Histidine Decarboxylase mRNA Expression Research Articles

Histamine in murine narcolepsy: What do genetic and immune models tell us?

An increased number of histaminergic neurons, identified by labeling histidine‐decarboxylase (HDC) its synthesis enzyme, was unexpectedly found in patients with narcolepsy type 1 (NT1). In quest for enlightenment, we evaluate whether an increase in HDC cell number and expression level would be detected in mouse models of the disease, in order to provide proof of concepts reveling possible mechanisms of compensation for the loss of orexin neurons, and/or of induced expression as a consequence of local neuroinflammation, a state that likely accompanies NT1. To further explore the compensatory hypothesis, we also study the noradrenergic wake‐promoting system. Immunohistochemistry for HDC, orexin, and melanin‐concentrating hormone (MCH) was used to count neurons. Quantitative‐PCR of HDC, orexin, MCH, and tyrosine‐hydroxylase was performed to evaluate levels of mRNA expression in the hypothalamus or the dorsal pons. Both quantifications were achieved in genetic and neuroinflammatory models of narcolepsy with major orexin impairment, namely the orexin‐deficient (Orex‐KO) and orexin‐hemagglutinin (Orex‐HA) mice respectively. The number of HDC neurons and mRNA expression level were unchanged in Orex‐KO mice compared to controls. Similarly, we found no change in tyrosine‐hydroxylase mRNA expression in the dorsal pons between groups. Further, despite the presence of protracted local neuroinflammation as witnessed by the presence of reactive microglia, we found no change in the number of neurons nor the expression of HDC in Orex‐HA mice compared to controls. Importantly, no correlation was found in all conditions between HDC and orexin. Our findings indicate that, in mice, the expression of histamine and noradrenalin, two wake‐promoting systems, are not modulated by orexin level whether the lack of orexin is constitutive or induced at adult age, showing thus no compensation. They also show no recruitment of histamine by local neuroinflammation. Further studies will be needed to further define the role of histamine in the pathophysiology of NT1.

Th2 cell-derived histamine is involved in nasal Th2 infiltration in mice.

Histamine derived from mast cells and basophils plays important roles in inducing allergic symptoms. Although T cells also produce histamine, the involvement of the histamine produced from T cells has remained enigmatic. We sought to reveal the roles of T helper 2 (Th2) cell-derived histamine in nasal allergic disorders. The histamine production from Th2 cells was measured by EIA. The mRNA expression of histidine decarboxylase (HDC) was measured by real-time PCR. To investigate the roles of Th2 cell-derived histamine in vivo, we analyzed an antigen-specific Th2 cell transfer mouse model. Th2 cells produced histamine by T cell receptor stimulation, and these properties were specific for Th2 cells, but not Th1 cells and naïve CD4 T cells. The histamine produced from Th2 cells was involved in the infiltrations of Th2 cells in response to antigen exposure. These results suggest that Th2 cell-derived histamine play important roles in nasal allergic disorders.

Compound 48/80 reduces the crop-emptying rate, likely through a histamine-associated pathway in chicks

Infectious conditions are associated with reduced food passage through the digestive tract in both mammals and chicks; however, the precise mechanism mediating this response in chicks remains unclear. The purpose of the present study was to determine if mast cells, a blood cell type which plays an important role in the immune system, might affect food passage through the digestive tract in chicks. Specifically, we performed intraperitoneal (IP) injections of compound 48/80, an inducer of mast cell degranulation, and measured crop emptying. The IP injection of compound 48/80 significantly reduced the crop-emptying rate, but it did not affect the proventriculus to small intestine transit rate or the number of defecations. We also found that IP-injected histamine, which is secreted by mast cells, also reduced the crop-emptying rate. In addition, IP injection of 2-pyridylethylamine (histamine H1 receptor agonist), but not dimaprit, (R)-(−)-α-methylhistamine, and VUF8430 (histamine H2, H3, and H4 receptor agonists, respectively), reduced the crop-emptying rate, implying that histamine reduces the crop emptying rate via the histamine H1 receptor. Finally, we found that IP injection of compound 48/80 reduced mRNA expression of histidine decarboxylase, a rate-limiting enzyme for histamine synthesis, in the esophagus and proventriculus at 1 h and the proventriculus and duodenum at 3 h after the injection. In sum, the present study suggests that the degranulation of mast cells causes a reduction in the crop-emptying rate, possibly via the histamine pathway in chicks.

Respiratory Chlamydia Infection Induce Release of Hepoxilin A3 and Histamine Production by Airway Neutrophils.

Background: Hepoxilins are biologically active metabolites of arachidonic acid that are formed through the 12-lipoxygenase pathway. Hepoxilin A3 is now known to be an important regulator of mucosal inflammation in response to infection by bacterial pathogens and was recently identified as a potent neutrophil chemoattractant in the intestinal mucosa. Our goal in this study was to determine if airway infection with Chlamydia in a murine model of allergic airway disease (AAD) induces hepoxilin secretion along with airway neutrophilia.Methods: We utilized an AAD adult Balb/c mouse model to evaluate airway pathology and immune response by assaying bronchoalveolar lavage (BAL) fluid cytokine, cellularity, histidine decarboxylase (HDC) as well as histamine released in response to in-vivo chlamydial antigen stimulation of purified airway neutrophils. Hepoxilin A3 production was determined by Western blot identification of 12-lipoxygenase precursor (12-LO).Results: Chlamydial infection induced increased production of IL-2, IL-12, TNF-α, and IFN-γ in BAL fluid compared to uninfected animals. Chlamydia-infected mice responded with robust airway neutrophil infiltration and upon induction of AAD increased their production of IL-4, IL-5, and IL-13 by >3 fold compared to unsensitized groups. In addition, 12-LO mRNA was upregulated in infected, but not in uninfected AAD mice, suggesting the production of hepoxilin A3. mRNA expression of HDC was induced only in neutrophils from the airways of Chlamydia-infected mice, but was not seen in AAD only or uninfected controls. When purified neutrophils from infected animals were challenged with chlamydial antigen in vitro there was significant histamine release.Conclusions: Our data confirms the production and release of hepoxilin A3 in the murine airways concomitant with airway neutrophilia in response to chlamydial infection. We further confirmed that Chlamydia provokes the production and release of histamine by these neutrophils. These findings suggest that neutrophils, provoked by Chlamydia infection can synthesize and release histamine, thereby contributing directly to airway inflammation.

Time-dependent effects of olanzapine treatment on the expression of histidine decarboxylase, H1 and H3 receptor in the rat brain: The roles in olanzapine-induced obesity

Antipsychotic treatment, particularly olanzapine and clozapine, induces severe obesity. The Histamine H1 receptor is considered to be an important contributor to olanzapine-induced obesity, however how olanzapine modulates the histaminergic system is not sufficiently understood. This study examined the effect of olanzapine on key molecules of the histaminergic system, including histidine decarboxylase (HDC), H1 receptor (H1R) and H3 receptor (H3R), in the brain at different stages of olanzapine-induced obesity. During short-term treatment (8-day), olanzapine increased hypothalamic HDC mRNA expression and H1R binding in the arcuate nucleus (Arc) and ventromedial hypothalamus (VMH), without changing H3R binding density. HDC mRNA and Arc H1R binding were positively correlated with increased food intake, feeding efficiency and weight gain. When the treatment was extended to 16 and 36 days, H1R binding was increased not only in the hypothalamic Arc and VMH but also in the brainstem dorsal vagal complex (DVC). The H1R bindings in the Arc, VMH and DVC were positively correlated with weight gain induced by olanzapine treatment. However, the expression of HDC and H3R mRNA was not increased. These results suggest that olanzapine time-dependently modulates histamine neurotransmission, which suggested the different neuronal mechanisms underlying different stages of weight gain development. Treatment targeting the H1R may be effective for both short- and long-term olanzapine-induced weight gain.

Timeline of Intestinal Adaptation After Malabsortive Surgery: Effect of Luminal Nutrients, Biliopancreatic Secretion, and Glutamine Supplementation.

The aim of this study was to study the process of intestinal adaptation in the three limbs of the small intestine after malabsorptive bariatric surgery: the biliopancreatic limb, the alimentary limb, and the common channel. These limbs are exposed to different stimuli, namely, gastrointestinal transit and nutrients in the alimentary limb, biliopancreatic secretions in the biliopancreatic limb, and a mix of both in the common channel. We also wished to investigate the effect of glutamine supplementation on the adaptation process. Three types of surgery were performed using a porcine model: biliopancreatic bypass (BPBP), massive (75%) short bowel resection as the positive control, and a sham operation (transection) as the negative control. We measured the height and width of intestinal villi, histidine decarboxylase (HDC) activity, and amount of HDC messenger RNA (mRNA) (standard diet or a diet supplemented with glutamine). An increase in HDC activity and mRNA expression was observed in the BPBP group. This increase coincided with an increase in the height and width of the intestinal villi. The increase in villus height was observed immediately after surgery and peaked at 2weeks. Levels remained higher than those observed in sham-operated pigs for a further 4weeks. The intestinal adaptation process in animals that underwent BPBP was less intense than in those that underwent massive short bowel resection and more intense than in those that underwent transection only. Supplementation with glutamine did not improve any of the parameters studied, although it did appear to accelerate the adaptive process.

Histamine 1 Receptor Blockade Enhances Eosinophil-Mediated Clearance of Adult Filarial Worms.

Filariae are tissue-invasive nematodes that cause diseases such as elephantiasis and river blindness. The goal of this study was to characterize the role of histamine during Litomosoides sigmodontis infection of BALB/c mice, a murine model of filariasis. Time course studies demonstrated that while expression of histidine decarboxylase mRNA increases throughout 12 weeks of infection, serum levels of histamine exhibit two peaks—one 30 minutes after primary infection and one 8 weeks later. Interestingly, mice treated with fexofenadine, a histamine receptor 1 inhibitor, demonstrated significantly reduced worm burden in infected mice compared to untreated infected controls. Although fexofenadine-treated mice had decreased antigen-specific IgE levels as well as lower splenocyte IL-5 and IFNγ production, they exhibited a greater than fourfold rise in eosinophil numbers at the tissue site where adult L. sigmodontis worms reside. Fexofenadine-mediated clearance of L. sigmodontis worms was dependent on host eosinophils, as fexofenadine did not decrease worm burdens in eosinophil-deficient dblGATA mice. These findings suggest that histamine release induced by tissue invasive helminths may aid parasite survival by diminishing eosinophilic responses. Further, these results raise the possibility that combining H1 receptor inhibitors with current anthelmintics may improve treatment efficacy for filariae and other tissue-invasive helminths.

Inhibition of Histamine-Stimulated Gastric Acid Secretion by Hydrogen Sulfide in Male Rats

Recently, hydrogen sulfide (H_2S) introduces as the third gaseous transmitter that has many physiologic and pharmacologic roles in the body. The aim of the present study was to investigate the effect of exogenously given H_2S on histamine-induced gastric acid secretion in rats. Thirtytwo male Wistar rats (150-200 g) were randomly assigned into 4 groups (8 per group). Animals were deprived of food but not water 24 h before the experiment and were randomly assigned into two control groups, distention-, and histamine-stimulated groups, and two NaHS-treated groups. To evaluate the effect of H_2S on histamine-induced gastric acid secretion, one group of animals were received an I.V. bolus of NaHS (a H_2S donor) at 80 μg/kg. To investigate the possible involved mechanism of the antisecretory effect of NaHS, mRNA expression of histidine decarboxylase (HDC) were evaluated by reverse-transcriptase PCR. The gastric acid output in response to histamine decreased by NaHS treatment (P＜0.01). Also the results showed that the level of gene expression of HDC was higher in NaHS-treated group than in control rats. The findings showed that the inhibitory effect of H_2S on gastric acid secretion was not related to a decrease in histamine release. It seems that up-regulation of HDC mRNA expression is secondary to inhibition of gastric acid secretion by NaHS.

Characterization of an avian histidine decarboxylase and localization of histaminergic neurons in the chicken brain

In mammals, it is established that histamine is a neurotransmitter and/or neuromodulator in the central nervous system. It is produced by the enzyme histidine decarboxylase (HDC) in the tuberomammillary nucleus of the posterior hypothalamus. However, HDC as well as histaminergic neurons have not yet been characterized in the avian brain. We have cloned the cDNA for HDC from the chicken hypothalamus and demonstrated that the chicken HDC sequence is highly homologous to the mammalian counterpart, and that the expressed protein shows high enzymatic activity. The expression of HDC mRNA at various sites in the brain was investigated using quantitative RT-PCR. The results showed that the HDC mRNA was highly expressed in the hypothalamic infundibulum. In situ hybridization analyses revealed that the cells containing HDC mRNA were localized in the medial mammillary nucleus of the hypothalamic infundibulum. Intracerebroventricular injection of histamine in chicks resulted in inhibition of feeding behavior. This is the first report of the characterization of histaminergic neurons in the avian brain, and our findings indicate that neuronal histamine exerts anorexigenic effects in chicks.

Involvement of Histaminergic System in the Anxiolytic-Like Activities of <i>Morus alba</i> Leaves in Mice

The aim of this study was to identify the effects of 85% methanolic extract of Morus alba leaves (EMA), which is a traditional herb, in mice. The effects of EMA on the anxiolytic-like behaviour were studied using the elevated plus maze (EPM) and hole-board test. To elucidate the mode of action of the anxiolytic-like effects of EMA, the mice were subjected to the co-administration of EMA (200 mg/kg, per os (p.o.)) and either antagonist. EMA (at 200 or 400 mg/kg) significantly increased the percentages of time-spent in the open arms and entries into the open arms of the EPM versus vehicle-treated control group (p<0.05). Moreover, in the hole-board test, EMA (200 and 400 mg/kg) significantly increased the number of head-dips versus vehicle-treated control group (p<0.05). However, there were no changes in the locomotor activity and myorelaxant effects in any group compared with the vehicle-treated control group. In addition, the anxiolytic-like effects of EMA were abolished by thioperamide (10 mg/kg, intraperitoneally (i.p.)), which is a histamine H3 receptor antagonist. Moreover, results from reverse transcription polymerase chain reaction (RT-PCR) also revealed that the amygdalal histidine decarboxylase mRNA expression levels in EMA (200 mg/kg)-treated group were significantly higher than those in the vehicle-treated controls (p<0.05). These results suggest that EMA might prove to be an effective anxiolytic agent and that EMA acts via the histaminergic system in central nerve system.

Expression patterns of corticotropin‐releasing factor, arginine vasopressin, histidine decarboxylase, melanin‐concentrating hormone, and orexin genes in the human hypothalamus

The hypothalamus regulates numerous autonomic responses and behaviors. The neuroactive substances corticotropin-releasing factor (CRF), arginine-vasopressin (AVP), histidine decarboxylase (HDC), melanin-concentrating hormone (MCH), and orexin/hypocretins (ORX) produced in the hypothalamus mediate a subset of these processes. Although the expression patterns of these genes have been well studied in rodents, less is known about them in humans. We combined classical histological techniques with in situ hybridization histochemistry to produce both 2D and 3D images and to visually align and quantify expression of the genes for these substances in nuclei of the human hypothalamus. The hypothalamus was arbitrarily divided into rostral, intermediate, and caudal regions. The rostral region, containing the paraventricular nucleus (PVN), was defined by discrete localization of CRF- and AVP-expressing neurons, whereas distinct relationships between HDC, MCH, and ORX mRNA-expressing neurons delineated specific levels within the intermediate and caudal regions. Quantitative mRNA signal intensity measurements revealed no significant differences in overall CRF or AVP expression at any rostrocaudal level of the PVN. HDC mRNA expression was highest at the level of the premammillary area, which included the dorsomedial and tuberomammillary nuclei as well as the dorsolateral hypothalamic area. In addition, the overall intensity of hybridization signal exhibited by both MCH and ORX mRNA-expressing neurons peaked in distinct intermediate and caudal hypothalamic regions. These results suggest that human hypothalamic neurons involved in the regulation of the HPA axis display distinct neurochemical patterns that may encompass multiple local nuclei.

A quantitative in situ hybridization protocol for formalin-fixed paraffin-embedded archival post-mortem human brain tissue

The use of radioactive in situ hybridization (ISH) to quantitatively determine low-to-moderate abundant mRNA expression in formalin-fixed, paraffin-embedded archival post-mortem human brain tissue is often limited by non-specific-deposits, visible as speckles. In the present study, optimal hybridization conditions were achieved for quantifying the mRNA expression of histidine decarboxylase (HDC) by a number of alterations in a routine protocol, which included (1) during purification of the oligo-probes, glycogen was omitted as a carrier for precipitation, (2) after precipitation, the labeled probe contained within the pellet was first dissolved in water instead of in hybridization buffer (HBF), (3) during hybridization, the dithiothreitol (DTT) concentration was increased from 200 to 800 mM in HBF, and (4) stringencies during hybridization and post-hybridization washes were increased by increasing the temperature. The effect of the adjustment was quantified on adjacent sections from 18 subjects (9 with Parkinson’s disease and 9 controls), by comparing the data from the standard and new protocol. The results showed that the improved protocol brought about significantly clearer background with higher signal-to-noise ratios ( p = 0.001). We propose that this protocol is also applicable for detection of other lower-abundant genes in human brain tissue and probably in other tissues as well. In the present study, this is not only illustrated for HDC ISH, but also for corticotrophin-releasing hormone mRNA expression in the hypothalamic paraventricular nucleus.

Hypothalamic neuronal histamine mediates the thyrotropin-releasing hormone-induced suppression of food intake.

We examined the involvement of thyrotropin-releasing hormone (TRH) and TRH type 1 and 2 receptors (TRH-R1 and TRH-R2, respectively) in the regulation of hypothalamic neuronal histamine. Infusion of 100 nmol TRH into the rat third cerebroventricle (3vt) significantly decreased food intake (p < 0.05) compared to controls infused with phosphate- buffered saline. This TRH-induced suppression of food intake was attenuated partially in histamine-depleted rats pre-treated with α-fluoromethylhistidine (a specific suicide inhibitor of histidine decarboxylase) and in mice with targeted disruption of histamine H1 receptors. Infusion of TRH into the 3vt increased histamine turnover as assessed by pargyline-induced accumulation of tele-methylhistamine (t-MH, a major metabolite of neuronal histamine in the brain) in the tuberomammillary nucleus (TMN), the paraventricular nucleus, and the ventromedial hypothalamic nucleus in rats. In addition, TRH-induced decrease of food intake and increase of histamine turnover were in a dose-dependent manner. Microinfusion of TRH into the TMN increased t-MH content, histidine decarboxylase (HDC) activity and expression of HDC mRNA in the TMN. Immunohistochemical analysis revealed that TRH-R2, but not TRH-R1, was expressed within the cell bodies of histaminergic neurons in the TMN of rats. These results indicate that hypothalamic neuronal histamine mediates the TRH-induced suppression of feeding behavior.

The CML-related oncoprotein BCR/ABL induces expression of histidine decarboxylase (HDC) and the synthesis of histamine in leukemic cells

AbstractBasophil numbers are typically elevated in chronic myeloid leukemia (CML) and increase during disease progression. Histamine is an essential mediator and marker of basophils and is highly up-regulated in CML. We examined the biochemical basis of histamine synthesis in CML cells. The CML-specific oncoprotein BCR/ABL was found to promote expression of histidine decarboxylase (HDC) and synthesis of histamine in Ba/F3 cells. Moreover, the BCR/ABL tyrosine kinase inhibitors imatinib (STI571) and nilotinib (AMN107) decreased histamine levels and HDC mRNA expression in BCR/ABL-transformed Ba/F3 cells, in the CML-derived basophil cell line KU812, and in primary CML cells. Synthesis of histamine was found to be restricted to the basophil compartment of the CML clone and to depend on signaling through the PI3-kinase pathway. CML cells also expressed histamine receptors (HRs), including HR-1, HR-2, HR-4, and histamine-binding CYP450 isoenzymes which also serve as targets of HR antagonists. The HR-1 antagonists loratadine and terfenadine, which bind to CYP450, were found to counteract proliferation of CML cells, whereas no growth inhibition was observed with the HR-1 antagonist fexofenadine which is not targeted or metabolized by CYP450. Moreover, DPPE, an inhibitor of histamine-binding CYP450 isoenzymes, produced growth inhibition in CML cells. Together, these data show that BCR/ABL promotes histamine production in CML cells and that certain HR-targeting drugs exert antileukemic effects on CML cells.

Dexamethasone Suppresses Histamine Synthesis by Repressing both Transcription and Activity of HDC in Allergic Rats

Histamine synthesized by histidine decarboxylase (HDC) from L-histidine is a major chemical mediator in the development of nasal allergy which is characterized by nasal hypersensitivity. However the regulatory mechanism of histamine synthesis by HDC remains to be elucidated. The objectives of the present study were to examine the changes of histamine content, HDC activity and HDC mRNA expression in the nasal mucosa of allergy model rats sensitized by the exposure to toluene diisocyanate (TDI) and to investigate the effect of dexamethasone on the above mentioned allergic parameters. Rats were sensitized and provocated by TDI and the nasal allergy-like behaviors were scored during a 10 minute period after provocation. Histamine content and HDC activity in the nasal mucosa were determined using fluorometric high performance liquid chromatography. The expression of HDC mRNA in nasal mucosa was determined using real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In TDI-sensitized rats, nasal allergy-like behaviors such as sneezing and watery rhinorrhea were induced. Histamine content, HDC activity and HDC mRNA expression in nasal mucosa were also significantly increased after TDI provocation. Pretreatment with dexamethasone significantly suppressed nasal allergy-like behaviors, up-regulation of histamine content, HDC activity and HDC mRNA induced by TDI in TDI-sensitized rats. These findings indicate that increased synthesis of histamine through up-regulation of HDC gene expression and HDC activity in nasal mucosa plays an important role in the development of nasal hypersensitivity. Repression of HDC gene expression and HDC activity by dexamethasone may underlie its therapeutic effect in the treatment of allergy.

BCR/ABL Induces Expression of Histidine Decarboxylase and Synthesis of Histamine in CML Cells.

Abstract Basophil numbers are typically elevated in patients with chronic myeloid leukemia (CML) and characteristically increase during disease progression. As a consequence, blood histamine levels are highly upregulated in CML. We examined the biochemical basis of production of histamine in CML cells and analyzed the effects of the CML-related oncoprotein BCR/ABL on the generation of this mediator. Expression of histamine and of histidine decarboxylase (HDC), the major enzyme involved in histamine synthesis, were examined in primary CML cells obtained from patients with chronic phase (CP) CML or accelerated phase (AP) CML with basophilia, in the CML-derived cell lines K562 and KU812, and in Ba/F3 cells inducibly expressing BCR/ABL on exposure to doxycycline (TonB.210-X cells). In all patients with AP-CML and basophilia, high levels of HDC mRNA and of histamine were detected, whereas in CP-CML cells only expressed low amounts of HDC and of histamine. HDC mRNA and histamine were detectable in the basophil-committed CML cell line KU812, but not in K562 cells. Exposure of primary CML cells or KU812 cells to the BCR/ABL tyrosine kinase inhibitors imatinib (1 μM; Novartis Pharma AG) or AMN107 (100 nM; Novartis Pharma AG) decreased the levels of histamine and expression of HDC in BCR/ABL-transformed cells. Moreover, BCR/ABL was found to promote the expression of HDC mRNA and to increase the levels of histamine in TonB.210-X cells. The BCR/ABL-induced synthesis of histamine in these cells was blocked by the PI3-kinase inhibitor LY294002, whereas neither the MEK inhibitor PD98059, nor the mTOR inhibitor rapamycin affected histamine levels. In conclusion, our data show that the CML-specific oncoprotein BCR/ABL induces expression of HDC and synthesis of histamine in leukemic cells through a pathway involving the PI3-kinase.

Increase in the level of histidine decarboxylase mRNA expression in nasal mucosa of rats sensitized by toluene diisocyanate.

Increase in the level of histidine decarboxylase mRNA expression in nasal mucosa of rats sensitized by toluene diisocyanate.

Transforming growth factor-alpha directly augments histidine decarboxylase and vesicular monoamine transporter 2 production in rat enterochromaffin-like cells.

For the production and vesicle storage of histamine, Enterochromaffin-like (ECL) cells express histidine decarboxylase (HDC) and vesicular monoamine transporter 2 (VMAT2). Although HDC and VMAT2 show dynamic changes during gastric ulcer healing, the control system of their expression has not been fully investigated. In the present study, we investigated the effect of transforming growth factor-alpha (TGF-alpha) and proinflammatory cytokines on HDC and VMAT2 expression in rat ECL cells. Time course changes in the expression of TGF-alpha during the healing of acetic acid-induced ulcers were studied. EGF receptor (EGFR) expression was also examined in ECL cells, whereas the direct effects of TGF-alpha and proinflammatory cytokines on HDC and VMAT2 expression in ECL cells were investigated using in vivo and in vitro models. During the process of ulcer healing, expression of TGF-alpha mRNA was markedly augmented. Furthermore, EGFR was identified in isolated ECL cells. TGF-alpha stimulated HDC and VMAT2 mRNA expression and protein production and also increased histamine release from ECL cells. Selective EGFR tyrosine kinase inhibitor tyrphostin AG1478 almost completely inhibited HDC and VMAT2 gene expression induced by TGF-alpha in vivo and in vitro. During gastric mucosal injury, TGF-alpha was found to stimulate ECL cell functions by increasing HDC and VMAT2 expression.

Modulation of the histaminergic system and behaviour by alpha-fluoromethylhistidine in zebrafish.

The functional role of histamine (HA) in zebrafish brains was studied. Zebrafish did not display a clear circadian variation in brain HA levels. Loading of zebrafish with l-histidine increased HA concentration in the brain. A single injection of the histidine decarboxylase (HDC) inhibitor, alpha-fluoromethylhistidine (alpha-FMH), gave rise to a rapid reduction in zebrafish brain HA. Low HDC activity in the brain after injections verified the effect of alpha-FMH. A reduction in the number of histaminergic fibres but not neurones and an increased expression of HDC mRNA was evident after alpha-FMH. Automated behavioural analysis after alpha-FMH injection showed no change in swimming activity, but abnormalities were detected in exploratory behaviour examined in a circular tank. No significant behavioural changes were detected after histidine loading. The time spent for performance in the T-maze was significantly increased in the first trial 4 days after alpha-FMH injections, suggesting that lack of HA may impair long-term memory. The rostrodorsal telencephalon, considered to correspond to the mammalian amygdala and hippocampus in zebrafish, is densely innervated by histaminergic fibres. These results suggest that low HA decreases anxiety and/or affects learning and memory in zebrafish, possibly through mechanisms that involve the dorsal forebrain.

Rat stomach ECL cells: mode of activation of histidine decarboxylase

Histidine decarboxylase (HDC) occurs in ECL cells in the oxyntic mucosa of rat stomach. It is activated by gastrin. Refeeding of fasted rats or treatment with the proton pump inhibitor omeprazole promptly raised the serum gastrin concentration and consequently the HDC activity and the HDC protein content of the oxyntic mucosa. The food- and omeprazole-induced increase in HDC mRNA expression in the oxyntic mucosa was modest by comparison. Blockade of translation (cycloheximide) but not transcription (actinomycin D) prevented the postprandial rise in HDC activity. The half-life of HDC activity (after blockade of translation) was 94 min in omeprazole-treated rats and 55 min in fasted controls. The rate of enzyme synthesis was estimated to be 15 times higher in omeprazole-treated rats than in fasted controls. Inhibition of histamine uptake into ECL-cell granules by reserpine, a blocker of the vesicular monoamine transporter type-2, lowered the HDC activity and prevented the gastrin-induced HDC activation. We suggest that HDC activation reflects enhanced transcription, translation and/or posttranslational enzyme activation as well as stabilization, and that a high cytosolic histamine concentration suppresses HDC activation.