A ketone ester diet exhibits anxiolytic and cognition-sparing properties,and lessens amyloid and tau pathologies in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) involves progressive accumulation of amyloid β-peptide (Aβ) and neurofibrillary pathologies, and glucose hypometabolism in brain regions critical for memory. The 3xTgAD mouse model was used to test the hypothesis that a ketone ester–based diet can ameliorate AD pathogenesis. Beginning at a presymptomatic age, 2 groups of male 3xTgAD mice were fed a diet containing a physiological enantiomeric precursor of ketone bodies (KET) or an isocaloric carbohydrate diet. The results of behavioral tests performed at 4 and 7 months after diet initiation revealed that KET-fed mice exhibited significantly less anxiety in 2 different tests. 3xTgAD mice on the KET diet also exhibited significant, albeit relatively subtle, improvements in performance on learning and memory tests. Immunohistochemical analyses revealed that KET-fed mice exhibited decreased Aβ deposition in the subiculum, CA1 and CA3 regions of the hippocampus, and the amygdala. KET-fed mice exhibited reduced levels of hyperphosphorylated tau deposition in the same regions of the hippocampus, amygdala, and cortex. Thus, a novel ketone ester can ameliorate proteopathic and behavioral deficits in a mouse AD model.     

Hypermetabolism in a triple-transgenic mouse model of Alzheimer's disease

A common feature of Alzheimer's disease (AD) is weight loss, even though there is often an increase in food intake in AD patients. The reasons for this weight loss are unknown, but may be due to increased energy expenditure (metabolic rate) or a reduction in energy intake. This was investigated in the present study, using a triple-transgenic (3xTgAD) mouse model of AD. Two-month-old 3xTgAD mice displayed greater food intake (17%) and body weight (34%) but no difference in metabolic rate, as compared with nontransgenic controls (non-Tg). At 12 months of age, 3xTgAD mice still consumed more food (30%), but their body weight was significantly lower (15%) than non-Tg controls. This reduction in body weight was accompanied by a significant rise in metabolic rate, indicated by greater oxygen consumption (24%) and carbon dioxide production (29%); the effects were also observed in 18-month-old 3xTgAD mice. These data demonstrate for the first time the existence of a hypermetabolic state in an experimental model of AD, but whether this can explain the weight loss observed in AD patients remains to be determined.     

L-type Ca currents at CA1 synapses,but not CA3 or dentate granule neuron synapses,are increased in 3xTgAD mice in an age-dependent manner

Abnormal neuronal excitability and impaired synaptic plasticity might occur before the degeneration and death of neurons in Alzheimer's disease (AD). To elucidate potential biophysical alterations underlying aberrant neuronal network activity in AD, we performed whole-cell patch clamp analyses of L-type (nifedipine-sensitive) Ca²⁺ currents (L-VGCC), 4–aminopyridine-sensitive K⁺ currents, and AMPA (2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid) and NMDA (N-methyl-D-aspartate) currents in CA1, CA3, and dentate granule neurons in hippocampal slices from young, middle-age, and old 3xTgAD mice and age-matched wild type mice. 3xTgAD mice develop progressive widespread accumulation of amyloid β-peptide, and selective hyperphosphorylated tau pathology in hippocampal CA1 neurons, which are associated with cognitive deficits, but independent of overt neuronal degeneration. An age-related elevation of L-type Ca²⁺ channel current density occurred in CA1 neurons in 3xTgAD mice, but not in wild type mice, with the magnitude being significantly greater in older 3xTgAD mice. The NMDA current was also significantly elevated in CA1 neurons of old 3xTgAD mice compared with in old wild type mice. There were no differences in the amplitude of K⁺ or AMPA currents in CA1 neurons of 3xTgAD mice compared with wild type mice at any age. There were no significant differences in Ca²⁺, K⁺, AMPA, or NMDA currents in CA3 and dentate neurons from 3xTgAD mice compared with wild type mice at any age. Our results reveal an age-related increase of L-VGCC density in CA1 neurons, but not in CA3 or dentate granule neurons, of 3xTgAD mice. These findings suggest a potential contribution of altered L-VGCC to the selective vulnerability of CA1 neurons to tau pathology in the 3xTgAD mice and to their degeneration in AD patients.     

High-fat diet aggravates amyloid-beta and tau pathologies in the 3xTg-AD mouse model

To investigate potential dietary risk factors of Alzheimer's disease (AD), triple transgenic (3xTg-AD) mice were exposed from 4 to 13 months of age to diets with a low n-3:n-6 polyunsaturated fatty acid (PUFA) ratio incorporated in either low-fat (5% w/w) or high-fat (35% w/w) formulas and compared with a control diet. The n-3:n-6 PUFA ratio was decreased independently of the dietary treatments in the frontal cortex of 3xTg-AD mice compared to non-transgenic littermates. Consumption of a high-fat diet with a low n-3:n-6 PUFA ratio increased amyloid-beta (Abeta) 40 and 42 concentrations in detergent-insoluble extracts of parieto-temporal cortex homogenates from 3xTg-AD mice. Low n-3:n-6 PUFA intake ratio increased insoluble tau regardless of total fat consumption, whereas high-fat diet incorporating a low n-3:n-6 PUFA ratio also increased soluble tau compared to controls. Moreover, the high-fat diet decreased cortical levels of the postsynaptic marker drebrin, while leaving presynaptic proteins synaptophysin, SNAP-25 and syntaxin 3 unchanged. Overall, these results suggest that high-fat consumption combined with low n-3 PUFA intake promote AD-like neuropathology.     

Protection of brain and pancreas from high-fat diet: effects of catechin and caffeine

To investigate the effect of a high-fat diet on brain and pancreas functions, we used SAMP10 mice that have characteristics of brain atrophy and cognitive dysfunction with aging. Simultaneously, we investigated the effect of green tea catechin consumption on high-fat diet feeding, because green tea catechin has been reported to improve brain atrophy, brain dysfunction and obesity. The body weight of mice fed a high-fat diet from 2 to 12 months was higher than that of the control, although the calorie intake was not. The high-fat diet also increased insulin secretion; however, the hypersecretion of insulin and obesity were suppressed when mice were fed a high-fat diet with green tea catechin and caffeine. Furthermore, brain atrophy was suppressed and the working memory, tested using Y-maze, improved in mice fed a high-fat diet containing green tea catechin and caffeine. The secretion of insulin might affect both obesity and brain function. A strong correlation was found between working memory and insulin release in mice fed a high-fat diet with green tea catechin and/or caffeine. The results indicate the protective effect of green tea catechin and caffeine on the functions of brain and pancreas in mice fed a high-fat diet.     

Chronic dietary alpha-lipoic acid reduces deficits in hippocampal memory of aged Tg2576 mice

Oxidative stress may play a key role in Alzheimer's disease (AD) neuropathology. Here, the effects of the antioxidant, alpha-lipoic acid (ALA) were tested on the Tg2576 mouse, a transgenic model of cerebral amyloidosis associated with AD. Ten-month old Tg2576 and wild type mice were fed an ALA-containing diet (0.1%) or control diet for 6 months and then assessed for the influence of diet on memory and neuropathology. ALA-treated Tg2576 mice exhibited significantly improved learning, and memory retention in the Morris water maze task compared to untreated Tg2576 mice. Twenty-four hours after contextual fear conditioning, untreated Tg2576 mice exhibited significantly impaired context-dependent freezing. ALA-treated Tg2576 mice exhibited significantly more context freezing than the untreated Tg2576 mice. Assessment of brain soluble and insoluble beta-amyloid levels revealed no differences between ALA-treated and untreated Tg2576 mice. Brain levels of nitrotyrosine, a marker of nitrative stress, were elevated in Tg2576 mice, while F2 isoprostanes and neuroprostanes, oxidative stress markers, were not elevated in the Tg2576 mice relative to wild type. These data indicate that chronic dietary ALA can reduce hippocampal-dependent memory deficits of Tg2576 mice without affecting beta-amyloid levels or plaque deposition.     

Disease-modified glycogen synthase kinase-3β intervention by melatonin arrests the pathology and memory deficits in an Alzheimer's animal model

The current therapies for Alzheimer's disease (AD) are merely palliative that cannot arrest the pathologic progression of the disease. Therefore, it is critical to develop treatments that can target the disease-modifying molecule(s). In the present study, we found that treatment of tg2576 mice with melatonin from 4–8 months of age did not improve the pathology or behavioral performance of the mice. However, remarkable attenuation of tau and β-amyloid pathologies with memory improvement were observed when melatonin was supplied from the age of 8–12 months or 4–12 months of the mice; more importantly, the improvements were still significant when the mice survived to old age. We also found that the disease stage-specific alteration of glycogen synthase kinase-3β (GSK-3β) but not protein phosphatase-2A, was correlated with the alterations of the pathology and behavior, and the timely targeting of GSK-3β was critical for the efficacy of melatonin. Our finding suggests that melatonin treatment only at proper timing could arrest AD by targeting the activated GSK-3β, which provides primary evidence for the importance and strategy in developing disease-modifying interventions of AD.     

Accumulation of neurofibrillary tangles and activated microglia is associated with lower neuron densities in the aphasic variant of Alzheimer’s disease

The neurofibrillary tangles (NFT) and amyloid‐ß plaques (AP) that comprise Alzheimer’s disease (AD) neuropathology are associated with neurodegeneration and microglial activation. Activated microglia exist on a dynamic spectrum of morphologic subtypes that include resting, surveillant microglia capable of converting to activated, hypertrophic microglia closely linked to neuroinflammatory processes and AD neuropathology in amnestic AD. However, quantitative analyses of microglial subtypes and neurons are lacking in non‐amnestic clinical AD variants, including primary progressive aphasia (PPA‐AD). PPA‐AD is a language disorder characterized by cortical atrophy and NFT densities concentrated to the language‐dominant hemisphere. Here, a stereologic investigation of five PPA‐AD participants determined the densities and distributions of neurons and microglial subtypes to examine how cellular changes relate to AD neuropathology and may contribute to cortical atrophy. Adjacent series of sections were immunostained for neurons (NeuN) and microglia (HLA‐DR) from bilateral language and non‐language regions where in vivo cortical atrophy and Thioflavin‐S‐positive APs and NFTs were previously quantified. NeuN‐positive neurons and morphologic subtypes of HLA‐DR‐positive microglia (i.e., resting [ramified] microglia and activated [hypertrophic] microglia) were quantified using unbiased stereology. Relationships between neurons, microglia, AD neuropathology, and cortical atrophy were determined using linear mixed models. NFT densities were positively associated with hypertrophic microglia densities (P < 0.01) and inversely related to neuron densities (P = 0.01). Hypertrophic microglia densities were inversely related to densities of neurons (P < 0.01) and ramified microglia (P < 0.01). Ramified microglia densities were positively associated with neuron densities (P = 0.02) and inversely related to cortical atrophy (P = 0.03). Our findings provide converging evidence of divergent roles for microglial subtypes in patterns of neurodegeneration, which includes hypertrophic microglia likely driving a neuroinflammatory response more sensitive to NFTs than APs in PPA‐AD. Moreover, the accumulation of both NFTs and activated hypertrophic microglia in association with low neuron densities suggest they may collectively contribute to focal neurodegeneration characteristic of PPA‐AD.     

3xTgAD mice exhibit altered behavior and elevated Aβ after chronic mild social stress

Chronic stress may be a risk factor for developing Alzheimer's disease (AD), but most studies of the effects of stress in models of AD utilize acute adverse stressors of questionable clinical relevance. The goal of this work was to determine how chronic psychosocial stress affects behavioral and pathological outcomes in an animal model of AD, and to elucidate underlying mechanisms. A triple-transgenic mouse model of AD (3xTgAD mice) and nontransgenic control mice were used to test for an affect of chronic mild social stress on blood glucose, plasma glucocorticoids, plasma insulin, anxiety, and hippocampal amyloid β-particle (Aβ), phosphorylated tau (ptau), and brain-derived neurotrophic factor (BDNF) levels. Despite the fact that both control and 3xTgAD mice experienced rises in corticosterone during episodes of mild social stress, at the end of the 6-week stress period 3xTgAD mice displayed increased anxiety, elevated levels of Aβ oligomers and intraneuronal Aβ, and decreased brain-derived neurotrophic factor levels, whereas control mice did not. Findings suggest 3xTgAD mice are more vulnerable than control mice to chronic psychosocial stress, and that such chronic stress exacerbates Aβ accumulation and impairs neurotrophic signaling.     

Neuropathology of dementia with Lewy bodies in advanced age: A comparison with Alzheimer disease

Dementia with Lewy Bodies (DLB) is a common neurodegenerative disorder of the aging population characterized by α-synuclein accumulation in cortical and subcortical regions. Although neuropathology in advanced age has been investigated in dementias such as Alzheimer Disease (AD), severity of the neuropathology in the oldest old with DLB remains uncharacterized. For this purpose we compared characteristics of DLB cases divided into three age groups 70–79, 80–89 and ≥90 years (oldest old). Neuropathological indicators and levels of synaptophysin were assessed and correlated with clinical measurements of cognition and dementia severity. These studies showed that frequency and severity of DLB was lower in 80–89 and ≥90 year cases compared to 70–79 year old group but cognitive impairment did not vary with age. The extent of AD neuropathology correlated with dementia severity only in the 70–79 year group, while synaptophysin immunoreactivity more strongly associated with dementia severity in the older age group in both DLB and AD. Taken together these results suggest that the oldest old with DLB might represent a distinct group.     

Effects of dietary fat on spontaneous metastasis of Lewis lung carcinoma in mice

The present study assessed the effects of dietary fat on spontaneous metastasis of Lewis lung carcinoma in mice. Three-week old male C57BL/6 mice were fed the AIN-93G diet or a 45% fat diet (% kcal.) for 7 weeks before they were subcutaneously injected with 2.5 × 10⁵ viable carcinoma cells. The primary tumor was resected 2 weeks later, and mice were maintained on their respective diets for an additional 2 weeks. The high-fat diet significantly increased body weight and abdominal adipose weight compared to the AIN-93G diet. Feeding mice the 45% fat diet resulted in a two-fold increase in the number of lung metastases (P < 0.05), a 35% increase in tumor cross-sectional area, and a 50% increase in tumor volume compared to mice fed the AIN-93G diet. There were no differences in plasma concentrations of TIMP-1, IL-1β, VEGF and MCP-1 in non-tumor-bearing mice fed the AIN-93G diet or the high-fat diet, but significant increases in these cytokines in tumor-bearing mice fed the AIN-93G diet compared to the non-tumor-bearing mice fed the same diet (P < 0.05 for each comparison). Further significant increases in these cytokines in tumor-bearing mice fed the 45% fat diet compared to the same tumor-bearing mice fed the AIN-93G diet (P < 0.05 for each comparison). The high-fat diet significantly increased plasma leptin and significantly decreased plasma adiponectin compared to the AIN-93G diet in both non-tumor-bearing and tumor-bearing mice. Results of the present study demonstrated that the high-fat diet enhanced spontaneous metastasis of Lewis lung carcinoma in mice and that this aggressiveness was accompanied with significant increases in plasma concentrations of angiogenic cytokines, suggesting that dietary fat affects metastasis by promoting angiogenic processes.     

Allopregnanolone restores hippocampal-dependent learning and memory and neural progenitor survival in aging 3xTgAD and nonTg mice

We previously demonstrated that allopregnanolone (APα) increased proliferation of neural progenitor cells and reversed neurogenic and cognitive deficits prior to Alzheimer's disease (AD) pathology (Wang, J.M., Johnston, P.B., Ball, B.G., Brinton, R.D., 2005. The neurosteroid allopregnanolone promotes proliferation of rodent and human neural progenitor cells and regulates cell-cycle gene and protein expression. J. Neurosci. 25, 4706-4718; Wang, J.M., Singh, C., Liu, L., Irwin, R.W., Chen, S., Chung, E.J., Thompson, R.F., Brinton, R.D., 2010. Allopregnanolone reverses neurogenic and cognitive deficits in mouse model of Alzheimer's disease. Proc. Natl. Acad. Sci. U. S. A. 107, 6498-6503). Herein, we determined efficacy of APα to restore neural progenitor cell survival and associative learning and memory subsequent to AD pathology in male 3xTgAD mice and their nontransgenic (nonTg) counterparts. APα significantly increased survival of bromodeoxyuridine positive (BrdU+) cells and hippocampal-dependent associative learning and memory in 3xTgAD mice in the presence of intraneuronal amyloid beta (Aβ) whereas APα was ineffective subsequent to development of extraneuronal Aβ plaques. Restoration of hippocampal-dependent associative learning was maximal by the first day and sustained throughout behavioral training. Learning and memory function in APα-treated 3xTgAD mice was 100% greater than vehicle-treated and comparable to maximal normal nonTg performance. In aged 15-month-old nonTg mice, APα significantly increased survival of bromodeoxyuridine-positive cells and hippocampal-dependent associative learning and memory. Results provide preclinical evidence that APα promoted survival of newly generated cells and restored cognitive performance in the preplaque phase of AD pathology and in late-stage normal aging.     

阿尔茨海默病合并2型糖尿病模型小鼠海马血管损伤与认知改变

目的 探讨2型糖尿病（T2DM）对阿尔茨海默病（AD）脑血管发育的影响,及其对AD病理发生的影响机制。 方法 40只6月龄APP/PS1转基因小鼠及同窝野生型小鼠采用高糖高脂饲料喂养6个月后,即各组小鼠12月龄时,连续4 d腹腔注射 1% 链脲佐菌素溶液,建立AD合并T2DM模型小鼠及单纯T2DM模型小鼠。设立4个组别：正常对照组、AD组、T2DM组、AD合并T2DM组,每组小鼠各10只。通过小鼠跳台实验检测小鼠学习记忆能力,墨汁灌注观察小鼠海马区血管形态,油红O染色、免疫荧光实验检测小鼠海马区各病理指标变化。 结果 与正常对照组相比,AD合并T2DM模型小鼠学习与记忆能力明显下降(P<0.05),海马区血管变细、密度明显减低(P<0.05),脂质沉积增多并出现小血管渗漏,且其海马区β-淀粉样前体蛋白裂解酶1（BACE-1）、核因子（NF)-κB与基质金属蛋白酶（MMP)-9表达增多(P<0.05)。 结论 T2DM对小鼠学习记忆功能起负作用,通过促进AD病理变化加速AD模型小鼠脑血管病变,MMP-9的异常表达也可能是引起AD血管病变的原因之一。     

Personality and resilience to Alzheimer’s disease neuropathology: a prospective autopsy study

Alzheimer’s disease (AD) neuropathology is found at autopsy in approximately 30% of cognitively normal older individuals. We examined whether personality traits are associated with such resilience to clinical dementia in individuals with AD neuropathology. Broad factors and specific facets of personality were assessed up to 28 years (mean 11 ± 7 years) before onset of dementia and up to 30 years (mean 15 ± 7 years) before death in a cohort (n = 111) evaluated for AD neuropathology at autopsy. Individuals with higher baseline scores on vulnerability to stress, anxiety, and depression (neuroticism: odds ratio, 2.0; 95% confidence interval, 1.2–3.5), or lower scores on order and competence (conscientiousness: odds ratio, 0.4; 95% confidence interval, 0.2–0.9) were less likely to remain asymptomatic in the presence of AD neuropathology. Neuroticism (r = 0.26), low agreeableness (r = −0.34), and some facets were also significantly associated with advanced stages of neurofibrillary tangles, but the associations between personality traits and risk of clinical dementia were mostly unchanged by controlling for the extent of neurofibrillary tangles and Aβ neuritic plaques. In sum, a resilient personality profile is associated with lower risk or delay of clinical dementia even in persons with AD neuropathology.     

Intermediate methylation epigenotype and its correlation to KRAS mutation in conventional colorectal adenoma

Calpains are cysteine proteinases that selectively cleave proteins in response to calcium signals. Exacerbated activation of calpain has been implicated as a major component in the signaling cascade that leads to β-amyloid (Aβ) production and tau hyperphosphorylation in Alzheimer's disease (AD). In this study, we analyzed the potential therapeutic efficacy of inhibiting the activation of calpain by a novel calpain inhibitor in aged 3xTgAD mice with well-established cognitive impairment, plaques, and tangles. The administration of a novel inhibitor of calpain, A-705253, attenuated cognitive impairment and synaptic dysfunction in a dose-dependent manner in 3xTgAD mice. Inhibition of calpain lowered Aβ(40) and Aβ(42) levels in both detergent-soluble and detergent-insoluble fractions and also reduced the total number and size of thioflavin S-positive fibrillar Aβ deposits. Mechanistically, these effects were, in part, explained by a down-regulation of β-secretase 1 (BACE1) and an up-regulation of ATP-binding cassette transporter A1 (ABCA1) expression, which, in turn, contributed to reduced production and increased clearance of Aβ, respectively. Moreover, A-705253 decreased the activation of cyclin-dependent kinase 5 (CDK5) and thereby diminished the hyperphosphorylation of tau. Finally, blockage of calpain activation reduced the astrocytic and microglial responses associated with AD-like pathological characteristics in aged 3xTgAD mice. Our data provide relevant functional and molecular insights into the beneficial therapeutic effects of inhibiting calpain activation for the management of AD.     

Impaired spatial memory in APP-overexpressing mice on a homocysteinemia-inducing diet

Consumption of a diet that significantly elevates homocysteine (homocysteinemia) induces cell death in the CA3 hippocampal subfield in amyloid precursor protein (APP) over-expressing transgenic mice but not in wild-type controls. We assessed behavioral and other neuropathological effects of a homocysteinemia-inducing diet in aged APP-overexpressing mice. Starting at 16-18 months of age, mice were fed either a treatment diet lacking folate, choline, and methionine, and supplemented with homocysteine, or a control diet containing normal amounts of folate, choline and methionine but no homocysteine. After 5 months on the experimental diets, performance on a delayed non-matching-to-position working-memory task was unimpaired. In contrast, spatial reference memory in the water maze was impaired in transgenic mice on the treatment diet. Transgenic mice had higher homocysteine levels than wild-type mice even when fed the control diet, suggesting an effect of genotype on homocysteine metabolism. Methyl-donor deficiency did not alter amyloid deposition in the transgenic mice. These results suggest that disrupted homocysteine metabolism may induce Abeta-associated memory impairments and neurodegeneration in APP overexpressing mice.     

Age‐Dependent Effect of β‐Amyloid Toxicity on Basal Forebrain Cholinergic Neurons and Inflammation in the Rat Brain

Beta‐amyloid (Aβ) accumulation, neuroinflammation, basal forebrain cholinergic loss and hippocampal degeneration are well‐described pathologies associated with Alzheimer's disease (AD). However, the role that age plays in the susceptibility of the brain to these AD pathologies and the relationships between them is still not well understood. This study investigated the age‐related response to intracerebroventricular injection of Aβ_25–35 in 3‐, 6‐ and 9‐month‐old rats. Aβ toxicity resulted in an age‐related increase in cholinergic loss and microglial activation in the basal forebrain along with neuronal loss in the hippocampal CA3 subfield. Performance in the Morris water maze revealed impairments in long‐term reference memory in 6‐month‐old Aβ administered animals, which was not seen in 3‐month‐old animals. These results support a role of Aβ administration in inducing age‐dependent cholinergic loss and neuroinflammation, and additionally provide evidence for a more age‐appropriate model of adult‐onset Aβ toxicity demonstrating pathological changes that reflect the early stages of AD pathogenesis including neuroinflammation, cholinergic loss and beginning stages of memory impairment.     

Plasma leptin and insulin in C57BI/6J mice on a high-fat diet: relation to subsequent changes in body weight

It has been proposed that leptin and insulin through central effects are involved in the regulation of energy balance and body weight. Whether circulating leptin or insulin levels predict subsequent changes in body weight is, however, not known. We examined plasma leptin and insulin at 2, 3, 6, 9 and 12 months of age in C57BI/6J mice given a normal diet (n = 12) or a high-fat diet (58% fat on a caloric base; n = 15). Plasma leptin levels increased by age and correlated with body weight in the entire material (r = 0.81, P < 0.001). Also plasma insulin increased by high-fat diet and correlated across all age periods with body weight (r = 0.56, P < 0.001). In mice, given normal diet, plasma leptin or insulin did not correlate to subsequent changes in body weight at any of the time points studied. However, in mice given the high-fat diet, plasma leptin at 6 (r = -0.57, P = 0.027) and 9 months of age (r = -0.56, P = 0.042) as well as plasma insulin at 6 (r = - 0.51, P = 0.049) and 9 months (r = -0.58, P = 0.037) correlated inversely to the change in body weight during the subsequent 3-month period. Hence, both leptin and insulin are negative predictors for future weight gain in high-fat fed mice. This suggests that when the regulation of body weight is challenged by a high-fat diet, leptin and insulin act to restrain or prevent future weight gain. This in turn may suggest that impairment of these (probably central) actions of leptin and insulin might underlie excessive increase in body weight under such conditions.