Leptin receptor deficiency confers resistance to behavioral effects of fluoxetine and desipramine via separable substrates

Obese male zucker rats show basilar dendritic retraction in the medial prefrontal cortex

Obesity, a prevalent disorder, predisposes individuals to metabolic syndrome, type 2 diabetes mellitus, and high blood pressure. Obesity has been investigated in various organisms that display genetic, high-fat, and high-carbohydrate diet (HFCD)-induced obesity. Recent studies have found that both male and female Zucker rats, which are genetically obese, exhibit alterations in dendritic arborization of neurons in certain structures of the central nervous system. Therefore, the present study aimed to analyze dendritic arborization and dendritic spine density of pyramidal neurons in the medial prefrontal cortex (mPFC) of obese adult male Zucker rats using the Golgi-Cox method and Sholl analysis. Obese male Zucker rats exhibit increased body weight and high concentrations of glucose, triglycerides, and cholesterol. Analysis of mPFC pyramidal neurons in these rats revealed basilar dendritic retraction at a medium distance from the soma, in addition to a reduction in total basilar dendritic length, without any changes in dendritic spine density. These findings are consistent with previous reports, indicating that changes in dendritic retraction may occur as a result of the leptin receptor mutation itself, in addition to the reduction in dendritic arborization observed in other regions of the central nervous system in rats. Furthermore, we suggest the possibility that biological processes modulated by the mPFC, such as foraging and social behavior, are also affected.

Major depressive disorder: biomarkers and biosensors

Depressive disorders belong to highly heterogeneous psychiatric diseases. Loss of in interest in previously enjoyed activities and a depressed mood are the main characteristics of major depressive disorder (MDD). Moreover, due to significant heterogeneity in clinical presentation and lack of applicable biomarkers, diagnosis and treatment remains challenging. Identification of relevant biomarkers would allow for improved disease classification and more personalized treatment strategies. Herein, we review the current state of these biomarkers and then discuss diagnostic techniques of aimed to specifically target these analytes using state of the art biosensor technology.

Effects of the Combination of the C1473G Mutation in the Tph2 Gene and Lethal Yellow Mutations in the Raly-Agouti Locus on Behavior, Brain 5-HT and Melanocortin Systems in Mice

Tryptophan hydroxylase 2 (TPH2) is the key and rate-limited enzyme of serotonin (5-HT) synthesis in the brain. The C1473G mutation in the Tph2 gene results in a two-fold decrease in enzyme activity in the mouse brain. The lethal yellow (A^Y) mutation in the Raly-Agouti locus results in the overexpression of the Agouti gene in the brain and causes obesity and depressive-like behavior in mice. Herein, the possible influences of these mutations and their combination on body mass, behavior, brain 5-HT and melanocortin systems in mice of the B6-1473CC/aa. B6-1473CC/A^Ya, B6-1473GG/aa are investigated. B6-1473GG/A^Ya genotypes were studied. The 1473G and A^Y alleles increase the activity of TPH2 and the expression of the Agouti gene, respectively, but they do not alter 5-HT and 5-HIAA levels or the expression of the genes Tph2, Maoa, Slc6a4, Htr1a, Htr2a, Mc3r and Mc4r in the brain. The 1473G allele attenuates weight gain and depressive-like immobility in the forced swim test, while the A^Y allele increases body weight gain and depressive-like immobility. The combination of these alleles results in hind limb dystonia in the B6-1473GG/A^Ya mice. This is the first evidence for the interaction between the C1473G and A^Y mutations.

Interactive Effects of Serum Leptin Levels and Physical Comorbidity on the Pharmacotherapeutic Response of Depressive Disorders

OBJECTIVE

To investigate individual and interactive associations of baseline serum leptin levels and physical comorbidity with short- and long-term treatment outcomes in outpatients with depressive disorders who received stepwise antidepressant treatment in a naturalistic prospective study design.

METHODS

Baseline serum leptin levels were measured, and the number of concurrent physical disorders ascertained from 1,094 patients. These patients received initial antidepressant monotherapy; then, for patients with an insufficient response or who experienced uncomfortable side effects, treatment was administered using alternative strategies every 3 weeks in the acute treatment phase (at 3, 6, 9, and 12 weeks) and every 3 months in the continuation treatment phase (at 6, 9, and 12 months). Then, 12-week and 12-month remission, defined as a Hamilton Depression Rating Scale score of ≤7, was estimated.

RESULTS

In multivariable logistic regression analyses, individual effects were found only between higher baseline serum leptin levels and 12-week non-remission. Significant interactive effects between higher leptin levels and fewer physical disorders (< 2 physical disorders) on 12-week non-remission were observed. However, neither individual nor interactive effects between leptin levels and physical comorbidity were associated with 12-month remission.

CONCLUSION

The combination of serum leptin level and number of physical disorders may be a useful predictor of short-term treatment responses in patients with depressive disorders receiving pharmacotherapy.

Association Between Self-rating Depression Scores and Total Ghrelin and Adipokine Serum Levels in a Large Population-Based Sample

Background

Ghrelin and the adipokines leptin and adiponectin have been suggested to be involved in mood and anxiety regulation and to be altered in affective disorders. However, studies investigating the association between ghrelin, leptin and adiponectin and depressive symptomatology are scarce but might contribute to a better understanding of their involvement in mood regulation. We thus aimed investigating the association between depressive symptomatology and total ghrelin as well as leptin and adiponectin serum levels in a large population-based sample.

Methods

Total serum ghrelin, adiponectin and leptin levels were determined in 1666 subjects of a population-based cross-sectional study ("LIFE"). The Center for Epidemiological Studies Depression Scale (CES-D) and the Inventory of Depressive Symptoms - Self Rating (IDS-SR) were administered. Multiple linear regression analyses were conducted to examine the association between total serum ghrelin, leptin and adiponectin and the intensity of depressive symptoms.

Results

In the total sample (n = 1,092), neither ghrelin nor leptin or adiponectin serum levels showed a significant association with CES-D or IDS-SR sum scores (N = 1,092) or in depressed/non-depressed subjects. Leptin serum levels showed a significantly positive association with IDS-SR sum scores in elderly men (≥60 years; β = 0.122, 95% CI: 0.009; 0.236; p = 0.035).

Conclusion

Our study suggests that peripheral levels of ghrelin and adipokines in a cross-sectional study design might not be sufficient to measure their involvement in depression, suggesting that associations are more complex and multi-layered.

Depression with atypical neurovegetative symptoms shares genetic predisposition with immuno-metabolic traits and alcohol consumption

BACKGROUND

Depression is a highly prevalent and heterogeneous disorder. This study aims to determine whether depression with atypical features shows different heritability and different degree of overlap with polygenic risk for psychiatric and immuno-metabolic traits than other depression subgroups.

METHODS

Data included 30 069 European ancestry individuals from the UK Biobank who met criteria for lifetime major depression. Participants reporting both weight gain and hypersomnia were classified as ↑WS depression (N = 1854) and the others as non-↑WS depression (N = 28 215). Cases with non-↑WS depression were further classified as ↓WS depression (i.e. weight loss and insomnia; N = 10 142). Polygenic risk scores (PRS) for 22 traits were generated using genome-wide summary statistics (Bonferroni corrected p = 2.1 × 10-4). Single-nucleotide polymorphism (SNP)-based heritability of depression subgroups was estimated.

RESULTS

↑WS depression had a higher polygenic risk for BMI [OR = 1.20 (1.15-1.26), p = 2.37 × 10-14] and C-reactive protein [OR = 1.11 (1.06-1.17), p = 8.86 × 10-06] v. non-↑WS depression and ↓WS depression. Leptin PRS was close to the significance threshold (p = 2.99 × 10-04), but the effect disappeared when considering GWAS summary statistics of leptin adjusted for BMI. PRS for daily alcohol use was inversely associated with ↑WS depression [OR = 0.88 (0.83-0.93), p = 1.04 × 10-05] v. non-↑WS depression. SNP-based heritability was not significantly different between ↑WS depression and ↓WS depression (14.3% and 12.2%, respectively).

CONCLUSIONS

↑WS depression shows evidence of distinct genetic predisposition to immune-metabolic traits and alcohol consumption. These genetic signals suggest that biological targets including immune-cardio-metabolic pathways may be relevant to therapies in individuals with ↑WS depression.

The menace of obesity to depression and anxiety prevalence

The incidence of depression and anxiety is amplified by obesity. Mounting evidence reveals that the psychiatric consequences of obesity stem from poor diet, inactivity, and visceral adipose accumulation. Resulting metabolic and vascular dysfunction, including inflammation, insulin and leptin resistance, and hypertension, have emerged as key risks to depression and anxiety development. Recent research advancements are exposing the important contribution of these different corollaries of obesity and their impact on neuroimmune status and the neural circuits controlling mood and emotional states. Along these lines, this review connects the clinical manifestations of depression and anxiety in obesity to our current understanding of the origins and biology of immunometabolic threats to central nervous system function and behavior.

The Role of Fgf9 in the Antidepressant Effects of Exercise and Fluoxetine in Chronic Unpredictable Mild Stress Mice

OBJECTIVE

The neurotrophic hypothesis of depression posits that stress and depression decrease neurotrophic factor expression in brain, whereas antidepressants and exercise can contribute to the blockade of stress effects and produce antidepressant effects. Fibroblast growth factor 9 (FGF9), a member of the fibroblast growth factor (FGF) family, has been reported to be dysregulated in depression. The present study aimed to determine whether and how Fgf9 mediates the antidepressant effects of fluoxetine and exercise in chronic unpredictable mild stress (CUMS) mice.

METHODS

Male C57BL/6 mice were exposed to CUMS for 7 weeks. From the fourth week, CUMS-exposed mice were subjected to fluoxetine treatment or swimming exercise for 4 weeks. Forced swim test, tail suspension test, and hole-board test were used to assess behaviors of mice. Real-time polymerase chain reaction was used to examine hippocampal messenger RNA levels of Fgf9, Fgf2, FgfR1, FgfR2, and FgfR3. Western blotting was used to examine the protein levels of Fgf9, protein kinase B (Akt), and phosphorylation of Akt at Ser473 in mouse hippocampus.

RESULTS

Our results demonstrated that CUMS induced depression-like behaviors, which were reversed by fluoxetine treatment and swimming exercise. Moreover, we found that CUMS resulted in a dysregulation of Fgf9, Fgf2, and FgfR2 expression, whereas fluoxetine and swimming restored the FGF expression in CUMS-exposed mice. An analysis of the proteins suggests that the antidepressant effects of fluoxetine and exercise in CUMS-exposed mice were associated with ameliorated Fgf9/Akt signaling.

CONCLUSIONS

Our findings have demonstrated that swimming exercise mimics the antidepressant effects of fluoxetine by regulating Fgf9 in CUMS-exposed mice, which may offer new mechanism-based therapeutic targets for depression.

High-fat diet induces neuroinflammation and reduces the serotonergic response to escitalopram in the hippocampus of obese rats

Clinical studies indicate that obese individuals have an increased risk of developing co-morbid depressive illness and that these patients have reduced responses to antidepressant therapy, including selective serotonin reuptake inhibitors (SSRIs). Obesity, a condition of chronic mild inflammation including obesity-induced neuroinflammation, is proposed to contribute to decreases in synaptic concentrations of neurotransmitters like serotonin (5HT) by decreasing 5HT synthesis in the dorsal raphe nucleus (DRN) and/or affecting 5HT reuptake in DRN target regions like the hippocampus. In view of these observations, the goal of the current study was to examine inflammatory markers and serotonergic dynamics in co-morbid obesity and depression. Biochemical and behavioral assays revealed that high-fat diet produced an obesity and depressive-like phenotype in one cohort of rats and that these changes were marked by increases in key pro-inflammatory cytokines in the hippocampus. In real time using fast scan cyclic voltammetry (FSCV), we observed no changes in basal levels of hippocampal 5HT; however responses to escitalopram were significantly impaired in the hippocampus of obese rats compared to diet resistant rats and control rats. Further studies revealed that these neurochemical observations could be explained by increases in serotonin transporter (SERT) expression in the hippocampus driven by elevated neuroinflammation. Collectively, these results demonstrate that obesity-induced increases in neuroinflammation adversely affect SERT expression in the hippocampus of obese rats, thereby providing a potential synaptic mechanism for reduced SSRI responsiveness in obese subjects with co-morbid depressive illness.

Integrating the monoamine and cytokine hypotheses of depression: Is histamine the missing link?

Psychiatric diseases, like depression, largely affect the central nervous system (CNS). While the underlying neuropathology of depressive illness remains to be elucidated, several hypotheses have been proposed as molecular underpinnings for major depressive disorder, including the monoamine hypothesis and the cytokine hypothesis. The monoamine hypothesis has been largely supported by the pharmaceuticals that target monoamine neurotransmitters as a treatment for depression. However, these antidepressants have come under scrutiny due to their limited clinical efficacy, side effects, and delayed onset of action. The more recent, cytokine hypothesis of depression is supported by the ability of immune-active agents to induce "sickness behaviour" akin to that seen with depression. However, treatments that more selectively target inflammation have yielded inconsistent antidepressive results. As such, neither of these hypotheses can fully explain depressive illness pathology, implying that the underlying neuropathological mechanisms may encompass aspects of both theories. The goal of the current review is to integrate these two well-studied hypotheses and to propose a role for histamine as a potential unifying factor that links monoamines to cytokines. Additionally, we will focus on stress-induced depression, to provide an updated perspective of depressive illness research and thereby identify new potential targets for the treatment of major depressive disorder.

Meta-analysis of cognitive and behavioral tests in leptin- and leptin receptor-deficient mice

Leptin is a hormone produced by adipocytes that regulates food intake and metabolism. Leptin-related gene-deficient mice, such as db/db and ob/ob mice, are widely used to study diabetes and its related diseases. However, broad effects of leptin appear to cause variability in behavioral test results. We performed a meta-analysis of major behavioral tests in db/db and ob/ob mice. These mice exhibited significant impairments in the Morris water maze, forced swim, novel object recognition, Y-maze, tail suspension, and light-dark box tests, whereas the elevated plus maze and open field tests did not reveal significant changes. We also performed correlation and regression analyses between the animals' performances and the experimental protocols and conditions. The memory-related tests were characterized by the correlations of their results with animal age, while the performances in the elevated plus-maze and forced swim tests were affected by the width of the devices used. In conclusion, db/db and ob/ob mice mainly exhibit memory deficits and depression-like behavior, although experimenters should be aware of animal age and device size in conducting experiments.

The Way to a Human's Brain Goes Through Their Stomach: Dietary Factors in Major Depressive Disorder

Globally, more than 250 million people are affected by depression (major depressive disorder; MDD), a serious and debilitating mental disorder. Currently available treatment options can have substantial side effects and take weeks to be fully effective. Therefore, it is important to find safe alternatives, which act more rapidly and in a larger number of patients. While much research on MDD focuses on chronic stress as a main risk factor, we here make a point of exploring dietary factors as a somewhat overlooked, yet highly promising approach towards novel antidepressant pathways. Deficiencies in various groups of nutrients often occur in patients with mental disorders. These include vitamins, especially members of the B-complex (B6, B9, B12). Moreover, an imbalance of fatty acids, such as omega-3 and omega-6, or an insufficient supply with minerals, including magnesium and zinc, are related to MDD. While some of them are relevant for the synthesis of monoamines, others play a crucial role in inflammation, neuroprotection and the synthesis of growth factors. Evidence suggests that when deficiencies return to normal, changes in mood and behavior can be, at least in some cases, achieved. Furthermore, supplementation with dietary factors (so called "nutraceuticals") may improve MDD symptoms even in the absence of a deficiency. Non-vital dietary factors may affect MDD symptoms as well. For instance, the most commonly consumed psychostimulant caffeine may improve behavioral and molecular markers of MDD. The molecular structure of most dietary factors is well known. Hence, dietary factors may provide important molecular tools to study and potentially help treat MDD symptoms. Within this review, we will discuss the role of dietary factors in MDD risk and symptomology, and critically discuss how they might serve as auxiliary treatments or preventative options for MDD.

Systemic TNF-α blockade attenuates anxiety and depressive-like behaviors in db/db mice through downregulation of inflammatory signaling in peripheral immune cells

Research studies have indicated that the comorbidity burden of mood disorders and obesity is reasonably high. Insulin signaling has been shown to modulate multiple physiological functions in the brain, indicating its association with neuropsychiatric diseases, including mood disorders. Leptin is a hormone responsible for regulating body weight and insulin homeostasis. Previous studies on db/db mice (a mouse model that carries a spontaneous genetic mutation in leptin receptor Lepr^db) have shown that they exhibit inflammation as well as neurobehavioral traits associated with mood. Therefore, targeting inflammatory pathways such as TNF-α may be an effective strategy in the treatment of obesity-linked mood disorders. The objective of this study was to investigate the effect of long-term administration of etanercept (a TNF-α blocker) on anxiety and depressive-like behaviors in db/db mice. This was performed using light/dark box, forced swim, and open field tests with lean littermate wild type (WT) mice serving as a control group. Using flow cytometry in peripheral blood, we further examined the molecular effects of etanercept on NF-κB p65, TNF-α, IL-17A, and TLR-4 expressing CD4+, CD8+, and CD14+ cells in the peripheral blood. Our data show that peripheral administration of etanercept decreased these cells in db/db mice. Furthermore, our results indicated that peripheral administration of etanercept reduced anxiety and depressive-like behaviors. Therefore, targeting TNF-α signaling might be an effective strategy for modulating obesity-associated depression and anxiety.

Circulating leptin, cortisol and gender differences associated with anorexia or obesity in depression

Objectives: To assess the role of circulating cortisol and leptin in depression associated with anorexia or obesity.Methods: Two hundred and fifty depressed patients presenting to the outpatient clinic of a psychiatric hospital and 250 non-depressed healthy volunteers were included in the study. The subjects of both groups were sub-grouped based upon their gender and BMI. Serum cortisol and leptin were determined by using respective ELISA kits.Results: The number of depressed than non-depressed subjects was three-fold higher in obese BMI groups of both genders. There were more depressed than non-depressed subjects in the underweight male BMI groups and in the overweight female BMI groups. There was a BMI-related increase in serum leptin and a decrease in serum cortisol in both genders. Depression in underweight BMI groups of both genders was associated with a decrease in serum leptin and an increase in cortisol. Higher serum leptin in obese BMI group was associated with a decrease in serum cortisol.Conclusions: Obesity is a risk factor for depression. The shift from typical to atypical depression is due to an inhibitory effect of higher circulating leptin on HPA axis activity and subsequent decrease in the lipolytic effects of cortisol.

Effects of disrupted ghrelin receptor function on fear processing, anxiety and saccharin preference in mice

BACKGROUND

Obesity is a risk factor for stress-related mental disorders such as post-traumatic stress disorder. The underlying mechanism through which obesity affects mental health remains poorly understood but dysregulation of the ghrelin system may be involved. Stress increases plasma ghrelin levels, which stimulates food intake as a potential stress-coping mechanism. However, diet-induced obesity induces ghrelin resistance which in turn may have deleterious effects on stress-coping. In our study, we explored whether disruption of ghrelin receptor function though high-fat diet or genetic ablation affects fear processing, anxiety-like behavior and saccharin preference in mice.

METHODS

Adult male C57BL6/J mice were placed on a standard diet or high-fat diet for a total period of 8 weeks. We first established that high-fat diet exposure for 4 weeks elicits ghrelin resistance, evidenced by a blunted hyperphagic response following administration of a ghrelin receptor agonist. We then carried out an experiment in which we subjected mice to auditory fear conditioning after 4 weeks of diet exposure and evaluated effects on fear extinction, anxiety-like behavior and saccharin preference. To explore whether fear conditioning as such may influence the effect of diet exposure, we also subjected mice to auditory fear conditioning prior to diet onset and 4 weeks later we investigated auditory fear extinction, anxiety-like behavior and saccharin preference. In a final experiment, we further assessed lack of ghrelin receptor function by investigating auditory fear processing, anxiety-like behavior and saccharin preference in ghrelin receptor knockout mice and their wild-type littermates.

RESULTS

High-fat diet exposure had no significant effect on auditory fear conditioning and its subsequent extinction or on anxiety-like behavior but significantly lowered saccharin preference. Similarly, ghrelin receptor knockout mice did not differ significantly from their wild-type littermates for auditory fear processing or anxiety-like behavior but showed significantly lower saccharin preference compared to wild-type littermates.

CONCLUSION

Taken together, our data suggest that disruption of ghrelin receptor function per se does not affect fear or anxiety-like behavior but may decrease saccharin preference in mice.

The associations of self-rated health with cardiovascular risk proteins: a proteomics approach

Background

Though subjective, poor self-rated health (SRH) has consistently been shown to predict cardiovascular disease (CVD). The underlying mechanism is unclear. This study evaluates the associations of SRH with biomarkers for CVD, aiming to explore potential pathways between poor SRH and CVD.

Methods

Based on the Malmö Diet and Cancer Cardiovascular Cohort study, a targeted proteomics approach was used to assess the associations of SRH with 88 cardiovascular risk proteins, measured in plasma from 4521 participants without CVD. The false discovery rate (FDR) was controlled using the Benjamini and Hochberg method. Covariates taken into consideration were age, sex, traditional CVD risk factors (low-density lipoprotein cholesterol, systolic blood pressure, anti-hypertensive medication, diabetes, body mass index, smoking), comorbidity, life-style and psycho-social factors (education level, living alone, alcohol consumption, low physical activity, psychiatric medication, sleep duration, and unemployment).

Results

Age and sex-adjusted associations with SRH was found for 34 plasma proteins. Nine of them remained significant after adjustments for traditional CVD risk factors. After further adjustment for comorbidity, life-style and psycho-social factors, only leptin (β = − 0.035, corrected p = 0.016) and C–C motif chemokine 20 (CCL20; β = − 0.054, corrected p = 0.016) were significantly associated with SRH.

Conclusions

Poor SRH was associated with raised concentrations of many plasma proteins. However, the relationships were largely attenuated by adjustments for CVD risk factors, comorbidity and psycho-social factors. Leptin and CCL20 were associated with poor SRH in the present study and could potentially be involved in the SRH–CVD link.

Impairment of cognitive flexibility in type 2 diabetic db/db mice

Impaired executive function is a major peril for patients with type 2 diabetes, reducing quality of life and ability for diabetes management. Despite the significance of this impairment, few animal models of type 2 diabetes examine domains of executive function such as cognitive flexibility or working memory. Here, we evaluated these executive function domains in db/db mice, an established model of type 2 diabetes, at 10 and 24 weeks of age. The db/db mice showed impaired cognitive flexibility in the Morris water maze reversal phase. However, the db/db mice did not show apparent working memory disturbance in the spatial working memory version of the Morris water maze or in the radial water maze. We also examined axon initial segments (AIS) and nodes of Ranvier, key axonal domains for action potential initiation and propagation. AIS were significantly shortened in medial prefrontal cortex and hippocampus of 26-week-old db/db mice compared with controls, similar to our previous findings in 10-week-old mice. Nodes of Ranvier in corpus callosum, previously shown to be unchanged at 10 weeks, were elongated at 26 weeks, suggesting an important role for this domain in disease progression. Together, the findings help establish db/db mice as a model of impaired cognitive flexibility in type 2 diabetes and advance our understanding of its pathophysiology.

Metformin Promotes Anxiolytic and Antidepressant-Like Responses in Insulin-Resistant Mice by Decreasing Circulating Branched-Chain Amino Acids

Epidemiological studies indicate that insulin resistance (IR), a hallmark of type 2 diabetes, is associated with an increased risk of major depression. Here, we demonstrated that male mice fed a high-fat diet (HFD) exhibited peripheral metabolic impairments reminiscent of IR accompanied by elevated circulating levels of branched-chain amino acids (BCAAs), whereas both parameters were normalized by chronic treatment with metformin (Met). Given the role of BCAAs in the regulation of tryptophan influx into the brain, we then explored the activity of the serotonin (5-HT) system. Our results indicated that HFD-fed mice displayed impairment in the electrical activity of dorsal raphe 5-HT neurons, attenuated hippocampal extracellular 5-HT concentrations and anxiety, one of the most visible and early symptoms of depression. On the contrary, Met stimulated 5-HT neurons excitability and 5-HT neurotransmission while hindering HFD-induced anxiety. Met also promoted antidepressant-like activities as observed with fluoxetine. In light of these data, we designed a modified HFD in which BCAA dietary supply was reduced by half. Deficiency in BCAAs failed to reverse HFD-induced metabolic impairments while producing antidepressant-like activity and enhancing the behavioral response to fluoxetine. Our results suggest that Met may act by decreasing circulating BCAAs levels to favor serotonergic neurotransmission in the hippocampus and promote antidepressant-like effects in mice fed an HFD. These findings also lead us to envision that a diet poor in BCAAs, provided either alone or as add-on therapy to conventional antidepressant drugs, could help to relieve depressive symptoms in patients with metabolic comorbidities.SIGNIFICANCE STATEMENT Insulin resistance in humans is associated with increased risk of anxiodepressive disorders. Such a relationship has been also found in rodents fed a high-fat diet (HFD). To determine whether insulin-sensitizing strategies induce anxiolytic- and/or antidepressant-like activities and to investigate the underlying mechanisms, we tested the effects of metformin, an oral antidiabetic drug, in mice fed an HFD. Metformin reduced levels of circulating branched-chain amino acids, which regulate tryptophan uptake within the brain. Moreover, metformin increased hippocampal serotonergic neurotransmission while promoting anxiolytic- and antidepressant-like effects. Moreover, a diet poor in these amino acids produced similar beneficial behavioral property. Collectively, these results suggest that metformin could be used as add-on therapy to a conventional antidepressant for the comorbidity between metabolic and mental disorders.

Hippocampal brain-derived neurotrophic factor determines recruitment of anatomically connected networks after stress in diabetic mice

Diabetes increases adrenal steroids in humans and animal models, but potential interactions with psychological stress remain poorly understood. Diabetic rodents exhibit anxiety and reductions in hippocampal brain-derived neurotrophic factor (BDNF) expression, and these studies investigated whether loss of BDNF-driven hippocampal activity promotes anxiety and disinhibits the HPA axis. Mice with genetic obesity and diabetes (db/db) received intrahippocampal injections of lentivirus for BDNF overexpression (db/db-BDNFOE), and Wt mice received lentiviral constructs for BDNF knockdown (Wt-BDNFKD). Behavioral anxiety and glucocorticoid responses to acute restraint were compared with mice that received a fluorescent reporter (Wt-GFP, db/db-GFP). These experiments revealed that changes in hippocampal BDNF were necessary and sufficient for behavioral anxiety and HPA axis disinhibition. To examine patterns of stress-induced regional activity, we used algorithmic detection of cFos and automated segmentation of forebrain regions to generate maps of functional covariance, which were subsequently aligned with anatomical connectivity weights from the Brain Architecture Management database. db/db-GFP mice exhibited reduced activation of the hippocampal ventral subiculum (vSub) and anterior bed nucleus of stria terminalis (aBNST), and increases in the paraventricular hypothalamus (PVH), relative to Wt-GFP. BDNFKD recapitulated this pattern in Wt mice, and BDNFOE normalized activation of the vSub > aBNST > PVH pathway in db/db mice. Analysis of forebrain activation revealed largely overlapping patterns of network disruption in db/db-GFP and Wt-BDNFKD mice, implicating BDNF-driven hippocampal activity as a determinant of stress vulnerability in both the intact and diabetic brain.

Leptin in depression: a potential therapeutic target

Leptin, produced and secreted by white adipose tissue, plays a critical role in regulating body weight, food intake, and energy metabolism. Recently, several studies have identified an underlying role for leptin in regulation of mood and cognition via regulation of synaptic changes in the brain that have been associated with antidepressant-like actions. Brain neural plasticity occurs in response to a range of intrinsic and extrinsic stimuli, including those that may mediate the effects of antidepressants. Neural plasticity theories of depression are thought to explain multiple aspects of depression and the effects of antidepressants. It is also well documented that leptin has effects on neural plasticity. This review summarizes the recent literature on the role of leptin in neural plasticity in order to elaborate the possible mechanism of leptin’s antidepressant-like effects. Recent findings provide new insights into the underlying mechanisms of neural plasticity in depression. Leptin may influence these mechanisms and consequently constitute a possible target for novel therapeutic approaches to the treatment of depression.

Swimming exercise reverses CUMS-induced changes in depression-like behaviors and hippocampal plasticity-related proteins

BACKGROUND

Stress-induced failed resilience of brain plasticity can contribute to the onset and recurrence of depression. Chronic stress has been reported to open windows of epigenetic plasticity in hippocampus. However, how hippocampal plasticity underlies depression-like behaviors and how it adapts in response to stress has not been addressed. The present study aimed to investigate the signaling mechanisms of CUMS affecting hippocampal plasticity-related proteins expression and the regulation of swimming exercise in mice.

METHODS

Male C57BL/6 mice were subjected to chronic unpredictable mild stress (CUMS) for 7 weeks. From the 4th week, CUMS mice were trained in a moderate swimming program for a total of 4 weeks. A videocomputerized tracking system was used to record behaviors of animals for a 5-min session. Real-time PCR and Western Blotting were used to examine gene expression in mouse hippocampus.

RESULTS

Our results demonstrated that CUMS induced depression-like behaviors, which were reversed by swimming exercise. Moreover, the behavioral changes induced by CUMS and exercise were correlated with hippocampal plasticity-related proteins expression of growth-associated protein-43 (GAP-43) and synaptophysin (SYN). The molecular mechanisms regulating this plasticity may include SIRT1/mircoRNA, CREB/BDNF, and AKT/GSK-3β signaling pathways.

LIMITATIONS

We did not establish a correlation between depression-like behaviors induced by chronic stress and epigenetic changes of hippocampal plasticity, either a causal molecular signaling underling this plasticity.

CONCLUSIONS

Our findings have identified swimming exercise effects on CUMS-induced changes in depression-like behaviors and hippocampal plasticity-related proteins, which provide a framework for developing new strategies to treat stress-induced depression.

OGT-related mitochondrial motility is associated with sex differences and exercise effects in depression induced by prenatal exposure to glucocorticoids

BACKGROUND

Prenatal exposure to glucocorticoids (GCs) has been found to trigger abnormal behaviors and deleterious neurological effects on offspring both in animals and in humans. The sex differences in depression have been replicated in numerous studies across cultures, persisting throughout the reproductive years. As an X-linked gene in rodents and in humans, O-GlcNAc transferase (OGT) may provide a novel perspective for the sex differences in depression.

METHODS

In the last third of pregnancy (gestational day 14-21), rats were subcutaneously administered either 0.13mg/kg dexamethasone-21-phosphate disodium salt (0.1mg/kg DEX) or vehicle (0.9% saline) once a day for 7 days. Adolescent (4 weeks) offspring were then trained in a swimming program or not.

RESULTS

Here we found that adult offspring rats exposed to DEX prenatally exhibited sex-specific depression-like behaviors, males being more vulnerable than females. Swimming exercise ameliorated the above-mentioned depressive syndromes, which may be a compensatory effect for male disadvantage suffering from prenatal stress. Furthermore, the effects of prenatal DEX exposure and swimming exercise on depression were associated with OGT-related mitochondrial motility, including PINK1/Parkin pathway and AKT/GSK3β pathway.

LIMITATIONS

Representative kymographs of mitochondrial motility were not detected and no causal effects were obtained by OGT gene overexpression or gene knockout in this study.

CONCLUSIONS

Our results provide a new perspective for better understanding sex differences and exercise effects in depression and may offer new mechanism-based therapeutic targets for depression.

Antidepressant-Like Effects of Acupuncture-Insights From DNA Methylation and Histone Modifications of Brain-Derived Neurotrophic Factor

Sensitive and stable biomarkers that facilitate depression detection and monitor the antidepressant efficiency are currently unavailable. Thus, the objective is to investigate the potential of DNA methylation and histone modifications of brain-derived neurotrophic factor (BDNF) in monitoring severity and antidepressive effects of acupuncture. The depression rat model was imitated by social isolation and chronic unpredicted mild stress (CUMS). The expression of serum BDNF was detected by enzyme-linked immunosorbent assay (ELISA), the hippocampal BDNF, acetylation levels in histone H3 lysine 9 (acH3K9), and HDAC2 by Western blot, the hippocampal mRNA of BDNF by RT-polymerase chain reaction (PCR). The DNA methylation patterns of the promoter I of BDNF was detected by MS-PCR. We investigated that the expression of BDNF in serum and hippocampus were significantly downregulated compared with controls. The same trend was found in mRNA of BDNF. Notably, acupuncture reversed the downregulation of BDNF in serum and hippocampus and mRNA of BDNF compared with model group. Acupuncture reversed the CUMS-induced downregulation of hippocampal acH3K9. On the contrary, the CUMS-induced upregulation of hippocampal HDAC2 in model group was significantly reversed by acupuncture. Collectively, the antidepressant effect of acupuncture might be mediated by regulating the DNA methylation and histone modifications of BDNF, which may represent novel biomaker for detection of depression and monitoring severity and antidepressive effects.

Metabolic and Microbiota Measures as Peripheral Biomarkers in Major Depressive Disorder

Advances in understanding the role of the microbiome in physical and mental health are at the forefront of medical research and hold potential to have a direct impact on precision medicine approaches. In the past 7 years, we have studied the role of microbiota-brain communication on behavior in mouse models using germ-free mice, mice exposed to antibiotics, and healthy specific pathogen free mice. Through our work and that of others, we have seen an amazing increase in our knowledge of how bacteria signal to the brain and the implications this has for psychiatry. Gut microbiota composition and function are influenced both by genetics, age, sex, diet, life experiences, and many other factors of psychiatric and bodily disorders and thus may act as potential biomarkers of the gut-brain axis that could be used in psychiatry and co-morbid conditions. There is a particular need in major depressive disorder and other mental illness to identify biomarkers that can stratify patients into more homogeneous groups to provide better treatment and for development of new therapeutic approaches. Peripheral outcome measures of host-microbe bidirectional communication have significant translational value as biomarkers. Enabling stratification of clinical populations, based on individual biological differences, to predict treatment response to pharmacological and non-pharmacological interventions. Here we consider the links between co-morbid metabolic syndrome and depression, focusing on biomarkers including leptin and ghrelin in combination with assessing gut microbiota composition, as a potential tool to help identify individual differences in depressed population.

Leptin Increases Expression of 5-HT2B Receptors in Astrocytes Thus Enhancing Action of Fluoxetine on the Depressive Behavior Induced by Sleep Deprivation

The long-lasting loss of sleep is a generally acknowledged risk factor for the occurrence of major depressive disorder (MDD), whereas sleep abnormalities being a key clinic symptom of the MDD. In our previous work, we demonstrated that the sleep deprivation (SD) stimulates activation of nucleotide-binding domain and leucine-rich repeat protein-3 (NLRP3) inflammasomes as well as the release of IL-1β and IL-18 from astrocytes. However, the underlying mechanism connecting SD and MDD still requires further study. Apart of the secretion of the pro-inflammatory cytokines, SD affects production of brain-derived neurotrophic factor (BDNF) while release of BDNF from astrocytes appears a key contributor to mood disorders. If and how the activation of NLRP3 inflammasome following SD affects the level of BDNF remains unknown. Antidepressant fluoxetine acts through astroglial 5-hydroxytryptamine receptor 2B (5-HT_2B); these receptors are also related to the sleep-wake cycle. Contribution of leptin to MDD has been discovered recently, although the mechanistic links between leptin and the depressive-like behaviors has not been revealed. In this study, we discovered: (i) that activation of NLRP3 inflammasome was involved in the depressive-like behaviors induced by SD; (ii) decrease in BDNF following SD required the activation of NLRP3 inflammasomes; (iii) leptin augmented the anti-depressive action of fluoxetine through an increase in expression of astrocytic 5-HT_2B receptors. We suggest that decrease in BDNF by the activated NLRP3 inflammasomes in astrocytes is the key pathological event of the depressive-like behaviors induced by SD, while the combined treatment with fluoxetine and leptin improves therapeutic outcome for the depression induced by SD.

Genetic Association of Major Depression With Atypical Features and Obesity-Related Immunometabolic Dysregulations

IMPORTANCE

The association between major depressive disorder (MDD) and obesity may stem from shared immunometabolic mechanisms particularly evident in MDD with atypical features, characterized by increased appetite and/or weight (A/W) during an active episode.

OBJECTIVE

To determine whether subgroups of patients with MDD stratified according to the A/W criterion had a different degree of genetic overlap with obesity-related traits (body mass index [BMI] and levels of C-reactive protein [CRP] and leptin).

DESIGN, SETTING, AND PATIENTS

This multicenter study assembled genome-wide genotypic and phenotypic measures from 14 data sets of the Psychiatric Genomics Consortium. Data sets were drawn from case-control, cohort, and population-based studies, including 26 628 participants with established psychiatric diagnoses and genome-wide genotype data. Data on BMI were available for 15 237 participants. Data were retrieved and analyzed from September 28, 2015, through May 20, 2017.

MAIN OUTCOMES AND MEASURES

Lifetime DSM-IV MDD was diagnosed using structured diagnostic instruments. Patients with MDD were stratified into subgroups according to change in the DSM-IV A/W symptoms as decreased or increased.

RESULTS

Data included 11 837 participants with MDD and 14 791 control individuals, for a total of 26 628 participants (59.1% female and 40.9% male). Among participants with MDD, 5347 (45.2%) were classified in the decreased A/W and 1871 (15.8%) in the increased A/W subgroups. Common genetic variants explained approximately 10% of the heritability in the 2 subgroups. The increased A/W subgroup showed a strong and positive genetic correlation (SE) with BMI (0.53 [0.15]; P = 6.3 × 10-4), whereas the decreased A/W subgroup showed an inverse correlation (-0.28 [0.14]; P = .06). Furthermore, the decreased A/W subgroup had a higher polygenic risk for increased BMI (odds ratio [OR], 1.18; 95% CI, 1.12-1.25; P = 1.6 × 10-10) and levels of CRP (OR, 1.08; 95% CI, 1.02-1.13; P = 7.3 × 10-3) and leptin (OR, 1.09; 95% CI, 1.06-1.12; P = 1.7 × 10-3).

CONCLUSIONS AND RELEVANCE

The phenotypic associations between atypical depressive symptoms and obesity-related traits may arise from shared pathophysiologic mechanisms in patients with MDD. Development of treatments effectively targeting immunometabolic dysregulations may benefit patients with depression and obesity, both syndromes with important disability.

Desipramine rescues age-related phenotypes in depression-like rats induced by chronic mild stress

AIMS

Our previous finding demonstrates that major depressive disorder can mediate accelerated aging in rats. Desipramine is a typical tricyclic antidepressant, and can provide neuroprotection and counteract depression-like behaviors. However, whether desipramine can rescue age-related phenotypes in depressed individuals is not understood. In the present study, we investigated the physiological function of desipramine on rescuing the age-related phenotypes in these animals.

MAIN METHODS

The rats were induced by chronic mild stress paradigm, and the depression-like behaviors of rats were detected by sucrose intake test, open field test (OFT) and forced swimming test (FST). Then the depressed rats were treated by desipramine.

KEY FINDINGS

Desipramine administration was effective in counteracting depression-like behaviors by increasing the sucrose solution intake, reducing the immobility time in the FST, and increasing total distance travelled and numbers of grid line crossed in the OFT. Moreover, desipramine treatment was able to reduce the oxidative damage to rat liver, and to increase the expression of telomerase reverse transcriptase (TERT), leading to correspondingly restored telomerase activity.

SIGNIFICANCE

Our findings identify that one function of desipramine may partly be to rescue age-related phenotypes in depressed individuals induced by chronic stress.

Venlafaxine exerts antidepressant effects possibly by activating MAPK-ERK1/2 and P13K-AKT pathways in the hippocampus

Serotonin noradrenaline reuptake inhibitors are effective antidepressant drugs, which include venlafaxine and duloxetine. Venlafaxine is commonly used in a clinical context, but the molecular biological mechanisms behind its effects have not been fully determined. Here, we explored the potential biological effects of venlafaxine on mouse hippocampus. Mice were randomly divided into two groups and injected daily with 0.9% NaCl solution or venlafaxine. A GC-MS-based metabolomic approach was used to identify possible metabolic differences between these groups, and the key proteins involved in the relevant pathways were validated by western blotting. In our experiments, 27 hippocampal metabolites that distinguished the venlafaxine group from the control group were identified. These differential metabolites were subjected to Ingenuity Pathway Analysis, which revealed that they were strongly related to two metabolic pathways (MAPK-ERK1/2 and P13K-AKT signaling pathways). Six key proteins, BDNF, p-c-Raf, p-MAPK, p-MEK, p-AKT, and CREB, were verified by western blotting and the results were consistent with the differential metabolites identified by GC-MS. This study sheds light on the biological mechanisms underlying the effects of venlafaxine.

Role of the adipose PPARγ-adiponectin axis in susceptibility to stress and depression/anxiety-related behaviors

Adaptive responses to stressful stimuli involving behavioral, emotional and metabolic changes are orchestrated by the nervous and endocrine systems. Adipose tissue has been recognized as a highly active metabolic and endocrine organ, secreting adipokines that operate as hormones to mediate the crosstalk with other organs including the brain. The role of adipose tissue in sensing and responding to emotional stress and in behavioral regulation, however, remains largely unknown. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is a key transcriptional factor controlling adipokine gene expression. Here we show that chronic social defeat stress decreases messenger RNA and protein levels of PPARγ in adipose tissue of susceptible but not resilient mice, which was correlated with social avoidance behavior. A corresponding reduction in adipose adiponectin production was observed in susceptible mice. Rosiglitazone, a blood-brain barrier-impermeant PPARγ-selective agonist, elicited antidepressant- and anxiolytic-like behavioral effects in wild-type mice, with a concurrent increase in plasma adiponectin levels. These effects of rosiglitazone were absent in mice lacking adiponectin but having normal PPARγ expression in adipose tissue and brain. Moreover, pretreatment with the PPARγ-selective antagonist GW9662 blocked rosiglitazone-induced adiponectin expression and antidepressant/anxiolytic-like effects. Together, these results suggest that the behavioral responses to rosiglitazone are mediated through PPARγ-dependent induction of adiponectin. Our findings support an important role for the adipose PPARγ-adiponectin axis in susceptibility to stress and negative emotion-related behaviors. Selectively targeting PPARγ in adipose tissue may offer novel strategies for combating depression and anxiety.

Leptin Dysregulation Is Specifically Associated With Major Depression With Atypical Features: Evidence for a Mechanism Connecting Obesity and Depression

BACKGROUND

Obesity-related dysregulation of leptin signaling (e.g., hyperleptinemia due to central functional resistance) may affect mood. However, evidence for leptin dysregulation in major depressive disorder (MDD) is conflicting. Inconclusive findings may be attributable to heterogeneity of MDD, aggregating biologically different subtypes. We examined the relationship of leptin with MDD, its common subtypes (typical and atypical), and clinical features.

METHODS

The sample consisted of participants (aged 18 to 65 years) from the Netherlands Study of Depression and Anxiety with current (n = 1062) or remitted (n = 711) MDD and healthy control subjects (n = 497). Diagnoses of MDD and subtypes were based on DSM-IV symptoms. Additional symptoms were measured with the Inventory of Depressive Symptomatology. Blood levels of leptin and adiposity indexes (body mass index and waist circumference) were assessed.

RESULTS

As compared to control subjects, higher leptin was associated with the atypical MDD subtype both for remitted (n = 144, odds ratio = 1.53, 95% confidence interval = 1.16-2.03, p = .003) and current (n = 270, odds ratio = 1.90, 95% confidence interval = 1.51-2.93, p = 5.3e-8) cases. This association was stronger for increasing adiposity levels (leptin by body mass index interaction, p < .02), strengthening the hypothesis of the involvement of leptin resistance. No association with leptin was found for overall MDD or the typical subtype. Among currently depressed patients, higher leptin was associated with key symptoms identifying the atypical subtype, such as hyperphagia, increased weight, and leaden paralysis.

CONCLUSIONS

Leptin dysregulation (resistance) may represent an underlying mechanism connecting obesity and MDD with atypical features. Development of treatment effectively targeting leptin resistance may benefit patients with atypical depression characterized by obesity-related metabolic alterations.

Antidepressant-like effect of valproic acid-Possible involvement of PI3K/Akt/mTOR pathway

RATIONALE

Few studies suggest that antidepressants exert their effects by activating some signaling pathways, including the phosphatidylinositol 3-kinase (PI3K). Moreover, valproic acid (VPA) activates the PI3K pathway. Thus, here we investigated the antidepressant-like effect of VPA and if its effect is related to PI3K/Akt/mTOR activation.

METHODS

C57Bl/6 (WT) and PI3Kγ^-/- mice received VPA injections (30, 100 or 300mg/kg, i.p.) and 30min after they were submitted to the forced swimming (FS), tail suspension (TS) and open field (OF) tests. Another group was pretreated with rapamycin (5mg/kg, i.p.) 150min before VPA administration. Akt phosphorylation levels were measured by Western blotting.

RESULTS

In WT mice, VPA (30mg/kg) reduced the immobility time in both FS and TS tests. However, VPA (300mg/kg) increased the immobility time in FS test. All doses of VPA did not alter locomotor activity. In PI3Kγ^-/- mice, none of the doses revealed antidepressant-like effect. However, in the OF test, the lower dose of VPA increased the travelled distance in comparison with vehicle group. An increase in Akt phosphorylation levels was observed in WT, but not in PI3Kγ^-/- mice. Finally, the pretreatment of WT mice with rapamycin abolished the antidepressant-like effect of VPA (30mg/kg) in FS test.

CONCLUSION

These data suggest that the antidepressant-like effects of VPA might depend on PI3K and mTOR activation. Thus, more studies are necessary to investigate the mechanisms involved in the antidepressant-like effect induced by VPA in order to investigate novel therapeutic targets for the treatment of depression.

Leptin receptor knockout-induced depression-like behaviors and attenuated antidepressant effects of exercise are associated with STAT3/SOCS3 signaling

Relatively little has been known about pathophysiological mechanisms contributing to the development of neuropsychiatric symptoms in the context of metabolic syndrome. Impaired leptin signaling activation in db/db mice has been proposed as a potential link between behavioral and metabolic disorders. Our previous studies have shown that exercise has the beneficial effects on a depression-like and insulin-resistant state in mice. The present study aimed to determine whether and how leptin receptor knockout (db/db) induces depression-like behaviors, and to identify the antidepressant effects of swimming exercise in db/db mice. Our results support the validity of db/db mice as an animal model to study depression with metabolic abnormalities, but fail to confirm the improvement of exercise on depression. LepRb knockout-induced depression-like behaviors are associated with STAT3/SOCS3 signaling but independent of IKKβ/NFκB signaling. Our findings suggest the potential importance of LepRb as an exercise-regulated target for depression, also representing a new target underlying treatment-resistant depression.

Obesity and neuroinflammatory phenotype in mice lacking endothelial megalin

BACKGROUND

The multiligand receptor megalin controls the brain uptake of a number of ligands, including insulin and leptin. Despite the role of megalin in the transport of these metabolically relevant hormones, the role of megalin at the blood-brain-barrier (BBB) has not yet been explored in the context of metabolic regulation.

METHODS

Here we investigate the role of brain endothelial megalin in energy metabolism and leptin signaling using an endothelial cell-specific megalin deficient (EMD) mouse model.

RESULTS

We found megalin is important to protect mice from developing obesity and metabolic syndrome when mice are fed a normal chow diet. EMD mice developed neuroinflammation, by triggering several pro-inflammatory cytokines, displayed reduced neurogenesis and mitochondrial deregulation.

CONCLUSIONS

These results implicate brain endothelial megalin expression in obesity-related metabolic changes through the leptin signaling pathway proposing a potential link between obesity and neurodegeneration.

Antidepressant-like activity of sildenafil following acute and subchronic treatment in the forced swim test in mice: effects of restraint stress and monoamine depletion

Sildenafil is a highly effective oral agent for the treatment of erectile dysfunction of multiple etiologies. Although in clinical practice sildenafil is often used in depressed patients, its influence on the pathophysiology of depression remains unclear. The aim of the present study was to evaluate the antidepressant-like activity following acute and subchronic treatment with sildenafil in naïve mice as well as in mice with reserpine- and restraint stress-induced depressive-like behavior. Since corticosterone is released in response to acute stress, we also aimed to assess the influence of sildenafil on serum corticosterone level in non-stressed and stressed animals. The antidepressant activity of sildenafil was assessed in the forced swim test. Corticosterone serum level was determined by using ELISA method, while brain and serum sildenafil level via HPLC method. Sildenafil administered acutely exerted an antidepressant-like effect. Subchronic (14 days) administration of sildenafil resulted only in a weak antidepressant-like effect when evaluated 24 h after the last dose. Acute but not subchronic sildenafil administration reversed the reserpine- and stress-induced immobility in the forced swim test. The lack of effects of sildenafil after subchronic treatment could have been related to its complete elimination from the brain within 24 h from the last injection. Interestingly, acute administration of sildenafil produced a marked increase in serum corticosterone level in both non-stressed and stressed animals. Sildenafil exerts differential effects in the forced swim test after acute and subchronic administration. Further studies on the antidepressant activity of sildenafil are required.

Anxiolytic-like effects of leptin on fixed interval responding

Leptin has been shown to affect energy homeostasis, learning and memory, and some models of anxiolytic action. However, leptin has produced inconsistent results in previous non-operant behavioural tests of anxiety. Here, we test the anxiolytic potential of leptin in an operant paradigm that has produced positive results across all classes of anxiolytic so far tested. Rats were tested in the Fixed Interval 60 Seconds (FI60) task following administration of 0/0.5/1.0mg/kg (i.p.) leptin or an active anxiolytic control of 5mg/kg (i.p.) chlordiazepoxide (CDP). By the end of the 14days of testing in the FI60 task, 0.5mg/kg leptin released suppressed responding in a manner similar to CDP, and 1.0mg/kg leptin produced a relative depression in responding, a similar outcome pattern to previously tested 5HT-agonist anxiolytics. This suggests that leptin behaves similarly to established serotonergic anxiolytics such as buspirone and fluoxetine; with the delay in development of effect during testing, and the inverted-U dose-response curve explaining the inconsistent behaviour of leptin in behavioural tests of anxiety, as this type of pattern is common to serotonergic anxiolytics.

Incoordination among Subcellular Compartments Is Associated with Depression-Like Behavior Induced by Chronic Mild Stress

BACKGROUND

Major depressive disorder is characterized as persistent low mood. A chronically stressful life in genetically susceptible individuals is presumably the major etiology that leads to dysfunctions of monoamine and hypothalamus-pituitary-adrenal axis. These pathogenic factors cause neuron atrophy in the limbic system for major depressive disorder. Cell-specific pathophysiology is unclear, so we investigated prelimbic cortical GABAergic neurons and their interaction with glutamatergic neurons in depression-like mice.

METHODS

Mice were treated with chronic unpredictable mild stress for 3 weeks until they expressed depression-like behaviors confirmed by sucrose preference, Y-maze, and forced swimming tests. The structures and functions of GABAergic and glutamatergic units in prelimbic cortices were studied by cell imaging and electrophysiology in chronic unpredictable mild stress-induced depression mice vs controls.

RESULTS

In depression-like mice, prelimbic cortical GABAergic neurons show incoordination among the subcellular compartments, such as decreased excitability and synaptic outputs as well as increased reception from excitatory inputs. GABAergic synapses on glutamatergic cells demonstrate decreased presynaptic innervation and increased postsynaptic responsiveness.

CONCLUSIONS

Chronic unpredictable mild stress-induced incoordination in prelimbic cortical GABAergic and glutamatergic neurons dysregulates their target neurons, which may be the pathological basis for depressive mood. The rebalance of compatibility among subcellular compartments would be an ideal strategy to treat neural disorders.

High-fat diet-induced metabolic disorders impairs 5-HT function and anxiety-like behavior in mice

BACKGROUND AND PURPOSE

The link between type 2 diabetes mellitus (T2DM) and depression is bidirectional. However, the possibility that metabolic disorders may elicit anxiogenic-like/depressive-like symptoms or alter the efficacy of antidepressant drugs remains poorly documented. This study explored the influence of T2DM on emotionality and proposed a therapeutic strategy that might be used in depressed diabetic patients.

EXPERIMENTAL APPROACH

Mice were fed a high-fat diet (HFD) and subjected to a full comprehensive metabolic and behavioural analysis to establish correlations between metabolic and psychiatric disorders. In vivo intra-hippocampal microdialysis was also applied to propose a mechanism underpinning the phenotype of mice fed the HFD. Finally, we tested whether chronic administration of the selective 5-HT reuptake inhibitor escitalopram or HFD withdrawal could reverse HFD-induced metabolic and behavioural anomalies.

KEY RESULTS

The increased body weight, hyperglycaemia and impaired glucose tolerance in response to HFD were correlated with anxiogenic-like/depressive-like symptoms. Moreover, this phenotype was associated with decreased extracellular 5-HT levels in the hippocampus which may result from increased sensitivity of the dorsal raphe 5-HT1A autoreceptor. Interestingly, the beneficial effect of prolonged administration of escitalopram was abolished in HFD-fed mice. On the contrary, HFD withdrawal completely reversed metabolic impairments and positively changed symptoms of anxiety, although some behavioural anomalies persisted.

CONCLUSIONS AND IMPLICATIONS

Our data provide clear-cut evidence that both pathologies are finely correlated and associated with impaired 5-HT mediated neurotransmission in the hippocampus. Further experiments are warranted to define the most adequate strategy for the treatment of such co-morbidity.

LINKED ARTICLES

This article is part of a themed section on Updating Neuropathology and Neuropharmacology of Monoaminergic Systems. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.13/issuetoc.

Leptin/LepRb in the Ventral Tegmental Area Mediates Anxiety-Related Behaviors

BACKGROUND

Leptin, an adipose-derived hormone, has been implicated in emotional regulation. We have previously shown that systemic administration of leptin produces anxiolytic-like effects and deletion of the leptin receptor, LepRb, in midbrain dopamine neurons leads to an anxiogenic phenotype. This study investigated whether activation or deletion of LepRb in the ventral tegmental area of adult mice is capable of inducing anxiolytic and anxiogenic effects, respectively.

METHODS

Mice were cannulated in the ventral tegmental area and received bilateral intra-ventral tegmental area infusions of leptin or the JAK2/STAT3 inhibitor AG490. Anxiety-like behaviors were assessed using the elevated plus-maze, light-dark box, and novelty suppressed feeding tests. Deletion of LepRb in the ventral tegmental area was achieved by bilateral injection of AAV-Cre into the ventral tegmental area of adult Lepr(flox/flox) mice. Anxiety-related behaviors were evaluated 3 weeks after viral injection.

RESULTS

Intra-ventral tegmental area infusions of leptin reduced anxiety-like behaviors, as indicated by increased percent open-arm time and open-arm entries in the elevated plus-maze test, increased time spent in the light side and decreased latency to enter the light side of the light-dark box, and decreased latency to feed in the novelty suppressed feeding test. Blockade of JAK2/STAT3 signaling in the ventral tegmental area by AG490 attenuated the anxiolytic effect produced by systemic administration of leptin. Lepr(flox/flox) mice injected with AAV-Cre into the ventral tegmental area showed decreased leptin-induced STAT3 phosphorylation and enhanced anxiety-like behaviors in the elevated plus-maze test and the novelty suppressed feeding test.

CONCLUSIONS

These findings suggest that leptin-LepRb signaling in the ventral tegmental area plays an important role in the regulation of anxiety-related behaviors.

Sex-Specific and Estrous Cycle-Dependent Antidepressant-Like Effects and Hippocampal Akt Signaling of Leptin

Sex differences in the incidence of depression and antidepressant treatment responses are well documented. Depression is twice as common in women as in men. Recent studies indicate that low levels of leptin, an adipocyte-derived hormone, are associated with increased symptoms of depression in women. Leptin has been shown to produce antidepressant-like effects in male rodents. In the present study, we examined sex differences and estrous cycle variations in antidepressant-like responses to leptin. Leptin administration significantly reduced immobility, a putative measure of behavioral despair, in the forced swim test in intact female mice in the proestrus phase but not in the diestrus phase of the estrous cycle. Moreover, leptin administration stimulated Akt phosphorylation in the hippocampus of female mice in proestrus but not in diestrus, in correlation with its differential behavioral effects in these two phases of the cycle. Leptin-induced behavioral responses and stimulation of hippocampal Akt phosphorylation in female mice were abolished by ovariectomy. By contrast, the antidepressant-like effect of leptin in male mice was not affected by gonadectomy (castration). Pretreatment with 17β-estradiol restored sensitivity to the effects of leptin on behavior and hippocampal Akt phosphorylation in ovariectomized female mice. These results suggest leptin regulates depression-like behavior and hippocampal Akt signaling in a sex-specific and estrous cycle-dependent manner.

Involvement of normalized NMDA receptor and mTOR-related signaling in rapid antidepressant effects of Yueju and ketamine on chronically stressed mice

Yueju, a Traditional Chinese Medicine formula, exhibited fast-onset antidepressant responses similar to ketamine. This study focused on assessing the rapid and persistent antidepressant efficacy of Yueju and ketamine in chronically stressed mice and its association with alternations in prefrontal N-methyl-D-aspartate (NMDA) receptor and mammalian target of rapamycin (mTOR)-related activity. Chronic mild stress (CMS) led to deficits in sucrose preference test (SPT), forced swim test, tail suspension test, and novelty-suppressed feeding test, which were improved differently by acute Yueju or ketamine administration. The improvement in SPT started as soon as 2 hours post Yueju and ketamine but lasted for 6 days only by Yueju. Body weight was regained by Yueju more than ketamine at post-drug administration day (PAD) 6. CMS decreased phosphorylation of the mTOR effectors 4E-BP1 and p70S6K, their upstream regulators ERK and Akt, and downstream targets including synaptic protein GluR1. Yueju or ketamine reversed these changes at PAD 2, but only Yueju reversed phosphor-Akt at PAD 6. CMS selectively and lastingly increased NMDA receptor subunit NR1 expression, which was reversed by ketamine or Yueju at PAD 2 but only by Yueju at PAD 6. These findings suggest that NR1 and Akt/mTOR signaling are important therapeutic targets for depression.

Ondansetron attenuates co-morbid depression and anxiety associated with obesity by inhibiting the biochemical alterations and improving serotonergic neurotransmission

In our earlier study we reported the antidepressant activity of ondansetron in obese mice. The present study investigates the effect of ondansetron on depression and anxiety associated with obesity in experimental mice with biochemical evidences. Male Swiss albino mice were fed with high fat diet (HFD) for 14weeks to induce obesity. Then the subsequent treatment with ondansetron (0.5 and 1mg/kg, p.o.), classical antidepressant escitalopram (ESC) (10mg/kg, p.o.) and vehicle (distilled water 10ml/kg, p.o.) was given once daily for 28days. Behavioral assay for depression including sucrose preference test, forced swim test (FST) and anxiety such as light dark test (LDT) and hole board test (HBT) were performed in obese mice. Furthermore, in biochemical estimations oral glucose tolerance test (OGTT), plasma leptin, insulin, corticosterone, brain oxidative stress marker malonaldehyde (MDA), antioxidant reduced glutathione (GSH) and serotonin assays were performed. Results indicated that HFD fed obese mice showed severe depressive and anxiety-like behaviors. Chronic treatment with ondansetron inhibited the co-morbid depression and anxiety in obese mice by increasing sucrose consumption in sucrose preference test and reducing the immobility time in FST, increasing time and transitions of light chamber in LDT, improving head dip and crossing scores in HBT compared to HFD control mice. Ondansetron in obese mice inhibited glucose sensitivity in OGTT, improved plasma leptin and insulin sensitivity, reversed hypothalamic pituitary adrenal (HPA) axis hyperactivity by reducing the corticosterone concentration, restored brain pro-oxidant/anti-oxidant balance by inhibiting MDA and elevating GSH concentrations and facilitated serotonergic neurotransmission. In conclusion, ondansetron reversed the co-morbid depression and anxiety associated with obesity in experimental mice by attenuating the behavioral and biochemical abnormalities.

Role of neuroinflammation in the emotional and cognitive alterations displayed by animal models of obesity

Obesity is associated with a high prevalence of mood disorders and cognitive dysfunctions in addition to being a significant risk factor for important health complications such as cardiovascular diseases and type 2 diabetes. Identifying the pathophysiological mechanisms underlying these health issues is a major public health challenge. Based on recent findings, from studies conducted on animal models of obesity, it has been proposed that inflammatory processes may participate in both the peripheral and brain disorders associated with the obesity condition including the development of emotional and cognitive alterations. This is supported by the fact that obesity is characterized by peripheral low-grade inflammation, originating from increased adipose tissue mass and/or dysbiosis (changes in gut microbiota environment), both of which contribute to increased susceptibility to immune-mediated diseases. In this review, we provide converging evidence showing that obesity is associated with exacerbated neuroinflammation leading to dysfunction in vulnerable brain regions associated with mood regulation, learning, and memory such as the hippocampus. These findings give new insights to the pathophysiological mechanisms contributing to the development of brain disorders in the context of obesity and provide valuable data for introducing new therapeutic strategies for the treatment of neuropsychiatric complications often reported in obese patients.

Search for common targets of lithium and valproic acid identifies novel epigenetic effects of lithium on the rat leptin receptor gene

Epigenetics may have an important role in mood stabilizer action. Valproic acid (VPA) is a histone deacetylase inhibitor, and lithium (Li) may have downstream epigenetic actions. To identify genes commonly affected by both mood stabilizers and to assess potential epigenetic mechanisms that may be involved in their mechanism of action, we administered Li (N = 12), VPA (N = 12), and normal chow (N = 12) to Brown Norway rats for 30 days. Genomic DNA and mRNA were extracted from the hippocampus. We used the mRNA to perform gene expression analysis on Affymetrix microarray chips, and for genes commonly regulated by both Li and VPA, we validated expression levels using quantitative real-time PCR. To identify potential mechanisms underlying expression changes, genomic DNA was bisulfite treated for pyrosequencing of key CpG island 'shores' and promoter regions, and chromatin was prepared from both hippocampal tissue and a hippocampal-derived cell line to assess modifications of histones. For most genes, we found little evidence of DNA methylation changes in response to the medications. However, we detected histone H3 methylation and acetylation in the leptin receptor gene, Lepr, following treatment with both drugs. VPA-mediated effects on histones are well established, whereas the Li effects constitute a novel mechanism of transcriptional derepression for this drug. These data support several shared transcriptional targets of Li and VPA, and provide evidence suggesting leptin signaling as an epigenetic target of two mood stabilizers. Additional work could help clarify whether leptin signaling in the brain has a role in the therapeutic action of Li and VPA in bipolar disorder.