Takahiko Shiina

Tachykinins and their functions in the gastrointestinal tract

Abstract.In the gastrointestinal tract, tachykinins are peptide neurotransmitters in nerve circuits that regulate intestinal motility, secretion, and vascular functions. Tachykinins also contribute to transmission from spinal afferents that innervate the gastrointestinal tract and have roles in the responses of the intestine to inflammation. Tachykinins coexist with acetylcholine, the primary transmitter of excitatory neurons innervating the muscle, and act as a co-neurotransmitter of excitatory neurons. Excitatory transmission is mediated through NK1 receptors (primarily on interstitial cells of Cajal) and NK2 receptors on the muscle. Tachykinins participate in slow excitatory transmission at neuro-neuronal synapses, through NK1 and NK3 receptors, in both ascending and descending pathways affecting motility. Activation of receptors (NK1 and NK2) on the epithelium causes fluid secretion. Tachykinin receptors on immune cells are activated during inflammation of the gut. Finally, tachykinins are released from the central terminals of gastrointestinal afferent neurons in the spinal cord, particularly in nociceptive pathways.

Macrophage-derived cytokine and nitric oxide profiles in type I and type II diabetes mellitus: effect of thymoquinone.

Comparing macrophage-derived cytokine and nitric oxide (NO) profiles in type I and type II diabetes mellitus (DM); and determining whether thymoquinone (TQ) has any modulatory effect were the main objectives of the present study. Peritoneal macrophages have been collected from Otsuka Long-Evans Tokushima Fatty (OLETF) as a model for type II DM and its control Long-Evans Tokushima Otsuka (LETO) rats, as well as from streptozotocin (STZ)-injected LETO ones as a model for type I DM. The cells were cultured and incubated with or without TQ (10 µM) in the absence or presence of lipopolysaccharide (LPS; 1 µg/ml). The same parameters have been also assessed in sera of the used animals with or without TQ treatment (3 mg/kg) under both LPS-stimulated (10 mg/kg) and unstimulated conditions. Nitrite, IL-1β and TNF-α were significantly higher in macrophage supernatants and sera of the acutely affected STZ-LETO rats either with or without LPS stimulation compared to corresponding controls. On the other hand, chronically diabetic OLETF rats’ macrophage supernatants showed significant decreases of IL-1β and TNF-α levels upon LPS stimulation or even without stimulation (IL-1β); and insignificant increase in nitrite concentration, which turned significant upon LPS stimulation. Sera of these animals, however, showed significant increase in TNF-α level. TQ normalised the elevated nitrite and cytokine profiles both in vitro and in vivo, yet had no significant effect on the already decreased parameters in chronically affected OLETF rats. These data suggest that there is a tendency for macrophage inflammatory products to increase in acute type I and to decrease in chronic type II DM; and that TQ has the potential to normalise the elevated levels of these macrophage-derived inflammatory mediators.

Contrasting effects of ghrelin and des-acyl ghrelin on the lumbo-sacral defecation center and regulation of colorectal motility in rats

Background  We have previously demonstrated that a centrally penetrant ghrelin receptor agonist enhances colorectal motility, through activation of the lumbo‐sacral defecation center (L6‐S1 region of the spinal cord) in rats. In the present study, we examined the effects of the native peptide and its non‐acylated counterpart in eliciting this stimulatory effect on colorectal motility.

Targeted disruption of MAIL, a nuclear IκB protein, leads to severe atopic dermatitis-like disease

MAIL (molecule-possessing ankyrin repeats induced by lipopolysaccharide) is a nuclear IκB protein that is also termed interleukin-1-inducible nuclear ankyrin repeat protein or inhibitor of nuclear factor κB (IκB) ζ. In this study, we generated Mail–/– mice to investigate the roles of MAIL in whole organisms. Mail–/– mice grew normally until 4–8 weeks after birth, when they began to develop lesions in the skin of the periocular region, face, and neck. MAIL mRNA and protein were constitutively expressed in the skin of wild type controls, especially in the keratinocytes. Serum IgE was higher in Mail–/– mice than in normal. Histopathological analysis indicated that the Mail–/– skin lesions appeared to be atopic dermatitis (AD) eczema with inflammatory cell infiltration. In addition, markedly elevated expression of some chemokines such as thymus and activation-regulated chemokine was detected in the Mail–/– skin lesions, similar to that observed in the skin of patients with AD. In Mail–/– mice, MAIL-deficient keratinocytes might be activated to produce chemokines and induce intraepidermal filtration of inflammatory cells, resulting in the onset of the AD-like disease. These findings suggest that MAIL is an essential molecule for homeostatic regulation of skin immunity. The Mail–/– mouse is a valuable new animal model for research on AD.

Inhibitory effects of zingerone, a pungent component of Zingiber officinale Roscoe, on colonic motility in rats

Ginger (rhizome of Zingiber officinale Roscoe) is an herbal medicine for the treatment of gastrointestinal disorders including constipation and diarrhea. Zingerone is a likely active constituent responsible for the antidiarrheal activity of ginger. The current study was designed to characterize pharmacological actions of zingerone on colonic motility. To evaluate pharmacological effects of zingerone on colonic motility, we used isolated colonic segments from rats, in which mechanical responses were recorded in the longitudinal direction. In addition, we evaluated the effects on colonic motility in vivo by measuring intraluminal pressure changes and expelled fluid volume from the colon in anesthetized rats. Zingerone was applied to the lumen of the colon to allow the drug to access from the mucosal side. Zingerone inhibited spontaneous contractile movements in the isolated colonic segments in a dose-dependent manner. The inhibitory effects of zingerone on colonic movements were not affected by pretreatment with capsazepine, a typical antagonist of transient receptor potential vanilloid 1. In addition, tetrodotoxin, a blocker of voltage-dependent sodium channels on neurons, did not affect the suppression of colonic movements by zingerone, suggesting that zingerone acts on the smooth muscles directly. Zingerone also attenuated colonic motility in vivo without affecting blood pressure and heart rate. The effects were reversible and reproducible. Our findings suggest that zingerone can inhibit colonic motility via direct action on smooth muscles. Zingerone might exert beneficial therapeutic effects on hypermotility-induced diarrhea by abrogating excessive gastrointestinal motility.

Tachykinins are involved in local reflex modulation of vagally mediated striated muscle contractions in the rat esophagus via tachykinin NK1 receptors

The objective of the present study was to investigate the hypothesis of the presence of a local neural reflex modulating the vagally mediated contractions of striated muscle in the rat esophagus and to determine the possible involvement of tachykinins in such a local neural reflex. Electrical stimulation of the vagus nerve evoked twitch contractile responses that were abolished by d-tubocurarine (5 microM). Capsaicin (1-100 microM) inhibited the vagally mediated twitch contractions o f the normal rat esophageal preparations concentration-dependently but not those of the neonatally capsaicin-treated ones. NG-nitro-L-arginine methyl ester (100 microM), a nitric oxide synthase inhibitor, blocked the inhibitory effect of capsaicin and exogenous application of a nitric oxide donor (1 mM) inhibited the vagally mediated twitch contractions. Capsaicin suppressed acetylcholine release from the normal rat esophageal segments evoked by vagus nerve stimulation but not that from the neonatally capsaicin-treated ones. A selective tachykinin NK1 receptor antagonist (0.1 or 1 microM) attenuated the inhibitory effect of capsaicin. However, antagonists of tachykinin NK2, tachykinin NK3 and calcitonin gene-related peptide receptors (1 microM) did not have any effect. A tachykinin NK1 receptor agonist (1 or 5 microM) inhibited the vagally mediated twitch contractions, which was prevented by NG-nitro-L-arginine methyl ester (100 microM). These data suggest that the rat esophagus might have a local neural reflex inhibiting the vagally mediated striated muscle motility, which consists of capsaicin-sensitive sensory neurons and myenteric nitrergic neurons, and that tachykinins might be involved in the neural reflex through tachykinin NK1 receptors.

Central A1-receptor activation associated with onset of torpor protects the heart against low temperature in the Syrian hamster

Body temperature drops dramatically during hibernation, but the heart retains the ability to contract and is resistant to induction of arrhythmia. Although adaptive changes in the heart prior to hibernation may be involved in the cold-resistant property, it remains unclear whether these changes are sufficient for maintaining cardiac pulsatility under an extreme hypothermic condition. We forcibly induced hypothermia in Syrian hamsters by pentobarbital anesthesia combined with cooling of the animals. This allows reproduction of a hypothermic condition in the absence of possible hibernation-specific reactions. Unlike hypothermia in natural hibernation, the forced induction of hypothermia caused atrioventricular block. Furthermore, J-waves, which are typically observed during hypothermia in nonhibernators, were recorded on an ECG. The origin of the J-wave seemed to be related to irreversible injury of the myocardium, because J-waves remained after recovery of body temperature. An abnormal ECG was also found when hypothermia was induced in hamsters that were well adapted to a cold and darkened environment or hamsters that had already experienced hibernation. These results suggest that acclimatization prior to hibernation does not have a crucial effect at least on acquisition of cardiac resistance to low temperature. In contrast, an abnormal ECG was not observed in the case of hypothermia induced by central administration of an adenosine A1-receptor agonist and subsequent cooling, confirming the importance of the adenosine system for inducing hibernation. Our results suggest that some specific mechanisms, which may be driven by a central adenosine system, operate for maintaining the proper cardiac pulsatility under extreme hypothermia.

Galanin modulates vagally induced contractions in the mouse oesophagus

Abstract  Nitrergic myenteric neurons co‐innervating motor endplates were previously shown to inhibit vagally induced contractions of striated muscle in the rodent oesophagus. Immunohistochemical demonstration of putative co‐transmitters, e.g. galanin, in enteric neurons prompted us to study a possible role of galanin in modulating vagally mediated contractions in an in vitro vagus nerve‐oesophagus preparation of the mouse. Galanin (1–16) (1–100 nmol L−1), in the presence of the peptidase inhibitor, phenanthroline monohydrate, inhibited vagally induced contractions in a concentration‐dependent manner (control: 100%; galanin 1 nmol L−1: 95.6 ± 1.6%; galanin 10 nmol L−1: 57.3 ± 6.5%; galanin 100 nmol L−1: 31.2 ± 8.1%, n = 5). The non‐selective galanin receptor antagonist, galantide (100 nmol L−1), blocked the inhibitory effect of galanin (10 nmol L−1) while the selective non‐galanin receptor 1 and galanin receptor 3 antagonists, M871 (1 μmol L−1) and SNAP37889 (100 nmol L−1), respectively, and the nitric oxide synthase inhibitor, NG‐nitro‐l‐arginine methyl ester (l‐NAME) (200 μmol L−1), failed to affect this galanin‐induced response. Simultaneous application of galantide (100 nmol L−1) and l‐NAME (200 μmol L−1) significantly reduced the inhibitory effect of capsaicin (30 μmol L−1) on vagally induced contractions when compared with its effect in the presence of l‐NAME alone or in combination with the selective galanin receptor 2 or 3 antagonists. An inhibitory effect of piperine on vagally induced contractions was reduced neither by galantide nor by l‐NAME. Immunohistochemistry revealed galanin immunoreactive myenteric neurons and nerve fibres intermingling with cholinergic vagal terminals at motor endplates. These data suggest that galanin from co‐innervating enteric neurons co‐operates with nitric oxide in modulating vagally induced contractions in the mouse oesophagus.

Neurally released ATP mediates endothelium‐dependent hyperpolarization in the circular smooth muscle cells of chicken anterior mesenteric artery

The object of the present study was to clarify the neurotransmitter(s) controlling membrane responses to electrical field stimulation (EFS) in the circular smooth muscle cells of first‐order branches of chicken anterior mesenteric artery. EFS (five pulses at 20 Hz, 1 ms) evoked a hyperpolarization of amplitude −21.6±1.2 mV, total duration 21.8±1.2 s and latency 641.7±81.9 ms. The response was tetrodotoxin‐sensitive and nonadrenergic noncholinergic (NANC) in nature. The NANC response was blocked by the nonspecific purinergic antagonist, suramin, indicating that the response is mediated by the neurotransmitter adenosine 5′‐triphosphate (ATP). Either desensitization or blockade of P2Y receptor with its putative agonist 2‐methylthioATP (1 μM for 30 min) or with its antagonist cibacron blue F3GA (10 μM), respectively, abolished the purinergic hyperpolarization. PPADS at concentrations up to 100 μM had no effect on the EFS‐induced response, indicating that this response is mediated through P2Y, but not P2X, receptor. In addition, the response was completely abolished by two specific P2Y1 receptor antagonists, namely, MRS 2179 (300 nM) and A3P5PS (10 μM). Removal of the endothelium abolished the purinergic hyperpolarization, which was converted, in some preparations, to a small depolarization, indicating that the hyperpolarizing response is endothelium‐dependent. The present study suggests that in first‐order branches of chicken anterior mesenteric artery, ATP released from perivascular nerves may diffuse to the endothelium‐activating P2Y1 receptor to induce release of an inhibitory substance that mediates hyperpolarization in the circular smooth muscle.

Extract of grains of paradise and its active principle 6-paradol trigger thermogenesis of brown adipose tissue in rats

Grains of paradise (GP) is a species of the ginger family, Zingiberaceae, extracts of which have a pungent, peppery taste due to an aromatic ketone, 6-paradol. The aim of this study was to explore the thermogenic effects of GP extracts and of 6-paradol. Efferent discharges from sympathetic nerves entering the interscapular brown adipose tissue were recorded. Intragastric injection of a GP extract or 6-paradol enhanced the efferent discharges of the sympathetic nerves in a dose-dependent manner. The enhanced nerve discharges were sustained for as long as 3h. The rats did not become desensitized to the stimulatory effects these compounds on sympathetic nerve activity. The tissue temperature of brown adipose tissue showed significant increase in rats injected with 6-paradol. These results demonstrate that GP extracts and 6-paradol activate thermogenesis in brown adipose tissue, and may open up new avenues for the regulation of weight loss and weight maintenance.