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

Cross talk mechanism of disturbed sleep patterns in neurological and psychological disorders

The incidence and prevalence of sleep disorders continue to increase in the elderly populace, particularly those suffering from neurodegenerative and neuropsychiatric disorders. This not only affects the quality of life but also accelerates the progression of the disease. There are many reasons behind sleep disturbances in such patients, for instance, medication use, nocturia, obesity, environmental factors, nocturnal motor disturbances and depressive symptoms. This review focuses on the mechanism and effects of sleep dysfunction in neurodegenerative and neuropsychiatric disorders. Wherein we discuss disturbed circadian rhythm, signaling cascade and regulation of genes during sleep deprivation. Moreover, we explain the perturbation in brainwaves during disturbed sleep and the ocular perspective of neurodegenerative and neuropsychiatric manifestations in sleep disorders. Further, as the pharmacological approach is often futile and carries side effects, therefore, the non-pharmacological approach opens newer possibilities to treat these disorders and widens the landscape of treatment options for patients.

Alzheimer's disease and sleep disorders: Insights into the possible disease connections and the potential therapeutic targets

One of the comorbid conditions in an individual with Alzheimer's disease is a sleep disorder. Clinical features of sleep disorders involve various sleep disturbances such as Obstructive Sleep Apnea (OSAS), Excessive Daytime Sleepiness (EDS), Rapid Eye Movement (REM), Breathing Disorders, Periodic limb movements in sleep (PLMS), etc. The primary tools used for the identification of such disturbances are Polysomnography (PSG) and Wrist actigraphy. This review will highlight and explains the different approaches used in the treatment of sleep disorders. Non-pharmacological treatments include Peter Hauri rules, sleep education program, and light therapy which play a key role in the regulation of sleep-wake cycles. Pharmacological therapy described in this article may be useful in treating sleep destruction in patients with Alzheimer's disease. Along with the Non-pharmacological and pharmacological treatment, here we discuss five commonly recognized plant-based nutraceuticals with hypothesized impact on sleep disorders: caffeine, chamomile, cherries, L-tryptophan, and valerian by the proper emphasis on the known mechanism of their action.

The Treatment of Sleep Dysfunction in Neurodegenerative Disorders

Sleep dysfunction is highly prevalent across the spectrum of neurodegenerative conditions and is a key determinant of quality of life for both patients and their families. Mounting recent evidence also suggests that such dysfunction exacerbates cognitive and affective clinical features of neurodegeneration, as well as disease progression through acceleration of pathogenic processes. Effective assessment and treatment of sleep dysfunction in neurodegeneration is therefore of paramount importance; yet robust therapeutic guidelines are lacking, owing in part to a historical paucity of effective treatments and trials. Here, we review the common sleep abnormalities evident in neurodegenerative disease states and evaluate the latest evidence for traditional and emerging interventions, both pharmacological and nonpharmacological. Interventions considered include conservative measures, targeted treatments of specific clinical sleep pathologies, established sedating and alerting agents, melatonin, and orexin antagonists, as well as bright light therapy, behavioral measures, and slow-wave sleep augmentation techniques. We conclude by providing a suggested framework for treatment based on contemporary evidence and highlight areas that may emerge as major therapeutic advances in the near future.

On-the-road driving performance after use of the antihistamines mequitazine and l-mequitazine, alone and with alcohol

OBJECTIVE

Previous studies demonstrated that mequitazine produces mild sedation after single doses. Its enantiomer, l-mequitazine, has a stronger potency for the H1 receptor. The aim of the current study was to assess the effects of l-mequitazine and mequitazine, alone and with alcohol, on driving.

METHODS

Twenty-five healthy volunteers were treated with l-mequitazine 2.5, 5.0 and 10 mg, mequitazine 10 mg and placebo, alone and in combination with alcohol in a double-blind crossover design. Driving performance was assessed using the standardized highway driving test in normal traffic. Its primary measure is the Standard Deviation of the Lateral Position (SDLP). Secondary measures consisted of an auditory word learning test during driving, and subjective measures of driving performance.

RESULTS

L-mequitazine 2.5 and 5.0 mg showed no effect on SDLP in the highway driving test, while SDLP significantly increased after l-mequitazine 10 mg (alone +1.59 cm; with alcohol +1.41 cm) and mequitazine 10 mg (with alcohol +1.17 cm). Alcohol significantly impaired all performance measures (SDLP +2.63 cm) but did not interact with the effects of treatment. Subjective measures indicated that participants were aware of the impairing effects of alcohol, but not of l-mequitazine and mequitazine.

CONCLUSION

L-mequitazine can be considered safe to drive in dosages of 2.5 and 5.0 mg. L-mequitazine 10 mg led to mild driving impairment. Alcohol impaired all performance measures and added to the effects of l-mequitazine and mequitazine.

Synthetic consciousness: the distributed adaptive control perspective

Understanding the nature of consciousness is one of the grand outstanding scientific challenges. The fundamental methodological problem is how phenomenal first person experience can be accounted for in a third person verifiable form, while the conceptual challenge is to both define its function and physical realization. The distributed adaptive control theory of consciousness (DACtoc) proposes answers to these three challenges. The methodological challenge is answered relative to the hard problem and DACtoc proposes that it can be addressed using a convergent synthetic methodology using the analysis of synthetic biologically grounded agents, or quale parsing. DACtoc hypothesizes that consciousness in both its primary and secondary forms serves the ability to deal with the hidden states of the world and emerged during the Cambrian period, affording stable multi-agent environments to emerge. The process of consciousness is an autonomous virtualization memory, which serializes and unifies the parallel and subconscious simulations of the hidden states of the world that are largely due to other agents and the self with the objective to extract norms. These norms are in turn projected as value onto the parallel simulation and control systems that are driving action. This functional hypothesis is mapped onto the brainstem, midbrain and the thalamo-cortical and cortico-cortical systems and analysed with respect to our understanding of deficits of consciousness. Subsequently, some of the implications and predictions of DACtoc are outlined, in particular, the prediction that normative bootstrapping of conscious agents is predicated on an intentionality prior. In the view advanced here, human consciousness constitutes the ultimate evolutionary transition by allowing agents to become autonomous with respect to their evolutionary priors leading to a post-biological Anthropocene.This article is part of the themed issue 'The major synthetic evolutionary transitions'.

The effect of histamine on changes in mental energy and fatigue after a single bout of exercise

The purpose of this research was to determine if histamine, acting on brain H1 receptors, influences changes in feelings of energy and fatigue or cognitive test performance after acute exercise. Women (n=20) with low vigor and high fatigue were administered the H1 antagonist drug doxepin hydrocholoride (6 mg) in tomato juice and tomato juice alone (placebo) in a randomized, double-blinded, cross-over experiment before performing 30 min of light intensity cycling exercise and completing energy, fatigue, sleepiness, and motivation scales, and cognitive tasks. After exercise, mental fatigue increased for the doxepin condition (p=0.014) but not placebo (p=0.700), while mental energy decreased for both PLA and DOX (p<0.001) and cognitive task performance was unaffected. It is inferred that histamine binding to H1 receptors in the brain has a role in exercise-induced reductions in mental fatigue, but not increases in energy.

Diphenhydramine's role in death investigations: an examination of diphenhydramine prevalence in 2 US geographical areas

PURPOSE

Diphenhydramine (DPH), an over-the-counter first-generation H1 receptor antagonist, is not a common drug of abuse; however, it is encountered in cases of overdose both in the clinical setting and in death investigations. The toxicology laboratories in the Tarrant County Medical Examiner's Office and the District of Columbia Office of The Chief Medical Examiner analyze antemortem and postmortem specimens. Presented are the findings of this evaluation and detailed histories of cases involving DPH.

METHODS

Toxicology reports, autopsy reports, and death investigator narratives were obtained in cases involving DPH at toxic and lethal levels in which this compound was the primary cause or a contributing factor in the death.

RESULTS

Blood concentrations were quantified at a range of 2870 to 21,263 ng/mL. A rare occurrence of DPH abuse via documented intravenous administration leading to death is presented. The cases presented here generally involved much higher concentrations of DPH and an older population than those in previous published data regarding DPH's role in death investigation and abuse.

CONCLUSIONS

As people seek legal alternative drugs to abuse and with the ease of obtaining information via online forums, there is a potential to see an increase in the number of cases involving excessive use of DPH.

Safe prescribing of physical health medication in patients with dementia

OBJECTIVE

The prescription of multiple medications for older people is common, despite concerns over the dangers associated with this. Older adults are particularly vulnerable to adverse effects of medication, and this is an even greater risk in patients with dementia. Many drugs used for physical health conditions can negatively affect cognition. Our aim was to identify areas of concern and which drugs to avoid in patients with dementia.

DESIGN

A review of the literature was carried out using Pubmed, Medline and Embase.

RESULTS

Many drugs used for physical health conditions may worsen the symptoms of dementia. They do this either by negating the effects of cognitive enhancers or through direct adverse effects on cognition

CONCLUSIONS

Where evidence exists, we provide guidance as to the safest drugs to prescribe in particular clinical situations. Anticholinergic drugs should be avoided in dementia wherever possible. Effective pain management is important in older patients, but caution should be used when selecting an opioid analgesic because of their adverse central effects. Cardiac drugs have overall negligible effects on cognition, although some have been reported to cause delirium.

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.

Cerebrospinal fluid norepinephrine and cognition in subjects across the adult age span

Adequate central nervous system noradrenergic activity enhances cognition, but excessive noradrenergic activity may have adverse effects on cognition. Previous studies have also demonstrated that noradrenergic activity is higher in older than younger adults. We aimed to determine relationships between cerebrospinal fluid (CSF) norepinephrine (NE) concentration and cognitive performance by using data from a CSF bank that includes samples from 258 cognitively normal participants aged 21-100 years. After adjusting for age, gender, education, and ethnicity, higher CSF NE levels (units of 100 pg/mL) are associated with poorer performance on tests of attention, processing speed, and executive function (Trail Making A: regression coefficient 1.5, standard error [SE] 0.77, p = 0.046; Trail Making B: regression coefficient 5.0, SE 2.2, p = 0.024; Stroop Word-Color Interference task: regression coefficient 6.1, SE 2.0, p = 0.003). Findings are consistent with the earlier literature relating excess noradrenergic activity with cognitive impairment.

Effects of single therapeutic doses of promethazine, fexofenadine and olopatadine on psychomotor function and histamine-induced wheal- and flare-responses: a randomized double-blind, placebo-controlled study in healthy volunteers

Since most first-generation antihistamines have undesirable sedative effects on the central nervous systems (CNS), newer (second-generation) antihistamines have been developed to improve patients’ quality of life. However, there are few reports that directly compare the antihistaminic efficacy and impairment of psychomotor functions. We designed a double-blind, placebo controlled, crossover study to concurrently compare the clinical effectiveness of promethazine, a first-generation antihistamine, and fexofenadine and olopatadine, second-generation antihistamines, by measuring their potency as peripheral inhibitors of histamine-induced wheal and flare. Further, we investigated their sedative effects on the CNS using a battery of psychomotor tests. When single therapeutic doses of fexofenadine (60 mg), olopatadine (5 mg) and promethazine (25 mg) were given in a double-blind manner to 24 healthy volunteers, all antihistamines produced a significant reduction in the wheal and flare responses induced by histamine. In the comparison among antihistamines, olopatadine showed a rapid inhibitory effect compared with fexofenadine and promethazine, and had a potent effect compared with promethazine. In a battery of psychomotor assessments using critical flicker fusion, choice reaction time, compensatory tracking, rapid visual information processing and a line analogue rating scale as a subjective assessment of sedation, promethazine significantly impaired psychomotor function. Fexofenadine and olopatadine had no significant effect in any of the psychomotor tests. Promethazine, fexofenadine and olopatadine did not affect behavioral activity, as measured by wrist actigraphy. These results suggest that olopatadine at a therapeutic dose has greater antihistaminergic activity than promethazine, and olopatadine and fexofenadine did not cause cognitive or psychomotor impairment.

Additive effects of a cholinesterase inhibitor and a histamine inverse agonist on scopolamine deficits in humans

RATIONALE

Enhancement of histaminergic neurotransmission or histaminergic plus cholinergic neurotransmission may represent novel strategies for improving cognition in Alzheimer's disease.

OBJECTIVE

To evaluate the effects of a novel histamine H3 receptor inverse agonist (MK-3134), an acetylcholinesterase inhibitor (donepezil), and their combination in attenuating the cognitive impairment associated with scopolamine.

METHODS

Thirty-one subjects were randomized, and 28 completed this double-blind, placebo-controlled, five-period crossover study. Cognition was assessed using the Groton Maze Learning Task (GMLT) as the primary outcome measure. The two primary hypotheses were that donepezil 10 mg and MK-3134 25 mg, respectively, would attenuate scopolamine (0.5 mg)-induced impairment as measured by the GMLT over the first 12 h after scopolamine administration (AUC(1-12)  (h)). A secondary hypothesis was that the combination of donepezil and MK-3134 would attenuate scopolamine-induced cognitive impairment to a greater extent than either agent alone as measured by the GMLT AUC(1-12 h).

RESULTS

The primary and secondary hypotheses were not met. Upon examining the time course of the scopolamine effects (an exploratory objective), peak effects were generally observed around 2 h after scopolamine administration. Administration of MK-3134 or donepezil improved performance on the GMLT at the 2-h time point, rather than AUC(1-12 h), compared with scopolamine alone. Moreover, it appeared that the combination of MK-3134 and donepezil blunted the scopolamine effect to a greater extent than either drug alone.

CONCLUSIONS

Exploratory analyses provide evidence for cognitive improvement through inverse agonism of the H3 histamine receptor and for cooperation between human cholinergic and histaminergic neurotransmitter systems. (ClinicalTrials.gov trial registration number: NCT01181310).

Sleep neurobiology from a clinical perspective

Many neurochemical systems interact to generate wakefulness and sleep. Wakefulness is promoted by neurons in the pons, midbrain, and posterior hypothalamus that produce acetylcholine, norepinephrine, dopamine, serotonin, histamine, and orexin/hypocretin. Most of these ascending arousal systems diffusely activate the cortex and other forebrain targets. NREM sleep is mainly driven by neurons in the preoptic area that inhibit the ascending arousal systems, while REM sleep is regulated primarily by neurons in the pons, with additional influence arising in the hypothalamus. Mutual inhibition between these wake- and sleep-regulating regions likely helps generate full wakefulness and sleep with rapid transitions between states. This up-to-date review of these systems should allow clinicians and researchers to better understand the effects of drugs, lesions, and neurologic disease on sleep and wakefulness.

Drug targets for cognitive enhancement in neuropsychiatric disorders

The investigation of novel drug targets for treating cognitive impairments associated with neurological and psychiatric disorders remains a primary focus of study in central nervous system (CNS) research. Many promising new therapies are progressing through preclinical and clinical development, and offer the potential of improved treatment options for neurodegenerative diseases such as Alzheimer's disease (AD) as well as other disorders that have not been particularly well treated to date like the cognitive impairments associated with schizophrenia (CIAS). Among targets under investigation, cholinergic receptors have received much attention with several nicotinic agonists (α7 and α4β2) actively in clinical trials for the treatment of AD, CIAS and attention deficit hyperactivity disorder (ADHD). Both glutamatergic and serotonergic (5-HT) agonists and antagonists have profound effects on neurotransmission and improve cognitive function in preclinical experiments with animals; some of these compounds are now in proof-of-concept studies in humans. Several histamine H3 receptor antagonists are in clinical development not only for cognitive enhancement, but also for the treatment of narcolepsy and cognitive deficits due to sleep deprivation because of their expression in brain sleep centers. Compounds that dampen inhibitory tone (e.g., GABA(A) α5 inverse agonists) or elevate excitatory tone (e.g., glycine transporter inhibitors) offer novel approaches for treating diseases such as schizophrenia, AD and Down syndrome. In addition to cell surface receptors, intracellular drug targets such as the phosphodiesterases (PDEs) are known to impact signaling pathways that affect long-term memory formation and working memory. Overall, there is a genuine need to treat cognitive deficits associated with many neuropsychiatric conditions as well as an increasingly aging population.

Effects of the use of hypnotics on cognition

Hypnotic drugs are intended to induce sedation and promote sleep. As a result, they have deteriorating effects on cognitive performance following intake. Most hypnotics are benzodiazepine receptor agonists which can have effects on memory in addition to their sedative effects. Other sedating drugs, such as histamine H1 antagonists or melatonin agonists, may have less effect on memory and learning. Hypnotics with other mechanisms of action are currently being investigated for efficacy and safety. For patients using hypnotic drugs, the effects on cognition are relevant to the extent that a drug dose affects daytime performance. Use of benzodiazepine hypnotics is associated with increased risk of car accidents and falling. Therefore, most hypnotics are studied to determine whether they produce residual sedation and impairing effects on performance the morning after bedtime use. Experimental studies using a standardized driving test clearly show that some drugs and doses produce severe residual effects, whereas others seem to have no or only minor impairing effects on next-day performance. No hypnotic has been found yet to improve daytime performance. Studies on long-term use of benzodiazepine hypnotics suggest that effects on daytime performance may diminish over time due to tolerance. However, there are also studies showing that performance may improve after discontinuation of chronic benzodiazepine use, which suggests that tolerance may not be complete.