Vulnerability to dietary n-3 polyunsaturated fatty acid deficiency after exposure to early stress in rats

Enduring effects of early-life adversity on reward processes: A systematic review and meta-analysis of animal studies

Two-thirds of individuals experience adversity during childhood such as neglect, abuse or highly-stressful events. Early-life adversity (ELA) increases the life-long risk of developing mood and substance use disorders. Reward-related deficits has emerged as a key endophenotype of such psychiatric disorders. Animal models are invaluable for studying how ELA leads to reward deficits. However, the existing literature is heterogenous with difficult to reconcile findings. To create an overview, we conducted a systematic review containing multiple meta-analyses regarding the effects of ELA on reward processes overall and on specific aspects of reward processing in animal models. A comprehensive search identified 120 studies. Most studies omitted key details resulting in unclear risk of bias. Overall meta-analysis showed that ELA significantly reduced reward behaviors (SMD: -0.42 [-0.60; -0.24]). The magnitude of ELA effects significantly increased with longer exposure. When reward domains were analyzed separately, ELA only significantly dampened reward responsiveness (SMD: -0.525[-0.786; -0.264]) and social reward processing (SMD: -0.374 [-0.663; -0.084]), suggesting that ELA might lead to deficits in specific reward domains.

Interactions between a polygenic risk score for plasma docosahexaenoic fatty acid concentration, eating behaviour, and body composition in children

BACKGROUND

The relationship between eating behaviour and current body weight has been described. However little is known about the effect of polyunsaturated fatty acids (PUFA) in this relationship. Genetic contribution to a certain condition is derived from a combination of small effects from many genetic variants, and polygenic risk scores (PRS) summarize these effects. A PRS based on a GWAS for plasma docosahexaenoic fatty acid (DHA) has been created, based on SNPs from 9 genes.

OBJECTIVE

To analyze the interaction between the PRS for plasma DHA concentration, body composition and eating behaviour (using the Children Eating Behaviour Questionnaire) in childhood.

SUBJECTS/METHODS

We analyzed a subsample of children from the Maternal, Adversity, Vulnerability and Neurodevelopment (MAVAN) cohort with PRS and measurements of eating behaviour performed at 4 years of age (n = 210), 6 y (n = 177), and body fat determined by bioelectric impedance at 4 y and 6 y or by air displacement plethysmography and dual-energy X-ray absorptiometry at 8 y (n = 42 and n = 37). PRS was based on the GWAS from Lemaitre et al. 2011 (p threshold = p < 5*10-6), and a median split created low and high PRS groups (high PRS = higher DHA level).

RESULTS

In ALSPAC children, we observed an association between PRS and plasma DHA concentration (β = 0.100, p < 0.01) and proportion (β = 0.107, p < 0.01). In MAVAN, there were interactions between PRS and body fat on pro-intake scores in childhood, in which low PRS and higher body fat were linked to altered behaviour. There were also interactions between PRS and pro-intake scores early in childhood on body fat later in childhood, suggesting that the genetic profile and eating behaviour influence the development of adiposity at later ages.

CONCLUSIONS

A lower PRS (lower plasma PUFA) can be a risk factor for developing higher body fat associated with non-adaptive eating behaviour in childhood; it is possible that the higher PRS (higher plasma PUFA) is a protective feature.

Life-course effects of early life adversity exposure on eating behavior and metabolism

Environmental variations in early life influence brain development, making individuals more vulnerable to psychiatric and metabolic disorders. Early life stress (ELS) has a strong impact on the development of eating behavior. However, eating is a complex behavior, determined by an interaction between signals of energy homeostasis, neuronal circuits involved in its regulation, and circuits related to rewarding properties of the food. Although mechanisms underlying ELS-induced altered feeding behavior are not completely understood, evidence suggest that the effects of ELS on metabolic, mood, and emotional disorders, as well as reward system dysfunctions can contribute directly or indirectly to altered feeding behavior. The focus of this chapter is to discuss the effects of ELS on eating behavior and metabolism, considering different factors that control appetite such as energy homeostasis, hedonic properties of the food, emotional and cognitive status. After highlighting classic studies on the association between ELS and eating behavior alterations, we discuss how exposure to adversity can interact with genetics characteristics to predict variable outcomes.

N-3 PUFA improved post-menopausal depression induced by maternal separation and chronic mild stress through serotonergic pathway in rats-effect associated with lipid mediators

Early life maternal separation (MS) increases the vulnerability to depression in rats with chronic mild stress (CMS). N-3 polyunsaturated fatty acids (PUFA) improved depressive behaviors in rats with acute stress; however, their effects on rats with MS+CMS were not apparent. The purpose of the present study was to investigate the hypothesis that lifetime n-3 PUFA supplementation improves post-menopausal depression through the serotonergic and glutamatergic pathways while modulating n-3 PUFA-derived metabolites. Female rats were fed diets of either 0% n-3 PUFA during lifetime or 1% energy n-3 PUFA during pre-weaning, post-weaning, or lifetime periods. Rats were allocated to non-MS or MS groups and underwent CMS after ovariectomy. N-3 PUFA increased brain n-3 PUFA-derived endocannabinoid/oxylipin levels, and reversed depressive behaviors. N-3 PUFA decreased blood levels of adrenocorticotropic hormone and corticosterone, and brain expressions of corticotropin-releasing factor and miRNA-218, which increased the expression of the glucocorticoid receptor. N-3 PUFA decreased the expression of tumor necrosis factor-α, interleukin (IL)-6, IL-1β, and prostaglandin E₂, while increased the expression of miRNA-155. N-3 PUFA also increased brainstem serotonin levels and hippocampal expression of the serotonin-1A receptor, cAMP response element-binding protein (CREB), phospho-CREB, and brain-derived neurotrophic factor. However, n-3 PUFA did not affect brain expression of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subtype 1, N-methyl-D-aspartate receptor subtype 2B, or miRNA-132. Moreover, n-3 PUFA exposure during lifetime caused greater effects than pre- and post-weaning periods. The present study suggested that n-3 PUFA improved depressive behaviors through serotonergic pathway while modulating the metabolites of n-3 PUFA in post-menopausal depressed rats with chronic stress.

Endocannabinoids and aging-Inflammation, neuroplasticity, mood and pain

Aging is associated with changes in hormones, slowing of metabolism, diminished physiological processes, chronic inflammation and high exposure to oxidative stress factors, generally described as the biological cost of living. Lifestyle interventions of diet and exercise can improve the quality of life during aging and lower diet-related chronic disease. The endocannabinoid system (ECS) has important effects on systemic metabolism and physiological systems, including the central and peripheral nervous systems. Exercise can reduce the loss of muscle mass and improve strength, and increase the levels of endocannabinoids (eCB) in brain and blood. Although the ECS exerts controls on multiple systems throughout life it affords benefits to natural aging. The eCB are synthesized from polyunsaturated fatty acids (PUFA) and the primary ones are produced from arachidonic acid (n-6 PUFA) and others from the n-3 PUFA, namely eicosapentaenoic and docosahexaenoic acids. The eCB ligands bind to their receptors, CB1 and CB2, with effects on appetite stimulation, metabolism, immune functions, and brain physiology and neuroplasticity. Dietary families of PUFA are a primary factor that can influence the types and levels of eCB and as a consequence, the downstream actions when the ligands bind to their receptors. Furthermore, the association of eCB with the synthesis of oxylipins (OxL) is a connection between the physiological actions of eCB and the lipid derived immunological OxL mediators of inflammation. OxL are ubiquitous and influence neuroinflammation and inflammatory processes. The emerging actions of eCB on neuroplasticity, well-being and pain are important to aging. Herein, we present information about the ECS and its components, how exercise and diet affects specific eCB, their role in neuroplasticity, neuroinflammation, pain, mood, and relationship to OxL. Poor nutrition status and low nutrient intakes observed with many elderly are reasons to examine the role of dietary PUFA actions on the ECS to improve health.

N-3 PUFA Have Antidepressant-like Effects Via Improvement of the HPA-Axis and Neurotransmission in Rats Exposed to Combined Stress

Early life and adulthood stress increase vulnerability for mental illness, and eventually trigger depression. N-3 polyunsaturated fatty acids (PUFA) have antidepressant effects, but their effect on rats exposed to combined stress has been not investigated. This study aimed to investigate whether n-3 PUFA supplementation had antidepressant-like effects in rat models of depression induced by a combination of chronic mild stress (CMS) and maternal separation (MS) through the modulation of the hypothalamic-pituitary-adrenal (HPA) axis and neurotransmission. Rats were fed the n-3 PUFA diet during the pre-weaning or post-weaning period or for lifetime, and allocated to different groups based on the type of induced stress: non-stress (NS), CMS + MS, or CMS alone. N-3 PUFA improved the depressive behaviors of the CMS alone and CMS + MS groups and modulated the HPA-axis by reducing the circulating adrenocorticotropic hormone, corticosterone, and corticotropin-releasing factor expression, and increasing glucocorticoid receptor expression. N-3 PUFA also modulated brain phospholipid fatty acid concentration, thus reducing inflammatory cytokines; improved the serotonergic pathway, thus increasing the expression of the brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), serotonin-1A receptor, and serum levels of serotonin; but did not affect glutamatergic neurotransmission. Furthermore, n-3 PUFA decreased the hippocampal expression of microRNA-218 and -132, increased that of microRNA-155, and its lifetime supplementation was more beneficial than pre- or post-weaning supplementation. This study suggests that n-3 PUFA has an antidepressant effect in rats exposed to combined stress, through the improvement of the HPA-axis abnormalities, the BDNF-serotonergic pathway, and the modulation of microRNAs.

Effects of maternal deprivation stress and maternal dietary of n-3 polyunsaturated fatty acids on the neurobehavioral development of male offspring

Objectives: Early-life stress and polyunsaturated fatty acids (PUFAs) have profound effects on brain development. Polyunsaturated fatty acids (PUFAs) are essential nutrients and normal components for development. The aims of this study are to investigate the effects of maternal deprivation (MD) stress and maternal dietary of n-3 PUFAs on the physical and neurobiological developments of offspring.Methods: According to the content of n-3 PUFAs in diets, female dams were divided into three groups (n = 6-7): deficiency, control and supplementary. MD paradigm was performed 6 h a day from postnatal days (PND) 1 to PND 14. The physical parameters and neurobehavioral tests were measured.Results: Different effects of MD stress, maternal diet and time on physical and neurobehavioral developments were observed. There was an interaction among stress, diet and time on body weight. MD stress markedly decreased weight among different diet groups, while deficiency diet significantly increased weight on PND 21 in N-MD pups and on PND 14 in MD pups. Moreover, MD stress delayed fur appearance and eye opening, whereas deficiency diet accelerated eye opening. On cliff avoidance and rearing frequency, MD pups performed worse; however a subtle delay on the surface righting was observed in supplementary group. Additionally, MD pups performed worse on PND 14 in forelimb grip. Unfortunately, there were no significant effects on incisor eruption, locomotion frequency and negative geotaxis.Discussion: This study suggests that early MD and inadequate intake of n-3 PUFAs are harmful to optimal growth and neurobehavioral development.

Maternal separation in rodents: a journey from gut to brain and nutritional perspectives

The developmental period constitutes a critical window of sensitivity to stress. Indeed, early-life adversity increases the risk to develop psychiatric diseases, but also gastrointestinal disorders such as the irritable bowel syndrome at adulthood. In the past decade, there has been huge interest in the gut-brain axis, especially as regards stress-related emotional behaviours. Animal models of early-life adversity, in particular, maternal separation (MS) in rodents, demonstrate lasting deleterious effects on both the gut and the brain. Here, we review the effects of MS on both systems with a focus on stress-related behaviours. In addition, we discuss more recent findings showing the impact of gut-directed interventions, including nutrition with pre- and probiotics, illustrating the role played by gut microbiota in mediating the long-term effects of MS. Overall, preclinical studies suggest that nutritional approaches with pro- and prebiotics may constitute safe and efficient strategies to attenuate the effects of early-life stress on the gut-brain axis. Further research is required to understand the complex mechanisms underlying gut-brain interaction dysfunctions after early-life stress as well as to determine the beneficial impact of gut-directed strategies in a context of early-life adversity in human subjects.

Anxiolytic- and Antidepressant-Like Effects of Fish Oil-Enriched Diet in Brain-Derived Neurotrophic Factor Deficient Mice

Despite significant advances in the understanding of the therapeutic activity of antidepressant drugs, treatment-resistant depression is a public health issue prompting research to identify new therapeutic strategies. Evidence strongly suggests that nutrition might exert a significant impact on the onset, the duration and the severity of major depression. Accordingly, preclinical and clinical investigations demonstrated the beneficial effects of omega-3 fatty acids in anxiety and mood disorders. Although the neurobiological substrates of its action remain poorly documented, basic research has shown that omega-3 increases brain-derived neurotrophic factor (BDNF) levels in brain regions associated with depression, as antidepressant drugs do. In contrast, low BDNF levels and hippocampal atrophy were observed in animal models of depression. In this context, the present study compared the effects of long-lasting fish oil-enriched diet, an important source of omega-3 fatty acids, between heterozygous BDNF^+/- mice and their wild-type littermates. Our results demonstrated lower activation of Erk in BDNF^+/- mice whereas this deficit was rescued by fish oil-enriched diet. In parallel, BDNF^+/- mice displayed elevated hippocampal extracellular 5-HT levels in relation with a local decreased serotonin transporter protein level. Fish oil-enriched diet restored normal serotonergic tone by increasing the protein levels of serotonin transporter. At the cellular level, fish oil-enriched diet increased the pool of immature neurons in the dentate gyrus of BDNF^+/- mice and the latter observations coincide with its ability to promote anxiolytic- and antidepressant-like response in these mutants. Collectively, our results demonstrate that the beneficial effects of long-term exposure to fish oil-enriched diet in behavioral paradigms known to recapitulate diverse abnormalities related to the depressive state specifically in mice with a partial loss of BDNF. These findings contrast with the mechanism of action of currently available antidepressant drugs for which the full manifestation of their therapeutic activity depends on the enhancement of serotoninergic and BDNF signaling. Further studies are warranted to determine whether fish oil supplementation could be used as an add-on strategy to conventional pharmacological interventions in treatment-resistant patients and relevant animal models.

The effects of early life stress on reward processing

Early life stress (ELS), in the form of childhood maltreatment, abuse, or neglect, increases the risk for psychiatric sequelae later in life. The neurobiology of response to early stress and of reward processing overlap substantially, leading to the prediction that reward processing may be a primary mediator of the effects of early life stress. We describe a growing body of literature investigating the effects of early life stressors on reward processing in animals and humans. Despite variation in the reviewed studies, an emerging pattern of results indicates that ELS results in deficits of ventral striatum-related functions of reward responsiveness and approach motivation, especially when the stressor is experienced in early in development. For stressors experienced later in the juvenile period and adolescence, the animal literature suggests an opposite effect, in which ELS results in increased hedonic drive. Future research in this area will help elucidate the transdiagnostic impact of early life stress, and therefore potentially identify and intervene with at-risk youth, prior to the emergence of clinical psychopathology.

Effects of eicosapentaenoic acid and docosahexaenoic acid on anxiety-like behavior in socially isolated rats

The effects of fish oil for improving mental health have been reported. The present study was undertaken to compare the effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on anxiety-like behavior using a rat model. Experimental diets enriched in EPA or DHA as glycerides were prepared. Rats were exposed to social isolation stress and fed the experimental diet for 14 days. The results of behavioral tests revealed that rats fed the EPA-enriched diet exhibited less anxiety-like behavior than rats fed the control or DHA-enriched diets. Furthermore, EPA suppressed anxiety-like behavior only in socially isolated rats. The increase in EPA contents in the brain phospholipid fraction by feeding EPA-enriched diet was more significant than that of DHA by feeding DHA-enriched diet. These results suggest that dietary EPA is more anxiolytic than DHA in rats exposed to social isolation stress and is effective in increasing EPA content in brain membranes.

Impulsivity-based thrifty eating phenotype and the protective role of n-3 PUFAs intake in adolescents

The goal of the present study was to investigate whether intrauterine growth restriction (IUGR) affects brain responses to palatable foods and whether docosahexaenoic acid (DHA, an omega-3 fatty acid that is a primary structural component of the human brain) serum levels moderate the association between IUGR and brain and behavioral responses to palatable foods. Brain responses to palatable foods were investigated using a functional magnetic resonance imaging task in which participants were shown palatable foods, neutral foods and non-food items. Serum DHA was quantified in blood samples, and birth weight ratio (BWR) was used as a proxy for IUGR. The Dutch Eating Behavior Questionnaire (DEBQ) was used to evaluate eating behaviors. In the contrast palatable food > neutral items, we found an activation in the right superior frontal gyrus with BWR as the most important predictor; the lower the BWR (indicative of IUGR), the greater the activation of this region involved in impulse control/decision making facing the viewing of palatable food pictures versus neutral items. At the behavioral level, a general linear model predicting external eating using the DEBQ showed a significant interaction between DHA and IUGR status; in IUGR individuals, the higher the serum DHA, the lower is external eating. In conclusion, we suggest that IUGR moderates brain responses when facing stimuli related to palatable foods, activating an area related to impulse control. Moreover, higher intake of n-3 PUFAs can protect IUGR individuals from developing inappropriate eating behaviors, the putative mechanism of protection would involve decreasing intake in response to external food cues in adolescents/young adults.

n-3 PUFAs have beneficial effects on anxiety and cognition in female rats: Effects of early life stress

Stressful life events, especially those in early life, can exert long-lasting changes in the brain, increasing vulnerability to mental illness especially in females. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) play a critical role in the development and function of the central nervous system (CNS). Thus, we investigated the influence of an eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA) (80% EPA, 20% DHA) n-3 PUFAs mixture on stress-related behavioural and neurobiological responses. Sprague-Dawley female rats were subjected to an early-life stress, maternal separation (MS) procedure from postnatal days 2 to 12. Non-separated (NS) and MS rats were administered saline, EPA/DHA 0.4g/kg/day or EPA/DHA 1g/kg/day, respectively. In adulthood, EPA/DHA treated animals had a dose dependent reduction in anxiety in NS rats. Furthermore, cognitive performance in the novel object recognition task (NOR) was improved by EPA/DHA treatment in NS animals only. EPA/DHA 1g/kg/day decreased behavioural despair in the forced swim test. Notably, EPA/DHA high dose increased the translocation of GRs into the nucleus of NS rat hippocampus. However, the levels of mBDNF remained unchanged in all the experimental groups. The corticosterone response to an acute stress was blunted in MS rats and this was further attenuated by pre-treatment with EPA/DHA. Immune response and monoamine neurotransmission were significantly altered by early-life stress. In conclusion, our study supports the view that n-3 PUFAs are beneficial in neurodevelopmentally normal animals but have little positive benefit in animals exposed to early life stress.

Poor infant inhibitory control predicts food fussiness in childhood - A possible protective role of n-3 PUFAs for vulnerable children

Intrauterine growth restriction (IUGR) children are more impulsive towards a sweet reward and have altered feeding behavior in adulthood. We hypothesized that early life inhibitory control predicts feeding behaviors later on in childhood, and the consumption of n-3 PUFAs during infancy may protect IUGR children from developing problematic feeding behaviors. 156 children had information on the Early Childhood Behavior Questionnaire (ECBQ) at 18 months, Food Frequency Questionnaire at 48 months and Children׳s Eating Behavior Questionnaire (CEBQ) at 72 months. There was a significant negative correlation between inhibitory control at 18 months and food fussiness at 72 months. A GLM model predicting food fussiness at 72 months showed significant interaction between n-3 PUFAs, inhibitory control and IUGR, with higher intakes associated with decreased risk for fussiness in IUGR children with poor inhibitory control. Deficits in early inhibitory control predict later food fussiness, and higher intakes of n-3 PUFAs in infancy may protect IUGR children from developing such behavior later.

The role of polyunsaturated fatty acids and GPR40 receptor in brain

Polyunsaturated fatty acids (PUFAs) are found in abundance in the nervous system. They perform significant functions for example boosting synaptogenesis, neurogenesis, inducing antinociception, stimulating gene expression and neuronal activity, preventing apoptosis and neuroinflammation. G-protein-coupled receptor 40 (GPR40), also called free fatty acid receptor 1 (FFA1), is ubiquitously expressed in various regions of the human brain including the olfactory bulb, midbrain, medulla oblongata, hippocampus, hypothalamus, cerebral cortex, cerebellum and in the spinal cord. GPR40, when binding with polyunsaturated fatty acids (PUFAs) has shown promising therapeutic potential. This review presents current knowledge regarding the pharmacological properties of GPR40 and addresses its functions in brain, with a focus on neurodevelopment & neurogenesis. Furthermore, the demonstration of GPR40 involvement in several neuropathological conditions such as apoptosis, inflammatory pain, Alzheimer's disease and Parkinson's disease. Although the results are encouraging, further research is needed to clarify their role in the treatment of inflammatory pain, Alzheimer's disease and Parkinson's disease. This article is part of the Special Issue entitled 'Lipid Sensing G Protein-Coupled Receptors in the CNS'.

Correlation between n-3 polyunsaturated fatty acids consumption and BDNF peripheral levels in adolescents

Background

Although several studies have reported an association between mental disorders and serum levels of brain-derived neurotrophic factor (BDNF), this association is still poorly understood. The study of factors associated with both BDNF levels and mental disorders, such as n-3 polyunsaturated fatty acids (n-3 PUFAs), may help to elucidate the mechanisms mediating the relationship between the two variables. Therefore, the present study aimed to evaluate whether the intake n-3 PUFAs correlates with serum levels of BDNF.

Findings

This study involved 137 adolescents drawn from a community sample, including a group with high levels of anxiety, assessed using the Screen for Children and Anxiety Related Emotional Disorders. Blood samples were collected and serum BDNF levels were measured. n-3 PUFAs were estimated using a food frequency questionnaire for adolescents. Correlations were performed to assess the association between n-3 PUFAs intake and BDNF levels. Effects of potential confounders (total fat consumption, age, gender and anxiety) were examined using linear regression models. There was a direct correlation between n-3 PUFAs consumption and serum BDNF levels, which remained significant even after accounting for potential confounders.

Conclusions

We were able to detect a correlation between n-3 PUFAs intake and peripheral BDNF levels. Our study was limited by its small sample size, and our external validity may be restricted by the oversampling of anxious adolescents. Our findings may help determine the nature of the association between mental disorders and serum levels of BDNF. However, more studies are needed to elucidate the possible mechanisms by which n-3 PUFAs intake affects BDNF levels, and how this may lead to an increased vulnerability to psychiatric disorders.