Major changes in the brain histamine system of the ground squirrel Citellus lateralis during hibernation.
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Hibernation in mammals such as the rodent hibernator Citellus lateralis is a physiological state in which CNS activity is endogenously maintained at a very low, but functionally responsive, level. The neurotransmitter histamine is involved in the regulation of diurnal rhythms and body temperature in nonhibernators and, therefore, could likely play an important role in maintaining the hibernating state. In this study, we show that histamine neuronal systems undergo major changes during hibernation that are consistent with such a role. Immunohistochemical mapping of histaminergic fibers in the brains of hibernating and nonhibernating golden-mantled ground squirrels (C. lateralis) showed a clear increase in fiber density during the hibernating state. The tissue levels of histamine and its first metabolite tele-methylhistamine were also elevated throughout the brain of hibernating animals, suggesting an increase in histamine turnover during hibernation, which occurs without an increase in histidine decarboxylase mRNA expression. This hibernation-related apparent augmentation of histaminergic neurotransmission was particularly evident in the hypothalamus and hippocampus, areas of importance to the control of the hibernating state, in which tele-methylhistamine levels were increased more than threefold. These changes in the histamine neuronal system differ from those reported for the metabolic pattern in other monoaminergic systems during hibernation, which generally indicate a decrease in turnover. Our results suggest that the influence of histamine neuronal systems may be important in controlling CNS activity during hibernation. (+info)
Comparison of functional antagonism between isoproterenol and M2 muscarinic receptors in guinea pig ileum and trachea.
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The ability of the M2 muscarinic receptor to mediate an inhibition of the relaxant effects of forskolin and isoproterenol was investigated in guinea pig ileum and trachea. In some experiments, trachea was first treated with 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) mustard to inactivate M3 receptors. The contractile response to oxotremorine-M was measured subsequently in the presence of both histamine (10 microM) and isoproterenol (10 nM). Under these conditions, [[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5, 11-dihydro-6H-pyrido[2,3b]-[1,4]benzodiazepine-6-one (AF-DX 116) antagonized the contractile response to oxotremorine-M in a manner consistent with an M3 mechanism. However, when the same experiment was repeated using forskolin (4 microM) instead of isoproterenol, the response to oxotremorine-M exhibited greater potency and was antagonized by AF-DX 116 in a manner consistent with an M2 mechanism. We also measured the effects of pertussis toxin treatment on the ability of isoproterenol to inhibit the contraction elicited by a single concentration of either histamine (0.3 microM) or oxotremorine-M (40 nM) in both the ileum and trachea. Pertussis toxin treatment had no significant effect on the potency of isoproterenol for inhibiting histamine-induced contractions in the ileum and trachea. In contrast, pertussis toxin treatment enhanced the relaxant potency of isoproterenol against oxotremorine-M-induced contractions in the ileum but not in the trachea. Also, pertussis toxin treatment enhanced the relaxant potency of forskolin against oxotremorine-M-induced contractions in the ileum and trachea. We investigated the relaxant potency of isoproterenol when very low, equi-effective (i.e., 20-34% of maximal response) concentrations of either histamine or oxotremorine-M were used to elicit contraction. Under these conditions, isoproterenol exhibited greater relaxant potency against histamine in the ileum but exhibited similar relaxant potencies against histamine and oxotremorine-M in the trachea. Following 4-DAMP mustard treatment, a low concentration of oxotremorine-M (10 nM) had no contractile effect in either the ileum or trachea. Nevertheless, in 4-DAMP mustard-treated tissue, oxotremorine-M (10 nM) reduced the relaxant potency of isoproterenol against histamine-induced contractions in the ileum, but not in the trachea. We conclude that in the trachea the M2 receptor mediates an inhibition of the relaxant effects of forskolin, but not isoproterenol, and the decreased relaxant potency of isoproterenol against contractions elicited by a muscarinic agonist relative to histamine is not due to activation of M2 receptors but rather to the greater contractile stimulus mediated by the M3 receptor compared with the H1 histamine receptor. (+info)
Potent mast cell degranulation and vascular permeability triggered by urocortin through activation of corticotropin-releasing hormone receptors.
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Urocortin (Ucn) is related to corticotropin-releasing hormone (CRH), and both are released in the brain under stress where they stimulate CRH 1 and 2 receptors (CRHR). Outside the brain, they may have proinflammatory actions through activation of mast cells, which are located perivascularly close to nerve endings and degranulate in response to acute psychological stress. Here, we report that a concentration of intradermal Ucn as low as 10 nM induced dose-dependent rat skin mast cell degranulation and increased vascular permeability. This effect appeared to be equipotent to that of calcitonin gene-related peptide and neurotensin. Ucn-induced skin vasodilation was inhibited by pretreatment with the mast cell stabilizer disodium cromoglycate (cromolyn) and was absent in the mast cell-deficient W/Wv mice. The selective nonpeptide CRH receptor 1 antagonist, antalarmin and the nonselective peptide antagonist astressin both reduced vascular permeability triggered by Ucn but not that by Substance P or histamine. In contrast, the peptide antagonist alpha-helical CRH-(9-41) reduced the effect of all three. The vasodilatory effect of Ucn was largely inhibited by pretreatment with H1 receptor antagonists, suggesting that histamine is the major mediator involved in vitro. Neuropeptide depletion of sensory neurons, treatment with the ganglionic blocker hexamethonium, or in situ skin infiltration with the local anesthetic lidocaine did not affect Ucn-induced vascular permeability, indicating that its in situ effect was not mediated through the peripheral nervous system. These results indicate that Ucn is one of the most potent triggers of rat mast cell degranulation and skin vascular permeability. This effect of Ucn may explain stress-induced disorders, such as atopic dermatitis or psoriasis, and may lead to new forms of treatment. (+info)
Dynamic and quantitative Ca2+ measurements using improved cameleons.
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Cameleons are genetically-encoded fluorescent indicators for Ca2+ based on green fluorescent protein variants and calmodulin (CaM). Because cameleons can be targeted genetically and imaged by one- or two-photon excitation microscopy, they offer great promise for monitoring Ca2+ in whole organisms, tissues, organelles, and submicroscopic environments in which measurements were previously impossible. However, the original cameleons suffered from significant pH interference, and their Ca2+-buffering and cross-reactivity with endogenous CaM signaling pathways was uncharacterized. We have now greatly reduced the pH-sensitivity of the cameleons by introducing mutations V68L and Q69K into the acceptor yellow green fluorescent protein. The resulting new cameleons permit Ca2+ measurements despite significant cytosolic acidification. When Ca2+ is elevated, the CaM and CaM-binding peptide fused together in a cameleon predominantly interact with each other rather than with free CaM and CaM-dependent enzymes. Therefore, if cameleons are overexpressed, the primary effect is likely to be the unavoidable increase in Ca2+ buffering rather than specific perturbation of CaM-dependent signaling. (+info)
On the mechanism of histaminergic inhibition of glutamate release in the rat dentate gyrus.
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1. Histaminergic depression of excitatory synaptic transmission in the rat dentate gyrus was investigated using extracellular and whole-cell patch-clamp recording techniques in vitro. 2. Application of histamine (10 microM, 5 min) depressed synaptic transmission in the dentate gyrus for 1 h. This depression was blocked by the selective antagonist of histamine H3 receptors, thioperamide (10 microM). 3. The magnitude of the depression caused by histamine was inversely related to the extracellular Ca2+ concentration. Application of the N-type calcium channel blocker omega-conotoxin (0. 5 or 1 microM) or the P/Q-type calcium channel blocker omega-agatoxin (800 nM) did not prevent depression of synaptic transmission by histamine. 4. The potassium channel blocker 4-aminopyridine (4-AP, 100 microM) enhanced synaptic transmission and reduced the depressant effect of histamine (10 microM). 4-AP reduced the effect of histamine more in 2 mM extracellular calcium than in 4 mM extracellular calcium. 5. Histamine (10 microM) did not affect the amplitude of miniature excitatory postsynaptic currents (mEPSCs) and had only a small effect on their frequency. 6. Histaminergic depression was not blocked by an inhibitor of serine/threonine protein kinases, H7 (100 microM), or by an inhibitor of tyrosine kinases, Lavendustin A (10 microM). 7. Application of adenosine (20 microM) or the adenosine A1 agonist N6-cyclopentyladenosine (CPA, 0.3 microM) completely occluded the effect of histamine (10 microM). 8. We conclude that histamine, acting on histamine H3 receptors, inhibits glutamate release by inhibiting presynaptic calcium entry, via a direct G-protein-mediated inhibition of multiple calcium channels. Histamine H3 receptors and adenosine A1 receptors act upon a common final effector to cause presynaptic inhibition. (+info)
Mediators of anaphylaxis but not activated neutrophils augment cholinergic responses of equine small airways.
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Neutrophilic inflammation in small airways (SA) and bronchospasm mediated via muscarinic receptors are features of chronic obstructive pulmonary disease in horses (COPD). Histamine, serotonin, and leukotrienes (LTs) are reported to be involved in the exacerbation of COPD, and currently, histamine has been shown to increase tension response to electrical field simulation (EFS) in equine SA. We tested the effects of these mediators and the effects of activated neutrophils on the cholinergic responses in SA. Histamine, serotonin, and LTD4 had a synergistic effect on EFS responses and only an additive effect on the tension response to exogenous ACh or methacholine. Atropine and TTX entirely eliminated the EFS-induced tension response in the presence of all three inflammatory mediators, indicating that augmentation of the EFS response applies only to the endogenous cholinergic response. Neutrophils isolated from control and COPD-affected horses were activated by zymosan, producing 18.1 +/- 2.3 and 25.0 +/- 2.3 nmol superoxide. 10(6) cells-1. 30 min-1, respectively. However, in contrast to the profound effect of mediators, incubation of SA for over 1 h in a suspension of up to 30 x 10(6) zymosan-treated neutrophils/ml did not significantly affect EFS responses of SA isolated from either control or COPD-affected horses. We conclude that in equine SA 1) the endogenous cholinergic responses are subject to strong facilitation by inflammatory mediators; 2) activated neutrophils do not affect cholinergic responses in SA; and 3) in acute bouts of equine COPD, histamine, LTD4, and serotonin (mediators primarily associated with type I allergic reaction) rather than mediators derived from neutrophils most likely contribute to increased cholinergic airway tone. (+info)
Exhaled nitric oxide; relationship to clinicophysiological markers of asthma severity.
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Bronchial asthma is an airway disorder associated with bronchial hyperresponsiveness, variable airflow obstruction and elevated levels of nitric oxide (NO) in exhaled air. The variables all reflect, in part, the underlying airway inflammation in this disease. To understand their interrelationships we have investigated the relationship between exhaled NO levels and clinicophysiological markers of asthma severity. Twenty-six steroid naive atopic asthmatics participated in the analysis. All were given diary cards and were asked to record their peak expiratory flow (PEF) rates twice daily together with their asthma symptom scores and beta-agonist use. Diary cards were collected 2 weeks later and measurements of exhaled NO levels, FEV1 and histamine bronchial hyperreactivity (PC20 histamine) were undertaken. Exhaled NO levels were significantly higher in our study population than in normal control subjects and correlated negatively with PC20 histamine (r = -0.51; P = 0.008) and positively with PEF diurnal variability (r = 0.58; P = 0.002), but not with symptom scores, beta-agonist use of FEV1 (%). We conclude that a significant relationship exists between exhaled NO levels and the two characteristic features and markers of asthma severity, namely bronchial hyperreactivity and PEF diurnal variability. The lack of correlation between symptom score and beta-agonist use, of FEV1 (%) predicted and exhaled NO suggests that these measures are reflective of differing aspects of asthma. (+info)
Strain-dependent induction of allergic sensitization caused by peanut allergen DNA immunization in mice.
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To investigate the potential application of allergen gene immunization in the modulation of food allergy, C3H/HeSn (C3H) mice received i.m. injections of pAra h2 plasmid DNA encoding one of the major peanut allergens, Ara h2. Three weeks following pDNA immunization, serum Ara h2-specific IgG2a, IgG1, but not IgE, were increased significantly in a dose-dependent manner. IgG1 was 30-fold higher in multiply compared with singly immunized mice. Ara h2 or peanut protein injection of immunized mice induced anaphylactic reactions, which were more severe in multiply immunized mice. Heat-inactivated immune serum induced passive cutaneous anaphylaxis, suggesting that anaphylaxis in C3H mice was mediated by IgG1. IgG1 responses were also induced by intradermal injection of pAra h2, and by i.m. injection of pOMC, the plasmid DNA encoding the major egg allergen protein, ovomucoid. To elucidate whether the pDNA immunization-induced anaphylaxis was a strain-dependent phenomenon, AKR/J and BALB/c mice also received multiple i.m. pAra h2 immunizations. Injection of peanut protein into these strains at weeks 3 or 5 following immunization did not induce reactions. Although IgG2a was increased significantly from week 2 in AKR/J mice and from week 4 in BALB/c mice and remained elevated for at least 6 wk, no IgG1 or IgE was detected. These results indicate that the type of immune responses to pDNA immunization in mice is strain dependent. Consequently, models for studying human allergen gene immunization require careful selection of suitable strains. In addition, this suggests that similar interindividual variation is likely in humans. (+info)