Disrupted cholecystokinin type-A receptor (CCKAR) gene in OLETF rats

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

Parabrachial coding of sapid sucrose: relevance to reward and obesity

Cumulative evidence in rats suggests that the pontine parabrachial nuclei (PBN) are necessary for assigning hedonic value to taste stimuli. In a series of studies, our laboratory has investigated the parabrachial coding of sapid sucrose in normal and obese rats. First, using chronic microdialysis, we demonstrated that sucrose intake increases dopamine release in the nucleus accumbens, an effect that is dependent on oral stimulation and on concentration. The dopamine response was independent of the thalamocortical gustatory system but was blunted substantially by lesions of the PBN. Similar lesions of the PBN but not the thalamic taste relay diminished cFos activation in the nucleus accumbens caused by sucrose ingestion. Recent single-neuron recording studies have demonstrated that processing of sucrose-evoked activity in the PBN is altered in Otsuka Long Evans Tokushima Fatty (OLETF) rats, which develop obesity due to chronic overeating and express increased avidity to sweet. Compared with lean controls, taste neurons in OLETF rats had reduced overall sensitivity to sucrose and altered concentration responses, with decreased responses to lower concentrations and augmented responses to higher concentrations. The decreased sensitivity to sucrose was specific to NaCl-best neurons that also responded to sucrose, but the concentration effects were carried by the sucrose-specific neurons. Collectively, these findings support the hypothesis that the PBN enables taste stimuli to engage the reward system and, in doing so, influences food intake and body weight regulation. Obesity, in turn, may further alter the gustatory code via forebrain connections to the taste relays or hormonal changes consequent to weight gain.

Cocaine- and amphetamine-regulated transcript peptide immunoreactivity in the brain of the CCK-1 receptor deficient obese OLETF rat

Cocaine- and amphetamine-regulated transcript (CART) peptide is expressed in brain areas involved in homeostatic regulation and reward. CART has been shown to reduce food intake, but the underlying mechanisms and the relevance of this effect on obesity yet remain unknown. Therefore, we used immunohistochemistry to investigate the expression of CART peptide in various brain regions of the obese Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking the CCK-1 receptor. Analysis revealed that whereas the distribution of CART-peptide immunoreactive neurons and axonal networks was identical in OLETF rats and lean controls, the intensity of CART immunoreactivity was significantly reduced in the rostral part of the nucleus accumbens (p < 0.01), the basolateral complex of the amygdala (p < 0.05) and the rostro-medial nucleus of the solitary tract (p < 0.001) of the OLETF rats. These areas are involved in reward and integration of taste and viscerosensory information and have been previously associated with altered functions in this strain. The findings suggest that in addition to previously described deficits in peripheral satiety signals and augmented orexigenic regulation, the anorectic effect of CART peptide may also be diminished in OLETF rats.

Effects of combined olmesartan and pravastatin on glucose intolerance and cardiovascular remodeling in a metabolic-syndrome model

Hypertension and dyslipidemia frequently coexist in patients with progressive insulin resistance and thus constitute metabolic syndrome. We sought to determine the merits of combining an angiotensin II receptor blocker and a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor in treating this pathological condition. Five-week-old Otsuka Long-Evans Tokushima Fatty rats, a model of metabolic syndrome, were untreated or treated with olmesartan 3 mg kg(-1) per day, pravastatin 30 mg kg(-1) per day or their combination for 25 weeks. Long-Evans Tokushima Otsuka rats served as normal controls. The antihypertensive effect of olmesartan and the lipid-lowering properties of pravastatin were both augmented by the combination. The oral glucose tolerance test revealed that only the combined treatment significantly reduced the area under the time-glucose curve, which was accompanied by augmented adiponectin messenger RNA expression in epididymal adipose tissue. Although the total cardiac endothelial nitric oxide synthetase (eNOS) content did not significantly differ among the groups, the combined treatment significantly increased the content of dihydrofolate reductase, a key eNOS coupler. Dihydroethidium staining of the aorta showed that the combination most significantly attenuated superoxide production. Moreover, Azan-Mallory staining revealed that the combination most significantly limited the perivascular fibrosis and wall thickening of intramyocardial coronary arteries. In conclusion, the combination of olmesartan and pravastatin augmented adiponectin expression in white adipose tissue and improved glucose tolerance in a rat model of metabolic syndrome, which was associated with more significant ameliorations of cardiovascular redox state and remodeling than those by treatments with either agent alone.

Normal feeding and body weight in Fischer 344 rats lacking the cholecystokinin-1 receptor gene

A large body of evidence has demonstrated that one mechanism by which cholecystokinin (CCK) inhibits food intake through activation of CCK1 receptors (CCK1R) on vagal afferent neurons that innervate the gastrointestinal tract and project to the hindbrain. OLETF rats, which carry a spontaneous null mutation of the CCK1R, are hyperphagic, obese, and predisposed to type 2 diabetes. Recently, by introgressing the OLETF-derived, CCK1R-null gene onto a Fischer 344 genetic background, we have been able to generate a CCK1R-deficient, congenic rat strain, F344.Cck1r(-/-), that in contrast to OLETF rats, possesses a lean and normoglycemic phenotype. In the present study, the behavioral and neurobiological phenotype of this rat strain was characterized more fully. As expected, intraperitoneal injections of CCK-8 inhibited intake of chow and Ensure Plus and induced Fos responses in the area postrema and the gelatinosus, commissural and medial subdivisions of the nucleus tractus solitarius of wild-type F344.Cck1r(+/+) rats, whereas CCK-8 was without effect on food intake or Fos induction in the F344.Cck1r(-/-) rats. F344.Cck1r(-/-) and F344.Cck1r(+/+) rats did not differ in body weight and showed comparable weight gain when maintained on Ensure Plus for 2 weeks. Also, no difference was found in 24-h food intake, and dark-phase meal frequency or meal size between F344.Cck1r(+/+) and F344.Cck1r(-/-) rats. As expected, blockade of endogenous CCK action at CCK1R increased food intake and blocked the effects of peripheral CCK-8 in wild-type F344.Cck1r(+/+) rats. These results confirm that in rats with a F344 background, CCK-1R mediates CCK-8-induced inhibition of food intake and Fos activation in the hindbrain and demonstrate that selective genetic ablation of CCK1R is not associated with altered meal patterns, hyperphagia, or excessive weight gain on a palatable diet.

Altered pontine taste processing in a rat model of obesity

The increased palatability of modern diet contributes to eating beyond homeostatic need and in turn to the growing prevalence of obesity. How palatability is coded in taste-evoked neural activity and whether this activity differs between obese and lean remains unknown. To investigate this, we used extracellular single-unit recording in the second central gustatory relay, the pontine parabrachial nucleus while stimulating the tongue with various concentrations of sucrose (0.01-1.5 M) in Otsuka Long Evans Tokushima Fatty (OLETF) rats, lacking CCK-1R. The analyses included a total of 179 taste-responsive neurons in age-matched prediabetic, obese OLETF and lean Long Evans Tokushima Otsuka (LETO) controls. Compared with LETO, we found more NaCl-, and fewer sucrose-responsive neurons (67 vs. 47% and 14 vs. 32%), and an overall reduced response magnitude to sucrose in the OLETF rats. Further, in the obese rats there was a rightward shift in sucrose concentration-response functions relative to lean controls with a higher response-threshold (0.37+/-0.05 vs. 0.23+/-0.2 M, P<0.05) and maximal neural response to higher sucrose concentrations (0.96+/-0.07 vs. 0.56+/-0.5 M, P<0.001). These findings demonstrate altered central gustatory processing for sucrose in obese OLETF rat and further support the notion that palatability is encoded in the across neuron pattern.

Adaptation to lactation in OLETF rats lacking CCK-1 receptors: body weight, fat tissues, leptin and oxytocin

OBJECTIVE

To understand the adaptation to lactation of obese rats, by studying the interplay among the gut hormone cholecystokinin (CCK), the adiposity hormone leptin and the affiliation hormone oxytocin in modulating body mass and fat storage.

DESIGN

Strain differences were examined between Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking expression of functional CCK-1 receptors and Long Evans Tokushima Otsuka (LETO) controls, tested as nulliparous dams, at the 7 and 15th lactation day, at weaning (lactation day 22) or 8 weeks postweaning.

MEASUREMENTS

We measured body mass, fat pads (brown, retroperitoneal and inguinal) and inguinal adipocytes. Plasma levels of leptin and oxytocin were determined.

RESULTS

Fat depots of LETO female rats were larger during lactation compared to the levels found in postweaning and nulliparous female rats. LETO female rats gained weight and accumulated fat during pregnancy and lactation, returning to their normal fat levels postweaning. In contrast, OLETF female rats presented lower body weight and fat depots during the lactation period than nulliparous dams, and regained the weight and fat postweaning. Plasma leptin and oxytocin were highly correlated and followed the same pattern. OLETF leptin levels were highly correlated with fat depot and inguinal cell surface. No significant correlation was found for LETO parameters.

CONCLUSIONS

Pregnancy and lactation are energy-consuming events, which naturally induce female rats to increase food intake and accumulate fat. When challenged by the demands of rapidly growing preobese OLETF pups, OLETF dams' fat stores are reduced to lean, LETO levels. During lactation, sensitivity of the oxytocinergic neurons descending from the paraventricular nuclei to the nucleus of the solitary tract to CCK is reduced. We theorized that this pathway is not available to OLETF female rats that lack functional CCK-1 receptors to mediate the signal. The current study contributes to the understanding of the female body's adaptation to lactation.

Functional polymorphisms in inbred rat strains and their allele frequencies in commercially available outbred stocks

Polymorphisms that have been proven to influence gene functions are called functional polymorphisms. It is significant to know the distribution of functional polymorphisms in the rat, widely used in animal models for human diseases. In this study, we assessed 16 functional polymorphisms consisting of 3 coat color and 13 disease-associated genes in 136 rat strains, as a part of the genetic profiling program of the National Bio Resource Project for the Rat (NBRP-Rat). Polymorphisms of Cdkn1a, Fcgr3, Grp10, Lss, and Fdft1, which were proven to function in prostate tumorigenesis, glomerulonephritis, hyperphagia, and cholesterol biosynthesis, were shared among various inbred strains. These findings indicated that most rat strains harbored the disease-associated alleles and suggested that many unidentified functional polymorphisms might exist in inbred rat strains. The functional polymorphisms shared in inbred strains were also observed within outbred stocks available commercially. Therefore, this implies that experimental plans based on either rat inbred strains or outbred stocks need to be carefully designed with a full understanding of the genetic characteristics of the animals. To select the most suitable strains for experiments, the NBRP-Rat will periodically improve and update the genetic profiles of rat strains.

Cholecystokinin-A receptors regulate photic input pathways to the circadian clock

Daily behaviors are strongly dominated by internally generated circadian rhythms, but the underlying mechanisms remain unclear. In mammals, photoentrainment of behaviors to light-dark cycles involves signaling from both intrinsically photosensitive retinal ganglion cells and classic photoreceptor pathways to the suprachiasmatic nucleus (SCN). How classic photoreceptor pathways work with the photosensitive ganglion cells, however, is not fully understood. Although cholecystokinin (CCK) peptide has been shown to be present in a variety of vertebrate retinas, its function at a systems level is also unknown. In the present study we examined a possible role of CCK-A receptors in photoentrainment using CCK-A receptor knockout mice. The lacZ reporter gene within a gene-knockout cassette revealed precise localization of CCK-A receptors in the circadian clock system. We demonstrated that CCK-A receptors were located predominately on glycinergic amacrine cells but were rarely found on SCN neurons. Moreover, Ca(2+) imaging analysis demonstrated that the CCK-A agonist, CCK-8 sulfate (CCK-8s), mobilized intracellular Ca(2+) in amacrine cells but not glutamate-receptive SCN neurons. Furthermore, light pulse-induced mPer1/mPer2 gene expression in SCN, behavioral phase shifts, and the pupillary reflex were significantly reduced in CCK-A receptor knockout mice. These data indicate a novel function of CCK-A receptors in the nonimage-forming photoreception presumably via amacrine cell-mediated signal transduction pathways.

Effect of dietary omega 3 phosphatidylcholine on obesity-related disorders in obese Otsuka Long-Evans Tokushima fatty rats

Recent reports have shown that dietary phosphatidylcholine (PC) has various beneficial biological effects. Omega 3 polyunsaturated fatty acids (omega3 PUFAs) have also been reported to have lipid-lowering effects in animal models and human studies. In the present study, we investigated the effect of omega3 PUFAs containing PC (omega3-PC) on obesity-related disorders in Otsuka Long-Evans Tokushima fatty (OLETF) rats. Rats were fed semisynthetic diets that contained either 5% corn oil and 2% egg-PC or 5% corn oil and 2% omega3-PC for 4 weeks. During this 4 week feeding of the omega3-PC, the OLEFT rats showed a decrease of omental white adipose tissue weight. In addition, the omega3-PC diet significantly decreased liver weight and hepatic lipid levels in OLETF rats. These changes were attributable to the significant suppression of fatty acid synthase activity and significant enhancement in the activities of carnitine palmitoyltransferase and peroxisomal beta-oxidation. Moreover, the omega3-PC diet reduced serum glucose levels concomitant with the increase of serum adiponectin levels. These results show that compared with egg-PC, omega3-PC can prevent or alleviate obesity-related disorders through the suppression of fatty acid synthesis, enhancement of fatty acid beta-oxidation, and increase of the serum adiponectin level in OLETF rats.

Altered emotional behaviors in the diabetes mellitus OLETF type 1 congenic rat

GPR10 is a G-protein-coupled receptor expressed in thalamic and hypothalamic brain regions, including the reticular thalamic nucleus (RTN) and periventricular nucleus (Pev), and the endogenous ligand for this receptor, prolactin-releasing peptide (PrRP), has demonstrated regulatory effects on the stress response. We produced a congenic rat by introducing the Dmo1 allele from the OLETF rat which encodes the amino acid sequences of GPR10 with a truncated NH2-terminus, into the Brown-Norway background. Using receptor autoradiography, we determined a lack of specific [125I]PrRP binding in the RTN and Pev of these mutant rats compared to the control rats. Furthermore, intracerebroventricular injection of PrRP did not induce a significant increase of c-fos-like immunoreactivity in the paraventricular nucleus of the mutant rats compared to the control rats. The mutant rats also displayed a less anxious-like phenotype in three behavioral-based models of anxiety-like behavior (open field, elevated plus maze and defensive withdrawal test). These data show the mutant congenic rat, of which GPR10 neither binds nor responds to PrRP, expresses less anxious-like phenotypes. On the basis of these observations, the GPR10 might be a novel target for the developing new drugs against anxiety and/or other stress-related diseases.

Dopamine D2 receptors contribute to increased avidity for sucrose in obese rats lacking CCK-1 receptors

Accumulating evidence has indicated a link between dopamine signaling and obesity in both animals and humans. We have recently demonstrated heightened avidity to sapid sweet solutions in the obese cholecystokinin (CCK)-1 receptor deficient Otsuka Long Evans Tokushima fatty (OLETF) rat. To investigate the dopamine dependence and the respective contribution of D1 and D2 receptor subtypes in this phenomenon, real and sham intake of 0.3 M sucrose solution was compared between prediabetic, obese OLETF and age-matched lean Long-Evans Tokushima Otsuka (LETO) cohorts following peripheral (i.p.) administration of equimolar doses (50-800 nmol/kg) of the D1 (R-(+) 7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine, SCH23390) and D2 (raclopride) selective receptor antagonists. Both antagonists were potent in reducing sucrose intake in both strains with both drugs suppressing sham intake starting at lower doses than real intake (200 nmol/kg vs. 400 nmol/kg for SCH23390, and 400 nmol/kg vs. 600 nmol/kg for raclopride, respectively). Furthermore, when percent suppression of intake, a measure that controlled for the higher baseline sucrose intake by obese rats was analyzed, OLETF rats expressed an increased sensitivity to raclopride in reducing ingestion of sucrose with a 1.7- and 2.9-fold lower inhibitory dose threshold (ID50) for real and sham intake conditions, respectively, compared with LETO controls. In contrast, SCH23390 caused no differential strain effect with respect to dosage whether sucrose was real or sham fed. These findings demonstrate that D2 receptors are involved in heightened increased consumption of sucrose observed in the OLETF obese rat.

Stimulation of cholecystokinin-A receptors with GI181771X does not cause weight loss in overweight or obese patients

Cholecystokinin (CCK) decreases meal size through activation of CCK-A receptors on vagal afferents. We tested the hypothesis that the selective CCK-A agonist GI181771X induces weight loss in obese patients. Patients with body mass index > or = 30 or > or = 27 kg/m2 with concomitant risk factors were randomized to 24-week, double-blind treatment with different GI181771X doses or matching placebo together with a hypocaloric diet. The primary efficacy end point was the absolute change in body weight. To monitor pancreatic and gallbladder effects, patients underwent abdominal ultrasound and magnetic resonance imaging before and after treatment. We randomized 701 patients to double-blind treatment. GI181771X did not reduce body weight and had no effect on waist circumference or other cardiometabolic risk markers. Gastrointestinal side effects were more common with GI181771X than with placebo treatment, whereas hepatobiliary or pancreatic abnormalities did not occur. CCK-A by itself does not have a central role in long-term energy balance.

Altered basal and stimulated accumbens dopamine release in obese OLETF rats as a function of age and diabetic status

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat lacking the CCK-1 receptor is hyperphagic, prefers palatable and high-calorie meals, and gradually develops obesity and type 2 diabetes. To determine dopamine levels in this strain, we used in vivo quantitative (no net flux) microdialysis at three different ages representing nondiabetic (8 wk), prediabetic (18 wk), and diabetic (56 wk) stages in OLETF and age-matched lean Long-Evans Tokushima Otsuka (LETO) controls. Results showed significantly elevated basal dopamine levels in the caudomedial nucleus accumbens of OLETF rats compared with LETO at younger ages (8 wk: 20.10 +/- 5.61 nM vs. 15.85 +/- 5.63 nM; 18 wk: 7.37 +/- 3.71 nM vs. 4.75 +/- 1.25 nM, means +/- SD). In contrast, at 56 wk of age, a profound decline in extracellular dopamine concentrations was seen in both strains with a tendency for a greater effect in OLETF rats (1.78 +/- 0.40 nM vs. 2.39 +/- 0.42 nM). Further, extracellular fraction, an index for reuptake, was higher in 56-wk-old OLETF compared with LETO (0.648 +/- 0.049 vs. 0.526 +/- 0.057). Potassium-stimulated dopamine efflux revealed an increased capacity of vesicular pool in OLETF rats compared with LETO across all age groups with an accentuated strain difference at 56 wk. These findings demonstrate altered striatal dopamine functions (i.e., increased stimulated release and uptake) in obese OLETF rat. This could be due to the lack of functional CCK-1 receptors, or metabolic and hormonal factors associated with the development of obesity and insulin resistance, or both.

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.

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.

The genetic landscape of type 2 diabetes in mice

Inbred mouse strains provide genetic diversity comparable to that of the human population. Like humans, mice have a wide range of diabetes-related phenotypes. The inbred mouse strains differ in the response of their critical physiological functions, such as insulin sensitivity, insulin secretion, beta-cell proliferation and survival, and fuel partitioning, to diet and obesity. Most of the critical genes underlying these differences have not been identified, although many loci have been mapped. The dramatic improvements in genomic and bioinformatics resources are accelerating the pace of gene discovery. This review describes how mouse genetics can be used to discover diabetes-related genes, summarizes how the mouse strains differ in their diabetes-related phenotypes, and describes several examples of how loci identified in the mouse may directly relate to human diabetes.

Conditioned preference for sweet stimuli in OLETF rat: effects of food deprivation

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an outbred strain of Long- Evans Tokushima Otsuka rat (LETO) that lacks CCK-1 receptor expression, is hyperphagic and develops obesity and type-2 diabetes. The present study sought to assess how OLETF rats alter intake, preference, and conditioned preference of palatable solutions after acute food deprivation. Our results show that after 24 h chow restriction, LETO rats increase both sucrose intake and two-bottle sucrose preference relative to their free-fed baseline, whereas OLETF rats do not increase sucrose intake (0.3 M or 1.0 M sucrose) or preference (1.0 M vs. 0.3 M sucrose) when they are food deprived. In contrast, OLETF rats exhibit a higher conditioned flavor preference when sucrose is used as unconditioned stimulus (US) relative to LETO rats, whether overnight food restricted (81% vs. 71% for OLETF and LETO rats, respectively) or free fed (82% vs. 54% for OLETF and LETO rats, respectively) during the test. When a noncaloric saccharin solution is used as US, OLETF rats show a higher preference for the saccharin-associated flavor relative to LETO rats when nondeprived (76% vs. 58% for OLETF and LETO rats, respectively); however, neither strain shows differential conditioned flavor preference for saccharin in the deprivation state during the test. These findings suggest that OLETF rats fail to integrate postabsorptive and orosensory effects of sucrose in a conditioning setting to influence intake. Thus, it appears that OLETF rats form preferences for sucrose based largely on orosensory and hedonic properties of the solution, rather than caloric value.

Differential serum proteomic analysis in a model of metabolic disease

Protein profiling would aid in better understanding the pathophysiology of metabolic disease. Here, we report on differential proteomic analysis using an animal model of diabetes mellitus and associated metabolic disorders (Otsuka Long-Evans Tokushima Fatty rat). Serum was analyzed by a new two-dimensional liquid chromatography system which separated proteins by chromatofocusing and subsequent reversed-phase chromatography. This is the first application of this approach to differential serum proteomics. Differentially expressed proteins, identified with MALDI-TOF mass spectrometry, included apolipoproteins and alpha2-HS-glycoprotein. These findings add to our understanding of the underlying pathophysiology. This new proteomic analysis is a promising tool to elucidate disease mechanisms.

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.

Decreased gastric mechanodetection, but preserved gastric emptying, in CCK-1 receptor-deficient OLETF rats

Obese CCK-1 receptor-lacking Otsuka Long Evans Tokushima fatty (OLETF) rats are hyperphagic relative to control, nonmutant Long Evans Tokushima Otsuka (LETO) rats. This study sought to assess whether the overeating observed in OLETF rats is associated with changes in gastric emptying rates or detection of gastric volume. We performed experiments in both 12- and 29-wk-old OLETF and LETO rats to address possible alterations in gastric functions during the development of increased body weight and blood glucose abnormalities in OLETF rats. Gastric emptying of a 5-g solid chow test meal was not significantly different between strains at either 1, 2, or 4 h postmeal. When rats with ad libitum access to chow were tested, there were no significant differences in gastric emptying between strains at any time period despite OLETF rats consuming significantly more chow than LETO rats. Similar to solid food, 5-min gastric emptying of a 5-ml isosmotic and hyperosmotic saline or glucose load was not significantly different between strains. When the stomach was distended with a 15-ml semisolid chow load, there was no significance difference in emptying at either 1 or 2 h. No significant differences in gastric emptying were detected between 12- and 29-wk-old rats under any conditions. Both young and old OLETF rats, however, reduced sham intake significantly less compared with LETO rats during a brief period of gastric distension by 5- or 10-ml balloon inflation. Finally, OLETF rats showed decreased Fos expression in the nucleus of the solitary tract relative to LETO rats after an 8-ml gastric distension. These findings demonstrate that OLETF rats do not express deficits in controlling gastric emptying rates; however, they exhibit decreased behavioral and vagal responsiveness to gastric distension that may contribute to the increased meal size in these animals.

Isomer-specific anti-obese and hypolipidemic properties of conjugated linoleic acid in obese OLETF rats

Conjugated linoleic acid (CLA), a mixture of positional and geometric isomers of linoleic acid, has attracted considerable attention because of its potentially beneficial biologic effects both in vitro and in vivo. Our results clearly show the specific action of the 10trans,12cis-CLA isomer against hyperlipidemia and obesity in obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats. After 2 weeks of feeding with 10t,12c-CLA, but not 9cis,11trans-CLA, abdominal adipose tissue weight and serum and hepatic lipid levels in OLETF rats were lower than those in linoleic acid-fed rats. These effects were attributable to suppressed fatty acid synthesis and enhanced fatty acid beta oxidation in the liver on a 10t,12c-CLA diet. Additionally, we showed that mRNA expression of fatty acid synthase, carnitine palmitoyltransferase, leptin, and sterol regulatory element binding protein-1 was also regulated by 10t,12c-CLA. We suppose that 10t,12c-CLA reveals hypolipidemic and anti-obese activity through the alteration of mRNA expressions in the liver and white adipose tissue.

Stress and pain responses in rats lacking CCK1 receptors

CCK involvement in stress- and pain-responsiveness was examined by studying the behavior of infant (11-12-days-old) and adult OLETF rats that do not express CCK1 receptors. Infant odor- and texture-preferences were also assessed. We hypothesized that OLETF rats will show behavioral patterns similar to those previously observed after CCK1 antagonist administration. Rate of separation-induced ultrasonic vocalization was significantly greater in OLETF compared to controls, in two separate studies. Infant pups of the two strains did not differ in odor- and texture-preference tests. OLETF rats showed consistently longer hot-plate paw-lift (as infants, in two separate studies) and paw-lick (as adults) latencies.

SUMMARY

OLETF pups vocalized in isolation more than controls and showed relative hypoalgesic responses, evident also in adulthood, in concordance with the pharmacological literature.

Mutated G-protein-coupled receptor GPR10 is responsible for the hyperphagia/dyslipidaemia/obesity locus of Dmo1 in the OLETF rat

1. We have confirmed the Diabetes Mellitus OLETF type I (Dmo1) effect on hyperphagia, dyslipidaemia and obesity in the Otsuka Long-Evans Tokushima Fatty (OLETF) strain. The critical interval was narrowed down to 570 kb between D1Got258 to p162CA1 by segregation analyses using congenic lines. 2. Within the critical 570 kb region of the Dmo1 locus, we identified the G-protein-coupled receptor gene GPR10 as the causative gene mutated in the OLETF strain. The ATG translation initiation codon of GPR10 is changed into ATA in this strain and, so, is unavailable for the initiation of translation. 3. The GPR10 protein has a cognate ligand, namely prolactin-releasing peptide (PrRP). Centrally administered PrRP suppressed the food intake of congenic rats that have a Brown Norway derived Dmo1 region (i.e. with wild-type GPR10), but did not suppress that of the OLETF strain, indicating that GPR10 is without function and could explain hyperphagia in the OLETF strain. 4. Moreover, when restricted in food volume to the same level consumed by the congenic strain, OLETF rats showed few differences in the parameters of dyslipidaemia and obesity compared with congenic strains. 5. Taken together, these results demonstrate that the mutated GPR10 receptor is responsible for the hyperphagia leading to obesity and dyslipidaemia in the obese diabetic strain rat.

Disturbance of Response to Acute Thermal Pain in Naturally Occurring Cholecystokinin-A Receptor Gene Knockout Otsuka Long-Evans Tokushima Fatty (OLETF) Rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rats lack cholecystokinin-A receptor (CCK-AR) because of a genetic abnormality. We observed that body temperature homeostasis in response to changes in ambient temperature was deteriorated in OLETF rats, while the functions of the signal outputs from the hypothalamus to effectors were not impaired. Deteriorated homeostasis was also seen in CCK-AR deficient (-/-) mice. In the present study, we examined whether the sensory pathway involved in transmitting signals about temperature from the skin to the brain was impaired in OLETF rats. To elucidate the involvement of CCK-AR function, we conducted the same experiment in CCK-AR(-/-) mice. Responses to thermal pain were assessed using the Hargreaves' plantar test apparatus. Shortening of withdrawal latency was observed in OLETF rats compared to control rats, indicating thermal hyperalgesia. Behavioral responses following paw withdrawal were disturbed in OLETF rats. The 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid contents in the hippocampus and frontal cortex of OLETF rats were significantly higher than in those of the controls. CCK-AR(-/-) mice did not show any differences from wild-type mice. In conclusion, OLETF rats showed thermal hyperalgesia and disturbed responses to thermal pain, and an alteration of 5-HT function might have a role in this disturbance.

Effects of cholecystokinin (CCK)-8 on hypothalamic oxytocin-secreting neurons in rats lacking CCK-A receptor

Peripheral administration of cholecystokinin (CCK)-8 selectively activates oxytocin (OXT)-secreting neurons in the supraoptic (SON) and the paraventricular nuclei (PVN) with the elevation of plasma OXT level in rats. We examined the effects of intravenous (iv) administration of CCK-8 on the neuronal activity of hypothalamic OXT-secreting neurons and plasma OXT level in Otsuka Long-Evans Tokushima Fatty (OLETF) rats that have a congenital defect in the expression of the CCK-A receptor gene. In situ hybridization histochemistry (ISH) for c-fos mRNA revealed that the expression of the c-fos gene was not induced in the SON, the PVN, the nucleus of the tractus solitarius (NTS) and the area postrema (AP) 30 min after iv administration of CCK-8 (20 and 40 microg/kg) in OLETF rats. In Long-Evans Tokushima Otsuka (LETO) rats (controls), c-fos mRNA was detected abundantly in those nuclei 30 min after iv administration of CCK-8 (20 microg/kg). Immunohistochemistry for c-fos protein (Fos) showed that the distributions of Fos-like immunoreactivity (LI) were identical to the results obtained from ISH. Dual immunostaining for OXT and Fos revealed that Fos-LI was mainly observed in OXT-secreting neurons in the SON and the PVN of LETO rats 90 min after iv administration of CCK-8 (20 microg/kg). Radioimmunoassay for OXT and arginine vasopressin (AVP) showed that iv administration of CCK-8 did not cause significant change in the plasma OXT and AVP levels in OLETF rats, while iv administration of CCK-8 caused a significant elevation of plasma OXT level without changing the plasma AVP level in LETO rats. These results suggest that peripheral administration of CCK-8 may selectively activate the hypothalamic OXT-secreting neurons and brainstem neurons through CCK-A receptor in rats.

Brief intermittent access to sucrose differentially modulates prepulse inhibition and acoustic startle response in obese CCK-1 receptor deficient rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rats lack the CCK-1 receptor and are hyperphagic and obese. CCK-1 receptors play a role in prepulse inhibition (PPI) by modulating mesolimbic dopamine transmission, a modulator of sensorimotor gating. Therefore, the present study assessed the effects of brief, daily sucrose access on PPI and acoustic startle response (ASR) in OLETF rat and age-matched non-mutant Long-Evans Tokushima Otsuka (LETO) rats. The results revealed that OLETF rats with sucrose access showed an increased ASR [F(1,16) = 6.84; P < 0.01)], relative to sucrose receiving LETO rats. No significant sucrose effect (P = 0.283) on PPI was noted in OLETF rats, whereas sucrose receiving LETO rats had a significantly lower (P < 0.05) PPI percentage than non-sucrose controls. In contrast, sucrose-receiving OLETF rats expressed significantly higher PPI percentage than LETO rats with identical sucrose presentation (P < 0.01). Taken together, these results suggest that sucrose access alters PPI and ASR in general, and the CCK-1 receptors play a modulatory role in facilitating or inhibiting these responses, respectively. A similar effect may be contributory to the hyperphagic behavioral phenotype of obese animal models with altered central dopamine regulation.

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.

Independent ingestion and microstructure of feeding patterns in infant rats lacking CCK-1 receptors

Otsuka Long-Evans Tokushima fatty (OLETF) rats are a strain of Long-Evans Tokushima Otsuka (LETO) rats that do not express CCK-1 receptors, developing in adulthood, hyperphagia, obesity, and non-insulin-dependent diabetes mellitus (NIDDM). We examined weight gain and meal patterns during a 30-min independent ingestion test on postnatal days 2-4 and again on days 9-11 in OLETF and LETO rat pups. OLETF pups were significantly heavier compared with their LETO controls at both ages, and they consumed significantly more of the sweet milk diet. The difference in intake can be attributed to a significant increase in meal size and duration. Number of clusters and bursts of licking within a meal were greater in OLETF rat pups, with no difference between strains in burst and cluster size. Interlick interval (ILI) was not significantly different between OLETF and LETO pups. This measure decreased on days 9-11 compared with days 2-4 in both strains. Latency to start feeding was significantly shorter on days 2-4 in OLETF vs. LETO pups, but this difference disappeared at the second test at the older age. Two- to four-day-old OLETF pups consumed a larger volume of milk during the first minute of feeding, and their initial lick rate and decay of lick rate were significantly larger compared with their LETO controls. Lack of CCK-1 receptors, or other OLETF-related abnormalities, therefore, resulted in a satiation deficit, leading to increased meal size, hyperphagia, and increased weight gain as early as 2-4 postnatal days.

Altered taste sensitivity in obese, prediabetic OLETF rats lacking CCK-1 receptors

Otsuka Long-Evans Tokushima fatty (OLETF) rats lack the CCK-1 receptor, are hyperphagic, progressively become obese, and develop type-2 diabetes. We recently demonstrated an increased preference for both real and sham feeding of sucrose in this strain, suggesting altered orosensory sensitivity. To investigate taste functions, we used an automated gustometer with 10-s access to different concentrations of various sapid stimuli. Tests were repeated at 10 and 18 wk of age to assess the early and advanced stages of prediabetes, respectively. Compared with age-matched, nonmutant controls, the OLETF rats showed higher avidity for sucrose at both ages. This difference increased as a function of age and tastant concentration. An exaggerated response also occurred for saccharin, alanine, and fructose, but not for Polycose. Similarly, OLETF rats consumed monosodium-glutamate more at the lower concentrations compared with controls, an effect that age also accentuated. In contrast, there was no statistical strain or age differences in responses to NaCl, MgCl2, citric acid, quinine-HCl, and the trigeminal stimulus capsaicin. These findings demonstrate that compared with controls, OLETF rats differ in their gustatory functions with an overall augmented sensitivity for sweet that progresses during prediabetes. This effect explains their overconsumption of sweet solutions and may contribute to the overall hyperphagia and obesity in this strain.

Dietary effect of pomegranate seed oil rich in 9cis, 11trans, 13cis conjugated linolenic acid on lipid metabolism in obese, hyperlipidemic OLETF rats

Conjugated fatty acid, the general term of positional and geometric isomers of polyunsaturated fatty acids with conjugated double bonds, has attracted considerable attention because of its potentially beneficial biological effects. In the present study, dietary effect of pomegranate seed oil rich in punicic acid (9cis, 11trans, 13cis-conjugated linolenic acid; 9c, 11t, 13c-CLNA) on lipid metabolism was investigated in obese, hyperlipidemic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. After 2 weeks feeding period, OLETF rats revealed obesity and hyperlipidemia compared with their progenitor LETO rats. Feeding of the diet supplemented with 9% safflower oil and 1% pomegranate seed oil (9c, 11t, 13c-CLNA diet) did not affect abdominal white adipose tissue weights and serum lipid levels compared with the diet supplemented with 10% safflower oil (control diet) in OLETF rats. However, the accumulated hepatic triacylglycerol was markedly decreased by 9c, 11t, 13c-CLNA diet in OLETF rats. Activities of hepatic enzymes related to fatty acid synthesis and fatty acid beta-oxidation were not altered by 9c, 11t, 13c-CLNA diet. Levels of monounsaturated fatty acid (MUFA), major storage form of fatty acid, in serum triacylglycerol were markedly higher in obese, hyperlipidemic OLETF rats than in lean LETO rats. In addition, 9c, 11t, 13c-CLNA diet significantly decreased MUFA levels in OLETF rats. This is the first study showing that 9c, 11t, 13c-CLNA suppresses delta-9 desaturation in vivo, and we suggest that the alleviation of hepatic triacylglycerol accumulation by 9c, 11t, 13c-CLNA diet was, at least in part, attributable to the suppression of delta-9 desaturation in OLETF rats.

Physiological and pathological age-associated changes in diurnal rhythm of energy expenditure in rats

Although the idea that energy metabolism of rats decreases with age has been widely accepted, few studies with regard to the diurnal rhythm of energy expenditure have been reported. Whether age alone altered the diurnal rhythm of energy expenditure was examined in Sprague-Dawley (SD) rats. The same determination was conducted in Otsuka Long Evans Tokushima Fatty (OLETF) rats to examine the effect of insulin resistance and diabetes. OLETF rats were developed as a model of non-insulin-dependent diabetes mellitus (NIDDM) with mild obesity. The characteristic features of OLETF rats are late onset of hyperglycemia at about 18 weeks of age, followed by insulin deficiency at about 65 weeks. Age-associated changes in diurnal rhythm of energy expenditure were not observed in SD rats. In OLETF rats, the diurnal rhythm of energy expenditure with two peaks was observed at 8 weeks of age, while these two peaks disappeared at 24 weeks of age (with NIDDM). Then, the pattern of diurnal rhythm at 44 weeks of age (with advanced NIDDM) was resembled to that of 62 weeks of age (with insulin deficiency). In conclusion, we clarified the changes in diurnal rhythm of energy expenditure associated with the progress of diabetes, while age alone did not alter the diurnal rhythm.

Increased oral and decreased intestinal sensitivity to sucrose in obese, prediabetic CCK-A receptor-deficient OLETF rats

CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rats are hyperphagic and develop obesity and Type 2 diabetes. In this strain, taste preference functions have not been investigated. Therefore, a series of short-access, two-bottle tests were performed in age-matched prediabetic OLETF and nonmutant Long-Evans Tokushima Otsuka (LETO) rats to investigate preference for sucrose (0.03, 0.1, 0.3, or 1.0 M) presented with a choice of water. To discern orosensory from postgastric factors that may contribute to this preference, in a separate experiment, rats were allowed to sham feed sucrose in the absence or presence of duodenal sucrose infusion (0.3, 0.6, or 1.0 M). In the two-bottle real-feeding tests, OLETF rats exhibited a greater preference for 0.3 M sucrose (91.2 +/- 1.7 and 78.5 +/- 3.4% for OLETF and LETO, respectively; P < 0.01) and 1.0 M sucrose (65.3 +/- 1.2 and 57.5 +/- 2.7% for OLETF and LETO, respectively; P < 0.05) than LETO rats. OLETF rats also sham fed less of the lowest (0.03 M; 33.8 +/- 4.8 and 58.3 +/- 7.3 ml for OLETF and LETO, respectively; P < 0.05) and more of the highest (1.0 M; 109.9 +/- 6.5 and 81.0 +/- 3.9 ml for OLETF and LETO, respectively; P < 0.01) concentration of sucrose relative to LETO rats. Finally, intraduodenal sucrose infusions (0.6 and 1.0 M) produced a smaller reduction of 0.3 M sham sucrose intake [14.1 +/- 8.1 vs. 52.5 +/- 3.3 ml and 49.4 +/- 8.0 vs. 82.4 +/- 3.2 ml for 0.6 M (P < 0.01) and 1.0 M (P < 0.05) infusions in OLETF and LETO, respectively]. These findings demonstrate that OLETF rats display an increased preference for sucrose, an effect that is at least partially influenced by the orosensory stimulating effect of sucrose. This enhanced responsiveness to oral stimulation, coupled with the deficit in responding to the postingestive feedback of intestinal sucrose, may contribute additively to the development of hyperphagia and weight gain in OLETF rats.

Absence of the cholecystokinin-A receptor deteriorates homeostasis of body temperature in response to changes in ambient temperature

The circadian rhythm of the body core temperature (Tc) and the effects of changes in ambient temperatures on the homeostasis of Tc in Otsuka Long Evans Tokushima Fatty (OLETF) rats, which are naturally occurring cholecystokinin (CCK)-A receptor (CCK-AR) gene knockout (−/−) rats, were examined. In addition, the peripheral responses to warming or cooling of the preoptic and anterior hypothalamic region (PO/AH) were determined. The circadian rhythm of Tc in OLETF rats was similar to that in Long-Evans Tokushima (LETO) rats; this rhythm was characterized by a higher Tc during the dark period and a lower Tc during the light period. When the ambient temperature was changed within the limits of 0°C to 30°C, the changes in Tc of LETO rats were associated with the changes in ambient temperature, whereas those in OLETF rats were dissociated from the temperature changes. The OLETF rats showed a large hysteresis. The peripheral responses to warming or cooling of PO/AH, including shivering of the neck muscle and changes in skin temperature of the tail and footpad, were similar in OLETF and LETO rats. To confirm the role of CCK-AR in the regulation of body temperature, the values of Tc in the CCK-AR(−/−) mice were compared with those in CCK-B receptor (CCK-BR) (−/−), CCK-AR(−/−)BR(−/−), and wild-type mice. In the mice, the circadian rhythms of Tc were the same, regardless of the genotype. Mice without CCK-AR showed larger hysteresis than mice with CCK-AR. From these results, we conclude that the lack of CCK-AR causes homeostasis of Tc in rats and mice to deteriorate.

Gastrins, cholecystokinins and gastrointestinal cancer

The gastrointestinal peptide hormones gastrin and cholecystokinin (CCK) are well known for their ability to stimulate gastric acid secretion and pancreatic enzyme secretion, respectively. The suggestion that gastrin and CCK might also promote the development of cancers of the gastrointestinal tract has been controversial, but an increasing body of evidence now supports the view that the amidated and non-amidated forms of gastrin act as growth factors via different receptors in different regions of the gut. For example, animal experiments indicate that amidated gastrins are involved in cellular differentiation and repair in the gastric mucosa, and synergize with Helicobacter pylori infection in the development of gastric carcinoma. In contrast, non-amidated gastrins stimulate colonic mucosal growth, accelerate the early steps in colorectal carcinoma formation, and are elevated in the tumour and circulation of patients with colorectal cancer. Although human pancreatic carcinomas express CCK-1 and CCK-2 receptors, the role of gastrins and CCK in pancreatic carcinogenesis is yet to be established. Further investigation of the possible role of the CCK-2 receptor in gastric and pancreatic neoplasia, and of the hypothesis that gastrin precursors act as autocrine growth factors in colorectal carcinoma, is warranted. However, therapies aimed at the gastrins must be targeted to the relevant gastrin/gastrin receptor combination.

The melanocortin agonist melanotan II increases insulin sensitivity in OLETF rats

Effects of peripheral administration of melanotan II (MTII), a melanocortin agonist, on insulin sensitivity and glucose tolerance were examined in Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Subcutaneous administration of MTII with osmotic mini-pumps decreased food intake and body weight in OLETF rats. MTII group showed more sensitivity to insulin compared with that allowed to eat ad libitum or pair-fed group in insulin tolerance tests on day 9. MTII group also showed significantly lower glucose values than ad libitum group in glucose tolerance tests on days 11 and 23. Thus, MTII increased insulin sensitivity and improved glucose tolerance in OLETF rats.

Differential roles for cholecystokinin a receptors in energy balance in rats and mice

Although cholecystokinin A (CCK-A) receptors (CCK-AR) mediate the feeding inhibitory actions of CCK in both rats and mice, the absence of CCK-AR results in species-specific phenotypes. The lack of CCK-AR in Otsuka Long-Evans Tokushima fatty (OLETF) rats results in hyperphagia and obesity. We have suggested that demonstrated increases in meal size and elevated levels of dorsomedial hypothalamic (DMH) neuropeptide Y (NPY) gene expression may contribute to this phenotype. In contrast to OLETF rats, CCK-AR(-/-) mice have normal total daily food intake and do not develop obesity. To assess the basis underlying the different phenotypes in rats and mice lacking CCK-AR, we characterized meal patterns in CCK-AR(-/-) mice and determined whether CCK-AR(-/-) mice exhibited an alteration in DMH NPY gene expression. We demonstrate that although CCK-AR(-/-) mice show a similar dysregulation in meal size as OLETF rats, they do not have an elevation in DMH NPY mRNA expression levels. In fact, intact mice have no CCK-AR in the DMH. Furthermore, in intact rats, NPY and CCK-AR are colocalized in DMH neurons, and parenchymal injection of CCK into the DMH reduces food intake and down-regulates DMH NPY mRNA expression. These results suggest that although CCK-AR plays a role in the mediation of CCK actions in the control of meal size in both rats and mice, CCK-AR seems to contribute to modulating DMH NPY levels only in rats. The deficit in CCK's action in the control of DMH NPY gene expression may play a major role in the obese phenotype in OLETF rats.

Regulation of rat pancreatic CCKB receptor and somatostatin expression by insulin

The cholecystokinin B receptor (CCK(B)R) is localized on pancreatic endocrine somatostatin delta-cells. Pancreatic somatostatin content was increased in diabetic rats. The mechanisms involved in this phenomenon are unknown, and we believe insulin is involved. In this study, four groups of rats were used: controls, streptozotocin-induced diabetic, streptozotocin-induced diabetic with insulin, and streptozotocin-induced diabetic with insulin and its cessation. Rats were killed after 7-28 days of treatment for diabetes, and somatostatin mRNA expression and pancreatic somatostatin content, CCK(B)R mRNA and protein expression evaluation in total pancreas and purified islets, and the cellular localization of somatostatin and CCK(B)R in islets was measured. Data indicate that diabetes is established after 7 days, is controlled by insulin, and reappears after treatment cessation. Pancreatic somatostatin mRNA expression and somatostatin content were increased during diabetes, normalized during insulin treatment, and reaugmented after treatment cessation. Gland and islet CCK(B)R mRNA and protein almost disappeared during diabetes; CCK(B) mRNA reappeared in response to insulin, but the protein did not. Confocal microscopy confirmed data obtained on somatostatin and CCK(B)R as established biochemically in the course of the treatments. In conclusion, these data strongly suggest that insulin can negatively control pancreatic somatostatin mRNA and hormone content and positively control CCK(B)R mRNA; the CCK(B)R protein appears to be delayed.

Enhancement of electroacupuncture-induced analgesic effect in cholecystokinin-A receptor deficient rats

Previously, we have showed that the cholecystokinin (CCK)-A receptor expression in hypothalamus is closely related with the responsiveness of electroacupuncture (EA)-mediated analgesic effects in rats. In order to confirm this observation more directly in vivo, the EA-mediated analgesic effects are compared between Otsuka Long-Evans Tokushima Fatty (OLETF) rats, the natural knockout rats with the homozygously disrupted CCK-A receptor gene, with Long-Evans Tokushima Otsuka (LETO) rats. They were stimulated at the zusanli (ST36) acupoint without using anesthetics or holders. The tail flick latency (TFL) test was performed to quantify analgesic effects and then the mean TFL increase ratios were calculated. OLETF rats showed a mean increase of 53% and LETO rats showed a mean increase of 31% of TFL. Our results suggest that the analgesic effect of acupuncture is closely related with the amount of CCK-A receptor expression.

The 10trans, 12cis isomer of conjugated linoleic acid promotes energy metabolism in OLETF rats

OBJECTIVE

We investigated the effect of conjugated linoleic acid (CLA) on energy metabolism in Otsuka Long-Evans Tokushima Fatty (OLETF) rats.

METHODS

In experiment 1, male OLETF rats were fed either control diet, 10% safflower oil or CLA diet, 9% safflower oil plus 1% CLA for 4 wk. In experiment 2, male OLETF rats were fed either 9c,11t-CLA diet, 9% safflower oil plus 1% 9c,11t-CLA-rich oil or 10t,12c-CLA diet, 9% safflower oil plus 1% 10t,12c-CLA-rich oil for 10 d.

RESULTS

In experiment 1, after 4 wk of feeding, serum and hepatic triacylglycerol concentrations in the CLA group were decreased significantly as compared with the control group. The CLA diet increased oxygen consumption and energy expenditure as compared with the control diet in OLETF rats. In experiment 2, a significant reduction of serum and hepatic triacylglycerol concentrations was seen in the 10t,12c-CLA group as opposed to the 9c,11t-CLA group. Oxygen consumption and energy expenditure were significantly higher in the 10t,12c-CLA group than in the 9c,11t-CLA group.

CONCLUSIONS

These results demonstrated that the hypolipidemic effect and the enhancement of energy metabolism by CLA can be attributed to the effect of the 10t,12c-CLA isomer.

What we know and what we need to know about the role of endogenous CCK in psychostimulant sensitization

The unique distribution of CCK and its receptors and its co-localization with dopamine makes it ideally situated to pay a role in dopamine-mediated reward and psychostimulant sensitization. A number of studies support the hypothesis that CCK acting through the CCK 1 and CCK 2 receptors is an endogenous modulator of dopamine neurotransmission. Behavioral studies with CCK antagonists and CCK 1 receptor mutant rats support a role for endogenous CCK in behavioral sensitization to psychostimulants. CCK microdialysis studies in the nucleus accumbens (NAC) have demonstrated that extracellular CCK is increased in the NAC by psychostimulants, providing neurochemical evidence that CCK could be involved in the behavioral response to psychostimulants. A model for how CCK may be acting in multiple brain regions to foster sensitization is presented and the gaps in our knowledge about the role of CCK in psychostimulant sensitization are described.

The 10trans,12cis isomer of conjugated linoleic acid suppresses the development of hypertension in Otsuka Long-Evans Tokushima fatty rats

Conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of linoleic acid found in beef, lamb, and dairy products. CLA has attracted considerable attention over the past several decades because of its potentially beneficial biological effects, including protective effects against several cancers, atherosclerosis, and obesity. Here we provide the first evidence that the 10trans,12cis-CLA isomer is able to suppress increases in blood pressure during the onset of obesity in OLETF rats. After 3 weeks of feeding with 10t,12c-CLA, systolic blood pressure was significantly lowered compared with rats fed linoleic acid or 9c,11t-CLA. Abdominal adipose tissue weight was also significantly lowered in rats fed 10t,12c-CLA, but not in those which were fed 9c,11t-CLA. In addition, we found that the relative mRNA expressions of angiotensinogen and leptin were suppressed by 10t,12c-CLA in adipose tissue. We speculate that the antihypertensive effect of 10t,12c-CLA can be attributed to the lowered secretion of hypertensive adipocytokines from abdominal adipose tissues.

Treatment for hyperglycemia promotes pancreatic regeneration in rats without CCK-1 receptor gene expression

INTRODUCTION AND AIM

Recent studies have suggested that CCK is not essential for normal pancreatic growth in mice. We examined whether the treatment of hyperglycemia participates in a non-CCK-1-receptor-mediated mechanism of pancreatic regeneration after partial (30%) pancreatectomy (Px) with use of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model for type 2 diabetes mellitus without CCK-1 receptor gene expression.

METHODOLOGY

Male OLETF rats were divided into five groups at 24 weeks of age. The first group was killed to examine the pancreas at 24 weeks of age (PrePx). The second group underwent a midline laparotomy and received a standard rat chow (ShamPx). The remaining three groups of rats received one of the following three treatments after Px: a standard rat chow (PxC), a diet containing acarbose (PxA), or a standard rat chow and once-daily subcutaneous injection of insulin (PxI) for 8 weeks.

RESULTS

PxC rats had significantly higher serum glucose levels than did PxA and PxI rats. Pancreatic weight and pancreatic contents of protein in PxA and PxI rats were significantly higher than in PxC rats. The pancreas in PxC rats was atrophic, and marked inflammatory cell infiltration was observed in the pancreas. In addition, tumor necrosis factor-alpha (TNFalpha) was expressed in the inflammatory cells, acinar cells, and islets in PxC rats. However, histologic alterations, including expression of TNFalpha, remained at a minimum in PxA and PxI rats.

CONCLUSION

We conclude that the control of serum glucose levels plays an important role in preventing pancreatic atrophy and participates in the non-CCK-1-receptor-mediated mechanisms of pancreatic growth in rats.

Physical activity prevented age-related decline in energy metabolism in genetically obese and diabetic rats, but not in control rats

Laboratory rats are normally confined to cages that markedly restrict their physical activity. In these rats, the resting energy expenditure accounts for 90% of the total daily energy expenditure, while the daily physical activity in humans consumes 30% of the total daily energy expenditure. Otsuka Long Evans Tokushima Fatty (OLETF) rats have been developed as a model of non-insulin-dependent diabetes mellitus (NIDDM) with mild obesity, and obesity is an important factor that induces diabetes in this strain. We implemented a running-wheel exercise regimen that was the equivalent of normal physical activity to provide light exercise for OLETF rats. The purpose of the study was to determine if light exercise improves the age-related decline in energy metabolism and glucose intolerance in OLETF rats. The effects were also compared in control Long Evans Tokushima (LETO) rats. From 12 to 46 weeks of age, the rats performed a running-wheel exercise (3000 m/day). Energy metabolism was determined at 8-week intervals. The typical increase in body weight was significantly decreased in OLETF rats in response to exercise, while no significant effect was observed in LETO rats. Energy expenditure and basal metabolic rate (BMR) per kilogram body weight (not whole-body weight) were increased by exercise in OLETF rats, but not in LETO rats. At 46 weeks of age, after exercise, the blood glucose and hemoglobin (Hb)A1c levels, as well as the plasma levels of insulin, triglyceride, cholesterol, and leptin significantly decreased in OLETF rats, while only the plasma levels of cholesterol and leptin significantly decreased in LETO rats. Light exercise thus appears to be beneficial for preventing age-related decline in energy metabolism and glucose intolerance in OLETF rats.

Role of CCK-A receptor for pancreatic function in mice: a study in CCK-A receptor knockout mice

INTRODUCTION

The cholecystokinin (CCK) family of peptides and receptors is present throughout the brain and gastrointestinal tract. The CCK receptors can be pharmacologically subdivided into two subtypes: CCK-A and CCK-B. CCK-A receptor is enriched in the pancreas of mice.

AIMS

To determine pancreatic functions in a CCK-A receptor deficient mouse mutant generated by gene targeting in embryonic stem cells. The targeting vector contained lacZ and neo insertions in exon 2.

METHODOLOGY

To examine exocrine functions, amylase release from the dispersed acini in vitro was examined. In the in vivo study, the mixture of bile-pancreatic juice was collected, and amylase, bicarbonate, and bile acid outputs were determined after the administration of various stimulants. The cystic duct of the gallbladder and the pylorus were ligated to exclude the involvement of gallbladder contraction and gastric acid. Pancreatic enzyme content was measured, and histologic examinations by HE and lacZ staining were conducted. To examine endocrine functions, oral glucose tolerance test (2 g/kg) was determined.

RESULTS

The body weight, pancreatic wet weight, and enzyme content in the pancreas were similar among the three genotypes. Amylase release in vivo and in vitro and bicarbonate secretion in vivo were not stimulated by CCK-8 in CCK-AR (-/-) mice, whereas the responses to other stimulants were substantial in (-/-) mice. Administration of secretin did not increase bicarbonate secretion regardless of genotype. A normal glucose tolerance was observed in (-/-) mice. Acinar cells, islets, and duct cells were stained by lacZ, and HE staining revealed no pathologic findings.

CONCLUSION

The CCK-A receptor is important for pancreatic exocrine secretion, but not essential for maintaining glucose concentration and pancreatic growth in mice.

Phenotypes of mice with invalidation of cholecystokinin (CCK(1) or CCK(2)) receptors

Cholecystokinin (CCK) is a peptide originally discovered in the gastrointestinal tract, but also found in high density in the mammalian brain. This peptide has been shown to be involved in numerous physiological functions such as feeding behavior, central respiratory control and cardiovascular tonus, vigilance states, memory processes, nociception, emotional and motivational responses. CCK interacts with nanomolar affinites with two different receptors designated CCK(1) and CCK(2). Primarily, the functional role of these binding sites in the brain and the periphery has been investigated thanks to the development of potent and selective CCK receptor antagonists and agonists. However, several studies have yielded conflicting data. Knockout mice provide unique opportunities to analyse diverse aspects of gene function in vivo. This review highlights recent progress in our understanding of the role of CCK(1) and CCK(2) receptors obtained by using mice with genetic invalidation of CCK(1) or CCK(2) receptors or natural CCK receptors mutants. The limits of this approach is discussed and some results were compared to those obtained by pharmacological blockade of CCK receptors by selective antagonists.

Actions of CCK in the controls of food intake and body weight: lessons from the CCK-A receptor deficient OLETF rat

The OLETF rat, lacking CCK-A receptors, provides an important model for identifying roles for CCK in the controls of food intake and body weight. OLETF rats are obese and diabetic and express deficits in the control of the size of individual meals. Meal size in OLETF rats is doubled and although meal number is decreased, the decrease is not sufficient to prevent hyperphagia. Analyses of patterns of hypothalamic gene expression in OLETF rats indicate the presence of a primary deficit in DMH NPY signaling. These data suggest an important role for CCK in controlling NPY expression in a population of non-leptin regulated hypothalamic neurons. In the absence of this control, NPY is overexpressed, contributing to hyperphagia and obesity. Thus, the obesity in the OLETF rats may be the outcome of two regulatory disruptions, one depending upon a peripheral within meal satiety pathway and the other depending upon a central pathway critical to overall energy balance.

A peroxisome proliferator-activated receptor gamma agonist influenced daily profile of energy expenditure in genetically obese diabetic rats

Otsuka Long Evans Tokushima Fatty (OLETF) rats were developed as a model of non-insulin-dependent diabetes mellitus (NIDDM) with mild obesity. We reported that the daily profiles of energy expenditure associated with two peaks (one between 05:00 and 08:00 and the other between 20:00 and 22:00) were observed at 8 weeks of age (without NIDDM), while these two peaks disappeared at 24 weeks of age with NIDDM. As a new anti-diabetic drug, a peroxisome proliferator-activated receptor y agonist pioglitazone hydrochloride has been developed, we examined whether pioglitazone normalized daily profiles of energy expenditure at 24 weeks of age. A control diet and pioglitazone (0.1%)-containing diet were fed from 6 weeks of age. The two peaks of daily profiles of energy expenditure, which disappeared in OLETF rats with the control diet at 24 weeks of age, were reproduced by administration of pioglitazone. The respiratory quotient was lower and fat derived energy used for combustion was increased by pioglitazone at both ages. The body weight, daily food intake, plasma levels of fat, insulin, leptin and the wet weight of visceral fat were not influenced, but the levels of blood hemoglobin Alc and plasma tumor necrosis factor a were decreased by pioglitazone. Administration of pioglitazone improved daily profiles of energy expenditure via affecting glucose and fat metabolisms.