Chow Feeding Research Articles

Changes of lipid levels in mice with hypoxic pulmonary arterial hypertension

To observe the changes of lipid levels in mice with pulmonary hypertension induced by hypoxia. The animal model of hypoxic pulmonary hypertension was established by exposing the mice to isobaric hypoxic chamberfor 3 weeks (23 h/d, regular chow feed). Twenty male C57BL/6 mice were randomlydivided into normoxia group and hypoxia group (n=10). The concentrations of total cholesterol, low density lipoprotein (LDL) and high density lipoprotein (HDL) in plasma were detected by Elisa method.The mRNA levels of HMG-CoAreductase (HMGCR), low density lipoprotein receptor (LDLR), scavenger receptor class B1 (SR-B1), and sterol regulatory element-binding factor-2 (SREBF2) in liverwere measured by real-time PCR. ① The right ventricular systolic pressure (RVSP) and the weight ratio of right ventricle (RV) to left ventricle plus septum (LV+S) of hypoxia group were significantly higher than those of normoxia group (P<0.05).② The concentrations of HDL and HDL/LDL in plasma were significantly higher in hypoxia group, compared with normoxia group (P<0.05).③The mRNA levels of LDLR and SR-B1in liver were significantly down-regulated in hypoxia group(P<0.05).④RVSP were significantly negative correlated with HDL/LDL, the gene expression of LDLR and SR-B1 (P<0.05). Abnormal lipid metabolism participates in the pathological proceeding of pulmonary hypertension induced by hypoxia.

Removal of high-fat diet after chronic exposure drives binge behavior and dopaminergic dysregulation in female mice

A significant contributor to the obesity epidemic is the overconsumption of highly palatable, energy dense foods. Chronic intake of palatable foods is associated with neuroadaptations within the mesocorticolimbic dopamine system adaptations which may lead to behavioral changes, such as overconsumption or bingeing. We examined behavioral and molecular outcomes in mice that were given chronic exposure to a high-fat diet (HFD; 12weeks), with the onset of the diet either in adolescence or adulthood. To examine whether observed effects could be reversed upon removal of the HFD, animals were also studied 4weeks after a return to chow feeding. Most notably, female mice, particularly those exposed to HFD starting in adolescence, demonstrated the emergence of binge-like behavior when given restricted access to a palatable food. Further, changes in dopamine-related gene expression and dopamine content in the prefrontal cortex were observed. Some of these HFD-driven phenotypes reversed upon removal of the diet, whereas others were initiated by removal of the diet. These findings have implications for obesity management and interventions, as both pharmacological and behavioral therapies are often combined with dietary interventions (e.g., reduction in calorie dense foods).

Loss of Protein Kinase C Alpha Disrupts Mean Arterial Pressure and Diurnal Rhythm

The sodium‐chloride cotransporter (NCC) is an essential regulator of sodium transport in the distal convoluted tubule (DCT). As such, functional aberrations will lead to dysregulation of sodium homeostasis and blood pressure. Although this role is well accepted, the mechanisms accounting for increased distal nephron sodium reabsorption is not completely understood. Previously published data from the Pharmacogenomic Evaluation of Antihypertensive Responses (PEAR) Study revealed that a single nucleotide polymorphism (SNP) in PKC‐α increases sensitivity to thiazide diuretics. To date, it is unknown whether this SNP is a gain or loss of function of PKC‐α. To investigate whether PKC‐α may be altering blood pressure via NCC, PKC‐α KO (PKC KO) and PKC Control (CTL) mice were used to measure blood pressure via radiotelemetry after normal and high salt (HS, 4%) dietary manipulations and Western blot analysis performed using kidney lysates. Using radiotelemetry (DSI) measurements obtained over an active and sleeping time periods, we report a significant decrease in mean arterial pressure (MAP) in the PKC KO mice as compared to control at baseline (111±1.3mmHg vs 120±2.4mmHg, n=12–16, p&lt;0.001). When comparing active vs. sleeping MAP, PKC KO mice had depressed MAP during both time periods, yet blood pressure differences (day vs. night) double during active periods (5.4±1.3mmHg PKC KO vs. 10.9±3.9mmHg PKC CTL, n=6–7). These differences were abolished with HS chow feeding (17.3mmHg PKC KO vs. 16.1mmHg PKC CTRL, n=4). To determine a possible mechanism for this phenomenon, whole kidney lysate was used to assay for total NCC protein. Total NCC protein was significantly increased in PKC KO mice at baseline, and continued during HS chow feeding, as compared to PKC CTL. In addition, PKC KO mice exhibited a diuresis with both normal and HS feeding. Our data suggest that lack of PKC‐α leads to decreased MAPs and diuresis, which may lead to increased total NCC expression to compensate. In addition, PKC KO mice exhibited an aberrant diurnal rhythm, which was recovered with HS diet suggesting that PKC‐α may be necessary to maintain sodium homeostasis.Support or Funding InformationNIDDK085097‐ RSH 2T32DK7656‐21 Emory Renal Division‐BMW

The brain renin-angiotensin system plays a crucial role in regulating body weight in diet-induced obesity in rats.

Reduced weight gain after treatment with AT1 receptor antagonists may involve a brain-related mechanism. Here, we investigated the role of the brain renin-angiotensin system on weight regulation and food behaviour, with or without additional treatment with telmisartan. Transgenic rats with a brain-specific deficiency in angiotensinogen (TGR(ASrAOGEN)) and the corresponding wild-type, Sprague Dawley (SD) rats were fed (3months) with a high-calorie cafeteria diet (CD) or standard chow. SD and TGR(ASrAOGEN) rats on the CD diet were also treated with telmisartan (8mg·kg(-1) ·d(-1) , 3months). Compared with SD rats, TGR(ASrAOGEN) rats (i) had lower weights during chow feeding, (ii) did not become obese during CD feeding, (iii) had normal baseline leptin plasma concentrations independent of the feeding regimen, whereas plasma leptin of SD rats was increased due to CD, (iv) showed a reduced energy intake, (v) had a higher, strain-dependent energy expenditure, which is additionally enhanced during CD feeding, (vi) had enhanced mRNA levels of pro-opiomelanocortin and (vii) showed improved glucose control. Weight gain and energy intake in rats fed the CD diet were markedly reduced by telmisartan in SD rats but only to a minor extent in TGR(ASrAOGEN) rats. The brain renin-angiotensin system affects body weight regulation, feeding behaviour and metabolic disorders. When angiotensin II levels are low in brain, rats are protected from developing diet-induced obesity and obesity-related metabolic impairments. We further suggest that telmisartan at least partly lowers body weight via a CNS-driven mechanism.

Effects of lisdexamfetamine and s-citalopram, alone and in combination, on effort-related choice behavior in the rat.

Effort-related motivational symptoms, such as anergia, psychomotor retardation, and fatigue, are an important aspect of depression and other disorders. Motivational symptoms are resistant to some treatments, including serotonin transport (SERT) inhibitors. Tests of effort-based choice using operant behavior tasks (e.g., concurrent lever pressing/ chow feeding tasks) can be used as animal models of motivational symptoms. Tests of effort-related choice allow animals to choose between high-effort actions that lead to more highly valued rewards vs. low-effort alternatives that lead to less valued rewards (i.e., less preferred or lower magnitude). Rats treated with the vesicular monoamine transport inhibitor tetrabenazine, or the cytokine interleukin-1β (IL-1β), which are associated with depressive symptoms in humans, can alter effort-related choice, reducing selection of the high effort alternative (lever pressing) while increasing intake of freely available chow. The present studies focused upon the ability of lisdexamfetamine (LDX) to increase exertion of effort in rats responding on effort-based choice tasks under several different conditions. LDX attenuated the shift from fixed ratio 5 lever pressing to chow intake induced by tetrabenazine and IL-1β. In contrast, the SERT inhibitor s-citalopram failed to reverse the effects of tetrabenazine. When given in combination with tetrabenazine+s-citalopram, LDX significantly increased lever pressing output compared to tetrabenaine+citalopram alone. LDX also increased work output in rats responding on a progressive ratio/chow feeding choice task. LDX can increase work output in rats responding on effort-based choice tasks, which may have implications for understanding the neurochemistry of motivational symptoms in humans.

Change of endoplasmic reticulum stress-related molecules in the course of sciatic nerve injury of diabetic rats

Objective To investigate the dynamic changes of endoplasmic reticulum stress-related molecules including glucose regulated protein (GRP78), C/EBP homologous protein (CHOP), and caspase-12 in sciatic nerve of diabetic rats and explore its mechanisms. Methods Rats were randomly divided into normal control group (NC) and diabetes mellitus group (DM) that were induced by intraperitoneal injection of Streptozocin after 4 weeks of high-fat chow feeding. Sciatic nerves were isolated for three times at 4 weeks, 8 weeks and 12 weeks after induction of diabetes. The expressions of GRP78, CHOP, and caspase-12 were detected with quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analyses. The morphology of sciatic nerve was investigated with electron microscope. Results With the extension of the course, demyelinating and axonal injury appeared in sciatic nerve of diabetic rats. The expressions of GRP78 mRNA and protein in DM group were significantly higher than NC group at 4 weeks and 8 weeks after induction of diabetes(P<0.05, P<0.01). The expressions of CHOP mRNA and protein in DM group were significantly higher than NC group at 8 weeks and 12 weeks after induction of diabetes (P<0.05). The expressions of caspase-12 mRNA and protein in DM group were significantly higher than NC group at 8 weeks after induction of diabetes(P<0.05, P<0.01). Conclusions Endoplasmic reticulum stress-related molecules (GRP78, CHOP, and caspase-12) contributed to the peripheral nerve injury of diabetic rats, and displayed dynamic changes. Key words: Endoplasmic reticulum; Stress; Diabetic neuropathies/ME; Peripheral nervous system diseases/CO/ME; Membrane proteins/ME; Transcription factor CHOP/ME; Caspase 12/ME

Abstract 11679: Similarities Between the Villi of the Jejunum and the Human Artery Wall May Contribute to Diet-Induced Dyslipidemia and Systemic Inflammation in LDLR Null Mice

In early atherosclerosis, LDL in the human artery wall is seeded with reactive oxygen species resulting in the formation of oxidized phospholipids that promote infiltration of monocytes, which convert into macrophages. We recently reported that supplementing standard mouse chow with lysophosphatidylcholine (LysoPC) 18:1 caused dyslipidemia and systemic inflammation in LDLR null mice. We now report that feeding chow supplemented with LysoPC 18:1 (1 mg LysoPC 18:1 per gram chow) or feeding a Western diet (WD) to LDLR null mice results in an increase in oxidized phospholipids in the villi of the jejunum as detected with the E06 antibody. On a diet of standard mouse chow, 2.2 ± 0.2% of the area of the villi of the jejunum stained positively for oxidized phospholipids. After two weeks of feeding standard mouse chow supplemented with LysoPC 18:1 or feeding WD, the area staining positively for oxidized phospholipids increased to 4.0 ± 0.5%, and 7.3 ± 0.8%, respectively (p = 0.0043, and p &lt; 0.0001, respectively). If 0.06% by weight of a concentrate of transgenic tomato expressing an apoA-I mimetic peptide (Tg6F) was added to the chow supplemented with LysoPC 18:1 or was added to WD, the area staining positively for oxidized phospholipids decreased to 2.1 ± 0.3%, and 2.3 ± 0.4%, respectively (p = 0.0029, and p &lt;0.0001, respectively). Concomitant with the increase in oxidized phospholipids there was a significant increase in macrophages as detected by F4/80 staining. On chow 0.8 ± 0.2% of the area of the villi of the jejunum stained positively for macrophages. After two weeks of feeding chow supplemented with LysoPC 18:1 or feeding WD, the area staining positively for macrophages increased to 1.6 ± 0.2%, and 4.4 ± 0.4%, respectively (p = 0.0095, and p &lt; 0.0001, respectively). If 0.06% by weight of Tg6F was added to the chow supplemented with LysoPC 18:1 or was added to WD, the area staining positively for macrophages decreased to 0.9 ± 0.2%, and 3.0 ± 0.3%, respectively (p = 0.0169, and p &lt; 0.0001, respectively). These data support the hypothesis that LysoPC 18:1 and WD lead to a sequence of events in the villi of jejunum that is very similar to that seen in the human artery wall, and may contribute to diet-induced dyslipidemia and systemic inflammation in LDLR null mice.

Contribution of brown adipose tissue activity to the control of energy balance by GLP-1 receptor signalling in mice.

We assessed the contribution of glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) signalling to thermogenesis induced by high-fat diet (HFD) consumption. Furthermore, we determined whether brown adipose tissue (BAT) activity contributes to weight loss induced by chronic subcutaneous treatment with the GLP-1R agonist, liraglutide, in a model of diet-induced obesity. Metabolic phenotyping was performed using indirect calorimetry in wild-type (WT) and Glp1r-knockout (KO) mice during chow and HFD feeding at room temperature and at thermoneutrality. In a separate study, we investigated the contribution of BAT thermogenic capacity to the weight lowering effect induced by GLP-1 mimetics by administering liraglutide (10 or 30nmolkg(-1)day(-1) s.c.) to diet-induced obese (DIO) mice for 6 or 4weeks, respectively. In both studies, animals were subjected to a noradrenaline (norepinephrine)-stimulated oxygen consumption [Formula: see text] test. At thermoneutrality, HFD-fed Glp1r-KO mice had similar energy expenditure (EE) compared with HFD-fed WT controls. However, HFD-fed Glp1r-KO mice exhibited relatively less EE when housed at a cooler standard room temperature, and had relatively lower [Formula: see text] in response to a noradrenaline challenge, which is consistent with impaired BAT thermogenic capacity. In contrast to the loss of function model, chronic peripheral liraglutide treatment did not increase BAT activity as determined by noradrenaline-stimulated [Formula: see text] and BAT gene expression. These data suggest that although endogenous GLP-1R signalling contributes to increased BAT thermogenesis, this mechanism does not play a significant role in the food intake-independent body weight lowering effect of the GLP-1 mimetic liraglutide in DIO mice.

Enhanced mitochondrial superoxide scavenging does not improve muscle insulin action in the high fat-fed mouse.

Improving mitochondrial oxidant scavenging may be a viable strategy for the treatment of insulin resistance and diabetes. Mice overexpressing the mitochondrial matrix isoform of superoxide dismutase (sod2tg mice) and/or transgenically expressing catalase within the mitochondrial matrix (mcattg mice) have increased scavenging of O2˙ˉ and H2O2, respectively. Furthermore, muscle insulin action is partially preserved in high fat (HF)-fed mcattg mice. The goal of the current study was to test the hypothesis that increased O2˙ˉ scavenging alone or in combination with increased H2O2 scavenging (mtAO mice) enhances in vivo muscle insulin action in the HF-fed mouse. Insulin action was examined in conscious, unrestrained and unstressed wild type (WT), sod2tg, mcattg and mtAO mice using hyperinsulinemic-euglycemic clamps (insulin clamps) combined with radioactive glucose tracers following sixteen weeks of normal chow or HF (60% calories from fat) feeding. Glucose infusion rates, whole body glucose disappearance, and muscle glucose uptake during the insulin clamp were similar in chow- and HF-fed WT and sod2tg mice. Consistent with our previous work, HF-fed mcattg mice had improved muscle insulin action, however, an additive effect was not seen in mtAO mice. Insulin-stimulated Akt phosphorylation in muscle from clamped mice was consistent with glucose flux measurements. These results demonstrate that increased O2˙ˉ scavenging does not improve muscle insulin action in the HF-fed mouse alone or when coupled to increased H2O2 scavenging.

Long-term high fat feeding of rats results in increased numbers of circulating microvesicles with pro-inflammatory effects on endothelial cells.

Obesity and type 2 diabetes lead to dramatically increased risks of atherosclerosis and CHD. Multiple mechanisms converge to promote atherosclerosis by increasing endothelial oxidative stress and up-regulating expression of pro-inflammatory molecules. Microvesicles (MV) are small ( < 1 μm) circulating particles that transport proteins and genetic material, through which they are able to mediate cell-cell communication and influence gene expression. Since MV are increased in plasma of obese, insulin-resistant and diabetic individuals, who often exhibit chronic vascular inflammation, and long-term feeding of a high-fat diet (HFD) to rats is a well-described model of obesity and insulin resistance, we hypothesised that this may be a useful model to study the impact of MV on endothelial inflammation. The number and cellular origin of MV from HFD-fed obese rats were characterised by flow cytometry. Total MV were significantly increased after feeding HFD compared to feeding chow (P< 0·001), with significantly elevated numbers of MV derived from leucocyte, endothelial and platelet compartments (P< 0·01 for each cell type). MV were isolated from plasma and their ability to induce reactive oxygen species (ROS) formation and vascular cell adhesion molecule (VCAM)-1 expression was measured in primary rat cardiac endothelial cells in vitro. MV from HFD-fed rats induced significant ROS (P< 0·001) and VCAM-1 expression (P= 0·0275), indicative of a pro-inflammatory MV phenotype in this model of obesity. These findings confirm that this is a useful model to further study the mechanisms by which diet can influence MV release and subsequent effects on cardio-metabolic health.

Intestinal Insulin Receptor Contributes to Elevated Cholesterol and Stem, Enteroendocrine, and Paneth Cell Adaptations to Obesity

Background The insulin receptor (IR) regulates nutrient uptake and utilization in multiple organs, but its role in the intestinal epithelium is not defined. Methods: We generated and characterized lean and obese mice with intestinal epithelial cell (IEC)-specific IR deletion (IRΔIEC) and littermate controls (IRfl/fl) using chow or high-fat diet (HFD) feeding to test the hypothesis that loss of IEC-IR will alter intestinal growth, biomarkers of intestinal epithelial stem cells (IE­­­SC) or other lineages, and metabolic responses to HFD. Results: In lean IRΔIEC mice there was little effect on any parameter measured. During HFD-induced obesity, both IRfl/fl and IRΔIEC mice exhibited increased body mass, impaired glucose tolerance, and decreased Paneth cell number. Obese IRfl/fl mice exhibited increases in circulating cholesterol, numbers enteroendocrine cells (EEC), mRNAs encoding a cholesterol transporter and incretins glucose-dependent insulinotrophic peptide and glucagon, and IESC biomarkers. All these effects were significantly attenuated or lost in obese IRΔIEC mice. Conclusions Our findings provide novel evidence that although IEC-IR is not required for normal intestinal growth, during HFD-induced obesity, IEC-IR contributes to increases in plasma cholesterol, EEC number, and increased mRNAs marking IESC and encoding proteins involved cholesterol handing and insulin regulation. Grants: F31 AG040943 (SFA), NIH DK040247-19 (PKL).

Acute consumption of a high-fat diet prior to ischemia-reperfusion results in cardioprotection through NF-κB-dependent regulation of autophagic pathways

Previous studies have demonstrated improvement of cardiac function occurs with acute consumption of a high-fat diet (HFD) after myocardial infarction (MI). However, no data exist addressing the effects of acute HFD upon the extent of injury after MI. This study investigates the hypothesis that short-term HFD, prior to infarction, protects the heart against ischemia-reperfusion (I/R) injury through NF-κB-dependent regulation of cell death pathways in the heart. Data show that an acute HFD initiates cardioprotection against MI (&gt;50% reduction in infarct size normalized to risk region) after 24 h to 2 wk of HFD, but protection is completely absent after 6 wk of HFD, when mice are reported to develop pathophysiology related to the diet. Furthermore, cardioprotection after 24 h of HFD persists after an additional 24 h of normal chow feeding and was found to be dependent upon NF-κB activation in cardiomyocytes. This study also indicates that short-term HFD activates autophagic processes (beclin-1, LC-3) preischemia, as seen in other protective stimuli. Increases in beclin-1 and LC-3 were found to be NF-κB-dependent, and administration of chloroquine, an inhibitor of autophagy, abrogated cardioprotection. Our results support that acute high-fat feeding mediates cardioprotection against I/R injury associated with a NF-κB-dependent increase in autophagy and reduced apoptosis, as has been found for ischemic preconditioning.

Effect of diet on preference and intake of sucrose in obese prone and resistant rats.

Increased orosensory stimulation from palatable diets and decreased feedback from gut signals have been proposed as contributing factors to obesity development. Whether altered taste functions associated with obesity are common traits or acquired deficits to environmental factors, such as a high-energy (HE)-diet, however, is not clear. To address this, we examined preference and sensitivity of increasing concentrations of sucrose solutions in rats prone (OP) and resistant (OR) to obesity during chow and HE feeding and measured lingual gene expression of the sweet taste receptor T1R3. When chow-fed, OP rats exhibited reduced preference and acceptance of dilute sucrose solutions, sham-fed less sucrose compared to OR rats, and had reduced lingual T1R3 gene expression. HE-feeding abrogated differences in sucrose preference and intake and lingual T1R3 expression between phenotypes. Despite similar sucrose intakes however, OP rats consumed significantly more total calories during 48-h two-bottle testing compared to OR rats. The results demonstrate that OP rats have an innate deficit for sweet taste detection, as illustrated by a reduction in sensitivity to sweets and reduced T1R3 gene expression; however their hyperphagia and subsequent obesity during HE-feeding is most likely not due to altered consumption of sweets.

Over-expression of Follistatin-like 3 attenuates fat accumulation and improves insulin sensitivity in mice

ObjectiveFollistatin-like 3 (fstl3), a natural inhibitor of members of the TGF-β family, increases during resistance training in human plasma. Fstl3 primarily binds myostatin and activin A, and thereby inhibits their functions. We hypothesize that blocking myostatin and activin A signalling through systemic fstl3 over-expression protects against diet-induced obesity and insulin resistance. MethodsFstl3 was over-expressed by DNA electrotransfer in tibialis anterior, quadriceps and gastrocnemius muscles in female C57BL/C mice, and the mice were subsequently randomized to chow or high-fat feeding. Body weight, food intake, fat accumulation by MR scanning, and glucose, insulin and glucagon tolerance were evaluated, as was the response in body weight and metabolic parameters to 24h fasting. Effects of fstl3 on pancreatic insulin and glucagon content, and pancreatic islet morphology were determined. ResultsFstl3 over-expression reduced fat accumulation during high-fat feeding by 16%, and liver fat by 50%, as determined by MRI. No changes in body weight were observed, while the weight of the transfected muscles increased by 10%. No transcriptional changes were found in the subcutaneous adipose tissue. Fstl3 mice displayed improved insulin sensitivity and muscle insulin signalling. In contrast, glucose tolerance was impaired in high-fat fed fstl3 mice, which was explained by increased hepatic glucagon sensitivity and glucose output, as well as a decrease in the pancreatic insulin/glucagon ratio. Accordingly, fstl3 transfection improved counter-regulation to 24h fasting. ConclusionFstl3 over-expression regulates insulin and glucagon sensitivities through increased muscular insulin action, as well as increased hepatic glucagon sensitivity and pancreatic glucagon content.

Genetic determinants of atherosclerosis, obesity, and energy balance in consomic mice.

Metabolic diseases such as obesity and atherosclerosis result from complex interactions between environmental factors and genetic variants. A panel of chromosome substitution strains (CSSs) was developed to characterize genetic and dietary factors contributing to metabolic diseases and other biological traits and biomedical conditions. Our goal here was to identify quantitative trait loci (QTLs) contributing to obesity, energy expenditure, and atherosclerosis. Parental strains C57BL/6 and A/J together with a panel of 21 CSSs derived from these progenitors were subjected to chronic feeding of rodent chow and atherosclerotic (females) or diabetogenic (males) test diets, and evaluated for a variety of metabolic phenotypes including several traits unique to this report, namely fat pad weights, energy balance, and atherosclerosis. A total of 297 QTLs across 35 traits were discovered, two of which provided significant protection from atherosclerosis, and several dozen QTLs modulated body weight, body composition, and circulating lipid levels in females and males. While several QTLs confirmed previous reports, most QTLs were novel. Finally, we applied the CSS quantitative genetic approach to energy balance, and identified three novel QTLs controlling energy expenditure and one QTL modulating food intake. Overall, we identified many new QTLs and phenotyped several novel traits in this mouse model of diet-induced metabolic diseases.

The VMAT-2 inhibitor tetrabenazine affects effort-related decision making in a progressive ratio/chow feeding choice task: reversal with antidepressant drugs.

Behavioral activation is a fundamental feature of motivation, and organisms frequently make effort-related decisions based upon evaluations of reinforcement value and response costs. Furthermore, people with major depression and other disorders often show anergia, psychomotor retardation, fatigue, and alterations in effort-related decision making. Tasks measuring effort-based decision making can be used as animal models of the motivational symptoms of depression, and the present studies characterized the effort-related effects of the vesicular monoamine transport (VMAT-2) inhibitor tetrabenazine. Tetrabenazine induces depressive symptoms in humans, and also preferentially depletes dopamine (DA). Rats were assessed using a concurrent progressive ratio (PROG)/chow feeding task, in which they can either lever press on a PROG schedule for preferred high-carbohydrate food, or approach and consume a less-preferred lab chow that is freely available in the chamber. Previous work has shown that the DA antagonist haloperidol reduced PROG work output on this task, but did not reduce chow intake, effects that differed substantially from those of reinforcer devaluation or appetite suppressant drugs. The present work demonstrated that tetrabenazine produced an effort-related shift in responding on the PROG/chow procedure, reducing lever presses, highest ratio achieved and time spent responding, but not reducing chow intake. Similar effects were produced by administration of the subtype selective DA antagonists ecopipam (D1) and eticlopride (D2), but not by the cannabinoid CB1 receptor neutral antagonist and putative appetite suppressant AM 4413, which suppressed both lever pressing and chow intake. The adenosine A2A antagonist MSX-3, the antidepressant and catecholamine uptake inhibitor bupropion, and the MAO-B inhibitor deprenyl, all reversed the impairments induced by tetrabenazine. This work demonstrates the potential utility of the PROG/chow procedure as a rodent model of the effort-related deficits observed in depressed patients.

Hypothalamic gliosis associated with high-fat diet feeding is reversible in mice: a combined immunohistochemical and magnetic resonance imaging study.

Gliosis, the activation of astrocyte and microglial cell populations, is a hallmark of central nervous system injury and is detectable using either immunohistochemistry or in vivo magnetic resonance imaging (MRI). Obesity in rodents and humans is associated with gliosis of the arcuate nucleus, a key hypothalamic region for the regulation of energy homeostasis and adiposity, but whether this response is permanent or reversible is unknown. Here we combine terminal immunohistochemistry analysis with serial, noninvasive MRI to characterize the progression and reversibility of hypothalamic gliosis in high-fat diet (HFD)-fed mice. The effects of HFD feeding for 16 weeks to increase body weight and adiposity relative to chow were nearly normalized after the return to chow feeding for an additional 4 weeks in the diet-reversal group. Mice maintained on the HFD for the full 20-week study period experienced continued weight gain associated with the expected increases of astrocyte and microglial activation in the arcuate nucleus, but these changes were not observed in the diet-reversal group. The proopiomelanocortin neuron number did not differ between groups. Although MRI demonstrated a positive correlation between body weight, adiposity, and the gliosis-associated T2 signal in the mediobasal hypothalamus, it did not detect the reversal of gliosis among the HFD-fed mice after the return to chow diet. We conclude that hypothalamic gliosis associated with 16-week HFD feeding is largely reversible in rodents, consistent with the reversal of the HFD-induced obesity phenotype, and extend published evidence regarding the utility of MRI as a tool for studying obesity-associated hypothalamic gliosis in vivo.

Dietary effects on resting metabolic rate in C57BL/6 mice are differentially detected by indirect (O2/CO2 respirometry) and direct calorimetry.

Resting metabolic rate (RMR) studies frequently involve genetically-manipulated mice and high fat diets (HFD). We hypothesize that the use of inadequate methods impedes the identification of novel regulators of RMR. This idea was tested by simultaneously measuring RMR by direct calorimetry and respirometry in C57BL/6J mice fed chow, 45% HFD, and then returned to chow. Comparing results during chow feeding uncovered an underestimation of RMR by respirometry (0.010 ± 0.001 kcal/h, P < 0.05), which is equivalent in magnitude to ∼2% of total daily caloric turnover. RMR during 45% HFD feeding was increased by respirometry (+0.013 ± 0.003 kcal/h, P < 0.05), but not direct calorimetry (+0.001 ± 0.002 kcal/h). Both methods indicated that return to chow reduced RMR compared to HFD, though direct calorimetry indicated a reduction below the initial chow fed state (−0.019 ± 0.004 kcal/h versus baseline, P < 0.05) that was not detected by respirometry (−0.003 ± 0.002 kcal/h versus baseline). These results highlight method-specific interpretations of the effects of dietary interventions upon RMR in mice, and prompt the reevaluation of preclinical screening methods used to identify novel RMR modulators.

Enhanced amelioration of high-fat diet-induced fatty liver by docosahexaenoic acid and lysine supplementations.

Fatty liver disease is the most common pathological condition in the liver. Here, we generated high-fat diet-(HFD-) induced nonalcoholic fatty liver disease (NAFLD) in mice and tested the effects of docosahexaenoic acid (DHA) and lysine during a four-week regular chow (RC)feeding. Our results showed that 1% lysine and the combination of 1% lysine + 1% DHA reduced body weight. Moreover, serum triglyceride levels were reduced by 1% DHA and 1% lysine, whereas serum alanine transaminase activity was reduced by 1% DHA and 1% DHA + 0.5% lysine. Switching to RC reduced hepatic lipid droplet accumulation, which was further reduced by the addition of DHA or lysine. Furthermore, the mRNA expressions of hepatic proinflammatory cytokines were suppressed by DHA and combinations of DHA + lysine, whereas the mRNA for the lipogenic gene, acetyl-CoA carboxylase 1 (ACC1), was suppressed by DHA. In the gonadal adipose tissues, combinations of DHA and lysine inhibited mRNA expression of lipid metabolism-associated genes, including ACC1, fatty acid synthase, lipoprotein lipase, and perilipin. In conclusion, the present study demonstrated that, in conjunction with RC-induced benefits, supplementation with DHA or lysine further ameliorated the high-fat diet-induced NAFLD and provided an alternative strategy to treat, and potentially prevent, NAFLD.

Effects of Fasting on Plasma Lipoprotein(a) in Cynomolgus Monkeys: Preliminary Experiments Results

Plasma lipoprotein(a) (Lp(a)) is known to be a strong independent risk factor for ischemic heart disease. However, it is not easily modulated by drugs that are presently available. Lp(a) is not present in many experimental animals except for Old World monkeys. In this study, we examined whether cynomolgus monkeys are useful model for research of human plasma Lp(a), and observed that plasma Lp(a) in cynomolgus monkeys varied as much as humans. As a result of 4 day-fasting in cynomolgus monkeys, the plasma Lp(a) level decreased in a monkey with originally high Lp(a) level. The Lp(a) level continued to decrease even 3 days after banana feeding, but returned to the original level 3 days after monkey chow feeding. On the other hand, in a monkey with low Lp(a) level, fasting had no effect on the Lp(a) level. However, in the third monkey having originally high Lp(a) level, the Lp(a) was not affected by decreasing the amount of monkey chow feeding by 50%. In summary, we found that cynomolgus monkeys may be an useful model for studying the effects of food on plasma Lp(a) in place of humans, and that high Lp(a) level may be controllable by strict diet regulation.