Imipramine protects against the deleterious effects of chronic corticosterone on depression-like behavior, hippocampal reelin expression, and neuronal maturation

Sex-dependent effects of early life stress on network and behavioral states

Background

Adverse childhood experiences (ACEs) are associated with numerous detriments in health, including increased vulnerability to psychiatric illnesses. Early life stress (ELS) in rodents has been shown to effectively model several of the behavioral and endocrine impacts of ACEs and has been utilized to investigate the underlying mechanisms contributing to disease. However, the precise neural mechanisms responsible for mediating the impact of ELS on vulnerability to psychiatric illnesses remain largely unknown.

Methods

We use behavior, immunoassay, in vivo LFP recording, histology, and patch clamp to describe the effects of ELS on stress behaviors, endocrinology, network states, protein expression, and cellular physiology in male and female mice.

Results

We demonstrate that a murine maternal separation (MS) ELS model causes sex-dependent alterations in behavioral and hormonal responses following an acute stressor. Local field potential (LFP) recordings in the basolateral amygdala (BLA) and frontal cortex (FC) reveal similar sex-dependent alterations at baseline, in response to acute ethological stress, and during fear memory extinction, supporting a large body of literature demonstrating that these network states contribute to stress reactivity and vulnerability to psychiatric illnesses. Sex differences were accompanied by altered physiology of BLA principal neurons in males and BLA PV interneurons in females.

Conclusions

Collectively, these results implicate novel, sex-dependent mechanisms through which ACEs may impact psychiatric health, involving altered cellular physiology and network states involved in emotional processing.

Molecular Mechanisms of Reelin in the Enteric Nervous System and the Microbiota-Gut-Brain Axis: Implications for Depression and Antidepressant Therapy

Current pharmacological treatments for depression fail to produce adequate remission in a significant proportion of patients. Increasingly, other systems, such as the microbiome-gut-brain axis, are being looked at as putative novel avenues for depression treatment. Dysbiosis and dysregulation along this axis are highly comorbid with the severity of depression symptoms. The endogenous extracellular matrix protein reelin is present in all intestinal layers as well as in myenteric and submucosal ganglia, and its receptors are also present in the gut. Reelin secretion from subepithelial myofibroblasts regulates cellular migration along the crypt-villus axis in the small intestine and colon. Reelin brain expression is downregulated in mood and psychotic disorders, and reelin injections have fast antidepressant-like effects in animal models of depression. This review seeks to discuss the roles of reelin in the gastrointestinal system and propose a putative role for reelin actions in the microbiota-gut-brain axis in the pathogenesis and treatment of depression, primarily reflecting on alterations in gut epithelial cell renewal and in the clustering of serotonin transporters.

Emotional behaviors as well as the hippocampal reelin expression in C57BL/6N male mice chronically treated with corticosterone

Depression is a common psychiatric disorder affecting around 300 million people worldwide. Serum cortisol and glucocorticoid levels in humans are reportedly higher in patients with depression compared to controls. Furthermore, rodents repeatedly treated with exogenous corticosterone (CORT), a glucocorticoid in rodents, exhibit deficits in emotional behaviors. To confirm the availability of mice with chronic CORT treatment as an animal model of depression, we investigated the effect of chronic CORT treatment on depression-like behavioral and neuropathological phenotypes in C57BL/6N male mice. Behavioral studies showed depression- and anxiety-like behaviors in mice treated with CORT compared with control mice in the forced-swim and elevated-plus maze tests. Additionally, treated mice represented anhedonia and social behavior impairments in the sucrose preference and social interaction tests, respectively. Brains of depression patients have altered expression of reelin, an extracellular matrix protein involved in neuronal development and function. Likewise, in the present study, mice with chronic CORT treatment also exhibited reelin downregulation in cells of the hippocampus. Hence, we investigated therapeutic effects of reelin supplementation on CORT-induced behavioral abnormalities in mice. Microinjections of recombinant reelin protein into the hippocampus did not rescue behavioral deficits in mice with chronic CORT treatment. These results suggest that C57BL/6N male mice chronically treated with CORT are a suitable animal depression model, in which depressive behaviors may occur independently of the alternation of hippocampal Reelin expression.

Reelin Rescues Behavioral, Electrophysiological, and Molecular Metrics of a Chronic Stress Phenotype in a Similar Manner to Ketamine

Over the past decade, ketamine, an NMDA receptor antagonist, has demonstrated fast-acting antidepressant effects previously unseen with monoaminergic-based therapeutics. Concerns regarding psychotomimetic effects limit the use of ketamine for certain patient populations. Reelin, an extracellular matrix glycoprotein, has shown promise as a putative fast-acting antidepressant in a model of chronic stress. However, research has not yet demonstrated the changes that occur rapidly after peripheral reelin administration. To address this key gap in knowledge, male Long-Evans rats underwent a chronic corticosterone (CORT; or vehicle) paradigm (40 mg/kg, 21 d). On day 21, rats were then administered an acute dose of ketamine (10 mg/kg, i.p.), reelin (3 µg, i.v.), or vehicle. Twenty-four hours after administration, rats underwent behavioral or in vivo electrophysiological testing before killing. Immunohistochemistry was used to confirm changes in hippocampal reelin immunoreactivity. Lastly, the hippocampus was microdissected from fresh tissue to ascertain whole cell and synaptic-specific changes in protein expression through Western blotting. Chronic corticosterone induced a chronic stress phenotype in the forced swim test and sucrose preference test (SPT). Both reelin and ketamine rescued immobility and swimming, however reelin alone rescued latency to immobility. In vivo electrophysiology revealed decreases in hippocampal long-term potentiation (LTP) after chronic stress which was increased significantly by both ketamine and reelin. Reelin immunoreactivity in the dentate gyrus paralleled the behavioral and electrophysiological findings, but no significant changes were observed in synaptic-level protein expression. This exploratory research supports the putative rapid-acting antidepressant effects of an acute dose of reelin across behavioral, electrophysiological, and molecular measures.

Connecting Dots between Mitochondrial Dysfunction and Depression

Mitochondria are the prime source of cellular energy, and are also responsible for important processes such as oxidative stress, apoptosis and Ca2+ homeostasis. Depression is a psychiatric disease characterized by alteration in the metabolism, neurotransmission and neuroplasticity. In this manuscript, we summarize the recent evidence linking mitochondrial dysfunction to the pathophysiology of depression. Impaired expression of mitochondria-related genes, damage to mitochondrial membrane proteins and lipids, disruption of the electron transport chain, higher oxidative stress, neuroinflammation and apoptosis are all observed in preclinical models of depression and most of these parameters can be altered in the brain of patients with depression. A deeper knowledge of the depression pathophysiology and the identification of phenotypes and biomarkers with respect to mitochondrial dysfunction are needed to help early diagnosis and the development of new treatment strategies for this devastating disorder.

Intravenous Reelin Treatment Rescues Atrophy of Spleen White Pulp and Correlates to Rescue of Forced Swim Test Immobility and Neurochemical Alterations Induced by Chronic Stress

Reelin, an extracellular matrix protein with putative antidepressant-like properties, becomes dysregulated by chronic stress. Improvement in cognitive dysfunction and depression-like behavior induced by chronic stress has been reported with both intrahippocampal and intravenous Reelin treatment but the mechanisms responsible are not clear. To determine if treatment with Reelin modifies chronic stress-induced dysfunction in immune organs and whether this relates to behavioral and/or neurochemical outcomes, spleens were collected from both male (n = 62) and female (n = 53) rats treated with daily corticosterone injections for three weeks that received Reelin or vehicle. Reelin was intravenously administered once on the final day of chronic stress, or repeatedly, with weekly treatments throughout chronic stress. Behavior was assessed during the forced swim test and the object-in-place test. Chronic corticosterone caused significant atrophy of the spleen white pulp, but treatment with a single shot of Reelin restored white pulp in both males and females. Repeated Reelin injections also resolved atrophy in females. Correlations were observed between recovery of white pulp atrophy and recovery of behavioral deficits and expression of both Reelin and glutamate receptor 1 in the hippocampus, supporting a role of the peripheral immune system in the recovery of chronic stress-induced behaviors following treatment with Reelin. Our data adds to research indicating Reelin could be a valuable therapeutic target for chronic stress-related disorders including major depression.

Sex differences in basal reelin levels in the paraventricular hypothalamus and in response to chronic stress induced by repeated corticosterone in rats

Repeated exposure to the stress hormone corticosterone results in depressive-like behaviours paralleled by the downregulation of hippocampal reelin expression. Reelin is expressed in key neural populations involved in the stress response, but whether its hypothalamic expression is sex-specific or involved in sex-specific vulnerability to stress is unknown. Female and male rats were treated with either daily vehicle or corticosterone injections (40 mg/kg) for 21 days. Thereafter, they were subjected to several behavioural tasks before being sacrificed to allow the analysis of reelin expression in hypothalamic nuclei. The basal density of reelin-positive cells in males was significantly higher in the paraventricular nucleus (19 %) and in the medial preoptic area (51 %) compared to females. Chronic corticosterone injections increased the immobility time in the forced swim test in males (107 %) and females (108 %) and decreased the exploration of the elevated plus maze in males (34 %). Corticosterone also caused a significant decrease in the density of reelin-positive cells in males, in both ventrodorsal (37 %) and ventrolateral (32 %) subdivisions of the paraventricular nucleus, while not affecting females. Moreover, in the paraventricular nucleus of males, 30 % of the basal reelin-positive cells co-expressed oxytocin while only 17.5 % did in females, showing a positive correlation between reelin and oxytocin levels. Chronic corticosterone did not significantly affect co-localization levels. For the first time, this study shows that there is a sexually dimorphic subpopulation of reelin-positive neurons in the paraventricular nucleus that can be differentially affected by chronic stress.

BKM120 alters the migration of doublecortin-positive cells in the dentate gyrus of mice

BKM120 is an inhibitor of class I phosphoinositide 3-kinases and its anti-cancer effects have been demonstrated in various solid cancer models. BKM120 is highly brain permeable and has been reported to induce mood disturbances in clinical trials. Therefore, we examined whether BKM120 produces anxiety- and depression-like behaviors in mice, as with patients receiving BKM120 in clinical trials. In this study, repeated BKM120 treatment (2.0 or 5.0mg/kg, i.p., five times at 12-h interval) significantly induced anxiety- and depression-like behaviors in mice. Although abnormal changes in hippocampal neurogenesis have been suggested to, at least in part, associated with the pathogenesis of depression and anxiety, BKM120 did not affect the incorporation of 5-bromo-2'-deoxyuridine or the expression of doublecortin (DCX); however, it significantly enhanced the radial migration of DCX-positive cells in the dentate gyrus. BKM120-induced changes in migration were not accompanied by obvious neuronal damage in the hippocampus. Importantly, BKM120-induced anxiety- and depression-like behaviors were positively correlated with the extent of DCX-positive cell migration. Concomitantly, p-Akt expression was significantly decreased in the dentate gyrus. Moreover, the expression of p-c-Jun N-terminal kinase (JNK), p-DCX, and Ras homolog family member A (RhoA)-GTP decreased significantly, particularly in aberrantly migrated DCX-positive cells. Together, the results suggest that repeated BKM120 treatment enhances the radial migration of DCX-positive cells and induces anxiety- and depression-like behaviors by regulating the activity of Akt, JNK, DCX, and RhoA in the dentate gyrus. It also suggests that the altered migration of adult-born neurons in the dentate gyrus plays a role in mood disturbances.

Reelin has antidepressant-like effects after repeated or singular peripheral injections

Chronic stress is a significant risk factor for depression onset. The effects of chronic stress can be studied preclinically using a corticosterone (CORT)-administration paradigm that results in a phenotype of depressive-like behavior associated with neurochemical abnormalities in brain regions like the hippocampus. We have recently shown that intrahippocampal infusions of Reelin have a fast effect in normalizing CORT-induced behavioral and neurochemical alterations. Reelin is also expressed in multiple peripheral systems and is found in blood plasma which prompted us to investigate whether peripheral intravenous (i.v.) Reelin injections could also result in antidepressant (ATD)-like actions. Repeated i.v. injections of Reelin were effective in rescuing the CORT-induced increases in forced-swim-test immobility in male and female rats, decreases in Reelin-immunopositive cells in the dentate gyrus subgranular zone, and expression of hippocampal GABA_Aβ 2/3, GluA1, and GluN2B receptors. However, Reelin had only a partial effect on the number and maturation rate of dentate gyrus newborn cells. CORT and Reelin did not affect open field test behavior. After evaluating the effects of multiple Reelin injections, we demonstrated that a single Reelin injection administered at the end of CORT treatment could rescue in 24 h the behavioral (forced-swim-test and object-in-place test), as well as neurochemical effects of CORT. These findings show that i.v. injections of Reelin have fast ATD-like effects associated with the restoration of hippocampal neurochemical deficits. Although additional mechanistic and pharmacokinetic studies are necessary, our data open the possibility to develop Reelin-based therapeutics with putative fast-ATD activity.

The Role of MeCP2 in Regulating Synaptic Plasticity in the Context of Stress and Depression

Methyl-CpG-binding protein 2 (MeCP2) is a transcriptional regulator that is highly abundant in the brain. It binds to methylated genomic DNA to regulate a range of physiological functions implicated in neuronal development and adult synaptic plasticity. MeCP2 has mainly been studied for its role in neurodevelopmental disorders, but alterations in MeCP2 are also present in stress-related disorders such as major depression. Impairments in both stress regulation and synaptic plasticity are associated with depression, but the specific mechanisms underlying these changes have not been identified. Here, we review the interplay between stress, synaptic plasticity, and MeCP2. We focus our attention on the transcriptional regulation of important neuronal plasticity genes such as BDNF and reelin (RELN). Moreover, we provide evidence from recent studies showing a link between chronic stress-induced depressive symptoms and dysregulation of MeCP2 expression, underscoring the role of this protein in stress-related pathology. We conclude that MeCP2 is a promising target for the development of novel, more efficacious therapeutics for the treatment of stress-related disorders such as depression.

New Strategies for the Treatment of Neuropsychiatric Disorders Based on Reelin Dysfunction

Reelin is an extracellular matrix protein that is mainly produced in Cajal-Retzius cells and controls neuronal migration, which is important for the proper formation of cortical layers in the developmental stage of the brain. In the adult brain, Reelin plays a crucial role in the regulation of N-methyl-D-aspartate receptor-dependent synaptic function, and its expression decreases postnatally. Clinical studies showed reductions in Reelin protein and mRNA expression levels in patients with psychiatric disorders; however, the causal relationship remains unclear. Reelin-deficient mice exhibit an abnormal neuronal morphology and behavior, while Reelin supplementation ameliorates learning deficits, synaptic dysfunctions, and spine loss in animal models with Reelin deficiency. These findings suggest that the neuronal deficits and brain dysfunctions associated with the down-regulated expression of Reelin are attenuated by enhancements in its expression and functions in the brain. In this review, we summarize findings on the role of Reelin in neuropsychiatric disorders and discuss potential therapeutic approaches for neuropsychiatric disorders associated with Reelin dysfunctions.

How Stress Influences the Dynamic Plasticity of the Brain’s Extracellular Matrix

Diffuse and structured extracellular matrix (ECM) comprise ∼20% of the brain’s volume and play important roles in development and adult plasticity. Perineuronal nets (PNNs), specialized ECM structures that surround certain types of neurons in the brain, emerge during the postnatal period, making their development and maintenance potentially sensitive to experience. Recent studies have shown that stress affects diffuse ECM as well as PNNs, and that such effects are dependent on life stage and brain region. Given that the ECM participates in synaptic plasticity, the generation of neuronal oscillations, and synchronous firing across brain regions, all of which have been linked to cognition and emotional regulation, ECM components may be candidate therapeutic targets for stress-induced neuropsychiatric disease. This review considers the influence of stress over diffuse and structured ECM during postnatal life with a focus on functional outcomes and the potential for translational relevance.

The effects of neonatal procedural pain and maternal isolation on hippocampal cell proliferation and reelin concentration in neonatal and adult male and female rats

Preterm births accounted for over 10% of all U.S. live births in 2019 and the rate is rising. Neonatal stressors, especially procedural pain, experienced by preterm infants in the neonatal intensive care unit (NICU) have been associated with neurodevelopmental impairments. Parental care can alleviate stress during stressful or painful procedures; however, infants in the NICU often receive reduced parental care compared with their peers. Animal studies suggest that decreased maternal care similarly impairs neurodevelopment but also influences the effects of neonatal pain. It is important to mimic both stressors in animal models of neonatal stress exposure. In this study, researchers investigated the individual and combined impact of neonatal pain and maternal isolation on reelin protein levels and cellular proliferation in the hippocampal dentate gyrus of 8 days old and adult rats. Exposure to either stressor individually, but not both, increased reelin levels in the dentate gyrus of adult females without significantly altering reelin levels in adult males. However, cell proliferation levels at either age were unaffected by the early-life stressors. These results suggest that each early-life stressor has a unique effect on markers of brain development and more research is needed to further investigate their distinct influences.

Antidepressant effects of curcumin-coated iron oxide nanoparticles in a rat model of depression

The antidepressant effect of curcumin-coated iron oxide nanoparticles (Cur-IONPs) was investigated in the current study using depression rat model induced by reserpine. IONPs were synthesized by curcumin as a reducing agent producing Cur-IONPs. Rats were divided into control, depression rat model, and depressed rats treated with Cur-IONPs. After treatment rat behavior was evaluated using forced swimming test (FST). Serotonin (5-HT), norepinephrine (NE), dopamine (DA), monoamine oxidase (MAO), acetylcholinesterase (AchE), Na⁺, K⁺, ATPase, lipid peroxidation (MDA), reduced glutathione (GSH), glutathione-s-transferase (GST) and nitric oxide (NO) were measured in the cortex and hippocampus. In depressed rats, FST showed increased immobilization time and reduced swimming time. This was associated with a significant decrease in 5-HT, NE, DA and GSH and a significant increase in MDA and NO levels and GST, MAO, AchE and Na⁺, K⁺, ATPase activities in the cortex and hippocampus. Treatment with Cur-NONPs for two weeks increased the swimming time reduced the immobility time, and elevated 5-HT, NE and DA levels. Cur-IONPs attenuated the oxidative stress induced by reserpine and restored the MAO, AchE and Na⁺, K⁺, ATPase. The present green method used curcumin in the IONPs synthesis and has several merits; obtaining nanoform of iron oxide, increasing the bioavailability of curcumin and reducing the oxidative stress induced by iron. The present antidepressant effect of Cur-IONPs could be attributed to the ability of Cur-IONPs to restore monoamine neurotransmitter levels by increasing their synthesis and reducing their metabolism. In addition, the antioxidant activity of curcumin prevented oxidative stress in the depressed rats.

Maternal Deprivation in Rats Decreases the Expression of Interneuron Markers in the Neocortex and Hippocampus

Early life stress has profound effects on the development of the central nervous system. We exposed 9-day-old rat pups to a 24 h maternal deprivation (MD) and sacrificed them as young adults (60-day-old), with the aim to study the effects of early stress on forebrain circuitry. We estimated numbers of various immunohistochemically defined interneuron subpopulations in several neocortical regions and in the hippocampus. MD rats showed reduced numbers of parvalbumin-expressing interneurons in the CA1 region of the hippocampus and in the prefrontal cortex, compared with controls. Numbers of reelin-expressing and calretinin-expressing interneurons were also reduced in the CA1 and CA3 hippocampal areas, but unaltered in the neocortex of MD rats. The number of calbinin-expressing interneurons in the neocortex was similar in the MD rats compared with controls. We analyzed cell death in 15-day-old rats after MD and found no difference compared to control rats. Thus, our results more likely reflect the downregulation of markers than the actual loss of interneurons. To investigate synaptic activity in the hippocampus we immunostained for glutamatergic and inhibitory vesicular transporters. The number of inhibitory synapses was decreased in the CA1 and CA3 regions of the hippocampus in MD rats, with the normal number of excitatory synapses. Our results indicate complex, cell type-specific, and region-specific alterations in the inhibitory circuitry induced by maternal deprivation. Such alterations may underlie symptoms of MD at the behavioral level and possibly contribute to mechanisms by which early life stress causes neuropsychiatric disorders, such as schizophrenia.

Patient oriented research in mental health: matching laboratory to life and beyond in Canada

As patient-oriented research gains popularity in clinical research, the lack of patient input in foundational science grows more evident. Research has shown great utility in active partnerships between patient partners and scientists, yet many researchers are still hesitant about listening to the voices of those with lived experience guide and shape their experiments. Mental health has been a leading area for patient movements such as survivor-led research, however the stigma experienced by these patients creates difficulties not present in other health disciplines. The emergence of COVID-19 has also created unique circumstances that need to be addressed. Through this lens, we have taken experiences from our patient partners, students, and primary investigator to create recommendations for the better facilitation of patient-oriented research in foundational science in Canada. With these guidelines, from initial recruitment and leading to sustaining meaningful partnerships, we hope to encourage other researchers that patient-oriented research is necessary for the future of mental health research and foundational science.

Altered acoustic startle, prepulse facilitation, and object recognition memory produced by corticosterone withdrawal in male rats

The symptoms of human depression often include cognitive deficits. However, cognition is not frequently included in the behavioral assessments conducted in preclinical models of depression. For example, it is well known that repeated corticosterone (CORT) injections in rodents produce depression-like behavior as measured by the forced swim test, sucrose preference test, and tail suspension test, but the cognitive impairments produced by repeated CORT have not been thoroughly examined. The purpose of this experiment was to assess the effect of repeated CORT injections on several versions of object recognition memory and modulation of the acoustic startle response by relatively low intensity prepulses, along with the more traditional assessment of depression-like behavior using the forced swim test. Rats received 21 days of CORT (40 mg/kg) or vehicle injections followed by a battery of behavioral tests. Importantly, during behavioral testing CORT treatment did not occur (CORT withdrawal). Corticosterone decreased body weight, increased immobility in the forced swim test, lowered startle amplitudes, and facilitated responding to trials with a short interval (30 ms) between the prepulse and pulse. Corticosterone also impaired both object location and object-in-place recognition memory, while sparing performance on object recognition memory. Collectively, our data suggest that CORT produces selective disruptions in prepulse facilitation, object location, and object-in-place recognition memory, and that these impairments should be considered as part of the phenotype produced by repeated CORT, and perhaps chronic stress.

Chronic stress followed by social isolation promotes depressive-like behaviour, alters microglial and astrocyte biology and reduces hippocampal neurogenesis in male mice

Unpredictable chronic mild stress (UCMS) is one of the most commonly used, robust and translatable models for studying the neurobiological basis of major depression. Although the model currently has multiple advantages, it does not entirely follow the trajectory of the disorder, whereby depressive symptomology can often present months after exposure to stress. Furthermore, patients with depression are more likely to withdraw in response to their stressful experience, or as a symptom of their depression, and, in turn, this withdrawal/isolation can further exacerbate the stressful experience and the depressive symptomology. Therefore, we investigated the effect(s) of 6 weeks of UCMS followed by another 6 weeks of social isolation (referred to as UCMSI), on behaviour, corticosterone stress responsivity, immune system functioning, and hippocampal neurogenesis, in young adult male mice. We found that UCMSI induced several behavioural changes resembling depression but did not induce peripheral inflammation. However, UCMSI animals showed increased microglial activation in the ventral dentate gyrus (DG) of the hippocampus and astrocyte activation in both the dorsal and ventral DG, with increased GFAP-positive cell immunoreactivity, GFAP-positive cell hypertrophy and process extension, and increased s100β-positive cell density. Moreover, UCMSI animals had significantly reduced neurogenesis in the DG and reduced levels of peripheral vascular endothelial growth factor (VEGF) - a trophic factor produced by astrocytes and that stimulates neurogenesis. Finally, UCMSI mice also had normal baseline corticosterone levels but a smaller increase in corticosterone following acute stress, that is, the Porsolt Swim Test. Our work gives clinically relevant insights into the role that microglial and astrocyte functioning, and hippocampal neurogenesis may play in the context of stress, social isolation and depression, offering a potentially new avenue for therapeutic target.

Severe life stress, mitochondrial dysfunction, and depressive behavior: A pathophysiological and therapeutic perspective

Mitochondria are responsible for providing our cells with energy, as well as regulating oxidative stress and apoptosis, and considerable evidence demonstrates that mitochondria-related alterations are prevalent during chronic stress and depression. Here, we discuss how chronic stress may induce depressive behavior by potentiating mitochondrial allostatic load, which ultimately decreases energy production, elevates the generation of harmful reactive oxygen species, damages mitochondrial DNA and increases membrane permeability and pro-apoptotic factor release. We also discuss how mitochondrial insults can exacerbate the immune response, contributing to depressive symptomology. Furthermore, we illustrate how depression symptoms are associated with specific mitochondrial defects, and how targeting of these defects with pharmacological agents may be a promising avenue for the development of novel, more efficacious antidepressants. In summary, this review supports the notion that severe psychosocial stress induces mitochondrial dysfunction, thereby increasing the vulnerability to developing depressive symptoms.

Facilitating Granule Cell Survival and Maturation in Dentate Gyrus With Baicalin for Antidepressant Therapeutics

Baicalin isolated from Scutellaria baicalensis possesses antidepressant abilities through its relation to hippocampal neurogenesis. Current research has found that baicalin can promote the proliferation of hippocampal granule cells, however, the detailed mechanism of baicalin on the survival and maturation of hippocampal granule cells has yet to be sufficiently explored. The purpose of this study was to evaluate whether baicalin could facilitate the survival and maturation of hippocampal granule cells, and to explore its potential mechanism. The chronic corticosterone (CORT)-induced mouse model of depression was used to assess antidepressant-like effects of baicalin and to illuminate possible molecular mechanisms by which baicalin affects hippocampal neurogenesis. The survival and maturation of granule cells were measured by immunohistochemistry, immunofluorescence and Golgi staining. The expression of Phosphatidylinositol 3-kinase (PI3K)/Protein kinase B (AKT)/glycogen synthase kinase-3β (GSK3β)/β-catenin pathway related proteins were measured by western blot analysis. PI3K inhibitor LY292002 and AKT inhibitor Perifosine were administered to HT-22 cells to explore the relationship between the PI3K/AKT/GSK3β/β-catenin pathway and baicalin. The results of the study illustrated that baicalin significantly decreased chronic CORT-induced depressive-like behaviors and reduced serum corticosterone levels. In addition, baicalin (administered at 60 mg/kg) reversed chronic CORT-induced lesions on hippocampal granule cells. Moreover, baicalin significantly increased the phosphorylation rate of PI3K, AKT, GSK3β, and total β-catenin. The study found that administration of LY292002/Perifosine counteracted the effects of baicalin in HT-22 cells. These results demonstrate that baicalin can alleviate chronic CORT-induced depressive-like behaviors through promoting survival and maturation of adult-born hippocampal granule cells and exhibiting protective effect on hippocampal neuron morphology. We propose the underlying mechanisms involve the activation of the PI3K/AKT/GSK3β/β-catenin pathway.

Ketamine Rescues Hippocampal Reelin Expression and Synaptic Markers in the Repeated-Corticosterone Chronic Stress Paradigm

Depression is the leading cause of disability worldwide, which necessitates novel therapeutics and biomarkers to approach treatment of this neuropsychiatric disorder. To assess potential mechanisms underlying the fast-acting antidepressant actions of ketamine we used a repeated corticosterone paradigm in adult male rats to assess the effects of ketamine on reelin-positive cells, a protein largely implicated in the pathophysiology of depression. We also assessed the effects of reelin and ketamine on hippocampal and cerebellar synpatosomes, and on serotonin transporter clustering in peripheral lymphocytes to determine reelin and ketamine's impact at the synaptic and peripheral levels. Reelin and ketamine similarly rescue synaptic expression of mTOR and p-mTOR that were decreased by corticosterone. Reelin, but not ketamine, was able to rescue patterns of serotonin transporter clustering in the periphery. These findings display ketamine as a powerful modulator of reelin expression and lend strength to further evaluation of the putative fast antidepressant-like actions of reelin.

Fast-acting antidepressant-like effects of Reelin evaluated in the repeated-corticosterone chronic stress paradigm

The present report examines the effects of repeated or single intrahippocampal Reelin infusions on measures of depressive-like behavior, cognition, and hippocampal neurogenesis in the repeated-corticosterone (CORT) paradigm. Rats received subcutaneous injections of CORT for 3 weeks and Reelin was infused through an inserted canula in the left hippocampus on days 7, 14, and 21, or only on day 21 of CORT injections. CORT increased immobility in the forced-swim test and impaired object-location memory. Notably, these effects were reversed by both repeated and single-Reelin infusions. CORT decreased both the number and complexity of doublecortin-labeled maturing newborn neurons in the dentate gyrus subgranular zone, and a single-Reelin infusion increased the number but not complexity of newborn neurons, while repeated Reelin infusions restored both. Injection of the AMPA antagonist CNQX blocked the rescue of the behavioral phenotype by Reelin but did completely block the effects of Reelin on hippocampal neurogenesis. Reelin is able to rescue the deficits in AMPA, NMDA, GABAA receptors, mTOR and p-mTOR induced by CORT. These novel results demonstrate that a single intrahippocampal Reelin infusion into the dorsal hippocampus has fast-acting antidepressant-like effects, and that some of these effects may be at least partially independent of Reelin actions on hippocampal neurogenesis.

Interaction of reelin and stress on immobility in the forced swim test but not dopamine-mediated locomotor hyperactivity or prepulse inhibition disruption: Relevance to psychotic and mood disorders

RATIONALE

Psychotic disorders, such as schizophrenia, as well as some mood disorders, such as bipolar disorder, have been suggested to share common biological risk factors. One such factor is reelin, a large extracellular matrix glycoprotein that regulates neuronal migration during development as well as numerous activity-dependent processes in the adult brain. The current study sought to evaluate whether a history of stress exposure interacts with endogenous reelin levels to modify behavioural endophenotypes of relevance to psychotic and mood disorders.

METHODS

Heterozygous Reeler Mice (HRM) and wildtype (WT) controls were treated with 50mg/L of corticosterone (CORT) in their drinking water from 6 to 9weeks of age, before undergoing behavioural testing in adulthood. We assessed methamphetamine-induced locomotor hyperactivity, prepulse inhibition (PPI) of acoustic startle, short-term spatial memory in the Y-maze, and depression-like behaviour in the Forced-Swim Test (FST).

RESULTS

HRM genotype or CORT treatment did not affect methamphetamine-induced locomotor hyperactivity, a model of psychosis-like behaviour. At baseline, HRM showed decreased PPI at the commonly used 100msec interstimulus interval (ISI), but not at the 30msec ISI or following challenge with apomorphine. A history of CORT exposure potentiated immobility in the FST amongst HRM, but not WT mice. In the Y-maze, chronic CORT treatment decreased novel arm preference amongst HRM, reflecting reduced short-term spatial memory.

CONCLUSION

These data confirm a significant role of endogenous reelin levels on stress-related behaviour, supporting a possible role in both bipolar disorder and schizophrenia. However, an interaction of reelin deficiency with dopaminergic regulation of psychosis-like behaviour remains unclear.

Red wine polyphenols reverse depressive-like behaviors in mice induced by repeated corticosterone treatment

The aim of this study was to investigate the antidepressant-like effect of red wine phenolic extracts in mouse model exposed to exogenous corticosterone. The results showed that 3-week corticosterone injections caused depression-like behavior in mice, as indicated by the significant decrease in sucrose consumption and increase immobility time in the forced swimming test (FST). Red wine phenolic extracts treatment significantly reduced serum corticosterone levels. Moreover, it was found that red wine phenolic extract increased the brain-derived neurotrophic factor protein (BNDF) and tropomyosin-related kinase B (TrkB) phosphorylation and cAMP-responsive element binding protein (CREB) phosphorylation levels in the hippocampus and prefrontal cortex. However, K252a, an inhibitor of TrkB, completely abolished those antidepressant-like effects. These results suggested that the red wine phenolic extracts produce an antidepressant-like effect in corticosteronetreated mice, at least in part, which is possibly mediated by modulating hypothalamic-pituitary-adrenal (HPA) axis, BDNF, TrkB and CREB phosphorylation levels in the brain region of mice.

A Role for Matrix Metalloproteases in Antidepressant Efficacy

Major depressive disorder is a debilitating condition that affects approximately 15% of the United States population. Though the neurophysiological mechanisms that underlie this disorder are not completely understood, both human and rodent studies suggest that excitatory/inhibitory (E/I) balance is reduced with the depressive phenotype. In contrast, antidepressant efficacy in responsive individuals correlates with increased excitatory neurotransmission in select brain regions, suggesting that the restoration of E/I balance may improve mood. Enhanced excitatory transmission can occur through mechanisms including increased dendritic arborization and synapse formation in pyramidal neurons. Reduced activity of inhibitory neurons may also contribute to antidepressant efficacy. Consistent with this possibility, the fast-acting antidepressant ketamine may act by selective inhibition of glutamatergic input to GABA releasing parvalbumin (PV)-expressing interneurons. Recent work has also shown that a negative allosteric modulator of the GABA-A receptor α subunit can improve depression-related behavior. PV-expressing interneurons are thought to represent critical pacemakers for synchronous network events. These neurons also represent the predominant GABAergic neuronal population that is enveloped by the perineuronal net (PNN), a lattice-like structure that is thought to stabilize glutamatergic input to this cell type. Disruption of the PNN reduces PV excitability and increases pyramidal cell excitability. Various antidepressant medications increase the expression of matrix metalloproteinases (MMPs), enzymes that can increase pyramidal cell dendritic arborization and spine formation. MMPs can also cleave PNN proteins to reduce PV neuron-mediated inhibition. The present review will focus on mechanisms that may underlie antidepressant efficacy, with a focus on monoamines as facilitators of increased matrix metalloprotease (MMP) expression and activation. Discussion will include MMP-dependent effects on pyramidal cell structure and function, as well as MMP-dependent effects on PV expressing interneurons. We conclude with discussion of antidepressant use for those at risk for Alzheimer’s disease, and we also highlight areas for further study.

Fetal exposure to high levels of maternal glucocorticoids alters reelin signaling in the prefrontal cortex of rat pups

Maternal stress (MS) is associated with various neuropsychiatric disorders and cognitive impairment in the offspring. However, it is unclear how early life stress alters the pup's brain development and how it contributes to the pathology of neuropsychiatric disorders later in life. Reelin is a large extracellular matrix glycoprotein that plays essential roles in early brain development such as neural migration, synaptic development, and maturation. Dysregulation of reelin and its signaling proteins is associated with the emergence of neuropsychiatric disorders in adulthood. This study examined the effect of repeated maternal Carbenoxolone (CBX) injection during late gestation on reelin signaling in the prefrontal cortex (PFC) of rat pups. CBX is a selective 11β-HSD2 enzyme inhibitor that promotes the direct transfer of maternal corticosteroids (CORT) to the fetus. Therefore, treatment with CBX can mimic the animal model of early life exposure to high levels of maternal stress hormone. In this study, pregnant rats were injected daily with either saline or CBX during gestation day (GD) 14-21, and the levels of reelin and its signaling proteins were examined in the PFC of rat pups at different postnatal age from P0-P21. The main result of this study is the repeated maternal CBX injections during GD14-21 acutely increase reln mRNA and protein expression in the PFC of rat pups at birth (P0) and follow by a significant decrease during P7-P14. The treatment also causes long term decreases in the amount of VLDLR and Dab1 which are the downstream signaling proteins for the reelin pathway, at least until P21. Our results indicated that fetal exposure to high levels of maternal CORT interferes with reelin signaling which might have profound effects on cortical development associated with neuropsychiatric disorders later in life.

Patterns of Membrane Protein Clustering in Peripheral Lymphocytes as Predictors of Therapeutic Outcomes in Major Depressive Disorder

There is an utmost necessity of developing novel biomarkers of depression that result in a more efficacious use of current antidepressant drugs. The present report reviews and discusses a recent series of experiments that focused on analysis of membrane protein clustering in peripheral lymphocytes as putative biomarkers of therapeutic efficacy for major depressive disorder. This review recapitulates how the ideas were originated, and the main findings demonstrated that analysis of serotonin transporter and serotonin 2 A receptor clustering in peripheral lymphocytes of naïve depression patients resulted in a discrimination of two subpopulations of depressed patients that showed a differential response upon 8 weeks of antidepressant treatment. The paper also reviews the usefulness of animal models of depression for an initial evaluation of membrane protein clustering in lymphocytes, which provides a screening tool to determine additional proteins to be further evaluated in depression patients. Finally, the present review provides a brief discussion of the general field of biomarkers of depression in relation to therapeutic outcomes and suggests additional ideas to provide extra value to the reviewed studies.

Exploring the Potential Antidepressant Mechanisms of TNFα Antagonists

Human and animal studies suggest an intriguing relationship between the immune system and the development of depression. Some peripherally produced cytokines, such as TNF-α, can cross the blood brain barrier and result in activation of brain microglia which produces additional TNF-α and fosters a cascade of events including decreases in markers of synaptic plasticity and increases in neurodegenerative events. This is exemplified by preclinical studies, which show that peripheral administration of pro-inflammatory cytokines can elicit depression-like behavior. Importantly, this depression-like behavior can be ameliorated by anti-cytokine therapies. Work in our laboratory suggests that TNF-α is particularly important for the development of a depressive phenotype and that TNF-α antagonists might have promise as novel antidepressant drugs. Future research should examine rates of inflammation at baseline in depressed patients and whether anti-inflammatory agents could be included as part of the treatment regimen for depressive disorders.

Melanin-Concentrating Hormone (MCH) and MCH-R1 in the Locus Coeruleus May Be Involved in the Regulation of Depressive-Like Behavior

BACKGROUND

Previous anatomical and behavioral studies have shown that melanin-concentrating hormone is involved in the modulation of emotional states. However, little is known about brain regions other than the dorsal raphe nucleus that relate the melanin-concentrating hormone-ergic system to depressive states. Numerous studies have shown that the locus coeruleus is involved in the regulation of depression and sleep. Although direct physiological evidence is lacking, previous studies suggest that melanin-concentrating hormone release in the locus coeruleus decreases neuronal discharge. However, remaining unclear is whether the melanin-concentrating hormone-ergic system in the locus coeruleus is related to depressive-like behavior.

METHOD

We treated rats with an intra-locus coeruleus injection of melanin-concentrating hormone, intracerebroventricular injection of melanin-concentrating hormone, or chronic subcutaneous injections of corticosterone to induce different depressive-like phenotypes. We then assessed the effects of the melanin-concentrating hormone receptor 1 antagonist SNAP-94847 on depressive-like behavior in the forced swim test and the sucrose preference test.

RESULTS

The intra-locus coeruleus and intracerebroventricular injections of melanin-concentrating hormone and chronic injections of corticosterone increased immobility time in the forced swim test and decreased sucrose preference in the sucrose preference test. All these depressive-like behaviors were reversed by an intra-locus coeruleus microinjection of SNAP-94847.

CONCLUSIONS

These results suggest that the melanin-concentrating hormone-ergic system in the locus coeruleus might play an important role in the regulation of depressive-like behavior.

Changes in Membrane Protein Clustering in Peripheral Lymphocytes in an Animal Model of Depression Parallel Those Observed in Naïve Depression Patients: Implications for the Development of Novel Biomarkers of Depression

Naïve depression patients show alterations in serotonin transporter (SERT) and serotonin 2A (5HT2A) receptor clustering in peripheral lymphocytes, and these alterations have been proposed as a biomarker of therapeutic efficacy in major depression. Repeated corticosterone (CORT) induces a consistent depression-like phenotype and has been widely used as an animal model to study neurobiological alterations underlying the depressive symptoms. In this experiment, we used the CORT paradigm to evaluate whether depression-like behavior is associated with similar changes in the pattern of SERT and 5HT2A membrane protein clustering as those observed in depression patients. We also analyzed the clustering of other proteins expressed in lipid rafts in lymphocytes. Rats received daily CORT or vehicle injections for 21 consecutive days. Afterward they underwent the forced swim test to evaluate depression-like behavior, and isolated lymphocytes were analyzed by immunocytochemistry coupled to image-analysis to study clustering parameters of the SERT, 5HT2A receptor, dopamine transporter (DAT), Beta2 adrenergic receptor (β2AR), NMDA 2B receptor (NR2B), Pannexin 1 (Pnx1), and prion cellular protein (PrPc). Our results showed that CORT increases the size of protein clusters for all proteins with the exception of β 2AR, which is decreased. CORT also increased the number of clusters for Pnx1 and PrPc only. Overall, these results indicate that alterations in SERT and 5HT2A protein clustering in naïve depression patients are paralleled by changes seen in an animal model of depression. The CORT paradigm may be a useful screen for examining additional proteins in lymphocytes as a preliminary step prior to their analysis as biomarkers of depression in human blood samples.

Longitudinal in vivo Diffusion Tensor Imaging Detects Differential Microstructural Alterations in the Hippocampus of Chronic Social Defeat Stress-Susceptible and Resilient Mice

Background: Microstructural alterations in the hippocampus may underlie stress-related disorders and stress susceptibility. However, whether these alterations are pre-existing stress vulnerability biomarkers or accumulative results of chronic stress remain unclear. Moreover, examining the whole hippocampus as one unit and ignoring the possibility of a lateralized effect of stress may mask some stress effects and contribute to the heterogeneity of previous findings. Methods: After C57BL/6 mice were exposed to a 10-day chronic social defeat stress (CSDS) paradigm, different stress phenotypes, i.e., susceptible (n = 10) and resilient (n = 7) mice, were discriminated by the behavior of the mice in a social interaction test. With in vivo diffusion tensor imaging (DTI) scans that were conducted both before and after the stress paradigm, we evaluated diffusion properties in the left and right, dorsal (dHi) and ventral hippocampus (vHi) of experimental mice. Results: A significantly lower fractional anisotropy (FA) was found in the right vHi of the susceptible mice prior to the CSDS paradigm than that found in the resilient mice, suggesting that pre-existing microstructural abnormalities may result in stress susceptibility. However, no significant group differences were found in the post-stress FA values of any of the hippocampal regions of interest (ROIs). In addition, mean diffusivity (MD) and radial diffusivity (RD) values were found to be significantly greater only in the right dHi of the resilient group compared to those of the susceptible mice. Furthermore, a significant longitudinal decrease was only observed in the right dHi RD value of the susceptible mice. Moreover, the social interaction (SI) ratio was positively related to post-stress left MD, right dHi MD, and right dHi RD values and the longitudinal right dHi MD percent change. Meanwhile, a negative relationship was detected between the SI ratio and bilateral mean of the post-stress left relative to right vHi FA value, highlighting the important role of right hippocampus in stress-resilience phenotype. Conclusion: Our findings demonstrated different longitudinal microstructural alterations in the bilateral dHi and vHi between stress-susceptible and resilient subgroups and indicated a right-sided lateralized stress effect, which may be useful in the diagnosis and prevention of stress-related disorders as well as their intervention.

The impact of body mass index in gene expression of reelin pathway mediators in individuals with schizophrenia and mood disorders: A post-mortem study

The objective of this study was to compare the expression of genes involved in the reelin pathway, in the post-mortem brain of individuals with schizophrenia (SZ) and mood disorders (MD) with a healthy control (HC) group; and to investigate the role f body mass index (BMI) as a potential mediator. The "Gene Expression in Postmortem dlPFC and Hippocampus from Schizophrenia and Mood Disorders" study holds microarray data on individuals with SZ, MD and HCs (from whom 849 specimens are from the dlPFC and 579 from the hippocampus). mRNA data was obtained using HumanHT-12 v4 BeadChip arrays (Illumina). Multivariate analysis of covariance were used to investigate the main effects of group and relevant covariates on RELNm, NOTCH1, GRIN1m, GRIN3A, CAMK2Gm, CAMK2A, CAMK2Bm, CAMK2N2, GRIN2Bm, GRIN2A, CREBBPm, APOE, LDLR and DAB1 gene expression. In the dlPFC, individuals with SZ had higher expression, relative to HCs, of APOE. Individuals with MD had higher expression, relative to HCs, of CAMK2A, CAMK2N2, and GRIN2Bm. Moreover, individuals with MD had higher expression, relative to SZ patients, of CAMK2N2. There were significant group by BMI effects for expression of RELN, CAMK2A, CAMK2N2, and GRIN2A. In the hippocampus, individuals with MD had lower expression, relative to HCs, of APOE. The results of this study suggest that the expression of genes related to the reelin pathway could be different between individuals with SZ and MD and healthy controls, with a greater vulnerability associated with greater BMI.

Mitochondria and Mood: Mitochondrial Dysfunction as a Key Player in the Manifestation of Depression

Human and animal studies suggest an intriguing link between mitochondrial diseases and depression. Although depression has historically been linked to alterations in monoaminergic pharmacology and adult hippocampal neurogenesis, new data increasingly implicate broader forms of dampened plasticity, including plasticity within the cell. Mitochondria are the cellular powerhouse of eukaryotic cells, and they also regulate brain function through oxidative stress and apoptosis. In this paper, we make the case that mitochondrial dysfunction could play an important role in the pathophysiology of depression. Alterations in mitochondrial functions such as oxidative phosphorylation (OXPHOS) and membrane polarity, which increase oxidative stress and apoptosis, may precede the development of depressive symptoms. However, the data in relation to antidepressant drug effects are contradictory: some studies reveal they have no effect on mitochondrial function or even potentiate dysfunction, whereas other studies show more beneficial effects. Overall, the data suggest an intriguing link between mitochondrial function and depression that warrants further investigation. Mitochondria could be targeted in the development of novel antidepressant drugs, and specific forms of mitochondrial dysfunction could be identified as biomarkers to personalize treatment and aid in early diagnosis by differentiating between disorders with overlapping symptoms.

Peripheral Etanercept Administration Normalizes Behavior, Hippocampal Neurogenesis, and Hippocampal Reelin and GABAA Receptor Expression in a Preclinical Model of Depression

Depression is a serious psychiatric disorder frequently comorbid with autoimmune disorders. Previous work in our lab has demonstrated that repeated corticosterone (CORT) injections in rats reliably increase depressive-like behavior, impair hippocampal-dependent memory, reduce the number and complexity of adult-generated neurons in the dentate gyrus, decrease hippocampal reelin expression, and alter markers of GABAergic function. We hypothesized that peripheral injections of the TNF-α inhibitor etanercept could exert antidepressant effects through a restoration of many of these neurobiological changes. To test this hypothesis, we examined the effect of repeated CORT injections and concurrent injections of etanercept on measures of object-location and object-in-place memory, forced-swim test behavior, hippocampal neurogenesis, and reelin and GABA β2/3 immunohistochemistry. CORT increased immobility behavior in the forced swim test and impaired both object-location and object-in-place memory, and these effects were reversed by etanercept. CORT also decreased both the number and complexity of adult-generated neurons, but etanercept restored these measures back to control levels. Finally, CORT decreased the number of reelin and GABA β2/3-ir cells within the subgranular zone of the dentate gyrus, and etanercept restored these to control levels. These novel results demonstrate that peripheral etanercept has antidepressant effects that are accompanied by a restoration of cognitive function, hippocampal neurogenesis, and GABAergic plasticity, and suggest that a normalization of reelin expression in the dentate gyrus could be a key component underlying these novel antidepressant effects.

DNA methylation and antipsychotic treatment mechanisms in schizophrenia: Progress and future directions

Antipsychotic response in schizophrenia is a complex, multifactorial trait influenced by pharmacogenetic factors. With genetic studies thus far providing little biological insight or clinical utility, the field of pharmacoepigenomics has emerged to tackle the so-called "missing heritability" of drug response in disease. Research on psychiatric disorders has only recently started to assess the link between epigenetic alterations and treatment outcomes. DNA methylation, the best characterised epigenetic mechanism to date, is discussed here in the context of schizophrenia and antipsychotic treatment outcomes. The majority of published studies have assessed the influence of antipsychotics on methylation levels in specific neurotransmitter-associated candidate genes or at the genome-wide level. While these studies illustrate the epigenetic modifications associated with antipsychotics, very few have assessed clinical outcomes and the potential of differential DNA methylation profiles as predictors of antipsychotic response. Results from other psychiatric disorder studies, such as depression and bipolar disorder, provide insight into what may be achieved by schizophrenia pharmacoepigenomics. Other aspects that should be addressed in future research include methodological challenges, such as tissue specificity, and the influence of genetic variation on differential methylation patterns.

Antidepressant and pro-neurogenic effects of agmatine in a mouse model of stress induced by chronic exposure to corticosterone

Agmatine is an endogenous neuromodulator that has been shown to have beneficial effects in the central nervous system, including antidepressant-like effects in animals. In this study, we investigated the ability of agmatine (0.1mg/kg, p.o.) and the conventional antidepressant fluoxetine (10mg/kg, p.o.) to reverse the behavioral effects and morphological alterations in the hippocampus of mice exposed to chronic corticosterone (20mg/kg, p.o.) treatment for a period of 21days as a model of stress and depressive-like behaviors. Chronic corticosterone treatment increased the immobility time in the tail suspension test (TST), but did not cause anhedonic-like and anxiety-related behaviors, as assessed with the splash test and the open field test (OFT), respectively. Of note, the depressive-like behaviors induced by corticosterone were accompanied by a decrease in hippocampal cell proliferation, although no changes in hippocampal neuronal differentiation were observed. Our findings provide evidence that, similarly to fluoxetine, agmatine was able to reverse the corticosterone-induced depressive-like behaviors in the TST as well as the deficits in hippocampal cell proliferation. Additionally, fluoxetine but not agmatine, increased hippocampal differentiation. Agmatine, similar to fluoxetine, was capable of increasing both dendritic arborization and length in the entire dentate hippocampus, an effect more evident in the ventral portion of the hippocampus, as assessed with the modified Sholl analysis. Altogether, our results suggest that the increase in hippocampal proliferation induced by agmatine may contribute, at least in part, to the antidepressant-like response of this compound in this mouse model of stress induced by chronic exposure to corticosterone.

Adult hippocampal neuroplasticity triggers susceptibility to recurrent depression

Depression is a highly prevalent and recurrent neuropsychiatric disorder associated with alterations in emotional and cognitive domains. Neuroplastic phenomena are increasingly considered central to the etiopathogenesis of and recovery from depression. Nevertheless, a high number of remitted patients experience recurrent episodes of depression, remaining unclear how previous episodes impact on behavior and neuroplasticity and/or whether modulation of neuroplasticity is important to prevent recurrent depression. Through re-exposure to an unpredictable chronic mild stress protocol in rats, we observed the re-appearance of emotional and cognitive deficits. Furthermore, treatment with the antidepressants fluoxetine and imipramine was effective to promote sustained reversion of a depressive-like phenotype; however, their differential impact on adult hippocampal neuroplasticity triggered a distinct response to stress re-exposure: while imipramine re-established hippocampal neurogenesis and neuronal dendritic arborization contributing to resilience to recurrent depressive-like behavior, stress re-exposure in fluoxetine-treated animals resulted in an overproduction of adult-born neurons along with neuronal atrophy of granule neurons, accounting for an increased susceptibility to recurrent behavioral changes typical of depression. Strikingly, cell proliferation arrest compromised the behavior resilience induced by imipramine and buffered the susceptibility to recurrent behavioral changes promoted by fluoxetine. This study shows that previous exposure to a depressive-like episode impacts on the behavioral and neuroanatomical changes triggered by subsequent re-exposure to similar experimental conditions and reveals that the proper control of adult hippocampal neuroplasticity triggered by antidepressants is essential to counteract recurrent depressive-like episodes.

Interaction Effect of Social Isolation and High Dose Corticosteroid on Neurogenesis and Emotional Behavior

Hypercortisolemia is one of the clinical features found in depressed patients. This clinical feature has been mimicked in animal studies via application of exogenous corticosterone (CORT). Previous studies suggested that CORT can induce behavioral disturbance in anxious-depressive like behavior, which is associated with suppressed neurogenesis. Hippocampal neurogenesis plays an important role in adult cognitive and behavioral regulation. Its suppression may thus lead to neuropsychiatric disorders. Similar to the effects of CORT on the animals’ depression-like behaviors and neurogenesis, social deprivation has been regarded as one factor that predicts poor prognosis in depression. Furthermore, social isolation is regarded as a stressor to social animals including experimental rodents. Hence, this study aims to examine if social isolation would induce further emotional or anxiety-like behavior disturbance and suppress neurogenesis in an experimental model that was repeatedly treated with CORT. Sprague-Dawley rats were used in this study to determine the effects of different housing conditions, either social isolated or group housing, in vehicle-treated control and CORT-treated animals. Forced swimming test (FST), open field test (OFT) and social interaction test (SIT) were used to assess depression-like, anxiety-like and social behaviors respectively. Immunohistochemistry was performed to quantify the number of proliferative cells and immature neurons in the hippocampus, while dendritic maturation of immature neurons was analyzed by Sholl analysis. Social isolation reduced latency to immobility in FST. Furthermore, social isolation could significantly reduce the ratio of doublecortin and bromodeoxyuridine (BrdU) positive cells of the neurogenesis assay under CORT-treated condition. The current findings suggested that the behavioral and neurological effect of social isolation is dependent on the condition of hypercortisolemia. Furthermore, social isolation may possibly augment the signs and symptoms of depressed patients with potential alteration in neurogenesis.

The exercise-glucocorticoid paradox: How exercise is beneficial to cognition, mood, and the brain while increasing glucocorticoid levels

Exercise is known to have beneficial effects on cognition, mood, and the brain. However, exercise also activates the hypothalamic-pituitary-adrenal axis and increases levels of the glucocorticoid cortisol (CORT). CORT, also known as the "stress hormone," is considered a mediator between chronic stress and depression and to link various cognitive deficits. Here, we review the evidence that shows that while both chronic stress and exercise elevate basal CORT levels leading to increased secretion of CORT, the former is detrimental to cognition/memory, mood/stress coping, and brain plasticity, while the latter is beneficial. We propose three preliminary answers to the exercise-CORT paradox. Importantly, the elevated CORT, through glucocorticoid receptors, functions to elevate dopamine in the medial prefrontal cortex under chronic exercise but not chronic stress, and the medial prefrontal dopamine is essential for active coping. Future inquiries may provide further insights to promote our understanding of this paradox.

Schisandra chinensis produces the antidepressant-like effects in repeated corticosterone-induced mice via the BDNF/TrkB/CREB signaling pathway

The present study aimed to examine the antidepressant-like effects and the possible mechanisms of Schisandra chinensis on depressive-like behavior induced by repeated corticosterone injections in mice. Here we evaluated the effect of an ethanol extract of the dried fruit of S. chinensis (EESC) on BDNF/TrkB/CREB signaling in the hippocampus and the prefrontal cortex. Three weeks of corticosterone injections in mice resulted in depressive-like behavior, as indicated by the significant decrease in sucrose consumption and increase the immobility time in the forced swim test, but without any influence on the locomotor activity. Further, there was a significant increase in serum corticosterone level and a significant downregulation of BDNF/TrkB/CREB signaling pathway in the hippocampus and prefrontal cortex in CORT-treated mice. Treatment of mice with EESC (600mg/kg) significantly ameliorated all the behavioral and biochemical changes induced by corticosterone. Moreover, pharmacological inhibition of BDNF signaling by K252a abolished entirely the antidepressant-like effect triggered by chronic EESC treatment. These results suggest that EESC produces an antidepressant-like effect in CORT-induced depression in mice, which is possibly mediated, at least in part, by rectifying the stress-based hypothalamic-pituitary-adrenal (HPA) axis dysfunction paradigm and upregulation of BDNF/TrkB/CREB signaling pathway.