Roles of glutamate signaling in preclinical and/or mechanistic models of depression

Arketamine for cognitive impairment in psychiatric disorders

Cognitive impairment has been observed in patients with various psychiatric disorders, including schizophrenia, major depressive disorder (MDD), and bipolar disorder (BD). Although modern therapeutic drugs can improve certain symptoms (i.e., psychosis, depression) in these patients, these drugs have not been found to improve cognitive impairment. The N-methyl-D-aspartate receptor antagonist (R,S)-ketamine has attracted attention as a rapidly acting antidepressant. In addition to its robust antidepressant effects, (R,S)-ketamine has been suggested to improve cognitive impairment in patients with MDD and BD, despite causing cognitive impairment in healthy control subjects. (R,S)-ketamine is a racemic mixture of equal amounts of (R)-ketamine (or arketamine) and (S)-ketamine (or esketamine). Arketamine has been found to have more potent antidepressant-like actions than esketamine in rodents. Interestingly, arketamine, but not esketamine, has been suggested to improve phencyclidine-induced cognitive deficits in mice. Furthermore, arketamine has been suggested to ameliorate cognitive deficits in rodent offspring after maternal immune activation. In the current article, it is proposed that arketamine has therapeutic potential for treating cognitive impairment in patients with psychiatric disorders. Additionally, the potential role of the gut-microbiome-brain axis in cognitive impairment in psychiatric disorders is discussed.

Traxoprodil Produces Antidepressant-Like Behaviors in Chronic Unpredictable Mild Stress Mice through BDNF/ERK/CREB and AKT/FOXO/Bim Signaling Pathway

Traxoprodil is a selective N-methyl-d-aspartate receptor subunit 2B (NR2B) receptor inhibitor with rapid and long-lasting antidepressant effects. However, the appropriate dosage, duration of administration, and underlying mechanism of traxoprodil's antidepressant effects remain unclear. The purpose of this study is to compare the antidepressant effects of traxoprodil in different doses and different durations of administration and to explore whether traxoprodil exerts antidepressant effects via the brain-derived neurotrophic factor/extracellular signal-regulated kinase/cAMP-response element binding protein (BDNF/ERK/CREB) and protein kinase B/Forkhead box O/building information modelling (AKT/FOXO/Bim) signaling pathway. Mice were randomly divided into control group, chronic unpredictable mild stress (CUMS) + vehicle group, CUMS + traxoprodil (10 mg/kg, 20 mg/kg, and 40 mg/kg) groups, and CUMS + fluoxetine (5 mg/kg) group, followed by a forced swimming test, tail suspension test, and sucrose preference test. Western blotting and immunohistochemistry were used to measure the protein expression of BDNF, p-ERK1/2, p-CREB, NR2B, AKT, FOXO1, FOXO3a, and Bim. Compared with the control group, CUMS treatment increased immobility time; decreased sucrose preference; reduced expression of BDNF, p-ERK1/2, and p-CREB; and increased expression of AKT, FOXO, and Bim in the hippocampus. These alterations were ameliorated by administration of 20 mg/kg or 40 mg/kg of traxoprodil after 7 or 14 days of administration and with 10 mg/kg of traxoprodil or 5 mg/kg of fluoxetine after 21 days of administration. At the 7-day and 14-day timepoints, traxoprodil displayed dose-dependent antidepressant effects, with 20 and 40 mg/kg doses of traxoprodil producing rapid and strong antidepressant effects. However, at 21 days of administration, 10 and 20 mg/kg doses of traxoprodil exerted more pronounced antidepressant effects. The mechanism of traxoprodil's antidepressant effects may be closely related to the BDNF/ERK/CREB and AKT/FOXO/Bim signaling pathway.

Downregulation of surface AMPA receptor expression in the striatum following prolonged social isolation, a role of mGlu5 receptors

Major depressive disorder is a common and serious mood illness. The molecular mechanisms underlying the pathogenesis and symptomatology of depression are poorly understood at present. Multiple neurotransmitter systems are believed to be implicated in depression. Increasing evidence supports glutamatergic transmission as a critical element in depression and antidepressant activity. In this study, we investigated adaptive changes in expression of AMPA receptors in a key limbic reward structure, the striatum, in response to an anhedonic model of depression. Prolonged social isolation in adult rats caused anhedonic/depression- and anxiety-like behavior. In these depressed rats, surface levels of AMPA receptors, mainly GluA1 and GluA3 subunits, were reduced in the nucleus accumbens (NAc). Surface GluA1/A3 expression was also reduced in the caudate putamen (CPu) following chronic social isolation. No change was observed in expression of presynaptic synaptophysin, postsynaptic density-95, and dendritic microtubule-associated protein 2 in the striatum. Noticeably, chronic treatment with the metabotropic glutamate (mGlu) receptor 5 antagonist MTEP reversed the reduction of AMPA receptors in the NAc and CPu. MTEP also prevented depression- and anxiety-like behavior induced by social isolation. These data indicate that adulthood prolonged social isolation induces the adaptive downregulation of GluA1/A3-containing AMPA receptor expression in the limbic striatum. mGlu5 receptor activity is linked to this downregulation, and antagonism of mGlu5 receptors produces an antidepressant effect in this anhedonic model of depression.

Blood Glutamate Scavenging With Pyruvate as a Novel Preventative and Therapeutic Approach for Depressive-Like Behavior Following Traumatic Brain Injury in a Rat Model

Depression is a common and serious complication following traumatic brain injury (TBI). Both depression and TBI have independently been associated with pathologically elevated extracellular brain glutamate levels. In the setting of TBI, blood glutamate scavenging with pyruvate has been widely shown as an effective method to provide neuroprotection by reducing blood glutamate and subsequent brain glutamate levels. Here we evaluate pyruvate as a novel approach in the treatment and prevention of post-TBI depression-like behavior in a rat model. Rats were divided into five groups: (1) sham-operated control with pyruvate, (2) sham-operated control with placebo, (3) post-TBI with placebo, (4) post-TBI given preventative pyruvate, and (5) post-TBI treated with pyruvate. These groups had an equal number of females and males. Rats were assessed for depressive-like behavior, neurological status, and glutamate levels in the blood and brain. Post-TBI neurological deficits with concurrent elevations in glutamate levels were demonstrated, with peak glutamate levels 24 h after TBI. Following TBI, the administration of either prophylactic or therapeutic pyruvate led to reduced glutamate levels, improved neurologic recovery, and improved depressive-like behavior. Glutamate scavenging with pyruvate may be an effective prophylactic and therapeutic option for post-TBI depression by reducing associated elevations in brain glutamate levels.

Molecular mechanisms underlying the antidepressant actions of arketamine: beyond the NMDA receptor

The discovery of robust antidepressant actions exerted by the N-methyl-D-aspartate receptor (NMDAR) antagonist (R,S)-ketamine has been a crucial breakthrough in mood disorder research. (R,S)-ketamine is a racemic mixture of equal amounts of (R)-ketamine (arketamine) and (S)-ketamine (esketamine). In 2019, an esketamine nasal spray from Johnson & Johnson was approved in the United States of America and Europe for treatment-resistant depression. However, an increasing number of preclinical studies show that arketamine has greater potency and longer-lasting antidepressant-like effects than esketamine in rodents, despite the lower binding affinity of arketamine for the NMDAR. In clinical trials, non-ketamine NMDAR-related compounds did not exhibit ketamine-like robust antidepressant actions in patients with depression, despite these compounds showing antidepressant-like effects in rodents. Thus, the rodent data do not necessarily translate to humans due to the complexity of human psychiatric disorders. Collectively, the available studies indicate that it is unlikely that NMDAR plays a major role in the antidepressant action of (R,S)-ketamine and its enantiomers, although the precise molecular mechanisms underlying antidepressant actions of (R,S)-ketamine and its enantiomers remain unclear. In this paper, we review recent findings on the molecular mechanisms underlying the antidepressant actions of (R,S)-ketamine and its potent enantiomer arketamine. Furthermore, we discuss the possible role of the brain-gut-microbiota axis and brain-spleen axis in stress-related psychiatric disorders and in the antidepressant-like action of arketamine. Finally, we discuss the potential of arketamine as a treatment for cognitive impairment in psychiatric disorders, Parkinson's disease, osteoporosis, inflammatory bowel diseases, and stroke.

R (-)-methoxetamine exerts rapid and sustained antidepressant effects and fewer behavioral side effects relative to S (+)-methoxetamine

The newfound antidepressant efficacy of ketamine has provided opportunities for the development of new-generation, rapid-acting, glutamate-based antidepressants. We previously identified that methoxetamine (MXE), a ketamine analog, and an N-Methyl-d-aspartate (NMDA) receptor antagonist, produced rapid and sustained antidepressant effects in mice. MXE (R, S (±)-MXE) is a racemic mixture containing equal parts of S (+)-MXE and R (-)-MXE. However, studies have yet to investigate the antidepressant effects of its enantiomers. Here, we examined the potential antidepressant properties and behavioral side effects of S- and R-MXE in mice. Both S- and R-MXE showed significant NMDA receptor affinity and appreciable inhibitory activity on serotonin transporter. Also, S- and R-MXE (10 mg kg^-1) exerted antidepressant effects and increased gamma waves (electroencephalography) but were inhibited by NBQX (an AMPA receptor antagonist). Subsequently, they increased mammalian target of rapamycin phosphorylation and AMPA receptor subunits GluA1 and GluA2 protein levels in the hippocampus or prefrontal cortex. Furthermore, they increased 5HT2a and 5HT2c receptor mRNA levels in the prefrontal cortex, with their antidepressant effects inhibited by ketanserin (a 5HT2a/c receptor antagonist). Taken together, S-MXE and R-MXE elicit antidepressant effects that are probably mediated via glutamatergic and serotonergic mechanisms. Unlike S-MXE, R-MXE did not induce prepulse inhibition deficits, hyperlocomotion, conditioned place preference, and locomotor sensitization, although it acutely altered motor coordination. This suggests that R-MXE induces fewer behavioral side effects and is a safer antidepressant than S-MXE. Overall, this study provides significant implications for future research on the next generation of rapid-acting, glutamate-based antidepressant drugs.

Rutin via Increase in the CA3 Diameter of the Hippocampus Exerted Antidepressant-Like Effect in Mouse Model of Maternal Separation Stress: Possible Involvement of NMDA Receptors

Methods

Mouse neonates were exposed to MS paradigm 3 hours daily from postnatal days (PND) 2 to 14. The control and MS mice were divided separately into 16 groups (n = 8) (8 groups for each set) including mice that received normal saline, mice that received rutin at doses of 10, 50, and 100 mg/kg, mice that received NMDA at a dose of 150 mg/kg, mice that received ketamine (NMDA antagonist) at a dose of 0.25 mg/kg, mice that received NMDA antagonist plus a subeffective dose of rutin, and mice that received NMDA plus an effective dose of rutin. Forced swimming test (FST) was performed. Afterwards, the hippocampus was evaluated in cases of histopathological changes as well as expression of NR2A and NR2B genes.

Results

Rutin significantly reduced immobility time in the FST. The expression of NR2A and NR2B subunits of NMDA receptor in MS mice was significantly higher than that in the control group. Rutin significantly decreased the expression of NR2B and NR2A subunits in the hippocampus. The CA3 diameter and percentage of dark neurons in the hippocampus of MS mice significantly decreased and increased, respectively, which partially reversed following rutin administration.

Conclusion

Rutin, partially, through a neuroprotective effect on the hippocampus exerted antidepressant-like effect. We concluded that NMDA receptors, at least in part, mediated the beneficial effect of rutin.

Repeated ketamine administration redeems the time lag for citalopram's antidepressant-like effects

Current available antidepressants exhibit low remission rate with a long response lag time. Growing evidence has demonstrated acute sub-anesthetic dose of ketamine exerts rapid, robust, and lasting antidepressant effects. However, a long term use of ketamine tends to elicit its adverse reactions. The present study aimed to investigate the antidepressant-like effects of intermittent and consecutive administrations of ketamine on chronic unpredictable mild stress (CUMS) rats, and to determine whether ketamine can redeem the time lag for treatment response of classic antidepressants. The behavioral responses were assessed by the sucrose preference test, forced swimming test, and open field test. In the first stage of experiments, all the four treatment regimens of ketamine (10 mg/kg ip, once daily for 3 or 7 consecutive days, or once every 7 or 3 days, in a total 21 days) showed robust antidepressant-like effects, with no significant influence on locomotor activity and stereotype behavior in the CUMS rats. The intermittent administration regimens produced longer antidepressant-like effects than the consecutive administration regimens and the administration every 7 days presented similar antidepressant-like effects with less administration times compared with the administration every 3 days. In the second stage of experiments, the combination of ketamine (10 mg/kg ip, once every 7 days) and citalopram (20 mg/kg po, once daily) for 21 days caused more rapid and sustained antidepressant-like effects than citalopram administered alone. In summary, repeated sub-anesthestic doses of ketamine can redeem the time lag for the antidepressant-like effects of citalopram, suggesting the combination of ketamine and classic antidepressants is a promising regimen for depression with quick onset time and stable and lasting effects.

Linkage of Non-receptor Tyrosine Kinase Fyn to mGlu5 Receptors in Striatal Neurons in a Depression Model

The Src family kinase (SFK) is a subfamily of non-receptor tyrosine kinases. The SFK member Fyn is enriched at synaptic sites in the limbic reward circuit and plays a pivotal role in the regulation of glutamate receptors. In this study, we investigated changes in phosphorylation and function of the two key SFK members (Fyn and Src) and SFK interactions with a metabotropic glutamate (mGlu) receptor in the limbic striatum of adult rats in response to chronic passive stress, i.e., prolonged social isolation which is a pre-validated animal paradigm modeling depression in adulthood. In rats that showed typical anhedonic/depression-like behavior after chronic social isolation, phosphorylation of SFKs at a conserved and activation-associated autophosphorylation site (Y416) was not altered in the two subdivisions of the striatum, the nucleus accumbens and caudate putamen. The total level of phosphorylation and kinase activity of individual Fyn and Src immunopurified from the striatum also remained stable after social isolation. Noticeably, Fyn and Src were found to interact with a G_αq-coupled mGlu5 receptor in striatal neurons. The interaction of Fyn with mGlu5 receptors was selectively elevated in socially isolated rats. Moreover, social isolation induced an increase in surface expression of striatal mGlu5 receptors, which was reduced by an SFK inhibitor. These results indicate that Fyn interacts with mGlu5 receptors in striatal neurons. Adulthood social isolation in rats enhances the Fyn-mGlu5 interaction, which appears to be critical for the upregulation of surface mGlu5 receptor expression in striatal neurons.

Involvement of glutamate and serotonin transmitter systems in male sex determination in Daphnia pulex

Environmental sex determination occurs in many organisms, however the means by which environmental stimuli are translated into endocrine messages remains poorly understood. The N-methyl-ᴅ-aspartate receptor (NMDAR) was evaluated as a candidate neural sensor of environmental signals linking environmental cues to endocrine responses using the crustacean Daphnia pulex. NMDAR agonists, modulators, and antagonists were evaluated for their ability to impact D. pulex male sex determination during early stages of reproductive maturity under conditions that simulated seasonal change. The antagonists MK-801 and desipramine significantly increased male sex determination. Both chemicals are also modulators of serotonergic and noradrenergic systems, thus, we evaluated several modulators of monoamine neurotransmission in an effort to discern which signaling pathways might contribute to male sex determination. Compounds that altered serotonergic signaling also stimulated male sex determination. The involvement of the glutamate and monoamine signaling in male sex determination was supported by the increase in mRNA levels of related receptors and transporters under conditions that stimulate male sex determination. Further, mRNA levels of components of the terminal endocrine pathway responsible for male sex determination were also elevated under stimulatory conditions. Overall, we provide evidence that glutamatergic and serotonergic systems function upstream of the endocrine regulation of male sex determination in early life stage daphnids.

Blood glutamate scavenging as a novel glutamate-based therapeutic approach for post-stroke depression

Post-stroke depression (PSD) is a major complication of stroke that significantly impacts functional recovery and quality of life. While the exact mechanism of PSD is unknown, recent attention has focused on the association of the glutamatergic system in its etiology and treatment. Minimizing secondary brain damage and neuropsychiatric consequences associated with excess glutamate concentrations is a vital part of stroke management. The blood glutamate scavengers, oxaloacetate and pyruvate, degrade glutamate in the blood to its inactive metabolite, 2-ketoglutarate, by the coenzymes glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT), respectively. This reduction in blood glutamate concentrations leads to a subsequent shift of glutamate down its concentration gradient from the blood to the brain, thereby decreasing brain glutamate levels. Although there are not yet any human trials that support blood glutamate scavengers for clinical use, there is increasing evidence from animal research of their efficacy as a promising new therapeutic approach for PSD. In this review, we present recent evidence in the literature of the potential therapeutic benefits of blood glutamate scavengers for reducing PSD and other related neuropsychiatric conditions. The evidence reviewed here should be useful in guiding future clinical trials.

Recent Studies on Anti-Depressant Bioactive Substances in Selected Species from the Genera Hemerocallis and Gladiolus: A Systematic Review

Herbal therapy is a potential alternative applied to pharmacological alleviation of depression symptoms and treatment of this disorder, which is predicted by the World Health Organization (WHO) to be the most serious health problem worldwide over the next several years. It has been well documented that many herbs with psychotropic effects have far fewer side effects than a variety of pharmaceutical agents used by psychiatrists for the treatment of depression. This systematic review presents literature data on the antidepressant activity of representatives of the genera Hemerocallis (H. fulva and H. citrina Baroni, family Xanthorrhoeaceae) and Gladiolus (G. dalenii, family Iridaceae) and on biologically active compounds and their mechanisms of action to consider the application of herbal preparations supporting the treatment of depression.

Implication of NMDA-NO pathway in the antidepressant-like effect of ellagic acid in male mice

Depression is one the common psychiatric disorders through the world. Nitric oxide (NO) and N-methyl-d-aspartate receptor (NMDA-R) are involved in the pathophysiology of depression. Previous studies have been reported various pharmacological properties for ellagic acid (EA). We aimed to evaluate possible involvement of NMDA-NO pathway in the antidepressant-like effect of EA. To do this, we used relevant behavioral tests to evaluate depressive-like behavior. In order to find effective and sub-effective doses of agents, mice treated with EA (6.25, 12.5, 25, 50 and 100 mg/kg), L-NAME (5 and 10 mg/kg), L-arg (25 and 50 mg/kg), NMDA (75 and 150 mg/kg) and ketamine (0.25 and 0.5 mg/kg). Furthermore, mice were treated with combination of sub-effective dose of EA plus sub-effective doses of L-NAME and/or ketamine as well as treated with effective dose of EA in combination of effective doses of L-arg and/or NMDA. Level of NO and gene expression of NR2A and NR2B subunits of NMDA-R were assessed in the hippocampus. Results showed that EA dose dependently provoked antidepressant-like effects and also decreased the hippocampal NO level as well as expression of NMDA-Rs. Co-administration of sub-effective doses of L-NAME or ketamine with sub-effective dose of EA potentiated the effect of EA on behaviors, NO level as well as NMDA-Rs gene expression in the hippocampus. However, co-treatment of effective dose of EA with effective doses of L-arg or NMDA mitigated effects of EA. In conclusion, our data suggested that NMDA-NO, partially at least, are involved in the antidepressant-like effect of EA.

Zinc signaling and epilepsy

Evidence from both preclinical and clinical studies suggest the importance of zinc homeostasis in seizures/epilepsy. Undoubtedly, zinc, via modulation of a variety of targets, is necessary for maintaining the balance between neuronal excitation and inhibition, while an imbalance between excitation and inhibition underlies seizures. However, the relationship between zinc signaling and seizures/epilepsy is complex as both extracellular and intracellular zinc may produce either protective or detrimental effects. This review provides an overview of preclinical/behavioral, functional and molecular studies, as well as clinical data on the involvement of zinc in the pathophysiology and treatment of seizures/epilepsy. Furthermore, the potential of targeting elements associated with zinc signaling or homeostasis and zinc levels as a therapeutic strategy for epilepsy is discussed.

Alterations in mGlu5 receptor expression and function in the striatum in a rat depression model

Major depressive disorder is a common form of mental illness. Many brain regions are implicated in the pathophysiology and symptomatology of depression. Among key brain areas is the striatum that controls reward and mood and is involved in the development of core depression-like behavior in animal models of depression. While molecular mechanisms in this region underlying depression-related behavior are poorly understood, the glutamatergic input to the striatum is believed to play a role. In this study, we investigated changes in metabotropic glutamate (mGlu) receptor expression and signaling in the striatum of adult rats in response to prolonged (10-12 weeks) social isolation, a pre-validated animal paradigm modeling depression in adulthood. We found that mGlu5 receptor protein levels in the striatum were increased in rats that showed typical depression- and anxiety-like behavior after chronic social isolation. This increase in mGlu5 receptor expression was seen in both subdivisions of the striatum, the nucleus accumbens and caudate putamen. At subcellular and subsynaptic levels, mGlu5 receptor expression was elevated in surface membranes at synaptic sites. In striatal neurons, the mGlu5-associated phosphoinositide signaling pathway was augmented in its efficacy after prolonged social isolation. These data indicate that the mGlu5 receptor is a sensitive substrate of depression. Adulthood social isolation leads to the up-regulation of mGlu5 receptor expression and function in striatal neurons.

Metabolomics of Major Depressive Disorder and Bipolar Disorder: Overview and Future Perspective

Major depressive disorder (MDD) and bipolar disorder (BD) are the most common mood disorders. They are etiologically related, but clinically distinct psychiatric illnesses. Their shared clinical features result in high rates of misdiagnosis due to a lack of biomarkers that allow their differentiation. BD is more frequently misdiagnosed as MDD because of overlapping symptomology, often later onset of mania, and frequent occurrence of depressive episodes in patients with BD. Misdiagnosis is also increased when patients with BD present symptoms indicative of a clinically significant depressive episode, but are premorbid for manic symptoms, or previous manic states not recognized. Therefore, the development of specific biomarkers for these disorders would be invaluable for establishing the correct diagnosis and treatment of MDD and BD. This chapter presents an overview and future perspective of the identification of biomarkers for mood disorders using metabolomics.

Intranasal Stem Cell Treatment as a Novel Therapy for Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) represents a major health problem in Western society due to high mortality and morbidity, and the relative young age of patients. Currently, efficacious therapeutic options are very limited. Mesenchymal stem cell (MSC) administration has been shown to improve functional outcome and lesion size in experimental models of stroke and neonatal hypoxic-ischemic brain injury. Here, we studied the therapeutic potential of intranasally administered bone marrow-derived MSCs relatively late postinsult using a rat endovascular puncture model for SAH. Six days after induction of SAH, rats were treated with MSCs or vehicle through nasal administration. Intranasal MSC treatment significantly improved sensorimotor and mechanosensory function at 21 days after SAH. Gray and white matter loss was significantly reduced by MSC treatment and the number of NeuN⁺ neurons around the lesion increased due to MSC treatment. Moreover, intranasal MSC administration led to a sharp decrease in SAH-induced activation of astrocytes and microglia/macrophages in the lesioned hemisphere, especially of M2-like (CD206⁺) microglia/macrophages. Interestingly, MSC administration also decreased SAH-induced depression-like behavior in association with a restoration of tyrosine hydroxylase expression in the substantia nigra and striatum. We show here for the first time that intranasal MSC administration reverses the devastating consequences of SAH, including regeneration of the cerebral lesion, functional recovery, and treatment of comorbid depression-like behavior.

Elevated peripheral blood glutamate levels in major depressive disorder

PURPOSE

There is growing evidence that glutamatergic signaling may be involved in major depressive disorder (MDD). In regard to peripheral blood glutamate changes in MDD, inconsistent findings have been reported. The purpose of the present study was to evaluate whether blood glutamate levels differed between MDD patients and control participants.

MATERIALS AND METHODS

We conducted a systematic review and meta-analysis of 12 association studies between blood glutamate levels and MDD in a total of 529 MDD patients and 590 controls. Subsequently, we conducted subgroup analyses and a meta-regression analysis to examine the sources of potential heterogeneity.

RESULTS

A random effects model showed that blood glutamate levels were significantly higher in MDD patients than in controls (standardized mean difference=0.54, 95% CI=0.27-0.82, p=8.5×10^-5) with high heterogeneity (I²=75.0%, p<0.05). Subgroup analyses showed elevated glutamate levels in MDD patients compared with controls in plasma, but not serum studies, and in studies using high-performance liquid chromatography but not with mass spectrometry for glutamate assay. A meta-regression analysis showed no effects of age, gender, medication use, sample size, and published year on blood glutamate levels.

CONCLUSION

Our findings suggest that altered glutamate levels may be implicated in MDD, which provides further evidence of glutamatergic dysfunction in MDD.

Alterations in amino acid levels in mouse brain regions after adjunctive treatment of brexpiprazole with fluoxetine: comparison with (R)-ketamine

RATIONALE

Brexpiprazole, a serotonin-dopamine activity modulator, is approved in the USA as an adjunctive therapy to antidepressants for treating major depressive disorders. Similar to the N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine, the combination of brexpiprazole and fluoxetine has demonstrated antidepressant-like effects in animal models of depression.

OBJECTIVES

The present study was conducted to examine whether the combination of brexpiprazole and fluoxetine could affect the tissue levels of amino acids [glutamate, glutamine, γ-aminobutyric acid (GABA), D-serine, L-serine, and glycine] that are associated with NMDAR neurotransmission.

METHODS

The tissue levels of amino acids in the frontal cortex, striatum, hippocampus, and cerebellum were measured after a single [or repeated (14 days)] oral administration of vehicle, fluoxetine (10 mg/kg), brexpiprazole (0.1 mg/kg), or a combination of the two drugs. Furthermore, we measured the tissue levels of amino acids after a single administration of the NMDAR antagonist (R)-ketamine.

RESULTS

A single injection of the combination of fluoxetine and brexpiprazole significantly increased GABA levels in the striatum, the D-serine/L-serine ratio in the frontal cortex, and the glycine/L-serine ratio in the hippocampus. A repeated administration of the combination significantly altered the tissue levels of amino acids in all regions. Interestingly, a repeated administration of the combination significantly decreased the D-serine/L-serine ratio in the frontal cortex, striatum, and hippocampus. In contrast, a single administration of (R)-ketamine significantly increased the D-serine/L-serine ratio in the frontal cortex.

CONCLUSIONS

These results suggested that alterations in the tissue levels of these amino acids may be involved in the antidepressant-like effects of the combination of brexpiprazole and fluoxetine.

Short- and long-term antidepressant effects of ketamine in a rat chronic unpredictable stress model

OBJECTIVE

This research was aimed to evaluate the behaviors of short- or long-term antidepressant effects of ketamine in rats exposed to chronic unpredictable stress (CUS).

BACKGROUND

Ketamine, a glutamate noncompetitive NMDA receptor antagonist, regulates excitatory amino acid functions, such as anxiety disorders and major depression, and plays an important role in synaptic plasticity and learning and memory.

METHODS

After 42 days of CUS model, male rats received either a single injection of ketamine (10 mg/kg; day 43) or 15 daily injections (days 43-75). The influence of ketamine on behavioral reactivity was assessed 24 hr (short-term) or 7 weeks after ketamine treatment (long-term). Behavioral tests used to assess the effects of these treatments included the sucrose preference (SP), open field (OF), elevated plus maze (EPM), forced swimming (FS), and water maze (WM) to detect anxiety-like behavior (OF and EPM), forced swimming (FS), and water maze (WM). Results: Short-term ketamine administration resulted in increases of body weight gain, higher sensitivity to sucrose, augmented locomotor activity in the OF, more entries into the open arms of the EPM, along increased activity in the FS test; all responses indicative of reductions in depression/despair in anxiety-eliciting situations. No significant differences in these behaviors were obtained under conditions of long-term ketamine administration (p > .05). The CUS + Ketamine group showed significantly increased activity as compared with the CUS + Vehicle group for analysis of the long-term effects of ketamine (*p < .05). Nor were significant differences obtained in learning and memory performance in rats receiving ketamine (p > .05).

CONCLUSION

Taken together these findings demonstrate that a short-term administration of ketamine induced rapid antidepressant-like effects in adult male rats exposed to CUS conditions, effects that were not observed in response to the long-term treatment regime.

The Emerging Role for Zinc in Depression and Psychosis

Zinc participation is essential for all physiological systems, including neural functioning, where it participates in a myriad of cellular processes. Converging clinical, molecular, and genetic discoveries illuminate key roles for zinc homeostasis in association with clinical depression and psychosis which are not yet well appreciated at the clinical interface. Intracellular deficiency may arise from low circulating zinc levels due to dietary insufficiency, or impaired absorption from aging or medical conditions, including alcoholism. A host of medications commonly administered to psychiatric patients, including anticonvulsants, oral medications for diabetes, hormones, antacids, anti-inflammatories and others also impact zinc absorption. Furthermore, inefficient genetic variants in zinc transporter molecules that transport the ion across cellular membranes impede its action even when circulating zinc concentrations is in the normal range. Well powered clinical studies have shown beneficial effects of supplemental zinc in depression and it important to pursue research using zinc as a potential therapeutic option for psychosis as well. Meta-analyses support the adjunctive use of zinc in major depression and a single study now supports zinc for psychotic symptoms. This manuscript reviews the biochemistry and bench top evidence on putative molecular mechanisms of zinc as a psychiatric treatment.

The combination of plasma glutamate and physical impairment after acute stroke as a potential indicator for the early-onset post-stroke depression

OBJECTS

The present study aimed to investigate the relationship of plasma glutamate levels with the early-onset of post-stroke depression (PSD) and to further explore the prognostic value of plasma glutamate combined with clinical characteristics for the early-onset PSD in the acute ischemic stroke patients.

METHODS

Seventy-four patients who admitted to the hospital within 24h of acute ischemic stroke were consecutively recruited and followed up for 2weeks. The Beck Depression Inventory (BDI) and 17-item Hamilton Depression Rating Scale (HAMD-17) were used to screen for depressive symptoms 14days after stroke. Diagnoses of depression were made in accordance with DSM-IV. Plasma glutamate levels were determined by High Performance Liquid Chromatography (HPLC) on days 1 and 14 after stroke for all patients.

RESULTS

Plasma glutamate levels were significantly lower in PSD patients than those of non-PSD patients on day 1 after stroke. ROC curve analyses revealed an AUC (area under the ROC curve) of 0.724 (95% CI: 0.584-0.863, p=0.004) and of 0.669 (95% CI: 0.523-0.814, p=0.030) for National Institute of Health Stroke Scale (NIHSS) scores and plasma glutamate levels on day 1 respectively. Combined ROC analyses using the two factors revealed the highest AUC of 0.804 (95% CI: 0.685-0.922, P<0.0001).

CONCLUSIONS

These results indicated an association between the early-onset PSD and a low plasma glutamate level following acute ischemic stroke. The combination of reduced plasma glutamate levels and physical impairment (determined by NIHSS) 1day after acute ischemic stroke was a potential diagnostic indicator for early-onset PSD.

Antidepressant Effects of (+)-MK-801 and (-)-MK-801 in the Social Defeat Stress Model

BACKGROUND

Current data on antidepressant action of the N-methyl-D-aspartate receptor antagonist, (+)-MK-801, is inconsistent. This study was conducted to examine the effects of (+)-MK-801 and its less potent stereoisomer, (-)-MK-801, in the social defeat stress model of depression.

METHODS

The antidepressant effects of (+)-MK-801 (0.1mg/kg) and (-)-MK-801 (0.1mg/kg) in the social defeat stress model were examined.

RESULTS

In the tail suspension and forced swimming tests, both stereoisomers significantly attenuated increased immobility time in susceptible mice. In the sucrose preference test, (+)-MK-801, but not (-)-MK-801, significantly enhanced reduced sucrose consumption 2 or 4 days after a single dose. However, no antianhedonia effects were detected 7 days after a single dose of either stereoisomer.

CONCLUSIONS

Both stereoisomers of MK-801 induced rapid antidepressant effects in the social defeat stress model, although neither produced a long-lasting effect (7 days).

Microbiota-driven transcriptional changes in prefrontal cortex override genetic differences in social behavior

Gene-environment interactions impact the development of neuropsychiatric disorders, but the relative contributions are unclear. Here, we identify gut microbiota as sufficient to induce depressive-like behaviors in genetically distinct mouse strains. Daily gavage of vehicle (dH2O) in nonobese diabetic (NOD) mice induced a social avoidance behavior that was not observed in C57BL/6 mice. This was not observed in NOD animals with depleted microbiota via oral administration of antibiotics. Transfer of intestinal microbiota, including members of the Clostridiales, Lachnospiraceae and Ruminococcaceae, from vehicle-gavaged NOD donors to microbiota-depleted C57BL/6 recipients was sufficient to induce social avoidance and change gene expression and myelination in the prefrontal cortex. Metabolomic analysis identified increased cresol levels in these mice, and exposure of cultured oligodendrocytes to this metabolite prevented myelin gene expression and differentiation. Our results thus demonstrate that the gut microbiota modifies the synthesis of key metabolites affecting gene expression in the prefrontal cortex, thereby modulating social behavior.

DOI:http://dx.doi.org/10.7554/eLife.13442.001

A combination of genes and environmental factors underlie an individual’s risk of developing a mental illness. Among the environmental factors, it is becoming clear that communication between the gut and the brain is involved, but we do not understand how these two organs communicate. Our gut contains a variety of bacteria that help us to digest food and there is some evidence that changes in these bacterial communities can influence our mental health.

Transplanting feces from one individual to the gut of another is one way to alter the communities of bacteria in the gut. Here, Gacias et al. investigated whether fecal transplants are sufficient to induce social avoidance behavior – a symptom of depression – in mice. The experiments show that introducing specific combinations of bacteria into the gut is indeed able to cause healthy adult mice to avoid social interactions. This effect was caused by changes in the “myelin” sheath that surrounds many nerve fibers and could be prevented by giving the mice antibiotics, which decreased the number of bacteria in the gut.

Further experiments revealed that the mice that became depressed after fecal transplants had higher levels of a molecule called cresol, which is produced by certain gut bacteria. Gacias et al. found that cresol is able to reduce the amount of myelin produced by brain cells. Therefore, these findings show that changing the communities of bacteria in the gut can result in the accumulation of molecules that influence social behavior. Future work will aim to identify bacteria that can reduce the amount of cresol produced in the gut, which may have the potential to treat depression.

DOI:http://dx.doi.org/10.7554/eLife.13442.002

Microendophenotypes of psychiatric disorders: phenotypes of psychiatric disorders at the level of molecular dynamics, synapses, neurons, and neural circuits

Psychiatric disorders are caused not only by genetic factors but also by complicated factors such as environmental ones. Moreover, environmental factors are rarely quantitated as biological and biochemical indicators, making it extremely difficult to understand the pathological conditions of psychiatric disorders as well as their underlying pathogenic mechanisms. Additionally, we have actually no other option but to perform biological studies on postmortem human brains that display features of psychiatric disorders, thereby resulting in a lack of experimental materials to characterize the basic biology of these disorders. From these backgrounds, animal, tissue, or cell models that can be used in basic research are indispensable to understand biologically the pathogenic mechanisms of psychiatric disorders. In this review, we discuss the importance of microendophenotypes of psychiatric disorders, i.e., phenotypes at the level of molecular dynamics, neurons, synapses, and neural circuits, as targets of basic research on these disorders.

Comparison of ketamine, 7,8-dihydroxyflavone, and ANA-12 antidepressant effects in the social defeat stress model of depression

RATIONALE

Brain-derived neurotrophic factor (BDNF) and signaling at its receptor, tropomyosin-related kinase B (TrkB), are implicated in the rapid and long-lasting antidepressant effects of ketamine. Moreover, a TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF), and/or TrkB antagonist, ANA-12, shows antidepressant effects in animal models of depression.

OBJECTIVE

The objective of this study is to compare the influence of ketamine, 7,8-DHF, and ANA-12 on antidepressant activity in the social defeat stress model.

RESULTS

In the tail suspension and forced swimming tests, ketamine, 7,8-DHF, or ANA-12 markedly attenuated the increased immobility time in depressed mice compared with the vehicle-treated group. In the sucrose preference test, all drugs significantly improved the reduced preference in depressed mice at both 1 and 3 days after a single dose. Antidepressant effect of ketamine, but not 7,8-DHF or ANA-12, was still detectable 7 days after a single dose. Western blot analyses showed that ketamine, but not 7,8-DHF or ANA-12, markedly attenuated reduced levels of BDNF and postsynaptic density protein 95 (PSD-95) in the prefrontal cortex (PFC), dentate gyrus (DG), and CA3 of the hippocampus in depressed mice 8 days after a single dose. Furthermore, ketamine markedly increased reduced levels of GluA1 in the PFC and DG of depressed mice. In contrast, ketamine showed no effect against increased levels of BDNF, PSD-95, and GluA1 observed in the nucleus accumbens of depressed mice.

CONCLUSIONS

Compared with 7,8-DHF and ANA-12, ketamine is a longer-lasting antidepressant in the social defeat stress model, and synaptogenesis may be required for the mechanisms that promote sustained antidepressant effects of ketamine.

Persistent neuropathic pain increases synaptic GluA1 subunit levels in core and shell subregions of the nucleus accumbens

The nucleus accumbens (NAc) is a key component of the brain reward system, and it is composed of core and shell subregions. Glutamate transmission through AMPA-type receptors in both core and shell of the NAc has been shown to regulate reward- and aversion-type behaviors. Previous studies have additionally demonstrated a role for AMPA receptor signaling in the NAc in chronic pain states. Here, we show that persistent neuropathic pain, modeled by spared nerve injury (SNI), selectively increases the numbers of GluA1 subunits of AMPA receptors at the synapse of both core and shell subregions. Such increases are not observed, however, for the GluA2 subunits. Furthermore, we find that phosphorylation at Ser845-GluA1 is increased by SNI at both core and shell subregions. These results demonstrate that persistent neuropathic pain increases AMPA receptor delivery to the synapse in both NAc core and shell, implying a role for AMPA receptor signaling in these regions in pain states.

Evidence for the involvement of NMDA receptors in the antidepressant-like effect of nicotine in mouse forced swimming and tail suspension tests

RATIONALE

The antidepressant action of acute nicotine administration in clinical and animal studies is well recognized. But the underlying mechanism for this effect has not been carefully discovered.

OBJECTIVES

We attempted to evaluate the possible role of N-Methyl-D-aspartate (NMDA) receptors in the antidepressant-like effect of nicotine.

METHODS

After the assessment of locomotor activity in the open-field test, forced swimming test (FST) and tail suspension test (TST) were used to evaluate the antidepressant-like effect of nicotine in mice. We performed intraperitoneal administration of nicotine at different doses and periods before the tests. To assess the possible involvement of NMDA receptors, non-effective doses of NMDA antagonists and an NMDA agonist were obtained and were administered simultaneously with the non-effective and effective doses of nicotine, respectively.

RESULTS

Nicotine (0.2 mg/kg, 30 min before FST/TST) significantly reduced the immobility time of mice similar to fluoxetine (20 mg/kg). Nicotine did not affect the locomotor behavior of mice in open-field test. Co-administration of non-effective doses of NMDA receptor antagonists, ketamine (1 or 0.3 mg/kg), MK-801 (0.05 or 0.005 mg/kg), and magnesium sulfate (10 or 5 mg/kg) with nicotine (0.1 or 0.03 mg/kg) had remarkable synergistic antidepressant effect in both FST and TST. Also, non-effective NMDA (75 or 30 mg/kg) reversed the anti-immobility effect of nicotine (0.2 mg/kg) on mouse FST and TST.

CONCLUSIONS

Our study has for the first time confirmed that the antidepressant-like effect of nicotine on mice is NMDA-mediated, and nicotine presumably exerts this effect by antagonizing the glutamatergic NMDA receptors.

AMPA Receptor-mTOR Activation is Required for the Antidepressant-Like Effects of Sarcosine during the Forced Swim Test in Rats: Insertion of AMPA Receptor may Play a Role

Sarcosine, an endogenous amino acid, is a competitive inhibitor of the type I glycine transporter and an N-methyl-d-aspartate receptor (NMDAR) coagonist. Recently, we found that sarcosine, an NMDAR enhancer, can improve depression-related behaviors in rodents and humans. This result differs from previous studies, which have reported antidepressant effects of NMDAR antagonists. The mechanisms underlying the therapeutic response of sarcosine remain unknown. This study examines the role of mammalian target of rapamycin (mTOR) signaling and α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor (AMPAR) activation, which are involved in the antidepressant-like effects of several glutamatergic system modulators. The effects of sarcosine in a forced swim test (FST) and the expression levels of phosphorylated mTOR signaling proteins were examined in the absence or presence of mTOR and AMPAR inhibitors. In addition, the influence of sarcosine on AMPAR trafficking was determined by analyzing the phosphorylation of AMPAR subunit GluR1 at the PKA site (often considered an indicator for GluR1 membrane insertion in neurons). A single injection of sarcosine exhibited antidepressant-like effects in rats in the FST and rapidly activated the mTOR signaling pathway, which were significantly blocked by mTOR inhibitor rapamycin or the AMPAR inhibitor 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX) pretreatment. Moreover, NBQX pretreatment eliminated the ability of sarcosine to stimulate the phosphorylated mTOR signaling proteins. Furthermore, GluR1 phosphorylation at its PKA site was significantly increased after an acute in vivo sarcosine treatment. The results demonstrated that sarcosine exerts antidepressant-like effects by enhancing AMPAR–mTOR signaling pathway activity and facilitating AMPAR membrane insertion.

Highlights

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A single injection of sarcosine rapidly exerted antidepressant-like effects with a concomitant increase in the activation of the mammalian target of rapamycin mTOR signaling pathway.

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The antidepressant-like effects of sarcosine occur through the activated AMPAR–mTOR signaling pathway.

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Sarcosine could enhance AMPAR membrane insertion via an AMPAR throughput.

Advancing understanding of executive function impairments and psychopathology: bridging the gap between clinical and cognitive approaches

Executive function (EF) is essential for successfully navigating nearly all of our daily activities. Of critical importance for clinical psychological science, EF impairments are associated with most forms of psychopathology. However, despite the proliferation of research on EF in clinical populations, with notable exceptions clinical and cognitive approaches to EF have remained largely independent, leading to failures to apply theoretical and methodological advances in one field to the other field and hindering progress. First, we review the current state of knowledge of EF impairments associated with psychopathology and limitations to the previous research in light of recent advances in understanding and measuring EF. Next, we offer concrete suggestions for improving EF assessment. Last, we suggest future directions, including integrating modern models of EF with state of the art, hierarchical models of dimensional psychopathology as well as translational implications of EF-informed research on clinical science.

The role of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in depression: central mediators of pathophysiology and antidepressant activity?

Depression is a major psychiatric disorder affecting more than 120 million people worldwide every year. Changes in monoaminergic transmitter release are suggested to take part in the pathophysiology of depression. However, more recent experimental evidence suggests that glutamatergic mechanisms might play a more central role in the development of this disorder. The importance of the glutamatergic system in depression was particularly highlighted by the discovery that N-methyl-D-aspartate (NMDA) receptor antagonists (particularly ketamine) exert relatively long-lasting antidepressant like effects with rapid onset. Importantly, the antidepressant-like effects of NMDA receptor antagonists, but also other antidepressants (both classical and novel), require activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Additionally, expression of AMPA receptors is altered in patients with depression. Moreover, preclinical evidence supports an important involvement of AMPA receptor-dependent signaling and plasticity in the pathophysiology and treatment of depression. Here we summarize work published on the involvement of AMPA receptors in depression and discuss a possible central role for AMPA receptors in the pathophysiology, course and treatment of depression.

GABAergic control of depression-related brain states

The GABAergic deficit hypothesis of major depressive disorders (MDDs) posits that reduced γ-aminobutyric acid (GABA) concentration in brain, impaired function of GABAergic interneurons, altered expression and function of GABA(A) receptors, and changes in GABAergic transmission dictated by altered chloride homeostasis can contribute to the etiology of MDD. Conversely, the hypothesis posits that the efficacy of currently used antidepressants is determined by their ability to enhance GABAergic neurotransmission. We here provide an update for corresponding evidence from studies of patients and preclinical animal models of depression. In addition, we propose an explanation for the continued lack of genetic evidence that explains the considerable heritability of MDD. Lastly, we discuss how alterations in GABAergic transmission are integral to other hypotheses of MDD that emphasize (i) the role of monoaminergic deficits, (ii) stress-based etiologies, (iii) neurotrophic deficits, and (iv) the neurotoxic and neural circuit-impairing consequences of chronic excesses of glutamate. We propose that altered GABAergic transmission serves as a common denominator of MDD that can account for all these other hypotheses and that plays a causal and common role in diverse mechanistic etiologies of depressive brain states and in the mechanism of action of current antidepressant drug therapies.

Variations of glutamate concentration within synaptic cleft in the presence of electromagnetic fields: an artificial neural networks study

Glutamate is an excitatory neurotransmitter that is released by the majority of central nervous system synapses and is involved in developmental processes, cognitive functions, learning and memory. Excessive elevated concentrations of Glu in synaptic cleft results in neural cell apoptosis which is called excitotoxicity causing neurodegenerative diseases. Hence, we investigated the possibility of extremely low frequency electromagnetic fields (ELF-EMF) as a risk factor which is able to change Glu concentration in synaptic clef. Synaptosomes as a model of nervous terminal were exposed to ELF-EMF for 15-55 min in flux intensity range from 0.1 to 2 mT and frequency range from 50 to 230 Hz. Finally, all raw data by INForm v4.02 software as an artificial neural network program was analyzed to predict the effect of whole mentioned range spectra. The results showed the tolerance of all effects between the ranges from -35 to +40 % compared to normal state when glutamatergic systems exposed to ELF-EMF. It indicates that glutamatergic system attempts to compensate environmental changes though release or reuptake in order to keep the system safe. Regarding to the wide range of ELF-EMF acquired in this study, the obtained outcomes have potential for developing treatments based on ELF-EMF for some neurological diseases; however, in vivo experiments on the cross linking responses between glutamatergic and cholinergic systems in the presence of ELF-EMF would be needed.

Beyond Monoamines-Novel Targets for Treatment-Resistant Depression: A Comprehensive Review

Major depressive disorder (MDD) is a leading cause of disability worldwide. Current first line therapies target modulation of the monoamine system. A large variety of agents are currently available that effectively alter monoamine levels; however, approximately one third of MDD patients remain treatment refractory after adequate trials of multiple monoamine based therapies. Therefore, patients with treatment-resistant depression (TRD) may require modulation of pathways outside of the classic monoamine system. The purpose of this review was thus to discuss novel targets for TRD, to describe their potential mechanisms of action, the available clinical evidence for these targets, the limitations of available evidence as well as future research directions. Several alternate pathways involved in the patho-etiology of TRD have been uncovered including the following: inflammatory pathways, the oxidative stress pathway, the hypothalamic-pituitary-adrenal (HPA) axis, the metabolic and bioenergetics system, neurotrophic pathways, the glutamate system, the opioid system and the cholinergic system. For each of these systems, several targets have been assessed in preclinical and clinical models. Preclinical models strongly implicate these pathways in the patho-etiology of MDD. Clinical trials for TRD have been conducted for several novel targets; however, most of the trials discussed are small and several are uncontrolled. Therefore, further clinical trials are required to assess the true efficacy of these targets for TRD. As well, several promising novel agents have been clinically tested in MDD populations, but have yet to be assessed specifically for TRD. Thus, their applicability to TRD remains unknown.

Rapid-onset antidepressant efficacy of glutamatergic system modulators: the neural plasticity hypothesis of depression

Depression is a devastating psychiatric disorder widely attributed to deficient monoaminergic signaling in the central nervous system. However, most clinical antidepressants enhance monoaminergic neurotransmission with little delay but require 4-8 weeks to reach therapeutic efficacy, a paradox suggesting that the monoaminergic hypothesis of depression is an oversimplification. In contrast to the antidepressants targeting the monoaminergic system, a single dose of the N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine produces rapid (within 2 h) and sustained (over 7 days) antidepressant efficacy in treatment-resistant patients. Glutamatergic transmission mediated by NMDARs is critical for experience-dependent synaptic plasticity and learning, processes that can be modified indirectly by the monoaminergic system. To better understand the mechanisms of action of the new antidepressants like ketamine, we review and compare the monoaminergic and glutamatergic antidepressants, with emphasis on neural plasticity. The pathogenesis of depression may involve maladaptive neural plasticity in glutamatergic circuits that may serve as a new class of targets to produce rapid antidepressant effects.

Glutamate transporter 1-mediated antidepressant-like effect in a rat model of chronic unpredictable stress

In recent years, more attention has been paid to the role of the glutamate transporter 1 (GLT-1, EAAT2) in major depressive disorder (MDD). However, experimental data on brain GLT-1 levels are, to some extent, inconsistent in human postmortem and animal studies. These discrepancies imply that the role of GLT-1 in the pathophysiology of MDD and the action of antidepressants remain obscure. This work was designed to study the impact of chronic unpredictable stress (CUS) for 2 sessions per day for 35 days and four weeks of fluoxetine (FLX) on depressive-like behaviors in rats, as well as the concomitant expression of the GLT-1 protein in the hippocampus. Behavioral changes were assessed by the sucrose preference and open field tests. GLT-1 levels were detected by immunohistchemistry and Western blot analysis. Our study demonstrated that the animals exposed to CUS showed depressive-like behaviors and exhibited a significant decrease in GLT-1 expression in the hippocampus. Chronic FLX treatment reversed the behavioral deficits and the CUS-induced decrease in GLT-1 levels. Taken together, our results support the reduction of GLT-1 in human postmortem studies in MDD and suggest that GLT-1 may be involved in the antidepressant activity of FLX. Our studies further support the notion that GLT-1 is an attractive candidate molecule associated with the fundamental processes of MDD and may be a potential, and novel pharmacological target for the treatment of MDD.

Plasma levels of glutamate during stroke is associated with development of post-stroke depression

BACKGROUND

Depression is a frequent mood disorder that affects around 33% of stroke patient. Our aim was to test the possible association between plasma glutamate and the development of post-stroke depression (PSD) in Chinese patients.

METHODS

The subjects were first-ever acute ischemic stroke (AIS) patients who were hospitalized during the period from November 2011 to September 2013. Clinical information and stroke severity was collected at admission. Neurological and neuropsychological evaluations were conducted at the 3-month follow-up. Plasma glutamate levels were analyzed at baseline using liquid chromatography followed by tandem mass spectrometry. Glutamate oxaloacetate transaminase (GOT), glutamate-pyruvate transaminase (GPT) and blood markers were also tested. Multivariate analyses were performed using logistic regression models.

RESULTS

During the study period, 209 patients were included in the analysis. Seventy patients (33.5%) were diagnosed as having major depression at 3 month. Patients with major depression showed higher levels of plasma glutamate [299 (235-353) vs. 157 (108-206) μM, P<0.0001] and lower GOT [14 (11-20) vs. 21 (15-32)U/L, P<0.0001] at admission. In multivariate analyses, plasma glutamate and GOT were independent predictors of PSD at 3 months [odds ratio (OR): 1.03 (1.02-1.04), P<0.0001; 0.84 (0.75-0.97), P=0.003]. Plasma levels of glutamate >205 μM were independently associated with PSD (OR, 21.3; 95% CI, 8.28-67.36, P<0.0001), after adjustment for possible variables.

CONCLUSION

The present study demonstrates a strong relationship between plasma glutamate and GOT levels at admission and the development of PSD within 3 months. Further studies are necessary to confirm this association, which may open the way to the proposal of new therapeutic options.

Antidepressant Effects of Ketamine on Depression-like Behavior in Juvenile Mice after Neonatal Dexamethasone Exposure

Objective

Pediatric depression is associated with significant functional impairment at school and at work. Recently, we reported on depression-like behavior in juvenile mice neonatally exposed to dexamethasone (DEX) as a potential animal model for pediatric depression. The N-methyl-D-aspartate (NMDA) receptor antagonist ketamine has promoted rapid and long-lasting antidepressant effects in patients with treatment-resistant major depression. This study was conducted to examine whether ketamine had antidepressant effects in juvenile mice after neonatal DEX exposure.

Methods

A single dose (10 mg/kg) of ketamine or vehicle was injected into juvenile mice at days 29-32 after neonatal DEX (or saline) exposure (days 1-3). The sucrose preference test, tail suspension test, and forced swimming test were performed 24, 40, and 46 hours, respectively, after injection of ketamine.

Results

Ketamine (10 mg/kg) significantly improved depression-like behavior in DEX-treated juvenile mice.

Conclusion

This finding suggests that ketamine confers antidepressant effects in an animal model of pediatric depression.

Use of antipsychotics in the treatment of depressive disorders

Summary

There is a long history of using antipsychotic medications in the treatment of depressive disorders. Atypical antipsychotics, which have fewer side effects than traditional antipsychotics, have been used as monotherapy or adjunctively with antidepressants to treat depressive disorders with or without psychotic symptoms. The antidepressant effect of atypical antipsychotics involves regulation of monoamine, glutamate, gamma-aminobutyric acid (GABA), cortisol, and neurotrophic factors. To date, the United States Food and Drug Administration (USFDA) has approved aripiprazole and quetiapine slow-release tablets as adjunctive treatment for depressive disorders, and the combination of olanzapine and fluoxetine for the treatment of treatment-resistant depression. When using atypical antipsychotics in the treatment of depressed patients, clinicians need to monitor patients for the emergence of adverse effects including extrapyramidal symptoms (EPS), weight gain, and hyperglycemia.

Behavioural screening of zebrafish using neuroactive traditional Chinese medicine prescriptions and biological targets

The mechanism of the therapeutic action of antidepressants remains uncertain in traditional Chinese medicine (TCM). In this study, we selected 7 classical TCM prescriptions and utilised an automatic video-tracking system to monitor the rest/wake behaviour of larval zebrafish at 4 days post-fertilisation (dpf) for 48 hours. We found that the curative effects of the prescriptions were dose-dependent. K-means clustering was performed according to the shared behavioural phenotypes of the zebrafish. The results revealed that the rest/wake behavioural profiles induced by the same class of prescriptions were similar. A correlation analysis was conducted between the TCM prescriptions and the known compounds. The results showed that the TCM prescriptions correlated well with some well-known compounds. Therefore, we predicted that they may share a similar mechanism of action. This paper describes the first study to combine TCM research with zebrafish rest/wake behaviour in vivo and presents a powerful approach for the discovery of the mechanism of action of TCM prescriptions.

[Ketamine in acute and severe major depressive disorder]

CONTEXT

Depression is a frequent, severe and expensive illness. Approximately 20% of depressive episodes are resistant to classic antidepressants. Glutamatergic antagonists, in particular ketamine, established a new, rapid and robust therapeutic approach in resistant depression.

RESULTS

The main results in the literature show a rapid and robust antidepressant effect of ketamine, with infra-anesthesic posology (0.5mg/kg) administered in intravenous way. Positive effects are observed on depressive symptoms, suicidal thoughts, and there is a potential synergic action when used in the induction of anesthesia for electroconvulsive therapy. However, effects only last shortly. Side effects are mostly reversible and of mild intensity, no severe consequences were reported.

LIMITS

Limits are the lack of power of the included studies, due to small sample sizes, and the scarcity of studies. Misuse of ketamine is an important issue to be taken into account, and few data about ketamine addiction potential and its long-term effects are published at the moment.

Antidepressant-like activity of magnesium in the chronic mild stress model in rats: alterations in the NMDA receptor subunits

Recent data suggests that the glutamatergic system is involved in the pathophysiology and treatment of major depressive disorder (MDD) and that the N-methyl-D-aspartate (NMDA) receptor is a potential target for antidepressant drugs. The magnesium ion blocks the ion channel of the NMDA receptor and prevents its excessive activation. Some preclinical and clinical evidence suggests also that magnesium may be useful in the treatment of depression. The present study investigated the effect of magnesium treatment (10, 15 and 20 mg/kg, given as magnesium hydroaspartate) in the chronic mild stress (CMS) model of depression in rats. Moreover, the effect of CMS and magnesium (with an effective dose) on the level of the proteins related to the glutamatergic system (GluN1, GluN2A, GluN2B and PSD-95) in the hippocampus, prefrontal cortex (PFC) and amygdala were examined. A significant reduction in the sucrose intake induced by CMS was increased by magnesium treatment at a dose of 15 mg/kg, beginning from the third week of administration. Magnesium did not affect this behavioural parameter in the control animals. CMS significantly increased the level of the GluN1 subunit in the amygdala (by 174%) and GluN2A in the hippocampus (by 191%), both of which were significantly attenuated by magnesium treatment. Moreover, magnesium treatment in CMS animals increased the level of GluN2B (by 116%) and PSD-95 (by 150%) in the PFC. The present results for the first time demonstrate the antidepressant-like activity of magnesium in the animal model of anhedonia (CMS), thus indicating the possible involvement of the NMDA/glutamatergic receptors in this activity.