Procognitive impact of ciproxifan (a histaminergic H3 receptor antagonist) on contextual memory retrieval after acute stress

Anxiolytic- and antidepressive-like effects of harmaline in mice are mediated via histamine H3 receptor blockade

Many neuropsychiatric disorders can be caused by neurotransmitter dysfunction. Experimental studies have demonstrated that histamine and the harmaline affect physiological processes through interaction with other neurotransmitter systems. The objective of these experiments was to investigate the involvement of the histaminergic system in the effects of harmaline on anxiety- and depressive-related effects in male NMRI mice. Behavioral tests were employed to evaluate anxiety-related symptoms (elevated plus maze; EPM), depressive-like symptoms (forced swim test; FST), and cognitive decline (step-down test). The histamine H3 receptor (H3R) agonist α-methylhistamine dihydrobromide (α-MH; 5 mg/kg, i.p.) had anxiolytic- and depressive-like effects, while the H3R antagonist thioperamide (10 mg/kg, i.p.) showed an antidepressive-like property. The subthreshold dose of α-MH resulted in an increase in the tendency of mice treated with the harmaline (2.5 mg/kg) to remain in the EPM open-arms. A subthreshold dose of thioperamide (5 mg/kg) increased the time spent in the open-arms in mice treated with harmaline (2.5 and 5 mg/kg) while a high dose of harmaline decreased the immobility time. Furthermore, two higher doses of harmaline resulted in a reduction in the number of open-arm entries. Similarly, mice administered with thioperamide and a low dose of harmaline decreased locomotor activity in the EPM. Ultimately, the combined thioperamide and harmaline did not impair memory retrieval of mice. These experiments demonstrate that the histaminergic system is implicated in the anxiety- and depressive-related effects of harmaline. The combination of thioperamide and harmaline is effective in treating anxiety and depression without having an adverse effect on memory formation.

Targeting Microglia in Neuroinflammation: H3 Receptor Antagonists as a Novel Therapeutic Approach for Alzheimer's Disease, Parkinson's Disease, and Autism Spectrum Disorder

Histamine performs dual roles as an immune regulator and a neurotransmitter in the mammalian brain. The histaminergic system plays a vital role in the regulation of wakefulness, cognition, neuroinflammation, and neurogenesis that are substantially disrupted in various neurodegenerative and neurodevelopmental disorders. Histamine H3 receptor (H3R) antagonists and inverse agonists potentiate the endogenous release of brain histamine and have been shown to enhance cognitive abilities in animal models of several brain disorders. Microglial activation and subsequent neuroinflammation are implicated in impacting embryonic and adult neurogenesis, contributing to the development of Alzheimer's disease (AD), Parkinson's disease (PD), and autism spectrum disorder (ASD). Acknowledging the importance of microglia in both neuroinflammation and neurodevelopment, as well as their regulation by histamine, offers an intriguing therapeutic target for these disorders. The inhibition of brain H3Rs has been found to facilitate a shift from a proinflammatory M1 state to an anti-inflammatory M2 state, leading to a reduction in the activity of microglial cells. Also, pharmacological studies have demonstrated that H3R antagonists showed positive effects by reducing the proinflammatory biomarkers, suggesting their potential role in simultaneously modulating crucial brain neurotransmissions and signaling cascades such as the PI3K/AKT/GSK-3β pathway. In this review, we highlight the potential therapeutic role of the H3R antagonists in addressing the pathology and cognitive decline in brain disorders, e.g., AD, PD, and ASD, with an inflammatory component.

Cognitive Deficits Found in a Pro-inflammatory State are Independent of ERK1/2 Signaling in the Murine Brain Hippocampus Treated with Shiga Toxin 2 from Enterohemorrhagic Escherichia coli

Shiga toxin 2 (Stx2) from enterohemorrhagic Escherichia coli (EHEC) produces hemorrhagic colitis, hemolytic uremic syndrome (HUS), and acute encephalopathy. The mortality rate in HUS increases significantly when the central nervous system (CNS) is involved. Besides, EHEC also releases lipopolysaccharide (LPS). Many reports have described cognitive dysfunctions in HUS patients, the hippocampus being one of the brain areas targeted by EHEC infection. In this context, a translational murine model of encephalopathy was employed to establish the deleterious effects of Stx2 and the contribution of LPS in the hippocampus. The purpose of this work is to elucidate the signaling pathways that may activate the inflammatory processes triggered by Stx2, which produces cognitive alterations at the level of the hippocampus. Results demonstrate that Stx2 produced depression-like behavior, pro-inflammatory cytokine release, and NF-kB activation independent of the ERK1/2 signaling pathway, while co-administration of Stx2 and LPS reduced memory index. On the other hand, LPS activated NF-kB dependent on ERK1/2 signaling pathway. Cotreatment of Stx2 with LPS aggravated the pathologic state, while dexamethasone treatment succeeded in preventing behavioral alterations. Our present work suggests that the use of drugs such as corticosteroids or NF-kB signaling inhibitors may serve as neuroprotectors from EHEC infection.

Amelioration of cognition impairments in the valproic acid-induced animal model of autism by ciproxifan, a histamine H3-receptor antagonist

Autism spectrum disorder is a neurodevelopmental disorder characterized by deficits in social communication and repetitive behavior. Many studies show that the number of cognitive impairmentscan be reduced by antagonists of the histamine H3 receptor (H3R). In this study, the effects of ciproxifan (CPX) (1 and 3 mg/kg, intraperitoneally) on cognitive impairments in rat pups exposed to valproic acid (VPA) (600 mg/kg, intraperitoneally) wereexamined on postnatal day 48-50 (PND 48-50) using marble-burying task (MBT), open field, novel object recognition (NOR), and Passive avoidance tasks. Famotidine (FAM) (10, 20, and 40 mg/kg, intraperitoneally) was also used to determine whether histaminergic neurotransmission exerts its procognitive effects via H2 receptors (H2Rs). Furthermore, a histological investigation was conducted to assess the degree of degeneration of hippocampal neurons. The results revealed that repetitive behaviors increased in VPA-exposed rat offspring in the MBT. In addition, VPA-exposed rat offspring exhibited more anxiety-like behaviors in the open field than saline-treated rats. It was found that VPA-exposed rat offspring showed memory deficits in NOR and Passive avoidance tasks. Our results indicated that 3 mg/kg CPX improved cognitive impairments induced by VPA, while 20 mg/kg FAM attenuated them. We concluded that 3 mg/kg CPX improved VPA-induced cognitive impairments through H3Rs. The histological assessment showed that the number of CA1 neurons decreased in the VPA-exposed rat offspring compared to the saline-exposed rat offspring, but this decrease was not significant. The histological assessment also revealed no significant differences in CA1 neurons in VPA-exposed rat offspring compared to saline-exposed rat offspring. However, CPX3 increased the number of CA1 neurons in the VPA + CPX3 group compared to the VPA + Saline group, but this increase was not significant. This study showed that rats prenatally exposed to VPA exhibit cognitive impairments in the MBT, open field, NOR, and Passive avoidance tests, which are ameliorated by CPX treatment on PND 48-50. In addition, morphological investigations showed that VPA treatment did not lead to neuronal degeneration in the CA1 subfield of the hippocampus in rat pups.

Two-hour acute restraint stress facilitates escape behavior and learning outcomes through the activation of the Cdk5/GR P S211 pathway in male mice

Acute stress exerts pleiotropic actions on learning behaviors. The induced negative effects are sometimes adopted to measure the efficacy of particular drugs. Until now, there are no detailed experimental data on the time-gradient effects of acute stress. Here, we developed the time gradient acute restraint stress (ARS) model to precisely assess the roles of different restrain times on inducing acute stress. Time gradient ARS facilitates escape behaviors and learning outcomes, peaking at 2 h-ARS and then declining to baseline at 3.5 h-ARS as confirmed by time gradient post-stress data. Furthermore, time gradient ARS activates glucocorticoid receptor (GR) phosphorylation site at Serine211 (P S221) as an inverted V-shaped pattern peaking at 2 h-ARS, whereas that of the GR phosphorylation site at Serine226 (P S226) from 2 h-ARS to 3.5 h-ARS. The 2 h-ARS but not 3.5 h-ARS enhances synaptic plasticity and genes transcription associated with learning and memory in the hippocampus of male mice. The Cdk5 inhibitor, roscovitine, blocks this facilitation effect by intervening in GR phosphorylation at Serine211 in the 2 h-ARS mice. Altogether, these findings show that the time gradient ARS selectively activates GR phospho-isoforms and differentially influences the behaviors along with maintaining a relationship between 2 h-ARS and Cdk5/GR P S211-mediated transcriptional activity.

Histamine H3 receptor antagonist, ciproxifan, alleviates cognition and synaptic plasticity alterations in a valproic acid-induced animal model of autism

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication and cognitive behaviors. Histamine H3 receptor (H3R) antagonists are considered as therapeutic factors for treating cognitive impairments.

OBJECTIVES

The aim of the present study was to evaluate the effects of the H3R antagonist, ciproxifan (CPX), on cognition impairment especially, spatial learning memory, and synaptic plasticity in the CA1 region of the hippocampus in autistic rats.

METHODS

Pregnant rats were injected with either valproic acid (VPA) (600 mg/kg, i.p.) or saline on an embryonic day 12.5 (E12.5). The effects of the H3R antagonist, ciproxifan (CPX) (1, 3 mg/kg, i.p.), were investigated on learning and memory in VPA-exposed rat pups and saline-exposed rat pups using Morris water maze (MWM) and social interaction tasks. The H2R antagonist, famotidine (FAM) (10, 20, 40 mg/kg, i.p.), was used to determine whether brain histaminergic neurotransmission exerted its procognitive effects through the H2R. In addition, synaptic reinforcement was evaluated by in vivo field potential recording.

RESULTS

The results showed that VPA-exposed rat pups had significantly lower sociability and social memory performance compared to the saline rats. VPA-exposed rat pups exhibited learning and memory impairments in the MWM task. In addition, VPA caused suppression of long-term potentiation (LTP) in the CA1 area of the hippocampus. Our results demonstrated that CPX 3 mg/kg improved VPA-induced cognitive impairments and FAM 20 mg/kg attenuated cognitive behaviors as well as electrophysiological properties.

CONCLUSIONS

CPX 3 mg/kg improved VPA-induced impairments of LTP as well as learning and memory deficits through H2R.

Revisiting Preclinical Observations of Several Histamine H3 Receptor Antagonists/Inverse Agonists in Cognitive Impairment, Anxiety, Depression, and Sleep-Wake Cycle Disorder

A relationship appears to exist between dysfunction of brain histamine (HA) and various neuropsychiatric brain disorders. The possible involvement of brain HA in neuropathology has gained attention recently, and its role in many (patho)physiological brain functions including memory, cognition, and sleep-wake cycle paved the way for further research on the etiology of several brain disorders. Histamine H3 receptor (H3R) evidenced in the brains of rodents and humans remains of special interest, given its unique position as a pre- and postsynaptic receptor, controlling the synthesis and release of HA as well as different other neurotransmitters in different brain regions, respectively. Despite several disappointing outcomes for several H3R antagonists/inverse agonists in clinical studies addressing their effectiveness in Alzheimer's disease (AD), Parkinson's disease (PD), and schizophrenia (SCH), numerous H3R antagonists/inverse agonists showed great potentials in modulating memory and cognition, mood, and sleep-wake cycle, thus suggesting its potential role in neurocognitive and neurodegenerative diseases such as AD, PD, SCH, narcolepsy, and major depression in preclinical rodent models. In this review, we present preclinical applications of selected H3R antagonists/inverse agonists and their pharmacological effects on cognitive impairment, anxiety, depression, and sleep-wake cycle disorders. Collectively, the current review highlights the behavioral impact of developments of H3R antagonists/inverse agonists, aiming to further encourage researchers in the preclinical drug development field to profile the potential therapeutic role of novel antagonists/inverse agonists targeting histamine H3Rs.

The 3-iodothyronamine (T1AM) and the 3-iodothyroacetic acid (TA1) indicate a novel connection with the histamine system for neuroprotection

The 3-iodothyronamine (T1AM) and 3-iodothryoacetic acid (TA1), are endogenous occurring compounds structurally related with thyroid hormones (THs, the pro-hormone T4 and the active hormone T3) initially proposed as possible mediators of the rapid effects of T3. However, after years from their identification, the physio-pathological meaning of T1AM and TA1 tissue levels remains an unsolved issue while pharmacological evidence indicates both compounds promote in rodents central and peripheral effects with mechanisms which remain mostly elusive. Pharmacodynamics of T1AM includes the recognition of G-coupled receptors, ion channels but also biotransformation into an active metabolite, i.e. the TA1. Furthermore, long term T1AM treatment associates with post-translational modifications of cell proteins. Such array of signaling may represent an added value, rather than a limit, equipping T1AM to play different functions depending on local expression of targets and enzymes involved in its biotransformation. Up to date, no information regarding TA1 mechanistic is available. We here review some of the main findings describing effects of T1AM (and TA1) which suggest these compounds interplay with the histaminergic system. These data reveal T1AM and TA1 are part of a network of signals involved in neuronal plasticity including neuroprotection and suggest T1AM and TA1 as lead compounds for a novel class of atypical psychoactive drugs.

The 4-Hole-Board Test for Assessment of Long-Term Spatial Memory in Mice

The hole-board test has been used in rodents since the early 60s to measure exploratory behavior, locomotor activity and cognitive function. The test is based on rodents' natural curiosity and attraction for novelty. Basically, the hole-board consists of a small square arena with an extractable platform as floor, which has a set of equally spaced circular holes on its surface. In this article, we describe the protocol of a 4-hole-board test allowing the assessment of long-term spatial memory in mice without the employment of water or food restriction, painful stimuli (as electrical shocks) or any aversive condition (as forced swimming or exposure to intense light). Four holes are present on the floor of the square arena (one for each of its four quadrants). Mice released in the arena spontaneously approach the holes and explore them by briefly inserting the snout inside, a behavior defined as nose-poking (or head-dipping). If, after 24 hr, rodents are re-exposed to the hole-board, the novelty of the holes decreases. Animals with an intact long-term memory will show a reduction of the frequency of nose-poking into the holes. The total number of nose-pokes on day 1 is an index of exploration, while the percentage of decrease in nose-poking on day 2 represents an index of long-term spatial memory. Number of quadrant crossings is scored as a control measure for locomotor activity, which with the present protocol should remain stable across the days of testing. Indeed, the 4-hole-board test represents a stress-free and animal-friendly option to evaluate long-term spatial memory. In the present paper, we provide detailed description of the hole-board apparatus and step-by-step protocol for assessment of spatial memory in mice. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Validation of the 4-hole-board Basic Protocol 2: Evaluation of long-term spatial memory through the 4-hole-board test.

Role of toll-like receptor 4 antagonist Lipopolysaccharide-Rhodobacter sphaeroides on acute stress-induced voluntary ethanol preference and drinking behaviour: In vivo Swiss Albino mouse model

The present study focused on investigating the effect of toll-like receptor 4 (TLR4) antagonist Lipopolysaccharide-Rhodobacter sphaeroides(LPS-RS) on acute, stress-induced voluntary ethanol preference and drinking behaviour, neuronal components activation, and gene expression associated with stress and addictive behaviour. This study involved the exposure of restraint stress and social isolation using Swiss Albino mice. Two-bottle choice ethanol preference analysis was used in the evaluation of voluntary ethanol seeking and drinking behaviour. Several behavioural assessments were carried out to assess fear and anxiety-like behaviour, neuromuscular ability, motor coordination and locomotion. Morphological and immunoreactivity analysis and gene expression analysis were done after the completion of behavioural assessments. TLR4 antagonist LPS-RS treated stressed-mice showed a significant decrease in ethanol drinking compared with stressed mice. Behavioural results showed that stress exposure induced fear and anxiety-like behaviour; however; no significant deficit was found on motor coordination, neuromuscular ability, locomotion and exploratory behaviour among groups. Morphological analysis showed no significant change in the prefrontal cortex and hippocampus among all groups, while immunoreactivity analysis showed higher expression of c-Fos in prefrontal cortex and hippocampus, higher TLR4 expression in the prefrontal cortex and glial fibrillary acidic protein (GFAP) in hippocampus among stressed-animals. Stressed-mice also showed significant increase in TLR4, Nuclear Factor-Kappa B (NF-kB), inducible nitric oxide synthase (iNOS), dopamine receptor D2 (DRD₂), cyclic adenosine monophosphate (cAMP) response element binding protein-1 (CREB-1) and opioid receptor MU-1 (OPRM-1) genes expression compared with control and LPS-RS treated stressed-mice. As a conclusion, the antagonism of TLR4 could provide therapeutic value in the treatment of stress-induced addiction.

Ameliorating effects of histamine H3 receptor antagonist E177 on acute pentylenetetrazole-induced memory impairments in rats

Histamine H3 receptors (H3Rs) are involved in several neuropsychiatric diseases including epilepsy. Therefore, the effects of H3R antagonist E177 (5 and 10 mg/kg, intraperitoneal (i.p.)) were evaluated on acute pentylenetetrazole (PTZ)-induced memory impairments, oxidative stress levels (glutathione (GSH), malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD)), various brain neurotransmitters (histamine (HA), acetylcholine (ACh), γ-aminobutyric acid (GABA)), and glutamate (Glu), acetylcholine esterase (AChE) activity, and c-fos protein expression in rats. E177 (5 and 10 mg/kg, i.p.) significantly prolonged step-through latency (STL) time in single-trial passive avoidance paradigm (STPAP), and shortened transfer latency time (TLT) in elevated plus maze paradigm (EPMP) (all P < 0.05). Moreover, and in the hippocampus of PTZ-treated animals, E177 mitigated abnormal levels of AChE activity, ACh and HA (all P < 0.05), but failed to modify brain levels of GABA and Glu. Furthermore, E177 alleviated hippocampal oxidative stress by significantly decreasing the elevated levels of MDA, and increasing the abnormally decreased level of GSH (all P < 0.05). Furthermore, E177 reduced elevated levels of hippocampal c-fos protein expression in hippocampal tissues of PTZ-treated animals (all P < 0.05). The observed results propose the potential of H3R antagonist E177 with an added advantage of avoiding cognitive impairment, emphasizing the H3Rs as a prospective target for future pharmacological management of epilepsy with associated memory impairments.

Antagonism of Histamine H3 receptors Alleviates Pentylenetetrazole-Induced Kindling and Associated Memory Deficits by Mitigating Oxidative Stress, Central Neurotransmitters, and c-Fos Protein Expression in Rats

Histamine H3 receptors (H3Rs) are involved in several neuropsychiatric diseases including epilepsy. Therefore, the effects of H3R antagonist E177 (5 and 10 mg/kg, intraperitoneal (i.p.)) were evaluated on the course of kindling development, kindling-induced memory deficit, oxidative stress levels (glutathione (GSH), malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD)), various brain neurotransmitters (histamine (HA), acetylcholine (ACh), γ-aminobutyric acid (GABA)), and glutamate (GLU), acetylcholine esterase (AChE) activity, and c-Fos protein expression in pentylenetetrazole (PTZ, 40 mg/kg) kindled rats. E177 (5 and 10 mg/kg, i.p.) significantly decreased seizure score, increased step-through latency (STL) time in inhibitory avoidance paradigm, and decreased transfer latency time (TLT) in elevated plus maze (all P < 0.05). Moreover, E177 mitigated oxidative stress by significantly increasing GSH, CAT, and SOD, and decreasing the abnormal level of MDA (all P < 0.05). Furthermore, E177 attenuated elevated levels of hippocampal AChE, GLU, and c-Fos protein expression, whereas the decreased hippocampal levels of HA and ACh were modulated in PTZ-kindled animals (all P < 0.05). The findings suggest the potential of H3R antagonist E177 as adjuvant to antiepileptic drugs with an added advantage of preventing cognitive impairment, highlighting the H3Rs as a potential target for the therapeutic management of epilepsy with accompanied memory deficits.

Procognitive impact of ciproxifan (a histaminergic H3 receptor antagonist) on contextual memory retrieval after acute stress

AIM

Although cognitive deficits commonly co-occur with stress-related emotional disorders, effect of procognitive drugs such as histaminergic H₃ receptor antagonists are scarcely studied on memory retrieval in stress condition.

METHODS

Experiment 1. Memory of two successive spatial discriminations (D1 then D2) 24 hours after learning was studied in a four-hole board in mice. H3 receptor antagonist ciproxifan (ip 3 mg/kg) and acute stress (three electric footshocks; 0.9 mA; 15 ms) were administered 30 and 15 minutes respectively before memory retrieval test. Fos immunostaining was performed to evaluate the neural activity of several brain areas. Experiment 2. Effects of ciproxifan and acute stress were evaluated on anxiety-like behavior in the elevated plus maze and glucocorticoid activity using plasma corticosterone assay.

RESULTS

Experiment 1. Ciproxifan increased memory retrieval of D2 in nonstress condition and of D1 in stress one. Ciproxifan mitigated the stress-induced increase of Fos expression in the prelimbic and infralimbic cortex, the central and basolateral amygdala and the CA1 of dorsal hippocampus. Experiment 2. Ciproxifan dampened the stress-induced anxiety-like behavior and plasma corticosterone increase.

CONCLUSION

Ciproxifan improved contextual memory retrieval both in stress and nonstress conditions without exacerbating behavioral and endocrine responses to stress. Overall, these data suggest potential usefulness of H₃ receptor antagonists as cognitive enhancer both in nonstress and stress conditions.