High-fat diet feeding alters olfactory-, social-, and reward-related behaviors of mice independent of obesity

Translational science approaches for food insecurity research

Food insecurity is a pervasive problem that impacts health and well-being across the lifespan. The human research linking food insecurity to poor metabolic and behavioral health outcomes is inherently correlational and suffers from a high degree of variability both between households and even within the same household over time. Further, food insecurity is impacted by societal and political factors that are largely out of the control of individuals, which narrows the range of intervention strategies. Animal models of food insecurity are being developed to address some of the barriers to mechanistic research. However, animal models are limited in their ability to consider some of the more complex societal elements of the human condition. We believe that understanding the role that food insecurity plays in ingestive behavior and chronic disease requires a truly translational approach, and that understanding the health impacts of this complex social phenomenon requires understanding both its psychological and physiological dimensions. This brief review will outline some key features of food insecurity, highlighting those that are amenable to investigation with controlled animal models and identifying areas where integrating animal and human studies can improve our understanding of the psychological burden and health impacts of food insecurity. In the interest of brevity, this review will largely focus on food insecurity in the United States, as the factors that contribute to food insecurity vary considerably across the globe.

Changes in reward-induced neural activity upon Cafeteria Diet consumption

Excessive consumption of highly palatable foods rich in sugar and fat, often referred to as "junk" or "fast" foods, plays a central role in the development of obesity. The highly palatable characteristics of these foods activate hedonic and motivational mechanisms to promote food-seeking behavior and overeating, which is largely regulated by the brain reward system. Excessive junk food consumption can alter the functioning of this reward system, but exact mechanisms of these changes are still largely unknown. This study investigated whether long-term junk food consumption, in the form of Cafeteria (CAF) diet, can alter the reward system in adult, female Long-Evans rats, and whether different regimes of CAF diet influence the extent of these changes. To this end, rats were exposed to a 6-week diet with either standard chow, or ad libitum daily access to CAF diet, 30 % restricted but daily access to CAF diet, or one-day-a-week (intermittent) ad libitum access to CAF diet, after which c-Fos expression in the Nucleus Accumbens (NAc), Prefrontal Cortex (PFC), and Ventral Tegmental Area (VTA) following consumption of a CAF reward of choice was examined. We found that all CAF diet regimes decreased c-Fos expression in the NAc-shell when presented with a CAF reward, while no changes in c-Fos expression upon the different diet regimes were found in the PFC, and possibly the VTA. Our data suggests that long-term junk food exposure can affect the brain reward system, resulting in an attenuated activity of the NAc-shell.

Short-term consumption of highly processed diets varying in macronutrient content impair the sense of smell and brain metabolism in mice

OBJECTIVE

Food processing greatly contributed to increased food safety, diversity, and accessibility. However, the prevalence of highly palatable and highly processed food in our modern diet has exacerbated obesity rates and contributed to a global health crisis. While accumulating evidence suggests that chronic consumption of such foods is detrimental to sensory and neural physiology, it is unclear whether its short-term intake has adverse effects. Here, we assessed how short-term consumption (<2 months) of three diets varying in composition and macronutrient content influence olfaction and brain metabolism in mice.

METHODS

The diets tested included a grain-based standard chow diet (CHOW; 54% carbohydrate, 32% protein, 14% fat; #8604 Teklad Rodent diet , Envigo Inc.), a highly processed control diet (hpCTR; 70% carbohydrate, 20% protein, 10% fat; #D12450B, Research Diets Inc.), and a highly processed high-fat diet (hpHFD; 20% carbohydrate, 20% protein, 60% fat; #D12492, Research Diets Inc.). We performed behavioral and metabolic phenotyping, electro-olfactogram (EOG) recordings, brain glucose metabolism imaging, and mitochondrial respirometry in different brain regions. We also performed RNA-sequencing (RNA-seq) in the nose and across several brain regions, and conducted differential expression analysis, gene ontology, and network analysis.

RESULTS

We show that short-term consumption of the two highly processed diets, but not the grain-based diet, regardless of macronutrient content, adversely affects odor-guided behaviors, physiological responses to odorants, transcriptional profiles in the olfactory mucosa and brain regions, and brain glucose metabolism and mitochondrial respiration.

CONCLUSIONS

Even short periods of highly processed food consumption are sufficient to cause early olfactory and brain abnormalities, which has the potential to alter food choices and influence the risk of developing metabolic disease.

Chronic hyperpalatable diet induces impairment of hippocampal-dependent memories and alters glutamatergic and fractalkine axis signaling

Chronic consumption of hyperpalatable and hypercaloric foods has been pointed out as a factor associated with cognitive decline and memory impairment in obesity. In this context, the integration between peripheral and central inflammation may play a significant role in the negative effects of an obesogenic environment on memory. However, little is known about how obesity-related peripheral inflammation affects specific neurotransmission systems involved with memory regulation. Here, we test the hypothesis that chronic exposure to a highly palatable diet may cause neuroinflammation, glutamatergic dysfunction, and memory impairment. For that, we exposed C57BL/6J mice to a high sugar and butter diet (HSB) for 12 weeks, and we investigated its effects on behavior, glial reactivity, blood-brain barrier permeability, pro-inflammatory features, glutamatergic alterations, plasticity, and fractalkine-CX3CR1 axis. Our results revealed that HSB diet induced a decrease in memory reconsolidation and extinction, as well as an increase in hippocampal glutamate levels. Although our data indicated a peripheral pro-inflammatory profile, we did not observe hippocampal neuroinflammatory features. Furthermore, we also observed that the HSB diet increased hippocampal fractalkine levels, a key chemokine associated with neuroprotection and inflammatory regulation. Then, we hypothesized that the elevation on glutamate levels may saturate synaptic communication, partially limiting plasticity, whereas fractalkine levels increase as a strategy to decrease glutamatergic damage.

Fingolimod Modulates the Gene Expression of Proteins Engaged in Inflammation and Amyloid-Beta Metabolism and Improves Exploratory and Anxiety-Like Behavior in Obese Mice

Obesity is considered a risk factor for type 2 diabetes mellitus, which has become one of the most important health problems, and is also linked with memory and executive function decline. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that regulates cell death/survival and the inflammatory response via its specific receptors (S1PRs). Since the role of S1P and S1PRs in obesity is rather obscure, we examined the effect of fingolimod (an S1PR modulator) on the expression profile of genes encoding S1PRs, sphingosine kinase 1 (Sphk1), proteins engaged in amyloid-beta (Aβ) generation (ADAM10, BACE1, PSEN2), GSK3β, proapoptotic Bax, and proinflammatory cytokines in the cortex and hippocampus of obese/prediabetic mouse brains. In addition, we observed behavioral changes. Our results revealed significantly elevated mRNA levels of Bace1, Psen2, Gsk3b, Sphk1, Bax, and proinflammatory cytokines, which were accompanied by downregulation of S1pr1 and sirtuin 1 in obese mice. Moreover, locomotor activity, spatially guided exploratory behavior, and object recognition were impaired. Simultaneously, fingolimod reversed alterations in the expressions of the cytokines, Bace1, Psen2, and Gsk3b that occurred in the brain, elevated S1pr3 mRNA levels, restored normal cognition-related behavior patterns, and exerted anxiolytic effects. The improvement in episodic and recognition memory observed in this animal model of obesity may suggest a beneficial effect of fingolimod on central nervous system function.

Adult mice with noise-induced hearing loss exhibited temporal ordering memory deficits accompanied by microglia-associated neuroplastic changes in the medial prefrontal cortex

Acquired peripheral hearing loss in midlife is considered the primary modifiable risk factor for dementia, while the underlying pathological mechanism remains poorly understood. Excessive noise exposure is the most common cause of acquired peripheral hearing loss in modern society. This study was designed to investigate the impact of noise-induced hearing loss (NIHL) on cognition, with a focus on the medial prefrontal cortex (mPFC), a brain region that is involved in both auditory and cognitive processes and is highly affected in patients with cognitive impairment. Adult C57BL/6 J mice were randomly assigned to a control group and seven noise groups: 0HPN, 12HPN, 1DPN, 3DPN, 7DPN, 14DPN, and 28DPN, which were exposed to broadband noise at a 123 dB sound pressure level (SPL) for 2 h and sacrificed immediately (0 h), 12 h, or 1, 3, 7, 14, or 28 days post-noise exposure (HPN, DPN), respectively. Hearing assessment, behavioral tests, and neuromorphological studies in the mPFC were performed in control and 28DPN mice. All experimental animals were included in the time-course analysis of serum corticosterone (CORT) levels and mPFC microglial morphology. The results illustrated that noise exposure induced early-onset transient serum CORT elevation and permanent moderate-to-severe hearing loss in mice. 28DPN mice, in which permanent NIHL has been verified, exhibited impaired performance in temporal order object recognition tasks concomitant with reduced structural complexity of mPFC pyramidal neurons. The time-course immunohistochemical analysis in the mPFC revealed significantly higher morphological microglial activation at 14 and 28 DPN, preceded by a remarkably higher amount of microglial engulfed postsynaptic marker PSD95 at 7 DPN. Additionally, lipid accumulation in microglia was observed in 7DPN, 14DPN and 28DPN mice, suggesting a driving role of lipid handling deficits following excessive phagocytosis of synaptic elements in delayed and sustained microglial abnormalities. These findings provide fundamentally novel information concerning mPFC-related cognitive impairment in mice with NIHL and empirical evidence suggesting the involvement of microglial malfunction in the mPFC neurodegenerative consequences of NIHL.

Impact of short and long exposure to cafeteria diet on food intake and white adipose tissue lipolysis mediated by glucagon-like peptide 1 receptor

Introduction

The modern food environment facilitates excessive calorie intake, a major driver of obesity. Glucagon-like peptide 1 (GLP1) is a neuroendocrine peptide that has been the basis for developing new pharmacotherapies against obesity. The GLP1 receptor (GLP1R) is expressed in central and peripheral tissues, and activation of GLP1R reduces food intake, increases the expression of thermogenic proteins in brown adipose tissue (BAT), and enhances lipolysis in white adipose tissue (WAT). Obesity decreases the efficiency of GLP1R agonists in reducing food intake and body weight. Still, whether palatable food intake before or during the early development of obesity reduces the effects of GLP1R agonists on food intake and adipose tissue metabolism remains undetermined. Further, whether GLP1R expressed in WAT contributes to these effects is unclear.

Methods

Food intake, expression of thermogenic BAT proteins, and WAT lipolysis were measured after central or peripheral administration of Exendin-4 (EX4), a GLP1R agonist, to mice under intermittent-short exposure to CAF diet (3 h/d for 8 days) or a longer-continuous exposure to CAF diet (24 h/d for 15 days). Ex-vivo lipolysis was measured after EX4 exposure to WAT samples from mice fed CAF or control diet for 12 weeks. .

Results

During intermittent-short exposure to CAF diet (3 h/d for 8 days), third ventricle injection (ICV) and intra-peritoneal administration of EX4 reduced palatable food intake. Yet, during a longer-continuous exposure to CAF diet (24 h/d for 15 days), only ICV EX4 administration reduced food intake and body weight. However, this exposure to CAF diet blocked the increase in uncoupling protein 1 (UCP1) caused by ICV EX4 administration in mice fed control diet. Finally, GLP1R expression in WAT was minimal, and EX4 failed to increase lipolysis ex-vivo in WAT tissue samples from mice fed CAF or control diet for 12 weeks. .

Discussion

Exposure to a CAF diet during the early stages of obesity reduces the effects of peripheral and central GLP1R agonists, and WAT does not express a functional GLP1 receptor. These data support that exposure to the obesogenic food environment, without the development or manifestation of obesity, can alter the response to GLP1R agonists. .

Impact of cafeteria diet and n3 supplementation on the intestinal microbiota, fatty acids levels, neuroinflammatory markers and social memory in male rats

OBJECTIVE

To assess the effects of omega-3 (n3) supplementation on intestinal microbiota, fatty acids profile, neuroinflammation, and social memory of cafeteria diet (CAF)-fed rats.

METHODS

Male Wistar rats were fed with CAF for 20 weeks. Omega-3 (500 mg/kg/day) was supplemented between the 16th and 20th week. Colon morphology, intestinal microbiota composition, short-chain fatty acids (SCFA) and lipopolysaccharide (LPS) in the plasma, fatty acids profile, TLR-4 and claudin-5 expressions in the brain, and social memory were investigated.

RESULTS

CAF reduced colon length, crypts' depth, and microbiota diversity, while n3 increased the Firmicutes/Bacteroidetes ratio. CAF increased SCFA plasma levels, but n3 reduced butyrate and isobutyrate in obese rats. LPS was increased in CAF-fed rats, and n3 decreased its levels. In the cerebral cortex, n3 increased caprylic, palmitic, stearic, tricosanoic, lignoceric, myristoleic, and linoleic acids. CAF increased palmitic acid and TLR-4 expression in the cerebral cortex while decreasing claudin-5 in the hippocampus. In the social memory test, CAF-fed animals showed greater social interaction with no effect of n3.

CONCLUSIONS

The lack of n3 effect in some of the evaluated parameters may be due to the severity of the obesity caused by CAF. However, n3 reduced LPS levels, suggesting its ability to reverse endotoxemia.

High-Fat Diet Exacerbates Autistic-Like Restricted Repetitive Behaviors and Social Abnormalities in CC2D1A Conditional Knockout Mice

Autism spectrum disorder (ASD) represents a heterogeneous group of neurodevelopmental disorders characterized by deficits in social communication, social interaction, and the presence of restricted repetitive behaviors. The cause of ASD involves complex interactions between genetic and environmental factors. Haploinsufficiency of the Coiled-coil and C2 domain containing 1A (Cc2d1a) gene is causally linked to ASD, and obesity has been associated with worse outcomes for ASD. High-fat diet (HFD) feeding leads to the development of obesity and metabolic dysfunction; however, the effect of HFD on pre-existing autistic-like phenotypes remains to be clarified. Here, we report that male Cc2d1a conditional knockout (cKO) mice fed with HFD, from weaning onwards and throughout the experimental period, show a marked aggravation in autistic-like phenotypes, manifested in increased restricted repetitive behaviors and impaired performance in the preference for social novelty, but not in sociability and cognitive impairments assessed using the object location memory, novel object recognition, and Morris water maze tests. HFD feeding also results in increased numbers of reactive microglia and astrocytes, and exacerbates reductions in dendritic complexity and spine density of hippocampal CA1 pyramidal neurons. Furthermore, we demonstrate that chronic treatment with minocycline, a semisynthetic tetracycline-derived antibiotic, rescues the observed behavioral and morphological deficits in Cc2d1a cKO mice fed with HFD. Collectively, these findings highlight an aggravating role of HFD in pre-existing autistic-like phenotypes and suggest that minocycline treatment can alleviate abnormal neuronal morphology and behavioral symptoms associated with ASD resulted from the interplay between genetic and environmental risk factors.

The Role of Mu Opioid Receptors in High Fat Diet-Induced Reward and Potentiation of the Rewarding Effect of Oxycodone

Excessive high fat diet (HFD) consumption can induce food addiction, which is believed to involve the communication between the hypothalamus and mesolimbic dopaminergic neurons, originating in the ventral tegmental area (VTA) and projecting to the nucleus accumbens (NAc). These brain areas are densely populated with opioid receptors, raising the possibility that these receptors, and particularly mu opioid receptors (MORs), are involved in rewards elicited by palatable food. This study sought to investigate the involvement of MORs in HFD-induced reward and if there is any difference between male and female subjects in this response. We also assessed if exposure to HFD would alter the rewarding action of oxycodone, a relatively selective MOR agonist. The place conditioning paradigm was used as an animal model of reward to determine if short-time (STC, 2 h) or long-time (LTC, 16 h) conditioning with HFD induces reward or alters the rewarding action of oxycodone. Male and female C57BL/6J mice as well as MOR knockout and their wildtype littermates of both sexes were tested for basal place preference on day 1 and then conditioned with an HFD in one chamber and a regular chow diet (RCD) in another chamber for 2 h on alternate days. Three sets of STC were used, followed by a set of LTC. Each set of conditioning consisted of two conditioning with RCD and two conditioning with HFD. Mice were tested for place preference after each set of STC and again after LTC. Controls were conditioned with RCD in both conditioning chambers. Following the last place preference test, mice were treated with oxycodone and conditioned in the HFD-paired chamber and with saline in the RCD-paired chamber for one hour once a day to explore the possibility if the HFD could alter oxycodone reward. The result showed that HFD induced conditioned place preference (CPP) in male but not female subjects. However, oxycodone conditioning elicited reward in both male and female mice of the HFD group but not the control group, showing that prior conditioning with HFD potentiated the rewarding action of oxycodone. The latter response was mediated via MORs, as it was blunted in MOR knockout mice. Similarly, HFD-induced CPP was blunted in male MOR knockout mice, suggesting sexual dimorphism in this response.

Kinase signalling in excitatory neurons regulates sleep quantity and depth

Progress has been made in the elucidation of sleep and wakefulness regulation at the neurocircuit level^1,2. However, the intracellular signalling pathways that regulate sleep and the neuron groups in which these intracellular mechanisms work remain largely unknown. Here, using a forward genetics approach in mice, we identify histone deacetylase 4 (HDAC4) as a sleep-regulating molecule. Haploinsufficiency of Hdac4, a substrate of salt-inducible kinase 3 (SIK3)³, increased sleep. By contrast, mice that lacked SIK3 or its upstream kinase LKB1 in neurons or with a Hdac4^S245A mutation that confers resistance to phosphorylation by SIK3 showed decreased sleep. These findings indicate that LKB1-SIK3-HDAC4 constitute a signalling cascade that regulates sleep and wakefulness. We also performed targeted manipulation of SIK3 and HDAC4 in specific neurons and brain regions. This showed that SIK3 signalling in excitatory neurons located in the cerebral cortex and the hypothalamus positively regulates EEG delta power during non-rapid eye movement sleep (NREMS) and NREMS amount, respectively. A subset of transcripts biased towards synaptic functions was commonly regulated in cortical glutamatergic neurons through the expression of a gain-of-function allele of Sik3 and through sleep deprivation. These findings suggest that NREMS quantity and depth are regulated by distinct groups of excitatory neurons through common intracellular signals. This study provides a basis for linking intracellular events and circuit-level mechanisms that control NREMS.

Neuronal Nitric Oxide Synthase Regulates Depression-like Behaviors in Shortening-Induced Obese Mice

Shortening is mainly derived from the partial hydrogenation of palm oil and widely used in fast food. Food processed with shortening contains high levels of industrial trans fatty acids. Studies have shown that there is a correlation between industrial trans fatty acids, obesity, and depression. However, the regulatory effect of neuronal nitric oxide synthase (nNOS) on depression in obese patients is still unknown. The purpose of this study was to explore mood changes in obese mice fed a high shortening diet, and to determine the regulatory effect of nNOS on depressive-like behaviors in obese mice. We used a high shortening diet-induced obesity mouse model to systematically assess the metabolic response, behavioral changes, prefrontal and hippocampal nNOS protein levels, and the effect of nNOS inhibitors (7-nitroindole) on depression-like behavior in obese mice. Interestingly, obese mice on a 9-week high-shortening diet developed short-term spatial working memory impairment and anxiety-like behavior, and obesity may be a risk factor for cognitive impairment and mood disorders. In animals fed a high shortening diet for 12 weeks, obese mice developed depression-like behavior and had significantly elevated levels of nNOS protein expression in the hippocampus and prefrontal lobe. Administration of the nNOS inhibitor 7-nitroindole could improve depression-like behaviors in obese mice, further suggesting that inhibition of nNOS is helpful for depression associated with obesity.

Neurobiological Mechanisms Modulating Emotionality, Cognition and Reward-Related Behaviour in High-Fat Diet-Fed Rodents

Affective and substance-use disorders are associated with overweight and obesity-related complications, which are often due to the overconsumption of palatable food. Both high-fat diets (HFDs) and psychostimulant drugs modulate the neuro-circuitry regulating emotional processing and metabolic functions. However, it is not known how they interact at the behavioural level, and whether they lead to overlapping changes in neurobiological endpoints. In this literature review, we describe the impact of HFDs on emotionality, cognition, and reward-related behaviour in rodents. We also outline the effects of HFD on brain metabolism and plasticity involving mitochondria. Moreover, the possible overlap of the neurobiological mechanisms produced by HFDs and psychostimulants is discussed. Our in-depth analysis of published results revealed that HFDs have a clear impact on behaviour and underlying brain processes, which are largely dependent on the developmental period. However, apart from the studies investigating maternal exposure to HFDs, most of the published results involve only male rodents. Future research should also examine the biological impact of HFDs in female rodents. Further knowledge about the molecular mechanisms linking stress and obesity is a crucial requirement of translational research and using rodent models can significantly advance the important search for risk-related biomarkers and the development of clinical intervention strategies.

Assessments of prolonged effects of desflurane and sevoflurane on motor learning deficits in aged AppNL-G-F/NL-G-F mice

As the proportion of elderly in society increases, so do the number of older patients undergoing surgical procedures. This is concerning as exposure to anesthesia has been identified as a risk factor for Alzheimer's disease (AD). However, the causal relationship between clinical AD development and anesthesia remains conjectural. Preclinical studies have demonstrated that anesthesia, such as halothane, isoflurane, and sevoflurane, induces AD-like pathophysiological changes and cognitive impairments in transgenic mouse models of AD. Desflurane does not have these effects and is expected to have more potential for use in elderly patients, yet little is known about its effects, especially on non-cognitive functions, such as motor and emotional functions. Thus, we examined the postanesthetic effects of desflurane and sevoflurane on motor and emotional function in aged App^{NL-G-F/NL-G-F} (App-KI) mice. This is a recently developed transgenic mouse model of AD exhibiting amyloid β peptide (Aβ) amyloidosis and a neuroinflammatory response in an age-dependent manner without non-physiological amyloid precursor protein (APP) overexpression. Mice were subjected to a short behavioral test battery consisting of an elevated plus maze, a balance beam test, and a tail suspension test seven days after exposure to 8.0% desflurane for 6 h or 2.8% sevoflurane for 2 h. App-KI mice showed significant increments in the percentage of entry and time spent in open arms in the elevated plus maze, increments in the number of slips and latency to traverse for the balance beam test, increments in the limb clasping score, increments in immobile duration, and decrements in latency to first immobile episode for the tail suspension test compared to age-matched wild type (WT) controls. Desflurane- and sevoflurane-exposed App-KI mice showed a delayed decrement in the number of slips for each trial in the balance beam test, while air-treated App-KI mice rapidly improved their performance, and increased their clasping behavior in the tail suspension test. Furthermore, App-KI inhibited the change in membrane GluA3 following exposure to anesthetics in the cerebellum. These results suggest high validity of App-KI mice as an animal model of AD.

Olfactory system and energy metabolism: a two-way street

Olfactory perception guides daily decisions regarding food consumption, social interactions, and predator avoidance in all mammalian species. Volatile inputs, comprising odorants and pheromones, are relayed to the olfactory bulb (OB) from nasal sensory neurons cells and transferred to secondary processing regions within the brain. Olfaction has recently been shown to shape homeostatic and maladaptive processes of energy intake and expenditure through neuronal circuits involving the medial basal hypothalamus. Reciprocally, gastrointestinal hormones, such as ghrelin and leptin, the secretion of which depends on satiety and adiposity levels, might also influence olfactory sensitivity to alter food-seeking behaviors. Here, in addition to reviewing recent updates on identifying these neuronal networks, we also discuss how bidirectional neurocircuits existing between olfactory and energy processing centers can become dysregulated during obesity.

Effect of Metformin in Autistic BTBR T+Itpr3tf/J Mice Administered a High-Fat Diet

The biological mechanisms linking diet-related obesity and autism-related behaviors remain unclear. We aimed to characterize these interactions, focusing on gut microbiota, 5-hydroxytryptamine (5-HT) levels, and autistic behaviors in an animal model for autism; a high-fat diet (HFD) BTBR T+Itpr3tf/J (BTBR) mouse. In this model, we also examined the medication effects of metformin (Met) which is known to ameliorate several symptoms of autism spectrum disorder (ASD).Therefore, we hypothesized that HFD exacerbates BTBR autistic symptoms, which can be alleviated by Met, and the effects are associated with serotonin and the microbiota. As expected, compared with mice fed a normal diet, ten-week HFD-fed mice showed increased body weight, adiposity, and glucose levels. HFD consumption markedly aggravated repetitive behaviors in the self-grooming test. Met reduced HFD-induced hyperactivity. Notably, HFD intervention rescued sociability in the three-chamber sociability test. Furthermore, HFD stimulated tryptophan production, which was inhibited by Met. In contrast, 5-HT levels were lower in the gut and higher in the cortex in the HFD group. Moreover, Met suppressed inflammation in the hippocampus of HFD-fed mice by significantly downregulating the expression of pro-inflammatory cytokines (NF-κB, IL-17A, and IL-6). HFD increased the Firmicutes/Bacteroidetes ratio, and Met supplementation decreased richness while increasing bacterial diversity. We found that the abundance of gut microbiota (Lachnoclostridium, Anaerotruncus, Mucispirillum, and Lactococcus) was correlated with behavior scores and 5-HT levels. Overall, HFD consumption improved sociality in BTBR mice, which was related to the modulation of 5-HT levels and the composition of the microbiota. Met did not show any significant positive effects on the autism phenotype associated with HFD.

Metformin Alleviates Autistic-Like Behaviors Elicited by High-Fat Diet Consumption and Modulates the Crosstalk Between Serotonin and Gut Microbiota in Mice

The biological mechanisms linking diet-related obesity and autistic behaviors remain unclear. Metformin has proven to be beneficial in the treatment of many syndromes, including autism spectrum disorder. Therefore, the aim of this study was to assess whether metformin treatment could ameliorate metabolic and behavioral alterations in C57BL/6 mice kept on a high-fat diet (HFD), and whether these changes were related to modifications in the gut microbiota and 5-HT levels. As expected, ten weeks of HFD ingestion increased body weight, adiposity, and glucose levels. HFD-fed mice showed a marked aggravation of repetitive behaviors (marble burying and self-grooming), and this was prevented by metformin administration. In addition, HFD-fed mice increased the total distance travelled in the open field test. This hyperactivity was counteracted by metformin cotreatment. In the elevated plus maze test, HFD-fed mice showed a reduced number of entries into the open arms. Interestingly, both HFD and metformin cotreatment increased social interactions in the three-chamber test. HFD increased the levels of intestinal tryptophan and 5-hydroxyindoleacetic acid. Metformin stimulated gut tryptophan and promoted the synthesis of 5-HT in the HFD group. Lactococcus, Trichococcus, Romboutsia, and Faecalibaculum were enriched in HFD-fed mice, whereas the HFD group cotreated with metformin was enriched in Intestinimonas and L. reuteri. Faecalibacterium was positively correlated with sociability and 5-HT pathway components in mice that received metformin. In summary, HFD consumption elicited a complex phenotype comprising higher levels of anxiety-like and repetitive behaviors but also increased sociability. Metformin could potentially improve HFD-induced disorders in the autistic spectrum through a mechanism involving positive modulation of 5-HT levels in the gut and its microbiota composition.

Neuronal GHS-R Differentially Modulates Feeding Patterns under Normal and Obesogenic Conditions

The orexigenic hormone ghrelin increases food intake and promotes obesity through its receptor, growth hormone secretagogue receptor (GHS-R). We previously reported two neuron-specific GHS-R knockout mouse lines, namely pan-neuronal deletion by Syn1-cre and hypothalamic deletion by AgRP-cre, exhibiting differential diet-dependent effects on body weight. GHS-R deficiency in neurons elicited less pronounced metabolic effects under regular diet (RD) than high fat diet (HFD). While there was no difference in total food intake of HFD in either mouse line, Syn1-cre; Ghsrf/f mice showed much greater anti-obesity effect than that of AgRP-cre; Ghsrf/f mice. Meal feeding pattern is known to have a major impact on energy homeostasis and obesity development. Here, we investigated the feeding behaviors of these two neuron-specific GHS-R knockout mice under RD and HFD feeding, by assessing meal number, meal size, meal duration, and feeding frequency. Under the normal diet, RD-fed Syn1-cre; Ghsrf/f mice showed a decreased meal size in dark phase, while RD-fed AgRP-cre; Ghsrf/f mice showed an increased meal duration in dark phase. Under the obesogenic diet, HFD-fed Syn1-cre; Ghsrf/f mice displayed reduced meal numbers in light phase and increased feeding in both light and dark phases, whereas HFD-fed AgRP-cre; Ghsrf/f mice showed a decreased meal duration in the light phase only. Consistently, the expression of neuropeptides (Neuropeptide Y and Orexin) was increased in the hypothalamus of RD-fed Syn1-cre; Ghsrf/f mice, whereas the expression of cannabinoid receptor type 1 (CB1) was increased in the hypothalamus of HFD fed Syn1-cre; Ghsrf/f mice. Overall, feeding pattern changes were more pronounced in Syn1-cre; Ghsrf/f mice than that in AgRP-cre; Ghsrf/f mice, and HFD elicited greater alteration than RD. While AgRP-cre; Ghsrf/f mice consumed HFD meals faster during the day (showing shorter meal duration), Syn1-cre; Ghsrf/f mice ate few HFD meals during the light phase and ate slowly throughout the day (showing longer meal duration in both phases). Our findings reveal that neuronal GHS-R regulates energy homeostasis by altering feeding patterns, and differentially modulates feeding patterns in a site- and diet-dependent manner. The distinctive data in these two mouse lines also suggest that eating slowly during the optimal feeding period (dark phase for mice) may be beneficial in combating obesity.

Olfaction in the context of obesity and diabetes: Insights from animal models to humans

The olfactory system is at the crossroad between sensory processing and metabolic sensing. In addition to being the center of detection and identification of food odors, it is a sensor for most of the hormones and nutrients responsible for feeding behavior regulation. The consequences of modifications in body homeostasis, nutrient overload and alteration of this brain network in the pathological condition of food-induced obesity and type 2 diabetes are still not elucidated. The aim of this review was first to use both humans and animal studies to report on the current knowledge of the consequences of obesity and type 2 diabetes on odorant threshold and olfactory perception including identification discrimination and memory. We then discuss how olfactory processing can be modified by an alteration of the metabolic homeostasis of the organism and available elements on pharmacological treatments that regulate olfaction. We focus on data within the olfactory system but also on the interactions between the olfactory system and other brain networks impacted by metabolic diseases.

High fat diet-induced obesity leads to depressive and anxiety-like behaviors in mice via AMPK/mTOR-mediated autophagy

Depression is one of the most common mental illnesses in modern society. In recent years, several studies show that there are disturbances in lipid metabolism in depressed patients. High-fat diet may lead to anxiety and depression, but the mechanisms involved remain unclear. In our study, we found that 8 weeks of high-fat feeding effectively induced metabolic disorders, including obesity and hyperlipidemia in mice. Interestingly, the mice also showed depressive and anxiety-like behaviors. We further found activated microglia and astrocyte, increased neuroinflammation, decreased autophagy and BDNF levels in mice after high-fat feeding. Besides, high-fat feeding can also inhibit AMPK phosphorylation and induce mTOR phosphorylation. After treating with the mTOR inhibitor rapamycin, autophagy and BDNF levels were elevated. The number of activated microglia and astrocyte, and pro-inflammation levels were reduced. Besides, rapamycin can also reduce the body weight and serum lipid level in high fat feeding mice. Depressive and anxiety-like behaviors were also ameliorated to some extent after rapamycin treatment. In summary, these results suggest that high-fat diet-induced obesity may lead to depressive and anxiety-like behaviors in mice by inhibiting AMPK phosphorylation and promoting mTOR shift to phosphorylation to inhibit autophagy. Therefore, improving lipid metabolism or enhancing autophagy through the AMPK/mTOR pathway could be potential targets for the treatment of obesity depression.

Environmental enrichment ameliorates high-fat diet induced olfactory deficit and decrease of parvalbumin neurons in the olfactory bulb in mice

Overweight induced by high-fat diet (HFD) represents one of the major health concerns in modern societies, which can cause lasting peripheral and central metabolic disorders in all age groups. Specifically, childhood obesity could lead to life-long impact on brain development and functioning. On the other hand, environmental enrichment (EE) has been demonstrated to be beneficial for learning and memory. Here, we explored the impact of high-fat diet on olfaction and organization of olfactory bulb cells in adolescent mice, and the effect of EE intervention thereon. Puberty mice (3-week-old) fed with HFD for 10 weeks exhibited poorer odor sensitivity and olfactory memory relative to controls consuming standard chows. The behavioral deficits were rescued in the HFD group with EE intervention. Neuroanatomically, parvalbumin (PV) interneurons in the olfactory bulb (OB) were reduced in the HFD-fed animals relative to control, while EE intervention also normalized this alteration. In contrast, cells expressing calbindin (CB), doublecortin (DCX) in the OB were not altered. Our findings suggest that PV interneurons may play a crucial role in mediating the HFD-induced olfactory deficit in adolescent mice, and can also serve a protective effect of EE against the functional deficit.

Patterned Feeding of a Hyper-Palatable Food (Oreo Cookies) Reduces Alcohol Drinking in Rats

While a bidirectional positive link between palatable food intake and alcohol drinking has been suggested, several rodents studies report reduced alcohol drinking following palatable diets exposure. These studies utilized purified rodents’ diets high in sugar/fat; however, the effects of hyper-palatable food (HPF) rich in fat and sugar on alcohol drinking remain unclear. Furthermore, neural substrates involved in HPF-mediated changes in alcohol consumption are poorly understood. Therefore, the present study evaluated the effects of patterned feeding of a hyper-palatable food (Oreo cookies) on alcohol drinking as well as dopamine (DA) and serotonin (5-HT) content in rat’s mesocorticolimbic (medial-prefrontal cortex, orbitofrontal cortex, amygdala, and nucleus accumbens) circuitry. Male Long Evans rats received 8-weeks of intermittent (Mon, Tue, Wed) Oreo cookies access, which induced a patterned feeding, in which rats in the Oreo group overconsumed calories on HPF days whereas underconsumption was observed on chow only (Thu, Fri) days. Following HPF exposure, alcohol consumption was evaluated while patterned feeding continued. Alcohol intake in the Oreo group was significantly lower as compared to the chow controls. However, alcohol intake in the Oreo group increased to the levels seen in the group receiving chow following the suspension of patterned HPF feeding. Finally, DA levels in the nucleus accumbens were significantly greater, whereas its metabolite (DOPAC) levels were lower in the Oreo group compared to the chow controls. Surprisingly, 5-HT levels remained unaltered in all tested brain areas. Together, these data suggest that HPF-associated increased DA availability and reduced DA turnover within mesocorticolimbic circuitry may regulate alcohol drinking following patterned HPF feeding.

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.

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

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

Fibroblast Growth Factor 21 as a Potential Biomarker for Improved Locomotion and Olfaction Detection Ability after Weight Reduction in Obese Mice

Obesity is one of the most challenging diseases of the 21st century and is accompanied by behavioural disorders. Exercise, dietary adjustments, or time-restricted feeding are the only successful long-term treatments to date. Fibroblast growth factor 21 (FGF21) plays a key role in dietary regulation, but FGF21 resistance is prevalent in obesity. The aim of this study was to investigate in obese mice whether weight reduction leads to improved behaviour and whether these behavioural changes are associated with decreased plasma FGF21 levels. After establishing a model for diet-induced obesity, mice were subjected to three different interventions for weight reduction, namely dietary change, treadmill exercise, or time-restricted feeding. In this study, we demonstrated that only the combination of dietary change and treadmill exercise affected all parameters leading to a reduction in weight, fat, and FGF21, as well as less anxious behaviour, higher overall activity, and improved olfactory detection abilities. To investigate the interrelationship between FGF21 and behavioural parameters, feature selection algorithms were applied designating FGF21 and body weight as one of five highly weighted features. In conclusion, we concluded from the complementary methods that FGF21 can be considered as a potential biomarker for improved behaviour in obese mice after weight reduction.

Clusterin overexpression as a potential neuroprotective response to the pathological effects of high fat dieting on the brain reward system

High-fat diets (HFDs) can lead to pathological changes in the brain underlying several behavioral disturbances (e.g., reward deficiency). To further increase our knowledge of these associations, we studied the sucrose reward and the brain expression of clusterin, a protein that is overexpressed after several kind of brain damaging conditions. C57BL/6J male mice were differentially fed on an HFD or standard chow for 41 days and underwent 11 sucrose place conditioning sessions followed by 4 extinction sessions to monitor the effects of HFD on sucrose reward by means of free choice tests. We quantified clusterin expression by immunochemistry in the nucleus accumbens, dorsal striatum and cingulate cortex. HFD tended to provoke a transient potentiation in the acquisition of sucrose-conditioned place preference, but this effect was followed by a much more consistent reduction in sucrose preference, which spontaneously disappeared after 31 days of an HFD with no need for extinction learning. The HFD mice showed higher clusterin expression in the nucleus accumbens but not in the other brain areas studied. The results confirm that HFDs strongly influence the rewarding properties of palatable foods and suggest a direct connection with neurotoxic alterations in the brain reward system tagged by clusterin overexpression.

Examining the role of olfaction in dietary choice

Obesity is frequently caused by calorie-rich dietary choices across the animal kingdom. As prandial preference toward a high-fat diet develops in mice, an anti-preference or devaluation of a nutritionally balanced but less palatable standard chow diet occurs concomitantly. Although mechanistic insights underlying devaluation have been observed physiologically in the brain, it is unclear how peripheral sensory processing affects food choice. Because olfactory cues and odor perception help coordinate food preference and intake, we determine the role of smell in the targeted consumption of a high-fat diet and simultaneous devaluation of a standard chow diet. Using inaccessible food and loss-of-function manipulations, we find that olfactory information is neither sufficient nor necessary for both the acute and chronic selection of high-fat diet and coincident diminished value of standard diet. This work suggests alternative means are behind the immediate and sustained consumption of high-fat diet and concurrent standard diet devaluation.

Olfaction is considered integral to food choice and preference formation. Boone et al. use a behavioral approach to determine the salience of olfactory cues in diet selection. They find that olfaction is neither sufficient nor required for both high-fat-diet preference and standard diet devaluation.

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

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

Western Diet Accelerates the Impairment of Odor-Related Learning and Olfactory Memory in the Mouse

Olfactory dysfunction could be an early indicator of cognitive decline in type 2 diabetes (T2D). However, whether obesity affects olfaction in people with T2D is unclear. This question needs to be addressed, because most people with T2D are obese. Importantly, whether different contributing factors leading to obesity (e.g., different components of diet or gain in weight) affect specific olfactory functions and underlying mechanisms is unknown. We examined whether two T2D-inducing obesogenic diets, one containing a high proportion of fat (HFD) and one with moderate fat and high sugar (Western diet, WD), affect odor detection/discrimination, odor-related learning, and olfactory memory in the mouse. We also investigated whether the diets impair adult neurogenesis, GABAergic interneurons, and neuroblasts in the olfactory system. Here, we further assessed olfactory cortex volume and cFos expression-based neuronal activity. The WD-fed mice showed declined odor-related learning and olfactory memory already after 3 months of diet intake (p = 0.046), although both diets induced similar hyperglycemia and weight gain compared to those of standard diet-fed mice (p = 0.0001 and p < 0.0001, respectively) at this time point. Eight months of HFD and WD diminished odor detection (p = 0.016 and p = 0.045, respectively), odor-related learning (p = 0.015 and p = 0.049, respectively), and olfactory memory. We observed no changes in the investigated cellular mechanisms. We show that the early deterioration of olfactory parameters related to learning and memory is associated with a high content of sugar in the diet rather than with hyperglycemia or weight gain. This finding could be exploited for understanding, and potentially preventing, cognitive decline/dementia in people with T2D. The mechanisms behind this finding remain to be elucidated.

Modeling Diet-Induced Metabolic Syndrome in Rodents

Standardized animal models represent one of the most valuable tools available to understand the mechanism underlying the metabolic syndrome (MetS) and to seek for new therapeutic strategies. However, there is considerable variability in the studies conducted with this essential purpose. This review presents an updated discussion of the most recent studies using diverse experimental conditions to induce MetS in rodents with unbalanced diets, discusses the key findings in metabolic outcomes, and critically evaluates what we have been learned from them and how to advance in the field. The study includes scientific reports sourced from the Web of Science and PubMed databases, published between January 2013 and June 2020, which used hypercaloric diets to induce metabolic disorders, and address the impact of the diet on metabolic parameters. The collected data are used as support to discuss variables such as sex, species, and age of the animals, the most favorable type of diet, and the ideal diet length to generate metabolic changes. The experimental characteristics propose herein improve the performance of a preclinical model that resembles the human MetS and will guide researchers to investigate new therapeutic alternatives with confidence and higher translational validity.

Alteraciones del olfato en la obesidad

Aun cuando el sentido del olfato es fundamental para la percepción de los alimentos, su relación con la obesidad ha sido poco investigada. Este artículo es una revisión de la literatura sobre esa relación. La evidencia actual tanto en animales como en humanos apoya la hipótesis de que el olfato está alterado en esta condición. Estudios recientes señalan que los individuos obesos podrían tener una mayor sensibilidad a los olores de alimentos altos en calorías, y menor para los de bajo valor calórico incluidos los no asociados con alimentos. El estudio de la percepción quimiosensorial es un área prometedora para avanzar en el entendimiento de los mecanismos involucrados en la obesidad.

High-Fat Diet Enhances Working Memory in the Y-Maze Test in Male C57BL/6J Mice with Less Anxiety in the Elevated Plus Maze Test

Obesity is characterized by massive adipose tissue accumulation and is associated with psychiatric disorders and cognitive impairment in human and animal models. However, it is unclear whether high-fat diet (HFD)-induced obesity presents a risk of psychiatric disorders and cognitive impairment. To examine this question, we conducted systematic behavioral analyses in C57BL/6J mice (male, 8-week-old) fed an HFD for 7 weeks. C57BL/6J mice fed an HFD showed significantly increased body weight, hyperlocomotion in the open-field test (OFT) and Y-maze test (YMZT), and impaired sucrose preference in the sucrose consumption test, compared to mice fed a normal diet. Neither body weight nor body weight gain was associated with any of the behavioral traits we examined. Working memory, as assessed by the YMZT, and anxiety-like behavior, as assessed by the elevated plus maze test (EPMT), were significantly correlated with mice fed an HFD, although these behavioral traits did not affect the entire group. These results suggest that HFD-induced obesity does not induce neuropsychiatric symptoms in C57BL/6J mice. Rather, HFD improved working memory in C57BL/6J mice with less anxiety, indicating that an HFD might be beneficial under limited conditions. Correlation analysis of individual traits is a useful tool to determine those conditions.

Reduced alcohol drinking following patterned feeding: Role of palatability and acute contingent availability

Recent studies from our lab have demonstrated that intermittent high-fat diet access reduces alcohol drinking in rats. However, it was unclear if caloric overload, palatability, or diet itself triggered reduced alcohol drinking. It is also unknown if a similar paradigm could reduce relapse-like alcohol drinking. The presented study tested the hypothesis that acute intermittent palatable diet (PD) access would rescue relapse-like drinking and palatability, but not diet itself contributes to reduced drinking. Male Long Evans rats received six-weeks intermittent or chronic chow (controls) or PDs (high-fat diet, high-sugar diet) exposure, and alcohol testing occurred following PDs suspension. Alcohol intake was not significantly different among groups in either condition, suggesting that diet itself did not impact alcohol drinking. A subset of these rats received two-weeks intermittent PDs (Int-PDs) exposure and alcohol testing reinitiated while Int-PDs access continued. Alcohol intake significantly escalated (~137% compared to baseline; alcohol deprivation effect) in the chow controls, whereas it remained unchanged in PD groups. These data demonstrate the critical importance of acute intermittent PDs availability and its protective effect in relapse-like drinking. To assess the contribution of palatability in reduced alcohol drinking, a separate group of rats received two-weeks intermittent high-sugar diet (Int-HSD) or saccharin (Int-SAC) access and tested for alcohol drinking while Int-HSD/SAC continued. Alcohol drinking significantly decreased (~30%) in both HSD and SAC groups compared to the controls. These data identify the critical parameters by which acute intermittent PD access reduces alcohol drinking and could have important therapeutic implications in the management of alcoholism.

Altered behavior in mice overexpressing soluble ST2

Psychoneuroimmunological studies have clearly demonstrated that both cellular and humoral immunity are related to major depression. Soluble ST2 is regarded as a key molecule regulating immune system as well as cell proliferation. Indeed, soluble ST2 is reported to reduce IL-33-induced IL-6 and TNF-α production in macrophages and IL-33-induced IL-5 and IL-13 production in type 2 innate lymphoid cells. Elevated serum concentrations of soluble ST2 have been reported in patients with neuropsychiatric disorders, suggesting pathophysiological roles of soluble ST2 in behavioral phenotypes. Nevertheless, the relation between soluble ST2 and depressive behavior remain to be uncovered. To complement this point, we performed broad behavioral phenotyping, utilizing transgenic mice with a high concentration of serum ST2 in the present study. Soluble ST2 overexpression mice (ST2 Tg mice) were generated on a C3H/HeJ background. ST2 Tg mice crossed onto the BALB/c genetic background were used. Before starting tests, each mouse was observed in a clean cage for a general health check and neurological screening tests. In Experiment I, comprehensive behavioral phenotyping was performed to reveal the role of soluble ST2 on sensorimotor functions, anxiety-like behaviors, depression-like behaviors, social behaviors, and learning and memory functions. In Experiment II, to confirm the role of soluble ST2 on depression-like behaviors, a depression test battery (two bottle choice test, forced swimming test, and tail suspension test) was applied. The general health check indicated good general health and normal gross appearance for ST2 Tg mice. Further, the neurological reflexes of all the mice were normal. We found that soluble ST2 overexpression resulted in decreased social interaction. Moreover, depression-like behaviors of ST2 Tg mice were observed in two well-established behavioral paradigms, the forced swimming test and the tail suspension test. Nevertheless, hedonic reaction to sucrose was observed in ST2 Tg mice similar to WT mice. These results suggest the depression in the ST2 Tg mice. In conclusion, through a series of experiments, we established the animal model for assessing role of soluble ST2 in neuropsychiatric disorders, and revealed the possible involvement of soluble ST2 in depressive behavior.

Central and Peripheral Mechanisms in ApoE4-Driven Diabetic Pathology

Apolipoprotein E (APOE) ε4 gene allele and type 2 diabetes mellitus (T2DM) are prime risk factors for Alzheimer’s disease (AD). Despite evidence linking T2DM and apoE4, the mechanism underlying their interaction is yet to be determined. In the present study, we employed a model of APOE-targeted replacement mice and high-fat diet (HFD)-induced insulin resistance to investigate diabetic mechanisms associated with apoE4 pathology and the extent to which they are driven by peripheral and central processes. Results obtained revealed an intriguing pattern, in which under basal conditions, apoE4 mice display impaired glucose and insulin tolerance and decreased insulin secretion, as well as cognitive and sensorimotor characteristics relative to apoE3 mice, while the HFD impairs apoE3 mice without significantly affecting apoE4 mice. Measurements of weight and fasting blood glucose levels increased in a time-dependent manner following the HFD, though no effect of genotype was observed. Interestingly, sciatic electrophysiological and skin intra-epidermal nerve fiber density (IENFD) peripheral measurements were not affected by the APOE genotype or HFD, suggesting that the observed sensorimotor and cognitive phenotypes are related to central nervous system processes. Indeed, measurements of hippocampal insulin receptor and glycogen synthase kinase-3β (GSK-3β) activation revealed a pattern similar to that obtained in the behavioral measurements while Akt activation presented a dominant effect of diet. HFD manipulation induced genotype-independent hyperlipidation of apoE, and reduced levels of brain apoE in apoE3 mice, rendering them similar to apoE4 mice, whose brain apoE levels were not affected by the diet. No such effect was observed in the peripheral plasma levels of apoE, suggesting that the pathological effects of apoE4 under the control diet and apoE3 under HFD conditions are related to the decreased levels of brain apoE. Taken together, our data suggests that diabetic mechanisms play an important role in mediating the pathological effects of apoE4 and that consequently, diabetic-related therapy may be useful in treating apoE4 pathology in AD.

Behavioral and Neurobiological Consequences of Hedonic Feeding on Alcohol Drinking

A complex interplay of peripheral and central signaling mechanisms within the body of an organism maintains energy homeostasis. In addition, energy/food intake is modified by various external factors (e.g., palatability, food availability, social and environmental triggers). Highly palatable foods can provoke maladaptive feeding behavior, which in turn disrupts normal homeostatic regulation resulting in numerous health consequences. Furthermore, neuroendocrine peptides, traditionally considered to regulate appetite and energy homeostasis, also control the intake and reinforcing properties of alcohol and drugs of abuse. Therefore, dysregulated eating as a result of a hedonic/binge-like intake of hyper-palatable food may impact alcohol drinking behavior. Relevant in this case is the fact that eating disorders are highly comorbid with several neuropsychiatric conditions, including alcohol use disorder. The present review is intended to summarize the neurobiological and functional consequences of hedonic feeding on alcohol intake.

Oxytocin Ameliorates Impaired Behaviors of High Fat Diet-Induced Obese Mice

Excessive intake of fat is a major risk factor for lifestyle-related diseases such as heart disease and also affects brain function such as object recognition memory, social recognition, anxiety behavior, and depression-like behavior. Although oxytocin (OXT) has been reported to improve object recognition, social recognition, anxiety behavior, and depression-like behavior in specific conditions, previous studies did not explore the impact of OXT in high-fat diet (HFD)-fed mice. Furthermore, it remains unclear whether intake of HFD affects OXT/oxytocin receptor (OXTR) in the brain. Here, we demonstrated that peripheral OXT administration improves not only social recognition but also object recognition and depressive-like behavior in HFD-fed mice. In contrast, peripheral OXT administration to HFD-fed male mice increased fear and anxiety-related behavior. In addition, we observed that intake of HFD decreased OXTR and c-fos mRNA expression in the hippocampus, specifically. Furthermore, peripheral OXT administration increased OXT mRNA expression in the hypothalamus. Altogether, these findings suggest that OXT has the potential to improve various recognition memory processes via peripheral administration but also has side effects that increase fear-related behavior in males.

Feed restriction since lactation has reduced anxiety in adult Wistar rats

ABSTRACT Objective To evaluate the effects of macronutrients (protein, carbohydrate and/or lipid) in the diet of young adult (72 days) and adult (182 days) Wistar rats treated ad libitum and with 30% restriction from birth on anxiety in the elevated plus-maze. Methods We used 238 rats treated from birth, composing the groups: Control, Protein, Carbohydrate, Lipid, Carbohydrate and Lipid, Control Restriction, Protein Restriction, Carbohydrate Restriction, Lipid Restriction and Carbohydrate and Lipid Restriction. The animals were weighed at the beginning and at the end of the experiment and tested in the elevated plus-maze. Data were submitted to analysis of variance, followed by the Newman-Keuls Test (p<0.05). Results Among the animals treated ad libitum, the Control, Carbohydrate plus Lipid and Lipid gained more weight than the Carbohydrate and Protein; ad libitum animals gained more weight than those on restriction; among the restrictions, Carbohydrate Restriction rats were the ones that gained less weight. Diet-restricted animals exhibited reduced first-entry latency, greater percentage of entries and time spent, frequency of open arm extremity visits, head dipping (protected and unprotected), and length of stay in the central area of the elevated plus-maze. The animals with 182 days presented greater latency for first entry, reduced frequency of false entries and visits to the ends of the open arms and protected head dipping. Conclusion Food restricted animals, regardless of the macronutrient present in the diet, were less anxious and/or increased their impulsivity and those at 182 days were more anxious and/or with reduced impulsivity.

Prefrontal cortex inflammation and liver pathologies accompany cognitive and motor deficits following Western diet consumption in non-obese female mice

AIMS

The high sugar and lipid content of the Western diet (WD) is associated with metabolic dysfunction, non-alcoholic steatohepatitis, and it is an established risk factor for neuropsychiatric disorders. Our previous studies reported negative effects of the WD on rodent emotionality, impulsivity, and sociability in adulthood. Here, we investigated the effect of the WD on motor coordination, novelty recognition, and affective behavior in mice as well as molecular and cellular endpoints in brain and peripheral tissues.

MAIN METHODS

Female C57BL/6 J mice were fed the WD for three weeks and were investigated for glucose tolerance, insulin resistance, liver steatosis, and changes in motor coordination, object recognition, and despair behavior in the swim test. Lipids and liver injury markers, including aspartate-transaminase, alanine-transaminase and urea were measured in blood. Serotonin transporter (SERT) expression, the density of Iba1-positive cells and concentration of malondialdehyde were measured in brain.

KEY FINDINGS

WD-fed mice exhibited impaired glucose tolerance and insulin resistance, a loss of motor coordination, deficits in novel object exploration and recognition, increased helplessness, dyslipidemia, as well as signs of a non-alcoholic steatohepatitis (NASH)-like syndrome: liver steatosis and increased liver injury markers. Importantly, these changes were accompanied by decreased SERT expression, elevated numbers of microglia cells and malondialdehyde levels in, and restricted to, the prefrontal cortex.

SIGNIFICANCE

The WD induces a spectrum of behaviors that are more reminiscent of ADHD and ASD than previously recognized and suggests that, in addition to the impairment of impulsivity and sociability, the consumption of a WD might be expected to exacerbate motor dysfunction that is also known to be associated with adult ADHD and ASD.

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

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

Diet-induced obesity decreases rate-dependent depression in the Hoffmann's reflex in adult mice

Obesity is associated with balance and motor control deficits. We have recently shown that Group Ia muscle spindle afferents, the sensory arm of the muscle stretch reflex, are less responsive in mice fed a high-fat diet. Here we test the hypothesis that reflex excitability to sensory information from Group Ia muscle spindle afferents is altered in a mouse model of diet-induced obesity. We measured the anesthetized Hoffmann's or H-reflex, the electrical analog of the muscle stretch reflex. Adult mice of both sexes were fed a control diet (CD; 10% kcal from fat) or a high-fat diet (HFD; 60% kcal from fat) for 5, 10, or 15 weeks. We used three quantitative measures of H-reflex excitability: (1) H-reflex latency; (2) the percentage of motor neurons recruited from electrical stimulation of Group Ia muscle spindle afferents (Hmax /Mmax ); and (3) rate-dependent depression (RDD), the decrease in H-reflex amplitude to high frequency stimulation (20 stimuli at 5 Hz). A HFD did not significantly alter H latency (P = 0.16) or Hmax /Mmax ratios (P = 0.06), but RDD was significantly lower in HFD compared to CD groups (P < 0.001). Interestingly, HFD males exhibited decreased RDD compared to controls only after 5 and 10 weeks of feeding, but females showed progressive decreases in RDD that were only significant at 10 and 15 weeks on the HFD. These results suggest that high-fat feeding increases H-reflex excitability. Future studies are needed to determine whether these changes alter muscle stretch reflex strength and/or balance and to determine the underlying mechanism(s).

Differential Impact of Ad Libitum or Intermittent High-Fat Diets on Bingeing Ethanol-Mediated Behaviors

Background: Dietary factors have significant effects on the brain, modulating mood, anxiety, motivation and cognition. To date, no attention has been paid to the consequences that the combination of ethanol (EtOH) and a high-fat diet (HFD) have on learning and mood disorders during adolescence. The aim of the present work was to evaluate the biochemical and behavioral consequences of ethanol binge drinking and an HFD consumption in adolescent mice. Methods: Animals received either a standard diet or an HFD (ad libitum vs. binge pattern) in combination with ethanol binge drinking and were evaluated in anxiety and memory. The metabolic profile and gene expression of leptin receptors and clock genes were also evaluated. Results: Excessive white adipose tissue and an increase in plasma insulin and leptin levels were mainly observed in ad libitum HFD + EtOH mice. An upregulation of the Lepr gene expression in the prefrontal cortex and the hippocampus was also observed in ad libitum HFD groups. EtOH-induced impairment on spatial memory retrieval was absent in mice exposed to an HFD, although the aversive memory deficits persisted. Mice bingeing on an HFD only showed an anxiolytic profile, without other alterations. We also observed a mismatch between Clock and Bmal1 expression in ad libitum HFD animals, which were mostly independent of EtOH bingeing. Conclusions: Our results confirm the bidirectional influence that occurs between the composition and intake pattern of a HFD and ethanol consumption during adolescence, even when the metabolic, behavioral and chronobiological effects of this interaction are dissociated.

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.

Phaseolus vulgaris L. Extract: Alpha-Amylase Inhibition against Metabolic Syndrome in Mice

To examine the effects of the alpha-amylase inhibitor isoform 1 called phaseolamin, a standardized extract from white kidney beans (Phaseolus vulgaris L.) was tested against the hallmarks of metabolic syndrome. The efficacy of a per os repeated treatment with P. vulgaris extract (500 mg/kg) was compared with metformin (100 mg/kg) and atorvastatin (10 mg/kg) in a model of metabolic syndrome evoked by prolonged high fat diet (HFD; week 1 to week 19) in C57BL/6 mice. Bean extract and compounds administration started after metabolic syndrome establishment (week 11). P. vulgaris extract reduced the body weight overtime, as well as effectively lowered glycaemia, triglycerides, and cholesterol. On week 19, bean extract normalized the HFD-evoked tolerance to glucose and insulin. According to the phytochemical characterization, it inhibited the alpha-amylase activity. Animals treated with the extract were rescued from motor impairments and nociceptive threshold alterations induced by HFD. Specific organs analysis revealed that P. vulgaris extract decreased hepatic steatosis and lipid peroxidation in liver. It protected the heart from HFD oxidative alterations increasing the expression of the detoxifying enzymes catalase and glutathione reductase, and normalizing NADH dehydrogenase level. The histological analysis of aorta showed a protection about the development of fatty streaks in the muscular layers. In conclusion, a prolonged treatment with the standardized extract of P. vulgaris significantly reduced several pathological features related to a metabolic syndrome-like condition; a multifactorial approach that candidates this vegetal product as a possible therapeutic option against metabolic syndrome.

A Preventive Prebiotic Supplementation Improves the Sweet Taste Perception in Diet-Induced Obese Mice

Orosensory perception of sweet stimulus is blunted in diet-induced obese (DIO) rodents. Although this alteration might contribute to unhealthy food choices, its origin remains to be understood. Cumulative evidence indicates that prebiotic manipulations of the gut microbiota are associated with changes in food intake by modulating hedonic and motivational drive for food reward. In the present study, we explore whether a prebiotic supplementation can also restore the taste sensation in DIO mice. The preference and licking behavior in response to various sucrose concentrations were determined using respectively two-bottle choice tests and gustometer analysis in lean and obese mice supplemented or not with 10% inulin-type fructans prebiotic (P) in a preventive manner. In DIO mice, P addition reduced the fat mass gain and energy intake, limited the gut dysbiosis and partially improved the sweet taste perception (rise both of sucrose preference and number of licks/10 s vs. non-supplemented DIO mice). No clear effect on orosensory perception of sucrose was found in the supplemented control mice. Therefore, a preventive P supplementation can partially correct the loss of sweet taste sensitivity found in DIO mice, with the efficiency of treatment being dependent from the nutritional status of mice (high fat diet vs. regular chow).

Central and Peripheral Inflammation Link Metabolic Syndrome and Major Depressive Disorder

Metabolic syndrome and major depression are two of the most common and debilitating disorders worldwide, occurring with significant rates of comorbidity. Recent studies have uncovered that each of these conditions is associated with chronic, low-grade inflammation. This is characterized by increased circulating pro-inflammatory cytokines, altered leukocyte population frequencies in blood, accumulation of immune cells in tissues including the brain, and activation of these immune cells. Cytokines that become elevated during obesity can contribute to the progression of metabolic syndrome by directly causing insulin resistance. During chronic stress, there is evidence that these cytokines promote depression-like behavior by disrupting neurotransmitter synthesis and signal transduction. Animal models of obesity and depression have revealed a bi-directional relationship whereby high-fat feeding and chronic stress synergize and exacerbate metabolic dysregulation and behavioral abnormalities. Although far from conclusive, emerging evidence suggests that inflammation in the central and peripheral immune system may link metabolic syndrome to major depressive disorder. In this review, we will synthesize available data supporting this view and identify critical areas for future investigation.