Involvement of the brain serotonergic system in the locomotor stimulant effects of chlorpheniramine in Wistar rats: implication of postsynaptic 5-HT1A receptors

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.

Forced Swimming-Induced Depressive-like Behavior and Anxiety Are Reduced by Chlorpheniramine via Suppression of Oxidative and Inflammatory Mediators and Activating the Nrf2-BDNF Signaling Pathway

The first-generation antihistamine chlorpheniramine (CPA) is believed to have both anxiolytic and antidepressant properties. The current study sought to assess the mechanisms behind the antidepressant and anxiolytic effects of CPA therapy concerning oxidative stress, inflammation, and nuclear factor p45 for erythroid 2-Brain-derived neurotrophic factor (Nrf2-BDNF) signaling pathway in forced swimming-induced depressive-like behavior and anxiety. Eighteen male Wistar rats (180-200 gm) rats were separated into three groups (n = 6): a stressed group (acute stress) that underwent the forced swimming test (FST) and a stressed group that received pretreatment with CPA (10 mg/kg body weight) for 3 weeks (CPA + acute stress). Animals were subsequently put through the following behavioral tests after undergoing a forced swim test (FST) for 5 min: an immobility test, open field test, and elevated plus maze test. Serum cortisol levels were measured when the rats were euthanized at the end of the experiments. Brain neurotransmitters (cortisol, serotonin, and noradrenaline), oxidative stress (SOD and MDA), inflammatory (IL-6 and IL-1) biomarkers, and the Nrf2-BDNF signaling pathway in the hippocampus and cerebral cortex tissues was determined. CPA prevented stress-induced increases in cortisol levels (p < 0.0001), decreased brain neurotransmitters, and increased oxidative stress and inflammation. CPA also upregulated the Nrf2-BDNF signaling pathway. Thus, CPA mitigates depressive-like behavior and anxiety by inhibiting oxidative stress and inflammation and upregulating the Nrf2-BDNF signaling pathway in the brain tissues.

The anaesthetist, opioid analgesic drugs, and serotonin toxicity: a mechanistic and clinical review

Most cases of serotonin toxicity are provoked by therapeutic doses of a combination of two or more serotonergic drugs, defined as drugs affecting the serotonin neurotransmitter system. Common serotonergic drugs include many antidepressants, antipsychotics, and opioid analgesics, particularly fentanyl, tramadol, meperidine (pethidine), and methadone, but rarely morphine and other related phenanthrenes. Symptoms of serotonin toxicity are attributable to an effect on monoaminergic transmission caused by an increased synaptic concentration of serotonin. The serotonin transporter (SERT) maintains low serotonin concentrations and is important for the reuptake of the neurotransmitter into the presynaptic nerve terminals. Some opioids inhibit the reuptake of serotonin by inhibiting SERT, thus increasing the plasma and synaptic cleft serotonin concentrations that activate the serotonin receptors. Opioids that are good inhibitors of SERT (tramadol, dextromethorphan, methadone, and meperidine) are most frequently associated with serotonin toxicity. Tramadol also has a direct serotonin-releasing action. Fentanyl produces an efflux of serotonin, and binds to 5-hydroxytryptamine (5-HT)_1A and 5-HT_2A receptors, whilst methadone, meperidine, and more weakly tapentadol, bind to 5-HT_2A but not 5-HT_1A receptors. The perioperative period is a time where opioids and other serotonergic drugs are frequently administered in rapid succession, sometimes to patients with other serotonergic drugs in their system. This makes the perioperative period a relatively risky time for serotonin toxicity to occur. The intraoperative recognition of serotonin toxicity is challenging as it can mimic other serious syndromes, such as malignant hyperthermia, sepsis, thyroid storm, and neuroleptic malignant syndrome. Anaesthetists must maintain a heightened awareness of its possible occurrence and a readiness to engage in early treatment to avoid poor outcomes.

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.

Dextromethorphan, chlorphenamine and serotonin toxicity: case report and systematic literature review

The aim of this review was to describe a patient with serotonin toxicity after an overdose of dextromethorphan and chlorphenamine and to perform a systematic literature review exploring whether dextromethorphan and chlorphenamine may be equally contributory in the development of serotonin toxicity in overdose. A Medline literature review was undertaken to identify cases of serotonin toxicity due to dextromethorphan and/or chlorphenamine. Case reports were included if they included information on the ingested dose or plasma concentrations of dextromethorphan and/or chlorphenamine, information about co-ingestions and detailed clinical information to evaluate for serotonin toxicity. Cases were reviewed by two toxicologists and serotonin toxicity, defined by the Hunter criteria, was diagnosed when appropriate. The literature was then reviewed to evaluate whether chlorphenamine may be a serotonergic agent. One hundred and fifty-five articles of dextromethorphan or chlorphenamine poisoning were identified. There were 23 case reports of dextromethorphan, of which 18 were excluded for lack of serotonin toxicity. No cases were identified in which serotonin toxicity could be solely attributed to chlorphenamine. This left six cases of dextrometorphane and/or chlorphenamine overdose, including our own, in which serotonin toxicity could be diagnosed based on the presented clinical information. In three of the six eligible cases dextromethorphan and chlorphenamine were the only overdosed drugs. There is substantial evidence from the literature that chlorphenamine is a similarly potent serotonin re-uptake inhibitor when compared with dextrometorphan. Chlorphenamine is a serotonergic medication and combinations of chlorphenamine and dextromethorphan may be dangerous in overdose due to an increased risk of serotonin toxicity.

Dextromethorphan, chlorphenamine and serotonin toxicity: case report and systematic literature review

The aim of this review was to describe a patient with serotonin toxicity after an overdose of dextromethorphan and chlorphenamine and to perform a systematic literature review exploring whether dextromethorphan and chlorphenamine may be equally contributory in the development of serotonin toxicity in overdose. A Medline literature review was undertaken to identify cases of serotonin toxicity due to dextromethorphan and/or chlorphenamine. Case reports were included if they included information on the ingested dose or plasma concentrations of dextromethorphan and/or chlorphenamine, information about co-ingestions and detailed clinical information to evaluate for serotonin toxicity. Cases were reviewed by two toxicologists and serotonin toxicity, defined by the Hunter criteria, was diagnosed when appropriate. The literature was then reviewed to evaluate whether chlorphenamine may be a serotonergic agent. One hundred and fifty-five articles of dextromethorphan or chlorphenamine poisoning were identified. There were 23 case reports of dextromethorphan, of which 18 were excluded for lack of serotonin toxicity. No cases were identified in which serotonin toxicity could be solely attributed to chlorphenamine. This left six cases of dextrometorphane and/or chlorphenamine overdose, including our own, in which serotonin toxicity could be diagnosed based on the presented clinical information. In three of the six eligible cases dextromethorphan and chlorphenamine were the only overdosed drugs. There is substantial evidence from the literature that chlorphenamine is a similarly potent serotonin re-uptake inhibitor when compared with dextrometorphan. Chlorphenamine is a serotonergic medication and combinations of chlorphenamine and dextromethorphan may be dangerous in overdose due to an increased risk of serotonin toxicity.

Involvement of the brain histaminergic system in addiction and addiction-related behaviors: a comprehensive review with emphasis on the potential therapeutic use of histaminergic compounds in drug dependence

Neurons that produce histamine are exclusively located in the tuberomamillary nucleus of the posterior hypothalamus and send widespread projections to almost all brain areas. Neuronal histamine is involved in many physiological and behavioral functions such as arousal, feeding behavior and learning. Although conflicting data have been published, several studies have also demonstrated a role of histamine in the psychomotor and rewarding effects of addictive drugs. Pharmacological and brain lesion experiments initially led to the proposition that the histaminergic system exerts an inhibitory influence on drug reward processes, opposed to that of the dopaminergic system. The purpose of this review is to summarize the relevant literature on this topic and to discuss whether the inhibitory function of histamine on drug reward is supported by current evidence from published results. Research conducted during the past decade demonstrated that the ability of many antihistaminic drugs to potentiate addiction-related behaviors essentially results from non-specific effects and does not constitute a valid argument in support of an inhibitory function of histamine on reward processes. The reviewed findings also indicate that histamine can either stimulate or inhibit the dopamine mesolimbic system through distinct neuronal mechanisms involving different histamine receptors. Finally, the hypothesis that the histaminergic system plays an inhibitory role on drug reward appears to be essentially supported by place conditioning studies that focused on morphine reward. The present review suggests that the development of drugs capable of activating the histaminergic system may offer promising therapeutic tools for the treatment of opioid dependence.

Combined dextromethorphan and chlorpheniramine intoxication in impaired drivers

Dextromethorphan is a nonprescription antitussive which has been gaining in popularity as an abused drug, because of the hallucinogenic, dissociative, and intoxicating effects it produces at high doses. This report describes a series of eight drivers arrested for driving under the influence of the combined effects of dextromethorphan and chlorpheniramine, and a further four drivers under the influence of dextromethorphan alone. In the combined dextromethorphan/chlorpheniramine cases, blood dextromethorphan concentrations ranged from 150 to 1220 ng/mL (n = 8; mean 676 ng/mL, median 670 ng/mL), and chlorpheniramine concentrations ranged from 70 to 270 ng/mL (n = 8; mean 200 ng/mL, median 180 ng/mL). The four cases without chlorpheniramine present had blood dextromethorphan concentrations between 190 and 1000 ng/mL (mean 570 ng/mL, median 545 ng/mL). Some drivers had therapeutic concentrations of other drugs present. Drivers generally displayed symptoms of central nervous system (CNS) depressant intoxication, and there was gross evidence of impairment in their driving, including weaving, leaving the lane of travel, failing to obey traffic signals, and involvement in collisions. Drug Recognition Expert opinions confirmed that the subjects were under the influence of a drug in the CNS-depressant category.

Stress-induced hyperthermia is reduced by rapid-acting anxiolytic drugs independent of injection stress in rats

BACKGROUND

Stress-induced hyperthermia (SIH) is the transient rise in body temperature after encountering a stressor. The SIH response can be blocked by administration of various anxiolytic drugs prior to inducing stress. However, a drug injection involves handling and injection stress and therefore induces a SIH response itself. In the standard SIH test, drugs are therefore injected 60 min before stress induction to allow injection-induced hyperthermia to decline. This makes it difficult to study putative anxiolytic compounds with a short half-life. The present study therefore aimed to compare the effects of standard (stressful) and stress-free anxiolytic drug administration on the subsequent SIH response with a 10-minute injection-stressor interval.

METHODS

Anxiolytic drugs with short half-lives (midazolam, 8-OH-DPAT, nicotine) were injected subcutaneously in rats using either a stressful (manual injection) or stress-free injection (subcutaneous cannula) method 10 min before novel cage stress. Body temperature and locomotor activity were measured using telemetric transmitters.

RESULTS

Stressful and stress-free drug administration resulted in comparable drug effects on the stress-induced hyperthermia and locomotor responses in rats.

CONCLUSION

The present study shows that both stressful and stress-free drug injection shortly before a stressor results in reproducible attenuation of the SIH response in rats. In rats, a short injection-stressor interval can therefore be applied using the SIH model, enabling the study of putative anxiolytic drugs with short half-lives.

The effect of the 5-HT1A receptor agonist, 8-OH-DPAT, on motion-induced emesis in Suncus murinus

In the present study we evaluated the role of 5-HT(1A) receptors in mediating the inhibitory action of 8-OH-DPAT, a 5-HT(1A) receptor agonist, in motion sickness in Suncus murinus. 8-OH-DPAT (0.1 mg/kg, i. p) attenuated motion-induced emesis which was associated with an increase in the latency of the onset to the first emetic episode. Pre-treatment with methysergide (a 5-HT(1/2/7) receptor antagonist, 1.0 mg/kg, i. p.), WAY-100635 (a 5-HT(1A) receptor antagonist, 1.0 mg/kg, i. p.), SB269970A (a 5-HT(7) receptor antagonist, 1.0 and 5.0 mg/kg, i. p.), ondansetron (a 5-HT(3) receptor antagonist, 1.0 mg/kg, i. p) or GR13808 (a 5-HT(4) receptor antagonist, 0.5 mg/kg, i. p) failed to modify the inhibitory action of 8-OH-DPAT on motion sickness. Furthermore, the application of either methysergide, WAY-100635, SB269970A, ondansetron or GR13808 alone had no effect on motion sickness in its own right. These data indicate that neither 5-HT(1A) nor any 5-HT(2) receptor subtypes, 5-HT(3), 5-HT(4) and 5-HT(7) receptors are likely to be involved in the inhibition of motion-induced emesis mediated by 8-OH-DPAT.

Evidence that the 5-HT1A autoreceptor is an important pharmacological target for the modulation of cocaine behavioral stimulant effects

The psychostimulant effects of cocaine critically depend on the serotonergic (5-HT) system, of which the 5-HT1A receptor is an essential component. We recently showed divergent contributions of various pre- and postsynaptic 5-HT1A receptor populations to the behavioral effects of cocaine. Here, we further investigate the role of 5-HT1A autoreceptors in the acute and chronic stimulant effects of cocaine using 5-HT1A receptor ligands in autoreceptor preferring doses. In experiment 1, four groups of rats (N = 10) received either saline or the 5-HT1A agonist, 8-OHDPAT (0.05 mg/kg) 20 min prior to a saline or cocaine (10 mg/kg) injection on 9 consecutive days. In experiment 2, six groups (N = 10) were given either saline, the 5-HT1A antagonist, WAY 100635 (0.05 mg/kg) or 8-OHDPAT (0.05 mg/kg) plus WAY 100635 (0.05 mg/kg) 20 min before a saline or cocaine (10.0 mg/kg) treatment on 9 consecutive days. Initially, both the 8-OHDPAT and WAY 100635 pretreatments completely blocked the locomotor stimulant effects of cocaine whereas the combined 8-OHDPAT plus WAY 100635 pretreatment had no effect. In saline treated groups, neither the WAY 100635 nor the 8-OHDPAT plus WAY 100635 pretreatment influenced spontaneous activity levels, whereas the 8-OHDPAT alone severely reduced spontaneous activity. These effects persisted over the course of the 9 test sessions. A different pattern of results was obtained for the cocaine treatment groups. With repeated treatments, the WAY 100635 treatment always blocked the locomotor activation effect of cocaine, whereas the effects of 8-OHDPAT were transformed from an inhibition to an enhancement of cocaine locomotor stimulation. The combined 8-OHDPAT plus WAY 100635 pretreatment did not affect the stimulant effect of cocaine. These findings demonstrate that low dose autoreceptor preferring treatments with a 5-HT1A agonist and antagonist can strongly modify the behavioral stimulant effects of cocaine and suggest that the 5-HT1A autoreceptor may be an important pharmacological target for the development of treatments for cocaine addiction.

The 5-HT1A receptor and behavioral stimulation in the rat: effects of 8-OHDPAT on spontaneous and cocaine-induced behavior

RATIONALE

The contribution of the 5-HT(1A) somato-dendritic autoreceptor populations to spontaneous and cocaine-induced locomotion is unclear.

OBJECTIVES

To use a low dose range of +/-8-hydroxy-2-(di- n-propylamino)tetralin (8-OHDPAT) to preferentially stimulate 5-HT(1A) autoreceptors and a medium 8-OHDPAT dose range to stimulate both 5-HT(1A) autoreceptors and postsynaptic receptors as pretreatments prior to either saline or cocaine.

METHODS

In experiment 1, either a medium dose of 8-OHDPAT (0.4 mg/kg) or a low dose (0.05 mg/kg) was given as pretreatments 20 min before five separate 20-min open-field tests. In experiment 2, the pretreatments were changed to a low dose range of 8-OHDPAT (0.01-0.05 mg/kg), with or without WAY 100635 (0.01-0.05 mg/kg). In experiment 3, the 8-OHDPAT pretreatments (0.01, 0.025 or 0.05 mg/kg) were administered 20 min prior to saline or cocaine (10 mg/kg) tests. In experiment 4, a medium dose range (0.2-0.3 mg/kg) was given 20 min prior to saline or cocaine (10 mg/kg) tests.

RESULTS

Experiment 1 showed that 8-OHDPAT (0.4 mg/kg) tended to increase locomotor activity but that pretreatment with 0.05 mg/kg severely suppressed locomotor activity. In experiment 2, 8-OHDPAT in the low dose range inhibited locomotor activity and this effect was reversed by co-administration of WAY 100635. Experiment 3 showed that the low-dose 8-OHDPAT pretreatment reduced locomotor activity in saline but not cocaine tests. In experiment 4, 8-OHDPAT in the medium dose range enhanced locomotor activity in cocaine tests.

CONCLUSIONS

It is suggested that the facilitatory effect of 8-OHDPAT on cocaine-induced locomotor stimulation is mediated by inhibition of 5-HT(1A) somato-dendritic autoreceptors.