Diet-induced insulin resistance impairs hippocampal synaptic plasticity and cognition in middle-aged rats

The potential roles of excitatory-inhibitory imbalances and the repressor element-1 silencing transcription factor in aging and aging-associated diseases

Disruptions to the central excitatory-inhibitory (E/I) balance are thought to be related to aging and underlie a host of neural pathologies, including Alzheimer's disease. Aging may induce an increase in excitatory signaling, causing an E/I imbalance, which has been linked to shorter lifespans in mice, flies, and worms. In humans, extended longevity correlates to greater repression of genes involved in excitatory neurotransmission. The repressor element-1 silencing transcription factor (REST) is a master regulator in neural cells and is believed to be upregulated with senescent stimuli, whereupon it counters hyperexcitability, insulin/insulin-like signaling pathway activity, oxidative stress, and neurodegeneration. This review examines the putative mechanisms that distort the E/I balance with aging and neurodegeneration, and the putative roles of REST in maintaining neuronal homeostasis.

Palatable high-fat diet intake influences mnemonic and emotional aspects in female rats in an estrous cycle-dependent manner

Worldwide, the excessive consumption of fat and/or sugar has increased considerably. Palatable high-fat diets (HFDs) lead to metabolic disturbances and obesity, and impact emotional and cognitive processes. Previous studies in rodent models suggested that HFDs often cause multiple behavioral alterations, such as learning and memory deficits, and anxiety-like behaviors. Different sexes imply different behavioral and cognitive abilities; yet, most of these studies dealt with male or ovariectomized rats. We evaluated HFD effects in female rats submitted to different behavioral tasks, considering the effects of endogenous hormonal variations throughout estrous cycle. Female Wistar rats in each phase of the estrous cycle using commercial chow (CC) or HFD for 32 days. During treatment, behavioral assessments using sucrose preference (SP), elevated plus-maze (EPM), open field (OF) and novel-object recognition (NOR). At the end of the behavioral tests, animals were euthanized, and performed an immunohistochemical analysis of the brains by brain-derived neurotrophic factor (BDNF) and tyrosine hydroxylase (TH). The main results demonstrated that (1) HFD-fed rats had higher body mass gain and food intake, without altering caloric intake, (2) rats in diestrus had lower sucrose intake, (3) females in metestrus and diestrus showed deficits in the novel-object recognition memory. Furthermore, TH-immunoreactivity decreased in the dorsal striatum and BDNF in the hippocampus in HFD-fed females. These results suggest that HFD alters neurochemical and metabolic aspects that may induce phase-dependent behavioral changes in female rats.

Long-term diet-induced obesity does not lead to learning and memory impairment in adult mice

Obesity arising from excessive dietary fat intake is a risk factor for cognitive decline, dementia and neurodegenerative diseases, including Alzheimer’s disease. Here, we studied the effect of long-term high-fat diet (HFD) (24 weeks) and return to normal diet (ND) on behavioral features, microglia and neurons in adult male C57BL/6J mice. Consequences of HFD-induced obesity and dietary changes on general health (coat appearance, presence of vibrissae), sensory and motor reflexes, learning and memory were assessed by applying a phenotypic assessment protocol, the Y maze and Morris Water Maze test. Neurons and microglia were histologically analyzed within the mediobasal hypothalamus, hippocampus and frontal motor cortex after long-term HFD and change of diet. Long periods of HFD caused general health issues (coat alterations, loss of vibrissae), but did not affect sensory and motor reflexes, emotional state, memory and learning. Long-term HFD increased the microglial response (increased Iba1 fluorescence intensity, percentage of Iba1-stained area and Iba1 gene expression) within the hypothalamus, but not in the cortex and hippocampus. In neither of these regions, neurodegeneration or intracellular lipid droplet accumulation was observed. The former alterations were reversible in mice whose diet was changed from HFD to ND. Taken together, long periods of excessive dietary fat alone do not cause learning deficits or spatial memory impairment, though HFD-induced obesity may have detrimental consequences for cognitive flexibility. Our data confirm the selective responsiveness of hypothalamic microglia to HFD.

Crème de la Créature: Dietary Influences on Behavior in Animal Models

In humans, alterations in cognitive, motivated, and affective behaviors have been described with consumption of processed diets high in refined sugars and saturated fats and with high body mass index, but the causes, mechanisms, and consequences of these changes remain poorly understood. Animal models have provided an opportunity to answer these questions and illuminate the ways in which diet composition, especially high-levels of added sugar and saturated fats, contribute to brain physiology, plasticity, and behavior. Here we review findings from invertebrate (flies) and vertebrate models (rodents, zebrafish) that implicate these diets with changes in multiple behaviors, including eating, learning and memory, and motivation, and discuss limitations, open questions, and future opportunities.

Altered Brain Cholinergic and Synaptic Markers in Obese Zucker Rats

The association between obesity and loss of cognitive performance has been recognized. Although there are data regarding the metabolic alterations in obese conditions and the development of neuroinflammation, no clear evidence concerning obesity-related cholinergic and synaptic impairments in the frontal cortex and hippocampus has been reported yet. Here, we investigate different cholinergic and synaptic markers in 12-, 16-, and 20-week-old obese Zucker rats (OZRs) compared with lean littermate rats (LZRs), using immunochemical and immunohistochemical analysis. Consequently, OZRs showed body weight gain, hypertension, and dysmetabolism. In 20-week-old OZRs, the reduction of vesicular acetylcholine transporter (VAChT) and alpha7 nicotinic acetylcholine receptors (α7nAChR) occurred both in the frontal cortex and in the hippocampus, suggesting a cognitive dysfunction due to obesity and aging. Among the muscarinic receptors analyzed, the level of expression of type 1 (mAChR1) was lower in the hippocampus of the older OZRs. Finally, we showed synaptic dysfunctions in OZRs, with a reduction of synaptophysin (SYP) and synaptic vesicle glycoprotein 2B (SV2B) in 20-week-old OZRs, both in the frontal cortex and in the hippocampus. Taken together, our data suggest specific alterations of cholinergic and synaptic markers that can be targeted to prevent cognitive deficits related to obesity and aging.

Effects of apolipoprotein E isoform, sex, and diet on insulin BBB pharmacokinetics in mice

Age, apolipoprotein E (apoE) isoform, sex, and diet can independently affect the risk for the development of Alzheimer’s disease (AD). Additionally, synergy between some of these risk factors have been observed. However, the relation between the latter three risk factors has not been investigated. Central nervous system (CNS) insulin resistance is commonly involved in each of these risk factors. CNS insulin is primarily derived from the periphery in which insulin must be transported across the blood–brain barrier (BBB). Additionally, insulin can bind the brain endothelial cell to affect intracellular signaling. Therefore, we hypothesized CNS access to insulin could be affected by the combination of apoE isoform, sex, and diet. We analyzed insulin BBB pharmacokinetics in aged apoE targeted replacement (E3 and E4) male and female mice on a low-fat and high-fat diet. There were differences within males and females due to apoE genotype and diet in insulin interactions at the BBB. These sex-, diet-, and apoE isoform-dependent differences could contribute to the cognitive changes observed due to altered CNS insulin signaling.

Influence of HFD-induced precocious puberty on neurodevelopment in mice

BACKGROUND

Precocious puberty is frequently associated with obesity, which will lead to long-term effects, especially on growth and reproduction. However, the effect of precocious puberty on children's neurodevelopment is still unknown.

OBJECTIVES

Here we evaluated the effect of High fat diet (HFD)-induced precocious puberty on neurodevelopment and behaviors of animals.

METHODS

Ovaries sections were stained with hematoxylin-eosin (H&E) using standard techniques. Behavioral tests included elevated plus maze (EPM), open field exploration, Y-Maze, marble burying test, and novelty- suppressed feeding. The expression of genes related to puberty and neural development was detected by immunohistochemistry and Western blot.

RESULTS

Our results showed HFD-induced precocious puberty increased the risk-taking behavior and decreased memory of mice. The content of Tyrosine hydroxylase (TH) and Arginine vasopressin (AVP) in hypothalamus were higher in HFD group than control group. Although the recovery of normal diet will gradually restore the body fat and other physiological index of mice, the anxiety increases in adult mice, and the memory is also damaged.

CONCLUSIONS

These findings describe the sensitivity of mice brain to HFD-induced precocious puberty and the irrecoverability of neural damage caused by precocious puberty. Therefore, avoiding HFD in childhood is important to prevent precocious puberty and neurodevelopmental impairment in mice.

Effects of short-term exposure to genistein and overfeeding diet on the neural and retinal progenitor competence of adult zebrafish (Danio rerio)

Neurogenesis is a process that occurs throughout the life of a vertebrate. Among the different factors that may affect the natural occurrence of neurogenesis, obesity seems to decrease the proliferation capacity of progenitor neuronal cells. Conversely, the phytoestrogen genistein is known to attenuate some obesity effects beyond its neuroprotective action. Aiming to improve the understanding of how obesity and genistein trigger an impact on the neural and retinal progenitor competence of adult zebrafish, fish were exposed to genistein (GEN - 2 μg L^-1) alone or combined with two dietary groups (control and overfeed - OFD) for up to 9 weeks. Zebrafish were fed once per day with Artemia sp. in the control and GEN (2% of BW, control diet), and three times per day in the OFD and OFD + GEN groups (12% BW, overfeeding diet). To assess obesity induction, BMI, biometric parameters, and PPAR-γ protein were quantified. Afterwards, qRT-PCR and immunohistochemistry were performed to determine the cell proliferation and the presence of stem cells through PCNA and Sox-2. Our findings proved that overfeeding adult zebrafish increased the general growth and induced the development of fatty liver. However, for OFD + GEN, this effect was assuaged through the anti-adipogenic effect of GEN. This finding suggests that phytoestrogens could be beneficial to reduce the negative effects of obesity. Moreover, OF induced negative effects on retinal and brain homeostasis, decreasing the proliferation capacity of progenitor neuronal cells. With regard to retinal progenitor competence, genistein seems to mitigate the negative impacts of obesity, whereas the effects of obesity on the brain were exacerbated by this phytoestrogen which negatively influenced the homeostasis of zebrafish neural progenitor competence. This study highlighted the fact that the effects of phytoestrogens in adult neural progenitor competence are complex and could exhibit dissimilar effects depending on the tissue.

Blood-Brain Barrier Breakdown: An Emerging Biomarker of Cognitive Impairment in Normal Aging and Dementia

The blood–brain barrier (BBB) plays a vital role in maintaining the specialized microenvironment of the neural tissue. It separates the peripheral circulatory system from the brain parenchyma while facilitating communication. Alterations in the distinct physiological properties of the BBB lead to BBB breakdown associated with normal aging and various neurodegenerative diseases. In this review, we first briefly discuss the aging process, then review the phenotypes and mechanisms of BBB breakdown associated with normal aging that further cause neurodegeneration and cognitive impairments. We also summarize dementia such as Alzheimer's disease (AD) and vascular dementia (VaD) and subsequently discuss the phenotypes and mechanisms of BBB disruption in dementia correlated with cognition decline. Overlaps between AD and VaD are also discussed. Techniques that could identify biomarkers associated with BBB breakdown are briefly summarized. Finally, we concluded that BBB breakdown could be used as an emerging biomarker to assist to diagnose cognitive impairment associated with normal aging and dementia.

Short-term high-fat diet induces cognitive decline, aggression, and anxiety-like behavior in adult zebrafish

Obesity is a global health problem with high prevalence and defined by a high body mass index (BMI). Several comorbidities affecting the central nervous system (CNS) are associated with obesity (e.g., neurodegenerative diseases, cognitive deficit, and psychobehavioral disturbs). The zebrafish (Danio rerio) has been considered a suitable model organism to investigate the neurobehavioral features of various human diseases. Here, we verify the impact of a high-fat diet (HFD) on the CNS by specifically assessing the effects of short-term HFD on anxiety-like responses, aggression, social preference, and memory, which are essential behaviors for survival and reproduction. Animals were separated in three experimental groups. The standard diet group (SD) received 7.5 mg/fish of dry food, while HFD groups received 5 mg/fish dry food plus 7.5 (HFD-7.5) or 15 mg/fish (HFD-15) of chicken egg yolk daily. Dietary fat content (w/w) was approximately 6.5%, 16.9%, and 21.1%, respectively. We performed behavioral tests and morphometric analyses after two weeks of HFD. In comparison to SD animals, HFD groups showed typical obesogenic responses with increases in BMI, abdominal length, and body weight. HFD individuals also showed increased aggression and anxiety-like behaviors in the mirror-induced aggression and novel tank diving tests, respectively. Interestingly, HFD did not change the social preference behavior, mean swimming speed or spontaneous activity levels, while the HFD-15 group showed cognitive deficits in the inhibitory avoidance test. Collectively, this "proof-of-concept" study is the first report to characterize the effects of short-term HFD on different behavioral domains of zebrafish with high degree of face validity. Moreover, our data reinforce the growing utility of zebrafish to explore the neurobehavioral basis of obesity, providing clinically translatable data, complementing the existing rodent models and supporting future mechanistic studies.

The impact of saturated fat, added sugar and their combination on human hippocampal integrity and function: A systematic review and meta-analysis

Paralleling animal research, there is emerging evidence that a Western-style (WS) diet - high in saturated fat and added sugar - impairs human hippocampal functioning. However, the conditions under which this occurs are not fully understood and there have been published failures to detect such effects. To date, there has been no systematic review or meta-analysis of relevant human studies. We undertook a systematic database search and review. Twenty studies were identified, two experimental, with the remainder correlational. The latter were included in a meta-analyses on the impact of WS-diet and its macronutrient components on human hippocampal function. Effects of age and sex were also examined. A WS-diet adversely impacted human hippocampal volume and functioning, with a small-pooled effect size. No effects were found for individual macronutrients. There was a high-level of study heterogeneity, which was not fully explained by study/sample characteristics. This may arise via the wide range of assessment tools used to measure both dietary intake and hippocampal functioning. Overall, a WS-diet clearly impacts human hippocampal functioning as in animals.

Of 'junk food' and 'brain food': how parental diet influences offspring neurobiology and behaviour

Unhealthy lifestyles and mental health problems are increasingly prevalent globally. Not only are 'junk food'-induced overweight and obesity risk factors for the development of brain disorders but they are also associated intergenerationally with ill health. Here, we reflect on the current knowledge of how maternal and paternal diet influences offspring brain development and behaviour, potentially predisposing children to mental health problems. Mounting evidence indicates diet-induced maternal and paternal programming of infant metabolism and neurobehavioural function, with potential downstream effects on mental health and resilience. Beyond the central nervous system (CNS), the microbiota-gut-brain axis has emerged as an important mediator of host physiology. We discuss how intergenerational seeding of the gut microbiome via parental lineage can influence offspring gut health and neurobiology.

High fat diet and its effects on cognitive health: alterations of neuronal and vascular components of brain

It has been well recognized that intake of diets rich in saturated fats could result in development of metabolic disorders such as type 2 diabetes mellitus, obesity and cardiovascular diseases. Recent studies have suggested that intake of high fat diet (HFD) is also associated with cognitive dysfunction. Various preclinical studies have demonstrated the impact of short and long term HFD feeding on the biochemical and behavioural alterations. This review summarizes studies and the protocols used to assess the impacts of HFD feeding on cognitive performance in rodents. Further, it discuss the key mechanisms that are altered by HFD feeding, such as, insulin resistance, oxidative stress, neuro-inflammation, transcriptional dysregulation and loss of synaptic plasticity. Along with these, HFD feeding also alters the vascular components of brain such as loss of BBB integrity and reduced cerebral blood flow. It is highly possible that these factors are responsible for the development of cognitive deficits as a result of HFD feeding.

The Impact of Obesity on Microglial Function: Immune, Metabolic and Endocrine Perspectives

Increased life expectancy in combination with modern life style and high prevalence of obesity are important risk factors for development of neurodegenerative diseases. Neuroinflammation is a feature of neurodegenerative diseases, and microglia, the innate immune cells of the brain, are central players in it. The present review discusses the effects of obesity, chronic peripheral inflammation and obesity-associated metabolic and endocrine perturbations, including insulin resistance, dyslipidemia and increased glucocorticoid levels, on microglial function.

Long-Term Overconsumption of Sugar Starting at Adolescence Produces Persistent Hyperactivity and Neurocognitive Deficits in Adulthood

Sugar has become embedded in modern food and beverages. This has led to overconsumption of sugar in children, adolescents, and adults, with more than 60 countries consuming more than four times (>100 g/person/day) the WHO recommendations (25 g/person/day). Recent evidence suggests that obesity and impulsivity from poor dietary habits leads to further overconsumption of processed food and beverages. The long-term effects on cognitive processes and hyperactivity from sugar overconsumption, beginning at adolescence are not known. Using a well-validated mouse model of sugar consumption, we found that long-term sugar consumption, at a level that significantly augments weight gain, elicits an abnormal hyperlocomotor response to novelty and alters both episodic and spatial memory. Our results are similar to those reported in attention deficit and hyperactivity disorders. The deficits in hippocampal-dependent learning and memory were accompanied by altered hippocampal neurogenesis, with an overall decrease in the proliferation and differentiation of newborn neurons within the dentate gyrus. This suggests that long-term overconsumption of sugar, as that which occurs in the Western Diet might contribute to an increased risk of developing persistent hyperactivity and neurocognitive deficits in adulthood.

Towards development of a novel screening method for identifying Alzheimer's disease risk: Raman spectroscopy of blood serum and machine learning

There is an urgent clinical need for a fast and effective method for diagnosing Alzheimer's disease (AD). The identification of AD in its most initial stages, at which point treatment could provide maximum therapeutic benefits, is not only likely to slow down disease progression but to also potentially provide a cure. However, current clinical detection is complicated and requires a combination of several methods based on significant clinical manifestations due to widespread neurodegeneration. As such, Raman spectroscopy with machine learning is investigated as a novel alternative method for detecting AD in its earliest stages. Here, blood serum obtained from rats fed either a standard diet or a high-fat diet was analyzed. The high-fat diet has been shown to initiate a pre-AD state. Partial least squares discriminant analysis combined with receiver operating characteristic curve analysis was able to separate the two rat groups with 100% accuracy at the donor level during external validation. Although further work is necessary, this research suggests there is a potential for Raman spectroscopy to be used in the future as a successful method for identifying AD early on in its progression, which is essential for effective treatment of the disease.

Blood lipid markers are associated with hippocampal viscoelastic properties and memory in humans

Age-related memory loss shares similar risk factors as cardiometabolic diseases including elevated serum triglycerides (TGs) and low-density lipoprotein cholesterol (LDL-C) and reduced high-density lipoprotein cholesterol (HDL-C). The mechanisms linking these aberrant blood lipids to memory loss are not completely understood but may be partially mediated by reduced integrity of the hippocampus (HC), the primary brain structure for encoding and recalling memories. In this study, we tested the hypothesis that blood lipid markers are independently associated with memory performance and HC viscoelasticity-a noninvasive measure of brain tissue microstructural integrity assessed by high-resolution magnetic resonance elastography (MRE). Twenty-six individuals across the adult lifespan were recruited (14 M/12 F; mean age: 42 ± 15 y; age range: 22-78 y) and serum lipid profiles were related to episodic memory and HC viscoelasticity. All subjects were generally healthy without clinically abnormal blood lipids or memory loss. Episodic memory was negatively associated with the TG/HDL-C ratio. HC viscoelasticity was negatively associated with serum TGs and the TG/HDL-C ratio, independent of age and in the absence of associations with HC volume. These data, although cross-sectional, suggest that subtle differences in blood lipid profiles in healthy adults may contribute to a reduction in memory function and HC tissue integrity.

Ablation of dynamin-related protein 1 promotes diabetes-induced synaptic injury in the hippocampus

Dynamin-related protein 1 (Drp1)-mediated mitochondrial dysfunction is associated with synaptic injury in the diabetic brain. However, the dysfunctional mitochondria by Drp1 deletion in the diabetic brain are poorly understood. Here, we investigated the effects of neuron-specific Drp1 deletion on synaptic damage and mitophagy in the hippocampus of a high-fat diet (HFD)/streptozotocin (STZ)-induced diabetic mice. HFD/STZ-induced diabetic mice exhibited metabolic disturbances and synaptic damages. Floxed Drp1 mice were crossed with Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα)-Cre mice, to generate neuron-specific Drp1 knockout (Drp1cKO) mice, which showed marked mitochondrial swelling and dendritic spine loss in hippocampal neurons. In particular, diabetic Drp1cKO mice exhibited an increase in dendritic spine loss and higher levels of oxidative stress and neuroinflammation compared with diabetic wild-type (WT) mice. Diabetic WT mice generally displayed increased Drp1-induced small mitochondrial morphology in hippocampal neurons, but large mitochondria were prominently observed in diabetic Drp1cKO mice. The levels of microtubule-associated protein 1 light-chain 3 and lysosomal-associated membrane protein 1 proteins were significantly increased in the hippocampus of diabetic Drp1cKO mice compared with diabetic WT mice. The inhibition of Drp1 adversely promotes synaptic injury and neurodegeneration in the diabetic brain. The findings suggest that the exploratory mechanisms behind Drp1-mediated mitochondrial dysfunction could provide a possible therapeutic target for diabetic brain complications.

Obesogenic Diets Cause Alterations on Proteins and Theirs Post-Translational Modifications in Mouse Brains

Obesity constitutes a major global health threat and is associated with a variety of diseases ranging from metabolic and cardiovascular disease, cancer to neurodegeneration. The hallmarks of neurodegeneration include oxidative stress, proteasome impairment, mitochondrial dysfunction and accumulation of abnormal protein aggregates as well as metabolic alterations. As an example, in post-mortem brain of patients with Alzheimer’s disease (AD), several studies have reported reduction of insulin, insulin-like growth factor 1 and insulin receptor and an increase in tau protein and glycogen-synthase kinase-3β compared to healthy controls suggesting an impairment of metabolism in the AD patient’s brain. Given these lines of evidence, in the present study we investigated brains of mice treated with 2 obesogenic diets, high-fat diet (HFD) and high-glycaemic diet (HGD), compared to mice fed with a standard diet (SD) employing a quantitative mass spectrometry-based approach. Moreover, post-translational modified proteins (phosphorylated and N-linked glycosylated) were studied. The aim of the study was to identify proteins present in the brain that are changing their expression based on the diet given to the mice. We believed that some of these changes would highlight pathways and molecular mechanisms that could link obesity to brain impairment. The results showed in this study suggest that, together with cytoskeletal proteins, mitochondria and metabolic proteins are changing their post-translational status in brains of obese mice. Specifically, proteins involved in metabolic pathways and in mitochondrial functions are mainly downregulated in mice fed with obesogenic diets compared to SD. These changes suggest a reduced metabolism and a lower activity of mitochondria in obese mice. Some of these proteins, such as PGM1 and MCT1 have been shown to be involved in brain impairment as well. These results might shed light on the well-studied correlation between obesity and brain damage. The results presented here are in agreement with previous findings and aim to open new perspectives on the connection between diet-induced obesity and brain impairment.

Catecholaminergic stimulation restores high-sucrose diet-induced hippocampal dysfunction

Increasing evidence suggests that long-term consumption of high-caloric diets increases the risk of developing cognitive dysfunctions. In the present study, we assessed the catecholaminergic activity in the hippocampus as a modulatory mechanism that is altered in rats exposed to six months of a high-sucrose diet (HSD). Male Wistar rats fed with this diet developed a metabolic disorder and showed impaired spatial memory in both water maze and object location memory (OLM) tasks. Intrahippocampal free-movement microdialysis showed a diminished dopaminergic and noradrenergic response to object exploration during OLM acquisition compared to rats fed with normal diet. In addition, electrophysiological results revealed an impaired long-term potentiation (LTP) of the perforant to dentate gyrus pathway in rats exposed to a HSD. Local administration of nomifensine, a catecholaminergic reuptake inhibitor, prior to OLM acquisition or LTP induction, improved long-term memory and electrophysiological responses, respectively. These results suggest that chronic exposure to HSD induces a hippocampal deterioration which impacts on cognitive and neural plasticity events negatively; these impairments can be ameliorated by increasing or restituting the affected catecholaminergic activity.

Western Diet Induces Impairment of Liver-Brain Axis Accelerating Neuroinflammation and Amyloid Pathology in Alzheimer's Disease

Alzheimer's disease (AD) is an aging-dependent, irreversible neurodegenerative disorder and the most common cause of dementia. The prevailing AD hypothesis points to the central role of altered cleavage of amyloid precursor protein (APP) and formation of toxic amyloid-β (Aβ) deposits in the brain. The lack of efficient AD treatments stems from incomplete knowledge on AD causes and environmental risk factors. The role of lifestyle factors, including diet, in neurological diseases is now beginning to attract considerable attention. One of them is western diet (WD), which can lead to many serious diseases that develop with age. The aim of the study was to investigate whether WD-derived systemic disturbances may accelerate the brain neuroinflammation and amyloidogenesis at the early stages of AD development. To verify this hypothesis, transgenic mice expressing human APP with AD-causing mutations (APPswe) were fed with WD from the 3rd month of age. These mice were compared to APPswe mice, in which short-term high-grade inflammation was induced by injection of lipopolysaccharide (LPS) and to untreated APPswe mice. All experimental subgroups of animals were subsequently analyzed at 4-, 8-, and 12-months of age. APPswe mice at 4- and 8-months-old represent earlier pre-plaque stages of AD, while 12-month-old animals represent later stages of AD, with visible amyloid pathology. Already short time of WD feeding induced in 4-month-old animals such brain neuroinflammation events as enhanced astrogliosis, to a level comparable to that induced by the administration of pro-inflammatory LPS, and microglia activation in 8-month-old mice. Also, WD feeding accelerated increased Aβ production, observed already in 8-month-old animals. These brain changes corresponded to diet-induced metabolic disorders, including increased cholesterol level in 4-months of age, and advanced hypercholesterolemia and fatty liver disease in 8-month-old mice. These results indicate that the westernized pattern of nourishment is an important modifiable risk factor of AD development, and that a healthy, balanced, diet may be one of the most efficient AD prevention methods.

Neuritin inhibits astrogliosis to ameliorate diabetic cognitive dysfunction

Earlier, it was shown that reversing the downregulation of neuritin expression in the brain improves central neuropathy in diabetic rats. We investigated the protective mechanism of neuritin in diabetic cognitive dysfunction via astrocytes. Further, the impact of the overexpression of neuritin in the cortex and the hippocampus on diabetic cognitive dysfunction and astrogliosis in type 2 diabetic (db/db) mice was assessed. Antagonists were used to inhibit the JAK2/STAT3 signaling pathway in U-118MG, an astrocyte cell line. Immunofluorescence, Western blotting, and real-time PCR were performed. Neuritin overexpression in the hippocampus of db/db mice significantly ameliorated cognitive dysfunction, hippocampal neuronal impairment, and synaptic plasticity deterioration, and inhibited astrogliosis and the JAK2/STAT3 signaling pathway in the hippocampus. Neuritin suppressed the JAK2/STAT3 signaling pathway to inhibit lipopolysaccharide-induced gliosis in U-118MG cells. It was observed that neuritin regulates the JAK2/STAT3 signaling pathway in astrocytes to inhibit astrogliosis and improve diabetic cognitive dysfunction.

Evaluation of the effectiveness of macaíba palm seed kernel (Acrocomia intumescens drude) on anxiolytic activity, memory preservation and oxidative stress in the brain of dyslipidemic rats

Macaíba palm seed kernel is a source of lipids and phenolic compounds. The objective of this study was to evaluate the effects of macaíba palm seed kernel on anxiety, memory, and oxidative stress in the brain of health and dyslipidemic rats. Forty rats were used, divided into 4 groups (n = 10 each): control (CONT), dyslipidemic (DG), kernel (KG), and Dyslipidemic kernel (DKG). Dyslipidemia was induced using a high fat emulsion for 14 days before treatment. KG and DKG received 1000 mg/kg of macaíba palm seed kernel per gavage for 28 days. After treatment, anxiety tests were carried out using the Open Field Test (OFT), Elevated Plus Maze (EPM), and the Object Recognition Test (ORT) to assess memory. In the animals’ brain tissue, levels of malondialdehyde (MDA) and total glutathione (GSH) were quantified to determine oxidative stress. The data were treated with Two Way ANOVA followed by Tukey (p <0.05). Results demonstrated that the animals treated with kernel realized more rearing. DG and KG groomed less compared with CONT and DKG compared with all groups in OFT. KG spent more time in aversive open arms compared with CONT and DKG compared with all groups in EPM. Only DKG spent more time in the central area in EMP. KG and DKG showed a reduction in the exploration rate and MDA values (p <0.05). Data showed that macaíba palm seed kernel consumption induced anxiolytic-like behaviour and decreased lipids peroxidation in rats’ brains. On the other hand, this consumption by healthy and dyslipidemic animals compromises memory.

The chemical chaperon 4-phenyl butyric acid restored high-fat diet- induced hippocampal insulin content and insulin receptor level reduction along with spatial learning and memory deficits in male rats

This study assessed the effect of a chronic high-fat diet (HFD) on plasma and hippocampal insulin and corticosterone levels, the hippocampus insulin receptor amount, and spatial learning and memory with or without receiving 4-phenyl butyric acid (4-PBA) in male rats. Rats were divided into high-fat and normal diet groups, then each group was subdivided into dimethyl sulfoxide (DMSO) and 4-PBA groups. After weaning, the rats were fed with HFD for 20 weeks. Then, 4-PBA or DMSO were injected for 3 days. Subsequently, oral glucose tolerance test was done. On the following day, spatial memory tests were performed. Then the hippocampus Bip, Chop, insulin, corticosterone, and insulin receptor levels were determined. HFD increased plasma glucose, leptin and corticosterone concentrations, hippocampus Bip, Chop and corticosterone levels, food intake, abdominal fat weight and body weight along with impaired glucose tolerance. It decreased plasma insulin, and insulin content, and its receptor amount in hippocampus. HFD lengthened escape latency and shortened the duration spent in target zone. 4-PBA administration improved the HFD- induced adverse changes. Chronic HFD possibly through the induction of endoplasmic reticulum (ER) stress and subsequent changes in the levels of hippocampal corticosterone, insulin and insulin receptor along with possible leptin resistance caused spatial learning and memory deficits.

Nutrition-based interventions for mood disorders

Introduction: 'Nutritional Psychiatry' is an emerging area of research that has great potential as an adjunctive tool for the prevention and treatment of diverse neuropsychiatric disorders. Several nutrition-related aspects, such as obesity, dietary patterns, gut microbiome composition and gut permeability, bioactive food compounds, and nutrients can influence pathways implicated in the pathophysiology of mood disorders.Areas covered: Here, the authors review the current evidence on nutrition-mood interaction and nutrition-based treatments for the two main mood disorders, i.e., major depressive disorder and bipolar disorder.Expert opinion: Consistent evidence from observational studies has pointed out the association between a 'healthy' diet, generally characterized by a higher intake of fruits, vegetables, legumes, nuts, whole grains, and good quality sources of protein (i.e. fish and/or seafood), and decreased risk of mood disorders and the parallel association between a 'Western' diet pattern and increased risk. However, only a few clinical trials have evaluated the effect of nutritional interventions on the treatment of these conditions. The bidirectional interaction between the brain and the gut, named 'brain-gut-microbiome axis' or 'gut-brain axis', plays a key role in the link between nutrition and mood disorders. Therefore, nutrition-based strategies for gut microbiota modulation are promising fields in mood disorders.

Understanding the Link Between Maternal Overnutrition, Cardio-Metabolic Dysfunction and Cognitive Aging

Obesity has long been identified as a global epidemic with major health implications such as diabetes and cardiovascular disease. Maternal overnutrition leads to significant health issues in industrial countries and is one of the risk factors for the development of obesity and related disorders in the progeny. The wide accessibility of junk food in recent years is one of the major causes of obesity, as it is low in nutrient content and usually high in salt, sugar, fat, and calories. An excess of nutrients during fetal life not only has immediate effects on the fetus, including increased growth and fat deposition in utero, but also has long-term health consequences. Based on human studies, it is difficult to discern between genetic and environmental contributions to the risk of disease in future generations. Consequently, animal models are essential for studying the impact of maternal overnutrition on the developing offspring. Recently, animal models provided some insight into the physiological mechanisms that underlie developmental programming. Most of the studies employed thus far have focused only on obesity and metabolic dysfunctions in the offspring. These studies have advanced our understanding of how maternal overnutrition in the form of high-fat diet exposure can lead to an increased risk of obesity in the offspring, but many questions remain open. How maternal overnutrition may increase the risk of developing brain pathology such as cognitive disabilities in the offspring and increase the risk to develop metabolic disorders later in life? Further, does maternal overnutrition exacerbate cognitive- and cardio-metabolic aging in the offspring?

Impaired brain fractalkine-CX3CR1 signaling is implicated in cognitive dysfunction in diet-induced obese mice

INTRODUCTION

A diet high in saturated fat is well known to affect neuronal function and contribute to cognitive decline in experimental animals and humans. Fractalkine released from neurons acts on its receptor, CX3C chemokine receptor 1 (CX3CR1), in the microglia to regulate several brain functions. The present study addressed whether fractalkine-CX3CR1 signaling in the brain, especially the hippocampus, contributes to the cognitive deficits observed in diet-induced obese (DIO) mice.

RESEARCH DESIGN AND METHODS

Mice were given 60% high-fat diet for 16 weeks. The expression of fractalkine and CX3CR1 in the hippocampus, amygdala and prefrontal cortex of DIO mice was analyzed. Cognitive ability in the Y-maze test and hippocampal glutamate receptors and synaptic markers were observed in DIO and CX3CR1 antagonist-treated mice. Regulation of fractalkine and CX3CR1 expression in the hippocampus was examined following administration of a selective insulin-like growth factor-1 (IGF-1) receptor inhibitor and a tyrosine receptor kinase B (TrkB) antagonist in normal mice.

RESULTS

DIO mice exhibited significant cognitive deficits in the Y-maze test and decrease in fractalkine and CX3CR1 in the hippocampus and amygdala compared with mice fed a control diet (CD mice). Administration of the CX3CR1 antagonist 18a in normal mice induced significant cognitive deficits in the Y-maze test. DIO mice and CX3CR1 antagonist-treated mice exhibited significant decreases in protein levels of NMDA (N-methyl-D-aspartate) receptor subunit (NR2A), AMPA (α-amino-5-methyl-3-hydroxy-4-isoxazole propionate) receptor subunit (GluR1) and postsynaptic density protein 95 in the hippocampus compared with their respective controls. Furthermore, plasma IGF-1 and hippocampal brain-derived neurotrophic factor were significantly decreased in DIO mice compared with CD mice. Administration of a selective IGF-1 receptor inhibitor and a TrkB antagonist in normal mice significantly decreased fractalkine and CX3CR1 in the hippocampus.

CONCLUSIONS

These findings indicate that the cognitive decline observed in DIO mice is due, in part, to reduced fractalkine-CX3CR1 signaling in the corticolimbic system.

The impact of insulin on the serotonergic system and consequences on diabetes-associated mood disorders

The idea that insulin could influence emotional behaviours has long been suggested. However, the underlying mechanisms have yet to be solved and there is no direct and clear-cut evidence demonstrating that such action involves brain serotonergic neurones. Indeed, initial arguments in favour of the association between insulin, serotonin and mood arise from clinical or animal studies showing that impaired insulin action in type 1 or type 2 diabetes causes anxiety- and depressive symptoms along with blunted plasma and brain serotonin levels. The present review synthesises the main mechanistic hypotheses that might explain the comorbidity between diabetes and depression. It also provides a state of knowledge of the direct and indirect experimental evidence that insulin modulates brain serotonergic neurones. Finally, it highlights the literature suggesting that antidiabetic drugs present antidepressant-like effects and, conversely, that serotonergic antidepressants impact glucose homeostasis. Overall, this review provides mechanistic insights into how insulin signalling alters serotonergic neurotransmission and related behaviours bringing new targets for therapeutic options.

Nutritional Status and Diet Style Affect Cognitive Function in Alcoholic Liver Disease

Malnutrition and cognitive dysfunction are typical features of alcoholic liver disease (ALD) and are correlated with the development of complications. The aim of this study is to explore the effect of nutritional state and diet on cognitive function in ALD. A total of 43 patients with compensated alcoholic cirrhosis were enrolled, and a neuropsychological test was assessed according to body mass index (BMI, <22 and ≥22). In the ALD animal study, mice were divided into five groups (n = 9/group; normal liquid, 5% EtOH + regular liquid, 5% EtOH + high-carbohydrate liquid, 5% EtOH + high-fat liquid, and 5% EtOH + high-protein liquid diet) and fed the same calories for eight weeks. To assess cognitive function, we performed T-maze studies weekly before/after alcohol binging. In cognitive function (BMI < 22/≥22), language score of Korea mini-mental state (7.4 ± 1.4/7.9 ± 0.4), Boston naming (11.7 ± 2.7/13.0 ± 1.8), forward digit span (6.7 ± 1.8/7.5 ± 1.6), Korean color word stroop (24.2 ± 26.5/43.6 ± 32.4), and interference score (33.9 ± 31.9/52.3 ± 33.9) revealed significant differences. In the T-maze test, alcohol significantly delayed the time to reach food, and binge drinking provided a temporary recovery in cognition. The alcohol-induced delay was significantly reduced in the high-carbohydrate and high-fat diet groups. Synaptic function exhibited no changes in all groups. Cognitive dysfunction is affected by nutritional status and diet in ALD.

The insulin resistance by triglyceride glucose index and risk for dementia: population-based study

Background

Insulin resistance is suggested to have negative effects on cognition; however, results from large population studies are lacking. In this study, the potential relationships between the triglyceride glucose (TyG) index, a simple surrogate marker of insulin resistance, and dementia were evaluated using a large-scale population dataset.

Methods

This was a retrospective, observational, cohort study using data from the National Health Information Database from 2009 to 2015 and included 5,586,048 participants 40 years age or older. The TyG index was used as a measure of insulin resistance, and participants were divided into quartiles based on TyG index. The incidence of dementia was assessed using hazard ratios (HRs) estimated with Cox proportional hazard modeling.

Results

During a median follow-up of 7.21 years, dementia was diagnosed in 142,714 (2.55%) participants. Alzheimer’s disease (AD) and vascular dementia (VD) were diagnosed in 74.3% and 12.5% of the participants. Multivariate-adjusted HRs for patients in the TyG index 4th quartile were higher for dementia (HRs = 1.14; 95% confidence interval [CI] 1.12–1.16), AD (HRs = 1.12; 95% CI 1.09–1.14), and VD (HRs = 1.18; 95% CI 1.12–1.23) compared with the 1st quartile of TyG index; however, this had a small effect size (Cohen’s d = 0.10, 0.08, and 0.13, respectively). These effects were independent of age, sex, smoking status, physical activity, body mass index, systolic blood pressure, and total cholesterol.

Conclusion

In this large population study, TyG index was associated with an increased risk of dementia, including AD and VD, that was independent of traditional cardiovascular risk factors, although the effect size of the TyG index was small.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-020-00758-4.

Sweet but Bitter: Focus on Fructose Impact on Brain Function in Rodent Models

Fructose consumption has drastically increased during the last decades due to the extensive commercial use of high-fructose corn syrup as a sweetener for beverages, snacks and baked goods. Fructose overconsumption is known to induce obesity, dyslipidemia, insulin resistance and inflammation, and its metabolism is considered partially responsible for its role in several metabolic diseases. Indeed, the primary metabolites and by-products of gut and hepatic fructolysis may impair the functions of extrahepatic tissues and organs. However, fructose itself causes an adenosine triphosphate (ATP) depletion that triggers inflammation and oxidative stress. Many studies have dealt with the effects of this sugar on various organs, while the impact of fructose on brain function is, to date, less explored, despite the relevance of this issue. Notably, fructose transporters and fructose metabolizing enzymes are present in brain cells. In addition, it has emerged that fructose consumption, even in the short term, can adversely influence brain health by promoting neuroinflammation, brain mitochondrial dysfunction and oxidative stress, as well as insulin resistance. Fructose influence on synaptic plasticity and cognition, with a major impact on critical regions for learning and memory, was also reported. In this review, we discuss emerging data about fructose effects on brain health in rodent models, with special reference to the regulation of food intake, inflammation, mitochondrial function and oxidative stress, insulin signaling and cognitive function.

Acylated Ghrelin as a Multi-Targeted Therapy for Alzheimer's and Parkinson's Disease

Much thought has been given to the impact of Amyloid Beta, Tau and Alpha-Synuclein in the development of Alzheimer's disease (AD) and Parkinson's disease (PD), yet the clinical failures of the recent decades indicate that there are further pathological mechanisms at work. Indeed, besides amyloids, AD and PD are characterized by the culminative interplay of oxidative stress, mitochondrial dysfunction and hyperfission, defective autophagy and mitophagy, systemic inflammation, BBB and vascular damage, demyelination, cerebral insulin resistance, the loss of dopamine production in PD, impaired neurogenesis and, of course, widespread axonal, synaptic and neuronal degeneration that leads to cognitive and motor impediments. Interestingly, the acylated form of the hormone ghrelin has shown the potential to ameliorate the latter pathologic changes, although some studies indicate a few complications that need to be considered in the long-term administration of the hormone. As such, this review will illustrate the wide-ranging neuroprotective properties of acylated ghrelin and critically evaluate the hormone's therapeutic benefits for the treatment of AD and PD.

The cafeteria diet: A standardized protocol and its effects on behavior

Obesity is a major health risk, with junk food consumption playing a central role in weight gain, because of its high palatability and high-energy nutrients. The Cafeteria (CAF) diet model for animal experiments consists of the same tasty but unhealthy food products that people eat (e.g. hot dogs and muffins), and considers variety, novelty and secondary food features, such as smell and texture. This model, therefore, mimics human eating patterns better than other models. In this paper, we systematically review studies that have used a CAF diet in behavioral experiments and propose a standardized CAF diet protocol. The proposed diet is ad libitum and voluntary; combines different textures, nutrients and tastes, including salty and sweet products; and it is rotated and varied. Our summary of the behavioral effects of CAF diet show that it alters meal patterns, reduces the hedonic value of other rewards, and tends to reduce stress and spatial memory. So far, no clear effects of CAF diet were found on locomotor activity, impulsivity, coping and social behavior.

Cognition, Brain Structure, and Brain Function in Individuals with Obesity and Related Disorders

PURPOSE OF REVIEW

Obesity is one of the most serious public health concerns. Excess adipose tissue, particularly with a centralized distribution, is associated with cognitive decline. Indeed, obesity has been associated with a number of adverse changes in brain function and structure that can be detected by neuroimaging techniques. These obesity-associated changes in the brain are associated with cognitive dysfunction.

RECENT FINDINGS

While the pathways by which excess adipose tissue affects brain function are not fully understood, available evidence points towards insulin resistance, inflammation, and vascular dysfunction, as possible mechanisms responsible for the observed relations between obesity and cognitive impairment. It appears that weight loss is related to better brain and cognitive outcomes and that cognitive impairment due to obesity may be reversible.

Metabolic regulation of aging and age-related disease

Inquiry into relationships between energy metabolism and brain function requires a uniquely interdisciplinary mindset, and implementation of anti-aging lifestyle strategies based on this work also involves consistent mental and physical discipline. Dr. Mark P. Mattson embodies both of these qualities, based on the breadth and depth of his work on neurobiological responses to energetic stress, and on his own diligent practice of regular exercise and caloric restriction. Dr. Mattson created a neurotrophic niche in his own laboratory, allowing trainees to grow their skills, form new connections, and eventually migrate, forming their own labs while remaining part of the extended lab family. In this historical review, we highlight Dr. Mattson's many contributions to understanding neurobiological responses to physical exercise and dietary restriction, with an emphasis on the mechanisms that may underlie neuroprotection in ageing and age-related disease. On the occasion of Dr. Mattson's retirement from the National Institute on Aging, we highlight his foundational work on metabolism and neuroplasticity by reviewing the context for these findings and considering their impact on future research on the neuroscience of aging.

Effects of dietary fat manipulation on cognition in mice and rats: protocol for a systematic review and meta-analysis

INTRODUCTION AND OBJECTIVE

The Western diet that comprises high levels of long-chain saturated fats and sugar is associated not only with metabolic disorders such as obesity and type 2 diabetes but also has been recently linked to brain changes and cognitive dysfunction. However, in animal studies, reported effects are variable, and the mechanisms underlying these effects are unclear. In the proposed review, we aim to summarise the diverse evidence of the effects of so-called 'high-fat' and ketogenic diets on behavioural measures of cognition in postweaning mice and rats, relative to animals on standard diets and to determine potential underlying mechanisms of high-fat diet-induced effects.

SEARCH STRATEGY

A comprehensive search strategy was designed to retrieve studies reporting use of a high-fat or ketogenic diet in postweaning mice and rats that included cognitive assessments. Three databases (Medline, SCOPUS and Web of Science) were searched and 4487 unique references were retrieved.

SCREENING AND ANNOTATION

Studies were screened for inclusion by two independent reviewers, with 330 studies retained for analysis. Characteristics of disease model choice, experimental design, intervention use and outcome assessment are to be extracted using the Systematic Review Facility (http://syrf.org.uk/) tool. Studies will be assessed for study quality and risk of bias and confidence of mechanistic involvement.

DATA MANAGEMENT AND REPORTING

For cognitive outcomes, effect sizes will be calculated using normalised mean difference and summarised using a random effects model. The contribution of potential sources of heterogeneity to the observed effects of diet on cognition will be assessed using multivariable meta-regression, with partitioning of heterogeneity as a sensitivity analysis. A preliminary version of this protocol was published on 9 April 2019 on the Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies website (http://www.dcn.ed.ac.uk/camarades/research.html%23protocols).

ETHICS AND DISSEMINATION

No ethical approval is required as there are no subjects in the proposed study.

Not only metformin, but also D-allulose, alleviates metabolic disturbance and cognitive decline in prediabetic rats

BACKGROUND

Prediabetes can be characterized as obesity with metabolic disturbance, leading to cognitive decline and brain pathologies. D-allulose administration in obese animals decreased metabolic disturbance. However, the comparative effects of D-allulose and metformin on cognition and brain functions in the diet-induced prediabetic condition are unclear. We assume that both D-allulose and metformin equally restore cognition and brain functions in prediabetic rats to an equal extent.

MATERIALS AND METHODS

Fifty-six rats were randomly divided into two groups: a control and diet-induced prediabetic group which had received a normal diet (ND) and a high-fat diet (HFD) for 24 weeks, respectively. After dietary protocol had been followed for 12 weeks, ND rats were given solely drinking water daily for 12 weeks. HFD-prediabetic rats randomly received drinking water with either D-allulose (1.9 g/kg/day of D-allulose) or metformin (300 mg/kg/day of metformin) for 12 weeks. Following this, cognition and brain parameters were determined.

RESULTS

Brain oxidative stress, mitochondrial dysfunction, microglial hyper-activation, apoptosis, brain insulin insensitivity, hippocampal synaptic dysfunction, and cognitive decline were observed in prediabetic rats. D-allulose and metformin equally attenuated brain oxidative stress, brain mitochondrial ROS production, hippocampal apoptosis, brain insulin insensitivity, hippocampal synaptic dysfunction, resulting in improved learning process in prediabetic rats. Metformin conferred greater advantage on the amelioration of brain mitochondrial dysfunction and brain microglial hyper-activation than D-allulose, resulting in improvement in both learning and memory processes in prediabetic rats.

CONCLUSIONS

Not only metformin, but also D-allulose, has beneficial effects on the enhancement of brain function and cognition in prediabetic condition.

Bidirectional modulation of hippocampal and amygdala synaptic plasticity by post-weaning obesogenic diet intake in male rats: Influence of the duration of diet exposure

Obesity is a chronic condition associated with adverse memory and emotional outcomes in humans and animal models. We have recently demonstrated that post-weaning (i.e., periadolescent) high-fat diet (HFD)-induced obesity has opposite effect on hippocampal and amygdala-dependent memory in rodents: while HFD consumption impairs spatial and relational memory, it enhances cue-dependent emotional memory. However, it is still not clear whether this bidirectional HFD effect on memory is related to bidirectional alterations of hippocampal and amygdala synaptic plasticity and if it is influenced by the duration of diet intake. In the current study, we compared in male rats the impact of 2-3 and 6-7 months of HFD intake starting at weaning, thus covering adolescence, on in vivo long-term potentiation (LTP) recorded simultaneously in the hippocampal area CA1 and the basolateral amygdala (BLA). As expected, 6-7 months of HFD intake abolished LTP in the CA1 and enhanced LTP in the BLA. However, 2-3 months of of HFD exposure enhanced LTP in both CA1 and BLA suggesting a transient compensatory mechanism in hippocampus. These results indicate that post-weaning HFD intake progressively leads to bidirectional modulation of hippocampal and amygdala synaptic plasticity, as we previously demonstrated for related memory processes, yet with a different temporal dynamic.

Treadmill exercise in obese maternal rats during pregnancy improves short-term memory through neurogenesis in the hippocampus of rat pups

Maternal obesity is known to increase the likelihood of offspring becoming obese, high blood pressure, and other metabolic disorders. After inducing obesity, the effect of treadmill exercise in maternal rats during pregnancy on short-term memory was investigated in relation to neurogenesis in rat pups. Short-term memory was declined in rat pups born to obese maternal rats, and treadmill running during pregnancy alleviated short-term memory impairment in rat pups born to obese maternal rats. The number of doublecortin (DCX)-positive and 5-bro-mo-2′-deoxyuridine (BrdU)-positive cells in the hippocampal dentate gyrus was decreased in rat pups born to obese maternal rats. Treadmill running during pregnancy increased the number of DCX-positive and BrdU-positive cells in rat pups born to obese maternal rats. Expression of brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (TrkB) in the hippocampus was decreased in the rat pups born to obese maternal rats. Treadmill running during pregnancy increased the expressions of BDNF and TrkB in rat pups born to obese maternal rats. Enhancing effect of short-term memory by treadmill exercise may be due to increased neurogenesis through activation of the BDNF-TrkB signaling pathway by treadmill exercise.

Switching from high-fat feeding (HFD) to regular diet improves metabolic and behavioral impairments in middle-aged female mice

Obesity represents a risk factor for metabolic syndrome and cardiovascular and psychiatric disorders. Excessive caloric intake, particularly in dietary fats, is an environmental factor that contributes to obesity development. Thus, the observation that switching from long-standing dietary obesity to standard diet (SD) can ameliorate the high-fat diet-induced metabolic, memory, and emotionality-related impairments are particularly important. Herein we investigated whether switching from the high-fat diet (HFD) to SD could improve the metabolic and behavioral impairments observed in middle-aged females C57Bl/6 mice. During twelve weeks, the animals received a high-fat diet (61 % fat) or SD diet. After 12-weeks, the HFD group's diet was switched to SD for an additional four weeks. It was observed a progressive deleterious effect of HFD in metabolic and behavioral parameters in mice. After four weeks of HFD-feeding, the animals showed glucose intolerance and increased locomotor activity. A subsequent increase in the body mass gain, hyperglycemia, and depressive-like behavior was observed after eight weeks, and memory impairments after twelve weeks. After replacing the HFD to SD, it was observed an improvement of metabolic (loss of body mass, normal plasma glucose levels, and glucose tolerance) and behavioral (absence of memory and emotional alterations) parameters. These results demonstrate the temporal development of metabolic and behavioral impairments following HFD in middle-age female mice and provide new evidence that these alterations can be improved by switching back the diet to SD.

Added sugar and dietary fiber consumption are associated with creativity in preadolescent children

Objectives: Creativity requires the ability to combine existing mental representations in new ways and depends, in part, on the hippocampus. Hippocampal function is, in turn, affected by a number of health factors, including aerobic fitness, excess adiposity, and diet. Specifically, in rodent studies, diets high in saturated fatty acids and sugar - hallmarks of a western diet- have been shown to negatively impact hippocampal function and thereby impair performance on cognitive tasks that require the hippocampus. Yet relatively few studies have examined the relationship between diet and hippocampal-dependent cognition in children. Methods: The current study therefore sought to explore the relationship of several diet quality markers including dietary lipids (saturated fatty acids and omega-3 fatty acids), simple carbohydrates (added sugars), and dietary fiber with creativity in preadolescent children. Participants (N = 57; mean age = 9.1 years) completed the Verbal Form of the Torrance Test of Creative Thinking (TTCT), a standardized test of creativity known to require the hippocampus. Additionally, participants completed a 3-day food intake record with the assistance of a parent, underwent dual energy x-ray absorptiometry (DXA) to assess central adiposity, and VO2max testing to assess aerobic fitness. Results: Added sugar intake was negatively associated, and dietary fiber was positively associated with overall TTCT performance. These relationships were sustained even after controlling for key covariates. Discussion: These findings are among the first to report an association between added sugar consumption and hippocampal-dependent cognition during childhood and, given the key role of the hippocampus in learning and memory, as well as creative thinking, have potential educational and public health implications.

Metabolic Defects Caused by High-Fat Diet Modify Disease Risk through Inflammatory and Amyloidogenic Pathways in a Mouse Model of Alzheimer's Disease

High-fat diet (HFD) has been shown to accelerate Alzheimer’s disease (AD) pathology, but the exact molecular and cellular mechanisms remain incompletely understood. Moreover, it is unknown whether AD mice are more susceptible to HFD-induced metabolic dysfunctions. To address these questions, we used 5xFAD mice as an Alzheimer’s disease model to study the physiological and molecular underpinning between HFD-induced metabolic defects and AD pathology. We systematically profiled the metabolic parameters, the gut microbiome composition, and hippocampal gene expression in 5xFAD and wild type (WT) mice fed normal chow diet and HFD. HFD feeding impaired energy metabolism in male 5xFAD mice, leading to increased locomotor activity, energy expenditure, and food intake. 5xFAD mice on HFD had elevated circulating lipids and worsened glucose intolerance. HFD caused profound changes in gut microbiome compositions, though no difference between genotype was detected. We measured hippocampal mRNAs related to AD neuropathology and neuroinflammation and showed that HFD elevated the expression of apoptotic, microglial, and amyloidogenic genes in 5xFAD mice. Pathway analysis revealed that differentially regulated genes were involved in insulin signaling, cytokine signaling, cellular stress, and neurotransmission. Collectively, our results showed that 5xFAD mice were more susceptible to HFD-induced metabolic dysregulation and suggest that targeting metabolic dysfunctions can ameliorate AD symptoms via effects on insulin signaling and neuroinflammation in the hippocampus.

The effects of exercise treatment on learning and memory ability, and cognitive performance in diet-induced prediabetes animals

Changes associated with cognitive function in the high-fat high-carbohydrate diet-induced prediabetes animal model and effect of exercise remain unclear. Rats were randomly assigned to the following groups (n = 6): non-diabetic (ND), prediabetic (PD), intermittent exercising PD (PD + IE) and regular exercising PD (PD + RE). After exercise cessation, oral glucose tolerance (OGT), Novel Object Recognition Test (NORT) and Morris-Water Maze (MWM) tests were performed to assess cognitive function. After sacrifice, malonaldehyde, glutathione peroxidase, interleukin-1β and dopamine concentration in the prefrontal cortex (PFC) and hippocampus were measured. Impaired OGT response in PD animals was accompanied by poor performance on behavioural tasks. This was associated with increased oxidative stress markers and impaired dopamine neurotransmission as evidence by elevated dopamine concentration in the PFC and hippocampal tissue. Improved OGT response by exercise was coupled with improved performance on behavioural tasks, oxidative stress markers and increased interleukin-1β concentration. In regular exercise, this was further coupled with improved dopamine neurotransmission. Cognitive function was affected during prediabetes in animals. This was partly due to oxidative stress and impaired dopamine neurotransmission. Both intermittent and regular exercise improved cognitive function. This was partly mediated by improved glucose tolerance and oxidative stress as well as a subclinical increase in interleukin-1β concentration. In regular exercise, this was further mediated by improved dopamine neurotransmission.

Chronic NaHS treatment improves spatial and passive avoidance learning and memory and anxiety-like behavior and decreases oxidative stress in rats fed with a high-fat diet

Cognitive function is impaired by increased consumption of a high-fat diet (HFD). Also, HFD consumption can alter hydrogen sulfide (H₂S) metabolism. H₂S is an important signaling molecule with antioxidant effects that regulates multiple functions in the brain. In the present study, we investigated the effect of sodium hydrosulfide (NaHS, an H₂S donor) on cognitive impairment and oxidative stress changes induced by HFD consumption. Following 11 weeks of HFD regimes in Wistar rats, elevated plus-maze (EPM), Morris water maze (MWM), and passive avoidance learning (PAL) tasks were used to evaluate the anxiety-like behavior and spatial and passive learning and memory, respectively. Daily intraperitoneal injection of NaHS was done during the dietary regimen. Serum and hippocampal oxidative stress biomarkers (malondialdehyde (MDA), total antioxidant capacity (TAC), and total oxidant status (TOS)) were measured. We demonstrated that treatment with NaHS ameliorated the impairment in the retrieval of reference memory and passive avoidance learning. Moreover, HFD increased anxiety-like behavior, which was reversed by the administration of NaHS. Additionally, the increase in MDA and TOS and the decrease in TAC induced by HFD in the serum and hippocampus were significantly reduced following administration of NaHS. These results indicate that NaHS could significantly ameliorate HFD-induced spatial and passive learning and memory impairment and anxiety-like behavior, at least in part, via its antioxidant activities. Therefore, the administration of NaHS can provide a therapeutic approach for HFD-induced memory impairment.

Sex-Dependent Wheel Running Effects on High Fat Diet Preference, Metabolic Outcomes, and Performance on the Barnes Maze in Rats

Excessive and prolonged intake of highly palatable, high fat (HF) foods contributes to the pathogenesis of obesity, metabolic syndrome, and cognitive impairment. Exercise can restore energy homeostasis and suppress HF diet preference in rats. However, it is unclear if exercise confers similar protection against the detrimental outcomes associated with a chronic HF diet preference and feeding in both sexes. We used our wheel running (WR) and two-diet choice (chow vs. HF) paradigm to investigate the efficacy of exercise in reversing HF diet-associated metabolic and cognitive dysregulation in rats, hypothesizing that beneficial effects of exercise would be more pronounced in males. All WR rats showed HF diet avoidance upon running initiation, and males, but not females, had a prolonged reduction in HF diet preference. Moreover, exercise only improved glucose tolerance and insulin profile in males. Compared to sedentary controls, all WR rats improved learning to escape on the Barnes maze. Only WR females increased errors made during subsequent reversal learning trials, indicating a sex-dependent effect of exercise on behavioral flexibility. Taken together, our results suggest that exercise is more effective at attenuating HF-associated metabolic deficits in males, and highlights the importance of developing sex-specific treatment interventions for obesity and cognitive dysfunction.

Effects of metformin on recognition memory and hippocampal neuroplasticity in rats with metabolic syndrome

Metabolic syndrome (MS) is a health problem that is characterized by body fat accumulation, hypertension, dyslipidemia, and hyperglycemia; recently, it has been demonstrated that MS also damages memory processes. The first-line drug in the treatment of MS and type 2 diabetes mellitus is metformin, which is an antihyperglycemic agent. This drug has been shown to produce neuroprotection and to improve memory processes. However, the mechanism involved in this neuroprotection is unknown. A 90-day administration of metformin improved the cognitive processes of rats with MS as evaluated by the novel object recognition test, and this finding could be explained by an increase in the neuronal spine density and spine length. We also found that metformin increased the immunoreactivity of synaptophysin, sirtuin-1, AMP-activated protein kinase, and brain-derived neuronal factor, which are important plasticity markers. We conclude that metformin is an important therapeutic agent that increases neural plasticity and protects cognitive processes. The use of this drug is important in the minimization of the damage caused by MS.

Interplay between Peripheral and Central Inflammation in Obesity-Promoted Disorders: The Impact on Synaptic Mitochondrial Functions

The metabolic dysfunctions induced by high fat diet (HFD) consumption are not limited to organs involved in energy metabolism but cause also a chronic low-grade systemic inflammation that affects the whole body including the central nervous system. The brain has been considered for a long time to be protected from systemic inflammation by the blood–brain barrier, but more recent data indicated an association between obesity and neurodegeneration. Moreover, obesity-related consequences, such as insulin and leptin resistance, mitochondrial dysfunction and reactive oxygen species (ROS) production, may anticipate and accelerate the physiological aging processes characterized by systemic inflammation and higher susceptibility to neurological disorders. Here, we discussed the link between obesity-related metabolic dysfunctions and neuroinflammation, with particular attention to molecules regulating the interplay between energetic impairment and altered synaptic plasticity, for instance AMP-activated protein kinase (AMPK) and Brain-derived neurotrophic factor (BDNF). The effects of HFD-induced neuroinflammation on neuronal plasticity may be mediated by altered brain mitochondrial functions. Since mitochondria play a key role in synaptic areas, providing energy to support synaptic plasticity and controlling ROS production, the negative effects of HFD may be more pronounced in synapses. In conclusion, it will be emphasized how HFD-induced metabolic alterations, systemic inflammation, oxidative stress, neuroinflammation and impaired brain plasticity are tightly interconnected processes, implicated in the pathogenesis of neurological diseases.

Intranasal insulin ameliorates cognitive impairment in a rat model of Parkinson's disease through Akt/GSK3β signaling pathway

AIMS

Parkinson's disease dementia (PDD) is one of the most common non-motor symptoms of advanced Parkinson's disease (PD). This study aimed to determine whether intranasal insulin has protective effects on cognition in the rat PD model induced by 6-hydroxylase dopamine (6-OHDA) through the insulin signaling pathway.

MATERIALS AND METHODS

The rats were given intranasal insulin administration for six weeks after unilateral medial forebrain bundle (MFB) injection of 6-OHDA. Then a series of cognitive-behavioral tests, immunofluorescence, and immunoblotting was performed on the rats.

KEY FINDINGS

The results demonstrated that the injection of 6-OHDA in the unilateral MFB damaged working memory and long-term habituation of rats in the T-maze rewarded alternation test and hole-board test. Besides, rats with unilateral 6-OHDA injury performed poorly in terms of escape latency and average speed during the hidden platform training phase rather than in the probe trial of the Morris Water Maze (MWM) test. Immunofluorescence results showed that unilateral 6-OHDA injury in MFB led to the massive death of ipsilateral-substantia nigra (SN) tyrosine hydroxylase (TH)-positive neurons. Western blot results further indicated that 6-OHDA-induced necrosis of ipsilateral-SN dopaminergic neurons reduced the levels of p-Akt (Ser473) and p-GSK3β (Ser9) in the ipsilateral-hippocampus.

SIGNIFICANCE

These findings provide a solid evidence base for the relationship between PD cognitive impairment and insulin signaling pathways.

Chronic high-fat diet consumption induces an alteration in plasma/brain neurotensin signaling, metabolic disturbance, systemic inflammation/oxidative stress, brain apoptosis, and dendritic spine loss

Chronic high-fat diet (HFD) consumption caused not only negative effects on obesity and metabolic disturbance, but also instigated several brain pathologies, including dendritic spine loss. In addition, alterations in plasma/brain neurotensin (NT) levels and NT signaling were observed in obesity. However, the mechanistic link between the NT levels in plasma and brain, NT signaling, and peripheral/brain pathologies following prolonged HFD consumption still needs to be elucidated. We hypothesized that an increase in peripheral/brain NT signaling were associated with peripheral/brain pathologies after prolonged HFD consumption. Male Wistar rats (n = 24) were given either a normal diet (ND) or a HFD for 12 and 40 weeks. At the end of each time course, metabolic parameters and plasma NT levels were measured. Rats were then decapitated and the brains were examined the levels of brain NT, hippocampal reactive oxygen species, the number of Iba-1 positive cells, the dendritic spine densities, and the expression of NT-, mitophagy-, autophagy-, and apoptotic-related proteins. The findings showed an increase in the level of plasma NT with dyslipidemia, metabolic disturbances, systemic inflammation/oxidative stress, and hippocampal pathologies in rats fed HFD for 12 and 40 weeks. The expression of brain NT signaling and brain apoptosis were markedly increased after 40 weeks of HFD feeding. These results indicated that the alteration in the level of circulating/brain NT and its downstream signaling were associated with central and peripheral pathologies after long-term HFD intake. Therefore, these alterations in NT level or its signaling could be considered as a therapeutic target in treating obesity.

Interplay between hormones and exercise on hippocampal plasticity across the lifespan

The hippocampus is a brain structure known to play a central role in cognitive function (namely learning and memory) as well as mood regulation and affective behaviors due in part to its ability to undergo structural and functional changes in response to intrinsic and extrinsic stimuli. While structural changes are achieved through modulation of hippocampal neurogenesis as well as alterations in dendritic morphology and spine remodeling, functional (i.e., synaptic) changes can be noted through the strengthening (i.e., long-term potentiation) or weakening (i.e., long-term depression) of the synapses. While age, hormone homeostasis, and levels of physical activity are some of the factors known to module these forms of hippocampal plasticity, the exact mechanisms through which these factors interact with each other at a given moment in time are not completely understood. It is well known that hormonal levels vary throughout the lifespan of an individual and it is also known that physical exercise can impact hormonal homeostasis. Thus, it is reasonable to speculate that hormone modulation might be one of the various mechanisms through which physical exercise differently impacts hippocampal plasticity throughout distinct periods of an individual's life. The present review summarizes the potential relationship between physical exercise and different types of hormones (namely sex, metabolic, and stress hormones) and how this relationship may mediate the effects of physical activity during three distinct life periods, adolescence, adulthood, and senescence. Overall, the vast majority of studies support a beneficial role of exercise in maintaining hippocampal hormonal levels and consequently, hippocampal plasticity, cognition, and mood regulation.