Activation of α7 nicotinic receptors suppresses sucrose addiction in mice

The mesolimbic dopamine system is important for the rewarding and motivational aspects of consuming rewarding and palatable food. Nicotinic receptors are present in the mesolimbic dopamine system and enhance the reinforcement of drugs of abuse. In this study, we examined the involvement of nicotine receptor subtypes in sucrose addiction in a sucrose preference paradigm. Sucrose preference and intake in mice increased in proportion to stepwise increases in sucrose concentrations. Moreover, sucrose preference and intake following sucrose withdrawal in mice were increased in comparison with the first set of trials. In the present study, α7, but not α4 and β2, nicotinic receptor subunit mRNA was decreased in the nucleus accumbens, but not in the hypothalamus, after sucrose withdrawal and subsequent sucrose intake. Administration of an agonist for α7, but not α4 and β2, nicotinic receptors suppressed the enhancement of sucrose preference and intake following sucrose withdrawal. These findings indicate that α7 nicotinic receptor activation suppresses sucrose addiction in a sucrose preference test in mice.

SARS-CoV-2 Infection among Medical Institution Faculty and Healthcare Workers in Tokyo, Japan

Objective To consider effective measures against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in medical institutions, this study estimated the SARS-CoV-2 infection rate among healthcare workers (HCWs) in Tokyo, Japan, and determined the specific findings for mild coronavirus disease 2019 (COVID-19) cases. Methods This study analyzed the results of serologic tests to detect immunoglobulin G antibodies against SARS-CoV-2 and evaluated the demographic and clinical characteristics of the faculty and HCWs at a Tokyo medical institution in August 2020. The demographic and clinical characteristics of participants with antibody-positive results were compared to those of participants with antibody-negative results. Materials This study recruited 2,341 faculty and HCWs at a Tokyo medical institution, 21 of whom had a COVID-19 history. Results Of the 2,320 participants without a COVID-19 history, 20 (0.862%) had positive serologic test results. A fever and dysgeusia or dysosmia occurred with greater frequency among the participants with positive test results than in those with negative results [odds ratio (OR), 5.475; 95% confidence interval (CI), 1.960-15.293 and OR, 24.158; 95% CI, 2.693-216.720, respectively]. No significant difference was observed in the positivity rate between HCWs providing medical care for COVID-19 patients using adequate protection and other HCWs (OR, 2.514; 95% CI, 0.959-6.588). Conclusion To reduce the risk of COVID-19 spread in medical institutions, faculty and HCWs should follow standard and necessary transmission-based precautions, and those with a fever and dysgeusia or dysosmia should excuse themselves from work as soon as possible.

Impaired brain fractalkine-CX3CR1 signaling is implicated in cognitive dysfunction in diet-induced obese mice

INTRODUCTION

A diet high in saturated fat is well known to affect neuronal function and contribute to cognitive decline in experimental animals and humans. Fractalkine released from neurons acts on its receptor, CX3C chemokine receptor 1 (CX3CR1), in the microglia to regulate several brain functions. The present study addressed whether fractalkine-CX3CR1 signaling in the brain, especially the hippocampus, contributes to the cognitive deficits observed in diet-induced obese (DIO) mice.

RESEARCH DESIGN AND METHODS

Mice were given 60% high-fat diet for 16 weeks. The expression of fractalkine and CX3CR1 in the hippocampus, amygdala and prefrontal cortex of DIO mice was analyzed. Cognitive ability in the Y-maze test and hippocampal glutamate receptors and synaptic markers were observed in DIO and CX3CR1 antagonist-treated mice. Regulation of fractalkine and CX3CR1 expression in the hippocampus was examined following administration of a selective insulin-like growth factor-1 (IGF-1) receptor inhibitor and a tyrosine receptor kinase B (TrkB) antagonist in normal mice.

RESULTS

DIO mice exhibited significant cognitive deficits in the Y-maze test and decrease in fractalkine and CX3CR1 in the hippocampus and amygdala compared with mice fed a control diet (CD mice). Administration of the CX3CR1 antagonist 18a in normal mice induced significant cognitive deficits in the Y-maze test. DIO mice and CX3CR1 antagonist-treated mice exhibited significant decreases in protein levels of NMDA (N-methyl-D-aspartate) receptor subunit (NR2A), AMPA (α-amino-5-methyl-3-hydroxy-4-isoxazole propionate) receptor subunit (GluR1) and postsynaptic density protein 95 in the hippocampus compared with their respective controls. Furthermore, plasma IGF-1 and hippocampal brain-derived neurotrophic factor were significantly decreased in DIO mice compared with CD mice. Administration of a selective IGF-1 receptor inhibitor and a TrkB antagonist in normal mice significantly decreased fractalkine and CX3CR1 in the hippocampus.

CONCLUSIONS

These findings indicate that the cognitive decline observed in DIO mice is due, in part, to reduced fractalkine-CX3CR1 signaling in the corticolimbic system.

The distributions of hematologic and biochemical values in healthy high-school adolescents in Japan

Laboratory tests of adolescents are often interpreted by using reference intervals derived from adults, even though these populations differ in their physical and physiologic characteristics and disease susceptibility. Therefore, to examine the distribution of laboratory values specific for adolescents, we analyzed hematologic and biochemical measurements obtained from 12,023 healthy Japanese adolescents (ages 15 through 18 years; male, 9165; female, 2858) during 2009 through 2018. Distributions were shown as medians with 95% (2.5th and 97.5th percentiles) of values and were compared with those from previous studies that examined similar Asian populations. There were some differences between hematologic parameters, serum creatinine and uric acid concentration, and lipid levels of Japanese adults and adolescents. In comparison with other Asian populations, the distributions of serum uric acid and high-density-lipoprotein cholesterol in the present study were slightly higher than those in the other studies. Although further research is need, the distributions of hematologic and biochemical tests in adolescents may have the potential to facilitate the early identification and management of disease in this population.

Neuronal cells derived from human induced pluripotent stem cells as a functional tool of melanocortin system

BACKGROUND

The preparation of human neurons derived from human induced pluripotent stem (iPS) cells can serve as a potential tool for evaluating the physiological and pathophysiological properties of human neurons and for drug development.

METHODS

In the present study, the functional activity in neuronal cells differentiated from human iPS cells was observed.

RESULTS

The differentiated cells expressed mRNAs for classical neuronal markers (microtubule-associated protein 2, β-tubulin III, calbindin 1, synaptophysin and postsynaptic density protein 95) and for subunits of various excitatory and inhibitory transmitters (NR1, NR2A, NR2B, GABA_A α1). Moreover, the differentiated cells expressed neuropeptides and receptors which are predominantly present in the hypothalamus. The expression of mRNA for preopiomelanocortin, agouti-related protein (AgRP), melanocortin-3 receptor (MC3R) and melanocortin-4 receptor (MC4R) increased in culture with a peak on Day 30 which subsequently decreased at Day 45. Immunoreactivities for MC3R and MC4R were also observed in cells differentiated from human iPS cells. Application of a potent agonist for MC3R and MC4R, [Nle4, D-Phe7]-α-melanocyte-stimulating hormone, significantly increased intracellular cAMP levels, but this was suppressed by AgRP (83-132) and SHU9119.

CONCLUSIONS

These findings offer the possibility for drug developments using neurons differentiated from normal or disease-associated human iPS cells.

Brain-specific natriuretic peptide receptor-B deletion attenuates high-fat diet-induced visceral and hepatic lipid deposition in mice

C-type natriuretic peptide (CNP) and its receptor, natriuretic peptide receptor-B (NPR-B), are abundantly distributed in the hypothalamus. To explore the role of central CNP/NPR-B signaling in energy regulation, we generated mice with brain-specific NPR-B deletion (BND mice) by crossing Nestin-Cre transgenic mice and mice with a loxP-flanked NPR-B locus. Brain-specific NPR-B deletion prevented body weight gain induced by a high-fat diet (HFD), and the mesenteric fat and liver weights were significantly decreased in BND mice fed an HFD. The decreased liver weight in BND mice was attributed to decreased lipid accumulation in the liver, which was confirmed by histologic findings and lipid content. Gene expression analysis revealed a significant decrease in the mRNA expression levels of CD36, Fsp27, and Mogat1 in the liver of BND mice, and uncoupling protein 2 mRNA expression was significantly lower in the mesenteric fat of BND mice fed an HFD than in that of control mice. This difference was not observed in the epididymal or subcutaneous fat. Although previous studies reported that CNP/NPR-B signaling inhibits SNS activity in rodents, SNS is unlikely to be the underlying mechanism of the metabolic phenotype observed in BND mice. Taken together, CNP/NPR-B signaling in the brain could be a central factor that regulates visceral lipid accumulation and hepatic steatosis under HFD conditions. Further analyses of the precise mechanisms will enhance our understanding of the contribution of the CNP/NPR-B system to energy regulation.

Intracerebroventricular administration of C-type natriuretic peptide suppresses food intake via activation of the melanocortin system in mice

C-type natriuretic peptide (CNP) and its receptor are abundantly distributed in the brain, especially in the arcuate nucleus (ARC) of the hypothalamus associated with regulating energy homeostasis. To elucidate the possible involvement of CNP in energy regulation, we examined the effects of intracerebroventricular administration of CNP on food intake in mice. The intracerebroventricular administration of CNP-22 and CNP-53 significantly suppressed food intake on 4-h refeeding after 48-h fasting. Next, intracerebroventricular administration of CNP-22 and CNP-53 significantly decreased nocturnal food intake. The increment of food intake induced by neuropeptide Y and ghrelin was markedly suppressed by intracerebroventricular administration of CNP-22 and CNP-53. When SHU9119, an antagonist for melanocortin-3 and melanocortin-4 receptors, was coadministered with CNP-53, the suppressive effect of CNP-53 on refeeding after 48-h fasting was significantly attenuated by SHU9119. Immunohistochemical analysis revealed that intracerebroventricular administration of CNP-53 markedly increased the number of c-Fos-positive cells in the ARC, paraventricular nucleus, dorsomedial hypothalamus, ventromedial hypothalamic nucleus, and lateral hypothalamus. In particular, c-Fos-positive cells in the ARC after intracerebroventricular administration of CNP-53 were coexpressed with α-melanocyte-stimulating hormone immunoreactivity. These results indicated that intracerebroventricular administration of CNP induces an anorexigenic action, in part, via activation of the melanocortin system.

[An approach toward CNS dysfunction associated with metabolic syndrome; implication of leptin, which is a key molecule of obesity, in depression associated with obesity]

Obesity is the most critical factor in the pathology of metabolic syndrome (MetS), and is associated with an increased risk of depression. The imbalance of hormones and neural peptides which are involved in energy regulation are observed in obesity. It becomes evident that these hormones and neural peptides also affect mood. Leptin plays a pivotal role in energy regulation mainly acting in the hypothalamus of the brain. Although obese humans and rodents usually have high circulating levels of leptin, leptin neither reduces food intake nor increases energy expenditure. This paradoxical situation in obesity has been termed "leptin resistance", which is considered to be a central dogma for obesity. Based on these observations, we examined the functional significance of leptin in the regulation of the depressive state in diet-induced obese (DIO) mice. Our recent study demonstrated that DIO mice showed severe depressive behavior without response to the antidepressant effect of leptin, which is, in part, due to the impairment of leptin action in the hippocampus (Yamada, et al., Endocrinology, 2011). MetS and CNS dysfunction might have common pathological bases vulnerable to these disorders. Our future direction is to investigate a new treatment strategy of MetS by analyzing CNS dysfunction associated with obesity.

Impairment of fear-conditioning responses and changes of brain neurotrophic factors in diet-induced obese mice

Recent epidemiological studies demonstrate that obesity is related to a high incidence of cognitive impairment. In the present study, cognitive behaviours in diet-induced obese (DIO) mice fed 60% high-fat diet for 16 weeks were compared with those in mice fed a control diet (CD) in fear-conditioning tests including both contextual and cued elements that preferentially depend on the hippocampus and amygdala, respectively. Furthermore, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) content in the brain areas was examined in both CD and DIO mice. In fear-conditioning tests, the freezing percentages of both contextual fear and cued fear responses in DIO mice were significantly lower than in CD mice. BDNF content in the cerebral cortex and hippocampus of DIO mice was significantly lower than that in CD mice. Its receptor, full-length TrkB, in the amygdala of DIO mice was significantly decreased compared to that in CD mice, although not in the cerebral cortex, hippocampus and hypothalamus. By contrast, NT-3 content in the hippocampus, amygdala and hypothalamus of DIO mice was significantly higher than that in CD mice. Its receptor, full-length TrkC, was not significantly different between CD and DIO mice. The present study demonstrates that DIO mice show impairment of both hippocampus-dependent contextual and amygdala-dependent cued responses in the fear-conditioning tests, as well as an imbalance in the interaction between the BDNF and NT-3 systems in the cerebral cortex, hippocampus and amygdala related to cognition and fear.

Salivary cortisol levels are associated with outcomes of weight reduction therapy in obese Japanese patients

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis can increase the risk of cardiovascular disease (CVD). However, the detailed relationships of HPA axis activity with weight reduction and CVD risk factors in obese patients have not been examined. This study was designed to elucidate the associations of salivary cortisol levels with weight reduction and CVD risk factors in obese patients. As a marker of HPA axis activity, we measured the morning salivary cortisol levels of 83 obese Japanese outpatients. We also examined metabolic parameters, inflammatory markers, and indicators of arterial stiffness, that is, the pulse wave velocity and cardio-ankle vascular index. All 83 obese patients underwent 3-month weight reduction therapy with lifestyle modification. At the baseline, multivariate regression analysis revealed that only logarithmic transformation of C-reactive protein (β = 0.258, P < .05) and cardio-ankle vascular index (β = 0.233, P < .05) were independent determinants of the salivary cortisol levels. However, other metabolic parameters were not significantly associated with the salivary cortisol levels. In addition, lower salivary cortisol levels and higher body weight at the baseline were the only independent determinants of successful weight loss through the weight reduction therapy (P < .01). The present study demonstrates that the baseline morning salivary cortisol levels are significantly associated with the levels of an inflammatory marker, arterial stiffness, and successful weight reduction in obese patients. Therefore, salivary cortisol could be a useful marker for assessing and managing body weight and CVD risk factors in obese patients.