The arcuate nucleus of the hypothalamus (ARH) is a key component of hypothalamic pathways regulating energy balance, and leptin is required for normal development of ARH projections. Diet-induced obesity (DIO) has a polygenic mode of inheritance, and DIO individuals develop the metabolic syndrome when a moderate amount of fat is added to the diet. Here we demonstrate that rats selectively bred to develop DIO, which are known to be leptin resistant before they become obese, have defective ARH projections that persist into adulthood. Furthermore, the ability of leptin to activate intracellular signaling in ARH neurons in vivo and to promote ARH neurite outgrowth in vitro is significantly reduced in DIO neonates. Thus, animals that are genetically predisposed toward obesity display an abnormal organization of hypothalamic pathways involved in energy homeostasis that may be the result of diminished responsiveness of ARH neurons to the trophic actions of leptin during postnatal development.

There is growing evidence that the postnatal environment can have a major impact on the development of obesity and insulin resistance in offspring. We postulated that cross-fostering obesity-prone offspring to lean, obesity-resistant dams would ameliorate their development of obesity and insulin resistance, while fostering lean offspring to genetically obese dams would lead them to develop obesity and insulin resistance as adults. We found that obesity-prone pups cross-fostered to obesity-resistant dams remained obese but did improve their insulin sensitivity as adults. In contrast, obesity-resistant pups cross-fostered to genetically obese dams showed a diet-induced increase in adiposity, reduced insulin sensitivity, and associated changes in hypothalamic neuropeptide, insulin, and leptin receptors, which might have contributed to their metabolic defects. There was a selective increase in insulin levels and differences in fatty acid composition of obese dam milk which might have contributed to the increased adiposity, insulin resistance, and hypothalamic changes in obesity-resistant cross-fostered offspring. These results demonstrate that postnatal factors can overcome both genetic predisposition and prenatal factors in determining the development of adiposity, insulin sensitivity, and the brain pathways that mediate these functions. diet-induced obesity; hypothalamus; milk; development; plasticity; Agouti-related peptide; leptin MATERNAL INTAKE of a high-fat diet and the presence of obesity during pregnancy and lactation promote obesity in offspring, particularly in individuals with an obesity-prone genetic background (21,32,36,55). However, there is growing evidence that a variety of manipulations during the postnatal environment can override prenatal factors and increase the risk of developing metabolic disorders such as obesity and diabetes later in life. Raising pups in small litters leads to increased milk intake and the development of obesity, whereas raising pups in large litters has the opposite effect (16,23,26). Administration of insulin during early postnatal development results in obesity and altered development of hypothalamic neuropeptide systems involved in energy homeostasis (22, 50). Cross-fostering pups is another method of assessing the role of the postnatal environment in later development. A single study in mice has demonstrated that fostering inbred obesity-prone mouse pups with obesity-resistant dams attenuates their obesity, whereas fostering obesity-resistant pups with obesity-prone dams causes them to develop obesity and insulin resistance (51).Unlike many rodent models, the majority of human obesity is inherited as a polygenic disorder (6). For that reason, we have used a rat model of diet-induced obesity (DIO), in which obesity is also inherited as a polygenic trait (33, 38) in association with insulin resistance (33), hypertension (14), and hyperlipidemia (62). These rats also have several abnormalities of brain function, which antedate and may contribute to the later development o...

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide ( 1 ). Dyslipidemia has been shown to be one of the most potent risk factors for coronary heart disease (CHD) ( 2, 3 ). Dyslipidemia is characterized by elevated plasma cholesterol, especially low density lipoprotein cholesterol (LDL-c) levels. Management of dyslipidemia is considered throughout the primary and secondary prevention of CHD ( 4 ). For the past 20 years, the statin (3-hydroxy-3-methylglutaryl CoA reductase inhibitors) class of cholesterol-lowering drugs has been used for the treatment of hypercholesterolemia, either alone or in combination with other classes of lipid-lowering drugs Abstract In an attempt to understand the applicability of various animal models to dyslipidemia in humans and to identify improved preclinical models for target discovery and validation for dyslipidemia, we measured comprehensive plasma lipid profi les in 24 models. These included fi ve mouse strains, six other nonprimate species, and four nonhuman primate (NHP) species, and both healthy animals and animals with metabolic disorders. Dyslipidemic humans were assessed by the same measures. Plasma lipoprotein profi les, eight major plasma lipid fractions, and FA compositions within these lipid fractions were compared both qualitatively and quantitatively across the species. Given the importance of statins in decreasing plasma low-density lipoprotein cholesterol for treatment of dyslipidemia in humans, the responses of these measures to simvastatin treatment were also assessed for each species and compared with dyslipidemic humans. NHPs, followed by dog, were the models that demonstrated closest overall match to dyslipidemic humans. For the subset of the dyslipidemic population with high plasma triglyceride levels, the data also pointed to hamster and db/db mouse as representative models for practical use in target validation. Most traditional models, including rabbit, Zucker diabetic fatty rat, and the majority of mouse models, did not demonstrate overall similarity to dyslipidemic humans in this study . -