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Histamine has the ability to influence the activity of immune cells including neutrophils and plays a pivotal role in inflammatory processes, which are a complex network of cellular and humoral events. One of the main functions manifested by activated neutrophils is oxidative burst, which is linked to the production of reactive oxygen species; therefore, the effects of histamine receptor agonists and antagonists on the oxidative burst of neutrophils is reviewed. A role for the well-characterized histamine H1 and H2 receptors in this process is discussed and compared to that of the recently discovered H4 receptor., (© 2013 The Authors. British Journal of Pharmacology © 2013 The British Pharmacological Society.)

The role of the basolateral amygdala (BLA) in the consolidation of aversive memory is well established. Here we investigate the involvement of the histaminergic system in BLA on this variable. Rats were chronically implanted with bilateral cannulae in the BLA and after recovery were trained in a one-trial step-down inhibitory avoidance task. Immediately after training histaminergic compounds either alone or in combination were infused through the cannulae. Memory was assessed in test sessions carried out 24 h after the training session. Post-training histamine (1-10 nmol; 0.5 μl/side) enhanced consolidation and the histamine H₃ receptor antagonist thioperamide (50 nmol; 0.5 μl/side) impaired memory consolidation. The effect was shared by the histamine N-methyltransferase inhibitor SKF-91844 (50 nmol; 0.5 μl/side) as well as by the H₃ receptor agonist imetit (10 nmol; 0.5 μl/side). The promnesic action of histamine was unaffected by the H₁ receptor antagonist pyrilamine (50 nmol; 0.5 μl/side). The H1 receptor agonist pyridylethylamine (10 nmol; 0.5 μl/side), the H₂ agonist dimaprit (10 nmol; 0.5 μl/side) and the H₂ antagonist ranitidine (50 nmol; 0.5 μl/side) were ineffective. Histaminergic compounds infused into the BLA had no effect on open-field or elevated plus-maze behaviour. The data show that histamine induces a dose-dependent mnemonic effect in rats and indicate that this reflects a role of endogenous histamine in the BLA mediated by H₃ receptors.

The histamine H4 receptor (H4R) is expressed primarily on cells involved in inflammation and immune responses. Recently, it has been reported the functional expression of H4R within neurons of the central nervous system, but their role has been poorly understood. The present study aimed to elucidate the physiopathological role of cerebral H4R in animal models by the intracerebroventricular administration of the H4R agonist VUF 8430 (20-40 μg per mouse). Selectivity of results was confirmed by the prevention of the effects produced by the H4R antagonist JNJ 10191584 (3-9 mg/kg p.o.). Neuronal H4R activation induced acute thermal antinociception, indicating that neuronal histamine H4R might be involved in the production of antinociception in the absence of an inflammatory process. An anxiolytic-like effect of intensity comparable to that exerted by diazepam, used as reference drug, was produced in the light-dark box test. VUF 8430 reversed the scopolamine-induced amnesia in the passive avoidance test and showed anorexant activity in food deprived mice. Conversely, the H4R activation did not modify the immobility time in the tail suspension test. Rotarod performance test was employed to demonstrate that the effects observed following the administration of VUF 8430 and JNJ 10191584 were not due to impaired motor function of animals. Furthermore, both compounds did not alter spontaneous mobility and exploratory activity in the hole board test. These results show the antinociceptive, antiamnesic, anxiolytic and anorexant effects induced by neuronal H4R agonism, suggesting that H4 modulators may have broader utility further the control of inflammatory and immune processes., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Experiments on isolated preparations of varicose human great saphenous vein revealed different sensitivity of the distal and proximal portions to P2X receptor agonist α,β-methylene-ATP, but not to norepinephrine and histamine. It is suggested that restructuring of the P2 receptor system plays an important role in the pathogenesis of varicose veins, which affects the trunk of the great saphenous vein in varying degrees.

There is evidence that H2R blockade improves ischemia/reperfusion (I/R) injury, but the underlying cellular mechanisms remain unclear. Histamine is known to increase vascular permeability and induce apoptosis, and these effects are closely associated with endothelial and mitochondrial dysfunction, respectively. Here, we investigated whether activation of the histamine H2 receptor (H2R) exacerbates myocardial I/R injury by increasing mitochondrial and endothelial permeability. Serum histamine levels were measured in patients with coronary heart disease, while the influence of H2R activation was assessed on mitochondrial and endothelial function in cultured cardiomyocytes or vascular endothelial cells, and myocardial I/R injury in mice. The serum histamine level was more than twofold higher in patients with acute myocardial infarction than in patients with angina or healthy controls. In neonatal rat cardiomyocytes, histamine dose-dependently reduced viability and induced apoptosis. Mitochondrial permeability and the levels of p-ERK1/2, Bax, p-DAPK2, and caspase 3 were increased by H2R agonists. In cultured human umbilical vein endothelial cells (HUVECs), H2R activation increased p-ERK1/2 and p-moesin levels and also enhanced permeability of HUVEC monolayer. All of these effects were abolished by the H2R blocker famotidine or the ERK inhibitor U0126. After I/R injury or permanent ischemia, the infarct size was reduced by famotidine and increased by an H2R agonist in wild-type mice. In H2R KO mice, the infarct size was smaller; myocardial p-ERK1/2, p-DAPK2, and mitochondrial Bax were downregulated. These findings indicate that H2R activation exaggerates myocardial I/R injury by promoting myocardial mitochondrial dysfunction and by increasing cardiac vascular endothelial permeability.

G protein-coupled receptor signaling does not result from sequential activation of a linear pathway of proteins/enzymes, but rather from complex interactions of multiple, branched signaling routes, i.e., signaling networks. In this work we present an exhaustive study of the cross-talk between H1 and H2 histamine receptors (H1R and H2R) in U937 cells and Chinese hamster ovary-transfected cells. By desensitization assays we demonstrated the existence of a crossdesensitization between both receptors independent of protein kinase A or C. H1R-agonist stimulation inhibited cell proliferation and induced apoptosis in U937 cells following treatment of 48 hours. H1R-induced antiproliferative and apoptotic response was inhibited by an H2R agonist suggesting that the cross-talk between both receptors modifies their function. Binding and confocal microscopy studies revealed cointernalization of both receptors upon treatment with the agonists. To evaluate potential heterodimerization of the receptors, sensitized emission fluorescence resonance energy transfer experiments were performed in human embryonic kidney 293T cells using H1R-cyan fluorescent protein and H2R-yellow fluorescent protein. To our knowledge these findings may represent the first demonstration of agonist-induced heterodimerization of the H1R and H2R. In addition, we also show that the inhibition of the internalization process did not prevent receptor crossdesensitization, which was mediated by G protein-coupled receptor kinase 2. Our study provides new insights into the complex signaling network mediated by histamine and further knowledge for the rational use of its ligands.

The accessory medulla (aMe) is the pacemaker that controls circadian activity rhythms in the cockroach Rhyparobia maderae. Not much is known about the classical neurotransmitters of input pathways to the cockroach circadian system. The circadian pacemaker center receives photic input from the compound eye, via unknown excitatory and GABAergic inhibitory entrainment pathways. In addition, neuropeptidergic inputs couple both pacemaker centers. A histamine-immunoreactive centrifugal neuron connects the ventral aMe with projection areas in the lateral protocerebrum and may provide non-photic inputs. To identify neurotransmitters of input pathways to the circadian clock with Fura-2-dependent Ca(2+) imaging, primary cell cultures of the adult aMe were stimulated with acetylcholine (ACh), as the most prominent excitatory, and histamine, as common inhibitory neurotransmitter. In most of aMe neurons, ACh application caused dose-dependent increases in intracellular Ca(2+) levels via ionotropic nicotinic ACh receptors. These ACh-dependent rises in Ca(2+) were mediated by mibefradil-sensitive voltage-activated Ca(2+) channels. In contrast, histamine application decreased intracellular Ca(2+) levels in only a subpopulation of aMe cells via H2-type histamine receptor chloride channels. Thus, our data suggest that ACh is part of the light entrainment pathway while histamine is involved in a non-photic input pathway to the ventral circadian clock of the Madeira cockroach.

By using brain slice preparations and extracellular recordings, the effect of histamine on spontaneous firing activities of neurons in the inferior vestibular nucleus (IVN), a key structure responsible for integration of vestibular, multisensory, and cerebellar inputs, in rats was investigated. Perfusing slices with histamine (1-10μM) elicited an excitatory response on IVN neurons. The responses were not blocked by low Ca(2+)/high Mg(2+) medium, indicating a direct postsynaptic effect of the amine. Furthermore, the histamine-induced excitation was partially blocked by selective histamine H1 receptor antagonist mepyramine (1μM) and H2 receptor antagonist ranitidine (1μM), respectively. Co-application of mepyramine and ranitidine nearly totally antagonized the histamine-induced excitation. Additionally, both selective H1 receptor agonist 2-pyridylethylamine (30-300μM) and H2 receptor agonist dimaprit (10-100μM) effectively mimicked the excitatory action of histamine on IVN neurons. Moreover, selective H4 antagonist JNJ7777120 (10μM) and agonist VUF8430 (30-300μM) had no effect on IVN neurons. These results demonstrate that histamine excites IVN neurons via postsynaptic H1 and H2 rather than H4 receptors, and suggest that the central histaminergic system actively modulate all four major vestibular nuclei including the IVN and may subsequently influence the vestibular nuclei-related reflexes and functions., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Purpose: To learn whether locally expressed and systemic mediators might modulate the cholinergically induced transepithelial Cl(-) fluxes that underlie lacrimal fluid production., Methods: Reconstituted epithelial monolayers were exposed to a submaximal dose of the muscarinic agonist, carbachol (CCh), or to one of several paracrine mediators for 18 hours, then acutely stimulated with an optimal dose of CCh. Secretory Cl(-) fluxes were assessed as negative short-circuit currents (ISC)., Results: Exposure to IL-6 at concentrations of 1 and 10 ng/mL and IL-1β at 10 ng/mL significantly decreased CCh-induced Cl(-) secretion. Prolactin decreased CCh-induced Cl(-) secretion, but the extent of the decrease diminished as the prolactin concentration increased from 20 to 200 ng/mL. CCh, 10 μM, prevented CCh, 100 μM, from eliciting Cl(-) secretion. Exposure to histamine, 10 mM, prevented formation of confluent monolayers. Exposure to histamine, 1 mM, decreased CCh-induced Cl(-) secretion, whereas exposure to 5-HT, 1 mM, potentiated CCh-induced Cl(-) secretion., Conclusions: Chronic exposure to inflammatory cytokines may significantly impair cholinergically induced lacrimal fluid production. Concentrations of prolactin within the high range of normal values also may impair fluid production, but this effect is reversed at levels associated with pregnancy. Autonomic neurotransmitters and paracrine mediators that signal through different G protein-coupled receptors appear to exert varying influences, which range from complete suppression to potentiation of cholinergically induced fluid production. Thus, some hormones and paracrine mediators may impair secretion in apparently homeostatic glands as well as diseased glands, whereas mediators produced by certain immune cell infiltrates may actually enhance fluid formation.

Numerous studies have demonstrated that brain histamine plays a crucial role in learning and memory and histamine H3 receptor inverse agonists (H3R inverse agonists) have been proposed to treat cognitive disorders. Pitolisant (BF2.649, 1-{3-[3-(4-chlorophenyl)propoxy]propyl}piperidine, hydrochloride) was the first H3R inverse agonist that has been tested in human trials and is well tolerated. The present study investigated whether Pitolisant (0.625-20mg/kg, i.p.) improves consolidation and reconsolidation processes in the fear conditioning task in female C57BL/6J mice. We also tested whether Pitolisant reverses memory deficits induced by the non-competitive N-methyl-d-aspartate (NMDA) antagonist dizocilpine (MK-801). Our results indicate that post-training systemic injections of Pitolisant facilitated consolidation of contextual fear memory and reversed amnesia induced by an i.p. injection of 0.12 mg/kg dizocilpine. In addition, none of the doses of Pitolisant we have tested after reactivation (reexposure to the context in which training took place 48 h earlier) affected reconsolidation, whereas dizocilpine disrupted it. However, Pitolisant was able to reverse the deficit in reconsolidation induced by 0.12 mg/kg dizocilpine. The present results are the first demonstration that Pitolisant is effective in improving consolidation processes in the fear condition task and add further evidence to its potential for treating cognitive disorders., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Antihistamines are thought to antagonize histamine and prevent it from binding to the histamine H1 receptor (H1R). However, recent studies indicate that antihistamines are classified into two groups, i.e., inverse agonists and neutral antagonists on the basis of their ability to down-regulate the constitutive activity of H1R. As H1R is an allergy-sensitive gene whose expression influences the severity of allergic symptoms, inverse agonists should more potently alleviate allergic symptoms than neutral antagonists by inhibiting H1R constitutive activity. Therefore, it is important to assess inverse agonistic activity of antihistamines. Here we report a novel assay method using HeLa cells expressing H1R endogenously for evaluation of inverse agonistic activity of antihistamines. Pretreatment with inverse agonists down-regulated H1R gene expression below to its basal level. On the other hand, basal H1R mRNA expression was unchanged by neutral antagonist pretreatment. Both inverse agonists and neutral antagonists suppressed histamine-induced H1R mRNA elevation. Classification of antihistamines on the basis of their suppressive activity of basal H1R gene expression was consistent with that of inositol phosphate accumulation in H1R-overexpressed cells. Our data suggest that the assay method using HeLa cells is more convenient and useful than the existing methods and may contribute to develop new antihistamines with inverse agonistic activity., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Aim: Histamine released from mast cell degranulation participates in the pathogenesis of ischemia/reperfusion injury. The purpose of our study was to define the role of histamine in hypoxia/reoxygenation mediated liver cell injury and to elucidate the underlying mechanism in vitro., Methods: Histamine alone or in combination with H1 receptor antagonist (pyrilamine), H2 receptor antagonist (cimetidine) or H3/4 receptor antagonist (thioperamide) at different concentrations before hypoxia was added to rat liver BRL-3A cell which was subjected to 24h hypoxia followed by 4h reoxygenation. Cell proliferation, apoptosis and the changes of ultrastructure were assessed, and MDA contents, SOD activities and ALT levels were quantified as well., Results: Histamine (from 10(-3) to 10(-9) M) did not affect the growth of BRL-3A cells without hypoxia treatment. However, histamine 10(-8)M significantly lowered the growth of BRL-3A cells challenged by hypoxia/reoxygenation, accompanied with concomitant elevations in MDA contents and decreases in SOD activities, all these changes were blocked by cimetidine, not by pyrilamine or thioperamide. However, histamine (above 10(-6) M) did not show exacerbating effects in BRL-3A cell subjected to hypoxia/reoxygenation., Conclusion: Histamine at low concentrations (10(-7)-10(-9) M) aggravates hypoxia/reoxygenation mediated BRL-3A damage through histamine H2 receptor., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Histamine exerts diverse effects on immune regulation through four types of histamine receptors (HRs). Among them, type 1 receptor (H1R) plays an important role in allergic inflammation. Dendritic cells (DCs), which express at least three types of HRs, are professional antigen-presenting cells controlling the development of allergic inflammation. However, the molecular mechanisms involved in H1R-mediated NF-ĸB signaling of DCs remain poorly defined., Methods: Bone-marrow (BM)-derived DCs (BM-DCs) were treated with H1R inverse agonists to interrupt basal H1R-mediated signaling. The crosstalk of H1R-mediated signaling and the NF-ĸB pathway was examined by NF-ĸB cellular activity using a luciferase reporter assay, NF-ĸB subunit analysis using Western blotting and TNF-α promoter activity using chromatin immunoprecipitation., Results: Blockage of H1R signaling by inverse agonists significantly inhibited TNF-α and IL-6 production of BM-DCs. H1R-specific agonists were able to enhance TNF-α production, but this overexpression was significantly inhibited by NF-ĸB inhibitor. The H1R inverse agonist ketotifen also suppressed cellular NF-ĸB activity, suggesting crosstalk between H1R and NF-ĸB signaling in DCs. After comprehensive analysis of NF-ĸB subunits, c-Rel protein expression was significantly down-regulated in ketotifen-treated BM-DCs, which led to inhibition of the promoter activity of TNF-α. Finally, adoptive transfer of the ketotifen-treated BM-DCs did not induce significant allergic airway inflammation compared to that of control cells in vivo., Conclusions: Our results suggest that c-Rel controls H1R-mediated proinflammatory cytokine production in DCs. This study provides a potential mechanism of H1R-mediated signaling and NF-ĸB pathway crosstalk in allergic inflammation., (Copyright © 2012 S. Karger AG, Basel.)

Histamine is a biogenic amine that exerts its biological effects as a neurotransmitter and local mediator via four histamine receptor (HR) subtypes (H(x)Rs) - H(1)R, H(2)R, H(3)R, and H(4)R - belonging to the superfamily of G-protein-coupled receptors (GPCRs). All four H(x)Rs exhibit pronounced differences in agonist and/or antagonist pharmacology among various species orthologs. The species differences constitute a problem for animal experiments and drug development. This problem applies to GPCRs with diverse ligands. Here, we summarize our current knowledge on H(x)R orthologs as a case study for species-dependent activity of GPCR ligands. We show that species-specific pharmacology also provides unique opportunities to study important aspects of GPCR pharmacology in general, including ligand-binding sites, the roles of extracellular domains in ligand binding and receptor activation, agonist-independent (constitutive) receptor activity, thermodynamics of ligand/receptor interaction, receptor-activation mechanisms, and ligand-specific receptor conformations., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The superior vestibular nucleus (SVN), which holds a key position in vestibulo-ocular reflexes and nystagmus, receives direct hypothalamic histaminergic innervations. By using rat brainstem slice preparations and extracellular unitary recordings, we investigated the effect of histamine on SVN neurons and the underlying receptor mechanisms. Bath application of histamine evoked an excitatory response of the SVN neurons, which was not blocked by the low-Ca(2+)/high-Mg(2+) medium, indicating a direct postsynaptic effect of the amine. Selective histamine H1 receptor agonist 2-pyridylethylamine and H2 receptor agonist dimaprit, rather than VUF8430, a selective H4 receptor agonist, mimicked the excitation of histamine on SVN neurons. In addition, selective H1 receptor antagonist mepyramine and H2 receptor antagonist ranitidine, but not JNJ7777120, a selective H4 receptor antagonist, partially blocked the excitatory response of SVN neurons to histamine. Moreover, mepyramine together with ranitidine nearly totally blocked the histamine-induced excitation. Immunostainings further showed that histamine H1 and H2 instead of H4 receptors existed in the SVN. These results demonstrate that histamine excites the SVN neurons via postsynaptic histamine H1 and H2 receptors, and suggest that the central histaminergic innervation from the hypothalamus may actively bias the SVN neuronal activity and subsequently modulate the SVN-mediated vestibular functions and gaze control., (Copyright © 2012 S. Karger AG, Basel.)

Objective: In this work, role of hypoxia in respiratory system on live and exited newborns weight 250-3000g.) which have died due to different reasons is studied., Methods: Response of tracheal rings in acetylcholine and histamine in different molar concentrations (10(-4), 10(-3), 10(-2), 10(-1) mol/dm3) was monitored. Study of the tracheal smooth musculature (TSM) tonus was performed in 12 tracheal preparations obtained from the newborns exited due to different reasons., Results: Based on the functional analysis of the isolated tracheal preparations, we have concluded that the cases born with lung atelectasis have caused significant response ofTSM to Acetylcholine and Histamine (p > 0.01). In cases of control group, which has exited due to different reasons from lung inflammatory processes (e.g.: pneumonia, bronchopneumonia, cerebral hemorrhage), Acetylcholine and Histamine have also caused significant constriction of tracheal smooth musculature., Conclusion: Results suggest that exited cases with lung atelectasis (hypoxemia) and cases of lung inflammatory processes have significant constrictor action to Acetylcholine and Histamine in tracheobronchial system.

Background/aims: Histamine remains the main mediator of allergic conjunctivitis and induces interleukin (IL)-6 and IL-8 production in human conjunctival epithelial cells (HCEC). The purpose of the present study was to determine whether histamine induced IL-6 and IL-8 expression in HCEC, and to describe the relationship between human calcium-activated chloride channel (hCLCA) 1 activity and IL-6 and IL-8 expression., Methods: HCEC were isolated from human conjunctiva and cultured at an air-liquid interface. IL-6 and IL-8 mRNA expression was examined by real-time PCR, and IL-6 and IL-8 secretion was measured by ELISA after stimulation of HCEC with histamine., Results: Histamine upregulated IL-6 and IL-8 expression and IL-6 and IL-8 secretion in a dose-dependent manner in HCEC. Niflumic acid (NFA), an hCLCA blocker, reduced histamine-induced IL-6 and IL-8 expression., Conclusion: Histamine-induced IL-6 and IL-8 production could be attenuated by NFA, an hCLCA blocker., (Copyright © 2013 S. Karger AG, Basel.)

Aim: The aim of our study was to investigate the functional roles of H3R agonist and antagonist in the development of hepatic functions impairment in immunized rabbits., Methods: The study comprised of six groups containing 18 rabbits in each. Group-I (negative control) and group-II (positive control) received sterile distilled water intramuscularly while Group III-VI received histamine (100 µgkg-1, s.c.), R-[-]-α-methylhistamine (H3R-agonist, 10 µgkg-1, s.c.), iodophenpropit (H3R-antagonist, 1 µgkg-1, i.m.), and the combination of iodophenpropit (1 µgkg-1, i.m.) plus histamine (100 µgkg-1, s.c.), respectively, b.i.d. (12 hours [8 am and 8 pm]) for 10 days. Groups II-VI were immunized on day 3 with intravenous injection of sheep red blood cells (1×109 cells/ml)., Results: On each experimental day, the mean values of serum enzymes and bilirubin in group-I and group-II showed no changes while in groups III, IV, V, and VI, these enzymes and bilirubin levels showed significant changes (p<0.05), when compared with their values within the group. Profile of ALT and AST production revealed that ALT and AST levels moderately were changed due to degeneration of the liver., Conclusion: Our results suggest that R-[-]-α-methylhistamine showed moderate, and histamine and iodophenpropit showed mild degeneration of liver functions; while iodophenpropit plus histamine showed hepatic functions similar to control group. This study suggests that H3R antagonist in combination with histamine may be a non-toxic therapeutic target for histamine research (Fig. 7, Ref. 28). Text in PDF www.elis.sk.

In acute experiments in conscious rabbits was studied protective action of selective blocker of histamine H3-receptor betahistine (2mg/kg i/v) against histological changes in precentral and postcentral gyrus, as well as in temporal lobe of cerebral cortex, thalamus, hypothalamus, and cerebellum, arising in case of modeling of whole body wide-frequency vibration. Betahistine attenuates edematous and degenerative changes in neurons and reciprocal glial reaction, caused by vibration, but does not eliminate edema in perivascular spaces. This effect may be related to the improvement of blood supply as a result of of vasodilatory action and decrease of oxygen consumption via vestibuloprotective effect.

The human histamine receptors hH(1)R and hH(2)R constitute important drug targets, and hH(3)R and hH(4)R have substantial potential in this area. Considering the species-specificity of pharmacology of H(x)R orthologs, it is important to analyze hH(x)Rs. Here, we summarize current knowledge of hH(x)Rs endogenously expressed in human cells and hH(x)Rs recombinantly expressed in mammalian and insect cells. We present the advantages and disadvantages of the various systems. We also discuss problems associated with the use of hH(x)R antibodies, an issue of general relevance for G-protein-coupled receptors (GPCRs). There is much greater overlap in activity of 'selective' ligands for other hH(x)Rs than the cognate receptor subtype than generally appreciated. Studies with native and recombinant systems support the concept of ligand-specific receptor conformations, encompassing agonists and antagonists. It is emerging that for characterization of hH(x)R ligands, one cannot rely on a single test system and a single parameter. Rather, multiple systems and parameters have to be studied. Although such studies are time-consuming and expensive, ultimately, they will increase drug safety and efficacy., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Mast cells (MC) occur normally in the testis with a species-specific distribution, yet their precise role remains unclear. Testicular MC express histidine decarboxylase (HDC), the unique enzyme responsible for histamine (HA) generation. Evidence to date supports a role for HA as a local regulator of steroidogenesis via functional H₁ and H₂ receptor subtypes (HRH1 and HRH2, respectively) present in Leydig cells. Given that HA is a well-known modulator of physiological and pathological proliferation in many different cell types, we aimed in the present study to evaluate whether HA might contribute to the regulation of Leydig cell number as well as to the control of androgen production. Herein, we demonstrate, to our knowledge for the first time, that MA-10 Leydig tumor cells, but not normal immature Leydig cells (ILC), exhibit a proliferative response upon stimulation with HA that involves HRH2 activation, transient elevation of cAMP levels, and increased extracellular signal-regulated kinase (ERK) phosphorylation. Our results also reveal that MA-10 cells show significantly heightened HDC expression compared to normal ILC or whole-testicular lysate and that inhibition of HDC activity decreases MA-10 cell proliferation, suggesting a possible correlation between autocrine overproduction of HA and abnormally increased proliferation in Leydig cells. The facts that germ cells are also both source and target of HA and that multiple testicular cells are susceptible to HA action underline the importance of the present study, which we hope will serve as a first step for further research into regulation of non-MC-related HDC expression within the testis and its significance for testicular function.

Purpose: The present work was carried out to reveal the involvement of histamine receptors at the neuro-melanophore junction of teleost, Oreochromis mossambicus., Methods: The isolated scale melanophores were assayed using the mean melanophore size index and their responses were recorded in presence of various concentrations of histamine along with H(1) and H(2) receptor specific agonists and antagonist and potentiator compound 48/80., Results: Melanophores showed high sensitivity to histamine and its specific agonists. Histamine caused a dose-dependent pigment aggregation, whereas 2-(2-Pyridyl) ethylamine (PEA), a specific H(1)R agonist also caused aggregation in a similar manner. Conversely, amthamine, a specific H(2)R agonist resulted in pigment dispersion. The effects were antagonized by mepyramine; specific H(1)R antagonist and ranitidine a specific H(2)R antagonist., Conclusion: It is concluded that O. mossambicus melanophores have both H(1) and H(2) receptors which mediate melanophore aggregation and dispersion respectively. Compound 48/80 augmented the melanin-aggregating and dispersing effects of PEA and amthamine. It is suggested that the effect of histamine is directly mediated through H1 and H2 receptors, whereas H1Rs may be predominantly involved in the aggregatory responses.

Post-consolidation immunotherapy with histamine dihydrochloride and interleukin-2 has been shown to improve leukemia-free survival in acute myeloid leukemia in a phase III trial. For this study, treatment efficacy was determined among 145 trial patients with morphological forms of acute myeloid leukemia as defined by the French-American-British classification. Leukemia-free survival was strongly improved in M4/M5 (myelomonocytic/monocytic) leukemia but not in M2 (myeloblastic) leukemia. We also analyzed histamine H(2) receptor expression by leukemic cells recovered from 26 newly diagnosed patients. H(2) receptors were typically absent from M2 cells but frequently expressed by M4/M5 cells. M4/M5 cells, but not M2 cells, produced reactive oxygen species that triggered apoptosis in adjacent natural killer cells. These events were significantly inhibited by histamine dihydrochloride. Our data demonstrate the presence of functional histamine H(2) receptors on human AML cells and suggest that expression of these receptors by leukemic cells may impact on the effectiveness of histamine-based immunotherapy.

The simpler, the better: H(3) histamine receptor (H(3)R) are of interest as therapeutic targets in cognitive and somnolence disorders. Here, lead optimization of H(3)R inverse agonists bearing a thiazolo[5,4-c]piperidine group gave rise to a clinical candidate with a much simpler unprecedented benzamide scaffold, displaying decreased hERG activity while maintaining high brain receptor occupancies., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Vitiligo is a progressive depigmenting disorder. Histamine has been shown to induce melanogenesis via histamine receptor 2, suggesting the possibility of histamine as a repigmenting agent for the treatment of vitiligo. However, the role and signaling mechanism of histamine are still unclear in melanogenesis, especially in relation to growth-differentiation factor-15, which is a protein belonging to transforming growth factor beta and found to be overexpressed in metastatic or malignant melanoma. We found that histamine induces growth-differentiation factor-15 in melanoma cell lines such as SK-MEL-2, B16F10, and melan-a cells. Therefore, in the present study, the role of growth-differentiation factor-15 in histamine-induced melanogenesis was investigated using gene silencing or overexpression of growth-differentiation factor-15 and histamine related compounds such as histamine, amthamine, and cimetidine. Gene silencing of growth-differentiation factor-15 suppressed histamine-induced proliferation, melanin production, tyrosinase activity, and chemotactic migration of SK-MEL-2 cells. Histamine-induced expression of tyrosinase, tyrosinase-related protein 1, and tyrosinase-related protein 2 was also suppressed by growth-differentiation factor-15 gene silencing. On the other hand, overexpression of growth-differentiation factor-15 using a plasmid containing growth-differentiation factor-15 in SK-MEL-2 cells increased melanin production and chemotactic migration. Amthamine induced expression of growth-differentiation factor-15 in a time and concentration dependent manner. Amthamine-induced expression of growth-differentiation factor-15 was suppressed by cimetidine. Our results suggest that growth-differentiation factor-15 is a new player in histamine-induced melanogenesis, which can help researchers to extend the knowledge of the role of the transforming growth factor beta family in melanogenesis and in skin pigment disorders such as vitiligo., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

We reported previously that natriuretic peptides, including brain natriuretic peptide (BNP), promote norepinephrine release from cardiac sympathetic nerves and dopamine release from differentiated pheochromocytoma PC12 cells. These proexocytotic effects are mediated by an increase in intracellular calcium secondary to cAMP/protein kinase A (PKA) activation caused by a protein kinase G (PKG)-mediated inhibition of phosphodiesterase type 3 (PDE3). The purpose of the present study was to search for novel means to prevent the proadrenergic effects of natriuretic peptides. For this, we focused our attention on neuronal inhibitory Gα(i/o)-coupled histamine H(3) and H(4) receptors. Our findings show that activation of neuronal H(3) and H(4) receptors inhibits the release of catecholamines elicited by BNP in cardiac synaptosomes and differentiated PC12 cells. This effect results from a decrease in intracellular Ca(2+) due to reduced intracellular cAMP/PKA activity, caused by H(3) and H(4) receptor-mediated PKG inhibition and consequent PDE3-induced increase in cAMP metabolism. Indeed, selective H(3) and H(4) receptor agonists each synergized with a PKG inhibitor and a PDE3 activator in attenuating BNP-induced norepinephrine release from cardiac sympathetic nerve endings. This indicates that PKG inhibition and PDE3 stimulation are pivotal for the H(3) and H(4) receptor-mediated attenuation of BNP-induced catecholamine release. Cardiac sympathetic overstimulation is characteristic of advanced heart failure, which was recently found not to be improved by the administration of recombinant BNP (nesiritide), despite the predicated beneficial effects of natriuretic peptides. Because excessive catecholamine release is likely to offset the desirable effects of natriuretic peptides, our findings suggest novel means to alleviate their adverse effects and improve their therapeutic potential.

Background and Purpose: Centrally acting histamine H(3) receptor ligands are proposed as potential treatments for obesity, although the value of inverse agonists at these receptors is still debated. Functional inhibition of H(3) autoreceptors activates neurones in a hypothalamic 'satiety' centre. The H(3) receptor antagonist, proxyfan was used as a tool to assess the action of histaminergic compounds in this model., Experimental Approach: We compared the actions of histamine on feeding with those of an H(3) receptor agonist (imetit) and inverse agonist (thioperamide) in rats and mice. Sites of action were identified by immunohistochemistry and the hypothalamic ventromedial nucleus (VMN) was investigated using electrophysiological techniques., Key Results: Central histamine or thioperamide decreased fast-induced feeding, whereas imetit increased feeding. Systemic thioperamide entered the brain to activate hypothalamic feeding centres and to reduce feeding without causing any adverse behaviours. Thioperamide activated neurones in the VMN through an action on histamine autoreceptors, whilst imetit had the opposite effect. Proxyfan administered alone did not affect either feeding or electrical activity. However, it blocked the actions of both thioperamide and imetit, acting as a neutral antagonist in this system., Conclusions and Implications: The H(3) receptor inverse agonist, thioperamide, potently reduced appetite without adverse behavioural effects. This action was blocked by proxyfan, acting as a neutral antagonist in this model and, therefore, this compound is useful in determining the selectivity of H(3) receptor-directed drugs. A major action of thioperamide is through presynaptic autoreceptors, inducing stimulation by endogenous histamine of postsynaptic H(1 ) receptors on anorectic hypothalamic neurones., (© 2012 The Authors. British Journal of Pharmacology © 2012 The British Pharmacological Society.)

The histamine H(2)-receptor (H(2)R) couples to G(S)-proteins and induces adenylyl cyclase-mediated cAMP accumulation. In human neutrophils and eosinophils, the H(2)R reduces chemotactic peptide-stimulated superoxide anion (O(2)(-)) formation. However, pharmacological characterization of the H(2)R in these cells is far from being complete. The aim of this study was to provide a comprehensive profiling of the H(2)R in neutrophils and eosinophils. Histamine inhibited O(2)(-) formation in human neutrophils more effectively than in eosinophils. H(2)R agonists mimicked the effects of histamine and H(2)R antagonists blocked the effects of histamine. We noticed multiple discrepancies in the potencies and efficacies of H(2)R agonists with respect to cAMP accumulation and inhibition of O(2)(-) formation in both cell types. There were also differences in the antagonist profiles between cAMP accumulation and inhibition of O(2)(-) formation in neutrophils. Moreover, the pharmacological profile of the recombinant H(2)R did not match the H(2)R profile in native cells. The H(2)R sequence identified in human neutrophils corresponds to the published H(2)R sequence, excluding the exclusive expression of a new H(2)R isoform as explanation for the differences. Very likely, the differences between ligands are explained by the existence of ligand-specific receptor conformations with unique affinities, potencies and efficacies. Thus, our data provide evidence for the notion that the concept of ligand-specific receptor conformations can be extended from recombinant systems to native cells., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Purpose: The purpose of this study was to determine the Ca(2+)-dependent cellular signaling pathways used by histamine to stimulate conjunctival goblet cell secretion., Methods: Cultured rat goblet cells were grown in RPMI 1640. Goblet cell secretion of high molecular weight glycoconjugates was measured by an enzyme-linked lectin assay. Intracellular [Ca(2+)] ([Ca(2+)](i)) was measured by loading cultured cells with the Ca(2+) sensitive dye fura-2. The level of [Ca(2+)](i) was measured using fluorescence microscopy. Extracellular regulated kinase (ERK) 2 was depleted using small interfering RNA (siRNA)., Results: Histamine-stimulated conjunctival goblet cell secretion of high molecular weight glycoproteins was blocked by removal of extracellular Ca(2+) and depletion of ERK2 by siRNA. Histamine increase in [Ca(2+)](i) was desensitized by repeated addition of agonist and blocked by a phospholipase C antagonist. Histamine at higher doses increased [Ca(2+)](i) by stimulating influx of extracellular Ca(2+), but at a lower dose released Ca(2+) from intracellular stores. Activation of each histamine receptor subtype (H(1)-H(4)) increased [Ca(2+)](i) and histamine stimulation was blocked by antagonists of each receptor subtype. The H(2) receptor subtype increase in [Ca(2+)](i) was cAMP dependent., Conclusions: We conclude that histamine activates phospholipase C to release intracellular Ca(2+) that induces the influx of extracellular Ca(2+) and activates ERK1/2 to stimulate conjunctival goblet cell mucous secretion, and that activation of all four histamine receptor subtypes can increase [Ca(2+)](i).

Background and Purpose: Betahistine, the main histamine drug prescribed to treat vestibular disorders, is a histamine H(3) receptor antagonist. Here, we explored the potential for modulation of the most recently cloned histamine receptor (H(4) receptor) to influence vestibular system function, using a selective H(4) receptor antagonist JNJ 7777120 and the derivate compound JNJ 10191584., Experimental Approach: RT-PCR was used to assess the presence of H(4) receptors in rat primary vestibular neurons. In vitro electrophysiological recordings and in vivo behavioural approaches using specific antagonists were employed to examine the effect of H(4) receptor modulation in the rat vestibular system., Key Results: The transcripts of H(4) and H(3) receptors were present in rat vestibular ganglia. Application of betahistine inhibited the evoked action potential firing starting at micromolar range, accompanied by subsequent strong neuronal depolarization at higher concentrations. Conversely, reversible inhibitory effects elicited by JNJ 10191584 and JNJ 7777120 began in the nanomolar range, without inducing neuronal depolarization. This effect was reversed by application of the selective H(4) receptor agonist 4-methylhistamine. Thioperamide, a H(3) /H(4) receptor antagonist, exerted effects similar to those of H(3) and H(4) receptor antagonists, namely inhibition of firing at nanomolar range and membrane depolarization above 100 µM. H(4) receptor antagonists significantly alleviated the vestibular deficits induced in rats, while neither betahistine nor thioperamide had significant effects., Conclusions and Implications: H(4) receptor antagonists have a pronounced inhibitory effect on vestibular neuron activity. This result highlights the potential role of H(4) receptors as pharmacological targets for the treatment of vestibular disorders., (© 2012 The Authors. British Journal of Pharmacology © 2012 The British Pharmacological Society.)

Histamine acts centrally to increase energy expenditure and reduce body weight by mechanisms not fully understood. It has been suggested that in the obese state hypothalamic histamine signaling is altered. Previous studies have also shown that histamine acting in the preoptic area controls thermoregulation. We aimed to study the influence of preoptic histamine on body temperature and energy homeostasis in control and obese mice. Activating histamine receptors in the preoptic area by increasing the concentration of endogenous histamine or by local injection of specific agonists induced an elevation of core body temperature and decreased respiratory exchange ratio (RER). In addition, the food intake was significantly decreased. The hyperthermic effect was associated with a rapid increase in mRNA expression of uncoupling proteins in thermogenic tissues, the most pronounced being that of uncoupling protein (UCP) 1 in brown adipose tissue and of UCP2 in white adipose tissue. In diet-induced obese mice histamine had much diminished hyperthermic effects as well as reduced effect on RER. Similarly, the ability of preoptic histamine signaling to increase the expression of uncoupling proteins was abolished. We also found that the expression of mRNA encoding the H1 receptor subtype in the preoptic area was significantly lower in obese animals. These results indicate that histamine signaling in the preoptic area modulates energy homeostasis by regulating body temperature, metabolic parameters and food intake and that the obese state is associated with a decrease in neurotransmitter's influence., (Copyright © 2012 IBRO. Published by Elsevier Ltd. All rights reserved.)

Histamine is involved in the central control of arousal, circadian rhythms and metabolism. The preoptic area, a region that contains thermoregulatory neurons is the main locus of histamine modulation of body temperature. Here we report that in mice, histamine activates H(2) subtype receptors in the medial preoptic nucleus (MPON) and induces hyperthermia. We also found that a population of glutamatergic MPON neurons express H(2) receptors and are excited by histamine or H(2) specific agonists. The agonists decreased the input resistance of the neuron and increased the depolarizing "sag" observed during hyperpolarizing current injections. Furthermore, at -60 mV holding potential, activation of H(2) receptors induced an inward current that was blocked by ZD7288, a specific blocker of the hyperpolarization activated cationic current (I(h)). Indeed, activation of H(2) receptors resulted in increased I(h) amplitude in response to hyperpolarizing voltage steps and a depolarizing shift in its voltage-dependent activation. The neurons excited by H(2) specific agonism expressed the HCN1 and HCN2 channel subunits. Our data indicate that at the level of the MPON histamine influences thermoregulation by increasing the firing rate of glutamatergic neurons that express H(2) receptors., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Itch and pain are common symptoms in skin disease. It has been suggested that negative emotions may play a role in itch and pain. To date, however, the role of emotions has only been studied for pain in experimental studies, not yet for itch., Objectives: To investigate the effects of negative and positive emotions on the sensitivity to itch and pain., Methods: Film fragments were used to induce a negative or positive emotional state in healthy women. Itch and pain were induced using the following somatosensory stimuli: electrical stimulation, histamine iontophoresis and the cold pressor test., Results: Results showed that the scores for itch and pain evoked by histamine and the cold pressor test, respectively, were significantly higher in the negative than in the positive emotion condition, whereas tolerance thresholds to electrical stimulation and the cold pressor test, and stimulus unpleasantness scores did not differ between the two conditions., Conclusions: These findings for the first time indicate in an experimental design that emotions play a role in sensitivity to somatosensory sensations of both itch and pain., (© 2012 The Authors. BJD © 2012 British Association of Dermatologists.)

After depletion of intracellular Ca2+ stores the capacitative response triggers an extracellular Ca2+ influx through store-operated channels (SOCs) which refills these stores. Our objective was to explore if human umbilical artery smooth muscle presented this response and if it was involved in the mechanism of serotonin- and histamine-induced contractions. Intracellular Ca2+ depletion by a Ca(2+)-free extracellular solution followed by Ca2+ readdition produced a contraction in artery rings which was inhibited by the blocker of Orai and TRPC channels 2-aminoethoxydiphenyl borate (2-APB), suggesting a capacitative response. In presence of 2-APB the magnitude of a second paired contraction by serotonin or histamine was significantly less than a first one, likely because 2-APB inhibited store refilling by capacitative Ca2+ entry. 2-APB inhibition of sarcoplasmic reticulum Ca2+ release was excluded because this blocker did not affect serotonin force development in a Ca(2+)-free solution. The PCR technique showed the presence of mRNAs for STIM proteins (1 and 2), for Orai proteins (1, 2 and 3) and for TRPC channels (subtypes 1, 3, 4 and 6) in the smooth muscle of the human umbilical artery. Hence, this artery presents a capacitative contractile response triggered by stimulation with physiological vasoconstrictors and expresses mRNAs for proteins and channels previously identified as SOCs.

Objective: Ischemic preconditioning and some drugs can protect tissues from injury by preserving microcirculation. This study evaluated vascular permeability in a hamster cheek pouch preparation using either short ischemic periods or bradykinin as preconditioning stimuli followed by 30 min of ischemia/reperfusion., Method: Sixty-six male hamsters were divided into 11 groups: five combinations of different ischemic frequencies and durations (one, three or five shorts periods of ischemia, separated by one or five minutes) with 10 min intervals between the ischemic periods, followed by 30 min ischemia/reperfusion; three or five 1 min ischemic periods with 10 min intervals between them followed by the topical application of histamine (2 µM); bradykinin (400 nM) followed by 30 min of ischemia/reperfusion; and three control groups (30 min of ischemia/reperfusion or histamine or bradykinin by themselves). Macromolecular permeability was assessed by injection of fluorescein-labeled dextran (FITC-dextran, MW= 150 kDa; 250 mg/Kg body weight), and the number of leaks/cm2 was counted using an intravital microscope and fluorescent light in the cheek pouch., Results: Plasma leakage (number of leaks/cm²) was significantly reduced by preconditioning with three and five 1 min ischemic periods, one and three 5 min ischemic periods and by bradykinin. Histamine-induced macromolecular permeability was also reduced after three periods of 5 min of ischemia., Conclusion: Short ischemic periods and bradykinin can function as preconditioning stimuli of the ischemia/reperfusion response in the hamster cheek pouch microcirculation. Short ischemic periods also reduced histamineinduced macromolecular permeability.

Histamine is a potent mediator in allergic inflammation with immunomodulatory properties. Since histamine was described to inhibit IL-12 production in human APCs, we hypothesized that also the expression of IL-27, a newly described member of the IL-12 family, which is present in inflammatory skin lesions, is modulated by histamine. Stimulation of human monocytes with histamine resulted in significant reduction of TLR ligand-induced IL-27 production in human monocytes. IL-27 subunits, p28 and EBI3, were down-regulated at the mRNA and protein level, whereas other cytokines, such as IL-6, IL-10, and TNF-α, were not influenced. Studies with histamine receptor-specific agonists and antagonists showed that the down-regulation of IL-27 was mediated via H(2)R and H(4)R but not H(1)R and H(3)R. Human KCs treated with supernatants of histamine-prestimulated monocytes induced significantly less CXCL10 than supernatants containing high levels of IL-27. DCs from H(4)R(-/-) mice responded to TLR simulation with higher IL-27 production as compared with WT mice. The down-regulation of IL-27 by histamine might be a new mechanism in the pathogenesis of inflammatory skin diseases, in particular, if increased concentrations of histamine are present at sites of inflammation, such as in chronic eczema and psoriasis.

The lack of classical lymph vessels within brain tissue complicates immune surveillance of the CNS, and therefore, cellular emigration out of the CNS parenchyma requires alternate pathways. Whereas invasion of blood-derived mononuclear cells and their transformation into ramified, microglia-like cells in areas of axonal degeneration across an intact BBB have been demonstrated, it still remained unclear whether these cells reside permanently, undergo apoptosis, or leave the brain to present antigen in lymphoid organs. With the use of ECL of mice and injection of GFP-expressing monocytes, we followed the appearance of injected cells in spleen and LNs and the migratory pathways in whole-head histological sections. Monocytes migrated from the lesion site to deep CLNs, peaking in number at Day 7, but they were virtually absent in spleen and in superficial CLNs and inguinal LNs until Day 21 after lesion/injection. In whole-head sections, GFP monocytes were found attached to the olfactory nerves and located within the nasal mucosa at 48 hpi. Thus, monocytes are capable of migrating from lesioned brain areas to deep CLNs and use the cribriform plate as an exit route.

A novel class of benzocinnolinones analogs of irdabisant were designed and synthesized as histamine H3R antagonists/inverse agonists. Modifications to the pyridazinone portion of the core and linker led to the identification of molecules with excellent target potency and selectivity with improved rat pharmacokinetic properties and reduced potential hERG liabilities., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Conclusion: The data suggest that histamine up-regulates MUC2 gene regulation and mucin production in airway epithelial cells through histamine 1 receptor (H1R). Histamine appears to play an important role in the early phase of mucin regulation, which might be effectively blocked by an H1R antagonist., Objective: Histamine is an important inflammatory mediator during the early phase of allergic response and antihistamine is known to have an ability to reduce mucus secretion in inflamed airways. The goal of the present study was to determine the effects of histamine on MUC2 gene expression and mucin secretion and to investigate the response to histamine 1 receptor (H1R) blocker in NCI-H292 cells and HM3-MUC2 cells., Methods: NCI-H292 cells, a human pulmonary mucoepidermoid carcinoma cell line, and HM3-MUC2 cells transfected with MUC2 promoter (-2,864/+19) pGL2 luciferase construct were used in the study. MUC2 mRNA expression was analyzed by RT-PCR for NCI-H292 cells and by luciferase assays for HM3-MUC2 cells. MUC2 protein production was determined by immunoassay and immunofluorescent stain in NCI-H292 cells., Results: Histamine increased MUC2 gene expression in a dose- and time-dependent manner. Peak response was reached at 12 h after histamine administration. MUC2 protein production was also dose-dependently increased, while it decreased with time in NCI-H292 cells. Pretreatment with histamine at a concentration of 1 mM induced MUC2 mRNAand protein production, which was equivalent to that caused by 10 µg/ml LPS, but less than that of 0.5 µM PMA. Histamine-induced MUC2 mRNA expression and mucin secretion were significantly suppressed by pretreatment with H1R antagonist.

Histamine is a mediator of inflammation in allergic disease and asthma. Stress activated protein kinases/c-jun N-terminal kinases (SAPK/JNK) are involved in asthma. This study examined the role of histamine receptors on the phosphorylation of SAPK/JNK in splenocytes. C57BL/6 mice splenocytes were treated with histamine (10⁻⁴ M to 10⁻¹¹ M), and its selective receptor agonists, phorbol 12 myristate 13-acetate (PMA) was used as a positive control, and phosphorylation of SAPK/JNK was determined. Histamine (10⁻⁴ M-10⁻⁸ M) inhibited phosphorylation of SAPK/JNK. H1R agonist betahistine (10⁻⁵ M) decreased SAPK/JNK phosphorylation and H2R agonist amthamine (10⁻⁵ M) did not show any significant effect. However, H3R agonist methimepip (10⁻⁶ M) and H4R agonist 4-methyl histamine (10⁻⁶ M), increased SAPK/JNK phosphorylation. We used TNFα knockout mice to determine if histamine regulated SAPK/JNK phosphorylation via TNFα. While the effects of histamine and H1 agonists were similar to that of wild type mice in inhibiting the phosphorylation of SAPK/JNK, the effects of H3 and H4 agonists differed in TNFα knockout mice splenocytes. Activation of H3 receptors decreased SAPK/JNK phosphorylation in TNFα knockout mice, as opposed to an increase in wild type mice, whereas H4 agonist did not show any significant effect on the phosphorylation of SAPK/JNK. This data showed that histamine acting through H4 receptors caused the phosphorylation of SAPK/JNK via TNFα. The role of H4 receptors in pro-inflammatory response is intriguing., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The histamine H4 receptor (H4R) is the youngest member of the histamine receptor family. Based on its predominant expression pattern in hematopoietic cells, the H4R is considered to be an interesting drug target for inflammatory disorders such as allergy and asthma. Since the identification and cloning of the H4R in 2000, drug discovery programs boosted the development of various H4R (specific) ligands. Differences between H4R orthologs in combination with available three-dimensional G protein-coupled receptor (GPCR) models have guided site-directed mutagenesis studies to gain insight in ligand binding and receptor activation. In addition, ongoing characterization of H4R-mediated signaling in transfected and native cells contributes to further unravel the (patho-) physiological functions of H4Rs.

Purpose: The purpose of this study was to determine the effect of histamine and its receptors on goblet cell secretion., Methods: Cultured rat and human goblet cells were grown in RPMI 1640. Goblet cell secretion of high molecular weight glycoconjugate was measured by an enzyme-linked lectin assay. Cultured rat goblet cells were homogenized and either RNA was isolated for RT-PCR or proteins were isolated for Western blot analysis for presence of histamine receptors subtypes H₁ through H₄. The localization of these receptors was determined in rat and human goblet cells by immunofluorescence microscopy., Results: Histamine stimulated goblet cell secretion in a concentration- and time-dependent manner. All four histamine receptors were present in cultured rat and human goblet cells. Use of agonists specific to individual histamine receptor subtypes indicated that the rank order of agonist stimulation was H₁ = H₃ > H₄ > H₂. Using antagonists specific to individual histamine receptor subtypes determined that H₂ and H₃, but not the H₁ and H₄, antagonists, inhibited histamine-stimulated conjunctival goblet cell secretion., Conclusions: Rat and human conjunctival goblet cells are a direct target of histamine, which induces secretion. All four histamine receptors are present in rat and human conjunctiva and are active in rat conjunctival goblet cells. These findings suggest that all four histamine receptor subtypes are important for conjunctival goblet cell secretion. Blockage of histamine receptor subtypes could prevent the excess mucus production associated with ocular allergy.

Background: Pruritus, or itch, is the most prevalent symptom of allergic and inflammatory skin disease. Although it is known that itch induces activation of a neural network in the brain, the temporal dynamics of the network as well as the pathophysiology and neurobiology are not well understood., Objectives: The study aimed to elucidate (i) the temporal dynamics of the itch response identified in earlier studies and (ii) the relationship between central and subjective responses to itch., Methods: Using a novel time-series analysis, we performed a double-blind, placebo-controlled, randomized, within-subject functional magnetic resonance imaging (fMRI) study of the cerebral processing of histamine-induced itch in healthy volunteers (n = 16) by tracking the 8-min period following a single skin prick., Results: Histamine-induced itch compared with saline resulted in significant area under the curve blood oxygen level dependent (BOLD) signal changes in the middle/superior temporal gyrus and right inferior frontal gyrus/insula. We observed negative itch-induced BOLD signal changes compared with saline in (i) the pregenual anterior cingulate cortex (ACC)/medial frontal gyrus, (ii) subgenual ACC/ventral striatum, (iii) bilateral temporal pole/parahippocampal gyrus and (iv) several regions within the cerebellum. We noted a trend significance in the left precentral gyrus part of the motor cortex. The BOLD signal change in several of these regions correlated with perception of itch intensity., Conclusions: In contrast to other fMRI studies we observed a multifocal negative signal. An improved understanding of both activated and deactivated brain regions during the itch response may in the long term facilitate development of more effective management strategies., (© 2012 The Authors. BJD © 2012 British Association of Dermatologists.)

Optimization of a series of aminomethyl ketone diamine H(3)R antagonists to reduce the brain exposure by lowering the pKa, led to molecules with improved pharmacokinetic properties. Compounds 9, 19, and 25 had high affinity for human H(3)R and demonstrated in vivo H(3)R functional activity in the rat dipsogenia model. Compound 9 displayed modest wake-promoting activity in the rat EEG/EMG model., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The effects of orexin-monoaminergic compound interactions on oxytocin release were studied in 14-day rat neurohypophyseal cell cultures prepared by an enzymatic dissociation technique. The oxytocin contents of the supernatants were determined by radioimmunoassay. Following the administration of orexin-A or orexin-B in increasing doses, significant changes were not observed in the oxytocin content of the supernatant media. The oxytocin level increased substantially in response to adrenaline, noradrenaline, serotonin, histamine, dopamine or K(+) treatment. Preincubation with orexin-A or orexin-B reduced the adrenaline-, histamine- or serotonin-induced oxytocin level increases, but the oxytocin concentrations of the supernatant media remained above the control level. There was no significant difference in decreasing effect between orexin-A and orexin-B. Neither orexin-A nor orexin-B induced changes in oxytocin release following monoaminergic compound treatment. The results indicate that the changes in oxytocin secretion induced by the monoaminergic system can be directly influenced by the orexin system. The effects of orexin on oxytocin release can be antagonized by an orexin-1 receptor-specific antagonist. It may be presumed that the orexins can play a role in the pathogenetic process of metabolic diseases (e.g. obesity) by reducing the effects of increased oxytocin release caused by monoaminergic compounds. The interactions between the monoaminergic and orexin systems regarding oxytocin secretion occur at both the hypothalamic and the neurohypophyseal levels., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Congenital insensitivity to pain with anhidrosis is a rare autosomal recessive hereditary disorder that is characterized by having both sensory neuropathy and anhidrosis. A 6-year-old Japanese boy presented with recurrent fever, lack of sweating, occult bone fractures and impaired pain sensation without mental retardation. Genetic analyses revealed compound heterozygous mutations in the NTRK1 gene that encodes TrkA, which is a receptor for nerve growth factor. While there were no apparent changes in the patient's dermal eccrine glands, the quantitative sudomotor axon reflex test with acetylcholine chloride revealed a complete loss of both the axon reflex-mediated and the directly activated sweat responses. On the other hand, the histamine prick test induced a normal weal response surrounded by a flare phenomenon. Notably, the patient felt both an itch sensation after histamine and a burning sensation after topical capsaicin application. Consistent with these findings, PGP9.5+ nerve fibre innervation of the papillary dermis was observed, although the fibres were completely absent around the eccrine glands. These findings suggest that there was a partial preservation of the nerve endings that express the H(1) receptor and/or TRPV1 in the upper dermis, even though there were mutations of the NTRK1 gene in this case., (© 2011 The Authors. BJD © 2011 British Association of Dermatologists.)

Background: There may be distinct pathways for transmission of histaminergic and nonhistaminergic itch, but all scratching behaviours elicited by histamine-dependent and histamine-independent pruritogens are diminished when spinal bombesin-recognized neurones are ablated., Aim: To investigate whether there is a difference in transmission of spinal itch signals between histamine-induced itch and nonhistamine-induced itch after neurotoxic destruction of spinal bombesin-recognized neurones., Methods: To ascertain the different relevance of spinal bombesin-recognized neurones in transmission of itch signals between these two classes of pruritogens, we determined the distribution of Fos-positive cells in the dorsal horn of spinal cord after stimulation with histamine (500 μg/site) and chloroquine (200 μg/site) in mice with spinal bombesin-recognized neurones ablated by intrathecal injection of bombesin-saporin (400 ng/5 μL)., Results: We found that after stimulation with both histamine and chloroquine, fewer Fos-positive cells were present in mice treated with bombesin-saporin compared with those treated with saporin alone. The reduction in Fos expression was greater with chloroquine than with histamine, and the distribution of Fos-positive cells was also different. We used biotin-labelled isolectin (IB)4, which labels one subset of C-fibres, and found that the percentages of Fos-positive cells in three areas (the dorsal to IB4-labelled region, the IB4-labelled region itself, and the ventral to IB4-labelled region) all changed significantly after intradermal injection of chloroquine, but not histamine, in mice treated with bombesin-saporin., Conclusions: These results suggest that spinal bombesin-recognized neurones are critical to both the histamine-dependent and histamine-independent pathways for itch, and that they mediate more nonhistaminergic than histaminergic sensation of itch in mice., (© The Author(s). CED © 2012 British Association of Dermatologists.)