Diet-induced obesity progressively alters cognition, anxiety-like behavior and lipopolysaccharide-induced depressive-like behavior: focus on brain indoleamine 2,3-dioxygenase activation

A YOLO based software for automated detection and analysis of rodent behaviour in the open field arena

Rodent models are important in mechanistic studies of the physiological and pathophysiological determinants of behaviour. The Open Field Test (OFT) is one of the most commonly utilised tests to assess rodent behaviour in a novel open environment. The key variables assessed in an OFT are general locomotor activity and exploratory behaviours and can be assessed manually or by automated systems. Although several automated systems exist, they are often expensive, difficult to use, or limited in the type of video that can be analysed. Here we describe a machine-learning algorithm - dubbed Cosevare - that uses a trained YOLOv3 DNN to identify and track movement of mice in the open-field arena. We validated Cosevare's capacity to accurately track locomotive and exploratory behaviour in 10 videos, comparing outputs generated by Cosevare with analysis by 5 manual scorers. Behavioural differences between control mice and those with diet-induced obesity (DIO) were also documented. We found the YOLOv3 based tracker to be accurate at identifying and tracking the mice within the open-field arena and in instances with variable backgrounds. Additionally, kinematic and spatial-based analysis demonstrated highly consistent scoring of locomotion, centre square duration (CSD) and entries (CSE) between Cosevare and manual scorers. Automated analysis was also able to distinguish behavioural differences between healthy control and DIO mice. The study found that a YOLOv3 based tracker is able to easily track mouse behaviour in the open field arena and supports machine learning as a potential future alternative for the assessment of animal behaviour in a wide range of species in differing environments and behavioural tests.

Legend of Weight Loss: a Crosstalk Between the Bariatric Surgery and the Brain

In recent years, plenty of researches have reported in obese individuals with abnormal brain processes implicated in homeostatic regulation, reward, emotion, memory, attention, and executive function in eating behaviors. Thus, treating obesity cannot remain "brainless." Behavioral and psychological interventions activate the food reward, attention, and motivation system, leading to minimal weight loss and high relapse rates. Pharmacotherapy is an effective weight loss method and regulate brain activity but with concerns about its brain function safety problems. Obesity surgery, the most effective therapy currently available for obesity, shows pronounced effects on brain activity, such as deactivation of reward and attention system, and activation of inhibition control toward food cues. In this review, we present an overview of alterations in the brain after the three common weight loss methods.

Brain-immune crosstalk in the treatment of major depressive disorder

A growing number of studies are pointing out the need for a conceptual shift from a brain-centered to a body-inclusive approach in mental health research. In this perspective, the link between the immune and the nervous system, which are deeply interconnected and continuously interacting, is one of the most important novel theoretical framework to investigate the biological bases of major depressive disorder and, more in general, mental illness. Indeed, depressed patients show high levels of inflammatory markers, administration of pro-inflammatory drugs triggers a depressive symptomatology and antidepressant efficacy is reduced by excessive immune system activation. A number of molecular and cellular mechanisms have been hypothesized to act as a link between the immune and brain function, thus representing potential pharmacologically targetable processes for the development of novel and effective therapeutic strategies. These include the modulation of the kynurenine pathway, the crosstalk between metabolic and inflammatory processes, the imbalance in acquired immune responses, in particular T cell responses, and the interplay between neural plasticity and immune system activation. In the personalized medicine approach, the assessment and regulation of these processes have the potential to lead, respectively, to novel diagnostic approaches for the prediction of treatment outcome according to the patient's immunological profile, and to improved efficacy of antidepressant compounds through immune modulation.

Saffron Extract-Induced Improvement of Depressive-Like Behavior in Mice Is Associated with Modulation of Monoaminergic Neurotransmission

Depressive disorders represent a major public health concern and display a continuously rising prevalence. Importantly, a large proportion of patients develops aversive side effects and/or does not respond properly to conventional antidepressants. These issues highlight the need to identify further therapeutic strategies, including nutritional approaches using natural plant extracts with known beneficial impacts on health. In that context, growing evidence suggests that saffron could be a particularly promising candidate. This preclinical study aimed therefore to test its antidepressant-like properties in mice and to decipher the underlying mechanisms by focusing on monoaminergic neurotransmission, due to its strong implication in mood disorders. For this purpose, the behavioral and neurobiochemical impact of a saffron extract, Safr’Inside™ (6.5 mg/kg per os) was measured in naïve mice. Saffron extract reduced depressive-like behavior in the forced swim test. This behavioral improvement was associated with neurobiological modifications, particularly changes in serotonergic and dopaminergic neurotransmission, suggesting that Safr’Inside™ may share common targets with conventional pharmacological antidepressants. This study provides useful information on the therapeutic relevance of nutritional interventions with saffron extracts to improve management of mood disorders.

Agomelatine effects on fat-enriched diet induced neuroinflammation and depression-like behavior in rats

Growing evidence suggests that a high fat diet (HFD) induces oxidative stress on the central nervous system (CNS), which predisposes to mood disorders and neuroinflammation. In this study we postulated that in addition to improving mood, antidepressant therapy would reverse inflammatory changes in the brain of rats exposed to a HFD. To test our hypothesis, we measured the effect of the antidepressant agomelatine (AGO) on anxiety- and depressive-like behaviors, as well as on CNS markers of inflammation in rats rendered obese. Agomelatine is an agonist of the melatonin receptors MT1 and MT2 and an antagonist of the serotonin receptors 5HT2B and 5HT2C. A subset of rats was also treated with lipopolysaccharides (LPS) to determine how additional neuroinflammation alters behavior and affects the response to the antidepressant. Specifically, rats were subjected to a 14-week HFD, during which time behavior was evaluated twice, first at the 10th week prior to LPS and/or agomelatine, and then at the 14th week after a bi-weekly exposure to LPS (250 μg/kg) and daily treatment with agomelatine (40 mg/kg). Immediately after the second behavioral testing we measured the proinflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6) and interleukin 1 beta (IL-1β), markers of oxidative stress thiobarbituric acid reactive substances (TABRS), catalase (CAT) and glutathione peroxidase (GPx), the growth factor BDNF, as well as the apoptosis marker caspase-3. Our results show that a HFD induced an anxiety-like behavior in the open field test (OFT) at the 10th week, followed by a depressive-like behavior in the forced swim test (FST) at the 14th week. In the prefrontal and hippocampal cortices of rats exposed to a HFD we noted an overproduction of TNF-α, IL-6, IL-1β, and TABRS, together with an increase in caspase-3 activity. We also observed a decrease in BDNF, as well as reduced CAT and GPx activity in the same brain areas. Treatment with agomelatine reversed the signs of anxiety and depression, and decreased the cytokines (TNF-α, IL-6 and IL-1β), TABRS, as well as caspase-3 activity. Agomelatine also restored BDNF levels and the activity of antioxidant enzymes CAT and GPx. Our findings suggest that the anxiolytic/antidepressant effect of agomelatine in obese rats could result from a reversal of the inflammatory and oxidative stress brought about by their diet.

Linking atypical depression and insulin resistance-related disorders via low-grade chronic inflammation: Integrating the phenotypic, molecular and neuroanatomical dimensions

Insulin resistance (IR) and related disorders, such as T2DM, increase the risk of major depressive disorder (MDD) and vice versa. Current evidence indicates that psychological stress and overeating can induce chronic low-grade inflammation that can interfere with glutamate metabolism in MDD as well as insulin signaling, particularly in the atypical subtype. Here we first review the interactive role of inflammatory processes in the development of MDD, IR and related metabolic disorders. Next, we describe the role of the anterior cingulate cortex in the pathophysiology of MDD and IR-related disorders. Furthermore, we outline how specific clinical features of atypical depression, such as hyperphagia, are more associated with inflammation and IR-related disorders. Finally, we examine the regional specificity of the effects of inflammation on the brain that show an overlap with the functional and morphometric brain patterns activated in MDD and IR-related disorders.

Dietary and metabolic risk of neuropsychiatric disorders: insights from animal models

Neuropsychiatric disorders are major causes of the global burden of diseases, frequently co-occurring with multiple co-morbidities, especially obesity, type 2 diabetes mellitus, non-alcoholic fatty liver disease and its various risk factors in the metabolic syndrome. While the determining factors of neuropsychiatric disorders are complex, recent studies have shown that there is a strong link between diet, metabolic state and neuropsychiatric disorders, including anxiety and depression. There is no doubt that rodent models are of great value for preclinical research. Therefore, this article focuses on a rodent model of chronic consumption of high-fat diet (HFD), and/or the addition of a certain amount of cholesterol or sugar, meanwhile, summarising the pattern of diet that induces anxiety/depressive-like behaviour and the underlying mechanism. We highlight how dietary and metabolic risk influence neuropsychiatric behaviour in animals. Changes in dietary patterns, especially HFD, can induce anxiety- or depression-like behaviours, which may vary by diet exposure period, sex, age, species and genetic background of the animals used. Furthermore, dietary patterns significantly aggravate anxiety/depression-like behaviour in animal models of neuropsychiatric disorders. The mechanisms by which diet induces anxiety/depressive-like behaviour may involve neuroinflammation, neurotransmitters/neuromodulators, neurotrophins and the gut-brain axis. Future research should be focused on elucidating the mechanism and identifying the contribution of diet and diet-induced metabolic risk to neuropsychiatric disorders, which can form the basis for future clinical dietary intervention strategies for neuropsychiatric disorders.

The Role of Hypothalamic Inflammation in Diet-Induced Obesity and Its Association with Cognitive and Mood Disorders

Obesity is often associated with cognitive and mood disorders. Recent evidence suggests that obesity may cause hypothalamic inflammation. Our aim was to investigate the hypothesis that there is a causal link between obesity-induced hypothalamic inflammation and cognitive and mood disorders. Inflammation may influence hypothalamic inter-connections with regions important for cognition and mood, while it may cause dysregulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis and influence monoaminergic systems. Exercise, healthy diet, and glucagon-like peptide receptor agonists, which can reduce hypothalamic inflammation in obese models, could improve the deleterious effects on cognition and mood.

Saturated Fatty Acid Intake Is Associated With Increased Inflammation, Conversion of Kynurenine to Tryptophan, and Delta-9 Desaturase Activity in Healthy Humans

Saturated fat ingestion has previously been linked to increases in inflammation. However the relationship between saturated fatty acid (SFA) intake and the kynureine:tryptophan ratio ([Kyn]:[Trp]), a marker of inflammation, has not been previously investigated. This study evaluated in healthy, middle aged, individuals (men = 48, women = 52), potential relationships between SFA intake, red blood cell (RBC) membrane SFAs and monounsaturated fatty acids (MUFA), the [Kyn]:[Trp] ratio, C-reactive protein (CRP), TNF-α and Δ9 desaturase activity. [Kyn]:[Trp] was positively associated with increases in Total fat (P = .034) intake, including Total SFA (P = .029) and Total MUFA (P = .042) intakes. Unexpectedly the [Kyn]:[Trp] ratio was inversely associated with the percentage of Total SFA (P = .004) and positively associated with percentage of Total MUFA (P = .012) present in the RBC membrane. We found a positive association between Δ9 desaturase activity, responsible for the desaturation of a various SFAs to MUFAs, and [Kyn]:[Trp] (P = .008). [Kyn]:[Trp] was also positively associated with CRP (P = .044), however no significant relationship between [Kyn]:[Trp] and TNF-α was found. This study shows for the first time that SFA consumption increases inflammatory pathways linked to increased tryptophan to kynurenine conversion, even in healthy humans. Our data also suggests that SFA linked increases in inflammation occur concomitantly with an upregulation of Δ9 desaturase activity resulting in increased desaturation of SFA substrates to their MUFA derivatives.

Low-dose alcohol ameliorated high fat diet-induced anxiety-related behavior via enhancing adiponectin expression and activating the Nrf2 pathway

Long-term high-fat-diet (HFD)-induced obesity is associated with many comorbidities, such as cognitive impairment and anxiety, which are increasing public health burdens that have gained prevalence in adolescents. Although low-dose alcohol could attenuate the risk of cardiovascular disease, its mechanism on HFD-induced anxiety-related behavior remains not clear. The mice were divided into 4 groups, Control (Con), Alcohol (Alc), HFD and HFD + Alc groups. To verify the effects of low-dose alcohol on HFD-induced anxiety-related behavior, the mice were fed with HFD for 16 weeks. At the beginning of week 13, the HFD-fed mice were administered intragastrically with low-dose alcohol (0.8 g kg^-1) for 4 weeks. After 4 weeks of oral administration, low-dose alcohol decreased body weight and Lee's index in HFD-induced obese mice. Moreover, low-dose alcohol alleviated the anxiety-related behaviors of obese mice in the open field test and the elevated plus maze test. The HFD-induced damage to the hippocampus was improved in hematoxylin-eosin staining assay in mice. In addition, low-dose alcohol also suppressed HFD-induced oxidative stress and increased HFD-suppressed adiponectin (APN) expression and nuclear factor erythroid 2-related factor 2 (Nrf2) activation in the hippocampus. Taken together, low-dose alcohol significantly ameliorates HFD-induced obesity, oxidative stress and anxiety-related behavior in mice, which might be related to APN upregulation, Nrf2 activation and related antioxidase expression including SOD1, HO-1, and catalase.

Dietary Fibers and Proteins Modulate Behavior via the Activation of Intestinal Gluconeogenesis

INTRODUCTION

Several studies have suggested that diet, especially the one enriched in microbiota-fermented fibers or fat, regulates behavior. The underlying mechanisms are currently unknown. We previously reported that certain macronutrients (fermentable fiber and protein) regulate energy homeostasis via the activation of intestinal gluconeogenesis (IGN), which generates a neural signal to the brain. We hypothesized that these nutriments might control behavior using the same gut-brain circuit.

METHODS

Wild-type and IGN-deficient mice were fed chow or diets enriched in protein or fiber. Changes in their behavior were assessed using suited tests. Hippocampal neurogenesis, extracellular levels of serotonin, and protein expression levels were assessed by immunofluorescence, in vivo dialysis, and Western blotting, respectively. IGN was rescued by infusing glucose into the portal vein of IGN-deficient mice.

RESULTS

We show here that both fiber- and protein-enriched diets exert beneficial actions on anxiety-like and depressive-like behaviors. These benefits do not occur in mice lacking IGN. Consistently, IGN-deficient mice display hallmarks of depressive-like disorders, including decreased hippocampal neurogenesis, basal hyperactivity, and deregulation of the hypothalamic-pituitary-adrenal axis, which are associated with increased expression of the precursor of corticotropin-releasing hormone in the hypothalamus and decreased expression of the glucocorticoid receptor in the hippocampus. These neurobiological alterations are corrected by portal glucose infusion mimicking IGN.

CONCLUSION

IGN translates nutritional information, allowing the brain to finely coordinate energy metabolism and behavior.

Mood disorders are associated with the reduction of brain derived neurotrophic factor in the hypocampus in rats submitted to the hipercaloric diet

Adipose tissue accumulation, resulting from the consumption of hypercaloric foods, can cause a dysfunction of the endocrine system. Such endocrine changes can influence the expression of various neurochemicals including brain-derived neurotrophic factor (BDNF) - associated with cognitive and emotional problems. Here, we investigated the effects of a hypercaloric diet on depression- and anxiety-like behaviors in young rats along with concomitant changes in BDNF expression levels in the hippocampus. Eight week-old Wistar rats (n = 20) were divided in: control diet (CD) group which received industrial food (n = 8) and hypercaloric diet (HD) group which received animal fat and soybean oil (n = 12). After 45 days on the diet, the animals were evaluated: body weight and blood biochemical analisys. Changes in mood disposition were evaluated using forced swim test and the elevated plus-maze, whereas hippocampal BDNF expression levels were quantified by ELISA. After 45 weeks, the CD group showed a significant increase in body weight relative to the HD group. However, the HD rats had a body fat percentage and exhibited increased level of the biochemical markers. Furthermore, the animals in the HD group presented increased immobility time in the forced swimming test, as well as reduced response to plus-maze test suggesting a depression- and anxiety-like emotional state. In addition, the HD group also showed lower BDNF expression levels in the hippocampus. This study demonstrates that a hypercaloric diet induced increase in adipose tissue concentration in young rats was associated with reduced hippocampal BDNF expression and resulted in an increase in depression- and anxiety-like behaviors. Graphical abstract.

Experimental Pulmonary Tuberculosis in the Absence of Detectable Brain Infection Induces Neuroinflammation and Behavioural Abnormalities in Male BALB/c Mice

Tuberculosis (TB) is a chronic infectious disease in which prolonged, non-resolutive inflammation of the lung may lead to metabolic and neuroendocrine dysfunction. Previous studies have reported that individuals coursing pulmonary TB experience cognitive or behavioural changes; however, the pathogenic substrate of such manifestations have remained unknown. Here, using a mouse model of progressive pulmonary TB, we report that, even in the absence of brain infection, TB is associated with marked increased synthesis of both inflammatory and anti-inflammatory cytokines in discrete brain areas such as the hypothalamus, the hippocampal formation and cerebellum accompanied by substantial changes in the synthesis of neurotransmitters. Moreover, histopathological findings of neurodegeneration and neuronal death were found as infection progressed with activation of p38, JNK and reduction in the BDNF levels. Finally, we perform behavioural analysis in infected mice throughout the infection, and our data show that the cytokine and neurochemical changes were associated with a marked onset of cognitive impairment as well as depressive- and anxiety-like behaviour. Altogether, our results suggest that besides pulmonary damage, TB is accompanied by an extensive neuroinflammatory and neurodegenerative state which explains some of the behavioural abnormalities found in TB patients.

Anti-Inflammatory Effects of Asian Fawn Lily (Erythronium japonicum) Extract on Lipopolysaccharide-Induced Depressive-Like Behavior in Mice

Neuroinflammation is associated with an increased risk of depression. Lipopolysaccharide (LPS) treatment is known to induce pro-inflammatory cytokine secretion and a depressive-like phenotype in mice. Although Erythronium japonicum exhibits various health benefits, the role of E. japonicum extract (EJE) in inflammation-associated depression is unknown. This study aimed to explore the anti-inflammatory effect of EJE on LPS-induced depressive symptoms in mice using the open field test (OFT), passive avoidance test (PAT), tail suspension test (TST), and forced swim test (FST). LPS-treated mice had significantly increased immobility time in the TST and FST, decreased step-through latency time in the PAT, and decreased locomotor activity in the OFT. However, administration of 100 and 300 mg/kg of EJE significantly improved these depressive-like behaviors. EJE also prevented the increase in mRNA levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and monocyte chemoattractant protein-1 (MCP-1), and the decrease in IL-10 levels by inhibiting nuclear factor-κB (NF-κB) subunit p65 phosphorylation. Additionally, LPS-treated mice showed markedly decreased brain-derived neurotrophic factor (BDNF) levels and phosphorylation of phosphoinositide 3-kinase (PI3K) and Akt, while EJE treatment significantly increased these levels in the hippocampus. These results suggest that EJE ameliorated LPS-induced depressive-like behavior by reducing LPS-induced neuroinflammation and activating the BDNF-PI3K/Akt pathway.

What animal models can tell us about long-term cognitive dysfunction following sepsis: A systematic review

Survivors of sepsis often develop long-term cognitive impairments. This review aimed at exploring the results of the behavioral tools and tests which have been used to evaluate cognitive dysfunction in different animal models of sepsis. Two independent investigators searched for sepsis- and cognition-related keywords. 6323 publications were found, of which 355 were selected based on their title, and 226 of these were chosen based on manuscript review. LPS was used to induce sepsis in 171 studies, while CLP was used in 55 studies. Inhibitory avoidance was the most widely used method for assessing aversive memory, followed by fear conditioning and continuous multi-trial inhibitory avoidance. With regard to non-aversive memory, most studies used the water maze, open-field, object recognition, Y-maze, plus maze, and radial maze tests. Both CLP and LPS models of sepsis were effective in inducing short- and long-term behavioral impairment. Our findings help elucidate the mechanisms involved in the pathophysiology of sepsis-induced cognitive changes, as well as the available methods and tests used to study this in animal models.

Maternal organophosphate flame-retardant exposure alters offspring feeding, locomotor and exploratory behaviors in a sexually-dimorphic manner in mice

Increased usage of organophosphate flame retardants (OPFRs) has led to detectable levels in pregnant women and neonates, which is associated with negative neurological outcomes. Therefore, we investigated if maternal OPFR exposure altered adult offspring feeding, locomotor, and anxiety-like behaviors on a low-fat (LFD) or high-fat diet (HFD). Wild-type C57Bl/6J dams were orally dosed with vehicle (sesame oil) or an OPFR mixture (1 mg/kg combination each of tris(1,3-dichloro-2-propyl)phosphate, triphenyl phosphate and tricresyl phosphate) from gestation day 7 to postnatal day 14. After weaning, pups were fed either a LFD or HFD until 19 weeks of age. Locomotor and anxiety-like behaviors were evaluated with the open field test, elevated plus maze, and metabolic cages. Feeding behaviors and meal patterns were analyzed by a Biological Data Acquisition System. Anogenital distance was reduced in OPFR-exposed male pups, but no effect was detected on adult body weight. We observed interactions of OPFR exposure and HFD consumption on locomotor and anxiety-like behavior in males, suggesting an anxiogenic effect while reducing overall nighttime activity. We also observed an interaction of OPFR exposure and HFD on weekly food intake and feeding behaviors. OPFR-exposed males consumed more total HFD than oil-exposed males during the 72-hour trial. However, when arcuate gene expression was analyzed, OPFR exposure induced Agrp expression in females, which would suggest greater orexigenic tone. Collectively, the implications of our study are that the behavioral effects of OPFR exposure are modulated by adult HFD consumption, which may influence the metabolic and neurological consequences of maternal OPFR exposure.

Western diet, obesity and bariatric surgery sequentially modulated anxiety, eating patterns and brain responses to sucrose in adult Yucatan minipigs

Palatable sweet/fatty foods overconsumption is a major risk factor for obesity and eating disorders, also having an impact on neuro-behavioural hedonic and cognitive components comparable to what is described for substance abuse. We hypothesized that Yucatan minipigs would show hedonic, cognitive, and affective neuro-behavioral shifts when subjected to western diet (WD) exposure without weight gain, after the onset of obesity, and finally after weight loss induced by caloric restriction with (RYGB) or without (Sham) gastric bypass. Eating behavior, cognitive and affective abilities were assessed with a spatial discrimination task (holeboard test) and two-choice feed tests. Brain responses to oral sucrose were mapped using 18F-FDG positron emission tomography. WD exposure impaired working memory and led to an “addiction-type” neuronal pattern involving hippocampal and cortical brain areas. Obesity induced anxiety-like behavior, loss of motivation, and snacking-type eating behavior. Weight loss interventions normalized the motivational and affective states but not eating behavior patterns. Brain glucose metabolism increased in gustatory (insula) and executive control (aPFC) areas after weight loss, but RYGB showed higher responses in inhibition-related areas (dorsal striatum). These results showed that diet quality, weight loss, and the type of weight loss intervention differently impacted brain responses to sucrose in the Yucatan minipig model.

Metformin: A Prospective Alternative for the Treatment of Chronic Pain

Metformin (biguanide) is a drug widely used for the treatment of type 2 diabetes. This drug has been used for 60 years as a highly effective antihyperglycemic agent. The search for the mechanism of action of metformin has produced an enormous amount of research to explain its effects on gluconeogenesis, protein metabolism, fatty acid oxidation, oxidative stress, glucose uptake, autophagy and pain, among others. It was only up the end of the 1990s and beginning of this century that some of its mechanisms were revealed. Metformin induces its beneficial effects in diabetes through the activation of a master switch kinase named AMP-activated protein kinase (AMPK). Two upstream kinases account for the physiological activation of AMPK: liver kinase B1 and calcium/calmodulin-dependent protein kinase kinase 2. Once activated, AMPK inhibits the mechanistic target of rapamycin complex 1 (mTORC1), which in turn avoids the phosphorylation of p70 ribosomal protein S6 kinase 1 and phosphatidylinositol 3-kinase/protein kinase B signaling pathways and reduces cap-dependent translation initiation. Since metformin is a disease-modifying drug in type 2 diabetes, which reduces the mTORC1 signaling to induce its effects on neuronal plasticity, it was proposed that these mechanisms could also explain the antinociceptive effect of this drug in several models of chronic pain. These studies have highlighted the efficacy of this drug in chronic pain, such as that from neuropathy, insulin resistance, diabetic neuropathy, and fibromyalgia-type pain. Mounting evidence indicates that chronic pain may induce anxiety, depression and cognitive impairment in rodents and humans. Interestingly, metformin is able to reverse some of these consequences of pathological pain in rodents. The purpose of this review was to analyze the current evidence about the effects of metformin in chronic pain and three of its comorbidities (anxiety, depression and cognitive impairment).

Sciatic Nerve Ligation Downregulates Mitochondrial Clusterin in the Rat Prefrontal Cortex

The concentration of the multifunctional protein clusterin is reduced in the plasma of subjects with degenerative scoliosis (DS) and carpal tunnel syndrome (CTS) but elevated in the cerebrospinal fluid of neuropathic pain patients successfully treated with spinal cord stimulation. The present work tries to increase the knowledge of pain-associated changes of plasma and brain clusterin by using an animal model of neuropathy. We studied the effects of sciatic nerve ligation on mechanical allodynia (von Frey test), anxiety (elevated plus maze test), plasma clusterin (enzyme-linked immunosorbent assay) and clusterin expression in the nucleus accumbens (NAC) and prefrontal cortex (PFC) of adult male Wistar rats (western blot). The possible modulatory role of high fat (HF) dieting was also studied, bearing in mind that obesity has been also reported to influence nociception, clusterin levels and prefrontal cortex activation. Animals with nerve ligation showed mechanical allodynia, anxiety and a marked downregulation of clusterin in the mitochondrial fraction of the prefrontal cortex. Animals fed on HF also exhibited a slight increase of the sensitivity to mechanical stimuli and anxiety; however, the diet did not potentiate the effects of nerve ligation. The results did not confirm a parallelism between neuropathy, obesity and alterations of plasma levels of clusterin, but strongly suggest that the protein could be involved in the functional reorganization of the prefrontal cortex which has been recently reported in chronic pain conditions.

Clinical Evidence of Antidepressant Effects of Insulin and Anti-Hyperglycemic Agents and Implications for the Pathophysiology of Depression-A Literature Review

Close connections between depression and type 2 diabetes (T2DM) have been suggested by many epidemiological and experimental studies. Disturbances in insulin sensitivity due to the disruption of various molecular pathways cause insulin resistance, which underpins many metabolic disorders, including diabetes, as well as depression. Several anti-hyperglycemic agents have demonstrated antidepressant properties in clinical trials, probably due to their action on brain targets based on the shared pathophysiology of depression and T2DM. In this article, we review reports of clinical trials examining the antidepressant effect of these medications, including insulin, metformin, glucagon like peptide-1 receptor agonists (GLP-1RA), and peroxisome proliferator-activated receptor (PPAR)-γ agonists, and briefly consider possible molecular mechanisms underlying the associations between amelioration of insulin resistance and improvement of depressive symptoms. In doing so, we intend to suggest an integrative perspective for understanding the pathophysiology of depression.

Immunological and behavioral responses to in vivo lipopolysaccharide administration in young and healthy obese and normal-weight humans

Obesity is associated with an increase prevalence of neuropsychiatric symptoms and diseases, such as depression. Based on the facts that pro-inflammatory cytokines are able to modulate behavior, and that obesity is characterized by a chronic low-grade inflammatory state, inflammation has been hypothesized to contribute to the neuropsychiatric comorbidity in obese individuals. However, a causal link between inflammation and the development of neuropsychiatric symptoms is hard to establish in humans. Here, we used an inflammatory stimulus, i.e. the intravenous injection of lipopolysaccharide (LPS), in a double-blind placebo-controlled design, to determine the vulnerability of obese individuals to inflammation-induced behavioral changes. The hypothesis was that obese individuals would show heightened behavioral response compared to normal-weight subjects for the same inflammatory stimulus, reflecting an increased sensitivity to the behavioral effects of pro-inflammatory cytokines. LPS (dose 0.8 ng/kg body weight, adjusted for estimated blood volume in obese subjects) and placebo (saline) were intravenously injected in 14 obese healthy subjects and 23 normal-weight healthy subjects in a within-subject, randomized, crossover design. LPS administration induced, in both groups, an acute increase in blood concentrations of cytokines (interleukin-6, tumor necrosis factor-α, and IL-10), as well as in body temperature, cortisol, norepinephrine, sickness symptoms, fatigue, negative mood, and state anxiety. There were little differences in the immune and behavioral responses to LPS between obese and normal-weight subjects, but the cortisol response to LPS was strongly attenuated in obese individuals. Higher percentage of body fat was related to a lower cortisol response to LPS. Taken together, the population of young and healthy obese individuals in this study did not exhibit an increased behavioral sensitivity to cytokines, but an attenuated cortisol response to the immune challenge. Future studies will need to determine whether additional physiological and psychological factors interact with the state of obesity to increase the risk for inflammation-induced neuropsychiatric symptoms.

Maternal obesity modulates sexually dimorphic epigenetic regulation and expression of leptin receptor in offspring hippocampus

Maternal obesity during pregnancy is associated with a greater risk for obesity and neurodevelopmental deficits in offspring. This developmental programming of disease is proposed to involve neuroendocrine, inflammatory, and epigenetic factors during gestation that disrupt normal fetal brain development. The hormones leptin and insulin are each intrinsically linked to metabolism, inflammation, and neurodevelopment, which led us to hypothesise that maternal obesity may disrupt leptin or insulin receptor signalling in the developing brain of offspring. Using a C57BL/6 mouse model of high fat diet-induced maternal obesity (mHFD), we performed qPCR to examine leptin receptor (Lepr) and insulin receptor (Insr) gene expression in gestational day (GD) 17.5 fetal brain. We found a significant effect of maternal diet and offspring sex on Lepr regulation in the developing hippocampus, with increased Lepr expression in female mHFD offspring (p < 0.05) compared to controls. Maternal diet did not alter hippocampal Insr in the fetal brain, or Lepr or Insr in prefrontal cortex, amygdala, or hypothalamus of female or male offspring. Chromatin immunoprecipitation revealed decreased binding of histones possessing the repressive histone mark H3K9me3 at the Lepr promoter (p < 0.05) in hippocampus of female mHFD offspring compared to controls, but not in males. Sex-specific deregulation of Lepr could be reproduced in vitro by exposing female hippocampal neurons to the obesity related proinflammatory cytokine IL-6, but not IL-17a or IFNG. Our findings indicate that the obesity-related proinflammatory cytokine IL-6 during pregnancy leads to sexually dimorphic changes in the modifications of histones binding at the Lepr gene promoter, and concomitant changes to Lepr transcription in the developing hippocampus. This suggests that exposure of the fetus to metabolic inflammatory molecules can impact epigenetic regulation of gene expression in the developing hippocampus.

Western diet-induced obesity disrupts the diurnal rhythmicity of hippocampal core clock gene expression in a mouse model

Western diet (WD) feeding disrupts core clock gene expression in peripheral tissues and contributes to WD-induced metabolic disease. The hippocampus, the mammalian center for memory, is also sensitive to WD feeding, but whether the WD disrupts its core clock is unknown. To this end, male mice were maintained on a WD for 16 weeks and diurnal metabolism, gene expression and memory were assessed. WD-induced obesity disrupted the diurnal rhythms of whole-body metabolism, markers of inflammation and hepatic gene expression, but did not disrupt diurnal expression of hypothalamic Bmal1, Npas2 and Per2. However, all measured core clock genes were disrupted in the hippocampus after WD feeding and the expression pattern of genes implicated in Alzheimer's disease and synaptic function were altered. Finally, WD feeding disrupted hippocampal memory in a task- and time-dependent fashion. Our results implicate WD-induced alterations in the rhythmicity of hippocampal gene expression in the etiology of diet-induced memory deficits.

High-fat diet negatively impacts both metabolic and behavioral health in outbred heterogeneous stock rats

Obesity is influenced by genetics and diet and has wide ranging comorbidities, including anxiety and depressive disorders. Outbred heterogeneous stock (HS) rats are used for fine-genetic mapping of complex traits and may be useful for understanding gene by diet interactions. In this study, HS rats were fed diets containing 60% kcal from fat (high-fat diet, HFD) or 10% kcal from fat (low-fat diet, LFD) and tested for metabolic (study 1) and behavioral (study 2) outcomes. In study 1, we measured glucose tolerance, fasting glucose and insulin, fat pad weights and despair-like behavior in the forced swim test (FST). In study 2, we assessed anxiety-like (elevated plus maze, EPM; open field test, OFT) and despair-like/coping (splash test, SpT; and FST) behaviors. Body weight and food intake were measured weekly in both studies. We found negative effects of HFD on metabolic outcomes, including increased body weight and fat pad weights, decreased glucose tolerance, and increased fasting insulin. We also found negative effects of HFD on despair-like/coping and anxiety-like behaviors. These include increased immobility in the FST, decreased open arm time in the EPM, and increased movement and rest episodes and decreased rearing in the OFT. The diet-induced changes in EPM and OFT were independent of overall locomotion. Additionally, diet-induced changes in OFT behaviors were independent of adiposity, while adiposity was a confounding factor for EPM and FST behavior. This work establishes the HS as a model to study gene by diet interactions affecting metabolic and behavioral health.

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.

Inflammation-Induced Tryptophan Breakdown is Related With Anemia, Fatigue, and Depression in Cancer

Many patients with cancer suffer from anemia, depression, and an impaired quality of life (QoL). These patients often also show decreased plasma tryptophan levels and increased kynurenine concentrations in parallel with elevated concentrations of Th1 type immune activation marker neopterin. In the course of anti-tumor immune response, the pro-inflammatory cytokine interferon gamma (IFN-γ) induces both, the enzyme indoleamine 2,3-dioxygenase (IDO) to degrade tryptophan and the enzyme GTP-cyclohydrolase I to form neopterin. High neopterin concentrations as well as an increased kynurenine to tryptophan ratio (Kyn/Trp) in the blood of cancer patients are predictive for a worse outcome. Inflammation-mediated tryptophan catabolism along the kynurenine pathway is related to fatigue and anemia as well as to depression and a decreased QoL in patients with solid tumors. In fact, enhanced tryptophan breakdown might greatly contribute to the development of anemia, fatigue, and depression in cancer patients. IDO activation and stimulation of the kynurenine pathway exert immune regulatory mechanisms, which may impair anti-tumor immune responses. In addition, tumor cells can degrade tryptophan to weaken immune responses directed against them. High IDO expression in the tumor tissue is associated with a poor prognosis of patients. The efficiency of IDO-inhibitors to inhibit cancer progression is currently tested in combination with established chemotherapies and with immune checkpoint inhibitors. Inflammation-mediated tryptophan catabolism and its possible influence on the development and persistence of anemia, fatigue, and depression in cancer patients are discussed.

Rapeseed oil fortified with micronutrients improves cognitive alterations associated with metabolic syndrome

Metabolic syndrome represents a major risk factor for severe comorbidities such as cardiovascular diseases or diabetes. It is also associated with an increased prevalence of emotional and cognitive alterations that in turn aggravate the disease and related outcomes. Identifying therapeutic strategies able to improve those alterations is therefore a major socioeconomical and public health challenge. We previously reported that both hippocampal inflammatory processes and neuronal plasticity contribute to the development of emotional and cognitive alterations in db/db mice, an experimental model of metabolic syndrome that displays most of the classical features of the syndrome. In that context, nutritional interventions with known impact on those neurobiological processes appear as a promising alternative to limit the development of neurobiological comorbidities of metabolic syndrome. We therefore tested here whether n-3 polyunsaturated fatty acids (n-3 PUFAs) associated with a cocktail of antioxidants can protect against the development of behavioral alterations that accompany the metabolic syndrome. Thus, this study aimed: 1) to evaluate if a diet supplemented with the plant-derived n-3 PUFA α-linolenic acid (ALA) and antioxidants (provided by n-3 PUFAs-rich rapeseed oil fortified with a mix of naturally constituting antioxidant micronutrients, including coenzyme Q10, tocopherol, and the phenolic compound canolol) improved behavioral alterations in db/db mice, and 2) to decipher the biological mechanisms underlying this behavioral effect. Although the supplemented diet did not improve anxiety-like behavior and inflammatory abnormalities, it reversed hippocampus-dependent spatial memory deficits displayed by db/db mice in a water maze task. It concomitantly changed subunit composition of glutamatergic AMPA and NMDA receptors in the hippocampus that has been shown to modulate synaptic function related to spatial memory. These data suggest that changes in local neuronal plasticity may underlie cognitive improvements in db/db mice fed the supplemented diet. The current findings might therefore provide valuable data for introducing new nutritional strategies for the treatment of behavioral complications associated with MetS.

The progress of gut microbiome research related to brain disorders

There is increasing evidence showing that the dynamic changes in the gut microbiota can alter brain physiology and behavior. Cognition was originally thought to be regulated only by the central nervous system. However, it is now becoming clear that many non-nervous system factors, including the gut-resident bacteria of the gastrointestinal tract, regulate and influence cognitive dysfunction as well as the process of neurodegeneration and cerebrovascular diseases. Extrinsic and intrinsic factors including dietary habits can regulate the composition of the microbiota. Microbes release metabolites and microbiota-derived molecules to further trigger host-derived cytokines and inflammation in the central nervous system, which contribute greatly to the pathogenesis of host brain disorders such as pain, depression, anxiety, autism, Alzheimer’s diseases, Parkinson’s disease, and stroke. Change of blood–brain barrier permeability, brain vascular physiology, and brain structure are among the most critical causes of the development of downstream neurological dysfunction. In this review, we will discuss the following parts:

Overview of technical approaches used in gut microbiome studies

Microbiota and immunity

Gut microbiota and metabolites

Microbiota-induced blood–brain barrier dysfunction

Neuropsychiatric diseases

■ Stress and depression

■ Pain and migraine

■ Autism spectrum disorders

Neurodegenerative diseases

■ Parkinson’s disease

■ Alzheimer’s disease

■ Amyotrophic lateral sclerosis

■ Multiple sclerosis

Cerebrovascular disease

■ Atherosclerosis

■ Stroke

■ Arteriovenous malformation

Conclusions and perspectives

Pioglitazone Attenuates Lipopolysaccharide-Induced Oxidative Stress, Dopaminergic Neuronal Loss and Neurobehavioral Impairment by Activating Nrf2/ARE/HO-1

The aim of the present study was to examine the neuroprotective potential of pioglitazone via activation of Nrf2/ARE-dependent HO-1 signaling pathway in chronic neuroinflammation and progressive neurodegeneration mouse model induced by lipopolysaccharide (LPS). After assessing spatial memory, anxiety and motor-coordination, TH+ neurons in substantia nigra (SN) were counted. The oxidative stress marker carbonyl protein levels and HO-1 enzyme activity were also evaluated. RT-qPCR was conducted to detect HO-1, Nrf2 and NF-κp65 mRNA expression levels and Nrf2 transcriptional activation of antioxidant response element (ARE) of HO-1 was investigated. Pioglitazone ameliorated LPS-induced dopaminergic neuronal loss, as well as mitigated neurobehavioral impairments. It enhanced Nrf2 mRNA expression, and augmented Nrf2/ARE-dependent HO-1 pathway activation by amplifying HO-1 mRNA expression. Moreover, it induced a significant decrease in NF-κB p65 mRNA expression, while reducing carbonyl protein levels and restoring the HO-1 enzyme activity. Interestingly, LPS induced Nrf2/antioxidant response element (ARE) of HO-1 activation, ultimately resulting in slight enhanced HO-1 mRNA expression. However, LPS elicited decrease in HO-1 enzyme activity. Zinc protoporphyrin-IX (ZnPPIX) administrated with pioglitazone abolished its effects in the LPS mouse model. The study results demonstrate that coordinated activation of Nrf2/ARE-dependent HO-1 pathway defense mechanism by the PPARγ agonist pioglitazone mediated its neuroprotective effects.

Modulation of high fat diet-induced microbiome changes, but not behaviour, by minocycline

An emerging novel therapeutic agent for major depressive disorder, minocycline, has the potential to influence both gut microbiome and inflammatory status. The present study showed that chronic high fat diet feeding led to changes in both behaviour and the gut microbiome in male mice, without an overt inflammatory response. The diet-induced behavioural changes were characterised as increased immobility in the forced swim test and changes in locomotor activities in the open field test. Minocycline significantly altered the gut microbiome, rendering a community distinctly different to both untreated healthy and diet-affected states. In contrast, minocycline did not reverse high fat diet-induced changes in behaviour.

Effect of High-Fat Diets on Oxidative Stress, Cellular Inflammatory Response and Cognitive Function

Cognitive dysfunction is linked to chronic low-grade inflammatory stress that contributes to cell-mediated immunity in creating an oxidative environment. Food is a vitally important energy source; it affects brain function and provides direct energy. Several studies have indicated that high-fat consumption causes overproduction of circulating free fatty acids and systemic inflammation. Immune cells, free fatty acids, and circulating cytokines reach the hypothalamus and initiate local inflammation through processes such as microglial proliferation. Therefore, the role of high-fat diet (HFD) in promoting oxidative stress and neurodegeneration is worthy of further discussion. Of particular interest in this article, we highlight the associations and molecular mechanisms of HFD in the modulation of inflammation and cognitive deficits. Taken together, a better understanding of the role of oxidative stress in cognitive impairment following HFD consumption would provide a useful approach for the prevention of cognitive dysfunction.

Association of high-fat diet with neuroinflammation, anxiety-like defensive behavioral responses, and altered thermoregulatory responses in male rats

Overweight and obesity are a worldwide pandemic affecting billions of people. These conditions have been associated with a chronic low-grade inflammatory state that is recognized as a risk factor for a range of somatic diseases as well as neurodevelopmental disorders, anxiety disorders, trauma- and stressor-related disorders, and affective disorders. We previously reported that the ingestion of a high-fat diet (HFD; 45% fat kcal/g) for nine weeks was capable of inducing obesity in rats in association with increased reactivity to stress and increased anxiety-related defensive behavior. In this study, we conducted a nine-week diet protocol to induce obesity in rats, followed by investigation of anxiety-related defensive behavioral responses using the elevated T-maze (ETM), numbers of FOS-immunoreactive cells after exposure of rats to the avoidance or escape task of the ETM, and neuroinflammatory cytokine expression in hypothalamic and amygdaloid nuclei. In addition, we investigated stress-induced cutaneous thermoregulatory responses during exposure to an open-field (OF). Here we demonstrated that nine weeks of HFD intake induced obesity, in association with increased abdominal fat pad weight, increased anxiety-related defensive behavioral responses, and increased proinflammatory cytokines in hypothalamic and amygdaloid nuclei. In addition, HFD exposure altered avoidance- or escape task-induced FOS-immunoreactivity within brain structures involved in control of neuroendocrine, autonomic, and behavioral responses to aversive stimuli, including the basolateral amygdala (BLA) and dorsomedial (DMH), paraventricular (PVN) and ventromedial (VMH) hypothalamic nuclei. Furthermore, rats exposed to HFD, relative to control diet-fed rats, responded with increased tail skin temperature at baseline and throughout exposure to an open-field apparatus. These data are consistent with the hypothesis that HFD induces neuroinflammation, alters excitability of brain nuclei controlling neuroendocrine, autonomic, and behavioral responses to stressful stimuli, and enhances stress reactivity and anxiety-like defensive behavioral responses.

Site-Specific Reprogramming of Macrophage Responsiveness to Bacterial Lipopolysaccharide in Obesity

The mechanisms by which obesity may alter immune responses to pathogens are poorly understood. The present study assessed whether the intrinsic responsiveness of resident macrophages to bacterial lipopolysaccharide (LPS) is reprogrammed in high-fat diet (HFD)-induced obesity. Macrophages from adipose tissue, lung alveoli, and the peritoneal cavity were extracted from obese rats on a HFD or from their lean counterparts, and subsequently studied in culture under identical conditions. CD45⁺/CD68⁺ cells (macrophages) were abundant in all cultures, and became the main producers of TNF-α upon LPS stimulation. But although all macrophage subpopulations responded to LPS with an M1-like profile of cytokine secretion, the TNF-α/IL-10 ratio was the lowest in adipose tissue macrophages, the highest in alveolar macrophages, and intermediary in peritoneal macrophages. What is more, diet exerted qualitatively distinct effects on the cytokine responses to LPS, with obesity switching adipose tissue macrophages to a more pro-inflammatory program and peritoneal macrophages to a less pro-inflammatory program, while not affecting alveolar macrophages. Such reprogramming was not associated with changes in the inflammasome-dependent secretion of IL-1β. The study further shows that the effects of diet on TNF-α/IL-10 ratios were linked to distinct patterns of NF-κB accumulation in the nucleus: while RelA was the NF-κB subunit most impacted by obesity in adipose tissue macrophages, cRel was the subunit affected in peritoneal macrophages. It is concluded that obesity causes dissimilar, site-specific changes in the responsiveness of resident macrophages to bacterial LPS. Such plasticity opens new avenues of investigation into the mechanisms linking obesity to pathogen-induced immune responses.

Baicalin ameliorates chronic mild stress-induced depression-like behaviors in mice and attenuates inflammatory cytokines and oxidative stress

The natural flavonoid glycoside baicalin (BA) produces a variety of pharmaceutical effects, particularly for psychiatric/neurological disorders. This study evaluated the behavioral and neuroprotective effects of BA in mice subjected to chronic unpredictable mild stress, a model of depression. BA (25 and 50 mg/kg) significantly increased sucrose consumption and reduced immobility times in the tail suspension and forced swim tests, demonstrating that BA alleviated depression-like behaviors. Moreover, BA reduced the levels of inflammatory cytokines, such as interleukin 1β, interleukin 6, and tumor necrosis factor α, in serum and in the hippocampus. BA also abrogated increases in NMDAR/NR2B and Ca²⁺/calmodulin-dependent protein kinase II, and the decrease in phosphorylated ERK and reactive oxygen species production in mice subjected to chronic unpredictable mild stress. These findings suggested that the antidepressive effects of BA are due to the regulation of an NMDAR/NR2B-ERK1/2-related pathway and inhibition of inflammatory cytokines and oxidative stress. Thus, BA represents a potential candidate drug for patients suffering from depression.

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.

Selective inhibition of intestinal 5-HT improves neurobehavioral abnormalities caused by high-fat diet mice

Recent literature reported the adverse effects of high-fat diet (HFD) on animal's emotional and cognitive function. An HFD-induced obesity/hyperlipidemia is accompanied by hormonal and neurochemical changes that can lead to depression. The important roles of gut-derived serotonin (5-Hydroxytryptamine, 5-HT) during this processing have been increasingly focused. Hence, to determine the potential role of gut-derived serotonin, HFD model was established in C57BL/6 mice. At the 4th week of feeding, a pharmacologic inhibitor of gut-derived 5-HT synthesis LP533401 (12.5 mg/kg/day), simvastatin (SIM) (5 mg/kg/day) and benzafibrate (BZ) (75 mg/kg/day) were administered for two weeks by oral gavage. Then, intraperitoneal glucose tolerance test (IPGTT), open field test (OFT), tail suspension test (TST), forced swim test (FST), sucrose preference test (SPT) were used to evaluate metabolic and neurobehavioral performances. Immunohistochemical staining, real-time quantitative PCR and other methods were to explore possible mechanisms. It was found that HFD feeding and drug treatments had some significant effects on neurobehaviors and brain: (1) All administrations reduced the total cholesterol (TC) and triglyceride (TG) parametric abnormality caused by HFD. LP533401 and SIM could significantly improve the impaired glucose tolerance, while BZ had no significant effect. (2) LP533401, SIM and BZ alleviated depression-like behavior of HFD mice in OFT, TST, FST and SPT. (3) LP533401 and SIM reversed the inhibition of Tryptophan Hydroxylase 2, Tph2 gene expression and the activation of Indoleamine 2,3-dioxy-Genase, IDO expression in HFD-treated brain, whereas BZ did not. (4) LP533401, SIM and BZ restored the inhibitory expression of 5-HT_1A receptor in HFD hippocampus. Conclusions: Selective inhibition of intestinal 5-HT can attenuate depressive-like behavior, reduce 5-HT_1AR impairment in hippocampus and correct abnormal 5-HT pathway in brain while ameliorating HFD-induced glucose intolerance. Further experiments are warranted to define the adequate strategy of targeting peripheral 5-HT for the treatment of such co-morbidity.

The Adipocyte Na/K-ATPase Oxidant Amplification Loop is the Central Regulator of Western Diet-Induced Obesity and Associated Comorbidities

Obesity has become a worldwide epidemic. We have previously reported that systemic administration of pNaKtide which targets the Na/K-ATPase oxidant amplification loop (NKAL) was able to decrease systemic oxidative stress and adiposity in mice fed a high fat and fructose supplemented western diet (WD). As adipocytes are believed to play a central role in the development of obesity and its related comorbidities, we examined whether lentiviral-mediated adipocyte-specific expression of NaKtide, a peptide derived from the N domain of the alpha1 Na/K-ATPase subunit, could ameliorate the effects of the WD. C57BL6 mice were fed a WD, which activated Na/K-ATPase signaling in the adipocytes and induced an obese phenotype and caused an increase in plasma levels of leptin, IL-6 and TNFα. WD also decreased locomotor activity, expression of the D2 receptor and tyrosine hydroxylase in brain tissue, while markers of neurodegeneration and neuronal apoptosis were increased following the WD. Selective adipocyte expression of NaKtide in these mice fed a WD attenuated all of these changes including the brain biochemical alterations and behavioral adaptations. These data suggest that adipocyte derived cytokines play an essential role in the development of obesity induced by a WD and that targeting the adipocyte NKAL loop may serve as an effective therapeutic strategy.

Nutritional Modulation of Immune and Central Nervous System Homeostasis: The Role of Diet in Development of Neuroinflammation and Neurological Disease

The gut-microbiome-brain axis is now recognized as an essential part in the regulation of systemic metabolism and homeostasis. Accumulating evidence has demonstrated that dietary patterns can influence the development of metabolic alterations and inflammation through the effects of nutrients on a multitude of variables, including microbiome composition, release of microbial products, gastrointestinal signaling molecules, and neurotransmitters. These signaling molecules are, in turn, implicated in the regulation of the immune system, either promoting or inhibiting the production of pro-inflammatory cytokines and the expansion of specific leukocyte subpopulations, such as Th17 and Treg cells, which are relevant in the development of neuroinflammatory and neurodegenerative conditions. Metabolic diseases, like obesity and type 2 diabetes mellitus, are related to inadequate dietary patterns and promote variations in the aforementioned signaling pathways in patients with these conditions, which have been linked to alterations in neurological functions and mental health. Thus, maintenance of adequate dietary patterns should be an essential component of any strategy aiming to prevent neurological pathologies derived from systemic metabolic alterations. The present review summarizes current knowledge on the role of nutrition in the modulation of the immune system and its impact in the development of neuroinflammation and neurological disease.

Access to a high resource environment protects against accelerated maturation following early life stress: A translational animal model of high, medium and low security settings

Early life exposure to a low security setting, characterized by a scarcity of resources and limited food access, increases the risk for psychiatric illness and metabolic dysfunction. We utilized a translational rat model to mimic a low security environment and determined how this manipulation affected offspring behavior, metabolism, and puberty. Because food insecurity in humans is associated with reduced access to healthy food options the "low security" rat manipulation combined a Western diet with exposure to a limited bedding and nesting manipulation (WD-LB). In this setting, dams were provided with limited nesting materials during the pups' early life (P2-P10). This manipulation was contrasted with standard rodent caging (SD) and environmental enrichment (EE), to model "medium security" and "high security" environments, respectively. To determine if transitioning from a low to high security environment improved outcomes, some juvenile WD-LB offspring were exposed to EE. Maternal care was impacted by these environments such that EE dams engaged in high quality care when on the nest, but spent less time on the nest than SD dams. Although WD-LB dams excessively chased their tails, they were very attentive to their pups, perhaps to compensate for limited resources. Offspring exposed to WD-LB only displayed subtle changes in behavior. However, WD-LB exposure resulted in significant metabolic dysfunction characterized by increased body weight, precocious puberty and alterations in the hypothalamic kisspeptin system. These negative effects of WD-LB on puberty and weight regulation were mitigated by EE exposure. Collectively, these studies suggest that both compensatory maternal care and juvenile enrichment can reduce the impact of a low security environment. Moreover, they highlight how utilizing diverse models of resource (in)stability can reveal mechanisms that confer vulnerability and resilience to early life stress.

Impacts of the late adulthood diet-induced obesity onset on behavior, immune function, redox state and life span of male and female mice

The aim of the present study was to investigate whether the late onset of diet-induced obesity (DIO) in middle-aged mice affected behavioral, immunological and oxidative stress parameters as well as life span of male and female mice. Also, it was analyzed whether the late DIO onset aggravated immunosenescence in old female mice. Late-adult male and female ICR/CD1 mice (28 weeks old) were fed either a high-fat diet or a standard diet during 14 weeks. After that, in these middle-aged (42 weeks old) diet-induced obese (DIO) and non-DIO controls, behavior as well as functions and redox state of peritoneal leukocytes were evaluated. These same parameters (excepting behavioral tests) were repeated when female mice were old (72 weeks old). The results showed lower exploratory activity and higher anxiety-like behavior in middle-aged male and female DIO than in controls. Moreover, these DIO animals from both sexes exhibited statistically significant impaired immune cell functions, such as chemotaxis of macrophages and lymphocytes, phagocytosis of macrophages, natural killer activity and lymphoproliferation in response to ConA and LPS, as well as an oxidative stress state in comparison with controls. Male DIO mice exhibited higher impairments in a variety of the evaluated parameters and a shorter life span than their female counterparts. In addition, female DIO mice, at old age, showed aggravated immunosenescence. In conclusion, the late DIO onset leads to impairments in behavior as well as in immune system functions of middle-aged male and female mice, males being significantly more affected than females.

The antidepressant effects of hesperidin on chronic unpredictable mild stress-induced mice

Hesperidin, a kind of citrus bioflavonoid distributed in foods including grapefruits, oranges and lemons, has many pharmacological activities. This study was aimed to evaluate the anti-depressant-like effect of hesperidin on chronic unpredictable mild stress (CUMS)-induced mice. Depressive-like behavior was detected by the sucrose preference test (SPT), tail suspension test (TST) and forced swimming test (FST). A 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay was performed to assess the cell viability of corticosterone-induced PC12 cells. The serum, hippocampal and cell supernatant concentrations of interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α were determined using enzyme-linked immunosorbent assay (ELISA) commercial kits. Furthermore, the protein expression levels of high-mobility group box 1 protein (HMGB1), receptor for advanced glycation end-products (RAGE)/NF-κB and brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) pathway in the hippocampus and corticosterone-induced PC12 cells were detected by Western blot. Our results showed that hesperidin (100, 200 mg/kg) significantly relieved depressive-like behaviors, including decreased sucrose consumption in sucrose preference test (SPT), immobility in the forced swimming test (FST), tail suspension test, and locomotor activity in the open field test (OFT). Hesperidin reduced inflammatory cytokine levels by attenuating the HMGB1/RAGE/NF-κB signaling pathway and BDNF/TrkB pathway both in vivo and in vitro. In conclusion, hesperidin possessed efficient neuroprotective effects on depression, which was associated with neuroinflammation mediated by the HMGB1/RAGE/NF-κB and BDNF/TrkB pathways.

Environmental Impoverishment, Aging, and Reduction in Mastication Affect Mouse Innate Repertoire to Explore Novel Environments and to Assess Risk

Studies indicate that inhibition of adequate masticatory function, due to soft diet, occlusal disharmony, or molar losses affects the cognitive behavior of rodents. However, no study has tested the effects on new environments exploration and risk assessment coupled with a combination of masticatory function rehabilitation and environmental enrichment. In the present report, we tested the hypothesis that age, environment, and masticatory changes may interact and alter exploratory patterns of locomotor activity and mice preferences in an open field (OF) arena. As OF arenas are widely used to measure anxiety-like behavior in rats and mice. We examined in an open arena, the exploratory and locomotor activities of mature (6-month-old; 6M), late mature (12-month-old; 12M), and aged (18-month-old; 18M) mice, subjected to distinct masticatory regimens and environments. Three different regimens of masticatory activity were used: continuous normal mastication with hard pellets (HD); normal mastication followed by reduced mastication with equal periods of pellets followed by soft powder – HD/SD; or rehabilitated masticatory activity with equal periods of HD, followed by powder, followed by pellets – HD/SD/HD). Under each diet regimen, half of the individuals were raised in standard cages [impoverished environment (IE)] and the other half in enriched cages [enriched environment (EE)]. Animals behavior on the open field (OF) task were recorded by webcam and analyzed with Any Maze software (Stöelting). The locomotor and exploratory activities in OF task declined with age, and this was particularly evident in 18M HD EE mice. Although all groups kept their preference by the peripheral zone, the outcomes were significantly influenced by interactions between environment, age, and diet. Independent of diet regime, 6M young mice maintained in an EE where voluntary exercise apparatus is available, revealed significant less body weight than all other groups. Although body weight differences were minimized as age progressed, 18M EE group revealed intragroup significant influence of diet regimens. We suggest that long life environmental enrichment reduces the tendency to avoid open/lit spaces (OF) and this is particularly influenced by masticatory activity. These measurements may be useful in discussions of anxiety-related tasks.

Brain tumor necrosis factor-α mediates anxiety-like behavior in a mouse model of severe obesity

Although the high prevalence of anxiety in obesity increasingly emerges as significant risk factor for related severe health complications, the underlying pathophysiological mechanisms remain poorly understood. Considering that chronic inflammation is a key component of obesity and is well known to impact brain function and emotional behavior, we hypothesized that it may similarly contribute to the development of obesity-related anxiety. This hypothesis was experimentally tested by measuring whether chronic food restriction, a procedure known to reduce inflammation, or chronic anti-inflammatory treatment with ibuprofen improved anxiety-like behavior and concomitantly decreased peripheral and/or hippocampal inflammation characterizing a model of severe obesity, the db/db mice. In both experiments, reduced anxiety-like behaviors in the open-field and/or elevated plus-maze were selectively associated with decreased hippocampal tumor necrosis factor-α (TNF-α) mRNA expression. Highlighting the causality of both events, chronic central infusion of the TNF-α blocker etanercept was then shown to be sufficient to improve anxiety-like behavior in db/db mice. Lastly, by measuring the impact of ex-vivo etanercept on hippocampal synaptic processes underlying anxiety-like behaviors, we showed that the anxiolytic effect of central TNF-α blockade likely involved modulation of synaptic transmission within the ventral hippocampus. Altogether, these results uphold the role of brain TNF-α in mediating obesity-related anxiety and provide important clues about how it may modulate brain function and behavior. They may therefore help to introduce novel therapeutic strategies to reduce anxiety associated with inflammatory conditions.

Ameliorative effect of fisetin against lipopolysaccharide and restraint stress-induced behavioral deficits via modulation of NF-κB and IDO-1

BACKGROUND

Fisetin, a plant active polyphenol, is well known for its antioxidant and free radical scavenging activities. The present study was designed to explore the detailed molecular mechanism underlying its neuroprotective effects.

METHODS

The young male mice were either administered a single dose of lipopolysaccharide (0.83 mg/kg) or subjected to restraint stress (6 h per day for 28 days) to induce behavioral deficits in different groups. Fisetin (15 mg/kg) was orally administered for the last 14 days of the study.

RESULTS

Lipopolysaccharide (LPS) as well as restraint stress (RS) exposure caused behavioral alterations (anxiety and depressive-like behavior). Gene expression analysis showed upregulation of nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB) and indoleamine 2,3-dioxygenase (IDO)-1 gene expression along with downregulation of Nrf-2 (nuclear factor erythroid 2-related factor 2), HO-1 (heme oxygenase-1), and ChAT (choline acetyltransferase) gene expression level in RS and RS+LPS groups. Fisetin administration significantly ameliorated behavioral and neurochemical deficits in LPS, RS, and RS+LPS groups.

CONCLUSION

These findings clearly indicated that fisetin administration improved behavioral functions and suppressed the NF-κB and IDO-1 (indoleamine 2,3-dioxygenase) activation along with their antioxidant effect, suggesting fisetin as an intriguing nutraceutical for the management of inflammation-associated neurological disorders.

FoxO1 regulates leptin-induced mood behavior by targeting tyrosine hydroxylase

PURPOSE

While leptin has been associated with various psycho-physiological functions, the molecular network in leptin-mediated mood regulation remains elusive.

METHODS

Anxiolytic behaviors and tyrosine hydroxylase (TH) levels were examined after leptin administration. Functional roles of STAT3 and FoxO1 in regulation of TH expression were investigated using in vivo and in vitro systems. A series of animal behavioral tests using dopaminergic neuron-specific FoxO1 KO (FoxO1 KO^DAT) were performed and investigated the roles of FoxO1 in regulation of mood behaviors.

RESULTS

Here, we show that administration of leptin induces anxiolytic-like phenotype through the activation of signal transducer and activator of transcription 3 (STAT3) and the inhibition of forkhead box protein O1 (FoxO1) in dopaminergic (DA) neurons of the midbrain. Specifically, STAT3 and FoxO1 directly bind to and exert opposing effects on tyrosine hydroxylase (TH) expression, where STAT3 acts as an enhancer and FoxO1 acts as a prominent repressor. Accordingly, suppression of the prominent suppressor FoxO1 by leptin strongly increased TH expression. Furthermore, our previous results showed that specific deletion of FoxO1 in DA neurons (FoxO1 KO^DAT) led to a profound elevation of TH activity and dopamine contents. Finally, FoxO1 KO^DAT mice exhibited enhanced leptin sensitivity as well as displayed reduced anxiety- and depression-like behaviors.

CONCLUSIONS

This work establishes a novel molecular mechanism of mood behavior regulation by leptin and suggests FoxO1 suppression by leptin might be a key for leptin-induced behavioral manifestation in DA neurons.