Strain difference in pituitary-adrenal axis between Wistar-Imamichi and Long Evans adult male rats.

In the present study, we used closed colony-Wistar-Imamichi (WI), inbred WI and Long Evans (LE) adult male rats to examine the secretion of ACTH and corticosterone in response to restraint stress. Blood (0.3 ml) was withdrawn through a jugular cannula at 0, 15, 30, 60 and 120 min after the onset of restraint stress. Plasma concentrations of ACTH and corticosterone increased after stress in all groups, but the responses of ACTH and corticosterone secretion were higher in LE rats than in WI rats. Present data suggest that the LE rat might be a good model as a high-response strain and the closed colony or the inbred WI rat might be a good model as a low-response strain in restraint stress experiments.     

Maternal obesity increases hypothalamic leptin receptor expression and sensitivity in juvenile obesity-prone rats

In rats selectively bred to develop diet-induced obesity (DIO) or to be diet-resistant (DR), DIO maternal obesity selectively enhances the development of obesity and insulin resistance in their adult offspring. We postulated that the interaction between genetic predisposition and factors in the maternal environment alter the development of hypothalamic peptide systems involved in energy homeostasis regulation. Maternal obesity in the current studies led to increased body and fat pad weights and higher leptin and insulin levels in postnatal day 16 offspring of both DIO and DR dams. However, by 6 wk of age, most of these intergroup differences disappeared and offspring of obese DIO dams had unexpected increases in arcuate nucleus leptin receptor mRNA, peripheral insulin sensitivity, diet- and leptin-induced brown adipose temperature increase and 24-h anorectic response compared with offspring of lean DIO, but not lean DR dams. On the other hand, while offspring of obese DIO dams did have the highest ventromedial nucleus melanocortin-4 receptor expression, their anorectic and brown adipose thermogenic responses to the melanocortin agonist, Melanotan II (MTII), did not differ from those of offspring of lean DR or DIO dams. Thus, during their rapid growth phase, juvenile offspring of obese DIO dams have alterations in their hypothalamic systems regulating energy homeostasis, which ameliorates their genetic and perinatally determined predisposition toward leptin resistance. Because they later go onto become more obese, it is possible that interventions during this time period might prevent the subsequent development of obesity.     

Spontaneous and conditioned behavior of Wistar and Long Evans rats

Spontaneous behavior (locomotion, feeding, drinking, and exploration in a two box apparatus) as well as conditioned behavior (passive and active avoidance responding, and freezing in the light-dark box apparatus) were studied in naive male Wistar and Long Evans rats. Concerning spontaneous behavior, Long Evans rats were more active during both light and dark periods, and showed better exploratory performance than Wistar rats. Concerning conditioned behavior, Long Evans rats acquired and retained better active and passive avoidance responses, and exhibited longer initial freezing than Wistar rats in the range of 0.6-1.4 mA footshocks. The results better define the important behavioral differences existing between the two strains, Long Evans rats showing consistently a higher level of alertness and a better conditioned performance.     

"Spatial memory in Long Evans and Rattus Norvegicus rats"

Rodents in search of food use visual environmental signals and complex spatial strategies and do not return to previously-visited locations, known as the win-shift strategy. The solution to the Olton Octagonal Maze (OOM) involves Working Memory (WM). A modified OOM was used that allows for measuring WM and Long Term Memory (LTM). The delayed spatial win-shift task consisted of a Training and Test phase separated by a delay. Prior to the Training phase, four arms were chosen at random and blocked, and food pellets were placed in the food cups of the four remaining open arms. Each rat was allowed to retrieve the pellets from the four open arms and then return to its home cage for the delay period (either 5 or 20 min). In the Test phase all 8 lanes were open, and the bait was placed in those blocked in the previous phase. Two experimental groups of rats, Long Evans and Norvegicus, and their corresponding control groups were trained. The experimental subjects performed Training-Delay-Test. The controls were only trained in the Test phase. Revisiting an arm previously explored in the 1st Phase was considered a LTM error. Revisiting an arm in the same trial constituted a WM error. It was concluded that the experimental groups do in fact possess LTM, with differences in favor of Norvegicus. There was no difference with respect to WM errors. The Norvegicus control group changes its strategy from allocentric to egocentric, which did not occur in the Long Evans control group.     

Sex differences in food hoarding behaviour of Long Evans rats

Food hoarding was examined in male and female Long Evans rats. During a three-week period the animals were regularly submitted to the testing procedures, with food pellets in the home cage being either unrestricted (first week), or restricted (second and third week). When food pellets were present ad libitum, the hoarding scores were low, lower in females than in males. When food deprivation was imposed (second week), the animals responded by hoarding more pellets. This increase was more pronounced in males than in females. During the third week the hoarding scores became more or less stable, with males hoarding significantly more pellets than females.     

Strain differences in response of Sprague-Dawley and Long Evans Hooded rats to the teratogen nitrofen

Administration of nitrofen (2,4-dichloro-4'-nitrodiphenyl ether) during organogenesis in rodents produces neonatal lethality accompanied by lung hypoplasia, diaphragmatic hernias, heart anomalies, and hydronephrosis. Different strains of rats, Long Evans Hooded (LEH) and Sprague-Dawley (SD), are reported to have different malformation responses to prenatal exposure, which could be due to true strain differences, to different levels and times of exposure, or to the use of different methods for detecting visceral malformations. In the present study, LEH, SD, and "virus-antibody-negative" SD (VAN-SD) rats were identically exposed to 0, 6.25, 12.5, or 25 mg/kg/day of nitrofen by gavage in corn oil on days 6 15 of gestation. At term, half of the litter was examined by the Wilson method of razorblade sectioning and the remainder by a modified Staples method of fresh visceral examination. The two methods were equally sensitive for detecting diaphragm, kidney, and lung anomalies, whereas heart malformations were more frequently identified with fresh visceral examination. The frequency of total malformations did not vary across strains at any dose, but there were substantial differences in the pattern of malformations in each strain. SD and VAN-SD rats responded similarly for all malformations, but had significantly higher incidences of diaphragm and lung anomalies than LEH rats. Conversely, LEH rats had significantly elevated levels of kidney anomalies compared to SD and VAN-SD rats, whereas frequency of heart malformations was low and comparable across strains. These results suggest that true strain differences exist in the pattern of malformation produced by prenatal exposure to nitrofen that may be based on genetic differences in embryonic susceptibility.     

Effects of housing density on Long Evans and Fischer 344 rats

At many breeding facilities, rats are housed at relatively high densities until they are 5 weeks old, at which point they are either shipped for research or rehoused at standard cage densities according to weight. The authors carried out a pilot study in Long Evans and in Fischer 344 rats to investigate whether continuing to house rats at high densities (24 in(2) floor space per rat) past the age of 5 weeks, through puberty and into adulthood would alter behavioral or physiological parameters compared with raising rats at standard densities (about 72 in(2) floor space per rat). After rats reached puberty, the authors rehoused them with unfamiliar cagemates. The researchers evaluated clinical and behavioral signs of stress, weight, blood glucose concentration, white blood cell count and serum corticosterone concentration. Overall, cage density had little effect on the parameters measured, though gender seemed to affect stress in Long Evans rats. The results suggest that rats of these strains can be raised at the higher densities tested until any age and regrouped with unfamiliar cagemates without compromising rats' welfare or subsequent experimental data.     

Maternal green tea extract supplementation to rats fed a high-fat diet ameliorates insulin resistance in adult male offspring

Maternal overnutrition is associated with increased risk of metabolic disorders in the offspring. This study tested the hypothesis that maternal green tea (GT) supplementation can alleviate metabolic derangements in high-fat-diet-fed rats born of obese dams. Female Sprague–Dawley rats were fed low-fat (LF, 7%), high-fat (HF, 30%) or HF diet containing 0.75% or 1.0% GT extract (GT1, GT2) prior to conception and throughout gestation and lactation. Both doses of GT significantly improved metabolic parameters of HF-fed lactating dams (P<.05). Birth weight and litter size of offspring from HF dams were similar, but GT supplementation led to lighter pups on day 21 (P<.05). The weaned male pups received HF, GT1 or GT2 diet (dam/pup diet groups: LF/HF, HF/HF, HF/GT1, HF/GT2, GT1/HF and GT2/HF). At week 13, they had similar weight but insulin resistance index (IRI), serum nonesterified fatty acid (NEFA) and liver triglyceride of rats born to GT dams were 57%, 23% and 26% lower, accompanied by improved gene/protein expressions related to lipid and glucose metabolism, compared with the HF/HF rats (P<.05). Although HF/GT1 and HF/GT2 rats had lower serum NEFA, their insulin and IRI were comparable to HF/HF rats. This study shows that metabolic derangements induced by an overnourished mother could be offset by supplementing GT to the maternal diet and that this approach is more effective than giving GT to offspring since weaning. Hence, adverse effects of developmental programming are reversible, at least in part, by supplementing bioactive food component(s) to the mother's diet.     

Enhanced sensitivity to methadone in adult rats perinatally exposed to methadone

Adult rats, maternally exposed to methadone during gestation and/or lactation, were evaluated for thermoregulatory and nociceptive responsiveness following a challenge with 5 mg/kg (i.p.) methadone. Prior to drug administration, female rats in the gestation and gestation-lactation groups and all male rats perinatally exposed to methadone were subnormal in body temperature. One hour after acute methadone injection, male control rats were hypothermic. All groups of methadone-treated offspring exhibited a marked lowering in body temperature with respect to their pre-injection levels, as well as in regard to values of methadone-administered control animals. Prior to drug administration, male rats of the gestation-lactation group and female rats of the gestation and lactation groups had elevated nociceptive thresholds. Except for male rats in the lactation group, animals treated with methadone perinatally had longer latencies in response to the hot-plate relative to their pre-injection values, as well as to levels of methadone-injected controls. Three days after acute methadone administration, some groups of rats subjected to this drug during gestation and/or lactation were found to be hypothermic and hypalgesic in respect to their pre-injection values, and also relative to control rats. These results suggest that exposure to methadone early in life can have a profound influence on drug response in adulthood.     

Leptin resistance in obesity is characterized by decreased sensitivity to proopiomelanocortin products

Obesity in normal animals has been demonstrated to be associated with a decrease in sensitivity to leptin especially as it relates to leptin's capacity to increase sympathetic nerve activity and enhance cardiovascular dynamics. In normal animals leptin has been demonstrated to exert significant regulatory responses by its capacity to increase proopiomelanocortin (POMC) expression and especially the increase in alpha melanocyte stimulating hormone (alphaMSH). These responses to leptin are blocked by a melanocortin-4 (MC-4) receptor antagonist. In this study we investigated the responsiveness of the sympathetic nervous system and cardiovascular system of high fat fed obese animals to the intracerebroventricular (ICV) administration of the POMC products alphaMSH and beta-endorphin (beta-END). We further investigated these responses in obese animals following leptin administration in the presence of MC-4 receptor and opioid receptor blockade. The ICV administration of leptin resulted in an increase in lumbar sympathetic nerve activity (LSNA) and mean arterial pressure (MAP) in normals but decreased it in the obese. The ICV administration of alphaMSH increased the LSNA and MAP in normal animals but to a lesser degree in obese animals. On the other hand beta-endorphin decreased the LSNA and MAP in normal animals but increased it in obese animals. Additionally ICV leptin administration in obese animals in the presence of MC-4 or opioid receptor blockade resulted in an increase in sympathetic activity and a pressor response. From these studies we conclude that obesity in high fat fed animals is characterized by a decreased sensitivity to alphaMSH and a paradoxical response to beta-endorphin and this altered responsiveness may be a factor in the altered leptin resistance characteristic of obese animals.     

Neonatal handling increases sensitivity to acute neurodegeneration in adult rats

Environmental stimuli during the perinatal period can result in persistent individual differences in neural viability and cognitive functions. Earlier studies have shown that brief daily maternal separation and/or handling of rat pups during the first weeks of life reduces stress reactivity during adulthood and attenuates neuronal loss and cognitive decline during aging. In the present study we examined whether neonatal handling also affects the sensitivity of the adult brain to an acute neurotoxic insult. Postnatally handled and nonhandled control rats were left undisturbed from weaning onwards until the age of 11 months. At this age, the animals were subjected to a neurotoxic challenge by unilateral infusion of 60 mM of the glutamate analogue N-methyl-D-aspartate (NMDA) into the nucleus basalis magnocellularis (NBM). The brains were collected to measure cholinergic cell and fiber loss. In the nonlesioned side of the brain, cholinergic cell number in the NBM and fiber density in the cortex were not different between postnatally handled and control rats. However, in the lesioned hemisphere handled animals exhibited a significantly higher loss of choline-acetyltransferase-immunoreactive and acetylcholinesterase-positive fibers in the somatosensory cortex. The present results provide evidence for an enhanced vulnerability of postnatally handled rats to acute neurodegeneration in contrast to the previously reported attenuation of spontaneous aging-related neurodegenerative processes.     

Effects of Dmo1 on obesity, dyslipidaemia and hyperglycaemia in the Otsuka Long Evans Tokushima Fatty strain

Whole-genome scans have identified Dmo1 as a major quantitative trait locus (QTL) for obesity and dyslipidaemia in the Otsuka Long Evans Tokushima Fatty (OLETF) rat. We have produced congenic rats for the Dmo1 locus, using marker-assisted speed congenic protocols, enforced by selective removal of other QTL regions (QTL-marker-assisted counterselection), to efficiently transfer chromosomal segments from non-diabetic Fischer 344 (F344) rats into the OLETF background. In the third generation of congenic animals, we observed a substantial therapeutic effect of the Dmo1 locus on lipid metabolism, obesity control and plasma glucose homeostasis. We conclude that single-allele correction of an impaired genetic pathway can generate a substantial therapeutic effect, despite the complex polygenic nature of type II diabetic syndromes.     

Reduced central leptin sensitivity in rats with diet-induced obesity

On low-fat chow diet, rats prone to diet-induced obesity (DIO) have increased arcuate nucleus neuropeptide Y (NPY) expression but similar leptin levels compared with diet-resistant (DR) rats (19). Here, body weight and leptin levels rose in DIO rats, and they defended their higher body weight after only 1 wk on a 31% fat high-energy (HE) diet. However, DIO NPY expression did not fall to DR levels until 4 wk when plasma leptin was 168% of DR levels. When switched to chow, DIO rats lost carcass fat (18). By 10 wk, leptin levels fell to 148% and NPY expression again rose to 150% of DR levels. During 4 wk of food restriction, DIO leptin fell by approximately 50% while NPY increased by 30%. While both returned to control levels by 8 wk, DIO rats still regained all lost weight when fed ad libitum. Finally, the anorexic effect of intracerebroventricular leptin (10 microg) was inversely correlated with subsequent 3-wk weight gain on HE diet. Thus NPY expression and food intake are less sensitive to the leptin's suppressive effects in DIO rats. While this may predispose them to develop DIO, it does not fully explain their defense of a higher body weight on HE diet.     

Non-shivering thermogenesis and obesity in adult diabetic Wistar fatty rats

1. Characteristics of resting and of norepinephrine (NE)-stimulated thermogenesis, and the glycemic response to NE were determined in adult male Wistar Fatty rats. Rats were maintained on Purina chow No. 5001 until 22 weeks of age, and fed semisynthetic diets containing 54% carbohydrate, 20% protein, 16% mixed fats, plus essential vitamins, minerals, and non-nutritive fiber from 22 until 30 weeks of age. 2. Obese rats were 50% heavier than lean throughout the study. Phenotype effects (obese greater than lean) were present for retroperitoneal (RP) and dorsal (DOR) white fat depot weight, adipocyte number per depot, and adipocyte lipid content. Epididymal mass and cellularity were similar in both phenotypes. 3. Interscapular brown adipose tissue (IBAT) mass, adipocyte size, and adipocyte number were greater in obese than in lean. Resting metabolic rates (RMR) of obese rats were lower than in lean, and increased 79% in lean but only 33% in obese animals following NE (200 micrograms/kg BW, s.c.) stimulation. 4. The glycemic response to NE occurred normally in both phenotypes, and resulted in a 3-fold increment in plasma glucose in lean rats and a 5-6-fold increase in plasma glucose in obese rats. 5. The results of this study are consistent with hyperplasia and hypertrophy of IBAT, RP and DOR depots, and indicate that the capacity for non-shivering thermogenesis is impaired in the obese phenotype of this strain in spite of peripheral sensitivity to NE and greater mass and cellularity of brown adipose tissue.     

Maternal response to environmental unpredictability

Mothers are expected to use environmental cues to modify maternal investment to optimize their fitness. However, when the environment varies unpredictably, cues may not be an accurate proxy of future conditions. Under such circumstances, selection favors a diversifying maternal investment strategy. While there is evidence that the environment is becoming more uncertain, the extent to which mothers are able to respond to this unpredictability is generally unknown. In this study, we test the hypothesis that Daphnia magna increase the variance in maternal investment in response to unpredictable variation in temperature consistent with global change predictions. We detected significant variability across temperature treatments in brood size, neonate size at birth, and time between broods. The estimated variability within‐brood size was higher (albeit not statistically significant) in mothers reared in unpredictable temperature conditions. We also detected a cross‐generational effect with the temperature history of mothers modulating the phenotypic response of F1's. Notably, our results diverged from the prediction that increased variability poses a greater risk to organisms than changes in mean temperature. Increased unpredictability in temperature had negligible effects on fitness‐correlated traits. Mothers in the unpredictable treatment, survived as long, and produced as many F1's during lifetime as those produced in the most fecund treatment. Further, increased unpredictability in temperature did not affect the probability of survival of F1's. Collectively, we provide evidence that daphnia respond effectively to thermal unpredictability. But rather than increasing the variance in maternal investment, daphnia respond to uncertainty by being a jack of all temperatures, master of none. Importantly, our study highlights the essential need to examine changes in variances rather than merely on means, when investigating maternal responses.     

Socs3 deficiency in the brain elevates leptin sensitivity and confers resistance to diet-induced obesity

Leptin is an adipocyte-derived hormone that plays a key role in energy homeostasis, yet resistance to leptin is a feature of most cases of obesity in humans and rodents. In vitro analysis suggested that the suppressor of cytokine signaling-3 (Socs3) is a negative-feedback regulator of leptin signaling involved in leptin resistance. To determine the functional significance of Socs3 in vivo, we generated neural cell-specific SOCS3 conditional knockout mice using the Cre-loxP system. Compared to their wild-type littermates, Socs3-deficient mice showed enhanced leptin-induced hypothalamic Stat3 tyrosine phosphorylation as well as pro-opiomelanocortin (POMC) induction, and this resulted in a greater body weight loss and suppression of food intake. Moreover, the Socs3-deficient mice were resistant to high fat diet-induced weight gain and hyperleptinemia, and insulin-sensitivity was retained. These data indicate that Socs3 is a key regulator of diet-induced leptin as well as insulin resistance. Our study demonstrates the negative regulatory role of Socs3 in leptin signaling in vivo, and thus suppression of Socs3 in the brain is a potential therapy for leptin-resistance in obesity.     

A genetic contribution to circulating cytokines and obesity in children

Cytokines are considered to be involved in obesity-related metabolic diseases. Study objectives are to determine the heritability of circulating cytokine levels, to investigate pleiotropy between cytokines and obesity traits, and to present genome scan results for cytokines in 1030 Hispanic children enrolled in VIVA LA FAMILIA Study. Cytokine phenotypes included monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-alpha), leptin, adiponectin, soluble intercellular adhesion molecule-1 (sICAM-1), transforming growth factor beta 1 (TGF-beta1), C-reactive protein (CRP), regulated upon activation, normal T-cell expressed and secreted (RANTES) and eotaxin. Obesity-related phenotypes included body mass index (BMI), fat mass (FM), truncal FM and fasting serum insulin. Heritabilities ranged from 0.33 to 0.97. Pleiotropy was observed between cytokines and obesity traits. Positive genetic correlations were seen between CRP, leptin, MCP-1 and obesity traits, and negative genetic correlations with adiponectin, ICAM-1 and TGF-beta1. Genome-wide scan of sICAM-1 mapped to chromosome 3 (LOD=3.74) between markers D3S1580 and D3S1601, which flanks the adiponectin gene (ADIPOQ). Suggestive linkage signals were found in other chromosomal regions for other cytokines. In summary, significant heritabilities for circulating cytokines, pleiotropy between cytokines and obesity traits, and linkage for sICAM-1 on chromosome 3q substantiate a genetic contribution to circulating cytokine levels in Hispanic children.     

The transcriptional profile of the kidney in Tsc2 heterozygous mutant Long Evans (Eker) rats compared to wild-type

Hereditary renal cell carcinoma (RCC) in Eker rats results from an inherited insertional mutation in the Tsc2 tumor suppressor gene and provides a valuable experimental model to characterize the function of the Tsc2 gene product, tuberin in vivo. The Tsc2 mutation predisposes the Eker rat to develop renal tumors at an early age. The exact mechanism of Tsc2 mediated tumor suppression is not known, however, there is evidence that it is most likely mediated by changes in cell cycle regulation via the PI3K/Akt pathway. The present study was designed to identify if gene expression was different in Tsc2 heterozygous mutant rat kidney compared to wild-type and if any of those differences are associated with tumorigenesis. cDNA microarray analysis of the untreated Tsc2 (+/-) mutant Long Evans (Eker) rat was compared to the Tsc2 (+/+) wild-type Long Evans rat to search for patterns that might be indicative of the intrinsic role of Tsc2. Of 4395 genes queried, 3.2% were significantly altered in kidneys from heterozygous mutant rats, of which 110 (76%) were up-regulated and 34 (24%) were down-regulated relative to the wild-type. The genes with altered expression belonged to the functional categories of cell cycle regulation, cell proliferation, cell adhesion and endocytosis. Many of these genes appear to be directly or indirectly regulated by the PI3K/Akt pathway. In addition to the PI3K/Akt pathway, other signaling pathways were also differentially expressed in Tsc2 mutant Eker rat kidneys compared to wild-type rats. The gene expression profiles of the Tsc2 heterozygous mutant and wild-type animals highlights new pathways for investigation that may be associated with the tumorigenic activity of tuberin loss and correlate with the enhanced susceptibility of the Tsc2 mutant animal's tendency to develop renal cell carcinoma.     

Maternal employment and childhood obesity in Russia

Existing research on childhood obesity shows that rising maternal employment is associated with increases in child weight. This paper aims to estimate the effect of maternal employment on childhood obesity in Russia, where obesity has been spreading quickly over the last 20 years. To address the endogeneity of maternal employment and estimate its effect on the weight outcomes of older siblings, I use plausibly exogenous variation in childcare enrolment for the youngest child in the household as an instrumental variable for maternal employment. Based on the Russian Longitudinal Monitoring Survey (RLMS-HSE), the results show that maternal employment leads to an increase in children’s BMI and in their probabilities of becoming overweight and obese. In exploring the potential underlying mechanisms, I find that maternal employment is related to less physical activity, to a higher probability of either watching TV or playing video games, and to poorer dietary habits among children.