Antihistamines: ABC for the pediatricians.

Antihistamines are currently one of the most commonly administered drugs in children. They are used to treat symptoms that depend on histamine release, namely allergic diseases, such as rhinitis, asthma, urticaria, and anaphylaxis. It is possible to distinguish first- and second-generation antihistamines. Pharmacological effects and therapeutic indications are similar, but second-generation antihistamines have fewer adverse effects because they are more selective for peripheral H1 receptors. Although they have been on the market for several years, there are still many adverse effects linked to the antihistamine safety profile, especially in the first years of life. Thus, many antihistamines are prescribed off-label, especially in children younger than 2 years of age, which is the age-group where most of the data on drug safety are lacking and many antihistamines are not recommended. This article aims to provide a practical update on the use of antihistamines in children.

Re-sensitization of desensitized histamine H1 receptors in the human skin takes more than 18 hours.

BACKGROUND: It is known since the time of testing histamine on pieces of guinea pig's jejunum that histamine receptors can develop insensitivity. The aim was to find evidence for desensitization of histamine H1 receptors in the human skin in vivo and, if found, to study the time for such receptors to regain normal sensitivity. MATERIALS AND METHODS: A skin prick test with histamine (10 mg mL-1 ) was set in areas where a large histamine wheal was evoked 2, 6, 18, 24 or 72 hours earlier. A skin prick test with histamine (10 mg mL-1 ) was also set in an area where an allergen wheal was evoked 2 or 6 hours earlier. Heights, diameters and areas were measured on photographs of side views of plaster casts of the evoked skin elevations. RESULTS: Histamine wheals, called test wheals, in areas where large histamine wheals were evoked 2, 6 or 18 hours earlier, were smaller than histamine wheals, called initial wheals, in earlier non-stimulated areas. Test wheals from the 18 hours experiment were smaller than test wheals from the 72 hours experiment. Test wheals evoked in areas where allergen wheals were evoked 2 or 6 hours earlier were smaller than corresponding initial wheals. CONCLUSION: Histamine-evoked wheals and IgE-mediated allergic wheals reduce the sensitivity of histamine H1 receptors in the human skin. It takes between 18 and 72 hours to restore the sensitivity. Similarities between the development of histamine wheals in the human skin and histaminergic migraine with aura are discussed.

Cetirizine use in childhood: an update of a friendly 30-year drug.

Cetirizine is a second-generation antihistamine, derived from the metabolism of hydroxyzine, highly specific for the H1 receptors, and with marked antiallergic properties. Although its history began more than 30 years ago, it remains one of the most used drugs in children with a leading role in the medical care of children with allergic diseases. Cetirizine use is licensed for paediatric patients for the treatment of allergic rhinitis, and chronic spontaneous urticaria, in Europe in children older than 2 years old and in the USA in children older than 6 months old. This review provides a practical update on the use of cetirizine in children and adolescents.

Signaling mechanism underlying the histamine-modulated action of hypoglossal motoneurons.

Histamine, an important modulator of the arousal states of the central nervous system, has been reported to contribute an excitatory drive at the hypoglossal motor nucleus to the genioglossus (GG) muscle, which is involved in the pathogenesis of obstructive sleep apnea. However, the effect of histamine on hypoglossal motoneurons (HMNs) and the underlying signaling mechanisms have remained elusive. Here, whole-cell patch-clamp recordings were conducted using neonatal rat brain sections, which showed that histamine excited HMNs with an inward current under voltage-clamp and a depolarization membrane potential under current-clamp via histamine H1 receptors (H1Rs). The phospholipase C inhibitor U-73122 blocked H1Rs-mediated excitatory effects, but protein kinase A inhibitor and protein kinase C inhibitor did not, indicating that the signal transduction cascades underlying the excitatory action of histamine on HMNs were H1R/Gq/11 /phospholipase C/inositol-1,4,5-trisphosphate (IP3). The effects of histamine were also dependent on extracellular Na(+) and intracellular Ca(2+), which took place via activation of Na(+)-Ca(2+) exchangers. These results identify the signaling molecules associated with the regulatory effect of histamine on HMNs. The findings of this study may provide new insights into therapeutic approaches in obstructive sleep apnea. We proposed the post-synaptic mechanisms underlying the modulation effect of histamine on hypoglossal motoneuron. Histamine activates the H1Rs via PLC and IP3, increases Ca(2+) releases from intracellular stores, promotes Na(+) influx and Ca(2+) efflux via the NCXs, and then produces an inward current and depolarizes the neurons. Histamine modulates the excitability of HMNs with other neuromodulators, such as noradrenaline, serotonin and orexin. We think that these findings should provide an important new direction for drug development for the treatment of obstructive sleep apnea.

A Novel Potent Sleep-Promoting Effect of Turmeric: Turmeric Increases Non-Rapid Eye Movement Sleep in Mice Via Histamine H1Receptor Blockade.

SCOPE: Turmeric has a broad spectrum of biological properties; however, the sleep-promoting effects of turmeric have not yet been reported. Thus, this study aims to investigate the effect of turmeric on sleep and the molecular mechanism underlying this effect. METHODS AND RESULTS: Pentobarbital-induce sleep test and sleep-wake profile assessment using recorded electroencephalography are used to evaluate the hypnotic effects of the turmeric extract (TE) compared to diazepam on sleep in mice. Additionally, the molecular mechanism of TE's sleep effect is investigated using ex vivo electrophysiological recordings from brain slices in histamine H1 receptor (H1 R) knockout mice. Oral administration of TE and diazepam significantly reduce sleep latency and increase non-rapid eye movement sleep (NREMS) duration without delta activity in mice. Like doxepin, TE inhibits the H1 R agonist (2-pyridylethylamine dihydrochloride)-induced increase in action potentials in the hypothalamic neurons. In animal tests using neurotransmitter agonists or antagonists, TE effect mimick H1 R antagonistic effect of doxepin. Additionally, both reduce sleep latency and increase NREMS in wild-type mice, although these effects are not observed in H1 R knockout mice. CONCLUSION: TE has a sleep-promoting effect owing to reduction in sleep latency and enhancement of NREMS via H1 R blockade; therefore, it could be useful in insomnia.

Crosstalk of hypothalamic chemerin, histamine, and AMPK in diet-and olanzapine-induced obesity in rats.

AIM: Contradiction overwhelms chemerin link to feeding behavior. Neither the chemerin central role on appetite regulation nor its relation to hypothalamic histamine and AMPK is verified. MAIN METHODS: Food intake, body weight and hypothalamic biochemical changes were assessed after a single intra-cerebroventricular or intraperitoneal injection (ip) (1 µg/kg or 16 µg/kg, respectively) or chronic ip administration (8 µg/kg/day) of chemerin for 14 or 28 days. Hypothalamic neurobiochemical changes in chemerin/histamine/AMPK induced by either 8-week high fat diet (HFD) or food restriction were also investigated. To confirm chemerin-histamine crosstalk, these neurobiochemical changes were assessed under settings of H1-receptor agonism and/or antagonism by betahistine and/or olanzapine, respectively for 3 weeks. KEY FINDINGS: Chemerin-injected rats exhibited anorexigenic behavior in both acute and chronic studies that was associated with a decreased AMPK activity in the arcuate nucleus (ARC). However, with long-term administration, chemerin anorexigenic effect gradually ceased. Contrarily to food restriction, 8-week HFD increased ARC expression of chemerin and its receptor CMKLR1, reducing food intake via an interplay of H1-receptors and AMPK activity. Blockage of H1-receptors by olanzapine disrupted chemerin signaling pathway with an increased AMPK activity, augmenting food intake. These changes were reversed to normal by betahistine coadministration. SIGNIFICANCE: Chemerin is an anorexigenic adipokine, whose dysregulation is implicated in diet, and olanzapine-induced obesity through a histamine/AMPK axis in the ARC. Hypothalamic chemerin/CMKLR1 expression is a dynamic time-dependent response to changes in body weight and/or food intake. Targeting chemerin as a novel therapeutic approach against antipsychotic- or diet-induced obesity is worth to be further delineated.

Focus on the cetirizine use in clinical practice: a reappraisal 30 years later.

Antihistamines are currently one of the most commonly administered categories of drugs. They are used to treat symptoms that are secondary to histamine release, which is typical of certain allergic conditions, including rhinitis, conjunctivitis, asthma, urticaria, and anaphylaxis. Cetirizine belongs to the second-generation family, so, it is very selective for peripheral H1 receptors, is potent and quickly relieves symptoms, exerts additional anti-allergic/anti-inflammatory effects, and is usually well-tolerated. It has been marketed 30 years ago. In these years, a remarkable body of evidence has been built. The current review provides a practical update on the use of cetirizine in clinical practice.

Contribution of potassium channels, beta2-adrenergic and histamine H1 receptors in the relaxant effect of baicalein on rat tracheal smooth muscle.

OBJECTIVES: Baicalein, a compound extracted from a variety of herbs, showed various pharmacological effects. This study evaluated the relaxant effects of baicalein and its underlying molecular mechanisms of action on rat's isolated tracheal smooth muscle. MATERIALS AND METHODS: Tracheal smooth muscle were contracted by 10 µM methacholine or 60 mM KCl and the effects of cumulative concentrations of baicalein (5, 10, 20 and 40 mg/ml) and theophylline (0.2, 0.4, 0.6 and 0.8 mM) were evaluated. To examine the possible mechanism(s) of the relaxant effect of baicalein, its effect was also evaluated on incubated tissues with atropine, indomethacin, diltiazem, N(G)-Nitro-L-arginine methyl ester (L-NAME), glibenclamide, propranolol and chlorpheniramine. RESULTS: A concentration-dependent and significant relaxant effect was seen for baicalein in non-incubated tissues contracted by KCl or methacholine (P<0.01 to P<0.001). No significant difference was seen between the relaxant effects of high concentrations of baicalein and theophylline. The relaxant effects of all concentrations of baicalein in incubated tissues with glibenclamide, propranolol and chlorpheniramine were significantly lower than non-incubated tissues (P<0.05 to P<0.001). Additionally, the EC50 values of baicalein in incubated tissue with propranolol was significantly higher than non-incubated condition (P<0.05). CONCLUSION: A potent relaxant effect comparable to the effect of theophylline was shown for baicalein, which was probably mediated via inhibition of histamine (H1) receptors, stimulation of beta2-adrenergic receptors and potassium channels activation.

Loratadine augments emotional blushing.

The aim of this study was to determine whether loratadine, a selective inverse agonist of peripheral histamine H1 receptors, would reduce emotional blushing. Loratadine (10 mg) or placebo was administered orally one hour before 31 healthy participants sang a children's nursery rhyme to evoke embarrassment and blushing. Skin blood flow was monitored via a laser Doppler probe attached to the cheek. Increases in facial blood flow while participants sang were greater in the loratadine than the placebo group (mean increase ±â€¯standard deviation 71 ±â€¯52% in the loratadine group versus 35 ±â€¯37%, p = .036). However, perceptions of blushing were similar in both groups. These findings suggest that loratadine augmented blushing rather than inhibiting it. Thus, histamine released during blushing may inhibit acute increases in facial blood flow by evoking H1 receptor-mediated vasoconstriction.

Brain Activation by H1 Antihistamines Challenges Conventional View of Their Mechanism of Action in Motion Sickness: A Behavioral, c-Fos and Physiological Study in Suncus murinus (House Musk Shrew).

Motion sickness occurs under a variety of circumstances and is common in the general population. It is usually associated with changes in gastric motility, and hypothermia, which are argued to be surrogate markers for nausea; there are also reports that respiratory function is affected. As laboratory rodents are incapable of vomiting, Suncus murinus was used to model motion sickness and to investigate changes in gastric myoelectric activity (GMA) and temperature homeostasis using radiotelemetry, whilst also simultaneously investigating changes in respiratory function using whole body plethysmography. The anti-emetic potential of the highly selective histamine H1 receptor antagonists, mepyramine (brain penetrant), and cetirizine (non-brain penetrant), along with the muscarinic receptor antagonist, scopolamine, were investigated in the present study. On isolated ileal segments from Suncus murinus, both mepyramine and cetirizine non-competitively antagonized the contractile action of histamine with pK b values of 7.5 and 8.4, respectively; scopolamine competitively antagonized the contractile action of acetylcholine with pA2 of 9.5. In responding animals, motion (1 Hz, 4 cm horizontal displacement, 10 min) increased the percentage of the power of bradygastria, and decreased the percentage power of normogastria whilst also causing hypothermia. Animals also exhibited an increase in respiratory rate and a reduction in tidal volume. Mepyramine (50 mg/kg, i.p.) and scopolamine (10 mg/kg, i.p.), but not cetirizine (10 mg/kg, i.p.), significantly antagonized motion-induced emesis but did not reverse the motion-induced disruptions of GMA, or hypothermia, or effects on respiration. Burst analysis of plethysmographic-derived waveforms showed mepyramine also had increased the inter-retch+vomit frequency, and emetic episode duration. Immunohistochemistry demonstrated that motion alone did not induce c-fos expression in the brain. Paradoxically, mepyramine increased c-fos in brain areas regulating emesis control, and caused hypothermia; it also appeared to cause sedation and reduced the dominant frequency of slow waves. In conclusion, motion-induced emesis was associated with a disruption of GMA, respiration, and hypothermia. Mepyramine was a more efficacious anti-emetic than cetirizine, suggesting an important role of centrally-located H1 receptors. The ability of mepyramine to elevate c-fos provides a new perspective on how H1 receptors are involved in mechanisms of emesis control.

Effect of Agonist and Antagonist on the In Vitro Contractility of Inflamed Vermiform Appendix.

INTRODUCTION: Appendicitis poses a great health problem worldwide. Previous studies demonstrated structural damage to neuronal network and interstitial cell of Cajal in appendicitis. Above observations suggest for the alterations in appendicular motility/contractility in appendicitis. But the mechanisms involved in mediating the contractility in inflamed vermiform appendix is not known till date. AIM: The present in vitro study was performed to find out the mechanisms responsible for contractility in the inflamed human vermiform appendix. MATERIALS AND METHODS: Contractions of the longitudinal muscle strips of inflamed appendix were recorded in vitro at 37±0.5°C. Control contractions were recorded for 30 min after an initial tension of 0.5 gram. Initially dose-response experiments of agonists (acetylcholine, serotonin and histamine) were performed separately and the dose that produced maximum contraction was determined with each agonist. This maximal dose of agonist was used to elicit contractions in next series of experiments before and after pre-treatment with appropriate antagonists like atropine, ondansetron (5-HT3 antagonist) and chlorpheniramine maleate respectively. RESULTS: Acetylcholine (ACh) and serotonin (5-HT) elicited maximum amplitude of contraction at 10 µM and 1 µM concentration respectively. These contractions were significantly blocked by prior exposure of muscle strips with atropine (100 µM) and ondansetron (10 µM). Histamine produced very low amplitude of contractions in comparison to ACh or 5-HT and did not exhibit dose-response relations. The histamine induced contractions were blocked by H1 antagonist chlorpheniramine maleate (100 µM). CONCLUSION: The observations suggested that the contractility of longitudinal muscle strips of inflamed vermiform appendix in human beings was predominantly mediated by muscarinic and serotonergic (5-HT3) mechanisms, whereas, histaminergic mechanisms played a minor role in mediating the contractility.

Na(+) -Ca(2+) Exchanger, Leak K(+) Channel and Hyperpolarization-Activated Cyclic Nucleotide-Gated Channel Comediate the Histamine-Induced Excitation on Rat Inferior Vestibular Nucleus Neurons.

AIMS: Antihistaminergic drugs have traditionally been used to treat vestibular disorders in the clinic. As a potential central target for antihistaminergic drugs, the inferior vestibular nucleus (IVN) is the largest subnucleus of the central vestibular nuclear complex and is considered responsible for vestibular-autonomic responses and integration of vestibular, cerebellar, and multisensory signals. However, the role of histamine on the IVN, particularly the underlying mechanisms, is still not clear. METHODS: Using whole-cell patch-clamp recordings on rat brain slices, histamine-induced effect on IVN neurons and the underlying receptor and ionic mechanisms were investigated. RESULTS: We found that histamine remarkably depolarized both spontaneous firing neurons and silent neurons in IVN via both histamine H1 and histamine H2 receptors. Furthermore, Na(+) -Ca(2+) exchangers (NCXs) and background leak K(+) channels linked to H1 receptors and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels coupled to H2 receptors comediate the histamine-induced depolarization on IVN neurons. CONCLUSION: These results demonstrate the multiple ionic mechanisms underlying the excitatory modulation of histamine/central histaminergic system on IVN neurons and the related vestibular reflexes and functions. The findings also suggest potential targets for the treatment of vestibular disorders in the clinic, at the level of ionic channels in central vestibular nuclei.

Dextromethorphan interactions with histaminergic and serotonergic treatments to reduce nicotine self-administration in rats.

Combining effective treatments with diverse mechanisms of action for smoking cessation may provide better therapy by targeting multiple points of control in the neural circuits underlying addiction. Previous research in a rat model has shown that dextromethorphan, which has α3ß4 nicotinic and NMDA glutamatergic antagonist actions, significantly decreases nicotine self-administration. We have found in the rat model that the H1 histamine antagonist pyrilamine and the serotonin 5HT2C agonist lorcaserin also significantly reduce nicotine self-administration. The current studies were conducted to determine the interactive effects of dextromethorphan with pyrilamine and lorcaserin on nicotine self-administration in rats. Young adult female rats were fitted with jugular IV catheters and trained to self-administer a nicotine infusion dose of 0.03-mg/kg/infusion. In an initial dose-effect function study of dextromethorphan, we found a monotonic decrease in nicotine self-administration over a dose range of 1 to 30-mg/kg with the lowest effective dose of 3-mg/kg. Then, with two separate cohorts of rats, dextromethorphan (0, 3.3, and 10-mg/kg) interactions with pyrilamine (0, 4.43, and 13.3-mg/kg) were investigated as well as interactions with lorcaserin (0, 0.3125 and 0.625-mg/kg). In the pyrilamine-dextromethorphan interaction study, an acute dose of pyrilamine (13.3-mg/kg) as well as an acute dose of dextromethorphan caused a significant decrease in nicotine self-administration. There were mutually augmenting effects of these two drugs. The combination of dextromethorphan (10-mg/kg) and pyrilamine (13.3-mg/kg) significantly lowered nicotine self-administration relative to either 10-mg/kg of dextromethorphan alone (p<0.05) or 13.3-mg/kg of pyrilamine alone (p<0.0005). In the lorcaserin-dextromethorphan study, an acute dose of lorcaserin (0.312-mg/kg) as well as an acute dose of dextromethorphan (10-mg/kg) caused a significant decrease in nicotine self-administration replicating previous findings. Augmenting interactions were observed with dextromethorphan and pyrilamine as well as lorcaserin. These findings suggest that combination therapy may be more effective smoking cessation treatments than monotherapy.

Infralimbic cortex controls core body temperature in a histamine dependent manner.

An increase in body temperature accelerates biochemical reactions and behavioral and physiological responses. A mechanism to actively increase body temperature would be beneficial during motivated behaviors. The prefrontal cortex is implicated in organizing motivated behavior; the infralimbic cortex, a subregion of the medial prefrontal cortex, has the necessary connectivity to serve the role of initiating such thermogenic mechanism at the beginning of the appetitive phase of motivated behavior; further, this cortex is active during motivated behavior and its disinhibition produces a marked behavioral and vegetative arousal increase, together with increases in histamine levels. We wanted to explore if this arousal was related to histaminergic activation after pharmacological infralimbic disinhibition and during the appetitive phase of motivated behavior. We measured core temperature and motor activity in response to picrotoxin injection in the infralimbic cortex, as well as during food-related appetitive behavior, evoked by enticing hungry rats with food. Pretreatment with the H1 receptor antagonist pyrilamine decreased thermal response to picrotoxin and enticement and completely blunted motor response to enticement. Motor and temperature responses to enticement were also completely abolished by infralimbic cortex inhibition with muscimol. To assess if this histamine dependent temperature increase was produced by an active sympathetic mediated thermogenic mechanism or was just a consequence of increased locomotor activity, we injected propranolol (i.p.), a ß adrenergic receptor blocker, before picrotoxin injection into the infralimbic cortex. Propranolol reduced the temperature increase without affecting locomotor activity. Altogether, these results suggest that infralimbic activation is necessary for appetitive behavior by inducing a motor and a vegetative arousal increase mediated by central histamine.

Betahistine ameliorates olanzapine-induced weight gain through modulation of histaminergic, NPY and AMPK pathways.

Olanzapine is widely used to treat schizophrenia and other disorders, but causes adverse obesity and other metabolic side-effects. Both animal and clinical studies have shown that co-treatment with betahistine (a histaminergic H1 receptor agonist and H3 receptor antagonist) is effective for ameliorating olanzapine-induced weight gain/obesity. To reveal the mechanisms underlying these effects, this study investigated the effects of co-treatment of olanzapine and betahistine (O+B) on expressions of histaminergic H1 receptor (H1R), AMP-activated protein kinase (AMPK), neuropeptide Y (NPY), and proopiomelanocortin (POMC) in the hypothalamus associated with reducing olanzapine-induced weight gain. Olanzapine significantly upregulated the mRNA and protein expressions of H1R, while O+B co-treatment significantly downregulated the H1R levels, compared to the olanzapine-only treatment group. The NPY mRNA expression was significantly enhanced by olanzapine, but it was significantly reversed by O+B co-treatment. The hypothalamic H1R expression was positively correlated with total food intake, and NPY expression. Olanzapine also increased AMPKα activation measured by the AMPKα phosphorylation (pAMPKα)/AMPKα ratio compared with controls, whereas O+B co-treatment decreased the pAMPKα/AMPKα ratio, compared with olanzapine only treatment. The pAMPKα/AMPKα ratio was positively correlated with total food intake and H1R expression. Although olanzapine administration decreased the POMC mRNA level, this level was not affected by O+B co-treatment. Therefore, these results suggested that co-treatment with betahistine may reverse olanzapine-induced body weight gain via the H1R-NPY and H1R-pAMPKα pathways.

Postsynaptic mechanisms underlying the excitatory action of histamine on medial vestibular nucleus neurons in rats.

BACKGROUND AND PURPOSE: Anti-histaminergic drugs have been widely used in the clinical treatment of vestibular disorders and most studies concentrate on their presynaptic actions. The present study investigated the postsynaptic effect of histamine on medial vestibular nucleus (MVN) neurons and the underlying mechanisms. EXPERIMENTAL APPROACH: Histamine-induced postsynaptic actions on MVN neurons and the corresponding receptor and ionic mechanisms were detected by whole-cell patch-clamp recordings on rat brain slices. The distribution of postsynaptic histamine H1, H2 and H4 receptors was mapped by double and single immunostaining. Furthermore, the expression of mRNAs for H1, H2 and H4 receptors and for subtypes of Na⁺ -Ca²âº exchangers (NCXs) and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels was assessed by quantitative real-time RT-PCR. KEY RESULTS: A marked postsynaptic excitatory effect, co-mediated by histamine H1 and H2 receptors, was involved in the histamine-induced depolarization of MVN neurons. Postsynaptic H1 and H2 rather than H4 receptors were co-localized in the same MVN neurons. NCXs contributed to the inward current mediated by H1 receptors, whereas HCN channels were responsible for excitation induced by activation of H2 receptors. Moreover, NCX1 and NCX3 rather than NCX2, and HCN1 rather than HCN2-4 mRNAs, were abundantly expressed in MVN. CONCLUSION AND IMPLICATIONS: NCXs coupled to H1 receptors and HCN channels linked to H2 receptors co-mediate the strong postsynaptic excitatory action of histamine on MVN neurons. These results highlight an active role of postsynaptic mechanisms in the modulation by central histaminergic systems of vestibular functions and suggest potential targets for clinical treatment of vestibular disorders.