Synergistic action of 5-HT2A antagonists and selective serotonin reuptake inhibitors in neuropsychiatric disorders

Discovery and in vitro Evaluation of Novel Serotonin 5-HT2A Receptor Ligands Identified Through Virtual Screening

The 5-HT2A receptor is a molecular target of high pharmacological importance. Ligands of this protein, particularly atypical antipsychotics, are useful in the treatment of numerous mental disorders, including schizophrenia and major depressive disorder. Structure-based virtual screening using a 5-HT2A receptor complex was performed to identify novel ligands for the 5-HT2A receptor, serving as potential antidepressants. From the Enamine screening library, containing over 4 million compounds, 48 molecules were selected for subsequent experimental validation. These compounds were tested against the 5-HT2A receptor in radioligand binding assays. From the tested batch, six molecules were identified as ligands of the main molecular target and were forwarded to a more detailed in vitro profiling. This included radioligand binding assays at 5-HT1A, 5-HT7, and D2 receptors and functional studies at 5-HT2A receptors. These compounds were confirmed to show a binding affinity for at least one of the targets tested in vitro. The success rate for the inactive template-based screening reached 17 %, while it was 9 % for the active template-based screening. Similarity and fragment analysis indicated the structural novelty of the identified compounds. Pharmacokinetics for these molecules was determined using in silico approaches.

Involvement of serotonergic receptors in depressive processes and their modulation by β-arrestins: A review

Over time, several studies have been conducted to demonstrate the functions of the neurotransmitter 5-hydroxytryptamine (5-HT), better known as serotonin. This neurotransmitter is associated with the modulation of various social and physiological behaviors, and its dysregulation has consequences at the behavioral level, leading to various neurophysiological disorders. Disorders such as anxiety, depression, schizophrenia, epilepsy, sexual disorders, and eating disorders, have been closely linked to variations in 5-HT concentrations and modifications in brain structures, including the raphe nuclei (RN), prefrontal cortex, basal ganglia, hippocampus, and hypothalamus, among others. The involvement of β-arrestin proteins has been implicated in the modulation of the serotonergic receptor response, as well as the activation of different signaling pathways related to the serotonergic system, this is particularly relevant in depressive disorders. This review will cover the implications of alterations in 5-HT receptor expression in depressive disorders in one hand and how β-arrestin proteins modulate the response mediated by these receptors in the other hand.

PET/CT study of dopamine transporter (DAT) binding with the triple reuptake inhibitor toludesvenlafaxine in rats and humans

PURPOSE

Toludesvenlafaxine is a recently developed antidepressant that belongs to the triple reuptake inhibitor class. Despite the in vitro evidence that toludesvenlafaxine inhibits the reuptake of serotonin (5-HT), norepinephrine (NE) and dopamine (DA), there is no in vivo evidence that toludesvenlafaxine binds to DAT and increases DA level, a mechanism thought to contribute to its favorable clinical performance.

METHODS

Positron emission tomography/computed tomography (PET/CT) was used to examine the DAT binding capacity in healthy rats and human subjects and microdialysis was used to examine the striatal DA level in rats. [18F]FECNT and [11C]CFT were used as PET/CT radioactive tracer for rat and human studies, respectively.

RESULTS

In rats, 9 mg/kg of toludesvenlafaxine hydrochloride (i.v.) followed by an infusion of 3 mg/kg via minipump led to the binding rate to striatum DAT at 3.7 - 32.41% and to hypothalamus DAT at 5.91 - 17.52% during the 45 min scanning period. 32 mg/kg oral administration with toludesvenlafaxine hydrochloride significantly increased the striatal DA level with the AUC0 - 180 min increased by 63.9%. In healthy volunteers, 160 mg daily toludesvenlafaxine hydrochloride sustained-release tablets for 4 days led to an average occupancy rates of DAT at 8.04% ± 7.75% and 8.09% ± 7.00%, respectively, in basal ganglion 6 h and 10 h postdose.

CONCLUSION

These results represent the first to confirm the binding of toludesvenlafaxine to DAT in both rats and humans using PET/CT, and its elevation of brain DA level, which may help understand the unique pharmacological and functional effects of triple reuptake inhibitors such as toludesvenlafaxine.

CLINICALTRIALS

GOV IDENTIFIERS

NCT05905120. Registered 14 June 2023. (retrospectively registered).

Multicomponent Synthesis of α-Branched Amines via a Zinc-Mediated Carbonyl Alkylative Amination Reaction

Methods for the synthesis of α-branched alkylamines are important due to their ubiquity in biologically active molecules. Despite the development of many methods for amine preparation, C(sp3)-rich nitrogen-containing compounds continue to pose challenges for synthesis. While carbonyl reductive amination (CRA) between ketones and alkylamines is the cornerstone method for α-branched alkylamine synthesis, it is sometimes limited by the sterically demanding condensation step between dialkyl ketones and amines and the more restricted availability of ketones compared to aldehydes. We recently reported a "higher-order" variant of this transformation, carbonyl alkylative amination (CAA), which utilized a halogen atom transfer (XAT)-mediated radical mechanism, enabling the streamlined synthesis of complex α-branched alkylamines. Despite the efficacy of this visible-light-driven approach, it displayed scalability issues, and competitive reductive amination was a problem for certain substrate classes, limiting applicability. Here, we report a change in the reaction regime that expands the CAA platform through the realization of an extremely broad zinc-mediated CAA reaction. This new strategy enabled elimination of competitive CRA, simplified purification, and improved reaction scope. Furthermore, this new reaction harnessed carboxylic acid derivatives as alkyl donors and facilitated the synthesis of α-trialkyl tertiary amines, which cannot be accessed via CRA. This Zn-mediated CAA reaction can be carried out at a variety of scales, from a 10 μmol setup in microtiter plates enabling high-throughput experimentation, to the gram-scale synthesis of medicinally-relevant compounds. We believe that this transformation enables robust, efficient, and economical access to α-branched alkylamines and provides a viable alternative to the current benchmark methods.

Progesterone receptor distribution in the human hypothalamus and its association with suicide

The human hypothalamus modulates mental health by balancing interactions between hormonal fluctuations and stress responses. Stress-induced progesterone release activates progesterone receptors (PR) in the human brain and triggers alterations in neuropeptides/neurotransmitters. As recent epidemiological studies have associated peripheral progesterone levels with suicide risks in humans, we mapped PR distribution in the human hypothalamus in relation to age and sex and characterized its (co-) expression in specific cell types. The infundibular nucleus (INF) appeared to be the primary hypothalamic structure via which progesterone modulates stress-related neural circuitry. An elevation of the number of pro-opiomelanocortin+ (POMC, an endogenous opioid precursor) neurons in the INF, which was due to a high proportion of POMC+ neurons that co-expressed PR, was related to suicide in patients with mood disorders (MD). MD donors who died of legal euthanasia were for the first time enrolled in a postmortem study to investigate the molecular signatures related to fatal suicidal ideations. They had a higher proportion of PR co-expressing POMC+ neurons than MD patients who died naturally. This indicates that the onset of endogenous opioid activation in MD with suicide tendency may be progesterone-associated. Our findings may have implications for users of progesterone-enriched contraceptives who also have MD and suicidal tendencies.

Trazodone in the Management of Major Depression Among Elderly Patients with Dementia: A Narrative Review and Clinical Insights

Objective

Major depressive disorder (MDD) often co-occurs with dementia and other neurological disorders, and treatment with antidepressants can improve symptoms, quality of life, and survival in these patients. This narrative review provides an expert opinion about the role and effectiveness of trazodone in the treatment of older adults with MDD and cognitive impairment due to physical illnesses, such as dementia.

Results

Because of its mechanism of action, trazodone can treat several depression symptoms often seen in people with dementia, including insomnia, agitation, anxiety, cognitive impairment, and irritability.

Conclusion

Trazodone may be beneficial for patients with dementia or other neurological disorders comorbid with MDD, especially when the clinical picture of depression includes or is comorbid to symptoms of insomnia, irritability, inner tension, anxiety, or psychomotor agitation.

D1R-5-HT2AR Uncoupling Reduces Depressive Behaviours via HDAC Signalling

Dopamine and serotonin signalling are associated with major depressive disorder, which is a prevalent life-threatening illness worldwide. Numerous FDA-approved dopamine/serotonin signalling-modifying drugs are available but are associated with concurrent side effects and limited efficacy. Thus, identifying and targeting their signalling pathway is crucial for improving depression treatment. Here, we determined that serotonin receptor 2A (5-HT2AR) abundantly forms a protein complex with dopamine receptor 1 (D1R) in high abundance via its carboxy-terminus in the brains of mice subjected to various chronic stress paradigms. Furthermore, the D1R/5-HT2AR interaction elicited CREB/ERK/AKT modulation during synaptic regulation. An interfering peptide (TAT-5-HT2AR-SV) agitated the D1R/5-HT2AR interaction and attenuated depressive symptoms accompanied by CREB/ERK molecule costimulation. Interestingly, HDAC antagonism but not TrkB antagonism reversed the antidepressant effect of competitive peptides. These findings revealed a novel D1R/5-HT2AR heteroreceptor complex mechanism in the pathophysiology of depression, and their uncoupling ameliorates depressive-like behaviours through HDAC-, and not BDNF-, dependent mechanisms.

Obsessive-compulsive disorder: Etiology, neuropathology, and cognitive dysfunction

BACKGROUND

This review provides an overview of obsessive-compulsive disorder (OCD) symptoms, including the four partially distinct subtypes of the disorder, current diagnostic criteria, and common comorbidities. Critically, it focuses on the etiology of OCD, including its underlying neuropathology, and examines cognitive dysfunction in OCD.

METHODS

This review study was conducted by library method.

RESULTS

We show how dysfunction in cortico-striato-thalamo-cortical (CSTC) circuits may underpin symptoms; and shed light on the putative neurochemistry within these loops such as the role of serotonin, dopamine, and glutamate systems. We also show how OCD is characterized by cognitive dysfunction including problems in cognitive flexibility, visuospatial memory, response inhibition, and goal-directed behavior, linked to aberrant activity within CSTC circuits.

CONCLUSIONS

In brief, research questions we shed light on include (1) what are the symptoms in OCD; (2) what is the etiology of the disorder and do existing models explain OCD; and (3) what are key cognitive deficits in OCD and do these improve with treatment?

Macronutrients and the state of happiness and mood in undergraduate youth of a military training course

BACKGROUND AND AIMS

Previous studies have reported a high prevalence of mental disorders among military organizations. Depression and anxiety are among the most important mental disorders, and depression, suicidal ideation, and violence have been found to be negatively associated with happiness and social support. Therefore, improving mood and increasing happiness can reduce the prevalence of mental disorders in military centers. Diet can improve happiness through specific molecular mechanisms and change our mood by affecting the chemical composition of the brain. Therefore, the present study examined the relationship between the quality and quantity of macronutrients in soldiers' diets with their mood and happiness.

METHODS

In the current cross-sectional study, 300 healthy soldiers were selected. Food intake data was collected using 168-item semi-quantitative food frequency questionnaire during the last year of their military training 2-year period. Then, we calculated the quality and quantity of macronutrients. Mood was assessed using the Profile of Mood States (POMS) questionnaire and happiness with the Oxford Happiness Questionnaire (OHQ).

RESULTS

The mean ± standard deviation of participants' age was 23.70 ± 1.76 years. A significant relationship was observed between mood score and carbohydrate quantity (OR: 0.32, 95% CI: 0.12-0.88, P-value for trend = 0.03). This suggests that increasing carbohydrate intake improved the participants' mood. No association was found between mood score with protein quantity (OR: 2.15, 95% CI: 0.80-5.75; P-value for trend = 0.12), and gram of fat intake (OR: 1.95, 95% CI: 0.74-5.13; P-value for trend = 0.15). None of the indicators related to macronutrient quality were significantly associated with happiness and mood scores in young soldiers (P ≥ 0.05).

CONCLUSIONS

Findings presented in this study showed that increased carbohydrate intake was significantly associated with better mood. However, mood is not related to the amount of proteins and fats and none of the parameters of macronutrient quality. Also, there was no significant relationship between the quantity and quality of macronutrients with happiness score.

An Overview of Physiologically-Based Pharmacokinetic Models for Forensic Science

A physiologically-based pharmacokinetic (PBPK) model represents the structural components of the body with physiologically relevant compartments connected via blood flow rates described by mathematical equations to determine drug disposition. PBPK models are used in the pharmaceutical sector for drug development, precision medicine, and the chemical industry to predict safe levels of exposure during the registration of chemical substances. However, one area of application where PBPK models have been scarcely used is forensic science. In this review, we give an overview of PBPK models successfully developed for several illicit drugs and environmental chemicals that could be applied for forensic interpretation, highlighting the gaps, uncertainties, and limitations.

The Burden of Carbohydrates in Health and Disease

Foods high in carbohydrates are an important part of a healthy diet, since they provide the body with glucose to support bodily functions and physical activity. However, the abusive consumption of refined, simple, and low-quality carbohydrates has a direct implication on the physical and mental pathophysiology. Then, carbohydrate consumption is postulated as a crucial factor in the development of the main Western diseases of the 21st century. We conducted this narrative critical review using MedLine (Pubmed), Cochrane (Wiley), Embase, and CinAhl databases with the MeSH-compliant keywords: carbohydrates and evolution, development, phylogenetic, GUT, microbiota, stress, metabolic health, consumption behaviors, metabolic disease, cardiovascular disease, mental disease, anxiety, depression, cancer, chronic kidney failure, allergies, and asthma in order to analyze the impact of carbohydrates on health. Evidence suggests that carbohydrates, especially fiber, are beneficial for the well-being and growth of gut microorganisms and consequently for the host in this symbiotic relationship, producing microbial alterations a negative effect on mental health and different organic systems. In addition, evidence suggests a negative impact of simple carbohydrates and refined carbohydrates on mood categories, including alertness and tiredness, reinforcing a vicious circle. Regarding physical health, sugar intake can affect the development and prognosis of metabolic disease, as an uncontrolled intake of refined carbohydrates puts individuals at risk of developing metabolic syndrome and subsequently developing metabolic disease.

In vitro and in vivo pharmacological characterization of dasotraline, a dual dopamine and norepinephrine transporter inhibitor in vivo

Inhibitors of dopamine transporters (DAT), norepinephrine transporters (NET) and serotonin transporters (SERT) are effective treatments for neuropsychiatric diseases. Dasotraline [(1R,4 S)- 4-(3,4-dichlorophenyl)- 1,2,3,4-tetrahydro-1-naphthalenamine, also known as SEP-225289) was evaluated for its inhibitory potency at DAT, NET and SERT using in vitro and in vivo assays. In vitro radiometric functional uptake studies showed preferential inhibition by dasotraline of hDAT (IC₅₀ =3 nM) and hNET (IC₅₀ =4 nM relative to hSERT(IC₅₀ =15 nM). In mouse ex vivo occupancy studies, dasotraline demonstrated total plasma concentration-dependent occupancy at DAT, NET and SERT. Determination of the TO₅₀ (50% transporter occupancy) were 32, 109 and 276 ng/ml, respectively. In SPECT imaging studies in baboons, dasotraline (0.2 mg/kg iv) displaced radiotracer binding to DAT by 87% but only 20% at NET and SERT. Rat microdialysis studies were performed in prefrontal cortex and striatum. Dasotraline produced sustained (>4 h) increases in dopamine and norepinephrine concentrations. Dasotraline was also more potent at increasing synaptic dopamine in the striatum, and norepinephrine in the prefrontal cortex than serotonin in these regions. In summary, dasotraline preferentially inhibits DAT and NET relative to SERT. Together, the occupancy and neurochemical profile of dasotraline provide a mechanistic basis for the treatment of diseases that have an underlying causality involving dopamine and norepinephrine dysfunction.

A serotonergic biobehavioral signature differentiates cocaine use disorder participants administered mirtazapine

Cocaine use disorder (CUD) patients display heterogenous symptoms and unforeseeable responses to available treatment approaches, highlighting the need to identify objective, accessible biobehavioral signatures to predict clinical trial success in this population. In the present experiments, we employed a task-based behavioral and pharmacogenetic-fMRI approach to address this gap. Craving, an intense desire to take cocaine, can be evoked by exposure to cocaine-associated stimuli which can trigger relapse during attempted recovery. Attentional bias towards cocaine-associated words is linked to enhanced effective connectivity (EC) from the anterior cingulate cortex (ACC) to hippocampus in CUD participants, an observation which was replicated in a new cohort of participants in the present studies. Serotonin regulates attentional bias to cocaine and the serotonergic antagonist mirtazapine decreased activated EC associated with attentional bias, with greater effectiveness in those CUD participants carrying the wild-type 5-HT2CR gene relative to a 5-HT2CR single nucleotide polymorphism (rs6318). These data suggest that the wild-type 5-HT2CR is necessary for the efficacy of mirtazapine to decrease activated EC in CUD participants and that mirtazapine may serve as an abstinence enhancer to mitigate brain substrates of craving in response to cocaine-associated stimuli in participants with this pharmacogenetic descriptor. These results are distinctive in outlining a richer "fingerprint" of the complex neurocircuitry, behavior and pharmacogenetics profile of CUD participants which may provide insight into success of future medications development projects.

Recent developments in the management of Huntington's disease

Huntington's disease (HD) is a rare, incurable, inheritedneurodegenerative disorder manifested by chorea, hyperkinetic, and hypokinetic movements. The FDA has approved only two drugs, viz. tetrabenazine, and deutetrabenazine, to manage the chorea associated with HD. However, several other drugs are used as an off-label to manage chorea and other symptoms such as depression, anxiety, muscle tremors, and cognitive dysfunction associated with HD. So far, there is no disease-modifying treatment available. Drug repurposing has been a primary drive to search for new anti-HD drugs. Numerous molecular targets along with a wide range of small molecules and gene therapies are currently under clinical investigation. More than 200 clinical studies are underway for HD, 75% are interventional, and 25% are observational studies. The present review discusses the small molecule clinical pipeline and molecular targets for HD. Furthermore, the biomarkers, diagnostic tests, gene therapies, behavioral and observational studies for HD were also deliberated.

Human Cortical Serotonin 2A Receptor Occupancy by Psilocybin Measured Using [11C]MDL 100,907 Dynamic PET and a Resting-State fMRI-Based Brain Parcellation

Psilocybin (a serotonin 2A, or 5-HT2A, receptor agonist) has shown preliminary efficacy as a treatment for mood and substance use disorders. The current report utilized positron emission tomography (PET) with the selective 5-HT2A receptor inverse agonist radioligand [11C]MDL 100,907 (a.k.a. M100,907) and cortical regions of interest (ROIs) derived from resting-state functional connectivity-based brain parcellations in 4 healthy volunteers (2 females) to determine regional occupancy/target engagement of 5-HT2A receptors after oral administration of a psychoactive dose of psilocybin (10 mg/70 kg). Average 5-HT2A receptor occupancy across all ROIs was 39.5% (± 10.9% SD). Three of the ROIs with greatest occupancy (between 63.12 and 74.72% occupancy) were within the default mode network (subgenual anterior cingulate and bilateral angular gyri). However, marked individual variability in regional occupancy was observed across individuals. These data support further investigation of the relationship between individual differences in the acute and enduring effects of psilocybin and the degree of regional 5-HT2A receptor occupancy.

Overcoming Depression with 5-HT2A Receptor Ligands

Depression is a multifactorial disorder that affects millions of people worldwide, and none of the currently available therapeutics can completely cure it. Thus, there is a need for developing novel, potent, and safer agents. Recent medicinal chemistry findings on the structure and function of the serotonin 2A (5-HT2A) receptor facilitated design and discovery of novel compounds with antidepressant action. Eligible papers highlighting the importance of 5-HT2A receptors in the pathomechanism of the disorder were identified in the content-screening performed on the popular databases (PubMed, Google Scholar). Articles were critically assessed based on their titles and abstracts. The most accurate papers were chosen to be read and presented in the manuscript. The review summarizes current knowledge on the applicability of 5-HT2A receptor signaling modulators in the treatment of depression. It provides an insight into the structural and physiological features of this receptor. Moreover, it presents an overview of recently conducted virtual screening campaigns aiming to identify novel, potent 5-HT2A receptor ligands and additional data on currently synthesized ligands acting through this protein.

5-HT Receptors and the Development of New Antidepressants

Serotonin modulates several physiological and cognitive pathways throughout the human body that affect emotions, memory, sleep, and thermal regulation. The complex nature of the serotonergic system and interactions with other neurochemical systems indicate that the development of depression may be mediated by various pathomechanisms, the common denominator of which is undoubtedly the disturbed transmission in central 5-HT synapses. Therefore, the deliberate pharmacological modulation of serotonergic transmission in the brain seems to be one of the most appropriate strategies for the search for new antidepressants. As discussed in this review, the serotonergic system offers great potential for the development of new antidepressant therapies based on the combination of SERT inhibition with different pharmacological activity towards the 5-HT system. The aim of this article is to summarize the search for new antidepressants in recent years, focusing primarily on the possibility of benefiting from interactions with various 5-HT receptors in the pharmacotherapy of depression.

A Complex Impact of Systemically Administered 5-HT2A Receptor Ligands on Conditioned Fear

BACKGROUND

Though drugs binding to serotonergic 5-HT2A receptors have long been claimed to influence human anxiety, it remains unclear if this receptor subtype is best described as anxiety promoting or anxiety dampening. Whereas conditioned fear expressed as freezing in rats is modified by application of 5-HT2A-acting drugs locally into different brain regions, reports on the effect of systemic administration of 5-HT2A receptor agonists and 5-HT2A antagonists or inverse agonists on this behavior remain sparse.

METHODS

We assessed the possible impact of systemic administration of 5-HT2A receptor agonists, 5-HT2A receptor inverse agonists, and a selective serotonin reuptake inhibitor (SSRI)-per se or in combination-on the freezing displayed by male rats when re-exposed to a conditioning chamber in which they received foot shocks 7 days earlier.

RESULTS

The 5-HT2A receptor agonists psilocybin and 25CN-NBOH induced a reduction in conditioned fear that was countered by pretreatment with 5-HT2A receptor inverse agonist MDL 100907. While both MDL 100907 and another 5-HT2A receptor inverse agonist, pimavanserin, failed to impact freezing per se, both compounds unmasked a robust fear-reducing effect of an SSRI, escitalopram, which by itself exerted no such effect.

CONCLUSIONS

The results indicate that 5-HT2A receptor activation is not a prerequisite for normal conditioned freezing in rats but that this receptor subtype, when selectively over-activated prior to expression, exerts a marked fear-reducing influence. However, in the presence of an SSRI, the 5-HT2A receptor, on the contrary, appears to counter an anti-freezing effect of the enhanced extracellular serotonin levels following reuptake inhibition.

Association between autism spectrum disorder and polymorphisms in genes encoding serotine and dopamine receptors

Dysfunctions of the neurotransmitter system are related to the development of many psychological diseases including autism spectrum disorder (ASD). Single nucleotide polymorphisms (SNPs) are correlated with varied susceptibility of ASD and response to treatments. The association between SNPs in genes encoding serotonin and dopamine receptors and childhood ASD was examined in a Chinese Han population. Both autistic children (n = 319) and age-and gender-matched healthy controls (n = 347) were recruited from a local district. Disease severity was evaluated by the childhood autism rating scale (CARS). SNPs of rs6311 and rs6313 in the serotonin receptor HTR2A gene, rs4630328 in the dopamine receptor D2 (DRD2) gene and rs167771 in the DRD3 gene were examined. The CC genotype of rs6311 was significantly associated with an increased risk of ASD (odds ratio (OD) = 1.8 vs TT, 95% confidence interval (CI): 1.2-2.8, P = 0.0085). Carriers of the C allele of rs6311 had a significantly higher risk of childhood ASD (OD =1.3, 95% CI = 1.1-1.7, P = 0.0094). A strong linkage disequilibrium was observed between rs6311 and rs6313 (D' = 0.93, r² = 0.86). There were significant correlations between haplotypes (T-A and C-G of rs6311-rs6313) and risk of childhood ASD. In contrast, the frequencies of genotypes and alleles of rs6313, rs4630328 and rs167771 were not significantly different between the case and control groups. All the SNPs examined were not associated with severity of the disease. Our study demonstrates that certain SNPs in the HTR2A gene, but not the DRD2 and DRD3, are associated with susceptibility to childhood ASD.

Early response to trazodone once-a-day in major depressive disorder: review of the clinical data and putative mechanism for faster onset of action

BACKGROUND

Most antidepressants have a delayed onset of action and must be administered for several weeks to generate therapeutic effects. Trazodone is a serotonin antagonist and reuptake inhibitor approved for the treatment of major depressive disorder. The once-a-day (OAD) formulation of trazodone has an improved tolerability profile compared to its conventional formulations. In this study, we systematically reviewed the evidence available for the antidepressant efficacy and early improvement in depressive symptoms with trazodone OAD treatment.

METHOD

We conducted a PubMed database search for randomized controlled trials published from 2005 to 2020.

RESULTS

Two studies, a placebo-controlled and an active-comparator (venlafaxine extended-release or XR) study were found. Both the studies demonstrated that trazodone exhibits antidepressant activity at a starting dose of 150 mg/day and results in statistically significant greater reduction in Hamilton Depression Rating Scale (HAM-D17) scores within 1 week of starting treatment compared to placebo or venlafaxine XR (P < .05). Trazodone also resulted in significant early improvement in the HAM-D17 sleep disturbance factor compared to placebo or venlafaxine XR at day 7 (P < .05). This clinical effect is supported by in vitro proprietary data for the affinity of trazodone for different target receptors. Activity at these receptors may underlie trazodone's fast antidepressant action.

CONCLUSIONS

Trazodone, if properly dosed, can be an effective antidepressant with early onset of action and good tolerability. Future studies designed to specifically evaluate onset and timing of improvement of depressive symptoms remain necessary to confirm and extend these results.

R (-)-methoxetamine exerts rapid and sustained antidepressant effects and fewer behavioral side effects relative to S (+)-methoxetamine

The newfound antidepressant efficacy of ketamine has provided opportunities for the development of new-generation, rapid-acting, glutamate-based antidepressants. We previously identified that methoxetamine (MXE), a ketamine analog, and an N-Methyl-d-aspartate (NMDA) receptor antagonist, produced rapid and sustained antidepressant effects in mice. MXE (R, S (±)-MXE) is a racemic mixture containing equal parts of S (+)-MXE and R (-)-MXE. However, studies have yet to investigate the antidepressant effects of its enantiomers. Here, we examined the potential antidepressant properties and behavioral side effects of S- and R-MXE in mice. Both S- and R-MXE showed significant NMDA receptor affinity and appreciable inhibitory activity on serotonin transporter. Also, S- and R-MXE (10 mg kg^-1) exerted antidepressant effects and increased gamma waves (electroencephalography) but were inhibited by NBQX (an AMPA receptor antagonist). Subsequently, they increased mammalian target of rapamycin phosphorylation and AMPA receptor subunits GluA1 and GluA2 protein levels in the hippocampus or prefrontal cortex. Furthermore, they increased 5HT2a and 5HT2c receptor mRNA levels in the prefrontal cortex, with their antidepressant effects inhibited by ketanserin (a 5HT2a/c receptor antagonist). Taken together, S-MXE and R-MXE elicit antidepressant effects that are probably mediated via glutamatergic and serotonergic mechanisms. Unlike S-MXE, R-MXE did not induce prepulse inhibition deficits, hyperlocomotion, conditioned place preference, and locomotor sensitization, although it acutely altered motor coordination. This suggests that R-MXE induces fewer behavioral side effects and is a safer antidepressant than S-MXE. Overall, this study provides significant implications for future research on the next generation of rapid-acting, glutamate-based antidepressant drugs.

Changing the Cortical Conductor's Tempo: Neuromodulation of the Claustrum

The claustrum is a thin sheet of neurons that is densely connected to many cortical regions and has been implicated in numerous high-order brain functions. Such brain functions arise from brain states that are influenced by neuromodulatory pathways from the cholinergic basal forebrain, dopaminergic substantia nigra and ventral tegmental area, and serotonergic raphe. Recent revelations that the claustrum receives dense input from these structures have inspired investigation of state-dependent control of the claustrum. Here, we review neuromodulation in the claustrum-from anatomical connectivity to behavioral manipulations-to inform future analyses of claustral function.

Somatostatin interneurons activated by 5-HT2A receptor suppress slow oscillations in medial entorhinal cortex

Serotonin (5-HT) is one of the major neuromodulators present in the mammalian brain and has been shown to play a role in multiple physiological processes. The mechanisms by which 5-HT modulates cortical network activity, however, are not yet fully understood. We investigated the effects of 5-HT on slow oscillations (SOs), a synchronized cortical network activity universally present across species. SOs are observed during anesthesia and are considered to be the default cortical activity pattern. We discovered that (±)3,4-methylenedioxymethamphetamine (MDMA) and fenfluramine, two potent 5-HT releasers, inhibit SOs within the entorhinal cortex (EC) in anesthetized mice. Combining opto- and pharmacogenetic manipulations with in vitro electrophysiological recordings, we uncovered that somatostatin-expressing (Sst) interneurons activated by the 5-HT_2A receptor (5-HT_2AR) play an important role in the suppression of SOs. Since 5-HT_2AR signaling is involved in the etiology of different psychiatric disorders and mediates the psychological effects of many psychoactive serotonergic drugs, we propose that the newly discovered link between Sst interneurons and 5-HT will contribute to our understanding of these complex topics.

Serotonin/dopamine interaction: Electrophysiological and neurochemical evidence

The interaction between serotonin (5-HT) and dopamine (DA) in the central nervous system (CNS) plays an important role in the adaptive properties of living animals to their environment. These are two modulatory, divergent systems shaping and regulating in a widespread manner the activity of neurobiological networks and their interaction. The concept of one interaction linking these two systems is rather elusive when looking at the mechanisms triggered by these two systems across the CNS. The great variety of their interacting mechanisms is in part due to the diversity of their neuronal origin, the density of their fibers in a given CNS region, the distinct expression of their numerous receptors in the CNS, the heterogeneity of their intracellular signaling pathway that depend on the cellular type expressing their receptors, and the state of activity of neurobiological networks, conditioning the outcome of their mutual influences. Thus, originally conceptualized as inhibition of 5-HT on DA neuron activity and DA neurotransmission, this interaction is nowadays considered as a multifaceted, mutual influence of these two systems in the regulation of CNS functions. These new ways of understanding this interaction are of utmost importance to envision the consequences of their dysfunctions underlined in several CNS diseases. It is also essential to conceive the mechanism of action of psychotropic drugs directly acting on their function including antipsychotic, antidepressant, antiparkinsonian, and drug of abuse together with the development of therapeutic strategies of Alzheimer's diseases, epilepsy, obsessional compulsive disorders. The 5-HT/DA interaction has a long history from the serendipitous discovery of antidepressants and antipsychotics to the future, rationalized treatments of CNS disorders.

Cortical influences of serotonin and glutamate on layer V pyramidal neurons

Layer V pyramidal neurons constitute principle output neurons of the medial prefrontal cortex (mPFC)/neocortex to subcortical regions including the intralaminar/midline thalamic nuclei, amygdala, basal ganglia, brainstem nuclei and the spinal cord. The effects of 5-hydroxytryptamine (5-HT) on layer V pyramidal cells primarily reflect a range of excitatory influences through 5-HT_2A receptors and inhibitory influences through non-5-HT_2A receptors, including 5-HT_1A receptors. While the 5-HT_2A receptor is primarily a postsynaptic receptor on throughout the apical dendritic field of 5-HT_2A receptors, activation of a minority of 5-HT_2A receptors also appears to increase spontaneous excitatory postsynaptic currents/potentials (EPSCs/EPSPs) via a presynaptic effect on thalamocortical terminals arising from the midline and intralaminar thalamic nuclei. Activation of 5-HT_2A receptors by the phenethylamine hallucinogen also appears to increase asynchronous release of glutamate upon the layer V pyramidal dendritic field, an effect that is suppressed by 5-HT itself through non-5-HT_2A receptors. Serotonergic hallucinogens acting on 5-HT_2A receptors also appears to increase gene expression of immediate early genes (iEG) and other receptors appearing to induce an iEG-like response like BDNF. Psychedelic hallucinogens acting on 5-HT_2A receptors also induce head twitches in rodents that appear related to induction of glutamate release. These electrophysiological, biochemical and behavioral effects of serotonergic hallucinogens appear to be related to modulating glutamatergic thalamocortical neurotransmission and/or shifting the balance toward 5-HT_2A receptor activation and away from non-5-HT_2A receptor activation. These 5-HT_2A receptor induced responses are modulated by feedback homeostatic mechanisms through mGlu₂, mGlu₄, and mGlu₈ presynaptic receptors on thalamocortical terminals. These 5-HT_2A receptor and glutamatergic interactions also appear to play a role on higher cortical functions of the mPFC such as motoric impulsivity and antidepressant-like behavioral responses on the differential-reinforcement-of low rate 72-s (DRL 72-s schedule). These mutually opposing effects between 5-HT_2A receptor and mGlu autoreceptor activation (e.g., blocking 5-HT_2A receptors and enhancing activity at mGlu₂ receptors) may play a clinical role with respect to currently prescribed or novel antidepressant drugs. Thus, there is an important balance between 5-HT_2A receptor activation and activation of mGlu autoreceptors on prefrontal cortical layer V pyramidal cells with respect to the electrophysiological, biochemical and behavioral effects serotonergic hallucinogenic drugs.

Spotlight on Pimavanserin Tartrate and Its Therapeutic Potential in the Treatment of Major Depressive Disorder: The Evidence to Date

Major depressive disorder (MDD) is widely prevalent and one of the leading causes of disability. Treatment outcomes remain suboptimal with 1 in 3 patients with MDD responding inadequately to commonly used antidepressants. Pimavanserin, an atypical antipsychotic that modulates serotonergic neurotransmission by selectively binding to serotonin receptor (2A and 2C) subtypes and without dopaminergic activity, may have the potential as an adjunctive treatment for MDD. In a phase 2 trial (n=203), addition of pimavanserin, as compared to placebo, to stable treatment with antidepressants was associated with greater reduction in 17-item Hamilton Depression Rating Scale score [HAMD, least square means (95% confidence interval) of -1.7 (-0.03, -3.37), p=0.039]. Furthermore, treatment with pimavanserin was associated with significantly greater improvement in specific symptoms associated with depression such as impaired sexual function, anxiety, sleepiness, and irritability. However, the availability of pimavanserin for clinical care of patients with MDD remains uncertain. Top-line results of phase 3 studies (n=298) that were announced by the sponsor found similar reductions in HAMD (mean baseline-to-week-5 reduction of 9.0 and 8.1, p=0.296) and rates of adverse events (58.1% and 54.7%) with addition of pimavanserin and placebo respectively to stable treatment with antidepressants. Given the potential benefit for specific symptoms such as impaired sexual function, anxiety and sleep/wakefulness disturbances, future studies that enrich for these symptoms may be needed to clarify the utility of adjunctive pimavanserin in treatment of patients with MDD.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Effect of adjunctive pimavanserin on suicidal ideation in patients with major depression: Analysis of the CLARITY study

BACKGROUND

Up to 15% of patients with major depressive disorder (MDD) attempt suicide and up to 2% complete suicide. This was a post-hoc analysis aimed to evaluate the risk of suicide ideation and behavior associated with adjunctive pimavanserin treatment in adults with MDD.

METHODS

CLARITY was a randomized, double-blind, placebo-controlled study in patients with MDD and an inadequate response to a selective serotonin reuptake inhibitor (SSRI) or serotonin-norepinephrine reuptake inhibitor (SNRI). For this post-hoc analysis, the primary endpoint was mean change from baseline for HAMD item 3 (suicide). The incidence of suicidal ideation or behavior was also assessed from the Columbia-Suicide Severity Rating Scale (C-SSRS) and reports of adverse events.

RESULTS

During Stage 1, LS mean change for HAMD Item 3 was reduced from baseline at each week with pimavanserin with a significant difference between pimavanserin and placebo at Week 3 (p=0.012, effect size: 0.431). At any post-baseline assessment, suicidal ideation on the C-SSRS was reported in 28 (18.1%) of patients with placebo and 9 (17.3%) with pimavanserin during Stage 1 and in 7 (20.7%) with placebo and 4 (13.8%) with pimavanserin during Stage 2. No events of suicidal behavior were observed with either placebo or pimavanserin.

LIMITATIONS

The post hoc nature, exclusion of patients with any history of suicide from the primary study, and the small number of patients who demonstrated evidence of suicidal ideation.

CONCLUSIONS

Adjunctive pimavanserin was not associated with an increase in suicidal ideation in patients with MDD. Further study is needed to verify these results.

Stimulation of 5-HT receptors in anterodorsal BNST guides fear to predictable and unpredictable threat

Through pharmacological manipulation of the serotonergic (5-Hydroxytryptamin, 5-HT) system, combined with behavioral analysis, we tested the hypothesis that fear responses to predictable and unpredictable threat are regulated through stimulation of 5-HT receptors (5-HT-R) in the anterodorsal section of the bed nucleus of the stria terminalis (adBNST). Local adBNST application of 5-HT1A-R antagonist WAY100635 and 5-HT1B-R antagonist NAS-181 before fear retrieval enhanced freezing, 24 h after predictable fear conditioning. In contrast, increased fear responses to unpredictable threat were blocked by 5-HT1A-R agonist Buspirone (given before conditioning or retrieval) and 5-HT1B-R agonist CP-94253 (applied before training). Prolonged fear responses were also blocked by local application of the 5-HT2A-R antagonist R-96544 before fear retrieval, and conversely, local application of the 5-HT2A-R agonist NBOH-2C-CN hydrochloride before fear retrieval enhanced freezing 24 h after predictable conditioning, indicating augmented fear responses. Activation of inhibitory 5-HT1A- or 5-HT1B-Rs and the blockade of the excitatory 5-HT2A-R before unpredictable fear conditioning significantly reduced freezing during retrieval. The results from this study suggest that modulation of inhibitory 5-HT1A/1B-R and/or excitatory 5-HT2A-R activity in the adBNST may represent potential targets for the development of new treatment strategies in anxiety disorders. In addition, this study supports the validity and reliability of the mouse model of modulated fear to predictable and unpredictable threats to study mechanisms of fear and anxiety in combination with pharmacological manipulations.

Expression of serotonin 1A and 2A receptors in molecular- and projection-defined neurons of the mouse insular cortex

The serotonin (5-HT) system is the target of multiple anxiolytics, including Buspirone, which is a partial agonist of the serotonin 1A receptor (5-HT1A). Similarly, ligands of the serotonin 2A receptor (5-HT2A) were shown to alter anxiety level. The 5-HT1A and 2A receptors are widely expressed across the brain, but the target region(s) underlying the influence of those receptors on anxiety remain unknown. Interestingly, recent studies in human and non-human primates have shown that the 5-HT1A and 5-HT2A binding potentials within the insular cortex (insula) are correlated to anxiety. As an initial step to define the function of 5-HT transmission in the insula, we quantified the proportion of specific neuronal populations of the insula expressing 5-HT1A or 5-HT2A. We analyzed seven neural populations, including three defined by a molecular marker (putative glutamate, GABA or parvalbumin), and four defined by their projections to different downstream targets. First, we found that more than 70% of putative glutamatergic neurons, and only 30% of GABAergic neurons express the 5-HT1A. Second, within insular projection neurons, 5-HT1A is highly expressed (75-80%) in the populations targeting one sub-nuclei of the amygdala (central or basolateral), or targeting the rostral or caudal sections of the lateral hypothalamus (LH). Similarly, 70% of putative glutamatergic neurons and only 30% of insular GABAergic neurons contain 5-HT2A. Finally, the 5-HT2A is present in a majority of insula-amygdala and insula-LH projection neurons (73-82%). These observations suggest that most glutamatergic neurons can respond to 5-HT through 5-HT1A or 5-HT2A in the insula, and that 5-HT directly affects a limited number of GABAergic neurons. This study defines a molecular and neuroanatomical map of the 5-HT system within the insular cortex, providing ground knowledge to identify the potential role of serotonergic modulation of selective insular populations in anxiety.

Central 5-HT receptors and their function; present and future

Since our review of central 5-HT receptors and their function twenty years ago, no new 5-HT receptor has been discovered and there is little evidence that this situation will change in the near future. Nevertheless, over this time significant progress has been made in our understanding of the properties of these receptors and in the clinical translation of this information, and some of these developments are highlighted herein. Such highlights include extensive mapping of 5-HT receptors in both animal and human brain, culminating in readily-accessible brain atlases of 5-HT receptor distribution, as well as emerging data on how 5-HT receptors are distributed within complex neural circuits. Also, a range of important pharmacological and genetic tools have been developed that allow selective 5-HT receptor manipulation, in cells through to whole organism models. Moreover, unexpected complexity in 5-HT receptor function has been identified including agonist-dependent signalling that goes beyond the pharmacology of canonical 5-HT receptor signalling pathways set down in the 1980s and 1990s. This new knowledge of 5-HT signalling has been extended by the discovery of combined signalling of 5-HT and co-released neurotransmitters, especially glutamate. Another important advance has been the progression of a large number of 5-HT ligands through to experimental medicine studies and clinical trials, and some such agents have already become prescribed therapeutic drugs. Much more needs to be discovered and understood by 5-HT neuropharmacologists, not least how the diverse signalling effects of so many 5-HT receptor types interact with complex neural circuits to generate neurophysiological changes which ultimately lead to altered cognitions and behaviour. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Depressive-like state sensitizes 5-HT1A and 5-HT1B auto-receptors in the dorsal raphe nucleus sub-system

Dorsal raphe (DR) and median raphe (MR) 5-HT neurons are two distinct sub-systems known to be regulated by 5-HT_1A and 5-HT_1B auto-receptors. Whether the auto-receptors in each sub-system are functionally altered in depressive-like state remains unknown. The present study is aimed to study a specific circuit (DR-ventral hippocampus and MR-dorsal hippocampus) within each sub-system to investigate changes in receptor sensitivity in the pathogenesis of depression. A mouse model of depression was developed through the social defeat paradigm, and was then treated with fluoxetine (FLX). 5-HT_1A auto-receptor in the neuronal cell body (DR or MR) and 5-HT_1B auto-receptor in the axonal terminal (ventral or dorsal hippocampus) were directly targeted by local perfusion of antagonists (5-HT_1A: WAY100635; 5-HT_1B: GR127935) through reverse microdialysis. Time courses of dialysate 5-HT measured at the axonal terminal were subsequently determined for each circuit. At baseline, 5-HT_1A and 5-HT_1B antagonists dose-dependently increased dialysate 5-HT, with sub-circuit specificity. In the depressive-like state, greater increases in dialysate 5-HT were observed only in the DR-ventral hippocampus circuit following local delivery of both antagonists, which were then fully restored following the FLX treatment. In contrast, no changes were observed in the MR-dorsal hippocampus circuit. Our results demonstrate differential changes in sensitivities of 5-HT_1A and 5-HT_1B auto-receptors in the DR-ventral hippocampus and MR-dorsal hippocampus circuits. 5-HT_1A and 5-HT_1B auto-receptors in the DR-ventral hippocampus circuit are sensitized in the depressive-like state. Taken together, these results suggest that the DR sub-system maybe the neural substrate mediating depressive phenotypes.

In silico identification of novel 5-HT2A antagonists supported with ligand- and target-based drug design methodologies

A wide range of neuropsychological disorders is caused by serotonin 5-HT_2A receptor (5-HT_2AR) malfunction. Therefore, this receptor had been frequently used as target in CNS drug research. To design novel potent 5-HT_2AR antagonists, we have combined ligand-based and target-based approaches. This study was performed on wide range of structurally diverse antagonists that were divided into three different clusters: clozapine, ziprasidone, and ChEMBL240876 derivatives. By performing the 50 ns long molecular dynamic simulations with each cluster representative in complex with 5-HT_2A receptor, we have obtained virtually bioactive conformations of the ligands and three different antagonist-bound, inactive, conformations of the 5-HT_2AR. These three 5-HT_2AR conformations were further used for docking studies and generation of the bioactive conformations of the data set ligands in each cluster. Subsequently, selected conformers were used for 3D-Quantitative Structure Activity Relationship (3D-QSAR) modelling and pharmacophore analysis. The reliability and predictive power of the created model was assessed using an external test set compounds and showed reasonable external predictability. Statistically significant variables were used to define the most important structural features required for 5-HT_2A antagonistic activity. Conclusions obtained from performed ligand-based (3D-QSAR) and target-based (molecular docking and molecular dynamics) methods were compiled and used as guidelines for rational drug design of novel 5-HT_2AR antagonists.Communicated by Ramaswamy H. Sarma.

Mapping the physiological and molecular markers of stress and SSRI antidepressant treatment in S100a10 corticostriatal neurons

In mood disorders, psychomotor and sensory abnormalities are prevalent, disabling, and intertwined with emotional and cognitive symptoms. Corticostriatal neurons in motor and somatosensory cortex are implicated in these symptoms, yet mechanisms of their vulnerability are unknown. Here, we demonstrate that S100a10 corticostriatal neurons exhibit distinct serotonin responses and have increased excitability, compared with S100a10-negative neurons. We reveal that prolonged social isolation disrupts the specific serotonin response which gets restored by chronic antidepressant treatment. We identify cell-type-specific transcriptional signatures in S100a10 neurons that contribute to serotonin responses and strongly associate with psychomotor and somatosensory function. Our studies provide a strong framework to understand the pathogenesis and create new avenues for the treatment of mood disorders.

Preclinical characterization of ACH-000029, a novel anxiolytic compound acting on serotonergic and alpha-adrenergic receptors

Anxiety disorders are serious and common mental diseases, yet there is still a need for the development of more effective anxiolytics with better safety profiles than benzodiazepines and serotonin reuptake inhibitors. The serotonergic and noradrenergic systems have reciprocal interactions and are intricately related to the pathogenesis of anxiety. In this study, the anxiolytic-like effect of the novel compound ACH-000029, 3-(2-(4-(2-methoxyphenyl) piperazine-1-yl) ethyl) quinazoline-4(3H)-one, is reported. This compound acts at selected serotonergic (5-HT1A and 5-HT1D partial agonism and 5-HT2A antagonism) and α-adrenergic (α-1A, 1B and 1D antagonism) receptors, with good selectivity over other G-protein-coupled receptors. ACH-000029 exhibited high blood-brain barrier permeation and acute anxiolytic effects in the marble burying (MB) and light-dark box (LDB) models of anxiety over the dose ranges of 8-32 mg/kg i.p. and 16-30 mg/kg p.o. The anxiolytic activity was comparable to that observed for serotonin reuptake inhibitors (paroxetine and fluoxetine) and benzodiazepines (alprazolam, diazepam and clobazam). The analysis of the whole-brain c-fos expression following oral dosing showed that ACH-000029 regulated regions highly associated with the processing of environmental stimuli and anxiety behavior, such as the amygdala, paraventricular nucleus of the thalamus, retrosplenial dorsal, pallidum, bed nuclei of the stria terminalis, and locus ceruleus. No safety concerns were identified for ACH-000029 in the functional observational battery up to 50 mg/kg i.p. and in the nonprecipitated withdrawal test up to 30 mg/kg p.o. twice daily for 20 days. This work supports the further development of ACH-000029 as a drug candidate for the treatment of anxiety disorders. The analysis of the in vitro pharmacology and brain regions regulated by this compound may also lead to the exploration of other indications within the psychiatry field.

An evaluation of lumateperone tosylate for the treatment of schizophrenia

Introduction: Schizophrenia, a devastating disorder with onset in adolescence or young adulthood, afflicts 1% of the population leading to severe social, educational, and occupational impairments. Lumateperone is a first-in-class investigational drug under development for the treatment of multiple neuropsychiatric and neurodegenerative disorders including schizophrenia. Its unique receptor affinity profile together with synergistic modulation of serotonergic, glutamatergic, and dopaminergic pathways imparts efficacy over a broad-spectrum of symptoms associated with schizophrenia.Areas covered: This narrative drug evaluation includes a review of lumateperone tosylate (lumateperone, ITI-007, ITI-722, Intra-Cellular Therapies, Inc.) for patients with schizophrenia. This review describes the receptor affinity profile, pharmacodynamics, pharmacokinetics, distribution, metabolism, and clinical trials that address how lumateperone could potentially emerge as an important therapeutic option for schizophrenia patients.Expert opinion: The unique pharmacological properties of lumateperone may provide the key to dramatically ameliorate the symptoms of schizophrenia as indicated by some clinical trials. Future clinical trials may be enhanced by the administration of more comprehensive long-term behavioral measures and utilization of molecular imaging to confirm the target engagement of the many possible sites of action. The results of ongoing and future studies will provide the evidence to determine if lumateperone will revolutionize the therapy of schizophrenia.

Spatiotemporal brain activation pattern following acute citalopram challenge is dose dependent and associated with neuroticism: A human phMRI study

BACKGROUND

The initial effects of selective serotonin reuptake inhibitors (SSRIs) in the human living brain are poorly understood. We carried out a 3T resting state fMRI study with pharmacological challenge to determine the brain activation changes over time following different dosages of citalopram.

METHODS

During the study, 7.5 mg i.v. citalopram was administered to 32 healthy subjects. In addition, 11.25 mg citalopram was administered to a subset of 9 subjects to investigate the dose-response. Associations with neuroticism (assessed by the NEO PI-R) of the emerging brain activation to citalopram was also investigated.

RESULTS

Citalopram challenge evoked significant activation in brain regions that are part of the default mode network, the visual network and the sensorimotor network, extending to the thalamus, and midbrain. Most effects appeared to be dose-dependent and this was statistically significant in the middle cingulate gyrus. Individual citalopram-induced brain responses were positively correlated with neuroticism scores and its subscales in specific brain areas; anxiety subscale scores in thalamus and midbrain and self-consciousness scores in middle cingulate gyrus. There were no sex differences.

LIMITATIONS

We investigated only healthy subjects and we used a relatively low sample size in the 11.25 mg citalopram analysis.

DISCUSSION

Our results suggest that SSRIs acutely induce an increased arousal-like state of distributed cortical and subcortical systems that is mediated by enhanced serotonin neurotransmission according to levels of neuroticism and underpins trait sensitivity to environmental stimuli and stressors. Studies in depression are needed to determine how therapeutic effects eventually emerge. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

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.

Depression- and anxiogenic-like behaviors induced by lipopolysaccharide in mice are reversed by a selenium-containing indolyl compound: Behavioral, neurochemical and computational insights involving the serotonergic system

Major depression and anxiety are highly incapacitating psychiatric disorders often present simultaneously, and the causal relationship between these disorders and inflammation are under extensive investigation. The treatment for this comorbidity still relies on drugs acting on the serotonergic neurotransmission, but the modulation of immune-inflammatory pathways has attained an increasing interest in the drug discovery. We have previously demonstrated that the selenoorganic compound 3-[(4-chlorophenyl)selanyl]-1-methyl-1H-indole (CMI) possess antioxidant, anti-inflammatory, antinociceptive and antidepressant-like effect in mice. Considering these pharmacological properties and the structural similarities between tryptophan, serotonin and CMI, the aim of the present study was to investigate whether CMI ameliorates depression- and anxiogenic-like behavior induced by lipopolysaccharide (LPS) in Swiss male mice by modulating the serotonergic system and reducing neuroinflammation. The administration of CMI (1 mg/kg, i.g) reversed the behavioral deficits induced by LPS (0.83 mg/kg, i.p) in the tail suspension test, splash test and elevated plus maze. The pre-treatment of mice with WAY100635 (5-HT_1A receptor antagonist), ketanserin (5-HT_2A/2C receptor antagonist) and ondansetron (5-HT₃ receptor antagonist) prevented the antidepressant- and anxiolytic-like effect elicited by CMI treatment after the LPS challenge. The administration of CMI also counteracted the increased expression of pro-inflammatory cytokines and indoleamine 2,3-dioxygenase (IDO) in the prefrontal cortex and hippocampus of mice challenged with LPS. Additionally, a molecular docking analysis showed that CMI binds to the active site of the serotonin transporter and IDO. These findings suggest that CMI reversed behavioral and biochemical alterations in the depression-anxiety comorbidity induced by LPS, possibly by modulation of neuroinflammatory mediators and the serotonergic system.

Insula serotonin 2A receptor binding and gene expression contribute to serotonin transporter polymorphism anxious phenotype in primates

Genetic variation in the serotonin transporter gene (SLC6A4) is associated with vulnerability to affective disorders and pharmacotherapy efficacy. We recently identified sequence polymorphisms in the common marmoset SLC6A4 repeat region (AC/C/G and CT/T/C) associated with individual differences in anxiety-like trait, gene expression, and response to antidepressants. The mechanisms underlying the effects of these polymorphisms are unknown, but a key mediator of serotonin action is the serotonin 2A receptor (5HT_2A). Thus, we correlated 5HT_2A binding potential (BP) and RNA gene expression in 16 SLC6A4 genotyped marmosets with responsivity to 5HT_2A antagonism during the human intruder test of anxiety. Voxel-based analysis and RNA measurements showed a reduction in 5HT_2A BP and gene expression specifically in the right posterior insula of individuals homozygous for the anxiety-related variant AC/C/G. These same marmosets displayed an anxiogenic, dose-dependent response to the human intruder after 5HT_2A pharmacological antagonism, while CT/T/C individuals showed no effect. A voxel-based correlation analysis, independent of SLC6A4 genotype, revealed that 5HT_2A BP in the adjacent right anterior insula and insula proisocortex was negatively correlated with trait anxiety scores. Moreover, 5HT_2A BP in both regions was a good predictor of the size and direction of the acute emotional response to the human intruder threat after 5HT_2A antagonism. Our findings suggest that genetic variation in the SLC6A4 repeat region may contribute to the trait anxious phenotype via neurochemical changes in brain areas implicated in interoceptive and emotional processing, with a critical role for the right insula 5HT_2A in the regulation of affective responses to threat.

Serotonin-induced hyperactivity in SSRI-resistant major depressive disorder patient-derived neurons

Selective serotonin reuptake inhibitors (SSRIs) are the most prescribed antidepressants. They regulate serotonergic neurotransmission, but it remains unclear how altered serotonergic neurotransmission may contribute to the SSRI resistance observed in approximately 30% of major depressive disorder (MDD) patients. Patient stratification based on pharmacological responsiveness and the use of patient-derived neurons may make possible the discovery of disease-relevant neural phenotypes. In our study from a large cohort of well-characterized MDD patients, we have generated induced pluripotent stem cells (iPSCs) from SSRI-remitters and SSRI-nonremitters. We studied serotonergic neurotransmission in patient forebrain neurons in vitro and observed that nonremitter patient-derived neurons displayed serotonin-induced hyperactivity downstream of upregulated excitatory serotonergic receptors, in contrast to what is seen in healthy and remitter patient-derived neurons. Our data suggest that postsynaptic forebrain hyperactivity downstream of SSRI treatment may play a role in SSRI resistance in MDD.

Genetic endophenotypes for insomnia of major depressive disorder and treatment-induced insomnia

Major depressive disorder (MDD) is primarily hinged on the presence of either low mood and/or anhedonia to previously pleasurable events for a minimum of 2 weeks. Other clinical features that characterize MDD include disturbances in sleep, appetite, concentration and thoughts. The combination of any/both of the primary MDD symptoms as well as any four of the other clinical features has been referred to as MDD. The challenge for replicating gene association findings with phenotypes of MDD as well as its treatment outcome is putatively due to stratification of MDD patients. Likelihood for replication of gene association findings is hypothesized with specificity in symptoms profile (homogenous clusters of symptom/individual symptoms) evaluated. The current review elucidates the genetic factors that have been associated with insomnia symptom of MDD phenotype, insomnia symptom as a constellation of neuro-vegetative cluster of MDD symptom, insomnia symptom of MDD as an individual entity and insomnia feature of treatment outcome. Homozygous CC genotype of 3111T/C, GSK3B-AT/TT genotype of rs33458 and haplotype of TPH1 218A/C were associated with insomnia symptom of MDD. Insomnia symptom of MDD was not resolved in patients with the A/A genotype of HTR2A-rs6311 when treated with SSRI. Homozygous short (SS) genotype-HTTLPR, GG genotype of HTR2A-rs6311 and CC genotype of HTR2A-rs6313 were associated with AD treatment-induced insomnia, while val/met genotype of BDNF-rs6265 and the TT genotype of GSK-3beta-rs5443 reduced it. Dearth of association studies may remain the bane for the identification of robust genetic endophenotypes in line with findings for genotypes of HTR2A-rs6311.

Sugar rush or sugar crash? A meta-analysis of carbohydrate effects on mood

The effect of carbohydrate (CHO) consumption on mood is much debated, with researchers reporting both mood improvements and decrements following CHO ingestion. As global consumption of sugar-sweetened products has sharply increased in recent years, examining the validity of claims of an association between CHOs and mood is of high importance. We conducted a systematic review and meta-analysis to evaluate the relationship between acute CHO ingestion and mood. We examined the time-course of CHO-mood interactions and considered the role of moderator variables potentially affecting the CHO-mood relationship. Analysis of 176 effect sizes (31 studies, 1259 participants) revealed no positive effect of CHOs on any aspect of mood at any time-point following their consumption. However, CHO administration was associated with higher levels of fatigue and less alertness compared with placebo within the first hour post-ingestion. These findings challenge the idea that CHOs can improve mood, and might be used to increase the public's awareness that the 'sugar rush' is a myth, inform health policies to decrease sugar consumption, and promote healthier alternatives.

5-HT2A receptor loss does not alter acute fluoxetine-induced anxiety and exhibit sex-dependent regulation of cortical immediate early gene expression

Background: Acute treatment with the selective serotonin reuptake inhibitor (SSRI), fluoxetine (Flx), induces anxiety-like behavioral effects. The serotonin_2A receptor (5-HT_2A) is implicated in the modulation of anxiety-like behavior, however its contribution to the anxiogenic effects of acute Flx remains unclear. Here, we examined the role of the 5-HT_2A receptor in the effects of acute Flx on anxiety-like behavior, serum corticosterone levels, neural activation and immediate early gene (IEG) expression in stress-responsive brain regions, using 5-HT_2A receptor knockout (5-HT_2A^−/−) mice of both sexes. Methods: 5-HT_2A^−/− and wild-type (WT) male and female mice received a single administration of Flx or vehicle, and were examined for anxiety-like behavior, serum corticosterone levels, FBJ murine osteosarcoma viral oncogene homolog peptide (c-Fos) positive cell numbers in stress-responsive brain regions of the hypothalamus and prefrontal cortex (PFC), and PFC IEG expression. Results: The increased anxiety-like behavior and enhanced corticosterone levels evoked by acute Flx were unaltered in 5-HT_2A^−/− mice of both sexes. 5-HT_2A^−/− female mice exhibited a diminished neural activation in the hypothalamus in response to acute Flx. Further, 5-HT_2A^−/− male, but not female, mice displayed altered baseline expression of several IEGs (brain-derived neurotrophic factor (Bdnf), Egr2, Egr4, FBJ osteosarcoma gene (Fos), FBJ murine osteosarcoma viral oncogene homolog B (Fosb), Fos-like antigen 2 (Fosl2), Homer scaffolding protein (Homer) 1-3 (Homer1-3), Jun proto-oncogene (Jun)) in the PFC. Conclusion: Our results indicate that the increased anxiety and serum corticosterone levels evoked by acute Flx are not influenced by 5-HT_2A receptor deficiency. However, the loss of function of the 5-HT_2A receptor alters the degree of neural activation of the paraventricular nucleus (PVN) of the hypothalamus in response to acute Flx, and baseline expression of several IEGs in the PFC in a sexually dimorphic manner.

Diminished responses to monoaminergic antidepressants but not ketamine in a mouse model for neuropsychiatric lupus

BACKGROUND

A significant proportion of patients suffering from major depression fail to remit following treatment and develop treatment-resistant depression. Developing novel treatments requires animal models with good predictive validity. MRL/lpr mice, an established model of systemic lupus erythematosus, show depression-like behavior.

AIMS

We evaluated responses to classical antidepressants, and associated immunological and biochemical changes in MRL/lpr mice.

METHODS AND RESULTS

MRL/lpr mice showed increased immobility in the forced swim test, decreased wheel running and sucrose preference when compared with the controls, MRL/MpJ mice. In MRL/lpr mice, acute fluoxetine (30 mg/kg, intraperitoneally (i.p.)), imipramine (10 mg/kg, i.p.) or duloxetine (10 mg/kg, i.p.) did not decrease the immobility time in the Forced Swim Test. Interestingly, acute administration of combinations of olanzapine (0.03 mg/kg, subcutaneously)+fluoxetine (30 mg/kg, i.p.) or bupropion (10 mg/kg, i.p.)+fluoxetine (30 mg/kg, i.p.) retained efficacy. A single dose of ketamine but not three weeks of imipramine (10 mg/kg, i.p.) or escitalopram (5 mg/kg, i.p.) treatment in MRL/lpr mice restored sucrose preference. Further, we evaluated inflammatory, immune-mediated and neuronal mechanisms. In MRL/lpr mice, there was an increase in autoantibodies' titers, [3H]PK11195 binding and immune complex deposition. There was a significant infiltration of the brain by macrophages, neutrophils and T-lymphocytes. p11 mRNA expression was decreased in the prefrontal cortex. Further, there was an increase in the 5-HT_2aR expression, plasma corticosterone and indoleamine 2,3-dioxygenase activity.

CONCLUSION

In summary, the MRL/lpr mice could be a useful model for Treatment Resistant Depression associated with immune dysfunction with potential to expedite antidepressant drug discovery.

In vitro pharmacological characterization of SPN-810M (molindone)

Background

Impulsive aggression (IA) is considered a maladaptive form of aggression that is reactive and overt and occurs outside of the acceptable social context. Many children and adolescents with attention-deficit/hyperactivity disorder (ADHD) display clinically significant aggression, with the predominant subtype being IA. However, there is currently no Food and Drug Administration-approved medication specifically to treat IA. The pathophysiology of IA is not fully understood, although it has been suggested to include the dopamine, norepinephrine, and serotonin systems.

Methods

SPN-810 (extended-release molindone) is being developed for the novel indication of IA and is currently being studied in patients treated for ADHD. Molindone is an indole derivative and a dopamine D₂ receptor antagonist.

Results

The in vitro pharmacological studies described in the current manuscript demonstrate that the active substance molindone (SPN-810M) is a potent antagonist for the dopamine receptors, D_2S and D_2L, and the serotonin receptor, 5-HT_2B, at therapeutic concentrations. The in vitro studies further demonstrate that the antagonist effect of SPN-810M is due to the parent drug and not the metabolites, and that the antagonism is not affected by the presence of norepinephrine or dopamine neurotransmitters. In addition, studies investigating the potential differential effects of the enantiomers of SPN-810M have demonstrated that the R(−) enantiomer is more potent than S(+), showing greater regulatory effect on D_2S and D_2L receptors.

Conclusion

Overall, the results of the in vitro SPN-810M pharmacological studies provide some insight into how SPN-810M modulates the serotonin and dopamine pathways that play a role in IA.

Interactions of Hallucinogens with the Glutamatergic System: Permissive Network Effects Mediated Through Cortical Layer V Pyramidal Neurons

Recordings made from layer V (L5) pyramidal cells of the prefrontal cortex (PFC) and neocortex in rodent slice preparations have shown that serotonin (5-hydroxytryptamine, 5-HT) and serotonergic hallucinogens induce an increase in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) in the apical dendritic field by activating 5-HT_2A receptors. Serotonergic hallucinogens induce late EPSCs and increase recurrent network activity when subcortical or mid-cortical regions are stimulated at low frequencies (e.g., 0.1 Hz). A range of agonists or positive allosteric modulators (PAMs) for mostly G_i/o-coupled receptors, including metabotropic glutamate₂ (mGlu₂), adenosine A₁, or μ-opioid receptors, suppress these effects of 5-HT_2A receptor stimulation. Furthermore, a range of mostly G_q/11-coupled receptors (including orexin₂ [OX₂]; α₁-adrenergic, and mGlu₅ receptors) similarly induce glutamate (Glu) release onto L5 pyramidal cells. Evidence implicates a number of brain regions in mediating these effects of serotonergic hallucinogens and G_q/11-coupled receptors including the midline and intralaminar thalamic nuclei, claustrum, and neurons in deep PFC. These effects on 5-HT_2A receptors and related GPCRs appear to play a major role in the behavioral effects of serotonergic hallucinogens, such as head twitches in rodents and higher order behaviors such as rodent lever pressing on the differential-reinforcement-of-low rate 72-s (DRL 72-s) schedule. This implies that the effects of 5-HT_2A receptor activation on the activity of L5 pyramidal cells may be responsible for mediating a range of behaviors linked to limbic circuitry with connectivity between the PFC, striatum, thalamus, claustrum, striatum, amygdala, and the hippocampal formation.