Comparative pharmacology of antipsychotics possessing combined dopamine D2 and serotonin 5-HT1A receptor properties

Micro-Infusion of 5-HT1a Receptor Antagonists into the Ventral Subiculum Ameliorate MK-801 Induced Schizophrenia-Like Behavior in Rats

Recent studies have shown that the 5-HT1a receptor (5-HT1aR) in the central 5-HT (Serotonergic) system is involved in the pathophysiology of schizophrenia through its various receptors, and the dysfunction of the ventral hippocampus may be a key causative factor in schizophrenia. To date, whether the 5-HT1a receptor is involved in ventral hippocampal dysfunction and its internal mechanism remain unclear. In this study, schizophrenia-like animal model was induced by intraperitoneal injection of aspartate receptor antagonist MK-801 in male Sprague Dawley rats, and the role of 5-HT1aR in this animal model was investigated by bilaterally micro-infusing the 5-HT1aR antagonist WAY100635 into the ventral subiculum (vSub) of the hippocampus of rats. Behavioral experiments such as open field test (OFT) and prepulse inhibition (PPI) were performed. The results showed that MK-801 induced hyperactivity and impaired prepulse inhibition in rats, whereas, micro-infusion of 5-HT1aR antagonist WAY100635 into the vSub ameliorated these phenomena. Immunofluorescence analysis revealed that WAY100635 significantly increased the c-Fos expression in vSub. Western blot and immunohistochemical analysis showed that MK-801 induced up-regulation of 5-HT1aR and phospho-extracellular regulated protein kinase (p-ERK) pathway, while micro-infusion of the WAY100635 down-regulated 5-HT1aR and p-ERK in the vSub. Therefore, the results of the present study suggested that in vSub, the 5-HT1aR antagonist WAY100635 may attenuate MK-801-induced schizophrenia-like activity by modulating excitatory neurons and downregulating p-ERK.

Augmentation therapy with serotonin1A receptor partial agonists on neurocognitive function in schizophrenia: A systematic review and meta-analysis

Background

In a previous meta-analysis, the use of serotonin1A(5-HT1A) receptor partial agonists of the azapirone class as an add-on therapy was associated with beneficial effects on positive symptoms and attention/processing speed in schizophrenia patients. This meta-analysis builds on that study by examining the effects of adjunctive treatment with 5-HT1A partial agonists in improving other domains of neurocognitive function in schizophrenia patients.

Methods

A literature search was performed from 1987 to May 2023 to identify randomized controlled trials. The standardized mean difference (SMD) with 95 % confidence intervals (CI) was calculated when there were two or more studies. Four studies, involving 313 patients, met the inclusion criteria and were used in the analysis.

Results

5-HT1A partial agonists (buspirone or tandospirone) did not have a significant effect on verbal learning (SMD = 0.08, 95 % CI = -0.31 to 0.47) or working memory (SMD = 0.15, 95 % CI = -0.09 to 0.39). Regarding executive functions (Wisconsin Card Sorting Test), positive but non-significant results were seen with the category number (SMD = 0.26, 95 % CI = -0.81 to 1.32), while non-significant effects were noted for percent preservation errors (SMD = -0.10, 95 % CI = -0.53 to 0.33).

Conclusions

The absence of any significant benefits in the cognitive domains studied here may have been due to the variance in the concomitant medication (typical vs atypical antipsychotic drugs), the level of cognition at baseline, or other factors. Further studies with various types of 5-HT1A agonists are warranted to examine the potential cognitive efficacy of stimulating these receptors.

In Vitro Comparison of Ulotaront (SEP-363856) and Ralmitaront (RO6889450): Two TAAR1 Agonist Candidate Antipsychotics

BACKGROUND

Trace amine-associated receptor-1 (TAAR1) agonists have been proposed as potential antipsychotics, with ulotaront and ralmitaront having reached clinical trials. While ulotaront demonstrated efficacy in a recent Phase II trial, a corresponding study studies of ralmitaront failed to show efficacy as a monotherapy or as an adjunct to atypical antipsychotics. In addition to TAAR1 agonism, ulotaront is a partial agonist at the serotonin 1A receptor (5-HT1AR). However, little is known about ralmitaront.

METHODS

We compared ulotaront and ralmitaront at TAAR1, 5-HT1AR, and dopamine D2 using luciferase complementation-based G protein recruitment, cAMP accumulation, and G protein-coupled inward rectifier potassium channel activation assays.

RESULTS

Ralmitaront showed lower efficacy at TAAR1 in G protein recruitment, cAMP accumulation, and GIRK activation assays. Moreover, ralmitaront lacked detectable activity at 5-HT1AR and dopamine D2.

CONCLUSIONS

Compared with ulotaront, ralmitaront shows lower efficacy and slower kinetics at TAAR1 and lacks efficacy at 5-HT1AR. These data may be relevant to understanding differences in clinical profiles of these 2 compounds.

Increased Metabolic Potential, Efficacy, and Safety of Emerging Treatments in Schizophrenia

Patients with schizophrenia experience a broad range of detrimental health outcomes resulting from illness severity, heterogeneity of disease, lifestyle behaviors, and adverse effects of antipsychotics. Because of these various factors, patients with schizophrenia have a much higher risk of cardiometabolic abnormalities than people without psychiatric illness. Although exposure to many antipsychotics increases cardiometabolic risk factors, mortality is higher in patients who are not treated versus those who are treated with antipsychotics. This indicates both direct and indirect benefits of adequately treated illness, as well as the need for beneficial medications that result in fewer cardiometabolic risk factors and comorbidities. The aim of the current narrative review was to outline the association between cardiometabolic dysfunction and schizophrenia, as well as discuss the confluence of factors that increase cardiometabolic risk in this patient population. An increased understanding of the pathophysiology of schizophrenia has guided discovery of novel treatments that do not directly target dopamine and that not only do not add, but may potentially minimize relevant cardiometabolic burden for these patients. Key discoveries that have advanced the understanding of the neural circuitry and pathophysiology of schizophrenia now provide possible pathways toward the development of new and effective treatments that may mitigate the risk of metabolic dysfunction in these patients. Novel targets and preclinical and clinical data on emerging treatments, such as glycine transport inhibitors, nicotinic and muscarinic receptor agonists, and trace amine-associated receptor-1 agonists, offer promise toward relevant therapeutic advancements. Numerous areas of investigation currently exist with the potential to considerably progress our knowledge and treatment of schizophrenia.

Cariprazine - an Alternative Treatment for Clozapine-resistant Schizophrenia?

Treatment-resistant schizophrenia (TRS) poses a significant therapeutic challenge in psychiatric practice. Clozapine is recognized as a treatment of choice in TRS but is not always effective in alleviating patients' symptoms. Additionally, clozapine therapy is associated with multiple side effects and monitoring requirements that often limit its use and negatively affect patients' compliance with the treatment. Although clozapine augmentation options are available, there is currently no alternative monotherapy proven to be effective in TRS. We present a case of a young man with TRS who failed to respond to appropriate trials of risperidone, aripiprazole and also clozapine, and who experienced impairing adverse effects of clozapine that made further clozapine treatment not only futile but also detrimental to his health. He was successfully treated with cariprazine monotherapy, which culminated in the remission of his both positive and negative symptoms of psychosis as well as in the marked improvement in social functioning. Cariprazine, a newer atypical antipsychotic endowed with a D3-preferring mode of action, may offer a better tolerated and more acceptable treatment option for patients with difficult-to-treat psychotic symptoms.

Seasonality of brain function: role in psychiatric disorders

Seasonality patterns are reported in various psychiatric disorders. The current paper summarizes findings on brain adaptations associated with seasonal changes, factors that contribute to individual differences and their implications for psychiatric disorders. Changes in circadian rhythms are likely to prominently mediate these seasonal effects since light strongly entrains the internal clock modifying brain function. Inability of circadian rhythms to accommodate to seasonal changes might increase the risk for mood and behavior problems as well as worse clinical outcomes in psychiatric disorders. Understanding the mechanisms that account for inter-individual variations in seasonality is relevant to the development of individualized prevention and treatment for psychiatric disorders. Despite promising findings, seasonal effects are still understudied and only controlled as a covariate in most brain research. Rigorous neuroimaging studies with thoughtful experimental designs, powered sample sizes and high temporal resolution alongside deep characterization of the environment are needed to better understand the seasonal adaptions of the human brain as a function of age, sex, and geographic latitude and to investigate the mechanisms underlying the alterations in seasonal adaptation in psychiatric disorders.

Dopamine D3/D2 Receptor Ligands Based on Cariprazine for the Treatment of Psychostimulant Use Disorders That May Be Dual Diagnosed with Affective Disorders

Highly selective dopamine D3 receptor (D3R) partial agonists/antagonists have been developed for the treatment of psychostimulant use disorders (PSUD). However, none have reached the clinic due to insufficient potency/efficacy or potential cardiotoxicity. Cariprazine, an FDA-approved drug for the treatment of schizophrenia and bipolar disorder, is a high-affinity D3R partial agonist (Ki = 0.22 nM) with 3.6-fold selectivity over the homologous dopamine D2 receptor (D2R). We hypothesized that compounds that are moderately D3R/D2R-selective partial agonists/antagonists may be effective for the treatment of PSUD. By systematically modifying the parent molecule, we discovered partial agonists/antagonists, as measured in bioluminescence resonance energy transfer (BRET)-based assays, with high D3R affinities (Ki = 0.14-50 nM) and moderate selectivity (<100-fold) over D2R. Cariprazine and two lead analogues, 13a and 13e, decreased cocaine self-administration (FR2; 1-10 mg/kg, i.p.) in rats, suggesting that partial agonists/antagonists with modest D3R/D2R selectivity may be effective in treating PSUD and potentially comorbidities with other affective disorders.

Dual 5-HT3 and 5-HT6 Receptor Antagonist FPPQ Normalizes Phencyclidine-Induced Disruption of Brain Oscillatory Activity in Rats

Schizophrenia is a severe mental disorder featuring psychotic, depressive, and cognitive alterations. Current antipsychotic drugs preferentially target dopamine D2-R and/or serotonergic 5-HT2A/1A-R. They partly alleviate psychotic symptoms but fail to treat negative symptoms and cognitive deficits. Here we report on the putative antipsychotic activity of (1-[(3-fluorophenyl)sulfonyl]-4-(piperazin-1-yl)-1H-pyrrolo[3,2-c]quinoline dihydrochloride) (FPPQ), a dual serotonin 5-HT3-R/5-HT6-R antagonist endowed with pro-cognitive properties. FPPQ fully reversed phencyclidine-induced decrease of low-frequency oscillations in the medial prefrontal cortex of anaesthetized rats, a fingerprint of antipsychotic activity. This effect was mimicked by the combined administration of the 5-HT3-R and 5-HT6-R antagonists ondansetron and SB-399 885, respectively, but not by either drug alone. In freely moving rats, FPPQ countered phencyclidine-induced hyperlocomotion and augmentation of gamma and high-frequency oscillations in medial prefrontal cortex, dorsal hippocampus, and nucleus accumbens. Overall, this supports that simultaneous blockade of 5-HT3R and 5-HT6-R-like that induced by FPPQ-can be a new target in antipsychotic drug development.

Binding of SEP-363856 within TAAR1 and the 5HT1A receptor: implications for the design of novel antipsychotic drugs

Current medications for schizophrenia typically modulate dopaminergic neurotransmission. While affecting positive symptoms, antipsychotic drugs have little clinical effect on negative symptoms and cognitive impairment. Moreover, newer 'atypical' antipsychotic drugs also have significant metabolic adverse-effects. The recent positive clinical trial of the novel drug candidate SEP-363856, which targets non-dopamine receptors (trace amine-associated receptor and the 5HT_1A receptor), is a potentially promising development for the management of schizophrenia. In this perspective, we briefly overview the role of TAAR1 and the 5HT_1A receptor in schizophrenia and explore the specific binding characteristics of SEP-363856 at these receptors. Molecular dynamics simulations (MDS) indicate that SEP-363856 interacts with a small, common set of conserved residues within the TAAR1 and 5HT_1A ligand-binding domain. The primary interaction of SEP-363856 involves binding to the negatively charged aspartate residue (Asp103^3.32, TAAR1; Asp116^3.32, 5HT_1A). In general, the binding of SEP-363856 within TAAR1 involves a greater number of aromatic contacts compared to 5HT_1A. MDS provides important insights into the molecular basis of binding site interactions of SEP-363856 with TAAR1 and the 5HT_1A receptor, which will be beneficial for understanding the pharmacological uniqueness of SEP-363856 and for the design of novel drug candidates for these newly targeted receptors in the treatment of schizophrenia and related disorders.

The 5-HT1A receptor as a serotonergic target for neuroprotection in cerebral ischemia

Cerebral ischemia due to stroke or cardiac arrest greatly affects daily functioning and the quality of life of patients and has a high socioeconomic impact due to the surge in their prevalence. Advances in the identification of an effective pharmacotherapy to promote neuroprotection and recovery after a cerebral ischemic insult are, however, limited. The serotonin 1A (5-HT_1A) receptor has been implicated in the regulation of several brain functions, including mood, emotions, memory, and neuroplasticity, all of which are deleteriously affected by cerebral ischemia. This review focuses on the specific roles and mechanisms of 5-HT_1A receptors in neuroprotection in experimental models of cerebral ischemia. We present experimental evidence that 5-HT_1A receptor agonists can prevent neuronal damage and promote functional recovery induced by focal and transient global ischemia in rodents. However, indiscriminate activation of pre-and postsynaptic by non-biased 5-HT_1A receptor agonists may be a limiting factor in the anti-ischemic clinical efficacy of these compounds since 5-HT_1A receptors in different brain regions can mediate diverging or even contradictory responses. Current insights are presented into the 'biased' 5-HT_1A post-synaptic heteroreceptor agonist NLX-101 (also known as F15599), a compound that preferentially and potently stimulates postsynaptic cortical pyramidal neurons without inhibiting firing of serotoninergic neurons, as a potential strategy providing neuroprotection in cerebral ischemic conditions.

Characterization of Dopamine Receptor Associated Drugs on the Proliferation and Apoptosis of Prostate Cancer Cell Lines

BACKGROUND

Dopamine Receptor (DR) gene family play an essential role in the regulation of Interleukin- 6 (IL-6) production. Our prior analysis of human prostate biopsy samples demonstrated the increased expression of IL-6 and a downregulating trend for dopamine receptor gene family.

OBJECTIVE

The objective was to investigate the expression of dopamine receptors, their catabolizing enzyme and IL-6 in prostate cancer cell lines and assess pharmacological effect of dopamine receptor modulators as a novel class of drugs repurposed for the treatment of prostate cancer.

METHODS

The therapeutic effect of dopamine, DR agonists, and DR antagonist were examined using LNCaP and PC3 cell lines. Cell viability and proliferation were assessed by MTT assay and proliferating cell nuclear antigen expression analysis, respectively. Furthermore, bax/bcl2 ratio, immunofluorescence assay and flow cytometric assay were performed for apoptosis analysis. RT- qPCR analysis was used to characterize the relative expression of dopamine-related genes, catabolic enzyme Catechol-o-Methyl-Transferase (COMT) and IL-6 before and after treatment to assess the therapeutic effects of drugs.

RESULTS

LNCaP cells express DRD1, DRD2, DRD5 and COMT genes and PC3 cells only express IL-6 gene. In-vitro, dopamine receptor agonists reduced cell viability of LNCaP and PC3 cells. In contrast, dopamine and dopamine receptor antagonist significantly increased tumor growth in PC3 cells.

CONCLUSION

Our results offer novel suggestion for a pathogenic role of dopamine receptor signaling in prostate cancer adenocarcinoma and indicates that modulators of DR- IL-6 pathway, including FDA-approved drug bromocriptine, might be utilized as novel drug repurposing strategy.

Development of a New Polymeric Nanocarrier Dedicated to Controlled Clozapine Delivery at the Dopamine D2-Serotonin 5-HT1A Heteromers

Clozapine, the second generation antipsychotic drug, is one of the prominent compounds used for treatment of schizophrenia. Unfortunately, use of this drug is still limited due to serious side effects connected to its unspecific and non-selective action. Nevertheless, clozapine still remains the first-choice drug for the situation of drug-resistance schizophrenia. Development of the new strategy of clozapine delivery into well-defined parts of the brain has been a great challenge for modern science. In the present paper we focus on the presentation of a new nanocarrier for clozapine and its use for targeted transport, enabling its interaction with the dopamine D₂ and serotonin 5-HT_1A heteromers (D₂-5-HT_1A) in the brain tissue. Clozapine polymeric nanocapsules (CLO-NCs) were prepared using anionic surfactant AOT (sodium docusate) as an emulsifier, and bio-compatible polyelectrolytes such as: poly-l-glutamic acid (PGA) and poly-l-lysine (PLL). Outer layer of the carrier was grafted by polyethylene glycol (PEG). Several variants of nanocarriers containing the antipsychotic varying in physicochemical parameters were tested. This kind of approach may enable the availability and safety of the drug, improve the selectivity of its action, and finally increase effectiveness of schizophrenia therapy. Moreover, the purpose of the manuscript is to cover a wide scope of the issues, which should be considered while designing a novel means for drug delivery. It is important to determine the interactions of a new nanocarrier with many cell components on various cellular levels in order to be sure that the new nanocarrier will be safe and won’t cause undesired effects for a patient.

Reasons for cannabidiol use: a cross-sectional study of CBD users, focusing on self-perceived stress, anxiety, and sleep problems

BACKGROUND

Public and medical interest in cannabidiol (CBD) has been rising, and CBD is now available from various sources. Research into the effects of low-dose CBD on outcomes like stress, anxiety, and sleep problems have been scarce, so we conducted an online survey of CBD users to better understand patterns of use, dose, and self-perceived effects of CBD.

METHODS

The sample consisted of 387 current or past-CBD users who answered a 20-question online survey. The survey was sent out to CBD users through email databases and social media. Participants reported basic demographics, CBD use patterns, reasons for use, and effects on anxiety, sleep, and stress.

RESULTS

The sample (N = 387) consisted of 61.2% females, mostly between 25 and 54 years old (72.2%) and primarily based in the UK (77.4%). The top 4 reasons for using CBD were self-perceived anxiety (42.6%), sleep problems (42.5%), stress (37%), and general health and wellbeing (37%). Fifty-four per cent reported using less than 50 mg CBD daily, and 72.6% used CBD sublingually. Adjusted logistic models show females had lower odds than males of using CBD for general health and wellbeing [OR 0.45, 95% CI 0.30-0.72] and post-workout muscle-soreness [OR 0.46, 95%CI 0.24-0.91] but had higher odds of using CBD for self-perceived anxiety [OR 1.60, 95% CI 0.02-2.49] and insomnia [OR 1.87, 95% CI 1.13-3.11]. Older individuals had lower odds of using CBD for general health and wellbeing, stress, post-workout sore muscles, anxiety, skin conditions, focusing, and sleep but had higher odds of using CBD for pain. Respondents reported that CBD use was effective for stress, sleep problems, and anxiety in those who used the drug for those conditions.

CONCLUSION

This survey indicated that CBD users take the drug to manage self-perceived anxiety, stress, sleep, and other symptoms, often in low doses, and these patterns vary by demographic characteristics. Further research is required to understand how low doses, representative of the general user, might impact mental health symptoms like stress, anxiety, and sleep problems.

Towards in vivo imaging of functionally active 5-HT1A receptors in schizophrenia: concepts and challenges

The serotonin 5-HT_1A receptor has attracted wide attention as a target for treatment of psychiatric disorders. Although this receptor is important in the pharmacological mechanisms of action of new-generation antipsychotics, its characterization remains incomplete. Studies based on in vitro molecular imaging on brain tissue by autoradiography, and more recently in vivo PET imaging, have not yielded clear results, in particular due to the limitations of current 5-HT_1A radiotracers, which lack specificity and/or bind to all 5-HT_1A receptors, regardless of their functional status. The new concept of PET neuroimaging of functionally active G-protein-coupled receptors makes it possible to revisit PET brain exploration by enabling new research paradigms. For the 5-HT_1A receptor it is now possible to use [¹⁸F]-F13640, a 5-HT_1A receptor radioligand with high efficacy agonist properties, to specifically visualize and quantify functionally active receptors, and to relate this information to subjects' pathophysiological or pharmacological state. We therefore propose imaging protocols to follow changes in the pattern of functional 5-HT_1A receptors in relation to mood deficits or cognitive processes. This could allow improved discrimination of different schizophrenia phenotypes and greater understanding of the basis of therapeutic responses to antipsychotic drugs. Finally, as well as targeting functionally active receptors to gain insights into the role of 5-HT_1A receptors, the concept can also be extended to the study of other receptors involved in the pathophysiology or therapy of psychiatric disorders.

Current Understanding of the Neurobiology of Agitation

Introduction

Managing agitation in the clinical setting is a challenge that many practitioners face regularly. Our evolving understanding of the etiological factors involved in aggressive acts has better informed our interventions through pharmacologic and behavioral strategies. This paper reviews the literature on the neurobiological underpinnings of aggressive behaviors, linking psychopathology with proposed mechanisms of action of psychiatric medications shown to be effective in mitigating agitation.

Methods

We performed a review of the extant literature using PubMed as a primary database. Investigation focused on neurobiology of agitation and its relation to the current evidence base for particular interventions.

Results

There are well-established pathways that can lead to increased autonomic response and the potential for violence. Psychopathology and substance-induced perceptual distortions may lead to magnification and overestimation of environmental threat, heightening the potential for aggression. Additional challenges have arisen with the advent of several novel drugs of abuse, many of which lead to atypical clinical presentations and which can elude standard drug screens. Our interventions still lean on the evidence base found in Project BETA (Best Practices in Evaluation and Treatment of Agitation). Although not a new drug and not included in the Project BETA guidelines, ketamine and its use are also discussed, given its unique pharmacology and potential benefits when other protocoled interventions have failed.

Conclusion

Aggression can occur due to manifold reasons in the clinical setting. Having an informed understanding of the possible determinants of agitation can help with more tailored responses to individual patients, limiting the unnecessary use of medications or of interventions that could be deemed forceful.

Targeting Serotonin1A Receptors for Treating Chronic Pain and Depression

The association of chronic pain with depression is becoming increasingly recognized. Treating both the conditions together is essential for an effective treatment outcome. In this regard, it is important to identify a shared mechanism involved in the association of chronic pain with depression. Central serotonin (5-hydroxytryptamine; 5-HT) neurotransmission has long been known to participate in the processing of signals related to pain. It also plays a key role in the pathogenesis and treatment of depression. Although functional responses to serotonin are mediated via the activation of multiple receptor types and subtypes, the 5-HT1A subtype is involved in the processing of nociception as well as the pathogenesis and treatment of depression. This receptor is located presynaptically, as an autoreceptor, on the perikaryon and dendritic spines of serotonin-containing neurons. It is also expressed as a heteroreceptor on neurons receiving input from serotonergic neurons. This arti-cle targets the 5-HT1A receptors to show that indiscriminate activation of pre and postsynaptic 5-HT1A receptors is likely to produce no therapeutic benefits; biased activation of the 5-HT heteroreceptors may be a useful strategy for treating chronic pain and depression individually as well as in a comorbid condition.

Identification of slit3 as a locus affecting nicotine preference in zebrafish and human smoking behaviour

To facilitate smoking genetics research we determined whether a screen of mutagenized zebrafish for nicotine preference could predict loci affecting smoking behaviour. From 30 screened F3 sibling groups, where each was derived from an individual ethyl-nitrosurea mutagenized F0 fish, two showed increased or decreased nicotine preference. Out of 25 inactivating mutations carried by the F3 fish, one in the slit3 gene segregated with increased nicotine preference in heterozygous individuals. Focussed SNP analysis of the human SLIT3 locus in cohorts from UK (n=863) and Finland (n=1715) identified two variants associated with cigarette consumption and likelihood of cessation. Characterisation of slit3 mutant larvae and adult fish revealed decreased sensitivity to the dopaminergic and serotonergic antagonist amisulpride, known to affect startle reflex that is correlated with addiction in humans, and increased htr1aa mRNA expression in mutant larvae. No effect on neuronal pathfinding was detected. These findings reveal a role for SLIT3 in development of pathways affecting responses to nicotine in zebrafish and smoking in humans.

Restless legs syndrome following the use of ziprasidone: a case report

Restless legs syndrome (RLS) is a common sleep-related movement disorder characterised by an uncomfortable urge to move the legs that occurs during periods of inactivity. Although there have been many case reports on antipsychotic-induced RLS, ziprasidone has never been reported as a cause of RLS. We present a case of a female patient with schizophrenia who presented with symptoms of RLS following the administration of high doses of ziprasidone added to quetiapine and valproate. The patient’s symptoms of RLS occurred following the administration and titration of ziprasidone to 160 mg, and were relieved upon reducing the dose to 120 mg/day. Other potential causative medications and differential diagnoses that could have caused similar symptoms were excluded. Clinicians should be aware of the potential for ziprasidone-induced RLS. Dopamine and serotonin interaction could be the mechanism underlying ziprasidone-induced RLS.

Genetic variants in dopamine receptors influence on heterodimerization in the context of antipsychotic drug action

Human dopamine D2 receptor (D₂R) gene has polymorphic variants, three of them alter its amino acid sequence: Val96Ala, Pro310Ser and Ser311Cys. Their functional role never became the object of extensive studies, even though there are some evidence that they correlate with schizophrenia. The present work reviews data indicating that these mutations play a role in dimer formation with dopamine D1 receptor (D₁R), with the strongest effect observed for Ser311Cys variant. Similarly, the affinity for antipsychotic drugs of this genetic variant depends on whether it is expressed together with D₁R or not. Better understanding of altered ability of genetic variants of D₂R to form dimers with D₁R, as well as of altered affinity for antipsychotic drugs, depending on the absence or presence of the second dopamine receptor is of great importance-since these two receptors are not always co-expressed in the same cell. It may well be that targeting new compounds toward the D₁R-D₂R dimers, which the most probably form under conditions of excessive dopamine release, will result in antipsychotic drugs devoid of serious side effects.

[Preclinical pharmacological profiles and clinical efficacy of the novel antipsychotic drug brexpiprazole (REXULTI® Tablets 1 mg, 2 mg)]

Brexpiprazole (Rexulti^®) is the second antipsychotic agent in the world with dopamine D2 receptor partial agonist which was developed by Otsuka Pharmaceutical Co. Ltd. It is categorized as 〝Serotonin- dopamine Activity Modulator (SDAM)〟 that regulates both serotoninergic and dopaminergic systems by acting as a partial agonist for serotonin 5-HT1A receptors and D2 receptors and as an antagonist for 5-HT2A receptors. In preclinical pharmacological studies, brexpiprazole showed the equivalent antipsychotic-like effects to those of other atypical antipsychotics. And it was suggested that brexpiprazole has the low potentials to induce extrapyramidal symptoms, hyperprolactinemia and tardive dyskinesia, with improvement effects on cognitive dysfunction. Furthermore, brexpiprazole has the weak effects on histamine H1 receptors which are associated with sedation and weight gain in clinical. In the clinical trials in patients with schizophrenia in both acute and maintenance phase, brexpiprazole showed improvement of antipsychotic effects against placebo, and low incidence of adverse events, e.g., extrapyramidal symptoms, hyperprolactinemia, and weight gain, as suggested in preclinical studies. Furthermore, brexpiprazole showed low incidence of metabolic abnormalities. In particular, brexpiprazole showed relatively low incidences of akathisia, insomnia and agitation which has been commonly reported with aripiprazole. This would be based on the pharmacological features of brexpiprazole that is more potent antagonism at 5-HT2A receptors and D2 receptors partial agonism with lower intrinsic activity compared to those of aripiprazole. In conclusion, brexpiprazole could be one of the antipsychotics with the most rational mechanism of action, and the better efficacy and safety/tolerability profiles would contribute to the treatment of patients with schizophrenia.

Randomized, double-blind, placebo-controlled study of F17464, a preferential D3 antagonist, in the treatment of acute exacerbation of schizophrenia

F17464, a highly potent preferential D3 antagonist, is a novel compound in development for schizophrenia treatment. This phase II, double-blind, randomized, placebo-controlled, parallel-group study in five European countries evaluated the efficacy and safety of F17464, 20 mg twice daily, versus placebo over 6 weeks in patients with acute exacerbation of schizophrenia. Change from baseline to Day 43 of the Positive and Negative Syndrome Scale (PANSS) total score was the primary outcome. The data from 134 randomized patients (67 per group) were analyzed (efficacy/safety). Using analysis of covariance (ANCOVA) after last observation carried forward (LOCF) imputation (primary analysis), the PANSS total score reduction was statistically significantly greater for F17464 than placebo treated subjects at endpoint (p = 0.014); using ANCOVA with Multiple Imputation (MI) method, the between-group difference was in favor of F17464 but did not reach statistical significance. Differences in PANSS positive and general psychopathology subscale score, Marder positive factor score, PANSS response, and PANSS resolution criteria were also statistically significant in favor of F17464 (p values < 0.05) using the LOCF method, with similar results as for the primary analysis using the MI method. Treatment-related adverse events (AEs) were reported in 49.3% and 46.3% of patients on F17464 and placebo, respectively. The most common AEs in F17464 group: insomnia, agitation, and increased triglycerides; worsening of schizophrenia/drug ineffective was less frequent in F17464. Interestingly, no weight gain, no extrapyramidal disorder except rare akathisia were observed under F17464. This 6-week trial demonstrated therapeutic efficacy of 40 mg/day F17464 in improving symptoms of acute exacerbation of schizophrenia with a favorable safety profile.

Potent Dopamine D2 Antagonists Block the Reward-Enhancing Effects of Nicotine in Smokers With Schizophrenia

Antipsychotics that are potent dopamine (DA) D2 receptor antagonists have been linked to elevated levels of nicotine dependence in smokers with schizophrenia. Because activation of D2 receptors mediates motivation for nicotine, we examined whether potent D2 antagonists would diminish nicotine's ability to stimulate reward processing-a mechanism that may drive compensatory increases in smoking. Smokers with schizophrenia (n = 184) were recruited and stratified into medication groups based on D2 receptor antagonist potency. The effects of smoking on reward function were assessed using a probabilistic reward task (PRT), administered pre- and post-smoking. The PRT used an asymmetrical reinforcement schedule to produce a behavioral response bias, previously found to increase under conditions (including smoking) that enhance mesolimbic DA signaling. Among the 98 participants with valid PRT data and pharmacotherapy that could be stratified into D2 receptor antagonism potency, a medication × smoking × block interaction emerged (P = .005). Post-hoc tests revealed a smoking × block interaction only for those not taking potent D2 antagonists (P = .007). This group exhibited smoking-related increases in response bias (P < .001) that were absent in those taking potent D2 antagonists (P > .05). Our findings suggest that potent D2 antagonists diminish the reward-enhancing effects of nicotine in smokers with schizophrenia. This may be a mechanism implicated in the increased rate of smoking often observed in patients prescribed these medications. These findings have important clinical implications for the treatment of nicotine dependence in schizophrenia.

Brexpiprazole has a low risk of dopamine D2 receptor sensitization and inhibits rebound phenomena related to D2 and serotonin 5-HT2A receptors in rats

Background

Long‐term antipsychotic treatment in patients with schizophrenia can induce supersensitivity psychosis and tardive dyskinesia which is thought to be caused by dopamine D₂ receptor sensitization. We evaluated the effects of brexpiprazole on D₂ receptor sensitivity after subchronic treatment in rats. We also evaluated whether brexpiprazole could suppress enhanced response to D₂ receptors in rats subchronically dosed with another atypical antipsychotic.

Methods

The maximum D₂ receptor density (B_max) and apomorphine (a D₂ receptor agonist)‐induced stereotypy were measured in rats orally dosed with vehicle, haloperidol (1 mg/kg), or brexpiprazole (4 or 30 mg/kg for B_max, 6 or 30 mg/kg for stereotypy) for 21 days. Then, effects of oral administrations of brexpiprazole (3 mg/kg), aripiprazole (10 mg/kg), and olanzapine (3 mg/kg) against increases in apomorphine‐induced hyperlocomotion and (±)‐2,5‐dimethoxy‐4‐iodoamphetamine hydrochloride (DOI: a 5‐HT_2A receptor agonist)‐induced head twitches were evaluated in rats subcutaneously treated with risperidone (1.5 mg/kg/d) via minipumps for 21 days.

Results

Haloperidol and brexpiprazole (30 mg/kg: approximately tenfold ED₅₀ of anti‐apomorphine‐induced stereotypy) but not brexpiprazole (4 or 6 mg/kg) significantly increased the B_max and apomorphine‐induced stereotypy. Brexpiprazole (3 mg/kg) and olanzapine (3 mg/kg) significantly suppressed both increases in apomorphine‐induced hyperlocomotion and also DOI‐induced head twitches in rats subchronically treated with risperidone, but aripiprazole (10 mg/kg) significantly suppressed only apomorphine‐induced hyperlocomotion.

Conclusion

Brexpiprazole has a low risk of D₂ receptor sensitization after a repeated administration and suppresses the rebound phenomena related to D₂ and 5‐HT_2A receptors after a repeated administration of risperidone.

Brexpiprazole has less potential to evoke dopamine D2 receptor supersensitivity in rats after repeated administration compared to haloperidol. In addition, brexpiprazole may have a lower risk for producing rebound symptoms associated with D2 receptor, 5‐HT2A receptor sensitization when switching from other antipsychotics such as risperidone.

Dopamine D2L Receptor Deficiency Causes Stress Vulnerability through 5-HT1A Receptor Dysfunction in Serotonergic Neurons

Mental disorders are caused by genetic and environmental factors. We here show that deficiency of an isoform of dopamine D₂ receptor (D₂R), D_2LR, causes stress vulnerability in mouse. This occurs through dysfunction of serotonin [5-hydroxytryptamine (5-HT)] 1A receptor (5-HT_1AR) on serotonergic neurons in the mouse brain. Exposure to forced swim stress significantly increased anxiety- and depressive-like behaviors in D_2LR knock-out (KO) male mice compared with wild-type mice. Treatment with 8-OH-DPAT, a 5-HT_1AR agonist, failed to alleviate the stress-induced behaviors in D_2LR-KO mice. In forced swim-stressed D_2LR-KO mice, 5-HT efflux in the medial prefrontal cortex was elevated and the expression of genes related to 5-HT levels was upregulated by the transcription factor PET1 in the dorsal raphe nucleus. Notably, D_2LR formed a heteromer with 5-HT_1AR in serotonergic neurons, thereby suppressing 5-HT_1AR-activated G-protein-activated inwardly rectifying potassium conductance in D_2LR-KO serotonergic neurons. Finally, D_2LR overexpression in serotonergic neurons in the dorsal raphe nucleus alleviated stress vulnerability observed in D_2LR-KO mice. Together, we conclude that disruption of the negative feedback regulation by the D_2LR/5-HT_1A heteromer causes stress vulnerability.SIGNIFICANCE STATEMENT Etiologies of mental disorders are multifactorial, e.g., interactions between genetic and environmental factors. In this study, using a mouse model, we showed that genetic depletion of an isoform of dopamine D₂ receptor, D_2LR, causes stress vulnerability associated with dysfunction of serotonin 1A receptor, 5-HT_1AR in serotonergic neurons. The D_2LR/5-HT_1AR inhibitory G-protein-coupled heteromer may function as a negative feedback regulator to suppress psychosocial stress.

Therapy of Schizoaffective Disorder and Paranoid Schizophrenia with Episodic Course

Background. The use of atypical antipsychotics in schizophrenia contributes to the reduction of psychotic, affective, negative and cognitive disorders.

Aims. To evaluate the effectiveness of ziprasidone therapy in patients with schizoaffective disorder and paranoid schizophrenia with episodic course.

Materials and methods. In accordance with ICD-10 there were 14 (63.6 %) people with schizoaffective disorder (F25), 8 (36.4 %) people with paranoid schizophrenia, episodic course (F20.x1). Treatment with ziprasidone lasted 42 days. The dose of ziprasidone in 6 patients (27.3 %) was 80 mg, in 10 patients (45.5 %) – 120 mg, in 6 patients (27.3 %) – 160 mg. Evaluation of the effectiveness of ziprasidone therapy was carried out using psychometric scales (PANSS, General clinical impression scale to assess the effectiveness of therapy – CGI-S, CGI-I), adverse events were registered with the UKU scale.

Results. The number of respondents was 19 (86.3 %) (reduction of the total score on the PANSS scale > 20 % of the pre-treatment level). Ziprasidone was effective in patients with schizoaffective disorder with a significant decrease in total score on PANSS subscales to the 14 th day of therapy (p < 0.05), with paranoid schizophrenia with episodic course – by the 21st day (p < 0.01). According to the CGI-S scale at the end of therapy, “borderline condition” was observed in 10 patients (52.6 %), mild severity – in 3 (15.8 %), normal condition – in 6 (31.6 %). CGI-I scale showed a significant improvement in 10 patients (52.6 %), marked improvement – in 9 patients (47.4 %). Among the mild adverse events that do not require discontinuation of the drug, we noted: weakness – in 3 patients (15.8 %), drowsiness – in 3 (15.8 %), impaired concentration – in 2 (10.5 %), orthostatic dizziness – in 2 (10.5 %), galactorrhea – in 1 (5.3 %).

Conclusions. Ziprasidone is an effective antipsychotic drug that has a safe tolerability profile. It can be used in patients with schizoaffective disorders and paranoid schizophrenia with episodic course.

Design of novel dopamine D2 and serotonin 5-HT2A receptors dual antagonists toward schizophrenia: An integrated study with QSAR, molecular docking, virtual screening and molecular dynamics simulations

The extrapyramidal side effects of schizophrenia treatment can be significantly reduced by simultaneously targeting dopamine D₂ and serotonin 5-HT_2A receptors. In this study, three-dimensional quantitative structure-activity relationship (3D-QSAR) models of D₂ receptor (CoMFA-1, q² = 0.767, r² = 0.969; CoMSIA-1, q² = 0.717, r² = 0.978) and 5-HT_2A receptor antagonists (CoMFA-2, q² = 0.703, r² = 0.946; CoMSIA-2, q² = 0.675, r² = 0.916) were successfully constructed using 35 tetrahydropyridopyrimidinone derivatives. Topomer CoMFA and HQSAR models were then constructed to further validate and supplement above models. Results showed that all models had good predictive power and stability. Contour map analysis revealed that the electrostatic and hydrophobic fields played vital roles in the bioactivity of dual antagonists. Molecular docking and molecular dynamic studies also suggested that the hydrogen bonding, electrostatic and hydrophobic interactions played key roles in the formation of stable binding sites. Meanwhile, several key residues like ASP114, TRP100, PHE389 of dopamine D₂ receptor and ASP134, PHE328, TRP324 of serotonin 5-HT_2A receptor were identified. Based on above findings, seven compounds were obtained through bioisostere replacement and ten compounds were designed by contour map analysis, in which the predicted activity of compounds S6 and DS2 were equivalent to that of the template compound 15. 3D-QSAR and ADMET predictions indicated that all newly designed compounds had great biological activity and physicochemical properties. Moreover, based on the best pharmacophore model, four compounds (Z1, Z2, Z3 and Z4) with new backbones were obtained by virtual screening. Overall, this study could provide theoretical guidance for the structural optimization, design and synthesis of novel dopamine D₂ and serotonin 5-HT_2A receptors dual antagonists. Abbreviations3D-QSARThree-dimensional quantitative structure-activity relationship5-HT_2ARSerotonin 5-hydroxytryptamine 5-HT_2A receptor5-HT_2CRSerotonin 5-hydroxytryptamine 5-HT_2C receptor receptorCADDComputer-aided drug designCoMFAComparative molecular field analysisCoMSIAComparative molecular similarity index analysisD₂RDopamine D(2) receptorGPCRG-protein coupled receptorPLSPartial least squares regressionHQSARHologram quantitative structure-activity relationship. Communicated by Ramaswamy H. Sarma.

Aripiprazole and Delusional Disorder

Delusional disorder is a relatively rare psychotic illness characterized by delusions with contents that are theoretically possible but highly unlikely, and an absence of the disorganized thought and negative symptoms characteristic of schizophrenia. The illness is rarely studied systematically and most guidance with regard to the treatment derives from case reports and small case series. Antipsychotic medications are the mainstay of treatment, but it is not clear whether any particular agent is more effective than others. We report the case of a patient with delusional disorder who had failed to respond to risperidone but improved markedly with aripiprazole. Aripiprazole may show promise as a treatment for delusional disorder, possibly as a result of its effects on both dopaminergic and serotonergic receptors.

Classics in Chemical Neuroscience: Risperidone

After the identification of the influence of serotonergic receptors in ameliorating the negative symptoms associated with schizophrenia, atypical antipsychotics were developed by incorporating dopamine and serotonin antagonism. Risperidone, sold under the trade name Risperdal, was the second atypical antipsychotic developed following clozapine but quickly became a first-line treatment for acute and chronic schizophrenia because of its preferential side effect profile. Despite initial Food and Drug Administration approval 25 years ago, risperidone continues to be a fundamental treatment for schizophrenia, bipolar I disorder, and autism-related irritability. It is on the World Health Organization's List of Essential Medicines for its balance of efficacy, safety, tolerability, and cost-effectiveness. In this review, we highlight the history and importance of risperidone as an atypical antipsychotic, in addition to its chemical synthesis, manufacturing, drug metabolism and pharmacokinetics, pharmacology, structure-activity relationship, indications, and adverse effects.

The preclinical discovery and development of cariprazine for the treatment of schizophrenia

INTRODUCTION

Cariprazine is approved in the United States and Europe for the treatment of manic or mixed episodes associated with bipolar I disorder and for the treatment of schizophrenia in adult patients. It is typically administered orally once a day (a dose range 1.5 - 6 mg/day), does require titration, and may be given with or without food. It has a half-life of 2 - 4 days with an active metabolite that has a terminal half-life of 2 - 3 weeks. Areas covered: This review article focuses on the preclinical discovery of cariprazine providing details regarding its pharmacological, behavioral, and neurochemical mechanisms and its contribution to clinical therapeutic benefits. This article is based on the available literature with respect to the preclinical and clinical findings and product labels of cariprazine. Expert opinion: Cariprazine shows highest affinity toward D₃ receptors, followed by D₂, 5-HT_2B, and 5-HT_1A receptors. It also shows moderate affinity toward σ₁, 5-HT_2A, and histamine H₁ receptors. Long-term administration of cariprazine altered the abundance of dopamine, serotonin, and glutamate receptor subtypes in different brain regions. All these mechanisms of cariprazine may contribute toward its unique preclinical profile and its clinically observed benefits in the treatment of schizophrenia, bipolar mania, and possibly other psychiatric disorders.

Repeated Clozapine Increases the Level of Serotonin 5-HT1AR Heterodimerization with 5-HT2A or Dopamine D2 Receptors in the Mouse Cortex

G-protein–coupled receptor (GPCR) heterodimers are new targets for the treatment of schizophrenia. Dopamine D₂ receptors and serotonin 5-HT_1A and 5-HT_2A receptors play an important role in neurotransmission and have been implicated in many human psychiatric disorders, including schizophrenia. Therefore, in this study, we investigated whether antipsychotic drugs (clozapine (CLZ) and haloperidol (HAL)) affected the formation of heterodimers of D₂–5-HT_1A receptors as well as 5-HT_1A–5-HT_2A receptors. Proximity ligation assay (PLA) was used to accurately visualize, for the first time, GPCR heterodimers both at in vitro and ex vivo levels. In line with our previous behavioral studies, we used ketamine to induce cognitive deficits in mice. Our study confirmed the co-localization of D₂/5-HT_1A and 5-HT_1A/5-HT_2A receptors in the mouse cortex. Low-dose CLZ (0.3 mg/kg) administered repeatedly, but not CLZ at 1 mg/kg, increased the level of D₂–5-HT_1A and 5-HT_1A–5-HT_2A heterodimers in the mouse prefrontal and frontal cortex. On the other hand, HAL decreased the level of GPCR heterodimers. Ketamine affected the formation of 5-HT_1A–5-HT_2A, but not D₂–5-HT_1A, heterodimers.

Antidepressant-Induced Activation in Children and Adolescents: Risk, Recognition and Management

The tolerability of antidepressants is poorly characterized in children and adolescents with depressive and anxiety disorders. Among adverse events that affect the tolerability of antidepressants in youth is activation, a cluster of symptoms that represent a hyperarousal event characterized by impulsivity, restlessness, and/or insomnia. This cluster of symptoms was first identified as a side effect of selective serotonin and selective serotonin norepinephrine inhibitors (SSRIs and SSNRIs) in the early 1990s; however, activation remains poorly characterized in terms of prevalence, risk factors, and pathophysiology. This article describes the pathophysiology of antidepressant-related activation, predictors of activation and its clinical management in youth with depressive and anxiety disorders who are treated with antidepressant medications.

The antipsychotic drug brexpiprazole reverses phencyclidine-induced disruptions of thalamocortical networks

Brexpiprazole (BREX), a recently approved antipsychotic drug in the US and Canada, improves cognitive dysfunction in animal models, by still largely unknown mechanisms. BREX is a partial agonist at 5-HT_1A and D₂ receptors and antagonist at α_1B- and α_2C-adrenergic and 5-HT_2A receptors all with a similar potency. The NMDA receptor antagonist phencyclidine (PCP), used as pharmacological model of schizophrenia, activates thalamocortical networks and decreases low frequency oscillations (LFO; <4 Hz). These effects are reversed by antipsychotics. Here we assessed the ability of BREX to reverse PCP-induced hyperactivity of thalamocortical circuits, and the involvement of 5-HT_1A receptors in its therapeutic action. BREX reversed PCP-induced neuronal activation at a lower dose in centromedial/mediodorsal thalamic nuclei (CM/MD; 0.5mg/kg) than in pyramidal medial prefrontal cortex neurons (mPFC, 2mg/kg), perhaps due to antagonism at α_1B-adrenoceptors, abundantly expressed in the thalamus. Conversely, a cumulative 0.5 mg/kg dose reversed a PCP-induced LFO decrease in mPFC but not in CM/MD. BREX reduced LFO in both areas, yet with a different dose-response, and moderately excited mPFC neurons. The latter effect was reversed by the 5-HT_1A receptor antagonist WAY-100635. Thus, BREX partly antagonizes PCP-induced thalamocortical hyperactivity, differentially in mPFC versus CM/MD. This regional selectivity may be related to the differential expression of α_1B-, α_2C-adrenergic and 5-HT_2A receptors in both regions and/or different neuronal types. Furthermore, the pro-cognitive properties of BREX may be related to the 5-HT_1A receptor-mediated increase in mPFC pyramidal neuron activity. Overall, the present data provide new insight on the brain elements involved in BREX's therapeutic actions.

Aripiprazole, A Drug that Displays Partial Agonism and Functional Selectivity

BACKGROUND

The treatment of schizophrenia is challenging due to the wide range of symptoms (positive, negative, cognitive) associated with the disease. Typical antipsychotics that antagonize D2 receptors are effective in treating positive symptoms, but extrapyramidal side-effects (EPS) are a common occurrence. Atypical antipsychotics targeting 5-HT2A and D2 receptors are more effective at treating cognitive and negative symptoms compared to typical antipsychotics, but these drugs also result in side-effects such as metabolic syndromes.

OBJECTIVE

To identify evidence in the literature that elucidates the pharmacological profile of aripiprazole.s.

METHODS

We searched PubMed for peer reviewed articles on aripiprazole and its clinical efficacy, side-effects, pharmacology, and effects in animal models of schizophrenia symptoms.

RESULTS

Aripiprazole is a newer atypical antipsychotic that displays a unique pharmacological profile, including partial D2 agonism and functionally selective properties. Aripiprazole is effective at treating the positive symptoms of schizophrenia and has the potential to treat negative and cognitive symptoms at least as well as other atypical antipsychotics. The drug has a favorable side-effect profile and has a low propensity to result in EPS or metabolic syndromes. Animal models of schizophrenia have been used to determine the efficacy of aripiprazole in symptom management. In these instances, aripiprazole resulted in the reversal of deficits in extinction, pre-pulse inhibition, and social withdrawal. Because aripiprazole requires a greater than 90% occupancy rate at D2 receptors to be clinically active and does not produce EPS, this suggests a functionally selective effect on intracellular signaling pathways.

CONCLUSION

A combination of factors such as dopamine system stabilization via partial agonism, functional selectivity at D2 receptors, and serotonin-dopamine system interaction may contribute to the ability of aripiprazole to successfully manage schizophrenia symptoms. This review examines these mechanisms of action to further clarify the pharmacological actions of aripiprazole.

Assessment of the relationship between food addiction and nutritional status in schizophrenic patients

OBJECTIVE

Obesity is one of today's most important public health problems. It is suggested that overeating and substance addiction show similarities, and addiction to food may be an important factor in the obesity epidemic. This study aimed to determine the prevalence of food addiction among schizophrenic patients and to examine the relationship between food addiction and anthropometric measurements and dietary nutrient intake.

METHODS

Study participants included a total of 104 schizophrenic outpatients, 62 females and 42 males. Food addiction was assessed by using the Yale Food Addiction Scale, and the anthropometric measurements of participants and their three-day food consumption were recorded.

RESULTS

This study found that more than half of the schizophrenic patients (60.6%) had food addiction, and that female schizophrenic patients had a higher prevalence (62.9%) of food addiction than male patients (57.1%). More than one-third of the schizophrenic patients with food addiction (41.3%) were found to be obese and their BMI, body weight, waist circumference, and body-fat ratio were higher than those of schizophrenic patients who did not have food addiction (P > 0.05). Moreover, the schizophrenic patients with food addiction were found to take significantly more energy, carbohydrate, and fat in their diet (P < 0.05).

CONCLUSION

It was observed that the development of food addiction in schizophrenic patients increased the risk of obesity and cardiovascular diseases, which were found to be at higher levels in these patients. Educational programs should be planned for these patients to acquire health dietary habits and to increase their physical activity levels, and an additional psychosocial support should be provided for patients with food addiction.

Extrapyramidal side effects of antipsychotics are linked to their association kinetics at dopamine D2 receptors

Atypical antipsychotic drugs (APDs) have been hypothesized to show reduced extrapyramidal side effects (EPS) due to their rapid dissociation from the dopamine D₂ receptor. However, support for this hypothesis is limited to a relatively small number of observations made across several decades and under different experimental conditions. Here we show that association rates, but not dissociation rates, correlate with EPS. We measured the kinetic binding properties of a series of typical and atypical APDs in a novel time-resolved fluorescence resonance energy transfer assay, and correlated these properties with their EPS and prolactin-elevating liabilities at therapeutic doses. EPS are robustly predicted by a rebinding model that considers the microenvironment of postsynaptic D₂ receptors and integrates association and dissociation rates to calculate the net rate of reversal of receptor blockade. Thus, optimizing binding kinetics at the D₂ receptor may result in APDs with improved therapeutic profile.

Atypical antipsychotics show reduced extrapyramidal side effects compared to first generation drugs. Here the authors use time-resolved FRET to measure binding kinetics, and show that side effects correlate with drug association rates to the D₂ receptor, while dissociation rates correlate with prolactin elevation.

Antinociceptive, antiallodynic and antihyperalgesic effects of the 5-HT1A receptor selective agonist, NLX-112 in mouse models of pain

BACKGROUND AND PURPOSE

NLX-112 (a.k.a. befiradol, F13640) is a drug candidate intended for the treatment of l-DOPA-induced dyskinesia. It is a highly selective serotonin 5-HT_1A receptor full agonist which has been previously tested in a variety of models of CNS effects including analgesic activity in rat. Its activity in mouse models of pain has not been previously investigated.

EXPERIMENTAL APPROACH

The activity of NLX-112 was tested in mouse models of acute pain (hot plate), tonic pain (intraplantar formalin test), in the oxaliplatin-induced neuropathic pain model of chemotherapy-induced peripheral neuropathy and in the streptozotocin (STZ)-induced model of painful diabetic neuropathy.

KEY RESULTS

The main findings indicate that (i) NLX-112 was markedly active in the formalin test with potent reduction of paw licking in both phases of the test (minimal effective dose (MED) 0.5 mg/kg i.p. and p.o. in acute phase, and 0.1 mg/kg i.p. and 1 mg/kg p.o. in late phase). The effects of NLX-112 in this test were completely abolished by the selective 5-HT_1A receptor antagonist, WAY100635; (ii) NLX-112 was active in the hot plate test and in the oxaliplatin-induced neuropathic pain model of chemotherapy-induced peripheral neuropathy, but at markedly higher doses (MED 2.5 mg/kg i.p.); (iii) NLX-112 was least active in the STZ-induced model of painful diabetic neuropathy (MED 5 mg/kg i.p.); (iv) NLX-112 did not affect locomotor activity.

CONCLUSIONS AND IMPLICATIONS

NLX-112 may have significant potential for treatment of tonic pain but may be less promising as a candidate for treatment of chemotherapy-induced or diabetic neuropathic pain.

The role of 5-HT receptors in depression

Depression is a polygenic and highly complex psychiatric disorder that remains a major burden on society. Antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), are some of the most commonly prescribed drugs worldwide. In this review, we will discuss the evidence that links serotonin and serotonin receptors to the etiology of depression and the mechanisms underlying response to antidepressant treatment. We will then revisit the role of serotonin in three distinct hypotheses that have been proposed over the last several decades to explain the pathophysiology of depression: the monoamine, neurotrophic, and neurogenic hypotheses. Finally, we will discuss how recent studies into serotonin receptors have implicated specific neural circuitry in mediating the antidepressant response, with a focus being placed on the hippocampus.

Classics in Chemical Neuroscience: Aripiprazole

Aripiprazole was the first antipsychotic developed to possess agonist properties at dopamine D₂ autoreceptors, a groundbreaking strategy that presented a new vista for schizophrenia drug discovery. The dopamine D₂ receptor is the crucial target of all extant antipsychotics, and all developed prior to aripiprazole were D₂ receptor antagonists. Extensive blockade of these receptors, however, typically produces extrapyramidal (movement) side effects, which plagued first-generation antipsychotics, such as haloperidol. Second-generation antipsychotics, such as clozapine, with unique polypharmacology and D₂ receptor binding kinetics, have significantly lower risk of movement side effects but can cause myriad additional ones, such as severe weight gain and metabolic dysfunction. Aripiprazole's polypharmacology, characterized by its unique agonist activity at dopamine D₂ and D₃ and serotonin 5-HT_1A receptors, as well as antagonist activity at serotonin 5-HT_2A receptors, translates to successful reduction of positive, negative, and cognitive symptoms of schizophrenia, while also mitigating risk of weight gain and movement side effects. New observations, however, link aripiprazole to compulsive behaviors in a small group of patients, an unusual side effect for antipsychotics. In this review, we discuss the chemical synthesis, pharmacology, pharmacogenomics, drug metabolism, and adverse events of aripiprazole, and we present a current understanding of aripiprazole's neurotherapeutic mechanisms, as well as the history and importance of aripiprazole to neuroscience.

Distinctive in vitro signal transduction profile of NLX-112, a potent and efficacious serotonin 5-HT1A receptor agonist

Objectives

NLX-112 (befiradol, F13640) is a selective serotonin 5-HT1A receptor agonist. Although it has been tested in vivo, little has been reported on its in vitro signal transduction profile.

Methods

NLX-112 was tested on G-protein activation, inhibition of adenylyl cyclase, ERK1/2 phosphorylation (pERK) and receptor internalization in recombinant cell lines. NLX-112 was also tested on G-protein activation in rat hippocampal membranes. Gα subunit mRNA expression in cell lines and rat brain tissue was quantified by quantitative PCR.

Key findings

For all signalling measures, NLX-112 exhibited agonist efficacy greater than for reference compounds ((±)8-OH-DPAT or buspirone), but similar to the endogenous agonist, serotonin, and was more potent for pERK than other responses. In rat hippocampal membranes, NLX-112 stimulated ‘total G-proteins' but, unlike (±)8-OH-DPAT and buspirone, was more potent for Gαo activation. Cell lines predominantly expressed Gαi1 and Gαi2 mRNA, with low levels of Gαo, whereas in rat brain Gαo subunits showed highest mRNA expression.

Conclusions

Unlike reference compounds, NLX-112 was a highly efficacious agonist in vitro, preferentially activating pERK in cell lines and Gαo proteins in rat hippocampal membranes. However, Gα subunit mRNA levels differ markedly between rat brain and cell lines, warranting caution when extrapolating from recombinant systems to native tissues.

Modulation of Synaptic Plasticity in the Cortex Needs to Understand All the Players

The prefrontal cortex (PFC) is involved in cognitive tasks such as working memory, decision making, risk assessment and regulation of attention. These functions performed by the PFC are supposed to rely on rhythmic electrical activity generated by neuronal network oscillations determined by a precise balance between excitation and inhibition balance (E/I balance) resulting from the coordinated activities of recurrent excitation and feedback and feedforward inhibition. Functional alterations in PFC functions have been associated with cognitive deficits in several pathologies such as major depression, anxiety and schizophrenia. These pathological situations are correlated with alterations of different neurotransmitter systems (i.e., serotonin (5-HT), dopamine (DA), acetylcholine…) that result in alterations of the E/I balance. The aim of this review article is to cover the basic aspects of the regulation of the E/I balance as well as to highlight the importance of the complementarity role of several neurotransmitters in the modulation of the plasticity of excitatory and inhibitory synapses. We illustrate our purpose by recent findings that demonstrate that 5-HT and DA cooperate to regulate the plasticity of excitatory and inhibitory synapses targeting layer 5 pyramidal neurons (L5PyNs) of the PFC and to fine tune the E/I balance. Using a method based on the decomposition of the synaptic conductance into its excitatory and inhibitory components, we show that concomitant activation of D1-like receptors (D1Rs) and 5-HT_1ARs, through a modulation of NMDA receptors, favors long term potentiation (LTP) of both excitation and inhibition and consequently does not modify the E/I balance. We also demonstrate that activation of D2-receptors requires functional 5-HT_1ARs to shift the E-I balance towards more inhibition and to favor long term depression (LTD) of excitatory synapses through the activation of glycogen synthase kinase 3β (GSK3β). This cooperation between different neurotransmitters is particularly relevant in view of pathological situations in which alterations of one neurotransmitter system will also have consequences on the regulation of synaptic efficacy by other neurotransmitters. This opens up new perspectives in the development of therapeutic strategies for the pharmacological treatment of neuronal disorders.

Involvement of presynaptic 5-HT1A receptors in the low propensity of brexpiprazole to induce extrapyramidal side effects in rats

Previous studies have shown that partial and full 5-HT_1A receptor agonists reduce antipsychotic-induced catalepsy. Consequently, some antipsychotics combining balanced efficacy between dopamine (DA) D₂ antagonism or partial agonism and 5-HT_1A receptor agonism have a low propensity to induce extrapyramidal side effects (EPS), as reflected by low cataleptogenic activity in rodents. In the present experiments, we attempted to explore the importance of pre- and postsynaptic 5-HT_1A agonistic properties of brexpiprazole and aripiprazole in the context of neurological side-effect liabilities. Additional measures of prefrontal cortical serotonin (5-HT) and DA levels using microdialysis were used to support that brexpiprazole has a preferential agonist effect on presynaptic 5-HT_1A receptors. Brexpiprazole (3.0 and 10mg/kg, p.o.) as well as aripiprazole (8.0 and 30mg/kg, p.o.) failed to induce catalepsy in rats. Brexpiprazole (10mg/kg, p.o.) significantly reduced the cataleptic response induced by haloperidol (0.63mg/kg, s.c.), while aripiprazole (1.0-100mg/kg, p.o.) failed to reverse the effect of haloperidol and only showed a numeric decrease at 10mg/kg, (p.o.). When 5-HT_1A receptors were blocked by the selective antagonist, WAY100635 (1.0mg/kg, s.c.), cataleptogenic properties of brexpiprazole (10mg/kg; p.o), but not aripiprazole (8.0 and 30mg/kg, p.o.) were unmasked. The ("biased") 5-HT_1A receptor agonists F15599 (postsynaptic preference) and F13714 (presynaptic preference) had differential effects on haloperidol-induced catalepsy: F13714 (0.16mg/kg, s.c.) counteracted catalepsy, whereas F15599 (0.040mg/kg, s.c.) had no significant effect at regionally-selective doses. These data support a role of presynaptic 5-HT_1A receptors in the anticataleptic effect of brexpiprazole. The selective 5-HT_2A antagonist M100907 (0.10mg/kg, s.c.) had no effect on haloperidol-induced catalepsy, arguing against a major role of 5-HT_2A receptors in the cataleptogenic profile of brexpiprazole. The findings with brexpiprazole were supported using microdialysis studies: Brexpiprazole (3.0 and 10mg/kg, p.o.) decreased extracellular 5-HT levels in the medial prefrontal cortex (mPFC), while it failed to affect extracellular DA in the same samples, suggesting that the 5-HT_1A agonist properties of brexpiprazole may be preferentially presynaptic. In conclusion, these results confirm that brexpiprazole and aripiprazole have low propensities to induce EPS. However, the low EPS risk of brexpiprazole is more likely dependent on its agonist properties on presynaptic 5-HT_1A receptors, while that of aripiprazole is less sensitive to 5-HT_1A receptor antagonism.