Diazepam and chlormethiazole attenuate the development of hyperthermia in an animal model of the serotonin syndrome

Serotonin syndrome: A rare yet crucial diagnosis

ABSTRACT

Serotonin syndrome is a rare, life-threatening toxidrome caused by serotonergic agents. This syndrome classically presents with a combination of mental status changes, autonomic hyperactivity, and neuromuscular abnormalities. However, diagnosing the condition is difficult because of its variable symptoms at presentation. As a result, serotonin syndrome often is underreported, making it harder to understand, recognize, and treat. Patients with this condition may present to primary or urgent care or an ED, and may become acutely symptomatic during an inpatient admission. Clinicians must be able to identify at-risk patients and intervene to prevent potentially lethal complications.

The serotonin toxidrome: shortfalls of current diagnostic criteria for related syndromes

INTRODUCTION

Serotonin syndrome (toxicity) describes adverse drug effects from toxic amounts of intra-synaptic central nervous system serotonin. A wide range of drugs have been implicated to cause serotonin toxicity, not all justifiably. The plausible agents all have a final common pathway resulting in a substantial increase in central nervous system serotonergic neurotransmission. Serotonin toxicity is characterized by neuromuscular excitation, mental status changes, and autonomic dysregulation. Signs and symptoms represent a spectrum of toxicity (mild to life-threatening) related to increasing serotonin concentrations. As there is no consensus on the threshold for "toxicity" or diagnostic criteria, the true incidence of serotonin toxicity is unknown. The incidence in overdose is easier to quantify and is reasonably common in serotonergic antidepressant overdoses. In a large case series of overdoses, moderate serotonin toxicity occurred in 14% of poisonings with a selective serotonin reuptake inhibitor. While half those ingesting a monoamine oxidase inhibitor in combination with a serotonergic agent in overdose exhibit at least moderately severe serotonin toxicity. In contrast, the incidence of serotonin toxicity in those on therapeutic serotonergic agents appears to be very low.

OBJECTIVES

To provide a narrative review of the current diagnostic criteria, utilizing case reports of fatalities to evaluate how many meet the various diagnostic criteria and propose practical solutions to resolve controversies in diagnosis.

METHODS

A review of serotonin toxicity diagnostic criteria in the English literature was completed by searching Embase and PubMed from January 1990 to July 2021 for the keywords "serotonin syndrome/toxicity" paired with "diagnostic criteria" or "diagnosis." Also, fatal cases of serotonin toxicity identified from a recent systematic review were independently examined to determine what diagnostic criteria were met and whether serotonin toxicity or another cause was most likely.

REVIEW OF DIAGNOSIS CRITERIA

Serotonin toxicity is a clinical diagnosis, four diagnostic criteria (Sternbach, Serotonin Syndrome Scale, Radomski, and Hunter) have been proposed. However, the Serotonin Syndrome Scale has not been validated in patients with serotonin toxicity and only utilized in those on a serotonergic agent. The remaining three criteria are utilized more widely but have undergone little refinement or validation.

REVIEW OF FATAL CASES

Shortfalls with diagnostic criteria can be illustrated by examining case fatalities. Of 55 fatal cases reviewed, 12 (22%) were unlikely to be serotonin toxicity. Sternbach and Radomski criteria were met by 25 (45%), 20 (36%) had insufficient data reported and 10 (18%) met an exclusion criterion. Few had sufficient information reported to determine whether Hunter Criteria were met, with only 13 (24%) documented as meeting the criteria, the remaining 42 (76%) had insufficient data.

RESOLVING SHORTFALLS IN CURRENT DIAGNOSTIC CRITERIA

As serotonin toxicity is a clinical diagnosis, issues arise when basing the diagnosis on symptom criteria alone, without considering whether the drug/s ingested increase central nervous system serotonin or whether there is an alternative diagnosis. This has resulted in case reports and government warnings for drugs that cannot plausibly cause significant serotonin toxicity (e.g., ondansetron and antipsychotics). We propose when assessing for a serotonin toxidrome, both the causative agent(s) and clinical scenario is considered to determine the likelihood of serotonin toxicity. Then the clinical features assessed, those with a moderate to high prior probability (e.g., serotonergic drug-drug interaction, overdose, recent initiation or increase in dose of serotonergic agent/s) could be diagnosed based on the Hunter criteria. However, those with a low probability (e.g., stable therapeutic doses of a serotonergic agent) require more specific and stringent criteria. Finally, we propose a minimum dataset for case reports/series of serotonin toxicity.

CONCLUSIONS

More complete and accurate reporting of serotonin toxicity cases is required in the future, to avoid further misleading associations that are physiologically implausible.

Serotonin Syndrome: Pathophysiology, Clinical Features, Management, and Potential Future Directions

Serotonin syndrome (SS) (also referred to as serotonin toxicity) is a potentially life-threatening drug-induced toxidrome associated with increased serotonergic activity in both the peripheral (PNS) and central nervous systems (CNS). It is characterised by a dose-relevant spectrum of clinical findings related to the level of free serotonin (5-hydroxytryptamine [5-HT]), or 5-HT receptor activation (predominantly the 5-HT_1A and 5-HT_2A subtypes), which include neuromuscular abnormalities, autonomic hyperactivity, and mental state changes. Severe SS is only usually precipitated by the simultaneous initiation of 2 or more serotonergic drugs, but the syndrome can also occur after the initiation of a single serotonergic drug in a susceptible individual, the addition of a second or third agent to long-standing doses of a maintenance serotonergic drug, or after an overdose. The combination of a monoamine oxidase inhibitor (MAOI), in particular MAO-A inhibitors that preferentially inhibit the metabolism of 5-HT, with serotonergic drugs is especially dangerous, and may lead to the most severe form of the syndrome, and occasionally death. This review describes our current understanding of the pathophysiology, clinical presentation and management of SS, and summarises some of the drugs and interactions that may precipitate the condition. We also discuss the newer novel psychoactive substances (NPSs), a growing public health concern due to their increased availability and use, and their potential risk to evoke the syndrome. Finally, we discuss whether the inhibition of tryptophan hydroxylase (TPH), in particular the neuronal isoform (TPH2), may provide an opportunity to pharmacologically target central 5-HT synthesis, and so develop new treatments for severe, life-threatening SS.

The Serotonin Syndrome: From Molecular Mechanisms to Clinical Practice

The serotonin syndrome is a medication-induced condition resulting from serotonergic hyperactivity, usually involving antidepressant medications. As the number of patients experiencing medically-treated major depressive disorder increases, so does the population at risk for experiencing serotonin syndrome. Excessive synaptic stimulation of 5-HT_2A receptors results in autonomic and neuromuscular aberrations with potentially life-threatening consequences. In this review, we will outline the molecular basis of the disease and describe how pharmacologic agents that are in common clinical use can interfere with normal serotonergic pathways to result in a potentially fatal outcome. Given that serotonin syndrome can imitate other clinical conditions, an understanding of the molecular context of this condition is essential for its detection and in order to prevent rapid clinical deterioration.

Case of Serotonin Syndrome Initially Presenting as Diffuse Body Pain

Patient: Female, 50

Final Diagnosis: Serotonin syndrome

Symptoms: Pain

Medication: —

Clinical Procedure: —

Specialty: General and Internal Medicine

A comparison of midazolam and dexmedetomidine for the recovery of serotonin syndrome in rats

Serotonin syndrome is a drug-related toxicity caused by excess serotonin within the central nervous system. We recently encountered a case of serotonin syndrome that developed in the early postoperative period that was successfully treated with intravenous dexmedetomidine. Although the prescriptive literature has commonly recommended sedation with benzodiazepines for controlling agitation in serotonin syndrome, the effectiveness of dexmedetomidine has also been reported in several clinical conditions. In the present study, we conducted a reverse translational experiment to compare the efficacy of dexmedetomidine and midazolam, at equi-sedative doses, on serotonergic toxicity-like responses in rats. Animals were subcutaneously injected with 0.75 mg/kg 8-OH-DPAT, a full 5-HT1A agonist. 8-OH-DPAT-treated rats showed serotonin syndrome-like behaviors (low body posture, forepaw treading), hyperlocomotion, and decreased body temperature, which were completely inhibited by pretreatment with WAY 100635, a selective 5-HT1A antagonist (n = 8). Intramuscular injection of midazolam (1.0 mg/kg) or dexmedetomidine (0.01 mg/kg), which comparably induced observable signs of sedation, was tested in the present study. Concomitant treatment with midazolam significantly attenuated the hyperlocomotion, but failed to affect traditional serotonin syndrome behaviors and body temperature in 8-OH-DPAT-treated rats (n = 8). On the other hand, concomitant treatment with dexmedetomidine significantly attenuated all of these parameters (n = 8). The present case and related reverse translational experiment demonstrate that dexmedetomidine may be more beneficial for the treatment of serotonin syndrome compared to the current recommended treatment with benzodiazepines.

The heat is on: Molecular mechanisms of drug-induced hyperthermia

Thermoregulation is an essential homeostatic process in which critical mechanisms of heat production and dissipation are controlled centrally in large part by the hypothalamus and peripherally by activation of the sympathetic nervous system. Drugs that disrupt the components of this highly orchestrated multi-organ process can lead to life-threatening hyperthermia. In most cases, hyperthermic agents raise body temperature by increasing the central and peripheral release of thermoregulatory neurotransmitters that ultimately lead to heat production in thermogenic effector organs skeletal muscle (SKM) and brown adipose tissue (BAT). In many cases hyperthermic drugs also decrease heat dissipation through peripheral changes in blood flow. Drug-induced heat production is driven by the stimulation of mechanisms that normally regulate the adaptive thermogenic responses including both shivering and non-shivering thermogenesis (NST) mechanisms. Modulation of the mitochondrial electrochemical proton/pH gradient by uncoupling protein 1 (UCP1) in BAT is the most well characterized mechanism of NST in response to cold, and may contribute to thermogenesis induced by sympathomimetic agents, but this is far from established. However, the UCP1 homologue, UCP3, and the ryanodine receptor (RYR1) are established mediators of toxicant-induced hyperthermia in SKM. Defining the molecular mechanisms that orchestrate drug-induced hyperthermia will be essential in developing treatment modalities for thermogenic illnesses. This review will briefly summarize mechanisms of thermoregulation and provide a survey of pharmacologic agents that can lead to hyperthermia. We will also provide an overview of the established and candidate molecular mechanisms that regulate the actual thermogenic processes in heat effector organs BAT and SKM.

Tramadol toxicity in a cat: case report and literature review of serotonin syndrome

OVERVIEW

Tramadol toxicity has not previously been reported in a cat.

CASE SUMMARY

This report describes the clinical signs, diagnosis and treatment of tramadol toxicity, manifesting as serotonin syndrome, in a cat in Australia.

PRACTICAL RELEVANCE

For any cat with suspicion of serotonin syndrome, in particular secondary to tramadol overdose, it is recommended that decontamination, monitoring and supportive care are instituted as soon as clinical signs develop. Prolonged hospitalisation may be required in the event of a severe overdose.

LITERATURE REVIEW

The literature relating to the pharmacology of tramadol and tramadol overdose, clinical manifestations of tramadol overdose, and serotonin syndrome in cats, humans and dogs is reviewed. Recommended treatment for tramadol overdose and serotonin syndrome is also discussed.

Animal models of the serotonin syndrome: a systematic review

The serotonin syndrome (SS) is a potentially life-threatening disorder in humans which is induced by ingestion of an overdose or by combination of two or more serotonin (5-HT)-enhancing drugs. In animals, acute administration of direct and indirect 5-HT agonists also leads to a set of behavioral and autonomic responses. In the current review, we provide an overview of the existing versions of the animal model of the SS. With a focus on studies in rats and mice, we analyze the frequency of behavioral and autonomic responses following administration of 5-HT-enhancing drugs and direct 5-HT agonists administered alone or in combination, and we briefly discuss the receptor mediation of these responses. Considering species differences, we identify a distinct set of behavioral and autonomic responses that are consistently observed following administration of direct and indirect 5-HT agonists. Finally, we discuss the importance of a standardized assessment of SS responses in rodents and the utility of animal models of the SS in translational studies, and provide suggestions for future research.

Serotonin syndrome: pills, thrills and shoulder aches

This case demonstrates an acute presentation of unwitnessed seizure causing typical injuries. Progress in hospital was complicated by worsening autonomic disturbance and agitation, typical for serotonin syndrome, suspected in light of recent selective serotonin reuptake inhibitor antidepressant initiation. Supportive care required treatment in the intensive care unit setting but full recovery ensued. This case not only reminds clinicians of the potential pitfalls in assessing postictal injured patients, but also that serotonin syndrome requires a high-index of diagnostic suspicion given the range of presenting features. Management ranges from simple withdrawal of the offending agent to specific therapies such as a cyproheptadine.

Treatment of four psychiatric emergencies in the intensive care unit

OBJECTIVES

To review the diagnosis and management of four selected psychiatric emergencies in the intensive care unit: agitated delirium, neuroleptic malignant syndrome, serotonin syndrome, and psychiatric medication overdose.

DATA SOURCES

Review of relevant medical literature.

DATA SYNTHESIS

Standardized screening for delirium should be routine. Agitated delirium should be managed with an antipsychotic and, possibly, dexmedetomidine in treatment-refractory cases. Delirium management should also include ensuring a calming environment and adequate pain control, minimizing benzodiazepines and anticholinergics, normalizing the sleep-wake cycle, providing sensory aids as required, and providing early physical and occupational therapy. Neuroleptic malignant syndrome should be treated by discontinuing dopamine blockers, providing supportive therapy, and possibly administering medications (benzodiazepines, dopamine agonists, and/or dantrolene) or electroconvulsive therapy, if indicated. Serotonin syndrome should be treated by discontinuing all serotonergic agents, providing supportive therapy, controlling agitation with benzodiazepines, and possibly administering serotonin2A antagonists. It is often unnecessary to restart psychiatric medications upon which a patient has overdosed in the intensive care unit, though withdrawal syndromes should be prevented, and communication with outpatient prescribers is vital.

CONCLUSIONS

Understanding the diagnosis and appropriate management of these four psychiatric emergencies is important to provide safe and effective care in the intensive care unit.

Toxicity of amphetamines: an update

Amphetamines represent a class of psychotropic compounds, widely abused for their stimulant, euphoric, anorectic, and, in some cases, emphathogenic, entactogenic, and hallucinogenic properties. These compounds derive from the β-phenylethylamine core structure and are kinetically and dynamically characterized by easily crossing the blood-brain barrier, to resist brain biotransformation and to release monoamine neurotransmitters from nerve endings. Although amphetamines are widely acknowledged as synthetic drugs, of which amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are well-known examples, humans have used natural amphetamines for several millenniums, through the consumption of amphetamines produced in plants, namely cathinone (khat), obtained from the plant Catha edulis and ephedrine, obtained from various plants in the genus Ephedra. More recently, a wave of new amphetamines has emerged in the market, mainly constituted of cathinone derivatives, including mephedrone, methylone, methedrone, and buthylone, among others. Although intoxications by amphetamines continue to be common causes of emergency department and hospital admissions, it is frequent to find the sophism that amphetamine derivatives, namely those appearing more recently, are relatively safe. However, human intoxications by these drugs are increasingly being reported, with similar patterns compared to those previously seen with classical amphetamines. That is not surprising, considering the similar structures and mechanisms of action among the different amphetamines, conferring similar toxicokinetic and toxicological profiles to these compounds. The aim of the present review is to give an insight into the pharmacokinetics, general mechanisms of biological and toxicological actions, and the main target organs for the toxicity of amphetamines. Although there is still scarce knowledge from novel amphetamines to draw mechanistic insights, the long-studied classical amphetamines-amphetamine itself, as well as methamphetamine and MDMA, provide plenty of data that may be useful to predict toxicological outcome to improvident abusers and are for that reason the main focus of this review.

The clinical toxicology of metamfetamine

INTRODUCTION

Metamfetamine is a highly addictive amfetamine analog that acts primarily as a central nervous system (CNS) stimulant. The escalating abuse of this drug in recent years has lead to an increasing burden upon health care providers. An understanding of the drug's toxic effects and their medical treatment is therefore essential for the successful management of patients suffering this form of intoxication.

AIM

The aim of this review is to summarize all main aspects of metamfetamine poisoning including epidemiology, mechanisms of toxicity, toxicokinetics, clinical features, diagnosis, and management.

METHODS

A summary of the literature on metamfetamine was compiled by systematically searching OVID MEDLINE and ISI Web of Science. Further information was obtained from book chapters, relevant news reports, and web material. Epidemiology. Following its use in the Second World War, metamfetamine gained popularity as an illicit drug in Japan and later the United States. Its manufacture and use has now spread to include East and South-East Asia, North America, Mexico, and Australasia, and its world-wide usage, when combined with amfetamine, exceeds that of all other drugs of abuse except cannabis. Mechanisms of toxicity. Metamfetamine acts principally by stimulating the enhanced release of catecholamines from sympathetic nerve terminals, particularly of dopamine in the mesolimbic, mesocortical, and nigrostriatal pathways. The consequent elevation of intra-synaptic monoamines results in an increased activation of central and peripheral α±- and β-adrenergic postsynaptic receptors. This can cause detrimental neuropsychological, cardiovascular, and other systemic effects, and, following long-term abuse, neuronal apoptosis and nerve terminal degeneration. Toxicokinetics. Metamfetamine is rapidly absorbed and well distributed throughout the body, with extensive distribution across high lipid content tissues such as the blood-brain barrier. In humans the major metabolic pathways are aromatic hydroxylation producing 4-hydroxymetamfetamine and N-demethylation to form amfetamine. Metamfetamine is excreted predominantly in the urine and to a lesser extent by sweating and fecal excretion, with reported terminal half-lives ranging from ∼5 to 30 h. Clinical features. The clinical effects of metamfetamine poisoning can vary widely, depending on dose, route, duration, and frequency of use. They are predominantly characteristic of an acute sympathomimetic toxidrome. Common features reported include tachycardia, hypertension, chest pain, various cardiac dysrhythmias, vasculitis, headache, cerebral hemorrhage, hyperthermia, tachypnea, and violent and aggressive behaviour. Management. Emergency stabilization of vital functions and supportive care is essential. Benzodiazepines alone may adequately relieve agitation, hypertension, tachycardia, psychosis, and seizure, though other specific therapies can also be required for sympathomimetic effects and their associated complications.

CONCLUSION

Metamfetamine may cause severe sympathomimetic effects in the intoxicated patient. However, with appropriate, symptom-directed supportive care, patients can be expected to make a full recovery.

Drugs and pharmaceuticals: management of intoxication and antidotes

The treatment of patients poisoned with drugs and pharmaceuticals can be quite challenging. Diverse exposure circumstances, varied clinical presentations, unique patient-specific factors, and inconsistent diagnostic and therapeutic infrastructure support, coupled with relatively few definitive antidotes, may complicate evaluation and management. The historical approach to poisoned patients (patient arousal, toxin elimination, and toxin identification) has given way to rigorous attention to the fundamental aspects of basic life support--airway management, oxygenation and ventilation, circulatory competence, thermoregulation, and substrate availability. Selected patients may benefit from methods to alter toxin pharmacokinetics to minimize systemic, target organ, or tissue compartment exposure (either by decreasing absorption or increasing elimination). These may include syrup of ipecac, orogastric lavage, activated single- or multi-dose charcoal, whole bowel irrigation, endoscopy and surgery, urinary alkalinization, saline diuresis, or extracorporeal methods (hemodialysis, charcoal hemoperfusion, continuous venovenous hemofiltration, and exchange transfusion). Pharmaceutical adjuncts and antidotes may be useful in toxicant-induced hyperthermias. In the context of analgesic, anti-inflammatory, anticholinergic, anticonvulsant, antihyperglycemic, antimicrobial, antineoplastic, cardiovascular, opioid, or sedative-hypnotic agents overdose, N-acetylcysteine, physostigmine, L-carnitine, dextrose, octreotide, pyridoxine, dexrazoxane, leucovorin, glucarpidase, atropine, calcium, digoxin-specific antibody fragments, glucagon, high-dose insulin euglycemia therapy, lipid emulsion, magnesium, sodium bicarbonate, naloxone, and flumazenil are specifically reviewed. In summary, patients generally benefit from aggressive support of vital functions, careful history and physical examination, specific laboratory analyses, a thoughtful consideration of the risks and benefits of decontamination and enhanced elimination, and the use of specific antidotes where warranted. Data supporting antidotes effectiveness vary considerably. Clinicians are encouraged to utilize consultation with regional poison centers or those with toxicology training to assist with diagnosis, management, and administration of antidotes, particularly in unfamiliar cases.

Review article: amphetamines and related drugs of abuse

Acute amphetamine toxicity is a relatively common clinical scenario facing the Australasian emergency medicine physician. Rates of use in Australasia are amongst the highest in the world. Clinical effects are a consequence of peripheral and central adrenergic stimulation producing a sympathomimetic toxidrome and a spectrum of central nervous system effects. Assessment aims to detect the myriad of possible complications related to acute amphetamine exposure and to institute interventions to limit associated morbidity and mortality. Meticulous supportive care aided by judicial use of benzodiazepines forms the cornerstone of management. Beta blockers are contraindicated in managing cardiovascular complications. Agitation and hyperthermia must be treated aggressively. Discharge of non-admitted patients from the emergency department should only occur once physiological parameters and mental state have returned to normal. All patients should receive education regarding the dangers of amphetamine use.

Drug-induced serotonin syndrome: a review

Serotonin syndrome, or serotonin toxicity (ST), is a clinical condition that occurs as a result of an iatrogenic drug-induced increase in intrasynaptic serotonin levels primarily resulting in activation of serotonin(2A) receptors in the central nervous system. The severity of symptoms spans a spectrum of toxicity that correlates with the intrasynaptic serotonin concentration. Although numerous drugs have been implicated in ST, life-threatening cases generally occur only when monoamine oxidase inhibitors are combined with either selective or nonselective serotonin re-uptake inhibitors. The triad of clinical features consists of neuromuscular hyperactivity, autonomic hyperactivity and altered mental status, which may present abruptly and progress rapidly. The awareness of ST is crucial not only in avoiding the unintentional lethal combination of therapeutic drugs but also in recognizing the clinical picture when it occurs so that treatment can be promptly initiated. In this review, the pathophysiology, clinical features, implicated drugs, diagnosis and treatment of ST are discussed.

Life-threatening serotonin toxicity due to a citalopram-fluconazole drug interaction: case reports and discussion

OBJECTIVE

To discuss two cases of life-threatening serotonin toxicity due to a drug interaction between citalopram and fluconazole and to review the pertinent literature.

METHODS

A Medline search without date limitation was conducted using the terms serotonin syndrome, serotonin toxicity, fluconazole and citalopram.

RESULTS AND DISCUSSION

Fluconazole inhibits CYP2C19. Citalopram is a substrate for 2C19 and inhibition of its metabolism may result in serotonin toxicity. Serotonin toxicity in oncology patients may not present with the classic constellation of signs typically described in the literature. Delirium may be the only presenting feature. Current level of evidence for treatment of serotonin toxicity is level 4 or 5 (case series and expert opinion). Nevertheless, there is a strong theoretical basis for treating serotonin toxicity in medical patients with a 5H(2A) blocker such as cyproheptadine.

CONCLUSIONS

Consultation-liaison psychiatrists and oncologists should be aware of this preventable and underrecognized interaction. Citalopram should be stopped or substituted prior to the concurrent administration of fluconazole, and in the event of toxicity, treatment with cyproheptadine has a favorable risk-benefit ratio despite a lack of randomized controlled data to support its use.

Characterization of serotonin-toxicity syndrome (toxidrome) elicited by 5-hydroxy-l-tryptophan in clorgyline-pretreated rats

Patients are at high risk of developing serotonin-toxicity syndrome (toxidrome) when they take multiple serotonergic drugs, particularly co-administered with monoamine oxidase inhibitors or 5-hydroxytryptamine (5-HT) reuptake blockers. The toxidrome can vary from mild to severe. The primary goal of the present study was to understand the relationship between behavioral signs and degrees of toxidrome induced by 5-hydroxy-l-tryptophan (5-HTP) in clorgylinized rats. The severity was obtained by scoring behavioral signs including head shakes, penile erection, forepaw treading, hind limb abduction, Straub tail and tremor. It was found that 5-HTP produced a dose-dependent increase in degrees of the toxidrome. Furthermore, correlation between the toxidrome and changes in body-core temperature (delta Tcor) was determined. There was hypothermia in the mild toxidrome (delta Tcor<-1 degrees C), high hyperthermia in the severe toxidrome (delta Tcor>+2 degrees C) and a small change in T(cor) in the moderate toxidrome (-1 degrees C<delta Tcor<+2 degrees C). Thus, delta Tcor in response to drugs can be used to estimate the severity of the toxidrome. The second attempt was to identify the receptors mediating those changes. 5-HT1A receptors were involved in the hypothermic response while 5-HT2A and NMDA receptors mediated head shakes, hyperthermia, forepaw treading and Straub tail. Lastly, antidotal effect of cyproheptadine and (+)-MK-801 was examined. Both drugs blocked hyperthermia and death. However, the effects on mortality became poor when the antidotes were injected 60 min after high hyperthermia had been induced. These findings demonstrate the importance of the time frame using antidotes in the treatment of the 5-HT toxidrome.

Serotonin syndrome associated with the use of escitalopram

Escitalopram is the newest selective serotonin reuptake inhibitor (SSRI) available for use in the United States. It has been approved for the treatment of major depression and generalized anxiety disorder. It is the S-enantiomer of the SSRI citalopram and is highly serotonin specific as it has minimal effect on the reuptake of dopamine or norepinephrine. It is also a well-tolerated medication, with a side-effect profile comparable to the other SSRIs. While a number of side effects have been seen during escitalopram therapy, such as insomnia, nausea, and increased sweating, there are no reported cases of serotonin syndrome associated with escitalopram therapy to date. We present the case of a 24-year-old woman who developed serotonin syndrome after an increase in her escitalopram to 30 mg/day. We will review the diagnostic criteria of serotonin syndrome and the clinical scenarios in which serotonin syndrome can develop. We will also discuss the proposed treatments and role that polypharmacology may play in the development of this clinical entity.

What's wrong with my mouse model?

Stress plays a key role in pathogenesis of anxiety and depression. Animal models of these disorders are widely used in behavioral neuroscience to explore stress-evoked brain abnormalities, screen anxiolytic/antidepressant drugs and establish behavioral phenotypes of gene-targeted or transgenic animals. Here we discuss the current situation with these experimental models, and critically evaluate the state of the art in this field. Noting a deficit of fresh ideas and especially new paradigms for animal anxiety and depression models, we review existing challenges and outline important directions for further research in this field.

Neuroleptic malignant syndrome and serotonin syndrome

This chapter is focused on drug-induced hyperthermia with special regard to use of antipsychotics and antidepressants for the treatment of schizophrenia and major depression, respectively. Neuroleptic malignant syndrome (NMS) develops during the use of neuroleptics, whereas serotonin syndrome is caused mainly by serotoninergic antidepressants. Although both syndromes show various symptoms, hyperthermia is the main clinical manifestation. In this review we describe the historical background, clinical manifestations, diagnosis, and differential diagnosis of these two syndromes based on our observations on the experimental and clinical data.

A review of serotonin toxicity data: implications for the mechanisms of antidepressant drug action

Data now exist from which an accurate definition for serotonin toxicity (ST), or serotonin syndrome, has been developed; this has also lead to precise, validated decision rules for diagnosis. The spectrum concept formulates ST as a continuum of serotonergic effects, mediated by the degree of elevation of intrasynaptic serotonin. This progresses from side effects through to toxicity; the concept emphasizes that it is a form of poisoning, not an idiosyncratic reaction. Observations of the degree of ST precipitated by overdoses of different classes of drugs can elucidate mechanisms and potency of drug actions. There is now sufficient pharmacological data on some drugs to enable a prediction of which ones will be at risk of precipitating ST, either by themselves or in combinations with other drugs. This indicates that some antidepressant drugs, presently thought to have serotonergic effects in animals, do not exhibit such effects in humans. Mirtazapine is unable to precipitate serotonin toxicity in overdose or to cause serotonin toxicity when mixed with monoamine oxidase inhibitors, and moclobemide is unable to precipitate serotonin toxicity in overdose. Tricyclic antidepressants (other than clomipramine and imipramine) do not precipitate serotonin toxicity and might not elevate serotonin or have a dual action, as has been assumed.

Hyperthermic Syndromes Induced by Toxins

Normal thermogenesis requires a complex interaction between systems that generate and dissipate heat. Serving as director of thermogenesis, the hypothalamus activates the sympathetic nervous system along with the thyroid and adrenal glands to respond to changes in body temperature. Working in concert, these systems result in heat generation by uncoupling of oxidative phosphorylation, combined with impaired heat dissipation through vasoconstriction. In this article, the authors discuss serotonin and sympathomimetic syndromes, neuroleptic malignant syndrome,and malignant hyperthermia and how these syndromes affect the hypothalamic and sympathetic nervous systems, resulting at times in severe hyperthermia. Current treatment recommendations and future trends in treatment are also discussed.

A systematic review of the serotonergic effects of mirtazapine in humans: implications for its dual action status

A systematic review of published work concerning mirtazapine was undertaken to assess possible evidence of serotonergic effects or serotonin toxicity (ST) in humans, because drug toxicity and interaction data from human over-doses is an useful source of information about the nature and potency of drug effects. There is a paucity of evidence for mirtazapine having effects on any indicator of serotonin elevation, which leads to an emphasis on ST as an important line of evidence. Mirtazapine is compared with its analogue mianserin, and other serotonergic drugs. Although mirtazapine is referred to as a dual-action 'noradrenergic and specific serotonergic drug' (NaSSA) little evidence to support that idea exists, except from initial microdialysis studies in animals showing small effects; those have not subsequently been replicated or substantiated by independent researchers. Also, new data indicate its affinity for Alpha 2 adrenoceptors is not different to mianserin. It appears to exhibit no serotonergic symptoms or toxicity in over-dose by itself, nor is there evidence that it precipitates ST in combination with monoamine oxidase inhibitors, as would be expected if it raises intra-synaptic serotonin levels. Mirtazapine has no demonstrable serotonergic effects in humans and there is insufficient evidence to designate it as a dual-action drug.

The pathophysiology of serotonin toxicity in animals and humans: implications for diagnosis and treatment

Serotonin toxicity (or serotonin syndrome) has become an increasingly common and important clinical problem in medicine over the last 15 years with the introduction of many new antidepressants that can cause increased levels of serotonin (5-HT) in the central nervous system (CNS). Severe and life-threatening cases are almost exclusively a result of combinations of antidepressants (usually monoamine oxidase inhibitors and selective serotonin reuptake inhibitors). Unfortunately, the term serotonin syndrome has a number of quite different meanings, and many people writing on this subject have failed to differentiate them. This has led to false conclusions regarding the 5-HT receptor subtypes responsible for the life-threatening effects in animal and human toxicity, and suggestions of ineffective treatment strategies. This review primarily addresses the serotonin receptor subtypes that underlie the clinical manifestations of excess CNS serotonin in humans and animals, and their implications for diagnosis and treatment. More specific diagnostic criteria for serotonin toxicity are required to identify situations when specific antidotes are likely to be useful. However, the mainstay of treatment of severe cases is good supportive care and early intubation and paralysis in life-threatening serotonin toxicity.

Toxin-induced hyperthermic syndromes

Toxin-induced hyperthermic syndromes are important to consider in the differential diagnosis of patients presenting with fever and muscle rigidity. If untreated, toxin-induced hyperthermia may result in fatal hyperthermia with multisystem organ failure. All of these syndromes have at their center the disruption of normal thermogenic mechanisms, resulting in the activation of the hypothalamus and sympathetic nervous systems.The result of this thermogenic dysregulation is excess heat generation combined with impaired heat dissipation. Although many similarities exist among the clinical presentations and pathophysiologies of toxin-induced hyperthermic syndromes, important differences exist among their triggers and treatments. Serotonin syndrome typically occurs within hours of the addition ofa new serotonergic agent or the abuse of stimulants such as MDMA or methamphetamine. Treatment involves discontinuing the offending agent and administering either a central serotonergic antagonist, such as cyproheptadine or chlorpromazine, a benzodiazepine, or a combination of the two. NMS typically occurs over hours to days in a patient taking a neuroleptic agent; its recommended treatment is generally the combination of a central dopamine agonist, bromocriptine or L-dopa, and dantrolene. In those patients in whom it is difficult to differentiate between serotonin and neuroleptic malignant syndromes, the physical examination may be helpful:clonus and hyperreflexia are more suggestive of serotonin syndrome,whereas lead-pipe rigidity is suggestive of NMS. In patients in whom serotonin syndrome and NMS cannot be differentiated, benzodiazepines represent the safest therapeutic option. MH presents rapidly with jaw rigidity, hyperthermia, and hypercarbia. Although it almost always occurs in the setting of surgical anesthesia, cases have occurred in susceptible individuals during exertion. The treatment of MH involves the use of dantrolene. Future improvements in understanding the pathophysiology and clinical presentations of these syndromes will undoubtedly result in earlier recognition and better treatment strategies.

Monoamine oxidase inhibitors, opioid analgesics and serotonin toxicity

Toxicity resulting from excessive intra-synaptic serotonin, historically referred to as serotonin syndrome, is now understood to be an intra-synaptic serotonin concentration-related phenomenon. Recent research more clearly delineates serotonin toxicity as a discreet toxidrome characterized by clonus, hyper-reflexia, hyperthermia and agitation. Serotonergic side-effects occur with serotonergic drugs, and overdoses of serotonin re-uptake inhibitors (SRIs) frequently produce marked serotonergic side-effects, and in 15% of cases, moderate serotonergic toxicity, but not to a severe degree, which produces hyperthermia and risk of death. It is only combinations of serotonergic drugs acting by different mechanisms that are capable of raising intra-synaptic serotonin to a level that is life threatening. The combination that most commonly does this is a monoamine oxidase inhibitor (MAOI) drug combined with any SRI. There are a number of lesser-known drugs that are MAOIs, such as linezolid and moclobemide; and some opioid analgesics have serotonergic activity. These properties when combined can precipitate life threatening serotonin toxicity. Possibly preventable deaths are still occurring. Knowledge of the properties of these drugs will therefore help to ensure that problems can be avoided in most clinical situations, and treated appropriately (with 5-HT(2A) antagonists for severe cases) if they occur. The phenylpiperidine series opioids, pethidine (meperidine), tramadol, methadone and dextromethorphan and propoxyphene, appear to be weak serotonin re-uptake inhibitors and have all been involved in serotonin toxicity reactions with MAOIs (including some fatalities). Morphine, codeine, oxycodone and buprenorphine are known not to be SRIs, and do not precipitate serotonin toxicity with MAOIs.

Gastric pentadecapeptide BPC 157 effective against serotonin syndrome in rats

Serotonin syndrome commonly follows irreversible monoamine oxidase (MAO)-inhibition and subsequent serotonin (5-HT) substrate (in rats with fore paw treading, hind limbs abduction, wet dog shake, hypothermia followed by hyperthermia). A stable gastric pentadecapeptide BPC 157 with very safe profile (inflammatory bowel disease clinical phase II, PL-10, PLD-116, PL-14736, Pliva) reduced the duration of immobility to a greater extent than imipramine, and, given peripherally, has region specific influence on brain 5-HT synthesis (alpha-[14C]methyl-L-tryptophan autoradiographic measurements) in rats, different from any other serotonergic drug. Thereby, we investigate this peptide (10 microg, 10 ng, 10 pg/kg i.p.) in (i) full serotonin syndrome in rat combining pargyline (irreversible MAO-inhibition; 75 mg/kg i.p.) and subsequent L-tryptophan (5-HT precursor; 100 mg/kg i.p.; BPC 157 as a co-treatment), or (ii, iii) using pargyline or L-tryptophan given separately, as a serotonin-substrate with (ii) pargyline (BPC 157 as a 15-min posttreatment) or as a potential serotonin syndrome inductor with (iii) L-tryptophan (BPC 157 as a 15 min-pretreatment). In all experiments, gastric pentadecapeptide BPC 157 contrasts with serotonin-syndrome either (i) presentation (i.e., particularly counteracted) or (ii) initiation (i.e., neither a serotonin substrate (counteraction of pargyline), nor an inductor for serotonin syndrome (no influence on L-tryptophan challenge)). Indicatively, severe serotonin syndrome in pargyline + L-tryptophan rats is considerably inhibited even by lower pentadecapeptide BPC 157 doses regimens (particularly disturbances such as hyperthermia and wet dog shake thought to be related to stimulation of 5-HT2A receptors), while the highest pentadecapeptide dose counteracts mild disturbances present in pargyline rats (mild hypothermia, feeble hind limbs abduction). Thereby, in severe serotonin syndrome, gastric pentadecapeptide BPC 157 (alone, no behavioral or temperature effect) has a beneficial activity, which is likely, particular, and mostly related to a rather specific counteraction of 5-HT2A receptors phenomena.

The role of the sympathetic nervous system and uncoupling proteins in the thermogenesis induced by 3,4-methylenedioxymethamphetamine

Body temperature regulation involves a homeostatic balance between heat production and dissipation. Sympathetic agents such as 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) can disrupt this balance and as a result produce an often life-threatening hyperthermia. The hyperthermia induced by MDMA appears to result from the activation of the sympathetic nervous system (SNS) and the hypothalamic-pituitary-thyroid/adrenal axis. Norepinephrine release mediated by MDMA creates a double-edged sword of heat generation through activation of uncoupling protein (UCP3) along with alpha1- and beta3-adrenoreceptors and loss of heat dissipation through SNS-mediated vasoconstriction. This review examines cellular mechanisms involved in MDMA-induced thermogenesis from UCP activation to vasoconstriction and how these mechanisms are related to other thermogenic conditions and potential treatment modalities.

5HT1A serotonin receptor agonists inhibit Plasmodium falciparum by blocking a membrane channel

To identify new leads for the treatment of Plasmodium falciparum malaria, we screened a panel of serotonin (5-hydroxytryptamine [5HT]) receptor agonists and antagonists and determined their effects on parasite growth. The 5HT1A receptor agonists 8-hydroxy-N-(di-n-propyl)-aminotetralin (8-OH-DPAT), 2,5-dimethoxy-4-iodoamphetamine, and 2,5-dimethoxy-4-bromophenylethylamine inhibited the growth of P. falciparum in vitro (50% inhibitory concentrations, 0.4, 0.7, and 1.5 microM, respectively). In further characterizing the antiparasitic effects of 8-OH-DPAT, we found that this serotonin receptor agonist did not affect the growth of Leishmania infantum, Trypanosoma cruzi, Trypanosoma brucei brucei, or Trichostrongylus colubriformis in vitro and did not demonstrate cytotoxicity against the human lung fibroblast cell line MRC-5. 8-OH-DPAT had similar levels of growth inhibition against several different P. falciparum isolates having distinct chemotherapeutic resistance phenotypes, and its antimalarial effect was additive when it was used in combination with chloroquine against a chloroquine-resistant isolate. In a patch clamp assay, 8-OH-DPAT blocked a P. falciparum surface membrane channel, suggesting that serotonin receptor agonists are a novel class of antimalarials that target a nutrient transport pathway. Since there may be neurological involvement with the use of 8-OH-DPAT and other serotonin receptor agonists in the treatment of falciparum malaria, new lead compounds derived from 8-OH-DPAT will need to be modified to prevent potential neurological side effects. Nevertheless, these results suggest that 8-OH-DPAT is a new lead compound with which to derive novel antimalarial agents and is a useful tool with which to characterize P. falciparum membrane channels.

Differences in hypothalamic Fos expressions between two heat stress conditions in conscious mice

Hyperthermia and dehydration were important physiological phenomena in heat stress. But, the degrees of these phenomena were changed by heat stress conditions, and the distinction between both phenomena is necessary for investigation of response for individual phenomenon. Heat stress at 34 degrees C for 60 min increased rectal temperature, and heat stress at 38.5 degrees C for 60 min further increased rectal temperature and increased osmolality in mice. We investigated the activated region in hypothalamus, which played a role in thermoregulation, fluid regulation and so on, using immunostaining for Fos protein under these conditions in conscious mice. At 34 degrees C, Fos-positive neurons increased in the median preoptic nucleus, lateral preoptic area and anterior hypothalamic area, which were known to be the thermoregulatory center, and the dorsomedial hypothalamic nucleus, which was known to control eating. At 38.5 degrees C, Fos-positive neurons further increased in the regions mentioned above and appeared in the lateral septal nucleus, medial preoptic area, lateral hypothalamic area and zona incerta, which were thought to be involved in thermoregulation and/or fluid regulation, and the paraventricular hypothalamic nucleus, supraoptic nucleus and supraoptic nucleus in the retrochiasmatic part, which were known to be involved in neuroendocrine effector systems. These results support that the activated regions in hypothalamus differed with heat stress conditions, which induced only hyperthermia and both hyperthermia and dehydration.

Systemic 5-hydroxy-L-tryptophan down-regulates the arcuate CART mRNA level in rats

This study was conducted to determine if serotonin (5-hydroxytryptamine; 5-HT) system correlates with the hypothalamic expression of cocaine-amphetamine-regulated transcript (CART) gene. Rats received intraperitoneal 5-hydroxy-L-tryptophan (5-HTP; a single or three daily injections at a dose of 100 mg/kg/10 ml), and CART mRNA level in the hypothalamus was examined by in situ hybridization at different time points. The 5-HT contents of the hypothalamus as well as the brainstem was increased persistently by 5-HTP injections, and food intake and body weight gain reduced. CART mRNA level decreased significantly in the hypothalamic arcuate nucleus by three daily 5-HTP, but not by a single injection. The pair-fed group of the chronic 5-HTP did not show a decrease in the arcuate CART mRNA level. The plasma leptin level markedly decreased in the chronic 5-HTP group, compared to the saline group, however, still higher than the pair-fed group with a statistical significance. These results suggest that 5-HT may suppress CART mRNA expression in the arcuate nucleus, not only by leptin signaling via its anorectic effect on the control of food intake, but also by some non-leptin mediated pathway.