Dopamine D3 receptor antagonism contributes to blonanserin-induced cortical dopamine and acetylcholine efflux and cognitive improvement

The dopamine D1 receptor positive allosteric modulator, DETQ, improves cognition and social interaction in aged mice and enhances cortical and hippocampal acetylcholine efflux

Dopamine (DA) D1 and D2 receptors (Rs) are critical for cognitive functioning. D1 positive allosteric modulators (D1PAMs) activate D1Rs without desensitization or an inverted U-shaped dose response curve. DETQ, [2-(2,6-dichlorophenyl)-1-((1S,3R)-3-(hydroxymethyl)-5-(2-hydroxypropan-2-yl)-1-methyl-3,4-dihydroisoquinolin-2(1H)-yl)ethan-1-one] is highly selective for the human D1Rs as shown in humanized D1R knock-in (hD1Ki) mice. Here, we have ascertained the efficacy of DETQ in aged [13-23-month-old (mo)] hD1Ki mice and their corresponding age-matched wild-type (WT; C57BL/6NTac) controls. We found that in aged mice, DETQ, given acutely, subchronically, and chronically, rescued both novel object recognition memory and social behaviors, using novel object recognition (NOR) and social interaction (SI) tasks, respectively without any adverse effect on body weight or mortality. We have also shown, using in vivo microdialysis, a significant decrease in basal DA and norepinephrine, increase in glutamate (Glu) and gamma-amino butyric acid (GABA) efflux with no significant changes in acetylcholine (ACh) levels in aged vs young mice. In young and aged hD1Ki mice, DETQ, acutely and subchronically increased ACh in the medial prefrontal cortex and hippocampal regions in aged hD1Ki mice without affecting Glu. These results suggest that the D1PAM mechanism is of interest as potential treatment for cognitive and social behavioral deficits in neuropsychiatric disorders including but not restricted to neurodegenerative disorders, such as Parkinson's disease.

Efficacy and safety of blonanserin versus risperidone in the treatment of schizophrenia: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

We conducted a systematic review and meta-analysis to evaluate the efficacy and safety of blonanserin and risperidone for the treatment of schizophrenia and to provide reliable pharmacotherapeutic evidence for in the clinical treatment of schizophrenia.

METHODS

We systematically searched the PubMed, Cochrane Library, Embase, Chinese Biomedical Literature Database (CBM), and China National Knowledge Infrastructure (CNKI) databases for head-to-head randomized controlled trials that compared blonanserin with risperidone for the treatment of schizophrenia. We extracted the following data: author, year, country, diagnostic criteria, sample size, course of treatment, dosage and outcomes. Our main endpoint was the changes in the Positive and Negative Syndrome Scale (PANSS) total scores. Meta-analysis of the included data was conducted by RevMan 5.3 software. We used the GRADE criteria to evaluate the certainty of the evidence.

RESULTS

A total of 411 studies were initially; 8 trials were eligible and were included in our analysis (N = 1386 participants). Regarding efficacy, there was no difference in changes in the PANSS total scores between the two groups (P > 0.05). In terms of safety, compared to risperidone, the incidence of serum prolactin increases and weight gain in the blonanserin group was lower (P<0.05), but the incidence of extrapyramidal symptoms (EPS) was higher (P<0.05).

CONCLUSION

The efficacy of blonanserin is similar to that of risperidone, but it is unclear whether blonanserin is more effective than risperidone at improving cognitive and social function. More high-quality studies are needed to verify the efficacy and safety of blonanserin in the future.

Effectiveness and safety of blonanserin for improving social and cognitive functions in patients with first-episode schizophrenia: a study protocol for a prospective, multicentre, single-arm clinical trial

INTRODUCTION

Both the pharmacological characteristics of blonanserin and its related small sample size studies suggest that blonanserin could alleviate social and cognitive dysfunctions in patients with schizophrenia. However, no large sample size studies have been performed so far. This study aimed to investigate the effectiveness and safety of blonanserin in improving social and cognitive functions in patients with first-episode schizophrenia.

METHODS AND ANALYSIS

This is a prospective, multicentre, single-arm clinical trial. A total of 188 patients with first-episode schizophrenia will be enrolled and will undergo a 0-7 day washout period before blonanserin administration. Doses of blonanserin will first be set to 4 mg P.O. twice per day after meals and gradually increased to 8-16 mg/d P.O., depending on patient's age and symptoms, for 26 weeks. Maximum dose of blonanserin will not be exceeding 24 mg/day. The primary endpoint of the study is the changes of Personal and Social Performance (PSP) score in patients from baseline to week 26. Secondary endpoints include changes in MATRICS consensus cognitive battery (MCCB), Paced Auditory Serial Addition Test (PASAT), grooved pegboard test (GPT), Positive and Negative Syndrome Scale (PANSS) total score and PANSS 5-factor subscale scores. Other endpoints include changes of serum brain-derived neurotrophic factor (BDNF) at corresponding visits and MRI results. Moreover, incidence of adverse events, changes in endocrine and metabolic profiles, renal, hepatic and sexual functions and extrapyramidal symptoms will be strictly monitored and recorded.

ETHICS AND DISSEMINATION

The study was approved by the ethics committee of the leading site Peking University Sixth Hospital (No. 2018-18), and all included patients are requested to provide written informed consent before enrolment. The study will be conducted according to the principles of the Declaration of Helsinki and follow the principles for clinical research.

TRIAL REGISTRATION NUMBER

NCT03784222.

Potential Mechanisms for Why Not All Antipsychotics Are Able to Occupy Dopamine D3 Receptors in the Brain in vivo

Dysfunctions of the dopaminergic system are believed to play a major role in the core symptoms of schizophrenia such as positive, negative, and cognitive symptoms. The first line of treatment of schizophrenia are antipsychotics, a class of medications that targets several neurotransmitter receptors in the brain, including dopaminergic, serotonergic, adrenergic and/or muscarinic receptors, depending on the given agent. Although the currently used antipsychotics display in vitro activity at several receptors, majority of them share the common property of having high/moderate in vitro affinity for dopamine D₂ receptors (D₂Rs) and D₃ receptors (D₃Rs). In terms of mode of action, these antipsychotics are either antagonist or partial agonist at the above-mentioned receptors. Although D₂Rs and D₃Rs possess high degree of homology in their molecular structure, have common signaling pathways and similar in vitro pharmacology, they have different in vivo pharmacology and therefore behavioral roles. The aim of this review, with summarizing preclinical and clinical evidence is to demonstrate that while currently used antipsychotics display substantial in vitro affinity for both D₃Rs and D₂Rs, only very few can significantly occupy D₃Rs in vivo. The relative importance of the level of endogenous extracellular dopamine in the brain and the degree of in vitro D₃Rs receptor affinity and selectivity as determinant factors for in vivo D₃Rs occupancy by antipsychotics, are also discussed.

Cognitive Deficit in Schizophrenia: From Etiology to Novel Treatments

Schizophrenia is a major mental illness characterized by positive and negative symptoms, and by cognitive deficit. Although cognitive impairment is disabling for patients, it has been largely neglected in the treatment of schizophrenia. There are several reasons for this lack of treatments for cognitive deficit, but the complexity of its etiology-in which neuroanatomic, biochemical and genetic factors concur-has contributed to the lack of effective treatments. In the last few years, there have been several attempts to develop novel drugs for the treatment of cognitive impairment in schizophrenia. Despite these efforts, little progress has been made. The latest findings point to the importance of developing personalized treatments for schizophrenia which enhance neuroplasticity, and of combining pharmacological treatments with non-pharmacological measures.

Pharmacology profile of F17464, a dopamine D3 receptor preferential antagonist

F17464 (N-(3-{4-[4-(8-Oxo-8H-[1,3]-dioxolo-[4,5-g]-chromen-7-yl)-butyl]-piperazin-1-yl}-phenyl)-methanesulfonamide, hydrochloride) is a new potential antipsychotic with a unique profile. The compound exhibits high affinity for the human dopamine receptor subtype 3 (hD3) (Ki = 0.17 nM) and the serotonin receptor subtype 1a (5-HT1a) (Ki = 0.16 nM) and a >50 fold lower affinity for the human dopamine receptor subtype 2 short and long form (hD2s/l) (Ki = 8.9 and 12.1 nM, respectively). [14C]F17464 dynamic studies show a slower dissociation rate from hD3 receptor (t1/2 = 110 min) than from hD2s receptor (t1/2 = 1.4 min) and functional studies demonstrate that F17464 is a D3 receptor antagonist, 5-HT1a receptor partial agonist. In human dopaminergic neurons F17464 blocks ketamine induced morphological changes, an effect D3 receptor mediated. In vivo F17464 target engagement of both D2 and 5-HT1a receptors is demonstrated in displacement studies in the mouse brain. F17464 increases dopamine release in the rat prefrontal cortex and mouse lateral forebrain - dorsal striatum and seems to reduce the effect of MK801 on % c-fos mRNA medium expressing neurons in cortical and subcortical regions. F17464 also rescues valproate induced impairment in a rat social interaction model of autism. All the neurochemistry and behavioural effects of F17464 are observed in the dose range 0.32-2.5 mg/kg i.p. in both rats and mice. The in vitro - in vivo pharmacology profile of F17464 in preclinical models is discussed in support of a therapeutic use of the compound in schizophrenia and autism.

Dopamine, Cognitive Impairments and Second-Generation Antipsychotics: From Mechanistic Advances to More Personalized Treatments

The pharmacological treatment of cognitive impairments associated with schizophrenia is still a major unmet clinical need. Indeed, treatments with available antipsychotics generate highly variable cognitive responses among patients with schizophrenia. This has led to the general assumption that antipsychotics are ineffective on cognitive impairment, although personalized medicine and drug repurposing approaches might scale down this clinical issue. In this scenario, evidence suggests that cognitive improvement exerted by old and new atypical antipsychotics depends on dopaminergic mechanisms. Moreover, the newer antipsychotics brexpiprazole and cariprazine, which might have superior clinical efficacy on cognitive deficits over older antipsychotics, mainly target dopamine receptors. It is thus reasonable to assume that despite more than 50 years of elusive efforts to develop novel non-dopaminergic antipsychotics, dopamine receptors remain the most attractive and promising pharmacological targets in this field. In the present review, we discuss preclinical and clinical findings showing dopaminergic mechanisms as key players in the cognitive improvement induced by both atypical antipsychotics and potential antipsychotics. We also emphasize the concept that these mechanistic advances, which help to understand the heterogeneity of cognitive responses to antipsychotics, may properly guide treatment decisions and address the unmet medical need for the management of cognitive impairment associated with schizophrenia.

Neurocognitive effects of atypical antipsychotics in patients with first-episode schizophrenia

Introduction: Cognitive impairment is a core feature of schizophrenia. The effects of atypical antipsychotics on the cognitive functions of patients with first-episode schizophrenia have not been comprehensively investigated so far. This study aims to compare neurocognitive effects of risperidone, olanzapine, and aripiprazole for first-episode schizophrenia.Methods: The study was a multicenter, randomized, open-label clinical trial. 546 patients were randomly divided into three medication groups, and followed up for 1 year. Cognitive performance was evaluated with a neuropsychological test battery. The Clinical trials.gov ID of the study is NCT01057849.Results: At 6 months, treatment resulted in significant improvements in all three groups in most cognitive domains except verbal learning and memory. At 12 months, three treatment groups had further improvements in three cognitive domains, but visual learning and memory performance dropped back to baseline.Conclusion: All three atypical antipsychotics tested in the study can potentially improve cognitive performance in first-episode schizophrenia, but no significant difference in the degree of improvement was found between drugs.

Dual-acting agents for improving cognition and real-world function in Alzheimer's disease: Focus on 5-HT6 and D3 receptors as hubs

To date, there are no interventions that impede the inexorable progression of Alzheimer's disease (AD), and currently-available drugs cholinesterase (AChE) inhibitors and the N-Methyl-d-Aspartate receptor antagonist, memantine, offer only modest symptomatic benefit. Moreover, a range of mechanistically-diverse agents (glutamatergic, histaminergic, monoaminergic, cholinergic) have disappointed in clinical trials, alone and/or in association with AChE inhibitors. This includes serotonin (5-HT) receptor-6 antagonists, despite compelling preclinical observations in rodents and primates suggesting a positive influence on cognition. The emphasis has so far been on high selectivity. However, for a multi-factorial disorder like idiopathic AD, 5-HT6 antagonists possessing additional pharmacological actions might be more effective, by analogy to "multi-target" antipsychotics. Based on this notion, drug discovery programmes have coupled 5-HT6 blockade to 5-HT4 agonism and inhibition of AchE. Further, combined 5-HT6/dopamine D3 receptor (D3) antagonists are of especial interest since D3 blockade mirrors 5-HT6 antagonism in exerting broad-based pro-cognitive properties in animals. Moreover, 5-HT6 and dopamine D3 antagonists promote neurocognition and social cognition via both distinctive and convergent actions expressed mainly in frontal cortex, including suppression of mTOR over-activation and reinforcement of cholinergic and glutamatergic transmission. In addition, 5-HT6 blockade affords potential anti-anxiety, anti-depressive and anti-epileptic properties, and antagonising 5-HT6 receptors may be associated with neuroprotective ("disease-modifying") properties. Finally D3 antagonism may counter psychotic episodes and D3 receptors themselves offer a promising hub for multi-target agents. The present article reviews the status of "R and D" into multi-target 5-HT6 and D3 ligands for improved treatment of AD and other neurodegenerative disorders of aging. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Effects of NBI-98782, a selective vesicular monoamine transporter 2 (VMAT2) inhibitor, on neurotransmitter efflux and phencyclidine-induced locomotor activity: Relevance to tardive dyskinesia and antipsychotic action

Valbenazine, a vesicular monoamine transporter 2 (VMAT2, SLC18A2) inhibitor, is a newly approved treatment for tardive dyskinesia. VMAT2 is present in the membrane of secretory vesicles and transports dopamine (DA), norepinephrine (NE), serotonin (5-HT), histamine, glutamate (Glu), and GABA into vesicles for presynaptic release. We utilized microdialysis in awake, freely moving mice to determine the effect of NBI-98782, the active metabolite of valbenazine, alone, or in combination with several antipsychotic drugs (APDs), to influence neurotransmitter efflux in the medial prefrontal cortex (mPFC), dorsal striatum (dSTR), hippocampus and nucleus accumbens (NAC); we also compared it with tetrabenazine, the prototypical VMAT2 inhibitor. Acute NBI-98782 and tetrabenazine decreased mPFC, dSTR, hippocampus, and NAC DA, 5-HT, and NE efflux, while increasing that of DOPAC, HVA, and 5-HIAA. Sub-chronic NBI-98782 (7 days) decreased baseline DA and 5-HT efflux in both mPFC and dSTR. NBI-98782 elicited similar effects on neurotransmitter efflux in sub-chronic NBI-98782-treated mice but also enhanced ACh and GABA; the decrease in DA efflux in mPFC and dSTR was not significant in the sc-treated animals. NBI-98782 suppressed clozapine-, olanzapine- and risperidone-induced DA efflux in both mPFC and dSTR, and ACh efflux in mPFC. NBI-98782 suppressed the haloperidol-induced DA efflux in dSTR, with minimal effect on GABA efflux. NBI-98782 attenuated PCP-induced DA, 5-HT, NE and Glu efflux, and AMPH-induced DA and NE efflux, in both mPFC and dSTR, as well as PCP- and AMPH-induced hyperlocomotion, suggesting possible beneficial antipsychotic effects.

The Role of Dopamine D3 Receptor Partial Agonism in Cariprazine-Induced Neurotransmitter Efflux in Rat Hippocampus and Nucleus Accumbens

Cariprazine is an approved antipsychotic and antidepressant which is a dopamine (DA) D₃-preferring D₃/D₂ receptor partial agonist, serotonin (5-HT) 5-HT_1A receptor partial agonist, and 5-HT_2B and 5-HT_2A receptor antagonist, a profile unique for atypical antipsychotic drugs. The purpose of this study was to clarify the effects of cariprazine and selective D₃ receptor ligands on neurotransmitter efflux in the rat nucleus accumbens (NAC) and ventral hippocampus (HIP), brain regions important for reality testing, rewarded behavior, and cognition. In vivo microdialysis was performed in awake, freely moving rats after administration of cariprazine; (+)-PD-128907 [(4aR,10bR)-3,4a,4,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol hydrochloride], a D₃ receptor-preferring agonist; and SB-277011A [trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolininecarboxamide hydrochloride], a selective D₃ receptor antagonist, alone or combined, and extracellular levels of multiple neurotransmitters and metabolites were measured in the NAC and HIP by ultraperformance liquid chromatography with tandem mass spectrometry. Cariprazine increased DA, norepinephrine (NE), and 5-HT efflux in both regions, whereas it increased glycine (Gly) and glutamate efflux only in the NAC and efflux of DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) only in the HIP. Similarly, SB-277011A increased DA, NE, DOPAC, and HVA, but not 5-HT, efflux in the NAC and HIP, and acetylcholine efflux in the HIP. Most of these effects of cariprazine and SB-277011A were fully or partially attenuated by the D₃ receptor agonist (+)-PD-128907, suggesting these effects of cariprazine are related to its D₃ receptor partial agonism, and that this mechanism, leading to diminished stimulation of D₃ receptors, may contribute to its efficacy in both schizophrenia and bipolar disorder. The possible role of Gly in the action of cariprazine is discussed. SIGNIFICANCE STATEMENT: The novel atypical antipsychotic drug cariprazine increased nucleus accumbens and hippocampal neurotransmitter efflux, similar to the actions of the D₃ receptor antagonist SB-277011A [trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolininecarboxamide hydrochloride]. The D₃ receptor-preferring agonist (+)-PD-128907 [(4aR, 10bR)-3,4a,4,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol hydrochloride], diminished the effects of both compounds on neurotransmitter efflux in both regions. These results suggested D3 receptor partial agonist activity of cariprazine, producing functional antagonism, may contribute to its efficacy in schizophrenia and bipolar disorder.

Blonanserin versus haloperidol in Japanese patients with schizophrenia: A phase 3, 8-week, double-blind, multicenter, randomized controlled study

OBJECTIVE

This Japanese, multicenter, randomized, double-blind trial, evaluating the efficacy and safety of blonanserin compared with haloperidol in patients with schizophrenia, was previously published by Murasaki in the Japanese language. In this article, we present the results of the trial based on full analysis dataset instead of per protocol dataset formerly reported and discuss the findings in light of the latest knowledge of pharmacological treatment for schizophrenia.

METHODS

A total of 265 patients were randomized to receive blonanserin (8 to 24 mg/d) or haloperidol (4 to 12 mg/d) twice daily for 8 weeks. Efficacy assessments included the Clinical Global Impressions-Improvement (CGI-I) and the Positive and Negative Syndrome Scale (PANSS).

RESULTS

Blonanserin was not inferior to haloperidol with a margin of 10% with respect to the improvement rate on CGI-I at end of study (60.5% vs 50.0%, P < 0.001). The decrease in the PANSS total score did not differ between the drugs (-10.3 vs -7.1). For the PANSS negative symptom score, the decrease was significantly greater with blonanserin than with haloperidol (P = 0.006). Blonanserin was well tolerated. The incidence of adverse events was similar for the two drugs. Extrapyramidal adverse events, sedation, hypotension, and prolactin increase were rarer with blonanserin than with haloperidol. No clinically important weight gain was observed.

CONCLUSIONS

Blonanserin is as effective as haloperidol for the treatment of schizophrenia. Blonanserin is more effective for negative symptoms with a lower risk of extrapyramidal symptoms compared with haloperidol.

Blonanserin ameliorates social deficit through dopamine-D3 receptor antagonism in mice administered phencyclidine as an animal model of schizophrenia

Blonanserin differs from other antipsychotic drugs, such as risperidone and olanzapine, and exhibits a higher affinity for dopamine-D_2/3 receptors than for serotonin 5-HT_2A receptors. We investigated the involvement of dopamine-D₃ receptors in the effect of blonanserin on the social deficit observed in an animal model of schizophrenia and sought to elucidate the molecular mechanism underlying its action. Mice received phencyclidine (PCP: 10 mg/kg/day, s.c.), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, once a day for 14 consecutive days. We then evaluated the sociability, using a social interaction test, and the expression of GluN1 subunit, an essential subunit of the NMDA receptors, in these mice. Blonanserin significantly ameliorated the PCP-induced social deficit, whereas olanzapine and haloperidol did not. This effect of blonanserin was antagonized by 7-OH-DPAT, a dopamine-D₃ receptor agonist, and SCH23390, a dopamine-D₁ receptor antagonist. However, the ameliorating effect of blonanserin was not inhibited by DOI, a serotonin 5-HT_2A receptor agonist. The PCP-induced social deficit was also ameliorated by U99194, a dopamine-D₃ receptor antagonist and SKF38393, a dopamine-D₁ receptor agonist, being effects antagonized by 7-OH-DPAT or SCH23390. Blonanserin significantly inhibited the decrease in the phosphorylation levels of GluN1 at Ser⁸⁹⁷ by protein kinase A (PKA) in the prefrontal cortex (PFC) in PCPadministered mice. These results suggest that activation of NMDA receptors due to Ser⁸⁹⁷-phosphorylation of GluN1 subunit, which is a step linked to dopamine-D₁ receptor-PKA signaling through dopamine-D₃ receptor antagonism in the PFC, is required for the ameliorating effect of blonanserin on the PCP-induced social deficit. These findings also provide in vivo evidence that blonanserin antagonism of the dopamine-D₃ receptors may be useful as a novel treatment strategy and that the dopamine-D₃ receptors can be a novel therapeutic target molecule for the social deficit observed in schizophrenia.

Antidepressant activities of escitalopram and blonanserin on prenatal and adolescent combined stress-induced depression model: Possible role of neurotrophic mechanism change in serum and nucleus accumbens

BACKGROUND

There has been number of studies suggesting experiences of adversity in early life interrelated subsequent brain development, however, neurobiological mechanisms confer risk for onset of psychiatric illness remains unclear.

METHODS

In order to elucidate the pathogenic mechanisms underlying early life adversity-induced refractory depression in more detail, we administered corticosterone (CORT) to adolescent rats with or without prenatal ethanol exposure followed by an antidepressant or antipsychotic and examined alterations in depressive and social function behaviors and brain-derived neurotrophic factor (BDNF) levels in serum, the hippocampus, anterior cingulate cortex, and nucleus accumbens.

RESULTS

The combined stress exposure of prenatal ethanol and adolescent CORT prolonged immobility times in the forced swim test (FST), and increased investigation times and numbers in the social interaction test (SIT). A treatment with escitalopram reversed depression-like behavior accompanied by reductions in BDNF levels in serum and the nucleus accumbens, while a treatment with blonanserin ameliorated abnormal social interaction behavior with reductions in serum BDNF levels.

LIMITATIONS

Further studies are needed to clarify the clinical evinces responding to these results, and many questions remain regarding the mechanisms by which refractory depression and antidepressant/antipsychotic treatments cause changes in serum and brain regional BDNF levels.

CONCLUSION

These results strongly implicate changes in BDNF levels in serum and the nucleus accumbens in the pathophysiology and treatment of early life combined stress-induced depression and highlight the therapeutic potential of escitalopram and new generation antipsychotic blonanserin for treatment-resistant refractory depression.

5-HT1A parital agonism and 5-HT7 antagonism restore episodic memory in subchronic phencyclidine-treated mice: role of brain glutamate, dopamine, acetylcholine and GABA

RATIONALE

The effect of atypical antipsychotic drugs (AAPDs), e.g., lurasidone, to improve cognitive impairment associated with schizophrenia (CIAS), has been suggested to be due, in part, to enhancing release of dopamine (DA), acetylcholine (ACh), and glutamate (Glu) in cortex and hippocampus.

RESULTS

The present study found acute lurasidone reversed the cognitive deficit in novel object recognition (NOR) in subchronic (sc) phencyclidine (PCP)-treated mice, an animal model for CIAS. This effect of lurasidone was blocked by pretreatment with the 5-HT_1AR antagonist, WAY-100635, or the 5-HT₇R agonist, AS 19. Lurasidone significantly increased medial prefrontal cortex (mPFC) ACh, DA, and Glu efflux, all of which were blocked by WAY-100635, with similar effects in the dorsal striatum (dSTR), except for the absence of an effect on Glu increase. AS 19 inhibited Glu, but not DA efflux, in the dSTR. The selective 5-HT₇R antagonist, SB-26970, increased mPFC DA, 5-HT, Glu, and, importantly, also GABA efflux and striatal DA, NE, 5-HT, and Glu efflux, indicating tonic inhibition of the release of these neurotransmitters by 5-HT₇R stimulation. These results provide new evidence that GABA release in the mPFC is tonically inhibited by 5-HT₇R stimulation and suggest that a selective 5-HT₇R antagonist might be clinically useful to enhance cortical GABAergic release. All SB-269970 effects were blocked by AS 19 or WAY-100635, suggesting 5-HT_1AR agonism is necessary for the release of these neurotransmitters by SB-269970. Lurasidone increased ACh, DA, and NE but not Glu efflux in mPFC and dSTR DA and Glu efflux in 5-HT₇ KO mice.

CONCLUSION

We conclude that lurasidone-induced Glu efflux in mPFC requires 5-HT₇R antagonism while its effects on cortical ACh and DA efflux are mainly due to 5-HT_1AR stimulation.

Antipsychotic-Induced Dopamine Supersensitivity Psychosis: Pharmacology, Criteria, and Therapy

The first-line treatment for psychotic disorders remains antipsychotic drugs with receptor antagonist properties at D2-like dopamine receptors. However, long-term administration of antipsychotics can upregulate D2 receptors and produce receptor supersensitivity manifested by behavioral supersensitivity to dopamine stimulation in animals, and movement disorders and supersensitivity psychosis (SP) in patients. Antipsychotic-induced SP was first described as the emergence of psychotic symptoms with tardive dyskinesia (TD) and a fall in prolactin levels following drug discontinuation. In the era of first-generation antipsychotics, 4 clinical features characterized drug-induced SP: rapid relapse after drug discontinuation/dose reduction/switch of antipsychotics, tolerance to previously observed therapeutic effects, co-occurring TD, and psychotic exacerbation by life stressors. We review 3 recent studies on the prevalence rates of SP, and the link to treatment resistance and psychotic relapse in the era of second-generation antipsychotics (risperidone, paliperidone, perospirone, and long-acting injectable risperidone, olanzapine, quetiapine, and aripiprazole). These studies show that the prevalence rates of SP remain high in schizophrenia (30%) and higher (70%) in treatment-resistant schizophrenia. We then present neurobehavioral findings on antipsychotic-induced supersensitivity to dopamine from animal studies. Next, we propose criteria for SP, which describe psychotic symptoms and co-occurring movement disorders more precisely. Detection of mild/borderline drug-induced movement disorders permits early recognition of overblockade of D2 receptors, responsible for SP and TD. Finally, we describe 3 antipsychotic withdrawal syndromes, similar to those seen with other CNS drugs, and we propose approaches to treat, potentially prevent, or temporarily manage SP.

Characterization of Behavioral, Signaling and Cytokine Alterations in a Rat Neurodevelopmental Model for Schizophrenia, and Their Reversal by the 5-HT6 Receptor Antagonist SB-399885

Post-weaning social isolation of rats produces neuroanatomical, neurochemical and behavioral alterations resembling some core features of schizophrenia. This study examined the ability of the 5-HT₆ receptor antagonist SB-399885 to reverse isolation-induced cognitive deficits, then investigated alterations in hippocampal cell proliferation and hippocampal and frontal cortical expression of selected intracellular signaling molecules and cytokines. Male Lister hooded rats (weaned on post-natal days 21-24 and housed individually or in groups of 3-4) received six i.p. injections of vehicle (1% Tween 80, 1 mL/kg) or SB-399885 (5 or 10 mg/kg) over a 2-week period starting 40 days post-weaning, on the days that locomotor activity, novel object discrimination (NOD), pre-pulse inhibition of acoustic startle and acquisition, retention and extinction of a conditioned freezing response (CFR) were assessed. Tissue was collected 24 h after the final injection for immunohistochemistry, reverse-phase protein microarray and western blotting. Isolation rearing impaired NOD and cue-mediated CFR, decreased cell proliferation within the dentate gyrus, and elevated hippocampal TNFα levels and Cdc42 expression. SB-399885 reversed the NOD deficit and partially normalized CFR and cell proliferation. These effects were accompanied by altered expression of several members of the c-Jun N-terminal Kinase (JNK) and p38 MAPK signaling pathways (including TAK1, MKK4 and STAT3). Although JNK and p38 themselves were unaltered at this time point hippocampal TAK1 expression and phosphorylation correlated with visual recognition memory in the NOD task. Continued use of this neurodevelopmental model could further elucidate the neurobiology of schizophrenia and aid assessment of novel therapies for drug-resistant cognitive symptoms.

Dopamine D3 receptor blockade rescues hyper-dopamine activity-induced deficit in novel object recognition memory

Patients afflicted with bipolar disorder demonstrate significant impairments in recognition and episodic memory during acute depressive and manic episodes. These impairments and the related pathophysiology may result from over-activation of the brain dopamine (DA) system. In order to model overactive DA transmission in a well-established novel object recognition (NOR) memory test, we used DA transporter knockdown (DAT-KD) mice, which exhibit reduced DAT expression and display hyper-dopaminergic phenotypes. DAT-KD mice exhibited impaired NOR memory compared to wild-type (WT) mice. This impairment was prevented by administration of FAUC365, a DA D₃ receptor (D₃R) selective antagonist, prior to object learning. Similarly, D₃R knockout (KO)/DAT-KD double mutant mice displayed performance in the NOR test that was comparable to WT mice, suggesting that deficiencies in NOR performance in DAT-KD mice can be compensated by diminishing D₃R signaling. GBR12909, a DAT blocker, also impaired NOR performance in WT mice, but not in D₃R KO mice. Impaired NOR performance in GBR12909-treated WT mice was also prevented by pretreatment with FAUC365. Together, these findings indicate that reduced DAT activity can impair recognition memory in the NOR test, and D₃R appears to be necessary to mediate this effect.

Antipsychotics promote GABAergic interneuron genesis in the adult rat brain: Role of heat-shock protein production

Current antipsychotics reduce positive symptoms and reverse negative symptoms in conjunction with cognitive behavioral issues with the goal of restoring impaired occupational and social functioning. However, limited information is available on their influence on gliogenesis or their neurogenic properties in adult schizophrenia brains, particularly on GABAergic interneuron production. In the present study, we used young adult subventricular zone (SVZ)-derived progenitor cells expressing proteoglycan NG2 cultures to examine the oligodendrocyte and GABAergic interneuron genesis effects of several kinds of antipsychotics on changes in differentiation function induced by exposure to the NMDA receptor antagonist MK-801. We herein demonstrated that antipsychotics promoted or restored changes in the oligodendrocyte/GABAergic interneuron differentiation functions of NG2(+) cells induced by the exposure to MK-801, which was considered to be one of the drug-induced schizophrenia model. We also demonstrated that antipsychotics restored heat-shock protein (HSP) production in NG2(+) cells with differentiation impairment. The antipsychotics olanzapine, aripiprazole, and blonanserin, but not haloperidol increased HSP90 levels, which were reduced by the exposure to MK-801. Our results showed that antipsychotics, particularly those recently synthesized, exerted similar GABAergic interneuron genesis effects on NG2(+) neuronal/glial progenitor cells in the adult rat brain by increasing cellular HSP production, and also suggest that HSP90 may play a crucial role in the pathophysiology of schizophrenia and is a key target for next drug development.

RP5063, an atypical antipsychotic drug with a unique pharmacologic profile, improves declarative memory and psychosis in mouse models of schizophrenia

Various types of atypical antipsychotic drugs (AAPDs) modestly improve the cognitive impairment associated with schizophrenia (CIAS). RP5063 is an AAPD with a diverse and unique pharmacology, including partial agonism at dopamine (DA) D₂, D₃, D₄, serotonin (5-HT)_1A, and 5-HT_2A receptors (Rs), full agonism at α₄β₂ nicotinic acetylcholine (ACh)R (nAChR), and antagonism at 5-HT_2B, 5-HT₆, and 5-HT₇Rs. Most atypical APDs are 5-HT_2A inverse agonists. The efficacy of RP5063 in mouse models of psychosis and episodic memory were studied. RP5063 blocked acute phencyclidine (PCP)-as well as amphetamine-induced hyperactivity, indicating antipsychotic activity. Acute administration of RP5063 significantly reversed subchronic (sc)PCP-induced impairment in novel object recognition (NOR), a measure of episodic memory, but not reversal learning, a measure of executive function. Co-administration of a sub-effective dose (SED) of RP5063 with SEDs of a 5-HT₇R antagonist, a 5-HT_1BR antagonist, a 5-HT_2AR inverse agonist, or an α₄β₂ nAChR agonist, restored the ability of RP5063 to ameliorate the NOR deficit in scPCP mice. Pre-treatment with a 5-HT_1AR, a D₄R, antagonist, but not an α₄β₂ nAChR antagonist, blocked the ameliorating effect of RP5063. Further, co-administration of scRP5063 prior to each dose of PCP prevented the effect of PCP to produce a deficit in NOR for one week. RP5063, given to scPCP-treated mice for one week restored NOR for one week only. Acute administration of RP5063 significantly increased cortical DA efflux, which may be critical to some of its cognitive enhancing properties. These results indicate that RP5063, by itself, or as an adjunctive treatment has a multifaceted basis for improving some cognitive deficits associated with schizophrenia.

Effectiveness of blonanserin for patients with drug treatment-resistant schizophrenia and dopamine supersensitivity: A retrospective analysis

OBJECTIVE

Dopamine supersensitivity psychosis (DSP) is one of the key factors contributing to the development of antipsychotic treatment-resistant schizophrenia (TRS). We investigated the efficacy of blonanserin, an atypical antipsychotic, for patients with TRS and DSP.

METHODS

In this 12-month retrospective follow-up study, we investigated the cases of eight consecutive patients with unstable TRS and DSP treated with blonanserin as an add-on therapy. We examined changes in scores for the Brief Psychiatric Rating Scale (BPRS), Clinical Global Impression-Severity of Illness (CGI-S) scale and the Global Assessment of Functioning scale (GAF) during the 12 months after the administration of blonanserin.

RESULTS

The patients' total scores on the BPRS and GAF scores were significantly improved by 3 months at the latest. Positive BPRS and CGI-S scores were also improved by 6 months at the latest. The total chlorpromazine-equivalent doses of antipsychotics were significantly reduced from 1462.3±499.6mg to 794.1±642.8mg (p=0.001) after 12 months of blonanserin treatment, with a favorable safety and tolerability profile.

CONCLUSIONS

Blonanserin may be a promising antipsychotic for the treatment of TRS and DSP.