Effects of Neonatal Overfeeding on Juvenile and Adult Feeding and Energy Expenditure in the Rat Aneta Stefanidis 1 , Sarah J. Spencer 1,2 * 1 Department of Physiology, Faculty of Medicine, Monash University, Melbourne, Victoria, Australia, 2 School of Health Sciences and Health Innovations Research Institute (HIRi), RMIT University, Melbourne, Victoria, Australia Abstract Overfeeding during perinatal life leads to an overweight phenotype that persists throughout the juvenile stage and into adulthood, however, the mechanim(s) underlying this effect are poorly understood. We hypothesized that obesity due to neonatal overfeeding is maintained by changes in energy expenditure and that these changes differ between males and females. We investigated feeding, physical activity, hormonal and metabolic alterations that occur in adult rats made obese by having been nursed in small litters (SL) compared with those from control litters (CL). There were no differences in absolute food intake between the groups, and juvenile and adult SL rats ate less chow per gram body weight than the CL did in the dark (active) phase. Juvenile, but not adult SL rats did have reduced whole body energy expenditure, but there were no differences between the groups by the time they reached adulthood. Adult SL females (but not males) had reduced brown adipose tissue (BAT) temperatures compared with CL in the first half of the dark phase. Our results indicate a persistent overweight phenotype in rats overfed as neonates is not associated with hyperphagia at any stage, but is reflected in reduced energy expenditure into the juvenile phase. The reduced dark phase BAT activity in adult SL females is not sufficient to reduce total energy expenditure at this stage of life and there is an apparently compensatory effect that prevents SL and CL from continuing to diverge in weight that appears between the juvenile and adult stages. Citation: Stefanidis A, Spencer SJ (2012) Effects of Neonatal Overfeeding on Juvenile and Adult Feeding and Energy Expenditure in the Rat. PLoS ONE 7(12): e52130. doi:10.1371/journal.pone.0052130 Editor: Thomas W.H. Kay, St. Vincent’s Institute, Australia Received July 2, 2012; Accepted November 15, 2012; Published December 14, 2012 Copyright: ß 2012 Stefanidis, Spencer. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by a Discovery Project Grant from the Australian Research Council to SJS (ARC; DP109339). SJS was supported by an NHMRC Peter Doherty Research Fellowship (465167) and an Endocrine Society of Australia Postdoctoral Fellowship, she is also an ARC Future Fellow (FT110100084). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: sarah.spencer@rmit.edu.au Introduction The nutritional environment in early life can be crucial in influencing body weight and has important consequences for metabolism and weight regulation throughout life. As such, overfeeding during the early postnatal period can lead to increased early weight gain that persists throughout the juvenile period and into adulthood [1,2,3,4]. Any predisposition to increased weight gain is a significant risk factor for persistent obesity and the variety of health complications that are associated with it, from type II diabetes to cardiovascular disease [1,5]. How the neonatal nutritional environment alters weight regulatory mechanisms, however, is poorly understood, and it is unknown if these mechanisms are affected in the same way in males and females. It has previously been established that both male and female rats raised in small litters (SL), where they have greater access to their mother’s milk, become overweight during the suckling period. Despite post-weaning access to identical diets to those of control litters (CL), SL rats continue to display this overweight phenotype as adults [1,2,3,4]. They also have some diabetogenic disturbances, such as impaired insulin-stimulated glucose transport [6]. Much attention has been focused on food intake and the hypothalamic mechanisms regulating feeding to explain how these SL rats maintain an overweight phenotype throughout life [1,7]. However, hyperphagia has not been consistently reported in this model. Several groups have noted no differences in food intake between CL and SL adult rats [3,8,9] and in cases where hyperphagia has been reported, this is either short-lived [10], and/ or can be attributed to the greater size of the animal [6,10,11,12]. That is, when corrected for overall body weight, SL rats do not generally eat more than CL, meaning they probably do not maintain their excess body weight through excess food intake. It is likely, therefore, that the major mechanism by which the SL rats stay overweight throughout life is via changes to metabolism and energy expenditure. In addition to increasing body weight by increasing food intake, reductions in energy expenditure can also contribute to the maintenance of an overweight phenotype [13]. For instance, there are strong indications that the ability of the interscapular brown adipose tissue (BAT) to thermoregulate and therefore increase energy expenditure may be compromised in overweight individ- uals. Down-regulation of BAT function has been observed in several genetic models of obesity, with ob/ob and db/db mice having reduced levels of BAT uncoupling protein (UCP) 1 [14,15], and obesity will develop, despite the absence of hyperphagia, in transgenic mice with a specific BAT ablation [16]. There are also indications that energy balance and propensity to become overweight may be differentially regulated in males and females. Male and female humans show differences in the propensity to become obese, with women often being more likely to develop obesity than their male counterparts and to present with indices of metabolic syndrome [17,18,19]. Men, on the other PLOS ONE | www.plosone.org 1 December 2012 | Volume 7 | Issue 12 | e52130