Recent advances in molecular biology have led to the investigation of the molecular mechanism by which chemicals such as odors and tastants are perceived by specific chemosensory organs. For example, G protein–coupled receptors expressed within the nasal epithelium and taste receptors in the oral cavity have been identified as odorant and taste receptors, respectively. However, there is much evidence to indicate that these chemosensory receptors are not restricted to primary chemosensory cells; they are also expressed and have function in other cells such as those in the airways and gastrointestinal (GI) tract. This short review describes the possible mechanisms by which taste signal transduction occurs in the oral cavity and tastants/nutrients are sensed in the GI tract by taste-like cells, mainly enteroendocrine and brush cells. Furthermore, it discusses the future perspectives of chemosensory studies.

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We reviewed the effect of monosodium glutamate (MSG) on the development and healing of nonsteroidal anti-inflammatory drug (NSAID)-induced small intestinal lesions in rats. Loxoprofen (60 mg/kg, p.o.) induced lesions in the small intestine within 24 h, accompanied by a decrease of Muc2 expression and an increase in enterobacterial invasion and inducible nitric oxide synthase (iNOS) expression. These lesions were prevented when MSG was given as a mixture of powdered food for 5 days before the loxoprofen treatment. This effect of MSG was accompanied by an increase in Muc2 expression / mucus secretion as well as the suppression of bacterial invasion and iNOS expression. These intestinal lesions healed spontaneously within 6 days, but the process was impaired by the repeated administration of low-dose loxoprofen (30 mg/kg) for 5 days after the ulceration, with the decrease of vascular endothelial derived growth factor (VEGF) expression and angiogenesis. The healing-impairing effect of loxoprofen was prevented by feeding 5% MSG for 5 days after the ulceration. These results suggest that MSG not only prevents loxoprofen-induced small intestinal damage but also promotes a healing of these lesions; the former is functionally associated with the increase in Muc2 expression / mucus secretion and the suppression of bacterial invasion and iNOS expression, while the latter is associated with the stimulation of VEGF expression/angiogenesis.

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The gustatory and visceral stimulation from food regulates digestion and nutrient utilization, and free glutamate (Glu) release from food is responsible for the umami taste perception that increases food palatability. The results of recent studies reveal a variety of physiological roles for Glu. For example, luminal applications of Glu into the mouth, stomach, and intestine increase the afferent nerve activities of the glossopharyngeal nerve, the gastric branch of the vagus nerve, and the celiac branch of the vagus nerve, respectively. Additionally, luminal Glu evokes efferent nerve activation of each branch of the abdominal vagus nerve. The intragastric administration of Glu activates several brain areas (e.g., insular cortex, limbic system, and hypothalamus) and has been shown to induce flavor-preference learning in rats. Functional magnetic resonance imaging of rats has shown that the intragastric administration of Glu activates the nucleus tractus solitarius, amygdala, and lateral hypothalamus. In addition, Glu may increase flavor preference as a result of its postingestive effect. Considering these results, we propose that dietary Glu functions as a signal for the regulation of the gastrointestinal tract via the gut–brain axis and contributes to the maintenance of a healthy life.

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Glycine is a non-essential amino acid that has indispensable roles in both excitatory and inhibitory neurotransmission via N-methyl-D-aspartate type glutamate receptors and glycine receptors, respectively. We recently reported that glycine ingestion before bedtime significantly ameliorated subjective sleep quality in individuals with insomniac tendencies. Oral administration of glycine to rats was found to induce a significant increase in the plasma and cerebrospinal fluid glycine concentrations and a significant decrease in the core body temperature associated with an increase in cutaneous blood flow. The decline in the core body temperature might be a mechanism underlying glycine’s effect on sleep, as the onset of sleep is known to involve a decrease in the core body temperature. Moreover, a low core body temperature is maintained during sleep in humans. Pharmacological studies investigating the mechanisms of glycine on sleep were also performed. In this review, we will describe both our recent findings regarding how and where orally administered glycine acts and findings from our rat study and human trials.

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The branched chain amino acids (BCAAs) leucine, isoleucine, and valine are the most abundant of the essential amino acids. BCAAs have recently been recognized as having functions other than simple nutrition. The importance of BCAAs as nutrient regulators in protein synthesis was recognized over 20 years ago. Leucine is the most potent of the BCAAs in stimulating muscle protein synthesis, while isoleucine and valine are much less effective. The signaling action of leucine in protein synthesis has been well studied, and the mechanisms are currently under investigation. However, the pharmacological effects of isoleucine and valine have not been clarified. It has recently been reported that, among the BCAAs, leucine and isoleucine act as signals in glucose metabolism. We revealed that isoleucine stimulates both glucose uptake in the muscle and whole body glucose oxidation, in addition to depressing gluconeogenesis in the liver, thereby leading to a hypoglycemic effect in rats. Based on these results, we speculate that isoleucine signaling accelerates catabolism of incorporated glucose for energy production and consumption.

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Although the antinociceptive effects of N-palmitoyl-ethanolamine (PEA) were first characterized nearly 50 years ago, the identity of the mechanism that mediates these actions has not been elucidated. The present study investigated the contribution of K⁺ channels on peripheral antinociception induced by the CB₂ agonist PEA. Nociceptive thresholds to mechanical paw stimulation of Wistar rats treated with intraplantar prostaglandin E₂ to induce hyperalgesia were measured, and other agents were also given by local injection. PEA (5, 10, and 20 μg/paw) elicited a local peripheral antinociceptive effect. This effect was antagonized by glibenclamide, a selective blocker of ATP-sensitive K⁺ channels (20, 40, and 80 μg/paw). In addition, neither the voltage-dependent K⁺ channel–specific blocker tetraethylammonium (30 μg/paw) nor the small and large conductance blockers of Ca²⁺-activated K⁺ channels, dequalinium (50 μg/paw) and paxilline (20 μg/paw), respectively, were able to block the local antinociceptive effect of PEA. These results indicate that the activation of ATP-sensitive K⁺ channels could be the mechanism that induces peripheral antinociception by PEA and that voltage-dependent K⁺ channels and small and large conductance Ca²⁺-activated K⁺ channels do not appear to be involved in this mechanism.

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This study examined the effect of norkurarinol on the toll-like receptor 3 (TLR3)-mediated signaling pathways and rotavirus replication. Norkurarinol, a lavandulylated flavanone, was isolated from the roots of Sophora flavescens, which has been shown to have anti-inflammatory activity. Norkurarinol suppressed the NF-κB and AP-1 inducible secreted embryonic alkaline phosphatase (SEAP) activity induced by poly(I:C), TLR3 ligand, in THP1-Blue-CD14 cells with IC₅₀ values of 20.9 μM. Norkurarinol also significantly suppressed the mRNA expression of pro-inflammatory and adhesive molecules induced by poly(I:C) and rotavirus infection. Pretreatment of norkurarinol blocked the NF-κB and AP-1 signaling pathway and the phosphorylation of MAPKs induced by poly(I:C). On the other hand, norkurarinol increased the level of IRF3 phosphorylation and IFNβ expression in a dose-dependent manner. Moreover, norkurarinol inhibited the rotavirus-induced cytopathic effects. These results suggest that norkurarinol can modulate the TLR3-mediated inflammatory responses and rotavirus replication.

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Abnormal proliferation of vascular smooth muscle cells (VSMCs) plays an essential role in the pathogenesis of vascular diseases, such as atherosclerosis, hypertension, and restenosis. Clitocybin A, a novel isoindolinone, isolated from the culture broth of mushroom Clitocybe aurantiaca has been reported to possess free radical scavenging activity. However, the antiproliferative effects of clitocybin A on VSMCs are unknown. In the present study, we investigated the effect of clitocybin A on platelet-derived growth factor (PDGF)-BB–induced proliferation of VSMCs and examined the molecular basis of the underlying mechanism. Clitocybin A inhibited DNA synthesis and cell proliferation. In accordance with these findings, clitocybin A blocked the PDGF-BB–inducible progression through G0/G1 to S phase of the cell cycle in synchronized cells and decreased the expression of cyclin-dependent kinase (CDK) 2, CDK4, cyclin D1, cyclin E, and proliferative cell nuclear antigen. In addition, clitocybin A inhibited the PDGF-BB–induced phosphorylation of phosphatidylinositol 3 kinase (PI3K) / Akt kinase. However, clitocybin A did not change the expression levels of extracellular signal-related kinase (ERK) 1/2, phospholipase C-γ1, and PDGF-Rβ phosphorylation. These results indicate that clitocybin A may inhibit VSMCs proliferation through G1 phase arrest by regulating the PI3K/Akt pathway.

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The aim of this study was to investigate the relaxant effect of insulin on the 5-hydroxytryptamine (5-HT)-induced constriction of the human endothelium-denuded saphenous vein (SV) and its signal transduction pathway. During the 5-HT-induced sustained constriction of vessels, insulin induced vasorelaxation in a concentration-dependent manner. This insulin-induced vasorelaxation was partially attenuated by L-NAME, a nitric oxide synthase (NOS) inhibitor, and was abolished by wortmannin, a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Insulin increased the Ser⁴⁷³ phosphorylation of Akt. Endothelial NOS and inducible NOS protein expressions were observed in SV smooth muscle when insulin induced relaxation of SV vessels preconstricted with 5-HT. Although insulin did not affect the total protein level of 5-HT_2A receptors, it decreased the particulate protein level and reciprocally increased the soluble protein level of 5-HT_2A receptors in a concentration-dependent manner. These results demonstrate that insulin can induce the internalization of 5-HT_2A receptors from the plasma membrane to the cytoplasm. The insulin-induced internalization of 5-HT_2A receptors was abolished by wortmannin but was not affected by L-NAME. These results suggest that the relaxant effect of insulin on 5-HT-induced vasoconstriction is mediated in part by the internalization of plasma membrane 5-HT_2A receptors and the production of nitric oxide via the PI3-K/Akt pathway.

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When cardiac tissue is exposed to hypoxia, myocytes are damaged, while fibroblasts are activated. However, it is unknown what changes are induced by hypoxia in cardiac fibroblasts. In this study, using the whole cell patch-clamp technique, we investigated the effect of hypoxia on membrane currents in fibroblasts primarily cultured from adult rat hearts. Cardiac fibroblasts were incubated for 24 h under normoxic or hypoxic conditions using Anaeropack. Hypoxia increased a current which reversed at around −20 mV in the cardiac fibroblasts. This current was inhibited by clotrimazole, which is an inhibitor of transient receptor potential melastatin 2 (TRPM2) channel and intermediate-conductance Ca²⁺-activated K⁺ channel (KCa3.1). ADP ribose in the pipette solution enhanced this current. Quantitative RT-PCR revealed that mRNA of TRPM2, but not that of KCa3.1, was increased by hypoxia. RNA interference of TRPM2 prevented the development of the hypoxia-induced current. H₂O₂, an activator of TRPM2 channel, induced a higher [Ca²⁺]_i elevation in hypoxia-exposed cardiac fibroblasts than that in normoxia-exposed cells. We conclude that hypoxia induces TRPM2 channel expression in adult rat cardiac fibroblasts.

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A sesquiterpene glycoside, cadin-2-en-1β-ol-1β-D-glucuronopyranoside (known as CR4-1), was isolated from Catharanthus roseus (Apocynaceae) hairy root cultures. C. roseus is widely used as an ornamental and medicinal plant and is cultivated mainly for its alkaloids. C. roseus has been reported to have pharmacologic properties such as anti-cancer, enzymatic anti–oxidant, and anti-diabetic effects. In this study, we demonstrated that CR4-1 significantly inhibited the in vitro invasion of MCF-7 human breast adenocarcinoma cells induced by 12-O-tetradecanoyl phorbol-13-acetate (TPA). Matrix metalloproteinases (MMPs) are known to be involved in cancer invasion and metastasis. Zymographic analysis showed that CR4-1 suppressed TPA-induced MMP-9 activity in a dose-dependent manner. We further demonstrated that CR4-1 suppressed the phosphorylation of extracellular signal-regulated protein kinase, but not p38 kinase or c-Jun N-terminal kinase (JNK). Moreover, CR4-1 attenuated TPA-induced degradation of κBα inhibitor (IκB-α). These results suggest that CR4-1 reduces the invasiveness of human cancer cells by suppressing MMP-9 expression through inhibition of the NF-κB signaling pathways.

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Cigarette smoking has been implicated in the initiation and progression of cardiovascular disorders and atherosclerosis. Here, we examined the effects of nicotine-free cigarette smoke extract (CSE) on the regulation of cardiovascular function. Rats were subcutaneously administered PBS or nicotine-free CSE at 0.05 to 1.5 mL/day per rat for 4 weeks. Blood pressure, cardiac function, and vascular responsiveness were measured at 4 weeks after administration. Furthermore, acute effects of nicotine-free CSE were also studied in the aorta isolated from normal rats. Blood pressure and left ventricular systolic pressure (LVSP) were significantly increased in the nicotine-free CSE–administered rats, but heart rate, dP/dt_max, and dP/dt_min were not affected. Endothelium-dependent relaxation by acetylcholine (ACh) in the nicotine-free CSE–treated rats was significantly attenuated compared to PBS-treated rats, but endothelium-independent relaxation by sodium nitroprusside (SNP) did not differ. Pretreatment with superoxide dismutase restored the attenuated ACh-induced relaxation. Contractions by phenylephrine, angiotensin II, and KCl did not differ between two groups. In vitro acute nicotine-free CSE treatment did not alter the response to ACh or SNP. These results suggest that chronic nicotine-free CSE administration impairs endothelial function by increased production of superoxide derived from the vascular wall components other than smooth muscles and induces slight hypertension accompanied with LVSP elevation.

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In the present study, we investigated the effect of aripiprazole, a dopamine system stabilizer, on ethanol-induced psychological and physiological dependence and anxiety-like behavior. First we determined the effect of aripiprazole, a dopamine system stabilizer, on the development and expression of ethanol-induced place preference. Both the development and expression of ethanol-induced place preference was significantly suppressed by treatment of aripiprazole. Next, the withdrawal score gradually increased with increasing duration after the withdrawal from ethanol for 6 days in vehicle-treated mice and the maximal score was observed 10 h after the ethanol withdrawal. Aripiprazole caused no changes in the withdrawal score as compared to vehicle-treated mice. Under these conditions we investigated the effect of aripiprazole on the anxiety-like behavior of ethanol physical dependent mice, which were animals subjected to ethanol vapor for 6 days. The significant decrease of time spent in the open arms and number of open arm entries characterize the anxiety-like behavior in ethanol physical dependent mice, compared to control mice. These decreases were reversed by treatment of aripiprazole, which were inhibited by WAY100635, a serotonin 5-HT_1A receptor antagonist. The present findings suggest that aripiprazole was efficient for reversing ethanol-induced place preference and anxiety-like behavior.

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Prostaglandin E₂ (PGE₂) is a key molecule involved in the neuroinflammatory processes that characterize amyotrophic lateral sclerosis (ALS). Although PGE₂ synthesis is regulated by PGE₂ synthases (PGESs), the pathological role of PGESs in ALS still remains unknown. Experiments were performed to elucidate the expression of PGESs and the localization of microsomal PGES-1 (mPGES-1) in neurons and glial cells in the spinal cord of ALS model (G93A) mice. Neurological symptom was observed in G93A mice from 14 weeks by the tail suspension test, and rotarod performances were decreased at 16 weeks and older. Western blotting revealed that the level of mPGES-1 was increased in G93A mice at 15 weeks and older. In contrast, the levels of cytosolic PGES and mPGES-2 did not change at any age. Immunohistochemical analysis demonstrated that age-dependent expression of mPGES-1 was found in motor neurons in G93A mice at 11 and 15 weeks. Immunoreactivity of mPGES-1 was also co-localized in Iba1-positive microglia in G93A mice at 15 weeks. These results suggest that mPGES-1 in motor neurons may play a role in the pathogenesis of ALS and that mPGES-1 may work sequentially in motor neurons and activated microglia to produce ALS symptoms in G93A mice.

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Anti-inflammatory effects of tocopherol (TOL) analogs have been attributed to their potent antioxidant activities. However, we and others have separately reported that γTOL or α-tocopheryl succinate (αTOS), despite their lower antioxidant activities, inhibit lipopolysaccharide (LPS)-induced production of prostaglandin E₂ (PGE₂) in macrophages and lung epithelial cells more effectively than αTOL. In the present study, we sought to directly analyze the effect of three TOL analogs (αTOL, αTOS, and γTOL) on LPS-induced production of pro-inflammatory mediators in macrophages. Our data demonstrated that the inhibitory effects of all three TOL analogs on nitric oxide production were very limited. In contrast, αTOS dose-dependently and significantly inhibited LPS-induced PGE₂ production in both RAW264.7 cells and peritoneal macrophages, whereas αTOL and γTOL were much less effective. Although αTOS had no effect on LPS-induced cyclooxygenase-2 expression, it did inhibit COX activity in intact cells. αTOS in combination with sulforaphane, a compound that blocked LPS-induced COX-2 expression, cooperatively and more significantly inhibited PGE₂ production. These findings suggest that αTOS is a more potent inhibitor of the pro-inflammatory mediator PGE₂. The inclusion of αTOS in vitamin supplements may further enhance the effectiveness of strategies for preventing diseases associated with inflammation.

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Rhubarb is a widely used traditional medicine and has been reported to elicit a number of biological effects including anti-inflammatory and antiplatelet effects. In the present study, we investigated the effects of anthraquinone derivatives isolated from rhubarb on platelet activity. Of four anthraquinone derivatives isolated from rhubarb examined, chrysophanol-8-O-glucoside (CP-8-O-glc) was found to have the most potent inhibitory effect on collagen- and thrombin-induced platelet aggregation. CP-8-O-glc–treated mice showed significantly prolonged bleeding times. Furthermore, CP-8-O-glc was found to have a significant inhibitory effect on rat platelet aggregation ex vivo and on thromboxane A₂ formation in vitro. In coagulation tests, CP-8-O-glc did not alter prothrombin time, and it prolonged the activated partial thromboplastin time. However, CP-8-O-glc only inhibited platelet phosphatidylserine exposure, but not exert direct inhibition on intrinsic factors. This study demonstrates the antiplatelet and anticoagulant effects of CP-8-O-glc and suggests that this compound might be of therapeutic benefit for the prevention of platelet-related cardiovascular diseases.

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The ultra-short acting, selective β₁-adrenergic antagonists landiolol and esmolol are widely used perioperatively; however, little is known about their acute direct actions on the heart. The current study utilized the Langendorff perfused heart system to measure changes in cardiac function and hemodynamics in response to each drug. Furthermore, electrophysiological analysis was performed on isolated ventricular myocytes. Direct application of esmolol significantly decreased systolic left ventricular pressure and heart rate at concentrations > 10 μM, while it dose-dependently increased coronary perfusion pressure. Esmolol also shortened the action potential duration (APD) in a concentration-dependent manner, an action maintained even when the delayed rectifier K⁺ current or ATP sensitive K⁺ current was blocked. Moreover, esmolol inhibited both the inward rectifier K⁺ current (I_K1) and the L-type Ca²⁺ current (I_CaL) and increased the outward current dose-dependently. In contrast, landiolol had minimal cardiac effects. In the Kyoto Model computer simulation, inhibition of either I_K1 or I_CaL alone failed to shorten the APD; however, an additional increase in the time-independent outward current caused shortening of the APD, equal to that induced by esmolol. In conclusion, esmolol directly inhibits cardiac performance significantly more so than landiolol, an effect revealed to be at least in part mediated by esmolol-induced APD shortening.

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Formaldehyde (FA) is irritating to the skin and is the main cause of sick building syndrome. However, the cutaneous reaction induced by long-term FA exposure has not been fully investigated. In our previous study, we demonstrated that repeated painting of 2% – 10% FA on mouse ears caused marked ear swelling and increased mRNA expression of transient receptor potential vanilloid 1 (TRPV1) and neurotrophins in the ear. TRPV1 is reported to be involved in neurogenic inflammation; therefore, in the present study, we investigated the role of TRPV1 in FA-induced skin inflammation using TRPV1 gene–knockout mice. Mice were painted with 5% FA once a week for 5 weeks, and ear swelling and mRNA expression were investigated. Ear swelling and increased expression of neurotrophins mRNA by FA provocation in wild-type mice were attenuated by disruption of the TRPV1 gene. Furthermore, painting with a threshold dose of capsaicin, which does not induce ear swelling in intact mice, caused marked ear swelling after painting the ear 5 times with FA, indicating that inflamed tissues after FA application are hypersensitive to various ligands of TRPV1 in mice. These results demonstrated that neurogenic inflammation via TRPV1 and neurotrophins could be involved in FA-induced dermatitis.

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We examined cytotoxic effects of nicotine/tar-free cigarette smoke extract (CSE) on C6 glioma cells. The CSE induced plasma membrane damage (determined by lactate dehydrogenase leakage and propidium iodide uptake) and cell apoptosis {determined by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] reduction activity and DNA fragmentation}. The cytotoxic activity decayed with a half-life of approximately 2 h at 37°C, and it was abolished by N-acetyl-L-cysteine and reduced glutathione. The membrane damage was prevented by catalase and edaravone (a scavenger of ^•OH) but not by superoxide dismutase, indicating involvement of ^•OH. In contrast, the CSE-induced cell apoptosis was resistant to edaravone and induced by authentic H₂O₂ or O₂⁻ generated by the xanthine/xanthine oxidase system, indicating involvement of H₂O₂ or O₂⁻ in cell apoptosis. Diphenyleneiodonium [NADPH oxidase (NOX) inhibitor] and bisindolylmaleimide I [BIS I, protein kinase C (PKC) inhibitor] abolished membrane damage, whereas they partially inhibited apoptosis. These results demonstrate that 1) a stable component(s) in the CSE activates PKC, which stimulates NOX to generate reactive oxygen species (ROS), causing membrane damage and apoptosis; 2) different ROS are responsible for membrane damage and apoptosis; and 3) part of the apoptosis is caused by oxidants independently of PKC and NOX.

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Cannabinoid agonists impair hippocampus-dependent learning and memory. Using mouse hippocampal slice preparations, we examined the effect of anandamide, an endogenous cannabinoid, on sharp wave–ripple (SW-R) complexes, which are believed to mediate memory consolidation during slow-wave sleep or behavioral immobility. Anandamide reduced the frequency of SW-Rs recorded from the CA3 region, and this effect was abolished by AM251, a cannabinoid CB1–receptor antagonist. We further addressed the action of anandamide using a functional multineuron calcium imaging technique. Anandamide reduced the firing rate of hippocampal neurons as well as disrupted the temporal coordination of their firings during SW-R.

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Isolation-induced abnormal behaviors are useful animal models for assessing potential anti-psychotic drugs. This study examined the effect of MGS0028, a selective metabotropic glutamate 2/3 receptor agonist, on abnormal behaviors such as hyperactivity, aggression, and deficits of prepulse inhibition in isolation-reared mice. MGS0028 attenuated hyperactivity and aggressive behaviors in isolation-reared mice. The agonist also reversed isolation rearing–induced deficits of prepulse inhibition. On the other hand, MGS0028 did not affect locomotor activity and prepulse inhibition in group-reared mice. These results suggest that the metabotropic glutamate 2/3 receptor agonist, MGS0028, is a potential compound for the treatment of psychiatric disorders.

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Multimodal analgesic approaches to manage acute and chronic pain are commonly used in humans. Here, we attempted to characterize a synergistic interaction between fentanyl, tramadol, and paracetamol on the inhibition of nociception in a model of visceral pain in mice. The three-drug combined treatment displayed a potent synergistic antinociceptive effect, together with a significant reduction of gastrointestinal transit inhibition. Furthermore, selective μ- and κ-opioid receptor antagonists reversed these synergistic antinociceptive effects, thus suggesting a pivotal role of the opioid system. Overall, this study presents accurate pre-clinical data that might be useful to improve the clinical management of opioid-mediated analgesia.

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