesting the antinociceptive activity is related to both spinal and supraspinal mechanisms. This drug also reduced the number of writhing behaviors indicating the presence of a peripherally mediated antinociceptive effect. Rota-rod testing displayed no notable effect on the motor activity of the animal supporting the conclusion that the observed antinociceptive effect is specific. The agomelatine-induced antinociceptive activity abrogated following pretreatment with naloxone (a non-selective opioid receptor antagonist, 5.48mg/kg, i.p.), which suggested the participation of opioid mechanisms to the antinociception. The possible contribution of μ, δ and ҡ subtypes of opioid receptors to the anti-nociceptive effect were evaluated using naloxonazine (7mg/kg, s.c.), naltrindole (0.99mg/kg, i.p.), and nor-binaltorphimine (1.03mg/kg, i.p.), respectively. Pretreatments using these antagonists abolished the antinociceptive activity of agomelatine in all of the nociceptive test paradigms used, which pointed out that μ, δ, and ҡ opioid receptors participated to the action of agomelatine on pain.

SIGNIFICANCE

These results demonstrated the therapeutic potential of agomelatine in the treatment of pain disorders.