Pathophysiology of depression and innovative treatments: remodeling glutamatergic synaptic connections

Advances in the study of NMDA receptors in depression pathogenesis and the antidepressant efficacy of their antagonists

N-methyl-D-aspartate receptors (NMDA receptors) play a crucial role as ionotropic glutamate receptors in regulating neuroplasticity, learning, memory, and a range of psychiatric disorders. Studies indicate that dysfunction of NMDA receptors is a key pathological mechanism in depression, where abnormal activation can result in neuronal excitotoxicity, excessive extracellular calcium ion accumulation, and disrupted neuroplasticity. As a non-competitive NMDA receptor antagonist, ketamine quickly relieves depressive symptoms by decreasing the activity of extracellular NMDA receptors and activating the mTOR signaling pathway. The treatment can improve severe depression and suicide thoughts within hours, but its potential for hallucinations, dissociative symptoms, and dependency restricts its broader application. Esketamine has demonstrated improvements in both side effects and efficacy and has received FDA approval, while other compounds with NMDA receptor modulating functions, such as memantine and rapastinel, are also showing potential in exploration. Future studies should concentrate on the molecular mechanisms of NMDA receptors, aiming to develop safer and more effective medications, and refine treatment strategies to offer personalized choices and longer-lasting efficacy for the treatment of depression.

Bioactive ketamine metabolite exerts in vivo neuroplastogenic effects to improve hippocampal function in a treatment-resistant depression model

An acute increase in excitatory synaptic transmission contributes to the rapid antidepressant actions of neuroplastogens, including ketamine and its bioactive metabolite, (2R,6R)-hydroxynorketamine (HNK). It is hypothesized that drug-induced metaplastic changes in synaptic strength account for therapeutically relevant behavioral adaptations in vivo. Using the plasticity-deficient Wistar Kyoto model of treatment-resistant depression, we demonstrate that (2R,6R)-HNK potentiates glutamatergic transmission, promotes synaptic strength, restores long-term potentiation (LTP), and reverses deficits in hippocampal-dependent synaptic activity and behavior. (2R,6R)-HNK selectively potentiated CA1 pyramidal neuron activity during novelty exploration and restored Schaffer collateral-dependent spatial recognition memory. Prior experience with spatial learning partially occluded LTP in control rats, an effect mimicked in LTP-impaired rats in which spatial learning deficits were reversed by (2R,6R)-HNK. These findings demonstrate that (2R,6R)-HNK exerts rapid neuroplastogenic effects in vivo, which improve cognitive function and promote adaptive changes in synaptic strength at functionally impaired synapses.

Delta opioid receptor agonists activate PI3K-mTORC1 signaling in parvalbumin-positive interneurons in mouse infralimbic prefrontal cortex to exert acute antidepressant-lie effects

The delta opioid receptor (DOP) is a promising target for novel antidepressants due to its potential for rapid action with minimal adverse effects; however, the functional mechanism underlying acute antidepressant actions remains elusive. We report that subcutaneous injection of the selective DOP agonist KNT-127 reduced immobility in the forced swimming test, and that this antidepressant-like response was reversed by intracerebroventricular injection of the selective mechanistic (or mammalian) target of rapamycin (mTOR) inhibitor rapamycin or the phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002. KNT-127 also alleviated social avoidance and reduced sucrose consumption (anhedonia) among chronic vicarious social defeat stress model mice, which were similarly reversed by PI3K and mTOR inhibitors. In addition, KNT-127 increased phosphorylation levels of the mTOR signaling-related proteins Akt and p70S6 kinase in medial prefrontal cortex as revealed by immunoblotting. In the forced swimming test, a microinfusion of KNT-127 and another DOP agonist SNC80 in the infralimbic prefrontal cortex (IL-PFC) attenuated the immobility, which were blocked by rapamycin and LY294002. Perfusion of KNT-127 onto IL-PFC slices increased miniature excitatory postsynaptic current frequency and reduced miniature inhibitory postsynaptic current frequency in pyramidal neurons as measured by whole-cell patch-clamping, and both responses were reversed by rapamycin. Imaging of brain slices from transgenic mice with DOP-promoter-driven green fluorescent protein revealed that most DOPs were expressed in parvalbumin-positive interneurons in the IL-PFC. These findings suggest that DOP agonists exert antidepressant-like actions by suppressing GABA release from parvalbumin-positive interneurons via the PI3K-Akt-mTORC1-p70S6 kinase pathway, thereby enhancing IL-PFC pyramidal neuron excitation.

Rapid hippocampal synaptic potentiation induced by ketamine metabolite (2R,6R)-hydroxynorketamine persistently primes synaptic plasticity

The pharmacologically active (R,S)-ketamine (ketamine) metabolite (2 R,6 R)-hydroxynorketamine (HNK) maintains ketamine's preclinical antidepressant profile without adverse effects. While hypotheses have been proposed to explain how ketamine and its metabolites initiate their antidepressant-relevant effects, it remains unclear how sustained therapeutic actions arise following drug elimination. To distinguish the physiological mechanisms involved in the rapid from sustained actions of HNK, we utilized extracellular electrophysiology combined with pharmacology to develop an in vitro hippocampal slice incubation model that exhibited pharmacological fidelity to the 1) rapid synaptic potentiation induced by HNK at the Schaffer collateral-CA1 (SC-CA1) synapse during bath-application to slices collected from mice, and 2) maintenance of metaplastic (priming) activity that enhanced N-methyl-D-aspartate receptor (NMDAR) activation-dependent long-term potentiation (LTP) hours after in vivo dosing. We used this model to reveal novel mechanisms engaged in HNK's temporally-sensitive antidepressant-relevant synaptic actions, finding that the induction of synaptic potentiation by HNK did not require NMDAR activity, but NMDAR activity was necessary to maintain synaptic priming. HNK required protein kinase A (PKA) activity to rapidly potentiate SC-CA1 neurotransmission to facilitate synaptic priming that persistently promoted LTP formation. HNK's rapid actions were blocked by inhibitors of adenylyl cyclase 1 (AC1), but not an AC5 inhibitor. We conclude that HNK rapidly potentiates SC-CA1 synaptic efficacy, which then stimulates priming mechanisms that persistently favor plasticity. Targeting such priming mechanisms may be an effective antidepressant strategy, and our incubation model may aid in revealing novel pharmacological targets.

Effects of tianeptine on mTORC1-mediated neuronal autophagy in primary rat hippocampal neurons under nutrient deprivation

The aim of this study was to investigate the effects of the antidepressant tianeptine on the mechanistic target of rapamycin complex 1(mTORC1)-mediated autophagy pathway in primary hippocampal neurons exposed to B27-deprived conditions. When primary hippocampal neurons were treated with tianeptine at doses of 1, 10, 50, and 100 µM for 3 days under B27-deprived conditions, we observed that it activated autophagy and increased the formation of autophagosomes through the upregulation of autophagic proteins, including autophagy-activating kinase 1 (ULK1), Beclin 1, LC3B-II/I, and p62. And at a concentration of 100 µM tianeptine, the decrease in mTORC1 phosphorylation induced by B27 deprivation was significantly reversed. Changes in the expression of autophagic proteins induced by B27 deprivation were reversed by tianeptine treatment in a concentration-dependent manner, and tianeptine significantly reduced the increase in LC3B membrane number induced by B27 deprivation, an effect that was blocked by pretreatment with rapamycin. In conclusion, tianeptine attenuated the activity of mTORC1-mediated autophagy in primary rat hippocampal neurons under B27-deprived conditions. These results may suggest a novel mechanism by which tianeptine may affect autophagy in neurons.

Demystifying the Antidepressant Mechanism of Action of Stinels, a Novel Class of Neuroplastogens: Positive Allosteric Modulators of the NMDA Receptor

Plastogens are a class of therapeutics that function by rapidly promoting changes in neuroplasticity. A notable example, ketamine, is receiving great attention due to its combined rapid and long-term antidepressant effects. Ketamine is an N-methyl-D-aspartate receptor (NMDAR) antagonist, and, in addition to its therapeutic activity, it is associated with psychotomimetic and dissociative side effects. Stinels-rapastinel, apimostinel, and zelquistinel-are also plastogens not only with rapid and long-term antidepressant effects but also with improved safety and tolerability profiles compared to ketamine. Previous descriptions of the mechanism by which stinels modulate NMDAR activity have been inconsistent and, at times, contradictory. The purpose of this review is to clarify the mechanism of action and contextualize stinels within a broader class of NMDAR-targeting therapeutics. In this review, we present the rationale behind targeting NMDARs for treatment-resistant depression and other psychiatric conditions, describe the various mechanisms by which NMDAR activity is regulated by different classes of therapeutics, and present evidence for the stinel mechanism. In contrast with previous descriptions of glycine-like NMDAR partial agonists, we define stinels as positive allosteric modulators of NMDAR activity with a novel regulatory binding site.

Genome-Wide Insights into Internalizing Symptoms in Admixed Latin American Children

BACKGROUND/OBJECTIVES

Internalizing disorders, including depression and anxiety, are major contributors to the global burden of disease. While the genetic architecture of these disorders in adults has been extensively studied, their early-life genetic mechanisms remain underexplored, especially in non-European populations. This study investigated the genetic mechanisms underlying internalizing symptoms in a cohort of Latin American children.

METHODS

This study included 1244 Brazilian children whose legal guardians completed the Child Behavior Checklist (CBCL) questionnaire. Genotyping was performed using the Illumina HumanOmni 2.5-8v1 BeadChip.

RESULTS

The genome-wide association analysis revealed a significant association of rs7196970 (p = 4.5 × 10-8, OR = 0.61), in the ABCC1 gene, with internalizing symptoms. Functional annotation highlighted variants in epigenetically active regulatory regions, with multiple variants linked to differential expression of ABCC1 across several human tissues. Pathway enrichment analysis identified 42 significant pathways, with notable involvement in neurobiological processes such as glutamatergic, GABAergic, and dopaminergic synapses.

CONCLUSIONS

This study identifies ABCC1 variants as novel genetic factors potentially associated with early-life internalizing symptoms. These results may contribute to future research on targeted interventions for childhood internalizing conditions.

Inhibition of prefrontal cortex parvalbumin interneurons mitigates behavioral and physiological sequelae of chronic stress in male mice

Chronic stress leads to hypofunction of the medial prefrontal cortex (mPFC), mechanisms of which remain to be determined. Enhanced activation of GABAergic of parvalbumin (PV) expressing interneurons (INs) is thought to play a role in stress-induced prefrontal inhibition. In this study, we tested whether chemogenetic inhibition of mPFC PV INs after chronic stress can rescue chronic stress-related behavioral and physiological phenotypes. Mice underwent 2 weeks of chronic variable stress (CVS) followed by a battery of behavioral tests known to be affected by chronic stress exposure, e.g. an open field (OF), novel object recognition (NOR), tail suspension test (TST), sucrose preference test (SPT), and light dark (LD) box. Inhibitory DREADDs were actuated by 3 mg/kg CNO administered 30 min prior to each behavioral test. CVS caused hyperactivity in the OF, reduced sucrose preference in the SPT (indicative of enhanced anhedonia), and increased anxiety-like behavior in the LD box. Inhibition of PV IN after stress mitigated these effects. In addition, CVS also resulted in reduced thymus weight and body weight loss, which were also mitigated by PV IN inhibition. Our results indicate that chronic stress leads to plastic changes in PV INs that may be mitigated by chemogenetic inhibition. Our findings implicate cortical GABAergic INs as a therapeutic target in stress-related diseases.

Research Progress on NMDA Receptor Enhancement Drugs for the Treatment of Depressive Disorder

Major depressive disorder (MDD) is a severe mental illness with a complex etiology. Currently, many medications employed in clinical treatment exhibit limitations such as delayed onset of action and a high incidence of adverse reactions. Therefore, there is a pressing need to develop antidepressants that exhibit enhanced efficacy and safety. The N-methyl-D-aspartate receptor (NMDAR), a distinctive glutamate-gated ion channel receptor, has been implicated in the onset and progression of depressive disorder, as evidenced by both preclinical and clinical research. The NMDAR antagonist, ketamine, exhibits rapid and sustained antidepressant effects, holding promise as a novel therapeutic approach for depressive disorder. However, its psychotomimetic impact and potential for addiction have restricted its widespread clinical application. Notably, over the past decade, studies have suggested that enhancing NMDAR functionality can produce antidepressant effects with improved safety, especially with the emergence of NMDAR-positive allosteric modulators (PAMs). We view this as a potential novel strategy for treating depression, forming the basis for the narrative review that follows.

Disruption of the autism-associated Pcdh9 gene leads to transcriptional alterations, synapse overgrowth, and defective network activity in the CA1

Protocadherins, a family of adhesion molecules with crucial role in cell-cell interactions, have emerged as key players in neurodevelopmental and psychiatric disorders. In particular, growing evidence links genetic alterations in Protocadherin 9 (PCDH9) gene with Autism Spectrum Disorder (ASD) and Major Depressive Disorder (MDD). Furthermore, Pcdh9 deletion induces neuronal defects in the mouse somatosensory cortex, accompanied by sensorimotor and memory impairment. However, the synaptic and molecular mechanisms of PCDH9 in the brain remain largely unknown, particularly concerning its impact on brain pathology. To address this question, we conducted a comprehensive investigation of PCDH9 role in the male mouse hippocampus at the ultrastructural, biochemical, transcriptomic, electrophysiological and network level. We show that PCDH9 mainly localizes at glutamatergic synapses and its expression peaks in the first week after birth, a crucial time window for synaptogenesis. Strikingly, Pcdh9 KO neurons exhibit oversized presynaptic terminal and postsynaptic density (PSD) in the CA1. Synapse overgrowth is sustained by the widespread up-regulation of synaptic genes, as revealed by single-nucleus RNA-seq (snRNA-seq), and the dysregulation of key drivers of synapse morphogenesis, including the SHANK2/CORTACTIN pathway. At the functional level, these structural and transcriptional abnormalities result into increased excitatory postsynaptic currents (mEPSC) and reduced network activity in the CA1 of Pcdh9 KO mice. In conclusion, our work uncovers Pcdh9 pivotal role in shaping the morphology and function of CA1 excitatory synapses, thereby modulating glutamatergic transmission within hippocampal circuits.Significance statement Converging evidence indicates that genetic alterations in Protocadherin 9 (PCDH9) gene are associated with Autism Spectrum Disorder (ASD) and Major Depressive Disorder (MDD). However, our understanding of PCDH9 physiological role and molecular mechanisms in the brain, as well as its connection to synaptic dysfunction and brain pathology, remains limited. Here we demonstrate that Pcdh9 regulates the transcriptional profile, morphology and function of glutamatergic synapses in the CA1, thereby tuning hippocampal network activity. Our results elucidate the molecular and synaptic mechanisms of a gene implicated in neurodevelopmental and psychiatric disorders, and suggest potential hippocampal alterations contributing to the cognitive deficits associated with these conditions.

The effect and mechanism of low-dose esketamine in neuropathic pain-related depression-like behavior in rats

BACKGROUND

Clinical evidence suggests that Esketamine (ESK) is an effective treatment for depression. However, the effects of Esketamine in treating depression-like behavior induced by neuropathic pain is unclear. The underlying molecular mechanisms require further investigation to provide new therapeutic targets for the treatment of clinical neuropathic pain-related depression.

METHODS

A neuropathic pain-related depression model was established in rats with spared nerve injury (SNI). Male Sprague-Dawley rats were randomly divided into four groups: Sham Group, SNI group, SNI + Normal Saline (NS) Group and SNI + ESK5mg/kg Group. Mechanical pain thresholds were measured to assess pain sensitivity in SNI rats. On the 14th day after surgery a forced swim test and sucrose preference test were used to evaluate the depressive-like behavior of rats in each group. Further, a proteomic analysis was used to quantify differentially expressed proteins. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were analyzed to explore the main protein targets of SNI in the medial prefrontal cortex. The expression of proteins was detected by Western blotting.

RESULTS

A neuropathic pain-related depression model was established. Compared with the Sham group, the mechanical pain threshold was decreased significantly (13.2 ± 1.0 vs. 0.7 ± 0.01 g n = 8), while immobility on the forced swim test was also decreased (93.1 ± 7.4 vs. 169.5 ± 9.6 s n = 8), and sucrose preference rate was significantly increased (98.8 ± 0.3 vs. 73.1 ± 1.4n = 7) in SNI group rats. Compared with the SNI + NS group, the mechanical pain threshold was not statistically significant, while immobility on the forced swim test was clearly decreased (161.1 ± 11.6 vs. 77.9 ± 5.0 s n = 8), and sucrose preference rate was significantly increased (53.1 ± 8.9 vs. 96.1 ± 1.4n = 7) in SNI + ESK5mg/kg group rats. To further investigate the underlying mechanism, we employed proteomics to identify proteins exhibiting more than a 1.2-fold difference (P < 0.05) in expression levels within each group for subsequent analysis. Relative to the Sham group, 88 downregulated and 104 up-regulated proteins were identified in the SNI group, while 120 and 84 proteins were up- and down-regulated in the Esketamine treatment group compared with the SNI + NS group. Compared with Sham group, the expressions of mGluR5 and Homer1a were up-regulated in the medial prefrontal cortex (mPFC) in SNI group (mGluR5:0.97 ± 0.05 vs 1.47 ± 0.15, Homer1a:1.03 ± 0.06 vs 1.46 ± 0.16n = 6), and down-regulated after intervention with Esketamine (mGluR5:1.54 ± 0.11 vs 1.06 ± 0.07, Homer1a:1.51 ± 0.13 vs 1.12 ± 0.34n = 6).

CONCLUSIONS

Low-dose Esketamine appeared to relieve depression-like behavior induced by neuropathic pain. The Homer1a-mGluR5 signaling pathway might be the mechanism of antidepressant effect of Esketamine.

Integrated Long Noncoding RNA and Messenger RNA Expression Analysis Identifies Molecules Specifically Associated With Resiliency and Susceptibility to Depression and Antidepressant Response

Background

Depression involves maladaptive processes impairing an individual's ability to interface with the environment appropriately. Long noncoding RNAs (lncRNAs) are gaining traction for their role in higher-order brain functioning. Recently, we reported that lncRNA coexpression modules may underlie abnormal responses to stress in rats showing depression-like behavior. The current study explored the global expression regulation of lncRNAs and messenger RNAs (mRNAs) in the hippocampus of rats showing susceptibility (learned helplessness [LH]) or resiliency (non-LH) to depression and fluoxetine response to LH (LH+FLX).

Methods

Multiple comparison analysis was performed with an analysis of variance via the aov and summary function in the R platform to identify the differential expression of mRNAs and lncRNAs among LH, non-LH, tested control, and LH+FLX groups. Weighted gene coexpression network analysis was used to identify distinctive modules and pathways associated with each phenotype. A machine learning analysis was conducted to screen the critical target genes. Based on the combined analysis, the regulatory effects of lncRNAs on mRNA expression were explored.

Results

Multiple comparison analyses revealed differentially expressed mRNAs and lncRNAs with each phenotype. Integrated bioinformatics analysis identified novel transcripts, specific modules, and regulatory pairs of mRNA-lncRNA in each phenotype. In addition, the machine learning approach predicted lncRNA-regulated Spp2 and Olr25 genes in developing LH behavior, whereas joint analysis of mRNA-lncRNA pairs identified Mboat7, Lmod1, I l 18, and Rfx5 genes in depression-like behavior and Adam6 and Tpra1 in antidepressant response.

Conclusions

The study shows a novel role for lncRNAs in the development of specific depression phenotypes and in identifying newer targets for therapeutic development.

Rapid Hippocampal Synaptic Potentiation Induced by Ketamine Metabolite ( 2R , 6R )-Hydroxynorketamine Persistently Primes Synaptic Plasticity

The pharmacologically active ( R , S )-ketamine (ketamine) metabolite ( 2R , 6R )-hydroxynorketamine (HNK) maintains ketamine's preclinical antidepressant profile without adverse effects. While hypotheses have been proposed to explain how ketamine and its metabolites initiate their antidepressant-relevant effects, it remains unclear how sustained therapeutic actions arise following drug elimination. To distinguish the physiological mechanisms involved in the rapid from sustained actions of HNK, we utilized extracellular electrophysiology combined with pharmacology to develop an in vitro hippocampal slice incubation model that exhibited pharmacological fidelity to the 1) rapid synaptic potentiation induced by HNK at the Schaffer collateral-CA1 (SC-CA1) synapse during bath-application to slices collected from mice, and 2) maintenance of metaplastic (priming) activity that lowered the threshold for N- methyl-D-aspartate receptor (NMDAR) activation-dependent long-term potentiation (LTP) hours after in vivo dosing. We then used this model to reveal novel druggable mechanisms engaged in HNK's temporally-sensitive antidepressant synaptic actions, finding that the induction of synaptic potentiation by HNK did not require NMDAR activity, but NMDAR activity was necessary to maintain synaptic priming. HNK required protein kinase A (PKA) activity to rapidly potentiate SC-CA1 neurotransmission to facilitate synaptic priming that persistently promoted LTP formation. HNK's rapid actions were blocked by inhibitors of adenylyl cyclase 1 (AC1), but not an AC5 inhibitor. We conclude that HNK rapidly potentiates SC-CA1 synaptic efficacy, which then stimulates priming mechanisms that persistently favor antidepressant-relevant plasticity. Targeting such priming mechanisms may be an effective antidepressant strategy, and using approaches such as our incubation model may aid in revealing novel pharmacological targets.

The Biomolecular Basis of Gut Microbiome on Neurological Diseases

The human gastrointestinal (GI) tract harbors many microorganisms, including viruses, protozoa, archaea, fungi, and bacteria. Altogether, these microbes constitute what we know as the gut microbiome (GM). These commensal communities have important implications for human health. They influence physiological processes through different mechanisms, including synthesizing neurotransmitters, regulating enzymatic pathways, and releasing molecules responsible for different signal pathways. The interaction between GM and brain function has been associated with the development and pathogenesis of neuropsychiatric diseases. This review discusses current studies targeting the regulation and modulation of GM in nerve, neuroendocrine, and immune pathways. Thus, we analyze current evidence on transcription, changes in composition, and specific interactions between the gut and brain from a biomolecular perspective. Special attention is paid to mood disorders and neurodegenerative diseases.

Inhibition of 14-3-3 proteins increases the intrinsic excitability of mouse hippocampal CA1 pyramidal neurons

14-3-3 proteins are a family of regulatory proteins that are abundantly expressed in the brain and enriched at the synapse. Dysfunctions of these proteins have been linked to neurodevelopmental and neuropsychiatric disorders. Our group has previously shown that functional inhibition of these proteins by a peptide inhibitor, difopein, in the mouse brain causes behavioural alterations and synaptic plasticity impairment in the hippocampus. Recently, we found an increased cFOS expression in difopein-expressing dorsal CA1 pyramidal neurons, indicating enhanced neuronal activity by 14-3-3 inhibition in these cells. In this study, we used slice electrophysiology to determine the effects of 14-3-3 inhibition on the intrinsic excitability of CA1 pyramidal neurons from a transgenic 14-3-3 functional knockout (FKO) mouse line. Our data demonstrate an increase in intrinsic excitability associated with 14-3-3 inhibition, as well as reveal action potential firing pattern shifts after novelty-induced hyperlocomotion in the 14-3-3 FKO mice. These results provide novel information on the role 14-3-3 proteins play in regulating intrinsic and activity-dependent neuronal excitability in the hippocampus.

Role of brain renin-angiotensin system in depression: A new perspective

Depression is a mood disorder characterized by abnormal thoughts. The pathophysiology of depression is related to the deficiency of serotonin (5HT), which is derived from tryptophan (Trp). Mitochondrial dysfunction, oxidative stress, and neuroinflammation are involved in the pathogenesis of depression. Notably, the renin-angiotensin system (RAS) is involved in the pathogenesis of depression, and different findings revealed that angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may be effective in depression. However, the underlying mechanism for the role of dysregulated brain RAS-induced depression remains speculative. Therefore, this review aimed to revise the conceivable role of ACEIs and ARBs and how these agents ameliorate the pathophysiology of depression. Dysregulation of brain RAS triggers the development and progression of depression through the reduction of brain 5HT and expression of brain-derived neurotrophic factor (BDNF) and the induction of mitochondrial dysfunction, oxidative stress, and neuroinflammation. Therefore, inhibition of central classical RAS by ARBS and ACEIs and activation of non-classical RAS prevent the development of depression by regulating 5HT, BDNF, mitochondrial dysfunction, oxidative stress, and neuroinflammation.

Antiretroviral drugs from multiple classes induce loss of excitatory synapses between hippocampal neurons in culture

Introduction: Antiretroviral (ARV) drugs have improved prognoses for people living with HIV. However, HIV-associated neurocognitive disorders (HAND) persist despite undetectable viral loads. Some ARVs have been linked to neuropsychiatric effects that may contribute to HAND. Synapse loss correlates with cognitive decline in HAND and synaptic deficits may contribute to the neuropsychiatric effects of ARV drugs. Methods: Using an automated high content assay, rat hippocampal neurons in culture expressing PSD95-eGFP to label glutamatergic synapses and mCherry to fill neuronal structures were imaged before and after treatment with 25 clinically used ARVs. Results and Discussion: At a concentration of 10 μM the protease inhibitors nelfinavir and saquinavir, the non-nucleoside reverse transcriptase inhibitors etravirine and the 8-OH metabolite of efavirenz, the integrase inhibitor bictegravir, and the capsid inhibitor lenacapavir produced synaptic toxicity. Only lenacapavir produced synapse loss at the nanomolar concentrations estimated free in the plasma, although all 4 ARV drugs induced synapse loss at Cmax. Evaluation of combination therapies did not reveal synergistic synaptic toxicity. Synapse loss developed fully by 24 h and persisted for at least 3 days. Bictegravir-induced synapse loss required activation of voltage-gated Ca2+ channels and bictegravir, etravirine, and lenacapavir produced synapse loss by an excitotoxic mechanism. These results indicate that select ARV drugs might contribute to neuropsychiatric effects in combination with drugs that bind serum proteins or in disease states in which synaptic function is altered. The high content imaging assay used here provides an efficient means to evaluate new drugs and drug combinations for potential CNS toxicity.

Hydroxynorketamine, but not ketamine, acts via α7 nicotinic acetylcholine receptor to control presynaptic function and gene expression

Ketamine is clinically used fast-acting antidepressant. Its metabolite hydroxynorketamine (HNK) shows a robust antidepressant effect in animal studies. It is unclear, how these chemically distinct compounds converge on similar neuronal effects. While KET acts mostly as N-methyl-d-aspartate receptor (NMDAR) antagonist, the molecular target of HNK remains enigmatic. Here, we show that KET and HNK converge on rapid inhibition of glutamate release by reducing the release competence of synaptic vesicles and induce nuclear translocation of pCREB that controls expression of neuroplasticity genes connected to KET- and HNK-mediated antidepressant action. Ro25-6981, a selective antagonist of GluN2B, mimics effect of KET indicating that GluN2B-containing NMDAR might mediate the presynaptic effect of KET. Selective antagonist of α7 nicotinic acetylcholine receptors (α7nAChRs) or genetic deletion of Chrna7, its pore-forming subunit, fully abolishes HNK-induced synaptic and nuclear regulations, but leaves KET-dependent cellular effects unaffected. Thus, KET or HNK-induced modulation of synaptic transmission and nuclear translocation of pCREB can be mediated by selective signaling via NMDAR or α7nAChRs, respectively. Due to the rapid metabolism of KET to HNK, it is conceivable that subsequent modulation of glutamatergic and cholinergic neurotransmission affects circuits in a cell-type-specific manner and contributes to the therapeutic potency of KET. This finding promotes further exploration of new combined medications for mood disorders.

Therapeutic potential of N-methyl-D-aspartate receptor modulators in psychiatry

N-methyl-D-aspartate (NMDA) receptors mediate a slow component of excitatory synaptic transmission, are widely distributed throughout the central nervous system, and regulate synaptic plasticity. NMDA receptor modulators have long been considered as potential treatments for psychiatric disorders including depression and schizophrenia, neurodevelopmental disorders such as Rett Syndrome, and neurodegenerative conditions such as Alzheimer's disease. New interest in NMDA receptors as therapeutic targets has been spurred by the findings that certain inhibitors of NMDA receptors produce surprisingly rapid and robust antidepressant activity by a novel mechanism, the induction of changes in the brain that well outlast the presence of drug in the body. These findings are driving research into an entirely new paradigm for using NMDA receptor antagonists in a host of related conditions. At the same time positive allosteric modulators of NMDA receptors are being pursued for enhancing synaptic function in diseases that feature NMDA receptor hypofunction. While there is great promise, developing the therapeutic potential of NMDA receptor modulators must also navigate the potential significant risks posed by the use of such agents. We review here the emerging pharmacology of agents that target different NMDA receptor subtypes, offering new avenues for capturing the therapeutic potential of targeting this important receptor class.

The role of cell adhesion molecule IgSF9b at the inhibitory synapse and psychiatric disease

Understanding perturbations in synaptic function between health and disease states is crucial to the treatment of neuropsychiatric illness. While genome-wide association studies have identified several genetic loci implicated in synaptic dysfunction in disorders such as autism and schizophrenia, many have not been rigorously characterized. Here, we highlight immunoglobulin superfamily member 9b (IgSF9b), a cell adhesion molecule thought to localize exclusively to inhibitory synapses in the brain. While both pre-clinical and clinical studies suggest its association with psychiatric diseases, our understanding of IgSF9b in synaptic maintenance, neural circuits, and behavioral phenotypes remains rudimentary. Moreover, these functions wield undiscovered influences on neurodevelopment. This review evaluates current literature and publicly available gene expression databases to explore the implications of IgSF9b dysfunction in rodents and humans. Through a focused analysis of one high-risk gene locus, we identify areas requiring further investigation and unearth clues related to broader mechanisms contributing to the synaptic etiology of psychiatric disorders.

Simvastatin ameliorates synaptic plasticity impairment in chronic mild stress-induced depressed mice by modulating hippocampal NMDA receptor

BACKGROUND

In our previous study, we showed simvastatin exerts an antidepressant effect and inhibits neuroinflammation. Given the role of synaptic impairment in depression development, we investigate the effect of simvastatin on synaptic plasticity in depression and the related mechanisms.

METHODS

Electrophysiological analysis, Golgi staining, and transmission electron microscope were performed to analyze the effect of simvastatin on synaptic impairment in depression. In addition, the localization and reactivity of N-methyl-D-aspartate receptor (NMDAR) subunits and the downstream signaling were investigated to explore the mechanism of simvastatin's effect on synaptic plasticity.

RESULTS

Simvastatin ameliorated the reduction of the magnitude of long-term potentiation (LTP) in Schaffer collateral-CA1, restored hippocampal dendritic spine density loss, improved the number of spine synapses, reversed the reduction in BrdU-positive cells in chronic mild stress (CMS)-induced depressed mice, and ameliorated NMDA-induced neurotoxicity in hippocampal neurons. Dysfunction of NMDAR activity in the hippocampus is associated with depression. Simvastatin treatment reversed the surface expression and phosphorylation changes of NMDAR subunits in NMDA-treated hippocampal neurons and depressed mice. In addition, simvastatin further increased the levels of mature BDNF, activating TrkB-Akt-mTOR signaling, which is critical for synaptic plasticity.

CONCLUSIONS

These findings suggest that simvastatin can improve the dysfunction of NMDAR and ameliorate hippocampal synaptic plasticity impairment in depressed mice.

D-mannose is a rapid inducer of ACSS2 to trigger rapid and long-lasting antidepressant responses through augmenting BDNF and TPH2 levels

The potentiation of synaptic plasticity and serotonin generation by brain-derived neurotrophic factor (BDNF) and tryptophan hydroxylase 2 (TPH2) is well characterized to facilitate rapid and long-lasting antidepressant actions. Therefore, the identification of the key protein that simultaneously controls both BDNF and TPH2 is important for the treatment of depression. We show here that a lack of acetyl-CoA synthetase short-chain family member 2 (ACSS2) causes impairments in BDNF-dependent synaptic plasticity and tryptophan hydroxylase 2 (TPH2)-mediated serotonin generation, thereby contributing to spontaneous and chronic restraint stress (CRS)-induced depressive-like behavior in mice. Conversely, D-mannose is identified as a rapid ACSS2 inducer and thus mediates rapid and long-lasting antidepressant-like effects. Mechanistically, acute and chronic D-mannose administration inhibits the phosphorylation of EF2 to increase BDNF levels and reverse the reduction of TPH2 histone acetylation and transcription. We reveal that ACSS2 promotes TPH2 histone acetylation and transcription with the requirement of AMPK activation. To elevate nuclear ACSS2 levels, D-mannose can rapidly and persistently activate AMPK via Ca2+-CAMKK2 and the lysosomal AXIN-LKB1 pathway to facilitate its fast-acting and persistent antidepressant responses. Taken together, the results presented here reveal that ACSS2 functions as a novel target to link rapid and persistent antidepressant actions and further suggest that D-mannose is a potential therapeutic agent to resist depression through its augmentation of the ACSS2 dependent BDNF and TPH2 pathways.

Effects of Antidepressant Medication on Brain-derived Neurotrophic Factor Concentration and Neuroplasticity in Depression: A Review of Preclinical and Clinical Studies

Depression is the most prevalent and debilitating disease with great impact on societies. Evidence suggests Brain-Derived Neurotrophic Factor (BDNF) plays an important role in pathophysiology of depression. Depression is associated with altered synaptic plasticity and neurogenesis. BDNF is the main regulatory protein that affects neuronal plasticity in the hippocampus. A wealth of evidence shows decreased levels of BDNF in depressed patients. Important literature demonstrated that BDNF-TrkB signaling plays a key role in therapeutic action of antidepressants. Numerous studies have reported anti-depressant effects on serum/plasma levels of BDNF and neuroplasticity which may be related to improvement of depressive symptoms. Most of the evidence suggested increased levels of BDNF after antidepressant treatment. This review will summarize recent findings on the association between BDNF, neuroplasticity, and antidepressant response in depression. Also, we will review recent studies that evaluate the association between postpartum depression as a subtype of depression and BDNF levels in postpartum women.

Sex-Dependent Effects of Chronic Restraint Stress on Mood-Related Behaviours and Neurochemistry in Mice

Anxiety and depressive disorders are closely associated; however, the pathophysiology of these disorders remains poorly understood. Further exploration of the mechanisms involved in anxiety and depression such as the stress response may provide new knowledge that will contribute to our understanding of these disorders. Fifty-eight 8-12-week-old C57BL6 mice were separated into experimental groups by sex as follows: male controls (n = 14), male restraint stress (n = 14), female controls (n = 15) and female restraint stress (n = 15). These mice were taken through a 4-week randomised chronic restraint stress protocol, and their behaviour, as well as tryptophan metabolism and synaptic proteins, were measured in the prefrontal cortex and hippocampus. Adrenal catecholamine regulation was also measured. The female mice showed greater anxiety-like behaviour than their male counterparts. Tryptophan metabolism was unaffected by stress, but some basal sex characteristics were noted. Synaptic proteins were reduced in the hippocampus in stressed females but increased in the prefrontal cortex of all female mice. These changes were not found in any males. Finally, the stressed female mice showed increased catecholamine biosynthesis capability, but this effect was not found in males. Future studies in animal models should consider these sex differences when evaluating mechanisms related to chronic stress and depression.

Ketamine and the Disinhibition Hypothesis: Neurotrophic Factor-Mediated Treatment of Depression

Ketamine is a promising alternative to traditional pharmacotherapies for major depressive disorder, treatment-resistant depression, and other psychiatric conditions that heavily contribute to the global disease burden. In contrast to the current standard of care medications for these disorders, ketamine offers rapid onset, enduring clinical efficacy, and unique therapeutic potential for use in acute, psychiatric emergencies. This narrative presents an alternative framework for understanding depression, as mounting evidence supports a neuronal atrophy and synaptic disconnection theory, rather than the prevailing monoamine depletion hypothesis. In this context, we describe ketamine, its enantiomers, and various metabolites in a range of mechanistic actions through multiple converging pathways, including N-methyl-D-aspartate receptor (NMDAR) inhibition and the enhancement of glutamatergic signaling. We describe the disinhibition hypothesis, which posits that ketamine's pharmacological action ultimately results in excitatory cortical disinhibition, causing the release of neurotrophic factors, the most important of which is brain-derived neurotrophic factor (BDNF). BDNF-mediated signaling along with vascular endothelial growth factor (VEGF) and insulin-like growth factor 1 (IGF-1) subsequently give rise to the repair of neuro-structural abnormalities in patients with depressive disorders. Ketamine's efficacious amelioration of treatment-resistant depression is revolutionizing psychiatric treatment and opening up fresh vistas for understanding the underlying causes of mental illness.

Long-term exposure changes the environmentally relevant bis(2-ethylhexyl) phthalate to be a neuro-hazardous substance disrupting neural homeostasis in emotional and cognitive functions

Bis(2-ethylhexyl) phthalate (DEHP) is the most used member of the phthalate class of compounds. Extensive use of this plasticizer allows daily exposure to humans via various routes. A positive relationship between DEHP exposure and neurobehavioral disorders is suspected. But, there are insufficient data on the harmfulness of neurobehavioral disorders caused by DEHP exposure, particularly at daily exposure levels. In this study, we assessed the consequences of daily DEHP ingestion (2 and 20 mg/kg diets) in male mice for at least 100 days and examined its effects on neuronal functions associated with neurobehavioral disorders, such as depression and cognitive decline. We found the marked depressive behaviors and reduced learning and memory function in the DEHP-ingestion groups, and that biomarkers related to chronic stress were increased in plasma and brain tissues. Long-term DEHP ingestion induced collapse of glutamate (Glu) and glutamine (Gln) homeostasis as a result of disruption of the Glu-Gln cycle in the medial prefrontal cortex and hippocampus. The reduced glutamatergic neurotransmission activity caused by DEHP ingestion was demonstrated using an electrophysiological method. This study revealed that long-term exposure to DEHP is hazardous and can cause neurobehavioral disorders, even at daily exposure levels.

Optogenetic stimulation of transmission from prelimbic cortex to nucleus accumbens core overcomes resistance to venlafaxine in an animal model of treatment-resistant depression

BACKGROUND

Our earlier study demonstrated that repeated optogenetic stimulation of afferents from ventral hippocampus (vHIP) to the prelimbic region of medial prefrontal cortex (mPFC) overcame resistance to antidepressant treatment in Wistar-Kyoto (WKY) rats. These results suggested that antidepressant resistance may result from an insufficiency of transmission from vHIP to mPFC. Here we examined whether similar effects can be elicited from major output of mPFC; the pathway from to nucleus accumbens core (NAc).

METHOD

WKY rats were subjected to Chronic Mild Stress and were used in two sets of experiments: 1) they were treated acutely with optogenetic stimulation of afferents to NAc core originating from the mPFC, and 2) they were treated with chronic (5 weeks) venlafaxine (10 mg/kg) and/or repeated (once weekly) optogenetic stimulation of afferents to NAc originating from either mPFC or vHIP.

RESULTS

Chronic mild stress procedure decreased sucrose intake, open arm entries on elevated plus maze, and novel object recognition test. Acute optogenetic stimulation of the mPFC-NAc and vHIP-NAc pathways had no effect in sucrose or plus maze tests, but increased object recognition. Neither venlafaxine nor mPFC-NAc optogenetic stimulation alone was effective in reversing the effects of CMS, but the combination of chronic antidepressant and repeated optogenetic stimulation improved behaviour on all three measures.

CONCLUSIONS

The synergism between venlafaxine and mPFC-NAc optogenetic stimulation supports the hypothesis that the mechanisms of non-responsiveness of WKY rats involves a failure of antidepressant treatment to restore transmission in the mPFC-NAc pathway. Together with earlier results, this implicates insufficiency in a vHIP-mPFC-NAc circuit in non-responsiveness to antidepressant drugs.

Early Clinical Experiences of Esketamine Nasal Spray in the UK in Adults with Treatment-Resistant Major Depressive Disorder: Advisory Panel Recommendations

PURPOSE

Treatment-resistant depression (TRD) is associated with profound morbidity for patients, placing a significant burden on those affected, the health service and wider society. Despite this, TRD remains chronically underserved in terms of viable treatment options. To address this gap, an advisory panel of psychiatrists and clinical researchers with experience in managing TRD convened to develop best practice statements on the use of esketamine nasal spray, one of the first TRD treatments to be licensed in 30 years.

METHODS

During a virtual meeting held on 12th November 2020, the advisory panel shared their experiences of using esketamine nasal spray in their clinical practice. The meeting focused on developing and refining recommendations for setting up and running an efficient esketamine nasal spray clinic for patients living with TRD. At the conclusion of the meeting, agreement was reached on all recommendation statements.

RESULTS

In setting up an esketamine nasal spray clinic, it is important to consider the logistical requirements involved and put measures in place to ensure it runs as efficiently as possible. Educating patients about the treatment and maintaining their well-being is paramount for preventing discontinuation. Putting in place checklists can be a useful strategy for ensuring treatment appointments run smoothly and safely.

CONCLUSION

Providing additional treatment options for the management of TRD, such as esketamine nasal spray, is likely to be key to improving the long-term outcomes of this underserved patient population.

Effect of transcranial magnetic stimulation on postural control of individuals with major depressive disorder: A case report

Accidental falls and major depressive disorder (MDD) are two common conditions associated with aging. Initial treatment of MDD often starts with administering antidepressants, followed by transcranial magnetic stimulation (TMS) for treatment-resistant individuals. The purpose of this case study was to determine the effect of repetitive TMS (rTMS) on postural control of an individual with MDD. A 44-year-old male with recurrent severe MDD was assessed for postural balance during eyes closed and eyes open conditions, pre and post three consecutive sessions receiving high-frequency rTMS (NeuroStar). Total excursion and velocity of sway significantly decreased following rTMS treatment when eyes were closed (p < 0.05). Power of the sway changed, but the changes were not statistically significant. The fractal dimension confidence circle area decreased significantly in eyes closed trials (p < 0.05). It appears that rTMS application can potentially impact postural steadiness in individuals with MDD. Our results warrant further studies with larger study samples.

NMDA Receptor Activation-Dependent Antidepressant-Relevant Behavioral and Synaptic Actions of Ketamine

Ketamine is a well-characterized NMDA receptor (NMDAR) antagonist, although the relevance of this pharmacology to its rapid (within hours of administration) antidepressant actions, which depend on mechanisms convergent with strengthening of excitatory synapses, is unclear. Activation of synaptic NMDARs is necessary for the induction of canonical long-term potentiation (LTP) leading to a sustained expression of increased synaptic strength. We tested the hypothesis that induction of rapid antidepressant effects requires NMDAR activation, by using behavioral pharmacology, western blot quantification of hippocampal synaptoneurosomal protein levels, and ex vivo hippocampal slice electrophysiology in male mice. We found that ketamine exerts an inverted U-shaped dose-response in antidepressant-sensitive behavioral tests, suggesting that an excessive NMDAR inhibition can prevent ketamine's antidepressant effects. Ketamine's actions to induce antidepressant-like behavioral effects, up-regulation of hippocampal AMPAR subunits GluA1 and GluA2, as well as metaplasticity measured ex vivo using electrically-stimulated LTP, were abolished by pretreatment with other non-antidepressant NMDAR antagonists, including MK-801 and CPP. Similarly, the antidepressant-like actions of other putative rapid-acting antidepressant drugs (2R,6R)-hydroxynorketamine (ketamine metabolite), MRK-016 (GABAAα5 negative allosteric modulator), and LY341495 (mGlu2/3 receptor antagonist) were blocked by NMDAR inhibition. Ketamine acted synergistically with an NMDAR positive allosteric modulator to exert antidepressant-like behavioral effects and activation of the NMDAR subunit GluN2A was necessary and sufficient for such relevant effects. We conclude rapid-acting antidepressant compounds share a common downstream NMDAR-activation dependent effector mechanism, despite variation in initial pharmacological targets. Promoting NMDAR signaling or other approaches that enhance NMDAR-dependent LTP-like synaptic potentiation may be an effective antidepressant strategy.SIGNIFICANCE STATEMENT The anesthetic and antidepressant drug ketamine is well-characterized as an NMDA receptor (NMDAR) antagonist; though, the relevance and full impact of this pharmacology to its antidepressant actions is unclear. We found that NMDAR activation, which occurs downstream of their initial actions, is necessary for the beneficial effects of ketamine and several other putative antidepressant compounds. As such, promoting NMDAR signaling, or other approaches that enhance NMDAR-dependent long-term potentiation (LTP)-like synaptic potentiation in vivo may be an effective antidepressant strategy directly, or acting synergistically with other drug or interventional treatments.

Role of group II metabotropic glutamate receptors in ketamine's antidepressant actions

Major Depressive Disorder (MDD) is a serious neuropsychiatric disorder afflicting around 16-17 % of the global population and is accompanied by recurrent episodes of low mood, hopelessness and suicidal thoughts. Current pharmacological interventions take several weeks to even months for an improvement in depressive symptoms to emerge, with a significant percentage of individuals not responding to these medications at all, thus highlighting the need for rapid and effective next-generation treatments for MDD. Pre-clinical studies in animals have demonstrated that antagonists of the metabotropic glutamate receptor subtype 2/3 (mGlu_2/3 receptor) exert rapid antidepressant-like effects, comparable to the actions of ketamine. Therefore, it is possible that mGlu₂ or mGlu₃ receptors to have a regulatory role on the unique antidepressant properties of ketamine, or that convergent intracellular mechanisms exist between mGlu_2/3 receptor signaling and ketamine's effects. Here, we provide a comprehensive and critical evaluation of the literature on these convergent processes underlying the antidepressant action of mGlu_2/3 receptor inhibitors and ketamine. Importantly, combining sub-threshold doses of mGlu_2/3 receptor inhibitors with sub-antidepressant ketamine doses induce synergistic antidepressant-relevant behavioral effects. We review the evidence supporting these combinatorial effects since sub-effective dosages of mGlu_2/3 receptor antagonists and ketamine could reduce the risk for the emergence of significant adverse events compared with taking normal dosages. Overall, deconvolution of ketamine's pharmacological targets will give critical insights to influence the development of next-generation antidepressant treatments with rapid actions.

Synapse Dysfunctions in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system (CNS) affecting nearly three million humans worldwide. In MS, cells of an auto-reactive immune system invade the brain and cause neuroinflammation. Neuroinflammation triggers a complex, multi-faceted harmful process not only in the white matter but also in the grey matter of the brain. In the grey matter, neuroinflammation causes synapse dysfunctions. Synapse dysfunctions in MS occur early and independent from white matter demyelination and are likely correlates of cognitive and mental symptoms in MS. Disturbed synapse/glia interactions and elevated neuroinflammatory signals play a central role. Glutamatergic excitotoxic synapse damage emerges as a major mechanism. We review synapse/glia communication under normal conditions and summarize how this communication becomes malfunctional during neuroinflammation in MS. We discuss mechanisms of how disturbed glia/synapse communication can lead to synapse dysfunctions, signaling dysbalance, and neurodegeneration in MS.

Role of neurotransmitters in immune-mediated inflammatory disorders: a crosstalk between the nervous and immune systems

Immune-mediated inflammatory diseases (IMIDs) are a group of common heterogeneous disorders, characterized by an alteration of cellular homeostasis. Primarily, it has been shown that the release and diffusion of neurotransmitters from nervous tissue could result in signaling through lymphocyte cell-surface receptors and the modulation of immune function. This finding led to the idea that the neurotransmitters could serve as immunomodulators. It is now manifested that neurotransmitters can also be released from leukocytes and act as autocrine or paracrine modulators. Increasing data indicate that there is a crosstalk between inflammation and alterations in neurotransmission. The primary goal of this review is to demonstrate how these two pathways may converge at the level of the neuron and glia to involve in IMID. We review the role of neurotransmitters in IMID. The different effects that these compounds exert on a variety of immune cells are also reviewed. Current and future developments in understanding the cross-talk between the immune and nervous systems will undoubtedly identify new ways for treating immune-mediated diseases utilizing agonists or antagonists of neurotransmitter receptors.

Therapeutic Implications of microRNAs in Depressive Disorders: A Review

MicroRNAs are hidden players in complex psychophysical phenomena such as depression and anxiety related disorders though the activation and deactivation of multiple proteins in signaling cascades. Depression is classified as a mood disorder and described as feelings of sadness, loss, or anger that interfere with a person’s everyday activities. In this review, we have focused on exploration of the significant role of miRNAs in depression by affecting associated target proteins (cellular and synaptic) and their signaling pathways which can be controlled by the attachment of miRNAs at transcriptional and translational levels. Moreover, miRNAs have potential role as biomarkers and may help to cure depression through involvement and interactions with multiple pharmacological and physiological therapies. Taken together, miRNAs might be considered as promising novel therapy targets themselves and may interfere with currently available antidepressant treatments.

Sex- and age-dependent effects of chronic corticosterone exposure on depressive-like, anxiety-like, and fear-related behavior: Role of amygdala glutamate receptors in the rat

Persistent glucocorticoid elevation consistent with chronic stress exposure can lead to psychopathology, including mood and anxiety disorders. Women and stress-exposed adolescents are more likely to be diagnosed with mood disorders, suggesting that sex and age are important factors in determining vulnerability, though much remains to be determined regarding the mechanisms underlying this risk. Thus, the aim of the present experiments was to use the chronic corticosterone (CORT) exposure paradigm, a model of depression-like behavior that has previously been established primarily in adult males, to determine the mood-related effects of CORT in female and adolescent rats. Depression- and anxiety-like effects in adulthood were determined using the sucrose preference (SPT), the forced swim test (FST), the elevated plus maze, and fear conditioning. Basolateral amygdala (BLA) and medial prefrontal cortex (mPFC) glutamate receptor subunit levels were then measured. In a subsequent experiment, adult male and female rats were tested for the effects of pharmacological activation (via AMPA) or inhibition (via NBQX) of AMPA receptors in the BLA on behavior in the FST. Overall, females showed reduced anxiety- and depressive-like behaviors relative to males. However, females treated with CORT in adolescence, but not adulthood, had increased immobility in the FST, indicative of depression-like behavior. In contrast, CORT did not alter behavior in adolescent-treated males, though the previously reported depression-like effect of adult CORT exposure was observed. Control females had higher expression of the AMPA receptor subunits GluA1 and GluA2/3 selectively in the BLA relative to males. Adolescent CORT treatment, however, decreased BLA GluA1 and GluA2/3 expression in females, but increased expression in males, consistent with the direction of depression-like behavioral effects. Male and female rats also demonstrated opposing patterns of response to BLA AMPA receptor modulation in the FST, with AMPA infusion magnifying the sex difference of decreased immobility in females. Overall, these experiments show that increased glutamate receptor function in the BLA may decrease the risk of developing depressive-like behavior, further supporting efforts to target glutamatergic receptors for the treatment of stress-related psychiatric disorders. These findings also support further focus on sex as a biological variable in neuropsychiatric research.

Interactions Among Brain-Derived Neurotrophic Factor and Neuroimmune Pathways Are Key Components of the Major Psychiatric Disorders

The purpose of this review is to summarize the current knowledge regarding the reciprocal associations between brain-derived neurotrophic factor (BDNF) and immune-inflammatory pathways and how these links may explain the involvement of this neurotrophin in the immune pathophysiology of mood disorders and schizophrenia. Toward this end, we delineated the protein-protein interaction (PPI) network centered around BDNF and searched PubMed, Scopus, Google Scholar, and Science Direct for papers dealing with the involvement of BDNF in the major psychosis, neurodevelopment, neuronal functions, and immune-inflammatory and related pathways. The PPI network was built based on the significant interactions of BDNF with neurotrophic (NTRK2, NTF4, and NGFR), immune (cytokines, STAT3, TRAF6), and cell-cell junction (CTNNB, CDH1) DEPs (differentially expressed proteins). Enrichment analysis shows that the most significant terms associated with this PPI network are the tyrosine kinase receptor (TRKR) and Src homology region two domain-containing phosphatase-2 (SHP2) pathways, tyrosine kinase receptor signaling pathways, positive regulation of kinase and transferase activity, cytokine signaling, and negative regulation of the immune response. The participation of BDNF in the immune response and its interactions with neuroprotective and cell-cell adhesion DEPs is probably a conserved regulatory process which protects against the many detrimental effects of immune activation and hyperinflammation including neurotoxicity. Lowered BDNF levels in mood disorders and schizophrenia (a) are associated with disruptions in neurotrophic signaling and activated immune-inflammatory pathways leading to neurotoxicity and (b) may interact with the reduced expression of other DEPs (CTNNB1, CDH1, or DISC1) leading to multiple aberrations in synapse and axonal functions.

Dysfunctional Heteroreceptor Complexes as Novel Targets for the Treatment of Major Depressive and Anxiety Disorders

Among mental diseases, major depressive disorder (MDD) and anxiety deserve a special place due to their high prevalence and their negative impact both on society and patients suffering from these disorders. Consequently, the development of novel strategies designed to treat them quickly and efficiently, without or at least having limited side effects, is considered a highly important goal. Growing evidence indicates that emerging properties are developed on recognition, trafficking, and signaling of G-protein coupled receptors (GPCRs) upon their heteromerization with other types of GPCRs, receptor tyrosine kinases, and ionotropic receptors such as N-methyl-D-aspartate (NMDA) receptors. Therefore, to develop new treatments for MDD and anxiety, it will be important to identify the most vulnerable heteroreceptor complexes involved in MDD and anxiety. This review focuses on how GPCRs, especially serotonin, dopamine, galanin, and opioid heteroreceptor complexes, modulate synaptic and volume transmission in the limbic networks of the brain. We attempt to provide information showing how these emerging concepts can contribute to finding new ways to treat both MDD and anxiety disorders.

Depression Symptoms and Mortality in Elderly Peruvian Navy Veterans: A Retrospective Cohort Study

Our study was design to determine the association between depressive symptoms and mortality in adults over 60 years old Navy Peruvian Veterans. We performed a retrospective cohort study based on a previous cohort study. A total of 1681 patients over 60 years old were included between 2010–2015. Demographic information, self-reported information about falls, physical frailty assessment, tobacco consumption, hypertension, Type 2 Diabetes Mellitus, Chronic Obstructive Pulmonary Disease and was collected. Depression was assessed by the short form of the Geriatric Depression Scale. We found that depressive symptoms were present in 24.9% of the participants and 40.5% of them died. Mortality risk in patients with depressive symptoms, physical frailty, and male sex was: RR of 23.1 (95% CI: 11.7–45.7), 3.84 (95% CI: 2.16–6.82), and 1.37 (95% CI: 1.07–1.75) respectively. We concluded that depressive symptoms in Peruvian retired military personnel and their immediate relatives are high and are significatively associated with mortality. Also, being male and frail was associated with an increased risk of death. This reinforces that early detection and assessment of depressive symptoms could be an opportunity to improve the health status of older adults.

Is (R)-ketamine a Potential Therapeutic Agent for Treatment-Resistant Depression with Less Detrimental Side Effects? A Review of Molecular Mechanisms Underlying Ketamine and its Enantiomers

Approximately one-third of individuals with major depressive disorder are resistant to conventional antidepressants (i.e., monoamine-based therapies), and, even among respondents, a proper therapeutic effect may require weeks of treatment. Ketamine, a racemic mixture of the two enantiomers, (R)-ketamine and (S)-ketamine, is an N-methyl-d-aspartate receptor (NMDAR) antagonist and has been shown to have rapid-acting antidepressant properties in patients with treatment-resistant depression (TRD). Although (R)-ketamine has a lower affinity for NMDAR, it presents greater potency and longer-lasting antidepressant properties, with no major side effects, than racemic ketamine or (S)-ketamine in preclinical findings. Thereby, ketamine and its enantiomers have not only an antagonistic effect on NMDAR but also a strong synaptogenic-modulatory effect, which is impaired in TRD pathophysiology. In this review, we summarize the current evidence regarding the modulation of neurotransmission, neuroplasticity, and neural network activity as putative mechanisms of these rapid-acting antidepressants, highlighting differences on intracellular signaling pathways of synaptic proteins such as mammalian target of rapamycin (mTOR), extracellular signal-regulated kinase (ERK) and brain-derived neurotrophic factor (BDNF). In addition, we discuss probable mechanisms involved in the side effects of ketamine and its enantiomers.

Electroacupuncture Ameliorates Depressive-Like State and Synaptic Deficits Induced by Hyper-Cholinergic Tone During Chronic Stress in Rats

BACKGROUND Major depressive disorder (MDD) is the leading cause of disability around the world. It is generally agreed that the central cholinergic system plays an important role in emotional regulation. Acetylcholine (ACh) is now a new target for antidepressants. Therefore, the aim of this study was to evaluate the effect of acupuncture on depressive behaviors, cholinergic tones, and synaptic plasticity in the prefrontal cortex (PFC) in chronic unpredictable mild stress (CUMS). MATERIAL AND METHODS We randomly divided 36 male Sprague-Dawley (SD) rats into the Normal group, Stress group, Physostigmine+stress (Phys+stress) group, and Electroacupuncture+physostigmine+stress (EA+Phys+stress) group. Rats underwent CUMS exposure for 42 days. After 28 days of CUMS, rats received physostigmine or EA treatment for 2 weeks. Rats in the Phys+stress and EA+Phys+stress group received an intraperitoneal injection of physostigmine (TOCRIS, UK, 5 mg/kg) daily. Rats in the EA+Phys+stress group also received EA stimulation at GV 20 (Baihui), GV 29 (Yintang), LI 4 (Hegu), and LR 3 (Taichong) daily for 2 weeks. RESULTS We found that EA ameliorated weight loss and the depressive-like behaviors in the sucrose preference test, novelty-suppressed feeding test, and open-field test. There was significantly decreased expression of ACh and increased expression of acetylcholinesterase (AChE) after EA treatment. Consistent with the behavior tests and cholinergic tones, there were increased spine density and expressions of synaptic proteins, including brain-derived neurotrophic factor (BDNF), glutamate receptor 1 (GluR1), glutamate receptor 2 (GluR2), postsynaptic density protein 95 (PSD95), and synapsin I in the PFC. CONCLUSIONS The results suggest that EA can reverse the depressive-like behaviors and synaptic deficits induced by hyper-cholinergic tone during chronic stress via the modulation of hyper-cholinergic tone.

Ingestion of Bis(2-ethylhexyl) phthalate (DEHP) during adolescence causes depressive-like behaviors through hypoactive glutamatergic signaling in the medial prefrontal cortex

Over the past decades, the production and use of hazardous chemicals has increased worldwide, and the incidence of neurological diseases is increasing proportionately. Among these chemicals, Bis(2-ethylhexyl) phthalate (DEHP) is the most common member of the phthalate family used as a plasticizer. The present study assessed the consequences of daily DEHP ingestion and its effects on brain functions related to depressive-like behaviors. Adolescent C57BL/6 male mice ingested different concentrations of DEHP in their diet (2, 20, and 200 mg/kg of diet), and behavioral changes in anxiety, despair, anhedonia, and sociality were investigated. DEHP exposure evoked depressive-like behaviors in a dose-dependent manner for each symptom. The levels of corticosterone and reactive oxygen species/reactive nitrogen species increased in DEHP-exposed groups, suggesting chronic stress-like responses. In the medial prefrontal cortex (mPFC), glutamate and glutamine were decreased, and glutamine synthetase showed lower activity compared to the control group, suggesting imbalanced glutamatergic signaling. Measuring the spontaneous excitatory postsynaptic current of glutamatergic neurons, we found that DEHP ingestion resulted in hypoactive glutamatergic signaling in the mPFC.

An Oppositional Tolerance Account for Potential Cognitive Deficits Caused by the Discontinuation of Antidepressant Drugs

Depression is the leading cause of disability worldwide, making antidepressant drugs the most used psychiatric drugs in the USA. Withdrawal effects and rebound symptoms frequently occur after the reduction and/or discontinuation of these drugs. Although these phenomena have been investigated with respect to the clinical symptomatology, no studies have systematically investigated the effects of withdrawal/rebound on general cognition. We present a novel framework based on the idea of allostatic adaptation, which allows to predict how different antidepressants likely impair different cognitive processes as a result of withdrawal and rebound effects. This framework relies on the assumptions that the type of cognitive impairments evoked by an antidepressant is determined by the targeted neurotransmitter systems, while the severity of deficits depends on its half-life. Our model predicts that the severity of detrimental cognitive withdrawal and rebound effects increases with a shorter half-life of the discontinued antidepressant drug. It further proposes drug-specific effects: antidepressants mainly targeting serotonin should primarily impair aversive and emotional processing, those targeting norepinephrine should impair the processing of alerting signals, those targeting dopamine should impair motivational processes and reward processing, and those targeting acetylcholine should impair spatial learning and memory. We hope that this framework will motivate further research to better understand and explain cognitive changes as a consequence of antidepressant discontinuation.

TAK-653, an AMPA receptor potentiator with minimal agonistic activity, produces an antidepressant-like effect with a favorable safety profile in rats

The N-methyl-d-aspartate receptor antagonist, ketamine, exhibits rapid and sustained antidepressant activity in patients with treatment-resistant depression (TRD), but its use is associated with psychotomimetic side effects. Evidence has suggested that the activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors followed by activation of the mechanistic target of rapamycin (mTOR) signaling pathway and production of brain derived neurotrophic factor (BDNF) protein may underlie the antidepressant efficacy of ketamine. In this study, we characterized the antidepressant-like effects of TAK-653, a novel AMPA receptor potentiator with virtually no agonistic activity. In rat primary cortical neurons, TAK-653 significantly increased phosphorylated and activated forms of mTOR and p70S6 kinase and their upstream regulators Akt and extracellular signal-regulated kinase (ERK). TAK-653 also significantly increased BDNF protein levels in rat primary cortical neurons. Ketamine at 30 mg/kg, i.p. produced antidepressant-like effects in the reduction of submissive behavior model (RSBM) in rats. Ketamine's antidepressant-like effect was blocked by pretreatment with the AMPA receptor antagonist NBQX at 10 mg/kg, i.p., indicating the essential role of AMPA receptor activation in the antidepressant-like effect of ketamine. Consistent with this finding, a sub-chronic administration of TAK-653 for 6 days produced significant antidepressant-like effect in the rat RSBM. Unlike ketamine, however, TAK-653 did not induce a hyperlocomotor response in rats, which is a behavioral index associated with psychotomimetic side effects in humans. TAK-653 may be a promising drug for the treatment of major depressive disorders including TRD with the potential for an improved safety profile compared with ketamine.

Neuromodulation of Hippocampal-Prefrontal Cortical Synaptic Plasticity and Functional Connectivity: Implications for Neuropsychiatric Disorders

The hippocampus-prefrontal cortex (HPC-PFC) pathway plays a fundamental role in executive and emotional functions. Neurophysiological studies have begun to unveil the dynamics of HPC-PFC interaction in both immediate demands and long-term adaptations. Disruptions in HPC-PFC functional connectivity can contribute to neuropsychiatric symptoms observed in mental illnesses and neurological conditions, such as schizophrenia, depression, anxiety disorders, and Alzheimer's disease. Given the role in functional and dysfunctional physiology, it is crucial to understand the mechanisms that modulate the dynamics of HPC-PFC communication. Two of the main mechanisms that regulate HPC-PFC interactions are synaptic plasticity and modulatory neurotransmission. Synaptic plasticity can be investigated inducing long-term potentiation or long-term depression, while spontaneous functional connectivity can be inferred by statistical dependencies between the local field potentials of both regions. In turn, several neurotransmitters, such as acetylcholine, dopamine, serotonin, noradrenaline, and endocannabinoids, can regulate the fine-tuning of HPC-PFC connectivity. Despite experimental evidence, the effects of neuromodulation on HPC-PFC neuronal dynamics from cellular to behavioral levels are not fully understood. The current literature lacks a review that focuses on the main neurotransmitter interactions with HPC-PFC activity. Here we reviewed studies showing the effects of the main neurotransmitter systems in long- and short-term HPC-PFC synaptic plasticity. We also looked for the neuromodulatory effects on HPC-PFC oscillatory coordination. Finally, we review the implications of HPC-PFC disruption in synaptic plasticity and functional connectivity on cognition and neuropsychiatric disorders. The comprehensive overview of these impairments could help better understand the role of neuromodulation in HPC-PFC communication and generate insights into the etiology and physiopathology of clinical conditions.

Microglia and BDNF at the crossroads of stressor related disorders: Towards a unique trophic phenotype

Stressors ranging from psychogenic/social to neurogenic/injury to systemic/microbial can impact microglial inflammatory processes, but less is known regarding their effects on trophic properties of microglia. Recent studies do suggest that microglia can modulate neuronal plasticity, possibly through brain derived neurotrophic factor (BDNF). This is particularly important given the link between BDNF and neuropsychiatric and neurodegenerative pathology. We posit that certain activated states of microglia play a role in maintaining the delicate balance of BDNF release onto neuronal synapses. This focused review will address how different "activators" influence the expression and release of microglial BDNF and address the question of tropomyosin receptor kinase B (TrkB) expression on microglia. We will then assess sex-based differences in microglial function and BDNF expression, and how microglia are involved in the stress response and related disorders such as depression. Drawing on research from a variety of other disorders, we will highlight challenges and opportunities for modulators that can shift microglia to a "trophic" phenotype with a view to potential therapeutics relevant for stressor-related disorders.

Hemoglobin A1c-levels and subsequent risk of depression in individuals with and without diabetes

BACKGROUND

It has been suggested that long-term glycemic load as reflected in plasma levels of Glycosylated Hemoglobin, Type A1C (HbA1c) is associated with higher risk of depression, however results have been conflicting. We examined the potential association between HbA1c and risk of depression in a large population-based cohort without baseline diabetes (the Glostrup cohort) defined by either self-reported diabetes, registry diagnosis of diabetes or use of antidiabetic medication at baseline and in a national diabetes cohort (the Danish Adult Diabetes Database).

METHODS

A total of 16,124 middle-aged individuals from the Glostrup cohort and 93,544 patients registered in the Danish Adult Diabetes Database were followed from the first registered HbA1c measurement (1999-2014) for subsequent diagnosis of depression or use of antidepressant medication in nation-wide Danish registers. The association was analyzed using a Cox proportional hazards regression model with HbA1c on both a continuous scale using restricted cubic splines and categorized based on the groups found in the spline model. We adjusted for relevant sociodemographic and clinical variables including previous depression and tested for interaction of both gender, insulin use and diabetes type.

RESULTS

During follow-up, 2694 (17%) in the Glostrup cohort and 29,234 (31%) in the diabetes cohort developed depression. In the Glostrup cohort, we found an indication of a positive linear association between HbA1c and depression in women, while no clear association was found in men. In patients with diabetes, we found a U-shaped association between HbA1c and depression in both men and women with the lowest risk estimates for HbA1c levels of 58 mmol/mol (7.5%) in men and of 60 mmol/mol (7.6%) in women. When HbA1c was categorized, men with the highest HbA1c-levels had significantly elevated risk of depression (HR_HbA1c>9.4 1.16 (95%CI 1.10-1.23)) after multifactorial adjustment compared to the reference group with HbA1c of 42.1-56.2 mmol/mol (6.0-7.3%). Women in the lowest and highest category of HbA1c had significantly higher risk of depression HR_HbA1c<6.0 1.15 (95% CI 1.09-1.22) and HR_HbA1c>9.3 1.10 (95% CI 1.04-1.16), respectively, compared to the reference group with HbA1c 42.1-55.0 mmol/mol (7.2-9.3%). There was a significant interaction with gender, but no interaction for insulin use or diabetes type.

CONCLUSIONS

In a population without baseline diabetes, higher HbA1c levels seemed associated with higher depression risk in women, whereas a U-shaped association was found in patients with known diabetes.

Determination of Diffusion Kinetics of Ketamine in Brain Tissue: Implications for in vitro Mechanistic Studies of Drug Actions

Ketamine has been in use for over 50 years as a general anesthetic, acting primarily through blockade of N-methyl-D-aspartate receptors in the brain. Recent studies have demonstrated that ketamine also acts as a potent and rapid-acting antidepressant when administered at sub-anesthetic doses. However, the precise mechanism behind this effect remains unclear. We examined the diffusion properties of ketamine in brain tissue to determine their effects in in vitro studies related to the antidepressant action of ketamine. Brain slices from adult mice were exposed to artificial cerebrospinal fluid (aCSF) containing ∼17 μM ketamine HCl for varying amounts of time. The amount of ketamine within each slice was then measured by tandem high-performance liquid chromatography - mass spectrometry to characterize the diffusion of ketamine into brain tissue over time. We successfully modeled the diffusion of ketamine into brain tissue using a mono-exponential function with a time constant of τ = 6.59 min. This curve was then compared to a one-dimensional model of diffusion yielding a diffusion coefficient of approximately 0.12 cm²⋅s^-1 for ketamine diffusing into brain tissue. The brain:aCSF partition coefficient for ketamine was determined to be approximately 2.76. Our results suggest that the diffusion properties of ketamine have a significant effect on drug concentrations achieved within brain tissue during in vitro experiments. This information is vital to determine the ketamine concentration necessary for in vitro slice preparation to accurately reflect in vivo doses responsible for its antidepressant actions.

Co-administration of cannabidiol and ketamine induces antidepressant-like effects devoid of hyperlocomotor side-effects

BACKGROUND AND PURPOSE

Although useful as a rapid-acting antidepressant drug, ketamine is known to induce psychotomimetic effects, which may interfere with its therapeutic use. Cannabidiol (CBD) is a non-psychostimulant compound from Cannabis sativa, which has shown promising antidepressant effects without inducing hyperlocomotion. AMPA receptor activation is involved in the antidepressant effect induced by ketamine, but its relevance for the effects of CBD is not known. Moreover, given that CBD has antipsychotic and antidepressant properties, it is unknown whether adding CBD to ketamine could potentiate the antidepressant properties of ketamine while also attenuating its psychostimulant effects.

EXPERIMENTAL APPROACH

S-Ketamine (2.5, 3, 5, 10, 30 mg/kg) and cannabidiol (3, 10, 30 mg/kg) were administered alone or in combination to male Swiss mice. Independent groups received NBQX (AMPA receptor antagonist) 5 min before administration of CBD or S-ketamine. The antidepressant-like effect was assessed in the forced swimming test (FST), and the open field test (OFT) evaluated the psychostimulant effect.

KEY RESULTS

CBD induced significant dose-dependent antidepressant effects without causing hyperlocomotion in the OFT. S-ketamine produced an antidepressant effect associated with hyperlocomotion in the higher dose. NBQX inhibited the antidepressant effect of both ketamine and CBD. Pretreatment with CBD (10 mg/kg) attenuated the ketamine-induced hyperlocomotion while preserving its antidepressant effect.

CONCLUSION

AND IMPLICATIONS: Similar to ketamine, the antidepressant-like effect elicited by CBD involves AMPA receptor activation. Additionally, CBD prevents the hyperlocomotion induced by S-ketamine without affecting its antidepressant-like effect. Our findings suggest that CBD and ketamine's combined administration can be a promising therapeutic strategy for achieving an appropriate antidepressant effect without unwanted side-effects. This article is part of the special issue on 'Cannabinoids'.

Diminished reward responsiveness is associated with lower reward network GluCEST: an ultra-high field glutamate imaging study

Low reward responsiveness (RR) is associated with poor psychological well-being, psychiatric disorder risk, and psychotropic treatment resistance. Functional MRI studies have reported decreased activity within the brain's reward network in individuals with RR deficits, however the neurochemistry underlying network hypofunction in those with low RR remains unclear. This study employed ultra-high field glutamate chemical exchange saturation transfer (GluCEST) imaging to investigate the hypothesis that glutamatergic deficits within the reward network contribute to low RR. GluCEST images were acquired at 7.0 T from 45 participants (ages 15-29, 30 females) including 15 healthy individuals, 11 with depression, and 19 with psychosis spectrum symptoms. The GluCEST contrast, a measure sensitive to local glutamate concentration, was quantified in a meta-analytically defined reward network comprised of cortical, subcortical, and brainstem regions. Associations between brain GluCEST contrast and Behavioral Activation System Scale RR scores were assessed using multiple linear regressions. Analyses revealed that reward network GluCEST contrast was positively and selectively associated with RR, but not other clinical features. Follow-up investigations identified that this association was driven by the subcortical reward network and network areas that encode the salience of valenced stimuli. We observed no association between RR and the GluCEST contrast within non-reward cortex. This study thus provides new evidence that reward network glutamate levels contribute to individual differences in RR. Decreased reward network excitatory neurotransmission or metabolism may be mechanisms driving reward network hypofunction and RR deficits. These findings provide a framework for understanding the efficacy of glutamate-modulating psychotropics such as ketamine for treating anhedonia.