Differential body weight and feeding responses to high-fat diets in rats and mice lacking cholecystokinin 1 receptors

Prior data demonstrated differential roles for cholecystokinin (CCK)1 receptors in maintaining energy balance in rats and mice. CCK1 receptor deficiency results in hyperphagia and obesity of Otsuka Long-Evans Tokushima Fatty (OLETF) rats but not in mice. To ascertain the role of CCK1 receptors in high-fat-diet (HFD)-induced obesity, we compared alterations in food intake, body weight, fat mass, plasma glucose, and leptin levels, and patterns of hypothalamic gene expression in OLETF rats and mice lacking CCK1 receptors in response to a 10-wk exposure to HFD. Compared with Long-Evans Tokushima Otsuka (LETO) control rats, OLETF rats on HFD had sustained overconsumption over the 10-wk period. High fat feeding resulted in greater increases in body weight and plasma leptin levels in OLETF than in LETO rats. In situ hybridization determinations revealed that, while HFD reduced neuropeptide Y (NPY) mRNA expression in both the arcuate nucleus (Arc) and the dorsomedial hypothalamus (DMH) of LETO rats, HFD resulted in decreased NPY expression in the Arc but not in the DMH of OLETF rats. In contrast to these results in OLETF rats, HFD increased food intake and induced obesity to an equal degree in both wild-type and CCK1 receptor(-/-) mice. NPY gene expression was decreased in the Arc in response to HFD, but was not detectable in the DMH in both wild-type and CCK1 receptor(-/-) mice. Together, these data provide further evidence for differential roles of CCK1 receptors in the controls of food intake and body weight in rats and mice.

Trisomy for the Down syndrome 'critical region' is necessary but not sufficient for brain phenotypes of trisomic mice

Trisomic Ts65Dn mice show direct parallels with many phenotypes of Down syndrome (DS), including effects on the structure of cerebellum and hippocampus. A small segment of Hsa21 known as the 'DS critical region' (DSCR) has been held to contain a gene or genes sufficient to cause impairment in learning and memory tasks involving the hippocampus. To test this hypothesis, we developed Ts1Rhr and Ms1Rhr mouse models that are, respectively, trisomic and monosomic for this region. Here, we show that trisomy for the DSCR alone is not sufficient to produce the structural and functional features of hippocampal impairment that are seen in the Ts65Dn mouse and DS. However, when the critical region is returned to normal dosage in trisomic Ms1Rhr/Ts65Dn mice, performance in the Morris water maze is identical to euploid, demonstrating that this region is necessary for the phenotype. Thus, although the prediction of the critical region hypothesis was disproved, novel gene dosage effects were identified, which help to define how trisomy for this segment of the chromosome contributes to phenotypes of DS.

Hyperphagia and obesity in OLETF rats lacking CCK-1 receptors

The brain-gut peptide cholecystokinin (CCK) inhibits food intake following peripheral or site directed central administration. Peripheral exogenous CCK inhibits food intake by reducing the size and duration of a meal. Antagonist studies have demonstrated that the actions of the exogenous peptide mimic those of endogenous CCK. Antagonist administration results in increased meal size and meal duration. The feeding inhibitory actions of CCK are mediated through interactions with CCK-1 receptors. The recent identification of the Otsuka-Long-Evans-Tokushima Fatty (OLETF) rat as a spontaneous CCK-1 receptor knockout model has allowed a more comprehensive evaluation of the feeding actions of CCK. OLETF rats become obese and develop non-insulin dependent diabetes mellitus (NIDDM). Consistent with the absence of CCK-1 receptors, OLETF rats do not respond to exogenous CCK. OLETF rats are hyperphagic and their increased food intake is characterized by a large increase in meal size with a decrease in meal frequency that is not sufficient to compensate for the meal size increase. Deficits in meal size control are evident in OLETF rats as young as 2 days of age. OLETF obesity is secondary to the increased food intake. Pair feeding to amounts consumed by intact control rats normalizes body weight, body fat and elevated insulin and glucose levels. Hypothalamic arcuate nucleus peptide mRNA expression in OLETF rats is appropriate to their obesity and is normalized by pair feeding. In contrast, pair fed and young pre-obese OLETF rats have greatly elevated dorsomedial hypothalamic (DMH) neuropeptide Y (NPY) mRNA expression. Elevated DMH NPY in OLETF rats appears to be a consequence of the absence of CCK-1 receptors. In intact rats NPY and CCK-1 receptors colocalize to neurons within the compact subregion of the DMH and local CCK administration reduces food intake and decreases DMH NPY mRNA expression. We have proposed that the absence of DMH CCK-1 receptors significantly contributes to the OLETF's inability to compensate for their meal size control deficit leading to their overall hyperphagia. Access to a running wheel and the resulting exercise normalizes food intake and body weight in OLETF rats. When given access to running wheels for 6 weeks shortly after weaning, OLETF rats do not gain weight to the same degree as sedentary OLETF rats and do not develop NIDDM. Exercise also prevents elevated levels of DMH NPY mRNA expression, suggesting that exercise exerts an alternative, non-CCK mediated, control on DMH NPY. The OLETF rat is a valuable model for characterizing actions of CCK in energy balance and has provided novel insights into interactions between exercise and food intake.

Hyperphagia and obesity of OLETF rats lacking CCK1 receptors: developmental aspects

Otsuka Long Evans Tokushima Fatty (OLETF) rats have a deletion in the gene encoding the cholecystokinin-1 (CCK1) receptor. This deletion prevents protein expression, making the OLETF rat a CCK1 receptor knockout model. Consistent with the absence of CCK1 receptors, OLETF rats do not reduce their food intake in response to exogenously administered CCK and consume larger than normal meals. This deficit in within-meal feedback signaling is evident in liquid as well as solid meals. Neonatal OLETF rats show similar differences in independent ingestion tests. Intake is higher and is reflected in greater licking behavior. Neonatal OLETF rats also have diminished latencies to consume and higher initial ingestion rats. Adult OLETF rats are hyperphagic and obese. Although arcuate nucleus peptide gene expression is apparently normal in OLETF rats, when obesity is prevented through pair-feeding to amounts consumed by control Long Evans Tokushima Otsuka (LETO) rats, dorsomedial hypothalamic NPY mRNA expression is significantly elevated in OLETF rats. NPY overexpression is also evident in preobese, juvenile OLETF rats suggesting a causal role for this overexpression in the hyperphagia and obesity. Running wheel exercise normalizes food intake and body weight in OLETF rats. When access to exercise is provided at a time when OLETF rats are obese, the effects are limited to the period of exercise. When running wheel access is available to younger, preobese OLETF rats, exercise results in long lasting reductions in food intake and body weight and improved glucose regulation. These lasting metabolic effects of exercise may be secondary to an exercise induced reduction in DMH NPY mRNA expression.

Leptin modulation of peripheral controls of meal size

Leptin reduces food intake through a specific effect on meal size. Investigations into how this within meal effect of leptin is mediated have demonstrated that leptin increases the ability of within meal inhibitory feedback signaling to limit intake and activate neurons within the nucleus of the solitary tract (NTS). Leptin's effects on neural activation can be demonstrated both as an increase in c-fos activation and as increase in electrophysiological activity in response to peripheral stimuli. Leptin can exert these effects through interactions at hypothalamic sites and activation of a descending pathway. NPY has opposite effect suggesting a role for reduced NPY signaling in the actions of leptin. Forebrain ventricular administration of a melanocortin agonist does not mimic the actions of leptin. As well as modulating within meal signaling through a descending pathway leptin, NPY and melanocortins could work directly at hindbrain integrative sites suggesting the possibility of distributed controls of meal size by anorexigenic and orexigenic signaling.

Weight gain and maternal behavior in CCK1 deficient rats

The OLETF rat model of obesity has been extensively studied as an adult model of hyperphagia-induced obesity. In order to better understand the early circumstances that make OLETF pups obese, we investigated body weight from postnatal day (PND) 1 and examined diurnal maternal behavior over the first three postpartum weeks by undisturbed observations. Male and female OLETF rats weighed significantly more than LETO controls from PND 1 until adulthood. Differences in nursing behavior were observed only in the third postnatal week: OLETF dams exhibited more frequent nursing. OLETF dams displayed less self-directed behaviors and activity, over the entire postpartum period examined. Taken together, these data demonstrate that OLETF males and females are heavier from birth and suggest that maternal factors may contribute to weight differences between the strains.

Bromocriptine reduces steatosis in obese rodent models

BACKGROUND/AIMS

Obesity is a risk factor for glucose intolerance, steatosis, and oxidative stress, characteristics of nonalcoholic fatty liver disease. Bromocriptine may have anti-obesity, insulin-sensitizing, lipolytic, and antioxidant properties. We, therefore, hypothesized that bromocriptine would improve markers of nonalcoholic fatty liver disease in obese rodent models.

METHODS

We performed a randomized, controlled experiment in genetically obese fatty Zucker rats and diet-induced obese rats to assess for behavioral and peripheral anti-obesity actions of bromocriptine (10mg/kg) that would improve nonalcoholic fatty liver disease.

RESULTS

Behaviorally, food intake decreased and locomotor activity increased in bromocriptine-treated fatty Zucker and dietary-induced obese rats. Peripherally, liver triglycerides were significantly reduced and hepatic manganese superoxide dismutase significantly increased in bromocriptine-treated fatty Zucker and diet-induced obese rats compared to controls. Blood glucose was significantly lower in bromocriptine-treated Zucker rats compared to fatty controls and was no different than that of lean controls.

CONCLUSIONS

Improvements in obesigenic behaviors, glucose tolerance, hepatic lipid accumulation, and mitochondrial oxidative stress observed in genetically obese and diet-induced obese rodents indicate that bromocriptine may be promising as a broad-based therapy for nonalcoholic fatty liver disease.

Gut peptide signaling in the controls of food intake

During a meal and after a meal, ingested nutrients alter the release of a variety of gut peptides that have the potential to modulate food intake. Such feedback peptide signaling can be conceptualized as having three outcomes: meal termination, inhibitory modulation of intake in subsequent meals, and orexigenic modulation. Cholecystokinin, pancreatic glucagons, and amylin are examples of peptides involved in meal termination. They are released rapidly with the onset of feeding and have short durations of action. Peptide YY(3-36) and glucagon-like peptide 1 are peptides for which longer-term feeding inhibitory actions have been proposed. They are released from the distal intestine and have longer durations of actions. Ghrelin is a gastric peptide that stimulates food intake after its exogenous administration. Plasma ghrelin levels fall with feeding and rise with food deprivation. All of these gut peptides have vagal or dorsal hindbrain mediation. Their potential as targets for the development of anti-obesity treatments is under study.

Abnormal social behaviors in young and adult rats neonatally infected with Borna disease virus

Autism spectrum disorders (ASD) have been the focus of a great deal of research and clinical speculation. This intense interest relates to both the perplexing pathogenesis and devastating consequences of these disorders. One of the obstacles to understanding the pathogenesis of autism and to developing efficient treatment has been the paucity of animal models that could be used for hypotheses-driven mechanistic studies of abnormal brain and behavior development and for the pre-clinical testing novel pharmacological treatments. In this report, we briefly review our animal model of ASD based on neonatal Borna disease virus (BDV) infection and present new data about abnormal social interaction in adult BDV-infected rats. We found that neonatal BDV infection profoundly affected social behaviors in adult rats. Compared to the control rats, both 90- and 180-day-old infected rats spent less time in active social interaction and more time in following their partners. In the intruder-resident test, the BDV-infected resident rats exhibited less aggression towards the intruders and showed more the following-the-intruder behavior. The following-the-partner behavior may be an example of "stereotypic" activity due to BDV-induced abnormal social communication between rats. The previously published results and present findings indicate that neonatal BDV infection significantly altered the normal pattern of social interaction in rats. Co-localization of activated microglia and dying Purkinje cells in BDV-infected rats suggests that the BDV model could be used to study a pathogenic link of Purkinje cell dropout and neuroinflammation to abnormal social behaviors.

Intracerebroventricular C75 decreases meal frequency and reduces AgRP gene expression in rats

3-Carboxy-4-alkyl-2-methylenebutyrolactone (C75), an inhibitor of fatty acid synthase and stimulator of carnitine palmitoyltransferase-1, reduces food intake and body weight in rodents when given systemically or centrally. Intracellular molecular mechanisms involving changes in cellular energy status are proposed to initiate the feeding and body weight reductions. However, effectors that lie downstream of these initial steps are not yet fully identified. Present experiments characterize the time courses of hypophagia and weight loss after single injections of C75 into the lateral cerebroventicle in rats and go on to identify specific meal pattern changes and coinciding alterations in gene expression for feeding-related hypothalamic neuropeptides. C75 reduced chow intake and body weight dose dependently. Although the principal effects occurred on the first day, weight losses relative to vehicle control were maintained over multiple days. C75 did not affect generalized locomotor activity. C75 began to reduce feeding after a 6-h delay. The hypophagia was due primarily to decreased meal number during 6–12 h without a significant effect on meal size, suggesting that central C75 reduced the drive to initiate meals. C75 prevented the anticipated hypophagia-induced increases in mRNA for AgRP in the arcuate nucleus at 22 h and at 6 h when C75 begins to suppress feeding. Overall, the data suggest that gene expression changes leading to altered melanocortin signaling are important for the hypophagic response to intracerebroventricular C75.

Lateral ventricular ghrelin and fourth ventricular ghrelin induce similar increases in food intake and patterns of hypothalamic gene expression

The gut peptide ghrelin has been shown to stimulate food intake after both peripheral and central administration, and the hypothalamic arcuate nucleus has been proposed to be the major site for mediating this feeding stimulatory action. Ghrelin receptors are widely distributed in the brain, and hindbrain ghrelin administration has been shown to potently stimulate feeding, suggesting that there may be other sites for ghrelin action. In the present study, we have further assessed potential sites for ghrelin action by comparing the ability of lateral and fourth ventricular ghrelin administration to stimulate food intake and alter patterns of hypothalamic gene expression. Ghrelin (0.32, 1, or 3.2 nmol) in the lateral or fourth ventricle significantly increased food intake in the first 4 h after injection, with no ventricle-dependent differences in degree or time course of hyperphagia. One nanomole of ghrelin into either the lateral or fourth ventricle resulted in similar increases in arcuate nucleus neuropeptide Y mRNA expression. Expression levels of agouti-related peptide or proopiomelanocortin mRNA were not affected by ghrelin administration. These data demonstrate that ghrelin can affect food intake and hypothalamic gene expression through interactions at multiple brain sites.

Recent advances in obesity: adiposity signaling and fat metabolism in energy homeostasis

Interactions between our conserved 'thrifty genotype' and current trends toward reduced physical activity and increased food intake are posited as the root cause of the rising prevalence of obesity in the modern era. The past decade has seen tremendous advances in our understanding of the physiological regulation of energy balance and adiposity, and important insights into the pathogenesis of obesity. We have gained a more comprehensive view of the energy homeostasis system from the discovery of the adiposity hormone leptin, the subsequent identification of hypothalamic and other brain neuropeptide systems controlling energy balance, and the progress in understanding the molecular mechanisms by which cells can sense and respond to changes in metabolic state. Numerous targets have been identified for potential pharmacological and genetic approaches to obesity management. Some of the most recent developments are prototypic compounds that manipulate fat metabolism, both in peripheral tissues and in the brain, to reduce body fat synthesis and storage and to increase fat oxidation, to reduce food intake, and to increase energy expenditure.

Looking for food in all the right places?

Examining a potential functional role for growth hormone secretagogue receptors in the hippocampus, Diano and colleagues (Diano et al., 2006), demonstrate novel actions of the orexigenic peptide ghrelin in hippocampal synaptic architecture, LTP, and learning and memory. These data suggest functional links between metabolic signaling and higher neural function.

Neurobiology of exercise

Voluntary physical activity and exercise training can favorably influence brain plasticity by facilitating neurogenerative, neuroadaptive, and neuroprotective processes. At least some of the processes are mediated by neurotrophic factors. Motor skill training and regular exercise enhance executive functions of cognition and some types of learning, including motor learning in the spinal cord. These adaptations in the central nervous system have implications for the prevention and treatment of obesity, cancer, depression, the decline in cognition associated with aging, and neurological disorders such as Parkinson's disease, Alzheimer's dementia, ischemic stroke, and head and spinal cord injury. Chronic voluntary physical activity also attenuates neural responses to stress in brain circuits responsible for regulating peripheral sympathetic activity, suggesting constraint on sympathetic responses to stress that could plausibly contribute to reductions in clinical disorders such as hypertension, heart failure, oxidative stress, and suppression of immunity. Mechanisms explaining these adaptations are not as yet known, but metabolic and neurochemical pathways among skeletal muscle, the spinal cord, and the brain offer plausible, testable mechanisms that might help explain effects of physical activity and exercise on the central nervous system.

The dorsal vagal complex as a site for cocaine- and amphetamine-regulated transcript peptide to suppress gastric emptying

Cocaine- and amphetamine-regulated transcript-derived peptides (CARTp) and corticotropin-releasing factor (CRF) alter feeding and gastrointestinal function after central administration, and the gastric inhibitory effects are mediated through CRF. We hypothesized that dorsal hindbrain effects of CARTp on gastric emptying are mediated by the vagus nerve and that the dorsal vagal complex (DVC) is a site of action for the gastric inhibitory effects of both CARTp and CRF. Rats were equipped with chronic intragastric fistulas and guide cannulas aimed at the fourth ventricle or the DVC. Fourth intracerebroventricular CARTp-induced suppression of 12 ml glucose (12.5%) gastric emptying during fill was blocked by subdiaphragmatic vagotomy. To establish whether the DVC may be a site of action for CARTp and/or CRF, intraparenchymal microinjections (0.25 microl) of CARTp (0.1 and 0.5 microg) and CRF (5 and 10 pmol) were administered in the DVC. Each dose, previously shown to be ineffective after fourth intracerebroventricular administration, suppressed gastric emptying during gastric fill vs. vehicle, but neither peptide changed gastric secretion volume or gastric acidity. The results indicate that the DVC is a target site for CRF and CARTp to inhibit gastric emptying and that the vagus mediates dorsal hindbrain effects of CARTp on gastric motor function.

Blockade of central GLP-1 receptors prevents CART-induced hypophagia and brain c-Fos expression

Central administration of both CART and GLP-1 reduces feeding and increases c-Fos in brain areas associated with food intake. To determine whether aspects of CART's effects were mediated through GLP-1's action, we examined whether the GLP-1 receptor antagonist des-His1-Glu9-exendin-4 (EX) blocked CART-induced feeding inhibition, and c-Fos activation. An i.c.v. dose of 100 microg EX blocked the feeding inhibitory action of 1 microg of CART i.c.v. and prevented CART-induced c-Fos expression at multiple hindbrain and hypothalamic sites. These data suggest that i.c.v. CART administration activates a central release of GLP-1 to inhibit feeding and produce widespread neural activation.

Chemical sympathectomy attenuates myenteric but not dorsal vagal complex Fos-like immunoreactivity induced by cholecystokinin-8 in the rat

Vagotomy and capsaicin treatment attenuate dorsal vagal complex (DVC) but not myenteric Fos-like immunoreactivity (Fos-LI) induced by cholecystokinin-8 (CCK-8). The goal of this experiment is to test the role of the sympathetic nervous system in the pathway by which CCK-8 increases myenteric Fos-LI. Adult male Sprague-Dawley rats were pretreated with guanethidine sulfate (40 mg/kg daily for 5 weeks) or vehicle intraperitoneally (IP), and injected with CCK-8 (40 microg/kg) or saline IP. Fos-LI was then quantified in the DVC and the myenteric neurons of the duodenum and jejunum using a diaminobenzidine reaction. Guanethidine pretreatment attenuated myenteric but not DVC Fos-LI induced by CCK-8. These findings demonstrate that sympathetic neurons play a role in mediating the myenteric Fos-LI response to CCK. They also suggest differential mediation of myenteric and DVC responses to CCK.

Strain differences in myenteric neuron number and CCK1 receptor mRNA expression may account for differences in CCK induced c-Fos activation

We utilized a diaminobenzidine reaction enhanced with nickel to compare dorsal vagal complex (DVC) and myenteric neuronal Fos-Like immunoreactivity (Fos-LI), in response to sulfated cholecystokinin-8 (CCK-8) (5, 10, 20, 40 microg/kg), among Sprague-Dawley (SD), Standard Long-Evans (SLE), Otsuka Long-Evans Tokushima Fatty (OLETF), and Long-Evans Tokushima Otsuka (LETO) rats. All rat strains but OLETF expressed Fos-LI in response to CCK-8. In addition, SD rats expressed more Fos-LI in the area postrema and myenteric neurons than SLE and LETO rats. To investigate the basis for these differences, we utilized cuprolinic blue staining, which stains neuronal cell bodies, to quantify the number of myenteric neurons, and a reverse transcriptase chain polymerase reaction to measure the gene expression of CCK(1) receptor in the gut. We found that SD rats have significantly more duodenal myenteric neurons than the other strains. In addition, this strain expressed significantly higher levels of the CCK(1) gene in both the duodenum and jejunum than the other strains. In conclusion, SD rats may express more myenteric Fos-LI in response to CCK due to increased numbers of myenteric neurons or more intestinal CCK(1) receptors than the other strains of rats.

Gut peptide signals in the control of food intake

Extract: During and following a meal, ingested nutrients come into contact with multiple sites in the gastrointestinal tract that have the potential to alter peptide and neural signaling. Such signals can serve as feedback mediators influencing current or subsequent food intake. Ingested nutrients accumulate within the stomach, activating gastric mechanoreceptors and providing a signal of gastric fullness. Even during a meal, some ingested nutrients pass from the stomach and contact intestinal receptors. Such contact results in gastrointestinal peptide release and the activation of neural fibers producing reflex alterations in gastrointestinal motor and secretory activity and providing feedback information about the volume and nature of ingested nutrients that could alter the size of the current meal or affect subsequent eating. Recent work has characterized the ability of multiple gut peptides to affect eating and, consistent with their different patterns of release around meals, various roles for these peptides in overall eating control have been suggested. With the current rapid increase in rates of obesity, peripheral peptides with the ability to affect food intake provide attractive targets for antiobesity drug development.

IL-6 induces regionally selective spinal cord injury in patients with the neuroinflammatory disorder transverse myelitis

Transverse myelitis (TM) is an immune-mediated spinal cord disorder associated with inflammation, demyelination, and axonal damage. We investigated the soluble immune derangements present in TM patients and found that IL-6 levels were selectively and dramatically elevated in the cerebrospinal fluid and directly correlated with markers of tissue injury and sustained clinical disability. IL-6 was necessary and sufficient to mediate cellular injury in spinal cord organotypic tissue culture sections through activation of the JAK/STAT pathway, resulting in increased activity of iNOS and poly(ADP-ribose) polymerase (PARP). Rats intrathecally infused with IL-6 developed progressive weakness and spinal cord inflammation, demyelination, and axonal damage, which were blocked by PARP inhibition. Addition of IL-6 to brain organotypic cultures or into the cerebral ventricles of adult rats did not activate the JAK/STAT pathway, which is potentially due to increased expression of soluble IL-6 receptor in the brain relative to the spinal cord that may antagonize IL-6 signaling in this context. The spatially distinct responses to IL-6 may underlie regional vulnerability of different parts of the CNS to inflammatory injury. The elucidation of this pathway identifies specific therapeutic targets in the management of CNS autoimmune conditions.

p53 mediates cellular dysfunction and behavioral abnormalities in Huntington's disease

We present evidence for a specific role of p53 in the mitochondria-associated cellular dysfunction and behavioral abnormalities of Huntington's disease (HD). Mutant huntingtin (mHtt) with expanded polyglutamine (polyQ) binds to p53 and upregulates levels of nuclear p53 as well as p53 transcriptional activity in neuronal cultures. The augmentation is specific, as it occurs with mHtt but not mutant ataxin-1 with expanded polyQ. p53 levels are also increased in the brains of mHtt transgenic (mHtt-Tg) mice and HD patients. Perturbation of p53 by pifithrin-alpha, RNA interference, or genetic deletion prevents mitochondrial membrane depolarization and cytotoxicity in HD cells, as well as the decreased respiratory complex IV activity of mHtt-Tg mice. Genetic deletion of p53 suppresses neurodegeneration in mHtt-Tg flies and neurobehavioral abnormalities of mHtt-Tg mice. Our findings suggest that p53 links nuclear and mitochondrial pathologies characteristic of HD.

Cholecystokinin-8 increases Fos-like immunoreactivity in the brainstem and myenteric neurons of rats through CCK1 receptors

To examine the role of cholecystokinin1 receptor (CCK1) in the activation of brainstem and myenteric neurons by CCK, we compared the ability of exogenous CCK-8 to induce Fos-like immunoreactivity (Fos-LI) in these neurons in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, lacking CCK1 receptors, and Long-Evans Tokushima Otsuka (LETO) controls. Five groups (n=4 rats per group) of OLETF rats, and five LETO control groups, were injected intraperitoneally (IP) with 5, 10, 20, and 40 microg/kg CCK-8 or saline. Forty-micrometer brainstem sections containing the area postrema, nucleus of the solitary tract, and the dorsal motor nucleus of the vagus, and myenteric neurons of the duodenum, jejunum, and ileum underwent a diaminobenzidine reaction enhanced with nickel to reveal Fos-LI. CCK-8 did not increase Fos-LI in any of the tested neurons in the OLETF rats. CCK-8 increased Fos-LI in the brainstem of the LETO rats in a dose dependent manner. In the LETO rats only 40 microg/kg CCK-8 increased Fos-LI in the myenteric plexus of the jejunum. This study demonstrates that CCK-8 activates the brainstem and myenteric neurons through the CCK1 receptor.

Leptin enhances feeding suppression and neural activation produced by systemically administered bombesin

Leptin amplifies feeding inhibition and neural activation produced by either cholecystokinin or intragastric preloads, suggesting that leptin may increase the efficacy of gastrointestinal meal-related signals. To determine whether leptin would similarly potentiate the feeding inhibitory actions of another putative satiety peptide, we evaluated the effects of third ventricular leptin administration on food intake and c-Fos activation in response to systemically administered bombesin (BN). Leptin (3.5 microg) was administered 1 h before either 0.9% saline or BN (0.32 and 1.0 nmol/kg) followed by 30-min access to Ensure liquid diet. Although neither leptin nor 0.32 nmol/kg BN alone suppressed Ensure intake, the combination reduced intake by 28%. The higher BN dose (1.0 nmol/kg) produced a significant suppression by itself but was further enhanced in the presence of leptin. Consistent with the behavioral results, c-Fos activation in the nucleus of the solitary tract was increased by combined dosages of leptin and 0.32 nmol/kg BN beyond the individual response to either peptide. In the presence of leptin, BN produced a 3.4- to 5.2-fold increase in the number of c-Fos-positive cells in the nucleus of the solitary tract compared with when BN was given alone. These data provide further support for the hypothesis that the effect of leptin on food intake may be mediated, in part, by modulating meal-related satiety signals.

Running wheel activity prevents hyperphagia and obesity in Otsuka long-evans Tokushima Fatty rats: role of hypothalamic signaling

Otsuka Long-Evans Tokushima fatty (OLETF) rats lacking cholecystokinin-A receptors are hyperphagic, obese, and diabetic. Although exercise attenuates OLETF rats' obesity, the mechanisms underlying the effects of exercise are unclear. In this study, we determined the effects of running wheel activity on patterns of body weight gain, food intake, and hypothalamic gene expression. We demonstrate that voluntary running activity beginning at 8 wk of age normalized meal patterns, food intake, body weight, and plasma levels of glucose and leptin in OLETF rats. During the initial exercise period, corticotropin-releasing factor (CRF) mRNA expression was significantly elevated in the dorsomedial hypothalamus (DMH) but not in the paraventricular nucleus in both OLETF and control Long-Evans Tokushima rats. In response to long-term exercise, arcuate nucleus (Arc) neuropeptide Y (NPY), and proopiomelanocortin as well as DMH NPY and CRF mRNA expression were increased in Long-Evans Tokushima rats. In contrast, whereas exercising OLETF rats had increased Arc NPY and DMH CRF expression, Arc proopiomelanocortin and DMH NPY mRNA levels were not elevated. Finally, we demonstrate that the effects of exercise on body weight in OLETF rats were long lasting. Although food intake and body weight were increased in OLETF rats when running wheels were locked, weights did not return to those of sedentary OLETF rats. Together, these data suggest that the elevation of DMH CRF expression may mediate the short-term feeding inhibitory effects of exercise and that exercise limits the elevation of DMH NPY expression to account for the overall prevention of OLETF rats' obesity.