Arcuate nucleus homeostatic systems reflect blood leptin concentration but not feeding behaviour during scheduled feeding on a high-fat diet in mice.

Hypothalamic homeostatic and forebrain reward-related genes were examined in the context of scheduled meal feeding without caloric restriction in C57BL/6 mice. Mice fed ad libitum but allowed access to a palatable high-fat (HF) diet for 2 hours a day rapidly adapted their feeding behaviour and consumed approximately 80% of their daily caloric intake during this 2-hour scheduled feed. Gene expression levels were examined during either the first or second hour of scheduled feeding vs 24 hours ad libitum feeding on the same HF diet. Gene expression of neuropeptide Y, agouti-related peptide, cocaine- and amphetamine-regulated transcript, pro-opiomelanocortin, long-form leptin receptor and suppressor of cytokine signalling-3 in the hypothalamic arcuate nucleus (ARC), as well as enkephalin, dynorphin, dopamine-2-receptor and dopamine-3-receptor in the nucleus accumbens (NAcc) in the forebrain, were measured by in situ hybridisation. Mice fed ad libitum on a HF diet had the highest total caloric intake, body weight gain, fat mass and serum leptin, whereas schedule-fed mice had a mild obese phenotype with intermediate total caloric intake, body weight gain, fat mass and serum leptin. The effects of feeding regime on ARC gene expression were emphasised by significant positive or negative correlations with body weight gain, fat mass and blood leptin, although they did not appear to be related to feeding behaviour in the schedule-fed groups (ie, the large, binge-type meals) and did not reveal any potential candidates for the regulation of these meals. Mechanisms underlying large meal/binge-type eating may be regulated by nonhomeostatic hedonic processes. However, assessment of opioid and dopamine receptor gene expression in the NAcc did not reveal evidence of involvement of these genes in regulating large meals. This complements our previous characterisation of ARC and NAcc genes in schedule-fed mice and rats, although it still leaves open the fundamental question about the underlying mechanisms of meal feeding.

Acute ghrelin changes food preference from a high-fat diet to chow during binge-like eating in rodents.

Ghrelin, an orexigenic hormone released from the empty stomach, provides a gut-brain signal that promotes many appetitive behaviours, including anticipatory and goal-directed behaviours for palatable treats high in sugar and/or fat. In the present study, we aimed to determine whether ghrelin is able to influence and/or may even have a role in binge-like eating behaviour in rodents. Accordingly, we used a palatable scheduled feeding (PSF) paradigm in which ad lib. chow-fed rodents are trained to 'binge' on a high-fat diet (HFD) offered each day for a limited period of 2 hours. After 2 weeks of habituation to this paradigm, on the test day and immediately prior to the 2-hour PSF, rats were administered ghrelin or vehicle solution by the i.c.v. route. Remarkably and unexpectedly, during the palatable scheduled feed, when rats normally only binge on the HFD, those injected with i.c.v. ghrelin started to eat more chow and chow intake remained above baseline for the rest of the 24-hour day. We identify the ventral tegmental area (VTA) (a key brain area involved in food reward) as a substrate involved because these effects could be reproduced, in part, by intra-VTA delivery of ghrelin. Fasting, which increases endogenous ghrelin, immediately prior to a palatable schedule feed also increased chow intake during/after the schedule feed but, in contrast to ghrelin injection, did not reduce HFD intake. Chronic continuous central ghrelin infusion over several weeks enhanced binge-like behaviour in palatable schedule fed rats. Over a 4-week period, GHS-R1A-KO mice were able to adapt and maintain large meals of HFD in a manner similar to wild-type mice, suggesting that ghrelin signalling may not have a critical role in the acquisition or maintenance in this kind of feeding behaviour. In conclusion, ghrelin appears to act as a modulating factor for binge-like eating behaviour by shifting food preference towards a more nutritious choice (from HFD to chow), with these effects being somewhat divergent from fasting.

Large, binge-type meals of high fat diet change feeding behaviour and entrain food anticipatory activity in mice.

Male C57BL/6 mice fed ad libitum on control diet but allowed access to a palatable high fat diet (HFD) for 2 h a day during the mid-dark phase rapidly adapt their feeding behaviour and can consume nearly 80% of their daily caloric intake during this 2 h-scheduled feed. We assessed food intake microstructure and meal pattern, and locomotor activity and rearing as markers of food anticipatory activity (FAA). Schedule fed mice reduced their caloric intake from control diet during the first hours of the dark phase but not during the 3-h period immediately preceding the scheduled feed. Large meal/binge-like eating behaviour during the 2-h scheduled feed was characterised by increases in both meal number and meal size. Rearing was increased during the 2-h period running up to scheduled feeding while locomotor activity started to increase 1 h before, indicating that schedule-fed mice display FAA. Meal number and physical activity changes were sustained when HFD was withheld during the anticipated scheduled feeding period, and mice immediately binged when HFD was represented after a week of this "withdrawal" period. These findings provide important context to our previous studies suggesting that energy balance systems in the hypothalamus are not responsible for driving these large, binge-type meals. Evidence of FAA in HFD dark phase schedule-fed mice implicates anticipatory processes in binge eating that do not involve immediately preceding hypophagia or regulatory homeostatic signalling.

Feeding and metabolic consequences of scheduled consumption of large, binge-type meals of high fat diet in the Sprague-Dawley rat.

Providing rats and mice with access to palatable high fat diets for a short period each day induces the consumption of substantial binge-like meals. Temporal food intake structure (assessed using the TSE PhenoMaster/LabMaster system) and metabolic outcomes (oral glucose tolerance tests [oGTTs], and dark phase glucose and insulin profiles) were examined in Sprague-Dawley rats given access to 60% high fat diet on one of 3 different feeding regimes: ad libitum access (HF), daily 2 h-scheduled access from 6 to 8 h into the dark phase (2 h-HF), and twice daily 1 h-scheduled access from both 1-2 h and 10-11 h into the dark phase (2×1 h-HF). Control diet remained available during the scheduled access period. HF rats had the highest caloric intake, body weight gain, body fat mass and plasma insulin. Both schedule-fed groups rapidly adapted their feeding behaviour to scheduled access, showing large meal/bingeing behaviour with 44% or 53% of daily calories consumed from high fat diet during the 2 h or 2×1 h scheduled feed(s), respectively. Both schedule-fed groups had an intermediate caloric intake and body fat mass compared to HF and control (CON) groups. Temporal analysis of food intake indicated that schedule-fed rats consumed large binge-type high fat meals without a habitual decrease in preceding intake on control diet, suggesting that a relative hypocaloric state was not responsible or required for driving the binge episode, and substantiating previous indications that binge eating may not be driven by hypothalamic energy balance neuropeptides. In an oGTT, both schedule-fed groups had impaired glucose tolerance with higher glucose and insulin area under the curve, similar to the response in ad libitum HF fed rats, suggesting that palatable feeding schedules represent a potential metabolic threat. Scheduled feeding on high fat diet produces similar metabolic phenotypes to mandatory (no choice) high fat feeding and may be a more realistic platform for mechanistic study of diet-induced obesity.

Impact of birth weight and gender on early postnatal hypothalamic energy balance regulatory gene expression in the young lamb.

Intra-uterine growth restriction (IUGR) is involved in developmental metabolic programming and here we test the hypothesis that IUGR affects the developing hypothalamic energy balance regulatory pathways in a sex-specific manner. This experiment investigated early postnatal hypothalamic gene expression for six primary leptin- and insulin-sensitive neuropeptides and receptors in male and female IUGR (n = 8 and 9, respectively) and normal (N) birth weight lambs (n = 8 per gender) gestated and suckled by overnourished mothers. IUGR lambs were smaller at birth, had increased fractional growth rates (FGR), lower final body weight (11 weeks) and similar body fat content compared with N lambs, while males had higher final body weight and insulinemia but lower body fat and leptinemia than females. In situ hybridization revealed greater gene expression in the hypothalamic arcuate nucleus at 11 weeks for anorexigenic genes in females and orexigenic genes in males, with no effect of IUGR. Leptinemia correlated with gene expression for neuropeptide Y (NPY, negatively) in both sexes and pro-opiomelanocortin (POMC, positively) in females but with leptin receptor (negatively) only in males. Current FGR for girth correlated negatively with gene expression for NPY in males and POMC in females. Neither IUGR nor gender affected suckling activity (proxy for appetite) assessed at 3 weeks, but final NPY gene expression correlated with suckling weight gain in males. This study has revealed no effect of IUGR on early postnatal hypothalamic energy balance gene expression but a major effect of gender associated with major sex differences in adiposity and leptinemia.

Arcuate nucleus homeostatic systems are not altered immediately prior to the scheduled consumption of large, binge-type meals of palatable solid or liquid diet in rats and Mice.

Meal feeding is a critical issue in the over-consumption of calories leading to human obesity. To investigate the mechanisms involved in the regulation of meal feeding in rodents, we studied a scheduled feeding regime that induces substantial food intake over short periods of time. Male Sprague-Dawley rats and C57BL6 mice were fed one of four palatable diets [45% fat pellet, 60% fat pellet or standard pellet supplemented with Ensure (EN; Abbott Laboratories, Maidenhead, UK) or 12.5% sucrose (SUC)] either ad lib. or with daily 2-h scheduled access and standard pellet available for 22 h. Energy balance gene expression in the hypothalamic arcuate nucleus (ARC) and nucleus accumbens (NAcc) reward gene expression were assessed by in situ hybridisation. Rats fed ad lib. on 45% or 60% fat diet were heavier and fatter than controls, and had reduced neuropeptide Y (NPY) gene expression in the ARC. Mice fed ad lib. on any of the palatable diets were heavier, fatter and had higher blood leptin than controls, and had reduced NPY and increased cocaine- and-amphetamine-regulated transcript mRNA in the ARC. Schedule-fed rats and mice quickly adapted their feeding behaviour to 2-h access on palatable food. Three schedule-fed groups binged: the percentage of daily calories consumed in 2 h on 45% fat diet, 60% fat diet or EN, respectively, was 55%, 63% and 49% in rats, and 86%, 86% and 45% in mice. However, changed feeding behaviour was not reflected in an induction of orexigenic neuropeptide or suppression of anorexigenic neuropeptide gene expression in the ARC, in the 2-h period prior to scheduled feeding. The mechanisms underlying large meal/binge-type eating may be regulated by nonhomeostatic processes involving other genes in the hypothalamus or other brain areas. However, assessment of opioid and dopamine receptor gene expression in the NAcc did not reveal evidence of the involvement of these genes in driving large meals, at least at the investigated time point.

Effects of altered glucose supply and adiposity on expression of hypothalamic energy balance regulatory genes in late gestation growth restricted ovine fetuses.

Intra-uterine growth restriction (IUGR) predisposes obesity in adulthood. This may be due to altered fetal nutrition causing sustained changes within the developing hypothalamic energy balance regulatory system. Using our established ovine model of IUGR, 130-day singleton fetuses (term=147 days) were obtained from growing adolescent mothers on control dietary intake (C), high intake (H) or H with growth hormone administration during either early (H+early GH) or late gestation (H+late GH) (n=6/group). GH increased maternal glycemia for the duration of treatment. H and H+early GH fetuses showed IUGR compared with C fetuses; body weight was partially restored in H+late GH fetuses, with 40% increased adiposity. In the fetal hypothalamic arcuate nucleus (ARC), cocaine- and amphetamine-regulated transcript mRNA (anorexigenic) was decreased in H fetuses and correlated across all groups with total fetal liver glycogen. Neuropeptide Y, agouti-related peptide (orexigenic) and proopiomelanocortin (anorexigenic) mRNAs were not different between groups. Insulin receptor mRNA in the ARC was increased in H, H+early GH and H+late GH fetuses and correlated negatively with fetal plasma insulin. Leptin receptor mRNA in the ARC correlated positively with fetal plasma leptin concentration and fetal fat content. Therefore, in IUGR fetuses, a key anorexigenic neuropeptide is sensitive to altered glucose supply and the hypothalamic leptin-signaling pathway is altered prenatally by increased adiposity and leptinemia. These changes could impact on postnatal energy balance regulation.