Nitric oxide mediates hyperphagia of obese Zucker rats: relation to specific changes in the microstructure of feeding behavior

Lipopolysaccharide-induced inflammation increases nitric oxide production in taste buds

Inducible nitric oxide synthase (iNOS) is expressed when cells are induced or stimulated by proinflammatory cytokines and/or bacterial lipopolysaccharide (LPS). iNOS is a downstream gene of the NF-κB pathway. Our previous studies demonstrated that five Nfkb genes are expressed in mouse taste epithelium and taste organoids. However, it is unclear whether activation of the NF-κB pathway could induce iNOS gene expression and increase nitric oxide (NO) production in taste buds. In this study, we investigated the expression of iNOS mRNA and protein after LPS stimulation. Our results showed that a subset of taste bud cells and taste neurons express iNOS proteins after LPS stimulation. In addition, isolated mouse taste epithelium can release NO after exposure to LPS ex vivo. In taste behavioral tests, the NO donor nitroprusside enhanced mouse aversive responses to salty, bitter, and sour taste compounds. The enhanced aversive responses were especially strong for salty taste. In conclusion, our results suggest that iNOS and NO may play a role in the inflammation-associated taste disturbances.

The Expanded Endocannabinoid System/Endocannabinoidome as a Potential Target for Treating Diabetes Mellitus

PURPOSE OF REVIEW

The endocannabinoid (eCB) system, i.e. the receptors that respond to the psychoactive component of cannabis, their endogenous ligands and the ligand metabolic enzymes, is part of a larger family of lipid signals termed the endocannabinoidome (eCBome). We summarize recent discoveries of the roles that the eCBome plays within peripheral tissues in diabetes, and how it is being targeted, in an effort to develop novel therapeutics for the treatment of this increasingly prevalent disease.

RECENT FINDINGS

As with the eCB system, many eCBome members regulate several physiological processes, including energy intake and storage, glucose and lipid metabolism and pancreatic health, which contribute to the development of type 2 diabetes (T2D). Preclinical studies increasingly support the notion that targeting the eCBome may beneficially affect T2D. The eCBome is implicated in T2D at several levels and in a variety of tissues, making this complex lipid signaling system a potential source of many potential therapeutics for the treatments for T2D.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Antiobesogenic role of endothelial nitric oxide synthase

The prevalence of obesity has increased remarkably in the past four decades. Because obesity can promote the development of type 2 diabetes and cardiovascular disease, understanding the mechanisms that engender weight gain and discovering safe antiobesity therapies are of critical importance. In particular, the gaseous signaling molecule, nitric oxide (NO), appears to be a central factor regulating adiposity and systemic metabolism. Obese and diabetic states are characterized by a deficit in bioavailable NO, with such decreases commonly attributed to downregulation of endothelial NO synthase (eNOS), loss of eNOS activity, or quenching of NO by its reaction with oxygen radicals. Gain-of-function studies, in which vascular-derived NO has been increased pharmacologically or genetically, reveal remarkable actions of NO on body composition and systemic metabolism. This review addresses the metabolic actions of eNOS and the potential therapeutic utility of harnessing its antiobesogenic effects.

L-arginine abolishes the hypothalamic serotonergic activation induced by central interleukin-1β administration to normal rats

IL-1β-induced anorexia may depend on interactions of the cytokine with neuropeptides and neurotransmitters of the central nervous system control of energy balance and serotonin is likely to be one catabolic mediator targeted by IL-1β. In the complex interplay involved in feeding modulation, nitric oxide has been ascribed a stimulatory action, which could be of significance in counteracting IL-1β effects.

The present study aims to explore the participation of the nitric oxide and the serotonin systems on the central mechanisms induced by IL-1β and the relevance of their putative interactions to IL-1β hypophagia in normal rats.

Serotonin levels were determined in microdialysates of the ventromedial hypothalamus after a single intracerebroventricular injection of 10 ng of IL-1β , with or without the pre-injection of 20 μg of the nitric oxide precursor L-arginine. IL-1β significantly stimulated hypothalamic serotonin extracellular levels, with a peak variation of 130 ±37% above baseline. IL- 1β also reduced the 4-h and the 24-h food intakes (by 23% and 58%, respectively). The IL-1β-induced serotonergic activation was abolished by the pre-injection of L-arginine while the hypophagic effect was unaffected.

The data showed that one central effect of IL-1β is serotonergic stimulation in the ventromedial hypothalamus, an action inhibited by nitric oxide activity. It is suggested that, although serotonin participates in IL-1β anorexia, other mechanisms recruited by IL-1β in normal rats are able to override the absence of the serotonergic hypophagic influence.

Club Drugs and HIV Infection: A Review

Club drug use is common among populations with human immunodeficiency virus (HIV) and populations at high risk for HIV infection. Club drugs have a myriad of acute and chronic medical consequences. Club drug-related visits to the emergency department and admissions for treatment of substance use have increased dramatically over the past 15 years. Most epidemiological data support the role of club drugs in increasing sexual risk behavior, with some studies demonstrating an independent association between use of certain club drugs and HIV infection. The direct influence of club drugs on progression of HIV disease remains to be determined; however, club drugs may interact with certain retroviral medications and have been associated with decreased adherence to medication. Clinicians should ask all patients about patterns of club drug use, counsel patients about the risks associated with club drug use, and refer patients to appropriate behavioral treatment programs for substance use when clinically indicated.

Simultaneous measurement of nitric oxide, blood glucose, and monoamines in the hippocampus of diabetic rat: an in vivo microdialysis study

The present study was undertaken to examine the relationships among the levels of nitric oxide (NO), monoamines, and blood glucose in the diabetic hippocampus. The levels of NO and monoamines (serotonin, 5-hydroxytryptamine [5-HT] and dopamine [DA]) were simultaneously measured in several experiments, using in vivo microdialysis techniques. We used both experimentally and spontaneously diabetic rats as the diabetic animal model, and compared the findings with those obtained from non-diabetic rats. The effects of the changed level of blood glucose due to insulin administration on the levels of NO, 5-HT, and DA were assessed. Total NO metabolite levels (NOx) were calculated as the sum of nitrite (NO2-) and nitrate (NO3-) levels. The results in the present study showed that: (1) the plasma levels of NOx in both diabetic rats were low compared to those in control rats, (2) the hippocampal NOx levels in both diabetic rats were almost the same as those in control rats, while the levels of 5-HT and DA were low in the diabetics, and (3) a sudden decrease in the plasma glucose level due to insulin administration reduced the NOx level as well as enhanced the 5-HT level in the diabetic hippocampus, a finding consistent with the results of 7 days administration of insulin. Taken together, these findings suggest that changes in the plasma glucose level cause, at least in part, the changes in the levels of NOx and monoamines in the diabetic brain.

A nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester, attenuates lipoprivic feeding in mice

Possible involvement of nitric oxide (NO) in lipoprivic feeding was investigated in nondeprived male ICR mice adapted to a high-fat diet in a within-subjects design. Lipoprivation was induced by blocking fatty acid oxidation with Na-mercaptoacetate (MA), which produces a short-term increase in feeding in mice and rats. Food intake, measured at 1, 2, and 4 h following injection of 70 mg/kg of MA, was attenuated in a dose related manner with increasing pretreatment dose (1,10, 25 and 50 mg/kg sc) of the NO-synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), reaching statistical significance at 10 mg/kg of L-NAME at h1 when compared to vehicle control condition. The inactive isomer, D-NAME, was ineffective, thereby supporting stereospecific drug action and directly implicating NO. A control experiment measured general locomotor activity (grid crossings and rears) in an open arena under 10-50 mg/kg of L-NAME in the same mice; both measures were significantly different from vehicle condition only at the highest dose. These findings support involvement of NO in lipoprivic hyperphagia; they are consistent with and extend research linking NO and ingestive behaviors through use of NOS inhibitors. Possible influences of confounds were discussed.

Morphological study of orexin neurons in the hypothalamus of the Long-Evans rat, with special reference to co-expression of orexin and NADPH-diaphorase or nitric oxide synthase activities

Orexins, novel neuropeptides, are exclusively localized in the hypothalamus and implicated in the regulation of a variety of activities, including food intake and energy balance. Nitric oxide (NO), an unconventional neurotransmitter, is widely present in numerous brain regions including the hypothalamus, and has similar physiological roles to those of the orexins. The present study was undertaken to examine the distribution of orexin neurons and the presence of neuronal nitric oxide synthase (nNOS) in the orexin neurons to clarify whether NO interacts with the orexins in the neuronal regulation activities in the Long-Evans rat. We used two double-labeling methods: nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry in combination with orexin immunohistochemistry, and double-labeling fluorescent immunohistochemistry for orexin and nNOS. The majority of the orexin immunoreactive neurons were localized mainly in the areas of the dorsomedial hypothalamic nucleus (DMN), the dorsal part of the perifornical nucleus (PEF) and lateral hypothalamic area. The orexin immunoreactive cell bodies were medium in size, and triangular, round, elliptic, and fusiform in shape. The sizes and shapes of orexin neurons in the different parts were similar. Cell bodies coexpressing the orexin and nNOS or NADPH-d were present in the areas of the DMN and the PEF, and the nerve fibers containing orexin and nNOS were distributed in the DMN and PEF, arcuate nucleus (ARN) and ventromedial hypothalamic nucleus (VMH). These results provide morphological evidence that there exists a population of nNOS- or NADPH-d-/orexin-coexpressing neurons in the orexinergic cell group in the hypothalamus, and taken together with previous findings, suggest that NO may play a role in the mechanisms by which orexin neurons regulate food intake and energy balance.

Nicotine administration decreases nitric oxide synthase expression in the hypothalamus of food-deprived rats

Effect of nicotine on nitric oxide synthase (NOS) expression in various hypothalamic regions was investigated in rats via nicotineamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. Sprague-Dawley rats were divided into the fed group, the fed and nicotine-treated group, the food-deprived group, and the food-deprived and nicotine-treated group. The fed groups received abundant food and water, while food was withheld from the food-deprived groups for 48 h. The nicotine-treated groups were injected with nicotine. Following food deprivation, enhanced NAPDH-d expression was detected in the paraventricular nucleus, ventromedial hypothalamic nucleus, and lateral hypothalamic area of the hypothalamus. Nicotine administration to the food-deprived rats resulted in decreased NADPH-d positivity. The present results indicate that nicotine administration is effective in limiting the enhancement in NOS expression following food restriction.

Differential expression of nicotinamide adenine dinucleotide phosphate-diaphorase in hypothalamic areas of obese Zucker rats

Several studies have suggested that the activity of nitric oxide synthase (NOS) may be involved in the regulation of food intake in the genetically obese Zucker rats. In the present study, we investigated the expression of NOS in various hypothalamic regions of obese and lean Zucker rats using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry. Obese Zucker rats showed significantly lower staining intensities of NADPH-diaphorase-positive neurons in the paraventricular nucleus (PVN), lateral hypothalamic area (LHA) and ventromedial hypothalamic nucleus (VMH) than lean Zucker rats did. The differences in staining intensities between obese and lean Zucker rats were large in both the PVN and LHA, but such differences were relatively small in the VMH.

Leptin increases serotonin turnover by inhibition of brain nitric oxide synthesis

Leptin administration inhibits diencephalic nitric oxide synthase (NOS) activity and increases brain serotonin (5-HT) metabolism in mice. We evaluated food intake, body-weight gain, diencephalic NOS activity, and diencephalic content of tryptophan (TRP), 5-HT, hydroxyindoleacetic acid (5-HIAA), and 5-HIAA/5-HT ratio after intracerebroventricular (ICV) or intraperitoneal (IP) leptin injection in mice. Five consecutive days of ICV or IP leptin injections induced a significant reduction in neuronal NOS (nNOS) activity, and caused a dose-dependent increase of 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio. Diencephalic 5-HT metabolism showed a significant increase in 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio 3 hours after a single leptin injection. This effect was maintained for 3 hours and had disappeared by 12 hours after injection. After a single IP leptin injection, the peak for 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio was achieved at 6 hours. Single injections of ICV or IP leptin significantly increased diencephalic 5-HT content. Leptin-induced 5-HT increase was antagonized by the coadministration of L-arginine only when the latter was ICV injected, whereas D-arginine did not influence leptin effects on brain 5-HT content. Finally, in nNOS-knockout mice, the appetite-suppressant activity of leptin was strongly reduced, and the leptin-induced increase in brain 5-HT metabolism was completely abolished. Our results indicate that the L-arginine/NO pathway is involved in mediating leptin effects on feeding behavior, and demonstrate that nNOS activity is required for the effects of leptin on brain 5-HT turnover.

N(G)-nitro-L-arginine methyl ester reduces stress-related feeding in the rat tail-pinch model

A possible role of nitric oxide (NO) in stress-related feeding was investigated in male rats using the tail-pinch (TP) model, in within-subjects experimental designs. An initial experiment demonstrated a dose-related reduction in TP-induced solid food intake over a 10-min test period with increasing dose (10.25, and 50 mg/kg SC) of the NO-synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), reaching statistical significance at 25 mg/kg L-NAME when compared to vehicle control (p < 0.05). Pattern analysis further revealed a decrease both in total duration of food-directed oral behavior and in percentage of longer duration (> 60 s) oral behavior bouts with increasing dose of L-NAME; both measures reached statistical significance at 50 mg/kg (p < 0.01). Pretreatment with 500 mg/kg of the NO precursor, L-arginine (L-arg), resulted in partial but not significant reversal of the attenuating effect of 25 mg/kg L-NAME on food intake. Latency to begin eating or gnawing was not significantly affected by L-NAME. In a subsequent experiment, L-arg alone (500 and 750 mg/kg) did not significantly alter TP-induced food intake. It is cautiously suggested that these results implicate involvement of NO in TP-induced feeding.

Effects of a nitric oxide synthase inhibitor on 5-HT1A receptor agonist 8-OH-DPAT-induced hyperphagia in rats

We investigated nitric oxide (NO) involvement in the hyperphagia induced by the 5-HT1A receptor agonist 8-hydroxy-2-di-n-(propylamino)tetralin (8-OH-DPAT). A NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), dose dependently inhibited 8-OH-DPAT-induced eating in freely feeding rats. However, the inactive isomer D-NAME was without effect. The inhibitory effects of L-NAME on 8-OH-DPAT-induced hyperphagia were reversed by simultaneous administration of L-arginine. These results suggest that NO participates in the 8-OH-DPAT-induced hyperphagia which is elicited by activation of the 5-HT1A receptor.