A model of neglect during postnatal life heightens obesity-induced hypertension and is linked to a greater metabolic compromise in female mice

Guidelines for in vivo models of developmental programming of cardiovascular disease risk

Research using animals depends on the generation of offspring for use in experiments or for the maintenance of animal colonies. Although not considered by all, several different factors preceding and during pregnancy, as well as during lactation, can program various characteristics in the offspring. Here, we present the most common models of developmental programming of cardiovascular outcomes, important considerations for study design, and provide guidelines for producing and reporting rigorous and reproducible cardiovascular studies in offspring exposed to normal conditions or developmental insult. These guidelines provide considerations for the selection of the appropriate animal model and factors that should be reported to increase rigor and reproducibility while ensuring transparent reporting of methods and results.

Sex-specific sequels of early life stress on serine/threonine kinase activity in visceral adipose tissue from obese mice

Adverse childhood experiences (ACEs) are an established independent risk factor for chronic disease including obesity and hypertension; however, only women exposed to multiple ACEs show a positive relationship with BMI. Our lab has reported that maternal separation and early weaning (MSEW), a mouse model of early life stress, induces sex-specific mechanisms underlying greater blood pressure response to a chronic high fat diet (HF). Specifically, female MSEW mice fed a HF display exacerbated perigonadal white adipose tissue (pgWAT) expansion and a metabolic syndrome-like phenotype compared to control counterparts, whereas hypertension is caused by sympathoactivation in male MSEW mice. Thus, this study aimed to determine whether there is a sex-specific serine/threonine kinase (STKA) activity in pgWAT adipose tissue associated with early life stress. Frozen pgWAT was collected from MSEW and control, male and female mice fed a HF to assess STKA activity using the Pamstation12 instrument. Overall, MSEW induces significant reduction of 7 phosphokinases (|Z| >=1.5) in females (QIK, MLK, PKCH, MST, STE7, PEK, FRAY) and 5 in males (AKT, SGK, P38, MARK, CDK), while 15 were downregulated in both sexes (DMPK, PKA, PKG, RSK, PLK, DYRK, NMO, CAMK1, JNK, PAKA, RAD53, ERK, PAKB, PKD, PIM, AMPK). This data provides new insights into the sex-specific dysregulation of the molecular network controlling cellular phosphorylation signals in visceral adipose tissue and identifies possible target phosphokinases implicated in adipocyte hypertrophy as a result of exposure to early life stress. Identifying functional metabolic signatures is critical to elucidate the underlying molecular mechanisms behind the sex-specific obesity risk associated with early life stress.

Obese Male Mice Exposed to Early Life Stress Display Sympathetic Activation and Hypertension Independent of Circulating Angiotensin II

BACKGROUND

We have previously reported that male mice exposed to maternal separation and early weaning (MSEW), a model of early life stress, show sympathetic activation and increased blood pressure in response to a chronic high-fat diet. The goal of this study was to investigate the contribution of the renin-angiotensin-aldosterone system to the mechanism by which MSEW increases blood pressure and vasomotor sympathetic tone in obese male mice.

METHODS AND RESULTS

Mice were exposed to MSEW during postnatal life. Undisturbed litters served as controls. At weaning, both control and MSEW offspring were placed on a low-fat diet or a high-fat diet for 20 weeks. Angiotensin peptides in serum were similar in control and MSEW mice regardless of the diet. However, a high-fat diet induced a similar increase in angiotensinogen levels in serum, renal cortex, liver, and fat in both control and MSEW mice. No evidence of renin-angiotensin system activation was found in adipose tissue and renal cortex. After chronic treatment with enalapril (2.5 mg/kg per day, drinking water, 7 days), an angiotensin-converting enzyme inhibitor that does not cross the blood-brain barrier, induced a similar reduction in blood pressure in both groups, while the vasomotor sympathetic tone remained increased in obese MSEW mice. In addition, acute boluses of angiotensin II (1, 10, 50 μg/kg s.c.) exerted a similar pressor response in MSEW and control mice before and after enalapril treatment.

CONCLUSIONS

Overall, elevated blood pressure and vasomotor sympathetic tone remained exacerbated in MSEW mice compared with controls after the peripheral inhibition of angiotensin-converting enzyme, suggesting a mechanism independent of angiotensin II.

On the origins of sleep disordered breathing, cardiorespiratory and metabolic dysfunction: which came first, the chicken or the egg?

Sleep disordered breathing (SDB) is a complex, sex specific and highly heterogeneous group of respiratory disorders. Nevertheless, sleep fragmentation and repeated fluctuations of arterial blood gases for several hours per night are at the core of the problem; together, they impose significant stress to the organism with deleterious consequences on physical and mental health. SDB increases the risk of obesity, diabetes, depression and anxiety disorders; however, the same health issues are risk factors for SDB. So, which came first, the chicken or the egg? What causes the appearance of the first significant apnoeic events during sleep? These are important questions because although moderate to severe SDB affects ∼500 million adults globally, we still have a poor understanding of the origins of the disease, and the main treatments (and animal models) focus on the symptoms rather than the cause. Because obesity, metabolic dysfunction and stress-related neurological disorders generally appear progressively, we discuss how the development of these diseases can lead to specific anatomical and non-anatomical traits of SDB in males and females while considering the impacts of sex steroids. In light of the growing evidence indicating that the carotid bodies are important sensors of key metabolic and endocrine signals associated with stress and dysmetabolism, we propose that these organs play a key role in the process.

Early life stress exacerbates obesity in adult female mice via mineralocorticoid receptor-dependent increases in adipocyte triglyceride and glycerol content

Previously, we have shown that Maternal Separation and Early Weaning (MSEW) exacerbates high fat diet (HF)-induced visceral obesity in female offspring compared to normally reared female mice. Stress hormones such as glucocorticoids and mineralocorticoids are critical mediators in the process of fat expansion, and both can activate the mineralocorticoid receptor (MR) in the adipocyte. Therefore, this study aimed to, comprehend the specific effects of MSEW on adipose tissue basic homeostatic function, and investigate whether female MSEW mice show an exacerbated obesogenic response mediated by MR. Gonadal white adipose tissue (gWAT), a type of visceral fat, was collected to assess lipidomics, transcriptomics, and in vitro lipolysis assay. Obese female MSEW mice showed increased adiposity, elevated 44:2/FA 18:2 + NH4 lipid class and reduced mitochondrial DNA density compared to obese control counterparts. In addition, single-cell RNA sequencing in isolated pre- and mature adipocytes showed a ~9-fold downregulation of aquaglycerolporin 3 (Aqp3), a channel responsible for glycerol efflux in adipocytes. Obese MSEW mice showed high levels of circulating aldosterone and gWAT-derived corticosterone compared to controls. Further, the MR blocker spironolactone (Spiro, 100 mg/kg/day, 2 weeks) normalized the elevated intracellular glycerol levels, the greater in vitro lipolysis response, and the number of large size adipocytes in MSEW mice compared to the controls. Our data suggests that MR plays a role promoting adipocyte hypertrophy in female MSEW mice by preventing lipolysis via glycerol release in favor of triglyceride formation and storage.

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.

The Role of the Gut Microbiota in the Effects of Early-Life Stress and Dietary Fatty Acids on Later-Life Central and Metabolic Outcomes in Mice

Early-life stress (ELS) leads to increased vulnerability for mental and metabolic disorders. We have previously shown that a low dietary ω-6/ω-3 polyunsaturated fatty acid (PUFA) ratio protects against ELS-induced cognitive impairments. Due to the importance of the gut microbiota as a determinant of long-term health, we here study the impact of ELS and dietary PUFAs on the gut microbiota and how this relates to the previously described cognitive, metabolic, and fatty acid profiles. Male mice were exposed to ELS via the limited bedding and nesting paradigm (postnatal day (P)2 to P9 and to an early diet (P2 to P42) with an either high (15) or low (1) ω-6 linoleic acid to ω-3 alpha-linolenic acid ratio. 16S rRNA was sequenced and analyzed from fecal samples at P21, P42, and P180. Age impacted α- and β-diversity. ELS and diet together predicted variance in microbiota composition and affected the relative abundance of bacterial groups at several taxonomic levels in the short and long term. For example, age increased the abundance of the phyla Bacteroidetes, while it decreased Actinobacteria and Verrucomicrobia; ELS reduced the genera RC9 gut group and Rikenella, and the low ω-6/ω-3 diet reduced the abundance of the Firmicutes Erysipelotrichia. At P42, species abundance correlated with body fat mass and circulating leptin (e.g., Bacteroidetes and Proteobacteria taxa) and fatty acid profiles (e.g., Firmicutes taxa). This study gives novel insights into the impact of age, ELS, and dietary PUFAs on microbiota composition, providing potential targets for noninvasive (nutritional) modulation of ELS-induced deficits. IMPORTANCE Early-life stress (ELS) leads to increased vulnerability to develop mental and metabolic disorders; however, the biological mechanisms leading to such programming are not fully clear. Increased attention has been given to the importance of the gut microbiota as a determinant of long-term health and as a potential target for noninvasive nutritional strategies to protect against the negative impact of ELS. Here, we give novel insights into the complex interaction between ELS, early dietary ω-3 availability, and the gut microbiota across ages and provide new potential targets for (nutritional) modulation of the long-term effects of the early-life environment via the microbiota.

Adolescents' Perspectives on the Drivers of Obesity Using a Group Model Building Approach: A South African Perspective

Overweight and obesity increase the risk of a range of poor physiological and psychosocial health outcomes. Previous work with well-defined cohorts has explored the determinants of obesity and employed various methods and measures; however, less is known on the broader societal drivers, beyond individual-level influences, using a systems framework with adolescents. The aim of this study was to explore the drivers of obesity from adolescents' perspectives using a systems approach through group model building in four South African schools. Group model building was used to generate 4 causal loop diagrams with 62 adolescents aged 16-18 years. These maps were merged into one final map, and the main themes were identified: (i) physical activity and social media use; (ii) physical activity, health-related morbidity, and socio-economic status; (iii) accessibility of unhealthy food and energy intake/body weight; (iv) psychological distress, body weight, and weight-related bullying; and (v) parental involvement and unhealthy food intake. Our study identified meaningful policy-relevant insights into the drivers of adolescent obesity, as described by the young people themselves in a South African context. This approach, both the process of construction and the final visualization, provides a basis for taking a novel approach to prevention and intervention recommendations for adolescent obesity.

Early Life Stress, Brain Development, and Obesity Risk: Is Oxytocin the Missing Link?

Obesity disease results from a dysfunctional modulation of the energy balance whose master regulator is the central nervous system. The neural circuitries involved in such function complete their maturation during early postnatal periods, when the brain is highly plastic and profoundly influenced by the environment. This phenomenon is considered as an evolutionary strategy, whereby metabolic functions are adjusted to environmental cues, such as food availability and maternal care. In this timeframe, adverse stimuli may program the body metabolism to maximize energy storage abilities to cope with hostile conditions. Consistently, the prevalence of obesity is higher among individuals who experienced early life stress (ELS). Oxytocin, a hypothalamic neurohormone, regulates the energy balance and modulates social, emotional, and eating behaviors, exerting both central and peripheral actions. Oxytocin closely cooperates with leptin in regulating energy homeostasis. Both oxytocin and leptin impact the neurodevelopment during critical periods and are affected by ELS and obesity. In this review article, we report evidence from the literature describing the effect of postnatal ELS (specifically, disorganized/inconstant maternal care) on the vulnerability to obesity with a focus on the role of oxytocin. We emphasize the existing research gaps and highlight promising directions worthy of exploration. Based on the available data, alterations in the oxytocin system may in part mediate the ELS-induced susceptibility to obesity.

Epididymal Fat-Derived Sympathoexcitatory Signals Exacerbate Neurogenic Hypertension in Obese Male Mice Exposed to Early Life Stress

[Figure: see text].

Modulation of the Hypothalamic Nutrient Sensing Pathways by Sex and Early-Life Stress

There are sex differences in metabolic disease risk, and early-life stress (ES) increases the risk to develop such diseases, potentially in a sex-specific manner. It remains to be understood, however, how sex and ES affect such metabolic vulnerability. The hypothalamus regulates food intake and energy expenditure by sensing the organism's energy state via metabolic hormones (leptin, insulin, ghrelin) and nutrients (glucose, fatty acids). Here, we investigated if and how sex and ES alter hypothalamic nutrient sensing short and long-term. ES was induced in mice by limiting the bedding and nesting material from postnatal day (P)2-P9, and the expression of genes critical for hypothalamic nutrient sensing were studied in male and female offspring, both at P9 and in adulthood (P180). At P9, we observed a sex difference in both Ppargc1a and Lepr expression, while the latter was also increased in ES-exposed animals relative to controls. In adulthood, we found sex differences in Acacb, Agrp, and Npy expression, whereas ES did not affect the expression of genes involved in hypothalamic nutrient sensing. Thus, we observe a pervasive sex difference in nutrient sensing pathways and a targeted modulation of this pathway by ES early in life. Future research is needed to address if the modulation of these pathways by sex and ES is involved in the differential vulnerability to metabolic diseases.

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.

Effects of Early-Life Stress, Postnatal Diet Modulation and Long-Term Western-Style Diet on Peripheral and Central Inflammatory Markers

Early-life stress (ES) exposure increases the risk of developing obesity. Breastfeeding can markedly decrease this risk, and it is thought that the physical properties of the lipid droplets in human milk contribute to this benefit. A concept infant milk formula (IMF) has been developed that mimics these physical properties of human milk (Nuturis®, N-IMF). Previously, we have shown that N-IMF reduces, while ES increases, western-style diet (WSD)-induced fat accumulation in mice. Peripheral and central inflammation are considered to be important for obesity development. We therefore set out to test the effects of ES, Nuturis® and WSD on adipose tissue inflammatory gene expression and microglia in the arcuate nucleus of the hypothalamus. ES was induced in mice by limiting the nesting and bedding material from postnatal day (P) 2 to P9. Mice were fed a standard IMF (S-IMF) or N-IMF from P16 to P42, followed by a standard diet (STD) or WSD until P230. ES modulated adipose tissue inflammatory gene expression early in life, while N-IMF had lasting effects into adulthood. Centrally, ES led to a higher microglia density and more amoeboid microglia at P9. In adulthood, WSD increased the number of amoeboid microglia, and while ES exposure increased microglia coverage, Nuturis® reduced the numbers of amoeboid microglia upon the WSD challenge. These results highlight the impact of the early environment on central and peripheral inflammatory profiles, which may be key in the vulnerability to develop metabolic derangements later in life.

Cardiometabolic Syndrome: An Update on Available Mouse Models

Cardiometabolic syndrome (CMS), a disease entity characterized by abdominal obesity, insulin resistance (IR), hypertension, and hyperlipidemia, is a global epidemic with approximately 25% prevalence in adults globally. CMS is associated with increased risk for cardiovascular disease (CVD) and development of diabetes. Due to its multifactorial etiology, the development of several animal models to simulate CMS has contributed significantly to the elucidation of the disease pathophysiology and the design of therapies. In this review we aimed to present the most common mouse models used in the research of CMS. We found that CMS can be induced either by genetic manipulation, leading to dyslipidemia, lipodystrophy, obesity and IR, or obesity and hypertension, or by administration of specific diets and drugs. In the last decade, the ob/ob and db/db mice were the most common obesity and IR models, whereas Ldlr-/- and Apoe-/- were widely used to induce hyperlipidemia. These mice have been used either as a single transgenic or combined with a different background with or without diet treatment. High-fat diet with modifications is the preferred protocol, generally leading to increased body weight, hyperlipidemia, and IR. A plethora of genetically engineered mouse models, diets, drugs, or synthetic compounds that are available have advanced the understanding of CMS. However, each researcher should carefully select the most appropriate model and validate its consistency. It is important to consider the differences between strains of the same animal species, different animals, and most importantly differences to human when translating results.

Exacerbated obesogenic response in female mice exposed to early life stress is linked to fat depot-specific upregulation of leptin protein expression

Early life stress (ELS) is an independent risk factor for increased BMI and cardiometabolic disease risk later in life. We have previously shown that a mouse model of ELS, maternal separation and early weaning (MSEW), exacerbates high-fat diet (HF)-induced obesity only in adult female mice. Therefore, the aim of this study was to investigate 1) whether the short- and long-term effects of HF on leptin expression are influenced by MSEW in a sex-specific manner and 2) the potential epigenetic mechanisms underlying the MSEW-induced changes in leptin expression. After 1 wk of HF, both MSEW male and female mice displayed increased fat mass compared with controls (P < 0.05). However, only MSEW female mice showed elevated leptin mRNA expression in gonadal white adipose tissue (gWAT; P < 0.05). After 12 wk of HF, fat mass remained increased only in female mice (P < 0.05). Moreover, plasma leptin and both leptin mRNA and protein expression in gWAT were augmented in MSEW female mice compered to controls (P < 0.05), but not in MSEW male mice. This association was not present in subcutaneous WAT. Furthermore, among 16 CpG sites in the leptin promoter, we identified three hypomethylated sites in tissue from HF-fed MSEW female mice compared with controls (3, 15, and 16, P < 0.05). These hypomethylated sites showed greater binding of key adipogenic factors such as PPARγ (P < 0.05). Taken together, our study reveals that MSEW superimposed to HF increases leptin protein expression in a sex- and fat depot-specific fashion. Our data suggest that the mechanism by which MSEW increases leptin expression could be epigenetic.

Early life stress reduces voluntary exercise and its prevention of diet-induced obesity and metabolic dysfunction in mice

The development of obesity-related metabolic syndrome (MetS) involves a complex interaction of genetic and environmental factors. One environmental factor found to be significantly associated with MetS is early life stress (ELS). We have previously reported on our mouse model of ELS, induced by neonatal maternal separation (NMS), that displays altered regulation of the hypothalamic-pituitary-adrenal (HPA) axis and increased sensitivity in the urogenital organs, which was attenuated by voluntary wheel running. Here, we are using our NMS model to determine if ELS-induced changes in the HPA axis also influence weight gain and MetS. Naïve (non-stressed) and NMS male mice were given free access to a running wheel and a low-fat control diet at 4-weeks of age. At 16-weeks of age, half of the mice were transitioned to a high fat/sucrose (HFS) diet to investigate if NMS influences the effectiveness of voluntary exercise to prevent diet-induced obesity and MetS. Overall, we observed a greater impact of voluntary exercise on prevention of HFS diet-induced outcomes in naïve mice, compared to NMS mice. Although body weight and fat mass were still significantly higher, exercise attenuated fasting insulin levels and mRNA levels of inflammatory markers in epididymal adipose tissue in HFS diet-fed naïve mice. Only moderate changes were observed in exercised NMS mice on a HFS diet, although this could partially be explained by reduced running distance within this group. Interestingly, sedentary NMS mice on a control diet displayed impaired glucose homeostasis and moderately increased pro-inflammatory mRNA levels in epididymal adipose, suggesting that early life stress alone impairs metabolic function and negatively impacts the therapeutic effect of voluntary exercise.

Association between prolonged separation from parents and allostatic load among children in China

OBJECTIVE

To capture the association of exposure to prolonged separation from both parents early in life and allostatic load (AL), a measure of biological multi-system dysregulation.

METHODS

We used data from 557 7-12-year-old children enrolled in rural area of Chizhou city, Anhui Province, China. We computed an AL score based on eleven biomarkers representing four regulatory systems: immune/inflammatory system (high sensitivity C-reactive protein); metabolic system (body mass index; high density lipoprotein; low density lipoprotein, total cholesterol; triglycerides; fasting glucose; glycated hemoglobin; insulin) and cardiovascular system (systolic and diastolic blood pressure). Child's experiences of parent-child separation were collected a brief online questionnaire by parents of children.

RESULTS

More than 1 in 3 of our participants separated with both parents at age 6 or younger and nearly 1 in 10 persistently separated from both parents after birth. The AL score was significantly higher among children separated from both parents during early childhood (3.25 ± 1.98) or persistently since birth (3.48 ± 1.92), compared with those who did not separated from both parents (2.34 ± 1.53, F = 12.992, P<0.001). After adjustment of demographic covariates, body mass index as well as parent frequency of communication and parental warmth, children who separated from both parents in early childhood (β = 0.84, 95%CI:0.40, 1.28, P < 0.001) or persistently into adolescence (β = 1.27, 95%CI:0.43, 2.12, P = 0.003) evinced the highest levels of AL.

CONCLUSION

This study is the first to show an association between prolonged parent-child separation and physiological wear-and-tear as measured by AL, which provides potential insights into the biological mechanisms underpinning long-term health outcomes in contexts of parent-child separation.

Does early weaning shape future endocrine and metabolic disorders? Lessons from animal models

Obesity and its complications occur at alarming rates worldwide. Epidemiological data have associated perinatal conditions, such as malnutrition, with the development of some disorders, such as obesity, dyslipidemia, diabetes, and cardiovascular diseases, in childhood and adulthood. Exclusive breastfeeding has been associated with protection against long-term chronic diseases. However, in humans, the interruption of breastfeeding before the recommended period of 6 months is a common practice and can increase the risk of several metabolic disturbances. Nutritional and environmental changes within a critical window of development, such as pregnancy and breastfeeding, can induce permanent changes in metabolism through epigenetic mechanisms, leading to diseases later in life via a phenomenon known as programming or developmental plasticity. However, little is known regarding the underlying mechanisms by which precocious weaning can result in adipose tissue dysfunction and endocrine profile alterations. Here, the authors give a comprehensive report of the different animal models of early weaning and programming that can result in the development of metabolic syndrome. In rats, for example, pharmacological and nonpharmacological early weaning models are associated with the development of overweight and visceral fat accumulation, leptin and insulin resistance, and neuroendocrine and hepatic changes in adult progeny. Sex-related differences seem to influence this phenotype. Therefore, precocious weaning seems to be obesogenic for offspring. A better understanding of this condition seems essential to reducing the risk for diseases. Additionally, this knowledge can generate new insights into therapeutic strategies for obesity management, improving health outcomes.

The influence of psychological stress in early life on sexual maturation and sexual behavior in male and female rats

PURPOSE

We studied the influence of psychological stress during the early neonatal period on sexual maturation and sexual behavior in rats.

METHODS

Neonatal male and female rats were divided into control (C) and maternal separation (MS) groups (n = 20-24 per group). The pups in the MS groups were placed in isolation cages for 240 minutes/d from postnatal days 2-11. Vaginal opening (VO) in females and preputial separation (PS) in males (indicators of sexual maturation) were monitored, as was the estrous cycle in females. Thereafter, sexual behavior was monitored twice at 13 and 15 weeks of age.

RESULTS

As for sexual maturation, the onset of PS occurred significantly earlier in the MS group than in the C group, whereas the onset of VO did not differ between the groups. The length of the estrous cycle did not differ between the groups. The frequencies of sexual behaviors did not differ between the groups in either sex.

CONCLUSIONS

In conclusion, early-life psychological stress induced by MS advanced sexual maturation in male rats, whereas it did not affect sexual maturation in female rats. On the other hand, early-life psychological stress might not affect sexual behavior in adulthood in either sex.

Maternal Separation Induces Long-Term Alterations in the Cardiac Oxytocin Receptor and Cystathionine γ-Lyase Expression in Mice

We recently showed that blunt chest trauma reduced the expression of the myocardial oxytocin receptor (Oxtr), which was further aggravated by genetic deletion of the H₂S-producing enzyme cystathionine γ-lyase (CSE). Exogenous H₂S supplementation restored myocardial Oxtr expression under these conditions. Early life stress (ELS) is a risk factor for cardiovascular disease by affecting vascular and heart structures. Therefore, we tested the hypotheses that (i) ELS affects cardiac Oxtr and CSE expressions and (ii) Oxtr and CSE expression patterns depend on the duration of stress exposure. Thus, two stress paradigms were compared: long- and short-term separation stress (LTSS and STSS, respectively). Cardiac Oxtr expression was differentially affected by the two stress paradigms with a significant reduction after LTSS and a significant increase after STSS. CSE expression, which was significantly reduced in Oxtr^−/− knockout hearts, was downregulated and directly related to Oxtr expression in LTSS hearts (r = 0.657, p = 0.012). In contrast, CSE expression was not related to Oxtr upregulation in STSS. Plasma Oxt levels were not affected by either ELS paradigm. The coincidence of LTSS-induced reduction of cardiac Oxtr and reduced CSE expression may suggest a novel pathophysiological link between early life adversities and increased risk for the development of cardiovascular disorders in adulthood.

Female Mice Exposed to Postnatal Neglect Display Angiotensin II-Dependent Obesity-Induced Hypertension

Background We have previously reported that female mice exposed to maternal separation and early weaning (MSEW), a model of early life stress, show exacerbated diet-induced obesity associated with hypertension. The goal of this study was to test whether MSEW promotes angiotensin II-dependent hypertension via activation of the renin-angiotensin system in adipose tissue. Methods and Results MSEW was achieved by daily separations from the dam and weaning at postnatal day 17, while normally reared controls were weaned at postnatal day 21. Female controls and MSEW weanlings were placed on a low-fat diet (LF, 10% kcal from fat) or high-fat diet (HF, 60% kcal from fat) for 20 weeks. MSEW did not change mean arterial pressure in LF-fed mice but increased it in HF-fed mice compared with controls (P<0.05). In MSEW mice fed a HF, angiotensin II concentration in plasma and adipose tissue was elevated compared with controls (P<0.05). In addition, angiotensinogen concentration was increased solely in adipose tissue from MSEW mice (P<0.05), while angiotensin-converting enzyme protein expression and activity were similar between groups. Chronic enalapril treatment (2.5 mg/kg per day, drinking water, 7 days) reduced mean arterial pressure in both groups of mice fed a HF (P<0.05) and abolished the differences due to MSEW. Acute angiotensin II-induced increases in mean arterial pressure (10 μg/kg SC) were attenuated in untreated MSEW HF-fed mice compared to controls (P<0.05); however, this response was similar between groups in enalapril-treated mice. Conclusions The upregulation of angiotensinogen and angiotensin II in adipose tissue could be an important mechanism by which female MSEW mice fed a HF develop hypertension.

Determining sample size adequacy for animal model studies in nutrition research: limits and ethical challenges of ordinary power calculation procedures

Animal models are widely used in the field of nutrition research. Scientifically and ethically sound experiments need an adequate number of experimental units. The use of 5-10 units is common, but such sample sizes can be justified for large effect sizes only. We reviewed animal model studies recently published in selected journals in the field of nutrition sciences. We performed a simulation study aimed at determining the adequate sample size for normality assessment. We then performed power calculations for a number of statistical tests commonly found in rodent model studies in nutrition research. Among the selected papers, sample sizes ranged from 6-18 units per group. None of them justified the sample size. However, such sample sizes do not allow for normality testing, thus, graphical approaches should be used. Parametric approaches result in higher statistical power when compared to their non-parametric counterparts. Repeated measures analysis should always be preferred, when possible.

Childhood adversity and mechanistic links to hypertension risk in adulthood

Adverse childhood experiences (ACEs), defined as traumatic events in childhood that range from various forms of abuse to household challenges and dysfunction, have devastating consequences on adult health. Epidemiological studies in humans and animal models of early life stress (ELS) have revealed a strong association and insight into the mechanistic link between ACEs and increased risk of cardiovascular disease (CVD). This review focuses on the mechanistic links of ACEs in humans and ELS in mice and rats to vasoactive factors and immune mediators associated with CVD and hypertension risk, as well as sex differences in these phenomena. Major topics of discussion in this review are as follows: (a) epidemiological associations between ACEs and CVD risk focusing on hypertension, (b) evidence for association of ACE exposures to immune-mediated and/or vasoactive pathways, (c) rodent models of ELS-induced hypertension risk, (d) proinflammatory mediators and vasoactive factors as mechanisms of ELS-induced hypertension risk. We also provide some overall conclusions and directions of further research. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Correlations of PPARα and PPARγ expressions with 1H-MRS quantified hepatic fat content in pups of rats that experienced intrauterine growth restriction

Background: Proton magnetic resonance spectroscopy (¹H-MRS) measurement of hepatic fat content in intrauterine growth restriction rats has rarely been reported. This study was to explore the association of peroxisome proliferator-activated receptor alpha and gamma (PPARα and PPARγ) expression with ¹H-MRS quantified hepatic fat content in offspring of rats that experienced intrauterine growth restriction (IUGR).Methods and findings: IUGR was established by feeding a low-protein diet to female rats during pregnancy. Male pups of IUGR rats were weighed, liver tissues were collected at the ages of 1 day and 1, 3, 8 and 12 weeks post birth. Visceral adipose tissues (VATs) were collected at 3, 8, and 12 weeks post birth. Male pups also received conventional magnetic resonance imaging and ¹H-MRS using a 3.0 T whole-body MR scanner at 3, 8, and 12 weeks post birth. The peak area ratios in the MR spectra were calculated to determine hepatic lipid content. The expression of PPARα protein was detected by Western blot. The expression of PPARα mRNA was measured by real-time quantitative PCR. Significantly lower PPARα protein and mRNA expression were observed in liver tissues of male pups of IUGR rats at 1 day and 1, 3, 8, and 12 weeks post birth compared to male pups of control rats. In contrast, significantly higher PPARγ protein and mRNA expression were observed in VATs of male pups of IUGR rats at 3, 8, and 12 weeks post birth compared to male pups of control rats. PPARα protein and mRNA expression in the liver negatively correlated with the hepatic fat content (r = -0.611, -0.607, respectively), whereas PPARγ protein and mRNA expression in VATs positively correlated with the hepatic fat content (r = 0.659, 0.668, respectively).Conclusion: ¹H-MRS allows noninvasive assessment of hepatic fat content in rats. PPARα protein and mRNA expression were significantly decreased in the livers of rats, whereas PPARγ protein and mRNA expression was significantly increased in VATs in pups of IUGR rats.