Depression-related behavior and mechanical allodynia are blocked by 3-(4-fluorophenylselenyl)-2,5-diphenylselenophene in a mouse model of neuropathic pain induced by partial sciatic nerve ligation

Glutathione Peroxidase-like Antioxidant Activity of 1,3-Benzoselenazoles: Synthesis and In Silico Molecular Docking Studies as Pancreatic Lipase Inhibitors

The synthesis of 1,3-benzoselenazoles was achieved by the reaction of corresponding bis[3-amino-N-(p-tolyl)benzamide-2-yl] diselenide, bis[3-amino-N-(4-methoxyphenyl)benzamide-2-yl] diselenide, and bis[3-amino-N-(4-(dimethylamino)phenyl) benzamide-2-yl] diselenide with aryl aldehydes. The 1,3-benzoselenazoles continued to exist as planar molecules due to the presence of secondary Se···O interactions as revealed by the single-crystal X-ray analysis. The presence of secondary Se···O interactions in 1,3-benzoselenazoles was confirmed using natural bond orbital (NBO) and atoms in molecules (AIM) calculations. Nucleus-independent chemical shift (NICS) values suggested the presence of aromatic character in a five-membered benzoselenazole heterocyclic ring. The glutathione peroxidase (GPx)-like antioxidant activity of all 1,3-benzoselenazoles was assessed using a thiophenol assay, exhibiting greater antioxidant activity than Ph2Se2 used as a reference. The most active catalyst carrying a strong electron-donating group (-NMe2) at the ortho-position to the benzoselenazole ring was further investigated at different concentrations of thiophenol, H2O2, and 1,3-benzoselenazoles as catalyst for determining their catalytic parameters. Moreover, the potential applications of all 1,3-benzoselenazoles against pancreatic lipase (PL) have been identified using in silico interactions between the active sites of the 1LPB protein as evaluated using a molecular docking study.

Photoinduced Copper-Catalyzed 1,2-Difunctionalization of 1,3-Dienes with Aryl Diselenides

Described herein is a photoinduced copper-catalyzed 1,2-difunctionalization of 1,3-dienes. The selenium atom radical was generated by the visible light irradiation of diselenides, triggering radical addition with 1,3-dienes to form allyl radical intermediate. Subsequent rapid Z/E isomerization allowed for thermodynamically favorable intermediate formation and enabled copper catalyzed stereoselective functionalization with various nucleophiles.

The potent analgesia of intrathecal 2R, 6R-HNK via TRPA1 inhibition in LF-PENS-induced chronic primary pain model

BACKGROUND

Chronic primary pain (CPP) is an intractable pain of unknown cause with significant emotional distress and/or dysfunction that is a leading factor of disability globally. The lack of a suitable animal model that mimic CPP in humans has frustrated efforts to curb disease progression. 2R, 6R-hydroxynorketamine (2R, 6R-HNK) is the major antidepressant metabolite of ketamine and also exerts antinociceptive action. However, the analgesic mechanism and whether it is effective for CPP are still unknown.

METHODS

Based on nociplastic pain is evoked by long-term potentiation (LTP)-inducible high- or low-frequency electrical stimulation (HFS/LFS), we wanted to develop a novel CPP mouse model with mood and cognitive comorbidities by noninvasive low-frequency percutaneous electrical nerve stimulation (LF-PENS). Single/repeated 2R, 6R-HNK or other drug was intraperitoneally (i.p.) or intrathecally (i.t.) injected into naïve or CPP mice to investigate their analgesic effect in CPP model. A variety of behavioral tests were used to detect the changes in pain, mood and memory. Immunofluorescent staining, western blot, reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR) and calcium imaging of in cultured dorsal root ganglia (DRG) neurons by Fluo-8-AM were used to elucidate the role and mechanisms of 2R, 6R-HNK in vivo or in vitro.

RESULTS

Intrathecal 2R, 6R-HNK, rather than intraperitoneal 2R, 6R-HNK or intrathecal S-Ketamine, successfully mitigated HFS-induced pain. Importantly, intrathecal 2R, 6R-HNK displayed effective relief of bilateral pain hypersensitivity and depressive and cognitive comorbidities in a dose-dependent manner in LF-PENS-induced CPP model. Mechanically, 2R, 6R-HNK markedly attenuated neuronal hyperexcitability and the upregulation of calcitonin gene-related peptide (CGRP), transient receptor potential ankyrin 1 (TRPA1) or vanilloid-1 (TRPV1), and vesicular glutamate transporter-2 (VGLUT2) in peripheral nociceptive pathway. In addition, 2R, 6R-HNK suppressed calcium responses and CGRP overexpression in cultured DRG neurons elicited by the agonists of TRPA1 or/and TRPV1. Strikingly, the inhibitory effects of 2R, 6R-HNK on these pain-related molecules and mechanical allodynia were substantially occluded by TRPA1 antagonist menthol.

CONCLUSIONS

In the newly designed CPP model, our findings highlighted the potential utility of intrathecal 2R, 6R-HNK for preventing and therapeutic modality of CPP. TRPA1-mediated uprgulation of CGRP and neuronal hyperexcitability in nociceptive pathways may undertake both unique characteristics and solving process of CPP.

Brachial plexus avulsion induced changes in gut microbiota promotes pain related anxiety-like behavior in mice

Introduction

Brachial plexus avulsion (BPA) injury develops frequent and intense neuropathic pain, involving in both peripheral and central nervous systems. The incidence of anxiety or depression caused by BPA-induced neuropathic pain is high, but the underlying mechanism remains unclear.

Methods

We established a BPA mice model and assessed its negative emotions through behavioral tests. To further explore the role of the microbiota-gut-brain axis in the unique emotional behavior after BPA, we performed intestinal fecal 16s and metabolomics assays. Psychobiotics (PB) supplementation was administered to BPA mice to check the probiotics effects on BPA-induced anxiety behaviors.

Results

Pain related anxiety-like behavior was observed at the early stage after BPA (7 days), while no depression-like behavior was detected. Intriguingly, gut microbiota diversity was increased in BPA mice, and the most abundant probiotics, Lactobacillus, showed obvious changes. Lactobacillus_reuteri was significantly decreased in BPA mice. Metabolomics analysis showed that Lactobacillus_reuteri-related bile acid pathway and some neurotransmitter amino acids were significantly altered. Further PB (dominated by Lactobacillus_reuteri) supplementation could significantly relieve BPA-induced anxiety-like behaviors in mice.

Conclusion

Our study suggests that pathological neuralgia after BPA could alter intestinal microbiota diversity, especially Lactobacillus, and the changes in neurotransmitter amino acid metabolites may be the key reason for the onset of anxiety-like behaviors in BPA mice.

Paroxetine increases delta opioid responsiveness in sensory neurons

There are currently no Food and Drug Administration (FDA)-approved delta opioid receptor (DOR)-selective agonists, despite having fewer side effects in rodents and non-human primates compared to traditional mu opioid receptor (MOR) therapeutics (Vanderah, 2010). Targeting peripheral receptors is an attractive strategy to reduce abuse potential. However, peripheral opioid receptors do not readily respond to agonists unless primed by inflammation, which would limit their efficacy in non-inflammatory pain patients (Stein et al., 1989). It was recently identified that G protein-coupled receptor kinase 2 (GRK2) maintains DOR incompetence in non-inflamed nociceptors (Brackley et al., 2016; Brackley et al., 2017). Here, we report that paroxetine, a selective serotonin reuptake inhibitor and potent GRK2 inhibitor (Thal et al., 2012), reduces chronic GRK2 association with membrane DOR, thereby enhancing peripheral DOR-mediated analgesic competence in the absence of inflammation. Interestingly, paroxetine's effects on GRK2 in vivo are limited to peripheral tissues in the male rat. The effects of paroxetine on DOR competence are notably antagonized by GRK2 overexpression. This is the first study to suggest that paroxetine induces peripheral DOR analgesic competence through a GRK2-dependent mechanism, improving analgesic efficacy in non-inflamed tissue. Because paroxetine targets the protein that governs peripheral opioid receptor responsiveness, and does so in the absence of inflammation, we propose that paroxetine may be suitable as a co-therapy with peripherally-restrictive doses of opioids to improve analgesic efficacy in non-inflammatory pain conditions.Significance StatementOpioids that target MOR represent the gold-standard for analgesic healthcare, despite widespread abuse potential and the ongoing opioid-epidemic. Work herein uncovers the therapeutic potential of targeting peripheral DOR for analgesic utility with an FDA-approved GRK2 inhibitor paroxetine to boost efficacy and reduce side effect profiles. Analgesic pain management targeting DOR with increased efficacy through adjuvant paroxetine treatment could reduce over-reliance on MOR agonist opioids for pain relief and usher in new options for analgesia.

Treatment with 5-fluoro-2-oxindole Increases the Antinociceptive Effects of Morphine and Inhibits Neuropathic Pain

The efficacy of µ-opioid receptors (MOR) in neuropathic pain is low and with numerous side effects that limited their use. Chronic neuropathic pain is also linked with emotional disorders that aggravate the sensation of pain and which treatment has not been resolved. This study investigates whether the administration of an oxindole, 5-fluoro-2-oxindole, could inhibit the nociceptive and emotional behaviors and increase the effectiveness of morphine via modulating the microglia and activating the nuclear factor erythroid-2 related factor 2 (Nrf2) signaling pathway and MOR expression. In C57BL/6 mice with neuropathic pain provoked by the total constriction of sciatic nerve we studied the effects of 10 mg/kg 5-fluoro-2-oxindole in: (i) the allodynia and hyperalgesia caused by the injury; (ii) the anxiety- and depressive-like behaviors; (iii) the local antinociceptive actions of morphine; (iv) the expression of CD11b/c (a microglial marker), the antioxidant and detoxificant enzymes Nrf2, heme oxygenase 1 (HO-1) and NAD(P)H:quinone oxidoreductase-1 (NQO1), and of MOR in the spinal cord and hippocampus. Results showed that the inhibition of the main nociceptive symptoms and the anxiety- and depressive-like behaviors induced by 5-fluoro-2-oxindole were accompanied with the suppression of microglial activation and the activation of Nrf2/HO-1/NQO1 signaling pathway in the spinal cord and/or hippocampus. This treatment also potentiated the pain-relieving activities of morphine by normalizing the reduced MOR expression. This work demonstrates the antinociceptive, anxiolytic and antidepressant effects of 5-fluoro-2-oxindole, suggests a new strategy to enhance the antinociceptive actions of morphine and proposes a new mechanism of action of oxindoles during chronic neuropathic pain.

Synthesis of 3,4-Bis(Butylselanyl)Selenophenes and 4-Alkoxyselenophenes Promoted by Oxone®

We describe herein an alternative transition-metal-free procedure to access 3,4-bis(butylselanyl)selenophenes and the so far unprecedented 3-(butylselanyl)-4-alkoxyselenophenes. The protocol involves the 5-endo-dig electrophilic cyclization of 1,3-diynes promoted by electrophilic organoselenium species, generated in situ through the oxidative cleavage of the Se-Se bond of dibutyl diselenide using Oxone^® as a green oxidant. The selective formation of the title products was achieved by controlling the solvent identity and the amount of dibutyl diselenide. By using 4.0 equiv of dibutyl diselenide and acetonitrile as solvent at 80 °C, four examples of 3,4-bis(butylselanyl)selenophenes were obtained in moderate to good yields (40–78%). When 3.0 equiv of dibutyl diselenide were used, in the presence of aliphatic alcohols as solvent/nucleophiles under reflux, 10 3-(butylselanyl)-4-alkoxyselenophenes were selectively obtained in low to good yields (15–80%).

Toxicology and pharmacology of synthetic organoselenium compounds: an update

Here, we addressed the pharmacology and toxicology of synthetic organoselenium compounds and some naturally occurring organoselenium amino acids. The use of selenium as a tool in organic synthesis and as a pharmacological agent goes back to the middle of the nineteenth and the beginning of the twentieth centuries. The rediscovery of ebselen and its investigation in clinical trials have motivated the search for new organoselenium molecules with pharmacological properties. Although ebselen and diselenides have some overlapping pharmacological properties, their molecular targets are not identical. However, they have similar anti-inflammatory and antioxidant activities, possibly, via activation of transcription factors, regulating the expression of antioxidant genes. In short, our knowledge about the pharmacological properties of simple organoselenium compounds is still elusive. However, contrary to our early expectations that they could imitate selenoproteins, organoselenium compounds seem to have non-specific modulatory activation of antioxidant pathways and specific inhibitory effects in some thiol-containing proteins. The thiol-oxidizing properties of organoselenium compounds are considered the molecular basis of their chronic toxicity; however, the acute use of organoselenium compounds as inhibitors of specific thiol-containing enzymes can be of therapeutic significance. In summary, the outcomes of the clinical trials of ebselen as a mimetic of lithium or as an inhibitor of SARS-CoV-2 proteases will be important to the field of organoselenium synthesis. The development of computational techniques that could predict rational modifications in the structure of organoselenium compounds to increase their specificity is required to construct a library of thiol-modifying agents with selectivity toward specific target proteins.

Synthesis of benzo[b]chalcogenophenes fused to selenophenes via intramolecular electrophilic cyclization of 1,3-diynes

We describe herein an alternative and transition-metal-free procedure for the access of benzo[b]chalcogenophenes fused to selenophenes via intramolecular cyclization of 1,3-diynes. This efficient protocol involves a double cyclization of 1,3-diynyl chalcogen derivatives promoted by the electrophilic species of organoselenium generated in situ by the oxidative cleavage of the Se-Se bond of dibutyl diselenide using Oxone® in acetonitrile as solvent in an open-flask at 80 °C. In this study, 15 selenophenes with broad substrate scope were prepared in moderate to excellent yields (55-98%) with short reaction times (0.5-3.0 h).

Recent Advances in the Synthesis of Selenophenes and Their Derivatives

The selenophene derivatives are an important class of selenium-based heterocyclics. These compounds play an important role in prospecting new drugs, as well as in the development of new light-emitting materials. During the last years, several methods have been emerging to access the selenophene scaffold, employing a diversity of cyclization-based synthetic strategies, involving specific reaction partners and particularities. This review presents a comprehensive discussion on the recent advances in the synthesis of selenophene-based compounds, starting from different precursors, highlighting the main differences, the advantages, and limitations among them.

Preclinical Considerations about Affective Disorders and Pain: A Broadly Intertwined, yet Often Under-Explored, Relationship Having Major Clinical Implications

Background: Pain, a distinctive undesirable experience, encompasses several different and fluctuating presentations across varying mood disorders. Therefore, the present narrative review aimed to shed further light on the matter, accounting for both experimental animal models and clinical observations about major depressive disorder (MDD) pathology. Method: Major databases were inquired from inception until April 2016 for records about MDD and pain. Results: Pain and MDD are tightly associated with each other in a bi-directional fashion. Several cross-sectional and retrospective studies indicated a high presence of pain in the context of mood disorders, including MDD (up to 65%), but also increased prevalence rates in the case of mood disorders documented among people with a primary diagnosis of either psychological or somatic pain (prevalence rates exceeding 45%). The clinical implications of these observations suggest the need to account for mood and pain manifestations as a whole rather than distinct entities in order to deliver more effective interventions. Limitations: Narrative review, lack of systematic control groups (e.g., people with the primary diagnosis at review, but not the associated comorbidity as a study) to allow reliable comparisons. Prevalence rates and clinical features associated with pain varied across different studies as corresponding operational definitions did. Conclusions: Pain may have a detrimental effect on the course of mood disorders-the opposite holds. Promoting a timely recognition and management of such an often neglected comorbidity would therefore represent a primary goal toward the delivery of effective, multi-disciplinary care.

Behavioral Effects of Continuously Administered Bergamot Essential Oil on Mice With Partial Sciatic Nerve Ligation

Neuropathic pain is an intractable chronic pain condition that is mainly caused by allodynia. We had previously reported that intra-plantar administration of bergamot essential oil (BEO) containing an aromatic compound significantly suppressed partial sciatic nerve ligation (PSNL)-induced mechanical allodynia via opioid mu receptors in mice. However, it has also been reported that the inhalation of BEO reduced formalin-induced nociceptive responses. Therefore, we aimed to elucidate whether the analgesic action of BEO is mediated by olfactory stimulation through volatile components. In the current study, BEO was continuously administered with an osmotic pump during PSNL surgery, and the effects on mice behavior were examined pharmacologically using a double activity monitoring system, which can detect two-dimensional planar motion in a cage with an infrared beam sensor as well as active motion with a running wheel. Here, we report that the two-dimensional planar activity significantly increased in mice with PSNL in the light phase (from 8 o’clock to 20 o’clock) but not in the dark phase (from 20 o’clock to 8 o’clock) from the second day after surgery. However, this increase was not observed when BEO was continuously administered. The effect of BEO on the two-dimensional planar counts in mice with PSNL was antagonized by naloxone hydrochloride. Regarding the running wheel activity, the number of rotations decreased by PSNL in the dark phase from the 8th day after surgery. However, this was not apparent with BEO use. The effect of BEO on the number of rotations was also antagonized by naloxone hydrochloride. Furthermore, inhalation of BEO in PSNL mice did not affect mechanical allodynia or the two-dimensional planar motion or running wheel activities. These findings indicate that BEO exhibits an analgesic action, which is mediated by opioid receptors and not by the olfactory system.

Persistent pain induces mood problems and memory loss by the involvement of cytokines, growth factors, and supraspinal glial cells

Lesions of peripheral nerves lead to pain, hyperalgesia, and psychological comorbidities. However, the relationship between mood disorders and neuropathic pain is unclear, as well as the underlying mechanisms related to these disorders. Therefore, we investigated if nerve injury induces depression, anxiety, and cognitive impairment and if there were changes in cytokines, growth factors, and glial cell activation in cortical sites involved in processing pain and mood in animals with nerve injury. Nerve injury was induced by partial sciatic nerve ligation (PSNL) in male Swiss mice and compared to sham-operated animals. Nociceptive behavioral tests to mechanical and thermal (heat and cold) stimuli confirmed the development of hyperalgesia. We further examined mood disorders and memory behaviors. We show nerve injury induces a decrease in mechanical withdrawal thresholds and thermal latency to heat and cold. We also show that nerve injury causes depressive-like and anxiety-like behaviors as well as impairment in short-term memory in mice. There were increases in proinflammatory cytokines as well as Brain-Derived Neurotrophic Factor (BDNF) in the injured nerve. In the spinal cord, there were increases in both pro and anti-inflammatory cytokines, as well as of BDNF and Nerve Growth Factor (NGF). Further, in our data was a decrease in the density of microglia and astrocytes in the hippocampus and increased microglial density in the prefrontal cortex, areas associated with neuropathic pain conditions.

Treatment with slow-releasing hydrogen sulfide donors inhibits the nociceptive and depressive-like behaviours accompanying chronic neuropathic pain: Endogenous antioxidant system activation

BACKGROUND

Therapies to treat chronic neuropathic pain and its associated comorbidities are limited. Recent studies demonstrated that the administration of slow-releasing hydrogen sulfide (H₂S) donors inhibited chemotherapy-induced neuropathic pain. However, the antidepressant or anxiolytic effects of these compounds and their mechanisms of action during chronic neuropathic pain have not been evaluated.

AIMS

To determine whether the administration of two slow-releasing H₂S donors, allyl isothiocyanate (A-ITC) and phenyl isothiocyanate (P-ITC), inhibits the nociceptive and emotional disorders associated with chronic neuropathic pain.

METHODS

In C57BL/6 male mice with neuropathic pain caused by the chronic constriction of the sciatic nerve, we assessed the effects of intraperitoneal administration of A-ITC and P-ITC in (a) the mechanical allodynia, thermal hyperalgesia and thermal allodynia induced by nerve ligation; (b) the anxiety- and depressive-like behaviours linked with neuropathic pain; (c) glial activation and mitogen-activated protein kinases phosphorylation, and (d) expression of the antioxidant enzymes, heme oxygenase 1 (HO-1), NADPH quinone oxidoreductase1, and glutathione S-transferase mu-1 (GSTM1), and alpha-1 (GSTA1), in hippocampus and prefrontal cortex (PFC).

RESULTS

Both treatments inhibited the allodynia and hyperalgesia, depressive-like behaviours, astroglial activation, and the extracellular signal-regulated kinase 1/2 phosphorylation but were unable to abolish the anxiety-like behaviours accompanying neuropathic pain. A-ITC and P-ITC also augmented the expression of HO-1, GSTM1, and GSTA1 in the hippocampus and/or PFC.

CONCLUSIONS

The administration of slow-releasing H₂S donors might be a promising treatment for the management of chronic neuropathic pain and some associated comorbidities via inhibiting the inflammatory and plasticity changes, and activating the endogenous antioxidant responses.

Sexual dimorphism in cognitive disorders in a murine model of neuropathic pain

BACKGROUND

A sex-difference in susceptibility to chronic pain is well-known. Although recent studies have begun to reveal the sex-dependent mechanisms of nerve injury-induced pain sensitization, sex differences in the affective and cognitive brain dysfunctions associated with chronic pain have not been investigated. Therefore, we tested whether chronic pain leads to affective and cognitive disorders in a mouse neuropathic pain model and whether those disorders are sexually dimorphic.

METHODS

Chronic neuropathic pain was induced in male and female mice by L5 spinal nerve transection (SNT) injury. Pain sensitivity was measured with the von Frey test. Affective behaviors such as depression and anxiety were assessed by the forced swim, tail suspension, and open field tests. Cognitive brain function was assessed with the Morris water maze and the novel object location and novel object recognition tests.

RESULTS

Mechanical allodynia was induced and maintained for up to 8 weeks after SNT in both male and female mice. Depressive- and anxiety-like behaviors were observed 8 weeks post-SNT injury regardless of sex. Chronic pain-induced cognitive deficits measured with the Morris water maze and novel object location test were seen only in male mice, not in female mice.

CONCLUSIONS

Chronic neuropathic pain is accompanied by anxiety- and depressive-like behaviors in a mouse model regardless of sex, and male mice are more vulnerable than female mice to chronic pain-associated cognitive deficits.

The molecular neurobiology of chronic pain-induced depression

The increasing number of individuals with comorbidities poses an urgent need to improve the management of patients with multiple co-existing diseases. Among these comorbidities, chronic pain and mood disorders, two long-lasting disabling conditions that significantly reduce the quality of life, could be cited first. The recent development of animal models accelerated the studies focusing on the underlying mechanisms of the chronic pain and depression/anxiety comorbidity. This review provides an overview of clinical and pre-clinical studies performed over the past two decades addressing the molecular aspects of the comorbid relationship of chronic pain and depression. We thus focused on the studies that investigated the molecular characteristics of the comorbid relationship between chronic pain and mood disorders, especially major depressive disorders, from the genetic and epigenetic point of view to key neuromodulators which have been shown to play an important role in this comorbidity.

Copper-Catalyzed Decarboxylative/Click Cascade Reaction: Regioselective Assembly of 5-Selenotriazole Anticancer Agents

A simple and efficient Cu-catalyzed decarboxylative/click reaction for the preparation of 1,4-disubstituted 5-arylselanyl-1,2,3-triazoles from propiolic acids, diselenides, and azides has been developed. The mechanistic study revealed that the intermolecular AAC reaction of an alkynyl selenium intermediate occurred. The resulting multisubstituted 5-seleno-1,2,3-triazoles were tested for in vitro anticancer activity by MTT assay, and compounds 4f, 4h, and 4p showed potent cancer cell-growth inhibition activities.

Opioid system contribution to the antidepressant-like action of m-trifluoromethyl-diphenyl diselenide in mice: A compound devoid of tolerance and withdrawal syndrome

Animal and clinical researches indicate that the opioid system exerts a crucial role in the etiology of mood disorders and is a target for intervention in depression treatment. This study investigated the contribution of the opioid system to the antidepressant-like action of acute or repeated m-trifluoromethyl-diphenyl diselenide administration to Swiss mice. m-Trifluoromethyl-diphenyl diselenide (50 mg/kg, intragastric) produced an antidepressant-like action in the forced swimming test from 30 min to 24 h after treatment. This effect was blocked by the µ and δ-opioid receptor antagonists, naloxonazine (10 mg/kg, intraperitoneally) and naltrindole (3 mg/kg, intraperitoneally), and it was potentiated by a κ-opioid receptor antagonist, norbinaltrophimine (1 mg/kg, subcutaneously ). Combined treatment with subeffective doses of m-trifluoromethyl-diphenyl diselenide (10 mg/kg, intragastric) and morphine (1 mg/kg, subcutaneously) resulted in a synergistic antidepressant-like effect. The opioid system contribution to the m-trifluoromethyl-diphenyl diselenide antidepressant-like action was also demonstrated in the modified tail suspension test, decreasing mouse immobility and swinging time and increasing curling time, results similar to those observed using morphine, a positive control. Treatment with m-trifluoromethyl-diphenyl diselenide induced neither tolerance to the antidepressant-like action nor physical signs of withdrawal, which could be associated with the fact that m-trifluoromethyl-diphenyl diselenide did not change the mouse cortical and hippocampal glutamate uptake and release. m-Trifluoromethyl-diphenyl diselenide treatments altered neither locomotor nor toxicological parameters in mice. These findings demonstrate that m-trifluoromethyl-diphenyl diselenide elicited an antidepressant-like action by direct or indirect μ and δ-opioid receptor activation and the κ-opioid receptor blockade, without inducing tolerance, physical signs of withdrawal and toxicity.

p,p'-Methoxyl-diphenyl diselenide elicits an antidepressant-like effect in mice without discontinuation anxiety phenotype

Major depressive disorder is the most severe and debilitating disease among psychiatric illnesses. The abrupt interruption of antidepressant treatment may lead to a complex physiological and neuropsychiatric syndrome. The organoselenium compound (MeOPhSe)₂ has been reported to have neuroprotective properties in animal models. The study aimed to investigate the effects of single or repeated administration of (MeOPhSe)₂ on depressive-like behavior and if the compound administration, and its discontinuation, may affect the anxiolytic-like phenotype in Swiss mice. The results showed that repeated intragastric administration of (MeOPhSe)₂ (dose range: 0.1-5mg/kg), different from a single administration, reduced the immobility time in the mouse tail suspension test. A single administration of (MeOPhSe)₂ at a dose of 5mg/kg decreased the immobility time, increased the swimming time and did not alter the climbing behavior in the modified forced swimming test (mFST). Repeated administration of (MeOPhSe)₂ decreased the immobility time, did not alter the swimming time and increased the climbing behavior in the mouse mFST. Repeated administration of (MeOPhSe)₂ at a dose of 5mg/kg elicited a mouse anxiolytic-like phenotype in the elevated plus maze and light-dark tests. Markers of hepatic and renal function tests were not altered by repeated administration of (MeOPhSe)₂ to mice. The findings indicate that a single or repeated administration of (MeOPhSe)₂ elicited an antidepressant-like action in mice. Moreover, repeated treatment with (MeOPhSe)₂ produced an anxiolytic-like action in mice and its profile remained stable after discontinuation.

Selective inhibition of MAO-A activity results in an antidepressant-like action of 2-benzoyl 4-iodoselenophene in mice

Depression is a leading cause of disability worldwide. For this reason, the aim of this study was to investigate the possible antidepressant-like activity of 2-benzoyl-4-iodoselenophene (C₁₇H₁₁IOSe), a selenophene compound, in two well-consolidated behavioral assays for screening antidepressant activity (forced swimming test and tail suspension test) in mice. In order to investigate the mechanism of action of C₁₇H₁₁IOSe, it was investigated the activities of cerebral enzymes: monoamine oxidase MAO A and B and Na⁺, K⁺ ATPase, and if an inhibitor of serotonin synthesis, p-chlorophenylalanine (pCPA) (100mg/kg) blocks the antidepressant-like effect of C₁₇H₁₁IOSe. Swiss mice received (C₁₇H₁₁IOSe) (5-50mg/kg) or canola oil by the intragastric (i.g.) route before behavioral tests. The results showed that C₁₇H₁₁IOSe at dose range of 5-50mg/kg decreased immobility time in the tail suspension test. In the forced swimming test, C₁₇H₁₁IOSe reduced the immobility time at the doses of 10 and 50mg/kg. C₁₇H₁₁IOSe differently affected the cerebral cortical Na⁺, K⁺ ATPase; the effects on this enzyme were dependent of the dose tested. At a dose of 10mg/kg, the compound increased Na⁺, K⁺ ATPase activity, while the activity was inhibited at a dose of 50mg/kg. pCPA blocked the antidepressant-like action of C₁₇H₁₁IOSe in mice. Therefore, C₁₇H₁₁IOSe (5-50mg/kg) selectively inhibited MAO-A activity in cerebral cortices of mice. The modulation of serotonergic system contributed to the antidepressant-like action of C₁₇H₁₁IOSe in mice.

Plant Natural Product Puerarin Ameliorates Depressive Behaviors and Chronic Pain in Mice with Spared Nerve Injury (SNI)

Simultaneous relief of the pain from body and brain remains an ongoing challenge. The aim of the present study was to clarify whether plant-derived isoflavone puerarin could ameliorate comorbid depression and pain. We investigated the effects of puerarin on depressive-like behaviors and neuropathic pain in C57BL/6 N mice with spared nerve injury (SNI). After SNI surgery, mice were allowed to recover spontaneously for 7 days and subsequently treated with puerarin, anti-depressant citalopram, and analgesic ibuprofen, alone or in combination, for 8 or 14 days. Forced swim test and tail suspension test were used to assess depressive-like behaviors, whereas von Frey filament test was used to estimate the sensitivity to the mechanical stimulation. Our results suggested that puerarin effectively ameliorated depression and pain in SNI mice although citalopram exhibited anti-depressant activity. In contrast, ibuprofen showed lesser activities against SNI-induced depression and pain. Further mechanistic studies revealed the uniqueness of puerarin as follows: (1) puerarin did not recover SNI-induced depletion of reduced glutathione and loss of superoxide dismutase (SOD), whereas citalopram and ibuprofen showed somewhat antioxidant activities; (2) puerarin markedly promoted the activation of CREB pathway although puerarin and citalopram activated ERK pathway to the same extent; (3) puerarin rapidly and persistently induced brain-derived neurotrophic factor (BDNF) expression whereas citalopram only induced BDNF expression after a prolonged stimulation. Collectively, these results suggest that puerarin may ameliorate the SNI-induced depression and pain via activating ERK, CREB, and BDNF pathways. Puerarin may serve as new lead compound for the development of novel therapeutics for depression and pain comorbidity.

High Times for Painful Blues: The Endocannabinoid System in Pain-Depression Comorbidity

Depression and pain are two of the most debilitating disorders worldwide and have an estimated cooccurrence of up to 80%. Comorbidity of these disorders is more difficult to treat, associated with significant disability and impaired health-related quality of life than either condition alone, resulting in enormous social and economic cost. Several neural substrates have been identified as potential mediators in the association between depression and pain, including neuroanatomical reorganization, monoamine and neurotrophin depletion, dysregulation of the hypothalamo-pituitary-adrenal axis, and neuroinflammation. However, the past decade has seen mounting evidence supporting a role for the endogenous cannabinoid (endocannabinoid) system in affective and nociceptive processing, and thus, alterations in this system may play a key role in reciprocal interactions between depression and pain. This review will provide an overview of the preclinical evidence supporting an interaction between depression and pain and the evidence supporting a role for the endocannabinoid system in this interaction.

Enhanced serotonin and mesolimbic dopamine transmissions in a rat model of neuropathic pain

In humans, affective consequences of neuropathic pain, ranging from depression to anxiety and anhedonia, severely impair quality of life and are a major disease burden, often requiring specific medications. Depressive- and anxiety-like behaviors have also been observed in animal models of peripheral nerve injury. Dysfunctions in central nervous system monoamine transmission have been hypothesized to underlie depressive and anxiety disorders in neuropathic pain. To assess whether these neurons display early changes in their activity that in the long-term might lead to chronicization, maladaptive plasticity and affective consequences, we carried out in vivo extracellular single unit recordings from serotonin neurons in the dorsal raphe nucleus (DRN) and from dopamine neurons in ventral tegmental area (VTA) in the spared nerve injury (SNI) model of neuropathic pain in rats. Extracellular dopamine levels and the expression of dopamine D1, D2 receptors and tyrosine hydroxylase (TH) were measured in the nucleus accumbens. We report that, two weeks following peripheral nerve injury, discharge rate of serotonin DRN neurons and burst firing of VTA dopamine cells are enhanced, when compared with sham-operated animals. We also observed higher extracellular dopamine levels and reduced expression of D2, but not D1, receptors and TH in the nucleus accumbens. Our study confirms that peripheral neuropathy induces changes in the serotonin and dopamine systems that might be the early result of chronic maladaptation to persistent pain. The allostatic activation of these neural systems, which mirrors that already described as a consequence of stress, might lead to depression and anxiety previously observed in neuropathic animals but also an attempt to cope positively with the negative experience.

Differential roles of hippocampal glutamatergic receptors in neuropathic anxiety-like behavior after partial sciatic nerve ligation in rats

BACKGROUND

Neuropathic pain evoked by nerve injury is frequently accompanied by deterioration of emotional behaviors, but the underlying signaling mechanisms remain elusive. Glutamate (Glu) is the major mediator of excitatory synaptic transmission throughout the brain, and abnormal activity of the glutamatergic system has been implicated in the pathophysiology of pain and associated emotional comorbidities. In this study we used the partial sciatic nerve ligation (PSNL) model of neuropathic pain in rats to characterize the development of anxiety-like behavior, the expression of glutamatergic receptors, and the phosphorylation of extracellular signal-regulated kinase (ERK) in the hippocampus, the region that encodes memories related to emotions.

RESULTS

We found that the mechanical withdrawal threshold was significantly reduced and an anxiety-like behavior was increased as determined via open field tests and elevated plus-maze tests at 28 days after injury. No significant differences were found in the ratio of sucrose preference and immobility time detected by sucrose preference tests and forced swimming tests respectively, possibly due to the timing factor. The expression of N-methyl-D-aspartate (NMDA) receptor subtypes NR1 and NR2B, but not NR2A, GluR1, or GluR2 (the main subtype of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA] receptor) in the hippocampus of injured rats was significantly reduced. Moreover, PSNL resulted in decreased phosphorylation of ERK1/2 in the hippocampus. Intriguingly, treatment with D-serine (a co-agonist of NMDA receptor, 1 g/kg intraperitoneally) reduced the anxiety-like behavior but not the mechanical hypersensitivity induced by PSNL.

CONCLUSIONS

PSNL can induce significant anxiety-like but not depression-like behavior, and trigger down-regulation of NMDA but not AMPA receptors in the hippocampus at 28 days after injury.

ERK1/2 phosphorylation is involved in the antidepressant-like action of 2,5-diphenyl-3-(4-fluorophenylseleno)-selenophene in mice

We investigated the antidepressant-like action of 5 compounds belonging to the selenophene class. The involvement of ERK and CREB activation in this action was also demonstrated. In the experiment 1, time-course and dose-response effect of H-DPS, CH3-DPS, Cl-DPS, F-DPS and CF3-DPS were accompanied in the mouse forced swimming test (FST). Firstly, animals received compounds at a dose of 50mg/kg, by intragastric (i.g.) route, at different times (15-240 min) before test. Results showed that the peak of maximum anti-despair behavior induced by Cl-DPS, F-DPS and CF3-DPS was at 30 min; maximum effect of H-DPS and CH3-DPS was found at 60 min, which was maintained until 120 min. Regarding dose-response effect, all compounds reduced immobility time and increased latency for the first episode of immobility at a dose of 50mg/kg. In addition, F-DPS also showed antidepressant-like action at a dose of 25mg/kg, whilst H-DPS, CH3-DPS, Cl-DPS and CF3-DPS were not effective at lower doses. Thus, F-DPS was chosen for further investigation of its mechanism of action. Experiment 2 showed that treatment of animals with F-DPS (50 mg/kg, i.g.) significantly increased phosphorylated ERK1/2 levels in the prefrontal cortex and hippocampus; however, pCREB levels were not affected. Additionally, in the experiment 3 anti-immobility effect of F-DPS was completely blocked by pretreatment of animals with PD 98,059, an inhibitor of ERK phosphorylation, suggesting that ERK signalling activation is involved in its antidepressant-like action in mice. Together our data appoint F-DPS as a promising molecule for the development of a new antidepressant therapy.

Pain and depression comorbidity: a preclinical perspective

Pain and depression are two highly prevalent and deleterious disorders with significant socioeconomic impact to society. Clinical observations have long recognized the co-existence and interactions of pain and depression. However, the underlying mechanisms of pain-depression comorbidity and their dynamic interactions remain largely unknown. Preclinical animal studies may provide critical information for the understanding of this important comorbidity. This review analyzed the current preclinical evidence of interactions between pain and depression, which generally supports the causative relationship of the two conditions. In addition, the analysis proposed to apply domain interplay concept in future model development of pain-depression comorbidity and mechanism studies. The application of spectrum-centered animal models will better the understanding of pain-depression dyad and foster the development of more effective therapeutic strategies.