NMDA and AMPA receptors are involved in the antidepressant-like activity of tianeptine in the forced swim test in mice

Coadministration of tianeptine alters behavioral parameters and levels of neurotrophins in a chronic model of Maple Syrup Urine disease

Maple Syrup Urine Disease (MSUD) is caused by the deficiency in the activity of the branched-chain α-ketoacid dehydrogenase complex (BCKDC), resulting in the accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine, and their respective branched-chain α-keto acids. Patients with MSUD are at high risk of developing chronic neuropsychiatric disorders; however, the pathophysiology of brain damage in these patients remains unclear. We hypothesize that MSUD can cause depressive symptoms in patients. To test our hypothesis, Wistar rats were submitted to the BCAA and tianeptine (antidepressant) administration for 21 days, starting seven days postnatal. Depression-like symptoms were assessed by testing for anhedonia and forced swimming after treatments. After the last test, the brain structures were dissected for the evaluation of neutrophins. We demonstrate that chronic BCAA administration induced depressive-like behavior, increased BDNF levels, and decreased NGF levels, suggesting a relationship between BCAA toxicity and brain damage, as observed in patients with MSUD. However, the administration of tianeptine was effective in preventing behavioral changes and restoring neurotrophins levels.

Glycine/NMDA Receptor Pathway Mediates the Rapid-onset Antidepressant Effect of Alkaloids From Trichilia Monadelpha

INTRODUCTION

Major depressive disorder is often associated with suicidal tendencies, and this condition accentuates the need for rapid-acting antidepressants. We previously reported that Alkaloids (ALK) from Trichilia monadelpha possess antidepressant action in acute animal models of depression and that this effect is mediated through the monoamine and L-arginine-NO-cGMP pathways. This study investigated the possible rapid-onset antidepressant effect of ALK from T. monadelpha and its connection with the glycine/NMDA receptor pathway.

METHODS

The onset of ALK action from T. monadelpha was evaluated using the Open Space Swim Test (OSST), a chronic model of depression. The modified forced swimming and tail suspension tests were used to assess the effect of the ALK on the glycine/NMDA receptor pathway. The Instutute of Cancer Research (ICR) mice were treated with either ALK (30-300 mg/kg, orally [PO]), imipramine (3-30 mg/kg, PO), fluoxetine (3-30 mg/kg, PO), or saline. To identify the role of glycine/NMDA receptor pathway in the effect of ALK, we pretreated mice with a partial agonist of the glycine/NMDA receptor, D-cycloserine (2.5 mg/kg, intraperitoneally [IP]), and an agonist of glycine/NMDA receptor, D-serine (600 mg/kg, IP), before ALK administration.

RESULTS

ALK reversed immobility in mice after the second day of drug treatment in the OSST. In contrast, there was a delay in the effects induced by fluoxetine and imipramine. ALK also increased mean swimming and climbing scores in mice. ALK was more efficacious than imipramine and fluoxetine in reducing immobility and increasing distance traveled. It is noteworthy that ALK was less potent than fluoxetine and imipramine. D-cycloserine potentiated mobility observed in the ALK- and fluoxetine-treated mice. In contrast, D-serine decreased mobility in the ALK-treated mice.

CONCLUSION

The study results suggest that ALK from T. monadelpha exhibits rapid antidepressant action in mice, and the glycine/NMDA receptor pathway possibly mediates the observed effect.

Pharmacological Screening of Mangifera indica Seeds for Antidepressant-like Action Along with a Mechanistic Study

Depression is emerging as a major global issue. There are several antidepressants available in the market, but their efficacy is usually unpredictable. Therefore, there is a need to find an alternative therapeutic agent with better therapeutic efficacy and availability. In the current investigation, the antidepressant-like action of the aqueous methanolic extract of Mangifera indica seeds (25, 50, and 100 mg/kg) was evaluated by two predictive models like the tail suspension test and forced swimming test along with the determination of the mechanism of action working behind this action. The results of the acute treatment with the extract show a dose-dependent reduction in the duration of immobility in both models. The antidepressant-like action of the extract (100 mg/kg) was blocked by the administration of p-chlorophenyl alanine, α-methyl-p-tyrosine, prazosin, and sulpiride while remaining unaffected with propranolol. In contrast, the administration of d-serine along with the extract (a full agonist of glycine/N-methyl-d-aspartate, NMDA, receptors) diminished the anti-immobility action. The administration of the extract along with nitro-l-arginine-methyl ester synergizes into the anti-immobility action of the extract, and intake of l-arginine remained unable to effect this action, whereas sildenafil blocks the effect. The antidepressant-like action of the extract is probably due to the involvement of serotonergic and adrenergic (mainly α receptors are involved) systems, an NMDA receptor complex, and the nitric oxide pathway.

Tianeptine antagonizes the reduction of PV+ and GAD67 cells number in dorsal hippocampus of socially isolated rats

Adult male rats exposed to chronic social isolation (CSIS) show depressive- and anxiety-like behaviors and reduce the numbers of parvalbumin-positive (PV+) interneurons in the dorsal hippocampus. We aimed to determine whether tianeptine (Tian), administered during the last three weeks of a six-week-social isolation (10 mg/kg/day), may reverse CSIS-induced behavioral changes and antagonize the CSIS-induced reduction in the number of PV+ interneurons. We also studied whether Tian affects the GABA-producing enzyme GAD67+ cells, in Stratum Oriens (SO), Stratum Pyramidale (SP), Stratum Radiatum (SR) and Stratum Lacunosum Moleculare (LM) of CA1-3, as well as in molecular layer-granule cell layer (ML-GCL) and Hilus (H) of the dentate gyrus (DG). CSIS-induced reduction in the number of PV+ cells was layer/subregion-specific with the greatest decrease in SO of CA2. Reduction in the number of PV+ cells was significantly higher than GAD67+ cells, indicating that PV+ cells are the main target following CSIS. Tian reversed CSIS-induced behavior phenotype and antagonized the reduction in the number of PV+ and GAD67+ cells in all subregions. In controls, Tian led to an increase in the number of PV+ and GAD67+ cells in SP of all subregions and PV+ interneurons in ML-GCL of DG, while treatment during CSIS, compared to CSIS alone, resulted with an increase of PV+ interneurons in SO and SP CA1, SP CA2/CA3 and ML-GCL DG with simultaneous increase in GAD67+ cells in all CA1, LM CA2, SO/SR/LM CA3. Data show that Tian offers protection from CSIS via modulation of the dorsal hippocampal GABAergic system.

Tianeptine, an atypical pharmacological approach to depression

The introduction of the first antidepressants in the 50s of the 20th century radically changed the treatment of depression, while providing information on pathophysiological aspects of this disease. New antidepressants drugs (agomelatine, tianeptine, vortioxetine) are providing data that give rise to pathophysiological hypotheses of depression that differ from the classic monoaminergic theory. In this sense, tianeptina, an atypical drug by its mechanism of differential action, contributes to clarify that in depression there is more than monoamines. Thus, tianeptine does not modify the rate of extracellular serotonin, so it does not increase or decrease the reuptake of serotonin. Chronic administration of tianeptine does not alter the density or affinity of more than a hundred classical receptors related to depression. Recently, a weak action of tianeptine on Mu opioid receptors has been described that could explain the release of dopamine in the limbic system and its participation in the modulation of glutamatergic mechanisms. These mechanisms support the hypothesis of the possible mechanism of action of this antidepressant. Tianeptine is an antidepressant, with anxiolytic properties, that can improve somatic symptoms. Tianeptine as a glutamatergic modulator, among other mechanisms, allows us to approach depression from a different point of view than other antidepressants.

Effects of Magnesium Supplementation on Unipolar Depression: A Placebo-Controlled Study and Review of the Importance of Dosing and Magnesium Status in the Therapeutic Response

Animal studies using tests and models have demonstrated that magnesium exerts an antidepressant effect. The literature contains few studies in humans involving attempts to augment antidepressant therapy with magnesium ions. The purpose of our study was to assess the efficacy and safety of antidepressant treatment, in combination with magnesium ions. A total of 37 participants with recurrent depressive disorder who developed a depressive episode were included in this study. As part of this double-blind study, treatment with the antidepressant fluoxetine was accompanied with either magnesium ions (120 mg/day as magnesium aspartate) or placebo. During an 8-week treatment period, each patient was monitored for any clinical abnormalities. Moreover, serum fluoxetine and magnesium levels were measured, and pharmaco-electroencephalography was performed. The fluoxetine + magnesium and fluoxetine + placebo groups showed no significant differences in either Hamilton Depression Rating Scale (HDRS) scores or serum magnesium levels at any stage of treatment. Multivariate statistical analysis of the whole investigated group showed that the following parameters increased the odds of effective treatment: lower baseline HDRS scores, female gender, smoking, and treatment augmentation with magnesium. The parameters that increased the odds of remission were lower baseline HDRS scores, shorter history of disease, the presence of antidepressant-induced changes in the pharmaco-EEG profile at 6 h after treatment, and the fact of receiving treatment augmented with magnesium ions. The limitation of this study is a small sample size.

Pharmacokinetic study of tianeptine and its active metabolite MC5 in rats following different routes of administration using a novel liquid chromatography tandem mass spectrometry analytical method

Tianeptine is an atypical antidepressant with a unique mechanism of action and recently it has been also reported that its major metabolite, compound MC5, possesses pharmacological activity similar to that of the parent drug. The current study aims to investigate the pharmacokinetics (PK) of both tianeptine and MC5 after intravenous or intraperitoneal administration of the parent drug as well as the metabolic ratio of MC5 in rats. To achieve these goals an LC-MS/MS method using the small sample volume for the quantitation of tianeptine and its active metabolite MC5 in rat plasma and liver perfusate has been developed and validated. Following an intravenous administration of tianeptine pharmacokinetic parameters were calculated by non-compartmental analysis. The average tianeptine volume of distribution at steady state was 2.03 L/kg and the systemic clearance equaled 1.84 L/h/kg. The mean elimination half-lives of tianeptine and MC5 metabolite were 1.16 and 7.53 h, respectively. The hepatic clearance of tianeptine determined in the isolated rat liver perfusion studies was similar to the perfusate flow rate despite the low metabolic ratio of MC5. Mass spectrometric analysis of rat bile indicated that tianeptine and MC5 metabolite are eliminated with bile as glucuronide and glutamine conjugates. Bioavailability of tianeptine after its intraperitoneal administration was 69%. The PK model with a metabolite compartment developed in this study for both tianeptine and MC5 metabolite after two routes of administration may facilitate tianeptine dosage selection for the prospective pharmacological experiments.

Antidepressive effects of ginsenoside Rg1 via regulation of HPA and HPG axis

BACKGROUND

Hypothalamic-pituitary-adrenal (HPA) axis hyperactivity is a well-established pathological feature of major depression, accompanied by the persistent increase of glucocorticoid level and the dysfunction of hypothalamic-pituitary-gonadal (HPG) axis. Ginsenoside Rg1 (Rg1) is one of the most active ingredients of Panax ginseng, which has various biological activity.

OBJECTIVE

This study aimed to investigate the antidepressive effects of Rg1 and elucidate its impact on neuroendocrine system.

METHODS

The antidepressive effects of Rg1 were first analysed in mice, and was further identified in the chronic-unpredictable-mild-stress (CUMS) model and the gonadectomized (GDX) model. The effects of Rg1 on depression-like behaviour were analysed by the forced swimming test (FST), tail suspension test (TST), sucrose preference test, and measurement of pentobarbital-induced sleep. The serum corticosterone and testosterone levels were detected by ELISA. The protein levels of glucocorticoid receptor (GR) and androgen receptor (AR) were analysed by western blot and immunohistochemistry analysis.

RESULTS

Rg1 significantly decreased the immobility time of mice in FST and TST. Furthermore, Rg1 alleviated anhedonia and hopelessness, decreased serum corticosterone level, and increased serum testosterone level, and the GR protein level in the PFC and hippocampus of the CUMS-treated rats. Moreover, Rg1 improved sleep disruption, down-regulated the serum corticosterone level, and increased AR protein level in the PFC of the GDX-treated mice.

CONCLUSION

Together, these studies suggest that Rg1 displayed antidepressant activity through the modulation of the HPA and the HPG axis. These findings provide new mechanism involved in the antidepressive effects of Rg1 and propose theoretical clues for clinical therapies.

The effects of desipramine, fluoxetine, or tianeptine on changes in bulbar BDNF levels induced by chronic social instability stress and inflammation

BACKGROUND

Stress is a major predisposing factor in the development of psychiatric disorders and potential source of augmented inflammatory processes in the brain. Increasing body of evidence shows an important role of alterations in the olfactory bulbs (OBs) function in stress-related disorders. The aim of the present study was to investigate the impact of antidepressants on the alterations of brain-derived neurotrophic factor (BDNF) induced by lipopolysaccharide (LPS) in female rats subjected to chronic social instability stress (CSIS).

METHODS

9 weeks old female rats were subjected to CSIS and injected ip once daily with desipramine (10 mg/kg), fluoxetine (5 mg/kg), or tianeptine (10 mg/kg) for 4 weeks. On the last day of the experiment, rats being at the estrus phase of cycle were injected ip with LPS (1 mg/kg) or saline.

RESULTS

The BDNF mRNA and protein levels were evaluated in the olfactory bulbs. and the BDNF protein levels were measured in plasma. A single LPS administration in the stressed rats resulted in significant decrease in the bulbar BDNF mRNA, but not in the protein level. Chronic administration of desipramine, fluoxetine, or tianeptine increased the BDNF mRNA expression and protein levels in the LPS-injected stressed rats. There was no effect of the studied antidepressants on the reduction of the plasma BDNF protein level induced by CSIS and LPS.

CONCLUSIONS

These results suggest that studied antidepressants were effective in inhibiting the impact of LPS on BDNF expression in the stressed rats what may be significant for beneficial action of this drugs.

Influence of the selective antagonist of the NR2B subunit of the NMDA receptor, traxoprodil, on the antidepressant-like activity of desipramine, paroxetine, milnacipran, and bupropion in mice

Pre-clinical and clinical studies indicated that a blockade of the NMDA receptor complex creates new opportunities for the treatment of affective disorders, including depression. The aim of the present study was to assess the influence of traxoprodil (10 mg/kg) on the activity of desipramine (10 mg/kg), paroxetine (0.5 mg/kg), milnacipran (1.25 mg/kg), and bupropion (10 mg/kg), each at sub-therapeutic doses. Moreover, brain levels of traxoprodil and tested agents were determined using HPLC. The obtained results were used to ascertain the nature of occurring interaction between traxoprodil and studied antidepressants. The experiment was carried out on naïve adult male Albino Swiss mice. Traxoprodil and other tested drugs were administered intraperitoneally. The influence of traxoprodil on the activity of selected antidepressants was evaluated in forced swim test (FST). Locomotor activity was estimated to exclude false positive/negative data. To assess the influence of traxoprodil on the concentration of used antidepressants, their levels were determined in murine brains using HPLC. Results indicated that traxoprodil potentiated activity of all antidepressants examined in FST and the observed effects were not due to the increase in locomotor activity. Only in the case of co-administration of traxoprodil and bupropion, increased bupropion concentrations in brain tissue were observed. All tested agents increased the traxoprodil levels in the brain. Administration of a sub-active dose of traxoprodil with antidepressants from different chemical groups, which act via enhancing monoaminergic transduction, caused the antidepressant-like effect in FST in mice. The interactions of traxoprodil with desipramine, paroxetine, milnacipran, and bupropion occur, at least partially, in the pharmacokinetic phase.

Pharmacokinetic/pharmacodynamic considerations for epilepsy - depression comorbidities

INTRODUCTION

Epilepsy may be frequently associated with psychiatric disorders and its co-existence with depression usually results in the reduced quality of life of patients with epilepsy. Also, the efficacy of antiepileptic treatment in depressed patients with epilepsy may be significantly reduced.

AREAS COVERED

Results of experimental studies indicate that antidepressants co-administered with antiepileptic drugs may either increase their anticonvulsant activity, remain neutral or decrease the protective action of antiepileptic drugs in models of seizures. Apart from purely pharmacodynamic interactions, pharmacokinetic mechanisms have been proven to contribute to the final outcome. We report on clinical data regarding the pharmacokinetic interactions of enzyme-inducing antiepileptic drugs with various antidepressants, whose plasma concentration may be significantly reduced. On the other hand, antidepressants (especially selective serotonin reuptake inhibitors) may influence the metabolism of antiepileptics, in many cases resulting in the elevation of plasma concentration of antiepileptic drugs.

EXPERT OPINION

The preclinical data may provide valuable clues on how to combine these two groups of drugs - antidepressant drugs neutral or potentiating the anticonvulsant action of antiepileptics are recommended in this regard. Avoidance of antidepressants clearly decreasing the convulsive threshold or decreasing the anticonvulsant efficacy of antiepileptic drugs (f.e. bupropion or mianserin) in patients with epilepsy is recommended.

Antidepressant-Like Effect of the Leaves of Pseudospondias microcarpa in Mice: Evidence for the Involvement of the Serotoninergic System, NMDA Receptor Complex, and Nitric Oxide Pathway

Depression continues to be a major global health problem. Although antidepressants are used for its treatment, efficacy is often inconsistent. Thus, the search for alternative therapeutic medicines for its treatment is still important. In this study, the antidepressant-like effect of Pseudospondias microcarpa extract (30-300 mg kg(-1), p.o.) was investigated in two predictive models of depression--forced swimming test and tail suspension test in mice. Additionally, the mechanism(s) of action involved were assessed. Acute treatment with the extract dose dependently reduced immobility of mice in both models. The antidepressant-like effect of the extract (100 mg kg(-1), p.o.) was blocked by p-chlorophenylalanine and cyproheptadine but not prazosin, propranolol, or yohimbine. Concomitant administration of D-cycloserine and the extract potentiated the anti-immobility effect. In contrast, D-serine, a full agonist of glycine/NMDA receptors, abolished the effects. Anti-immobility effects of PME were prevented by pretreatment of mice with L-arginine (750 mg kg(-1), i.p.) and sildenafil (5 mg kg(-1), i.p.). On the contrary, pretreatment of mice with L-NAME (30 mg kg(-1), i.p.) or methylene blue (10 mg kg(-1), i.p.) potentiated its effects. The extract produces an antidepressant-like effect in the FST and TST that is dependent on the serotoninergic system, NMDA receptor complex, and the nitric oxide pathway.

The depressogenic-like effect of acute and chronic treatment with dexamethasone and its influence on the activity of antidepressant drugs in the forced swim test in adult mice

There is a close relationship between chronic stress, glucocorticoids and depression. Psychiatric and cognitive symptoms resembling major depression have been observed in patients experiencing elevated glucocorticoid levels, and a high percentage of people suffering from depression have undergone a stressful event/events prior to the onset of this mental disorder. In our study, we investigated whether acute and chronic treatment of dexamethasone induces depression-like behavior in mice and if dexamethasone therapy influences the activity of antidepressant drugs with diverse modes of action. The antidepressant-like effect was assessed by the forced swim test in adult mice. The depressogenic-like activity of dexamethasone turned out to be dose-dependent: only the highest tested dose of the glucocorticoid (i.e., 64μg/kg) given as a single injection increased immobility time, whereas 16μg/kg/day of dexamethasone (but not 4μg/kg/day) administered repeatedly induced a significant alteration in animal behavior. These depressogenic doses of dexamethasone (i.e., 64μg/kg and 16μg/kg/day for an acute and repeated administration, respectively) diminished the antidepressant potential of the therapeutic doses of imipramine (10mg/kg), amitriptyline (10mg/kg), tianeptine (25mg/kg), mianserin (10mg/kg), citalopram (15mg/kg) and moclobemide (25mg/kg). Two main findings of our study should be particularly underlined: (1) both single and repeated administration of dexamethasone evoked a depression-like behavior of mice, (2) both single and repeated administration of dexamethasone were able to modify the activity of the antidepressant agents from various pharmacological groups, which may lead to a considerable reduction in the efficacy of pharmacotherapy prescribed for patients with mood disorders.

The role of NMDA receptors in the pathophysiology and treatment of mood disorders

Mood disorders such as major depressive disorder and bipolar disorder are chronic and recurrent illnesses that cause significant disability and affect approximately 350 million people worldwide. Currently available biogenic amine treatments provide relief for many and yet fail to ameliorate symptoms for others, highlighting the need to diversify the search for new therapeutic strategies. Here we present recent evidence implicating the role of N-methyl-D-aspartate receptor (NMDAR) signaling in the pathophysiology of mood disorders. The possible role of NMDARs in mood disorders has been supported by evidence demonstrating that: (i) both BPD and MDD are characterized by altered levels of central excitatory neurotransmitters; (ii) NMDAR expression, distribution, and function are atypical in patients with mood disorders; (iii) NMDAR modulators show positive therapeutic effects in BPD and MDD patients; and (iv) conventional antidepressants/mood stabilizers can modulate NMDAR function. Taken together, this evidence suggests the NMDAR system holds considerable promise as a therapeutic target for developing next generation drugs that may provide more rapid onset relief of symptoms. Identifying the subcircuits involved in mood and elucidating the role of NMDARs subtypes in specific brain circuits would constitute an important step toward the development of more effective therapies with fewer side effects.

The effects of ifenprodil on the activity of antidepressant drugs in the forced swim test in mice

BACKGROUND

According to reports in the literature, more than 30% of depressive patients fail to achieve remission. Therapy with the conventional antidepressant drugs may induce the serious adverse reactions. Moreover, its benefits may be seen at least 2-4 weeks after the first dose. Therefore, the alternative strategies for prevention and treatment of depression are sought. The main aim of our study was to assess the effects of ifenprodil given at a non-active dose (10mg/kg) on the activity of antidepressant agents from diverse pharmacological groups.

METHODS

The antidepressant-like effect was assessed by the forced swim test in mice.

RESULTS

Ifenprodil potentiated the antidepressant-like effect of imipramine (15mg/kg) and fluoxetine (5mg/kg) while did not reduce the immobility time of animals which simultaneously received reboxetine (2.5mg/kg) or tianeptine (15mg/kg).

CONCLUSION

The concomitant administration of certain commonly prescribed antidepressant drugs that affect the serotonergic neurotransmission (i.e., typical tricyclic antidepressants and selective serotonin reuptake inhibitors) with a negative modulator selectively binding to the GluN1/N2B subunits of the NMDA receptor complex (i.e., ifenprodil) may induce a more pronounced antidepressant-like effect than monotherapy. However, these findings still need to be confirmed in further experiments.

Involvement of NMDA and AMPA receptors in the antidepressant-like activity of antidepressant drugs in the forced swim test

BACKGROUND

The involvement of glutamate system (particularly the NMDA and AMPA receptors) in the mechanism of antidepressant activity was demonstrated in preclinical and clinical studies.

METHODS

In the present study, we investigated the effect of NMDA and AMPA receptors' ligands (agonists and antagonists) on the antidepressant-like activity of escitalopram, milnacipran, imipramine and reboxetine in the forced swim test in mice.

RESULTS

Antidepressant activity (reduction in immobility time) of escitalopram and milnacipran but not of imipramine and reboxetine was antagonized by N-methyl-D-aspartate acid. CGP37849 (antagonist of the NMDA receptor) enhanced the antidepressant activity of all examined antidepressants. On the other hand, CX614 (a potentiator/positive allosteric modulator of the AMPA receptor) enhanced the antidepressant activity of imipramine and reboxetine but not of escitalopram and milnacipran in this test. NBQX (the AMPA receptor antagonist) did not influence the antidepressant activity of all tested agents.

CONCLUSIONS

The data indicate the complex interactions following the activation or blockade of the NMDA and AMPA receptors with antidepressant drugs. The general phenomenon is the enhancing effect of the NMDA receptor antagonism on the antidepressant activity. Moreover, is can be concluded that the activity of antidepressants with a serotonergic mechanism of action can be inhibited by NMDA activation, while antidepressants with a noradrenergic mechanism of action are dependent on AMPA receptor transmission.

Dietary magnesium restriction reduces amygdala-hypothalamic GluN1 receptor complex levels in mice

Reduced daily intake of magnesium (Mg(2+)) is suggested to contribute to depression. Indeed, preclinical studies show dietary magnesium restriction (MgR) elicits enhanced depression-like behaviour establishing a causal relationship. Amongst other mechanisms, Mg(2+) gates the activity of N-methyl-D-asparte (NMDA) receptors; however, it is not known whether reduced dietary Mg(2+) intake can indeed affect brain NMDA receptor complexes. Thus, the aim of the current study was to reveal whether MgR induces changes in brain NMDA receptor subunit composition that would indicate altered NMDA receptor regulation. The results revealed that enhanced depression-like behaviour elicited by MgR was associated with reduced amygdala-hypothalamic protein levels of GluN1-containing NMDA complexes. No change in GluN1 mRNA levels was observed indicating posttranslational changes were induced by dietary Mg(2+) restriction. To reveal possible protein interaction partners, GluN1 immunoprecipitation and proximity ligation assays were carried out revealing the expected GluN1 subunit association with GluN2A, GluN2B, but also novel interactions with GluA1, GluA2 in addition to known downstream signalling proteins. Chronic paroxetine treatment in MgR mice normalized enhanced depression-like behaviour, but did not alter protein levels of GluN1-containing NMDA receptors, indicating targets downstream of the NMDA receptor. Collectively, present data demonstrate that dietary MgR alters brain levels of GluN1-containing NMDA receptor complexes, containing GluN2A, GluN2B, AMPA receptors GluA1, GluA2 and several protein kinases. These data indicate that the modulation of dietary Mg(2+) intake may alter the function and signalling of this receptor complex indicating its involvement in the enhanced depression-like behaviour elicited by MgR.

Effects of ifenprodil on the antidepressant-like activity of NMDA ligands in the forced swim test in mice

Multiple pre-clinical and clinical studies clearly displayed implication of the NMDA receptors in development of depressive disorders since a variety of NMDA receptor antagonists exhibit an antidepressant-like effect. The main aim of our study was to assess the influence of ifenprodil - an allosteric modulator selectively binding at the NR2B subunit on the performance in the forced swim test in mice of various NMDA receptor ligands interacting with distinct components of the NMDA receptor complex. Ifenprodil at a dose of 10mg/kg enhanced the antidepressant-like effect of CGP 37849 (a competitive NMDA receptor antagonist, 0.312mg/kg), L-701,324 (an antagonist at glycine site, 1mg/kg), MK-801 (a non-competitive antagonist, 0.05mg/kg) and d-cycloserine (a partial agonist of a glycine site, 2.5mg/kg) but it did not shorten the immobility time of animals which concurrently received an inorganic modulator of the NMDA receptor complex, such as Zn(2+) (2.5mg/kg) or Mg(2+) (10mg/kg). On the other hand, the antidepressant-like effect of ifenprodil (20mg/kg) was reversed by N-methyl-d-aspartic acid (an agonist at the glutamate site, 75mg/kg) or d-serine (an agonist at the glycine site, 100nmol/mouse). In conclusion, the antidepressant-like potential of ifenprodil given concomitantly with NMDA ligands was either reinforced (in the case of both partial agonist and antagonists, except for magnesium and zinc) or diminished (in the case of conventional full agonists).

Metabotropic glutamate 2/3 receptor antagonists improve behavioral and prefrontal dopaminergic alterations in the chronic corticosterone-induced depression model in mice

Metabotropic glutamate 2/3 (mGlu2/3) receptor antagonists have an antidepressant-like effect, but the exact mechanism still remains unclear. This study examined the effects of mGlu2/3 receptor antagonists in chronic corticosterone-treated mice which could be used as an animal model of depression. In the forced swim test, the mGlu2/3 receptor antagonists MGS0039 (1.0 mg/kg, i.p.) and LY341495 (0.3 mg/kg, i.p) significantly reduced the increased immobility time of mice pretreated with corticosterone (20 mg/kg, s.c.) for 21 days, while desipramine (30 mg/kg, i.p.) and fluoxetine (30 mg/kg, i.p.) did not. The antidepressant-like effect of LY341495 was not blocked by the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor antagonist NBQX (10 mg/kg, i.p.). Systemic administration of LY341495 did not affect basal release of glutamate, dopamine or serotonin in the prefrontal cortex of the control or chronic corticosterone-treated mice. Chronic corticosterone markedly enhanced high K(+)-induced release of dopamine, but not serotonin or glutamate, in the prefrontal cortex. This neurochemical change was blocked by systemic administration of MGS0039 and LY341495, but not desipramine or fluoxetine. These results suggest that chronic corticosterone-treated mice could be used as an animal model of treatment-resistant depression. This study also suggests that the prefrontal dopaminergic system is involved in the antidepressant-like effect of mGlu2/3 receptor antagonists in the chronic corticosterone-induced depression model.