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• The degree of fluid satiety differentially affects taste-aversive memory formation. • H3 receptor activation in the insular cortex disrupted CTA only under fluid deprivation regimen. • RAMH in the insular cortex decreases novel appetitive response only in the ad libitum regime. • H3 receptor activation during ad libitum conditioning accelerates aversive memory extinction. Conditioned taste aversion (CTA) is a robust associative learning; liquid deprivation during this conditioning allows researchers to obtain readable measures of associative learning. Recent research suggests that thirst could be a crucial motivator that modulates conditioning and memory extinction processes, highlighting the importance of the body's internal state during learning. Furthermore, the histaminergic system is one of the major modulatory systems controlling several behavioral and neurobiological functions, such as feeding, water intake, and nociception. Therefore, this research aimed to assess the effect of H3 histaminergic receptor activation in the insular cortex (IC) during CTA. For this, we conditioned adult male Wistar rats under two regimens: water deprivation and water ad libitum. A classical CTA protocol was used for water deprivation. Before CTA acquisition, 10 μM R-α-methylhistamine (RAMH), an H3 receptor agonist, was injected into the IC. Results showed that RAMH injections decreased CTA in water-deprived rats without affecting the significant aversion conditioning in rats that were given water ad libitum. Moreover, RAMH accelerated the process of aversive memory extinction under ad libitum water conditions. According to our findings, the degree of liquid satiety differentially affected taste-aversive memory formation, and H3 histamine receptors were more involved under water deprivation conditions during acquisition. However, these receptors modulated the strength of aversive conditioning by altering the rate of aversive memory extinction in the absence of deprivation. In conclusion, histaminergic activity in the IC may influence taste memory dynamics through different mechanisms depending on the degree of liquid satiety or deprivation during conditioning. [ABSTRACT FROM AUTHOR]

Virulent Klebsiella oxytoca strains are associated with gut and lung pathologies, yet our understanding of the molecular signals governing pathogenesis remains limited. Here, we characterized a family of K. oxytoca pyrazine and pyrazinone autoinducers and explored their roles in microbial and host signaling. We identified the human mucin capping sugar Neu5Ac as a selective elicitor of leupeptin, a protease inhibitor prevalent in clinical lung isolates of K. oxytoca, and leupeptin-derived pyrazinone biosynthesis. Additionally, we uncovered a separate pyrazine pathway, regulated by general carbohydrate metabolism, derived from a broadly conserved PLP-dependent enzyme. While both pyrazine and pyrazinone signaling induce iron acquisition responses, including enterobactin biosynthesis, pyrazinone signaling enhances yersiniabactin virulence factor production and selectively activates the proinflammatory human histamine receptor H4 (HRH4). Our findings suggest that the availability of specific carbohydrates delineates distinct autoinducer pathways in K. oxytoca that may have differential effects on bacterial virulence and host immune responses. Differential carbohydrate metabolism elicits distinct pyrazine and pyrazinone autoinducer signalling pathways in Klebsiella oxytoca, which impact bacterial virulence programs. [ABSTRACT FROM AUTHOR]

Background/Objectives: Autism spectrum disorder (ASD) is a neurodevelopmental condition marked by social interaction difficulties, repetitive behaviors, and immune dysregulation with elevated pro-inflammatory markers. Autophagic deficiency also contributes to social behavior deficits in ASD. Histamine H3 receptor (H3R) antagonism is a potential treatment strategy for brain disorders with features overlapping ASD, such as schizophrenia and Alzheimer's disease. Methods: This study investigated the effects of sub-chronic systemic treatment with the H3R antagonist E159 on social deficits, repetitive behaviors, neuroinflammation, and autophagic disruption in male BTBR mice. Results: E159 (2.5, 5, and 10 mg/kg, i.p.) improved stereotypic repetitive behavior by reducing self-grooming time and enhancing spontaneous alternation in addition to attenuating social deficits. It also decreased pro-inflammatory cytokines in the cerebellum and hippocampus of treated BTBR mice. In BTBR mice, reduced expression of autophagy-related proteins LC3A/B and Beclin 1 was observed, which was elevated following treatment with E159, attenuating the disruption in autophagy. The co-administration with the H3R agonist MHA (10 mg/kg, i.p.) reversed these effects, highlighting the role of histaminergic neurotransmission in observed behavioral improvements. Conclusions: These preliminary findings suggest the therapeutic potential of H3R antagonists in targeting neuroinflammation and autophagic disruption to improve ASD-like behaviors. [ABSTRACT FROM AUTHOR]

Izuforant is a selective, and potent histamine H4 receptor (H4R) antagonist developed to treat atopic dermatitis (AD). There is an unmet medical need for therapeutic agents to control inflammation and pruritus. Izuforant is a strong candidate for this task based on the findings of non‐clinical studies showing that inhibition of the histamine‐mediated signaling pathway via H4R by izuforant results in decreased pruritus and inflammation. This study aimed to evaluate the clinical pharmacokinetic (PK) and pharmacodynamic (PD) profiles of izuforant. Dose‐block‐randomized, double‐blind, placebo‐controlled, single‐ and multiple ascending dose studies were conducted in 64 healthy volunteers. For the single ascending dose (SAD) study, 10–600 mg izuforant was administered to the designated groups. For the multiple ascending dose (MAD) study, 100–400 mg izuforant was administered to three groups. The clinical pharmacokinetic (PK) profile of izuforant was evaluated using plasma and urine concentrations. Blood sampling for the PD assay, which measured imetit‐induced eosinophil shape changes (ESC), was also conducted. A one‐compartment PK model described the distribution and elimination profiles of izuforant. An imetit‐induced ESC inhibition test was established and validated for PD evaluation as a measure of the H4R antagonistic effect. ESC inhibition was observed even at doses as low as 10 mg; however, this inhibition became stronger and lasted longer as the dose increased. All izuforant doses were well tolerated, and no discontinuations due to adverse events (AE) or deaths were reported. [ABSTRACT FROM AUTHOR]

This study attempted to clarify the role of histamine H1 receptors in epilepsy by exploring the effects of agonists and inverse agonists on the rundown of the current induced by iterative applications of NMDA or GABA in primary neuronal culture. Mepyramine, a classical H1‐receptor antagonist/inverse agonist, increased the NMDA current by about 40% during the first minutes of recording. This effect was concentration‐dependent, maximal at 10 nM, and mimicked by triprolidine, another antagonist/inverse agonist. No endogenous histamine was detected in the cultures by a selective immunoassay; both compounds were acting as inverse agonists. Indicating a high constitutive activity of the H1 receptor in this system, histamine did not affect the NMDA rundown, including its settlement, but significantly reversed the effect of mepyramine. A similar pattern was obtained with 2,3 bromophenyl histamine, a selective H1‐receptor agonist. The initial increase induced by the two inverse agonists was followed by the same rundown as in controls. H1‐ and NMDA receptors are colocalized in most cultured neuronal cells. Mepyramine and histamine did not affect the GABA rundown. Our findings suggest an interaction between H1‐ and NMDA receptors. Inactivation of the H1‐receptor by its inverse agonists delays the settlement of the NMDA rundown, which may underlie their proconvulsant effect reported in clinics. Therefore, H1‐receptor constitutive activity and the effect of histamine revealed in its absence, tend to facilitate the initiation of the rundown, which is consistent with the anticonvulsant properties of histamine via activation of H1‐receptors reported in many studies. [ABSTRACT FROM AUTHOR]

Aim Methods Results Conclusion Postmortem brain studies offer enormous opportunities to study molecular mechanisms associated with suicide. In the present study, conventional [35S]GTPγS binding assay and its version‐up method ([35S]GTPγS binding/immunoprecipitation assay) were applied to postmortem human hippocampal membranes prepared from suicide victims and control subjects.By using conventional [35S]GTPγS binding assay, functional activations of Gi/o proteins coupled with multiple GPCRs (5‐HT1A receptor, α2A‐adrenoceptor, M2/M4 mAChRs, adenosine A1 receptor, histamine H3 receptor, group II mGlu, GABAB receptor, μ‐opioid receptor, δ‐opioid receptor, and NOP receptor) were detected by using 15 different agonists. Furthermore, 5‐HT2A receptor‐ and M1 mAChR‐mediated Gαq/11 activation and adenosine A1 receptor‐mediated Gαi‐3 activation were detectable by means of [35S]GTPγS binding/immunoprecipitation assay.No significant differences in pharmacological parameters of all concentration‐response curves investigated were found between suicide victims and control subjects. Significant correlations were obtained for the maximal percent increases between some distinct signaling pathways.Although only preliminary and auxiliary results were obtained as to the potential differences between suicide victims and control subjects because of the limited number of subjects as well as unmatched age and postmortem delay, adenosine A1 receptor‐mediated Gαi/o activation and 5‐HT2A receptor‐mediated Gαq/11 activation appear worth focusing on in the future investigations. This study also indicates the possibility that some distinct signaling pathways are interrelated with each other, for example, functional activations of Gi/o proteins coupled to M2/M4 mAChR and 5‐HT1A receptor, NOP receptor, and GABAB receptor, and NOP receptor and δ‐opioid receptor. [ABSTRACT FROM AUTHOR]

Objective(s): In the present study, the relaxant effect of crocetin on tracheal smooth muscle cells (TSM) and its possible mechanisms were evaluated. Materials and Methods: The study was conducted on 54 male Wistar rats in 8 groups. TSM was contracted by methacholine (10 μM) and KCl (60 mM), and the relaxant effects of four cumulative concentrations of crocetin, petal extract of saffron, and theophylline were examined on non-incubated and TSM incubated with propranolol, chlorpheniramine, diltiazem, atropine, glibenclamide, and indomethacin were investigated. Results: In non-incubated TSM contracted by methacholine or KCl, crocetin and theophylline showed concentration-dependent relaxant effects (all, P<0.001). However, various concentrations of crocetin showed significantly lower relaxant effects compared to those of theophylline (all, P<0.001). In the methacholine-induced contraction of TSM, the relaxation effect of the last concentration of crocetin in the TSM incubated with propranolol was lower than in non-incubated TSM (P<0.05). In the incubated TSM with chlorpheniramine, the relaxant effects of the two last concentrations of crocetin were significantly lower than in the non-incubated tissues contracted by KCl (P<0.05 and P<0.0). The levels of EC50 crocetin in the incubated TSM with glibenclamide, chlorpheniramine, and indomethacin were markedly lower than in non-incubated (all, P<0.05). Conclusion: The results showed potent relaxation effects of crocetin on TSM and were suggested to be through stimulation of ß-adrenergic receptors, inhibition of histamine (H1 ) receptors, and potassium channel opening mechanisms. [ABSTRACT FROM AUTHOR]

Histamine is one of the most important and extensively studied biological molecules in the human body. It plays a constitutive role within almost every bodily system, but most notably within the stomach, where it regulates acid secretion, the central nervous system, where it acts as a neurotransmitter, the cardiovascular system, where it affects cardiac output and vascular permeability, and it has a well-established role in allergy and anaphylaxis. Histamine exerts its effects through four distinct receptor subtypes: H1, H2, H3 and H4. Predominantly, though not exclusively, these take the form of G-protein-coupled receptors. Clinically used antihistamines demonstrate inverse agonism to the histamine receptor and drugs are available with activity at H1, H2 and H3 receptors. H1 antihistamines are used in the treatment of allergy, and are classified as either first or second generation. First-generation antihistamines have significant sedative side effects. H2 antihistamines are predominantly used for the treatment of gastrooesophageal reflux and peptic ulcer disease; however, the most widely used of these, ranitidine, has been withdrawn from use due to (impurity related) safety concerns. H3 antihistamines have been explored for the treatment of neurological disease and to date the only licensed H3 antihistamine is used for the treatment of narcolepsy. Multiple uses have been suggested for H4 antihistamines, including immunomodulation, the treatment of asthma and even as an analgesic. However, no (commercially available) drug exists as of yet. [ABSTRACT FROM AUTHOR]

The article discusses the creation of the World Wide Approved Drug (WWAD) database, which aims to provide comprehensive information on medicines approved for therapeutic use worldwide. The database collects data from National Medicine Registers (NMRs) and official documentation from medicines regulatory authorities (MRAs) of different countries. The article emphasizes the need for a unified resource that aggregates information on worldwide approved medicines and highlights the challenges in accessing and processing this data. The World Wide Approved Drugs (WWAD) database is a comprehensive resource that provides information on low molecular weight pharmaceutical substances from 71 countries and regions. It includes data on drug names, chemical structures, therapeutic indications, molecular targets, and biological activities. The database can be used for various purposes, including searching for information on approved drugs, drug repositioning, data enrichment, and assessing the novelty of investigated compounds. The WWAD database is freely available for academic use through the Way2Drug platform. This document contains a list of references and citations from various scientific articles and databases related to topics such as computational chemistry, drug discovery, drug repurposing, and regulatory approval of drugs. The references cover a range of subjects including the use of artificial intelligence and machine learning in drug discovery, the development of databases for drug repurposing, and the analysis of drug approvals by regulatory agencies. The document provides a comprehensive list of sources that library patrons can use to further their research on these topics. [Extracted from the article]

Autism spectrum disorder (ASD) is one of the leading causes of distorted social communication, impaired speech, hyperactivity, anxiety, and stereotyped repetitive behaviour. The aetiology of ASD is complex; therefore, multiple drugs have been suggested to manage the symptoms. Studies with histamine H3 receptor (H3R) blockers and acetylcholinesterase (AchE) blockers are considered potential therapeutic agents for the management of various cognitive impairments. Therefore, the aim of this study was to evaluate the neuro-behavioural effects of Betahistine, an H3R antagonist, and Donepezil, an acetylcholinesterase inhibitor on Swiss albino mouse model of autism. The mice were intraperitoneally injected with valproic acid (VPA) on the embryonic 12.5th day to induce autism-like symptoms in their offspring. This induced autism-like symptoms persists throughout the life. After administration of different experimental doses, various locomotor tests: Open Field, Hole-Board, Hole Cross and behavioural tests by Y-Maze Spontaneous Alternation and histopathology of brain were performed and compared with the control and negative control (NC1) groups of mice. The behavioural Y-Maze test exhibits significant improvement (p <0.01) on the short term memory of the test subjects upon administration of lower dose of Betahistine along with MAO-B inhibitor Rasagiline once compared with the NC1 group (VPA-exposed mice). Furthermore, the tests showed significant reduction in locomotion in line crossing (p <0.05), rearing (p <0.001) of the Open Field Test, and the Hole Cross Test (p <0.01) with administration of higher dose of Betahistine. Both of these effects were observed upon administration of acetylcholinesterase inhibitor, Donepezil. Brain-histopathology showed lower neuronal loss and degeneration in the treated groups of mice in comparison with the NC1 VPA-exposed mice. Administration of Betahistine and Rasagiline ameliorates symptoms like memory deficit and hyperactivity, proving their therapeutic effects. The effects found are dose dependent. The findings suggest that H3R might be a viable target for the treatment of ASD. [ABSTRACT FROM AUTHOR]

Repurposing utilizes existing drugs with known safety profiles and discovers new uses by combining experimental and computational approaches. The integration of computational methods has greatly advanced drug repurposing, offering a rational approach and reducing the risk of failure in these efforts. Recognizing the potential for drug repurposing, we employed our Iterative Stochastic Elimination (ISE) algorithm to screen known drugs from the DrugBank database. Repurposing in our hands is based on computer models of the actions of ligands: the ISE algorithm is a machine learning tool that creates ligand-based models by distinguishing between the physicochemical properties of known drugs and those of decoys. The models are large sets of "filters" made out, each, of molecular properties. We screen and score external sets of molecules (in our case- the DrugBank molecules) by our agonism and antagonism models based on published data (i.e., IC50, Ki, or EC50) and pick the top-scoring molecules as candidates for experiments. Such agonist and antagonist models for six G-protein coupled receptors (GPCRs) families facilitated the identification of repurposing opportunities. Our screening revealed 5982 new potential molecular actions (agonists, antagonists), which suggest repurposing candidates for the cannabinoid 2 (CB2), histamine (H1, H3, and H4), and dopamine 3 (D3) receptors, which may be useful to treat conditions such as neuroinflammation, obesity, allergic dermatitis, and drug abuse. These sets of best candidates should now be examined by experimentalists: based on previous such experiments, there is a very high chance of discovering novel highly bioactive molecules. [ABSTRACT FROM AUTHOR]

Histamine (HA), a biogenic monoamine, exerts its pleiotropic effects through four H1R–H4R histamine receptors, which are also expressed in brain tissue. Together with the projections of HA-producing neurons located within the tuberomammillary nucleus (TMN), which innervate most areas of the brain, they constitute the histaminergic system. Thus, while remaining a mediator of the inflammatory reaction and immune system function, HA also acts as a neurotransmitter and a modulator of other neurotransmitter systems in the central nervous system (CNS). Although the detailed causes are still not fully understood, neuroinflammation seems to play a crucial role in the etiopathogenesis of both neurodevelopmental and neurodegenerative (neuropsychiatric) diseases, such as autism spectrum disorders (ASDs), attention-deficit/hyperactivity disorder (ADHD), Alzheimer's disease (AD) and Parkinson's disease (PD). Given the increasing prevalence/diagnosis of these disorders and their socioeconomic impact, the need to develop effective forms of therapy has focused researchers' attention on the brain's histaminergic activity and other related signaling pathways. This review presents the current state of knowledge concerning the involvement of HA and the histaminergic system within the CNS in the development of neurodevelopmental and neurodegenerative disorders. To this end, the roles of HA in neurotransmission, neuroinflammation, and neurodevelopment are also discussed. [ABSTRACT FROM AUTHOR]

Background Clostridium difficile infection (CDI) is a debilitating nosocomial infection. C. difficile produces toxins A and B, which cause inflammation. Existing therapies have issues with recurrence, cost, and safety. We aim to discover a safe, effective, and economical nonmicrobiological therapeutic approach against CDI. Methods We included human primary peripheral blood mononuclear cells (PBMCs), fresh human colonic explants, and humanized HuCD34-NCG mice. Toxin A+B+ VPI 10463 and A−B+ ribotype 017 C. difficile strains were used. We used single-cell RNA profiling and high-throughput screening to find actionable toxin B–dependent pathways in PBMCs. Results Histamine 1 receptor–related drugs were found among the hit compounds that reversed toxin-mediated macrophage inflammatory protein (MIP) 1α expression in PBMCs. We identified loratadine as the safest representative antihistamine for therapeutic development. Loratadine inhibited toxin B–induced MIP-1α secretion in fresh human colonic tissues. Oral loratadine (10 mg/kg/d) maintained survival, inhibited intestinal CCl3 messenger RNA expression, and prevented vancomycin-associated recurrence in the VPI 10463–infected mice and ribotype 017-infected hamsters. Splenocytes from loratadine-treated mice conferred anti-inflammatory effects to the VPI 10463–infected T/B-cell-–deficient Rag −/− mice. Oral loratadine suppressed human MIP-1α expression in monocytes/macrophages in toxin B–expressing ribotype 017-infected humanized HuCD34-NCG mice. Conclusions Loratadine may be repurposed to optimize existing therapies against CDI. [ABSTRACT FROM AUTHOR]

This document is a letter to the editor discussing paradoxical urticaria reactions to H1-antihistamines. The authors report on nine patients with paradoxical urticaria who experienced hives from different classes of H1-antihistamines. The cause of this reaction is still unclear, but it may be related to mast cell degranulation or disruption of the arachidonic acid metabolism pathway. Physicians should be aware of this diagnosis and perform an allergy work-up, including skin testing, in patients suspected of having paradoxical urticaria. The letter includes a table summarizing the clinical characteristics and allergy work-up of the identified cases. [Extracted from the article]

Histamine H3 receptor (H3R) antagonists, such as betahistine (BHTE), have shown significant potential in treating central nervous system (CNS) disorders due to their neuroprotective properties. This study investigated BHTE's effects on lipopolysaccharide (LPS)-induced neurotoxicity, which is associated with neuroinflammation and neurodegeneration. Rats were divided into groups and pre-treated with BHTE (5 or 10 mg/kg, p.o.) for 30 days, followed by LPS administration (1 mg/kg, i.p.) for 4 consecutive days to induce neurotoxicity. LPS exposure resulted in cognitive impairment, as evidenced by performance deficits in maze tests, and a significant reduction in brain acetylcholine (ACh) levels. Additionally, LPS led to increased neuroinflammation, oxidative stress, mitochondrial dysfunction, and apoptosis. Pre-treatment with BHTE effectively counteracted these effects, improving cognitive performance and restoring ACh levels. BHTE significantly reduced LPS-induced increases in pro-inflammatory markers (COX-2, TNF-α, and IL-6) while enhancing anti-inflammatory cytokines (IL-10 and TGF-β1). Furthermore, BHTE improved mitochondrial function by increasing enzyme levels (MRCC-I, II, and IV) and boosted anti-apoptotic (Bcl-2) and antioxidant defenses (GSH and catalase). BHTE also reduced apoptosis markers, including pro-apoptotic protein caspase-3, and oxidative stress marker malondialdehyde (MDA). Molecular modeling studies revealed that BHTE effectively binds to key enzymes involved in neuroinflammation and apoptosis (AChE, COX-2, and caspase-3), with binding free energies between 4 and 5 kcal/mol, interacting with critical residues. These findings underscore BHTE's multifaceted neuroprotective effects against LPS-induced neurotoxicity, offering potential therapeutic avenues for managing neuroinflammation and related neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Doxepin is an antihistamine and tricyclic antidepressant that binds to the histamine H1 receptor (H1R) with high affinity. Doxepin is an 85:15 mixture of the E‐ and Z‐isomers. The Z‐isomer is well known to be more effective than the E‐isomer, whereas based on the crystal structure of the H1R/doxepin complex, the hydroxyl group of Thr1123.37 is close enough to form a hydrogen bond with the oxygen atom of the E‐isomer. The detailed binding characteristics and reasons for the differences remain unclear. In this study, we analyzed doxepin isomers bound to the receptor following extraction from a purified H1R protein complexed with doxepin. The ratio of the E‐ and Z‐isomers bound to wild‐type (WT) H1R was 55:45, indicating that the Z‐isomer was bound to WT H1R with an approximately 5.2‐fold higher affinity than the E‐isomer. For the T1123.37V mutant, the E/Z ratio was 89:11, indicating that both isomers have similar affinities. Free energy calculations using molecular dynamics (MD) simulations also reproduced the experimental results of the relative binding free energy differences between the isomers for WT and T1123.37V. Furthermore, MD simulations revealed that the hydroxyl group of T1123.37 did not form hydrogen bonds with the E‐isomer, but with the adjacent residues in the binding pocket. Analysis of the receptor‐bound doxepin and MD simulations suggested that the hydroxyl group of T1123.37 contributes to the formation of a chemical environment in the binding pocket, which is slightly more favorable for the Z‐isomer without hydrogen bonding with doxepin. [ABSTRACT FROM AUTHOR]

Objective(s): In the present study, the relaxant effect of crocetin on tracheal smooth muscle cells (TSM) and its possible mechanisms were evaluated.Materials and Methods: The study was conducted on 54 male Wistar rats in 8 groups. TSM was contracted by methacholine (10 μM) and KCl (60 mM), and the relaxant effects of four cumulative concentrations of crocetin, petal extract of saffron, and theophylline were examined on non-incubated and TSM incubated with propranolol, chlorpheniramine, diltiazem, atropine, glibenclamide, and indomethacin were investigated. Results: In non-incubated TSM contracted by methacholine or KCl, crocetin and theophylline showed concentration-dependent relaxant effects (all, P

Cadaverine is an endogenous metabolite produced by the gut microbiome with various activity in physiological and pathological conditions. However, whether cadaverine regulates pain or itch remains unclear. In this study, we first found that cadaverine may bind to histamine 4 receptor (H4R) with higher docking energy score using molecular docking simulations, suggesting cadaverine may act as an endogenous ligand for H4R. We subsequently found intradermal injection of cadaverine into the nape or cheek of mice induces a dose-dependent scratching response in mice, which was suppressed by a selective H4R antagonist JNJ-7777120, transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine and PLC inhibitor U73122, but not H1R antagonist or TRPA1 antagonist or TRPV4 antagonist. Consistently, cadaverine-induced itch was abolished in Trpv1 −/− but not Trpa1 −/− mice. Pharmacological analysis indicated that mast cells and opioid receptors were also involved in cadaverine-induced itch in mice. scRNA-Seq data analysis showed that H4R and TRPV1 are mainly co-expressed on NP2, NP3 and PEP1 DRG neurons. Calcium imaging analysis showed that cadaverine perfusion enhanced calcium influx in the dissociated dorsal root ganglion (DRG) neurons, which was suppressed by JNJ-7777120 and capsazepine, as well as in the DRG neurons from Trpv1 −/− mice. Patch-clamp recordings found that cadaverine perfusion significantly increased the excitability of small diameter DRG neurons, and JNJ-7777120 abolished this effect, indicating involvement of H4R. Together, these results provide evidences that cadaverine is a novel endogenous pruritogens, which activates H4R/TRPV1 signaling pathways in the primary sensory neurons. [ABSTRACT FROM AUTHOR]

The future of therapy for neurodegenerative diseases (NDs) relies on new strategies targeting multiple pharmacological pathways. Our research led to obtaining the compound AR71 [(E)-3-(3,4,5-trimethoxyphenyl)-1-(4-(3-(piperidin-1-yl)propoxy)phenyl)prop-2-en-1-one], which has high affinity for human H3R (Ki = 24 nM) and selectivity towards histamine H1 and H4 receptors (Ki > 2500 nM), and showed anti-inflammatory activity in a model of lipopolysaccharide-induced inflammation in BV-2 cells. The presented tests confirmed its antagonist/inverse agonist activity profile and good metabolic stability while docking studies showed the binding mode to histamine H1, H3, and H4 receptors. In in vitro tests, cytotoxicity was evaluated at three cell lines (neuroblastoma, astrocytes, and human peripheral blood mononuclear cells), and a neuroprotective effect was observed in rotenone-induced toxicity. In vivo experiments in a mouse neuropathic pain model demonstrated the highest analgesic effects of AR71 at the dose of 20 mg/kg body weight. Additionally, AR71 showed antiproliferative activity in higher concentrations. These findings suggest the need for further evaluation of AR71's therapeutic potential in treating ND and CNS cancer using animal experimental models. [ABSTRACT FROM AUTHOR]

Prenatal alcohol exposure can have persistent effects on learning, memory, and synaptic plasticity. Previous work from our group demonstrated deficits in long-term potentiation (LTP) of excitatory synapses on dentate gyrus granule cells in adult offspring of rat dams that consumed moderate levels of alcohol during pregnancy. At present, there are no pharmacotherapeutic agents approved for these deficits. Prior work established that systemic administration of the histaminergic H3R inverse agonist ABT-239 reversed deficits in LTP observed following moderate PAE. The present study examines the effect of a second H3R inverse agonist, SAR-152954, on LTP deficits following moderate PAE. We demonstrate that systemic administration of 1 mg/kg of SAR-152954 reverses deficits in potentiation of field excitatory post-synaptic potentials (fEPSPs) in adult male rats exposed to moderate PAE. Time-frequency analyses of evoked responses revealed PAE-related reductions in power during the fEPSP, and increased power during later components of evoked responses which are associated with feedback circuitry that are typically not assessed with traditional amplitude-based measures. Both effects were reversed by SAR-152954. These findings provide further evidence that H3R inverse agonism is a potential therapeutic strategy to address deficits in synaptic plasticity associated with PAE. • The H3R inverse agonist SAR-152954 reversed LTP deficits in the dentate gyrus following prenatal alcohol exposure (PAE). • These outcomes align with results obtained previously with the H3R inverse agonist ABT-239. • Time-frequency analyses provide a sensitive measure of PAE effects on baseline evoked responses and LTP. • SAR-152954 was associated with numerical, non-significant, decreases in input/output responses for PAE and control offspring. [ABSTRACT FROM AUTHOR]

Globally, hepatitis C virus (HCV) and coronavirus disease 2019 (COVID‐19) are the most common causes of death due to the lack of early predictive and diagnostic tools. Therefore, research for a new biomarker is crucial. Inflammatory biomarkers are critical central players in the pathogenesis of viral infections. IL‐18, produced by macrophages in early viral infections, triggers inflammatory biomarkers and interferon production, crucial for viral host defense. Finding out IL‐18 function can help understand COVID‐19 pathophysiology and predict disease prognosis. Histamine and its receptors regulate allergic lung responses, with H1 receptor inhibition potentially reducing inflammation in severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection. angiotensin‐converting enzyme 2 (ACE‐2) receptors on cholangiocytes suggest liver involvement in SARS‐CoV‐2 infection. The current study presents the potential impact of circulating acetylcholine, histamine, IL‐18, and interferon‐Alpha as diagnostic tools in HCV, COVID‐19, and dual HCV‐COVID‐19 pathogenesis. The current study was a prospective cross‐section conducted on 188 participants classified into the following four groups: Group 1 COVID‐19 (n = 47), Group 2 HCV (n = 47), and Group 3 HCV‐COVID‐19 patients (n = 47), besides the healthy control Group 4 (n = 47). The levels of acetylcholine, histamine, IL‐18, and interferon‐alpha were assayed using the ELISA method. Liver and kidney functions within all groups showed a marked alteration compared to the healthy control group. Our statistical analysis found that individuals with dual infection with HCV‐COVID‐19 had high ferritin levels compared to other biomarkers while those with COVID‐19 infection had high levels of D‐Dimer. The histamine, acetylcholine, and IL‐18 biomarkers in both COVID‐19 and dual HCV‐COVID‐19 groups have shown discriminatory power, making them potential diagnostic tests for infection. These three biomarkers showed satisfactory performance in identifying HCV infection. The IFN‐Alpha test performed well in the HCV‐COVID‐19 group and was fair in the COVID‐19 group, but it had little discriminative value in the HCV group. Moreover, our findings highlighted the pivotal role of acetylcholine, histamine, IL‐18, and interferon‐Alpha in HCV, COVID‐19, and dual HCV‐COVID‐19 infection. Circulating levels of acetylcholine, histamine, IL‐18, and interferon‐Alpha can be potential early indicators for HCV, COVID‐19, and dual HCV‐COVID‐19 infection. We acknowledge that further large multicenter experimental studies are needed to further investigate the role biomarkers play in influencing the likelihood of infection to confirm and extend our observations and to better understand and ultimately prevent or treat these diseases. [ABSTRACT FROM AUTHOR]

Dopamine and histamine receptors D2R and H3R are G protein-coupled receptors (GPCRs) which can establish physical receptor–receptor interactions (RRIs), leading to homo/hetero-complexes in a dynamic equilibrium. Although D2R and H3R expression has been detected within the carotid body (CB), their possible heterodimerization has never been demonstrated. The aim of this work was to verify D2R and H3R colocalization in the CB, thus suggesting a possible interplay that, in turn, may be responsible of specific D2R and H3R antagonistic functional implications. The CBs of both Sprague–Dawley rats (n = 5) and human donors (n = 5) were dissected, and immunolocalization of D2R and H3R was performed; thereafter, in situ proximity ligation assay (PLA) was developed. According to experimental evidence (immunohistochemistry and double immunofluorescence), all the samples displayed positive D2R and H3R elements; hence, PLA assay followed by confocal microscopy analysis was positive for D2R and H3R RRIs. Additionally, D2R and H3R heterodimers were mainly detected in type I cells (βIII-tubulin-positive cells), but type II cells’ involvement cannot be excluded. RRIs may play a role in functional modulation of CB cells; investigating RRIs in the CB may guide toward the comprehension of its plastic changes and fine regulatory role while also unveiling their possible clinical implications. [ABSTRACT FROM AUTHOR]

Fear memory is essential for survival and adaptation, yet excessive fear memories can lead to emotional disabilities and mental disorders. Despite previous researches have indicated that histamine H1 receptor (H1R) exerts critical and intricate effects on fear memory, the role of H1R is still not clarified. Here, we show that deletion of H1R gene in medial septum (MS) but not other cholinergic neurons selectively enhances contextual fear memory without affecting cued memory by differentially activating the dentate gyrus (DG) neurons in mice. H1R in cholinergic neurons mediates the contextual fear retrieval rather than consolidation by decreasing acetylcholine release pattern in DG. Furthermore, selective knockdown of H1R in the MS is sufficient to enhance contextual fear memory by manipulating the retrieval-induced neurons in DG. Our results suggest that H1R in MS cholinergic neurons is critical for contextual fear retrieval, and could be a potential therapeutic target for individuals with fear-related disorders. Neural mechanism underlying fear memory process is not fully understood. Here, the authors report that histamine H1 receptor (H1R) in medial septum cholinergic neurons is critical for contextual fear retrieval, serving as a promising target for related neurological disease. [ABSTRACT FROM AUTHOR]

Atherosclerosis (AS) is a chronic inflammatory arterial disease, in which abnormal lipid metabolism and foam cell formation play key roles. Histamine is a vital biogenic amine catalyzed by histidine decarboxylase (HDC) from L-histidine. Histamine H1 receptor (H1R) antagonist is a commonly encountered anti-allergic agent in the clinic. However, the role and mechanism of H1R in atherosclerosis have not been fully elucidated. Here, we explored the effect of H1R on atherosclerosis using Apolipoprotein E-knockout (ApoE−/−) mice with astemizole (AST, a long-acting H1R antagonist) treatment. The results showed that AST increased atherosclerotic plaque area and hepatic lipid accumulation in mice. The result of microarray study identified a significant change of endothelial lipase (LIPG) in CD11b+ myeloid cells derived from HDC-knockout (HDC−/−) mice compared to WT mice. Blocking H1R promoted the formation of foam cells from bone marrow-derived macrophages (BMDMs) of mice by up-regulating p38 mitogen-activated protein kinase (p38 MAPK) and LIPG signaling pathway. Taken together, these findings demonstrate that blocking H1R signal aggravates atherosclerosis by promoting abnormal lipid metabolism and macrophage-derived foam cell formation via p38 MAPK-LIPG signaling pathway. Key messages: Blocking H1R signal with AST aggravated atherosclerosis and increased hepatic lipid accumulation in high-fat diet (HFD)-fed ApoE−/− mice. Blocking H1R signal promoted macrophage-derived foam cell formation via p38 MAPK-LIPG signaling pathway. [ABSTRACT FROM AUTHOR]

Depression and anxiety disorders, prevalent neuropsychiatric conditions that frequently coexist, limit psychosocial functioning and, consequently, the individual's quality of life. Since the pharmacological treatment of these disorders has several limitations, the search for effective and secure antidepressant and anxiolytic compounds is welcome. Vitamin D has been shown to exhibit neuroprotective, antidepressant, and anxiolytic properties. Therefore, this study aimed to explore new molecular targets of calcitriol, the active form of vitamin D, through integrated bioinformatic analysis. Calcitriol targets were predicted in SwissTargetPrediction server (2019 version). The disease targets were collected by the GeneCards database searching the keywords "depression" and "anxiety". Gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to analyze the intersections of targets. Network analyses were carried out using GeneMania server (2023 version) and Cytoscape (V. 3.9.1.) software. Molecular docking predicted the main targets of the network and Ligplot predicted the main intermolecular interactions. Our study showed that calcitriol may interact with multiple targets. The main targets found are the vitamin D receptor (VDR), histamine H3 receptor (H3R), endocannabinoid receptors 1 and 2 (CB1 and CB2), nuclear receptor NR1H3, patched-1 (PTCH1) protein, opioid receptor NOP, and phosphodiesterase enzymes PDE3A and PDE5A. Considering the role of these targets in the pathophysiology of depression and anxiety, our findings suggest novel putative mechanisms of action of vitamin D as well as new promising molecular targets whose role in these disorders deserves further investigation. [ABSTRACT FROM AUTHOR]

Background: Numerous studies highlight the critical role that neural histamine plays in feeding behavior, which is controlled by central histamine H3 and H1 receptors. This is the fundamental motivation for the increased interest in creating histamine H3 receptor antagonists as anti-obesity medications. On the other hand, multiple other neurotransmitter systems have been identified as pharmacotherapeutic targets for obesity, including sigma-2 receptor systems. Interestingly, in our previous studies in the rat excessive eating model, we demonstrated a significant reduction in the development of obesity using dual histamine H3/sigma-2 receptor ligands. Moreover, we showed that compound KSK-94 (structural analog of Abbott's A-331440) reduced the number of calories consumed, and thus acted as an anorectic compound. Therefore, in this study, we extended the previous research and studied the influence of KSK-94 on adipose tissue collected from animals from our previous experiment. Methods: Visceral adipose tissue was collected from four groups of rats (standard diet + vehicle, palatable diet + vehicle, palatable diet + KSK-94, and palatable diet + bupropion/naltrexone) and subjected to biochemical, histopathological, and immunohistochemical studies. Results: The obtained results clearly indicate that compound KSK-94 prevented the hypertrophy and inflammation of visceral adipose tissue, normalized the levels of leptin, resistin and saved the total reduction capacity of adipose tissue, being more effective than bupropion/naltrexon in these aspects. Moreover, KSK-94 may induce browning of visceral white adipose tissue. Conclusion: Our study suggests that dual compounds with a receptor profile like KSK-94, i.e., targeting histamine H3 receptor and, to a lesser extent, sigma-2 receptor, could be attractive therapeutic options for patients at risk of developing obesity or with obesity and some metabolic disorders. However, more studies are required to determine its safety profile and the exact mechanism of action of KSK-94. [ABSTRACT FROM AUTHOR]

Dry skin is common to many pruritic diseases and is difficult to improve with oral traditional antihistamines. Recently, increasing evidence indicated that histamine H4 receptor (H4R) plays an important role in the occurrence and development of pruritus. Extracellular signal‐regulated kinase (ERK) phosphorylation activation in the spinal cord mediates histamine‐induced acute and choric itch. However, whether the histamine H4 receptor regulates ERK activation in the dry skin itch remains unclear. In the study, we explore the role of the histamine H4 receptor and p‐ERK in the spinal cord in a dry skin mouse model induced by acetone–ether–water (AEW). q‐PCR, Western blot, pharmacology and immunofluorescence were applied in the study. We established a dry skin itch model by repeated application of AEW on the nape of neck in mice. The AEW mice showed typically dry skin histological change and persistent spontaneous scratching behaviour. Histamine H4 receptor, instead of histamine H1 receptor, mediated spontaneous scratching behaviour in AEW mice. Moreover, c‐Fos and p‐ERK expression in the spinal cord neurons were increased and co‐labelled with GRPR‐positive neurons in AEW mice. Furthermore, H4R agonist 4‐methyhistamine dihydrochloride (4‐MH)induced itch. Both 4‐MH‐induced itch and the spontaneous itch in AEW mice were blocked by p‐ERK inhibitor U0126. Finally, intrathecal H4R receptor antagonist JNJ7777120 inhibited spinal p‐ERK expression in AEW mice. Our results indicated that spinal H4R mediates itch via ERK activation in the AEW‐induced dry skin mice. [ABSTRACT FROM AUTHOR]

Introduction: Colorectal cancer is a highly aggressive and metastatic cancer with inadequate clinical outcomes. Given the crucial role of histamine and histamine receptors in colorectal carcinogenesis, this study aimed at exploring the anticancer effects of terfenadine against colorectal cancer HCT116 cells and elucidate its underlying mechanism. Methods: Herein, we examined the effect of terfenadine on growth and proliferation of HCT116 cells in vitro and in vivo. Various experimental techniques such as flow cytometry, western blot, immunoprecipitation, luciferase assay were employed to unveil the mechanism of cell death triggered by terfenadine. Results: Terfenadine markedly attenuated the viability of HCT116 cells by abrogating histamine H1 receptor (H1R) signaling. In addition, terfenadine modulated the balance of Bax and Bcl-2, triggering cytochrome c discharge in the cytoplasm, thereby stimulating the caspase cascade and poly-(ADP-ribose) polymerase (PARP) degradation. Moreover, terfenadine suppressed murine double minute-2 (Mdm2) expression, whereas p53 expression increased. Terfenadine suppressed STAT3 phosphorylation and expression of its gene products by inhibiting MEK/ERK and JAK2 activation in HCT116 cells. Furthermore, treatment with U0126, a MEK inhibitor, and AG490, a JAK2 inhibitor, dramatically diminished the phosphorylations of ERK1/2 and JAK2, respectively, leading to STAT3 downregulation. Likewise, terfenadine diminished the complex formation of MEK1/2 with β-arrestin 2. In addition, terfenadine dwindled the phosphorylation of PKC substrates. Terfenadine administration (10 mg/kg) substantially retarded the growth of HCT116 tumor xenografts in vivo. Conclusion: Terfenadine induces the apoptosis of HCT116 cells by abrogating STAT3 signaling. Overall, this study supports terfenadine as a prominent anticancer therapy for colorectal cancer. [ABSTRACT FROM AUTHOR]

G‐protein‐coupled receptors (GPCRs) transmit downstream signals predominantly via G‐protein pathways. However, the conformational basis of selective coupling of primary G‐protein remains elusive. Histamine receptors H2R and H3R couple with Gs‐ or Gi‐proteins respectively. Here, three cryo‐EM structures of H2R‐Gs and H3R‐Gi complexes are presented at a global resolution of 2.6‐2.7 Å. These structures reveal the unique binding pose for endogenous histamine in H3R, wherein the amino group interacts with E2065.46 of H3R instead of the conserved D1143.32 of other aminergic receptors. Furthermore, comparative analysis of the H2R‐Gs and H3R‐Gi complexes reveals that the structural geometry of TM5/TM6 determines the primary G‐protein selectivity in histamine receptors. Machine learning (ML)‐based structuromic profiling and functional analysis of class A GPCR–G‐protein complexes illustrate that TM5 length, TM5 tilt, and TM6 outward movement are key determinants of the Gs and Gi/o selectivity among the whole Class A family. Collectively, the findings uncover the common structural geometry within class A GPCRs that determines the primary Gs‐ and Gi/o‐coupling selectivity. [ABSTRACT FROM AUTHOR]

Introduction: Brain histamine is considered an endogenous anticonvulsant and histamine H1 receptor. H1R antagonists have, in earlier studies, been found to induce convulsions. Moreover, research during the last two decades has provided more information concerning the anticonvulsant activities of histamine H3R (H3R) antagonists investigated in a variety of animal epilepsy models. Methods: Therefore, the in vivo anticonvulsant effect of the H3R antagonist DL76, with proven high in vitro affinity, in vitro selectivity profile, and high in vivo antagonist potency in mice against maximal electroshock (MES)-induced seizures in mice, was assessed. Valproic acid (VPA) was used as a reference antiepileptic drug (AED). In addition, DL76 was tested for its reproductive and fetal toxicity in the same animal species. Results and discussion: Our observations showed that acute systemic administration (intraperitoneal; i.p.) of DL76 (7.5 mg/kg, 15 mg/kg, 30 mg/kg, and 60 mg/kg, i.p.) provided significant and dose-dependent protection against MES-induced seizures in female and male mice. Moreover, the DL76- provided protective effects were comparable to those offered by the VPA and were reversed when animals were co-administered the CNS-penetrant selective H3R agonist R-(a)-methylhistamine (RAM, 10 mg/kg, i.p.). Furthermore, the administration of single (7.5 mg/kg, 15 mg/kg, 30 mg/kg, or 60 mg/kg, i.p.) or multiple doses (3 × 15 mg/kg, i.p.) of H3R antagonist DL76 on gestation days (GD) 8 or 13 failed to affect the maternal body weight of mice when compared with the control mice group. No significant alterations were detected in the average number of implantations and resorptions between the control and DL76-treated groups at the early stages of gestation and the organogenesis period. In addition, no significant differences in the occurrence of skeletal abnormalities, urogenital abnormalities, exencephaly, exomphalos, facial clefts, and caudal malformations were observed. The only significant abnormalities witnessed in the treated groups of mice were in the length of long bones and body length. In conclusion, the novel H3R antagonist DL76 protected test animals against MES-induced seizures and had a low incidence of reproductive and fetal malformation with decreased long bone lengths in vivo, signifying the potential therapeutic value of H3R antagonist DL76 for future preclinical as well as clinical development for use in the management of epilepsy. [ABSTRACT FROM AUTHOR]

Diarrhea caused by gut motility involves 5‐HT3 serotonin receptor (5‐HT3R) antagonist, M3 muscarinic acetylcholine receptor (M3‐AchR), and H1 histamine receptor (H1R) via their respective agonist. Papaya (Carica papaya L.) leaf is an herbal medicine to treat diarrhea in Indonesia, though this has not yet been proven scientifically. This study aimed to determine the antidiarrheal properties of papaya leaf through in vivo and in silico studies. In the mice model, papaya leaves were infused with distilled water and subjected to in vivo antidiarrheal study using castor oil‐induced diarrhea. In silico molecular docking study of nineteen secondary metabolites was carried out on the M3‐AchR (PDB ID: 5ZHP) using AutoDock Tools 1.5.6, while ADMET was predicted by pre‐ADMET. The results showed that papaya leaf infusion caused a decrease in the total number of feces, an increase in the onset time of diarrhea, a reduction in the frequency of diarrhea, and an increase in the percentage of inhibition of diarrhea. Quercetin 3‐rutinoside, a flavonoid glycoside, is potentially an antidiarrheal remedy at M3‐AchR. ADMET prediction showed good distribution on the target and was not toxic, but absorption needed to be considered. We concluded that the antidiarrheal activity of papaya leaf infusion was dose‐dependent. Based on a molecular docking study, the flavonoid glycoside was very effective as an antidiarrheal remedy. ADMET prediction showed a specific distribution to the target and was not toxic. [ABSTRACT FROM AUTHOR]

Background: Allergic disorders, prevalent global health concerns, afflict a substantial portion of the world's population. These maladies result from an exaggerated immune system response to ordinarily innocuous substances, such as pollen, dust mites, and specific dietary components. Clinical manifestations of this heightened immune response include itching, swelling, and respiratory impairment, often accompanied by releasing mediators like histamine. The pathophysiological mechanisms of allergy disorders are intricate, arising from a complex interplay between genetic and environmental factors. While clinical presentations may vary, all allergy conditions share a common foundation in the dysregulated immune response to allergens. Result: The current aim of this study was to identify innovative anti-allergic agents capable of inhibiting histamine and effectively mitigating allergic reactions by utilizing the computer-aided drug design approach by discovery studio (DS) 2022 v 23.1.1 package. The overarching aim was identifying potential drug candidates targeting the active site within the histamine H1 receptor complex; therefore, a collection of 4000 small druggable compounds was curated from ZINC, PubChem, and DRUG BANK databases sources. Four compounds appeared as promising candidates after assessing docking scores and binding energies. Notably, Compound ID 34154, recognized as tymazoline, showed the highest affinity for the H1 receptor of 3RZE, suggesting it may be the most promising choice for more research. Further chemoinformatic and ADMET (absorption, distribution, metabolism, excretion, and toxicity) analyses were conducted to assess the drug-like qualities of this chosen molecule. In addition, bioisosteric substitution techniques were employed to enhance tymazoline's ADMET characteristics. Conclusion: Tymazoline shows strong binding affinity with 3RZE and verified all the drug-likeness criteria to inhibit the allergic disorders. Furthermore, molecular dynamics (MD) studies corroborated tymazoline's potential as an anti-allergic agent, demonstrating contact between the ligand and the receptor that is well defined and stable. [ABSTRACT FROM AUTHOR]

Background: Polyoxyethylene hydrogenated castor oil (HCO ethoxylates) is a nonionic surfactant used as an excipient for ointments and injections in human and veterinary drugs. Several polyethylene glycol (PEG) derivatives can be obtained depending on the number of moles of ethylene oxide (EO). HCO ethoxylates have the potential to cause anaphylactoid reactions. There is little published information about these types of reactions in dogs. Objective: To determine the potential for HCO‐ethoxylate‐containing drugs to cause anaphylactoid reactions in dogs, employing intradermal testing (IDT) with various concentrations of HCO ethoxylates (HCO‐25, ‐40, ‐60 and ‐80). Animals: Four healthy male laboratory dogs. Materials and Methods: We performed IDT with drugs containing HCO ethoxylates and HCO ethoxylates alone to determine threshold concentrations. The IDT scores and threshold concentrations were compared. Analysis of skin biopsies from IDT sites was used to measure the percentage of degranulated mast cells. The effect of histamine at IDT sites was investigated by pre‐treatment with an antihistamine. Results: All HCO‐ethoxylate‐containing drugs caused a wheal‐and‐flare reaction. The threshold concentrations (0.001% and 0.00001%) of each HCO‐ethoxylate depended on the number of moles of EO (p < 0.05). Mast cell degranulation was enhanced by all HCO ethoxylates. The HCO‐60‐induced reaction was suppressed by an oral antihistamine. Conclusions and Clinical Relevance: The threshold concentration can serve as a consideration for developing safe new drug formulations and for clinical decision‐making around using drugs containing PEG derivatives. IDT is useful to predict the risk of adverse effects. Antihistamines could demonstrate a prophylactic effect. [ABSTRACT FROM AUTHOR]

Background: Periodontitis preceded by gingivitis is the most common form of periodontal disease and occurs due to the interaction of microorganisms present in the complex bacterial aggregates of dental plaque biofilm and their metabolism products with periodontal tissues. Histamine is a heterocyclic biogenic amine acting via four types of receptors. Histamine H3 receptors act as presynaptic auto/heteroreceptors to regulate the release of histamine and other neurotransmitters. Aim: Since the nervous system is able to regulate the progression of the inflammatory process and bone metabolism, the aim of this study was to investigate the effects of DL76, which acts as an antagonist/inverse agonist of H3 receptors, on the course of experimental periodontitis. Materials and methods: This study was conducted in 24 mature male Wistar rats weighing 245–360 g, aged 6–8 weeks. A silk ligature was placed on the second maxillary molar of the right maxilla under general anesthesia. From the day of ligating, DL76 and 0.9% NaCl solutions were administered subcutaneously for 28 days in the experimental and control groups, respectively. After the experiment, histopathological, immunohistochemical and radiological examinations were performed. Results: Ligation led to the development of the inflammatory process with lymphocytic infiltration, increased epithelial RANKL and OPG expression as well as bone resorption. DL76 evoked a reduction in (1) lymphocytic infiltration, (2) RANKL and OPG expression as well as (3) bone resorption since the medians of the mesial and distal interdental spaces in the molars with induced periodontitis were 3.56-fold and 10-fold lower compared to the corresponding values in saline-treated animals with periodontitis. Conclusion: DL76 is able to inhibit the progression of experimental periodontitis in rats, as demonstrated by a reduction in the inflammatory cell infiltration, a decrease in the RANKL/RANK OPG pathway expression and a reduction in the alveolar bone resorption. [ABSTRACT FROM AUTHOR]

OBJECTIVE To examine the potential of galangin in a mouse model of ovalbumin (OVA)-induced allergic rhinitis (AR), as chronic AR, induced by immunoglobulin-E (IgE), leads to histamine release and nasal inflammation, and although galangin exhibits antiasthmatic and anti-inflammatory potential, its effect on AR is yet to be investigated. ANIMALS 126 BALB/c mice. METHODS AR induction involved sensitizing female mice with OVA (5%, 500 µL, IP) for 14 days. Post OVA challenge, the mice were divided into 7 groups (n = 18/group), including normal, AR control, montelukast (10 mg/kg), galangin (5, 10, and 20 mg/kg), and per se (galangin [20 mg/kg] treatment. Various outcomes were evaluated, including nasal symptoms, histopathology, biochemistry, and nasal lavage fluid inflammatory cytokines and signaling pathways in nasal mucosal to assess galangin potential in AR. RESULTS In AR mice, galangin (10 and 20 mg/kg) significantly (P < .05) reduced sneezing, rubbing, and nasal discharge post-OVA challenge. Galangin treatment attenuated (P < .05) elevated serum histamine, ß-hexosaminidase, IgE, and Immunoglobulin G1 levels in AR control mice. Additionally, galangin significantly (P < .05) decreased OVA-induced alterations in IL-4, IL-6, IL-13, and interferon-γ levels in nasal lavage fluid compared to AR control mice. Western blot analysis demonstrated that galangin lowered OVA-induced AR by significantly (P < .05) downregulating the phosphorylated protein kinase B and mammalian target of rapamycin-protein expressions while markedly (P < .05) upregulating the glycogen synthase kinase-3ß protein expressions in nasal mucosal. Galangin also significantly ameliorated (P < .05) the OVA-induced histological aberrations in the nasal mucosa, reflected by reduced eosinophil infiltration, hyperplasia, and edema. CLINICAL RELEVANCE Galangin exhibits antihistaminic and anti-inflammatory effects in AR mice by regulating IgE-mediated histamine and inflammatory release and modulating the phosphatidylinositol 3-kinase/Ak strain transforming/mammalian target of rapamycin pathways. [ABSTRACT FROM AUTHOR]

Background Allergies often present challenges in managing itch and the effects of histamine. Cooling agents that act via transient receptor potential melastatin 8 (TRPM8) agonism have shown potential in itch management. However, animal studies on itch have limitations, as animals cannot communicate subjective events and their fur-coated skin differs from that of humans. Human studies offer more direct and reliable information. Objectives To investigate the effects of a specific TRPM8 agonist gel (cryosim-1) on itch induced by various pruritogens in human skin. Methods Calcium imaging experiments determined the binding of cryosim-1 and histamine to their respective receptors. Thirty healthy volunteers underwent skin prick tests with pruritogens and a control vehicle. Itch and pain intensity were measured using a numerical rating scale (NRS) across 10 min. Participants were randomly assigned to pretreatments with vehicle or TRPM8 agonist gel. Tests were repeated at a later date, and skin moisture, transepidermal water loss and mechanical sensitivity were measured. Results The in vitro study confirmed that histamine is not a TRPM8 agonist and cryosim-1 does not act as an agonist or antagonist on the human histamine 1 receptor. The TRPM8 agonist gel significantly reduced the itch intensity for all pruritogens compared with the vehicle-only gel. It also reduced itch NRS and the integrated itch score. Mechanical sensitivity was also reduced. Conclusions The specific TRPM8 agonist gel effectively suppressed human skin itch induced by various pruritogens. These versatile actions suggest that cooling agents may be promising treatments for multiple forms of itch stimuli. [ABSTRACT FROM AUTHOR]

Background Cholinergic urticaria (CholU) is a common subtype of chronic inducible urticaria, where signs and symptoms (e.g. pruritic wheals and angioedema) are triggered by sweating due to physical exercise, passive warming and by other sweat-inducing situations. While guidelines recommend treatment with second-generation H1 antihistamines, approximately 90% of patients report uncontrolled disease. Targeting the histamine 4 receptor (H4R) has shown promise in preclinical/clinical studies of allergic/inflammatory diseases. Izuforant (LEO 152020) is a selective oral H4R antagonist with expected dual antipruritic and anti-inflammatory effects. Objectives To assess the effects of izuforant in adults with CholU, a common type of chronic urticaria driven by histamine and characterized by high skin levels of H4R expression. Methods This was a phase IIa randomized double-blind placebo-controlled multicentre crossover trial where patients with CholU with an inadequate response to ≥ 1 standard dose of H1 antihistamine received izuforant 100 mg twice daily or placebo (EUCTR2020-004961-38-DE; NCT04853992). The primary endpoint was change from baseline in Urticaria Activity Score. Exploratory endpoints included CholU activity score over 7 days, urticaria control test, Physician Global Assessment, patient global assessment of severity (PGA-S), provocation tests, Dermatology Life Quality Index and CholU quality of life (CholU-QoL). Pharmacokinetic and pharmacodynamic parameters, and serum biomarkers were assessed, as well as safety and tolerability. Results Nineteen patients were randomized and included in the full analysis set; 18 completed treatment [mean (SD) age 29.5 (9.8) years; mean (SD) CholU duration 8.0 (6.3) years]. The primary and most of prespecified exploratory endpoints were not met; there were significant improvements in PGA-S for izuforant vs. placebo (P = 0.02), and nonsignificant improvements for other endpoints in quality of life and histamine skin prick test. All adverse events (AEs) experienced with izuforant were considered mild. The most frequently reported (> 1 patient) were nausea (three patients) and upper abdominal pain (two patients), occurring more frequently with izuforant vs. placebo (one patient each). There were no treatment-related serious AEs and no patient receiving izuforant discontinued the study. Treatment with izuforant did not cause downregulation of H4R. Conclusions This is the first study to explore the role of H4R as a therapeutic target in urticaria. Targeting H4R with izuforant was well tolerated but did not demonstrate significant improvements vs. placebo in the primary endpoint and all but one prespecified exploratory endpoint in CholU. [ABSTRACT FROM AUTHOR]

Mas‐related G protein‐coupled receptor X2 (MrgprX2) is acknowledged as a mast cell‐specific receptor, playing a crucial role in orchestrating anaphylactoid responses through mast cell degranulation. It holds promise as a target for regulating allergic and inflammatory diseases mediated by mast cells. Polygonum cuspidatum (PC) has shown notable anti‐anaphylactoid effects, while its pharmacologically active components remain unclear. In this study, we successfully utilized MrgprX2 high‐expressing cell membrane chromatography (CMC), in conjunction with liquid chromatography‐mass spectrometry (LC‐MS), to identify active anti‐anaphylactoid components in PC. Our study pinpointed polydatin, resveratrol, and emodin‐8‐O‐β‐d‐glucoside as potential anti‐anaphylactoid compounds in PC. Their anti‐anaphylactoid activities were evaluated through β‐aminohexosidase and histamine release assays, demonstrating a concentration‐dependent inhibition for both β‐aminohexosidase and histamine release. This approach, integrating MrgprX2 high‐expression CMC with LC‐MS, proves effective in screening potential anti‐anaphylactoid ingredients in natural herbal medicines. The findings from this study illuminated the anti‐anaphylactoid properties of specific components in PC and provided an efficient method for the drug development of natural products. [ABSTRACT FROM AUTHOR]

Background: Atopic dermatitis (AD) is a highly prevalent inflammatory skin disorder characterized by episodic exacerbations and remissions. Why the clinically healthy skin of AD patients becomes rapidly inflamed and very pruritic is poorly understood. Objective: To investigate cowhage‐ and histamine‐induced itch and skin expression levels of their target receptors in lesional and non‐lesional skin of AD, compared to the skin of patients with psoriasis, chronic spontaneous urticaria (CSU) and healthy subjects. Methods: Patients with AD, psoriasis and chronic spontaneous urticaria (CSU) as well as healthy control subjects (HC) (n = 20 each) were assessed for differences in itch parameters, neurogenic flare reaction and local blood flow responses to skin provocations with cowhage and histamine. Skin biopsies from 10 AD, 10 psoriasis,11 CSU and 12 HC were obtained to assess expression of protease‐activated receptors 2 and 4 (PAR‐2, PAR‐4), histamine H1 and H4 receptors (H1R, H4R), and mast cells. Results: Provocation of non‐lesional skin of AD patients with cowhage resulted in prolonged itch (p = 0.020), which was not observed in psoriasis and CSU. Significantly prolonged and more intense cowhage‐ and histamine‐induced itch (for duration, peak and overall intensity) was also observed in lesional AD skin. Diminished neurogenic flare reaction and blood flow after histamine provocation were shown in AD and psoriasis patients. Non‐lesional AD skin along with lesional AD and psoriasis skin showed an increased expression of PAR‐2 and PAR‐4, H1R and H4R. Mast cell number was higher in lesional AD and psoriasis skin (p = 0.006 and p = 0.006, respectively). Conclusion: The non‐lesional skin of AD patients markedly differs from healthy skin in cowhage‐induced itch responses and the expression of receptors for proteases and histamine. Proactive therapeutic interventions that downregulate these receptors may prevent episodic exacerbation in AD. [ABSTRACT FROM AUTHOR]

IntroductionAlzheimer's disease (AD) is a progressive neurodegenerative disorderfeaturing a brain accumulation of extracellular β-amyloidplaques (Aβ) and intracellular neurofibrillary tautangles (NFTs). Although cognitive decline is a disease-defining symptom of AD, sleep dysfunction, a common symptom often preceding cognitive decline, hasrecently gained more attention as a core AD symptom. Polysomnography and othersleep measures show sleep fragmentation with shortening of N3 sleep togetherwith excessive daytime sleepiness (EDS) and sundowning as the main findings in AD patients. The latter reflects dysfunction of the wake-promoting neurons (WPNs), including histaminergic neurons (HAN) located in thetuberomammillary nucleus (TMN) of the posterior hypothalamus, which projectunmyelinated axons to various parts of the brain. Histamine's role in cognitionand arousal is broadly recognized. Selective targeting of histaminergic subtype-3 and 4 receptors show therapeutic potential in rodent models of AD andaging.MethodBased on PubMed, Scopus, and google scholar databases search, this review summarizes the current knowledge on the histaminergic system in AD and aging, its therapeutic potential in AD, and highlight areas where moreresearch is needed.ResultsAnimal studies have demonstrated that pharmacological manipulation of histaminergic receptors or histamine supplementation improves cognition in AD models. However, measurements of HA or HA metabolite levels in the human brainand CSF present contradictory reports due to either lack of power or controls for known confounders.DiscussionSystemic studies including broad age, sex, neuropathological diagnosis, and disease stage are warranted to fill the gap in our current understanding of the histaminergic neurotransmitter/neuromodulator system in humans, especially age-related changes, and therapeuticpotential of histamine in AD-related dysfunction.

Dm9 neurons in Drosophila have been proposed as functional homologs of horizontal cells in the outer retina of vertebrates. Here we combine genetic dissection of neuronal circuit function, two-photon calciumimaging in Dm9 and inner photoreceptors, and immunohistochemical analysis to reveal novel insights into the functional role of Dm9 in early visual processing. Our experiments show that Dm9 receive input from all four types of inner photoreceptor R7p, R7y, R8p, and R8y. Histamine released from all types R7/R8 directly inhibits Dm9 via the histamine receptorOrt, and outweighs simultaneous histamine-independent excitation of Dm9 by UV-sensitive R7. Dm9 in turn provides inhibitory feedback to all R7/R8, which is sufficient for color-opponent processing in R7 but not R8. Color opponent processing in R8 requires additional synaptic inhibition by R7 of the same ommatidium via axo-axonal synapses and the second Drosophila histamine receptor HisCl1. Notably, optogenetic inhibition of Dm9 prohibits color opponent processing in all types of R7/R8 and decreases intracellular calciumin photoreceptor terminals. The latter likely results fromreduced release of excitatory glutamate from Dm9 and shifts overall photoreceptor sensitivity toward higher light intensities. In summary, our results underscore a key role of Dm9 in color opponent processing in Drosophila and suggest a second role of Dm9 in regulating light adaptation in inner photoreceptors. These novel findings on Dm9 are indeed reminiscent of the versatile functions of horizontal cells in the vertebrate retina. [ABSTRACT FROM AUTHOR]

Histamine, a bioactive component in certain foods such as Huangjiu has been associated with liver injury and disrupted intestinal balance. This study explored the potential therapeutic effects of fucoidan (FCD) in mitigating histamine-induced imbalances in mice. We found that FCD mitigated liver injury, reducing transaminases, oxidative stress, and inflammation. Histological improvements included decreased cell infiltration and necrosis. FCD restored tight junction proteins and suppressed inflammation-related genes. Western blot analysis revealed FCD's impact on TGF-β1, p-AKT, AKT, CYP2E1, Grp78, NLRP3, Cas-1, and GSDMD. Gut LPS levels decreased with FCD. Gut microbiota analysis showed FCD's modulation effect, reducing Firmicutes and increasing Bacteroides. FCD demonstrates potential in alleviating histamine-induced liver injury, regulating inflammation, and influencing gut microbiota. Further research exploring higher dosages and additional parameters is warranted. [ABSTRACT FROM AUTHOR]

Background: Although immune checkpoint blockade (ICB) therapy has proven to be extremely effective at managing certain cancers, its efficacy in treating pancreatic ductal adenocarcinoma (PDAC) has been limited. Therefore, enhancing the effect of ICB could improve the prognosis of PDAC. In this study, we focused on the histamine receptor H1 (HRH1) and investigated its impact on ICB therapy for PDAC. Methods: We assessed HRH1 expression in pancreatic cancer cell (PCC) specimens from PDAC patients through public data analysis and immunohistochemical (IHC) staining. The impact of HRH1 in PCCs was evaluated using HRH1 antagonists and small hairpin RNA (shRNA). Techniques including Western blot, flow cytometry, quantitative reverse transcription polymerase chain reaction (RT-PCR), and microarray analyses were performed to identify the relationships between HRH1 and major histocompatibility complex class I (MHC-I) expression in cancer cells. We combined HRH1 antagonism or knockdown with anti-programmed death receptor 1 (αPD-1) therapy in orthotopic models, employing IHC, immunofluorescence, and hematoxylin and eosin staining for assessment. Results: HRH1 expression in cancer cells was negatively correlated with HLA-ABC expression, CD8+ T cells, and cytotoxic CD8+ T cells. Our findings indicate that HRH1 blockade upregulates MHC-I expression in PCCs via cholesterol biosynthesis signaling. In the orthotopic model, the combined inhibition of HRH1 and αPD-1 blockade enhanced cytotoxic CD8+ T cell penetration and efficacy, overcoming resistance to ICB therapy. Conclusions: HRH1 plays an immunosuppressive role in cancer cells. Consequently, HRH1 intervention may be a promising method to amplify the responsiveness of PDAC to immunotherapy. [ABSTRACT FROM AUTHOR]

Network oscillation in the anterior cingulate cortex (ACC) plays a key role in attention, novelty detection and anxiety; however, its involvement in cognitive impairment caused by acute systemic inflammation is unclear. To investigate the acute effects of systemic inflammation on ACC network oscillation and cognitive function, we analyzed cytokine level and cognitive performance as well as network oscillation in the mouse ACC Cg1 region, within 4 hours after lipopolysaccharide (LPS, 30 μg/kg) administration. While the interleukin-6 concentration in the serum was evidently higher in LPS-treated mice, the increases in the cerebral cortex interleukin-6 did not reach statistical significance. The power of kainic acid (KA)-induced network oscillation in the ACC Cg1 region slice preparation increased in LPS-treated mice. Notably, histamine, which was added in vitro, increased the oscillation power in the brain slices from LPS-untreated mice; for the LPS-treated mice, however, the effect of histamine was suppressive. In the open field test, frequency of entries into the center area showed a negative correlation with the power of network oscillation (0.3 μM of KA, theta band (3–8 Hz); 3.0 μM of KA, high-gamma band (50–80 Hz)). These results suggest that LPS-induced systemic inflammation results in increased network oscillation and a drastic change in histamine sensitivity in the ACC, accompanied by the robust production of systemic pro-inflammatory cytokines in the periphery, and that these alterations in the network oscillation and animal behavior as an acute phase reaction relate with each other. We suggest that our experimental setting has a distinct advantage in obtaining mechanistic insights into inflammatory cognitive impairment through comprehensive analyses of hormonal molecules and neuronal functions. [ABSTRACT FROM AUTHOR]

Context: The advancement in the development of second-generation drugs in the field of antihistamines represents a significant milestone in the management of allergic diseases, targeting the effects of histamine. The efficacy of bilastine in treating allergic disorders has sparked interest in investigating its polymorphism, a crucial property that impacts quality, safety, and effectiveness as per regulatory guidelines. This study examines the polymorphism of bilastine, focusing on two crystalline forms labeled as Form I and Form II. Utilizing advanced analytical techniques, the research explores the structural characteristics and molecular interactions within these forms. Geometric parameters, such as bond lengths, bond angles, and torsion angles, are examined to comprehend molecular conformations and crystal packing arrangements. Hydrogen bonding, covalent bonds, and van der Waals forces contribute to the unique supramolecular arrangements in these forms. This study provides a significant contribution to understanding bilastine's polymorphism, offering critical insights to researchers and regulatory bodies to ensure the quality, efficacy, and safety of antihistamine products. Methods: The molecular conformation of two bilastine forms was obtained through DFT with the exchange–correlation functional M06-2X and the 6–311 + + G(d,p) basis set, and the results were compared with the experimental X-ray. The atomic coordinates were obtained directly from the crystalline structures, and charge transfer was also investigated using frontier molecular orbitals (HOMO and LUMO), and MEP map in order to evaluate the energies associated with charge transfers and regions of high electron affinity. The geometric and topological parameters and intermolecular interactions in the crystals were analyzed using Hirshfeld Surface. [ABSTRACT FROM AUTHOR]

In the present study, the mechanisms involved in scopolamine-induced memory impairment have been investigated. The molecular events that take place during memory mostly include mechanisms that are seen in the acquisition phase. Results showed that one of the mechanisms of memory destruction caused by scopolamine, in addition to weakening the cholinergic system, is the indirect effect of scopolamine on other neurotransmitter systems, including the glutamatergic system. Scopolamine injection increases dopamine by inhibiting M2/4 muscarinic autoreceptors. These autoreceptors are located on dopaminergic presynaptic neurons, and their activation reduces the release of dopamine. Therefore, blocking these autoreceptors by scopolamine can increase the release of dopamine. Both D1 and D2 receptors are involved in learning and memory processes. In general, stimulation of dopamine D1 receptors follows an inverted U-shaped dose-response curve, meaning that both insufficient and excessive amounts of dopamine cause memory impairment. Therefore, an indirect effect on the dopaminergic system can be one of the scopolamine-induced memory impairment mechanisms. Effects on cell membrane potential and neuron plasticity, and interaction with acetylcholine are among other mechanisms. Serotonin plays a complex role in memory and learning. Serotonin receptors (5-HT2A) also play a role in memory function by affecting calcium transport. This action is similar to dopamine and other G-protein-coupled receptors, which activate phospholipase C, enter calcium into the cell, and activate calcineurin. Activation of 5-HT2A and 5-HT4 receptors by specific agonists of these receptors enhances long-term potentiation (LTP), which plays a significant role in memory. On the other hand, specific 5-HT3 receptor antagonist improves LTP. The 5-HT6 receptor antagonist can improve memory function. Therefore, different serotonin receptors have different roles in memory function, and the interaction between scopolamine and these receptors needs further study. It has been shown that histamine increases the secretion of acetylcholine in the hippocampus, and postsynaptic H1 and presynaptic H3 receptors play a major role in memory and learning; however, whether scopolamine can cause memory impairment through interaction with histamine receptors has been not reviewed. [ABSTRACT FROM AUTHOR]

Allergic rhinitis (AR) is a prevalent inflammatory condition affecting millions globally, with current treatments often associated with significant side effects. To seek safer and more effective alternatives, natural sources like Urtica dioica (UD) are being explored. However, UD's mechanism of action remains unknown. Therefore, to elucidate it, we conducted an in silico evaluation of UD phytochemicals' effects on known therapeutic targets of allergic rhinitis: histamine receptor 1 (HR1), neurokinin 1 receptor (NK1R), cysteinyl leukotriene receptor 1 (CLR1), chemoattractant receptor-homologous molecule expressed on type 2 helper T cells (CRTH2), and bradykinin receptor type 2 (BK2R). The docking analysis identified amentoflavone, alpha-tocotrienol, neoxanthin, and isorhamnetin 3-O-rutinoside as possessing a high affinity for all the receptors. Subsequently, molecular dynamics (MD) simulations were used to analyze the key interactions; the free energy of binding was calculated through Generalized Born and Surface Area Solvation (MMGBSA), and the conformational changes were evaluated. Alpha-tocotrienol exhibited a high affinity while also inducing positive conformational changes across all targets. Amentoflavone primarily affected CRTH2, neoxanthin targeted NK1R, CRTH2, and BK2R, and isorhamnetin-3-O-rutinoside acted on NK1R. These findings suggest UD's potential to treat AR symptoms by inhibiting these targets. Notably, alpha-tocotrienol emerges as a promising multi-target inhibitor. Further in vivo and in vitro studies are needed for validation. [ABSTRACT FROM AUTHOR]

The present work intends to provide a closer look at histamine in Drosophila. This choice is motivated firstly because Drosophila has proven over the years to be a very simple, but powerful, model organism abundantly assisting scientists in explaining not only normal functions, but also derangements that occur in higher organisms, not excluding humans. Secondly, because histamine has been demonstrated to be a pleiotropic master molecule in pharmacology and immunology, with increasingly recognized roles also in the nervous system. Indeed, it interacts with various neurotransmitters and controls functions such as learning, memory, circadian rhythm, satiety, energy balance, nociception, and motor circuits, not excluding several pathological conditions. In view of this, our review is focused on the knowledge that the use of Drosophila has added to the already vast histaminergic field. In particular, we have described histamine's actions on photoreceptors sustaining the visual system and synchronizing circadian rhythms, but also on temperature preference, courtship behavior, and mechanosensory transmission. In addition, we have highlighted the pathophysiological consequences of mutations on genes involved in histamine metabolism and signaling. By promoting critical discussion and further research, our aim is to emphasize and renew the importance of histaminergic research in biomedicine through the exploitation of Drosophila, hopefully extending the scientific debate to the academic, industry, and general public audiences. [ABSTRACT FROM AUTHOR]

The modulation of biological processes with light-sensitive chemical probes promises precise temporal and spatial control. Yet, the design and synthesis of suitable probes is a challenge for medicinal chemists. This article introduces a photocaging strategy designed to modulate the pharmacology of histamine H3 receptors (H3R) and H4 receptors (H4R). Employing the photoremovable group BODIPY as the caging entity for two agonist scaffolds—immepip and 4-methylhistamine—for H3R and H4R, respectively, we synthesized two BODIPY-caged compounds, 5 (VUF25657) and 6 (VUF25678), demonstrating 10–100-fold reduction in affinity for their respective receptors. Notably, the caged H3R agonist, VUF25657, exhibits approximately a 100-fold reduction in functional activity. The photo-uncaging of VUF25657 at 560 nm resulted in the release of immepip, thereby restoring binding affinity and potency in functional assays. This approach presents a promising method to achieve optical control of H3R receptor pharmacology. [ABSTRACT FROM AUTHOR]

Considering the importance of pain and stress, we decided to investigate the intra‐anterior cingulate cortex (ACC) microinjection of histamine and mepyramine alone and concurrently on acute pain induced by hot plate following restraint stress in male rats. 24‐gauge, 10 mm stainless steel guide cannula was implanted over the ACC in the incised scalp of 4 groups. Restraint stress in healthy rats produced a significant increase (p <.05) in the pain threshold. The simultaneous microinjection of 4 μg/side histamine and 8 μg/side mepyramine as a histaminergic system inverse agonist in healthy nonrestraint animals did not affect the pain threshold. Although Histamine decreased the threshold of pain meaningfully, mepyramine elevated it in a significant manner (p <.05). In the restrained animals, intra‐ACC microinjection of histamine produced no significant impact on the pain threshold. However, intra‐ACC microinjection of mepyramine before histamine, significantly (p <.01) altered the result and enhanced the threshold of pain. The results of our study demonstrated that histaminergic neurons have an important role in the processing of pain in the ACC following restraint stress. [ABSTRACT FROM AUTHOR]