Short exposure to a diet rich in both fat and sugar or sugar alone impairs place, but not object recognition memory in rats

Short-term high fat diet impairs memory, exacerbates the neuroimmune response, and evokes synaptic degradation via a complement-dependent mechanism in a mouse model of Alzheimer's disease

Alzheimer's Disease (AD) is a neurodegenerative disease characterized by profound memory impairments, synaptic loss, neuroinflammation, and hallmark pathological markers. High-fat diet (HFD) consumption increases the risk of developing AD even after controlling for metabolic syndrome, pointing to a role of the diet itself in increasing risk. In AD, the complement system, an arm of the immune system which normally tags redundant or damaged synapses for pruning, becomes pathologically overactivated leading to tagging of healthy synapses. While the unhealthy diet to AD link is strong, the underlying mechanisms are not well understood in part due to confounding variables associated with long-term HFD which can independently influence the brain. Therefore, we experimented with a short-term diet regimen to isolate the diet's impact on brain function without causing obesity. This project investigated the effect of short-term HFD on 1) memory, 2) neuroinflammation including complement, 3) AD pathology markers, 4) synaptic markers, and 5) in vitro microglial synaptic phagocytosis in the 3xTg-AD mouse model. Following the consumption of either standard chow or HFD, 3xTg-AD and non-Tg mice were tested for memory impairments. In a separate cohort of mice, levels of hippocampal inflammatory markers, complement proteins, AD pathology markers, and synaptic markers were measured. For the last set of experiments, BV2 microglial phagocytosis of synapses was evaluated. Synaptoneurosomes isolated from the hippocampus of 3xTg-AD mice fed chow or HFD were incubated with equal numbers of BV2 microglia. The number of BV2 microglia that phagocytosed synaptoneurosomes was tracked over time with a live-cell imaging assay. Finally, we incubated BV2 microglia with a complement receptor inhibitor (NIF) and repeated the assay. Behavioral analysis showed 3xTg-AD mice had significantly impaired long-term contextual and cued fear memory compared to non-Tg mice that was further impaired by HFD. HFD significantly increased inflammatory markers and complement expression while decreasing synaptic marker expression only in 3xTg-AD mice, without altering AD pathology markers. Synaptoneurosomes from HFD-fed 3xTg-AD mice were phagocytosed at a significantly higher rate than those from chow-fed mice, suggesting the synapses were altered by HFD. The complement receptor inhibitor blocked this effect in a dose-dependent manner, demonstrating the HFD-mediated increase in phagocytosis was complement dependent. This study indicates HFD consumption increases neuroinflammation and over-activates the complement cascade in 3xTg-AD mice, resulting in poorer memory. The in vitro data point to complement as a potential mechanistic culprit and therapeutic target underlying HFD's influence in increasing cognitive vulnerability to AD.

Association between a body shape index and cognitive impairment among us older adults from a cross-sectional survey of the NHANES 2011-2014

PURPOSE

This study aimed to assess the relationship between A Body Shape Index (ABSI) and cognitive impairment among older adults in the United States.

METHODS

This cross-sectional study analyzed cognitive function in 2,752 individuals aged 60 and older using data from the 2011-2014 National Health and Nutrition Examination Survey (NHANES). Cognitive assessments were conducted using the Immediate Recall Test (IRT), Delayed Recall Test (DRT), Animal Fluency Test (AFT), and Digit Symbol Substitution Test (DSST). A Body Shape Index (ABSI) was calculated from waist circumference (WC), weight, and height. The relationship between ABSI and cognitive outcomes was examined through multifactorial linear regression, smooth curve fitting, and subgroup and interaction analyses.

RESULTS

With complete data, 2752 persons 60 and older participated in the study. After adjusting for covariables, these results showed statistically significant negative relationships between ABSI, IRT, and DSST scores. The negative correlation between DSST and ABSI is more substantial in males than females. There is less of a negative link between ABSI, AFT, and DSST among drinkers who consume 12 or more drinks annually compared to those who consume less. Furthermore, compared to individuals without high blood pressure(HBP), those who suffered HBP showed a more significant negative connection between ABSI and AFT.

CONCLUSION

Lower cognitive function was linked to higher ABSI.

High sugar consumption for seven days in adult mice increased blood glucose variability, induced an anxiolytic effect and triggered oxidative stress in cerebral cortex

Brain function is highly altered by glucose toxicity related to diabetes. High consumption of sugar in normal conditions is suspected to affect as well brain integrity. The present study investigates the possible effects of short-term exposure to high sugar diet on brain redox homeostasis in healthy mice. Male adult healthy mice were divided into two groups: control (CG) and sugar-exposed group (SG), that was exposed continually to 10% of glucose in drinking water for 7 days and 20% sucrose pellets food. Behavior, blood glucose variability and cerebral cortex oxidative stress biomarkers were measured at the end of exposure. Animals exposed to the high sugar diet expressed a significant increase in blood glucose levels and high glucose variability compared to control. These animals expressed as well anxiolytic behavior as revealed by the plus maze test. Exposure to the sugar diet altered redox homeostasis in the brain cortex as revealed by an increase in lipid peroxidation and the activity of antioxidant enzymes superoxide dismutase (SOD) and glutathione-s-transferase (GST). On the other hand, catalase (CAT) activity was decreased, and reduced glutathione (GSH) level was not altered compared to control. Further studies are required to understand the mechanisms trigging oxidative stress (OS) in the brain in response to short term exposure to high sugar diet and glucose fluctuations.

High-Caloric Diets in Adolescence Impair Specific GABAergic Subpopulations, Neurogenesis, and Alter Astrocyte Morphology

We compared the effects of two different high-caloric diets administered to 4-week-old rats for 12 weeks: a diet rich in sugar (30% sucrose) and a cafeteria diet rich in sugar and high-fat foods. We focused on the hippocampus, particularly on the gamma-aminobutyric acid (GABA)ergic system, including the Ca2+-binding proteins parvalbumin (PV), calretinin (CR), calbindin (CB), and the neuropeptides somatostatin (SST) and neuropeptide Y (NPY). We also analyzed the density of cholinergic varicosities, brain-derived neurotrophic factor (BDNF), reelin (RELN), and cyclin-dependent kinase-5 (CDK-5) mRNA levels, and glial fibrillary acidic protein (GFAP) expression. The cafeteria diet reduced PV-positive neurons in the granular layer, hilus, and CA1, as well as NPY-positive neurons in the hilus, without altering other GABAergic populations or overall GABA levels. The high-sugar diet induced a decrease in the number of PV-positive cells in CA3 and an increase in CB-positive cells in the hilus and CA1. No alterations were observed in the cholinergic varicosities. The cafeteria diet also reduced the relative mRNA expression of RELN without significant changes in BDNF and CDK5 levels. The cafeteria diet increased the number but reduced the length of the astrocyte processes. These data highlight the significance of determining the mechanisms mediating the observed effects of these diets and imply that the cognitive impairments previously found might be related to both the neuroinflammation process and the reduction in PV, NPY, and RELN expression in the hippocampal formation.

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.

Effects of metformin on behavioral alterations produced by chronic sucrose consumption in male rats

Excessive consumption of sugary drinks negatively impacts the developing brain, producing long-lasting behavioral and metabolic disorders. Here, we study whether treatment with the antihyperglycemic agent metformin prevents some of the anxiety and memory alterations produced by chronic sucrose consumption. Male Sprague-Dawley rats had unrestricted access to water (control group) and a bottle containing a 10% sucrose solution (sucrose group, SUC) for 35 days. In parallel, a group of animals from SUC received metformin (25 mg/kg or 50 mg/kg, orally; MET 25 and MET 50 groups, respectively). After 2 weeks of metformin treatment, the animals weighed less than controls. SUC and MET 50 groups compensated for the caloric intake from the sugary solution by consuming less chow. In contrast, total energy intake in MET 25 was higher than the rest of the groups, but they still weighed less than control and SUC groups, suggesting that at this concentration, metformin delays body growth. The animals were then tested for the open field (OF), elevated plus maze (EPM) and novel object location (NOL) tests. In the OF, SUC animals spent more time in the central zone of the arena, evidenced by an increased number of entries and the distance traveled there. In the EPM, SUC animals spent more time in the open arms and less time in the central square. Metformin treatment prevented the decreased anxiety observed in SUC animals in the OF and EPM. In the NOL test, SUC animals showed less interest in novelty and metformin treatment did not improve this alteration. The preference for open spaces in the OF and EPM were associated with increased serum triglycerides (TG) and malondialdehyde levels in the medial prefrontal cortex (mPFC) and the hippocampus (HIP), while poor memory performance was associated with high basal blood glucose levels. In conclusion, the decreased anxiety-like behavior produced by chronic sucrose consumption was prevented by metformin treatment, through a mechanism that probably involves normalization of TG levels and decreased oxidative stress in mPFC and HIP.

A Comprehensive Review of the Effects of Glycemic Carbohydrates on the Neurocognitive Functions Based on Gut Microenvironment Regulation and Glycemic Fluctuation Control

Improper glycemic carbohydrates (GCs) consumption can be a potential risk factor for metabolic diseases such as obesity and diabetes, which may lead to cognitive impairment. Although several potential mechanisms have been studied, the biological relationship between carbohydrate consumption and neurocognitive impairment is still uncertain. In this review, the main effects and mechanisms of GCs' digestive characteristics on cognitive functions are comprehensively elucidated. Additionally, healthier carbohydrate selection, a reliable research model, and future directions are discussed. Individuals in their early and late lives and patients with metabolic diseases are highly susceptible to dietary-induced cognitive impairment. It is well known that gut function is closely related to dietary patterns. Unhealthy carbohydrate diet-induced gut microenvironment disorders negatively impact cognitive functions through the gut-brain axis. Moreover, severe glycemic fluctuations, due to rapidly digestible carbohydrate consumption or metabolic diseases, can impair neurocognitive functions by disrupting glucose metabolism, dysregulating calcium homeostasis, oxidative stress, inflammatory responses, and accumulating advanced glycation end products. Unstable glycemic status can lead to more severe neurological impairment than persistent hyperglycemia. Slow-digested or resistant carbohydrates might contribute to better neurocognitive functions due to stable glycemic response and healthier gut functions than fully gelatinized starch and nutritive sugars.

The influence of ultra-processed food consumption on reward processing and energy intake: Background, design, and methods of a controlled feeding trial in adolescents and young adults

BACKGROUND

The greatest age-related weight gain occurs in the early/mid-20s. Overall dietary quality among adolescents and emerging adults (age 18-25) is poor, with ultra-processed foods (UPF) representing more than two-thirds of adolescents' total energy intake (i.e., 68%). UPF consumption may impact cognitive and neurobiological factors that influence dietary decision-making and energy intake (EI). To date, no research has addressed this in this population.

METHODS

Participants aged 18-25 will undergo two 14-day controlled feeding periods (81% UPF, 0% UPF) using a randomly assigned crossover design, with a 4-week washout between conditions. Brain response to a UPF-rich milkshake, as well as behavioral measures of executive function, will be evaluated before and after each diet. Following each diet, measurements include ad libitum buffet meal EI, food selection, eating rate, and eating in the absence of hunger (EAH). Prior to initiating recruitment, controlled diet menus, buffet, and EAH snacks were developed and evaluated for palatability. Sensory and texture attributes of buffet and EAH snack foods were also evaluated.

RESULTS

Overall diet palatability was rated "like very much" (8)/"like moderately"(7) (UPF: 7.6 ± 1.0; Non-UPF: 6.8 ± 1.5). Subjective hardness rating (range = 1-9 [1 = soft, 9 = hard] was similar between UPF and Non-UPF buffet and snack items (UPF:4.22 ± 2.19, Non-UPF: 4.70 ± 2.03), as was the objective measure of hardness (UPF: 2874.33 ± 2497.06 g, Non-UPF: 2243.32 ± 1700.51 g).

CONCLUSIONS

Findings could contribute to an emerging neurobiological understanding of the effects of UPF consumption including energy overconsumption and weight gain among individuals at a critical developmental stage.

The Effect of Fat Intake with Increased Omega-6-to-Omega-3 Polyunsaturated Fatty Acid Ratio in Animal Models of Early and Late Alzheimer's Disease-like Pathogenesis

This work aims to clarify the effect of dietary polyunsaturated fatty acid (PUFA) intake on the adult brain affected by amyloid pathology. McGill-R-Thy1-APP transgenic (Tg) rat and 5xFAD Tg mouse models that represent earlier or later disease stages were employed. The animals were exposed to a control diet (CD) or an HFD based on corn oil, from young (rats) or adult (mice) ages for 24 or 10 weeks, respectively. In rats and mice, the HFD impaired reference memory in wild-type (WT) animals but did not worsen it in Tg, did not cause obesity, and did not increase triglycerides or glucose levels. Conversely, the HFD promoted stronger microglial activation in Tg vs. WT rats but had no effect on cerebral amyloid deposition. IFN-γ, IL-1β, and IL-6 plasma levels were increased in Tg rats, regardless of diet, while CXCL1 chemokine levels were increased in HFD-fed mice, regardless of genotype. Hippocampal 3-nitrotyrosine levels tended to increase in HFD-fed Tg rats but not in mice. Overall, an HFD with an elevated omega-6-to-omega-3 ratio as compared to the CD (25:1 vs. 8.4:1) did not aggravate the outcome of AD regardless of the stage of amyloid pathology, suggesting that many neurobiological processes relevant to AD are not directly dependent on PUFA intake.

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.

The Connection between Chronic Liver Damage and Sporadic Alzheimer's Disease: Evidence and Insights from a Rat Model

Junk foods are typically low in essential nutrients, such as vitamins, minerals, and antioxidants. They are also loaded with trans fats and saturated fats, which can increase the level of triglycerides in the blood. High triglyceride levels can contribute to the development of non-alcoholic fatty liver disease (NAFLD), a condition where excess fat accumulates in the liver. A high intake of junk foods can lead to insulin resistance, a condition where the body's cells become less responsive to insulin. A diet lacking in nutrients and loaded with unwanted toxins can impair the liver's ability to detoxify harmful substances and damage its overall function. It is known that the regular consumption of junk food can be linked to memory impairment and cognitive decline. Several studies have shown that diets high in unhealthy fats, sugars, and processed foods can negatively impact brain health, including memory function. In this study, Wistar rats were used to model Late-Onset Alzheimer's Disease (LOAD), which was inspired by knowledge of the liver-brain axis's role in causing dementia. The model mimicked junk-food-induced liver-brain damage, and was developed by using the toxins d-galactosamine, ethanol and d-galactose. To begin with, the model rats demonstrated insulin resistance, a characteristic of LOAD patients. Glucose levels in both the brain and liver tissues were significantly elevated in the model, paralleling clinical findings in LOAD patients. High glucose levels in the brain lead to the increased production of advanced glycation end-products (AGEs), which, along with amyloid beta, harm neighbouring neurons. Histopathological analysis revealed deformed glial nodules, apoptotic neurons, and amyloid plaques in the brain section in the later stages of the disease. Simultaneously, the liver section displayed features of cirrhosis, including an effaced lobular architecture and the extravasation of red blood cells. Liver enzymes ALT, AST and ALP were consistently elevated with disease progression. Furthermore, immunohistochemistry confirmed the presence of amyloid precursor protein (APP) in the diseased brain. The positive expression of Hypoxia-Inducible Factor 3-Alpha (HIF3A) in the brain indicated hypoxic conditions, which is consistent with other LOAD studies. This model also exhibited damaged intestinal villi and excessive bowel and urinary incontinence, indicating malnutrition and a disturbed gut microbiome, which is also consistent with LOAD patients. Bioinformatics analysis on serum protein suggests a few affected molecular pathways, like the amyloid secretase pathway, androgen/oestrogen/progesterone biosynthesis, the apoptosis signalling pathway, the insulin/IGF pathway-protein kinase B signalling cascade, the Metabotropic glutamate receptor group I pathway, the Wnt signalling pathway, etc. Behavioural analysis confirmed memory decline and the loss of muscle strength with disease progression. Overall, this rat model of LOAD sheds valuable light on LOAD pathology and highlights the potential link between liver dysfunction, particularly induced by the excessive consumption of junk food, and LOAD. This study contributes to a deeper understanding of the complex molecular mechanisms involved in LOAD, paving the way for new possibilities in therapeutic interventions.

Habitual intake of fat and sugar is associated with poorer memory and greater impulsivity in humans

The vicious cycle model of obesity suggests that repeated habitual intake of a diet high in fat and sugar (HFS) results in impairment in hippocampal function which in turn increases impulsive behaviours, making it harder to resist unhealthy diet choices. Evidence from studies with rodents consistently show switching to a HFS diet impairs performance on hippocampally-sensitive memory tasks. The limited literature in humans also suggest impaired memory and increased impulsivity related to higher habitual HFS intake. However, these changes in memory and impulsivity have been looked at independently. To investigate how these effects are inter-related, three experiments were conducted where relative HFS intake was related to measures of memory and impulsivity. In Experiment 1 (90 female participants), HFS was associated with higher scores on the Everyday Memory Questionnaire-revised (EMQ), and higher scores on the total, Attention (BISatt) and Motor (BISmot) sub-scales of the Barratt Impulsiveness Scale (BIS11). Experiment 2 (84 women and 35 men), replicated the association between HFS and EMQ, and also found HFS related to poorer performance on the hippocampally-sensitive 4 mountain (4MT) memory task. The association between HFS intake and the BISatt replicated, but there were no significant associations with other BIS11 measures or delay-discounting for monetary rewards. Experiment 3 (199 women and 87 men) replicated the associations between DFS and 4MT and EMQ, and also found an association with overall recall, but not response inhibition, from a Remembering Causes Forgetting task: HFS was also significantly associated with BIS total, BISatt and BISmot. In all three studies these associations remained when potential confounds (BMI, age, gender, hunger state, restrained and disinhibited eating) were controlled for. Mediation analysis found that the effect of HFS on memory at least part mediated the relationship between HFS and impulsivity in Experiments 1 and 3, but not 2. Overall these data provide some support for the vicious cycle model, but also suggest that trait impulsivity may be a risk factor for poor dietary choice.

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.

High-Fat-Sugar Diet is Associated with Impaired Hippocampus-Dependent Memory in Humans

Overconsumption of high-fat and high-sugar (HFS) diet may affect the hippocampus, and consequently, memory functions. Yet, converging evidence is needed to demonstrate that the type of memory affected by HFS diet consumption is indeed hippocampus dependent. Moreover, the extent to which HFS diet can also affect executive functioning, and indirectly affect memory requires further examination. In this online study, we asked 349 young adults to report their HFS diet consumption and complete a word memory task, the Everyday Memory Questionnaire, and importantly two memory tasks that have been shown to robustly engage the hippocampus, i.e., the Pattern Separation and Associative Memory Tasks. Participants also completed two executive functioning tasks, the Trail Making Task (TMT) and the Stroop Task. These measures assess attention/cognitive flexibility and the ability to inhibit cognitive interference, respectively. After controlling for confounding variables, we found that participants who reported higher level consumption of a HFS diet performed worse on the Pattern Separation Task and that higher HFS intake was significantly associated with poorer TMT task performance and longer Stroop average reaction time (RT). TMT and Stroop RT scores indicative of reduced executive function also partially mediated the relationship between HFS diet and memory performance on the pattern separation task. Taken together, our results provide converging evidence that HFS diet may impair hippocampus-dependent memory. HFS diet may also affect executive functioning and indirectly impair memory function. The findings are consistent with human subject and animal studies and call for further investigations on the psychological and neural mechanisms underlying the dietary effects on cognitive processes.

Binge eating, overeating and food addiction: Approaches for examining food overconsumption in laboratory rodents

Overeating ranges in severity from casual overindulgence to an overwhelming drive to consume certain foods. At its most extreme, overeating can manifest as clinical diagnoses such as binge eating disorder or bulimia nervosa, yet subclinical forms of overeating such as emotional eating or uncontrolled eating can still have a profoundly negative impact on health and wellbeing. Although rodent models cannot possibly capture the full spectrum of disordered overeating, studies in laboratory rodents have substantially progressed our understanding of the neurobiology of overconsumption. These experimental approaches range from simple food-exposure protocols that promote binge-like eating and the development of obesity, to more complex operant procedures designed to examine distinct 'addiction-like' endophenotypes for food. This review provides an overview of these experimental approaches, with the view to providing a comprehensive resource for preclinical investigators seeking to utilize behavioural models for studying the neural systems involved in food overconsumption.

Short-term Cafeteria Diet Is Associated with Fat Mass Accumulation, Systemic and Amygdala Inflammation, and Anxiety-like Behavior in Adult Male Wistar Rats

Obesity is linked to metabolic, hormonal and biochemical alterations, and is also a risk factor for behavioral disorders. Evidence suggests that these disorders may be related to the consumption of hypercaloric diets, fat mass accumulation and changes in inflammation and redox status. Although much is known about the chronic effects of hypercaloric diets on mental health, few studies have evaluated the consequences of short-term exposure of these diets on behavior. The aim of this study was to evaluate nutritional, behavioral (anxiety-like), inflammatory and redox status parameters in adult male Wistar rats exposed to short-term cafeteria diet. Adult Wistar male rats (90 days-old; n = 12/group) received, during 14 days, the diets: Control- standard diet; Simple Cafeteria Diet (SCD)- homogeneous cafeteria diet. Varied Cafeteria Diet (VCD)- cafeteria diet with rotation and variation. Nutritional analyzes and tests for anxiety-like behaviors were performed, in addition to inflammatory and redox status measurements in blood and amygdala. The SCD group showed higher fat energy intake, while the VCD group consumed more energy from carbohydrates. SCD and VCD showed higher fat mass accumulation, in addition to higher levels of TNFα, INFγ, TBARS and FRAP in the blood. Also, SCD and VCD groups reported high levels of TNFα in the amygdala. Regarding behavioral evaluations, SCD and VCD groups showed anxiogenesis in the elevated plus maze, light-dark box, and open field tests. Therefore, the two cafeteria diets induced obesity and systemic inflammation, which in turn, resulted in an increase in amygdala TNFα levels and anxiety-like behaviors in Wistar rats.

Effects of High-Fat and High-Fat High-Sugar Diets in the Anxiety, Learning and Memory, and in the Hippocampus Neurogenesis and Neuroinflammation of Aged Rats

High-caloric diets induce several deleterious alterations in the human body, including the brain. However, information on the effects of these diets on the elderly brain is scarce. Therefore, we studied the effects of 2 months of treatment with high-fat (HF) and high-fat-high-sugar (HFHS) diets on aged male Wistar rats at 18 months. Anxiety levels were analyzed using the open-field and plus-maze tests, while learning and memory processes were analyzed using the Morris water maze test. We also analyzed neurogenesis using doublecortin (DCX) and neuroinflammation using glial fibrillary acidic protein (GFAP). In aged rats, the HFHS diet impaired spatial learning, memory, and working memory and increased anxiety levels, associated with a reduction in the number of DCX cells and an increase in GFAP cells in the hippocampus. In contrast, the effects of the HF diet were lighter, impairing spatial memory and working memory, and associated with a reduction in DCX cells in the hippocampus. Thus, our results suggest that aged rats are highly susceptible to high-caloric diets, even if they only started in the elderly, with an impact on cognition and emotions. Furthermore, diets rich in saturated fats and sugar are more detrimental to aged rats than high-fat diets are.

Association Between Consumption of Ultraprocessed Foods and Cognitive Decline

Importance

Although consumption of ultraprocessed food has been linked to higher risk of cardiovascular disease, metabolic syndrome, and obesity, little is known about the association of consumption of ultraprocessed foods with cognitive decline.

Objective

To investigate the association between ultraprocessed food consumption and cognitive decline in the Brazilian Longitudinal Study of Adult Health.

Design, Setting, and Participants

This was a multicenter, prospective cohort study with 3 waves, approximately 4 years apart, from 2008 to 2017. Data were analyzed from December 2021 to May 2022. Participants were public servants aged 35 to 74 years old recruited in 6 Brazilian cities. Participants who, at baseline, had incomplete food frequency questionnaire, cognitive, or covariate data were excluded. Participants who reported extreme calorie intake (<600 kcal/day or >6000 kcal/day) and those taking medication that could negatively interfere with cognitive performance were also excluded.

Exposures

Daily ultraprocessed food consumption as a percentage of total energy divided into quartiles.

Main Outcomes and Measures

Changes in cognitive performance over time evaluated by the immediate and delayed word recall, word recognition, phonemic and semantic verbal fluency tests, and Trail-Making Test B version.

Results

A total of 15 105 individuals were recruited and 4330 were excluded, leaving 10 775 participants whose data were analyzed. The mean (SD) age at the baseline was 51.6 (8.9) years, 5880 participants (54.6%) were women, 5723 (53.1%) were White, and 6106 (56.6%) had at least a college degree. During a median (range) follow-up of 8 (6-10) years, individuals with ultraprocessed food consumption above the first quartile showed a 28% faster rate of global cognitive decline (β = -0.004; 95% CI, -0.006 to -0.001; P = .003) and a 25% faster rate of executive function decline (β = -0.003, 95% CI, -0.005 to 0.000; P = .01) compared with those in the first quartile.

Conclusions and Relevance

A higher percentage of daily energy consumption of ultraprocessed foods was associated with cognitive decline among adults from an ethnically diverse sample. These findings support current public health recommendations on limiting ultraprocessed food consumption because of their potential harm to cognitive function.

Different Sources of Sugar Consumption and Cognitive Performance in Older Adults: Data From the National Health and Nutrition Examination Survey 2011-2014

OBJECTIVES

Excess sugar consumption, particularly in sugar-sweetened beverages (SSBs), has been linked to poor cognitive performance. We aimed to assess the association of consumption of total sugar, as well as the consumption of SSBs, solid desserts, and 100% fruit juice with cognitive performance among older adults.

METHODS

Consumption of total sugar, SSBs, solid desserts, and 100% fruit juice were obtained from the 24-hr recall interview. Cognitive performance was evaluated using the Consortium to Establish a Registry for Alzheimer's Disease word list, the Animal Fluency Test, and the Digit Symbol Substitution Test. Binary logistic regression models were used to evaluate the association between consumption of sugar (total and from different sources) and cognitive performance.

RESULTS

A total of 1,938 participants aged 60 years or older from the National Health and Nutrition Examination Survey 2011-2014 were included. Compared to the lowest tertile, the highest tertile of total sugar consumption was independently associated with higher odds of low memory performance (odds ratio [OR] = 1.87, 95% confidence interval [CI] = 1.00; 3.50, p = .049). Consumption of SSBs was associated with higher risk of low memory (OR = 1.58, 95% CI = 1.11; 2.25, p = .014), whereas consumption of solid desserts was associated with lower risk of low verbal fluency performance (OR = 0.62, 95% CI = 0.41; 0.95, p = .032).

DISCUSSION

Higher consumption of total sugars and SSBs was associated with lower memory performance, while consumption of solid desserts was associated with higher verbal fluency performance.

Obesity-Induced Brain Neuroinflammatory and Mitochondrial Changes

Obesity is defined as abnormal and excessive fat accumulation, and it is a risk factor for developing metabolic and neurodegenerative diseases and cognitive deficits. Obesity is caused by an imbalance in energy homeostasis resulting from increased caloric intake associated with a sedentary lifestyle. However, the entire physiopathology linking obesity with neurodegeneration and cognitive decline has not yet been elucidated. During the progression of obesity, adipose tissue undergoes immune, metabolic, and functional changes that induce chronic low-grade inflammation. It has been proposed that inflammatory processes may participate in both the peripheral disorders and brain disorders associated with obesity, including the development of cognitive deficits. In addition, mitochondrial dysfunction is related to inflammation and oxidative stress, causing cellular oxidative damage. Preclinical and clinical studies of obesity and metabolic disorders have demonstrated mitochondrial brain dysfunction. Since neuronal cells have a high energy demand and mitochondria play an important role in maintaining a constant energy supply, impairments in mitochondrial activity lead to neuronal damage and dysfunction and, consequently, to neurotoxicity. In this review, we highlight the effect of obesity and high-fat diet consumption on brain neuroinflammation and mitochondrial changes as a link between metabolic dysfunction and cognitive decline.

Long-Term Memory Function Impairments following Sucrose Exposure in Juvenile versus Adult Rats

We previously described that excessive consumption of sucrose during youth produces fear memory and anxiety-like behavior in adulthood. Here, we evaluated whether high cognitive function is also affected by studying early sucrose consumption in object recognition memory (NOR). Male Sprague Dawley rats were tested for short-term, long-term, and consolidated NOR after 25 days of unlimited sucrose access in juvenile (PD 25–50) or adult age (PD 75–100). All rats spent equal time exploring the two objects during the sample phase T1. When animals were exposed for 2, 24 h or 7 days later to a copy of the objects presented in T1 and a novel object, the sucrose-exposed juvenile group failed to distinguish between the familiar and the novel objects in contrast with the rest of the groups. Sucrose-exposed animals developed hypertriglyceridemia and glucose intolerance, but juvenile animals showed increased fasting glycemia and sustained the glucose intolerance longer. Moreover, sucrose decreased hippocampal proBDNF expression in juveniles while it was increased in adults, and sucrose also increased RAGE expression in adults. The NOR exploration ratio correlated negatively with basal glycemia and positively with proBDNF. Taken together, these data suggest that sucrose-induced alterations in glucose metabolism may contribute to a long-term decline in proBDNF and impaired recognition memory.

Feeding the Brain: Effect of Nutrients on Cognition, Synaptic Function, and AMPA Receptors

In recent decades, traditional eating habits have been replaced by a more globalized diet, rich in saturated fatty acids and simple sugars. Extensive evidence shows that these dietary factors contribute to cognitive health impairment as well as increase the incidence of metabolic diseases such as obesity and diabetes. However, how these nutrients modulate synaptic function and neuroplasticity is poorly understood. We review the Western, ketogenic, and paleolithic diets for their effects on cognition and correlations with synaptic changes, focusing mainly (but not exclusively) on animal model studies aimed at tracing molecular alterations that may contribute to impaired human cognition. We observe that memory and learning deficits mediated by high-fat/high-sugar diets, even over short exposure times, are associated with reduced arborization, widened synaptic cleft, narrowed post-synaptic zone, and decreased activity-dependent synaptic plasticity in the hippocampus, and also observe that these alterations correlate with deregulation of the AMPA-type glutamate ionotropic receptors (AMPARs) that are crucial to neuroplasticity. Furthermore, we explored which diet-mediated mechanisms modulate synaptic AMPARs and whether certain supplements or nutritional interventions could reverse deleterious effects, contributing to improved learning and memory in older people and patients with Alzheimer’s disease.

Appetitive interoception, the hippocampus and western-style diet

Obesity, Type 2 diabetes and other metabolic disorders continue to pose serious challenges to human health and well-being. An important source of these challenges is the overconsumption of saturated fats and sugar, main staples of what has been called the Western-style diet (WD). The current paper describes a theoretical model and supporting evidence that links intake of a WD to interference with a specific brain substrate that underlies processing of interoceptive signals of hunger and satiety. We review findings from rats and humans that the capacity of these signals to modulate the strength of appetitive and eating behavior depends on the functional integrity of the hippocampus and the learning memory operations it performs. Important among these operations is the use of contextual information to retrieve memories that are associated with other events. Within our framework, satiety provides an interoceptive context that informs animals that food cues and appetitive behavior will not be followed by rewarding postingestive outcomes. This serves to prevent those cues and responses from retrieving those reward memories. The findings reviewed provide evidence that consuming a WD and the high amounts of saturated fat and sugar it contains (a) is associated with the emergence of pathophysiologies to which the hippocampus appears selectively vulnerable (b) impairs hippocampal-dependent learning and memory (HDLM) and (c) weakens behavioral control by interoceptive hunger and satiety contextual stimuli. It is hypothesized that these consequences of WD intake may establish the conditions for a vicious cycle of further WD intake, obesity, and potentially cognitive decline.

Overnutrition Induced Cognitive Impairment: Insulin Resistance, Gut-Brain Axis, and Neuroinflammation

Overnutrition-related obesity has become a worldwide epidemic, and its prevalence is expected to steadily rise in the future. It is widely recognized that obesity exerts negative impacts on metabolic disorders such as type 2 diabetes mellitus (T2DM) and cardiovascular diseases. However, relatively fewer reports exist on the impairment of brain structure and function, in the form of memory and executive dysfunction, as well as neurogenerative diseases. Emerging evidence indicates that besides obesity, overnutrition diets independently induce cognitive impairments via multiple mechanisms. In this study, we reviewed the clinical and preclinical literature about the detrimental effects of obesity or high-nutrition diets on cognitive performance and cerebral structure. We mainly focused on the role of brain insulin resistance (IR), microbiota-gut-brain axis, and neuroinflammation. We concluded that before the onset of obesity, short-term exposure to high-nutrition diets already blunted central responses to insulin, altered gut microbiome composition, and activated inflammatory mediators. Overnutrition is linked with the changes in protein expression in brain insulin signaling, leading to pathological features in the brain. Microbiome alteration, bacterial endotoxin release, and gut barrier hyperpermeability also occur to trigger mental and neuronal diseases. In addition, obesity or high-nutrition diets cause chronic and low-grade systematic inflammation, which eventually spreads from the peripheral tissue to the central nervous system (CNS). Altogether, a large number of unknown but potential routes interact and contribute to obesity or diet-induced cognitive impairment. The challenge for future research is to identify effective interventions involving dietary shifts and personalized therapy targeting the underlying mechanisms to prevent and improve cognition deficits.

Horizons in Human Aging Neuroscience: From Normal Neural Aging to Mental (Fr)Agility

While aging is an important risk factor for neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, age-related cognitive decline can also manifest without apparent neurodegenerative changes. In this review, we discuss molecular, cellular, and network changes that occur during normal aging in the absence of neurodegenerative disease. Emerging findings reveal that these changes include metabolic alterations, oxidative stress, DNA damage, inflammation, calcium dyshomeostasis, and several other hallmarks of age-related neural changes that do not act on their own, but are often interconnected and together may underlie age-related alterations in brain plasticity and cognitive function. Importantly, age-related cognitive decline may not be reduced to a single neurobiological cause, but should instead be considered in terms of a densely connected system that underlies age-related cognitive alterations. We speculate that a decline in one hallmark of neural aging may trigger a decline in other, otherwise thus far stable subsystems, thereby triggering a cascade that may at some point also incur a decline of cognitive functions and mental well-being. Beyond studying the effects of these factors in isolation, considerable insight may be gained by studying the larger picture that entails a representative collection of such factors and their interactions, ranging from molecules to neural networks. Finally, we discuss some potential interventions that may help to prevent these alterations, thereby reducing cognitive decline and mental fragility, and enhancing mental well-being, and healthy aging.

Hedgehog Signal Defect Leading to Familial Exudative Vitreoretinopathy-Like Disease and Gastrointestinal Malformation

Objectives:

The aim of the study was to present a new genetic association presenting with gastrointestinal tract malformations (GTMs) and familial exudative vitreoretinopathy (FEVR)-like disease and review the genetics of Hedgehog signaling.

Materials and Methods:

Three neonates were diagnosed with FEVR-like retinal vascular disease upon routine ophthalmological examination during hospitalization in the neonatal surgical intensive care unit for GTMs. Genetic analysis of the neonates was performed.

Results:

Gestational age of the neonates was 39, 38, and 39 weeks and birth weights were 3,500, 3,600, and 3,300 grams, respectively. All six eyes of the three infants were treated by laser photocoagulation. Recurrence was not seen in any of the eyes. Genetical analysis of all the neonates diagnosed with FEVR-like disease revealed defects in the Hedgehog pathway.

Conclusion:

FEVR is a genetically well-defined retinal vascular disease. The current study is the first to show an association between FEVR-like retinal vascular disease and GTMs. This study demonstrates the importance of the Hedgehog pathway in retinal vascular and gut development.

The Effect of Dietary Fat and Sucrose on Cognitive Functioning in Mice Lacking Insulin Signaling in Neuropeptide Y Neurons

Obesogenic diets can produce hippocampal insulin resistance and impairments to hippocampal-dependent cognition. This study investigated the effect of disrupted insulin signaling in Neuropeptide Y (NPY) neurons on diet-induced deficits in hippocampal-dependent memory. Wild-type mice and mice that had a targeted knockout of insulin receptors on NPY cells (IR^lox/lox;NPY^Cre/+) were given ad libitum access to a high-fat diet (high fat; HF), 10% sucrose solution (high sugar; HS), both high-fat diet and sucrose solution (high fat, high sugar; HFHS), or a normal fat control chow for 12 weeks. Mice were tested in the Morris Water Maze (MWM), a hippocampal-dependent spatial memory task. Glucose homeostasis was assessed via a glucose tolerance test. Independent of genotype, consumption of HF, but not HS, diet increased energy intake, body weight, and plasma leptin, and impaired glucose tolerance. Disrupted insulin signaling in NPY cells and dietary interventions did not significantly affect the ability of mice to learn the location of the platform in the MWM. However, for IR^lox/lox control mice, consumption of HF, but not HS, diet resulted in reduced time spent in the target quadrant during the probe trial, suggesting a hippocampal-dependent memory deficit. IR^lox/lox;NPY^Cre/+ mice had poor performance in the probe trial regardless of diet, suggesting a floor effect. This study did not find adverse effects of chronic sucrose intake on metabolic outcomes or hippocampal-dependent memory. These data also suggest that the effects of HF diet on hippocampal-dependent memory may be dependent on insulin signaling in hippocampal NPY cells.

Caloric restriction in mice improves short-term recognition memory and modifies the neuroinflammatory response in the hippocampus of male adult offspring

Restrictive diets (RD) can influence the inflammatory phenotype of dams and their offspring. Thus, this study aimed to evaluate the effects of caloric restriction on the neuroinflammatory profile in the hippocampus and the short-term recognition memory of male offspring from RD-fed dams. Mice dams received standard diet ad libitum (CONT) or restrictive diet (RD; 30% reduction of CONT consumption) during pregnancy and lactation. Male pups were weaned at 21 days and randomly divided into two groups that received CONT or RD; groups were named according to maternal/offspring diets: CONT/CONT, CONT/RD, RD/CONT, and RD/RD. At 90 days old, short-term memory was assessed by the object recognition test (ORT); the inflammatory state of the hippocampus was analyzed by gene expression of sirtuin-1 (Sirt1) and inflammasome Nlrp3; and by protein expression of toll-like receptor-4 (TLR-4) and zonula occludens-1 (ZO-1). Our results showed an improvement in short-term memory in RD-fed offspring. The expression of Sirt1 was higher in RD/CONT compared to CONT/CONT and decreased in RD/RD compared to CONT/RD. Nlrp3 gene expression showed an offspring effect, being decreased in RD-fed mice. TLR-4 expression was higher in RD/CONT compared to CONT/CONT, similarly to ZO-1 expression. However, ZO-1 also showed a maternal diet effect and increased expression in the offspring of RD dams. Our findings demonstrate that caloric restriction improved short-term recognition memory. However, a restrictive diet should be applied with caution; depending on the offspring's diet, it may not benefit the neuroinflammatory phenotype or cognition.

The health effect of probiotics on high-fat diet-induced cognitive impairment, depression and anxiety: A cross-species systematic review

Obesity is a complex disease with many co-morbidities, including impaired cognitive functions. Obese individuals often contain an aberrant microbiota. Via the microbiota-gut-brain axis, the altered microbiota composition can affect cognition or induce anxiety- or depressive-like behavior. Probiotics have been shown to alleviate both obesity- and neurobehavioral disorder-related symptoms. Here, we evaluated previously published results on the effectiveness of probiotic intervention in alleviating obesity- or high-fat diet (HFD)-related cognitive impairment, depression and anxiety. A systematic search was performed in PubMed, Embase, and Google Scholar until June 2021 to identify relevant articles. Seventeen studies were included: one human and sixteen animal studies. Overall, the findings support the beneficial health effect of probiotics on HFD-induced cognitive impairment and anxiety. However, the results suggest that multi-strain probiotic treatments should be used with caution, especially in the absence of HFD-induced impairment. Future studies should overcome the large variation in study design and high risk of bias found in the current evidence. Nevertheless, probiotic treatment, in particular using the Lactobacillus genus, seems promising.

COVCOG 1: Factors Predicting Physical, Neurological and Cognitive Symptoms in Long COVID in a Community Sample. A First Publication From the COVID and Cognition Study

Since its first emergence in December 2019, coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has evolved into a global pandemic. Whilst often considered a respiratory disease, a large proportion of COVID-19 patients report neurological symptoms, and there is accumulating evidence for neural damage in some individuals, with recent studies suggesting loss of gray matter in multiple regions, particularly in the left hemisphere. There are a number of mechanisms by which COVID-19 infection may lead to neurological symptoms and structural and functional changes in the brain, and it is reasonable to expect that many of these may translate into cognitive problems. Indeed, cognitive problems are one of the most commonly reported symptoms in those experiencing "Long COVID"-the chronic illness following COVID-19 infection that affects between 10 and 25% of patients. The COVID and Cognition Study is a part cross-sectional, part longitudinal, study documenting and aiming to understand the cognitive problems in Long COVID. In this first paper from the study, we document the characteristics of our sample of 181 individuals who had experienced COVID-19 infection, and 185 who had not. We explore which factors may be predictive of ongoing symptoms and their severity, as well as conducting an in-depth analysis of symptom profiles. Finally, we explore which factors predict the presence and severity of cognitive symptoms, both throughout the ongoing illness and at the time of testing. The main finding from this first analysis is that that severity of initial illness is a significant predictor of the presence and severity of ongoing symptoms, and that some symptoms during the initial illness-particularly limb weakness-may be more common in those that have more severe ongoing symptoms. Symptom profiles can be well described in terms of 5 or 6 factors, reflecting the variety of this highly heterogenous condition experienced by the individual. Specifically, we found that neurological/psychiatric and fatigue/mixed symptoms during the initial illness, and that neurological, gastrointestinal, and cardiopulmonary/fatigue symptoms during the ongoing illness, predicted experience of cognitive symptoms.

High sucrose diet does not impact spatial cognition in rats using advanced touchscreen technology

INTRODUCTION

Western diets, including those consisting of saturated fats, simple sugars and processed foods, is rising at an unprecedented rate. These lead to obesity and metabolic diseases, and possibly cognitive deficits. Exploring this, recent studies demonstrate marked impairment in spatial learning in rodents exposed to high-sugar diets. We utilised advanced touchscreen technology to assess several spatial and non-spatial components of cognition in rats chronically exposed to a high sucrose diet.

METHODS

Male Wistar rats received 70 ml of 10% sucrose solution each day, or control tap water, persisting for the experiment duration (total n = 32). After 5 weeks of diet, rats performed Pairwise Discrimination, Location Discrimination, or Progressive Ratio tasks on automated touchscreens, and performance compared between groups.

RESULTS

Sucrose rats consumed all the sugar solution provided to them, and had significantly increased caloric intake, compared to controls (p < 0.0001). However, in all tests, we found no significant difference in cognitive performance between Sucrose and Control treated rats. This included the number of trials for acquisition, and reversal, in Pairwise Discrimination, and number of trials required to complete Location Discrimination (p > 0.05 for all outcomes). No differences were observed in perseverative behaviour, motivation levels, or processing speed.

CONCLUSION

Our study found no evidence to suggest that chronic consumption of sucrose impairs cognition, including both spatial and non-spatial learning tasks. These findings suggest that not all aspects of spatial cognition are negatively impacted by high sugar diet in rodents, and that particular use of touchscreen technology may probe different aspects of cognition than traditional tasks.

Schizophrenia-associated SAP97 mutations increase glutamatergic synapse strength in the dentate gyrus and impair contextual episodic memory in rats

Mutations in the putative glutamatergic synapse scaffolding protein SAP97 are associated with the development of schizophrenia in humans. However, the role of SAP97 in synaptic regulation is unclear. Here we show that SAP97 is expressed in the dendrites of granule neurons in the dentate gyrus but not in the dendrites of other hippocampal neurons. Schizophrenia-related perturbations of SAP97 did not affect CA1 pyramidal neuron synapse function. Conversely, these perturbations produce dramatic augmentation of glutamatergic neurotransmission in granule neurons that can be attributed to a release of perisynaptic GluA1-containing AMPA receptors into the postsynaptic densities of perforant pathway synapses. Furthermore, inhibiting SAP97 function in the dentate gyrus was sufficient to impair contextual episodic memory. Together, our results identify a cell-type-specific synaptic regulatory mechanism in the dentate gyrus that, when disrupted, impairs contextual information processing in rats.

The effects of SAP97 mutations associated with schizophrenia on synaptic function are unclear. Here, the authors show that schizophrenia-related SAP97 mutations enhance glutamatergic synapse strength in the dentate gyrus, impairing contextual episodic memory in rats.

Ten-week high fat and high sugar diets in mice alter gut-brain axis cytokines in a sex-dependent manner

Diets high in fat and sugar induce inflammation throughout the body, particularly along the gut-brain axis; however, the way these changes in immune signaling mediate one another remains unknown. We investigated cytokine changes in the brain and colon following prolonged high fat or sugar diet in female and male adult C57BL/6 mice. Ten weeks of high fat diet increased levels of TNFα, IL-1β, IL-6, IFNγ, and IL-10 in the female hippocampus and altered cytokines in the frontal cortex of both sexes. High sugar diet increased hippocampal cytokines and decreased cytokines in the diencephalon and frontal cortex. In the colon, high fat diet changed cytokine expression in both sexes, while high sugar diet only increased TNFα in males. Causal mediation analysis confirmed that colon IL-10 and IL-6 mediate high fat diet-induced neuroimmune changes in the female hippocampus and male frontal cortex. Additionally, high fat diet increased food consumption and weight gain in both sexes, while high sugar diet decreased male weight gain. These findings reveal a novel causal link between gut and brain inflammation specific to prolonged consumption of high fat, not high sugar, diet. Importantly, this work includes females which have been under-represented in diet research, and demonstrates that diet-induced neuroinflammation varies by brain region between sexes. Furthermore, our data suggest female brains are more vulnerable than males to inflammatory changes following excessive fat and sugar consumption, which may help explain the increased risk of inflammation-associated psychiatric conditions in women who eat a Western Diet rich in both dietary components.

A Long-Term Energy-Rich Diet Increases Prefrontal BDNF in Sprague-Dawley Rats

Findings of the effect of high-fat feeding including “Cafeteria Diets” (CAF) on brain-derived neurotrophic factor (BDNF) in the hippocampus (HIP) and prefrontal cortex (PFC) in rodents are conflicting. CAF is a non-standardized, highly palatable energy-rich diet composed by everyday food items for human consumption and is known to induce metabolic syndrome and obesity in rats. However, the highly palatable nature of CAF may counteract a negative effect of chronic stress on anticipatory behavior and synaptic plasticity in the hippocampus, hence represent a confounding factor (e.g., when evaluating functional effects on the brain). This study investigated the effects of a chronic, restricted access to CAF on BDNF, monoamine neurotransmitters, and redox imbalance in HIP and PFC in male rats. Our results show that CAF induced BDNF and its receptor TrkB in PFC compared to the controls (p < 0.0005). No differences in monoamine neurotransmitters were detected in either PFC or HIP. CAF increased dehydroascorbic acid and decreased malondialdehyde in PFC (p < 0.05), suggesting an early redox imbalance insufficient to induce lipid peroxidation. This study supports that a chronic CAF on a restricted schedule increases BDNF levels in the PFC of rats, highlighting that this may be a suboptimal feeding regime when investigating the effects of diet-induced obesity in the brain and emphasizing this as a point of attention when comparing the findings.

Sexually Dimorphic Effects of a Western Diet on Brain Mitochondrial Bioenergetics and Neurocognitive Function

A Western diet (WD), high in sugars and saturated fats, impairs learning and memory function and contributes to weight gain. Mitochondria in the brain provide energy for neurocognitive function and may play a role in body weight regulation. We sought to determine whether a WD alters behavior and metabolic outcomes in male and female rodents through impacting hippocampal and hypothalamic mitochondrial bioenergetics. Results revealed a sexually dimorphic macronutrient preference, where males on the WD consumed a greater percentage of calories from fat/protein and females consumed a greater percentage of calories from a sugar-sweetened beverage. Both males and females on a WD gained body fat and showed impaired glucose tolerance when compared to same-sex controls. Males on a WD demonstrated impaired hippocampal functioning and an elevated tendency toward a high membrane potential in hippocampal mitochondria. Comprehensive bioenergetics analysis of WD effects in the hypothalamus revealed a tissue-specific adaption, where males on the WD oxidized more fat, and females oxidized more fat and carbohydrates at peak energy demand compared to same-sex controls. These results suggest that adult male rats show a susceptibility toward hippocampal dysfunction on a WD, and that hypothalamic mitochondrial bioenergetics are altered by WD in a sex-specific manner.

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.

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.

Influence of pro-obesogenic dietary habits on stress-induced cognitive alterations in healthy adult volunteers

Stress is a fundamental biological response that can be associated with alterations in cognitive processes. Unhealthy dietary habits are proposed to modulate this effect, notably through their pro-inflammatory potential. This cross-sectional study aimed to evaluate the influence of an obesogenic dietary pattern with inflammatory potential on stress-induced cognitive alterations in healthy volunteers. Fifty healthy adult participants were stratified into two diet groups: obesogenic vs. non-obesogenic, based on their self-reported consumption of fat, sugar, and salt, assessed by the French National Program for Nutrition and Health questionnaire and a food frequency questionnaire. Serum high-sensitive C-reactive protein (hsCRP) was measured as a marker of systemic inflammation using ELISA. Verbal memory and sustained attention were evaluated through the Verbal Recognition Memory (VRM) test and the Rapid Visual Information Processing (RVP) test respectively, from the Cambridge Neuropsychological Test Automated Battery. Assessments were performed before and after exposure to the psychological stressor Trier Social Stress Test (TSST). Stress response was evaluated by subjective stress perception, salivary cortisol, blood pressure, and heart rate. Twenty-two participants (44%) presented an obesogenic diet. Systemic inflammation was significantly higher in the obesogenic diet group (p=0.005). The TSST induced a significant stress response, regardless of dietary habits (Time effect p < 0.001). In the whole sample, exposure to TSST was associated with cognitive changes in the form of impaired performance on the VRM test and overall improved RVP scores. However, the obesogenic diet group exhibited an increased total number of false alarms (Time x Diet: p=0.014) on the RVP test after TSST exposure as well as a greater impairment in immediate verbal recognition on the VRM test (Time x Diet: p=0.002). This effect was not associated with the inflammatory component of the obesogenic diet. These results suggest that an obesogenic diet may sensitize healthy individuals to the detrimental effects of acute stress on cognitive performance.

Effects of sleep deprivation of various durations on novelty-related object recognition memory and object location memory in mice

Sleep is essential for important physiological functions. Impairment of learning and memory function caused by lack of sleep is a common physiological phenomenon of which underlying changes in synaptic plasticity in the hippocampus are not well understood. The possible different effects of sleep deprivation (SD) lasting for various durations on learning and memory function and hippocampal synaptic plasticity are still not completely clear. In this study, we used a modified multiple platform method (MMPM) to induce rapid eye movement SD (REM SD), lasting for 24 h, 48 h, and 72 h, separately. The novel place recognition (NPR) and novel object recognition (NOR) tasks were used to test the novelty-related object recognition memory (ORM) and object location memory (OLM) of mice. Then, hippocampal synaptic plasticity was evaluated after all behavioural experiments. The results showed that REM SD played a key role in OLM but not in ORM. Specifically, 24 h REM SD improved novelty-related OLM, accompanied by a significantly increased hippocampal synaptic plasticity, including gain of dendritic spines, increased expression of hippocampal GluA1, and enhanced long-term potentiation (LTP), whereas 48 h REM SD showed no effect on OLM or the hippocampal synaptic plasticity mentioned above; however, 72 h REM SD impaired novelty-related OLM and weakened hippocampal synaptic plasticity, including serious loss of dendritic spines, decreased expression of hippocampal GluA1, and significantly attenuated LTP. Our results suggest that REM SD of various durations has different effects on both novelty-related OLM and hippocampal synaptic plasticity.

Cognitive impairment in obese rat model: role of glial cells

BACKGROUND

Obesity is a worldwide problem. Some studies revealed that it leads to deterioration of the cognitive function, regardless of age.

AIM OF THE STUDY

explore the effect of obesity on cognitive function in a rat model of obesity highlighting the role of glial cells.

MATERIALS AND METHODS

twenty adult male albino rats were assigned to two groups: group I: consumed normal diet, group II: consumed high-fat diet. Body Mass Index (BMI), serum glucose, insulin, HOMA IR and lipid profile were measured. Also, hippocampal expression of Brain derived neurotrophic factor (Bdnf), synapsin, Ionized calcium binding adaptor molecule 1 (Iba), nuclear factor erythroid -related factor 2 (Nrf2), Myelin basic protein (Mbp) were measured by real-time polymerase chain reaction. The Morris Water Maze is a test used to assess spatial learning and memory capacities of rats.

RESULTS

There was a high significant increase in lipid profile, serum glucose, insulin serum levels and HOMA-IR in obese groups with impaired Morris water maze performance compared to control group. There was a significant downregulation in hippocampal Bdnf and synapsin mRNA expression. In addition to decrease in Mbp mRNA expression (P < 0.001). This could be explained by oxidative stress through significant downregulation of Nrf2 mRNA, and inflammation observed in significant upregulation Iba mRNA gene expression in the obese group.

CONCLUSION

Many factors contribute to obesity associated cognitive impairment. In our study, we figured out the crucial roles of glial cells including microglial activation and oligodendrocytes affection with other underlying mechanisms including oxidative stress and hippocampal inflammation.

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.

Western diet as a trigger of Alzheimer's disease: From metabolic syndrome and systemic inflammation to neuroinflammation and neurodegeneration

An excess of saturated fatty acids and simple sugars in the diet is a known environmental risk factor of Alzheimer's disease (AD) but the holistic view of the interacting processes through which such diet may contribute to AD pathogenesis is missing. We addressed this need through extensive analysis of published studies investigating the effects of western diet (WD) on AD development in humans and laboratory animals. We reviewed WD-induced systemic alterations comprising metabolic changes, induction of obesity and adipose tissue inflammation, gut microbiota dysbiosis and acceleration of systemic low-grade inflammation. Next we provide an overview of the evidence demonstrating that WD-associated systemic alterations drive impairment of the blood-brain barrier (BBB) and development of neuroinflammation paralleled by accumulation of toxic amyloid. Later these changes are followed by dysfunction of synaptic transmission, neurodegeneration and finally memory and cognitive impairment. We conclude that WD can trigger AD by acceleration of inflammaging, and that BBB impairment induced by metabolic and systemic inflammation play the central role in this process. Moreover, the concurrence of neuroinflammation and Aβ dyshomeostasis, which by reciprocal interactions drive the vicious cycle of neurodegeneration, contradicts Aβ as the primary trigger of AD. Given that in 2019 the World Health Organization recommended focusing on modifiable risk factors in AD prevention, this overview of the sequential, complex pathomechanisms initiated by WD, which can lead from peripheral disturbances to neurodegeneration, can support future prevention strategies.

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.

Sex differences in recovery from cognitive and metabolic impairments induced by supplementary sucrose in rats

Consumption of beverages containing around 10% sucrose contributes to worldwide obesity. Studies using rats can increase understanding of the consequences of such consumption. The present experiment aimed to compare male and female rats, first, in terms of cognitive and metabolic impairments produced by excessive intakes of 10% sucrose solution (Stage 1:8 weeks) and, second, with regard to recovery once access to sucrose ceased (Stage 2:4 weeks). All animals had unrestricted access to chow and water throughout. The primary cognitive outcome was performance on a place recognition task. The primary metabolic outcome was retroperitoneal fat pad mass/kg bodyweight at cull, with body weight and glucose tolerance as secondary outcomes. In a 3 × 2 between-subject factorial design the first factor was whether rats had: (1) unlimited access to a 10% sucrose solution and water throughout both stages (Suc-Suc); (2) were switched from sucrose in the 8-week Stage 1 to water only in the 4-week Stage 2 (Suc-Water); or (3) had no access to sucrose in either stage (Water-Water). The second factor was sex. A major metabolic outcome was that of persistent adiposity in both males and females in the Suc-Water condition. As for place recognition, females in the Suc-Suc condition showed greater long-term resistance than males to the impact of excessive sucrose on spatial memory impairment. Overall, few sex differences were found in secondary metabolic outcomes.

A glucose-stimulated BOLD fMRI study of hypothalamic dysfunction in mice fed a high-fat and high-sucrose diet

The hypothalamus is the central regulator of energy homeostasis. Hypothalamic neuronal circuits are disrupted upon overfeeding, and play a role in the development of metabolic disorders. While mouse models have been extensively employed for understanding the mechanisms of hypothalamic dysfunction, functional magnetic resonance imaging (fMRI) on hypothalamic nuclei has been challenging. We implemented a robust glucose-induced fMRI paradigm that allows to repeatedly investigate hypothalamic responses to glucose. This approach was used to test the hypothesis that hypothalamic nuclei functioning is impaired in mice exposed to a high-fat and high-sucrose diet (HFHSD) for seven days. The blood oxygen level-dependent (BOLD) fMRI signal was measured from brains of mice under light isoflurane anaesthesia, during which a 2.6 g/kg glucose load was administered. The mouse hypothalamus responded to glucose but not saline administration with a biphasic BOLD fMRI signal reduction. Relative to controls, HFHSD-fed mice showed attenuated or blunted responses in arcuate nucleus, lateral hypothalamus, ventromedial nucleus and dorsomedial nucleus, but not in paraventricular nucleus. In sum, we have developed an fMRI paradigm that is able to determine dysfunction of glucose-sensing neuronal circuits within the mouse hypothalamus in a non-invasive manner.

Unravelling the impacts of western-style diets on brain, gut microbiota and cognition

The steady rise in the prevalence of obesity has been fostered by modern environments that reduce energy expenditure and encourage consumption of 'western'-style diets high in fat and sugar. Obesity has been consistently associated with impairments in executive function and episodic memory, while emerging evidence indicates that high-fat, high-sugar diets can impair aspects of cognition within days, even when provided intermittently. Here we review the detrimental effects of diet and obesity on cognition and the role of inflammatory and circulating factors, compromised blood-brain barrier integrity and gut microbiome changes. We next evaluate evidence for changing risk profiles across life stages (adolescence and ageing) and other populations at risk (e.g. through maternal obesity). Finally, interventions to ameliorate diet-induced cognitive deficits are discussed, including dietary shifts, exercise, and the emerging field of microbiome-targeted therapies. With evidence that poor diet and obesity impair cognition via multiple mechanisms across the human lifespan, the challenge for future research is to identify effective interventions, in addition to diet and exercise, to prevent and ameliorate adverse effects.

Eating behavior as a new frontier in memory research

The study of memory is commonly associated with neuroscience, aging, education, and eyewitness testimony. Here we discuss how eating behavior is also heavily intertwined-and yet considerably understudied in its relation to memory processes. Both are influenced by similar neuroendocrine signals (e.g., leptin and ghrelin) and are dependent on hippocampal functions. While learning processes have long been implicated in influencing eating behavior, recent research has shown how memory of recent eating modulates future consumption. In humans, obesity is associated with impaired memory performance, and in rodents, dietary-induced obesity causes rapid decrements to memory. Lesions to the hippocampus disrupt memory but also induce obesity, highlighting a cyclic relationship between obesity and memory impairment. Enhancing memory of eating has been shown to reduce future eating and yet, little is known about what influences memory of eating or how memory of eating differs from memory for other behaviors. We discuss recent advancements in these areas and highlight fruitful research pursuits afforded by combining the study of memory with the study of eating behavior.