Postnatal regulation of hypothalamic neuropeptide expression by leptin: implications for energy balance and body weight regulation

Maturational effect of leptin on CO2 chemosensitivity in newborn rats

BACKGROUND

Leptin augments central CO2 chemosensitivity and stabilizes breathing in adults. Premature infants have unstable breathing and low leptin levels. Leptin receptors are on CO2 sensitive neurons in the Nucleus Tractus Solitarius (NTS) and locus coeruleus (LC). We hypothesized that exogenous leptin improves hypercapnic respiratory response in newborn rats by improving central CO2 chemosensitivity.

METHODS

In rats at postnatal day (p)4 and p21, hyperoxic and hypercapnic ventilatory responses, and pSTAT and SOCS3 protein expression in the hypothalamus, NTS and LC were measured before and after treatment with exogenous leptin (6 µg/g).

RESULTS

Exogenous leptin increased the hypercapnic response in p21 but not in p4 rats (P ≤ 0.001). At p4, leptin increased pSTAT expression only in the LC, and SOCS3 expression in the NTS and LC; while at p21 pSTAT and SOCS3 levels were higher in the hypothalamus, NTS, and LC (P ≤ 0.05).

CONCLUSIONS

We describe the developmental profile of the effect of exogenous leptin on CO2 chemosensitivity. Exogenous leptin does not augment central CO2 sensitivity during the first week of life in newborn rats. The translational implication of these findings is that low plasma leptin levels in premature infants may not be contributing to respiratory instability.

IMPACT

Exogenous leptin does not augment CO2 sensitivity during the first week of life in newborn rats, similar to the developmental period when feeding behavior is resistant to leptin. Exogenous leptin increases CO2 chemosensitivity in newborn rats after the 3rd week of life and upregulates the expression of pSTAT and SOC3 in the hypothalamus, NTS and LC. Low plasma leptin levels in premature infants are unlikely contributors to respiratory instability via decreased CO2 sensitivity in premature infants. Thus, it is highly unlikely that exogenous leptin would alter this response.

Perinatal exposure to tributyltin affects feeding behavior and expression of hypothalamic neuropeptide Y in the paraventricular nucleus of adult mice

Organotins such as tributyltin chloride (TBT), are highly diffused environmental pollutants, which act as metabolism disrupting chemicals, i.e. may interfere with fat tissue differentiation, as well as with neuroendocrine circuits, thus impairing the control of energetic balance. We have previously demonstrated that adult exposure to TBT altered the expression of neuropeptides in the hypothalamus. In this study, we orally administered daily a solution containing oil, or TBT (0.25, 2.5, or 25 μg/kg body weight/day) to pregnant females from gestational day 8 until birth, and to their pups from day 0 until post-natal day 21. Our results showed that TBT exposure of female mice during gestation and of pups during lactation permanently altered the feeding efficiency of pups of both sexes and subcutaneous fat distribution in adult males. In addition, the neuropeptide Y system was affected at the level of the paraventricular nucleus, with a decrease in immunoreactivity in both sexes (significant in females for all TBT doses and in males only for intermediate TBT doses), while no effect was observed in other hypothalamic areas (arcuate, ventromedial and dorsomedial nuclei). Metabolic syndrome, as well as obesity and diabetes, which are significant health issues, are considered multifactorial diseases and may be caused by exposure to metabolic disruptors, both in adults and during perinatal life. In addition, our work indicates that TBT doses defined as the tolerably daily intake had a profound and sex-specific long-term effect.

Developmental programming of hypothalamic melanocortin circuits

The melanocortin system plays a critical role in the central regulation of food intake and energy balance. This system consists of neurons producing pro-opiomelanocortin (POMC), melanocortin receptors (MC4Rs), and the endogenous antagonist agouti-related peptide (AgRP). Pomc and Mc4r deficiency in rodents and humans causes early onset of obesity, whereas a loss of Agrp function is associated with leanness. Accumulating evidence shows that many chronic diseases, including obesity, might originate during early life. The melanocortin system develops during a relatively long period beginning during embryonic life with the birth of POMC and AgRP neurons and continuing postnatally with the assembly of their neuronal circuitry. The development of the melanocortin system requires the tight temporal regulation of molecular factors, such as transcription factors and axon guidance molecules, and cellular mechanisms, such as autophagy. It also involves a complex interplay of endocrine and nutritional factors. The disruption of one or more of these developmental factors can lead to abnormal maturation and function of the melanocortin system and has profound metabolic consequences later in life.

Neonatal leptin antagonism improves metabolic programming of postnatally overnourished mice

BACKGROUND/OBJECTIVES

Alteration of the perinatal nutritional environment is an important risk factor for the development of metabolic diseases in later life. The hormone leptin plays a critical role in growth and development. Previous studies reported that postnatal overnutrition increases leptin secretion during the pre-weaning period. However, a direct link between leptin, neonatal overnutrition, and lifelong metabolic regulation has not been investigated.

METHODS

We used the small litter mouse model combined with neonatal leptin antagonist injections to examine whether attenuating leptin during early life improves lifelong metabolic regulation in postnatally overnourished mice.

RESULTS

Postnatally overnourished mice displayed rapid weight gain during lactation and remained overweight as adults. These mice also showed increased adiposity and perturbations in glucose homeostasis in adulthood. Neonatal administration of a leptin antagonist normalized fat mass and insulin sensitivity in postnatally overnourished mice. These metabolic improvements were associated with enhanced sensitivity of hypothalamic neurons to leptin.

CONCLUSIONS

Early postnatal overnutrition causes metabolic alterations that can be permanently attenuated with the administration of a leptin antagonist during a restricted developmental window.

Amylin and Leptin interaction: Role During Pregnancy, Lactation and Neonatal Development

Amylin is co-secreted with insulin by pancreatic β-cells in response to a meal and produced by neurons in discrete hypothalamic brain areas. Leptin is proportionally secreted by the adipose tissue. Both hormones control food intake and energy homeostasis post-weaning in rodents. While amylin's main site of action is located in the area postrema (AP) and leptin's is located in the mediobasal hypothalamus, both hormones can also influence the other's signaling pathway; amylin has been shown enhance hypothalamic leptin signaling, and amylin signaling in the AP may rely on functional leptin receptors to modulate its effects. These two hormones also play major roles during other life periods. During pregnancy, leptin levels rise as a result of an increase in fat depot resulting in gestational leptin-resistance to prepare the maternal body for the metabolic needs during fetal development. The role of amylin is far less studied during pregnancy and lactation, though amylin levels seem to be elevated during pregnancy relative to insulin. Whether amylin and leptin interact during pregnancy and lactation remains to be assessed. Lastly, during brain development, amylin and leptin are major regulators of cell birth during embryogenesis and act as neurotrophic factors in the neonatal period. This review will highlight the role of amylin and leptin, and their possible interaction, during these dynamic time periods of pregnancy, lactation, and early development.

A new action of peptide hormones for survival in a low-nutrient environment

Malnutrition occurs when nutrient intake is too low for any reason and occurs regardless of gender or age. Therefore, besides loss of eating or digestive functionality due to illness, malnutrition can occur when a healthy individual undergoes an extreme diet and biases their nutrition, or when athletes exerts more energy than they can replenish through food. It has recently been reported that in Japan, the mortality rate of leaner individuals is equal to or higher than that of obese people. It is important to understand what homeostatic maintenance mechanism is behind this when the body is under hypotrophic conditions. Such mechanisms are generally endocranially controlled. We address this fundamental concern in this paper by focusing on peptide hormones. We introduce a mechanism for survival in a malnourished state via the regulation of food intake and temperature. Additionally, we will discuss the latest findings and future prospects for research on changes in the endocrine environment associated with malnutrition associated with exercise. We also review changes in next-generation endocrine environments when caused by malnutrition brought on by dieting.

Feeding circuit development and early-life influences on future feeding behaviour

A wide range of maternal exposures - undernutrition, obesity, diabetes, stress and infection - are associated with an increased risk of metabolic disease in offspring. Developmental influences can cause persistent structural changes in hypothalamic circuits regulating food intake in the service of energy balance. The physiological relevance of these alterations has been called into question because maternal impacts on daily caloric intake do not persist to adulthood. Recent behavioural and epidemiological studies in humans provide evidence that the relative contribution of appetitive traits related to satiety, reward and the emotional aspects of food intake regulation changes across the lifespan. This Opinion article outlines a neurodevelopmental framework to explore the possibility that crosstalk between developing circuits regulating different modalities of food intake shapes future behavioural responses to environmental challenges.

The undeveloped properties of GABA neurons in the ventral tegmental area promote energy intake for growth in juvenile rats

Juvenile animals show higher energy intake (EI) per body weight (BW) to meet the energy requirements for growth. However, the underlying mechanisms that induce high EI/BW in juvenile animals remain unknown. The EI from a control diet (CD) and high fat diet (HFD), as well as BW changes were compared between juvenile (3 weeks old) and adult (8 weeks old) rats. BW gain and EI were increased in the HFD-fed adult rats compared to the CD-fed adult rats. However, in the juvenile rats, there were no differences in BW gain and EI between the CD-fed and HFD-fed groups. The locomotor activity was significantly increased in HFD group compared with the CD group in juvenile, but not in adult rats. Gamma-aminobutyric acid (GABA) neurons in the VTA were found to remain undeveloped with less GABAergic input into dopamine neurons in the juvenile rats. The deletion of the VTA GABA neurons in the adult rats significantly increased CD consumption, but showed almost no change in HFD consumption. These data suggest that undeveloped properties of VTA GABA neurons in juvenile rats can promote higher EI regardless of high or less palatable feeding, and contribute to growth promotion.

DESACYLATED GHRELIN AND LEPTIN IN THE CORD BLOOD OF SMALL-FOR-GESTATIONAL-AGE NEWBORNS WITH INTRAUTERINE GROWTH RESTRICTION

Context

Ghrelin, in both its acylated and desacylated forms, and leptin can modulate fetal energy balance and development.

Objective

The aim of our study is to assess desacylated ghrelin (DAG) and leptin values and influence on intrauterine and postnatal growth in infants with intrauterine growth restriction.

Design subjects and methods

We performed a prospective study on 39 infants recruited over five months, 20 appropriate - for - gestational - age (AGA) infants and 19 small-for-gestational-age (SGA) infants, in which we measured DAG and leptin in the umbilical cord blood and we compared their respective values between the two groups, along with auxological parameters at birth and at 10 months of postnatal age.

Results

Our results show that both DAG and leptin have lower values in SGA infants and correlate with most of the anthropometrical parameters at birth. Both hormones correlate with weight at 10 months in SGA infants, but this correlation lacks in AGA infants. Whereas DAG in the cord blood can be considered a predictor for weight at 10 months (β=0.207, p=0.001), the same cannot be stated about leptin (β=0.078, p=0.195).

Conclusion

DAG and leptin are involved in both intrauterine and postnatal development, but the extent of their role is still to be determined.

Wired for eating: how is an active feeding circuitry established in the postnatal brain?

From birth, mammals have to find food and maximize caloric intake to ensure growth and survival. Suckling must be initiated quickly after birth and then maintained and controlled until weaning. It is a complex process involving interactions between sensory and motor neuronal pathways. Meanwhile, the control of food intake and energy homeostasis is progressively established via the development of hypothalamic circuits. The development of these circuits is influenced by hormonal and nutritional signals and can be disturbed in a variety of developmental disorders leading to long-term metabolic, behavioral and cognitive dysfunctions. This review summarizes our current knowledge of the neuronal circuits involved in early postnatal feeding processes.

Hormonal and nutritional regulation of postnatal hypothalamic development

The hypothalamus is a key centre for regulation of vital physiological functions, such as appetite, stress responsiveness and reproduction. Development of the different hypothalamic nuclei and its major neuronal populations begins prenatally in both altricial and precocial species, with the fine tuning of neuronal connectivity and attainment of adult function established postnatally and maintained throughout adult life. The perinatal period is highly susceptible to environmental insults that, by disrupting critical developmental processes, can set the tone for the establishment of adult functionality. Here, we review the most recent knowledge regarding the major postnatal milestones in the development of metabolic, stress and reproductive hypothalamic circuitries, in the rodent, with a particular focus on perinatal programming of these circuitries by hormonal and nutritional influences. We also review the evidence for the continuous development of the hypothalamus in the adult brain, through changes in neurogenesis, synaptogenesis and epigenetic modifications. This degree of plasticity has encouraging implications for the ability of the hypothalamus to at least partially reverse the effects of perinatal mal-programming.

Amylin Selectively Signals Onto POMC Neurons in the Arcuate Nucleus of the Hypothalamus

Amylin phosphorylates ERK (p-ERK) in the area postrema to reduce eating and synergizes with leptin to phosphorylate STAT3 in the arcuate (ARC) and ventromedial (VMN) hypothalamic nuclei to reduce food intake and body weight. The current studies assessed potential amylin and amylin-leptin ARC/VMN interactions on ERK signaling and their roles in postnatal hypothalamic pathway development. In amylin knockout mice, the density of agouti-related protein (AgRP)-immunoreactive (IR) fibers in the hypothalamic paraventricular nucleus (PVN) was increased, while the density of α-melanocyte-stimulating hormone (αMSH) fibers was decreased. In mice deficient of the amylin receptor components RAMP1/3, both AgRP and αMSH-IR fiber densities were decreased, while only αMSH-IR fiber density was decreased in rats injected neonatally in the ARC/VMN with an adeno-associated virus short hairpin RNA against the amylin core receptor. Amylin induced p-ERK in ARC neurons, 60% of which was present in POMC-expressing neurons, with none in NPY neurons. An amylin-leptin interaction was shown by an additive effect on ARC ERK signaling in neonatal rats and a 44% decrease in amylin-induced p-ERK in the ARC of leptin receptor-deficient and of ob/ob mice. Together, these results suggest that amylin directly acts, through a p-ERK-mediated process, on POMC neurons to enhance ARC-PVN αMSH pathway development.

Cocaine inhibits leptin-induced increase of the cocaine- and amphetamine-regulated transcript peptide in the nucleus accumbens in rats

Two well-known appetite-regulatory peptides, leptin and cocaine- and amphetamine-regulated transcript (CART), are known to be involved in the brain rewarding pathway. However, it is not yet known how they interact in the nucleus accumbens, an important region mediating the rewarding effects of drugs of abuse. Using the immunoassay method, we found that a microinjection of leptin into the nucleus accumbens core induces an immediate and transient increase of the CART peptide in this site, whereas these effects were inhibited by cocaine. These results expand the role of accumbal leptin to the regulation of the CART peptide and further suggest that possible interaction of these appetite-regulating peptides may be involved in cocaine-mediated rewarding effects.

Food Intake and Core Body Temperature of Pups and Adults in a db Mouse Line Deficient in the Long Form of the Leptin Receptor without Misty Mutation

Different involvement of leptin signaling in food intake (FI) and body temperature (BT) in pups and adults has been suggested. However, the leptin receptor (Lepr) long-form-deficient (db) mouse line has not been fully examined in pups. In the most available db mouse line, wild-type (WT) mice have a mutation in the dedicator of cytokinesis 7 gene, named misty, which was recently revealed to be involved in neuronal development. Therefore, we established a line of db mice without the misty mutation using natural mating. Adult (8 weeks of age) homozygous db/db mice displayed significantly higher core body weight (BW) and FI and significantly lower core BT than WT mice. However, postnatal (2 weeks of age) db/db mice displayed similar BW and milk intake and significantly lower core BT than WT mice. Correspondingly, adult and postnatal db/db mice exhibited altered mRNA levels of hypothalamic orexigenic and anorexigenic peptide in adults but not in pups. Additionally, db/db mice displayed significantly lower mRNA levels of brown adipose tissue uncoupling protein 1 at both ages. In conclusion, the db mouse line without the misty mutation clearly showed the different involvements of the Lepr long form in FI and BT in pups and adults.

Ghrelin and hypothalamic NPY/AgRP expression in mice are affected by chronic early-life stress exposure in a sex-specific manner

Early-life stress (ES) is a risk factor for metabolic disorders (e.g. obesity) with a notoriously higher prevalence in women compared to men. However, mechanisms underlying these effects remain elusive. The development of the hypothalamic feeding and metabolic regulatory circuits occurs mostly in the early sensitive postnatal phase in rodents and is tightly regulated by the metabolic hormones leptin and ghrelin. We have previously demonstrated that chronic ES reduces circulating leptin and alters adipose tissue metabolism early and later in life similarly in both sexes. However, it is unknown whether chronic ES might also affect developmental ghrelin and insulin levels, and if it induces changes in hypothalamic feeding circuits, possibly in a sex-dependent manner. We here show that chronic ES, in the form of exposure to limited nesting and bedding material from postnatal day (P)2 to P9 in mice, affects ghrelin levels differently, depending on the form of ghrelin (acylated vs desacylated), on age (P9 vs P14) and on sex, while insulin levels were similarly increased in both sexes after ES at P9. Even though ghrelin levels were more strongly affected in ES-exposed females, hypothalamic neuropeptide Y (NPY) and agouti-related peptide (AgRP) fiber density at P14 were similarly altered in both sexes by ES. In the paraventricular nucleus of the hypothalamus, both NPY and AgRP fiber density were increased, while in the arcuate nucleus of the hypothalamus, NPY was increased and AgRP unaltered. Additionally, the hypothalamic mRNA expression of ghrelin's receptor (i.e. growth hormone secretagogue receptor) was not affected by ES. Taken together, the specific alterations found in these important regulatory circuits after ES might contribute to an altered energy balance and feeding behavior in adulthood and thereby to an increased vulnerability to develop metabolic disorders.

Long-lived weight-reduced αMUPA mice show higher and longer maternal-dependent postnatal leptin surge

We investigated whether long-lived weight-reduced αMUPA mice differ from their wild types in postnatal body composition and leptin level, and whether these differences are affected by maternal-borne factors. Newborn αMUPA and wild type mice had similar body weight and composition up to the third postnatal week, after which αMUPA mice maintained lower body weight due to lower fat-free mass. Both strains showed a surge in leptin levels at the second postnatal week, initiating earlier in αMUPA mice, rising higher and lasting longer than in the wild types, mainly in females. Leptin level in dams' serum and breast milk, and in their pup's stomach content were also higher in αMUPA than in the WT during the surge peak. Leptin surge preceded the strain divergence in body weight, and was associated with an age-dependent decrease in the leptin:fat mass ratio-suggesting that postnatal sex and strain differences in leptin ontogeny are strongly influenced by processes independent of fat mass, such as production and secretion, and possibly outside fat tissues. Dam removal elevated corticosterone level in female pups from both strains similarly, yet mitigated the leptin surge only in αMUPA-eliminating the strain differences in leptin levels. Overall, our results indicate that αMUPA's postnatal leptin surge is more pronounced than in the wild type, more sensitive to maternal deprivation, less related to pup's total adiposity, and is associated with a lower post-weaning fat-free mass. These strain-related postnatal differences may be related to αMUPA's higher milk-borne leptin levels. Thus, our results support the use of αMUPA mice in future studies aimed to explore the relationship between maternal (i.e. milk-borne) factors, postnatal leptin levels, and post-weaning body composition and energy homeostasis.

Obesity Pathogenesis: An Endocrine Society Scientific Statement

Obesity is among the most common and costly chronic disorders worldwide. Estimates suggest that in the United States obesity affects one-third of adults, accounts for up to one-third of total mortality, is concentrated among lower income groups, and increasingly affects children as well as adults. A lack of effective options for long-term weight reduction magnifies the enormity of this problem; individuals who successfully complete behavioral and dietary weight-loss programs eventually regain most of the lost weight. We included evidence from basic science, clinical, and epidemiological literature to assess current knowledge regarding mechanisms underlying excess body-fat accumulation, the biological defense of excess fat mass, and the tendency for lost weight to be regained. A major area of emphasis is the science of energy homeostasis, the biological process that maintains weight stability by actively matching energy intake to energy expenditure over time. Growing evidence suggests that obesity is a disorder of the energy homeostasis system, rather than simply arising from the passive accumulation of excess weight. We need to elucidate the mechanisms underlying this "upward setting" or "resetting" of the defended level of body-fat mass, whether inherited or acquired. The ongoing study of how genetic, developmental, and environmental forces affect the energy homeostasis system will help us better understand these mechanisms and are therefore a major focus of this statement. The scientific goal is to elucidate obesity pathogenesis so as to better inform treatment, public policy, advocacy, and awareness of obesity in ways that ultimately diminish its public health and economic consequences.

Hypothalamic effects of neonatal diet: reversible and only partially leptin dependent

Early life diet influences metabolic programming, increasing the risk for long-lasting metabolic ill health. Neonatally overfed rats have an early increase in leptin that is maintained long term and is associated with a corresponding elevation in body weight. However, the immediate and long-term effects of neonatal overfeeding on hypothalamic anorexigenic pro-opiomelanocortin (POMC) and orexigenic agouti-related peptide (AgRP)/neuropeptide Y (NPY) circuitry, and if these are directly mediated by leptin, have not yet been examined. Here, we examined the effects of neonatal overfeeding on leptin-mediated development of hypothalamic POMC and AgRP/NPY neurons and whether these effects can be normalised by neonatal leptin antagonism in male Wistar rats. Neonatal overfeeding led to an acute (neonatal) resistance of hypothalamic neurons to exogenous leptin, but this leptin resistance was resolved by adulthood. While there were no effects of neonatal overfeeding on POMC immunoreactivity in neonates or adults, the neonatal overfeeding-induced early increase in arcuate nucleus (ARC) AgRP/NPY fibres was reversed by adulthood so that neonatally overfed adults had reduced NPY immunoreactivity in the ARC compared with controls, with no further differences in AgRP immunoreactivity. Short-term neonatal leptin antagonism did not reverse the excess body weight or hyperleptinaemia in the neonatally overfed, suggesting factors other than leptin may also contribute to the phenotype. Our findings show that changes in the availability of leptin during early life period influence the development of hypothalamic connectivity short term, but this is partly resolved by adulthood indicating an adaptation to the metabolic mal-programming effects of neonatal overfeeding.

Hyperleptinemia in Neonatally Overfed Female Rats Does Not Dysregulate Feeding Circuitry

Neonatal overfeeding during the first weeks of life in male rats is associated with a disruption in the peripheral and central leptin systems. Neonatally overfed male rats have increased circulating leptin in the first 2 weeks of life, which corresponds to an increase in body weight compared to normally fed counterparts. These effects are associated with a short-term disruption in the connectivity of neuropeptide Y (NPY), agouti-related peptide (AgRP), and pro-opiomelanocortin (POMC) neurons within the regions of the hypothalamus responsible for control of energy balance and food intake. Female rats that are overfed during the first weeks of their life experience similar changes in circulating leptin levels as well as in their body weight. However, it has not yet been studied whether these metabolic changes are associated with the same central effects as observed in males. Here, we hypothesized that hyperleptinemia associated with neonatal overfeeding would lead to changes in central feeding circuitry in females as it does in males. We assessed hypothalamic NPY, AgRP, and POMC gene expression and immunoreactivity at 7, 12, or 14 days of age, as well as neuronal activation in response to exogenous leptin in neonatally overfed and control female rats. Neonatally overfed female rats were hyperleptinemic and were heavier than controls. However, these metabolic changes were not mirrored centrally by changes in hypothalamic NPY, AGRP, and POMC fiber density. These findings are suggestive of sex differences in the effects of neonatal overfeeding and of differences in the ability of the female and male central systems to respond to changes in the early life nutritional environment.

Diet-induced obesity and prenatal undernutrition lead to differential neuroendocrine gene expression in the hypothalamic arcuate nuclei

Previously we reported that prenatal undernutrition (UN) leads to a dysregulation of appetite suppression through alterations in hypothalamic neuropeptide gene expression. In the current study, we expand our observations and investigate neuroendocrine transcriptional responses and central leptin sensitivity within the arcuate nucleus of rats exposed to prenatal UN or a postnatal high-fat diet (HF). Pregnant Wistar rats were fed a standard chow diet either ad libitum (AD) or at 30 % of AD intake throughout gestation (UN) resulting in either control or intrauterine growth-restricted female offspring. At weaning, AD offspring were fed either a chow (C) or a HF (30 % fat wt/wt) diet ad libitum for the remainder of the study, whereas UN offspring were fed a chow diet only. At ~142 days, AD and UN offspring received either recombinant rat leptin (L) or saline (S) subcutaneously for 14 days. Prenatal UN had a significant effect on hypothalamic NPY (P < 0.0001), AgRP (P < 0.01) and ObRb (P < 0.02) mRNA expression compared to AD chow-fed offspring. A postnatal HF diet had a significant effect on AgRP mRNA expression (P < 0.001), compared to AD chow-fed offspring, but no effect on NPY and ObRb expression. Leptin treatment, in both UN and HF offspring, was ineffective in reducing NPY and AgRP mRNA expression, and had no effect on ObRb expression. These findings suggest that prenatal UN and a postnatal HF diet lead to differential neuroendocrine gene expression in the hypothalamic arcuate nuclei and reduced sensitivity to leptin's anorexigenic effects.

In Utero Development of Fetal Thirst and Appetite: Potential for Programming

Thirst and appetite-mediated ingestive behavior develop and are likely programmed in utero, thus preparing for newborn and adult ingestive behavior. Fetal swallowing activity is markedly different from that of the adult, as spontaneous fetal swallowing occurs at a markedly (six-fold) higher rate compared with spontaneous adult drinking activity. This high rate of fetal swallowing is critical for the regulation of amniotic fluid volume and the development of the fetal gastrointestinal tract. Disordered fetal swallowing has been associated with both a decrease (oligohydramnios) and increase (polyhydramnios) in amniotic fluid volume. Both conditions are associated with a significant increase in perinatal morbidity and mortality, and limited treatment modalities are currently available. The mechanisms underlying the high rate of human fetal swallowing are regulated, in part, by tonic activity of central angiotensin II, glutamate N-methyl-D-aspartate receptors, and neuronal nitric oxide synthase. Fetal hypertonicity-mediated dipsogenesis is likely programmed in utero, as offspring of water-restricted ewes demonstrate a programmed syndrome of plasma hypertonicity, with significant hematologic and cardiovascular alterations. Similar to dipsogenic mechanisms, peripheral and central fetal orexic mechanisms also develop in utero, as demonstrated by increased fetal swallowing after both oral sucrose infusion and central injection of neuropeptide Y. The role of leptin in regulating fetal ingestive behavior is interesting because, contrary to actions in adults, leptin does not suppress fetal ingestive behavior. Teleologically, this may be of value during the newborn period, as unopposed appetite stimulatory mechanisms may facilitate rapid fetal and newborn weight gain. An adverse intrauterine environment, with altered fetal orexic factors during the critical developmental period of fetal life, may alter the normal setpoints of appetitive behavior and potentially lead to programming of adulthood hyperphagia and obesity. Further research is needed to delineate the mechanistic relationship between the intrauterine environment and the development of the setpoints of adult appetite and thirst.

Orexigenic Gene Expression in Late Gestation Ovine Foetal Hypothalamus is Sensitive to Maternal Undernutrition and Realimentation

Adverse nutritional effects on developing foetal hypothalamic appetitive pathways may contribute to programmed hyperphagia and obesity in intra-uterine growth-restricted, low birth weight offspring. In the present study, for the first time, hypothalamic gene expression for primary orexigenic and anorexigenic genes was examined in late gestation ovine foetuses (130 days; term=145 days) whose mothers were undernourished (UN) or well-nourished (C) throughout pregnancy, or transferred from UN to C on day 90 (UN-C). Pregnancies resulted from singleton embryo transfer into adolescent growing ewes. Body weight, carcass fat content and perirenal adipose tissue (PAT) mass were all lower for UN (n=9) than C (n=7) and intermediate for UN-C foetuses (n=6), with no effect of sex. PAT leptin gene expression (by the reverse transcriptase-polymerase chain reaction) was lower in UN than C and UN-C groups, and lower in males than females. Gene expression (by in situ hybridisation with radiolabelled riboprobes) in the arcuate nucleus was greater in UN than C foetuses for neuropeptide Y (NPY), agouti-related peptide (AGRP) and leptin receptor (OBRb) but not different for pro-opiomelanocortin and cocaine- and amphetamine-regulated transcript. Gene expression in UN-C foetuses was intermediate for NPY and AGRP and not different from C foetuses for OBRb. Gene expression for NPY, AGRP and OBRb correlated negatively with foetal carcass fat content and with PAT leptin gene expression across all groups. Males had greater mRNA expression for AGRP than females, with NPY and OBRb showing similar trends. Therefore, maternal undernutrition throughout pregnancy increased orexigenic gene expression in the late gestation foetal hypothalamus, and expression levels were largely normalised by improved maternal nutrition in the last third of pregnancy. These findings may have implications for avoiding or correcting prenatal programming of postnatal hyperphagia and obesity.

Developmental influences on circuits programming susceptibility to obesity

Suboptimal maternal nutrition exerts lasting impacts on obesity risk in offspring, but the direction of the effect is determined by the timing of exposure. While maternal undernutrition in early pregnancy is associated with increased body mass index, in later pregnancy it can be protective. The importance of the timing of maternal undernutrition is also observed in rodents, however, many of the processes that occur in the last trimester of human gestation are delayed to the postnatal period. Neonatal leptin administration exerts lasting impacts on susceptibility to obesity in rodents. Although leptin can influence the formation of hypothalamic circuits involved in homeostatic control of feeding during the postnatal period, these effects are too late to account for its ability to reverse adverse metabolic programming due to early gestational exposure to maternal undernutrition. This review presents an alternative framework for understanding the effects of neonatal leptin through influences on developing thermoregulatory circuits.

Early life origins of metabolic disease: Developmental programming of hypothalamic pathways controlling energy homeostasis

A wealth of animal and human studies demonstrate that perinatal exposure to adverse metabolic conditions - be it maternal obesity, diabetes or under-nutrition - results in predisposition of offspring to develop obesity later in life. This mechanism is a contributing factor to the exponential rise in obesity rates. Increased weight gain in offspring exposed to maternal obesity is usually associated with hyperphagia, implicating altered central regulation of energy homeostasis as an underlying cause. Perinatal development of the hypothalamus (a brain region key to metabolic regulation) is plastic and sensitive to metabolic signals during this critical time window. Recent research in non-human primate and rodent models has demonstrated that exposure to adverse maternal environments impairs the development of hypothalamic structure and consequently function, potentially underpinning metabolic phenotypes in later life. This review summarizes our current knowledge of how adverse perinatal environments program hypothalamic development and explores the mechanisms that could mediate these effects.

Blockage of the Neonatal Leptin Surge Affects the Gene Expression of Growth Factors, Glial Proteins, and Neuropeptides Involved in the Control of Metabolism and Reproduction in Peripubertal Male and Female Rats

Leptin (Lep) is important in the development of neuroendocrine circuits involved in metabolic control. Because both Lep and metabolism influence pubertal development, we hypothesized that early changes in Lep signaling could also modulate hypothalamic (HT) systems involved in reproduction. We previously demonstrated that a single injection of a Lep antagonist (Antag) on postnatal day (PND)9, coincident with the neonatal Lep peak, induced sexually dimorphic modifications in trophic factors and markers of cell turnover and neuronal maturation in the HT on PND13. Here, our aim was to investigate whether the alterations induced by Lep antagonism persist into puberty. Accordingly, male and female rats were treated with a pegylated super Lep Antag from PND5 to PND9 and killed just before the normal appearance of external signs of puberty (PND33 in females and PND43 in males). There was no effect on body weight, but in males food intake increased, subcutaneous adipose tissue decreased and HT neuropeptide Y and Agouti-related peptide mRNA levels were reduced, with no effect in females. In both sexes, the Antag increased HT mRNA levels of the kisspeptin receptor, G protein-coupled recepter 54 (Gpr54). Expression of the Lep receptor, trophic factors, and glial markers were differently affected in the HT of peripubertal males and females. Lep production in adipose tissue was decreased in Antag-treated rats of both sexes, with production of other cytokines being differentially regulated between sexes. In conclusion, in addition to the long-term effects on metabolism, changes in neonatal Lep levels modifies factors involved in reproduction that could possibly affect sexual maturation.

Early leptin intervention reverses perturbed energy balance regulating hypothalamic neuropeptides in the pre- and postnatal calorie-restricted female rat offspring

Pre- and postnatal calorie restriction is associated with postnatal growth restriction, reduced circulating leptin concentrations, and perturbed energy balance. Hypothalamic regulation of energy balance demonstrates enhanced orexigenic (NPY, AgRP) and diminished anorexigenic (POMC, CART) neuropeptide expression (PN21), setting the stage for subsequent development of obesity in female Sprague-Dawley rats. Leptin replenishment during the early postnatal period (PN2-PN8) led to reversal of the hypothalamic orexigenic:anorexigenic neuropeptide ratio at PN21 by reducing only the orexigenic (NPY, AgRP), without affecting the anorexigenic (POMC, CART) neuropeptide expression. This hypothalamic effect was mediated via enhanced leptin receptor (ObRb) signaling that involved increased pSTAT3/STAT3 but reduced PTP1B. This was further confirmed by an increase in body weight at PN21 in response to intracerebroventricular administration of antisense ObRb oligonucleotides (PN2-PN8). The change in the hypothalamic neuropeptide balance in response to leptin administration was associated with increased oxygen consumption, carbon dioxide production, and physical activity, which resulted in increased milk intake (PN14) with no change in body weight. This is in contrast to the reduction in milk intake with no effect on energy expenditure and physical activity observed in controls. We conclude that pre- and postnatal calorie restriction perturbs hypothalamic neuropeptide regulation of energy balance, setting the stage for hyperphagia and reduced energy expenditure, hallmarks of obesity. Leptin in turn reverses this phenotype by increasing hypothalamic ObRb signaling (sensitivity) and affecting only the orexigenic arm of the neuropeptide balance.

The interplay of early-life stress, nutrition, and immune activation programs adult hippocampal structure and function

Early-life adversity increases the vulnerability to develop psychopathologies and cognitive decline later in life. This association is supported by clinical and preclinical studies. Remarkably, experiences of stress during this sensitive period, in the form of abuse or neglect but also early malnutrition or an early immune challenge elicit very similar long-term effects on brain structure and function. During early-life, both exogenous factors like nutrition and maternal care, as well as endogenous modulators, including stress hormones and mediator of immunological activity affect brain development. The interplay of these key elements and their underlying molecular mechanisms are not fully understood. We discuss here the hypothesis that exposure to early-life adversity (specifically stress, under/malnutrition and infection) leads to life-long alterations in hippocampal-related cognitive functions, at least partly via changes in hippocampal neurogenesis. We further discuss how these different key elements of the early-life environment interact and affect one another and suggest that it is a synergistic action of these elements that shapes cognition throughout life. Finally, we consider different intervention studies aiming to prevent these early-life adversity induced consequences. The emerging evidence for the intriguing interplay of stress, nutrition, and immune activity in the early-life programming calls for a more in depth understanding of the interaction of these elements and the underlying mechanisms. This knowledge will help to develop intervention strategies that will converge on a more complete set of changes induced by early-life adversity.

CART in the regulation of appetite and energy homeostasis

The cocaine- and amphetamine-regulated transcript (CART) has been the subject of significant interest for over a decade. Work to decipher the detailed mechanism of CART function has been hampered by the lack of specific pharmacological tools like antagonists and the absence of a specific CART receptor(s). However, extensive research has been devoted to elucidate the role of the CART peptide and it is now evident that CART is a key neurotransmitter and hormone involved in the regulation of diverse biological processes, including food intake, maintenance of body weight, reward and addiction, stress response, psychostimulant effects and endocrine functions (Rogge et al., 2008; Subhedar et al., 2014). In this review, we focus on knowledge gained on CART's role in controlling appetite and energy homeostasis, and also address certain species differences between rodents and humans.

Developmental switch of leptin signaling in arcuate nucleus neurons

Leptin is well known for its role in the regulation of energy homeostasis in adults, a mechanism that at least partially results from the inhibition of the activity of NPY/AgRP/GABA neurons (NAG) in the arcuate nucleus of the hypothalamus (ARH). During early postnatal development in the rodent, leptin promotes axonal outgrowth from ARH neurons, and preautonomic NAG neurons are particularly responsive to leptin's trophic effects. To begin to understand how leptin could simultaneously promote axonal outgrowth from and inhibit the activity of NAG neurons, we characterized the electrochemical effects of leptin on NAG neurons in mice during early development. Here, we show that NAG neurons do indeed express a functional leptin receptor throughout the early postnatal period in the mouse; however, at postnatal days 13-15, leptin causes membrane depolarization in NAG neurons, rather than the expected hyperpolarization. Leptin action on NAG neurons transitions from stimulatory to inhibitory in the periweaning period, in parallel with the acquisition of functional ATP-sensitive potassium channels. These findings are consistent with the idea that leptin provides an orexigenic drive through the NAG system to help rapidly growing pups meet their energy requirements.

CART in the brain of vertebrates: circuits, functions and evolution

Cocaine- and amphetamine-regulated transcript peptide (CART) with its wide distribution in the brain of mammals has been the focus of considerable research in recent years. Last two decades have witnessed a steady rise in the information on the genes that encode this neuropeptide and regulation of its transcription and translation. CART is highly enriched in the hypothalamic nuclei and its relevance to energy homeostasis and neuroendocrine control has been understood in great details. However, the occurrence of this peptide in a range of diverse circuitries for sensory, motor, vegetative, limbic and higher cortical areas has been confounding. Evidence that CART peptide may have role in addiction, pain, reward, learning and memory, cognition, sleep, reproduction and development, modulation of behavior and regulation of autonomic nervous system are accumulating, but an integration has been missing. A steady stream of papers has been pointing at the therapeutic potentials of CART. The current review is an attempt at piecing together the fragments of available information, and seeks meaning out of the CART elements in their anatomical niche. We try to put together the CART containing neuronal circuitries that have been conclusively demonstrated as well as those which have been proposed, but need confirmation. With a view to finding out the evolutionary antecedents, we visit the CART systems in sub-mammalian vertebrates and seek the answer why the system is shaped the way it is. We enquire into the conservation of the CART system and appreciate its functional diversity across the phyla.

The over-expression of miR-200a in the hypothalamus of ob/ob mice is linked to leptin and insulin signaling impairment

Early in life, leptin plays a crucial role in hypothalamic neural organization. Leptin, most likely, controls neural gene expression conferring then specific phenotype regarding energy homeostasis. MicroRNAs are new regulators for several physiological functions, including the regulation of metabolism. However, the impact of leptin on hypothalamic microRNA patterns remains unknown. Here, we demonstrate that miR-200a, miR-200b and miR-429 are up-regulated in the hypothalamus of genetically obese and leptin deficient ob/ob mice. Leptin treatment down-regulates these miRNAs in ob/ob hypothalamus. The hypothalamic silencing of miR-200a increased the expression level of leptin receptor and insulin receptor substrate 2, reduced body weight gain, and restored liver insulin responsiveness. In addition, the overexpression of pre-miR-200a in a human neuroblastoma cell line impaired insulin and leptin signaling. These findings link the alteration of leptin and insulin signaling to the up-regulation of hypothalamic miR-200a which could be a new target for treatment of obesity.

The neuropathology of obesity: insights from human disease

Obesity, a pathologic state defined by excess adipose tissue, is a significant public health problem as it affects a large proportion of individuals and is linked with increased risk for numerous chronic diseases. Obesity is the result of fundamental changes associated with modern society including overnutrition and sedentary lifestyles. Proper energy homeostasis is dependent on normal brain function as the master metabolic regulator, which integrates peripheral signals, modulates autonomic outflow and controls feeding behavior. Therefore, many human brain diseases are associated with obesity. This review explores the neuropathology of obesity by examining brain diseases which either cause or are influenced by obesity. First, several genetic and acquired brain diseases are discussed as a means to understand the central regulation of peripheral metabolism. These diseases range from monogenetic causes of obesity (leptin deficiency, MC4R deficiency, Bardet-Biedl syndrome and others) to complex neurodevelopmental disorders (Prader-Willi syndrome and Sim1 deficiency) and neurodegenerative conditions (frontotemporal dementia and Gourmand's syndrome) and serve to highlight the central regulatory mechanisms which have evolved to maintain energy homeostasis. Next, to examine the effect of obesity on the brain, chronic neuropathologic conditions (epilepsy, multiple sclerosis and Alzheimer's disease) are discussed as examples of obesity leading to maladaptive processes which exacerbate chronic disease. Thus, obesity is associated with multiple pathways including abnormal metabolism, altered hormonal signaling and increased inflammation which act in concert to promote downstream neuropathology. Finally, the effect of anti-obesity interventions is discussed in terms of brain structure and function. Together, understanding human diseases and anti-obesity interventions leads to insights into the bidirectional interaction between peripheral metabolism and central brain function, highlighting the need for continued clinicopathologic and mechanistic studies of the neuropathology of obesity.

Leptin gene in rabbit: cloning and expression in mammary epithelial cells during pregnancy and lactation

Leptin is known as a cytokine mostly produced by fat cells and implicated in regulation of energy metabolism and food intake but has also been shown to be involved in many physiological mechanisms such as tissue metabolism and cell differentiation and proliferation. In particular, leptin influences the development of mammary gland. Although leptin expression in mammary gland has been studied in several species, no data are available in the rabbit. Leptin transcripts in this species have been described as being encoded by only two exons rather than three as in other species. Our focus was to clone and sequence the rabbit leptin cDNA and to prepare the recombinant biologically active protein for validation of the proper sequence and then to describe leptin expression in rabbit mammary gland during different stages of pregnancy and lactation. The leptin sequence obtained was compared with those of other species, and genome alignment demonstrated that the rabbit leptin gene is also encoded by three exons. Additionally, we analyzed the expression of leptin during pregnancy and lactation. Leptin mRNA was weakly expressed throughout pregnancy, whereas mRNA levels were higher during lactation, with a significant increase between days 3 and 16. Leptin transcripts and protein were localized in luminal epithelial cells, thus indicating that leptin synthesis occurs in this compartment. Therefore, mammary synthesized leptin may constitute a major regulator of mammary gland development by acting locally as an autocrine and/or paracrine factor. Furthermore, our results support the possible physiological role of leptin in newborns through consumption of milk.

The manifestation of cocaine-induced midline destructive lesion in bone tissue and its identification in human skeletal remains

Cocaine-induced midline destructive lesion (CIMDL) is a condition that may arise in response to chronic insufflation ("snorting") of cocaine. It is clinically diagnosed when the nasal septum, lateral nasal walls, and/or hard palate show signs of destruction in association with cocaine use. Although its true incidence is unknown, CIMDL is not an uncommon clinical finding amongst intranasal cocaine abusers and is likely to be encountered by forensic anthropologists and medical examiners working worldwide. Given the preponderance of drug abusers amongst the subjects of forensic casework, the ability to diagnose CIMDL in dry bone may provide crucial insight into an investigation and even help confirm an individual identification. This paper aims to make practicing forensic anthropologists aware of CIMDL. Through the analysis of existing clinical literature, patient CT scans, and histology sections, it works toward the establishment of formal diagnostic criteria for identifying CIMDL in human skeletal remains. Lytic destruction regularly involves the vomer and frequently extends to the perpendicular plate of the ethmoid, the palatal process of the maxillae or the palatine bones, and the inferior nasal conchae. The middle nasal conchae, medial walls of the maxillary sinuses, ethmoid sinuses, and cribriform plate are often damaged. Destruction may also implicate the superior nasal conchae, the orbit, and the sphenoid. Bones affected by CIMDL may contain necrotic lesions or may be absent entirely. Lesions show minimal, if any, signs of repair. The author proposes that this lack of new bone formation may be mediated by potentially elevated leptin levels in cocaine abusers and CIMDL patients and may be the key to differentiating CIMDL from other lytic processes of the midface.

Intermittent fasting dietary restriction regimen negatively influences reproduction in young rats: a study of hypothalamo-hypophysial-gonadal axis

Nutritional infertility is very common in societies where women fail to eat enough to match their energy expenditure and such females often present as clinical cases of anorexia nervosa. The cellular and molecular mechanisms that link energy balance and central regulation of reproduction are still not well understood. Peripheral hormones such as estradiol, testosterone and leptin, as well as neuropeptides like kisspeptin and neuropeptides Y (NPY) play a potential role in regulation of reproduction and energy balance with their primary target converging on the hypothalamic median eminence-arcuate region. The present study was aimed to explore the effects of negative energy state resulting from intermittent fasting dietary restriction (IF-DR) regimen on complete hypothalamo-hypophysial-gonadal axis in Wistar strain young female and male rats. Significant changes in body weight, blood glucose, estrous cyclicity and serum estradiol, testosterone and LH level indicated the negative role of IF-DR regimen on reproduction in these young animals. Further, it was elucidated whether serum level of metabolic hormone, leptin plays a mechanistic role in suppressing hypothalamo-hypophysial-gonadal (HPG) axis via energy regulators, kisspeptin and NPY in rats on IF-DR regimen. We also studied the effect of IF-DR regimen on structural remodeling of GnRH axon terminals in median eminence region of hypothalamus along with the glial cell marker, GFAP and neuronal plasticity marker, PSA-NCAM using immunostaining, Western blotting and RT-PCR. Together these data suggest that IF-DR regimen negatively influences reproduction in young animals due to its adverse effects on complete hypothalamus-hypophysial-gonadal axis and may explain underlying mechanism(s) to understand the clinical basis of nutritional infertility.

Development of the hypothalamic melanocortin system

The melanocortin system is a critical component of the forebrain and hindbrain regulatory systems involved in energy balance. This system is composed of pro-opiomelanocortin (POMC) neurons that act, in part, through the melanocortin-4 receptor (MC4R). Although the importance of the melanocortin system in controlling feeding has been established for two decades, the understanding of the developmental substrates underlying POMC and MC4R neuron development and function has just begun to emerge. The formation of the melanocortin system involves several discrete developmental steps that include the birth and fate specification of POMC- and MC4R-containing neurons and the extension and guidance of POMC axons to their MC4R-expressing target nuclei. Each of these developmental processes appears to require specific sets of genes and developmental cues that include perinatal hormones. Recent evidence has also highlighted the importance of perinatal nutrition in controlling the ultimate architecture of the melanocortin system.

PVN pathways controlling energy homeostasis

Research into the control of energy balance has tended to focus on discrete brain regions, such as the brainstem, medulla, arcuate nucleus of the hypothalamus, and neocortex. Recently, a larger picture has begun to emerge in which the coordinated communication between these areas is proving to be critical to appropriate regulation of metabolism. By serving as a center for such communication, the paraventricular nucleus of the hypothalamus (PVH) is perhaps the most important brain nucleus regulating the physiological response to energetic challenges. Here we review recent advances in the understanding of the circuitry and function of the PVH.

Neuron-restrictive silencer factor (NRSF) represses cocaine- and amphetamine-regulated transcript (CART) transcription and antagonizes cAMP-response element-binding protein signaling through a dual NRSE mechanism

Cocaine- and amphetamine-regulated transcript (CART) peptide plays a pivotal role in neuroprotection against stroke-related brain injury. However, the regulatory mechanism on CART transcription, especially the repression mechanism, is not fully understood. Here, we show that the transcriptional repressor neuron-restrictive silencer elements (NRSF, also known as REST) represses CART expression through direct binding to two NRSF-binding elements (NRSEs) in the CART promoter and intron 1 (named pNRSE and iNRSE, respectively). EMSA show that NRSF binds to pNRSE and iNRSE directly in vitro. ChIP assays show that NRSF recruits differential co-repressor complexes including CoREST and HDAC1 to these NRSEs. The presence of both NRSEs is required for efficient repression of CART transcription as indicated by reporter gene assays. NRSF overexpression antagonizes forskolin-mediated up-regulation of CART mRNA and protein. Ischemia insult triggered by oxygen-glucose deprivation (OGD) enhances NRSF mRNA levels and then NRSF antagonizes the CREB signaling on CART activation, leading to augmented cell death. Depletion of NRSF in combination with forskolin treatment increases neuronal survival after ischemic insult. These findings reveal a novel dual NRSE mechanism by which NRSF represses CART expression and suggest that NRSF may serve as a therapeutic target for stroke treatment.

Gene transcripts associated with BMI in the motor cortex and caudate nucleus of calorie restricted rhesus monkeys

Obesity affects over 500 million people worldwide, and has far reaching negative health effects. Given that high body mass index (BMI) and insulin resistance are associated with alterations in many regions of brain and that physical activity can decrease obesity, we hypothesized that in Rhesus monkeys (Macaca mulatta) fed a high fat diet and who subsequently received reduced calories BMI would be associated with a unique gene expression signature in motor regions of the brain implicated in neurodegenerative disorders. In the motor cortex with increased BMI we saw the upregulation of genes involved in apoptosis, altered gene expression in metabolic pathways, and the downregulation of pERK1/2 (MAPK1), a protein involved in cellular survival. In the caudate nucleus with increased BMI we saw the upregulation of known obesity related genes (the insulin receptor (INSR) and the glucagon-like peptide-2 receptor (GLP2R)), apoptosis related genes, and altered expression of genes involved in various metabolic processes. These studies suggest that the effects of high BMI on the brain transcriptome persist regardless of two months of calorie restriction. We hypothesize that active lifestyles with low BMIs together create a brain homeostasis more conducive to brain resiliency and neuronal survival.

Obesity, leptin, and Alzheimer's disease

Obesity has various deleterious effects on health largely associated with metabolic abnormalities including abnormal glucose and lipid homeostasis that are associated with vascular injury and known cardiac, renal, and cerebrovascular complications. Advanced age is also associated with increased adiposity, decreased lean mass, and increased risk for obesity-related diseases. Although many of these obesity- and age-related disease processes have long been subsumed to be secondary to metabolic or vascular dysfunction, increasing evidence indicates that obesity also modulates nonvascular diseases such as Alzheimer's disease (AD) dementia. The link between peripheral obesity and neurodegeneration will be explored, using adipokines and AD as a template. After an introduction to the neuropathology of AD, the relationship between body weight, obesity, and dementia will be reviewed. Then, population-based and experimental studies that address whether leptin modulates brain health and mitigates AD pathways will be explored. These studies will serve as a framework for understanding the role of adipokines in brain health.

Increased maternal fat consumption during pregnancy alters body composition in neonatal mice

Maternal overnutrition prior to and during gestation causes pronounced metabolic dysfunction in the adult offspring. However, less is known about metabolic adaptations in the offspring that occur independently of postnatal growth and nutrition. Therefore, we evaluated the impact of excess maternal dietary lipid intake on the in utero programming of body composition, hepatic function, and hypothalamic development in newborn (P0) offspring. Female mice were fed a low-fat (LF) or high-fat (HF) diet and were mated after 4, 12, and 23 wk. A subset of the obese HF dams was switched to the LF diet during the second (DR2) or third (DR3) pregnancies. The HF offspring accrued more fat mass than the LF pups, regardless of duration of maternal HF diet consumption or prepregnancy maternal adiposity. Increased neonatal adiposity was not observed in the DR3 pups. Liver weights were reduced in the HF offspring but not in the DR2 or DR3 pups. Offspring hepatic triglyceride content was reduced in the HF pups, but hepatic inflammation and expression of lipid metabolism genes were largely unaffected by maternal diet. Maternal diet did not alter the hypothalamic expression of orexigenic and anorexigenic neuropeptides in the offspring. Thus, the intrauterine programming of increased neonatal adiposity and reduced liver size by maternal overnutrition is evident in mice at birth and occurs prior to the development of maternal obesity. These observations demonstrate that dietary intervention during pregnancy minimizes the deleterious effects of maternal obesity on offspring body composition, potentially reducing the offsprings' risk of developing obesity and related diseases later in life.

Perinatal programming of body weight control by leptin: putative roles of AMP kinase and muscle thermogenesis

Breastfeeding, compared with infant-formula feeding, confers later protection against obesity. Leptin represents a candidate for the programming of the lean phenotype as suggested by 1) the presence of leptin in breast milk and its absence in infant formula, 2) a human study that showed a negative correlation between leptin concentrations in breast milk and body weights of infants until 2 y of age, and 3) intervention studies in animals. Milk-borne leptin and leptin synthesized in adipose tissue and the stomach may contribute to leptinemia in newborns. Studies in rodents suggested that early leptin treatment may program either a lean or obese phenotype, probably depending on the dose, route of administration, and timing of exposure to high leptin concentrations, whereas these studies also suggested the importance of the physiologic postnatal surge in leptinemia for the programming effect. Leptin oral administration at physiologic doses to neonate rats during the entire lactation period had later positive effects that prevented the animals from overweight and obesity and other metabolic alterations, which were particularly associated with feeding of a high-fat diet. High leptin sensitivity, which is associated with leanness, and leptin resistance in obesity may be programmed by the early life environment. The differential sensitivity to leptin implies a contribution of leptin-inducible energy expenditure to the adult phenotype. Available data have suggested the involvement of nonshivering thermogenesis induced by a leptin-AMP-activated protein kinase axis in oxidative muscles, which is based on lipid metabolism. Additional studies on the programming effects of leptin, mainly in response to the oral intake of leptin, are required.

Expression of cocaine- and amphetamine-regulated transcript in the rat forebrain during postnatal development

Cocaine- and amphetamine-regulated transcript (CART) is widespread in the rodent brain. CART has been implicated in many different functions including reward, feeding, stress responses, sensory processing, learning and memory formation. Recent studies have suggested that CART may also play a role in neural development. Therefore, in the present study we compared the distribution pattern and levels of CART mRNA expression in the forebrain of male and female rats at different stages of postnatal development: P06, P26 and P66. At 6 days of age (P06), male and female rats showed increased CART expression in the somatosensory and piriform cortices, indusium griseum, dentate gyrus, nucleus accumbens, and ventral premammillary nucleus. Interestingly, we found a striking expression of CART mRNA in the ventral posteromedial and ventral posterolateral thalamic nuclei. This thalamic expression was absent at P26 and P66. Contrastingly, at P06 CART mRNA expression was decreased in the arcuate nucleus. Comparing sexes, we found increased CART mRNA expression in the anteroventral periventricular nucleus of adult females. In other regions including the CA1, the lateral hypothalamic area and the dorsomedial nucleus of the hypothalamus, CART expression was not different comparing postnatal ages and sexes. Our findings indicate that CART gene expression is induced in a distinct temporal and spatial manner in forebrain sites of male and female rats. They also suggest that CART peptide participate in the development of neural pathways related to selective functions including sensory processing, reward and memory formation.

Developmental programming of energy balance and its hypothalamic regulation

Developmental programming is an important physiological process that allows different phenotypes to originate from a single genotype. Through plasticity in early life, the developing organism can adopt a phenotype (within the limits of its genetic background) that is best suited to its expected environment. In humans, together with the relative irreversibility of the phenomenon, the low predictive value of the fetal environment for later conditions in affluent countries makes it a potential contributor to the obesity epidemic of recent decades. Here, we review the current evidence for developmental programming of energy balance. For a proper understanding of the subject, knowledge about energy balance is indispensable. Therefore, we first present an overview of the major hypothalamic routes through which energy balance is regulated and their ontogeny. With this background, we then turn to the available evidence for programming of energy balance by the early nutritional environment, in both man and rodent models. A wealth of studies suggest that energy balance can indeed be permanently affected by the early-life environment. However, the direction of the effects of programming appears to vary considerably, both between and within different animal models. Because of these inconsistencies, a comprehensive picture is still elusive. More standardization between studies seems essential to reach veritable conclusions about the role of developmental programming in adult energy balance and obesity.