Emerging role of glutamate in the pathophysiology of major depressive disorder

A role for inflammatory metabolites as modulators of the glutamate N-methyl-D-aspartate receptor in depression and suicidality

BACKGROUND

Patients with depression and suicidality suffer from low-grade neuroinflammation. Pro-inflammatory cytokines activate indoleamine 2,3-dioxygenase, an initial enzyme of the kynurenine pathway. This pathway produces neuroactive metabolites, including quinolinic- and kynurenic acid, binding to the glutamate N-methyl-d-aspartate-receptor, which is hypothesized to be part of the neural mechanisms underlying symptoms of depression. We therefore hypothesized that symptoms of depression and suicidality would fluctuate over time in patients prone to suicidal behavior, depending on the degree of inflammation and kynurenine metabolite levels in the cerebrospinal fluid (CSF).

METHODS

We measured cytokines and kynurenine metabolites in CSF, collected from suicide attempters at repeated occasions over 2 years (total patient samples n=143, individuals n=30) and healthy controls (n=36). The association between the markers and psychiatric symptoms was assessed using the Montgomery Asberg Depression Rating Scale and the Suicide Assessment Scale.

RESULTS

Quinolinic acid was increased and kynurenic acid decreased over time in suicidal patients versus healthy controls. Furthermore, we found a significant association between low kynurenic acid and severe depressive symptoms, as well as between high interleukin-6 levels and more severe suicidal symptoms.

CONCLUSIONS

We demonstrate a long-term dysregulation of the kynurenine pathway in the central nervous system of suicide attempters. An increased load of inflammatory cytokines was coupled to more severe symptoms. We therefore suggest that patients with a dysregulated kynurenine pathway are vulnerable to develop depressive symptoms upon inflammatory conditions, as a result the excess production of the NMDA-receptor agonist quinolinic acid. This study provides a neurobiological framework supporting the use of NMDA-receptor antagonists in the treatment of suicidality and depression.

A randomized controlled trial of intranasal ketamine in major depressive disorder

BACKGROUND

The N-methyl-D-aspartate glutamate receptor antagonist ketamine, delivered via an intravenous route, has shown rapid antidepressant effects in patients with treatment-resistant depression. The current study was designed to test the safety, tolerability, and efficacy of intranasal ketamine in patients with depression who had failed at least one prior antidepressant trial.

METHODS

In a randomized, double-blind, crossover study, 20 patients with major depression were randomly assigned, and 18 completed 2 treatment days with intranasal ketamine hydrochloride (50 mg) or saline solution. The primary efficacy outcome measure was change in depression severity 24 hours after ketamine or placebo, measured using the Montgomery-Åsberg Depression Rating Scale. Secondary outcomes included persistence of benefit, changes in self-reports of depression, changes in anxiety, and proportion of responders. Potential psychotomimetic, dissociative, hemodynamic, and general adverse effects associated with ketamine were also measured.

RESULTS

Patients showed significant improvement in depressive symptoms at 24 hours after ketamine compared to placebo (t = 4.39, p < .001; estimated mean Montgomery-Åsberg Depression Rating Scale score difference of 7.6 ± 3.7; 95% confidence interval, 3.9-11.3). Response criteria were met by 8 of 18 patients (44%) 24 hours after ketamine administration compared with 1 of 18 (6%) after placebo (p = .033). Intranasal ketamine was well tolerated with minimal psychotomimetic or dissociative effects and was not associated with clinically significant changes in hemodynamic parameters.

CONCLUSIONS

This study provides the first controlled evidence for the rapid antidepressant effects of intranasal ketamine. Treatment was associated with minimal adverse effects. If replicated, these findings may lead to novel approaches to the pharmacologic treatment of patients with major depression.

In a randomized, double-blind clinical trial, adjuvant atorvastatin improved symptoms of depression and blood lipid values in patients suffering from severe major depressive disorder

BACKGROUND

The administration of statins seems to be a promising new avenue in the treatment of patients suffering from major depressive disorder (MDD), though patients suffering from severe MDD remain unstudied in this respect. The aim of the present study was therefore to investigate, in a randomized double-blind clinical trial, the influence of adjuvant atorvastatin on symptoms of depression in patients with MDD.

METHODS

A total of 60 patients suffering from MDD (mean age: 32.25 years; 53% males) received a standard medication of 40 mg/d citalopram. Next, patients were randomly assigned either to the atorvastatin group (20 mg/d) or to the placebo group. Blood lipid values were assessed at baseline and on completion of the study 12 weeks later. Experts rated depressive symptoms via Hamilton Depression Rating Scales (HDRS) at baseline and 3, 6 and 12 weeks later.

RESULTS

HDRS scores decreased over time; the significant Time by Group interaction showed that symptoms of depression decreased more in the atorvastatin than in the placebo group. Compared to the placebo group, in the atorvastatin group cholesterol, triglyceride, and Low Density Lipids (LDL) significantly decreased, and High Density Lipids (HDL) significantly increased over time. HDRS scores and blood lipid values were generally not associated.

CONCLUSIONS

The pattern of results suggests that adjuvant atorvastatin favorably influences symptoms of depression among patients with severe MDD. Given that after 12 weeks of monotherapy and adjuvant atorvastatin patients were still moderately to severely depressed, more powerful treatment algorithms such as augmentation and change of medication are highly recommended.

Muscle over mind

Depression is associated with elevated kynurenine levels, a tryptophan metabolite generated under stress and inflammatory conditions. Agudelo et al. (2014) now reveal how PGC-1α1 overexpression in muscle mimics anti-depressant effects of exercise by promoting kynurenine aminotransferase expression, likely preventing kynurenine from crossing the blood brain barrier to disrupt neural plasticity.

The dilemma of treatments for epileptic patients with depression

Depression is a state of low mood and aversion to activity. It may occur due to existence of other mental or physical diseases or from the medications for those illnesses. It is one of the leading sources of disability. Among these physical diseases, epilepsy is widely recognized as one of the main causes of depression. Patients with epilepsy are at high risk of developing depressive symptoms, and the suicide rates in patients with epilepsy have been reported to be much higher than in the general population. However, due to fears of lowering seizure threshold and adverse drug interactions between antidepressants and antiepileptic drugs, physician are reluctant to place patients with epilepsy on antidepressant medication. As a result, the question has been raised that what the best managements should be used to treat epileptic patients with depression. In this review, the currently used medications for antidepressants and antiepileptic drugs were summarized by their working targets in order to establish appropriate pharmacological management of depression and epilepsy. Despite the complex relationship between epilepsy and depression, coadministration of antidepressants and AEDs can still be done safely and effectively under the conditions of good clinical management. The ideal antidepressants for people with epilepsy should be efficacious but with few adverse effects, which will not antagonize GABAergic mechanisms or interfere with plasma anticonvulsant concentrations.

Mechanisms of NOS1AP action on NMDA receptor-nNOS signaling

NMDA receptors (NMDAR) are glutamate-gated calcium channels that play pivotal roles in fundamental aspects of neuronal function. Dysregulated receptor function contributes to many disorders. Recruitment by NMDARs of calcium-dependent enzyme nNOS via PSD95 is seen as a key contributor to neuronal dysfunction. nNOS adaptor protein (NOS1AP), originally described as a competitor of PSD95:nNOS interaction, is regarded an inhibitor of NMDAR-driven nNOS function. In conditions of NMDAR hyperactivity such as excitotoxicity, one expects NOS1AP to be neuroprotective. Conditions of NMDAR hypoactivity, as thought to occur in schizophrenia, might be exacerbated by NOS1AP. Indeed GWAS have implicated NOS1AP and nNOS in schizophrenia. Several studies now indicate NOS1AP can mediate rather than inhibit NMDAR/nNOS-dependent responses, including excitotoxic signaling. Yet the concept of NOS1AP as an inhibitor of nNOS predominates in studies of human disease genetics. Here we review the experimental evidence to evaluate this apparent controversy, consider whether the known functions of NOS1AP might defend neurons against NMDAR dysregulation and highlight specific areas for future investigation to shed light on the functions of this adaptor protein.

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.

The role of glutamate and its receptors in autism and the use of glutamate receptor antagonists in treatment

Glutamate is the major excitatory neurotransmitter in the brain and may be a key neurotransmitter involved in autism. Literature pertaining to glutamate and autism or related disorders (e.g., Fragile X syndrome) is reviewed in this article. Interest in glutamatergic dysfunction in autism is high due to increasing convergent evidence implicating the system in the disorder from peripheral biomarkers, neuroimaging, protein expression, genetics and animal models. Currently, there are no pharmaceutical interventions approved for autism that address glutamate deficits in the disorder. New treatments related to glutamatergic neurotransmission, however, are emerging. In addition, older glutamate-modulating medications with approved indications for use in other disorders are being investigated for re-tasking as treatments for autism. This review presents evidence in support of glutamate abnormalities in autism and the potential for translation into new treatments for the disorder.

Antidepressant-like effect of the mGluR5 antagonist MTEP in an astroglial degeneration model of depression

The glutamatergic predominance in the excitatory-inhibitory balance is postulated to be involved in the pathogenesis of depression. Such imbalance may be induced by astrocyte ablation which reduces glutamate uptake and increases glutamate level in the synaptic cleft. In the present study, we tried to ascertain whether astroglial degeneration in the prefrontal cortex could serve as an animal model of depression and whether inhibition of glutamatergic transmission by the mGluR5 antagonist MTEP could have antidepressant potential. Astrocytic toxins l-or dl-alpha-aminoadipic acid (AAA), 100μg/2μl, were microinjected, bilaterally into the rat medial prefrontal cortex (PFC) on the first and second day of experiment. MTEP (10mg/kg) or imipramine (30mg/kg) were administered on the fifth day. Following administration of MTEP or imipramine the forced swim test (FST) was performed for assessment of depressive-like behavior. The brains were taken out for analysis on day eight. The astrocytic marker, glial fibrillary acidic protein (GFAP) was quantified in PFC by Western blot method and by stereological counting of immunohistochemically stained sections. Both l-AAA and dl-AAA induced a significant increase in immobility time in the FST. This effect was reversed by imipramine, which indicates depressive-like effects of these toxins. A significant decrease in GFAP (about 50%) was found after l-AAA. Both the behavioral and GFAP level changes were prevented by MTEP injection. The obtained results indicate that the degeneration of astrocytes in the PFC by l-AAA may be a useful animal model of depression and suggest antidepressant potential of MTEP.

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.

Radiation Dosimetry of (18)F-FPEB in Humans

(18)F-3-fluoro-5-[(pyridin-3-yl)ethynyl]benzonitrile ((18)F-FPEB) is a potent and specific radioligand for the metabotropic glutamate receptor subtype 5 (mGluR5). Before undertaking clinical research studies with (18)F-FPEB, we performed studies of human radiation dosimetry.

METHODS

Serial whole-body scans were obtained in 9 healthy human subjects (5 men, 4 women) for 190-440 min after the intravenous administration of (18)F-FPEB. Radiation doses were estimated using the OLINDA/EXM software.

RESULTS

Peak organ doses were to the urinary bladder wall, 0.258 mGy/MBq (0.955 rad/mCi), and gallbladder wall, 0.193 mGy/MBq (0.716 rad/mCi). The effective dose was 0.025 mSv/MBq (0.0922 rem/mCi). The doses to the red marrow and spleen were 0.00797 mGy/MBq (0.0295 rad/mCi) and 0.00709 mGy/MBq (0.0262 rad/mCi), respectively. Reducing the urinary voiding interval to 60 or 90 min lowered the urinary bladder wall dose to 0.0885 mGy/MBq (0.327 rad/mCi) or 0.128 mGy/MBq (0.473 rad/mCi), respectively, and the effective dose to 0.0149 mSv/MBq (0.0551 rem/mCi) or 0.0171 mSv/MBq (0.0634 rem/mCi), respectively.

CONCLUSION

Urinary voiding should be performed during (18)F-FPEB studies to minimize radiation exposure to research subjects.

Effects of Brilliant Blue G on Serum Tumor Necrosis Factor-α Levels and Depression-like Behavior in Mice after Lipopolysaccharide Administration

OBJECTIVE

Accumulating evidence suggests that inflammation plays a role in the pathophysiology of major depression. The adenosine triphosphate (ATP)-sensitive P2X7 receptor (P2X7R) plays a crucial role in microglial activation caused by inflammation. The dye brilliant blue G (BBG) is a P2X7R antagonist. This study examined whether BBG shows antidepressant effects in an inflammation-induced model of depression.

METHODS

We examined the effects of BBG (12.5, 25, or 50 mg/kg) on serum tumor necrosis factor-α (TNF-α) levels after administering the bacterial endotoxin lipopolysaccharide (LPS; 0.5 mg/kg) and the effects of BBG (50 mg/kg) on depression-like behavior in the tail-suspension test (TST) and forced swimming test (FST).

RESULTS

Pretreatment with BBG (12.5, 25, or 50 mg/kg) significantly blocked the increase in serum TNF-α levels after a single dose of LPS (0.5 mg/kg). Furthermore, BBG (50 mg/kg) significantly attenuated the increase in immobility time in the TST and FST after LPS (0.5 mg/kg) administration.

CONCLUSION

The results suggest that BBG has anti-inflammatory and antidepressant effects in mice after LPS administration. Therefore, P2X7R antagonists are potential therapeutic drugs for inflammation-related major depression.

The effects of antidepressant treatment in prenatally stressed rats support the glutamatergic hypothesis of stress-related disorders

Abnormalities of synaptic transmission in the hippocampus represent an integral part of the altered programming triggered by early life stress, which enhances the vulnerability to stress-related disorders in the adult life. Rats exposed to prenatal restraint stress (PRS) develop enduring biochemical and behavioral changes characteristic of an anxious/depressive-like phenotype. Most neurochemical abnormalities in PRS rats are found in the ventral hippocampus, a region that encodes memories related to stress and emotions. We have recently demonstrated a causal link between the reduction of glutamate release in the ventral hippocampus and anxiety-like behavior in PRS rats. To confer pharmacological validity to the glutamatergic hypothesis of stress-related disorders, we examined whether chronic treatment with two antidepressants with different mechanisms of action could correct the defect in glutamate release and associated behavioral abnormalities in PRS rats. Adult unstressed or PRS rats were treated daily with either agomelatine (40 mg/kg, i.p.) or fluoxetine (5 mg/kg, i.p.) for 21 d. Both treatments reversed the reduction in depolarization-evoked glutamate release and in the expression of synaptic vesicle-associated proteins in the ventral hippocampus of PRS rats. Antidepressant treatment also corrected abnormalities in anxiety-/depression-like behavior and social memory performance in PRS rats. The effect on glutamate release was strongly correlated with the improvement of anxiety-like behavior and social memory. These data offer the pharmacological demonstration that glutamatergic hypofunction in the ventral hippocampus lies at the core of the pathological phenotype caused by early life stress and represents an attractive pharmacological target for novel therapeutic strategies.

[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.

The neurobiological pathogenesis of poststroke depression

Poststroke depression (PSD) is an important consequence after stroke, with negative impact on stroke outcome. The pathogenesis of PSD is complicated, with some special neurobiological mechanism, which mainly involves neuroanatomical, neuron, and biochemical factors and neurogenesis which interact in complex ways. Abundant studies suggested that large lesions in critical areas such as left frontal lobe and basal ganglia or accumulation of silent cerebral lesions might interrupt the pathways of monoamines or relevant pathways of mood control, thus leading to depression. Activation of immune system after stroke produces more cytokines which increase glutamate excitotoxicity, results in more cell deaths of critical areas and enlargement of infarctions, and, together with hypercortisolism induced by stress or inflammation after stroke which could decrease intracellular serotonin transporters, might be the key biochemical change of PSD. The interaction among cytokines, glucocorticoid, and neurotrophin results in the decrease of hippocampal neurogenesis which has been proved to be important for mood control and pharmaceutical effect of selective serotonin reuptake inhibitors and might be another promising pathway to understand the pathogenesis of PSD. In order to reduce the prevalence of PSD and improve the outcome of stroke, more relevant studies are still required to clarify the pathogenesis of PSD.

The role of mTOR in depression and antidepressant responses

The aim of this study was to characterize the mTOR signaling cascade in depression and the actions that antidepressant drugs have on this pathway. Herein, a literature review was performed by verification and comparison of textbooks and journal articles that describe the characterization of the mTOR signaling cascade and its relationship to depression and antidepressant drugs, especially ketamine. Postmortem studies have shown robust deficits in the mammalian target of rapamycin (mTOR) signaling in the prefrontal cortex of subjects diagnosed with major depressive disorder. However, besides the mTOR signaling pathway having an antidepressant response to various drugs, this seems to be more associated with antidepressant N-methyl-d-aspartate (NMDA) receptor antagonists, such as ketamine. The characterization of the mTOR signaling pathway in depression and its action in response to antidepressants show great potential for the identification of new therapeutic targets for the development of antidepressant drugs.

Recent progress in understanding subtype specific regulation of NMDA receptors by G Protein Coupled Receptors (GPCRs)

G Protein Coupled Receptors (GPCRs) are the largest family of receptors whose ligands constitute nearly a third of prescription drugs in the market. They are widely involved in diverse physiological functions including learning and memory. NMDA receptors (NMDARs), which belong to the ionotropic glutamate receptor family, are likewise ubiquitously expressed in the central nervous system (CNS) and play a pivotal role in learning and memory. Despite its critical contribution to physiological and pathophysiological processes, few pharmacological interventions aimed directly at regulating NMDAR function have been developed to date. However, it is well established that NMDAR function is precisely regulated by cellular signalling cascades recruited downstream of G protein coupled receptor (GPCR) stimulation. Accordingly, the downstream regulation of NMDARs likely represents an important determinant of outcome following treatment with neuropsychiatric agents that target selected GPCRs. Importantly, the functional consequence of such regulation on NMDAR function varies, based not only on the identity of the GPCR, but also on the cell type in which relevant receptors are expressed. Indeed, the mechanisms responsible for regulating NMDARs by GPCRs involve numerous intracellular signalling molecules and regulatory proteins that vary from one cell type to another. In the present article, we highlight recent findings from studies that have uncovered novel mechanisms by which selected GPCRs regulate NMDAR function and consequently NMDAR-dependent plasticity.

Chemokines and chemokine receptors in mood disorders, schizophrenia, and cognitive impairment: a systematic review of biomarker studies

The search for immune biomarkers in psychiatric disorders has primarily focused on pro-inflammatory cytokines. Other immune proteins including chemokines have been relatively neglected in such studies. Recent evidence has implicated chemokines in many neurobiological processes potentially relevant to psychiatric disorders, beyond their classical chemotactic functions. These may include neuromodulator effects, neurotransmitter-like effects, and direct/indirect regulation of neurogenesis. This systematic review presents the existing early evidence which supports an association of many chemokines with the psychiatric disorders: depression, bipolar disorder, schizophrenia, mild cognitive impairment and Alzheimer's disease. The non-specific association of chemokines including CXCL8 (IL-8), CCL2 (MCP-1), CCL3 (MIP-1α) and CCL5 (RANTES) with these disorders across diagnostic categories implies a generalised involvement of many chemokine systemic with psychiatric disease. Additional chemokines with great mechanistic relevance including CXCL12 (SDF-1) and CX3CL1 (fractalkine) have been rarely reported in the existing human literature and should be included in future clinical studies. The potential utility of these proteins as pathologically relevant biomarkers or therapeutic targets should be considered by future clinical and translational research.

Rethinking metabotropic glutamate receptor 5 pathological findings in psychiatric disorders: implications for the future of novel therapeutics

BACKGROUND

Pharmacological modulation of metabotropic glutamate receptor 5 (mGluR5) is of marked interest as a novel therapeutic mechanism to treat schizophrenia and major depression. However, the status of mGluR5 in the pathophysiology of these disorders remains unknown.

DISCUSSION

The majority of studies in the schizophrenia post-mortem brain indicate that total mGluR5 expression is unaltered. However, close examination of the literature suggests that these findings are superficial, and in actuality, a number of critical factors have not yet been considered; alterations may be highly dependent on brain region, neuronal population or molecular organisation in specific cellular compartments. A number of genetic knockout studies (mGluR5, Norbin, Homer1 etc.) continue to lend support to a role of mGluR5 in the pathology of schizophrenia, providing impetus to explore the regulation of mGluR5 beyond total mGluR5 protein and mRNA levels. With regards to major depression, preliminary evidence to date shows a reduction in total mGluR5 protein and mRNA levels; however, as in schizophrenia, there are no studies examining mGluR5 function or regulation in the pathological state. A comprehensive understanding of mGluR5 regulation in major depression, particularly in comparison to schizophrenia, is crucial as this has extensive implications for mGluR5 targeting novel therapeutics, especially considering that opposing modulation of mGluR5 is of therapeutic interest for these two disorders.

SUMMARY

Despite the complexities, examinations of post-mortem human brain provide valuable insights into the pathologies of these inherently human disorders. It is important, especially with regards to the identification of novel therapeutic drug targets, to have an in depth understanding of the pathophysiologies of these disorders. We posit that brain region- and cell type-specific alterations exist in mGluR5 in schizophrenia and depression, with evidence pointing towards altered regulation of this receptor in psychiatric pathology. We consider the implications of these alterations, as well as the distinction between schizophrenia and depression, in the context of novel mGluR5 based therapeutics.

Calcium-permeable AMPA receptors in the nucleus accumbens regulate depression-like behaviors in the chronic neuropathic pain state

Depression is a salient emotional feature of chronic pain. Depression alters the pain threshold and impairs functional recovery. To date, however, there has been limited understanding of synaptic or circuit mechanisms that regulate depression in the pain state. Here, we demonstrate that depression-like behaviors are induced in a rat model of chronic neuropathic pain. Using this model, we show that chronic pain selectively increases the level of GluA1 subunits of AMPA-type glutamate receptors at the synapses of the nucleus accumbens (NAc), a key component of the brain reward system. We find, in addition, that this increase in GluA1 levels leads to the formation of calcium-permeable AMPA receptors (CPARs). Surprisingly, pharmacologic blockade of these CPARs in the NAc increases depression-like behaviors associated with pain. Consistent with these findings, an AMPA receptor potentiator delivered into the NAc decreases pain-induced depression. These results show that transmission through CPARs in the NAc represents a novel molecular mechanism modulating the depressive symptoms of pain, and thus CPARs may be a promising therapeutic target for the treatment of pain-induced depression. More generally, these findings highlight the role of central glutamate signaling in pain states and define the brain reward system as an important region for the regulation of depressive symptoms of pain.

R (-)-ketamine shows greater potency and longer lasting antidepressant effects than S (+)-ketamine

The N-methyl-D-aspartate (NMDA) receptor antagonist ketamine is one of the most attractive antidepressants for treatment-resistant major depressive disorder (MDD). Ketamine (or RS (±)-ketamine) is a racemic mixture containing equal parts of R (-)-ketamine and S (+)-ketamine. In this study, we examined the effects of R- and S-ketamine on depression-like behavior in juvenile mice after neonatal dexamethasone (DEX) exposure. In the tail suspension test (TST) and forced swimming test (FST), both isomers of ketamine significantly attenuated the increase in immobility time, seen in DEX-treated juvenile mice at 27 and 29 h respectively, after ketamine injections. In the 1% sucrose preference test (SPT), both isomers significantly attenuated the reduced preference for 1% sucrose consumption in DEX-treated juvenile mice, 48 h after a ketamine injection. Interestingly, when immobility times were tested by the TST and FST at day 7, R-ketamine, but not S-ketamine, significantly lowered the increases in immobility seen in DEX-treated juvenile mice. This study shows that a single dose of R-ketamine produced rapid and long-lasting antidepressant effects in juvenile mice exposed neonatally to DEX. Therefore, R-ketamine appears to be a potent and safe antidepressant relative to S-ketamine, since R-ketamine may be free of psychotomimetic side effects.

Ketamine: synaptogenesis, immunomodulation and glycogen synthase kinase-3 as underlying mechanisms of its antidepressant properties

Major depressive disorder is an extremely debilitating condition affecting millions of people worldwide. Nevertheless, currently available antidepressant medications still have important limitations, such as a low response rate and a time lag for treatment response that represent a significant problem when dealing with individuals who are vulnerable and prone to self-harm. Recent clinical trials have shown that the N-methyl-D-aspartate receptor antagonist, ketamine, can induce an antidepressant response within hours, which lasts up to 2 weeks, and is effective even in treatment-resistant patients. Nonetheless, its use is limited due to its psychotomimetic and addictive properties. Understanding the molecular pathways through which ketamine exerts its antidepressant effects would help in the developing of novel antidepressant agents that do not evoke the same negative side effects of this drug. This review focuses specifically on the effects of ketamine on three molecular mechanisms that are relevant to depression: synaptogenesis, immunomodulation and regulation of glycogen synthase kinase-3 activity.

Zinc, magnesium and NMDA receptor alterations in the hippocampus of suicide victims

BACKGROUND

There is evidence for an association between suicidal behavior and depression. Accumulating data suggests that depression is related to a dysfunction of the brain's glutamatergic system, and that the N-methyl-d-aspartate (NMDA) receptor plays an important role in antidepressant activity. Zinc and magnesium, the potent antagonists of the NMDA receptor complex, are involved in the pathophysiology of depression and exhibit antidepressant activity.

METHODS

The present study investigated the potency of Zn(2+) and Mg(2+) to [(3)H] MK-801, which binds to the NMDA receptor channel in the hippocampus of suicide victims (n=17) and sudden death controls (n=6). Moreover, the concentrations of zinc and magnesium (by flame atomic absorption spectrometry) and levels of NMDA subunits (NR2A and NR2B) and PSD-95 protein (by Western blotting) were determined.

RESULTS

Our results revealed that there was a statistically significant decrease (by 29% and 40%) in the potency of zinc and magnesium (respectively) to inhibit [(3)H] MK-801 binding to NMDA receptors in the hippocampus in suicide tissue relative to the controls. These alterations were associated with increased NR2A (+68%) and decreases in both the NR2B (-46%) and PSD-95 (-35%) levels. Furthermore, lower concentrations (-9%) of magnesium (although not of zinc) were demonstrated in suicide tissue.

CONCLUSIONS

Our findings indicate that alterations in the zinc, magnesium and NMDA receptor complex in the hippocampus are potentially involved in the pathophysiology of suicide-related disorders (depression), which may lead to functional NMDA receptor hyperactivity.

Neurovascular unit dysfunction with blood-brain barrier hyperpermeability contributes to major depressive disorder: a review of clinical and experimental evidence

About one-third of people with major depressive disorder (MDD) fail at least two antidepressant drug trials at 1 year. Together with clinical and experimental evidence indicating that the pathophysiology of MDD is multifactorial, this observation underscores the importance of elucidating mechanisms beyond monoaminergic dysregulation that can contribute to the genesis and persistence of MDD. Oxidative stress and neuroinflammation are mechanistically linked to the presence of neurovascular dysfunction with blood-brain barrier (BBB) hyperpermeability in selected neurological disorders, such as stroke, epilepsy, multiple sclerosis, traumatic brain injury, and Alzheimer’s disease. In contrast to other major psychiatric disorders, MDD is frequently comorbid with such neurological disorders and constitutes an independent risk factor for morbidity and mortality in disorders characterized by vascular endothelial dysfunction (cardiovascular disease and diabetes mellitus). Oxidative stress and neuroinflammation are implicated in the neurobiology of MDD. More recent evidence links neurovascular dysfunction with BBB hyperpermeability to MDD without neurological comorbidity. We review this emerging literature and present a theoretical integration between these abnormalities to those involving oxidative stress and neuroinflammation in MDD. We discuss our hypothesis that alterations in endothelial nitric oxide levels and endothelial nitric oxide synthase uncoupling are central mechanistic links in this regard. Understanding the contribution of neurovascular dysfunction with BBB hyperpermeability to the pathophysiology of MDD may help to identify novel therapeutic and preventative approaches.

Modulation of the inflammatory response in rats chronically treated with the antidepressant agomelatine

Growing evidence suggests that the activation of the inflammatory/immune system contributes to depression pathogenesis, a hypothesis that might hold strong clinical implication. Indeed more than 30% of depressed patients fail to achieve remission, which poses the necessity to identify systems that may represent novel targets for medications. Accordingly, goal of this study was to evaluate the ability of the antidepressant agomelatine to modulate specific components of the immune response in the rat brain following an inflammatory challenge with lipopolysaccharide (LPS). To this aim, adult male rats were chronically treated with agomelatine before being acutely challenged with LPS 16 h after the last drug administration. Rats were sacrificed 2, 6, or 24h after the challenge and several components of the inflammatory response have been investigated by using real-time PCR or ELISA. We found that agomelatine significantly reduced the LPS-induced up-regulation of the pro-inflammatory cytokines interleukin-1β and interleukin-6 in the rat brain as well as at peripheral level. At central level, these effects are associated to the inhibition of NF-κB translocation as well as to alterations of mechanisms responsible for microglia activation. In addition, we found that agomelatine was also able to alter the expression of enzymes related to the kynurenine pathway that are thought to represent important mediators to inflammation-related depression. These data disclose novel properties that may contribute to the therapeutic effect of agomelatine providing evidence for a crucial role of specific components of the immune/inflammatory system in the antidepressant response and thereby in depression etiopathology.

Vulnerability versus resilience to prenatal stress in male and female rats; implications from gene expression profiles in the hippocampus and frontal cortex

Adverse life events during pregnancy may impact upon the developing fetus, predisposing prenatally stressed offspring to the development of psychopathology. In the present study, we examined the effects of prenatal restraint stress (PS) on anxiety- and depression-related behavior in both male and female adult Sprague-Dawley rats. In addition, gene expression profiles within the hippocampus and frontal cortex (FC) were examined in order to gain more insight into the molecular mechanisms that mediate the behavioral effects of PS exposure. PS significantly increased anxiety-related behavior in male, but not female offspring. Likewise, depression-related behavior was increased in male PS rats only. Further, male PS offspring showed increased basal plasma corticosterone levels in adulthood, whereas both PS males and females had lower stress-induced corticosterone levels when compared to controls. Microarray-based profiling of the hippocampus and FC showed distinct sex-dependent changes in gene expression after PS. Biological processes and/or signal transduction cascades affected by PS included glutamatergic and GABAergic neurotransmission, mitogen-activated protein kinase (MAPK) signaling, neurotrophic factor signaling, phosphodiesterase (PDE)/ cyclic nucleotide signaling, glycogen synthase kinase 3 (GSK3) signaling, and insulin signaling. Further, the data indicated that epigenetic regulation is affected differentially in male and female PS offspring. These sex-specific alterations may, at least in part, explain the behavioral differences observed between both sexes, i.e. relative vulnerability versus resilience to PS in male versus female rats, respectively. These data reveal novel potential targets for antidepressant and mood stabilizing drug treatments including PDE inhibitors and histone deacetylase (HDAC) inhibitors.

Systematic review and meta-analysis of serotonin transporter genotype and discontinuation from antidepressant treatment

There is evidence that 5-HTTLPR is associated with response following treatment from selective serotonin reuptake inhibitors (SSRIs). The short (S) allele has reduced serotonin transporter expression, compared to the long (L) allele, and has been reported to be associated with poorer response in Europeans, with the effect in other populations unclear. However the published literature is inconsistent. A systematic review and meta-analysis was performed to investigate the effect of 5-HTTLPR on discontinuation from antidepressant treatment. Data were obtained from 17 studies including 4309 participants. The principal outcome measure was the allelic odds ratio (OR) for the 5-HTTLPR S allele and discontinuation status. A random effects meta-analysis provided no evidence that the S allele was associated with increased odds of discontinuation from SSRIs in Europeans (OR 1.09, 95% CI 0.83-1.42, p=0.53; 10 studies, n=2504) but in East Asians there was evidence of a reduced odds of discontinuation (OR 0.28, 95% CI 0.12-0.64, p=0.002; 2 studies, n=136). There was a suggestion of small study bias (p=0.05). This meta-analysis provides no evidence of an association between 5-HTTLPR and discontinuation from antidepressant treatment in Europeans. The low number of studies in East Asian samples using SSRIs reduces confidence in our evidence that the S allele decreases the odds of discontinuation in this population. At present, there is no evidence of an association between 5-HTTLPR and discontinuation from SSRI treatment in a European population with further studies required to investigate its effects in different populations.

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).

Role of the NMDA receptor in cognitive deficits, anxiety and depressive-like behavior in juvenile and adult mice after neonatal dexamethasone exposure

Postnatal dexamethasone (DEX) therapy has been used to treat or prevent chronic lung disease after premature births. However, there are many reports of long-term negative neurodevelopmental sequelae following this treatment. In contrast, hydrocortisone (HYD), which has fewer neurodevelopment adverse effects, is used as an alternative for DEX. In this study, we report that neonatal DEX exposure (days 1-3) caused alterations of amino acids affecting N-methyl-d-aspartate (NMDA) receptor neurotransmission in mouse brains. Neonatal DEX, but not HYD, exposure (days 1-3) significantly decreased the GluN2B subunit of NMDA receptor in the hippocampus at juvenile and adult stages. Mice treated with DEX showed cognitive deficits, as well as anxiety and depressive-like behavior at juvenile and adult stages. In contrast, mice treated with HYD (days 1-3) showed no behavioral abnormalities at these stages. In the DEX suppression test, plasma levels of corticosterone in mice exposed neonatally to DEX and HYD were significantly higher at juvenile, but not adult stages. Pretreatment with Ro 63-1908, an antagonist at GluN2B subunit, 30min before each injection of DEX, prevented cognitive deficits, as well as anxiety and depressive-like behavior in juvenile and adult mice. Interestingly, subsequent repeated (days 29-33) administration of Ro 63-1908 or L701324, an antagonist of the glycine modulatory site on the NMDA receptor, significantly suppressed behavioral abnormalities in juvenile and adult mice after neonatal DEX exposure. These results indicate that neonatal DEX, but not HYD, exposure produced behavioral abnormalities in juvenile and adult mice by altering glutamatergic neurotransmission via the NMDA receptor. The NMDA receptor antagonists may prevent or treat these DEX-induced neonatal behavioral abnormalities in later life.

Glutamatergic GRIN2B and polyaminergic ODC1 genes in suicide attempts: associations and gene-environment interactions with childhood/adolescent physical assault

The complex etiology of suicidal behavior has frequently been investigated in relation to monoaminergic neurotransmission, but other neurosystems have shown alterations as well, involving excitatory glutamatergic and inhibitory γ-aminobutyric acid (GABA) molecular components, together with the modulating polyamines. Sufficiently powered and family-based association studies of glutamatergic and GABAergic genes with suicidal behavior are nonexistent, but several studies have been reported for polyamines. We therefore conducted, for the first time ever, an extensive family-based study of 113 candidate single-nucleotide polymorphisms (SNPs) located in 24 glutamatergic and GABA genes, in addition to interrelated polyaminergic genes, on the outcome of severe suicide attempts (SAs). The family-based analysis (n=660 trios) was supplemented with gene-environment interaction (G × E), case-control (n=519 controls) and subgroup analyses. The main observations were the previously unreported association and linkage of SNPs rs2268115 and rs220557 in GRIN2B, as well as of SNPs rs1049500 and rs2302614 in ODC1 (P<10(-2)). Furthermore, GRIN2B haplotypic associations were observed, in particular with a four-SNP AGGC haplotype (rs1805247-rs1806201-rs1805482-rs2268115; P<10(-5)), and a third SNP rs7559979 in ODC1 showed G × E with serious childhood/adolescent physical assault (P<10(-4)). SA subjects were characterized by transdiagnostic trait anger and past year alcohol-drug use disorders, but not by alcohol-drug use at SA, depression, anxiety or psychosis diagnoses. We also discuss a first ever confirmatory observation of SNP rs6526342 (polyaminergic SAT1) in SA, originally identified in completed suicides. The results suggest that specific genetic variants in a subset of glutamatergic (GRIN2B) and polyaminergic (ODC1) neurosystem genes may be of importance in certain suicidal subjects.

The involvement of ERK/CREB/Bcl-2 in depression-like behavior in prenatally stressed offspring rats

A number of studies reveal that prenatal stress (PS) may induce an increased vulnerability to depression in offspring. Some evidences indicate that extracellular signal-regulated kinase (ERK)-cyclic AMP responsive element binding protein (CREB) signal system may play an important role in the molecular mechanism of depression. In the present study, we examined the effects of prenatal restraint stress on depression-like behavior in one-month offspring Sprague-Dawley rats and expression of ERK2, CREB, B-cell lymphoma-2 (Bcl-2) mRNA in the hippocampus, prefrontal cortex and striatum to explore the potential role of ERK-CREB pathway in mediating the behavioral effects of PS exposure. Our findings demonstrated that PS increased immobility time in forced swimming test and decreased expression of ERK2, CREB, Bcl-2 mRNA in the hippocampus and prefrontal cortex of juvenile offspring rats except for CREB in hippocampus of male offspring. Changes induced by PS were partly prevented by MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist. These findings suggested that the ERK-CREB system might be related with the depression-like behavior in juvenile offspring rats subjected to PS, in which NMDA receptors might be involved.

Monitoring Neuroprotective Effects Using Positron Emission Tomography With [ 11 C]ITMM, a Radiotracer for Metabotropic Glutamate 1 Receptor

Background and Purpose—

Recent pharmacological evidence shows that antagonists for the metabotropic glutamate 1 (mGlu1) receptor exhibit neuroprotective effects in an ischemic brain. The aim of this study was to visualize the mGlu1 receptor and to monitor neuroprotective effects in a rat model of mild focal ischemia using positron emission tomography (PET) with N -[4-[6-(isopropylamino)pyrimidin-4-yl]-1,3-thiazol-2-yl]-4-[ 11 C]methoxy- N- methylbenzamide ([ 11 C]ITMM), a radiotracer for mGlu1.

Methods—

Rats were subjected to a 30-minute transient right middle cerebral artery occlusion. Saline or minocycline, a neuroprotective agent, was intravenously injected immediately after surgery and then daily during the subsequent 7 days. PET imaging with [ 11 C]ITMM was performed on the rats on days 1 to 7 after ischemia. In vitro autoradiography and histopathologic staining were conducted to confirm the results of in vivo PET.

Results—

PET with [ 11 C]ITMM demonstrated a gradual decrease of radioactivity in the ipsilateral sides of the ischemic brains. The radioactivity uptake ratio between the ipsilateral and contralateral sides also decreased with time. Minocycline treatment slowed down the decrease in the radioactivity level in the ipsilateral sides. Pretreatment with JNJ16259685, an mGlu1-selective ligand, significantly reduced brain radioactivity, confirming that the uptake of [ 11 C]ITMM primarily reflects mGlu1 levels in the brain regions, including the ischemic area. In vitro autoradiography and histopathology confirmed the changes in mGlu1 levels in the brains.

Conclusions—

[ 11 C]ITMM-PET may be a useful technique for characterizing the change in mGlu1 level during the occurrence and progression of neuronal damage and for evaluating the neuroprotective effects of drugs after ischemia.

Glutamate modulators as potential therapeutic drugs in schizophrenia and affective disorders

Severe psychiatric disorders such as schizophrenia are related to cognitive and negative symptoms, which often are resistant to current treatment approaches. The glutamatergic system has been implicated in the pathophysiology of schizophrenia and affective disorders. A key component is the dysfunction of the glutamatergic N-methyl-D-aspartate (NMDA) receptor. Substances regulating activation/inhibition of the NMDA receptor have been investigated in schizophrenia and major depression and are promising in therapeutic approaches of negative symptoms, cognition, and mood. In schizophrenia, add-on treatments with glycine, D-serine, D-alanine, D-cycloserine, D-amino acid oxidase inhibitors, glycine transporter-1 (GlyT-1) inhibitors (e.g., sarcosine, bitopertin) and agonists (e.g., LY2140023) or positive allosteric modulator (e.g., ADX71149) of group II metabotropic glutamate receptors (mGluRs) have been studied. In major depression, the NMDA receptor antagonists (e.g., ketamine, AZD6765), GluN2B subtype antagonists (e.g., traxoprodil, MK-0657), and partial agonists (e.g., D-cycloserine, GLYX-13) at the glycine site of the NMDA receptor have been proven to be effective in animal studies and first clinical trials. In addition, clinical studies of mGluR2/3 antagonist BCI-838 (a prodrug of BCI-632 (MGS0039)), mGluR2/3-negative allosteric modulators (NMAs) (e.g., RO499819, RO4432717), and mGluR5 NAMs (e.g., AZD2066, RO4917523) are in progress. Future investigations should include effects on brain structure and activation to elucidate neural mechanisms underlying efficacy of these drugs.

Ketamine regulates the presynaptic release machinery in the hippocampus

In the search for new drug targets, that may help point the way to develop fast-acting treatments for mood disorders, we have explored molecular pathways regulated by ketamine, an NMDA receptor antagonist, which has consistently shown antidepressant response within a few hours of administration. Using Sprague-Dawley rats we investigated the effects of ketamine on the presynaptic release machinery responsible for neurotransmitter release at 1, 2 and 4 h as well as 7 days after administration of a single subanesthetic dose of ketamine (15 mg/kg). A large reduction in the accumulation of SNARE complexes was observed in hippocampal synaptic membranes after 1, 2 and 4 h of ketamine administration. In parallel, we found a selective reduction in the expression of the synaptic vesicle protein synaptotagmin I and an increase in the levels of synapsin I in hippocampal synaptosomes suggesting a mechanism by which ketamine reduces SNARE complex formation, in part, by regulating the number of synaptic vesicles in the nerve terminals. Moreover, ketamine reduced Thr(286)-phosphorylated αCaMKII and its interaction with syntaxin 1A, which identifies CaMKII as a potential target for second messenger-mediated actions of ketamine. In addition, despite previous reports of ketamine-induced inhibition of GSK-3, we were unable to detect regulation of its activity after ketamine administration. Our findings demonstrate that ketamine rapidly induces changes in the hippocampal presynaptic machinery similar to those that are obtained only with chronic treatments with traditional antidepressants. This suggests that reduction of neurotransmitter release in the hippocampus has possible relevance for the rapid antidepressant effect of ketamine.

Glutamate-based antidepressants: preclinical psychopharmacology

Over the past 20 years, converging lines of evidence have both linked glutamatergic dysfunction to the pathophysiology of depression and demonstrated that the glutamatergic synapse presents multiple targets for developing novel antidepressants. The robust antidepressant effects of the N-methyl-D-aspartate receptor antagonists ketamine and traxoprodil provide target validation for this family of ionotropic glutamate receptors. This article reviews the preclinical evidence that it may be possible to develop glutamate-based antidepressants by not only modulating ionotropic (N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid) and metabotropic glutamate (mGlu) receptors, including mGlu2/3, mGLu5 and mGlu7 receptors, but also by altering synaptic concentrations of glutamate via specialized transporters such as glial glutamate transporter 1 (excitatory amino-acid transporter 2).

A 12-month naturalistic observation of three patients receiving repeat intravenous ketamine infusions for their treatment-resistant depression

BACKGROUND

Acute administration of subanesthestic doses of intravenous ketamine have been shown to elicit a rapid antidepressant response in patients with treatment-resistant depression. However, it remains to be seen if repeated doses over a longer period of time will have the same effects. Here, we assess the long-term efficacy of repeated intravenous ketamine infusions in three patients with high treatment-resistant depression via a naturalistic observation study.

METHOD

Three patients consented to intravenous ketamine infusions as a therapy for their treatment-resistant depression. Patients were administered ketamine at 0.5mg/kg of ideal body weight over 40 min followed by a saline flush until discharge. Severity of depressive symptoms was rated with the Montgomery-Asberg Depression Rating Scale.

RESULTS

All three patients responded to the ketamine infusions, but each went through an individualized course of treatment based on their own response.

LIMITATIONS

This was an open-label naturalistic observation without blinding, randomization, or a placebo control.

CONCLUSIONS

These cases add to the literature supporting the therapeutic effect of low-dose repeated intravenous ketamine for patients with treatment-resistant depression. Further study is needed to define the risks, benefits, indications, and contraindications of this potential treatment.

Acute atorvastatin treatment exerts antidepressant-like effect in mice via the L-arginine-nitric oxide-cyclic guanosine monophosphate pathway and increases BDNF levels

Atorvastatin is a synthetic and lipophilic statin that presents a good effect in decreasing cholesterol levels and is safe and well tolerated. Population-based studies have suggested a positive role of statins in reducing depression risk. This study aimed at investigating the atorvastatin effect in the tail suspension test (TST) and in the forced swimming test (FST). The participation of NMDA receptors and L-arginine-NO-cGMP in an atorvastatin antidepressant-like effect in the TST was evaluated. Acute atorvastatin administration (0.1-30 mg/kg) reduced the immobility time both in TST and FST. A similar effect was observed by using imipramine as a positive control in the TST and FST (1 and 0.1-1 mg/kg, p.o., respectively). An atorvastatin (0.1 mg/kg) antidepressant-like effect was prevented by the pretreatment of mice with NMDA (0.1 pmol/site, i.c.v.), L-arginine (750 mg/kg, i.p.) or sildenafil (5 mg/kg, i.p.). The administration of MK-801 (0.001 mg/kg, i.p.), ketamine (0.1 mg/kg, i.p.), 7-nitroindazole (50 mg/kg, i.p.), methylene blue (20 mg/kg, i.p.), or ODQ (30 pmol/site i.c.v.) in combination with a subeffective dose of atorvastatin (0.01 mg/kg, p.o.) reduced the immobility time in the TST compared to drugs alone, showing the participation of the pathway L-arginine-NO-cGMP. The administration of drugs did not produce any significant alteration in locomotor activity in the open-field test. Acute atorvastatin treatment (0.1-10.0 mg/kg, v.o.) increased the hippocampal BDNF levels, which is an effect that has not been observed in imipramine-treated mice. These results demonstrate that atorvastatin exerts an antidepressant-like effect and point to dependence on the inhibition of NMDA receptors and NO-cGMP synthesis, and on the increase of hippocampal BDNF levels.

Dysfunctional astrocytic regulation of glutamate transmission in a rat model of depression

Depression is usually associated with alterations in the monoaminergic system. However, new evidences suggest the involvement of the glutamatergic system in the aetiology of depression. Here we explored the glutamatergic system in a rat model of depression (i.e., the flinders sensitive line (FSL)) to reveal the mechanism underlying the emotional and cognitive aspects associated with the disease. We showed a dramatically elevated level of baseline glutamatergic synaptic transmission by whole-cell recordings as well as impairment in long-term potentiation induced by high-frequency stimulation in hippocampal slices from FSL rats compared with Sprague-Dawley rats. At behavioural level, FSL rats displayed recognition memory impairment in the novel object recognition test. Enantioselective chromatography analysis revealed lower levels of D-serine in the hippocampus of FSL rats and both synaptic plasticity and memory impairments were restored by administration of D-serine. We also observed dysfunctional astrocytic glutamate regulation including downregulation of the glia glutamate transporter GLAST as shown by western blot. One possibility is that the dysfunctional astrocytic glutamate reuptake triggers a succession of events, including the reduction of D-serine production as a safety mechanism to avoid NMDA receptor overactivation, which in turn causes the synaptic plasticity and memory impairments observed. These findings open up new brain targets for the development of more potent and efficient antidepressant drugs.

Tianeptine combination for partial or non-response to selective serotonin re-uptake inhibitor monotherapy

AIMS

The goal of this study was to assess the efficacy and tolerability of tianeptine in combination with selective serotonin re-uptake inhibitor (SSRI) in partial responders or non-responders to SSRI monotherapy.

METHODS

In this prospective, open-label, 6-week study, 150 patients with major depressive disorder who had previously not responded or partially responded to SSRI monotherapy were recruited. Tianeptine was given in combination with an SSRI for 6 weeks.

RESULTS

Significant improvements were observed in the mean scores of the Hamilton Depression Rating Scale (HDRS), Montgomery-Åsberg Depression Rating Scale (MADRS), and Clinical Global Impression-Severity (CGI-S). The change in the mean HDRS, MADRS, and CGI-S scores was significant from week 1. The response rates were 64.7% (HDRS) and 68.7% (MADRS), and the remission rates were 34.0% (HDRS) and 42.0% (MADRS) at week 6. Thirty-six patients (24.0%) reported adverse events that were determined by the investigator to be related to one of the study drugs. The tianeptine and SSRI combination was generally well-tolerated.

CONCLUSIONS

A combination strategy with tianeptine may be an effective and well-tolerated tool for patients who have failed to adequately respond to SSRI monotherapy.

Neonatal disruption of serine racemase causes schizophrenia-like behavioral abnormalities in adulthood: clinical rescue by d-serine

BACKGROUND

D-Serine, an endogenous co-agonist of the N-methyl-D-aspartate (NMDA) receptor, is synthesized from L-serine by serine racemase (SRR). Given the role of D-serine in both neurodevelopment and the pathophysiology of schizophrenia, we examined whether neonatal disruption of D-serine synthesis by SRR inhibition could induce behavioral abnormalities relevant to schizophrenia, in later life.

METHODOLOGY/PRINCIPAL FINDINGS

Neonatal mice (7-9 days) were injected with vehicle or phenazine methosulfate (Met-Phen: 3 mg/kg/day), an SRR inhibitor. Behavioral evaluations, such as spontaneous locomotion, novel object recognition test (NORT), and prepulse inhibition (PPI) were performed at juvenile (5-6 weeks old) and adult (10-12 weeks old) stages. In addition, we tested the effects of D-serine on PPI deficits in adult mice after neonatal Met-Phen exposure. Finally, we assessed whether D-serine could prevent the onset of schizophrenia-like behavior in these mice. Neonatal Met-Phen treatment reduced D-serine levels in the brain, 24 hours after the final dose. Additionally, this treatment caused behavioral abnormalities relevant to prodromal symptoms in juveniles and to schizophrenia in adults. A single dose of D-serine improved PPI deficits in adult mice. Interestingly, chronic administration of D-serine (900 mg/kg/day from P35 to P70) significantly prevented the onset of PPI deficits after neonatal Met-Phen exposure.

CONCLUSIONS/SIGNIFICANCE

This study shows that disruption of D-serine synthesis during developmental stages leads to behavioral abnormalities relevant to prodromal symptoms and schizophrenia, in later life. Furthermore, early pharmacological intervention with D-serine may prevent the onset of psychosis in adult.

Microglial dysregulation in psychiatric disease

Microglia, the brain's resident immune cells, are phagocytes of the macrophage lineage that have a key role in responding to inflammation and immune challenge in the brain. More recently, they have been shown to have a number of important roles beyond immune surveillance and response, including synaptic pruning during development and the support of adult neurogenesis. Microglial abnormalities have been found in several neuropsychiatric conditions, though in most cases it remains unclear whether these are causative or are a reaction to some other underlying pathophysiology. Here we summarize postmortem, animal, neuroimaging, and other evidence for microglial pathology in major depression, schizophrenia, autism, obsessive-compulsive disorder, and Tourette syndrome. We identify gaps in the existing literature and important areas for future research. If microglial pathology proves to be an important causative factor in these or other neuropsychiatric diseases, modulators of microglial function may represent a novel therapeutic strategy.

Schizophrenia is primed for an increased expression of depression through activation of immuno-inflammatory, oxidative and nitrosative stress, and tryptophan catabolite pathways

Schizophrenia and depression are two common and debilitating psychiatric conditions. Up to 61% of schizophrenic patients have comorbid clinical depression, often undiagnosed. Both share significant overlaps in underlying biological processes, which are relevant to the course and treatment of both conditions. Shared processes include changes in cell-mediated immune and inflammatory pathways, e.g. increased levels of pro-inflammatory cytokines and a Th1 response; activation of oxidative and nitrosative stress (O&NS) pathways, e.g. increased lipid peroxidation, damage to proteins and DNA; decreased antioxidant levels, e.g. lowered coenzyme Q10, vitamin E, glutathione and melatonin levels; autoimmune responses; and activation of the tryptophan catabolite (TRYCAT) pathway through induction of indoleamine-2,3-dioxygenase. Both show cognitive and neurostructural evidence of a neuroprogressive process. Here we review the interlinked nature of these biological processes, suggesting that schizophrenia is immunologically primed for an increased expression of depression. Such a conceptualization explains, and incorporates, many of the current perspectives on the nature of schizophrenia and depression, and has implications for the nature of classification and treatment of both disorders. An early developmental etiology to schizophrenia, driven by maternal infection, with subsequent impact on offspring immuno-inflammatory responses, creates alterations in the immune pathways, which although priming for depression, also differentiates the two disorders.

Glutamate concentration in the medial prefrontal cortex predicts resting-state cortical-subcortical functional connectivity in humans

Communication between cortical and subcortical regions is integral to a wide range of psychological processes and has been implicated in a number of psychiatric conditions. Studies in animals have provided insight into the biochemical and connectivity processes underlying such communication. However, to date no experiments that link these factors in humans in vivo have been carried out. To investigate the role of glutamate in individual differences in communication between the cortex--specifically the medial prefrontal cortex (mPFC)--and subcortical regions in humans, a combination of resting-state fMRI, DTI and MRS was performed. The subcortical target regions were the nucleus accumbens (NAc), dorsomedial thalamus (DMT), and periaqueductal grey (PAG). It was found that functional connectivity between the mPFC and each of the NAc and DMT was positively correlated with mPFC glutamate concentrations, whilst functional connectivity between the mPFC and PAG was negatively correlated with glutamate concentration. The correlations involving mPFC glutamate and FC between the mPFC and each of the DMT and PAG were mirrored by correlations with structural connectivity, providing evidence that the glutamatergic relationship may, in part, be due to direct connectivity. These results are in agreement with existing results from animal studies and may have relevance for MDD and schizophrenia.

Neuroinflammation and psychiatric illness

Multiple lines of evidence support the pathogenic role of neuroinflammation in psychiatric illness. While systemic autoimmune diseases are well-documented causes of neuropsychiatric disorders, synaptic autoimmune encephalitides with psychotic symptoms often go under-recognized. Parallel to the link between psychiatric symptoms and autoimmunity in autoimmune diseases, neuroimmunological abnormalities occur in classical psychiatric disorders (for example, major depressive, bipolar, schizophrenia, and obsessive-compulsive disorders). Investigations into the pathophysiology of these conditions traditionally stressed dysregulation of the glutamatergic and monoaminergic systems, but the mechanisms causing these neurotransmitter abnormalities remained elusive. We review the link between autoimmunity and neuropsychiatric disorders, and the human and experimental evidence supporting the pathogenic role of neuroinflammation in selected classical psychiatric disorders. Understanding how psychosocial, genetic, immunological and neurotransmitter systems interact can reveal pathogenic clues and help target new preventive and symptomatic therapies.

Connecting inflammation with glutamate agonism in suicidality

The NMDA-receptor antagonist ketamine has proven efficient in reducing symptoms of suicidality, although the mechanisms explaining this effect have not been detailed in psychiatric patients. Recent evidence points towards a low-grade inflammation in brains of suicide victims. Inflammation leads to production of quinolinic acid (QUIN) and kynurenic acid (KYNA), an agonist and antagonist of the glutamatergic N-methyl-D-aspartate (NMDA) receptor, respectively. We here measured QUIN and KYNA in the cerebrospinal fluid (CSF) of 64 medication-free suicide attempters and 36 controls, using gas chromatography mass spectrometry and high-performance liquid chromatography. We assessed the patients clinically using the Suicide Intent Scale and the Montgomery-Asberg Depression Rating Scale (MADRS). We found that QUIN, but not KYNA, was significantly elevated in the CSF of suicide attempters (P<0.001). As predicted, the increase in QUIN was associated with higher levels of CSF interleukin-6. Moreover, QUIN levels correlated with the total scores on Suicide Intent Scale. There was a significant decrease of QUIN in patients who came for follow-up lumbar punctures within 6 months after the suicide attempt. In summary, we here present clinical evidence of increased QUIN in the CSF of suicide attempters. An increased QUIN/KYNA quotient speaks in favor of an overall NMDA-receptor stimulation. The correlation between QUIN and the Suicide Intent Scale indicates that changes in glutamatergic neurotransmission could be specifically linked to suicidality. Our findings have important implications for the detection and specific treatment of suicidal patients, and might explain the observed remedial effects of ketamine.