Early maternal separation induces preference for sucrose and aspartame associated with increased blood glucose and hyperactivity

Effects of early-life stress followed by access to stevia or sucralose during adolescence on weight gain, glycemia, and anxiety-related behaviors in male and female rats

Early-life stress and subsequent high-calorie diets during adolescence are known to be risk factors for developing metabolic and psychological disorders. Although non-nutritive sweeteners such as stevia and sucralose have been a useful alternative to reduce sugar consumption, the effects of prolonged consumption of these sweeteners on metabolism and behavior in adolescents remain unclear. Here, we evaluated the effects of early-stress followed by access to stevia or sucralose during adolescence on weight gain, glycemia, and anxiety-related behaviors in male and female rats. During postnatal days (PNDs) 1-21, pups were separated twice a day, for 180 min each time, from their dam nest while non-separated pups served as controls. The pups were weaned, separated by sex and randomly distributed into the stevia, sucralose and water conditions. During PNDs 26-50, two bottles containing water and stevia or sucralose were placed in the animal home-cages, and body weight and blood glucose measures were scored. On PNDs 50 and 51, behavioral measures were obtained in the open-field test. Results showed that male rats consuming stevia reduced body weight gain, blood glucose and increased locomotion. Early-stress led to low blood glucose and alterations in anxiety and locomotion-related behaviors in a sex-dependent manner. Moreover, sucralose access during adolescence reversed the effects of early-stress on anxiety-related behaviors in female rats. The results suggest that the consumption of stevia and sucralose could be an alternative for the replacement of sugar-sweetened beverages, especially in adolescents who have had adverse early-life experiences.

Differential effects of perigestational consumption of sucrose-sweetened beverages on anxiety and depression-related behaviors in adult offspring: Sex disparity in a mouse model

Consumption of sucrose-sweetened drinks (SSDs) during pregnancy and breastfeeding can lead to various health and metabolism issues, but the potential impact on neurodevelopment and long-term effects remains unclear. This study aims to examine how maternal consumption of SSDs during gestation and lactation influences anxiety and depression-related behavior in adult offspring. Adult female CD-1 mice were randomly assigned to a control group (CG) or a sucrose group (SG) 2 weeks before gestation. The SG had 2 h of access to an SSD (15% w/w, 0.6 kcal/ml) for 2 weeks before mating, during pregnancy, and throughout lactation, totaling 8 weeks. Adult offspring were then evaluated for depressive-related behaviors and anxiety-related behaviors. Our findings reveal that perigestational consumption of SSDs does not lead to offspring presenting behaviors related to depression, but it does increase swimming behavior. However, maternal consumption of SSDs could impact the fighting response due to a diminished motivational component. In contrast, perigestational consumption of SSDs has apparent effects on anxiety-related behavior. Furthermore, female offspring appeared to be particularly vulnerable, exhibiting a higher anxiety index compared with controls. These findings indicate that females could be more vulnerable to the effects of maternal consumption of SSDs, being more susceptible to the presence of anxiety-related behaviors.

Aspartame and Its Metabolites Cause Oxidative Stress and Mitochondrial and Lipid Alterations in SH-SY5Y Cells

Due to a worldwide increase in obesity and metabolic disorders such as type 2 diabetes, synthetic sweeteners such as aspartame are frequently used to substitute sugar in the diet. Possible uncertainties regarding aspartame's ability to induce oxidative stress, amongst others, has led to the recommendation of a daily maximum dose of 40 to 50 mg per kg. To date, little is known about the effects of this non-nutritive sweetener on cellular lipid homeostasis, which, besides elevated oxidative stress, plays an important role in the pathogenesis of various diseases, including neurodegenerative diseases such as Alzheimer's disease. In the present study, treatment of the human neuroblastoma cell line SH-SY5Y with aspartame (271.7 µM) or its three metabolites (aspartic acid, phenylalanine, and methanol (271.7 µM)), generated after digestion of aspartame in the human intestinal tract, resulted in significantly elevated oxidative stress associated with mitochondrial damage, which was illustrated with reduced cardiolipin levels, increased gene expression of SOD1/2, PINK1, and FIS1, and an increase in APF fluorescence. In addition, treatment of SH-SY5Y cells with aspartame or aspartame metabolites led to a significant increase in triacylglycerides and phospholipids, especially phosphatidylcholines and phosphatidylethanolamines, accompanied by an accumulation of lipid droplets inside neuronal cells. Due to these lipid-mediating properties, the use of aspartame as a sugar substitute should be reconsidered and the effects of aspartame on the brain metabolism should be addressed in vivo.

Resistance exercise was safe for the pregnancy and offspring's development and partially protected rats against early life stress-induced effects

Promising evidence points to gestational physical exercise as the key to preventing various disorders that affect the offspring neurodevelopment, but there are no studies showing the impact of resistance exercise on offspring health. Thus, the aim of this study was to investigate whether resistance exercise during pregnancy is able to prevent or to alleviate the possible deleterious effects on offspring, caused by early life-stress (ELS). Pregnant rats performed resistance exercise throughout the gestational period:they climbed a sloping ladder with a weight attached to their tail, 3 times a week. Male and female pups, on the day of birth (P0), were divided into 4 experimental groups: 1) rats of sedentary mothers (SED group); 2) rats of exercised mothers (EXE group); 3) rats of sedentary mothers and submitted to maternal separation (ELS group) and 4) rats of exercised mothers and submitted to MS (EXE + ELS group). From P1 to P10, pups from groups 3 and 4 were separated from their mothers for 3 h/day. Maternal behavior was assessed. From P30, behavioral tests were performed and on P38 the animals were euthanized and prefrontal cortex samples were collected. Oxidative stress and tissue damage analysis by Nissl staining were performed. Our results demonstrate that male rats are more susceptible to ELS than females, showing impulsive and hyperactive behavior similar to that seen in children with ADHD. This behavior was attenuated by the gestational resistance exercise. Our results demonstrate, for the first time, that resistance exercise performed during pregnancy seems to be safe for the pregnancy and offspring's neurodevelopment and are effective in preventing ELS-induced damage only in male rats. Interestingly, resistance exercise during pregnancy improved maternal care and it is reasonable to propose that this finding may be related to the protective role on the animals neurodevelopment, observed in our study.

Maternal separation affects Anxiety like behavior begin in adolescence continue through adulthood and related to Dnmt3a expression

Early life stress, including maternal separation, is among one of the main causes of anxiety in adolescents. DNA methyltransferase 3A (Dnmt3a) is a key molecule that regulates DNA methylation and is found to be associated with anxiety-like behavior. It is not clear whether maternal separation affects anxiety levels in mice at different developmental stages, or whether Dnmt3a plays a role in this process. Here, by using open field test to exploring the effect of maternal separation on anxiety-like behavior in mice of different age, it was found that maternal separation could successfully induce anxiety-like behavior in adolescent mice, and which continued through adulthood. By using western blot, we found the levels of Dnmt3a in the hippocampus and cortex have shown different trends in maternal separation mice on P17. Further, by using immunostaining, we have found that the expression levels of Dnmt3a in the cortex and hippocampus were significantly different, and decreased to varying degrees with the age of mice, which being the reason for different trends. Our results provide an experimental basis for further development of anxiety/depression treatment programs more suitable for adolescence.

Sex-dependence and comorbidities of the early-life adversity induced mental and metabolic disease risks: Where are we at?

Early-life adversity (ELA) is a major risk factor for developing later-life mental and metabolic disorders. However, if and to what extent ELA contributes to the comorbidity and sex-dependent prevalence/presentation of these disorders remains unclear. We here comprehensively review and integrate human and rodent ELA (pre- and postnatal) studies examining mental or metabolic health in both sexes and discuss the role of the placenta and maternal milk, key in transferring maternal effects to the offspring. We conclude that ELA impacts mental and metabolic health with sex-specific presentations that depend on timing of exposure, and that human and rodent studies largely converge in their findings. ELA is more often reported to impact cognitive and externalizing domains in males, internalizing behaviors in both sexes and concerning the metabolic dimension, adiposity in females and insulin sensitivity in males. Thus, ELA seems to be involved in the origin of the comorbidity and sex-specific prevalence/presentation of some of the most common disorders in our society. Therefore, ELA-induced disease states deserve specific preventive and intervention strategies.

Inhibition of adult neurogenesis reduces avoidance behavior in male, but not female, mice subjected to early life adversity

Early life adversity (ELA) increases the risk of developing neuropsychiatric illnesses such as anxiety disorders. However, the mechanisms connecting these negative early life experiences to illness later in life remain unclear. In rodents, plasticity mechanisms, specifically adult neurogenesis in the ventral hippocampus, have been shown to be altered by ELA and important for buffering against detrimental stress-induced outcomes. The current study sought to explore whether adult neurogenesis contributes to ELA-induced changes in avoidance behavior. Using the GFAP-TK transgenic model, which allows for the inhibition of adult neurogenesis, and CD1 littermate controls, we subjected mice to an ELA paradigm of maternal separation and early weaning (MSEW) or control rearing. We found that mice with intact adult neurogenesis showed no behavioral changes in response to MSEW. After reducing adult neurogenesis, however, male mice previously subjected to MSEW had an unexpected decrease in avoidance behavior. This finding was not observed in female mice, suggesting that a sex difference exists in the role of adult-born neurons in buffering against ELA-induced changes in behavior. Taken together with the existing literature on ELA and avoidance behavior, this work suggests that strain differences exist in susceptibility to ELA and that adult-born neurons may play a role in regulating adaptive behavior.

Adult food choices depend on sex and exposure to early-life stress: Underlying brain circuitry, adipose tissue adaptations and metabolic responses

Exposure to early-life stress (ES) increases the risk to develop obesity later in life, and these effects may be sex-specific, but it is currently unknown what underlies the ES-induced metabolic vulnerability. We have previously shown that ES leads to a leaner phenotype under standard chow diet conditions, but to increased fat accumulation when exposed to an unhealthy obesogenic diet. However these diets were fed without a choice. An important, yet under investigated, element contributing to the development of obesity in humans is the choice of the food. There is initial evidence that ES leads to altered food choices but a thorough testing on how ES affects the choice of both the fat and sugar component, and if this is similar in males and females, is currently missing. We hypothesized that ES increases the choice for unhealthy foods, while it at the same time also affects the response to such a diet. In a mouse model for ES, in which mice are exposed to limited nesting and bedding material from postnatal day (P)2–P9, we investigated if ES exposure affected i) food choice with a free choice high-fat high-sugar diet (fcHFHS), ii) the response to such a diet, iii) the brain circuits that regulate food intake and food reward and iv) if such ES effects are sex-specific. We show that there are sex differences in food choice under basal circumstances, and that ES increases fat intake in females when exposed to a mild acute stressor. Moreover, ES impacts the physiologic response to the fcHFHS and the brain circuits regulating food intake in sex-specific manner. Our data highlight sex-specific effects of ES on metabolic functioning and food choice.

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Strong sex differences exist in food choice and metabolism in mice.

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Early-life stress (ES) increases fat intake in females after mild acute stress exposure.

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The physiological response to the diet is affected by ES in a sex-dependent manner.

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ES modulates the hedonic feeding circuitry.

Long-term activation of hippocampal glial cells and altered emotional behavior in male and female adult rats after different neonatal stressors

Early life stress increases the risk of developing psychiatric diseases in adulthood. Severe neonatal infections can also contribute to the development of affective illnesses. Stress and infections both trigger the immediate activation of the neuroimmune system. We compared the long-term effects of neonatal single or combined stress-immune challenges on emotional behavior and glial cell responses in the hippocampus. Male and female Sprague Dawley rats were randomly allocated across four conditions: (1) control + vehicle; (2) maternal separation (MS, 3 h/day on postnatal days [PN] 1-14) + vehicle; (3) control + lipopolysaccharide (LPS, 0.5. mg/kg, PN14); (4) MS + LPS. The rats' behaviors were analyzed from PN120 in males and from PN150 in diestrous females. LPS, but not MS, increased anxiety-like behavior in male rats; however, in females, it increased with both challenges. Depressive-like behavior increased after MS-but not LPS-in males and females. Combined stressors increased depressive-like behavior in both sexes. All stressors promoted microglial activation in CA3 and hilus in males and females. MS and LPS increased the astrocytic density within the male hilus, but LPS only increased it in CA3. MS prevented the rise in astrocytic density with LPS. In females, MS reduced the astrocytic population of the hilus and CA3 areas. Taken together, the behavioral and glial cell responses to early life challenges are sex-dependent and cell-type specific. This suggests a sexual dimorphism in the nature of the adverse event faced. These results have implications for understanding the emergence of psychiatric illnesses.

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.

Early-Life Stress Modulates Gut Microbiota and Peripheral and Central Inflammation in a Sex-Dependent Manner

Recent studies have reported that changes in gut microbiota composition could induce neuropsychiatric problems. In this study, we investigated alterations in gut microbiota induced by early-life stress (ELS) in rats subjected to maternal separation (MS; 6 h a day, postnatal days (PNDs) 1-21), along with changes in inflammatory cytokines and tryptophan-kynurenine (TRP-KYN) metabolism, and assessed the differences between sexes. High-throughput sequencing of the bacterial 16S rRNA gene showed that the relative abundance of the Bacteroides genus was increased and that of the Lachnospiraceae family was decreased in the feces of MS rats of both sexes (PND 56). By comparison, MS increased the relative abundance of the Streptococcus genus and decreased that of the Staphylococcus genus only in males, whereas the abundance of the Sporobacter genus was enhanced and that of the Mucispirillum genus was reduced by MS only in females. In addition, the levels of proinflammatory cytokines were increased in the colons (IFN-γ and IL-6) and sera (IL-1β) of the male MS rats, together with the elevation of the KYN/TRP ratio in the sera, but not in females. In the hippocampus, MS elevated the level of IL-1β and the KYN/TRP ratio in both male and female rats. These results indicate that MS induces peripheral and central inflammation and TRP-KYN metabolism in a sex-dependent manner, together with sex-specific changes in gut microbes.

Corticotropin-releasing factor infusion in the bed nucleus of the stria terminalis of lactating mice alters maternal care and induces behavioural phenotypes in offspring

The peripartum period is accompanied by numerous physiological and behavioural adaptations organised by the maternal brain. These changes are essential for adequate expression of maternal behaviour, thereby ensuring proper development of the offspring. The corticotropin-releasing factor (CRF) plays a key role in a variety of behaviours accompanying stress, anxiety, and depression. There is also evidence that CRF contributes to maladaptations during the peripartum period. We investigated the effects of CRF in the bed nucleus of the stria terminalis (BNST) of lactating mice during maternal care and analysed locomotor activity and anxiety-like behaviour in the offspring. The BNST has been implicated in anxiety behaviour and regulation of the stress response. The effects of intra-BNST CRF administration were compared with those induced by the limited bedding (LB) procedure, a model that produces altered maternal behaviour. BALB/cJ dams were exposed to five infusions of CRF or saline into the BNST in the first weeks after birth while the LB dams were exposed to limited nesting material from postnatal days (P) 2–9. Maternal behaviour was recorded in intercalated days, from P1-9. Offspring anxiety-like behaviour was assessed during adulthood using the open-field, elevated plus-maze, and light/dark tests. Both intra-BNST CRF and LB exposure produced altered maternal care, represented by decreased arched-back nursing and increased frequency of exits from the nest. These changes in maternal care resulted in robust sex-based differences in the offspring’s behavioural responses during adulthood. Females raised by CRF-infused dams exhibited increased anxiety-like behaviour, whereas males presented a significant decrease in anxiety. On the other hand, both males and females raised by dams exposed to LB showed higher locomotor activity. Our study demonstrates that maternal care is impaired by intra-BNST CRF administrations, and these maladaptations are similar to exposure to adverse early environments. These procedures, however, produce distinct phenotypes in mice during young adulthood and suggest sex-based differences in the susceptibility to poor maternal care.

Artificial sweeteners affect the glucose transport rate in the Caco-2/NCI-H716 co-culture model

BACKGROUND

Artificial sweeteners have been used widely as substitutes for sugar for several decades. In recent years they have been reported to be harmful to human health - especially to glucose absorption. However, as conclusions from previous studies using a single Caco-2 cell model were not consistent, further studies with a more suitable cell model are needed.

RESULTS

We established a co-culture model with enterocyte Caco-2 and enteroendocrine NCI-H716 cell lines cultured in transwell inserts. The effects of artificial sweeteners, enhancing the glucose transport rate, lasted for 60 min and then began to diminish. Most importantly, different artificial sweeteners with the same sweetness intensity had similar effects on glucose transport. The sodium / glucose co-transporter member 1 (SGLT1) mRNA expression levels increased significantly with an initial glucose concentration of 20 mM, while glucose transporter 2 (GLUT2) mRNA expression significantly increased with initial glucose concentrations of 20 mM and 60 mM.

CONCLUSION

Based on the Caco-2/NCI-H716 co-culture model, SGLT1 and GLUT2 mediated the enhancing effects of artificial sweeteners on glucose transport, depending on the sweetness intensity and initial glucose concentration.

Systematic review and meta-analysis: effects of maternal separation on anxiety-like behavior in rodents

The mechanisms by which childhood maltreatment increases anxiety is unclear, but a propensity for increased defensive behavior in rodent models of early life stress (ELS) suggests that work in rodents may clarify important mechanistic details about this association. A key challenge in studying the effects of ELS on defensive behavior in rodents is the plethora of inconsistent results. This is particularly prominent with the maternal separation (MS) literature, one of the most commonly used ELS models in rodents. To address this issue we conducted a systematic review and meta-analysis, examining the effects of MS on exploratory-defensive behavior in mice and rats using the open field test (OFT) and the elevated plus maze (EPM). This search yielded a total of 49 studies, 24 assessing the effect of MS on behavior in the EPM, 11 tested behavior in the OFT, and 14 studies provided data on both tasks. MS was associated with increased defensive behavior in rats (EPM: Hedge's g = -0.48, p = 0.02; OFT: Hedge's g = -0.33, p = 0.05), effect sizes that are consistent with the anxiogenic effect of early adversity reported in humans. In contrast, MS did not alter exploratory behavior in mice (EPM: Hedge's g = -0.04, p = 0.75; OFT: Hedge's g = -0.03, p = 0.8). There was a considerable amount of heterogeneity between studies likely related to the lack of standardization of the MS protocol. Together, these findings suggest important differences in the ability of MS to alter circuits that regulate defensive behaviors in mice and rats.

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.

Maternal deprivation alters nociceptive response in a gender-dependent manner in rats

The present study aimed at investigating both the early and long-term effects of maternal deprivation as well as gender on neuromotor reflexes, anxiety behavior and thermal nociceptive responses. A total of 64 Wistar rats pups (32 males, 32 females) were utilized and were deprived of their mother for 3 h/daily, from postnatal day 1 (P1) until P10. Successively, animals were divided into 2 groups: control group (C) - pups no subjected to intervention; and the maternal-deprived group (MD): pups subjected to maternal deprivation. The neuromotor reflexes were evaluated through the righting reflex and negative geotaxis tests; the exploratory behavior by open field test (OFT); the anxiety-like behavior by elevated plus-maze test (EPM); the thermal nociceptive responses byhot plate (HP) and tail-flick (TFL) tests. All the animals subjected to maternal deprivation showed a delayed reflex response at P8 in the negative geotaxis test. In contrast, the OFT at P20 identified an effect of gender on the outer crossings and grooming as well as an interaction between gender and maternal deprivation on latency. Additionally, effect of maternal deprivation in the open and closed arms as well as gender effect in the protected head-dipping (PHD) and non-protected head-dipping (NPHD) were observed at P20 (EPM). In contrast, there were a gender effect on latency and an interaction between gender and maternal deprivation on rearing at P42. Moreover, in nociceptive tests was observed an analgesic effect induced by maternal deprivation; however, in the TFL test, only deprived females showed this effect. Surprisingly, only control animals presented an ontogeny nociceptive effect in the HP testat P21 and P43, which may be related to an increase in the inhibitory nociceptive pathways throughout life. In this way, we suggest maternal deprivation to be able to anticipate the maturation of the inhibitory nociceptive pathway. In conclusion, maternal deprivation induced a delayed reflex response at P8 and altered the anxiety and nociceptive behaviors according to the time after exposure to this stressor, in a gender-specific manner.

Effect of developmental NMDAR antagonism with CGP 39551 on aspartame-induced hypothalamic and adrenal gene expression

Rationale

Aspartame (L-aspartyl phenylalanine methyl ester) is a non-nutritive sweetener (NNS) approved for use in more than 6000 dietary products and pharmaceuticals consumed by the general public including adults and children, pregnant and nursing mothers. However a recent prospective study reported a doubling of the risk of being overweight amongst 1-year old children whose mothers consumed NNS-sweetened beverages daily during pregnancy. We have previously shown that chronic aspartame (ASP) exposure commencing in utero may detrimentally affect adulthood adiposity status, glucose metabolism and aspects of behavior and spatial cognition, and that this can be modulated by developmental N-methyl-D-aspartate receptor (NMDAR) blockade with the competitive antagonist CGP 39551 (CGP). Since glucose homeostasis and certain aspects of behavior and locomotion are regulated in part by the NMDAR-rich hypothalamus, which is part of the hypothalamic-pituitary-adrenal- (HPA) axis, we have elected to examine changes in hypothalamic and adrenal gene expression in response to ASP exposure in the presence or absence of developmental NMDAR antagonism with CGP, using Affymetrix microarray analysis.

Results

Using 2-factor ANOVA we identified 189 ASP-responsive differentially expressed genes (DEGs) in the adult male hypothalamus and 2188 in the adrenals, and a further 23 hypothalamic and 232 adrenal genes significantly regulated by developmental treatment with CGP alone. ASP exposure robustly elevated the expression of a network of genes involved in hypothalamic neurosteroidogenesis, together with cell stress and inflammatory genes, consistent with previous reports of aspartame-induced CNS stress and oxidative damage. These genes were not differentially expressed in ASP mice with CGP antagonism. In the adrenal glands of ASP-exposed mice, GABA and Glutamate receptor subunit genes were amongst those most highly upregulated. Developmental NMDAR antagonism alone had less effect on adulthood gene expression and affected mainly hypothalamic neurogenesis and adrenal steroid metabolism. Combined ASP + CGP treatment mainly upregulated genes involved in adrenal drug and cholesterol metabolism.

Conclusion

ASP exposure increased the expression of functional networks of genes involved in hypothalamic neurosteroidogenesis and adrenal catecholamine synthesis, patterns of expression which were not present in ASP-exposed mice with developmental NMDAR antagonism.