Free-choice alcohol consumption in mice after application of the appetite regulating peptide leptin

BACKGROUND: Leptin has been shown to regulate food intake and energy expenditure. Very recently, associations of elevated leptin plasma levels during alcohol withdrawal with alcohol craving have been observed in humans. Therefore, we tested the hypothesis that the application of exogenous leptin modulates voluntary alcohol consumption in mice. METHODS: Sixteen mice (129/Sv x C57BL/6J) were habituated to ethanol consumption over a time period of 3 months. After a basal 2-week free-choice drinking phase, mice were separated into two groups (n = 8) according to weight and alcohol consumption. They received recombinant leptin (1 mg/kg) versus saline intraperitoneally daily for 10 days. After 4 days of free-choice consumption of ethanol (16% v/v) versus water, ethanol was withdrawn at day 4 and replaced at day 6 to test the occurrence of an alcohol deprivation effects. Fluid intake was evaluated by controlling the weight of the drinking tubes daily. RESULTS: Free-choice ethanol consumption after withdrawal was significantly elevated in mice after intraperitoneal injection of 1 mg/kg leptin (alcohol deprivation effect), but not during basal drinking. CONCLUSION: We suggest that leptin may enhance motivation for alcohol consumption in habituated mice after alcohol withdrawal.     

Influences of diabetes (db/db), obese (ob/ob) and dystrophic (dy/dy) genotype mutations on hind limb bone maturation: a morphometric, radiological and cytochemical indices analysis

The influences of single-gene missense mutations expressing diabetes (db/db), obese (ob/ob) or dystrophia (dy/dy) dysregulated metabolic syndromes on hind limb bone maturation and cytodevelopment in C57BL/KsJ mice were evaluated by radiological, macro- and cytomorphometric analysis of the resulting variances in os coxae, femur and tibia osteodevelopment indices relative to control parameters between 8 and 16 weeks of age. Associated with obesity and hyperglycaemic/hyperinsulinaemic states, both db/db and ob/ob mutants demonstrated significant suppression of hind limb maturation (length) and cytodensity indices relative to control growth parameters. By contrast, skeletal growth suppression induced by dy/dy mutation expression was associated with lean body mass and normoglycaemic/hypoinsulinaemic systemic endometabolic indices. In both db/db and ob/ob mutation syndromes, osteovascular, -interstitial and -cytolipidaemia were prominent cytochemical aberrations of the osteopaenic states relative to the dyslipidaemia/fibrodysplasia characteristic of dy/dy osteomaturation. Between 8 and 16 weeks of age, both ob/ob and db/db groups demonstrated extensive cortical interstitial (laminal) osteolipidaemia and suppressed cytodensities compared to control indices. These data demonstrate that the abnormal hyperglycaemic/hyperinsulinaemic endometabolic states associated with the expression of db/db and ob/ob genomutations promote extensive lipidaemia-induced osteopaenia, compromising hind limb osteomaturation and cytodensity indices, as compared to the hyperfibritic osteopaenia characteristic of dy/dy mutation syndromes. Recognized therapeutic modulation of the hypercytolipidaemic component of diabetes-obesity syndromes may prove to be effective towards amelioration of the deleterious influences of these expressed hyperglycaemic, dysregulated lipometabolic conditions on osteomaturation and cytodevelopment.     

Strain-dependent stimulation of growth in leptin-treated obese db/db mice

Leptin increases the proliferation of various cell types in vitro, and we reported that background strain influences the metabolic responses to leptin in db/db mice, which express short-form, but not long-form, leptin receptors. Here, we examined the effects of leptin on growth of young C57BL/Ks, C57BL/6J, and C57BL/3J db/db mice. Intraperitoneal infusions of 20 micro g leptin/d for 26 d increased the food intake of C57BL/6J mice by 15% (P < 0.01), but had no effect in C57BL/Ks db/db mice. Leptin-infused C57BL/6J db/db mice gained more weight ( approximately 20%; P < 0.04) than PBS-infused controls. The increased weight was sustained after leptin infusion ended. Leptin had no effect on weight gain or food intake of C57BL/3J db/db mice, which only express the soluble leptin receptor. A single leptin injection increased MAPK phosphorylation in liver by 40% (P < 0.001) and that in muscle tissues by 20% (P < 0.001) in C57BL/6J mice, but did not change phosphorylation in C57BL/3J db/db mice. These results suggest that leptin increases the weight gain of C57BL/6J db/db mice by activating the MAPK pathway through a mechanism that is dependent on short-form leptin receptors. This response may be masked by activation of the long-form receptor in wild-type animals that lose body fat during leptin treatment.     

Ciglitazone,a new hypoglycaemic agent. 4. Effect on pancreatic islets of C57BL/6J-ob/ob and C57BL/KsJ-db/db mice

Summary Pancreases of treated and control male C57BL/6J-ob/ob and C57BL/KsJ-db/db mice were evaluated by qualitative and morphometric microscopic techniques to determine the effects of chronic ciglitazone treatment on the morphology of cells and surface area and number of pancreatic islets. The cells of treated ob/ob and db/db mice displayed moderate to heavy granulation whereas most cells of untreated obese and diabetic mice were extensively degranulated. Although moderate proliferation of the rough endoplasmic reticulum and Golgi apparatus was evident in some cells of treated db/db mice, both groups of treated ob/ob and db/db mice displayed an improved pattern of insulin synthesis and storage. In contrast, the cells of untreated ob/ob and db/db mice were in a severe state of stress which was indicated by extensive hypertrophy of the rough endoplasmic reticulum, Golgi apparatus and mitochondria. Some cells of untreated db/ db mice also displayed lysosome aggregates indicative of early stages of necrosis. Morphometric analysis revealed that the surface area of islets of treated ob/ob mice was significantly smaller in comparison with that of untreated ob/ob mice. Since the surface area of islets of treated C57BL/6J-+/? mice (lean littermates of ob/ob mice) was less than that of treated ob/ob mice, the progression of islet hypertrophy in the obese mice was probably arrested or attenuated but not to the level of the treated +/? mice. The number of pancreatic islets was significantly greater in treated than in untreated db/ db mice. A majority of the islets of untreated db/db mice were atrophie and consisted of acinar and endocrine cells whereas most of the islets of treated db/db mice appeared to be intact and unremarkable. The results of this study suggest that ciglitazone is an effective hypoglycaemic agent which may directly or indirectly promote -cell regranulation and an improved pattern of insulin synthesis and storage in ob/ob and db/db mice. However, in treated db/db mice, there still was some evidence of stress in the cells. Overall, the prolonged treatment with ciglitazone also seemed to inhibit the hypertrophy of islets in ob/ob mice and protect the structural integrity and viability of islets in db/db mice.     

Development of ethanol withdrawal-related sensitization and relapse drinking in mice selected for high- or low-ethanol preference

Background: Previous studies have shown that high alcohol consumption is associated with low withdrawal susceptibility, while at the same time, other studies have shown that exposure to ethanol vapor increases alcohol drinking in rats and mice. In the present studies, we sought to shed light on this seeming contradiction using mice selectively bred for High‐ (HAP) and Low‐ (LAP) Alcohol Preference, first, assessing these lines for differences in signs of ethanol withdrawal and second, for differences in the efficacy of intermittent alcohol vapor exposure on elevating subsequent ethanol intake. Methods: Experiment 1 examined whether these lines of mice differed in ethanol withdrawal‐induced CNS hyperexcitability and the development of sensitization to this effect following intermittent ethanol vapor exposure. Adult HAP and LAP lines (replicates 1 and 2), and the C3H/HeNcr inbred strain (included as a control genotype for comparison purposes) received intermittent exposure to ethanol vapor and were evaluated for ethanol withdrawal‐induced seizures assessed by scoring handling‐induced convulsions (HIC). Experiment 2 examined the influence of chronic intermittent ethanol exposure on voluntary ethanol drinking. Adult male and female HAP‐2 and LAP‐2 mice, along with male C57BL/6J (included as comparative controls) were trained to drink 10% ethanol using a limited access (2 h/d) 2‐bottle choice paradigm. After stable baseline daily intake was established, mice received chronic intermittent ethanol vapor exposure in inhalation chambers. Ethanol intake sessions resumed 72 hours after final ethanol (or air) exposure for 5 consecutive days. Results: Following chronic ethanol treatment, LAP mice exhibited overall greater withdrawal seizure activity compared with HAP mice. In Experiment 2, chronic ethanol exposure/withdrawal resulted in a significant increase in ethanol intake in male C57BL/6J, and modestly elevated intake in HAP‐2 male mice. Ethanol intake for male control mice did not change from baseline levels of intake. In contrast, HAP‐2 female and LAP‐2 mice of both sexes did not show changes in ethanol intake as a consequence of intermittent ethanol exposure. Conclusions: Overall, these results indicate that the magnitude of ethanol withdrawal‐related seizures is inversely related to inherited ethanol intake preference. Additionally, intermittent ethanol vapor exposure appears more likely to affect high‐drinking mice (C57BL/6J and HAP‐2) than low drinkers, although these animals are less affected by ethanol withdrawal.     

Leptin modulates behavioral responses to sweet substances by influencing peripheral taste structures

Leptin is a hormone that regulates body weight homeostasis mainly via the hypothalamic functional leptin receptor Ob-Rb. Recently, we proposed that the taste organ is a new peripheral target for leptin. Leptin selectively inhibits mouse taste cell responses to sweet substances and thereby may act as a sweet taste modulator. The present study further investigated leptin action on the taste system by examining expression of Ob-Rb in taste cells and behavioral responses to sweet substances in leptin-deficient ob/ob, and Ob-Rb-deficient db/db mice and their normal litter mates. RT-PCR analysis showed that Ob-Rb was expressed in taste cells in all strains tested. The db/db mice, however, had a RT-PCR product containing an abnormal db insertion that leads to an impaired shorter intracellular domain. In situ hybridization analysis showed that the hybridization signals for normal Ob-Rb mRNA were detected in taste cells in lean and ob/ob mice but not in db/db mice. Two different behavioral tests, one using sweet-bitter mixtures as taste stimuli and the other a conditioned taste aversion paradigm, demonstrated that responses to sucrose and saccharin were significantly decreased after ip injection of leptin in ob/ob and normal littermates, but not in db/db mice. These results suggest that leptin suppresses behavioral responses to sweet substances through its action on Ob-Rb in taste cells. Such taste modulation by leptin may be involved in regulation for food intake.     

De novo cholesterol synthesis in three different animal models of diabetes

Summary Recent studies have demonstrated that cholesterol synthesis is increased two to threefold in the intestines of streptozotocin-induced diabetic rats. Cholesterol synthesis in tissues other than the intestines, including the liver, was not significantly altered by diabetes. In diabetic Chinese hamsters, cholesterol synthesis was increased 2.5-fold in both the small and large intestine. These observations are similar to our findings in diabetic rats and suggest that a stimulation of intestinal cholesterogenesis may be a uniform phenomenon in insulinopenic diabetes. In db/db mice, cholesterol synthesis was increased in both the liver and intestines but quantitatively the increase in hepatic cholesterogenesis was of much greater magnitude. Cholesterol feeding, which markedly inhibited hepatic cholesterol synthesis in both control and db/db mice, did not obliterate this difference in hepatic cholesterol synthesis. In ob/ob mice, the severity of the metabolic disturbances was less than that observed in db/db mice and no abnormalities in cholesterol synthesis were observed in animals ingesting a low cholesterol diet. However, in ob/ob mice fed a high cholesterol diet, hepatic cholesterol synthesis was increased. These observations suggest that in obese insulin resistant diabetic animals of milder severity, the abnormality in hepatic cholesterol synthesis manifests itself only when the animals are ingesting a high cholesterol diet. The results of this and previous studies suggest that in insulinopenic diabetes there is a stimulation of cholesterol synthesis that is localized to the intestines, whereas in obese, insulin-resistant diabetic animals, cholesterol synthesis is altered in the liver.     

腹腔注射分泌胰升血糖素样肽-1重组腺伴随病毒对db/db小鼠高血糖的影响

目的 观察腹腔注射分泌表达胰升血糖素样肽-1（GLP-1）的重组腺伴随病毒对db/db小鼠高血糖的纠正作用. 方法 将12只8周龄db/db小鼠随机分为对照组与实验组.测量体重、血糖.实验组腹腔注射分泌表达GLP-1的重组腺伴随病毒,对照组腹腔注射对照病毒.给药后分别于第2、4、6、8、10、12周测量体重,并检测血糖水平. 结果 随观察时间的延长,对照组体重、血糖呈上升趋势,实验组则下降.实验组2周时,体重（38.3±4.4）g,血糖（18.2±3.0）mmol/L,与对照组[（44.2±4.7）g、（22.6±4.5）mmol/L]比较,差异无统计学意义（P＞0.05）.第4～12周时实验组体重和血糖均低于对照组,两组间比较差异有统计学意义（P＜0.05）. 结论 通过腹腔注射分泌表达GLP-1的重组腺伴随病毒方式,可纠正db/db小鼠高血糖.     

A peptide leptin antagonist reduces food intake in rodents.

OBJECTIVE: The purpose of the present study was to investigate the continuing validity of the hypothesis that leptin is a physiologically important regulator of food intake, using the human leptin mutant R128Q leptin. DESIGN: In a cellular proliferation assay, based on BAF-3 cells transfected with the murine ObRb receptor, R128Q leptin was shown to be devoid of agonistic activity and to competitively inhibit the proliferative effects of leptin. To determine whether R128Q leptin was also an antagonist of leptin in vivo, the leptin mutant was injected intracerebroventricularly (i.c.v.) into rats in the absence and presence of leptin. R128Q was also injected intraperitoneally (i.p.) into ob/ob and into db/db mice expressing, respectively, either normal or defective ObRb receptors. RESULTS: R128Q was shown to be a competitive antagonist of leptin induced cellular proliferation in vitro. Surprisingly, in vivo R128Q leptin produced a strong dose-dependent decrease in food intake, and was only slightly less potent than leptin itself. In fasted rats, the inhibitory effects of leptin and R128Q leptin (i.c.v.) on post-fast refeeding were additive. Finally, R128Q leptin produced the same inhibition of food intake as leptin when injected i.p. in ob/ob mice and, like leptin, was inactive after i.p. injection to db/db mice. CONCLUSION: R128Q leptin is a leptin agonist in vivo, but behaves as an antagonist against leptin induced proliferation in vitro. The data demonstrate that the human leptin mutant R128Q leptin is not a suitable tool for investigating the physiological actions of leptin.     

Unique alterations of neuropeptide content in median eminence, amygdala, and dorsal vagal complex of 3- and 6-week-old diabetes mutant mice

The nature of the genetic defects which define the obese (ob) and diabetes (db) loci in mice remain unknown, but both produce similar syndromes when maintained in the same strain of mice. There is some evidence suggesting a lesion in the central nervous system (CNS) in db/db mice, while ob/ob mice appear to have a primary lesion outside the CNS. In a search for further evidence of a unique central lesion in db/db mice, we have examined neuropeptide content in selected, microdissected brain areas in both of these mutants and lean controls. In order to rule out possible interactions of the db mutation with the genetic background, diabetes mice of both C57BL/KsJ and C57BL/6J strains were studied. When concentrations of nine neuropeptide immunoreactivities were examined in up to seven microdissected areas of the brain, C57BL/6J ob/ob mice showed only one reproducible alteration, a lower content of beta-endorphin-like immunoreactivity (LI) in the preoptic area at both 3 and 6 weeks of age as compared with lean littermates. In contrast, db/db mice of both C57BL/6J and C57BL/KsJ strains exhibited alterations in a total of four peptides in three brain areas: lower concentration of somatostatin-LI in median eminence, higher Met-enkephalin-LI in dorsal vagal complex of the medulla oblongata, higher substance P-LI and lower vasoactive intestinal polypeptide (VIP)-LI in amygdala. The concentrations of the peptides studied in medial basal hypothalamus, lateral hypothalamus, substantia nigra, and preoptic area were not reproducibly altered in db/db mice. These data provide preliminary evidence for unique brain abnormalities in db/db mice in specific areas that are involved in processing of neural signals that can affect the islets of Langerhans, gonadotrophin secretory patterns, and many other visceral functions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuropeptide content in pancreas and pituitary of obese and diabetes mutant mice: strain and sex differences.

The nature of the primary genetic defects in ob/ob and db/db mice are unknown. Both the obese (ob) and diabetes (db) mutations produce similar, multicomponent obese-hyperinsulinemic syndromes when maintained in the same strain of mouse. In an attempt to find differences between these mutations in neuroendocrine function affecting the islets of Langerhans or the pituitary, tissue content of four neuropeptides that are known to be capable of influencing the rate of insulin secretion was examined in obese (ob/ob) and diabetes (db/db) mice. In the first study, C57BL/6Job/ob and control males were studied at 3, 4, and 11 weeks of age. In the second study, db/db mice of both sexes and two inbred strains (C57BL/6J and C57BL/KsJ), which differ markedly in the severity of expression of the diabetes phenotype, were studied at 3 weeks of age, before the development of hyperglycemia and secondary consequences thereof. Immunoreactive peptides were measured in acetic acid extracts of pancreas and pituitary. No differences between male ob/ob and db/db mice of the C57BL/6J strain were found. Marked sex differences in lean control mice were found at 3 weeks of age in pancreatic Met-enkephalin-LI and galanin-LI (with two- to threefold higher content in males). Low pancreatic content (50% to 70% lower than in control mice) of galanin-LI, Met-enkephalin-LI and Leu-enkephalin-LI was associated with hyperinsulinemia in male B6 ob/ob and db/db mice at 3 weeks of age, though not in B6 db/db females and not in BKs db/db mice of either sex.(ABSTRACT TRUNCATED AT 250 WORDS)     

2型糖尿病模型db/db小鼠海马超微结构观察

目的：观察2型糖尿病动物模型－C57BL／KsJ(db/db)小鼠海马超微结构变化,方法：糖尿病组：6周龄C57BL／KsJ(db/db)小鼠5只,尾静脉空腹血糖高于11．1mmol/L且肥胖,对照组;非糖尿病小鼠C57BL／KsJ5只,尾静脉空腹血糖低于6．0mmol/L,体重正常,于30周龄（成模第6个月要）时,灌注固定取脑,透射电镜下观察海马CAI区,结果：糖尿病小鼠海马超微结构发生显著改变包括锥体细胞退变,髓鞘崩解,突触变性等。结论：糖尿病所致海马超微结构改变可能与糖尿病学习记忆功能减退有关。     

Pharmacological profiles of a novel protein tyrosine phosphatase 1B inhibitor,JTT‐551

Aim: Protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin signalling, is a novel therapeutic target for type 2 diabetes mellitus. We evaluated in vitro and in vivo the pharmacological profiles of a new PTP1B inhibitor, JTT‐551: monosodium ({[5‐(1,1‐dimethylethyl)thiazol‐2‐yl]methyl} {[(4‐{4‐[4‐(1‐propylbutyl)phenoxy]methyl}phenyl)thiazol‐2‐yl]methyl}amino)acetate. Methods: PTP1B inhibitory activity and the inhibition mode were assayed with p‐nitrophenyl phosphate as a substrate, and the selectivity of JTT‐551 against other PTPs, including T‐cell protein tyrosine phosphatase (TCPTP), CD45 protein tyrosine phosphatase (CD45) and leucocyte common antigen‐related protein tyrosine phosphatase (LAR), was evaluated. Glucose uptake with JTT‐551 treatment was evaluated in L6 rat skeletal myoblasts (L6 cells). In the in vivo study, we investigated the effects on insulin receptor (IR) phosphorylation and blood chemical parameters with JTT‐551 administration in ob/ob mice and db/db mice. Results: JTT‐551 showed an inhibitory effect on PTP1B with a Ki value of 0.22 µM, and a mixed‐type inhibition mode. Ki values of TCPTP, CD45 and LAR were 9.3, 30 or higher and 30 or higher µM, respectively, and JTT‐551 exhibited clear selectivity against the other PTPs. Moreover, JTT‐551 increased the insulin‐stimulated glucose uptake in L6 cells. A single administration of JTT‐551 in ob/ob mice enhanced the IR phosphorylation of liver and reduced the glucose level. In db/db mice, chronic administration showed a hypoglycaemic effect without an acceleration of body weight gain. Conclusions: JTT‐551, a newly developed PTP1B inhibitor, improves glucose metabolism by enhancement of insulin signalling and could be useful in the treatment of type 2 diabetes mellitus.     

Activation of the cardiac ciliary neurotrophic factor receptor reverses left ventricular hypertrophy in leptin-deficient and leptin-resistant obesity

Disruption of the leptin signaling pathway within the heart causes left ventricular hypertrophy (LVH). Because human obesity is a syndrome of leptin resistance, which is not amenable to leptin treatment, the identification of parallel signal transduction pathways is of potential therapeutic value. Ciliary neurotrophic factor (CNTF), which acts parallel to leptin in the hypothalamus, is not previously recognized to have cardiac activity. We hypothesized that CNTF receptors are present on cardiomyocytes and their activation reverses LVH in both leptin-deficient ob/ob and leptin-resistant db/db mice. The localization of CNTF receptors (CNTFRalpha) to the sarcolemma in C57BL/6, ob/ob and db/db was confirmed in situ with immunohistochemistry, and immunoblotting (60 and 40 kDa) on isolated myocytes. ob/ob mice were randomly assigned to receive s.c. recombinant CNTF (CNTF(Ax15); 0.1 mg x kg(-1) per day; n = 11) calorie-restriction (n = 9), or feeding ad libitum (n = 11). db/db mice were allocated to three similar groups (n = 8, 7, and 8, respectively) plus a leptin group (1 mg x kg(-1) per day; n = 7). Echocardiography showed that CNTF(Ax15) reduced cardiac hypertrophy [posterior wall thickness decreased by 29 +/- 8% (P < 0.01) in ob/ob and by 21 +/- 3% in db/db mice (P < 0.01)], which was consistent with the reduction of myocyte width. Western blotting showed that leptin and CNTF(Ax15) activated Stat3 and ERK1/2 pathway in cultured adult mice cardiomyocytes and cardiac tissue from in ob/ob and db/db mice. Together, these findings support the role of a previously undescribed signaling pathway in obesity-associated cardiac hypertrophy and have therapeutic implications for patients with obesity-related cardiovascular disease and other causes of LVH.     

Brain-derived neurotrophic factor enhances glucose utilization in peripheral tissues of diabetic mice

AIMS: Repetitive subcutaneous or intracerebroventricular administration of brain-derived neurotrophic factor (BDNF) ameliorates glucose metabolism and enhances energy expenditure in obese diabetic C57BL/KsJ-db/db mice. To explore the mechanism of action through which BDNF regulates glucose metabolism, we examined the effects of BDNF on glucose utilization and norepinephrine (NE) content in peripheral tissues of diabetic mice. METHODS: [(14)C]2-deoxyglucose ([(14)C]2-DG) uptake into peripheral tissues was analysed after intravenous injection of [(14)C]2-DG in db/db and normal C57BL/6 mice, and [(14)C]2-DG uptake and NE content in peripheral tissues were analysed after subcutaneous administration of BDNF (20 mg/kg) to male db/db and normal mice for 8 days. RESULTS: [(14)C]2-DG uptake in the diaphragm, heart, gastrocnemius, soleus and interscapular brown adipose tissue (BAT) of db/db mice was significantly lower than in normal mice. Repetitive administration of BDNF to db/db mice for 8 days enhanced [(14)C]2-DG uptake in the diaphragm, heart, soleus, BAT and liver. The NE content in heart, skeletal muscle, interscapular BAT and liver of db/db mice given BDNF was high compared with db/db mice given vehicle, whereas no significant change in NE content in peripheral tissues was observed in normal mice given BDNF and those given vehicle. BDNF did not affect [(14)C]2-DG uptake or NE content in the white adipose tissue of db/db mice. CONCLUSIONS: These data indicate that BDNF ameliorates glucose metabolism by enhancement of glucose utilization in muscle and BAT, with this effect caused by modulation of the central and peripheral nervous systems.     

Reversal of type 2 diabetes in mice by products of malaria parasites: I. Effect of inactivated parasites

C57BL/KsJ-db/db and C57BL/KsJ-ob/ob mice are good models for studies on human obesity and type 2 diabetes. We have previously shown that infection with blood-stage malaria or injection of extracts from malaria-parasitized red blood cells induces hypoglycemia in normal mice and normalizes hyperglycemia in mice made moderately diabetic by streptozotocin. In the present study, we show that a single intravenous (IV) injection of Formalin-fixed Plasmodium yoelii YM (FFYM) preparation decreases blood glucose in db/db mice from an initial value of 19 mmol/L to a normal value of 7 mmol/L (P < .0001) for at least 24 hours and reduces food intake. Plasma insulin concentrations in db/db mice were not altered. FFYM was also active in normal and ob/ob mice, an effect associated with an increase in plasma insulin. Although the rate of weight gain in lean ob/+ and lean db/+ was not altered by this treatment, there was a significant reduction in weight gain in db/db and ob/ob mice (P < .001). We suggest that malaria-derived molecules, when fully characterized, may provide structural information for the development of new agents for the management of type 2 diabetes.     

Comparison of ethanol preference and neurochemical measures of mesolimbic dopamine and adenosine systems across different strains of mice

BACKGROUND: To extend the known phenotype of strains commonly used in the development of mutant mice, ethanol, saccharin, and caffeine preferences were examined in C57Bl/6J, CD-1, and hybrid C57Bl/6J x CD-1 mice. As dopaminergic mechanisms are inherently involved in the neuronal processing of many drugs of abuse (including ethanol), and an important role for adenosine-dopamine interactions has also been reported, the dopaminergic and purinergic neurochemical profiles of mice were compared against the consummatory phenotype observed. METHODS: Ethanol (5% v/v), saccharin (0.1% w/v), and caffeine (0.1% w/v) consumption and preference were examined using a 2-bottle free-choice paradigm. Dopamine and adenosine receptor and transporter mRNA and protein density were quantified using in situ hybridization histochemistry and in vitro autoradiography, respectively. RESULTS: C57Bl/6J and hybrid C57Bl/6J x CD-1 mice demonstrated a clear ethanol preference, voluntarily consuming large quantities of ethanol when given the choice between drinking vessels containing either ethanol or water. Conversely, CD-1 mice were characterized as ethanol-avoiding under the present paradigm. Differences in D(1) receptor mRNA between the strains were consistent with the observed behavioral differences in ethanol preference. The high ethanol-preferring phenotype of C57Bl/6J mice could not be directly linked to alterations in dopamine transporter neurochemistry and/or enkephalin levels as proposed by earlier researchers. Ethanol-seeking behavior appeared to correlate with D2 receptor expression, however, with evidence that ethanol-preferring mice also exhibit an increased density of D2 receptors within limbic dopaminergic projection nuclei. Interestingly, strain differences in the expression of the ethanol-sensitive nucleoside transporter paralleled differences in ethanol consumption, a novel finding consonant with purinergic involvement in dopamine-related behaviors. CONCLUSIONS: This study has highlighted the relevance of alterations in dopamine receptor expression and purinergic modulation within the mesolimbic pathway and predisposition toward the development of ethanol-seeking behavior.     

Ethanol preference is inversely correlated with ethanol-induced dopamine release in 2 substrains of C57BL/6 mice

BACKGROUND: The C57BL/6 mouse model has been used extensively in alcohol drinking studies, yet significant differences in ethanol preference between substrains exist. Differences in ethanol-induced dopamine release in the ventral striatum could contribute to this variability in drinking behavior as dopamine has been implicated in the reinforcing properties of ethanol. METHODS: A 2-bottle choice experiment investigated the difference in ethanol preference between C57BL/6J and C57BL/6NCrl animals. Microdialysis was used to determine dopamine release and ethanol clearance in these 2 substrains after intraperitoneal injections of 1.0, 2.0 and 3.0 g/kg ethanol or saline. RESULTS: C57BL/6J mice exhibited significantly greater ethanol preference and less ethanol-stimulated dopamine release compared with C57BL/6NCrl mice. The intraperitoneal injections of ethanol caused a significant increase in dopamine in both substrains at all 3 doses with significant differences between substrains at the 2 highest alcohol doses. Saline injections had a significant effect on dopamine release when given in a volume equivalent to the 3 g/kg ethanol dose. Ethanol pharmacokinetics were similar in the 2 substrains at all 3 doses. CONCLUSIONS: Ethanol-induced dopamine release in the ventral striatum may contribute to the differences in alcohol preference between C57BL/6J and C57BL/6NCrl mice.     

Endogenous Opioids Are Involved in the Genetically Determined High Preference for Ethanol Consumption

The link between endogenous opioid peptides and the genetic predisposition to preferentially consume ethanol was examined in alcohol preferring C57BL/6J mice compared with the alcohol nonpreferring DBA/2 mice. Concentrations of Met-enkephalin pentapeptide or precursor in various brain regions of potential relevance were not different between the two strains. C57BL/6J mice had a significantly lower pain threshold that could be increased by a selective mu-receptor opioid agonist [D-Ala2, MePhe4, Met(O)5-ol]-enkephalin. Treatment with this drug also decreased ethanol consumption in C57BL/6J mice. Increasing the synaptic half-life of endogenous enkephalins by the enkephalinase inhibitor kelatorphan also decreased ethanol consumption. Assay of endogenous enkephalin degrading activity showed increased enkephalinase activity in striatal issue of C57BL/6J compared with DBA/2 tissue. These results suggest that a relative lack of enkephalin peptides trans-synaptically, possibly resulting from enhanced enkephalin degradation may contribute to increase alcohol consumption in C57BL/6J mice.     

Increased expression of hypothalamic leptin receptor and adiponectin accompany resistance to dietary-induced obesity and infertility in female C57BL/6J mice

BACKGROUND: Obesity is strongly associated with female infertility, but the mechanisms underlying this relationship are largely unknown. METHODS: We investigated the effect of increasing dietary fat percentage upon body mass, hypothalamic neuropeptide gene expression, adipose hormone secretion and fertility in females of the inbred mouse strains C57BL/6J and DBA/2J. To assess the effect of obesity independent of dietary influence, we also compared these parameters in wild-type female C57BL/6J mice to those congenic for the obesogenic mutations ob/ob and A(y)/a. RESULTS: After 24 weeks, rather than exhibiting an obese, leptin-resistant phenotype like their female DBA/2J counterparts, wild-type female C57BL/6J mice remained lean, fertile and manifested increased hypothalamic LEPR-B expression. Although both mutant genotypes were associated with obesity and subfertility, ob/ob mice demonstrated significantly increased hypothalamic LEPR-B expression, whereas A(y)/a mice had a significant reduction. Interestingly, wild-type female C57BL/6J mice were noted to manifest significantly higher and lower levels of adiponectin and tissue plasminogen activator inhibitor-1 (tPAI-1), respectively, than weight-matched wild-type female DBA/2J mice. CONCLUSIONS: We conclude that (1) resistance to the obese-infertile phenotype in female C57BL/6J mice is associated with increased hypothalamic leptin receptor expression and alterations in adipokine levels consistent with decreased adipose tissue inflammation and (2) that long-standing hyperleptinemic obesity in mice is associated with a downregulation of the hypothalamic leptin receptor.