Effect of chronic corticosterone application on depression‐like behavior in C57BL/6N and C57BL/6J mice

Many studies using genetic mouse models are performed with animals on either one of the two closely related genetic backgrounds, C57BL/6J or C57BL/6N. These strains differ only in a few genetic loci, but have some phenotypic differences that also affect behavior. In order to determine the effects of chronic stress hormone exposure, which is relevant for the pathogenesis of psychiatric disorders, we investigated here the behavioral manifestations of long‐term increase in corticosterone levels. Thus, male mice from both sub‐strains were subcutaneously implanted with corticosterone (20 mg) or placebo pellets that released the hormone for a period of 21 days and resulted in significantly elevated plasma corticosterone levels. Corticosterone significantly increased food intake in B6N, but not in B6J mice. At various time points after pellet implantation, we performed tests relevant to activity and emotional behaviors. B6J mice displayed a generally higher activity in the home cage and the open field. Corticosterone decreased the activity. In B6N mice, corticosterone also decreased sucrose preference, worsened the coat state and increased forced swim immobility, while it had no effect in the B6J strain. Altogether, these results indicate that B6N mice are more sensitive to some of the effects of chronic corticosterone treatment than B6J mice.     

Substrain specific behavioral responses in male C57BL/6N and C57BL/6J mice to a shortened 21-hour day and high-fat diet

ABSTRACT

Altered circadian rhythms have negative consequences on health and behavior. Emerging evidence suggests genetics influences the physiological and behavioral responses to circadian disruption. We investigated the effects of a 21 h day (T = 21 cycle), with high-fat diet consumption, on locomotor activity, explorative behaviors, and health in male C57BL/6J and C57BL/6N mice. Mice were exposed to either a T = 24 or T = 21 cycle and given standard rodent chow (RC) or a 60% high-fat diet (HFD) followed by behavioral assays and physiological measures. We uncovered numerous strain differences within the behavioral and physiological assays, mainly that C57BL/6J mice exhibit reduced susceptibility to the obesogenic effects of (HFD) and anxiety-like behavior as well as increased circadian and novelty-induced locomotor activity compared to C57BL/6N mice. There were also substrain-specific differences in behavioral responses to the T = 21 cycle, including exploratory behaviors and circadian locomotor activity. Under the 21-h day, mice consuming RC displayed entrainment, while mice exposed to HFD exhibited a lengthening of activity rhythms. In the open-field and light-dark box, mice exposed to the T = 21 cycle had increased novelty-induced locomotor activity with no further effects of diet, suggesting daylength may affect mood-related behaviors. These results indicate that different circadian cycles impact metabolic and behavioral responses depending on genetic background, and despite circadian entrainment.     

Differential regulation of leptin expression and function in A/J vs. C57BL/6J mice during diet-induced obesity

Obesity-resistant (A/J) and obesity-prone (C57BL/6J) mice were weaned onto low-fat (LF) or high-fat (HF) diets and studied after 2, 10, and 16 wk. Despite consuming the same amount of food, A/J mice on the HF diet deposited less carcass lipid and gained less weight than C57BL/6J mice over the course of the study. Leptin mRNA was increased in white adipose tissue (WAT) in both strains on the HF diet but to significantly higher levels in A/J compared with C57BL/6J mice. Uncoupling protein 1 (UCP1) and UCP2 mRNA were induced by the HF diet in brown adipose tissue (BAT) and WAT of A/J mice, respectively, but not in C57BL/6J mice. UCP1 mRNA was also significantly higher in retroperitoneal WAT of A/J compared with C57BL/6J mice. The ability of A/J mice to resist diet-induced obesity is associated with a strain-specific increase in leptin, UCP1, and UCP2 expression in adipose tissue. The findings indicate that the HF diet does not compromise leptin-dependent regulation of adipocyte gene expression in A/J mice and suggest that maintenance of leptin responsiveness confers resistance to diet-induced obesity.     

Restoration of gallstone susceptibility by leptin in C57BL/6J ob/ob mice

The absence of leptin due to the ob mutation leads to obesity and confers resistance to diet-induced cholesterol gallstone formation in otherwise susceptible C57BL/6J mice. To investigate contributions of obesity and leptin to gallstone susceptibility, C57BL/6J ob/ob mice were treated daily with i.p. saline or recombinant murine leptin at low (1 microgram/g bw) or high (10 microgram/g bw) doses and were pair-fed a lithogenic diet (15% dairy fat, 1.25% cholesterol, 0.5% cholic acid). Weight loss in ob/ob mice increased in proportion to leptin dose, indicating that the lithogenic diet did not impair leptin sensitivity. In a dose-dependent manner, leptin promoted cholesterol crystallization and gallstone formation, which did not occur in saline-treated mice. Notwithstanding, leptin decreased biliary lipid secretion rates without enriching cholesterol in bile. Leptin did not affect bile salt hydrophobicity, but did increase the biliary content of the most abundant molecular species of phosphatidylcholine, 16:0-18:2. Treatment with leptin down-regulated 3-hydroxy-3-methylglutaryl CoA reductase and prevented cholesterol from accumulating in liver. Consistent with increased hepatic clearance, leptin decreased plasma HDL cholesterol concentrations. This was accommodated in liver without up-regulation of cholesterol 7alpha-hydroxylase or Acat. These data suggest that despite the lithogenic diet, endogenous sources constitute a significant proportion of biliary cholesterol during leptin-induced weight loss. Kinetic factors related to cholesterol nucleation, gallbladder contractility, or mucin secretion may have accounted for leptin-induced gallstone formation.     

Antiobesity effect of PEGylated conjugated linoleic acid on high-fat diet-induced obese C57BL/6J (ob/ob) mice: attenuation of insulin resistance and enhancement of antioxidant defenses

This study was designed to test that dietary conjugated linoleic acids (CLA) used in a mixture of cis-9,trans-11 and trans-10, cis-12 isomers (40% each in weight) coupled to poly(ethylene glycol) (PEG) as PEGylated CLA (PCLA) act as mediators inducing or inhibiting specific metabolic pathways in high-fat (HF)-fed obese C57BL/6J (ob/ob) mice. After an acclimatization period of 7 days, animals were given a normal (control) or HF diet, the latter being added either alone (HF) or with CLA, PEG or PCLA for 6 weeks. Although the food intakes were not different among the dietary groups, final body weights were significantly lower in the HF-PCLA group than in the HF group. Also the HF-PCLA diet strongly prevented the dramatic increase in blood low-density lipoprotein cholesterol observed with the HF diet, with no difference in high-density lipoprotein cholesterol between control, HF and HF-PCLA treatments. Furthermore, homeostasis model assessment levels showed a marked decrease in HF-PCLA-fed mice, preventing the increase found in mice fed the HF diet, and suggesting that PCLA lowered insulin resistance in HF-mice. The liver steatosis observed in mice fed the HF diet was also prevented by PCLA. Interestingly, the activity of mitochondrial glutathione peroxidase was increased by PCLA, which may enhance antioxidant defenses. Overall, PCLA exerted its beneficial effects through reduction of lipid accumulation and attenuation of insulin resistance induced by the HF diet in obese C57BL/6J (ob/ob) mice, which might confer to these products antiobesity properties in other species.     

Embryonic stem cells derived from C57BL/6J and C57BL/6N mice

Mouse embryonic stem (ES) cells with the C57BL/6 genetic background allow the generation of knockout mice without the need to backcross to C57BL/6. However, C57BL/6 ES cells whose pluripotency after homologous recombination has been confirmed are not yet available from public cell banks. To facilitate the use of ES cells derived from C57BL/6 sublines in both biologic and medical research, we demonstrated that the use of knockout serum replacement as a medium supplement and 8-cell blastomeres as recipient embryos allowed establishment of ES cells and production of germline chimeric mice, respectively. Under effective conditions, a large number of ES cell lines were established from C57BL/6J and C57BL/6N blastocysts. The majority of ES cells in many cell lines obtained from both strains showed a normal chromosome number. Germline chimeric mice were generated from C57BL/6J and C57BL/6N ES cells. Finally, the ES cell line B6J-S1UTR, derived from C57BL/6J, was used for successful production of gene knockout mice. C57BL/6J ES (B6J-S1UTR and B6J-23UTR) and C57BL/6N ES (B6N-22UTR) cells are available from the cell bank of the BioResource Center at RIKEN Tsukuba Institute (http://www.brc.riken.jp/lab/cell/english/).     

Protective effects of azelaic acid against high-fat diet-induced oxidative stress in liver, kidney and heart of C57BL/6J mice

Excess fat intake induces hyperinsulinaemia, increases nutrient uptake and lipid accumulation, amplifies ROS generation, establishes oxidative stress and morphological changes leading to tissue injury in the liver, kidney and heart of high-fat diet (HFD)-fed mice. The effect of azelaic acid (AzA), a C9 α,ω-dicarboxylic acid, against HFD-induced oxidative stress was investigated by assaying the activities and levels of antioxidants and oxidative stress markers in the liver, kidney and heart of C57BL/6J mice. Mice were segregated into two groups, one fed standard diet (NC) and the other fed high-fat diet (HFD) for 15 weeks. HFD-fed mice were subjected to intragastric administration of AzA (80 mg/kg BW)/RSG (10 mg/kg BW) during 11-15 weeks. Glucose, insulin, triglycerides, hepatic and nephritic markers were analysed in the plasma and the activity of enzymatic, non-enzymatic antioxidants and lipid peroxidation markers were examined in the plasma/erythrocytes, liver, kidney and heart of normal and experimental mice. We inferred significant decrease in enzymatic and non-enzymatic antioxidants along with significant increase in glucose, insulin, hepatic and nephritic markers, triglycerides and lipid peroxidation markers in HFD-fed mice. Administration of AzA could positively restore the levels of plasma glucose, insulin, triglycerides, hepatic and nephritic markers to near normal. AzA increased the levels of enzymatic and nonenzymatic antioxidants with significant reduction in the levels of lipid peroxidation markers. Histopathological examination of liver, kidney and heart substantiated these results. Hence, we put forward that AzA could counteract the potential injurious effects of HFD-induced oxidative stress in C57BL/6J mice.     

A High-Fat Diet Delays Age-Related Hearing Loss Progression in C57BL/6J Mice

Objective

Age-related hearing loss (AHL), or presbycusis, is the most common sensory disorder among the elderly. We used C57BL/6J mice as an AHL model to determine a possible association between AHL and a high-fat diet (HFD).

Methods

Forty C57BL/6J mice were randomly assigned to a control or HFD group. Each group was divided into the following subgroups: 1-, 3-, 5- and 12-month groups (HFD, n = 5/subgroup; control, n = 5/subgroup). Nine CBA/N-slc mice were also used as a 12-month control (n = 5) or 12-month HFD (n = 4) group. The mice were fed a HFD or normal (control) diet throughout this study. Hearing function was evaluated at 1, 3, 5 and 12 months using auditory evoked brainstem responses (ABRs). Spiral ganglion cells (SGCs) were also counted.

Results

The elevation of ABR thresholds (at 4 and 32 kHz) at 3 and 5 months was significantly suppressed in the HFD group compared with the control groups for C57BL/6J mice. After 12 months, the elevation of ABR thresholds was significantly suppressed in the HFD group at all frequencies for C57BL/6J mice. In contrast, CBA/N-slc mice displayed opposite outcomes, as ABR thresholds at all frequencies at 12 months were significantly elevated in the HFD group compared with the control group. For the C57BL/6J mice at 12 months, SGC numbers significantly decreased in all parts of the cochleae in the control group compared with the HFD groups. In contrast, for the CBA/N-slc mice, SGC numbers significantly decreased, particularly in the upper parts of the cochleae in the HFD group compared with the control groups.

Conclusions

The elevation in ABR thresholds and SGC loss associated with aging in the HFD-fed C57BL/6J mice were significantly suppressed compared with those in the normal diet-fed mice. These results suggest that HFD delays AHL progression in the C57B/6J mice.     

Endothelial expression of endoglin in normocholesterolemic and hypercholesterolemic C57BL/6J mice before and after atorvastatin treatment

Endoglin (CD105) is a homodimeric transmembrane glycoprotein strongly related to transforming growth factor (TGF)-beta signaling and many pathological states. In this study, we wanted to evaluate whether endoglin is expressed in normocholesterolemic and hypercholesterolemic C57BL/6J mice as well as whether it is affected by atorvastatin treatment in these mice. C57BL/6J mice were fed with chow diet or an atherogenic diet for 12 weeks after weaning. In 2 atorvastatin-treated groups, mice were fed the same diets (chow or atherogenic) as described above except atorvastatin was added at the dosage of 10 mg x kg(-1) x day(-1) for the last 8 weeks before euthanasia. Biochemical analysis of blood samples revealed that administration of atherogenic diet significantly increased levels of total cholesterol, VLDL, LDL, and decreased levels of HDL. Atorvastatin treatment resulted in a significant decrease in total cholesterol and VLDL only in mice fed by atherogenic diet. Quantitative stereological analysis revealed that atorvastatin significantly decreased endothelial expression of endoglin in C57BL/6J mice fed the atherogenic diet. In conclusion, we demonstrated that endothelial expression of endoglin is upregulated by hypercholesterolemia and decreased by the hypolipidemic effect of atorvastatin in C57BL/6J mice, suggesting that endoglin expression could be involved in atherogenesis.     

Effects of Excess Energy Intake on Glucose and Lipid Metabolism in C57BL/6 Mice

Excess energy intake correlates with the development of metabolic disorders. However, different energy-dense foods have different effects on metabolism. To compare the effects of a high-fat diet, a high-fructose diet and a combination high-fat/high-fructose diet on glucose and lipid metabolism, male C57BL/6 mice were fed with one of four different diets for 3 months: standard chow; standard diet and access to fructose water; a high fat diet; and a high fat diet with fructose water. After 3 months of feeding, the high-fat and the combined high-fat/high-fructose groups showed significantly increased body weights, accompanied by hyperglycemia and insulin resistance; however, the high-fructose group was not different from the control group. All three energy-dense groups showed significantly higher visceral fat weights, total cholesterol concentrations, and low-density lipoprotein cholesterol concentrations compared with the control group. Assays of basal metabolism showed that the respiratory quotient of the high-fat, the high-fructose, and the high-fat/high-fructose groups decreased compared with the control group. The present study confirmed the deleterious effect of high energy diets on body weight and metabolism, but suggested that the energy efficiency of the high-fructose diet was much lower than that of the high-fat diet. In addition, fructose supplementation did not worsen the detrimental effects of high-fat feeding alone on metabolism in C57BL/6 mice.     

Pancreatic lesions of small-obese mice (C57BL/6 J-ob/ob) with hyperglucagonemia

Male Small-obese mice (Small-ob) which derived from a C57BL/6 J-ob/ob mouse colony were examined histopathologically at 13-, 39-, and over 52-week-old. C57BL/6 J-ob mice (?/+: Non-ob, ob/ob: Ob) were studied as controls. In Small-ob mice, plasma glucagon concentration was higher than that of the Ob mice (this difference was highly significant), and serum levels for insulin was within normal limits. Microscopically, hypertrophy and hyperplasia of the islets of Langerhans were found only in the pancreas of Ob mice. The increase in the number of A-cells and the decrease in the number of B-cells were revealed immunohistochemically in the islets of Small-ob mice. These changes were more severe with advance of age. In the aged Small-ob mice, perivascular and periductular cell infiltration were found, but inflammatory change of islet tissue was not confirmed in any animals examined. Diabetic symptoms in Small-ob mice seems to stem from the disparity in insulin/glucagon (I/G) ratio associated with hyperglucagonemia which result from increased number of A-cells of pancreatic islets.     

Strain differences in response to acute hypoxia: CD-1 versus C57BL/6J mice.

Some mammals respond to hypoxia by lowering metabolic demand for oxygen and others by maximizing efficiency of oxygen usage: the former strategy is generally held to be the more effective. We describe within the same species one outbred strain (CD-1) that lowers demand and another inbred strain (C57BL/6J) that maximizes oxygen efficiency to markedly extend hypoxic tolerance. Unanesthetized adult male mice (Mus musculus, CD-1 and C57BL/6J) between 20 and 35 g were used. Sham-conditioned (SC) C57BL/6J mice survived severe hypoxia (4.5% O(2), balance N(2)) roughly twice as long as SC CD-1 mice (median 211 and 93.5 s, respectively; P < 0.0001). Following acute hypoxic conditioning (HC), C57BL/6J mice survived subsequent hypoxia 10 times longer than HC CD-1 mice (median 2,198 and 238 s respectively; P < 0.0001). Therefore, C57BL/6J mice are both naturally more tolerant to hypoxia and show a greater increase in hypoxic tolerance in response to hypoxic conditioning. Indirect calorimetry indicates that CD-1 mice lower mass-specific oxygen consumption (V'o(2) in ml O(2).kg(-1).min(-1)) and carbon dioxide production (V'co(2) in ml CO(2).kg(-1).min(-1)) in response to HC (P = 0.002 and P < 0.0001, respectively), but C57BL/6J mice maintain V'o(2) and V'co(2) after HC. Respiratory exchange ratio and fluorometric assay of plasma ketones suggest that C57BL/6J mice rapidly switch to ketone metabolism, a more efficient substrate, while CD-1 mice reduce overall metabolic activity. We conclude that under severe hypoxia in mice, switching fuel, possibly to ketones, while maintaining V'o(2), may confer a greater survival advantage than simply lowering demand.     

Genetic polymorphisms among C57BL/6 mouse inbred strains

Mice from the inbred C57BL/6 strain have been commonly used for the generation and analysis of transgenic and knockout animal models. However, several C57BL/6 substrains exist, and these are genetically and phenotypically different. In addition, each of these substrains can be purchased from different animal providers and, in some cases, they have maintained their breeding stocks separated for a long time, allowing genetic differences to accumulate due to individual variability and genetic drift. With the aim of describing the differences in the genotype of several C57BL/6 substrains, we applied the Illumina^® Mouse Medium Density Linkage Mapping panel, with 1,449 single nucleotide polymorphisms (SNPs), to individuals from ten C57BL/6-related strains: C57BL/6JArc, C57BL/6J from The Jackson Lab, C57BL/6J from Crl, C57BL6/JRccHsd, C57BL/6JOlaHsd, C57BL/6JBomTac, B6(Cg)-Tyr ^c?2j /J, C57BL/6NCrl, C57BL/6NHsd and C57BL/6NTac. Twelve SNPs were found informative to discriminate among the mouse strains considered. Mice derived from the original C57BL/6J: C57BL/6JArc, C57BL/6J from The Jackson Lab and C57BL/6J from Crl, were indistinguishable. Similarly, all C57BL/6N substrains displayed the same genotype, whereas the additional substrains showed intermediate cases with substrain-specific polymorphisms. These results will be instrumental for the correct genetic monitoring and appropriate mouse colony handling of different transgenic and knockout mice produced in distinct C57BL/6 inbred substrains.     

Effects of atherogenic diet consumption on lipoproteins in mouse strains C57BL/6 and C3H

Inbred mouse strains C57BL/6J (B6) (susceptible) and C3H/HeJ (C3H) (resistant) differ in atherosclerosis susceptibility due to a single gene, Ath-1. Plasma lipoproteins from female mice fed chow or an atherogenic diet displayed strain differences in lipoprotein particle sizes and apolipoprotein (apo) composition. High density lipoprotein (HDL) particle sizes were 9.5 +/- 0.1 nm for B6 and 10.2 +/- 0.1 nm for C3H. No major HDL particle size subclasses were observed. Plasma HDL level in the B6 strain was reduced by the atherogenic diet consumption while the HDL level in the resistant C3H mice was unaffected. The reduction in HDL in the B6 strain was associated with decreases in HDL apolipoproteins A-I(-34%) and A-II(-60%). The HDL apoC content in mice fed chow was two-fold higher in C3H than B6. Lipoproteins containing apolipoprotein B (VLDL, IDL, LDL) shifted from a preponderance of the B-100 (chow diet) to a preponderance of the B-48 (atherogenic diet). The LDL-particle size distribution was strain-specific with the chow diet but not genetically associated with the Ath-1 gene. In both strains on each diet, apolipoprotein E was largely distributed in the VLDL, LDL, and HDL fractions. The B6 strain became sixfold elevated in total lipoprotein E content which in the C3H strain was not significantly affected by diet. However, the C3H LDL apoE content was reduced. On both diets, the C3H strain exhibited apolipoprotein E levels comparable to the atherogenic diet-induced levels of the B6 mice.     

Restraint increases prolactin and REM sleep in C57BL/6J mice but not in BALB/cJ mice

Sleep is generally considered to be a recovery from prior wakefulness. The architecture of sleep not only depends on the duration of wakefulness but also on its quality in terms of specific experiences. In the present experiment, we studied the effects of restraint stress on sleep architecture and sleep electroencephalography (EEG) in different strains of mice (C57BL/6J and BALB/cJ). One objective was to determine if the rapid eye movement (REM) sleep-promoting effects of restraint stress previously reported for rats would also occur in mice. In addition, we examined whether the effects of restraint stress on sleep are different from effects of social defeat stress, which was found to have a non-REM (NREM) sleep-promoting effect. We further measured corticosterone and prolactin levels as possible mediators of restraint stress-induced changes in sleep. Adult male C57BL/6J and BALB/cJ mice were subjected to 1 h of restraint stress in the middle of the light phase. To control for possible effects of sleep loss per se, the animals were also kept awake for 1 h by gentle handling. Restraint stress resulted in a mild increase in NREM sleep compared with baseline, but, overall, this effect was not significantly different from sleep deprivation by gentle handling. In contrast, restraint stress caused a significant increase in REM sleep compared with handling in the C57BL/6J mice but not in BALB/cJ mice. Corticosterone levels were significantly and similarly elevated after restraint in both strains, but prolactin was increased only in the C57BL/6J mice. In conclusion, this study shows that the restraint stress-induced increase in REM sleep in mice is strongly strain dependent. The concomitant increases in prolactin and REM sleep in the C57BL/6J mice, but not in BALB/cJ mice, suggest prolactin may be involved in the mechanism underlying restraint stress-induced REM sleep. Furthermore, this study confirms that different stressors differentially affect NREM and REM sleep. Whereas restraint stress promotes REM sleep in C57BL/6J mice, we previously found that in the same strain, social defeat stress promotes NREM sleep. As such, studying the consequences of specific stressful stimuli may be an important tool to unravel both the mechanism and function of different sleep stages.     

Coffee and caffeine improve insulin sensitivity and glucose tolerance in C57BL/6J mice fed a high-fat diet

We have previously demonstrated that coffee and caffeine ameliorated hyperglycemia in spontaneously diabetic KK-A(y) mice. This present study evaluates the antidiabetic effects of coffee and caffeine on high-fat-diet-induced impaired glucose tolerance in C57BL/6J mice. C57BL/6J mice fed a high-fat diet were given regular drinking water (control group), or a 2.5-fold-diluted coffee or caffeine solution (200 mg/L) for 17 weeks. The ingestion of coffee or caffeine improved glucose tolerance, insulin sensitivity, and hyperinsulinemia when compared with mice in the control group. The adipose tissue mRNA levels of inflammatory adipocytokines (MCP-1 and IL-6) and the liver mRNA levels of genes related to fatty acid synthesis were lower in the coffee and caffeine groups than those in the control group. These results suggest that coffee and caffeine exerted an ameliorative effect on high-fat-diet-induced impaired glucose tolerance by improving insulin sensitivity. This effect might be attributable in part to the reduction of inflammatory adipocytokine expression.     

Hypolipidemic effect of young persimmon fruit in C57BL/6.KOR-ApoEshl mice

We investigated the hypolipidemic effects of young persimmon fruit (YP) on apolipoprotein E-deficient C57BL/6.KOR-ApoEshl mice. These mice exhibited higher plasma cholesterols, except for high-density lipoprotein (HDL), and lower plasma HDL cholesterol than C57BL/6.Cr mice that had the same genetic background as the C57BL/6.KOR-ApoEshl mice. Male C57BL/6.KOR-ApoEshl mice (n=5) were fed a diet supplemented with dry YP, Hachiya-kaki, at a concentration of 5% (w/w) for 10 weeks. YP treatment significantly lowered plasma chylomicron, very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) cholesterols, and triglyceride, and this response was accompanied by an elevation of fecal bile acid excretion. In the liver, sterol regulatory element binding protein-2 gene expression was significantly higher in mice fed YP, while the mRNA and protein levels of the LDL receptor did not change. These results indicate that acceleration of fecal bile acid excretion is a major mechanism of the hypolipidemic effect induced by YP in C57BL/6.KOR-ApoEshl mice.     

Initiation of hyperinsulinemia and hyperleptinemia is diet dependent in C57BL/6 mice.

C57BL/6 female mice were fed high fat diets containing different types of carbohydrate (sucrose or corn starch) and contents of cholesterol (0.03 % or 1 %) to identify early metabolic changes leading to increases in leptin levels and eventual insulin resistance. Under identical dietary fat conditions, type of carbohydrate and cholesterol content contributed to the timing of leptin increases. Mice fed a high-fat, high-sucrose diet showed early (4 weeks) and robust increases in circulating insulin and leptin levels (2-fold and 5-fold, respectively). In contrast, mice fed this diet with added cholesterol or with sucrose substituted by corn starch led to marked delays (8-10 weeks) in the elevations of insulin and leptin, although body weight gains were nearly identical among test diet groups. Thus, sucrose in combination with saturated fat played a specific role in initiating early metabolic changes associated with elevated leptin and insulin levels. Because leptin levels were most reflective of changes in insulin, our data support a role for insulin in determining plasma leptin levels in mice.     

Differential expression and regulation of myristoylated alanine-rich C kinase substrate (MARCKS) in the hippocampus of C57/BL6J and DBA/2J mice

The myristoylated alanine-rich C kinase substrate (MARCKS) is a major protein kinase C (PKC) substrate in brain that binds the inner surface of the plasma membrane, calmodulin, and cross-links filamentous actin, all in a PKC phosphorylation-reversible manner. MARCKS has been implicated in hippocampal-dependent learning and long-term potentiation (LTP). Previous studies have shown DBA/2 mice to exhibit poor spatial/contextual learning, impaired hippocampal LTP, and hippocampal mossy fiber hypoplasia, as well as reduced hippocampal PKC activity and expression relative to C57BL/6 mice. In the present study, we assessed the expression (mRNA and protein) and subcellular distribution (membrane and cytolsol) of MARCKS in the hippocampus and frontal cortex of C57BL/6 and DBA/2 mice using quantitative western blotting. In the hippocampus, total MARCKS mRNA and protein levels in C57BL/6J mice were significantly lower ( approximately 45%) compared with DBA/2J mice, and MARCKS protein was observed predominantly in the cytosolic fraction. MARCKS expression in frontal cortex did not differ significantly between strains. To examine the dynamic regulation of MARCKS subcellular distribution, mice from each strain were subjected to 60 min restraint stress and MARCKS subcellular distribution was determined 24 h later. Restraint stress resulted in a significant reduction in membrane MARCKS expression in C57BL/6J hippocampus but not in the DBA/2J hippocampus despite similar stress-induced increases in serum corticosterone. Restraint stress did not affect cytosolic or total MARCKS levels in either strain. Similarly, restraint stress (30 min) in rats also induced a significant reduction in membrane MARCKS, but not total or cytosolic MARCKS, in the hippocampus but not in frontal cortex. In rats, chronic lithium treatment prior to stress exposure reduced hippocampal MARCKS expression but did not affect the stress-induced reduction in membrane MARCKS. Collectively these data demonstrate higher resting levels of MARCKS in the hippocampus of DBA/2J mice compared to C57BL/6J mice, and that acute stress leads to a long-term reduction in membrane MARCKS expression in C57BL/6J mice and rats but not in DBA/2J mice. These strain differences in hippocampal MARCKS expression and subcellular translocation following stress may contribute to the differences in behaviors requiring hippocampal plasticity observed between these strains.     

Diet-induced obesity and hepatic gene expression alterations in C57BL/6J and ICAM-1-deficient mice

The effects of high-fat feeding on the development of obesity were evaluated in intercellular adhesion molecule-1 (ICAM-1) knockout and C57BL/6J (B6) male mice fed a high-fat diet for < or =50 days. Serum and tissues were collected at baseline and after 1, 11, and 50 days on the diet. After 11 days on the diet, ICAM-1-deficient, but not B6, mice developed fatty livers and showed a significant increase in inguinal fat pad weight. At day 50, ICAM-1-deficient mice weighed less, and their adiposity index and circulating leptin levels were significantly lower than those of B6 controls. To better understand the early differential response to the diet, liver gene expression was analyzed at three time points by use of Affymetrix GeneChips. In both strains, a similar pattern of gene expression was detected in response to the high-fat diet. However, sterol regulatory element-binding protein-1, apolipoprotein A4, and adipsin mRNAs were significantly induced in ICAM-1-deficient livers, suggesting that these genes and their associated pathways may be involved in the acute diet response observed in the knockout mice.