Histidine Decarboxylase Levels Research Articles

Histamine promotes mouse decidualization through stimulating epithelial amphiregulin release.

Accumulating evidence shows that inflammation is essential for embryo implantation and decidualization. Histamine, a proinflammatory factor that is present in almost all mammalian tissues, is synthesized through decarboxylating histidine by histidine decarboxylase (HDC). Although histamine is known to be essential for decidualization, the underlying mechanism remains undefined. In the present study, histamine had no obvious direct effects on in vitro decidualization in mice. However, the obvious differences in HDC protein levels between day 4 of pregnancy and day 4 of pseudopregnancy, as well as between delayed and activated implantation, suggested that the blastocyst may be involved in regulating HDC expression. Furthermore, blastocyst-derived tumor necrosis factor α (TNFα) significantly increased HDC levels in the luminal epithelium. Histamine increased the levels of amphiregulin (AREG) and disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) proteins, which was abrogated by treatment with famotidine, a specific histamine type 2 receptor (H2R) inhibitor, or by TPAI-1 (a specific inhibitor of ADAM17). Intraluminal injection of urocanic acid (HDC inhibitor) on day 4 of pregnancy significantly reduced the number of implantation sites on day 5 of pregnancy. TNFα-stimulated increases in HDC, AREG and ADAM17 protein levels was abrogated by urocanic acid, a specific inhibitor of HDC. Additionally, AREG treatment significantly promoted in vitro decidualization. Collectively, our data suggests that blastocyst-derived TNFα induces luminal epithelial histamine secretion, and histamine increases mouse decidualization through ADAM17-mediated AREG release.

Impact of moderate prenatal alcohol exposure on histaminergic neurons, histidine decarboxylase levels and histamine H2 receptors in adult rat offspring.

We have reported that moderate prenatal alcohol exposure (PAE) elevates histamine H3 receptor-mediated inhibition of glutamatergic neurotransmission in dentate gyrus (DG), and that the H3 receptor antagonist ABT-239 ameliorates PAE-induced deficits in DG long-term potentiation. Here, we investigated whether PAE alters other markers of histaminergic neurotransmission. Long-Evans rat dams voluntarily consumed either a 0% or a 5% ethanol solution 4h each day throughout gestation. Young adult female offspring from each prenatal treatment group were used in histidine decarboxylase (HDC) immunohistochemical studies of histamine neuron number in ventral hypothalamus, quantitative Western blotting studies of HDC expression in multiple brain regions, radiohistochemical studies of H2 receptor density in multiple brain regions, and in biochemical studies of H2 receptor-effector coupling in dentate gyrus. Rat dams consumed a mean of 1.90g of ethanol/kg/day during pregnancy. This level of consumption did not affect maternal weight gain, offspring birth weight, or litter size. PAE did not affect the number of HDC-positive neurons in ventral hypothalamus. However, HDC expression was reduced in frontal cortex, dentate gyrus, and cerebellum of PAE rats compared to controls. Specific [125I]-iodoaminopotentidine binding to H2 receptors was not altered in any of the brain regions measured, nor was basal or H2 receptor agonist-stimulated cAMP accumulation in DG altered in PAE rats compared to controls. These results suggest that not all markers of histaminergic neurotransmission are altered by PAE. However, the observation that HDC levels were reduced in the same brain regions where elevated H3 receptor-effector coupling was observed previously raises the question of whether a cause-effect relationship exists between HDC expression and H3 receptor function in affected brain regions of PAE rats. This relationship, along with the question of why these effects occur in some, but not all brain regions, requires more-detailed investigation.

Eosinophil cationic protein and histamine production by neutrophils from patients with periodontitis.

Periodontitis develops through an inflammatory process caused by an infection at the microbial biofilm, followed by tissue destruction mediated by leukocytes, which cause clinically significant destruction of connective tissue and bone. Several elements derived from the bacteria cause the inflammatory response and the release of mediators involved in destruction of the periodontium. There are number of inflammatory mediators released by leukocytes, mainly neutrophils, upon bacterial challenge. Neutrophils produce and release eosinophil cationic protein (ECP) and histamine, two important inflammatory mediators; however, their role has not been characterized in periodontal inflammation. Thus, the purpose of this study is to investigate whether neutrophils from patients with periodontitis can produce ECP and histamine in response to lipopolysaccharides (LPSs). ECP and histamine production in response to LPSs was analyzed by enzyme-linked immunosorbent assay. Expression of the histidine decarboxylase and ECP was also analyzed by flow cytometry and fluorescence microscopy in neutrophils from patients with periodontitis in response to LPS. It was found that neutrophils from patients with periodontitis express higher levels of histidine decarboxylase and ECP than those from healthy volunteers, and they also release higher levels of histamine. Findings described could represent new knowledge indicating neutrophils as a source of histamine and ECP in the progression of periodontitis.

Induced histamine regulates Ni elution from an implanted Ni wire in mice by downregulating neutrophil migration

Histamine regulates various inflammatory reactions. We have reported that the expression of histidine decarboxylase (HDC) was induced by subcutaneous implantation of nickel (Ni) wire. However, the source and functions of histamine in Ni elution and Ni wire-induced inflammation have not been completely studied. We aimed to elucidate the effects of de novo synthesized histamine on leucocyte infiltration and Ni elution. Implantation of Ni wire induced an increase in the Ni ion content of the surrounding tissues and serum and in the mRNA levels of HDC, a histamine-producing enzyme, macrophage inflammatory protein-2 (MIP-2), a chemoattractant for neutrophils, and monocyte chemoattractant protein-1 (MCP-1), a chemoattractant for monocytes. The Ni wire induced HDC expression even in mast cell-deficient WBB6F1-W/WV mice. In HDC knockout (HDC KO) mice, the Ni wire-induced increase in MIP-2 mRNA expression was significantly higher than that in wild-type mice but not MCP-1. MIP-2 expression was enhanced in histamine H2 receptor knockout (H2R KO) mice but not in WBB6F1-W/WV mice. Histamine inhibited NiCl2 -induced MIP-2 mRNA expression in mouse bone marrow-derived macrophages (BMDMs) obtained from wild-type mice; this inhibition was not observed in BMDMs from H2R KO mice. Ni elution increased in HDC KO mice, in which leucocyte infiltration also increased, and was suppressed in mice treated with neutrophil-specific antibody. These results suggest that the Ni wire induced HDC expression in non-mast cells and that, in the chronic phase of inflammation, endogenous histamine reduced Ni elution, probably through regulation of MIP-2 expression and neutrophil migration.

Mouse model of imiquimod-induced psoriatic itch.

Itch is a major indicator of psoriasis, but the underlying mechanisms behind this symptom are largely unknown. To investigate the neuronal mechanisms of psoriatic itch, we tested whether mice subjected to the imiquimod-induced psoriasis model exhibit itch-associated behaviors. Mice received daily topical applications of imiquimod to the rostral back skin for 7 days. Imiquimod-treated mice exhibited a significant increase in spontaneous scratching behavior directed to the treated area as well as touch-evoked scratching (alloknesis). To characterize this model, we measured the mRNA expression levels of pruritogens and itch-relevant receptors/channels using real-time reverse transcription PCR. The mRNA expression of MrgprA3, MrgprC11, and MrgprD decreased gradually over time in the dorsal root ganglion (DRG) cells. There was no significant change in the mRNA expression of TRPV1 or TRPA1 in DRG cells. TRPV4 mRNA expression was transiently increased in the DRG cells, whereas TRPM8 mRNA was significantly decreased. The mRNA expression levels of histidine decarboxylase and tryptophan hydroxylase 1, as well as the intensity of histamine and serotonin immunoreactivity, were transiently increased in the skin on day 2, returning to baseline by day 7. Histamine H1-receptor antagonists, chlorpheniramine and olopatadine, significantly inhibited spontaneous scratching on day 2, but not day 7. Neither chlorpheniramine nor olopatadine affected alloknesis on day 2 or day 7. These results may reflect the limited antipruritic effects of histamine H1-receptor antagonists on human psoriasis. The imiquimod-induced psoriasis model seems to be useful for the investigation of itch and its sensitization in psoriasis.

The histamine-synthesizing enzyme histidine decarboxylase is upregulated by keratinocytes in atopic skin.

Histamine is an abundant mediator accumulating in the skin of atopic patients, where it is thought to be derived from immune cells. While keratinocytes express histidine decarboxylase (HDC), levels of the enzyme in normal or diseased epidermis and factors that influence its expression in human keratinocytes are not known. To assess levels of HDC in inflammatory skin diseases and factors influencing its expression. Normal and filaggrin-insufficient human keratinocytes, organotypic epidermal models and skin samples were investigated for the expression of HDC. The effect of cytokines, bacterial and allergen stimuli exposure and functional changes in differentiation were evaluated in vitro. We detected abundant expression of the HDC protein in all models studied; expression was increased in atopic skin samples. Filaggrin-insufficient keratinocytes maintained HDC levels, but exposure of keratinocytes to thymic stromal lymphopoietin, tumour necrosis factor-α, lipopolysaccharide (LPS) and house dust mite (HDM) extract increased HDC expression in vitro. Furthermore, filaggrin expression in cultured keratinocytes increased following histamine depletion. Keratinocytes express abundant HDC protein, and the levels increase in atopic skin. LPS, HDM and cytokines, which are implicated in allergic inflammation, promote the expression of the enzyme and upregulate histamine levels in keratinocytes. Actively produced histamine influences keratinocyte differentiation, suggesting functional relevance of the axis to atopic dermatitis. The findings therefore identify a new point of therapeutic intervention.

Structural basis for the histamine synthesis by human histidine decarboxylase

Histamine is a bioactive amine responsible for a variety of physiological reactions, including allergy, gastric acid secretion, and neurotransmission. In mammals, histamine production from histidine is catalyzed by histidine decarboxylase (HDC). Mammalian HDC is a pyridoxal 5'-phosphate (PLP)-dependent decarboxylase and belongs to the same family as mammalian glutamate decarboxylase (GAD) and mammalian aromatic L-amino acid decarboxylase (AroDC). The decarboxylases of this family function as homodimers and catalyze the formation of physiologically important amines like GABA and dopamine via decarboxylation of glutamate and DOPA, respectively. Despite high sequence homology, both AroDC and HDC react with different substrates. For example, AroDC catalyzes the decarboxylation of several aromatic L-amino acids, but has little activity on histidine. Although such differences are known, the substrate specificity of HDC has not been extensively studied because of the low levels of HDC in the body and the instability of recombinant HDC, even in a well-purified form. However, knowledge about the substrate specificity and decarboxylation mechanism of HDC is valuable from the viewpoint of drug development, as it could help lead to designing of novel drugs to prevent histamine biosynthesis. We have determined the crystal structure of human HDC in complex with inhibitors, histidine methyl ester (HME) and alpha-fluoromethyl histidine (FMH). These structures showed the detailed features of the PLP-inhibitor adduct (external aldimine) in the active site of HDC. These data provided insight into the molecular basis for substrate recognition among the PLP-dependent L-amino acid decarboxylases.

Histidine Decarboxylase Deficiency Causes Tourette Syndrome: Parallel Findings in Humans and Mice

Tourette syndrome (TS) is characterized by tics, sensorimotor gating deficiencies, and abnormalities of cortico-basal ganglia circuits. A mutation in histidine decarboxylase (Hdc), the key enzyme for the biosynthesis of histamine (HA), has been implicated as a rare genetic cause. Hdc knockout mice exhibited potentiated tic-like stereotypies, recapitulating core phenomenology of TS; these were mitigated by the dopamine (DA) D2 antagonist haloperidol, a proven pharmacotherapy, and by HA infusion into the brain. Prepulse inhibition was impaired in both mice and humans carrying Hdc mutations. HA infusion reduced striatal DA levels; in Hdc knockout mice, striatal DA was increased and the DA-regulated immediate early gene Fos was upregulated. DA D2/D3 receptor binding was altered both in mice and in humans carrying the Hdc mutation. These data confirm histidine decarboxylase deficiency as a rare cause of TS and identify HA-DA interactions in the basal ganglia as an important locus of pathology.

Structure Analysis of Histidine Decarboxylase in Complex with Inhibitors

Histamine is a bioactive amine responsible for a variety of physiological reactions, including allergy, gastric acid secretion, and neurotransmission. In mammals, histamine production from histidine is catalyzed by histidine decarboxylase (HDC). Mammalian HDC is a pyridoxal 5'-phosphate (PLP)-dependent decarboxylase and belongs to the same family as mammalian glutamate decarboxylase (GAD) and mammalian aromatic L-amino acid decarboxylase (AroDC). The decarboxylases of this family function as homodimers and catalyze the formation of physiologically important amines like γ-aminobutyric acid (GABA), dopamine, and serotonin via decarboxylation of glutamate, 3,4-dihydroxyphenylalanine (DOPA), and 5-hydroxytryptophan, respectively. Despite high sequence homology, both AroDC and HDC react with different substrates. For example, AroDC catalyzes the decarboxylation of several aromatic L-amino acids, but has little activity on histidine. Although such differences are known, the substrate specificity of HDC has not been extensively studied because of the low levels of HDC in the body and the instability of recombinant HDC, even in a well-purified form. However, knowledge about the substrate specificity and decarboxylation mechanism of HDC is valuable from the viewpoint of drug development, as it could help lead to designing of novel drugs to prevent histamine biosynthesis.The structure of the mammalian HDC has not yet been reported. The three-dimensional structure will provide invaluable insights into the molecular basis of the histidine substrate specificity. We have determined the crystal structure of human HDC in complex with an inhibitor, histidine methyl ester (HME). This structure showed the detailed features of the PLP-inhibitor adduct (external aldimine) in the active site of HDC. Moreover, a comparison of the structure of HDC with that of AroDC revealed a key residue, Ser354, for substrate specificity. These data provided insight into the molecular basis for substrate recognition among the PLP-dependent L-amino acid decarboxylases.

Tryptanthrin ameliorates atopic dermatitis through down-regulation of TSLP

Atopic dermatitis (AD) is a common skin disease that greatly worsens quality of life. Thymic stromal lymphopoietin (TSLP) plays a decisive role in the development of AD. The purpose of this study is to examine whether tryptanthrin (TR) would suppress AD through the regulation of TSLP. We analyzed the effect of TR on the level of TSLP from phorbol myristate acetate/calcium ionophore A23187-activated human mast cell line, HMC-1 cells, in 2,4-dinitrofluorobenzene-induced AD-like skin lesions of NC/Nga mice, and in anti-CD3/anti-CD28-stimulated splenocytes. TR significantly suppressed the level of intracellular calcium and the production and mRNA expression of TSLP through the blockade of receptor-interacting protein 2/caspase-1/nuclear factor-κB pathway in the activated HMC-1 cells. TR also significantly suppressed the levels of histidine decarboxylase and IL-1β. Furthermore, TR ameliorated clinical symptoms in the AD model. TR significantly reduced the levels of TSLP, IL-4, IFN-γ, IL-6, TNF-α, thymus and activation-regulated chemokine, and caspase-1 in AD skin lesions. Also, TR significantly reduced the serum levels of histamine and IL-4 in the AD model. Finally, TR significantly inhibited the production of IL-4, IFN-γ, and TNF-α from the stimulated splenocytes. Taken together, TR exhibits the potential to be a therapeutic agent for AD through down-regulation of TSLP.

Neuronal histaminergic system in aging and age-related neurodegenerative disorders

The neuronal histaminergic system is involved in many physiological functions and is severely affected in age-related neurodegenerative diseases such as Parkinson's disease (PD) and Alzheimer's disease (AD). The properties of the neuronal histaminergic system in experimental animals and the alterations observed in postmortem brain material of PD or AD patients are reviewed. The production of neuronal histamine shows diurnal fluctuations in control subjects who had no neuropsychiatric disorders, while this fluctuation was strongly altered in patients with neurodegenerative diseases, including PD and AD. In addition, different alterations shown as expression levels of histidine decarboxylase (the key enzyme for histamine production), histamine-methyltransferase (the histamine deactivating enzyme), and histamine receptors (H1–4R) were found in various neurodegenerative disorders. Discrepancies between results from animal models and postmortem human brain material studies have made clear that the validation of animal models is absolutely necessary and that studies on patients and human postmortem material are essential to understand the changes of neuronal histaminergic system occurring in neuropsychiatric disorders.

Histidine decarboxylase expression influences the neofolliculogenesis of newborn mouse dermal cells

With the introduction of hair regeneration techniques using epidermal and dermal cells, hair follicle regeneration became much easier and faster. Current success has been dependent on the availability of cells from newborn or embryonic mice. We recently observed that the hair-inducing ability of newborn mouse dermal cells disappeared in the first few days of life and there was a drastic decrease of histidine decarboxylase (HDC) gene expression from postnatal day 0 (p0) to day 7 (p7). The aim of this study was to study the role of HDC in hair follicle induction. The mRNA levels of HDC in p0, p7 and p48 C57BL/6 mouse skin were checked with a real time reverse transcription polymerase chain reaction and immunohistochemistry. To test the effect of HDC, HDC expression in p0 mouse dermal cells was suppressed with small interfering RNA (siRNA) transfection. Mock treated and HDC siRNA treated cells were then injected with adult epidermal cells into nude mice skin. Three weeks later, the number, length and thickness of induced hairs were compared. Compared with p0, the mRNA level of HDC was much lower at p7 and p48. Immunohistochemical staining also revealed a marked decrease of HDC expression in p7 mice skin, compared with p0 skin. Hair patch assays showed that the HDC siRNA treated p0 dermal cells induced less hair follicle structures and shorter and thinner hair shafts than mock treated cells. HDC, whose expression is remarkably downregulated during the first few days after birth in dermal cells of mice, plays essential roles in the hair-inducing ability of newborn mouse dermal cells.

Increased expression of the histamine H4receptor subtype in hypertrophic differentiation of chondrogenic ATDC5 cells

Histamine has been regarded as an inflammatory mediator of arthritic disorders. We have previously reported that the expression of histamine H(4) receptor (H(4)R) mRNA in synovial tissues was significantly higher in patients with osteoarthritis (OA) compared to those with rheumatoid arthritis. Chondrocyte hypertrophy and endochondral ossification are essential processes in pathologic disorders such as osteophyte formation during OA progression. In the present study, we examined the expression of H(4) R during differentiation into hypertrophic chondrocytes in the ATDC5 cells, a widely used in vitro model of chondrogenic differentiation. Quantitative reverse transcription polymerase chain reaction showed that the levels of histidine decarboxylase and H(4)R mRNA on ATDC5 cells were increased in a time-dependent manner during the culture period. By contrast, the expressions of H(1)R and H(2)R were not increased from day 7 onwards. The mRNA expression of the hypertrophic chondrocyte marker type X collagen (COL X) was increased markedly from 14 to 21. Immunocytochemical analysis indicated that H(4)R staining was strongly immunoreactive on the plasma membrane of ATDC5 cells. Flow cytometry showed increased expression of H(4)R and COL X protein in ATDC5 chondrocytes. Furthermore, the majority of the COL X-positive cells expressed H(4) R throughout the culture period. In summary, we showed for the first time that H(4)R is expressed in ATDC5 chondrocytes. Moreover, we found that most hypertrophic chondrocytes express H(4)R, suggesting that this receptor might be associated with the differentiation of chondrocytes into hypertrophic cells, which are abnormally observed in joint lesions in OA.

Histidine Decarboxylase Is Identified as a Potential Biomarker of Intestinal Mucosal Injury in Patients with Acute Intestinal Obstruction

Various biomarkers currently used for the diagnosis of intestinal mucosal injury (IMI) in patients with acute intestinal obstruction have low sensitivity and specificity. In the present study, IMI, as indicated by the impaired expression of tight junction proteins, including zonula occludens-1, occludin and claudin-1, and inflammation were determined in colonic tissues of patients with 45 strangulated intestinal obstruction (STR-IO) and the adjacent "normal" colonic tissues of 35 patients with colon cancers by quantitative real-time polymerase chain reaction (QRT-PCR), Western blotting, immunohistochemistry and histological examination, respectively. Then, two-dimensional fluorescent difference gel electrophoresis coupled with linear trap quadrupole mass spectrometry was used to screen for potential biomarkers of IMI in the serum samples of 10 STR-IO, 10 simple intestinal obstruction (SIM-IO) and 10 normal healthy controls. A total of 35 protein spots were differentially expressed among the serum samples, and six of the proteins were identified as potential biomarkers. Among the six proteins, histidine decarboxylase (HDC) and ceruloplasmin (CP) were elevated significantly in patients with STR-IO, compared with patients with SIM-IO and healthy controls. Thus, HDC and CP were further validated by QRT-PCR, Western blotting, immunohistochemistry and enzyme-linked immunosorbent assay, respectively, in colonic tissues, serum and urine samples. Finally, the receiver operating characteristic curves were used to show the area under the curves of HDC, CP and several established biomarkers, followed by the determination of the appropriate cutoff values and their sensitivities and specificities. It was shown that for serum and urine, HDC levels achieved sensitivities and specificities compatible to or even greater than those of established biomarkers for the diagnosis of IMI in patients with acute intestinal obstruction, although further validation in a larger cohort is required.

High levels of histidine decarboxylase in the striatum of mice and rats

The neurotransmitter histamine is produced in the tuberomamillary nucleus of the posterior hypothalamus; these neurons project broadly throughout central nervous system. Histidine decarboxylase (HDC) synthesizes histamine from histidine; in the brain, its mRNA is expressed exclusively in the posterior hypothalamus. Histamine receptors are expressed throughout the forebrain, including in cortex, hippocampus, and basal ganglia, suggesting functional innervation of these structures. We investigated the distribution of HDC protein in dissected tissue from mouse and rat, anticipating that it would reflect the density of hypothalamic histaminergic axonal projections and thus qualitatively parallel the known distribution of histamine receptors. HDC protein was found at high levels in hypothalamus, as anticipated. Surprisingly, it was found at comparably high levels in mouse striatum. HDC protein was 10-fold lower in cortex, hippocampus, and cerebellum. Specificity of HDC detection by Western blot was confirmed using HDC knockout mice. Similar high levels of HDC protein were found in dissected striatum from rat. Striatum does not, however, contain comparably elevated of histamine, relative to other forebrain structures; we confirmed this fact using HPLC. This discrepancy between HDC protein and histamine levels in the striatum suggests that histamine metabolism and neurotransmission in basal ganglia may have unique characteristics, the details of which remain to be elucidated.

Neuronal histamine production remains unaltered in Parkinson's disease despite the accumulation of Lewy bodies and Lewy neurites in the tuberomamillary nucleus

Neuronal histamine production in the hypothalamic tuberomamillary nucleus (TMN) was hypothesized to change significantly in Parkinson's disease (PD) in relation to the accumulation of Lewy bodies/Lewy neurites (LBs/LNs). We measured the messenger ribonucleic acid (mRNA) levels of histidine decarboxylase (HDC), the key enzyme of histamine production, and the amount of LBs/LNs in the TMN by quantitative in situ hybridization and immunocytochemistry in postmortem human brain material of clinical PD (CPD), preclinical PD, and control subjects. No significant difference of histidine decarboxylase mRNA levels was observed among different clinical or Braak-PD stages, in spite of the strong accumulation of LBs/LNs in the TMN of clinical PD patients. We conclude that neuronal histamine production remains largely unaltered in PD despite the abundant LB/LN accumulation in the TMN.

Functional Increase of Brain Histaminergic Signaling in Huntington's Disease

To evaluate whether central histaminergic signaling in Huntington's disease (HD) patients is affected, we assessed mRNA levels of histidine decarboxylase (HDC), volume of and neuron number in the hypothalamic tuberomamillary nucleus (TMN) (HD n = 8, controls n = 8). In addition, we assessed histamine N-methyltransferase (HMT) and histamine receptor (H(1) R, H(2) R and H(3) R) mRNA levels in the inferior frontal gyrus (IFG) (n = 9 and 9) and caudate nucleus (CN) (n = 6 and 6) by real-time polymerase chain reaction. In HD patients, TMN volume and neuronal number was unaltered (P = 0.72, P = 0.25). The levels of HDC mRNA (P = 0.046), IFG HMT (P < 0.001), H(1) R (P < 0.001) and H(3) R mRNA levels (P = 0.011) were increased, while CN H(2) R and H(3) R mRNA levels were decreased (P = 0.041, P = 0.009). In HD patients, we observed a positive correlation between IFG H(3) R mRNA levels and CAG repeat length (P = 0.024) and negative correlations between age at onset of disease and IFG HMT (P = 0.015) and H(1) R (P = 0.021) mRNA levels. These findings indicate a functional increase in brain histaminergic signaling in HD, and provide a rationale for the use of histamine receptor antagonists.

A22 Hypothalamic changes in Huntington's disease

BackgroundIn recent years it has become increasingly clear that the hypothalamus might be affected in Huntington's disease (HD), and that this may underlie many features in this disease. Research on...

Histamine in the posterodorsal medial amygdala modulates cardiovascular reflex responses in awake rats

Centrally injected histamine (HA) affects heart rate (HR), arterial blood pressure (BP), and sympathetic activity in rats. The posterodorsal medial amygdala (MePD) has high levels of histidine decarboxylase, connections with brain areas involved with the modulation of cardiovascular responses, and is relevant for the pathogenesis of hypertension. However, there is no report demonstrating the role of the MePD histaminergic activity on the cardiovascular function in awake rats. The aims of the present work were: 1) to study the effects of two doses (10–100 nM) of HA microinjected in the MePD on basal cardiovascular recordings and on baroreflex- and chemoreflex-mediated responses; 2) to reveal whether cardiovascular reflex responses could be affected by MePD microinjections of (R)-α-methylhistamine (AH 3), an agonist of the inhibitory autoreceptor H 3; and, 3) to carry out a power spectral analysis to evaluate the contribution of the sympathetic and parasympathetic components in the variability of the HR and BP recordings. When compared with the control group (microinjected with saline, 0.3 μl), HA (10 nM) promoted an increase in the MAP 50, i.e. the mean value of BP at half of the HR range evoked by the baroreflex response. Histamine (100 nM) did not affect the baroreflex activity, but significantly decreased the parasympathetic component of the HR variability, increased the sympathetic/parasympathetic balance at basal conditions (these two latter evaluated by the power spectral analysis), and promoted an impairment in the chemoreflex bradycardic response. Microinjection of AH 3 (10 μM) led to mixed results, which resembled the effects of both doses of HA employed here. Present data suggest that cardiovascular changes induced by baroreceptors and chemoreceptors involve the histaminergic activity in the MePD. This neural regulation of reflex cardiovascular responses can have important implications for homeostatic and allostatic conditions and possibly for the behavioral displays modulated by the rat MePD.

Serotonin and histamine storage in mast cell secretory granules is dependent on serglycin proteoglycan

Serotonin and histamine are components of human and rodent mast cell secretory granules. Serotonin and histamine are stored in the same compartment as serglycin proteoglycan. Here we addressed the possibility that serglycin may be involved in their storage and/or release. The storage and release of histamine and serotonin was studied in bone marrow-derived mast cells (BMMCs) and in peritoneal mast cells from wild-type or serglycin-/- mice. Both serotonin and histamine storage in BMMCs was positively correlated with the degree of mast cell differentiation, and the amount of stored amine was reduced in serglycin-/- BMMCs compared with wild-type controls. The amounts of histamine/serotonin stored were reflected by the expression levels of histidine decarboxylase and tryptophan hydroxylase 1, respectively. Calcium ionophore activation resulted in serotonin/histamine release both from wild-type and serglycin-/- BMMCs. Interestingly, serotonin release was induced in cells lacking intracellular stores of serotonin, suggesting de novo synthesis. The knockout of serglycin affected the levels of stored and released mast cell serotonin and histamine to an even larger extent in in vivo-derived mast cells than in BMMCs. These results establish a previously assumed, but not proven, role of serglycin in storage of histamine and, further, establish for the first time that serotonin storage in mast cells is dependent on serglycin proteoglycan.