Functional neuroimaging of cognition impaired by a classical antihistamine, d-chlorpheniramine

Classics in Chemical Neuroscience: Deliriant Antihistaminic Drugs

Antihistaminic drugs are widely used clinically and have long been primarily known for their use to treat severe allergic conditions caused by histamine release. Antihistaminic drugs also exert central nervous system (CNS) effects, acting as anxiolytics, hypnotics, and neuroleptics. However, these drugs also have multiple serious neuropharmacological side-effects, inducing delirium, hyperarousal, disorganized behavior, and hallucinations. Due to their robust CNS effects, antihistamines are also increasingly abused, with occasional overdoses and life-threatening toxicity. Here, we discuss chemical and neuropharmacological aspects of antihistaminic drugs in both human and animal (experimental) models and outline their current societal and mental health importance as neuroactive substances.

Molecular mechanism of antihistamines recognition and regulation of the histamine H1 receptor

Histamine receptors are a group of G protein-coupled receptors (GPCRs) that play important roles in various physiological and pathophysiological conditions. Antihistamines that target the histamine H1 receptor (H1R) have been widely used to relieve the symptoms of allergy and inflammation. Here, to uncover the details of the regulation of H1R by the known second-generation antihistamines, thereby providing clues for the rational design of newer antihistamines, we determine the cryo-EM structure of H1R in the apo form and bound to different antihistamines. In addition to the deep hydrophobic cavity, we identify a secondary ligand-binding site in H1R, which potentially may support the introduction of new derivative groups to generate newer antihistamines. Furthermore, these structures show that antihistamines exert inverse regulation by utilizing a shared phenyl group that inserts into the deep cavity and block the movement of the toggle switch residue W4286.48. Together, these results enrich our understanding of GPCR modulation and facilitate the structure-based design of novel antihistamines.

Targeting Histamine and Histamine Receptors for Memory Regulation: An Emotional Perspective

Histamine has long been accepted as a pro-cognitive agent. However, lines of evidence have suggested that the roles of histamine in learning and memory processes are much more complex than previously thought. When explained by the spatial perspectives, there are many contradictory results. However, using emotional memory perspectives, we suspect that the histaminergic system may interplay with stress, reward inhibition, and attention to modulate emotional memory formation. The functional diversity of histamine makes it a viable target for clinical management of neuropsychiatric disorders. Here, we update the current knowledge about the functions of histamine in emotional memory and summarize the underlying molecular and neural circuit mechanisms. Finally, we review the main clinical studies about the impacts of histamine-related compounds on memory and discuss insights into future research on the roles of histamine in emotional memory. Despite the recent progress in histamine research, the histaminergic emotional memory circuits are poorly understood, and it is also worth verifying the functions of histamine receptors in a more spatiotemporally specific manner.

Old versus new antihistamines: Effects on cognition and psychomotor functions

Context

Antihistamines (AHs) are the most widely long-term therapeutic option to manage allergic diseases. This research aimed to study the effects of long-term administration of AHs: on cognitive (memory, mood, attention, sleep and executive function) and psychomotor performance.

Materials and Methods

This prospective, observational study for a total duration of 30 months was carried out at the Dermatology OPD in adult patients with dermatological condition who were newly prescribed either chlorpheniramine (4 mg, BD), levocetirizine (10 mg, OD), fexofenadine (180 mg, OD) or bepotastine (10 mg, BD) for at least 28 days as per inclusion and exclusion criteria after taking written informed consent. A detailed history of the patients, memory (using PGI memory scale) and psychomotor functions, Brief Mood Introspection Scale and Epworth Sleepiness Scale were assessed at baseline, 1 week and 4 weeks. Data obtained were analysed using paired sample t-test and one-way ANOVA followed by post hoc analysis (P-value <0.05 statistically significant).

Results

A total of 22 in chlorpheniramine group, 23 in levocetirizine group, 20 in fexofenadine group and 18 in bepotastine group were analysed. Chlorpheniramine and levocetirizine had deteriorating effects on cognitive and psychomotor performance, whereas fexofenadine and bepotastine showed positive effect on various cognitive and psychometric tasks. The study results showed chlorpheniramine and levocetirizine to be having sedative effects, whereas fexofenadine was nonsedating. In bepotastine group, no effect on sleep was observed. No significant difference in mood scores was observed in between chlorpheniramine, levocetirizine and fexofenadine groups. In bepotastine group, arousal calm and positive tired scores increased at 4 week as compared to baseline.

Conclusion

Patients with dermatological illnesses can be prescribed fexofenedine and bepotastine, as compared to chlorpheniramine and levocetirizine, and their cognitive and psychological functions should be evaluated periodically with suitable tests.

Migraine Pharmacological Treatment and Cognitive Impairment: Risks and Benefits

Migraine is a common neurological disorder impairing the quality of life of patients. The condition requires, as an acute or prophylactic line of intervention, the frequent use of drugs acting on the central nervous system (CNS). The long-term impact of these medications on cognition and neurodegeneration has never been consistently assessed. The paper reviews pharmacological migraine treatments and discusses their biological and clinical effects on the CNS. The different anti-migraine drugs show distinct profiles concerning neurodegeneration and the risk of cognitive deficits. These features should be carefully evaluated when prescribing a pharmacological treatment as many migraineurs are of scholar or working age and their performances may be affected by drug misuse. Thus, a reconsideration of therapy guidelines is warranted. Furthermore, since conflicting results have emerged in the relationship between migraine and dementia, future studies must consider present and past pharmacological regimens as potential confounding factors.

Pharmacogenomics for the efficacy and side effects of antihistamines

Antihistamines, especially H1 antihistamines, are widely used in the treatment of allergic diseases such as urticaria and allergic rhinitis, mainly for reversing elevated histamine and anti-allergic effects. Antihistamines are generally safe, but some patients experience adverse reactions, such as cardiotoxicity, central inhibition, and anticholinergic effects. There are also individual differences in antihistamine efficacy in clinical practice. The concept of individualized medicine has been deeply rooted in people's minds since it was put forward. Pharmacogenomics is the study of the role of inheritance in individual variations in drug response. In recent decades, pharmacogenomics has been developing rapidly, which provides new ideas for individualized medicine. Polymorphisms in the genes encoding metabolic enzymes, transporters, and target receptors have been shown to affect the efficacy of antihistamines. In addition, recent evidence suggests that gene polymorphisms influence urticaria susceptibility and antihistamine therapy. Here, we summarize current reports in this area, aiming to contribute to future research in antihistamines and clinical guidance for antihistamines use in individualized medicine.

Clinical practice guidelines for the management of atopic dermatitis 2018

Atopic dermatitis (AD) is a disease characterized by relapsing eczema with pruritus as a primary lesion. The current strategies to treat AD in Japan from the perspective of evidence-based medicine consist of three primary measures: (i) the use of topical corticosteroids and tacrolimus ointment as the main treatment for the inflammation; (ii) topical application of emollients to treat the cutaneous barrier dysfunction; and (iii) avoidance of apparent exacerbating factors, psychological counseling and advice about daily life. The guidelines present recommendations to review clinical research articles, evaluate the balance between the advantages and disadvantages of medical activities, and optimize medical activity-related patient outcomes with respect to several important points requiring decision-making in clinical practice.

Histamine H1 receptor on astrocytes and neurons controls distinct aspects of mouse behaviour

Histamine is an important neurotransmitter that contributes to various processes, including the sleep-wake cycle, learning, memory, and stress responses. Its actions are mediated through histamine H1-H4 receptors. Gene knockout and pharmacological studies have revealed the importance of H1 receptors in learning and memory, regulation of aggression, and wakefulness. H1 receptors are abundantly expressed on neurons and astrocytes. However, to date, studies selectively investigating the roles of neuronal and astrocytic H1 receptors in behaviour are lacking. We generated novel astrocyte- and neuron-specific conditional knockout (cKO) mice to address this gap in knowledge. cKO mice showed cell-specific reduction of H1 receptor gene expression. Behavioural assessment revealed significant changes and highlighted the importance of H1 receptors on both astrocytes and neurons. H1 receptors on both cell types played a significant role in anxiety. Astrocytic H1 receptors were involved in regulating aggressive behaviour, circadian rhythms, and quality of wakefulness, but not sleep behaviour. Our results emphasise the roles of neuronal H1 receptors in recognition memory. In conclusion, this study highlights the novel roles of H1 receptors on astrocytes and neurons in various brain functions.

Brain histamine H1 receptor occupancy after oral administration of desloratadine and loratadine

Some histamine H1 receptor (H1R) antagonists induce adverse sedative reactions caused by blockade of histamine transmission in the brain. Desloratadine is a second-generation antihistamine for treatment of allergic disorders. Its binding to brain H1Rs, which is the basis of sedative property of antihistamines, has not been examined previously in the human brain by positron emission tomography (PET). We examined brain H1R binding potential ratio (BPR), H1R occupancy (H1RO), and subjective sleepiness after oral desloratadine administration in comparison to loratadine. Eight healthy male volunteers underwent PET imaging with [11C]-doxepin, a PET tracer for H1Rs, after a single oral administration of desloratadine (5 mg), loratadine (10 mg), or placebo in a double-blind crossover study. BPR and H1RO in the cerebral cortex were calculated, and plasma concentrations of loratadine and desloratadine were measured. Subjective sleepiness was quantified by the Line Analogue Rating Scale (LARS) and the Stanford Sleepiness Scale (SSS). BPR was significantly lower after loratadine administration than after placebo (0.504 ± 0.074 vs 0.584 ± 0.059 [mean ± SD], P < 0.05), but BPR after desloratadine administration was not significantly different from BPR after placebo (0.546 ± 0.084 vs 0.584 ± 0.059, P = 0.250). The plasma concentration of loratadine was negatively correlated with BPR in subjects receiving loratadine, but that of desloratadine was not correlated with BPR. Brain H1ROs after desloratadine and loratadine administration were 6.47 ± 10.5% and 13.8 ± 7.00%, respectively (P = 0.103). Subjective sleepiness did not significantly differ among subjects receiving the two antihistamines and placebo. At therapeutic doses, desloratadine did not bind significantly to brain H1Rs and did not induce any significant sedation.

Antihistamines for Allergic Rhinitis Treatment from the Viewpoint of Nonsedative Properties

Antihistamines targeting the histamine H₁ receptor play an important role in improving and maintaining the quality of life of patients with allergic rhinitis. For more effective and safer use of second-generation drugs, which are recommended by various guidelines, a classification based on their detailed characteristics is necessary. Antihistamines for first-line therapy should not have central depressant/sedative activities. Sedative properties (drowsiness and impaired performance) are associated with the inhibition of central histamine neurons. Brain H₁ receptor occupancy (H₁RO) is a useful index shown to be correlated with indices based on clinical findings. Antihistamines are classified into non-sedating (<20%), less-sedating (20–50%), and sedating (≥50%) groups based on H₁RO. Among the non-sedating group, fexofenadine and bilastine are classified into “non-brain-penetrating antihistamines” based on the H₁RO. These two drugs have many common chemical properties. However, bilastine has more potent binding affinity to the H₁ receptor, and its action tends to last longer. In well-controlled studies using objective indices, bilastine does not affect psychomotor or driving performance even at twice the usual dose (20 mg). Upon selecting antihistamines for allergic rhinitis, various situations should be taken into our consideration. This review summarizes that the non-brain-penetrating antihistamines should be chosen for the first-line therapy of mild allergic rhinitis.

Effects of levocetirizine and diphenhydramine on regional glucose metabolic changes and hemodynamic responses in the human prefrontal cortex during cognitive tasks

OBJECTIVE

Antihistamines often have sedative side effects. This was the first study to measure regional cerebral glucose (energy) consumption and hemodynamic responses in young adults during cognitive tests after antihistamine administration.

METHODS

In this double-blind, placebo-controlled, three-way crossover study, 18 healthy young Japanese men received single doses of levocetirizine 5 mg and diphenhydramine 50 mg at intervals of at least six days. Subjective feeling, task performances, and brain activity were evaluated during three cognitive tests (word fluency, two-back, and Stroop). Regional cerebral glucose consumption changes were measured using positron emission tomography with [¹⁸ F]fluorodeoxyglucose. Regional hemodynamic responses were measured using near-infrared spectroscopy.

RESULTS

Energy consumption in prefrontal regions was significantly increased after antihistamine administration, especially diphenhydramine, whereas prefrontal hemodynamic responses, evaluated with oxygenated hemoglobin levels, were significantly lower with diphenhydramine treatment. Stroop test accuracy was significantly impaired by diphenhydramine, but not by levocetirizine. There was no significant difference in subjective sleepiness.

CONCLUSIONS

Physiological "coupling" between metabolism and perfusion in the healthy human brain may not be maintained under pharmacological influence due to antihistamines. This uncoupling may be caused by a combination of increased energy demands in the prefrontal regions and suppression of vascular permeability in brain capillaries after antihistamine treatment. Further research is needed to validate this hypothesis.

The clinical pharmacology of non-sedating antihistamines

We previously reported on brain H₁ receptor occupancy measurements of antihistamines in human brain using [¹¹C]doxepin and positron emission tomography (PET). We proposed the use of brain H₁ receptor occupancy to classify antihistamines objectively into three categories of sedating, less-sedating, and non-sedating antihistamines according to their sedative effects. Non-sedating antihistamines are recommended for the treatment of allergies such as pollinosis and atopic dermatitis because of their low penetration into the central nervous system. Physicians and pharmacists are responsible for fully educating patients about the risks of sedating antihistamines from pharmacological points of view. If a sedating antihistamine must be prescribed, its sedative effects should be thoroughly considered before choosing the drug. Non-sedating antihistamines should be preferentially used whenever possible as most antihistamines are equally efficacious, while adverse effects of sedating antihistamines can be serious. This review summarizes the pharmacological properties of clinically useful non-sedating antihistamines from the perspective of histamine function in the CNS.

Histamine H3 receptor as a potential target for cognitive symptoms in neuropsychiatric diseases

The potential contributions of the brain histaminergic system in neurodegenerative diseases, and the possiblity of histamine-targeting treatments is attracting considerable interests. The histamine H3 receptor (H3R) is expressed mainly in the central nervous system, and is, consequently, an attractive pharmacological target. Although recently described clinical trials have been disappointing in attention deficit hyperactivity disorder (ADHD) and schizophrenia (SCH), numerous H3R antagonists, including pitolisant, demonstrate potential in the treatment of narcolepsy, excessive daytime sleepiness associated with cognitive impairment, epilepsy, and Alzheimer's disease (AD). This review focuses on the recent preclinical as well as clinical results that support the relevance of H3R antagonists for the treatment of cognitive symptoms in neuropsychiatric diseases, namely AD, epilepsy and SCH. The review summarizes the role of histaminergic neurotransmission with focus on these brain disorders, as well as the effects of numerous H3R antagonists on animal models and humans.

A simulated car-driving study on the effects of acute administration of levocetirizine, fexofenadine, and diphenhydramine in healthy Japanese volunteers

OBJECTIVE

Antihistamines are often used for treating allergic rhinitis. However, many older antihistamines cause sedative side effects. The sedative effects of antihistamines on car-driving have been investigated. This has not been investigated for levocetirizine, a new-generation antihistamine, in Asian populations, and so we evaluated its sedative effects in healthy Japanese subjects.

METHODS

In this double-blind, placebo-controlled, four-way crossover study, healthy volunteers received single doses of levocetirizine 5 mg, fexofenadine 60 mg, diphenhydramine 50 mg, and placebo at intervals of at least 6 days. Simple brake reaction time and choice brake reaction time task (CBRT), a lateral tracking (LT) task, and a multiple task, a mixture of CBRT and LT task, were used to compare driving performance between the four drugs. Subjective sedation was also assessed.

RESULTS

The simple brake reaction time and CBRT, and the CBRT component of the multiple task, did not show any significant differences between the drugs. In contrast, the LT, both as a single parameter and as a component of the multiple task, showed significant differences between diphenhydramine and the newer-generation antihistamines in a manner that corresponds with subjective sedation.

CONCLUSIONS

Levocetirizine and fexofenadine did not impair psychomotor performance in subjects performing simulated car-driving tasks, while diphenhydramine did impair psychomotor performance in the subjects. Copyright © 2016 John Wiley & Sons, Ltd.

Treatment of allergic rhinitis and urticaria: a review of the newest antihistamine drug bilastine

Allergic rhinitis and urticaria are common allergic diseases that may have a major negative impact on patients' quality of life. Bilastine, a novel new-generation antihistamine that is highly selective for the H1 histamine receptor, has a rapid onset and prolonged duration of action. This agent does not interact with the cytochrome P450 system and does not undergo significant metabolism in humans, suggesting that it has very low potential for drug-drug interactions, and does not require dose adjustment in renal impairment. As bilastine is not metabolized and is excreted largely unchanged, hepatic impairment is not expected to increase systemic exposure above the drug's safety margin. Bilastine has demonstrated similar efficacy to cetirizine and desloratadine in patients with seasonal allergic rhinitis and, in a Vienna Chamber study, a potentially longer duration of action than fexofenadine in patients with asymptomatic seasonal allergic rhinitis. It has also shown significant efficacy (similar to that of cetirizine) and safety in the long-term treatment of perennial allergic rhinitis. Bilastine showed similar efficacy to levocetirizine in patients with chronic spontaneous urticaria and can be safely used at doses of up to fourfold higher than standard dosage (80 mg once daily). The fourfold higher than standard dose is specified as an acceptable second-line treatment option for urticaria in international guidelines. Bilastine is generally well tolerated, both at standard and at supratherapeutic doses, appears to have less sedative potential than other second-generation antihistamines, and has no cardiotoxicity. Based on its pharmacokinetic properties, efficacy, and tolerability profile, bilastine will be valuable in the management of allergic rhinitis and urticaria.

Bilastine: a new antihistamine with an optimal benefit-to-risk ratio for safety during driving

INTRODUCTION

Rational selection of a second-generation H1-antihistamine requires efficacy and safety considerations, particularly regarding central nervous system (CNS) effects (cognitive and psychomotor function), potential for driving impairment, minimal sedative effects and a lack of interactions. This review evaluates the key safety features of the non-sedating antihistamine, bilastine, during driving and in preventing road traffic accidents.

AREAS COVERED

Among the second-generation H1-antihistamines, sedative effects which can affect cognitive and psychomotor performance, and possibly driving ability, may not be similar. Bilastine is absorbed rapidly, undergoes no hepatic metabolism or cytochrome P450 interaction (minimal drug-drug interaction potential), and is a substrate for P-glycoprotein (limiting CNS entry). Positron emission tomography showed that, compared with other second-generation H1-antihistamines, bilastine has the lowest cerebral histamine H1-receptor occupancy. Bilastine 20 mg once daily (therapeutic dose) is non-sedating, does not enhance the effects of alcohol or CNS sedatives, does not impair driving performance and has at least similar efficacy as other second-generation H1-antihistamines in the treatment of allergic rhinoconjunctivitis and urticaria.

EXPERT OPINION

Current evidence shows that bilastine has an optimal benefit-to-risk ratio, meeting all conditions for contributing to safety in drivers who need antihistamines, and hence for being considered as an antihistamine of choice for drivers.

Histamine H1 receptor occupancy by the new-generation antipsychotics olanzapine and quetiapine: a positron emission tomography study in healthy volunteers

RATIONALE

Histamine H1 antagonists have hypnotic, appetite-promoting, and sedative side effects. Most second-generation antipsychotics have potent antagonistic effects on histamine H1 receptor (H1R). Positron emission tomography (PET) can measure the H1R occupancy (H1RO) in vivo, although there are no reports regarding antipsychotics.

OBJECTIVES

We studied the H1RO of olanzapine and quetiapine in vivo with respect to their plasma concentrations and subjective drowsiness by performing human PET imaging studies with [(11)C]doxepin, a potent PET ligand of H1R.

METHODS

Six healthy Japanese male volunteers were enrolled. Cross-randomized PET imaging was performed after a single oral administration of olanzapine (2.5 mg), quetiapine (25 mg), or placebo. PET data were analyzed by region of interest and voxel-by-voxel analysis. We concurrently measured plasma drug concentrations by liquid chromatography/tandem mass spectrometry and evaluated subjective sleepiness.

RESULTS

The binding potential ratios of olanzapine and quetiapine in the cerebral cortex were significantly lower than that of the placebo. The H1RO values of olanzapine and quetiapine in the cortex were approximately 61-80 and 56-81%, respectively. The binding potential ratios of the drugs were significantly lower than that of the placebo in the dorsolateral prefrontal and lateral temporal cortices, and anterior and posterior cingulate gyri. The H1RO values in the cortex were significantly correlated with subjective sleepiness but not plasma drug concentrations.

CONCLUSIONS

Olanzapine and quetiapine have high H1RO values in the human brain under their clinical minimum doses. This study provides a foundation of the properties by which new-generation antipsychotics block the central histaminergic system in humans.

Bilastine vs. hydroxyzine: occupation of brain histamine H1 -receptors evaluated by positron emission tomography in healthy volunteers

AIM

A close correlation exists between positron emission tomography (PET)-determined histamine H1 -receptor occupancy (H1 RO) and the incidence of sedation. Antihistamines with H1 RO <20% are classified as non-sedating. The objective was to compare the H1 RO of bilastine, a second generation antihistamine, with that of hydroxyzine.

METHODS

This randomized, double-blind, crossover study used PET imaging with [(11) C]-doxepin to evaluate H1 RO in 12 healthy males (mean age 26.2 years), after single oral administration of bilastine (20 mg), hydroxyzine (25 mg) or placebo. Binding potentials and H1 ROs were calculated in five cerebral cortex regions of interest: frontal, occipital, parietal, temporal, insula. Plasma bilastine concentrations, subjective sedation (visual analogue scale), objective psychomotor performance (digital symbol substitution test), physiological variables and safety (adverse events, AEs), were also evaluated.

RESULTS

The mean binding potential of all five regions of interest (total binding potential) was significantly greater with bilastine than hydroxyzine (mean value 0.26 vs. 0.13, P < 0.01; mean difference and 95% CI -0.130 [-0.155, 0.105]). There was no significant difference between bilastine and placebo. Overall H1 RO by bilastine was significantly lower than that by hydroxyzine (mean value -3.92% vs. 53.95%, P < 0.01; mean difference and 95% CI 57.870% [42.664%, 73.075%]). There was no significant linear relationship between individual bilastine plasma concentrations and total binding potential values. No significant between-treatment differences were observed for sedation and psychomotor performance. Twenty-six non-serious AEs were reported. Sleepiness or sedation was not reported with bilastine but appeared in some subjects with hydroxyzine.

CONCLUSIONS

A single oral dose of bilastine 20 mg had minimal H1 RO, was not associated with subjective sedation or objective impairment of psychomotor performance and was devoid of treatment-related sedative AEs, thus satisfying relevant subjective, objective and PET criteria as a non-sedating antihistamine.

Multifactorial determinants of cognition - Thyroid function is not the only one

Background

Since the 1960s hypothyroidism together with iodine deficiency have been considered to be a principal determinant of cognition development. Following iodine supplementation programs and improved treatment options for hypothyroidism this relation might not be valid in 2015. On the other hand neurosciences have added different inputs also related to cognition.

Scope of review

We will examine the characteristics of the original and current publications on thyroid function and cognition and also add some general determinants of intelligence and cognition. One central issue for us is the relation of stress to cognition knowing that both physical and psychological stress, are frequent elements in subjects with thyroid dysfunction. We have considered a special type of stress called pre-natal stress which can influence cognitive functions. Fear and anxiety can be intermingled requiring mechanisms of fear extinction.

Major conclusions

Recent studies have failed to show an influence of thyroid medication during pregnancy on intellectual development. Neuroscience offers a better explanation of cognition than hypothyroidism and iodine deficiency. Additional factors relevant to cognition are nutrition, infection, prenatal stress, and early life stress. In turn stress is related to low magnesium levels. Magnesium supplementation can correct both latent hypothyroidism and acquired mild cognitive deficits.

General significance

Cognition is a complex process that depends on many determinants and not only on thyroid function. Magnesium deficiency appears to be a basic mechanism for changes in thyroid function as well as of cognition.

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Untreated hypothyroidism, i.e. hypothyroxinemia, can influence IQ.

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Thyroxine administration to euthyroid pregnant women has no effect on cognition.

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The hippocampus and NMDA receptors play a central role in cognitive processes.

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Antenatal and early life stressors can influence cognition later in life.

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Stressors can lead to decreased levels of magnesium and demands supplementation.

Brain histamine H1 receptor occupancy measured by PET after oral administration of levocetirizine, a non-sedating antihistamine

OBJECTIVE

Histamine H1 receptor (H1R) antagonists often have sedative side effects, which are caused by the blockade of the neural transmission of the histaminergic neurons. We examined the brain H1R occupancy (H1RO) and the subjective sleepiness of levocetirizine, a new second-generation antihistamine, comparing fexofenadine, another non-sedating antihistamine, as a negative active control.

METHODS

Eight healthy volunteers underwent positron emission tomography (PET) imaging with [(11)C]doxepin, a PET tracer that specifically binds to H1Rs, after a single oral administration of levocetirizine (5 mg), fexofenadine (60 mg) or placebo in a double-blind crossover study. Binding potential ratios and H1ROs in the cerebral cortices regions were calculated using placebo. Subjective sleepiness was assessed with the Line Analogue Rating Scale and the Stanford Sleepiness Scale.

RESULTS

There was no significant difference between the mean brain H1RO after levocetirizine administration (8.1%; 95% CI: -9.8 to 26.0%) and fexofenadine administration (-8.0%; 95% CI: -26.7 to 10.6%). Similarly, subjective sleepiness was not significantly different between the two antihistamines and placebo. Neither subjective sleepiness nor plasma concentrations was significantly correlated with the brain H1RO of the two antihistamines.

CONCLUSION

At therapeutic dose, levocetirizine does not bind significantly to the brain H1Rs and does not induce significant sedation.

Antihistamine induced blood oxygenation level dependent response changes related to visual processes during sensori-motor performance

The histaminergic involvement in selective processes underlying its role in human sensori-motor performance is largely unknown. Recently, selective effects of central H₁-inverse agonism on sensory visual processes were observed in electrophysiological--but not behavioral data; a discrepancy suggested to result from speeded response-choice related processes. This study attempts to establish the effects on visual processes and identify putative compensatory mechanisms related to increased visual and response-choice task demands by assessing H₁-inverse agonism induced changes in blood oxygenation level dependent (BOLD) response. Twelve participants received oral doses of dexchlorpheniramine 4 mg, lorazepam 1 mg, and placebo in a three-way crossover designed study. Brain activity was assessed for choice reaction time task performance in a 3 T magnetic resonance scanner 2 h after drug administration. Participants responded with their left or right hand and index or middle finger as indicated by the laterality of stimulus presentation and identity of the stimulus, respectively. Stimuli were intact or visually degraded and responses were compatible or incompatible with the laterality of stimulus presentation. Both dexchlorpheniramine and lorazepam affected the BOLD response in the occipital cortex indicating affected visual information processing. Dexchlorpheniramine decreased BOLD response in the dorsal precuneus and left precentral gyrus as part of a motor network, which however might not be interpreted as a compensatory mechanism, but may be the upstream consequence of impaired visual processing.

Diphenhydramine dependence through deep intramuscular injection resulting in myonecrosis and prolonged QT interval

WHAT IS KNOWN AND OBJECTIVE

Diphenhydramine (DPH) is a first-generation antihistamine, which is useful in treating allergic reaction, and is usually considered innocuous. We describe a retired nurse with history of depression, who began to develop drug-seeking behaviour after her first receiving of an intramuscular (IM) DPH injection due to urticaria.

CASE SUMMARY

The 49-year-old patient had developed IM DPH dependence within 4 months. She needed to receive psychiatric inpatient treatment because of depressive mood, serious myonecrosis over injected sites, and prolongation of QT interval.

WHAT IS NEW AND CONCLUSION

This is the first reported case of DPH dependence through the IM route. Second-generation antihistamines might be better choices for patients with psychiatric illness by reason of their lower effects on central nervous system and lower risk of abuse.

Effects of sedative antidepressants on prefrontal cortex activity during verbal fluency task in healthy subjects: a near-infrared spectroscopy study

RATIONALE

Japanese researchers have recently conducted studies using near-infrared spectroscopy (NIRS) to help diagnose psychiatric disorders based on changes in brain activity. However, the influence of psychotropic drugs on NIRS measurements has not been clarified.

OBJECTIVE

To assess the effects of sedative antidepressants on prefrontal cortex activity in healthy subjects using NIRS in a double-blinded, placebo-controlled, crossover trial.

METHODS

Nineteen healthy males received nocturnal doses of mirtazapine 15 mg, trazodone 25 mg, or placebo for eight consecutive days in rotation, with a washout period of more than 1 week between each rotation. Subjects performed a verbal fluency task during NIRS on a total of seven occasions during the study period: more than a week prior to receiving the first dose of the first medication; and on days 2 and 9 of each rotation. The number of words correctly generated during the task (behavioral performance) was also recorded. Stanford Sleepiness Scale (SSS) scores were determined each day.

RESULTS

Mirtazapine 15 mg significantly increased oxyhemoglobin (oxy-Hb) concentration change in NIRS on day 9, compared to trazodone 25 mg and placebo. Mirtazapine 15 mg significantly increased SSS on day 2, compared to the other conditions. No significant differences in behavioral performance were observed.

CONCLUSIONS

Administration of mirtazapine for eight consecutive days affected oxy-Hb changes on NIRS. This result indicates that researchers should consider how certain types of antidepressant could influence brain function when the brain activity of patients with psychiatric disorders is assessed.

Sustaining attention to simple tasks: a meta-analytic review of the neural mechanisms of vigilant attention

Maintaining attention for more than a few seconds is essential for mastering everyday life. Yet, our ability to stay focused on a particular task is limited, resulting in well-known performance decrements with increasing time on task. Intriguingly, such decrements are even more likely if the task is cognitively simple and repetitive. The attentional function that enables our prolonged engagement in intellectually unchallenging, uninteresting activities has been termed vigilant attention. Here we synthesized what we have learned from functional neuroimaging about the mechanisms of this essential mental faculty. To this end, a quantitative meta-analysis of pertinent neuroimaging studies was performed, including supplementary analyses of moderating factors. Furthermore, we reviewed the available evidence on neural time-on-task effects, additionally considering information obtained from patients with focal brain damage. Integrating the results of both meta-analysis and review, we identified a set of mainly right-lateralized brain regions that may form the core network subserving vigilant attention in humans, including dorsomedial, mid- and ventrolateral prefrontal cortex, anterior insula, parietal areas (intraparietal sulcus, temporoparietal junction), and subcortical structures (cerebellar vermis, thalamus, putamen, midbrain). We discuss the potential functional roles of different nodes of this network as well as implications of our findings for a theoretical account of vigilant attention. It is conjectured that sustaining attention is a multicomponent, nonunitary mental faculty, involving a mixture of (a) sustained/recurrent processes subserving task-set/arousal maintenance and (b) transient processes subserving the target-driven reorienting of attention. Finally, limitations of previous studies are considered and suggestions for future research are provided.

Structure of the human histamine H1 receptor complex with doxepin

The biogenic amine histamine is an important pharmacological mediator involved in pathophysiological processes such as allergies and inflammations. Histamine H(1) receptor (H(1)R) antagonists are very effective drugs alleviating the symptoms of allergic reactions. Here we show the crystal structure of the H(1)R complex with doxepin, a first-generation H(1)R antagonist. Doxepin sits deep in the ligand-binding pocket and directly interacts with Trp 428(6.48), a highly conserved key residue in G-protein-coupled-receptor activation. This well-conserved pocket with mostly hydrophobic nature contributes to the low selectivity of the first-generation compounds. The pocket is associated with an anion-binding region occupied by a phosphate ion. Docking of various second-generation H(1)R antagonists reveals that the unique carboxyl group present in this class of compounds interacts with Lys 191(5.39) and/or Lys 179(ECL2), both of which form part of the anion-binding region. This region is not conserved in other aminergic receptors, demonstrating how minor differences in receptors lead to pronounced selectivity differences with small molecules. Our study sheds light on the molecular basis of H(1)R antagonist specificity against H(1)R.

Effects of olanzapine, sertindole and clozapine on MK-801 induced visual memory deficits in mice

We investigated the effects of the second generation antipsychotics olanzapine, sertindole and clozapine on visual recognition memory using the novel object recognition (NOR) test in naive and MK-801-treated animals. The effects of drug treatment on locomotion and anxiety were also determined using the open field test. Male Balb-c mice were treated with olanzapine (0.2, 0.4 and 0.6 mg/kg; i.p.), sertindole (0.63, 1.3 and 2.5mg/kg; s.c.) or clozapine (0.5 and 1mg/kg; i.p.), and cognitive deficits were induced by MK-801 (0.2mg/kg; i.p.) administration. Olanzapine treatment decreased the ratio index in the NOR test, whereas sertindole and clozapine had no effect in naive mice. MK-801-induced cognitive impairment was reversed by treatment with olanzapine, sertindole or clozapine. While olanzapine, sertindole and clozapine had no effect on the anxiety of naive mice as determined by the open field test, MK-801 significantly increased the total distance traveled, time spent in the center zone and the velocity of the animals. MK-801-induced effects on locomotion and anxiety in the open field test were reversed by olanzapine, sertindole or clozapine treatment. The results of the present study demonstrated that olanzapine, sertindole and clozapine improved cognition in MK-801 treated mice, and indicate that these drugs have a potential to improve cognition in schizophrenia.

Brain histamine H1 receptor occupancy of loratadine measured by positron emission topography: comparison of H1 receptor occupancy and proportional impairment ratio

AIMS

We have evaluated the sedative properties of H1-antihistamines by using positron emission tomography (PET) and ¹¹C-doxepin. The purpose of the present study was to measure histamine H1 receptor occupancy (H1RO) of loratadine 10 mg in patients with allergic rhinitis and to compare this occupancy with that of d-chlorpheniramine 2 mg, a first-generation antihistamine. We also compared our PET findings with the proportional impairment ratio reported by McDonald et al.

METHODS

The H1RO of loratadine 10 mg and d-chlorpheniramine 2 mg were evaluated in human brains in a double-blind and crossover design using ¹¹C-doxepin PET. Eleven young male patients with allergic rhinitis were examined by PET following oral single administration of loratadine 10 mg and d-chlorpheniramine 2 mg.

RESULTS

Loratadine 10 mg occupied 11.7 ± 19.5% of histamine H1 receptors in the cortex, whereas d-chlorpheniramine 2 mg occupied 53.0 ± 33.2% in the same area, suggesting a non-sedating property of loratadine at a dose of 10 mg. The H1RO values of loratadine and d-chlorpheniramine as well as those of previous studies were found to be significantly proportional to the proportional impairment ratio (r = 0.899).

CONCLUSION

Measurement of H1RO is a sensitive and absolute method to characterize the non-sedating property of drugs with H1 antagonistic activity.

Differential responding of autonomic function to histamine H₁ antagonism in irritable bowel syndrome

BACKGROUND

The role of histamine in the pathophysiology of irritable bowel syndrome (IBS) is largely unknown. Dysfunction of the autonomic nervous system (ANS) in IBS patients is also not fully confirmed. We hypothesized that blockade of histamine H₁ receptors affects ANS responses differently between IBS subjects and controls.

METHODS

Subjects were 12 IBS subjects and 12 age- and sex-matched controls. Either 100 μg kg⁻¹ chlorphenamine or the same amount of saline was administered on different days. The rectum was stimulated with electrical currents of 0 mA (sham) or 30 mA. Autonomic nervous system function was measured using mean arterial pressure (MAP), heart rate (HR), high frequency (HF) component of HR variability, low frequency/high frequency ratio (LF/HF ratio) and plasma catecholamines and histamine. Subjective perceived stress during the examination was evaluated on an ordinate scale.

KEY RESULTS

Mean arterial pressure showed significant effects of diagnosis (P < 0.05) and drug × diagnosis interaction (P < 0.05). The MAP significantly increased after chlorphenamine administration in IBS subjects, but not in controls. Heart rate revealed a significant drug effect (P < 0.001), which decreased after chlorphenamine administration in controls, but not in IBS subjects. Perceived stress significantly increased by rectal stimulation (P < 0.001) and a significant stimulus × diagnosis interaction (P < 0.05) was revealed, indicating greater reduction in IBS subjects by chlorphenamine.

CONCLUSION & INFERENCES

Sympathetic vasomotor tone in IBS subjects differentially responded on administration of a histamine H₁ antagonist to that of controls. These findings suggest an increased histaminergic activity in IBS subjects.

Next-day residual sedative effect after nighttime administration of an over-the-counter antihistamine sleep aid, diphenhydramine, measured by positron emission tomography

Antihistamines often are self-administered at night as over-the-counter (OTC) sleep aids, but their next-day residual sedative effect has never been evaluated using a reliable quantitative method such as positron emission tomography (PET). We performed a double-blind, placebo-controlled, crossover study in which we evaluated the residual effect the next day after nighttime administration of diphenhydramine, a commonly used OTC sleep aid, in terms of brain H₁ receptor occupancy (H₁RO) measured using ¹¹C-doxepin-PET. We also compared the results of diphenhydramine with those of bepotastine, a second-generation antihistamine. Eight healthy adult male subjects underwent PET measurement the morning (11:00) after random oral administration of diphenhydramine (50 mg), bepotastine (10 mg), or placebo the night before (23:00). Binding potential ratios and H₁ROs were calculated in different brain regions of interest such as the cingulate gyrus, frontotemporal cortex, and cerebellum. Subjective sleepiness and plasma drug concentration also were measured. Calculation of binding potential ratios revealed significantly lower values for diphenhydramine than for bepotastine or placebo in all regions of interest (P < 0.01). Cortical mean H₁RO after diphenhydramine treatment was 44.7% compared with 16.6% for bepotastine treatment (P < 0.01). Subjective sleepiness was not significantly different among the subjects treated with each test drug or the placebo. In conclusion, the next-day residual sedative effect after nighttime administration of the OTC sleep aid diphenhydramine was verified for the first time by direct PET measurement of H₁RO. Taking into account the possible hangover effect of OTC antihistamine sleep aids, care needs to be taken during their administration.

Cognitive domains affected by histamine H(1)-antagonism in humans: a literature review

The neurotransmitter histamine has been suggested to be involved in cognitive functioning. Generally, studies in animals have shown a decrease in performance after decreasing histamine neurotransmission and improved performance after increasing histamine neurotransmission. It is unclear, however, what role histamine plays in cognition in humans. Up until now, most data are derived from studies and reviews that aimed to assess the sedative potential of H(1)-antagonists and not the effects on cognition in particular. The objective of this paper is specifically to review which cognitive domains are affected by H(1)-antagonists. Taken together, 90 experimental studies on the performance effects of sedative H(1)-antagonists published between 1973 and 2009 were reviewed. Results showed that psychomotor skills and attention are most frequently impaired and memory the least. Tasks assessing memory that were affected usually required rapid responses. It was concluded that both the complexity of the task as well as the demand for information processing speed determines the sensitivity to the effects of central H(1)-antagonism. The importance of the sensitive cognitive domains to histaminergic dysfunction, as well as the relation between histamine related decrease in arousal and task performance deserve further research.

Dose dependency of brain histamine H(1) receptor occupancy following oral administration of cetirizine hydrochloride measured using PET with [11C]doxepin

AIMS

The strength of sedation due to antihistamines can be evaluated using positron emission tomography (PET). The purpose of the present study is to measure histamine H(1) receptor (H(1)R) occupancy following oral administration of cetirizine (10 and 20 mg) in order to examine dose dependency.

METHODS

Fifteen healthy male volunteers (age range, 20-35 years) were divided into 3 subgroups and were studied following single oral administration of cetirizine at 10 mg (n = 5) and 20 mg (n = 5) or hydroxyzine at 30 mg (n = 5) using PET with 11C-doxepin. Each subject was scanned also following the administration of placebo. Binding potential and H(1)RO values were calculated in the prefrontal and anterior cingulate cortices. Subjective sleepiness was also measured, and the correlation to H(1)RO was examined for each antihistamine.

RESULTS

The averaged H(1)ROs of cetirizine 10 mg, 20 mg, and hydroxyzine 30 mg in the prefrontal and cingulate cortices was 12.6%, 25.2%, and 67.6%, respectively. The H(1)RO of hydroxyzine 30 mg correlated well with subjective sleepiness (p < 0.001); however, those of cetirizine 10 and 20 mg showed no correlation with subjective sleepiness.

CONCLUSION

It was demonstrated that the brain penetration of orally administered cetirizine was dose-dependent. Cetirizine 10 mg, with its low H(1)RO and thus minimal sedation, could be more safely used than cetirizine 20 mg for the treatment of various allergic disorders.

Histamine in the nervous system

Histamine is a transmitter in the nervous system and a signaling molecule in the gut, the skin, and the immune system. Histaminergic neurons in mammalian brain are located exclusively in the tuberomamillary nucleus of the posterior hypothalamus and send their axons all over the central nervous system. Active solely during waking, they maintain wakefulness and attention. Three of the four known histamine receptors and binding to glutamate NMDA receptors serve multiple functions in the brain, particularly control of excitability and plasticity. H1 and H2 receptor-mediated actions are mostly excitatory; H3 receptors act as inhibitory auto- and heteroreceptors. Mutual interactions with other transmitter systems form a network that links basic homeostatic and higher brain functions, including sleep-wake regulation, circadian and feeding rhythms, immunity, learning, and memory in health and disease.

Brain histamine H1 receptor occupancy of orally administered antihistamines, bepotastine and diphenhydramine, measured by PET with 11C-doxepin

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

'Bepotastine besilate' is a novel second-generation antihistamine developed in Japan and its antiallergic effects have already been demonstrated by various studies. However, only a few clinical studies regarding its sedative property are available. In addition, histamine H(1) receptor occupancy (H(1)RO) of this new antihistamine has never been measured by positron emission tomography (PET).

WHAT THIS STUDY ADDS

This paper provides the first measurement result of cerebral H(1)RO of bepotastine besilate (approximately 15%) as determined by PET. This result is in accordance with the clinical classification of bepotastine as a second-generation antihistamine. In addition, the relationship between subjective sleepiness and cerebral H(1)RO of this second-generation antihistamine is demonstrated for the first time using a placebo-controlled crossover study design. AIMS Antihistamines are frequently used for treating various allergic diseases, but often induce sedation. The degree of sedation can be evaluated by measuring histamine H(1) receptor occupancy (H(1)RO) in the brain using positron emission tomography (PET). The aim was to measure H(1)RO of bepotastine, a new second-generation antihistamine, and to compare it with that of diphenhydramine.

METHODS

Eight healthy male volunteers (mean age +/- SD 24.4 +/- 3.3 years) were studied after single oral administration of bepotastine (10 mg), diphenhydramine (30 mg) or placebo, by PET imaging with (11)C-doxepin in a crossover study design. Binding potential ratio and H(1)ROs were calculated using placebo data and were compared between bepotastine and diphenhydramine in the anterior and posterior cingulate gyri (ACG and PCG, respectively), superior and inferior frontal cortices (SFC and IFC, respectively), orbitofrontal cortex (OFC), insular cortex (IC), lateral and medial temporal cortices (LTC and MTC, respectively), parietal cortex (PC), occipital cortex (OC) and sensorimotor cortex (SMC). Plasma concentration of each antihistamine was measured, and its correlation to H(1)RO was examined.

RESULTS

H(1)RO after bepotastine treatment was significantly lower than that after diphenhydramine treatment in all cortical regions (P < 0.001). Mean H(1)ROs of bepotastine and diphenhydramine were 14.7% and 56.4%, respectively. H(1)ROs of both bepotastine and diphenhydramine correlated to their respective drug plasma concentration (P < 0.001).

CONCLUSION

Oral bepotastine (10 mg), with its relatively low H(1)RO and thus minimal sedation, has the potential for use as a mildly or slightly sedative antihistamine in the treatment of various allergic disorders.

Effects of a sedative antihistamine, D-chlorpheniramine, on regional cerebral perfusion and performance during simulated car driving

OBJECTIVES

The sedative side effects of antihistamines have been recognized to be potentially dangerous in car driving, but the mechanism underlying these effects has not yet been elucidated to date. The aim of the present study is to examine regional cerebral blood flow (rCBF) responses during a simulated car-driving task following oral administration of D-chlorpheniramine using positron emission tomography (PET) and [15O]H2O, based on a single-blind cross-over study-design.

METHODS

Right-handed, healthy male volunteers (n = 14) drove a car in a simulated environment following oral administration of D-chlorpheniramine repetab 6 mg or placebo. Their rCBF was measured using PET with [15O]H2O in the following three conditions: (1) resting, (2) active driving, and (3) passive driving. All 'in-car' views during the simulated driving were videotaped and used for rating driving performance.

RESULTS

Performance evaluation revealed that the number of lane deviations significantly increased in the D-chlorpheniramine condition compared with the placebo condition (p < 0.01). Subjective sleepiness was not significantly different between the two drug conditions. The regions of diminished brain responses following D-chlorpheniramine treatment were detected in the parietal, temporal and visual cortices, and in the cerebellum. The regions of augmented rCBF responses were found in the orbitofrontal cortex and cerebellar vermis.

CONCLUSION

These results suggest that D-chlorpheniramine tends to suppress visuo-spatial cognition and visuo-motor coordinating functions rather than attention and motor functions during car driving.

Dimenhydrinate effect on cerebral oxygen status and salivary chromogranin-A during cognitive tasks

To investigate the effects of dimenhydrinate on cerebral oxygen status (COS; cerebral oxygenated hemoglobin concentration changes) and salivary chromogranin-A (CgA) during a cognitive test battery, a double-blind, placebo-controlled, randomized, crossover protocol was used to examine the effect of 50 mg of dimenhydrinate or placebo in 12 subjects. This test battery includes tests of both reaction time and fundamental cognitive ability and was used in the assessment of pilots. Poor cognitive performance was observed in the subjects taking dimenhydrinate. We used two-channel near-infrared spectroscopy to investigate the effects of dimenhydrinate on the COS. With the one exception of shifting attention task in the left forehead, no significant difference was found between dimenhydrinate and placebo during the tasks of the test battery. Under placebo treatment, on the other hand, CgA levels were significantly elevated during cognitive testing when compared with baseline. However, CgA levels were not significantly elevated above baseline following dimenhydrinate. The present study is one of the first to demonstrate that the first-generation antihistamine drugs altered the responses of salivary CgA during cognitive tasks. The changes in salivary CgA secretion, as a result of dimenhydrinate administration, may serve as a sensitive biomarker of a psychological status such as a drug-induced sedation during the performance of a cognitive test battery. Further studies, however, are required to examine the usefulness of this sensitive biomarker in investigation of psychological agents during cognitive tasks.

Comparison of diphenhydramine and modafinil on arousal and autonomic functions in healthy volunteers

Arousal is regulated by the interplay between wakefulness- and sleep-promoting nuclei. Major wakefulness-promoting nuclei are the histaminergic tuberomamillary nucleus (TMN) of the hypothalamus and the noradrenergic locus coeruleus (LC) of the pons, which also play a role in autonomic regulation. First generation antihistamines, such as diphenhydramine, are likely to cause sedation by blocking excitatory H1 histamine receptors in the cerebral cortex, and the anti-narcolepsy drug modafinil may promote wakefulness by activating the locus coeruleus. We compared the effects of single doses of diphenhydramine (75 mg) and modafinil (200 mg) on arousal and autonomic functions in 16 healthy male volunteers, using a placebo-controlled, balanced, double-blind design. Arousal was assessed by critical flicker fusion frequency (CFFF), visual analogue scales (VAS) and pupillary fatigue waves (Pupillographic Sleepiness Test (PST)). Autonomic functions measured included resting pupil diameter, light and darkness reflex responses, blood pressure, heart rate and salivation. Data were analysed with ANOVA, with multiple comparisons. Diphenhydramine had sedative effects as shown by reductions in CFFF, VAS alertness ratings and increases of the indices of pupillary fatigue. Modafinil had alerting effects as indicated by reductions in the measures of pupillary fatigue. Comparison of pre-post medication changes in pupil diameter showed a decrease after diphenhydramine and an increase after modafinil. Diphenhydramine reduced salivation, and modafinil increased systolic blood pressure. In conclusion, diphenhydramine and modafinil evoked opposite effects on arousal and sympathetic functions, which are likely to reflect their interaction with the central histaminergic and noradrenergic systems. Hyposalivation by diphenhydramine is likely to be due to its additional anticholinergic property.

Reversal of PCP-induced learning and memory deficits in the Morris' water maze by sertindole and other antipsychotics

RATIONALE

In humans, the N-methyl-D-aspartate antagonist phencyclidine (PCP) induces behavioral changes that mimic schizophrenia symptoms, including positive and negative symptoms as well as cognitive deficits. In clinic, the cognitive deficits are closely associated with functional outcome. Thus, improvement of cognition may have high impact on patients' daily life.

OBJECTIVE

In the present study, three second-generation antipsychotics (sertindole, risperidone, and clozapine) as well as the classical antipsychotic haloperidol were tested for the ability to reverse PCP-induced cognitive deficits in the Morris' water maze.

RESULTS

The second-generation antipsychotics reversed the PCP-induced cognitive impairment: sertindole (0.63-2.5 mg/kg, s.c.), risperidone (0.04 mg/kg, s.c.; whereas 0.08 and 0.16 mg/kg were without significant effect), and clozapine (0.63 mg/kg, s.c.; while 1.3 mg/kg was without significant effect). The significant effect of sertindole was observed from day 2 onwards, while clozapine and risperidone only had significant effect at day 3. The classical antipsychotic haloperidol (0.010-0.020 mg/kg, s.c.) was ineffective. No compounds influenced swimming speed at the doses used, indicating that motor function was preserved.

CONCLUSION

These results confirm that repeated PCP administration induces marked cognitive deficits. Further, second-generation antipsychotics like sertindole, clozapine, and risperidone within a certain, often narrow, dose range are able to reverse the impairment and thus might improve cognitive deficits in schizophrenic patients, whereas classical compounds like haloperidol lack this effect. The receptor mechanisms involved in the reversal of PCP's disruptive effect are discussed and likely include a delicate balance between effects on dopamine D(2), 5-HT(2A/6), alpha-adrenergic, muscarinic, and histaminergic H(1) receptors.

Creating more effective antidepressants: clues from the clinic

Antidepressant medications have eased the suffering of millions of people. In addition to treating depression, antidepressant drugs also treat several anxiety disorders. Unfortunately, there are problematic limitations with antidepressant agents, including a delayed therapeutic response and insufficient efficacy. Emerging evidence shows that atypical antipsychotic agents can be used as augmentation therapy in patients with poor responses to antidepressants. Future drugs combining key features of antidepressant and atypical antipsychotic agents could offer new promise for patients suffering from obsessive-compulsive disorder, post-traumatic stress disorder, panic disorder, generalized anxiety disorder and depression.

Selective cognitive dysfunction in mice lacking histamine H1 and H2 receptors

Previous pharmacological experiments provide conflicting findings that describe both facilitatory and inhibitory effects of neuronal histamine on learning and memory. Here, we examined learning and memory and synaptic plasticity in mice with a null mutation of gene coding histamine H1 or H2 receptor in order to clarify the role of these receptors in learning and memory processes. Learning and memory were evaluated by several behavioral tasks including object recognition, Barnes maze and fear conditioning. These behavioral tasks are highly dependent on the function of prefrontal cortex, hippocampus or amygdala. Object recognition and Barnes maze performance were significantly impaired in both H1 receptor gene knockout (H1KO) and H2 receptor gene knockout (H2KO) mice when compared to the respective wild-type (WT) mice. Conversely, both H1KO and H2KO mice showed better auditory and contextual freezing acquisition than their respective WT mice. Furthermore, we also examined long-term potentiation (LTP) in the CA1 area of hippocampus in H1KO and H2KO mice and their respective WT mice. LTP in the CA1 area of hippocampus was significantly reduced in both H1KO and H2KO mice when compared with their respective WT mice. In conclusion, our results demonstrate that both H1 and H2 receptors are involved in learning and memory processes for which the frontal cortex, amygdala and hippocampus interact.

The physiological and pathophysiological roles of neuronal histamine: an insight from human positron emission tomography studies

Histamine neurons are exclusively located in the posterior hypothalamus, and project their fibers to almost all regions of the human brain. Although a significant amount of research has been done to clarify the functions of the histaminergic neuron system in animals, a few studies have been reported on the roles of this system in the human brain. In past studies, we have been able to clarify some of the functions of histamine neurons using different methods, such as histamine-related gene knockout mice or human positron emission tomography (PET). The histaminergic neuron system is known to modulate wakefulness, the sleep-wake cycle, appetite control, learning, memory and emotion. Accordingly we have proposed that histamine neurons have a dual effect on the CNS, with both stimulatory and suppressive actions. As a stimulator, neuronal histamine is one of the most important systems that stimulate and maintain wakefulness. Brain histamine also functions as a suppressor in bioprotection against various noxious and unfavorable stimuli of convulsion, drug sensitization, denervation supersensitivity, ischemic lesions and stress susceptibility. This review summarizes our works on the functions of histamine neurons using human PET studies, including the development of radiolabeled tracers for histamine H1 receptors (H1R: (11)C-doxepin and (11)C-pyrilamine), PET measurements of H1R in depression, schizophrenia, and Alzheimer's disease (AD), and studies on the sedative effects of antihistamines using H(2)(15)O and H1R occupancy in the human brain. These molecular and functional PET studies in humans are useful for drug development in this millennium.

Sertindole, in contrast to clozapine and olanzapine, does not disrupt water maze performance after acute or chronic treatment

Cognitive deficits in schizophrenia are associated with poor functional outcome, and may be further aggravated by treatment with antipsychotics. In the present study the acute and chronic (3 weeks of treatment) effects of clozapine, olanzapine, and sertindole on performance in the Morris water maze in rats was compared, using pharmacologically and/or clinically relevant dose regimens. An experimental design consisting of three trials/day over 3 days was used. Performance was expressed as the distance and latency to find a submerged platform, as well as the percentage of "non-finders", i.e. percentage of trials where the rat was unable to find the platform within the total trial time of 60 s. Clozapine (40 mg/kg, p.o.) and olanzapine (2.5 mg/kg, s.c.) impaired water maze performance when given acutely. However, tolerance developed to the deficit induced by clozapine, whereas the olanzapine-mediated impairment was enhanced after chronic treatment. Sertindole (2.5 mg/kg, p.o.) had no disruptive effect on performance after either acute or chronic treatment. Exposure measurements confirmed that all three compounds were present in the serum at least at clinically effective concentrations. Thus, the three antipsychotics tested differentially affected rodent cognition, whereby sertindole appeared to have a lower potential than either clozapine or olanzapine to induce cognitive impairment. The hypothesis that the low potency of sertindole in inducing dopamine D2 receptor blockade, combined with lack of antimuscarinic and histamine H1 antagonist activity in vivo is discussed. Clearly further studies are needed to assess the potential cognition-enhancing effects of sertindole vs. other antipsychotics in a relevant animal model of schizophrenia.