Anorexia nervosa as a motivated behavior: Relevance of anxiety, stress, fear and learning

The high comorbidity between anorexia nervosa (AN) and anxiety disorders is well recognized. AN is a motivated behavioral disorder in which habit formation is likely to contribute to the persistence of abnormal eating and exercise behaviors. Secondary alterations in brain circuitry underlying the reward value of food and exercise, along with disturbances in neuroendocrine hunger and satiety signaling arising from starvation and excessive exercise, are likely contributors to the maintenance of anorectic behaviors in genetically vulnerable individuals. The potential role of fear conditioning in facilitating onset of AN, or of impaired fear extinction in contributing to the high relapse rates observed following weight restoration, is of interest. Evidence from animal models of anxiety and human laboratory studies indicate that low estrogen impairs fear extinction. Low estradiol levels in AN may therefore play a role in perpetuating fear of food and fat in recently weight restored patients. Translational models including the activity based anorexia (ABA) rodent model of AN, and neuroimaging studies of fear extinction and conditioning, could help clarify the underlying molecular mechanisms and neurocircuitry involved in food avoidance behaviors in AN. Moreover, the adaptation of novel treatment interventions with efficacy in anxiety disorders may contribute to the development of new treatments for this impairing disorder.

Wheel running decreases palatable diet preference in Sprague-Dawley rats

Physical activity has beneficial effects on not only improving some disease conditions but also by preventing the development of multiple disorders. Experiments in this study examined the effects of wheel running on intakes of chow and palatable diet e.g. high fat (HF) or high sucrose (HS) diet in male and female Sprague-Dawley rats. Experiment 1 demonstrated that acute wheel running results in robust HF or HS diet avoidance in male rats. Although female rats with running wheel access initially showed complete avoidance of the two palatable diets, the avoidance of the HS diet was transient. Experiment 2 demonstrated that male rats developed decreased HF diet preferences regardless of the order of diet and wheel running access presentation. Running associated changes in HF diet preference in females, on the other hand, depended on the testing schedule. In female rats, simultaneous presentation of the HF diet and running access resulted in transient complete HF diet avoidance whereas running experience prior to HF diet access did not affect the high preference for the HF diet. Ovariectomy in females resulted in HF diet preference patterns that were similar to those in male rats during simultaneous exposure of HF and wheel running access but similar to intact females when running occurred before HF exposure. Overall, the results demonstrated wheel running associated changes in palatable diet preferences that were in part sex dependent. Furthermore, ovarian hormones play a role in some of the sex differences. These data reveal complexity in the mechanisms underlying exercise associated changes in palatable diet preference.

Large litter rearing improves leptin sensitivity and hypothalamic appetite markers in offspring of rat dams fed high-fat diet during pregnancy and lactation

Maternal high-fat (HF) diet has long-term consequences on the offspring's metabolic phenotype. Here, we determined the effects of large litter (LL) rearing in offspring of rat dams fed HF diet during gestation and lactation. Pregnant Sprague-Dawley rats were maintained on standard chow (CHOW) or HF diet throughout gestation and lactation. Pups were raised in normal litters (NLs) (10 pups/dam) or LLs (16 pups/dam) during lactation, resulting in 4 groups: CHOW-NL, CHOW-LL, HF-NL, and HF-LL. The offspring were weaned onto to either CHOW or HF diet on postnatal day 21. Male and female pups with maternal HF diet (HF-NL) had greater body weight and adiposity, higher plasma leptin levels, impaired glucose tolerance, abnormal hypothalamic leptin signaling pathways (lower leptin receptor-b [OB-Rb] and signal transducer and activator of transcription 3, higher suppressor of cytokine signaling 3 mRNA expression) and appetite markers (lower neuropeptide Y and Agouti-related peptide mRNA expression), and reduced phospho-signal transducer and activator of transcription 3 level in response to leptin in the arcuate nucleus at weaning, whereas LL rearing normalized these differences. When weaned onto CHOW diet, adult male offspring from HF diet-fed dams continued to have greater adiposity, higher leptin levels, and lower hypothalamic OB-Rb, and LL rearing improved them. When weaned onto HF diet, both adult male and female offspring with maternal HF diet had greater body weight and adiposity, higher leptin levels, impaired glucose tolerance, lower OB-Rb, and higher suppressor of cytokine signaling 3 in hypothalamus compared with those of CHOW dams, whereas LL rearing improved most of them except male OB-Rb expression. Our data suggest that LL rearing improves hypothalamic leptin signaling pathways and appetite markers in an age- and sex-specific manner in this model.

Long term exendin-4 treatment reduces food intake and body weight and alters expression of brain homeostatic and reward markers

Repeated administration of the long-acting glucagon-like peptide 1 receptor agonist exendin-4 (EX-4) has been shown to reduce food intake and body weight and do so without a rebound increase in food intake after treatment termination. The current study examines the neural mechanisms underlying these actions. After 6 weeks of maintenance on a standard chow or a high-fat (HF) diet, male Sprague Dawley rats were treated with EX-4 (3.2 μg/kg, i.p., twice a day) or vehicle for 9 consecutive days. Food intake and body weight (BW) were monitored daily. Expression of the genes for the hypothalamic arcuate nucleus (ARC) peptides proopiomelanocortin (POMC), neuropeptide Y (NPY), and agouti gene-related protein was determined. Expression of the dopamine precursor tyrosine hydroxylase (TH) gene in the ventral tegmental area and genes for dopamine receptors 1 (D1R) and dopamine receptor 2 in the nucleus accumbens were also determined. Pair-fed groups were included to control for the effects of reduced food intake and BW. Treatment with EX-4 significantly decreased food intake and BW over the 9-day period in both the standard chow and HF groups. HF feeding decreased POMC without changing NPY/agouti gene-related protein gene expression in the ARC. Treatment with EX-4 increased POMC and decreased NPY expression independent of the reduction of food intake and BW. Mesolimbic TH and D1R gene expression were decreased significantly in chronic HF diet-fed rats, and these changes were reversed in both EX-4 and pair-fed conditions. These results suggest a role for increased POMC and decreased NPY expression in the ARC in the effects of EX-4 on food intake and BW. Our findings also suggest that EX-4 induced the recovery of mesolimbic TH and D1R expression in HF diet-fed rats may be secondary to HF intake reduction and/or weight loss.

Phosphorodiamidate morpholino oligomers suppress mutant huntingtin expression and attenuate neurotoxicity

Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the huntingtin (HTT) gene. Disease pathogenesis derives, at least in part, from the long polyglutamine tract encoded by mutant HTT. Therefore, considerable effort has been dedicated to the development of therapeutic strategies that significantly reduce the expression of the mutant HTT protein. Antisense oligonucleotides (ASOs) targeted to the CAG repeat region of HTT transcripts have been of particular interest due to their potential capacity to discriminate between normal and mutant HTT transcripts. Here, we focus on phosphorodiamidate morpholino oligomers (PMOs), ASOs that are especially stable, highly soluble and non-toxic. We designed three PMOs to selectively target expanded CAG repeat tracts (CTG22, CTG25 and CTG28), and two PMOs to selectively target sequences flanking the HTT CAG repeat (HTTex1a and HTTex1b). In HD patient-derived fibroblasts with expanded alleles containing 44, 77 or 109 CAG repeats, HTTex1a and HTTex1b were effective in suppressing the expression of mutant and non-mutant transcripts. CTGn PMOs also suppressed HTT expression, with the extent of suppression and the specificity for mutant transcripts dependent on the length of the targeted CAG repeat and on the CTG repeat length and concentration of the PMO. PMO CTG25 reduced HTT-induced cytotoxicity in vitro and suppressed mutant HTT expression in vivo in the N171-82Q transgenic mouse model. Finally, CTG28 reduced mutant HTT expression and improved the phenotype of Hdh(Q7/Q150) knock-in HD mice. These data demonstrate the potential of PMOs as an approach to suppressing the expression of mutant HTT.

Behavioral characterization of the hyperphagia synphilin-1 overexpressing mice

Synphilin-1 is a cytoplasmic protein that has been shown to be involved in the control of energy balance. Previously, we reported on the generation of a human synphilin-1 transgenic mouse model (SP1), in which overexpression of human synphilin-1 resulted in hyperphagia and obesity. Here, behavioral measures in SP1 mice were compared with those of their age-matched controls (NTg) at two time points: when there was not yet a group body weight difference (“pre-obese”) and when SP1 mice were heavier (“obese”). At both time points, meal pattern analyses revealed that SP1 mice displayed higher daily chow intake than non-transgenic control mice. Furthermore, there was an increase in meal size in SP1 mice compared with NTg control mice at the obese stage. In contrast, there was no meal number change between SP1 and NTg control mice. In a brief-access taste procedure, both “pre-obese” and “obese“ SP1 mice displayed concentration-dependent licking across a sucrose concentration range similar to their NTg controls. However, at the pre-obese stage, SP1 mice initiated significantly more trials to sucrose across the testing sessions and licked more vigorously at the highest concentration presented, than the NTg counterparts. These group differences in responsiveness to sucrose were no longer apparent in obese SP1 mice. These results suggest that at the pre-obese stage, the increased trials to sucrose in the SP1 mice reflects increased appetitive behavior to sucrose that may be indicative of the behavioral changes that may contribute to hyperphagia and development of obesity in SP1 mice. These studies provide new insight into synphilin-1 contributions to energy homeostasis.

Similarities and differences between "proactive" and "passive" stress-coping rats in responses to sucrose, NaCl, citric acid, and quinine

A stress-coping style describes a set of behavioral and physiological measures that characterize an individual's response to stressful stimuli. It would follow that different stress-coping styles are associated with differential sensitivity for taste stimuli. Animals with stress-coping characteristics better suited to an environment in which new foods are more frequently encountered may show enhanced orosensitivity to cues that signal toxins and/or nutritional value. Here, rats were categorized as "proactive" or "passive" based on results from a defensive burying test. Next, the brief-access taste procedure was used to compare unconditioned licking responses to a concentration array of compounds that humans describe as "sweet" (sucrose), "salty" (NaCl), "sour" (citric acid), and "bitter" (quinine) across the 2 groups. Both groups displayed concentration-dependent lick responses to sucrose, NaCl, citric acid, and quinine. The passive group initiated significantly fewer trials to sucrose than the proactive rats, but the groups did not significantly differ in trial initiation for the other 3 test compounds. Thus, differences in food intake, body weight, and glucose homeostasis between the stress-coping styles are not likely driven by alterations in orosensory responsivity. However, the current findings lend support to the hypothesis that the 2 groups differ in reward-related signaling mechanisms.

From fat fruit fly to human obesity

Obesity is a chronic metabolic disease that has become a global problem. Although a tremendous amount of effort has been spent to prevent and treat obesity, its etiology is still largely unknown and there are not yet sufficient strategies to control obesity. Recently, the fruit fly, Drosophila melanogaster, has become a useful model for studying metabolic homeostasis and obesity related disorders. The goal of this mini-review is to summarize the recent achievements of Drosophila models and to highlight the experimental protocols used in studying feeding behavior and energy homeostasis in the fly. The Drosophila models provide useful tools to understand obesity pathogenesis and to develop novel therapeutics.

Maternal high-fat diet during pregnancy and lactation reduces the appetitive behavioral component in female offspring tested in a brief-access taste procedure

Maternal high-fat diet appears to disrupt several energy balance mechanisms in offspring. Here, female offspring from dams fed a high-fat diet (HF) did not significantly differ in body weight compared with those fed chow (CHOW), when weaned onto chow diet. Yet when presented with both a chow and a high-fat diet, high-fat intake was significantly higher in HF compared with CHOW offspring. To assess taste-based responsiveness, offspring (12 wk old) were tested in 30-min sessions (10-s trials) to a sucrose concentration series in a brief-access taste test. Compared with CHOW, the HF offspring initiated significantly fewer trials but did not significantly differ in the amount of concentration-dependent licking. Thus, rather than affect lick response (consummatory), maternal diet affects spout approach (appetitive), which may be attributed to motivation-related mechanisms. Consistent with this possibility, naltrexone, an opioid receptor antagonist, further reduced trial initiation, but not licking in both groups. With naltrexone administration, the group difference in trial initiation was no longer evident, suggesting differences in endogenous opioid activity between the two groups. Relative expression of μ-opioid receptor in the ventral tegmental area was significantly lower in HF rats. When trial initiation was not required in one-bottle intake tests, no main effect of maternal diet on the intake of sucrose and corn oil emulsions was observed. Thus, the maternal high-fat diet-induced difference in diet preference is not likely due to changes in the sensory orosensory component of the taste stimulus but may depend on alterations in satiety signals or absorptive mechanisms.

Nutrient-specific feeding and endocrine effects of jejunal infusions in obese animals

Intestinal nutrient infusions result in variable decreases in food intake and body weight based on the nutrient type and the specific intestinal infusion site. We previously found that intrajejunal infusions of a fatty acid and glucose, but not casein hydrolysate, decreases food intake and body weight in lean chow-fed laboratory rats. To test whether obese, high fat-fed animals would show similar decreases in food intake and body weight in response to intrajejunal infusions of the same nutrients, equal kilocalorie loads of these nutrients (11.4 kcal) or vehicle were infused into the jejunum of obese, high fat-fed male Sprague-Dawley rats over 7 h/day for 5 consecutive days. Food intake was continuously monitored, and body weight was measured daily. After the infusion on the final day, rats were killed and plasma was collected. Similar to lean chow-fed rats, intrajejunal infusions of linoleic acid (LA) and glucose (Glu), but not casein hydrolysate (Cas), suppressed food intake with no compensatory increase in food intake after the infusion period. In contrast to lean chow-fed rats, only the LA, and not the Glu or Cas, produced decreases in body weight in the obese high fat-fed rat. There also were no differences in plasma glucagon-like peptide-1 levels in any of the nutrient infusion groups compared with saline infusion. These results suggest that there is a differential response to the same nutrients in lean vs. obese animals.

Analyses of meal patterns across dietary shifts

The direct controls of meal size can be categorized into positive signals such as those from the oral cavity and negative signals such as postoral inhibitory cues. It follows that the relative contribution of these signals, and in turn meal pattern parameters, change across periods of high-energy diet exposure. Here, we compared daily intake and meal pattern analysis in male Sprague-Dawley rats presented a high-energy diet for 6weeks then standard chow for ∼1week (HE), with those of standard chow fed controls (CHOW). These measures allow for evaluation of (1) whether there are distinct dynamic and static phases of DIO and if so, how they are characterized, (2) how meal patterns change across short and long term HE experience, and (3) ingestive behavioral changes when HE-fed animals are returned to standard chow. The HE animals showed significantly higher intake primarily driven by an increase in meal size compared to CHOW controls. This was most pronounced during the first several days of high-energy diet exposure thus characterizing the dynamic phase. Intake and meal size decreased with longer exposure to the diet but remained significantly higher than those of CHOW. Increased meal size could be driven by enhanced orosensory stimulation and/or reduced sensitivity to postoral inhibitory feedback. Distribution curves derived from histogram plots of meal size revealed both larger average meal size (right shift) and spread (standard deviation) thus it is tempting to speculate that more than one type of mechanism influences increased meal size. Meal number decreased suggesting post meal inhibitory signaling is relatively intact. However, this increase was insufficient to compensate for the increased meal size. When HE animals were switched to standard chow, daily intake and meal size decreased and eventually returned to values comparable to those of the CHOW rats. Meal number remained lower suggesting altered physiological mechanism(s) that underlie the control of ingestive behavior as a function of previous high-energy diet exposure.

Early postweaning exercise improves central leptin sensitivity in offspring of rat dams fed high-fat diet during pregnancy and lactation

Maternal high-fat (HF) diet has long-term consequences on the metabolic phenotype of the offspring. Here, we determined the effects of postweaning exercise in offspring of rat dams fed HF diet during gestation and lactation. Pregnant Sprague-Dawley rats were maintained on chow or HF diet throughout gestation and lactation. All pups were weaned onto chow diet on postnatal day (PND) 21. At 4 wk of age, male pups were given free access to running wheels (RW) or remained sedentary (SED) for 3 wk, after which all rats remained sedentary, resulting in four groups: CHOW-SED, CHOW-RW, HF-SED, and HF-RW. Male HF offspring gained more body weight by PND7 compared with CHOW pups and maintained this weight difference through the entire experiment. Three weeks of postweaning exercise did not affect body weight gain in either CHOW or HF offspring, but reduced adiposity in HF offspring. Plasma leptin was decreased at the end of the 3-wk running period in HF-RW rats but was not different from HF-SED 9 wk after the exercise period ended. At 14 wk of age, intracerebroventricular injection of leptin suppressed food intake in CHOW-SED, CHOW-RW, and HF-RW, while it did not affect food intake in HF-SED group. At death, HF-RW rats also had higher leptin-induced phospho-STAT3 level in the arcuate nucleus than HF-SED rats. Both maternal HF diet and postweaning exercise had effects on hypothalamic neuropeptide and receptor mRNA expression in adult offspring. Our data suggest that postweaning exercise improves central leptin sensitivity and signaling in this model.

Hypothalamic malonyl-CoA and the control of food intake

Fatty acid metabolism is implicated in the hypothalamic control of food intake. In this regard, malonyl-CoA, an intermediate in fatty acid synthesis, is emerging as a key player. Malonyl-CoA in the hypothalamus has been proposed as an anorectic mediator in the central control of feeding. A large body of evidence demonstrates that modulating hypothalamic activities of malonyl-CoA metabolic enzymes impacts food intake. Malonyl-CoA action appears to play a significant role in the intracellular signaling pathways underlying leptin anorectic effect in the arcuate nucleus. Ghrelin's hypothalamic effect on feeding may also involve the change in malonyl-CoA metabolism. Hypothalamic malonyl-CoA levels are altered in response to fasting and refeeding, suggesting physiological relevance of the changes in malonyl-CoA level in the controls of feeding and energy balance. Malonyl-CoA inhibits the acyltransferase activity of carnitine palmitoyltransferase-1 (CPT-1), and CPT-1 was considered as a downstream effector in hypothalamic malonyl-CoA effect on feeding. However, recent evidence has not been entirely consistent with this notion. In the arcuate nucleus, the inhibition of CPT-1 acyltransferase activity does not play an important role in the feeding effect of either leptin or cerulenin (a fatty acid synthase inhibitor) that requires the increase in malonyl-CoA level. Alternatively, the brain isoform of CPT-1 (CPT-1c) may act as a downstream target in the malonyl-CoA signaling pathways. CPT-1c does not possess a typical acyltransferase activity, and the exact molecular function of this protein is currently unknown. Recent data indicate it is involved in ceramide metabolism. Of relevance, in the arcuate nucleus, CPT-1c may link malonyl-CoA to ceramide metabolism to affect food intake.

Differential effects of central ghrelin on fatty acid metabolism in hypothalamic ventral medial and arcuate nuclei

Fatty acid metabolism is an important pathway involved in the hypothalamus-mediated control of food intake. Previous studies using whole hypothalamic tissue lysates have shown that fatty acid metabolism plays a key role in ghrelin's effect on feeding. Here, we report site-specific effects of central ghrelin on fatty acid metabolism in two critical hypothalamic nuclei, the ventral medial nucleus (VMN) and the arcuate nucleus (Arc). Intracerebroventricular administration of ghrelin to rats activates AMP-activated protein kinase in both the VMN and the Arc, while ghrelin treatment has a site-specific effect on fatty acid metabolic pathways in these two nuclei. In the VMN, central ghrelin increases the phosphorylation level of ACC, indicating the decrease in activity, and decreases the level of malonyl-CoA (the product of ACC). Malonyl-CoA is an inhibitor of carnitine palmitoyltransferase-1 (CPT-1) that is a key enzyme in mitochondrial fatty acid oxidation. Consistent with this action of malonyl-CoA on CPT-1, central ghrelin treatment increases the activity of CPT-1 in the VMN. In contrast, in the Arc, neither malonyl-CoA level nor CPT-1 activity is affected following central ghrelin. Taken together, our data suggest ghrelin exerts differential effects on fatty acid metabolic pathways in the VMN and the Arc.

Identification of hypothalamic neuron-derived neurotrophic factor as a novel factor modulating appetite

Disruption of finely coordinated neuropeptide signals in the hypothalamus can result in altered food intake and body weight. We identified neuron-derived neurotrophic factor (NENF) as a novel secreted protein through a large-scale screen aimed at identifying novel secreted hypothalamic proteins that regulate food intake. We observed robust Nenf expression in hypothalamic nuclei known to regulate food intake, and its expression was altered under the diet-induced obese (DIO) condition relative to the fed state. Hypothalamic Nenf mRNA was regulated by brain-derived neurotrophic factor (BDNF) signaling, itself an important regulator of appetite. Delivery of purified recombinant BDNF into the lateral cerebral ventricle decreased hypothalamic Nenf expression, while pharmacological inhibition of trkB signaling increased Nenf mRNA expression. Furthermore, recombinant NENF administered via an intracerebroventricular cannula decreased food intake and body weight and increased hypothalamic Pomc and Mc4r mRNA expression. Importantly, the appetite-suppressing effect of NENF was abrogated in obese mice fed a high-fat diet, demonstrating a diet-dependent modulation of NENF function. We propose the existence of a regulatory circuit involving BDNF, NENF, and melanocortin signaling. Our study validates the power of using an integrated experimental and bioinformatic approach to identify novel CNS-derived proteins with appetite-modulating function and reveals NENF as an important central modulator of food intake.

Palatable food avoidance and acceptance learning with different stressors in female rats

Stress activates the hypothalamus-pituitary-adrenal (HPA) axis leading to the release of glucocorticoids (GC). Increased activity of the HPA axis and GC exposure has been suggested to facilitate the development of obesity and metabolic syndrome. Nonetheless, different stressors can produce distinct effects on food intake and may support different directions of food learning e.g. avoidance or acceptance. This study examined whether interoceptive (LiCl and exendin-4) and restraint stress (RS) support similar or distinct food learning. Female rats were exposed to different stressors after their consumption of a palatable food (butter icing). After four palatable food-stress pairings, distinct intakes of the butter icing were observed in rats treated with different stressors. Rats that received butter icing followed by intraperitoneal injections of LiCl (42.3mg/kg) and exendin-4 (10μg/kg) completely avoided the palatable food with subsequent presentations. In contrast, rats experiencing RS paired with the palatable food increased their consumption of butter icing across trials and did so to a greater degree than rats receiving saline injections. These data indicate that interoceptive and psychosocial stressors support conditioned food avoidance and acceptance, respectively. Examination of c-Fos immunoreactivity revealed distinct neural activation by interoceptive and psychosocial stressors that could provide the neural basis underlying opposite direction of food acceptance learning.

Glucagon-like peptide 1 and appetite

Glucagon-like peptide 1 (GLP-1) and GLP-1 analogs have received much recent attention due to the success of GLP-1 mimetics in treating type II diabetes mellitus (T2DM), but these compounds may also have the potential to treat obesity. The satiety effect of GLP-1 may involve both within-meal enteroenteric reflexes, and across-meal central signaling mechanisms, that mediate changes in appetite and promote satiety. Here, we review data supporting the role of both peripheral and central GLP-1 signaling in the control of gastrointestinal motility and food intake. Understanding the mechanisms underlying the appetite-suppressive effects of GLP-1 may help in developing targeted treatments for obesity.

Estrogen-related receptor β deletion modulates whole-body energy balance via estrogen-related receptor γ and attenuates neuropeptide Y gene expression

Estrogen-related receptors (ERRs) α, β and γ are orphan nuclear hormone receptors with no known ligands. Little is known concerning the role of ERRβ in energy homeostasis, as complete ERRβ-null mice die mid-gestation. We generated two viable conditional ERRβ-null mouse models to address its metabolic function. Whole-body deletion of ERRβ in Sox2-Cre:ERRβ(lox/lox) mice resulted in major alterations in body composition, metabolic rate, meal patterns and voluntary physical activity levels. Nestin-Cre:ERRβ(lox/lox) mice exhibited decreased expression of ERRβ in hindbrain neurons, the predominant site of expression, decreased neuropeptide Y (NPY) gene expression in the hindbrain, increased lean body mass, insulin sensitivity, increased energy expenditure, decreased satiety and decreased time between meals. In the absence of ERRβ, increased ERRγ signaling decreased satiety and the duration of time between meals, similar to meal patterns observed for both the Sox2-Cre:ERRβ(lox/lox) and Nestin-Cre:ERRβ(lox/lox) strains of mice. Central and/or peripheral ERRγ signaling may modulate these phenotypes by decreasing NPY gene expression. Overall, the relative expression ratio between ERRβ and ERRγ may be important in modulating ingestive behavior, specifically satiety, gene expression, as well as whole-body energy balance.

Overexpression of neuropeptide Y in the dorsomedial hypothalamus increases trial initiation but does not significantly alter concentration-dependent licking to sucrose in a brief-access taste test

Evidence in the literature raises the possibility that alterations in neuropeptide Y (NPY) in the dorsomedial hypothalamus (DMH) may contribute to hyperphagia leading to body weight gain. Previously, we have shown that compared to AAVGFP controls, adeno-associated virus (AAV)-mediated overexpression of NPY in the DMH of lean rats resulted in significantly higher body weight gain that was attributed to increased food intake, and this was further exacerbated by a high-fat diet. Here, we tested AAVNPY and AAVGFP control rats in a brief-access taste procedure (10-s trials, 30-min sessions) to an array of sucrose concentrations under ad libitum and partial food and water access conditions. The test allows for some segregation of the behavioral components by providing a measure of trial initiation (appetitive) and unconditioned licks at each concentration (consummatory). Consistent with previous findings suggesting that NPY has a primary effect on appetitive function, overexpression of DMH NPY did not significantly alter concentration-dependent licking response to sucrose but when tested in a non-restricted food and water schedule, AAVNPY rats initiated significantly more sucrose trials compared to AAVGFP controls in a brief-access taste test.

Maternal high-fat diet during gestation or suckling differentially affects offspring leptin sensitivity and obesity

Maternal high-fat (HF) diet throughout gestation and suckling has long-term consequences on the offspring's metabolic phenotype. Here we determine the relative contribution of pre- or postnatal maternal HF diet on offspring's metabolic phenotype. Pregnant Sprague-Dawley rats were maintained on normal chow or HF diet throughout gestation and suckling. All litters were cross-fostered to chow or HF dams on postnatal day (PND)1, resulting in four groups. Body weight, body composition, and glucose tolerance were measured at weaning and in adulthood. Leptin sensitivity was assessed by signal transducer and activator of transcription (STAT)3 activation on PND10 and PND21. Pups cross-fostered to HF dams gained more body weight than chow pups by PND7 and persisted until weaning. Postnatal HF pups had greater adiposity, higher plasma leptin concentration, impaired glucose tolerance, and reduced phosphorylated STAT3 in response to leptin in the arcuate nucleus at weaning. After weaning, male offspring cross-fostered to HF dams were hyperphagic and maintained greater body weight than postnatal chow pups. Postnatal HF diet during suckling continued to impair glucose tolerance in male and female offspring in adulthood. Maternal HF diet during suckling has a greater influence in determining offspring's metabolic phenotype than prenatal HF diet exposure and could provide insight regarding optimal perinatal nutrition for mothers and children.

Altered Hypothalamic Signaling and Responses to Food Deprivation in Rats Fed a Low-Carbohydrate Diet

OBJECTIVE

To model how consuming a low-carbohydrate (LC) diet influences food intake and body weight.

RESEARCH METHODS AND PROCEDURES

Food intake and body weight were monitored in rats with access to chow (CH), LC-high-fat (HF), or HF diets. After 8 weeks, rats received intracerebroventricular injections of a melanocortin agonist (melanotan-II) and antagonist (SHU9119), and feeding responses were measured. At sacrifice, plasma hormones and hypothalamic expression of mRNA for proopiomelanocortin (POMC), melanocortin-4 receptor, neuropeptide Y (NPY), and agouti related protein (AgRP) were assessed. A second set of rats had access to diet (chow or LC-HF) for 4 weeks followed by 24 h food deprivation on two occasions, after which food intake and hypothalamic POMC, NPY, and AgRP mRNA expression were measured.

RESULTS

HF rats consumed more food and gained more weight than rats on CH or LC-HF diets. Despite similar intakes and weight gains, LC-HF rats had increased adiposity relative to CH rats. LC-HF rats were more sensitive to melanotan-II and less sensitive to SHU9119. LC-HF rats had increased plasma leptin and ghrelin levels and decreased insulin levels, and patterns of NPY and POMC mRNA expression were consistent with those of food-deprived rats. LC-HF rats did not show rebound hyperphagia after food deprivation, and levels NPY, POMC, and AgRP mRNA expression were not affected by deprivation.

DISCUSSION

Our results demonstrate that an LC diet influences multiple systems involved in the controls of food intake and body weight. These data also suggest that maintenance on an LC-HF diet affects food intake by reducing compensatory responses to food deprivation.

Disassociation between preprandial gut peptide release and food-anticipatory activity

Animals learn to anticipate a meal as evidenced by increases in premeal activity. This learned response appears to be independent of the nutrient status of an animal because food-anticipatory activity (FAA) can be seen after entrainment by a highly palatable food when rats remain ad libitum on chow. Mealtime feeding not only induces an increase in activity but also appears to entrain the secretion of various peptides prior to a meal including insulin, ghrelin, and glucagon-like peptide-1 (GLP-1). It is not clear whether these meal-anticipatory changes in peptides are causally associated with FAA. To assess whether FAA and preprandial peptide changes co-occur with meal entrainment using different diets, rats were conditioned to receive a 6-h chow meal, 6-h high-fat meal, or 2 h access of chocolate while ad libitum on chow in the middle of the light cycle. FAA was measured for 4 h prior to mealtime. Rats were then killed at 90, 60, and 30 min prior to mealtime and plasma was collected. Although the chocolate-entrained rats showed comparable FAA with the nonchocolate-entrained animals, they did not show anticipatory increases in the ghrelin or GLP-1. All entrainment conditions induced a decrease in insulin and an increase in glucose prior to mealtime. These data suggest that separate mechanisms may underlie the preprandial increases in ghrelin and GLP-1 and changes in FAA, insulin, and glucose.

A novel obesity model: synphilin-1-induced hyperphagia and obesity in mice

Aims

The pathogenesis of obesity remains incompletely understood and the exploration of the role of novel proteins in obesity may provide important insights into its causes and treatments. Here we report a previously unidentified role for synphilin-1 in the controls of food intake and body weight. Synphilin-1, a cytoplasmic protein, was initially identified as an interaction partner of alpha-synuclein, and has implications in Parkinson's disease pathogenesis related to protein aggregation.

Subjects and methods

To study the in vivo role of synphilin-1, we characterized a human synphilin-1 transgenic mouse (SP1) by assessing synphilin-1 expression, plasma parameters, food intake and spontaneous activity to determine the major behavioral changes and their consequences in the development of the obesity phenotype.

Results

Expression of human synphilin-1 in brain neurons in SP1 mice resulted in increased food intake, body weight and body fat. SP1 mice also displayed hyperinsulinemia, hyperleptinemia and impaired glucose tolerance. Pair-feeding SP1 mice to amounts consumed by non-transgenic mice prevented the increased body weight, adiposity, hyperinsulinemia and hyperleptinemia demonstrating that these were all the consequences of increased food intake. Transgenic expression of synphilin-1 was enriched in hypothalamic nuclei involved in feeding control, and fasting induced elevated endogenous synphilin-1 levels at these sites, suggesting that synphilin-1 is an important player in the hypothalamic energy balance regulatory system.

Conclusion

These studies identify a novel function of synphilin-1 in controlling food intake and body weight, and may provide a unique obesity model for future studies of obesity pathogenesis and therapeutics.