Methylphenidate prevents high-fat diet (HFD)-induced learning/memory impairment in juvenile mice

Long-term saturated fat-enriched diets impair hippocampal learning and memory processes in a sex-dependent manner

Consumption of saturated fat-enriched diets during adolescence has been closely associated with the reduction of hippocampal synaptic plasticity and the impairment of cognitive function. Nevertheless, the effect of long-term intake of these foods has not yet been studied. In the present study, we have investigated the effect of a treatment, lasting for 40 weeks, with a diet enriched in saturated fat (SOLF) on i) spatial learning and memory, ii) hippocampal synaptic transmission and plasticity, and iii) hippocampal gene expression levels in aged male and female mice. Our findings reveal that SOLF has a detrimental impact on spatial memory and synaptic plasticity mechanisms, such as long-term potentiation (LTP), and downregulates Gria1 expression specifically in males. In females, SOLF downregulates the gene expression of Gria1/2/3 and Grin1/2A/2B glutamate receptor subunits as well as some proinflammatory interleukins. These findings highlight the importance of considering sex-specific factors when assessing the long-term effects of high-fat diets on cognition and brain plasticity.

Extracellular vesicles released from microglia after palmitate exposure impact brain function

Dietary patterns that include an excess of foods rich in saturated fat are associated with brain dysfunction. Although microgliosis has been proposed to play a key role in the development of brain dysfunction in diet-induced obesity (DIO), neuroinflammation with cytokine over-expression is not always observed. Thus, mechanisms by which microglia contribute to brain impairment in DIO are uncertain. Using the BV2 cell model, we investigated the gliosis profile of microglia exposed to palmitate (200 µmol/L), a saturated fatty acid abundant in high-fat diet and in the brain of obese individuals. We observed that microglia respond to a 24-hour palmitate exposure with increased proliferation, and with a metabolic network rearrangement that favors energy production from glycolysis rather than oxidative metabolism, despite stimulated mitochondria biogenesis. In addition, while palmitate did not induce increased cytokine expression, it modified the protein cargo of released extracellular vesicles (EVs). When administered intra-cerebroventricularly to mice, EVs secreted from palmitate-exposed microglia in vitro led to memory impairment, depression-like behavior, and glucose intolerance, when compared to mice receiving EVs from vehicle-treated microglia. We conclude that microglia exposed to palmitate can mediate brain dysfunction through the cargo of shed EVs.

Western diet consumption impairs memory function via dysregulated hippocampus acetylcholine signaling

Western diet (WD) consumption during early life developmental periods is associated with impaired memory function, particularly for hippocampus (HPC)-dependent processes. We developed an early life WD rodent model associated with long-lasting HPC dysfunction to investigate the neurobiological mechanisms mediating these effects. Rats received either a cafeteria-style WD (ad libitum access to various high-fat/high-sugar foods; CAF) or standard healthy chow (CTL) during the juvenile and adolescent stages (postnatal days 26-56). Behavioral and metabolic assessments were performed both before and after a healthy diet intervention period beginning at early adulthood. Results revealed HPC-dependent contextual episodic memory impairments in CAF rats that persisted despite the healthy diet intervention. Given that dysregulated HPC acetylcholine (ACh) signaling is associated with memory impairments in humans and animal models, we examined protein markers of ACh tone in the dorsal HPC (HPCd) in CAF and CTL rats. Results revealed significantly lower protein levels of vesicular ACh transporter in the HPCd of CAF vs. CTL rats, indicating chronically reduced ACh tone. Using intensity-based ACh sensing fluorescent reporter (iAChSnFr) in vivo fiber photometry targeting the HPCd, we next revealed that ACh release during object-contextual novelty recognition was highly predictive of memory performance and was disrupted in CAF vs. CTL rats. Neuropharmacological results showed that alpha 7 nicotinic ACh receptor agonist infusion in the HPCd during training rescued memory deficits in CAF rats. Overall, these findings reveal a functional connection linking early life WD intake with long-lasting dysregulation of HPC ACh signaling, thereby identifying an underlying mechanism for WD-associated memory impairments.

Impact of high-fat diet on cognitive behavior and central and systemic inflammation with aging and sex differences in mice

Aging and age-related diseases are associated with cellular stress, metabolic imbalance, oxidative stress, and neuroinflammation, accompanied by cognitive impairment. Lifestyle factors such as diet, sleep fragmentation, and stress can potentiate damaging cellular cascades and lead to an acceleration of brain aging and cognitive impairment. High-fat diet (HFD) has been associated with obesity, metabolic disorders like diabetes, and cardiovascular disease. HFD also induces neuroinflammation, impairs learning and memory, and may increase anxiety-like behavior. Effects of a HFD may also vary between sexes. The interaction between Age- and Sex- and Diet-related changes in neuroinflammation and cognitive function is an important and poorly understood area of research. This study was designed to examine the effects of HFD on neuroinflammation, behavior, and neurodegeneration in mice in the context of aging or sex differences. In a series of studies, young (2-3 months) or old (12-13 months) C57BL/6J male mice or young male and female C57Bl/6J mice were fed either a standard diet (SD) or a HFD for 5-6 months. Behavior was assessed in Activity Chamber, Y-maze, Novel Place Recognition, Novel Object Recognition, Elevated Plus Maze, Open Field, Morris Water Maze, and Fear Conditioning. Post-mortem analyses assessed a panel of inflammatory markers in the plasma and hippocampus. Additionally, proteomic analysis of the hypothalamus, neurodegeneration, neuroinflammation in the locus coeruleus, and neuroinflammation in the hippocampus were assessed in a subset of young and aged male mice. We show that HFD increased body weight and decreased locomotor activity across groups compared to control mice fed a SD. HFD altered anxiety-related exploratory behavior. HFD impaired spatial learning and recall in young male mice and impaired recall in cued fear conditioning in young and aged male mice, with no effects on spatial learning or fear conditioning in young female mice. Effects of Age and Sex were observed on neuroinflammatory cytokines, with only limited effects of HFD. HFD had a more significant impact on systemic inflammation in plasma across age and sex. Aged male mice had induction of microglial immunoreactivity in both the locus coeruleus (LC) and hippocampus an effect that HFD exacerbated in the hippocampal CA1 region. Proteomic analysis of the hypothalamus revealed changes in pathways related to metabolism and neurodegeneration with both aging and HFD in male mice. Our findings suggest that HFD induces widespread systemic inflammation and limited neuroinflammation. In addition, HFD alters exploratory behavior in male and female mice, and impairs learning and memory in male mice. These results provide valuable insight into the impact of diet on cognition and aging pathophysiology.

Early- but not late-adolescent Western diet consumption programs for long-lasting memory impairments in male but not female rats

Early life Western diet (WD) consumption leads to impaired memory function, particularly for processes mediated by the hippocampus. However, the precise critical developmental window(s) during which WD exposure negatively impacts hippocampal function are unknown. Here, we exposed male and female rats to a WD model involving free access to a variety of high-fat and/or high-sugar food and drink items during either the early-adolescent period (postnatal days [PN] 26-41; WD-EA) or late-adolescent period (PN 41-56; WD-LA). Control (CTL) rats were given healthy standard chow throughout both periods. To evaluate long-lasting memory capacity well beyond the early life WD exposure periods, we performed behavioral assessments after both a short (4 weeks for WD-EA, 2 weeks for WD-LA) and long (12 weeks for WD-EA, 10 weeks for WD-LA) period of healthy diet intervention. Results revealed no differences in body weight or body composition between diet groups, regardless of sex. Following the shorter period of healthy diet intervention, both male and female WD-EA and WD-LA rats showed deficits in hippocampal-dependent memory compared to CTL rats. Following the longer healthy diet intervention period, memory impairments persisted in male WD-EA but not WD-LA rats. In contrast, in female rats the longer healthy diet intervention reversed the initial memory impairments in both WD-EA and WD-LA rats. Collectively, these findings reveal that early-adolescence is a critical period of long-lasting hippocampal vulnerability to dietary insults in male but not female rats, thus highlighting developmental- and sex-specific effects mediating the relationship between the early life nutritional environment and long-term cognitive health.

Early- but not late-adolescent Western diet consumption programs for long-lasting memory impairments in male but not female rats

Early life Western diet (WD) consumption leads to impaired memory function, particularly for processes mediated by the hippocampus. However, the precise critical developmental window(s) during which WD exposure negatively impacts hippocampal function are unknown. Here, we exposed male and female rats to a WD model involving free access to a variety of high-fat and/or high-sugar food and drink items during either the early-adolescent period (postnatal days [PN] 26-41; WD-EA) or late-adolescent period (PN 41-56; WD-LA). Control (CTL) rats were given healthy standard chow throughout both periods. To evaluate long-lasting memory capacity well beyond the early life WD exposure periods, we performed behavioral assessments after both a short (4 weeks for WD-EA, 2 weeks for WD-LA) and long (12 weeks for WD-EA, 10 weeks for WD-LA) period of healthy diet intervention. Results revealed no differences in body weight or body composition between diet groups, regardless of sex. Following the shorter period of healthy diet intervention, both male and female WD-EA and WD-LA rats showed deficits in hippocampal-dependent memory compared to CTL rats. Following the longer healthy diet intervention period, memory impairments persisted in male WD-EA but not WD-LA rats. In contrast, in female rats the longer healthy diet intervention reversed the initial memory impairments in both WD-EA and WD-LA rats. Collectively, these findings reveal that early-adolescence is a critical period of long-lasting hippocampal vulnerability to dietary insults in male but not female rats, thus highlighting developmental- and sex-specific effects mediating the relationship between the early life nutritional environment and long-term cognitive health.

Melanotan-II reverses memory impairment induced by a short-term HF diet

A high-fat (HF) diet has been shown to increase the risk of neurological impairments and neurodegenerative disorders. The melanotropins used in this study have been associated with diet-related disorders; however, there is an absence of studies on their effect on diet-induced neurobehavioral conditions. Here, we investigated the possible relationship among diet, Melanotan-II (MT-II) targeting melanotropin receptors, and the behavior of zebrafish (Danio rerio). Surprisingly, even a short-term HF diet lasting for ∼ 1 % of the zebrafish's life had a strong developmental effect. Zebrafish fed the HF diet showed an impairment in recognition memory, elevated anxiety levels, and reduced exploratory propensity after just three weeks compared to zebrafish fed the control diet. These HF diet-induced abnormalities were reversed by MT-II. Animals fed a HF diet and treated with MT-II demonstrated recognition memory, anxiety, and exploratory behavior similar to the control group. This study provides evidence that even a short-term HF diet has an impact on memory and emotions and is the first study to show that MT-II reverses these changes.

High-fat diet-induced dopaminergic dysregulation induces REM sleep fragmentation and ADHD-like behaviors

Consumption of a high-fat diet (HFD) has been associated with reduced wakefulness and various behavioral deficits, including anxiety, depression, and anhedonia. The dopaminergic system, which plays a crucial role in sleep and ADHD, is known to be vulnerable to chronic HFD. However, the association between HFD-induced behavioral and molecular changes remains unclear. Therefore, we investigated the effects of a HFD on the dopaminergic system and its association with behavioral deficits in male mice. The mice were divided into normal diet and HFD groups and were analyzed for sleep patterns, behavior tests, and transcription levels of dopamine-related genes in the brain. The HFD group showed decreased wakefulness, increased REM sleep with fragmented patterns, decreased time spent in the center zone of the open field test, shorter immobile time in the tail suspension test, impaired visuospatial memory, and reduced sucrose preference. Additionally, the HFD group had decreased mRNA levels of D1R, COMT, and DAT in the nucleus accumbens, which negatively correlated with REM sleep proportion and REM sleep bout count. The results suggest that HFD-induced behavioral deficits were resemblance to ADHD-like behavioral phenotypes and disturbs REM sleep by dysregulating the dopaminergic system.

Western diet consumption impairs memory function via dysregulated hippocampus acetylcholine signaling

Western diet (WD) consumption during development yields long-lasting memory impairments, yet the underlying neurobiological mechanisms remain elusive. Here we developed an early life WD rodent model to evaluate whether dysregulated hippocampus (HPC) acetylcholine (ACh) signaling, a pathology associated with memory impairment in human dementia, is causally-related to WD-induced cognitive impairment. Rats received a cafeteria-style WD (access to various high-fat/high-sugar foods; CAF) or healthy chow (CTL) during the juvenile and adolescent periods (postnatal days 26-56). Behavioral, metabolic, and microbiome assessments were performed both before and after a 30-day healthy diet intervention beginning at early adulthood. Results revealed CAF-induced HPC-dependent contextual episodic memory impairments that persisted despite healthy diet intervention, whereas CAF was not associated with long-term changes in body weight, body composition, glucose tolerance, anxiety-like behavior, or gut microbiome. HPC immunoblot analyses after the healthy diet intervention identified reduced levels of vesicular ACh transporter in CAF vs. CTL rats, indicative of chronically reduced HPC ACh tone. To determine whether these changes were functionally related to memory impairments, we evaluated temporal HPC ACh binding via ACh-sensing fluorescent reporter in vivo fiber photometry during memory testing, as well as whether the memory impairments could be rescued pharmacologically. Results revealed dynamic HPC ACh binding during object-contextual novelty recognition was highly predictive of memory performance and was disrupted in CAF vs. CTL rats. Further, HPC alpha-7 nicotinic receptor agonist infusion during consolidation rescued memory deficits in CAF rats. Overall, these findings identify dysregulated HPC ACh signaling as a mechanism underlying early life WD-associated memory impairments.

Amygdala activity and amygdala-hippocampus connectivity: Metabolic diseases, dementia, and neuropsychiatric issues

With rapid aging of the population worldwide, the number of people with dementia is dramatically increasing. Some studies have emphasized that metabolic syndrome, which includes obesity and diabetes, leads to increased risks of dementia and cognitive decline. Factors such as insulin resistance, hyperglycemia, high blood pressure, dyslipidemia, and central obesity in metabolic syndrome are associated with synaptic failure, neuroinflammation, and imbalanced neurotransmitter levels, leading to the progression of dementia. Due to the positive correlation between diabetes and dementia, some studies have called it "type 3 diabetes". Recently, the number of patients with cognitive decline due to metabolic imbalances has considerably increased. In addition, recent studies have reported that neuropsychiatric issues such as anxiety, depressive behavior, and impaired attention are common factors in patients with metabolic disease and those with dementia. In the central nervous system (CNS), the amygdala is a central region that regulates emotional memory, mood disorders, anxiety, attention, and cognitive function. The connectivity of the amygdala with other brain regions, such as the hippocampus, and the activity of the amygdala contribute to diverse neuropathological and neuropsychiatric issues. Thus, this review summarizes the significant consequences of the critical roles of amygdala connectivity in both metabolic syndromes and dementia. Further studies on amygdala function in metabolic imbalance-related dementia are needed to treat neuropsychiatric problems in patients with this type of dementia.

High-Fat Diet Consumption Induces Neurobehavioral Abnormalities and Neuronal Morphological Alterations Accompanied by Excessive Microglial Activation in the Medial Prefrontal Cortex in Adolescent Mice

The association between a high-fat diet (HFD) consumption and emotional/cognitive disorders is widely documented. One distinctive feature of the prefrontal cortex (PFC), a kernel emotion- and cognition-related brain region, is its protracted adolescent maturation, which makes it highly vulnerable to the detrimental effects of environmental factors during adolescence. Disruption of the PFC structure and function is linked to emotional/cognitive disorders, especially those that emerge in late adolescence. A HFD consumption is common among adolescents, yet its potential effects on PFC-related neurobehavior in late adolescence and any related underlying mechanisms are yet to be established. In the present study, adolescent (postnatal days 28-56) male C57BL/6J mice were fed a control diet (CD) or a HFD and underwent behavioral tests in addition to Golgi staining and immunofluorescence targeting of the medial PFC (mPFC). The HFD-fed adolescent mice exhibited anxiety- and depression-like behavior and abnormal mPFC pyramidal neuronal morphology accompanied by alterations in microglial morphology indicative of a heightened state of activation and increased microglial PSD95⁺ inclusions signifying excessive phagocytosis of the synaptic material in the mPFC. These findings offer novel insights into the neurobehavioral effects due to adolescent HFD consumption and suggest a contributing role in microglial dysfunction and prefrontal neuroplasticity deficits for HFD-associated mood disorders in adolescents.

Addiction-like behaviour towards high-fat high-sugar food predicts relapse propensity in both obesity prone and obesity resistant C57BL/6 J mice

Compulsive overeating of palatable food is thought to underlie some forms of obesity. Similarities are often observed in the behavioural symptomology and the neuropathophysiology underlying substance use disorder and compulsive overeating. As such, preclinical animal models which assess addiction-like behaviour towards food may assist the understanding of the neurobiology underlying overeating behaviour. Further, the relationship between these behaviours and the propensity for diet-induced obesity warrants examination. In this study we investigated the relationship between the propensity for diet-induced obesity (DIO) and addiction-like behaviour towards highly palatable food in C57BL/6 J mice as measured by a 3-criteria model. We also examined the extent to which performance on this 3-criteria model predicted two key hallmark features of addiction - resistance to extinction and relapse propensity (as measured by reinstatement of lever pressing). C57BL/6 J mice were allowed free access to a palatable diet for 8 weeks then separated by weight gain into DIO-prone and DIO-resistant subgroups. Access to palatable food was then restricted to daily operant self-administration sessions whereby addiction-like behaviour towards a high-fat high-sugar food reward was assessed using a 3-criteria model similar to that used to assess addiction-like behaviour towards drugs of abuse. In contrast to findings in rats, no difference in addiction-like behaviour towards food was observed between obesity prone (OP) and obesity resistant (OR) mice. Similarly, principal components analysis found no distinct patterns in the relationship between addiction-like behaviours across treatment groups. This suggests that the strain and species of rodent may be critical for studying the mechanisms underlying pathological overconsumption. Further analysis revealed that the extent of performance on the 3-criteria model correlated with the propensity for C57BL/6 J mice to both extinguish food seeking behaviour and "relapse" after a period of withdrawal. This finding was evident across all groups, regardless of DIO. Collectively, these data validate the 3-criteria model as a robust model to comprehensively assess food addiction-like behaviour in mice, regardless of prior food intake history.

Cardiovascular and lipid-lowering effects of a marine lipoprotein extract in a high-fat diet-induced obesity mouse model

Obesity is a major health challenge worldwide, with implications for diabetes, hypertension and cardiovascular disease (CVD). Regular consumption of dark-meat fish is linked to a lower incidence of CVD and associated metabolic disorders due to the presence of long-chain omega-3 fatty acid ethyl esters in fish oils. The aim of the present study was to determine whether a marine compound like a sardine lipoprotein extract (RCI-1502), regulates fat accumulation in the heart of a high-fat diet-induced (HFD) mouse model of obesity. To investigate its effects in the heart and liver, we conducted a randomized, 12-week placebo-controlled study in which we analyzed the expression of vascular inflammation markers, obesity biochemical patterns and related CVD pathologies. Male HFD-fed mice treated with a RCI-1502-supplemented diet showed reduced body weight, abdominal fat tissue and pericardial fat pad mass density without systemic toxicity. RCI-1502 significantly reduced triacylglyceride, low-density lipoprotein and total-cholesterol concentrations in serum, but increased HDL-cholesterol levels. Our data show that RCI-1502 is beneficial for reducing obesity associated with a long-term HFD, possibly by exerting a protective effect on lipidic homeostasis, indicated also by histopathological analysis. These results collectively indicate that RCI-1502 acts as a cardiovascular therapeutic nutraceutical agent, which modulates fat-induced inflammation and improves metabolic health.

A one month high fat diet disrupts the gut microbiome and integrity of the colon inducing adiposity and behavioral despair in male Sprague Dawley rats

High-fat diet (HFD) is associated with gut microbiome dysfunction and mental disorders. However, the time-dependence as to when this occurs is unclear. We hypothesized that a short-term HFD causes colonic tissue integrity changes resulting in behavioral changes. Rats were fed HFD or low-fat diet (LFD) for a month and gut microbiome, colon, and behavior were evaluated. Behavioral despair was found in the HFD group. Although obesity was absent, the HFD group showed increased percent weight gain, epididymal fat tissue, and leptin expression. Moreover, the HFD group had increased colonic damage, decreased expression of the tight junction proteins, and higher lipopolysaccharides (LPS) in serum. Metagenomic analysis revealed that the HFD group had more Bacteroides and less S24-7 which correlated with the decreased claudin-5. Finally, HFD group showed an increase of microglia percent area, increased astrocytic projections, and decreased phospho-mTOR. In conclusion, HFD consumption in a short period is still sufficient to disrupt gut integrity resulting in LPS infiltration, alterations in the brain, and behavioral despair even in the absence of obesity.

Melatonin treatment improves cognitive deficits by altering inflammatory and neurotrophic factors in the hippocampus of obese mice

Overweight and obesity are associated with an increased risk of developing dementia and cognitive deficits. Neuroinflammation is one of the most important mechanisms behind cognitive impairment in obese patients. In recent years, the neuroendocrine hormone melatonin has been suggested to have therapeutic effects for memory decline in several neuropsychiatric and neurological conditions. However, the effects of melatonin on cognitive function under obesity conditions still need to be clarified. The purpose of this study was to determine whether melatonin treatment can improve cognitive impairment in obese mice. To this end, male C57BL6 mice were treated with a high-fat diet (HFD) for 20 weeks to induce obesity. The animal received melatonin for 8 weeks. Cognitive functions were evaluated using the Y maze, object recognition test, and the Morris water maze. We measured inflammatory cytokines including tumor necrosis factor (TNF)-α, interferon (IFN)-γ, interleukin (IL)-17A, and brain-derived neurotrophic factor (BDNF) in the hippocampus of obese mice. Our results show that HFD-induced obesity significantly impaired working, spatial and recognition memory by increasing IFN-γ and IL-17A and decreasing BDNF levels in the hippocampus of mice. On the other hand, melatonin treatment effectively improved all cognitive impairments and reduced TNF-α, IFN-γ, and IL-17A and elevated BDNF levels in the hippocampus of obese mice. Taken together, this study suggests that melatonin treatment could have a beneficial role in the treatment of cognitive impairment in obesity.

Sex Differences in Cognition Across Aging

Sex and gender differences are seen in cognitive disturbances in a variety of neurological and psychiatry diseases. Men are more likely to have cognitive symptoms in schizophrenia whereas women are more likely to have more severe cognitive symptoms with major depressive disorder and Alzheimer's disease. Thus, it is important to understand sex and gender differences in underlying cognitive abilities with and without disease. Sex differences are noted in performance across various cognitive domains - with males typically outperforming females in spatial tasks and females typically outperforming males in verbal tasks. Furthermore, there are striking sex differences in brain networks that are activated during cognitive tasks and in learning strategies. Although rarely studied, there are also sex differences in the trajectory of cognitive aging. It is important to pay attention to these sex differences as they inform researchers of potential differences in resilience to age-related cognitive decline and underlying mechanisms for both healthy and pathological cognitive aging, depending on sex. We review literature on the progressive neurodegenerative disorder, Alzheimer's disease, as an example of pathological cognitive aging in which human females show greater lifetime risk, neuropathology, and cognitive impairment, compared to human males. Not surprisingly, the relationships between sex and cognition, cognitive aging, and Alzheimer's disease are nuanced and multifaceted. As such, this chapter will end with a discussion of lifestyle factors, like education and diet, as modifiable factors that can alter cognitive aging by sex. Understanding how cognition changes across age and contributing factors, like sex differences, will be essential to improving care for older adults.

Peanut (Arachis hypogaea) sprout prevents high-fat diet-induced cognitive impairment by improving mitochondrial function

This study was performed to evaluate the improvement effect of the ethyl acetate fraction from peanut (Arachis hypogaea) sprout (EFPS) on high-fat diet (HFD)-induced cognitive deficits in C57BL/6 mice. Mice were randomly divided four groups (n = 13) as control (normal chow), HFD, EFPS 20 (20 mg/kg of body weight; intragastric administration) and EFPS 50 (50 mg/kg of body weight; intragastric administration) groups. HFD was provide for 15 weeks excepting control group. EFPS ameliorated cognitive dysfunction in Y-maze, passive avoidance test and Morris water maze test. EFPS significantly improved glucose tolerance and serum lipid profile, and reduced body weight. EFPS ameliorated oxidative stress by regulating MDA levels and SOD activity in liver and brain tissues. In addition, EFPS restored brain mitochondrial dysfunction related to energy metabolism. Moreover, the bioactive compounds of EFPS were identified as di-caffeic acid, caffeic acid, dihydrokaempferol-hexoside, di-p-coumaroyl tartaric acid isomer and group B soyasaponins using ultra-performance liquid chromatography-quadrupole-time-of-flight (UPLC-Q-TOF) mass spectrometry. These results show that EFPS can improve cognitive functions in HFD-induced diabetic mice.

Peripheral and cognitive benefits of physical exercise in a mouse model of midlife metabolic syndrome

Despite national and international efforts for the prevention of metabolic syndrome and its underlying diseases/disorders, its prevalence is still rising, especially in the middle-aged population. In this study, we explore the effect of high fat diet on the development of metabolic syndrome in middle-aged mice and to evaluate the potential benefits of voluntary physical exercise on the periphery as well as brain cognitive function, and to explore the potential mechanisms. We found that metabolic syndrome developed at middle age significantly impairs cognitive function and the impairment is associated with gene dysregulation in metabolic pathways that are largely affecting astrocytes in the brain. Eight-week voluntary wheel running at a frequency of three times a week, not only improves peripheral glucose control but also significantly improves learning and memory. The improvement of cognitive function is associated with restoration of gene expression involved in energy metabolism in the brain. Our study suggests that voluntary physical exercise is beneficial for metabolic syndrome-induced peripheral as well as cognitive dysfunction and can be recommended as therapeutic intervention for metabolic syndrome and associated diseases.

β-Glucan-Rich Extract of Gray Oyster Mushroom, Pleurotus pulmonarius, Improves Object Recognition Memory and Hippocampus Morphology in Mice Fed a High-Fat Diet

Obesity may cause behavioral alterations, while maternal obesity can contribute to metabolic disorders in subsequent generations. The effect of β-glucan-rich Pleurotus pulmonarius (βgPp) was investigated on mouse neurobehavior and hippocampus and its offspring's hippocampus development. Female ICR mice were fed with normal diet (ND), ND with βgPp, high-fat diet (HFD), or HFD with βgPp for 3 months followed by behavioral test and mating. Immunohistochemistry for the expression of neuronal nuclear protein (NeuN) and ionized calcium binding adaptor molecule-1 (Iba-1) in the hippocampus was carried out. βgPp significantly enhanced short-term object recognition memory in HFD-fed mice. βgPp also ameliorated the histological alterations and neuronal loss and increased Iba-1-positive microglia in the hippocampus regions of HFD-fed mice and their male offspring. These findings demonstrated that βgPp supplementation attenuated the effects of HFD on object recognition memory and the alterations on the hippocampal regions of maternal mice and their male offspring.

Hippocampal Function Is Impaired by a Short-Term High-Fat Diet in Mice: Increased Blood-Brain Barrier Permeability and Neuroinflammation as Triggering Events

Worldwide, and especially in Western civilizations, most of the staple diets contain high amounts of fat and refined carbohydrates, leading to an increasing number of obese individuals. In addition to inducing metabolic disorders, energy dense food intake has been suggested to impair brain functions such as cognition and mood control. Here we demonstrate an impaired memory function already 3 days after the start of a high-fat diet (HFD) exposure, and depressive-like behavior, in the tail suspension test, after 5 days. These changes were followed by reduced synaptic density, changes in mitochondrial function and astrocyte activation in the hippocampus. Preceding or coinciding with the behavioral changes, we found an induction of the proinflammatory cytokines TNF-α and IL-6 and an increased permeability of the blood–brain barrier (BBB), in the hippocampus. Finally, in mice treated with a TNF-α inhibitor, the behavioral and BBB alterations caused by HFD-feeding were mitigated suggesting that inflammatory signaling was critical for the changes. In summary, our findings suggest that HFD rapidly triggers hippocampal dysfunction associated with BBB disruption and neuroinflammation, promoting a progressive breakdown of synaptic and metabolic function. In addition to elucidating the link between diet and cognitive function, our results might be relevant for the comprehension of the neurodegenerative process.

Consumption of dietary fat causes loss of olfactory sensory neurons and associated circuitry that is not mitigated by voluntary exercise in mice

Excess nutrition causes loss of olfactory sensory neurons (OSNs) and reduces odour discrimination and odour perception in mice. To separate diet-induced obesity from the consumption of dietary fat, we designed pair-feeding experiments whereby mice were maintained on isocaloric diets for 5 months, which prevented increased fat storage. To test our hypothesis that adiposity was not a prerequisite for loss of OSNs and bulbar projections, we used male and female mice with an odorant receptor-linked genetic reporter (M72tauLacZ; Olfr160) to visualize neural circuitry changes resulting from elevated fat in the diet. Simultaneously we monitored glucose clearance (diagnostic for prediabetes), body fat deposition, ingestive behaviours, select inflammatory markers and energy metabolism. Axonal projections to defined olfactory glomeruli were visualized in whole-mount brains, and the number of OSNs was manually counted across whole olfactory epithelia. After being pair fed a moderately high-fat (MHF) diet, mice of both sexes had body weight, adipose deposits, energy expenditure, respiratory exchange ratios and locomotor activity that were unchanged from control-fed mice. Despite this, they were still found to lose OSNs and associated bulbar projections. Even with unchanged adipocyte storage, pair-fed animals had an elevation in TNF cytokines and an intermediate ability for glucose clearance. Albeit improving health metrics, access to voluntary running while consuming an ad libitum fatty diet still precipitated a loss of OSNs and associated axonal projections for male mice. Our results support that long-term macronutrient imbalance can drive anatomical loss in the olfactory system regardless of total energy expenditure. KEY POINTS: Obesity can disrupt the structure and function of organ systems, including the olfactory system that is important for food selection and satiety. We designed dietary treatments in mice such that mice received fat, but the total calories provided were the same as in control diets so that they would not gain weight or increase adipose tissue. Mice that were not obese but consumed isocaloric fatty diets still lost olfactory neuronal circuits, had fewer numbers of olfactory neurons, had an elevation in inflammatory signals and had an intermediate ability to clear glucose (prediabetes). Mice were allowed access to running wheels while consuming fatty diets, yet still lost olfactory structures. We conclude that a long-term imbalance in nutrition that favours fat in the diet disrupts the olfactory system of mice in the absence of obesity.

Saturated and unsaturated fat diets impair hippocampal glutamatergic transmission in adolescent mice

Consumption of high-fat diets (HFD) has been associated with neuronal plasticity deficits and cognitive disorders linked to the alteration of glutamatergic disorders in the hippocampus. As young individuals are especially vulnerable to the effects of nutrients and xenobiotics on cognition, we studied the effect of chronic consumption of saturated (SOLF) and unsaturated oil-enriched foods (UOLF) on: i) spatial memory; ii) hippocampal synaptic transmission and plasticity; and iii) gene expression of glutamatergic receptors and hormone receptors in the hippocampus of adolescent and adult mice. Our results show that both SOLF and UOLF impair spatial short-term memory. Accordingly, hippocampal synaptic plasticity mechanisms underlying memory, and gene expression of NMDA receptor subunits are modulated by both diets. On the other hand, PPARγ gene expression is specifically down-regulated in adolescent SOLF individuals and up-regulated in adult UOLF mice.

Protective effects of krill oil on high fat diet-induced cognitive impairment by regulation of oxidative stress

Consumption of high fat diet (HFD) increases risk of cognitive impairment and memory deficit by elevation of oxidative stress in the brain. In this study, we investigated the protective effects of krill oil (KO) against HFD-induced cognitive impairment in mice. The mice were fed with HFD for 10 weeks, and then KO was orally administered at doses of 100, 200, or 500 mg/kg/d for 4 weeks. To evaluate the cognitive abilities, we carried out the behavior tests, such as T-maze, novel object recognition test, and Morris water maze test. The HFD-induced cognitive impairment mice showed impairments in both spatial memory and novel object cognitive abilities. However, administration of KO at doses of 100, 200, or 500 mg/kg/d improved spatial memory ability and novel object cognition by increase of the exploration of new route and novel object. In addition, KO-administered group improved learning and memory abilities, showing shorter latency to reach hidden platform compared with control group. Furthermore, levels of reactive oxygen species (ROS), lipid peroxidation, and nitric oxide (NO) were significantly elevated by consumption of HFD, indicating that consumption of HFD induces oxidative stress in the brain. However, administration of KO attenuated oxidative stress by decrease of the ROS levels, lipid peroxidation, and NO. This study suggests that KO improves HFD-induced cognitive impairment by attenuation of oxidative stress in the brain. Therefore, KO may play as a promising agent in treatment and prevention of HFD-induced cognitive impairment.

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.

High fat suppresses SOD1 activity by reducing copper chaperone for SOD1 associated with neurodegeneration and memory decline

High fat consumption leads to reactive oxygen species (ROS) which is associated with age-progressive neurological disorders. Cu/Zn superoxide dismutase (SOD1) is a critical enzyme against ROS. However, the relationship between SOD1 and the high-fat-induced ROS and neurodegeneration is poorly known. Here we showed that, upon treatment with a saturated fatty acid palmitic acid (PA), the SOD1 activity was decreased in mouse neuronal HT-22 cell line accompanied by elevation of ROS, but not in mouse microglial BV-2 cell line. We further showed that PA decreased the levels of copper chaperone for SOD1 (CCS) in HT-22 cells, which promoted the nuclear import of SOD1 and decreased its activity. We demonstrated that the reduction of CCS is involved in the PA-induced decrease of SOD1 activity and elevation of ROS. In addition, compared with the adult mice fed with a standard diet, the high-fat-diet adult mice presented an increase of plasma free fatty acids, reduction of hippocampal SOD1 activity and CCS, mitochondrial degeneration and long-term memory decline. Taken together, our findings suggest that the high-fat-induced lower CCS level is essential for SOD1 suppression which may be associated with neurodegeneration and cognitive decline.

Western Diet Consumption During Development: Setting the Stage for Neurocognitive Dysfunction

The dietary pattern in industrialized countries has changed substantially over the past century due to technological advances in agriculture, food processing, storage, marketing, and distribution practices. The availability of highly palatable, calorically dense foods that are shelf-stable has facilitated a food environment where overconsumption of foods that have a high percentage of calories derived from fat (particularly saturated fat) and sugar is extremely common in modern Westernized societies. In addition to being a predictor of obesity and metabolic dysfunction, consumption of a Western diet (WD) is related to poorer cognitive performance across the lifespan. In particular, WD consumption during critical early life stages of development has negative consequences on various cognitive abilities later in adulthood. This review highlights rodent model research identifying dietary, metabolic, and neurobiological mechanisms linking consumption of a WD during early life periods of development (gestation, lactation, juvenile and adolescence) with behavioral impairments in multiple cognitive domains, including anxiety-like behavior, learning and memory function, reward-motivated behavior, and social behavior. The literature supports a model in which early life WD consumption leads to long-lasting neurocognitive impairments that are largely dissociable from WD effects on obesity and metabolic dysfunction.

Sex Differences in Metabolic Recuperation After Weight Loss in High Fat Diet-Induced Obese Mice

Dietary intervention is a common tactic employed to curtail the current obesity epidemic. Changes in nutritional status alter metabolic hormones such as insulin or leptin, as well as the insulin-like growth factor (IGF) system, but little is known about restoration of these parameters after weight loss in obese subjects and if this differs between the sexes, especially regarding the IGF system. Here male and female mice received a high fat diet (HFD) or chow for 8 weeks, then half of the HFD mice were changed to chow (HFDCH) for 4 weeks. Both sexes gained weight (p < 0.001) and increased their energy intake (p < 0.001) and basal glycemia (p < 0.5) on the HFD, with these parameters normalizing after switching to chow but at different rates in males and females. In both sexes HFD decreased hypothalamic NPY and AgRP (p < 0.001) and increased POMC (p < 0.001) mRNA levels, with all normalizing in HFDCH mice, whereas the HFD-induced decrease in ObR did not normalize (p < 0.05). All HFD mice had abnormal glucose tolerance tests (p < 0.001), with males clearly more affected, that normalized when returned to chow. HFD increased insulin levels and HOMA index (p < 0.01) in both sexes, but only HFDCH males normalized this parameter. Returning to chow normalized the HFD-induced increase in circulating leptin (p < 0.001), total IGF1 (p < 0.001), IGF2 (p < 0.001, only in females) and IGFBP3 (p < 0.001), whereas free IGF1 levels remained elevated (p < 0.01). In males IGFBP2 decreased with HFD and normalized with chow (p < 0.001), with no changes in females. Although returning to a healthy diet improved of most metabolic parameters analyzed, fIGF1 levels remained elevated and hypothalamic ObR decreased in both sexes. Moreover, there was sex differences in both the response to HFD and the switch to chow including circulating levels of IGF2 and IGFBP2, factors previously reported to be involved in glucose metabolism. Indeed, glucose metabolism was also differentially modified in males and females, suggesting that these observations could be related.

High-fat diet and acute stress have different effects on object preference tests in rats during adolescence and adulthood

Meals of high-fat diet (HFD) during adolescence produce stronger impairments to memory during adolescence than adulthood, however recovery of memory from adolescent HFD is underexplored. In addition, many tests of rodent memory are confounded by aversive or food-based stimuli, making it difficult to determine baseline memory processing affected by HFD. Thus, we utilized three cohorts of rats (adolescent HFD, adult HFD, and adolescent HFD with recovery) to explore the effects of HFD at different ages on two traditional tests of memory based strictly on object exploration, novel object recognition and novel object location tests. To isolate stress as a variable, rats were tested either at baseline or with cold water swim occurring directly after object acquisition. Results show that preference for novel objects is impaired by stress across all groups, but HFD alone only impairs preference for novel objects during adolescence, although this recovers after switching to a control diet. Additionally, preference for an object in a new location is impaired by HFD in all age groups and fails to recover following diet change. Together the data suggest that stress and HFD differentially affect object preference, based on test type, except during the adolescent period. Because these tests are traditionally interpreted as memory processes dependent on two distinct brain regions, the hippocampus and perirhinal cortex, these results support that stress and HFD affect the hippocampus and perirhinal cortex differently. The data affirm that while perirhinal cortex-dependent behavior recovers, the adolescent period is susceptible to long-lasting dysfunctions of hippocampal behavior by HFD.

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.

Effect of Vigna angularis on High-Fat Diet-Induced Memory and Cognitive Impairments

High-fat diet (HFD)-induced obesity is related to cognitive and memory dysfunction. Much attention was focused on functional foods as a therapeutic strategy to treat cognitive decline by obesity. In the present study, we confirmed the protective effect of Vigna angularis (VA) on cognitive and memory impairment in an obese mouse model. For 16 weeks, mice were fed HFD and VA extract was administered during 4 weeks at 100 and 200 mg/kg. The cognitive abilities of HFD-induced mice were evaluated using behavioral tests. Compared with the control group, VA groups were improved spatial and recognition ability. In T-maze and novel object recognition tests, VA 100 and VA 200 groups showed increased ratios of exploration of a novel object/route compared to a familiar object/route. Moreover, VA 100 and VA 200 groups reached the platform faster than the control group in a Morris water maze test. Therefore, VA extract may protect against HFD-induced cognitive impairment and memory dysfunction. (PNU-IACUC; approval no. PNU-2019-2166).

Obesogenic diet-associated C-reactive protein predicts reduced central dopamine and corticostriatal functional connectivity in female rhesus monkeys

Alterations in dopamine (DA) signaling and reductions in functional connectivity (FC; a measure of temporal correlations of activity between different brain regions) within dopaminergic reward pathways are implicated in the etiology of psychopathology and have been associated with increased concentrations of inflammatory markers, including C-reactive protein. Peripheral and central inflammatory cytokines that have been shown to disrupt DA signaling and corticostriatal FC are associated with C-reactive protein, an acute phase reactant that is used translationally as a marker of systemic inflammation. One factor that can significantly increase systemic inflammation to produce neuroadaptations in reward pathways is a diet that results in fat mass accumulation (e.g. obesogenic diet). The current study in female rhesus monkeys maintained in a standard laboratory chow (n = 18) or on obesogenic diet (n = 16) for 12-months tested the hypothesis that an obesogenic diet would alter central DA and homovanillic acid (HVA) concentrations, and be associated with increased CRP concentrations and decreased FC between corticostriatal regions at 12-months following dietary intervention. We specifically assessed FC between the nucleus accumbens (NAcc) and two sub-regions of the prefrontal cortex (PFC) previously associated with CRP concentrations, the ventromedial PFC (vmPFC) and the orbitofrontal cortex (OFC), which are also involved in emotional and motivational salience assessment, and in goal-directed behavior, impulse control and the salience/value of food, respectively. Results showed that CSF DA concentrations were decreased (p = 0.002), HVA:DA ratios were increased (p = 0.016), and body mass index was increased (p = 0.047) over the 12-months of consuming an obesogenic diet. At 12-months, females maintained in the obesogenic diet exhibited higher CRP concentrations than females consuming chow-only (p = 0.008). Linear regression analyses revealed significant CRP by dietary condition interactions on DA concentrations (β = -5.10; p = 0.017) and HVA:DA ratios (β = 5.14; p = 0.029). Higher CRP concentrations were associated with lower CSF DA concentrations (r = -0.69; p = 0.004) and greater HVA:DA ratios only in females maintained in the obesogenic dietary condition (r = 0.58; p = 0.024). Resting-state magnetic resonance neuroimaging (rs-fMRI) in a subset of females from each diet condition (n = 8) at 12-months showed that higher CRP concentrations were associated decreased FC between the NAcc and subregions of the prefrontal cortex (PFC; p's < 0.05). Decreased FC between the NAcc and PFC subregions were also associated with lower concentrations of DA and greater HVA:DA ratios (p's < 0.05). Overall, these data suggest that increased inflammatory signaling driving heightened CRP levels may mediate the adverse consequences of obesogenic diets on DA neurochemistry and corticostriatal connectivity.

Abelmoschus Esculentus (L.) Moench's Peel Powder Improves High-Fat-Diet-Induced Cognitive Impairment in C57BL/6J Mice

Okra peel exhibits numerous therapeutic effects. This study explores the potential ameliorative effects of okra peel powder on high-fat-diet (HFD)-induced hypercholesterolemia and cognitive deficits. Thirty-six C57BL/6J male mice were randomly divided into six groups (n = 6 per group): (i) control, mice fed with a normal diet; (ii) HFD, mice fed with HFD; (iii) HFD-SIM, mice fed with HFD and given simvastatin (20 mg/kg/day); (iv) HFD-OP1; (v) HFD-OP2; (vi) HFD-OP3, mice fed with HFD and okra peel (200, 400, or 800 mg/kg/day, respectively). Following 10 weeks of treatments, the mice were subjected to the Morris water maze (MWM). Parameters such as weekly average body weight, food intake, and blood lipid profiles were also recorded. The HFD group showed a profound increase in total cholesterol and low-density lipoprotein concentration compared to the control group. All okra-treated and HFD-SIM groups performed better than the HFD group during acquisition trials, whereas only the HFD-OP1 produced a significantly higher number of entries into the platform zone during the probe trial. In sum, all three okra doses improved the learning ability of the mice. However, only the lowest dose of okra significantly improved the spatial reference memory retention.

Palmitoylethanolamide counteracts brain fog improving depressive-like behaviour in obese mice: Possible role of synaptic plasticity and neurogenesis

BACKGROUND AND PURPOSE

High-fat diet (HFD)-induced obesity is accompanied by metabolic and neurochemical changes that have been associated with depression. Recent studies indicate that palmitoylethanolamide (PEA) exerts metabolic effects and holds neuroprotective potential. However, studies on HFD exposure in mice which investigate the effects of PEA on monoamine system and synaptic plasticity are limited.

EXPERIMENTAL APPROACH

In C57Bl/6J male mice, obesity was established by HFD feeding for 12 weeks. Then, mice were treated with ultra-micronized PEA (30 mg·kg^-1 daily p.o.) or vehicle for 7 weeks along with HFD. Mice receiving chow diet and vehicle served as controls. Thereafter, depressive-, anhedonic-like behaviour and cognitive performance were measured. Monoamine analyses were performed on brain areas (nucleus accumbens, Nac; prefrontal cortex, PFC; hippocampus), and markers of synaptic plasticity and neurogenesis were evaluated in hippocampus.

KEY RESULTS

PEA limited depressive- and anhedonic-like behaviour, and cognitive deficits induced by HFD. PEA induced an increase in 5-HT levels in PFC, and a reduction of dopamine and 5-HT turnover in Nac and PFC, respectively. Moreover, PEA increased dopamine levels in the hippocampus and PFC. At a molecular level, PEA restored brain-derived neurotrophic factor signalling pathway in hippocampus and PFC, indicating an improvement of synaptic plasticity. In particular, PEA counteracted the reduction of glutamatergic synaptic density induced by HFD in the stratum radiatum of the CA1 of the hippocampus, where it also exhibited neurogenesis-promoting abilities.

CONCLUSION AND IMPLICATIONS

PEA may represent an adjuvant therapy to limit depressive-like behaviours and memory deficit, affecting monoamine homeostasis, synaptic plasticity and neurogenesis.

LINKED ARTICLES

This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.4/issuetoc.

Association between saturated fatty acid intake and depressive symptoms in midlife women: A prospective study

BACKGROUND

This prospective investigation examined relations between baseline dietary saturated fatty acid (SFA) intake of women at midlife and prevalence of depressive symptoms 4 years later.

METHODS

Women enrolled in the Study of Women's Health Across the Nation (SWAN) had measures of CES-D depression scores 4 years later and SFA intake at baseline. Logistic regression models were used to study prospective associations between SFA intake and depressive symptoms.

RESULTS

A total of 2400 women aged 42-52 years were included in the present study. The ORs of depressive symptoms in model 1 adjustment for baseline CES-D score indicated that baseline SFA intake was positively associated with depressive symptoms. After additional adjustment for age, race/ethnicity, education, financial strain, physical activity, smoking currently, BMI, menopausal status, VMS, chronic stress and use of antidepressant in model 2, the results were similar to those of the model 1. This association remained statistically significant and changed little when additional controlling for SHBG and FSH in fully adjusted model 3. The fully adjusted OR of depressive symptoms in model 3 was 2.423 (1.142-5.143) in quartile 4 (the highest) versus quartile 1 (the lowest) of the baseline SFA intake.

LIMITATIONS

Assessment of depression and SFA intake was based on a self-report scale.

CONCLUSIONS

Baseline SFA intake is a predictor for depressive symptoms assessed 4 years later in midlife women. This underlines the importance of targeting SFA intake in the prevention of major depression in midlife women.

Indole Tryptophan Metabolism and Cytokine S100B in Children with Attention-Deficit/Hyperactivity Disorder: Daily Fluctuations, Responses to Methylphenidate, and Interrelationship with Depressive Symptomatology

Background: Indole tryptophan metabolites (ITMs), mainly produced at the gastrointestinal level, participate in bidirectional gut-brain communication and have been implicated in neuropsychiatric pathologies, including attention-deficit/hyperactivity disorder (ADHD). Method: A total of 179 children, 5-14 years of age, including a healthy control group (CG, n = 49), and 107 patients with ADHD participated in the study. The ADHD group was further subdivided into predominantly attention deficit (PAD) and predominantly hyperactive impulsive (PHI) subgroups. Blood samples were drawn at 20:00 and 09:00 hours, and urine was collected between blood draws, at baseline and after 4.63 ± 2.3 months of methylphenidate treatment in the ADHD group. Levels and daily fluctuations of ITM were measured by tandem mass spectrometer, and S100B (as a glial inflammatory marker) by enzyme-linked immunosorbent assay. Factorial analysis of variance (Stata 12.0) was performed with groups/subgroups, time (baseline/after treatment), hour of day (morning/evening), and presence of depressive symptoms (DS; no/yes) as factors. Results: Tryptamine and indoleacetic acid (IAA) showed no differences between the CG and ADHD groups. Tryptamine exhibited higher evening values (p < 0.0001) in both groups. No changes were associated with methylphenidate or DS. At baseline, in comparison with the rest of study sample, PHI with DS+ group showed among them much greater morning than evening IAA (p < 0.0001), with treatment causing a 50% decrease (p = 0.002). Concerning indolepropionic acid (IPA) MPH was associated with a morning IPA decrease and restored the daily profile observed in the CG. S100B protein showed greater morning than evening concentrations (p = 0.001) in both groups. Conclusion: Variations in ITM may reflect changes associated with the presence of DS, including improvement, among ADHD patients.

Effects of Hypericum scabrum extract on dentate gyrus synaptic plasticity in high fat diet-fed rats

High-fat diet (HFD) can induce deficits in neural function, oxidative stress, and decrease hippocampal neurogenesis. Hypericum (H.) scabrum extract (Ext) contains compounds that could treat neurological disorders. This study aimed to examine the neuroprotective impacts of the H. scabrum Ext on hippocampal synaptic plasticity in rats that were fed HFD. Fifty-four male Wistar rats (220 ± 10 g) were randomly arranged in six groups: (1) HFD group; (2) HFD + Ext300 group; (3) HFD + Ext100 group; (4) Control group; (5) Ext 300 mg/kg group; (6) Ext 100 mg/kg group. These protocols were administrated for 3 months. After this stage, a stimulating electrode was implanted in the perforant pathway (PP), and a bipolar recording electrode was embedded into the dentate gyrus (DG). Long-term potentiation (LTP) was provoked by high-frequency stimulation (HFS) of the PP. Field excitatory postsynaptic potentials (EPSP) and population spikes (PS) were recorded at 5, 30, and 60 min after HFS. The HFD group exhibited a large and significant decrease in their PS amplitude and EPSP slope as compared to the control and extract groups. In reverse, H. scabrum administration in the HFD + Ext rats reversed the effect of HFD on the PS amplitude and EPSP slope. The results of the study support that H. scabrum Ext can inhibit diminished synaptic plasticity caused by the HFD. These effects are probably due to the extreme antioxidant impacts of the Ext and its capability to scavenge free radicals.

Amyloid beta and diabetic pathology cooperatively stimulate cytokine expression in an Alzheimer's mouse model

BACKGROUND

Diabetes is a risk factor for developing Alzheimer's disease (AD); however, the mechanism by which diabetes can promote AD pathology remains unknown. Diabetes results in diverse molecular changes in the brain, including dysregulation of glucose metabolism and loss of cerebrovascular homeostasis. Although these changes have been associated with increased Aβ pathology and increased expression of glial activation markers in APPswe/PS1dE9 (APP/PS1) mice, there has been limited characterization, to date, of the neuroinflammatory changes associated with diabetic conditions.

METHODS

To more fully elucidate neuroinflammatory changes associated with diabetes that may drive AD pathology, we combined the APP/PS1 mouse model with either high-fat diet (HFD, a model of pre-diabetes), the genetic db/db model of type 2 diabetes, or the streptozotocin (STZ) model of type 1 diabetes. We then used a multiplexed immunoassay to quantify cortical changes in cytokine proteins.

RESULTS

Our analysis revealed that pathology associated with either db/db, HFD, or STZ models yielded upregulation of a broad profile of cytokines, including chemokines (e.g., MIP-1α, MIP-1β, and MCP-1) and pro-inflammatory cytokines, including IL-1α, IFN-γ, and IL-3. Moreover, multivariate partial least squares regression analysis showed that combined diabetic-APP/PS1 models yielded cooperatively enhanced expression of the cytokine profile associated with each diabetic model alone. Finally, in APP/PS1xdb/db mice, we found that circulating levels of Aβ1-40, Aβ1-42, glucose, and insulin all correlated with cytokine expression in the brain, suggesting a strong relationship between peripheral changes and brain pathology.

CONCLUSIONS

Altogether, our multiplexed analysis of cytokines shows that Alzheimer's and diabetic pathologies cooperate to enhance profiles of cytokines reported to be involved in both diseases. Moreover, since many of the identified cytokines promote neuronal injury, Aβ and tau pathology, and breakdown of the blood-brain barrier, our data suggest that neuroinflammation may mediate the effects of diabetes on AD pathogenesis. Therefore, strategies targeting neuroinflammatory signaling, as well as metabolic control, may provide a promising strategy for intervening in the development of diabetes-associated AD.

Farnesoid X Receptor (FXR) Aggravates Amyloid-β-Triggered Apoptosis by Modulating the cAMP-Response Element-Binding Protein (CREB)/Brain-Derived Neurotrophic Factor (BDNF) Pathway In Vitro

Background

Alzheimer’s disease (AD), which results in cognitive deficits, usually occurs in older people and is mainly caused by amyloid beta (Aβ) deposits and neurofibrillary tangles. The bile acid receptor, farnesoid X receptor (FXR), has been extensively studied in cardiovascular diseases and digestive diseases. However, the role of FXR in AD is not yet understood. The purpose of the present study was to investigate the mechanism of FXR function in AD.

Material/Methods

Lentivirus infection, flow cytometry, real-time PCR, and western blotting were used to detect the gain or loss of FXR in cell apoptosis induced by Aβ. Co-immunoprecipitation was used to analyze the molecular partners involved in Aβ-induced apoptosis.

Results

We found that the mRNA and protein expression of FXR was enhanced in Aβ-triggered neuronal apoptosis in differentiated SH-SY5Y cells and in mouse hippocampal neurons. Overexpression of FXR aggravated Aβ-triggered neuronal apoptosis in differentiated SH-SY5Y cells, and this effect was further increased by treatment with the FXR agonist 6ECDCA. Molecular mechanism analysis by co-immunoprecipitation and immunoblotting revealed that FXR interacted with the cAMP-response element-binding protein (CREB), leading to decreased CREB and brain-derived neurotrophic factor (BDNF) protein levels. Low expression of FXR mostly reversed the Aβ-triggered neuronal apoptosis effect and prevented the reduction in CREB and BDNF.

Conclusions

These data suggest that FXR regulates Aβ-induced neuronal apoptosis, which may be dependent on the CREB/BDNF signaling pathway in vitro.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Examining Adolescence as a Sensitive Period for High-Fat, High-Sugar Diet Exposure: A Systematic Review of the Animal Literature

Animal studies suggest that poor nutrition (e.g., high-fat, high-sugar diets) may lead to impairments in cognitive functioning. Accumulating evidence suggests that the deleterious effects of these diets appear more pronounced in animals maintained on this diet early in life, consistent with the notion that the developing brain may be especially vulnerable to environmental insults. The current paper provides the first systematic review of studies comparing the effects of high-fat, high-sugar diet exposure during adolescence and adulthood on memory performance. The majority of studies (7/8) identified here report diet-induced memory problems when diet exposure began in adolescence but not adulthood. These findings lend support to the hypothesis that adolescence is a sensitive period during which palatable diets may contribute to negative neurocognitive effects. The current review explores putative mechanisms involved in diet-induced cognitive dysfunction and highlights promising areas for further research.

Anxiety-like behaviors and hippocampal nNOS in response to diet-induced obesity combined with exercise

A high-fat diet (HFD) and overweight status can induce hippocampal dysfunction, leading to depression and anxiety. Exercise has beneficial effects on emotional behaviors. We previously reported that exercise training rescues HFD-induced excess hippocampal neuronal nitric oxide synthase (nNOS) expression, which is a key regulator of anxiety. Here, we investigated anxiety-like behaviors and hippocampal nNOS expression in response to HFD combined with exercise. Mice were assigned to standard diet, HFD, or HFD with exercise groups for 12 weeks. We found that exercise during the final 6 weeks of the HFD regime improved 12 weeks of HFD-induced defecation, accompanied by rescue of excess nNOS expression. However, anxiety indicators in the elevated plus maze were unchanged. These effects were not apparent after only 1 week of exercise. In conclusion, 6 weeks of exercise training reduced HFD-related anxiety according to one of our measures (defecation), and reversed changes in the hippocampal nNOS/NO pathway.

Handling stress impairs learning through a mechanism involving caspase-1 activation and adenosine signaling

Acute stressors can induce fear and physiologic responses that prepare the body to protect from danger. A key component of this response is immune system readiness. In particular, inflammasome activation appears critical to linking stress to the immune system. Here, we show that a novel combination of handling procedures used regularly in mouse research impairs novel object recognition (NOR) and activates caspase-1 in the amygdala. In male mice, this handling-stress paradigm combined weighing, scruffing and sham abdominal injection once per hr. While one round of weigh/scruff/needle-stick had no impact on NOR, two rounds compromised NOR without impacting location memory or anxiety-like behaviors. Caspase-1 knockout (KO), IL-1 receptor 1 (IL-1R1) KO and IL-1 receptor antagonist (IL-RA)-administered mice were resistant to handling stress-induced loss of NOR. In addition, examination of the brain showed that handling stress increased caspase-1 activity 85% in the amygdala without impacting hippocampal caspase-1 activity. To delineate danger signals relevant to handling stress, caffeine-administered and adenosine 2A receptor (A2AR) KO mice were tested and found resistant to impaired learning and caspase-1 activation. Finally, mice treated with the β-adrenergic receptor antagonist, propranolol, were resistant to handling stress-induced loss of NOR and caspase-1 activation. Taken together, these results indicate that handling stress-induced impairment of object learning is reliant on a pathway requiring A2AR-dependent activation of caspase-1 in the amygdala that appears contingent on β-adrenergic receptor functionality.

Refractory diet-dependent changes in neural microstructure: Implications for microstructural endophenotypes of neurologic and psychiatric disease

Alterations in gut microbiome populations via dietary manipulation have been shown to induce diet-dependent changes in white matter microstructure. The purpose of this study is to examine the durability of these diet-induced microstructural alterations. We implemented a crossover experimental design where post-weaned male rats were assigned to one of four experimental diets. Following the administration of experimental diets and again following crossover and resumption of a normal diet, brains were imaged ex-vivo with diffusion tensor imaging. Following standard image preprocessing, tract-based spatial statistics and region-of-interest measurements were then calculated for all diffusion tensor indices. Voxel-wise differences in FA were identified in the high fat diet group when compared to animals receiving a control diet. Following crossover, there were new voxel-wise changes in both FA and TR that do not correspond to the regions previously identified. Animals crossed over from the high fiber diet demonstrate widespread and global changes in the diffusion tensor that stand in stark contrast to the minimal changes identified before crossover. While no significant differences between any of the diffusion metrics were identified in the high protein group before crossover, statistically significant decreased RD values were observed following resumption of a normal diet. Diet-induced changes in neural microstructure are durable changes that are unrecoverable following the resumption of a normal diet. We further show that in certain experimental diets, resumption of a normal diet can lead to further marked and unanticipated changes in white matter microstructure.

The Physical Burden of Immunoperception

The previous chapter introduced the ImmunoEmotional Regulatory System (IMMERS). Also, there was a brief discussion about psychological states/psychiatric disorders that so far have been linked to the IMMERS. The present chapter considers another aspect of the IMMERS in which physiological states/physical diseases can be fit to the IMMERS.

Neuroprotective effects of vitamin D on high fat diet- and palmitic acid-induced enteric neuronal loss in mice

Background

The role of vitamin D in obesity and diabetes is debated. Obese and/or diabetic patients have elevated levels of free fatty acids, increased susceptibility to gastrointestinal symptoms and are suggested to have altered vitamin D balance. The enteric nervous system is pivotal in regulating gastrointestinal activity and high fat diet (HFD) has been shown to cause loss of enteric neurons in ileum and colon. This study investigates the effect of vitamin D on HFD- and palmitic acid-induced enteric neuronal loss in vivo and in vitro.

Methods

Mice were fed either a normal diet (ND) or HFD supplemented with varying levels of vitamin D (from 0x to 20x normal vitamin D level) for 19 weeks. Ileum and colon were analyzed for neuronal numbers and remodeling. Primary cultures of myenteric neurons from mouse small intestine were treated with palmitic acid (4x10^-4M) and/or 1α,25-hydroxy-vitamin D3 (VD, 10^-11- 10^-7M) with or without modulators of lipid metabolism and VD pathways. Cultures were analyzed by immunocyto- and histochemical methods.

Results

Vitamin D supplementation had no effect on enteric neuronal survival in the ND group. HFD caused substantial loss of myenteric neurons in ileum and colon. Vitamin D supplementation between 0-2x normal had no effect on HFD-induced neuronal loss. Supplementation with 20x normal, prevented the HFD-induced neuronal loss. In vitro supplementation of VD prevented the palmitic acid-induced neuronal loss. The VD receptor (VDR) was not identified in enteric neurons. Enteric glia expressed the alternative VD receptor, protein disulphide isomerase family A member 3 (PDIA3), but PDIA3 was not found to mediate the VD response in vitro. Inhibition of peroxisome proliferator-activated receptor gamma (PPARγ) and immune neutralization of isocitrate lyase prevented the VD mediated neuroprotection to palmitic acid exposure.

Conclusions

Results show that VD protect enteric neurons against HFD and palmitic acid induced neuronal loss. The mechanism behind is suggested to be through activation of PPARγ leading to improved neuronal peroxisome function and metabolism of neuronal lipid intermediates.