Observations on the orexigenic hypothalamic neuropeptide Y-system in neonatally overfed weanling rats

Role of neonatal hyperleptinaemia on serum adiponectin and suppressor of cytokine signalling-3 expression in young rats

Previously we had shown that neonatal leptin treatment programmes for both hyperleptinaemia and hyperinsulinaemia, which lead to leptin resistance and low expression of the hypothalamic leptin receptor (OB-Rb) of rats aged 150 d. Here we investigated in young post-weaned rats (age 30 d) if leptin treatment during lactation induces leptin and insulin resistance and if those changes are accompanied by changes in the suppressor of cytokine signalling-3 (SOCS-3) expression and serum adiponectin concentration. After delivery, the pups were divided into two groups: (1) a leptin group (Lep) that were injected with leptin daily (8 microg/100 g body weight subcutaneously) for the first 10 d of lactation; (2) a control (C) group, receiving saline. After weaning (day 21), body weight was monitored until the animals were age 30 d. They were tested for food intake in response to either leptin (0.5 mg/kg body weight intraperitoneally) (CL, LepL) or saline (CSal, LepSal) when they were aged 30 d. The CL group showed lower food intake, but no response was observed in the LepL group, suggesting leptin resistance. The Lep group had hyperleptinaemia (five-fold), hyperinsulinaemia (+42.5%) and lower levels of serum adiponectin (-43.2%). The hypothalamic expression of OB-Rb was lower (-22%) and SOCS-3 was higher (+52.8%) in the Lep group. We conclude that neonatal leptin treatment programmes for leptin resistance as soon as 30 d and suggests that SOCS-3 appears to be of particular importance in this event. In the Lep group, the lower serum adiponectin levels were accompanied by higher serum insulin, indicating a probable insulin resistance.

Relevance of animal models to human eating disorders and obesity

BACKGROUND AND RATIONALE

This review addresses the role animal models play in contributing to our knowledge about the eating disorders anorexia nervosa (AN) and bulimia nervosa (BN) and obesity.

OBJECTIVES

Explore the usefulness of animal models in complex biobehavioral familial conditions, such as AN, BN, and obesity, that involve interactions among genetic, physiologic, psychological, and cultural factors.

RESULTS AND CONCLUSIONS

The most promising animal model to mimic AN is the activity-based anorexia rodent model leading to pathological weight loss. The paradigm incorporates reward elements of the drive for activity in the presence of an appetite and allows the use of genetically modified animals. For BN, the sham-feeding preparation in rodents equipped with a gastric fistula appears to be best suited to reproduce the postprandial emesis and the defects in satiety. Animal models that incorporate genes linked to behavior and mood may clarify biobehavioral processes underlying AN and BN. By contrast, a relative abundance of animal models has contributed to our understanding of human obesity. Both environmental and genetic determinants of obesity have been modeled in rodents. Here, we consider single gene mutant obesity models, along with models of obesigenic environmental conditions. The contributions of animal models to obesity research are illustrated by their utility for identifying genes linked to human obesity, for elucidating the pathways that regulate body weight and for the identification of potential therapeutic targets. The utility of these models may be further improved by exploring the impact of experimental manipulations on the behavioral determinants of energy balance.

Hypothalamic neuropeptide expression of juvenile and middle-aged rats after early postnatal food restriction

Rats subjected to early postnatal food restriction (FR) show persistent changes in energy balance. The hypothalamus plays a major role in the regulation of energy balance. Therefore, we hypothesized that early postnatal food restriction induces developmental programming of hypothalamic gene expression of neuropeptides involved in this regulation. In the hypothalamus of juvenile and middle-aged rats that were raised in control (10 pups) or FR litters (20 pups), gene expression was investigated for neuropeptide Y (NPY), agouti-related protein (AgRP), proopiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) in the arcuate nucleus (ARC); CRH and TRH in the paraventricular nucleus; and melanin-concentrating hormone (MCH) and orexin in the lateral hypothalamic area. Early postnatal FR acutely and persistently reduced body size. Juvenile FR rats had significantly reduced CART gene expression and increased MCH expression. In middle-aged FR rats, POMC and CART mRNA levels were significantly reduced. The ratio between expression of the ARC orexigenic peptides (NPY and AgRP) and anorexigenic peptides (POMC and CART) was increased in juvenile, but not in middle-aged, FR rats. These results suggest that in neonatal rats, FR already triggers the ARC, and to a lesser extent the lateral hypothalamic area, but not the paraventricular nucleus, to increase expression of orexigenic relative to anorexigenic peptides. In addition, with enduring small body size and normalized hypothalamic gene expression, the adult FR rats appeared to have accepted this smaller body size as normal. This suggests that the body weight set-point was differently programmed in animals with early postnatal FR.

Maternal nutrition and the programming of obesity: The brain

The increasing incidence of obesity in the developed and developing world in the last decade has led to a need to define our understanding of the physiological mechanisms which can predispose individuals to weight gain in infancy, childhood and adulthood. There is now a considerable body of evidence which has shown that the pathway to obesity may begin very early in life, and that exposure to an inappropriate level of nutrition during prenatal and/or early postnatal development can predispose individuals to obesity in later life The brain is at the heart of the regulation of appetite and food preferences, and it is increasingly being recognized that the development of central appetitive structures is acutely sensitive to the nutritional environment both before and immediately after birth. This review will summarize the body of work which has highlighted the critical role of the brain in the early origins of obesity and presents some perspectives as to the potential application of these research findings in the clinical setting.

Improved lactational nutrition and postnatal growth ameliorates impairment of glucose tolerance by uteroplacental insufficiency in male rat offspring

Intrauterine growth restriction and accelerated postnatal growth predict increased risk of diabetes. Uteroplacental insufficiency in the rat restricts fetal growth but also impairs mammary development and postnatal growth. We used cross fostering to compare the influence of prenatal and postnatal nutritional restraint on adult glucose tolerance, insulin secretion, insulin sensitivity, and hypothalamic neuropeptide Y content in Wistar Kyoto rats at 6 months of age. Bilateral uterine vessel ligation (restricted) to induce uteroplacental insufficiency or sham surgery (control) was performed on d-18 gestation. Control, restricted, and reduced (reducing litter size of controls to match restricted) pups were cross fostered onto a control or restricted mother 1 d after birth. Restricted pups were born small compared with controls. Restricted males, but not females, remained lighter up to 6 months, regardless of postnatal environment. By 10 wk, restricted-on-restricted males ate more than controls. At 6 months restricted-on-restricted males had increased hypothalamic neuropeptide Y content compared with other groups, and together with reduced-on-restricted males had increased retroperitoneal fat weight (percent body weight) compared with control-on-controls. Restricted-on-restricted males had impaired glucose tolerance, reduced first-phase insulin secretion, but unaltered insulin sensitivity, compared with control-on-controls. In males, being born small and exposed to an impaired lactational environment adversely affects adult glucose tolerance and first-phase insulin secretion, but improving lactation partially ameliorates this condition. This study identifies early life as a target for intervention to prevent later diabetes after prenatal restraint.

Regulation of fetal growth: consequences and impact of being born small

The first trimester of pregnancy is the time during which organogenesis takes place and tissue patterns and organ systems are established. In the second trimester the fetus undergoes major cellular adaptation and an increase in body size, and in the third trimester organ systems mature ready for extrauterine life. In addition, during that very last period of intrauterine life there is a significant increase in body weight. In contrast to the postnatal endocrine control of growth, where the principal hormones directly influencing growth are growth hormone (GH) and the insulin-like growth factors (IGFs) via the GH-IGF axis, fetal growth throughout gestation is constrained by maternal factors and placental function and is coordinated by growth factors. In general, growth disorders only become apparent postnatally, but they may well be related to fetal life. Thus, fetal growth always needs to be considered in the overall picture of human growth as well as in its metabolic development.

Maternal perinatal undernutrition drastically reduces postnatal leptin surge and affects the development of arcuate nucleus proopiomelanocortin neurons in neonatal male rat pups

A growing body of evidence suggests that maternal undernutrition sensitizes the offspring to the development of energy balance metabolic disorders such as type 2 diabetes, dyslipidemia, and obesity. The present study aimed at examining the impact of maternal undernutrition on leptin plasma levels in newborn male rats and on the arcuate nucleus proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons that are major leptin targets. Using a model of perinatal maternal 50% food-restricted diet (FR50) in the rat, we evaluated leptin plasma levels and hypothalamic POMC and NPY gene expression from postnatal day (PND) 4 to PND30 in both control and FR50 offspring. In control rats, a postnatal peak of plasma leptin was observed between PND4 and PND14 that reached a maximal value at PND10 (5.17 +/- 0.53 ng/ml), whereas it was dramatically reduced in FR50 pups with the higher concentration at PND7 (0.93 +/- 0.23 ng/ml). In FR50 animals, using semiquantitative RT-PCR and in situ hybridization, we showed that the hypothalamic POMC mRNA level was decreased from PND14 until PND30, whereas NPY gene expression was not significantly modified. In PND21 FR50 animals, we observed strikingly reduced immunoreactive beta-endorphin nerve fibers projecting to the hypothalamic paraventricular nucleus without affecting NPY projections. Our data showed that maternal undernutrition drastically reduces the postnatal surge of plasma leptin, disturbing particularly the hypothalamic wiring as well as the gene expression of the anorexigenic POMC neurons in male rat pups. These alterations might contribute to the adult metabolic disorders resulting from perinatal growth retardation.

Effects of uteroplacental insufficiency and reducing litter size on maternal mammary function and postnatal offspring growth

Human intrauterine growth restriction is often associated with uteroplacental insufficiency and a decline in nutrient and oxygen supply to the fetus. This study investigated the effects of uteroplacental insufficiency and intrauterine growth restriction (Restricted) or reducing litter size for normally grown pups (Reduced Litter) on maternal mammary development and function, milk composition, offspring milk intake, and their resultant effects on postnatal growth. Uteroplacental insufficiency was surgically induced by bilateral uterine vessel ligation on day 18 of gestation in the Wistar Kyoto rat. At birth, a group of sham control rats had their litter size reduced to five (Reduced Litter) to match that of the Restricted group. Cohorts of rats were terminally anesthetized on day 20 of gestation or day 6 of lactation, and a third group was studied throughout lactation. Restricted pups had a lower birth weight (by 16%) and litter size (by 36%) compared with controls, as well as reduced mammary parathyroid hormone-related protein content and milk ionic calcium concentrations associated with reduced total pup calcium. Restricted dams with lower circulating progesterone experienced premature lactogenesis, producing less milk per pup with altered composition compared with controls, further slowing growth during lactation. Reducing litter size of pups born of normal birth weight (Reduced Litter) was associated with decreased pup growth, highlighting the importance of appropriate controls. The present study demonstrates that uteroplacental insufficiency impairs mammary function, compromises milk quality and quantity, and reduces calcium transport into milk, further restraining postnatal growth.

Excess weight gain during the early postnatal period is associated with permanent reprogramming of brown adipose tissue adaptive thermogenesis

Excess weight gain during the early postnatal period increases the risk of persistent obesity into adulthood and impacts on the subsequent risk for metabolic and cardiovascular diseases. The current study investigated the long-term effect of early excess weight gain, through reduced nursing litter size, on body weight regulation and its relation to brown adipose tissue (BAT) thermogenesis. Animals raised in a small litter (SL, three pups per litter) were compared with those raised in a normal litter size (NL, eight pups per litter). BAT from young adult NL and SL rats, maintained under either ambient or cold conditions, were used for gene expression, morphological, and functional analysis. Compared with NL, SL rats showed excess weight gain, and adult SL animals had a reduced thermogenic capacity as displayed by lower levels of uncoupling protein 1 (UCP1). When exposed to cold, BAT from SL rats was less active and demonstrated reduced responsiveness to cold. Furthermore, reduction in transcript abundance of several lipid lipases and transcriptional regulators was observed in SL rats either at ambient temperature or under cold conditions. Finally, the expression of sympathetic beta 3-adrenergic receptor and the response to the sympathetic receptor agonist isoproterenol were decreased in SL rats. Overall, these observations provide the first evidence that postnatal excess weight gain results in abnormalities in BAT thermogenesis and sympathetic outflow, which likely increases susceptibility to obesity in adulthood.

Factors associated with newborn in-hospital weight loss: comparisons by feeding method, demographics, and birthing procedures

Full-term newborn normative weight loss and factors influencing this were determined through chart audits (n = 812) at 6 hospitals in Manitoba, Canada. The effects of parity, gestational age, birth weight, sex, length of stay, type of delivery (cesarean vs vaginal), epidural use, and type of infant feeding (exclusively breastfed, partially breastfed, exclusively formula-fed) on percentage weight loss in hospital were analyzed using multiple regression analysis. In-hospital weight loss was 5.09% +/- 2.89% (95% CI, 4.89-5.29), varying by feeding category: exclusively breastfed 5.49% +/- 2.60% (95% CI, 5.23-5.74), partially breastfed 5.52% +/- 3.02% (95% CI, 5.16-5.88), and formula-fed 2.43% +/- 2.12% (95% CI, 2.02-2.85). Factors significantly increasing the percentage weight loss included higher birth weight, female sex, epidural use, and longer hospital stay. Lower percentage weight loss was associated with greater gestational age and exclusive formula feeding. Parity and type of delivery were not significant. Controlling for demographic and delivery-related variables, exclusive formula feeding had the largest impact, with 3.1% less weight loss than exclusive breastfeeding.

Prenatal and postnatal pathways to obesity: different underlying mechanisms, different metabolic outcomes

Obesity and type 2 diabetes are worldwide health issues. The present paper investigates prenatal and postnatal pathways to obesity, identifying different metabolic outcomes with different effects on insulin sensitivity and different underlying mechanisms involving key components of insulin receptor signaling pathways. Pregnant Wistar rats either were fed chow ad libitum or were undernourished throughout pregnancy, generating either control or intrauterine growth restricted (IUGR) offspring. Male offspring were fed either standard chow or a high-fat diet from weaning. At 260 d of age, whole-body insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp, and other metabolic parameters were measured. As expected, high-fat feeding caused diet-induced obesity (DIO) and insulin resistance. Importantly, the insulin sensitivity of IUGR offspring was similar to that of control offspring, despite fasting insulin hypersecretion and increased adiposity, irrespective of postnatal nutrition. Real-time PCR and Western blot analyses of key markers of insulin sensitivity and metabolic regulation showed that IUGR offspring had increased hepatic levels of atypical protein kinase C zeta (PKC zeta) and increased expression of fatty acid synthase mRNA. In contrast, DIO led to decreased expression of fatty acid synthase mRNA and hepatic steatosis. The decrease in hepatic PKC zeta with DIO may explain, at least in part, the insulin resistance. Our data suggest that the mechanisms of obesity induced by prenatal events are fundamentally different from those of obesity induced by postnatal high-fat nutrition. The origin of insulin hypersecretion in IUGR offspring may be independent of the mechanistic events that trigger the insulin resistance commonly observed in DIO.

Prenatal exposure to undernutrition and programming of responses to high-fat feeding in the rat

Fetal undernutrition programmes risk of later metabolic disorders. Postnatal factors modify the programmed phenotype. This study aimed to assess the effects of a postnatal high-fat (HF) challenge on body weight gain, adiposity and gene expression following prenatal undernutrition. Pregnant rats were fed either a control diet or a low-protein (LP) diet, targeted at days 0-7 (LPE), days 8-14 (LPM), or days 15-22 (LPL) gestation. At 12 weeks of age offspring were either fed standard laboratory chow diet (4.13 % fat), or a 39.5 % fat diet, for 10 weeks. LP exposure had no effect on weight gain or abdominal fat in males. Females exposed to LP diet in utero exhibited a similar weight gain on HF diet as on the chow diet. Programming of fat deposition was noted in LPE females and males of the LPM and LPL groups (P = 0.019). Hypothalamic expression of galanin mRNA was similar in all groups, but expression of the galanin-2 receptor was modified by LP exposure in female offspring. Hepatic expression of sterol response element binding protein (SREBP-1c) was decreased by LP at both the mRNA (P = 0.008) and protein (P < 0.001) level. HF feeding increased expression of SREBP-1c mRNA three-fold in controls, with little response noted in the LP groups. Interactions of factors such as postnatal diet, age and sex act together with prenatal factors to determine metabolic function and responsiveness at any stage of postnatal life. This study further establishes a role for prenatal nutrition in programming the genes involved in lipid metabolism and appetite regulation.

Insulin resistance of hypothalamic arcuate neurons in neonatally overfed rats

Rats exposed to early postnatal overfeeding by rearing in small litters become hyperphagic, hyperleptinemic, and hyperinsulinemic throughout later life. Medial arcuate neurons are involved in body weight regulation. They were tested in brain slices of control and small-litter rats concerning differences in responses to insulin. Insulin induced suppression of firing in controls, whereas in small-litter rats inhibition was significantly reduced and activation increased. This could be observed in juvenile as well as adult rats. A gamma-aminobutyric acid type A receptor antagonist did not change the responses. Thus, negative feedback to the satiety signal insulin on medial arcuate neurons is reduced in neonatally overfed small-litter rats. This can be regarded as insulin resistance, which is induced during early development and persists in later life.

Neuropeptide Y in normal eating and in genetic and dietary-induced obesity

Neuropeptide Y (NPY) is one the most potent orexigenic peptides found in the brain. It stimulates food intake with a preferential effect on carbohydrate intake. It decreases latency to eat, increases motivation to eat and delays satiety by augmenting meal size. The effects on feeding are mediated through at least two receptors, the Y1 and Y5 receptors. The NPY system for feeding regulation is mostly located in the hypothalamus. It is formed of the arcuate nucleus (ARC), where the peptide is synthesized, and the paraventricular (PVN), dorsomedial (DMN) and ventromedial (VMN) nuclei and perifornical area where it is active. This activity is modulated by the hindbrain and limbic structures. It is dependent on energy availability, e.g. upregulation with food deprivation or restriction, and return to baseline with refeeding. It is also sensitive to diet composition with variable effects of carbohydrates and fats. Leptin signalling and glucose sensing which are directly linked to diet type are the most important factors involved in its regulation. Absence of leptin signalling in obesity models due to gene mutation either at the receptor level, as in the Zucker rat, the Koletsky rat or the db/db mouse, or at the peptide level, as in ob/ob mouse, is associated with increased mRNA abundance, peptide content and/or release in the ARC or PVN. Other genetic obesity models, such as the Otsuka-Long-Evans-Tokushima Fatty rat, the agouti mouse or the tubby mouse, are characterized by a diminution in NPY expression in the ARC nucleus and by a significant increase in the DMN. Further studies are necessary to determine the exact role of NPY in these latter models. Long-term exposure to high-fat or high-energy palatable diets leads to the development of adiposity and is associated with a decrease in hypothalamic NPY content or expression, consistent with the existence of a counter-regulatory mechanism to diminish energy intake and limit obesity development. On the other hand, an overactive NPY system (increased mRNA expression in the ARC associated with an upregulation of the receptors) is characteristic of rats or rodent strains sensitive to dietary-induced obesity. Finally, NPY appears to play an important role in body weight and feeding regulation, and while it does not constitute the only target for drug treatment of obesity, it may nevertheless provide a useful target in conjunction with others.

Programming of the appetite-regulating neural network: a link between maternal overnutrition and the programming of obesity?

The concept of a functional foetal "appetite regulatory neural network" is a new and potentially critical one. There is a growing body of evidence showing that the nutritional environment to which the foetus is exposed during prenatal and perinatal development has long-term consequences for the function of the appetite-regulating neural network and therefore the way in which an individual regulates energy balance throughout later life. This is of particular importance in the context of evidence obtained from a wide range of epidemiological studies, which have shown that individuals exposed to an elevated nutrient supply before birth have an increased risk of becoming obese as children and adults. This review summarises the key pieces of experimental evidence, by our group and others, that have contributed to our current understanding of the programming of appetite, and highlights the important questions that are yet to be answered. It is clear that this area of research has the potential to generate, within the next few years, interventions that could begin to alleviate the adverse long-term consequences of being exposed to an elevated nutrient supply before birth.

Developmental programming of obesity in mammals

Converging lines of evidence from epidemiological studies and animal models now indicate that the origins of obesity and related metabolic disorders lie not only in the interaction between genes and traditional adult risk factors, such as unbalanced diet and physical inactivity, but also in the interplay between genes and the embryonic, fetal and early postnatal environment. Whilst studies in man initially focused on the relationship between low birth weight and risk of adult obesity and metabolic syndrome, evidence is also growing to suggest that increased birth weight and/or adiposity at birth can also lead to increased risk for childhood and adult obesity. Hence, there appears to be increased risk of obesity at both ends of the birth weight spectrum. Animal models, including both under- and overnutrition in pregnancy and lactation lend increasing support to the developmental origins of obesity. This review focuses upon the influence of the maternal nutritional and hormonal environment in pregnancy in permanently programming appetite and energy expenditure and the hormonal, neuronal and autocrine mechanisms that contribute to the maintenance of energy balance in the offspring. We discuss the potential maternal programming 'vectors' and the molecular mechanisms that may lead to persistent pathophysiological changes resulting in subsequent disease. The perinatal environment, which appears to programme subsequent obesity, provides a potential therapeutic target, and work in this field will readily translate into improved interventional strategies to stem the growing epidemic of obesity, a disease which, once manifest, has proven particularly resistant to treatment.

Regulation of leptin synthesis and secretion before birth: implications for the early programming of adult obesity

A series of epidemiological, clinical and experimental studies have shown that there are associations between the fetal and neonatal nutritional environment and the amount and distribution of adipose tissue in adult life. This review considers the evidence for these relationships and discusses the potential impact of the prenatal nutritional experience on the development of the endocrine and neuroendocrine systems that regulate energy balance, with a particular emphasis on the role of the adipocyte-derived hormone, leptin. In the rodent, leptin derived from the mother may exert an important influence on the development of the appetite regulatory neural network and on the subsequent regulation of leptin synthesis and the risk for obesity in the offspring. In species such as the human and sheep, there is also recent evidence that the synthesis and secretion of adipocyte-derived hormones, such as leptin, are regulated in fetal life. Furthermore, the hypothalamic neuropeptides that regulate energy intake and expenditure in adult life are also present within the fetal brain and may be regulated by the prevailing level of maternal and hence fetal nutrient and hormonal signals, including leptin. This work is important in determining those initiating mechanisms within the 'fat-brain' axis in early life that precede the development of adult obesity.

GABAA receptor antagonists prevent abnormalities in leptin, insulin and amylin actions on paraventricular hypothalamic neurons of overweight rats

The hypothalamic regulatory system of body weight which develops in rats during critical periods of early postnatal life seems to express plastic changes depending on nutrition at that time. Adult rats previously exposed to early postnatal overnutrition by raising them in small litters become persistently predisposed to overweight, hyperphagia and hyperleptinaemia. The hypothesis was raised that feeding-related peptides could be involved through altered effects on neuronal activity of the regulatory systems of such rats. This was studied on brain slices of small-litter rats and normal-weight controls between days 60 and 120 of life. Neurons of the medial parvocellular part of the paraventricular nucleus were significantly activated by the adiposity signals leptin, insulin and amylin in controls. This is a kind of negative feedback, because activation of these neurons is known to be followed in vivo by increased energy expenditure. GABAergic mechanisms seem to affect these neuronal responses because the activating effects of insulin and amylin were reduced in the presence of a GABA(A) receptor antagonist. In overweight small-litter rats, however, the neuronal responses to the adiposity signals were significantly changed; activating effects were reduced and inhibitory effects increased. By means of blockade of GABA(A) receptors, significant alterations in the neuronal responses to leptin, insulin and amylin in small-litter rats were prevented. Responses to the peptides were reversed and now resembled those of controls. In conclusion, changes in neuronal wiring with GABAergic interneurons seem to contribute to a persistently reduced negative feedback of adiposity signals in early postnatally overfed rats.

Effects of perinatal overfeeding on mechanisms controlling food intake and body weight homeostasis

The prevalence of overweight and obesity in most developed countries has markedly increased during the last several decades. In addition to genetic, hormonal and metabolic influences, epigenetic environmental factors, such as fetal and neonatal nutrition, play a key role in the development of obesity. Interestingly, becoming overweight during critical developmental periods of fetal and/or neonatal life has been shown to continue throughout juvenile life into adulthood. In spite of this evidence, the specific biological mechanisms underlying this fetal/neonatal programming are not perfectly understood. However, it is clear that circulating hormones, such as insulin, leptin and ghrelin, play a critical role in the development and programming of hypothalamic circuits regulating food intake and bodyweight homeostasis.

The importance of catch-up growth after early malnutrition for the programming of obesity in male rat

OBJECTIVE

To investigate whether catch-up growth after maternal malnutrition would favor the development of obesity in adulthood.

RESEARCH METHODS AND PROCEDURES

Pregnant rats were submitted to protein or calorie restriction during the course of gestation. During lactation, pups were protein-restricted, normally fed, or overfed [reduced litter size, control (C) diet]. At weaning, rats were transferred to chow or to a hypercaloric diet (HCD) known to induce obesity. Body weight, food intake, blood parameters, glucose tolerance, adipocyte cellularity, and adipose factors contributing to cardiovascular disease development were measured.

RESULTS

Protein and calorie restriction during gestation led to growth retardation at birth. If malnutrition was prolonged throughout lactation, adult body weight was permanently reduced. However, growth-retarded offspring overfed during the suckling period underwent a rapid catch-up growth and became heavier than the normally fed Cs. Offspring of calorie-restricted rats gained more weight than those of dams fed protein-restricted diet. Feeding an HCD postnatally amplified the effect of calorie restriction, and offspring that underwent catch-up growth became more obese than Cs. The HCD was associated with hyperphagia, hyperglycemia, hyperinsulinemia, glucose intolerance, insulin resistance, and adipocyte hypertrophy. The magnitude of effects varied depending on the type and the timing of early malnutrition. The expression of genes encoding factors implicated in cardiovascular disease was also modulated differently by early malnutrition and adult obesity.

DISCUSSION

Catch-up growth immediately after early malnutrition should be a key point for the programming of obesity.

Metabolic imprinting: critical impact of the perinatal environment on the regulation of energy homeostasis

Epidemiological studies in humans suggest that maternal undernutrition, obesity and diabetes during gestation and lactation can all produce obesity in offspring. Animal models have allowed us to investigate the independent consequences of altering the pre- versus post-natal environments on a variety of metabolic, physiological and neuroendocrine functions as they effect the development in the offspring of obesity, diabetes, hypertension and hyperlipidemia (the 'metabolic syndrome'). During gestation, maternal malnutrition, obesity, type 1 and type 2 diabetes and psychological, immunological and pharmacological stressors can all promote offspring obesity. Normal post-natal nutrition can reduce the adverse impact of some of these pre-natal factors but maternal high-fat diets, diabetes and increased neonatal access to food all enhance the development of obesity and the metabolic syndrome in offspring. The outcome of these perturbations of the perinatal environmental is also highly dependent upon the genetic background of the individual. Those with an obesity-prone genotype are more likely to be affected by factors such as maternal obesity and high-fat diets than are obesity-resistant individuals. Many perinatal manipulations appear to promote offspring obesity by permanently altering the development of central neural pathways, which regulate food intake, energy expenditure and storage. Given their strong neurotrophic properties, either excess or an absence of insulin and leptin during the perinatal period are likely to be effectors of these developmental changes. Because obesity is associated with an increased morbidity and mortality and because of its resistance to treatment, prevention is likely to be the best strategy for stemming the tide of the obesity epidemic. Such prevention should begin in the perinatal period with the identification and avoidance of factors which produce permanent, adverse alterations in neural pathways which control energy homeostasis.

Perinatal overfeeding in rats results in increased levels of plasma leptin but unchanged cerebrospinal leptin in adulthood

OBJECTIVE

To study the effect of perinatal programming and overfeeding on the hypothalamic control mechanisms of food intake in adult rats.

DESIGN

Neonatal programming effects on body weight, food intake, central and peripheral leptin levels, hypothalamic neuropeptides, leptin receptors and central leptin responsiveness in adult rats.

MEASUREMENTS

Plasma and cerebrospinal fluid (CSF) leptin levels were analyzed using radioimmunoassay. Neuropeptide mRNA levels were analyzed using in situ hybridization. Leptin receptor mRNA levels were analyzed using reverse transcriptase-polymerase chain reaction.

RESULTS

Perinatally overfed rats growing up in small litters (SL) maintain their obese and hyperleptinemic phenotype in adulthood. However, leptin levels in CSF are abnormally low considering the plasmatic hyperleptinemia. In contrast to the already reported changes in perinatally overfed juvenile rats, perinatally overfed adult rats did not show any alteration in the expression of leptin receptor isoforms and evaluated neuropeptides. Moreover, SL adult rats showed a normal sensitivity regarding the inhibitory effect of intracerebroventricular leptin administration on food intake.

CONCLUSION

Perinatal overfeeding does not induce alterations in either the anorectic response to central leptin administration or expression of leptin receptors and neuropeptides in adulthood. The leptin resistance to peripheral leptin in SL adult rats may be related to impaired leptin transport across the blood-brain barrier.

Increased maternal nutrition alters development of the appetite‐regulating network in the brain

Individuals exposed to an increased nutrient supply before birth have a high risk of becoming obese children and adults. It has been proposed that exposure of the fetus to high maternal nutrient intake results in permanent changes within the central appetite regulatory network. No studies, however, have investigated the impact of increased maternal nutrition on the appetite regulatory network in species in which this network develops before birth, as in the human. In the present study, pregnant ewes were fed a diet which provided 100% (control, n = 8) or approximately 160% (well-fed, n = 8) of metabolizable energy requirements. Ewes were allowed to lamb spontaneously, and lambs were sacrificed at 30 days of postnatal age. All fat depots were dissected and weighed, and expression of the appetite-regulating neuropeptides and the leptin receptor (OBRb) were determined by in situ hybridization. Lambs of well-fed ewes had higher glucose (Glc) concentrations during early postnatal life (F = 5.93, P<0.01) and a higher relative subcutaneous (s.c.) fat mass at 30 days of age (34.9+/-4.7 g/kg vs. 22.8+/-3.3 g/kg; P<0.05). The hypothalamic expression of pro-opiomelanocortin was higher in lambs of well-fed ewes (0.48+/-0.09 vs. 0.28+/-0.04, P<0.05). In lambs of overnourished mothers, but not in controls, the expression of OBRb was inversely related to total relative fat mass (r2 = 0.50, P = 0.05, n = 8), and the direct relationship between the expression of the central appetite inhibitor CART and fat mass was lost. The expression of neuropeptide Y and AGRP was inversely related to total relative fat mass (NPY, r2 = 0.28, P<0.05; agouti-related peptide, r2 = 0.39, P<0.01). These findings suggest that exposure to increased nutrition before birth alters the responses of the central appetite regulatory system to signals of increased adiposity after birth.

Perinatal Nutrition and Hormone-Dependent Programming of Food Intake

It is increasingly accepted that alterations of the intrauterine and early postnatal nutritional, metabolic and hormonal environment may predispose individuals to development of diseases in later life. Results from studies of the offspring of diabetic mothers strongly support this hypothesis. It has also been suggested that being light at birth leads to an increased risk of the metabolic syndrome (Syndrome X) in later life (the Barker hypothesis). The pathophysiological mechanisms that underlie this programming are unclear. However, hormones are important environment-dependent organizers of the developing neuroendocrine-immune network, which regulates all the fundamental processes of life. Hormones can act as 'endogenous functional teratogens' when present in non-physiological concentrations, induced by alterations in the intrauterine or neonatal environment during critical periods of perinatal life. Perinatal hyperinsulinism is pathognomic in offspring of diabetic mothers. Early hyperinsulinism also occurs as a result of early postnatal overfeeding. In rats, endogenous hyperinsulinism, as well as peripheral or intrahypothalamic insulin treatment during perinatal development, may lead to 'malprogramming' of the neuroendocrine systems regulating body weight, food intake and metabolism. This results in an increased disposition to become obese and to develop diabetes throughout life. Similar malprogramming may occur due to perinatal hypercortisolism and hyperleptinism. With regard to 'small baby syndrome' and the thrifty phenotype hypothesis, we propose that early postnatal overfeeding of underweight newborns may substantially contribute to their long-term risk of obesity and diabetes. In summary, a complex malprogramming of the central regulation of body weight and metabolism may provide a general aetiopathogenetic concept, explaining perinatally acquired disposition to later disease and, thereby, opening a wide field for primary prevention.

Weight gain in the first week of life and overweight in adulthood: a cohort study of European American subjects fed infant formula

BACKGROUND

Successful prevention of obesity and related cardiovascular risk factors requires a clear understanding of its determinants over the life course. Rapid infancy weight gain is associated with childhood obesity, whereas low infancy weight is associated with coronary heart disease. Our aim was to identify during which periods in infancy weight gain is associated with adult obesity.

METHODS AND RESULTS

A cohort of European American formula-fed subjects, measured on 7 occasions during infancy as part of several infant formula studies, were contacted at age 20 to 32 years, when they reported usual adult weight and height. A life-course plot was used to identify critical periods of weight gain associated with adulthood overweight (body mass index > or =25 kg/m2). These associations were tested with logistic regressions. Data were available for 653 subjects (72% of eligible subjects). Approximately 32% of them were overweight adults. The period between birth and age 8 days was identified as potentially critical. After adjustment for important confounding factors, weight gain during the first week of life was associated with adulthood overweight status (OR for each 100-g increase 1.28, 95% CI 1.08 to 1.52), as was weight gain during the first 112 days of life (OR 1.04, 95% CI 1.01 to 1.08). Similar results were obtained after standardization with z scores from a reference population.

CONCLUSIONS

In formula-fed infants, weight gain during the first week of life may be a critical determinant for the development of obesity several decades later. These results contribute to the understanding of chronic disease programming and suggest new approaches to obesity prevention.

'Programming' of orexigenic and anorexigenic hypothalamic neurons in offspring of treated and untreated diabetic mother rats

Exposure to maternal diabetes in utero (GD) may 'program' for obesity. Orexigenic neuropeptides, like neuropeptide Y (NPY) and agouti-related peptide (AGRP), and anorexigenic neuropeptides, like proopiomelanocortin (POMC) and alpha-melanocyte-stimulating hormone (MSH), are decisively involved in body weight regulation. We investigated consequences of GD and its treatment by pancreatic islet transplantation in rats for development of neuropeptidergic neurons in the arcuate hypothalamic nucleus (ARC) in weanling offspring. In GD, islet transplantation on d15 of pregnancy led to normalized blood glucose. Sham-transplanted GD mothers (TSGD) remained hyperglycemic. Twenty-one-day-old TSGD offspring developed hypothalamic 'malorganization'. Despite of normal leptin and insulin levels in TSGD offspring, increased immunopositivity of NPY and AGRP appeared. TSGD offspring showed unchanged POMC, but decreased MSH-immunopositivity. In conclusion, untreated diabetes in pregnant rats leads to 'malprogramming' of hypothalamic neuropeptidergic neurons in offspring, probably contributing to later development of overweight. These acquired alterations are preventable by treatment of maternal GD.

Early dietary intervention: long-term effects on blood pressure, brain neuropeptide Y, and adiposity markers

Early life nutrition impacts on subsequent risk of obesity and hypertension. Several brain chemicals responsible for both feeding and cardiovascular regulation are altered in obesity. We examined effects of early postnatal overnutrition on blood pressure, brain neuropeptide Y (NPY), and adiposity markers. Rat pup litters were adjusted to either 3 or 12 male animals (overnutrition and control, respectively) on day 1 of life. After weaning, rats were given either a palatable high-fat diet or standard chow. Smaller litter pups were significantly heavier by 17 days of age. By 16 wk, the effect of litter size was masked by that of diet, postweaning. Small and normal litter animals fed a high-fat diet had similar increases in body weight, plasma insulin, leptin, and adiponectin concentrations, leptin mRNA, and fat masses relative to chow-fed animals. An increase in 11beta-hydroxysteroid dehydrogenase-1 mRNA in white adipose tissue, and a decrease in uncoupling protein-1 mRNA in brown adipose tissue in both small litter groups at 16 wk of age, may represent a programming effect of the altered litter size. NPY concentration in the paraventricular nucleus of the hypothalamus was reduced in high fat-fed groups. Blood pressure was significantly elevated at 13 wk in high-fat-fed animals. This study demonstrates that overnourishment during early postnatal development leads to profound changes in body weight at weaning, which tended to abate with maturation. Thus the effects of long-term dietary intervention postweaning can override those of litter size-induced obesity.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Function of neuropeptide Y and agouti-related protein at weaning: relation to corticosterone, dietary carbohydrate and body weight

Neuropeptide Y (NPY) and agouti-related protein (AgRP), potent stimulants of feeding, have been linked in adult rats to both corticosterone (CORT) and dietary carbohydrate. To understand the significance of this relationship early in life, measurements were taken of these parameters at different ages around weaning, in rats given a choice of macronutrient diets or maintained on a carbohydrate-rich diet. The results demonstrate that, in both male and female rat pups, the expression and production of NPY and AgRP in the arcuate nucleus (ARC) peak on postnatal day 21 (P21), compared to P15 before weaning and P27 after weaning. These elevated levels of peptide were associated with peak levels of CORT and glucose and also a strong, natural preference for carbohydrate at weaning, which accounted for 55-65% of the pups' total diet. In subgroups defined by their body weight at these stages, rats with as little as 4% lower body weight (compared to higher weight pups) had 30-60% greater expression of NPY and AgRP in the ARC and elevated levels of CORT, with no difference in leptin or insulin. This response was significantly more pronounced at P21 than at P15 or P27. The importance of carbohydrate during this stage was suggested by additional results showing elevated NPY expression, CORT levels, body weight and inguinal fat pad weights in P27 pups raised on a 65% carbohydrate diet vs. 45% carbohydrate. These results suggest that hypothalamic NPY and AgRP, together with CORT, have glucoregulatory as well as feeding stimulatory functions that help mediate the transition from suckling of a fat-rich diet to independent feeding of a carbohydrate-rich diet. During this critical period, the carbohydrate together with the peptides and CORT provide the important signals, including elevated glucose, that promote de novo lipogenesis and enable weanling animals to survive periods of food deprivation.

Impact of early neonatal breast-feeding on psychomotor and neuropsychological development in children of diabetic mothers

OBJECTIVE

In general, breast-feeding positively influences development of psychomotor function and cognition in children. Offspring of diabetic mothers (ODM) have delayed psychomotor and cognitive development. Recently, we observed a dose-dependent negative effect of early neonatal ingestion of breast milk from diabetic mothers (diabetic breast milk [DBM]) on the risk of overweight during early childhood. Here, we investigated the influence of early neonatal intake of DBM on neurodevelopment in ODM.

RESEARCH DESIGN AND METHODS

A total of 242 ODM were evaluated for age of achieving major developmental milestones (Denver Developmental Scale) according to the volume of DBM ingested during the first week of life, using Kruskal-Wallis and Kaplan-Meier analysis.

RESULTS

Children in the upper tertile of early neonatal ingestion of DBM achieved early psychomotor developmental milestones ("lifting head while prone," "following with eyes") earlier than those in lower tertiles (P = 0.002). In contrast, a delay in the onset of speaking was observed in children who had ingested larger volumes of DBM compared with those with lower DBM intake (P = 0.002). This negative impact of DBM ingestion was not confounded by birth characteristics, total milk intake, or socioeconomic/educational status.

CONCLUSIONS

Our data indicate differential effects of early neonatal DBM ingestion on psychomotor and cognitive development. Ingesting larger compared with smaller volumes of DBM may normalize early psychomotor development in ODM but delays onset of speaking as a parameter indicative of cognitive development. This effect may result from qualitative alterations in the composition of DBM. Further studies are urgently recommended on the benefits and harms of breast-feeding in ODM.

Early origins of obesity: programming the appetite regulatory system

There is evidence that changes in perinatal nutrition programme the development of relative fat mass and the regulation of appetite in adult life. These studies have been primarily in the rodent utilizing maternal overnutrition or undernutrition imposed at different stages of pregnancy and beyond, mapping of neuropeptide localization and activity and appropriate null mutant models. Whilst the rodent offers significant advantages in terms of a short gestation and the availability of useful transgenic and null mutant models, there are also advantages to using an animal model more akin to the human, in which all components of the 'fat-brain axis' are present before birth, such as the sheep. This review summarizes recent work on the expression and localization of the 'appetite regulatory' peptides in the fetal rodent and sheep hypothalamus and their potential role in the early programming of postnatal appetite and obesity.

Impact of glucose infusion on the structural and functional characteristics of adipose tissue and on hypothalamic gene expression for appetite regulatory neuropeptides in the sheep fetus during late gestation

In the present study, our aim was to determine whether intrafetal glucose infusion increases fetal adiposity, synthesis and secretion of leptin and regulates gene expression of the 'appetite regulatory' neuropeptides neuropepetide Y (NPY), agouti-related peptide (AGRP), pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) and receptors (leptin receptor (OB-Rb) and melancortin 3 receptor (MC3R)) within the fetal hypothalamus. Glucose (50% dextrose in saline) or saline was infused (7.5 ml h(-1)) into fetal sheep between 130 and 140 days gestation (term = 150 +/- 3 days gestation). Glucose infusion increased circulating glucose and insulin concentrations, mean lipid locule size (532.8 +/- 3.3 microm2 versus 456.7 +/- 14.8 microm2) and total unilocular fat mass (11.7 +/- 0.6 g versus 8.9 +/- 0.6 g) of the perirenal fat depot. The expression of OB-Rb mRNA was higher in the ventromedial nucleus compared to the arcuate nucleus of the hypothalamus in both glucose and saline infused fetuses (F= 8.04; P < 0.01) and there was a positive correlation between expression of OB-Rb and MC3R mRNA in the arcuate nucleus (r= 0.81; P < 0.005). Glucose infusion increased mRNA expression for POMC, but not for the anorectic neuropeptide CART, or the orexigenic neuropeptides NPY and AGRP, in the arcuate nucleus of the fetal hypothalamus. These findings demonstrate that increased circulating glucose and insulin regulate gene expression of the neuropeptides within the fetal hypothalamus that are part of the neural network regulating energy balance in adult life.

Hypothalamic neurons of postnatally overfed, overweight rats respond differentially to corticotropin-releasing hormones

Adult overweight rats previously subjected to early postnatal overnutrition in small litters are hyperphagic, hyperleptinemic and differ in emotional behaviour from rats of control litters. We proved the hypothesis that neurons of the hypothalamic regulatory system of body weight differentially react to peptides of the corticotropin-releasing factor (CRF) family in these overweight rats. Single unit activity was recorded in brain slices. In controls, CRF and the CRF(2) receptor agonist stresscopin-related peptide (SRP) predominantly activated neurons of the dorsomedial part of ventromedial hypothalamic nucleus (VMHDM), but in overweight rats, SRP induced a significant inhibition. Increased neuronal firing to CRF and SRP of the medial parvocellular part of paraventricular hypothalamic nucleus (PaMP) in controls similarly changed to more inhibition in overweight rats. Inhibition of neuronal activity in VMHDM and PaMP can contribute to reduce satiety signals and to decrease energy expenditure in rats. In contrast, medial arcuate (ArcM) neurons of controls were significantly inhibited by SRP, whereas neurons of overweight rats could also be activated. The difference in the expression of these response types was significant. Activation of ArcM neurons known to produce neuropeptide Y can increase food intake. The results are discussed in terms of a trophic action of leptin changing synaptic wiring and the expression of excitatory and inhibitory synapses. The altered responses of hypothalamic neurons in adult small-litter rats may reflect a general mechanism of neurochemical plasticity acquired during the postnatal critical differentiation period, thus leading to permanently altered function of the regulatory system of body weight.

A possible role of neuropeptide Y, agouti-related protein and leptin receptor isoforms in hypothalamic programming by perinatal feeding in the rat

AIM/HYPOTHESIS

Perinatal overfeeding predisposes humans and rats to obesity and diabetes in later life. One classical model for studying the effect of early feeding is manipulation of the size of rat litters. Rats growing up in small litters gain more weight than rats growing up in normal-sized litters. Interestingly, these obese rats maintain this phenotype in adulthood. Conversely, rats raised in large litters show a delay in growth and a decrease in body weight. The aim of this work was to assess the hypothalamic control mechanisms of food intake regulated by perinatal feeding.

METHODS

Leptin levels were analysed using RIA. Leptin receptor mRNA levels were analysed using RT-PCR. Neuropeptide mRNA levels were analysed using in situ hybridisation.

RESULTS

Perinatally overfed neonatal male rats exhibited hyperleptinaemia and a decrease in hypothalamic mRNA levels of the long isoform of the leptin receptor (OB-Rb), explaining their leptin resistance. Moreover, this obese model showed an increase in the mRNA expression of cocaine- and amphetamine-regulated transcript, neuropeptide Y and agouti-related protein in the hypothalamic arcuate nucleus (ARC). In contrast, perinatally underfed neonatal male rats with hypoleptinaemia showed an increase in hypothalamic mRNA of the short isoforms of the leptin receptor. Furthermore, they exhibited an increase in expression of neuropeptide Y and agouti-related protein in the ARC.

CONCLUSIONS/INTERPRETATION

Rats overfed during early postnatal life show a leptin-resistant state mediated by down-regulation of the hypothalamic OB-Rb. These data, together with the increased expression of neuropeptide Y and agouti-related protein in specific neurons in the ARC, might indicate the existence of regulated programming in this nucleus and may provide a new aetiopathogenic concept in susceptibility to obesity.

'Fetal programming' and 'functional teratogenesis': on epigenetic mechanisms and prevention of perinatally acquired lasting health risks

Alterations of the intrauterine and early postnatal nutritional, metabolic, and hormonal environment may cause predispositions to the development of disorders and diseases in later life. Mechanisms responsible for this perinatally acquired 'malprogramming' still remain unclear. It has long been known, however, that hormones are environment-dependent organizers of the developing 'neuroendocrine-immune network', which regulates all fundamental processes of life. When present in nonphysiological concentrations during critical ontogenetic periods, hormones can therefore also act as 'endogenous functional teratogens'. Fetal and neonatal hyperinsulinism is a pathognomic feature in the offspring of diabetic mothers. Perinatal hyperinsulinism also occurs due to early postnatal overfeeding. Data obtained by our group indicate that elevated insulin concentrations during critical periods of perinatal life may induce a lasting 'malprogramming' of neuroendocrine systems regulating body weight, food intake, and metabolism. Similar characteristics may occur due to perinatal hyperleptinism, hypercortisolism etc. Since mechanisms of early 'programming' of obesity, diabetes, and the metabolic syndrome X are unclear, a complex 'neuroendocrine malprogramming' of the regulation of body weight and metabolism may provide a general etiopathogenetic concept in this context, exemplarily revealing critical new implications for chances and challenges of perinatal preventive medicine in the future.

Altered action of dopamine and cholecystokinin on lateral hypothalamic neurons in rats raised under different feeding conditions

Single-unit activity was recorded in the lateral hypothalamus (LH) of adult Wistar rats anaesthetized with urethane. The rats were differently nourished till weaning by raising in small (SL), control (CL) or large litters (LL). They gained significantly different body weight leading to overweight in SL (mean: 428.4 g on day 90) and underweight in LL rats (mean 399.5 g) compared to CLs (414.5 g). The mean basal firing rate of LH neurons differed, it was lowest in SL and highest in LL rats. The proportion of neurons changing their firing rate by more than 30% in response to iontophoretically administered dopamine (DA) was significantly greater in SL (76%) than LL rats (54%). Effects of DA were significantly more often blocked by a D1 receptor antagonist in LL than CLs. The responsiveness to cholecystokinin (CCK) alone and coadministered with DA was also greater in SL than LL. Furthermore, the proportion of neurons inhibited by DA alone and in the presence of CCK was significantly greater in SL than LL rats. In conclusion, litter size and difference in nourishment during early postnatal development of rats seem to determine LH basal firing rate. The increased neuronal responsiveness to exogenous DA and CCK in neonatally overfed SL rats may indicate a decreased activity of these endogenous signals which normally contribute to limitation of energy intake.

Altered responses to orexigenic (AGRP, MCH) and anorexigenic (alpha-MSH, CART) neuropeptides of paraventricular hypothalamic neurons in early postnatally overfed rats

Food intake and energy expenditure are regulated by neuropeptides in the hypothalamus. While cocaine- and amphetamine-regulated transcript (CART) peptide and melanocortins such as alpha-melanocyte-stimulating hormone (alpha-MSH) are anorexigenic and increase energy expenditure, the endogenous melanocortin receptor antagonist agouti gene-related protein (AGRP), melanin-concentrating hormone (MCH) and neuropeptide Y (NPY) are orexigenic, anabolic peptides. Alterations in the regulatory balance may promote excessive weight gain. The action of these peptides on paraventricular hypothalamic neurons was studied in brain slices of overweight, adult rats previously subjected to early postnatal overfeeding in small litters of only three pups per mother, compared to 12 pups per dam in control litters. CART, melanocortins and NPY significantly excited paraventricular neurons of controls, whereas neurons of small-litter rats were mainly inhibited. Inhibition was dominant following administration of AGRP, MCH and NPY. The altered responses of paraventricular neurons in adult small-litter rats might reflect a general mechanism of neurochemical plasticity and 'malprogramming' of hypothalamic neuropeptidergic systems acquired during the postnatal critical differentiation period, thus leading to permanently altered function of these regulatory systems of body weight.

Ontogeny of the hypothalamic neuropeptide Y system

Early onset obesity and type II diabetes is rapidly becoming an epidemic, especially within the United States. This dramatic increase is likely due to many factors including both prenatal and postnatal environmental cues. The purpose of this review is to highlight some of the recent advances in our knowledge of the development of the hypothalamic circuits involved in the regulation of energy balance, with a focus on the neuropeptide Y (NPY) system. Unlike the adult rat, during the postnatal period NPY is transiently expressed in several hypothalamic regions, along with the expected expression within the arcuate nucleus (ARH). These transient populations of NPY neurons during the postnatal period may provide local NPY production to sustain the necessary energy intake during this critical growth phase. This may be physiologically important since ARH-NPY projections do not fully develop until the 3rd postnatal week. The significance of this ontogeny is that many peripheral metabolic signals have little effect of feeding prior to the development of the ARH projections. The essential questions now are whether prenatal and/or postnatal exposure to high levels of insulin or leptin during development can cause permanent changes in the function of hypothalamic circuits. It is vital to understand not only the natural development of the hypothalamic circuits that regulate energy homeostasis, but also their abnormal development caused by maternal and postnatal environmental cues. This will be pivotal for designing intervention and therapeutics to treat early onset obesity/type II diabetes, which may very well need to be different from those designed to prevent/treat adult onset obesity/type II diabetes.

Is breastfeeding protective against child obesity?

Recent studies suggest that breastfeeding reduces the risk of child obesity to a moderate extent. Of 11 studies that examined prevalence of overweight in children older than 3 years of age and that had a sample size of > or = 100 per feeding group, 8 showed a lower risk of overweight in children who had been breastfed, after controlling for potential confounders. The 3 "negative" studies lacked information on the exclusivity of breastfeeding. A dose-response relationship with duration of breastfeeding was observed in some, but not all, of the "positive" studies. Possible mechanisms include learned self-regulation of energy intake, metabolic programming in early life, and residual confounding by parental attributes. If the association is causal, the effect of breastfeeding is probably small compared to other factors that influence child obesity, such as parental overweight. Nonetheless, it may be of public health significance considering the current epidemic of child overweight.

Energy metabolism of young rats after early postnatal overnutrition

Early postnatal overnutrition (PNO) induced by restricting litter size in rats leads to increased body-weight (BW) and body-fat gain in later life. PNO rats are used as an animal model of moderate obesity and early hyperinsulinism. We investigated whether the increased adiposity could be due to a decreased energy expenditure. Male newborn Wistar rats were raised in litters of either two (SL) or twelve pups (NL), weaned at 4 weeks of age and subsequently fed ad libitum. BW was recorded continuously until 12 weeks of age. Daily energy intake, total daily energy expenditure (EE, measured by indirect calorimetry) and body composition were measured in weaned pups at 5, 8 and 12 weeks of age. SL rats displayed increased BW compared with NL rats from week 2 to 5 and again from week 10 to 12. Lean body mass, body fat and protein content and total EE were increased in SL rats at week 5. The same linear correlation described the relationship between BW and total EE in NL and SL rats. At week 8 to 12 no differences in energy metabolism could be found, but the total fat content was increased in SL rats at week 12. Energy balance, i.e. assimilated energy minus EE, was no different between SL and NL at any time that it was measured. We conclude that although PNO rats display increased adiposity in early life, there seem to be no long-lasting effects on energy metabolism in later life, even if a tendency to increased adiposity can still be detected.

Differential response to NPY of PVH and dopamine-responsive VMH neurons in overweight rats

Neuronal responses to neuropeptide Y and dopamine were recorded in brain slices of hypothalamic paraventricular (PVH) and ventromedial (VMH) nuclei in normal and hyperphagic overweight rats reared in small litters of three pups. NPY significantly activated PVH neurons of normal rats, but inhibited neurons of overweight rats. In the VMH, a significantly higher coincidence of inhibition induced by NPY and dopamine was found in overweight rats. Similar neuronal responses were evoked by a NPY Y5 receptor agonist. Effects of NPY could be blocked by a Y1 receptor antagonist. The altered response of PVH neurons to the feeding-inducing NPY and the increased inhibition by NPY and dopamine in the VMH might contribute to the persisting hyperphagia and overweight of postnatally overnourished rats.

Early nutrition and leptin concentrations in later life

BACKGROUND

Formula feeding or overweight in infancy may increase the later risk of obesity, but the mechanisms involved are uncertain. Because obesity is associated with high leptin concentrations relative to fat mass, programming of leptin concentrations may be one mechanism by which early nutrition influences later obesity.

OBJECTIVE

We tested the hypothesis that high nutrient intake or formula feeding in infancy programs greater leptin concentrations relative to fat mass in later life.

DESIGN

Serum leptin concentrations were measured by radioimmunoassay in 197 adolescents aged 13-16 y who were born preterm and randomly assigned at birth to receive either a nutrient-enriched preterm formula or banked donated breast milk (trial 1) or a preterm formula or a standard formula (trial 2). Fat mass was estimated with the use of bioelectrical impedance analysis.

RESULTS

After combining the results of trials 1 and 2 as planned, the ratio of leptin to fat mass was significantly greater in the children who received the preterm formula (geometric : 0.84 microg x L(-1) x kg(-1)) than in those who received standard formula or banked breast milk (0.62 microg x L(-1) x kg(-1); mean difference: 30.8%; 95% CI for difference: 8.4%, 53.2%; P = 0.007). The difference between the diet groups remained significant after adjustment for age, sex, Tanner stage, social class, and fat mass. Human milk intake was significantly associated with lower leptin concentrations relative to fat mass in adolescence (P = 0.023), independent of potential confounding factors.

CONCLUSION

Programming of relative leptin concentrations by early diet may be one mechanism that links early nutrition with later obesity.

Effects of litter size on sympathetic activity in young adult rats

Rearing animals in small litters induces a permanent increase in body weight and body fat. To determine whether changes in sympathoadrenal activity contribute to this effect, litter size was adjusted the day after birth and maintained until weaning at 21 days. Sympathetic nervous system (SNS) activity was measured in adult animals using [(3)H]norepinephrine ([(3)H]NE) turnover in peripheral tissues. Although litter size was without effect on [(3)H]NE turnover in chow-fed animals, acceleration of [(3)H]NE turnover by dietary sucrose was completely abolished in heart and attenuated in interscapular brown adipose tissue and kidney of rats reared in small litters. Body and epididymal fat-pad weights were heavier in rats reared in small litters; however, weight gain in response to dietary enrichment with sucrose did not differ as a function of litter size. Thus litter size alters dietary activation of the SNS, and this effect presumably reflects changes in central nervous system regulation.

Action of CCK and 5-HT on lateral hypothalamic neurons depends on early postnatal nutrition

Wistar rats grown up during the early postnatal life (3-21 days after birth) in artificially built normal, small or large lifters developed a significantly different body weight. This difference persisted also during adulthood when they had free access to food and water. The influence of iontophoretically administered cholecystokinin (CCK8S), serotonin (5-HT) or co-ejection of both on firing of lateral hypothalamic neurons was investigated in adult, urethane anesthetized rats of the three groups. The responsiveness to CCK8S was significantly higher in large- and small-litter rats than in the normal control group. The differences were greater in males than in females. They resulted in the male large-litter group from an increase of excitatory responses, whereas in the male small-litter group the proportion of inhibitory responses was augmented. Co-administration of 5-HT generally reduced the neuronal responsiveness. Especially in the large-litter group excitatory responses were significantly reduced. It may be speculated that the availability of food in the early postnatal life influences the development of the hypothalamic regulatory network in such a way that it stabilizes the high or low food ingestion all the life. At least in males, a changed responsiveness and type of response to cholecystokinin of lateral hypothalamic neurons might be involved in this altered regulation.

Novel expression of neuropeptide Y (NPY) mRNA in hypothalamic regions during development: region-specific effects of maternal deprivation on NPY and Agouti-related protein mRNA

During development there is novel expression of NPY mRNA in the dorsomedial hypothalamic nucleus (DMH) and perifornical region (PFR), in addition to the arcuate nucleus (ARH). Furthermore, NPY mRNA levels peak in all regions on postnatal d 16 (P16) and decrease to adult levels by P30. The purpose of the present study was to determine whether NPY and agouti-related protein (AGRP) mRNA expression in the different hypothalamic regions on P11 and P16 are similarly affected by fasting. An examination of the full rostral to caudal extent of the hypothalamus revealed two additional regions displaying novel NPY mRNA expression, the parvocellular division of the paraventricular nucleus (PVH) and lateral hypothalamus (LH). Maternal deprivation for 36 h, used to bring about a fast, similarly increased (23-29%) NPY and AGRP mRNA expression in the ARH on P11 and P16. In contrast, NPY expression in the DMH and PFR were significantly decreased (19-30% and 48-53%, respectively), whereas NPY mRNA levels in the PVH and LH were not altered by this treatment. The increase in NPY and AGRP mRNA expression in the ARH in response to maternal deprivation suggests that these neuronal populations respond to signals of energy balance. In contrast, NPY expression in the DMH, PFR, PVH, and LH is differentially regulated by maternal deprivation or other factors associated with maternal separation.

The effect of leptin treatment on the development of obesity in overfed suckling Wistar rats

OBJECTIVE

To identify the role of hyperleptinaemia in mediating the effects of early postnatal overfeeding in a rat strain known to be prone to manipulations of the early environment which result in predispositions for obesity and associated metabolic and cardiovascular disturbance in later life.

DESIGN

Wistar rats were reared in normal litters (NL, 10--12 pups) or small litters (SL, four pups) from postnatal day 3 and killed for determination of body composition and plasma leptin and insulin concentrations on day 7 or day 21 after having been treated with recombinant leptin (2 x 50 (pmol/g)/day) or saline from day 1.

RESULTS

Rearing in SL doubled the body fat content and plasma leptin levels in comparison to NL pups by 21 days of age. Under leptin-treatment throughout suckling age, NL pups remained leptin responsive, ie the difference in body fat content was progressively reduced relative to the controls. Until 7 days of age, despite the body fat content of untreated SL pups being 2-fold higher and their plasma leptin level 7-fold higher than that of NL pups, leptin treatment caused the same percentage decreases in body fat in SL than in NL pups. But in contrast to NL pups, the SL pups became leptin resistant thereafter. Plasma insulin levels in 7-day-old leptin-treated SL pups were 3-fold higher than in untreated littermates and 5-fold higher than in the NL groups.

CONCLUSION

Prophylactic leptin treatment does not prevent hyperinsulinaemia and excessive fat deposition in SL pups. On the other hand, selective hyperleptinaemia during suckling age does not trigger leptin resistance and obesity in NL pups. Rather than hyperleptinaemia per se, other factors associated with early postnatal overnutrition, for example, the concurrent hyperinsulinaemia, seem to play a pivotal role for the development of leptin-resistance and life-long obesity risk in SL rats.

Leptin responsiveness of juvenile rats: proof of leptin function within the physiological range

To bridge the gap between studies demonstrating leptin's role in protecting fat stores when food is scarce and other studies demonstrating the effects of treatment with leptin at doses that increase plasma levels to values found in overfed animals, we investigated whether leptin serves an adipostatic function within the normal range of free-feeding lean animals, i.e. within the very small range of endogenous plasma levels at which no leptin resistance occurs. For this purpose we applied recombinant leptin via mini-osmotic pumps to rats between 15 and 24 days of age and between 25 and 34 days of age and studied its dose-dependent effects on body mass and fat mass at plasma leptin concentrations extending down to the normal levels in lean animals. Using percentage change of fat mass (relative to that of saline-treated littermates) as the measure, a linear dose-response curve was found up to doses of 2 microg g(-1) day(-1), corresponding to plasma leptin concentrations between the normal physiological range and 50 ng ml(-1). In 15- to 24-day-old animals, analysis of the correlation (r = -0.89) between individual plasma concentrations and the corresponding leptin-induced changes of body fat content for a range extending down towards zero (i.e. towards the average fat content of the controls) yielded a zero value of 3.1 ng ml(-1), which was within the 2-4 ng ml(-1) range of plasma leptin concentrations found in the control pups. Likewise, regression analysis for the data from the 25- to 34-day-old pups (r = -0.88), for which the control range was 1-3 ng ml(-1), yielded a zero value of 1.9 ng ml(-1). We conclude that normal plasma leptin levels represent an adipostatic signal. Steady-state levels of plasma leptin in free-feeding lean animals thus provide a signal not only for protecting sufficiency but also for limiting increases of body fat stores.

Effects of intrauterine and early postnatal growth restriction on hypothalamic somatostatin gene expression in the rat

In the human, intrauterine growth retardation (IUGR) can result in persistent postnatal growth failure, which may be attributable, in part, to abnormal GH secretion. Whether putative alterations in GH secretion are the result of abnormalities intrinsic to the pituitary or reflect changes in the production of GH-releasing hormone or somatostatin (SS) is unknown. We tested the hypothesis that growth failure associated with IUGR or early postnatal food restriction (FR) is caused by a central defect in hypothalamic SS gene expression. Both models displayed persistent growth failure postnatally without any catch-up growth. We measured levels of SS mRNA levels in rats experimentally subjected to IUGR or FR. SS mRNA levels were measured by semiquantitative in situ hybridization throughout development. Levels of SS mRNA in the periventricular nucleus were significantly higher in both male and female IUGR rats in the juvenile and adult stages compared with matched controls (p < or = 0.05). FR was associated with higher SS mRNA levels only in neonatal female rats (p < or = 0.05). These results suggest that intrauterine malnutrition induces a persistent increase in the expression of SS mRNA in the periventricular nucleus, whereas early postnatal FR results in only a transient increase in SS gene expression. Because IGF-I levels were normal in juvenile IUGR and FR rats, central dysregulation of SS neurons does not appear to be the cause of early postnatal growth failure in either model. However, these observations are consistent with the hypothesis that nutritional stress at critical times during development can have persistent and potentially irreversible effects on organ function.