Effects of nonsedating histamine H1-antagonists on EEG activity and behavior in the cat

Neural signatures of sleep in zebrafish

Slow-wave sleep and rapid eye movement (or paradoxical) sleep have been found in mammals, birds and lizards, but it is unclear whether these neuronal signatures are found in non-amniotic vertebrates. Here we develop non-invasive fluorescence-based polysomnography for zebrafish, and show-using unbiased, brain-wide activity recording coupled with assessment of eye movement, muscle dynamics and heart rate-that there are at least two major sleep signatures in zebrafish. These signatures, which we term slow bursting sleep and propagating wave sleep, share commonalities with those of slow-wave sleep and paradoxical or rapid eye movement sleep, respectively. Further, we find that melanin-concentrating hormone signalling (which is involved in mammalian sleep) also regulates propagating wave sleep signatures and the overall amount of sleep in zebrafish, probably via activation of ependymal cells. These observations suggest that common neural signatures of sleep may have emerged in the vertebrate brain over 450 million years ago.

Induction of prolonged, continuous slow-wave sleep by blocking cerebral H₁ histamine receptors in rats

BACKGROUND AND PURPOSE

Classic H(1) histamine receptor (H(1)R) antagonists are non-selective for H(1)R and known to produce drowsiness. Modern antihistamines are more selective for H(1)R, and are 'non-drowsy' presumably due to reduced permeability through the blood-brain barrier. To characterize both histaminergic sleep regulation and the central actions of antihistamines, in the present study we analysed the effect of classic and modern antihistamines on rats' sleep using continuous i.c.v. infusions.

EXPERIMENTAL APPROACH

Effects of classic (d-chlorpheniramine; d-CPA) and second-generation (cetirizine) antihistamines on sleep were compared after i.p. injections or continuous i.c.v. infusions into rats. Fluorescent cetirizine/DBD-pz was synthesized to trace the approximate distribution of cerebral cetirizine. Furthermore, the effects of H(1) R antagonists on cultured preoptic neurons were examined using calcium imaging.

KEY RESULTS

d-CPA 4 mg·kg(-1) i.p. increased non-rapid eye movement (REM) sleep whereas 10-40 mg·kg(-1) d-CPA decreased non-REM sleep at dark onset time. Nocturnal i.c.v. infusions of d-CPA (10 µmol·100 µL(-1)·10 h(-1)) increased drowsiness but not non-REM sleep, whereas the same i.c.v. infusions of cetirizine significantly increased non-REM sleep, abolished REM sleep, and decreased wakefulness for more than 10 h. The medial preoptic area contained the greatest fluorescent labelling after i.c.v. cetirizine/DBD-pz infusions. Histamine-induced Ca(2+) increases in medial preoptic neurons were blocked by d-CPA or cetirizine, whereas d-CPA, but not cetirizine, increased Ca(2+) irrespective of antihistaminergic activity at ≥ 100 µM.

CONCLUSION AND IMPLICATIONS

The excitatory action of d-CPA may explain the seemingly inconsistent actions of d-CPA on sleep. Cerebral H(1)R inhibition by cetirizine induces synchronization of cerebral activity and prolonged, continuous slow-wave sleep.

First and second generation H₁ histamine receptor antagonists produce different sleep-inducing profiles in rats

First generation H₁ histamine receptor antagonists, such as d-chlorpheniramine (d-CPA) and diphenhydramine, produce drowsiness in humans. They are currently used as over-the-counter sleep aids. However, the mechanisms underlying drowsiness induced by these H₁ histamine receptor antagonists remain obscure because they produce heterogeneous receptor-independent actions. Ketotifen is a second generation H₁ histamine receptor antagonist which is more permeable to the brain than newer H₁ histamine receptor antagonists. Therefore, to access sleep-inducing profiles by H₁ histamine receptor blocking actions, the present study compared the dose-dependent effects of diphenhydramine and ketotifen (1-40 mg/kg, intraperitoneal injection at dark onset time) on daily sleep-wake patterns in rats. Ketotifen dose-dependently decreased rapid-eye-movement (REM) sleep and increased non-REM sleep by amplifying slow-wave electroencephalogram powers. Diphenhydramine at 4 mg/kg transiently increased non-REM sleep and reduced REM sleep similar to the effects of ketotifen. The larger injections of diphenhydramine (10-40 mg/kg), however, reduced non-REM sleep, abolished slow-wave enhancements and facilitated wakefulness. The bi-directional action of diphenhydramine on sleep is similar to our former results using d-CPA. Taken together, the arousal effects caused by over-dose administrations of the first generation H₁ histamine receptor antagonists may be mediated by H₁ histamine receptor-independent actions. To further examine the tolerance of ketotifen-induced sleep, 3 mg/kg ketotifen was injected daily for 5 days 3 h before light onset time. These experiments consistently enhanced non-REM-sleep at the end of the active phase of rats, suggesting that ketotifen may function as a desirable sleep aid although the coincidental REM sleep reduction requires attention.

Evaluation of diphenhydramine as a sedative for dogs

OBJECTIVE

To determine and compare levels of sedation achieved by IM administration of diphenhydramine, saline (0.9% NaCl) solution, and acepromazine in dogs.

DESIGN

Prospective randomized study.

ANIMALS

56 dogs.

PROCEDURE

Dogs were randomly assigned to receive diphenhydramine at 2, 4, or 8 mg/kg (0.9, 1.8, or 3.6 mg/lb, respectively) i.m.; acepromazine at 0.1 mg/kg (0.05 mg/lb) i.m.; or saline solution at 0.05 mL/kg (0.02 mL/lb) i.m. Sedation was assessed by use of a 6-category descriptive system based on observation and interaction.

RESULTS

Dogs in the acepromazine group had significantly higher sedation scores than did dogs in the saline solution or diphenhydramine groups at 30 minutes. Dogs in the diphenhydramine groups did not have significantly different sedation scores from dogs in the saline solution group at any time point.

CONCLUSIONS AND CLINICAL RELEVANCE

Diphenhydramine did not cause clinically appreciable sedation in healthy dogs. Diphenhydramine is not suitable as a sole sedative prior to general anesthesia in dogs.

The olfactory bulbectomised rat as a model of depression

Bilateral olfactory bulbectomy results in changes in behavior, and in the endocrine, immune and neurotransmitter systems, that simulates many of those seen in patients with major depression. The olfactory system in the rat forms a part of the limbic region in which the amygdala and hippocampus contribute to the emotional and memory components of behavior. However, the loss of olfaction alone, which results from bulbectomy, is not the major factor that contributes to the behavioral abnormalities as peripherally induced anosmia does not cause the same behavioral changes. Thus it would appear that bulbectomy causes a major dysfunction of the cortical-hippocampal-amygdala circuit that underlies the behavioral and other changes. These neuroanatomical areas also seem to be dysfunctional in the patient with major depression. Chronic, but not acute, administration of antidepressants largely corrects most the behavioral, endocrine, immune and neurotransmitter changes that occur following bulbectomy. Thus the olfactory bulbectomized rat is not only a model for detecting antidepressant activity but also one for exploring the inter-relationships between these systems that are also dysfunctional in patients with major depression.

Antihistamines in the management of allergic pruritus in dogs and cats

Antihistamines clearly have a place in the management of pruritus in the atopic dog and cat and, in this paper, important aspects of pharmacology and pharmacokinetics, adverse effects and precautions, and clinical use of these compounds are reviewed. Successful use of antihistamines is dependent on, among other considerations, the adherence to recommended doses and frequencies of administration, the recognition and control of concurrent and secondary factors, the willingness to try several different compounds, and the realisation that these agents are best employed in a preventive fashion.

Delirium. Advances in diagnosis, pathophysiology, and treatment

This article discusses research in the areas of morbidity and mortality, epidemiologic risk factors, phenomenology, pathophysiology, and treatment of delirium. Delirium assessment instruments are reviewed. The neuropathophysiologic understanding of delirium is discussed in the context of important CNS neural circuitry. Pharmacologic treatments of delirium in adults and children are outlined, with particular emphasis on intravenous use of butyrophenone neuroleptics.

Behavioural and immunological effects of the antihistamine terfenadine in olfactory bulbectomized rats

The effects of chronic treatment with the non-sedative histamine H1 receptor antagonist terfenadine (5 mg/kg, i.p.) for 16 days on some behavioural and immunological parameters were studied in the olfactory bulbectomized (OB) rat model of depression. In the open field apparatus, OB rats showed a significant increase in ambulation and rearing scores. Following terfenadine treatment, this hyperactivity was significantly attenuated. In untreated OB rats, neutrophils phagocytosis and lymphocyte proliferation were significantly suppressed. Terfenadine administration markedly reversed the suppression of these immunological parameters in the treated OB animals, but did not reverse the abnormalities in the differential white blood cell count caused by bulbectomy. These results suggest that the histamine H1 receptor antagonist terfenadine may have antidepressant properties and that terfenadine is effective in reversing some of behavioural and immune changes in the olfactory bulbectomized rat model of depression.

Asthma: An Important Disease to Otolaryngologists — Part II: Asthma Management Strategy

Asthma is a chronic inflammatory disease of the lower respiratory tract which is triggered by exposure to allergens or other airway irritants, and is commonly encountered in otolaryngologic practice. This three-part review is designed to assist otolaryngologists in effectively managing their asthmatic patients. In Part I, current information on the pathophysiology and increasing prevalence of asthma, its clinical variability, the assessment of asthma severity and methods for diagnosis of asthma were summarized. Part 11 discusses a tripartite strategy for asthma management, based on environmental controls, the use of anti-inflammatory therapies and patient education. In addition, pharmacologic treatments which are not primarily anti-inflammatory are reviewed in detail. The uses, effectiveness, side effects and suitability for drug combination therapy for mucolytic, anticholinergic, antihistamine, theophylline and beta agonist drugs are compared, and the disadvantages of beta antagonists are summarized. Part III concludes with an overview of antiinflammatory therapies for asthma control.

Loratadine. A reappraisal of its pharmacological properties and therapeutic use in allergic disorders

Loratadine is a long-acting antihistamine agent, exhibiting partial selectivity for peripheral histamine H1-receptors. To date, loratadine has been evaluated in allergic rhinitis, urticaria and, to a limited extent, in asthma. In several large controlled comparative clinical studies, loratadine was superior to placebo, faster acting than astemizole and as effective as azatadine, cetirizine, chlorpheniramine (chlorphenamine), clemastine, hydroxyzine, mequitazine and terfenadine in patients with allergic rhinitis and chronic urticaria. The clinical effectiveness of loratadine in asthma is at present unclear. Loratadine is well tolerated. At dosages of 10 mg daily, commonly reported adverse events were somnolence, fatigue and headache. Sedation occurred less frequently with loratadine than with azatadine, cetirizine, chlorpheniramine, clemastine and mequitazine. Serious ventricular arrhythmias, as reported with some other second generation histamine H1-receptor antagonists, have not been observed with loratadine to date. Thus, loratadine, with its attributes of once daily administration, fast onset of action and essentially nonsedating properties, would appear to be an appropriate first-line agent for the treatment of allergic rhinitis or urticaria.

Allergic Rhinosinusitis: The Total Rhinologic Disease

Allergic rhinosinusitis has three forms of therapy: pharmacotherapy, immunotherapy, and surgical therapy. Pharmacotherapeutically, there are six classes of drugs that give symptomatic relief: mucolytics, decongestants, anticholinergic agents, antihistamines, mast cell stabilizers, and corticosteroids. All six classes are discussed individually and in detail.

For immunotherapeutic therapy of allergic rhinosinusitis, there are four types of skin testing in current use: scratch testing, prick testing, single intradermal testing, and skin end point titration testing. Only the latter is able to quantitate the antigenicity of each antigen, and thus the treatment vial made from only this type of skin testing can adequately treat all antigens to which the patient is sensitive. These differences in testing and vial mixing are explained.

The last form of therapy is surgical therapy, which corrects the obstructive phenomenon caused by allergic rhinosinusitis. The procedures described are reduction inferior turbinectomies and endoscopic sinus surgery.

It is felt by the authors that the specialist who is uniquely positioned to offer a patient suffering from allergic rhinosinusitis all three forms of therapy is the rhinologist.