Potential link between antidepressant-like effects of ketamine and promotion of adult neurogenesis in the ventral hippocampus of mice

Ketamine's Amelioration of Fear Extinction in Adolescent Male Mice Is Associated with the Activation of the Hippocampal Akt-mTOR-GluA1 Pathway

Fear-related disorders, including post-traumatic stress disorder (PTSD), and anxiety disorders are pervasive psychiatric conditions marked by persistent fear, stemming from its dysregulated acquisition and extinction. The primary treatment for these disorders, exposure therapy (ET), relies heavily on fear extinction (FE) principles. Adolescence, a vulnerable period for developing psychiatric disorders, is characterized by neurobiological changes in the fear circuitry, leading to impaired FE and increased susceptibility to relapse following ET. Ketamine, known for relieving anxiety and reducing PTSD symptoms, influences fear-related learning processes and synaptic plasticity across the fear circuitry. Our study aimed to investigate the effects of ketamine (10 mg/kg) on FE in adolescent male C57 BL/6 mice at the behavioral and molecular levels. We analyzed the protein and gene expression of synaptic plasticity markers in the hippocampus (HPC) and prefrontal cortex (PFC) and sought to identify neural correlates associated with ketamine's effects on adolescent extinction learning. Ketamine ameliorated FE in the adolescent males, likely affecting the consolidation and/or recall of extinction memory. Ketamine also increased the Akt and mTOR activity and the GluA1 and GluN2A levels in the HPC and upregulated BDNF exon IV mRNA expression in the HPC and PFC of the fear-extinguished mice. Furthermore, ketamine increased the c-Fos expression in specific brain regions, including the ventral HPC (vHPC) and the left infralimbic ventromedial PFC (IL vmPFC). Providing a comprehensive exploration of ketamine's mechanisms in adolescent FE, our study suggests that ketamine's effects on FE in adolescent males are associated with the activation of hippocampal Akt-mTOR-GluA1 signaling, with the vHPC and the left IL vmPFC as the proposed neural correlates.

Potentiation of antidepressant effects: NPY1R agonist and ketamine synergy enhances TrkB signaling and neurogenesis in the ventral hippocampus

BACKGROUND

Major Depressive Disorder (MDD) poses a significant challenge to global health, with current treatments often limited by efficacy and onset delays. This study explores the synergistic antidepressant-like effects of an NPY1R agonist and Ketamine, targeting their neurobiological interactions within the ventral hippocampus.

RESEARCH DESIGN AND METHODS

Utilizing a preclinical model, this study administered Neuropeptide Y receptor 1 (NPY1R) agonist and Ketamine, both separately and in combination, through intracerebroventricular (icv) and intranasal (i.n.) routes. The Forced Swimming Test (FST) was employed to assess antidepressant-like activity, while in situ Proximity Ligation Assay and immunohistochemistry were used to examine NPY1R/TrkB heteroreceptor complexes and BDNF expression in the ventral dentate gyrus (DG), along with neurogenesis markers.

RESULTS

The combined treatment significantly reduced immobility in the FST, indicative of enhanced antidepressant-like effects, correlated with increased formation of NPY1R/TrkB complex and brain-derived neurotrophic factor (BDNF) expression in the ventral DG. These molecular alterations were associated with increased neurogenesis.

CONCLUSIONS

The coadministration of an NPY1R agonist and Ketamine in a rodent model demonstrated potentiated antidepressant responses through synergistic neurobiological pathways, including TrkB signaling and hippocampal neurogenesis. This indicates a novel therapeutic strategy for MDD, warranting further clinical investigation to fully understand its implications.

The impact of adult neurogenesis on affective functions: of mice and men

In most mammals, new neurons are not only produced during embryogenesis but also after birth. Soon after adult neurogenesis was discovered, the influence of recruiting new neurons on cognitive functions, especially on memory, was documented. Likewise, the late process of neuronal production also contributes to affective functions, but this outcome was recognized with more difficulty. This review covers hypes and hopes of discovering the influence of newly-generated neurons on brain circuits devoted to affective functions. If the possibility of integrating new neurons into the adult brain is a commonly accepted faculty in the realm of mammals, the reluctance is strong when it comes to translating this concept to humans. Compiling data suggest now that new neurons are derived not only from stem cells, but also from a population of neuroblasts displaying a protracted maturation and ready to be engaged in adult brain circuits, under specific signals. Here, we discuss the significance of recruiting new neurons in the adult brain circuits, specifically in the context of affective outcomes. We also discuss the fact that adult neurogenesis could be the ultimate cellular process that integrates elements from both the internal and external environment to adjust brain functions. While we must be critical and beware of the unreal promises that Science could generate sometimes, it is important to continue exploring the potential of neural recruitment in adult primates. Reporting adult neurogenesis in humankind contributes to a new vision of humans as mammals whose brain continues to develop throughout life. This peculiar faculty could one day become the target of treatment for mental health, cognitive disorders, and elderly-associated diseases. The vision of an adult brain which never stops integrating new neurons is a real game changer for designing new therapeutic interventions to treat mental disorders associated with substantial morbidity, mortality, and social costs.

Atrophy of bilateral nucleus accumbens in melancholic depression

Evidence from previous literature suggests that the nucleus accumbens (NAc), hippocampus, and amygdala play critical roles in the reward circuit. Meanwhile, it was also suggested that abnormalities in the reward circuit might be closely associated with the symptom of anhedonia of depression. However, few studies have investigated the structural alterations of the NAc, hippocampus, and amygdala in depression with anhedonia as the main clinical manifestation. Thus, the current study aimed to explore the structural changes of the subcortical regions among melancholic depression (MD) patients, especially in the NAc, hippocampus, and amygdala, to provide a theoretical basis for understanding the pathological mechanisms of MD. Seventy-two MD patients, 74 nonmelancholic depression (NMD) patients, and 81 healthy controls (HCs) matched for sex, age, and years of education were included in the study. All participants underwent T1-weighted MRI scans. Subcortical structure segmentation was performed using the FreeSurfer software. MD and NMD patients had reduced left hippocampal volume compared with HCs. Meanwhile, only MD patients had reduced bilateral NAc volumes. Moreover, correlation analyses showed correlations between left NAc volume and late insomnia and lassitude in MD patients. The reduced hippocampal volume may be related to the pathogenesis of major depressive disorder (MDD), and the reduced volume of the NAc may be the unique neural mechanism of MD. The findings of the current study suggest that future studies should investigate the different pathogenic mechanisms of different subtypes of MDD further to contribute to the development of individualized diagnostic and treatment protocols.

Antidepressant-like effect of acute dose of Naringin involves suppression of NR1 and activation of protein kinase A/cyclic adenosine monophosphate response element-binding protein/brain-derived neurotrophic factor signaling in hippocampus

Naringin (Nr) has been identified to have antidepressant-like effects through repeated treatment. However, the underlying mechanism of the rapid antidepressant-like effects of Nr was still unclear. The present study used behavioral tests, classic depressive model and pharmacological methods to reveal the rapid antidepressant-like potential of Nr. We found that a single dose of Nr (20 mg/kg) produced antidepressant-like action after 2 h in the tail suspension test (TST) and forced swimming test (FST). Moreover, ketamine-like effects were also demonstrated by using the chronic mild stress model (CMS) and learned helplessness (LH), and the results showed that Nr reversed all behavioral defects, TST, FST, source preference test (SPT) in CMS, and LH testing, TST, FST in LH model, at 2 h after a single administration. In addition, Nr (20 mg/kg) could improve the abnormal expressions of NMDA receptor NR1 and PKA/CREB/BDNF pathway in hippocampus 2 h after a single administration in CMS mice. Further investigation revealed that activation of NMDA receptors by NMDA (750 mg/kg) could block the antidepressant effects of acute administration of Nr (20 mg/kg). However, the inhibition of NMDA receptors by MK-801 (0.05 mg/kg) promoted the subdose of Nr (10 mg/kg) to have antidepressant effect, which was similar to the effective dose Nr (20 mg/kg). Taken together, acute dose of Nr produces rapid antidepressant-like action, and the underlying mechanism could be through inhibiting NMDA receptors in the hippocampus.

Intranasal Administration of Resolvin E1 Produces Antidepressant-Like Effects via BDNF/VEGF-mTORC1 Signaling in the Medial Prefrontal Cortex

Intracerebroventricular infusion of resolvin E1 (RvE1), a bioactive metabolite derived from eicosapentaenoic acid, exerts antidepressant-like effects in a mouse model of lipopolysaccharide (LPS)-induced depression; these effects are blocked by systemic injection of rapamycin, a mechanistic target of rapamycin complex 1 (mTORC1) inhibitor. Additionally, local infusion of RvE1 into the medial prefrontal cortex (mPFC) or dorsal hippocampal dentate gyrus (DG) produces antidepressant-like effects. To evaluate the potential of RvE1 for clinical use, the present study examined whether treatment with RvE1 via intranasal (i.n.) route, a non-invasive route for effective drug delivery to the brain, produces antidepressant-like effects in LPS-challenged mice using tail suspension and forced swim tests. Intranasal administration of RvE1 significantly attenuated LPS-induced immobility, and these antidepressant-like effects were completely blocked by an AMPA receptor antagonist or L-type voltage-dependent Ca2+ channel blocker. The antidepressant-like effects of both i.n. and intra-mPFC administrations of RvE1 were blocked by intra-mPFC infusion of a neutralizing antibody (nAb) for brain-derived neurotrophic factor (BDNF) or vascular endothelial growth factor (VEGF). Intra-mPFC infusion of rapamycin completely blocked the antidepressant-like effects of both i.n. and intra-mPFC administrations of RvE1 as well as those of intra-mPFC infusion of BDNF and VEGF. Moreover, i.n. RvE1 produced antidepressant-like effects via mTORC1 activation in the mPFC of a mouse model of repeated prednisolone-induced depression. Intra-dorsal DG infusion of BDNF and VEGF nAbs, but not rapamycin, blocked the antidepressant-like effects of i.n. RvE1. These findings suggest that i.n. administration of RvE1 produces antidepressant-like effects through activity-dependent BDNF/VEGF release in the mPFC and dorsal DG, and mTORC1 activation in the mPFC, but not in the dorsal DG. Thus, RvE1 can be a promising candidate for a novel rapid-acting antidepressant.

Ketamine and its metabolites: Potential as novel treatments for depression

Depression is a well-known serious mental illness, and the onset of treatment using traditional antidepressants is frequently delayed by several weeks. Moreover, numerous patients with depression fail to respond to therapy. One major breakthrough in antidepressant therapy is that subanesthetic ketamine doses can rapidly alleviate depressive symptoms within hours of administering a single dose, even in treatment-resistant patients. However, specific mechanisms through which ketamine exerts its antidepressant effects remain elusive, leading to concerns regarding its rapid and long-lasting antidepressant effects. N-methyl-d-aspartate receptor (NMDAR) antagonists like ketamine are reportedly associated with serious side effects, such as dissociative symptoms, cognitive impairment, and abuse potential, limiting the large-scale clinical use of ketamine as an antidepressant. Herein, we reviewed the pharmacological properties of ketamine and the mechanisms of action underlying the rapid antidepressant efficacy, including the disinhibition hypothesis and synaptogenesis, along with common downstream effector pathways such as enhanced brain-derived neurotrophic factor and tropomyosin-related kinase B signaling, activation of the mechanistic target of rapamycin complex 1 and transforming growth factor β1. We focused on evidence supporting the relevance of these potential mechanisms of ketamine and its metabolites in mediating the clinical efficacy of the drug. Given its reported antidepressant efficacy in preclinical studies and limited undesirable adverse effects, (R)-ketamine may be a safer, more controllable, rapid antidepressant. Overall, understanding the potential mechanisms of action of ketamine and its metabolites in combination with pharmacology may help develop a new generation of rapid antidepressants that maximize antidepressant effects while avoiding unfavorable adverse effects. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Autophagy promotes membrane trafficking of NR2B to alleviate depression by inhibiting AQP4 expression in mice

Depression is a high-incidence mental illness that seriously affects human health. AQP4 has been reported to be closely associated with depression, while the underlying mechanism is still unclear. This work aimed to investigate the functional role of AQP4 in depression. Depression mouse model was constructed by administration of chronic social defeat stress (CSDS). We found that AQP4 was highly expressed in the hippocampal tissues of CSDS mice. AQP4 knockdown alleviated depression and enhanced the expression of NR2B and PSD95 in CSDS mice. Moreover, primary hippocampal neurons were treated with N-methyl-d-aspartate (NMDA) to induce neuron injury. AQP4 overexpression repressed cell viability and promoted apoptosis of NMDA-treated primary hippocampal neurons. AQP4 up-regulation repressed the expression of NR2B (surface), and enhanced the expression of NR2B (intracellular), P-NR2B, CaMK II and CK2 in the NMDA-treated primary hippocampal neurons. The influence conferred by AQP4 up-regulation was abolished by KN-93 (CaMK II inhibitor) or TBB (CK2 inhibitor) treatment. Rapamycin treatment enhanced the expression of NR2B (surface), and repressed the expression of AQP4, NR2B (intracellular) and P-NR2B in the primary hippocampal neurons by activating autophagy. The activated autophagy alleviated depression in CSDS mice by repressing AQP4 expression. In conclusion, our data demonstrated that autophagy ameliorated depression by repressing AQP4 expression in mice, and AQP4 knockdown promoted membrane trafficking of NR2B and inhibited phosphorylation of NR2B via CaMK II/CK2 pathway. Thus, our work suggests that AQP4 may be a promising molecular target for the development of antidepressant drugs.

Drugs and Endogenous Factors as Protagonists in Neurogenic Stimulation

Neurogenesis is a biological process characterized by new neurons formation from stem cells. For decades, it was believed that neurons only multiplied during development and in the postnatal period but the discovery of neural stem cells (NSCs) in mature brain promoted a revolution in neuroscience field. In mammals, neurogenesis consists of migration, differentiation, maturation, as well as functional integration of newborn cells into the pre-existing neuronal circuit. Actually, NSC density drops significantly after the first stages of development, however in specific places in the brain, called neurogenic niches, some of these cells retain their ability to generate new neurons and glial cells in adulthood. The subgranular (SGZ), and the subventricular zones (SVZ) are examples of regions where the neurogenesis process occurs in the mature brain. There, the potential of NSCs to produce new neurons has been explored by new advanced methodologies and in neuroscience for the treatment of brain damage and/or degeneration. Based on that, this review highlights endogenous factors and drugs capable of stimulating neurogenesis, as well as the perspectives for the use of NSCs for neurological and neurodegenerative diseases.

Chondroitin sulfate proteoglycan is a potential target of memantine to improve cognitive function via the promotion of adult neurogenesis

BACKGROUND AND PURPOSE

Chondroitin sulfate proteoglycan (CSPG) constitutes the neurogenic niche in the hippocampus. The reduction of hippocampal neurogenesis is involved in aging-related cognitive decline and dementia. The purpose of this study is to find candidates that improve cognitive function by analyzing the effects of memantine (MEM), a therapeutic agent for Alzheimer's disease, on CSPG and adult hippocampal neurogenesis.

EXPERIMENTAL APPROACH

The effects of MEM on neurogenesis-related cells and CSPG content were assessed in the hippocampus of middle-aged mice. The MEM-induced alterations in gene expressions of neurotrophins and enzymes associated with biosynthesis and degradation of CSPG in the hippocampus were also measured. The effects of MEM on cognitive function were estimated using a behavioral test battery. The same set of behavioral tests was applied to evaluate the effects of pharmacological depletion of CSPG in the hippocampus.

KEY RESULTS

The densities of newborn granule cells and content of CSPG in the hippocampus were increased by MEM. The expression levels of the enzyme responsible for the biosynthesis CSPG were increased by MEM. The neurotrophin-related molecules were activated by MEM. Short- and long-term memory performance was improved by MEM. Pharmacological depletion of CSPG impairs the effects of MEM on cognitive improvement in middle-aged mice.

CONCLUSIONS AND IMPLICATIONS

MEM regulates the biosynthesis and degradation of CSPG, which may underlie the improvement of cognitive function via the promotion of adult hippocampal neurogenesis. These results imply that CSPG-related enzymes may be potentially attractive candidates for the treatment of aging-related cognitive decline.

Alleviation of cognitive deficits via upregulation of chondroitin sulfate biosynthesis by lignan sesamin in a mouse model of neuroinflammation

Lignans are plant-derived compounds that act as partial estrogen agonists. Chondroitin sulfate proteoglycans (CSPGs) represent one of the major components of the extracellular matrix (ECM). Here we aimed to understand the role of sesamin (SES), a major lignan compound, in the biosynthesis and degradation of CSPGs in the mouse hippocampus because CSPGs play a key role in the regulation of cognitive functions through the promotion of adult neurogenesis. The expression of the pro-inflammatory cytokine interleukin-1β was decreased by SES administration in the hippocampus of lipopolysaccharide (LPS)-treated mice, a model of neuroinflammation-induced cognitive deficits. The expression of genes related to biosynthesis and degradation of CSPGs in the hippocampus of LPS-treated mice was both increased and decreased by SES administration. Further, the diffuse ECM labeling of CSPGs by Wisteria floribunda agglutinin (WFA) in the hippocampus of LPS-treated mice was increased by SES administration. The densities of neural stem cells, late transit-amplifying cells, and newborn-granule cells in the hippocampus of LPS-treated mice were also increased by SES administration. Moreover, SES-induced alterations in gene expression, WFA labeling, and adult neurogenesis in LPS-treated mice were more evident in the dorsal hippocampus (center of cognition) than in the ventral hippocampus (center of emotion). Neither LPS nor SES administration affected locomotor activity, anxiety-like behavior, and depression-related behavior. However, impairments in contextual memory and sensorimotor gating in LPS-treated mice were recovered by SES administration. Our results show that SES can promote adult hippocampal neurogenesis through the upregulation of CSPGs, which may alleviate cognitive deficits induced by neuroinflammation.

Transcriptional Activation, Deactivation and Rebound Patterns in Cortex, Hippocampus and Amygdala in Response to Ketamine Infusion in Rats

Ketamine, an N-methyl-D-aspartate (NMDA)-receptor antagonist, is a recently revitalized treatment for pain and depression, yet its actions at the molecular level remain incompletely defined. In this molecular-pharmacological investigation in the rat, we used short- and longer-term infusions of high dose ketamine to stimulate neuronal transcription processes. We hypothesized that a progressively stronger modulation of neuronal gene networks would occur over time in cortical and limbic pathways. A continuous intravenous administration paradigm for ketamine was developed in rat consisting of short (1 h) and long duration (10 h, and 10 h + 24 h recovery) infusions of anesthetic concentrations to activate or inhibit gene transcription in a pharmacokinetically controlled fashion. Transcription was measured by RNA-Seq in three brain regions: frontal cortex, hippocampus, and amygdala. Cellular level gene localization was performed with multiplex fluorescent in situ hybridization. Induction of a shared transcriptional regulatory network occurred within 1 h in all three brain regions consisting of (a) genes involved in stimulus-transcription factor coupling that are induced during altered synaptic activity (immediate early genes, IEGs, such as c-Fos, 9–12 significant genes per brain region, p < 0.01 per gene) and (b) the Nrf2 oxidative stress-antioxidant response pathway downstream from glutamate signaling (Nuclear Factor Erythroid-Derived 2-Like 2) containing 12–25 increasing genes (p < 0.01) per brain region. By 10 h of infusion, the acute results were further reinforced and consisted of more and stronger gene alterations reflecting a sustained and accentuated ketamine modulation of regional excitation and plasticity. At the cellular level, in situ hybridization localized up-regulation of the plasticity-associated gene Bdnf, and the transcription factors Nr4a1 and Fos, in cortical layers III and V. After 24 h recovery, we observed overshoot of transcriptional processes rather than a smooth return to homeostasis suggesting an oscillation of plasticity occurs during the transition to a new phase of neuronal regulation. These data elucidate critical molecular regulatory actions during and downstream of ketamine administration that may contribute to the unique drug actions of this anesthetic agent. These molecular investigations point to pathways linked to therapeutically useful attributes of ketamine.

Rapid-Onset Antidepressant-Like Effect of Nelumbinis semen in Social Hierarchy Stress Model of Depression

Depression is a disease with increasing prevalence worldwide, and it is necessary to develop a therapeutic agent with better efficacy than existing antidepressant drugs. Antidepressants that act on the glutamatergic nervous system, such as ketamine, have a rapid-onset antidepressant effect and are effective against treatment-resistant depression. However, because of the addictive potential of ketamine, alternative substances without psychological side effects are recommended. In particular, many natural compounds have been tested for their antidepressant effects. The antidepressant effects of Nelumbinis semen (NS) have been tested in many studies, along with the various actions of NS on the glutamatergic system. Thus, it was expected that NS might have a rapid-onset antidepressant effect. To test the antidepressant potential, despair and anhedonic behaviors were measured after administering NS to mice exposed to social hierarchy stress (SHS), and biochemical changes in the prefrontal cortex and hippocampus were analyzed. NS reduced despair-like responses in the forced swim test and tail suspension test. Mice exposed to SHS showed depression-like responses such as increased despair, reduced hedonia, and an anxiety-like response in the novelty suppressed feeding test. NS, but not fluoxetine, improved those depression-like behaviors after acute treatment, and NBQX, an AMPA receptor blocker, inhibited the antidepressant-like effects of NS. The antidepressant-like effect of NS was related to enhanced phosphorylation of mTOR in the prefrontal cortex and dephosphorylation of GluR1 S845 in the hippocampus. Since NS has shown antidepressant-like potential in a preclinical model, it may be considered as a candidate for the development of antidepressants in the future.

Early-life stress induces emotional and molecular alterations in female mice that are partially reversed by cannabidiol

Gender is considered as a pivotal determinant of mental health. Indeed, several psychiatric disorders such as anxiety and depression are more common and persistent in women than in men. In the past two decades, impaired brain energy metabolism has been highlighted as a risk factor for the development of these psychiatric disorders. However, comprehensive behavioural and neurobiological studies in brain regions relevant to anxiety and depression symptomatology are scarce. In the present study, we summarize findings describing cannabidiol effects on anxiety and depression in maternally separated female mice as a well-established rodent model of early-life stress associated with many mental disorders. Our results indicate that cannabidiol could prevent anxiolytic- and depressive-related behaviour in early-life stressed female mice. Additionally, maternal separation with early weaning (MSEW) caused long-term changes in brain oxidative metabolism in both nucleus accumbens and amygdalar complex measured by cytochrome c oxidase quantitative histochemistry. However, cannabidiol treatment could not revert brain oxidative metabolism impairment. Moreover, we identified hyperphosphorylation of mTOR and ERK 1/2 proteins in the amygdala but not in the striatum, that could also reflect altered brain intracellular signalling related with to bioenergetic impairment. Altogether, our study supports the hypothesis that MSEW induces profound long-lasting molecular changes in mTOR signalling and brain energy metabolism related to depressive-like and anxiety-like behaviours in female mice, which were partially ameliorated by CBD administration.

Rapid-acting antidepressants and the circadian clock

A growing number of epidemiological and experimental studies has established that circadian disruption is strongly associated with psychiatric disorders, including major depressive disorder (MDD). This association is becoming increasingly relevant considering that modern lifestyles, social zeitgebers (time cues) and genetic variants contribute to disrupting circadian rhythms that may lead to psychiatric disorders. Circadian abnormalities associated with MDD include dysregulated rhythms of sleep, temperature, hormonal secretions, and mood which are modulated by the molecular clock. Rapid-acting antidepressants such as subanesthetic ketamine and sleep deprivation therapy can improve symptoms within 24 h in a subset of depressed patients, in striking contrast to conventional treatments, which generally require weeks for a full clinical response. Importantly, animal data show that sleep deprivation and ketamine have overlapping effects on clock gene expression. Furthermore, emerging data implicate the circadian system as a critical component involved in rapid antidepressant responses via several intracellular signaling pathways such as GSK3β, mTOR, MAPK, and NOTCH to initiate synaptic plasticity. Future research on the relationship between depression and the circadian clock may contribute to the development of novel therapeutic strategies for depression-like symptoms. In this review we summarize recent evidence describing: (1) how the circadian clock is implicated in depression, (2) how clock genes may contribute to fast-acting antidepressants, and (3) the mechanistic links between the clock genes driving circadian rhythms and neuroplasticity.

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.

The Mechanisms Behind Rapid Antidepressant Effects of Ketamine: A Systematic Review With a Focus on Molecular Neuroplasticity

The mechanism of action underlying ketamine's rapid antidepressant effects in patients with depression, both suffering from major depressive disorder (MDD) and bipolar disorder (BD), including treatment resistant depression (TRD), remains unclear. Of the many speculated routes that ketamine may act through, restoring deficits in neuroplasticity may be the most parsimonious mechanism in both human patients and preclinical models of depression. Here, we conducted a literature search using PubMed for any reports of ketamine inducing neuroplasticity relevant to depression, to identify cellular and molecular events, relevant to neuroplasticity, immediately observed with rapid mood improvements in humans or antidepressant-like effects in animals. After screening reports using our inclusion/exclusion criteria, 139 publications with data from cell cultures, animal models, and patients with BD or MDD were included (registered on PROSPERO, ID: CRD42019123346). We found accumulating evidence to support that ketamine induces an increase in molecules involved in modulating neuroplasticity, and that these changes are paired with rapid antidepressant effects. Molecules or complexes of high interest include glutamate, AMPA receptors (AMPAR), mTOR, BDNF/TrkB, VGF, eEF2K, p70S6K, GSK-3, IGF2, Erk, and microRNAs. In summary, these studies suggest a robust relationship between improvements in mood, and ketamine-induced increases in molecular neuroplasticity, particularly regarding intracellular signaling molecules.

Reviewing the Role of the Endocannabinoid System in the Pathophysiology of Depression

Major depressive disorder is a high-impact, debilitating disease and it is currently considered the most prevalent mental illness. It is associated with disability, as well as increased morbidity and mortality. Despite its significant repercussions in our society, its exact pathophysiology remains unclear and therefore, available antidepressant treatment options are limited and, in some cases, ineffective. In the past years, research has focused on the development of a multifactorial theory of depression. Simultaneously, evidence supporting the role of the endocannabinoid system in the neurobiology of neuropsychiatric diseases has emerged. Studies have shown that the endocannabinoid system strongly impacts neurotransmission, and the neuroendocrine and neuroimmune systems, which are known to be dysfunctional in depressive patients. Accordingly, common antidepressants were shown to have a direct impact on the expression of cannabinoid receptors throughout the brain. Therefore, the relationship between the endocannabinoid system and major depressive disorder is worth consideration. Nevertheless, most studies focus on smaller pieces of what is undoubtedly a larger mosaic of interdependent processes. Therefore, the present review summarizes the existing literature regarding the role of the endocannabinoid system in depression aiming to integrate this information into a holistic picture for a better understanding of the relationship between the two.

Ketamine as a Treatment for Anorexia Nervosa: A Narrative Review

Anorexia nervosa (AN) is a highly complex disorder to treat, especially in severe and enduring cases. Whilst the precise aetiology of the disorder is uncertain, malnutrition and weight loss can contribute to reductions in grey and white matter of the brain, impairments in neuroplasticity and neurogenesis and difficulties with cognitive flexibility, memory and learning. Depression is highly comorbid in AN and may be a barrier to recovery. However, traditional antidepressants are often ineffective in alleviating depressive symptoms in underweight patients with AN. There is an urgent need for new treatment approaches for AN. This review gives a conceptual overview for the treatment of AN with ketamine. Ketamine has rapid antidepressant effects, which are hypothesised to occur via increases in glutamate, with sequelae including increased neuroplasticity, neurogenesis and synaptogenesis. This article provides an overview of the use of ketamine for common psychiatric comorbidities of AN and discusses particular safety concerns and side effects. Potential avenues for future research and specific methodological considerations are explored. Overall, there appears to be ample theoretical background, via several potential mechanisms, that warrant the exploration of ketamine as a treatment for adults with AN.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

Many physiologic effects of l-glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, are mediated via signaling by ionotropic glutamate receptors (iGluRs). These ligand-gated ion channels are critical to brain function and are centrally implicated in numerous psychiatric and neurologic disorders. There are different classes of iGluRs with a variety of receptor subtypes in each class that play distinct roles in neuronal functions. The diversity in iGluR subtypes, with their unique functional properties and physiologic roles, has motivated a large number of studies. Our understanding of receptor subtypes has advanced considerably since the first iGluR subunit gene was cloned in 1989, and the research focus has expanded to encompass facets of biology that have been recently discovered and to exploit experimental paradigms made possible by technological advances. Here, we review insights from more than 3 decades of iGluR studies with an emphasis on the progress that has occurred in the past decade. We cover structure, function, pharmacology, roles in neurophysiology, and therapeutic implications for all classes of receptors assembled from the subunits encoded by the 18 ionotropic glutamate receptor genes. SIGNIFICANCE STATEMENT: Glutamate receptors play important roles in virtually all aspects of brain function and are either involved in mediating some clinical features of neurological disease or represent a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of this class of receptors will advance our understanding of many aspects of brain function at molecular, cellular, and system levels and provide new opportunities to treat patients.

Activation of Autophagy Ameliorates Age-Related Neurogenesis Decline and Neurodysfunction in Adult Mice

Adult neurogenesis is the ongoing generation of functional new neurons from neural progenitor cells (NPCs) in the mammalian brain. However, this process declines with aging, which is implicated in the recession of brain function and neurodegeneration. Understanding the mechanism of adult neurogenesis and stimulating neurogenesis will benefit the mitigation of neurodegenerative diseases. Autophagy, a highly conserved process of cellular degradation, is essential for maintaining cellular homeostasis and normal function. Whether and how autophagy affects adult neurogenesis remains poorly understood. In present study, we revealed a close connection between impaired autophagy and adult neurogenetic decline. Expression of autophagy-related genes and autophagic activity were significantly declined in the middle-adult subventricular/subgranular zone (SVZ/SGZ) homogenates and cultured NPCs, and inhibiting autophagy by siRNA interference resulted in impaired proliferation and differentiation of NPCs. Conversely, stimulating autophagy by rapamycin not only revitalized the viability of middle-adult NPCs, but also facilitated the neurogenesis in middle-adult SVZ/SGZ. More importantly, autophagic activation by rapamycin also ameliorated the olfactory sensitivity and cognitional capacities in middle-adult mice. Taken together, our results reveal that compromised autophagy is involved in the decline of adult neurogenesis, which could be reversed by autophagy activation. It also shed light on the regulation of adult neurogenesis and paves the way for developing a therapeutic strategy for aging and neurodegenerative diseases.

Ketamine: Neuroprotective or Neurotoxic?

Ketamine, a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist, has been employed clinically as an intravenous anesthetic since the 1970s. More recently, ketamine has received attention for its rapid antidepressant effects and is actively being explored as a treatment for a wide range of neuropsychiatric syndromes. In model systems, ketamine appears to display a combination of neurotoxic and neuroprotective properties that are context dependent. At anesthetic doses applied during neurodevelopmental windows, ketamine contributes to inflammation, autophagy, apoptosis, and enhances levels of reactive oxygen species. At the same time, subanesthetic dose ketamine is a powerful activator of multiple parallel neurotrophic signaling cascades with neuroprotective actions that are not always NMDAR-dependent. Here, we summarize results from an array of preclinical studies that highlight a complex landscape of intracellular signaling pathways modulated by ketamine and juxtapose the somewhat contrasting neuroprotective and neurotoxic features of this drug.

Disrupting phosphorylation of Tyr-1070 at GluN2B selectively produces resilience to depression-like behaviors

Drugs targeting N-methyl-D-aspartate receptors (NMDARs) have been approved to treat major depressive disorder (MDD); however, the presence of undesirable psychotomimetic and cognitive side effects may limit their utility. In this study, we show that the phosphorylation levels of the GluN2B subunit at tyrosine (Y) 1070 increase in mice after both acute and chronic restraint stress (CRS) exposure. Preventing GluN2B-Y1070 phosphorylation via Y1070F mutation knockin produces effects similar to those of antidepressants but does not affect cognitive or anxiety-related behaviors in subject mice. Mechanistically, the Y1070F mutation selectively reduces non-synaptic NMDAR currents and increases the number of excitatory synapses in the layer 5 pyramidal neurons of medial prefrontal cortex (mPFC) but not in the hippocampus. Altogether, our study identifies phosphorylation levels of GluN2B-Y1070 in the mPFC as a dynamic, master switch guarding depressive behaviors, suggesting that disrupting the Y1070 phosphorylation of GluN2B subunit has the potential for developing new antidepressants.

Stress-Related Dysfunction of Adult Hippocampal Neurogenesis-An Attempt for Understanding Resilience?

Newborn neurons in the adult hippocampus are regulated by many intrinsic and extrinsic cues. It is well accepted that elevated glucocorticoid levels lead to downregulation of adult neurogenesis, which this review discusses as one reason why psychiatric diseases, such as major depression, develop after long-term stress exposure. In reverse, adult neurogenesis has been suggested to protect against stress-induced major depression, and hence, could serve as a resilience mechanism. In this review, we will summarize current knowledge about the functional relation of adult neurogenesis and stress in health and disease. A special focus will lie on the mechanisms underlying the cascades of events from prolonged high glucocorticoid concentrations to reduced numbers of newborn neurons. In addition to neurotransmitter and neurotrophic factor dysregulation, these mechanisms include immunomodulatory pathways, as well as microbiota changes influencing the gut-brain axis. Finally, we discuss recent findings delineating the role of adult neurogenesis in stress resilience.

Comparison effects of chronic sleep deprivation on juvenile and young adult mice

Sleeplessness leads to a spectrum of neuropsychiatric disorders, affecting both juveniles and young adults. Studies have shown different sleep patterns at different stages of development. However, the molecular mechanisms underlying the effects of the same chronic sleep deprivation (CSD) on behaviours of juveniles and young adults remain elusive. Here, we aimed to evaluate the effects of CSD (6 days, 19 h per day) on anxiety-like behaviour, cognitive performance and molecular alterations in juvenile and young adult mice. Change in body weight suggested impaired physical development in CSD animals, specifically juveniles gaining weight at a lower rate and young adults losing weight. Behavioural performance indicated that CSD had little effect on spatial memory, but induced analogous anxiety-like phenotypes in both juveniles and young adults, as evidenced by no significant difference in the Y-maze experiment (Y-M) or the Morris water maze experiment (MWM), as well as the decreased open-arm distance percentage in the elevated plus maze experiment (EPM). In addition, CSD reduced the N-methyl-D-aspartic receptor subunit 2B (NR2B) and postsynaptic density protein 95 (PSD95) levels in juveniles, but these were increased in young adults. In conclusion, our results suggested that although CSD resulted in analogous anxiety-like behaviours in both juvenile and young adult mice, the underlying mechanisms might be different, which was indicated by the opposite change of synaptic proteins under CSD. These findings may help to better understand the important role of sleep and have constructive significance for human health.

Immunoregulation and antidepressant effect of ketamine

Major depressive disorder (MDD) is a common mental health disorder that brings severe disease burden worldwide. Traditional antidepressants are mainly targeted at monoamine neurotransmitters, with low remission rates and high recurrence rates. Ketamine is a noncompetitive glutamate N-methyl-d-aspartate receptor (NMDAR) antagonist, and its rapid and powerful antidepressant effects have come to light. Its antidepressant mechanism is still unclarified. Research found that ketamine had not only antagonistic effect on NMDAR but also strong immunomodulatory effect, both of which were closely related to the pathophysiology of MDD. Although there are many related studies, they are relatively heterogeneous. Therefore, this review mainly describes the immune mechanisms involved in MDD and how ketamine plays an antidepressant role by regulating peripheral and central immune system, including peripheral inflammatory cytokines, central microglia, and astrocytes. This review summarizes the related research, finds out the deficiencies of current research, and provides ideas for future research and the development of novel antidepressants.

Repurposing Ketamine in Depression and Related Disorders: Can This Enigmatic Drug Achieve Success?

Repurposing ketamine in the therapy of depression could well represent a breakthrough in understanding the etiology of depression. Ketamine was originally used as an anesthetic drug and later its use was extended to other therapeutic applications such as analgesia and the treatment of addiction. At the same time, the abuse of ketamine as a recreational drug has generated a concern for its psychotropic and potential long-term effects; nevertheless, its use as a fast acting antidepressant in treatment-resistant patients has boosted the interest in the mechanism of action both in psychiatry and in the wider area of neuroscience. This article provides a comprehensive overview of the actions of ketamine and intends to cover: (i) the evaluation of its clinical use in the treatment of depression and suicidal behavior; (ii) the potential use of ketamine in pediatrics; (iii) a description of its mechanism of action; (iv) the involvement of specific brain areas in producing antidepressant effects; (v) the potential interaction of ketamine with the hypothalamic-pituitary-adrenal axis; (vi) the effect of ketamine on neuronal transmission in the bed nucleus of stria terminalis and on its output; (vii) the evaluation of any gender-dependent effects of ketamine; (viii) the interaction of ketamine with the inflammatory processes involved in depression; (ix) the evaluation of the effects observed with single or repeated administration; (x) a description of any adverse or cognitive effects and its abuse potential. Finally, this review attempts to assess whether ketamine's use in depression can improve our knowledge of the etiopathology of depression and whether its therapeutic effect can be considered an actual cure for depression rather than a therapy merely aimed to control the symptoms of depression.

Targeting the dysfunction of glutamate receptors for the development of novel antidepressants

Increasing evidence indicates that dysfunction of glutamate receptors is involved in the pathophysiology of major depressive disorder (MDD). Although accumulating efforts have been made to elucidate the applications and mechanisms underlying antidepressant-like effects of ketamine, a non-selective antagonist of N-methyl-d-aspartate receptor (NMDAR), the role of specific glutamate receptor subunit in regulating depression is not completely clear. The current review aims to discuss the relationships between glutamate receptor subunits and depressive-like behaviors. Research literatures were searched from inception to July 2020. We summarized the alterations of glutamate receptor subunits in patients with MDD and animal models of depression. Animal behaviors in response to dysfunction of glutamate receptor subunits were also surveyed. To fully understand mechanisms underlying antidepressant-like effects of modulators targeting glutamate receptors, we discussed effects of each glutamate receptor subunit on serotonin system, synaptic plasticity, neurogenesis and neuroinflammation. Finally, we collected most recent clinical applications of glutamate receptor modulators and pointed out the limitations of these candidates in the treatment of MDD.

Increasing Adult Hippocampal Neurogenesis Promotes Resilience in a Mouse Model of Depression

Many studies evaluated the functional role of adult hippocampal neurogenesis (AHN) and its key role in cognitive functions and mood regulation. The effects of promoting AHN on the recovery of stress-induced symptoms have been well studied, but its involvement in stress resilience remains elusive. We used a mouse model enabling us to foster AHN before the exposure to unpredictable chronic mild stress (UCMS) to evaluate the potential protective effects of AHN on stress, assessing the depressive-like phenotype and executive functions. For this purpose, an inducible transgenic mouse model was used to delete the pro-apoptotic gene Bax from neural progenitors four weeks before UCMS, whereby increasing the survival of adult-generated neurons. Our results showed that UCMS elicited a depressive-like phenotype, highlighted by a deteriorated coat state, a higher immobility duration in the tail suspension test (TST), and a delayed reversal learning in a water maze procedure. Promoting AHN before UCMS was sufficient to prevent the development of stressed-induced behavioral changes in the TST and the water maze, reflecting an effect of AHN on stress resilience. Taken together, our data suggest that increasing AHN promotes stress resilience on some depressive-like symptoms but also in cognitive symptoms, which are often observed in MD.

Iridoids from Gardeniae fructus ameliorates depression by enhancing synaptic plasticity via AMPA receptor-mTOR signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Gardeniae fructus is a traditional Chinese herb which exerts antidepressant effect. However, its effective constituent and potential mechanism are still unknown.

AIM OF THE STUDY

To examine whether iridoids, a type of monoterpenoids from Gardeniae fructus (IGF), exerts antidepressant effect by enhancing synaptic plasticity via AMPA receptor-mTOR signaling.

MATERIALS AND METHODS

The antidepressant effect of IGF (15 mg/kg; 30 mg/kg; 45 mg/kg) was investigated in spatial restraint stress (SRS)-induced mice. The expression levels of AMPA receptor-mTOR signaling and synaptic proteins were measured by Western blot, dendritic spine density was observed in Golgi staining. AMPA receptor (AMPAR) inhibitor NBQX and mTOR inhibitor Rapamycin were employed to determine the roles of AMPAR and mTOR signaling in IGF-induced antidepressant effects.

RESULTS

After IGF administration, the expression of the AMPA glutamate receptor Glutamate Receptor 1 (GluA1) was inhibited in SRS mice. We also observed a trend toward the up-regulation of the mammalian target of Rapamycin (mTOR) protein kinase, p70 ribosomal protein S6K (P70S6K) and eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1). The protein levels of Synapsin-1 and PSD-95 were decreased after SRS challenge, along with declined dendritic spine density, which were all reversed with IGF treatment. Furthermore, the treatment efficacy of IGF were blocked with AMPA receptor inhibitor NBQX or mTOR inhibitor Rapamycin.

CONCLUSION

IGF exerted antidepressive-like effects by stimulating AMPAR-mTOR signaling regulated synaptic plasticity enhancement. This work provided an important basis for developing IGF and Gardeniae fructus as potential anti-depressants.

The unique plasticity of hippocampal adult-born neurons: Contributing to a heterogeneous dentate

The dentate gyrus (DG) of the hippocampus is evolutionarily conserved as one of the few sites of adult neurogenesis in mammals. Although there is clear evidence that neurogenesis is necessary for healthy hippocampal function, whether adult-born neurons are simply integrated into existing hippocampal networks to serve a similar purpose to that of developmentally born neurons or whether they represent a discrete cell population with unique functions remains less clear. In this review, we consider evidence for discrete cellular, synaptic, and structural features of adult-born DG neurons, suggesting that neurogenesis contributes to the formation of a heterogeneous DG. We therefore propose that hippocampal neurogenesis creates a specialized neuronal subpopulation that may play a key role in hippocampal functions like episodic memory. We note critical gaps in this extensive body of work, including a general failure to include female animals in relevant research and a need for more precise consideration of intrahippocampal neuroanatomy.

Ketamine and the Future of Rapid-Acting Antidepressants

The therapeutic onset of traditional antidepressants is delayed by several weeks and many depressed patients fail to respond to treatment altogether. In contrast, subanesthetic ketamine can rapidly alleviate symptoms of depression within hours of a single administration, even in patients who are considered treatment-resistant. Ketamine is thought to exert these effects by restoring the integrity of neural circuits that are compromised in depression. This hypothesis stems in part from preclinical observations that ketamine can strengthen synaptic connections by increasing glutamate-mediated neurotransmission and promoting rapid neurotrophic factor release. An improved understanding of how ketamine, and other novel rapid-acting antidepressants, give rise to these processes will help foster future therapeutic innovation. Here, we review the history of antidepressant treatment advances that preceded the ketamine discovery, critically examine mechanistic hypotheses for how ketamine may exert its antidepressant effects, and discuss the impact this knowledge has had on ongoing drug discovery efforts.

Evaluation of the antidepressive property of β-hydroxybutyrate in mice

β-hydroxybutyrate, a ketone body metabolite, has been shown to suppress depression-like behavior in rodents. In this study, we examined its antidepressive property in acute and chronic administration modes in mice by using forced swim test and tail suspension test. Results showed that the decrease effect of β-hydroxybutyrate (300 mg/kg) on immobility time in the tail suspension test and forced swim test in stress-naive mice began to be significant at day 11. In a dose-dependent experiment, β-hydroxybutyrate treatment (11 days) showed significant antidepressant activities at the dose of 200 and 300 mg/kg. Unlike fluoxetine, β-hydroxybutyrate treatment (300 mg/kg) showed no antidepressant activities in the acute (1 hour before the test) and three times administration mode within 24 hours (1, 5, and 24 hours before the test). But in a co-administration mode, β-hydroxybutyrate (100 mg/kg) -fluoxetine (2.5 mg/kg) co-administration exhibited an obvious antidepressant activity in the tail suspension test and forced swim test. Further analysis showed that the antidepressant effects of β-hydroxybutyrate and fluoxetine were not associated with the change in mouse locomotor activity. Furthermore, both chronic β-hydroxybutyrate treatment and β-hydroxybutyrate-fluoxetine co-treatment suppressed chronic unpredictable stress-induced increase in immobility time in the tail suspension test and forced swim test as well as chronic unpredictable stress-induced decrease in mouse body weight. Taken together, these results indicate that β-hydroxybutyrate (1) needs a relatively long time to show comparable behavioral activity to that of fluoxetine in assays that are sensitive to the behavioral effects of established antidepressant compounds and (2) can augment the antidepressant action of a sub-therapeutic dose of fluoxetine.

Regulation of Neurogenesis by Organic Cation Transporters: Potential Therapeutic Implications

Neurogenesis is the process by which new neurons are generated from neural stem cells (NSCs), which are cells that have the ability to proliferate and differentiate into neurons, astrocytes, and oligodendrocytes. The process is essential for homeostatic tissue regeneration and the coordination of neural plasticity throughout life, as neurons cannot regenerate once injured. Therefore, defects in neurogenesis are related to the onset and exacerbation of several neuropsychiatric disorders, and therefore, the regulation of neurogenesis is considered to be a novel strategy for treatment. Neurogenesis is regulated not only by NSCs themselves, but also by the functional microenvironment surrounding the NSCs, known as the "neurogenic niche." The neurogenic niche consists of several types of neural cells, including neurons, glial cells, and vascular cells. To allow communication with these cells, transporters may be involved in the secretion and uptake of substrates that are essential for signal transduction. This chapter will focus on the involvement of polyspecific solute carriers transporting organic cations in the possible regulation of neurogenesis by controlling the concentration of several organic cation substrates in NSCs and the neurogenic niche. The potential therapeutic implications of neurogenesis regulation by these transporters will also be discussed.

Hippocampal volume, function, and related molecular activity in anorexia nervosa: A scoping review

INTRODUCTION

Anorexia nervosa (AN) is a serious and persistent eating disorder, characterized by severe dietary restriction and weight loss, with a third of patients developing a  severe-enduring form. The factors contributing to this progression are poorly understood, although there is evidence for impairments in neural structures such as the hippocampus, an area particularly affected by malnutrition and chronic stress.

AREAS COVERED

This study aimed to map the evidence for alterations in hippocampal volume, function, and related molecular activity in anorexia nervosa. PubMed, PsycINFO, and Web of Science were searched for studies related to hippocampal function and integrity using a range of methodologies, such as neuropsychological paradigms, structural and functional magnetic resonance imaging, and analysis of blood components.

EXPERT OPINION

Thirty-nine studies were included in this review. The majority were neuroimaging studies, which found hippocampus-specific volumetric and functional impairments. Neuropsychological studies showed evidence for a specific memory and learning impairments. There was some evidence for molecular abnormalities (e.g. cortisol), although these were few studies. Taken together, our review suggests that the hippocampus might be a particular region of interest when considering neurobiological approaches to understanding AN. These findings warrant further investigation and may lead to novel treatment approaches.

Application of stem cell biology in treating neurodegenerative diseases

BACKGROUND

The appropriate strategies are needed for stimulating the endogenous neurogenesis or introducing extrinsic neural progenitors, which could be harnessed as the regenerative resources for cueing the neurodegenerations. Adult neurogenesis is the endogenous continuing physiology in limited brain regions such as hippocampus, olfactory system, and hypothalamus. Besides adult neurogenesis, induced pluripotent stem cells (iPSCs) induced functional neurons could be another option for regenerative therapies.

OBJECTIVE

Current studies are trying to improve the adult neurogenesis and enable the iPSCs induced neurons into neural regeneration. Methods: Here in this review, we mainly introduced the recent progress in neural stem cell biology and its application in the treatment of the neurodegenerations. We main separated the strategy in summarizing the mediators and potential targets to promoting endogenous neural regeneration and transplantation of neural progenitors.

CONCLUSION

By collecting and comparing the advantages disadvantages between above-mentioned two strategies, we will offer the insight on future development of stem cell therapy in treating neurodegenerative patients.

Steps towards standardized quantification of adult neurogenesis

New neurons are generated in adult mammals. Adult hippocampal neurogenesis is considered to play an important role in cognition and mental health. The number and properties of newly born neurons are regulatable by a broad range of physiological and pathological conditions. To begin to understand the underlying cellular mechanisms and functional relevance of adult neurogenesis, many studies rely on quantification of adult-born neurons. However, lack of standardized methods to quantify new neurons is impeding research reproducibility across laboratories. Here, we review the importance of stereology, and propose why and how it should be applied to the study of adult neurogenesis.

Ketamine in Bipolar Disorder: A Review

Bipolar disorder (BD) is a psychiatric illness associated with high morbidity, mortality and suicide rate. It has neuroprogressive course and a high rate of treatment resistance. Hence, there is an unquestionable need for new BD treatment strategies. Ketamine appears to have rapid antidepressive and antisuicidal effects. Since most of the available studies concern unipolar depression, here we present a novel insight arguing that ketamine might be a promising treatment for bipolar disorder.

Neurotrophic mechanisms underlying the rapid and sustained antidepressant actions of ketamine

Clinical and preclinical studies have demonstrated that depression, one of the most common psychiatric illnesses, is associated with reduced levels of neurotrophic factors, including brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), contributing to neuronal atrophy in the prefrontal cortex (PFC) and hippocampus, and reduced hippocampal adult neurogenesis. Conventional monoaminergic antidepressants can block/reverse, at least partially, these deficits in part via induction of BDNF and/or VEGF, although these drugs have significant limitations, notably a time lag for therapeutic response and low response rates. Recent studies reveal that ketamine, an N-methyl-d-aspartate receptor antagonist produces rapid (within hours) and sustained (up to a week) antidepressant actions in both patients with treatment-resistant depression and rodent models of depression. Rodent studies also demonstrate that ketamine rapidly increases BDNF and VEGF release and/or expression in the medial PFC (mPFC) and hippocampus, leading to increase in the number and function of spine synapses in the mPFC and enhancement of hippocampal neurogenesis. These neurotrophic effects of ketamine are associated with the antidepressant effects of this drug. Together, these findings provide evidence for a neurotrophic mechanism underlying the rapid and sustained antidepressant actions of ketamine and pave the way for the development of rapid and more effective antidepressants with fewer side effects than ketamine.