Dopamine D2 receptors as treatment targets in schizophrenia

ADGRG1, an adhesion G protein-coupled receptor, forms oligomers

G protein-coupled receptor (GPCR) oligomerization is a highly debated topic in the field. While initially believed to function as monomers, current literature increasingly suggests that these cell surface receptors, spanning almost all GPCR families, function as homo- or hetero-oligomers. Yet, the functional consequences of these oligomeric complexes remain largely unknown. Adhesion GPCRs (aGPCRs) present an intriguing family of receptors characterized by their large and multi-domain N-terminal fragments (NTFs), intricate activation mechanisms, and the prevalence of numerous splice variants in almost all family members. In the present study, bioluminescence energy transfer (BRET) and Förster resonance energy transfer (FRET) were used to study the homo-oligomerization of adhesion G protein-coupled receptor G1 (ADGRG1; also known as GPR56) and to assess the involvement of NTFs in these receptor complexes. Based on the results presented herein, we propose that ADGRG1 forms 7-transmembrane-driven homo-oligomers on the plasma membrane. Additionally, Stachel motif interactions appear to influence the conformation of these receptor complexes.

Cognitive Effects of Reducing First-Generation Antipsychotic Dose Compared to Switching to Ziprasidone in Long-Stay Patients with Schizophrenia

Background: Cognitive impairment is a core symptom of schizophrenia and is associated with functional outcomes. Improving cognitive function is an important treatment goal. Studies have reported beneficial cognitive effects of the second-generation antipsychotic (SGA) ziprasidone. Reducing the dose of first-generation antipsychotics (FGA) might also improve cognitive function. This study compared the cognitive effects in long-stay patients who were randomized to groups who underwent FGA dose reduction or switched to ziprasidone. Methods: High-dose FGA was reduced to an equivalent of 5 mg of haloperidol in 10 patients (FGA-DR-condition), and 13 patients switched to ziprasidone 80 mg b.i.d. (ZIPRA condition). Five domains of cognitive function were assessed before dose reduction or switching (T0) and after 1 year (T1). This study was approved by the ethics committee of the Open Ankh (CCMO number 338) and registered at the Netherlands Trial Register (code 5864). Results: Non-significant deterioration was seen in all cognitive domains studied in the FGA-DR condition, whereas there was a non-significant improvement in all cognitive domains in the ZIPRA condition. The most robust difference between conditions, in favor of ziprasidone, was in executive function. Conclusions: In patients with severe chronic schizophrenia, ziprasidone had a non-significant and very modest beneficial effect on cognitive function compared with FGA dose reduction. Larger trials are needed to further investigate this effect.

The Natural Protoalkaloid Methyl-2-Amino-3-Methoxybenzoate (MAM) Alleviates Positive as well as Cognitive Symptoms in Rat and Mouse Schizophrenia Models

The development of new antipsychotics with pro-cognitive properties and less side effects represents a priority in schizophrenia drug research. In this study, we present for the first time a preclinical exploration of the effects of the promising natural atypical antipsychotic Methyl-2-Amino-3- Methoxybenzoate (MAM), a brain-penetrable protoalkaloid from the seed of the plant Nigella damascena. Using animal models related to hyperdopaminergic activity, namely the pharmacogenetic apomorphine (D2/D1 receptor agonist)-susceptible (APO-SUS) rat model and pharmacologically induced mouse and rat models of schizophrenia, we found that MAM reduced gnawing stereotypy and climbing behaviours induced by dopaminergic agents. This predicts antipsychotic activity. In line, MAM antagonized apomorphine-induced c-Fos and NPAS4 mRNA levels in post-mortem brain nucleus accumbens and dorsolateral striatum of APO-SUS rats. Furthermore, phencyclidine (PCP, an NMDA receptor antagonist) and 2,5-Dimethoxy-4-iodoamphetamine (DOI, a 5HT2A/2C receptor agonist) induced prepulse inhibition deficits, reflecting the positive symptoms of schizophrenia, which were rescued by treatment with MAM and atypical antipsychotics alike. Post-mortem brain immunostaining revealed that MAM blocked the strong activation of both PCP- and DOI-induced c-Fos immunoreactivity in a number of cortical areas. Finally, during a 28-day subchronic treatment regime, MAM did not induce weight gain, hyperglycemia, hyperlipidemia or hepato- and nephrotoxic effects, side effects known to be induced by atypical antipsychotics. MAM also did not show any cataleptic effects. In conclusion, its brain penetrability, the apparent absence of preclinical side effects, and its ability to antagonize positive and cognitive symptoms associated with schizophrenia make MAM an exciting new antipsychotic drug that deserves clinical testing.

Molecular dynamics and free energy calculations of clozapine bound to D2 and H1 receptors reveal a cardiometabolic mitigated derivative

Most atypical antipsychotics derive from a high dropout of drug treatments due to adverse cardiometabolic side effects. These side effects are caused, in part, by the H1 receptor blockade. The current work sought a clozapine derivative with a reduced affinity for the H1 receptor while maintaining its therapeutic effect linked to D2 receptor binding. Explicit molecular dynamics simulations and end-point free energy calculations of clozapine in complex with the D2 and H1 receptors embedded in cholesterol-rich lipid bilayers were performed to analyze the intermolecular interactions and address the relevance of clozapine-functional groups. Based on that, free energy perturbation calculations were performed to measure the change in free energy of clozapine structural modifications. Our results indicate the best clozapine derivative is the iodine atom substitution for chlorine. The latter is mainly due to electrostatic interaction loss for the H1 receptor, while the halogen orientation out of the D2 active site reduces the impact on the affinity.Communicated by Ramaswamy H. Sarma.

Dopamine partial agonists: a discrete class of antipsychotics

Worldwide, there are now three marketed dopamine D2 partial agonists: aripiprazole, brexpiprazole and cariprazine. These three drugs share a number of properties other than their action at D2 receptors. Pharmacologically, they are 5HT2 antagonists and D3 and 5HT1A partial agonists but with little or no alpha-adrenergic, anticholinergic or antihistaminic activity. They also share a long duration of action. Clinically, D2 partial agonists are effective antipsychotics and generally have useful antimanic and antidepressant activity. They are usually well tolerated, causing akathisia and insomnia only at the start of treatment, and are non-sedating. These drugs also share a very low risk of increased prolactin and of weight gain and accompanying metabolic effects. They may also have a relatively low risk of tardive dyskinesia. There is some evidence that they are preferred by patients to dopamine antagonists. Individual dopamineD2 partial agonists have much in common and as a group they differ importantly from dopamine D2 antagonists. Dopamine D2 partial agonists should be considered a distinct class of antipsychotics.Key pointsD2 partial agonists share many pharmacological and clinical propertiesD2 partial agonists differ in several important respects from D2 antagonistsD2 partial agonists should be considered a discrete class of antipsychotics.

Optical Control of Dopamine D2-like Receptors with Cell-Specific Fast-Relaxing Photoswitches

Dopamine D2-like receptors (D2R, D3R, and D4R) control diverse physiological and behavioral functions and are important targets for the treatment of a variety of neuropsychiatric disorders. Their complex distribution and activation kinetics in the brain make it difficult to target specific receptor populations with sufficient precision. We describe a new toolkit of light-activatable, fast-relaxing, covalently taggable chemical photoswitches that fully activate, partially activate, or block D2-like receptors. This technology combines the spatiotemporal precision of a photoswitchable ligand (P) with cell type and spatial specificity of a genetically encoded membrane anchoring protein (M) to which the P tethers. These tools set the stage for targeting endogenous D2-like receptor signaling with molecular, cellular, and spatiotemporal precision using only one wavelength of light.

Dopamine agonists in Parkinson's disease: Impact of D1-like or D2-like dopamine receptor subtype selectivity and avenues for future treatment

Dopamine agonists (DAs) have demonstrated efficacy for the treatment of Parkinson's disease (PD) but are limited by adverse effects (AEs). DAs can vary considerably in their receptor subtype selectivity and affinity, chemical composition, receptor occupancy, and intrinsic activity on the receptor. Most currently approved DAs for PD treatment primarily target D2/D3 (D2-like) dopamine receptors. However, selective activation of D1/D5 (D1-like) dopamine receptors may enable robust activation of motor function while avoiding AEs related to D2/D3 receptor agonism. Full D1/D5 receptor-selective agonists have been explored in small, early-phase clinical studies, and although their efficacy for motor symptoms was robust, challenges with pharmacokinetics, bioavailability, cardiovascular AEs, and dyskinesia rates similar to levodopa prevented clinical advancement. Generally, repeated dopaminergic stimulation with full DAs is associated with frontostriatal dysfunction and sensitization that may induce plastic changes in the motor system, and neuroadaptations that produce long-term motor and nonmotor complications, respectively. Recent preclinical and clinical studies suggest that a D1/D5 receptor-selective partial agonist may hold promise for providing sustained, predictable, and robust motor control, while reducing risk for motor complications (e.g., levodopa-induced dyskinesia) and nonmotor AEs (e.g., impulse control disorders and excessive daytime sleepiness). Clinical trials are ongoing to evaluate this hypothesis. The potential emerging availability of novel dopamine receptor agonists with selective dopamine receptor pharmacology suggests that the older terminology "dopamine agonist" may need revision to distinguish older-generation D2/D3-selective agonists from D1/D5-selective agonists with distinct efficacy and tolerability characteristics.

Lu AF35700 reverses the phencyclidine-induced disruption of thalamo-cortical activity by blocking dopamine D1 and D2 receptors

Antipsychotic drugs of different chemical/pharmacological families show preferential dopamine (DA) D₂ receptor (D₂-R) vs. D₁ receptor (D₁-R) affinity, with the exception of clozapine, the gold standard of schizophrenia treatment, which shows a comparable affinity for both DA receptors. Here, we examined the ability of Lu AF35700 (preferential D₁-R>D₂-R antagonist), to reverse the alterations in thalamo-cortical activity induced by phencyclidine (PCP), used as a pharmacological model of schizophrenia. Lu AF35700 reversed the PCP-induced alteration of neuronal discharge and low frequency oscillation (LFO, 0.15-4 Hz) in thalamo-cortical networks. Likewise, Lu AF35700 prevented the increased c-fos mRNA expression induced by PCP in thalamo-cortical regions of awake rats. We next examined the contribution of D₁-R and D₂-R to the antipsychotic reversal of PCP effects. The D₂-R antagonist haloperidol reversed PCP effects on thalamic discharge rate and LFO. Remarkably, the combination of sub-effective doses of haloperidol and SCH-23390 (DA D₁-R antagonist) fully reversed the PCP-induced fall in thalamo-cortical LFO. However, unlike with haloperidol, SCH-23390 elicited different degrees of potentiation of the effects of low clozapine and Lu AF35700 doses. Overall, the present data support a synergistic interaction between both DA receptors to reverse the PCP-induced alterations of oscillatory activity in thalamo-cortical networks, possibly due to their simultaneous blockade in direct and indirect pathways of basal ganglia. The mild potentiation induced by SCH-23390 in the case of clozapine and Lu AF35700 suggests that, at effective doses, these agents reverse PCP effects through the simultaneous blockade of both DA receptors.

Movement disorders associated with substance use in adults living in precarious housing or homelessness

OBJECTIVE

Many individuals living in precarious housing or homelessness have multimorbid illnesses, including substance use, psychiatric, and neurological disorders. Movement disorders (MDs) associated substance use are amongst the poorly studied subtopics of drug-induced MDs. The aim of the present study was, therefore, to determine the proportion affected and severity of different signs of MDs, as well as their associations with substance use in a community-based sample of precariously housed and homeless individuals.

METHODS

Participants were recruited from an impoverished urban neighborhood and were assessed for substance dependence and self-reported substance use (alcohol, cannabis, cocaine, methamphetamine, nicotine, and opioids), as well as for the severity of signs of MDs (akathisia, dyskinesia, dystonia, and parkinsonism). Adjusted regression models were used to estimate the associations of the severity of signs with the frequency of substance use over the past 4 weeks and with the baseline diagnosis of substance dependence.

RESULTS

The proportion of the sample with clinically relevant signs of MDs in any of the four categories was 18.6% (n = 401), and these participants demonstrated lower levels of functioning than those without signs. Of the different types of substance use, only methamphetamine (its frequency of use and dependence) was significantly associated with greater severity of overall signs of MDs. Frequency of methamphetamine use significantly interacted with age and sex, whereby older female participants exhibited the greatest overall severity with increased methamphetamine use. Of the different signs of MDs, methamphetamine use frequency was positively associated with the severity of trunk/limb dyskinesia and hypokinetic parkinsonism. Relative to no use, concurrent use of antipsychotics demonstrated lower severity of trunk/limb dyskinesia and greater severity of hypokinetic parkinsonism with methamphetamine use, and greater severity of dystonia with cocaine use.

CONCLUSIONS

Our study found a high proportion of MDs in a relatively young sample, and their severity was consistently associated with methamphetamine use, moderated by participant demographics and antipsychotic use. These disabling sequelae represent an important and understudied neurological condition that may affect quality of life and will require further study.

The Role of Dopamine D3 Receptors, Dysbindin, and Their Functional Interaction in the Expression of Key Genes for Neuroplasticity and Neuroinflammation in the Mouse Brain

Cognitive impairment in schizophrenia remains a clinically and pharmacologically unsolved challenge. Clinical and preclinical studies have revealed that the concomitant reduction in dysbindin (DYS) and dopamine receptor D3 functionality improves cognitive functions. However, the molecular machinery underlying this epistatic interaction has not yet been fully elucidated. The glutamate NMDA receptors and the neurotrophin BDNF, with their established role in promoting neuroplasticity, may be involved in the complex network regulated by the D3/DYS interaction. Furthermore, as inflammation is involved in the etiopathogenesis of several psychiatric diseases, including schizophrenia, the D3/DYS interaction may affect the expression levels of pro-inflammatory cytokines. Thus, by employing mutant mice bearing selective heterozygosis for D3 and/or DYS, we provide new insights into the functional interactions (single and synergic) between these schizophrenia susceptibility genes and the expression levels of key genes for neuroplasticity and neuroinflammation in three key brain areas for schizophrenia: the prefrontal cortex, striatum, and hippocampus. In the hippocampus, the epistatic interaction between D3 and DYS reversed to the wild-type level the downregulated mRNA levels of GRIN1 and GRIN2A were observed in DYS +/- and D3 +/- mice. In all the areas investigated, double mutant mice had higher BDNF levels compared to their single heterozygote counterparts, whereas D3 hypofunction resulted in higher pro-inflammatory cytokines. These results may help to clarify the genetic mechanisms and functional interactions involved in the etiology and development of schizophrenia.

G protein-coupled receptors in neurodegenerative diseases and psychiatric disorders

Neuropsychiatric disorders are multifactorial disorders with diverse aetiological factors. Identifying treatment targets is challenging because the diseases are resulting from heterogeneous biological, genetic, and environmental factors. Nevertheless, the increasing understanding of G protein-coupled receptor (GPCR) opens a new possibility in drug discovery. Harnessing our knowledge of molecular mechanisms and structural information of GPCRs will be advantageous for developing effective drugs. This review provides an overview of the role of GPCRs in various neurodegenerative and psychiatric diseases. Besides, we highlight the emerging opportunities of novel GPCR targets and address recent progress in GPCR drug development.

Schizophrenia Synaptic Pathology and Antipsychotic Treatment in the Framework of Oxidative and Mitochondrial Dysfunction: Translational Highlights for the Clinics and Treatment

Schizophrenia is a worldwide mental illness characterized by alterations at dopaminergic and glutamatergic synapses resulting in global dysconnectivity within and between brain networks. Impairments in inflammatory processes, mitochondrial functions, energy expenditure, and oxidative stress have been extensively associated with schizophrenia pathophysiology. Antipsychotics, the mainstay of schizophrenia pharmacological treatment and all sharing the common feature of dopamine D2 receptor occupancy, may affect antioxidant pathways as well as mitochondrial protein levels and gene expression. Here, we systematically reviewed the available evidence on antioxidants' mechanisms in antipsychotic action and the impact of first- and second-generation compounds on mitochondrial functions and oxidative stress. We further focused on clinical trials addressing the efficacy and tolerability of antioxidants as an augmentation strategy of antipsychotic treatment. EMBASE, Scopus, and Medline/PubMed databases were interrogated. The selection process was conducted in respect of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria. Several mitochondrial proteins involved in cell viability, energy metabolism, and regulation of oxidative systems were reported to be significantly modified by antipsychotic treatment with differences between first- and second-generation drugs. Finally, antioxidants may affect cognitive and psychotic symptoms in patients with schizophrenia, and although the evidence is only preliminary, the results indicate that further studies are warranted.

Novel Multimodal Salicylamide Derivative with Antidepressant-like, Anxiolytic-like, Antipsychotic-like, and Anti-Amnesic Activity in Mice

Depression, anxiety, and schizophrenia may coexist in psychiatric patients. Moreover, these disorders are very often associated with cognitive impairments. However, pharmacotherapy of these conditions remains challenging due to limited drug effectiveness or numerous side effects. Therefore, there is an urgent need to develop novel multimodal compounds that can be used to treat depression, anxiety, and schizophrenia, as well as memory deficits. Thus, this study aimed to evaluate the potential antidepressant-like, anxiolytic-like, antipsychotic-like effects, and anti-amnesic properties, of the novel arylpiperazine derivative of salicylamide, JJGW07, with an affinity towards serotonin 5-HT1A, 5-HT2A, and 5-HT7 and dopamine D2 receptors. Firstly, we investigated the compound's affinity for 5-HT6 receptors and its functional activity by using in vitro assays. JJGW07 did not bind to 5-HT6 receptors and showed antagonistic properties for 5-HT1A, 5-HT2A, 5-HT7, and D2 receptors. Based on the receptor profile, we performed behavioral studies in mice to evaluate the antidepressant-like, anxiolytic-like, and antipsychotic-like activity of the tested compound using forced swim and tail suspension tests; four-plate, marble-burying, and elevated plus maze tests; and MK-801- and amphetamine-induced hyperlocomotion tests, respectively. JJGW07 revealed antidepressant-like properties in the tail suspension test, anxiolytic-like effects in the four-plate and marble-burying tests, and antipsychotic-like activity in the MK-801-induced hyperlocomotion test. Importantly, the tested compound did not induce catalepsy and motor impairments or influence locomotor activity in rodents. Finally, to assess the potential procognitive and anti-amnesic properties of JJGW07, we used passive avoidance and object recognition tests in mice. JJGW07 demonstrated positive effects on long-term emotional memory and also ameliorated MK-801-induced emotional memory impairments in mice, but showed no procognitive properties in the case of recognition memory. Our results encourage the search for new compounds among salicylamide derivatives, which could be model structures with multitarget mechanisms of action that could be used in psychiatric disorder therapy.

Recent advances in dopamine D2 receptor ligands in the treatment of neuropsychiatric disorders

Dopamine is a biologically active amine synthesized in the central and peripheral nervous system. This biogenic monoamine acts by activating five types of dopamine receptors (D_1-5 Rs), which belong to the G protein-coupled receptor family. Antagonists and partial agonists of D₂ Rs are used to treat schizophrenia, Parkinson's disease, depression, and anxiety. The typical pharmacophore with high D₂ R affinity comprises four main areas, namely aromatic moiety, cyclic amine, central linker and aromatic/heteroaromatic lipophilic fragment. From the literature reviewed herein, we can conclude that 4-(2,3-dichlorophenyl), 4-(2-methoxyphenyl)-, 4-(benzo[b]thiophen-4-yl)-1-substituted piperazine, and 4-(6-fluorobenzo[d]isoxazol-3-yl)piperidine moieties are critical for high D₂ R affinity. Four to six atoms chains are optimal for D₂ R affinity with 4-butoxyl as the most pronounced one. The bicyclic aromatic/heteroaromatic systems are most frequently occurring as lipophilic appendages to retain high D₂ R affinity. In this review, we provide a thorough overview of the therapeutic potential of D₂ R modulators in the treatment of the aforementioned disorders. In addition, this review summarizes current knowledge about these diseases, with a focus on the dopaminergic pathway underlying these pathologies. Major attention is paid to the structure, function, and pharmacology of novel D₂ R ligands, which have been developed in the last decade (2010-2021), and belong to the 1,4-disubstituted aromatic cyclic amine group. Due to the abundance of data, allosteric D₂ R ligands and D₂ R modulators from patents are not discussed in this review.

Epilepsy and Autism Spectrum Disorder (ASD): The Underlying Mechanisms and Therapy Targets Related to Adenosine

Epilepsy and autism spectrum disorder (ASD) are highly mutually comorbid, suggesting potential overlaps in genetic etiology, pathophysiology, and neurodevelopmental abnormalities. Adenosine, an endogenous anticonvulsant and neuroprotective neuromodulator of the brain, has been proved to affect the process of epilepsy and ASD. On the one hand, adenosine plays a crucial role in preventing the progression and development of epilepsy through adenosine receptordependent and -independent ways. On the other hand, adenosine signaling can not only regulate core symptoms but also improve comorbid disorders in ASD. Given the important role of adenosine in epilepsy and ASD, therapeutic strategies related to adenosine, including the ketogenic diet, neuromodulation therapy, and adenosine augmentation therapy, have been suggested for the arrangement of epilepsy and ASD. There are several proposals in this review. Firstly, it is necessary to further discuss the relationship between both diseases based on the comorbid symptoms and mechanisms of epilepsy and ASD. Secondly, it is important to explore the role of adenosine involved in epilepsy and ASD. Lastly, potential therapeutic value and clinical approaches of adenosine-related therapies in treating epilepsy and ASD need to be emphasized.

Antipsychotic- and Anxiolytic-like Properties of a Multimodal Compound JJGW08 in Rodents

Schizophrenia is a chronic mental illness, which remains difficult to treat. A high resistance to the available therapies, their insufficient efficacy, and numerous side effects are the reasons why there is an urgent need to develop new antipsychotics. This study aimed to assess the antipsychotic-like effects of JJGW08, a novel arylpiperazine alkyl derivative of salicylamide, in rodents. First, considering the JJGW08 receptor profile, we investigated the compound's intrinsic activity towards dopamine D₂ and serotonin 5-HT_1A, 5-HT_2A, and 5-HT₇ receptors using functional assays. Next, we assessed the effect of JJGW08 on MK-801- and amphetamine-induced hyperlocomotion, its risk of inducing catalepsy and impairing motor coordination, as well as the anxiolytic-like effects in the four-plate and marble burying tests in mice. Finally, we investigated the antipsychotic-like properties of JJGW08 in rats using MK-801-induced hyperlocomotion and prepulse inhibition tests. We found that JJGW08 showed antagonistic properties at dopamine D₂ and serotonin 5-HT_1A, 5-HT_2A, and 5-HT₇ receptors. However, the effect on the 5-HT_2A and 5-HT₇ receptors was very weak. Moreover, the tested compound showed an antipsychotic-like effect in MK-801- and amphetamine-induced hyperlocomotion but not in a prepulse inhibition test in rats. Notably, JJGW08 demonstrated anxiolytic-like properties in both behavioral tests. Importantly, the compound did not induce catalepsy or motor coordination impairment in mice at antipsychotic-like doses. Our study suggests it is worth searching for new potential antipsychotics among arylpiperazine alkyl derivatives of salicylamide.

Glutamatergic dysfunction in Schizophrenia

The NMDA-R hypofunction model of schizophrenia started with the clinical observation of the precipitation of psychotic symptoms in patients with schizophrenia exposed to PCP or ketamine. Healthy volunteers exposed to acute low doses of ketamine experienced mild psychosis but also negative and cognitive type symptoms reminiscent of the full clinical picture of schizophrenia. In rodents, acute systemic ketamine resulted in a paradoxical increase in extracellular frontal glutamate as well as of dopamine. Similar increase in prefrontal glutamate was documented with acute ketamine in healthy volunteers with ¹H-MRS. Furthermore, sub-chronic low dose PCP lead to reductions in frontal dendritic tree density in rodents. In post-mortem ultrastructural studies in schizophrenia, a broad reduction in dendritic complexity and somal volume of pyramidal cells has been repeatedly described. This most likely accounts for the broad, subtle progressive cortical thinning described with MRI in- vivo. Additionally, prefrontal reductions in the obligatory GluN₁ subunit of the NMDA-R has been repeatedly found in post-mortem tissue. The vast ¹H-MRS literature in schizophrenia has documented trait-like small increases in glutamate concentrations in striatum very early in the illness, before antipsychotic treatment (the same structure where increased pre-synaptic release of dopamine has been reported with PET). The more recent genetic literature has reliably detected very small risk effects for common variants involving several glutamate-related genes. The pharmacological literature has followed two main tracks, directly informed by the NMDA-R hypo model: agonism at the glycine site (as mostly add-on studies targeting negative and cognitive symptoms); and pre-synaptic modulation of glutamatergic release (as single agents for acute psychosis). Unfortunately, both approaches have failed so far. There is little doubt that brain glutamatergic abnormalities are present in schizophrenia and that some of these are related to the etiology of the illness. The genetic literature directly supports a non- specific etiological role for glutamatergic dysfunction. Whether NMDA-R hypofunction as a specific mechanism accounts for any important component of the illness is still not evident. However, a glutamatergic model still has heuristic value to guide future research in schizophrenia. New tools to jointly examine brain glutamatergic, GABA-ergic and dopaminergic systems in-vivo, early in the illness, may lay the ground for a next generation of clinical trials that go beyond dopamine D2 blockade.

Assessing the effects of antipsychotic medications on schizophrenia functional analysis: a postmortem proteome study

Antipsychotic drugs (APDs) are effective in treating positive symptoms of schizophrenia (SCZ). However, they have a substantial impact on postmortem studies. As most cohorts lack samples from drug-naive patients, many studies, rather than understanding SCZ pathophysiology, are analyzing the drug effects. We hypothesized that comparing SCZ-altered and APD-influenced signatures derived from the same cohort can provide better insight into SCZ pathophysiology. For this, we performed LCMS-based proteomics on dorsolateral prefrontal cortex (DLPFC) samples from control and SCZ subjects and used statistical approaches to identify SCZ-altered and APD-influenced proteomes, validated experimentally using independent cohorts and published datasets. Functional analysis of both proteomes was contrasted at the biological-pathway, cell-type, subcellular-synaptic, and drug-target levels. In silico validation revealed that the SCZ-altered proteome was conserved across several studies from the DLPFC and other brain areas. At the pathway level, SCZ influenced changes in homeostasis, signal-transduction, cytoskeleton, and dendrites, whereas APD influenced changes in synaptic-signaling, neurotransmitter-regulation, and immune-system processes. At the cell-type level, the SCZ-altered and APD-influenced proteomes were associated with two distinct striatum-projecting layer-5 pyramidal neurons regulating dopaminergic-secretion. At the subcellular synaptic level, compensatory pre- and postsynaptic events were observed. At the drug-target level, dopaminergic processes influenced the SCZ-altered upregulated-proteome, whereas nondopaminergic and a diverse array of non-neuromodulatory mechanisms influenced the downregulated-proteome. Previous findings were not independent of the APD effect and thus require re-evaluation. We identified a hyperdopaminergic cortex and drugs targeting the cognitive SCZ-symptoms and discussed their influence on SCZ pathology in the context of the cortico-striatal pathway.

Translational relevance of forward genetic screens in animal models for the study of psychiatric disease

Psychiatric disorders represent a significant burden in our societies. Despite the convincing evidence pointing at gene and gene-environment interaction contributions, the role of genetics in the etiology of psychiatric disease is still poorly understood. Forward genetic screens in animal models have helped elucidate causal links. Here we discuss the application of mutagenesis-based forward genetic approaches in common animal model species: two invertebrates, nematodes (Caenorhabditis elegans) and fruit flies (Drosophila sp.); and two vertebrates, zebrafish (Danio rerio) and mice (Mus musculus), in relation to psychiatric disease. We also discuss the use of large scale genomic studies in human populations. Despite the advances using data from human populations, animal models coupled with next-generation sequencing strategies are still needed. Although with its own limitations, zebrafish possess characteristics that make them especially well-suited to forward genetic studies exploring the etiology of psychiatric disorders.

Cell type-specific mechanism of Setd1a heterozygosity in schizophrenia pathogenesis

Schizophrenia (SCZ) is a chronic, serious mental disorder. Although more than 200 SCZ-associated genes have been identified, the underlying molecular and cellular mechanisms remain largely unknown. Here, we generated a Setd1a (SET domain containing 1A) haploinsufficiency mouse model to understand how this SCZ-associated epigenetic factor affects gene expression in brain regions highly relevant to SCZ. Single-cell RNA sequencing revealed that Setd1a heterozygosity causes highly variable transcriptional adaptations across different cell types in prefrontal cortex (PFC) and striatum. The Foxp2+ neurons exhibit the most prominent gene expression changes among the different neuron subtypes in PFC, which correlate with changes in histone H3 lysine 4 trimethylation. Many of the genes dysregulated in Setd1a+/- mice are involved in neuron morphogenesis and synaptic function. Consistently, Setd1a+/- mice exhibit certain behavioral features of patients with SCZ. Collectively, our study establishes Setd1a+/- mice as a model for understanding SCZ and uncovers a complex brain region- and cell type-specific dysregulation that potentially underlies SCZ pathogenesis.

Identifying dopamine supersensitivity through a randomized controlled study of switching to aripiprazole from other antipsychotic agents in patients with schizophrenia

BACKGROUND

Aripiprazole has been reported to worsen psychotic symptoms when switching from other antipsychotics, possibly due to dopamine supersensitivity psychosis.

OBJECTIVE

This study aimed to explore the predictors and possible underlying mechanisms of aripiprazole-related psychotic exacerbation.

METHODS

We conducted an 8-week, open-label, randomized controlled study from October 2007 to September 2009, assigning patients with a primary diagnosis of schizophrenia or schizoaffective disorder to switch from other antipsychotics to aripiprazole with 2-week dual administration, and then to taper off the original agents in fast (n = 38, within 1 week) or slow (n = 41, within 4 weeks) strategies. Positive and Negative Syndrome Scale (PANSS) was examined at day 0, 7, 14, 28, 56. Aripiprazole-related exacerbation (ARE) was defined positive as a 2-point increase in delusion/hallucination dimension score within 28 days compared with baseline. Baseline demographic, clinical and intervention-related variables were compared between the ARE+ and ARE- groups.

RESULTS

Of the 79 randomized patients, 21 fulfilled the criteria of ARE+ , and 46 were classified as ARE-. Fourteen patients in the ARE+ group had worsening psychotic symptoms in the first and second weeks. Compared with the ARE- group, the ARE+ group had a higher baseline chlorpromazine equivalent dose (405.8 ± 225.8 mg vs 268.1 ± 165.4 mg, p = 0.007) and was associated with prescription of first-generation antipsychotics (p = 0.038).

CONCLUSIONS

A higher dose of original antipsychotics and prescription of first-generation antipsychotics may be associated with a higher risk of ARE. The underlying mechanism might be covert dopamine supersensitivity psychosis. These findings may help to identify high-risk patients and guide appropriate treatment strategies.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT00545467.

Tardive dyskinesia

Tardive dyskinesia is a group of hyperkinetic and hypokinetic movement disorders, following the administration of dopamine receptor-blocking drugs. The severity of these syndromes varies from soft forms to the development of life-degrading situations. Phenomenologically tardive dyskinesia can be represented both in isolation and in various combinations. Recognition of these syndromes early in the development of tardive dyskinesia can optimize therapeutic treatment and reduce the risk of severe complications. As a means of treatment, deutetrabenazine or valbenazine are used as first-line drugs, with resistance to therapy and in severe cases, drugs of other groups are used (amantadine, baclofen, botulinum toxin type A, clonazepam, donepezil, gabapentin, ginkgo biloba, levetiracetam, melatonin, pregabalin, thiamine, verapamil, vitamin B6, vitamin E). Our own experience of 12 patients with tardive dystonia showed the effeciency of local injections of botulinum toxin.

Covert Dyskinesia With Aripiprazole: Tip of the Iceberg? A Case Report and Literature Review

BACKGROUND

Tardive dyskinesia (TD) is an involuntary movement disorder most commonly involving the tongue, lips, and face and less commonly the trunk and limbs. Although TD is historically associated with conventional antipsychotics, it still occurs with newer agents. Covert dyskinesia (CD), a form of TD, occurs after the discontinuation of antipsychotics, and it differs from other withdrawal emergent dyskinesia by its persistence for more than 8 to 12 weeks after discontinuation of dopamine receptor-blocking agents. Although initially reported in the 1960s with conventional antipsychotics, multiple recent reports describe several cases in association with aripiprazole (APZ).

METHODS

We used PubMed and the Google Scholar for CD reports during the past 20 years. We also report a recent case ofCD.

RESULTS

We identified 11 case reports of CD. Six were related to APZ, 3 to risperidone, 1 to amisulpride, and 1 to haloperidol. Our patient was an 81-year-old woman with a history of major depressive disorder who was admitted for worsening depression. Before hospitalization, she had been on APZ 5 mg/d for 2 years, but it was discontinued 4 months prior, and then she developed repetitive involuntary movements in her tongue, lips, and jaw 2 months after APZ discontinuation. The Abnormal Involuntary Movement Scale score was 5. Reinstating APZ a few months later led to disappearance of movements.

CONCLUSIONS

Literature to date suggests that APZ is the atypical antipsychotic most commonly reported with CD. A possible risk might be APZ's unique mechanism of action and its association with akathisia. Following up patients with serial Abnormal Involuntary Movement Scale after antipsychotic discontinuation is recommended.

Radioligand and computational insight in structure - Activity relationship of saccharin derivatives being ipsapirone and revospirone analogues

Schizophrenia and depression are diseases that significantly impede human functioning in society. Current antidepressant drugs are not fully effective. According to literature data, the effect on D₂R or 5-HT_1AR can effectively reduce the symptoms of depression or schizophrenia. Recent research hypothetized that the synergism of both of these receptors can improve the effectiveness of therapy. Ipsapirone, a representative of long-chain arylpiperazines, is a known 5-HT_1AR ligand that has antidepressant effect. This compound has no affinity for the D₂R. Bearing in mind, we decided to design ligands with improved affinity to D₂R and confirmed that in some cases elongation of the carbon linker or arylpiperazine exchange may have beneficial influence on the binding to D2R and 5-HT1AR. Four groups of ligands being ipsapirone analogues with butyl, pentyl, hexyl and stiffened xylene chains were designed. All compounds were obtained in solvent-free reactions supported by a microwave irradiation with an efficiency mainly above 60%. All ligands containing 1-(2-pyrimidinyl)piperazine exhibited high affinity to 5-HT_1AR. In this case, chemical modifications within the chain did not affect the affinity to D₂R. In the case of ligands containing 1-phenylpiperazine, 1-(3-trifluoromethylphenyl)piperazine, 1-(1-naphthyl)piperazine, and 1-(4-chlorophenyl)piperazine, elongation of carbon linker increases of affinity to D₂R. For ligands containing 1- (2-pyridyl) piperazine, and 1-(2,3-dichlorophenyl)piperazine, we observed an opposite effect. For ligands containing 1-phenylpiperazine, 1-(2-methoxyphenyl)piperazine and 1-(2-pyridyl)piperazine, chain elongation had no effect on 5-HT_1AR binding. In turn of ligands containing 1-(3-trifluoromethylphenyl)piperazine and 1- (2,3-dichlorophenyl)piperazine, we observed that elongation of carbon linker has a positive influence to 5-HT_1AR. Molecular modelling was used to support the SAR study.

The High Affinity Dopamine D2 Receptor Agonist MCL-536: A New Tool for Studying Dopaminergic Contribution to Neurological Disorders

The dopamine D₂ receptor exists in two different states, D₂^high and D_2low; the former is the functional form of the D₂ receptor and associates with intracellular G-proteins. The D₂ agonist [³H]MCL-536 has high affinity for the D₂ receptor (K_d 0.8 nM) and potently displaces the binding of (R-(-)-N-n-propylnorapomorphine (NPA; K_i 0.16 nM) and raclopride (K_i 0.9 nM) in competition binding assays. Here, we further characterize [³H]MCL-536. [³H]MCL-536 was metabolically stable, with about 75% of the compound remaining intact after 1 h incubation with human liver microsomes. Blood-brain barrier penetration in rats was good, attaining at 15 min a % injected dose per gram of wet tissue (%ID/g) of 0.28 in males versus 0.42 in females in the striatum. Specific uptake ratios ([%ID/g striatum]/[%ID/g cerebellum]) were stable in males during the first 60 min and in females up to 15-30 min. The D₂-rich striatum exhibited the highest uptake and slowest washout compared to D₂-poor cortex or cerebellum. In peripheral organs, uptake peaked at 15 min but declined to baseline at 60 min, indicating good clearance from the body. In vitro autoradiography on transaxial and coronal brain sections showed specific binding of [³H]MCL-536, which was abolished by preincubation with D₂/D₃ ligands sulpiride, NPA, and raclopride and in the presence of the stable GTP analogue guanylylimidodiphosphate. In amphetamine-sensitized animals, striatal binding was higher than in controls, indicating specificity for the D₂^high receptor state. [³H]MCL-536's unique properties make it a valuable tool for research on neurological disorders involving the dopaminergic system like Parkinson's disease or schizophrenia.

The histamine H3R and dopamine D2R/D3R antagonist ST-713 ameliorates autism-like behavioral features in BTBR T+tf/J mice by multiple actions

Several brain neurotransmitters, including histamine (HA), acetylcholine (ACh), and dopamine (DA) are suggested to be involved in several brain disorders including cognitive deficits, depression, schizophrenia, anxiety, and narcolepsy, all of which are comorbid with Autism spectrum disorder (ASD). Therefore, the ameliorative effects of the novel multiple-active compound ST-713 with high binding affinities at histamine H3 receptor (H3R), dopamine D2sR and D3R on ASD-like behaviors in male BTBR T+tf/J mice model were assessed. ST-713 (3-(2-chloro-10H-phenothiazin-10-yl)-N-methyl-N-(4-(3-(piperidin-1-yl)propoxy)benzyl)propan-1-amine; 2.5, 5, and 10 mg/kg, i.p.) ameliorated dose-dependently social deficits, and significantly alleviated the repetitive/compulsive behaviors of BTBR mice (all P < 0.05). Moreover, ST-713 modulated disturbed anxiety levels, but failed to obliterate increased hyperactivity of tested mice. Furthermore, ST-713 (5 mg/kg) attenuated the increased levels of hippocampal and cerebellar protein expressions of NF-κB p65, COX-2, and iNOS in BTBR mice (all P < 0.05). The ameliorative effects of ST-713 on social parameters were entirely reversed by co-administration of the H3R agonist (R)-α-methylhistamine or the anticholinergic drug scopolamine. The obtained results demonstrate the potential of multiple-active compounds for the therapeutic management of neuropsychiatric disorders, e.g. ASD.

Modulating the Neuromodulators: Dopamine, Serotonin, and the Endocannabinoid System

Dopamine (DA), serotonin (5-hydroxytryptamine, 5-HT), and endocannabinoids (ECs) are key neuromodulators involved in many aspects of motivated behavior, including reward processing, reinforcement learning, and behavioral flexibility. Among the longstanding views about possible relationships between these neuromodulators is the idea of DA and 5-HT acting as opponents. This view has been challenged by emerging evidence that 5-HT supports reward seeking via activation of DA neurons in the ventral tegmental area. Adding an extra layer of complexity to these interactions, the endocannabinoid system is uniquely placed to influence dopaminergic and serotonergic neurotransmission. In this review we discuss how these three neuromodulatory systems interact at the cellular and circuit levels. Technological advances that facilitate precise identification and control of genetically targeted neuronal populations will help to achieve a better understanding of the complex relationship between these essential systems, and the potential relevance for motivated behavior.

The Multi-Targeting Ligand ST-2223 with Histamine H3 Receptor and Dopamine D2/D3 Receptor Antagonist Properties Mitigates Autism-Like Repetitive Behaviors and Brain Oxidative Stress in Mice

Autism spectrum disorder (ASD) is a complex heterogeneous neurodevelopmental disorder characterized by social and communicative impairments, as well as repetitive and restricted behaviors (RRBs). With the limited effectiveness of current pharmacotherapies in treating repetitive behaviors, the present study determined the effects of acute systemic treatment of the novel multi-targeting ligand ST-2223, with incorporated histamine H₃ receptor (H₃R) and dopamine D₂/D₃ receptor affinity properties, on ASD-related RRBs in a male Black and Tan BRachyury (BTBR) mouse model of ASD. ST-2223 (2.5, 5, and 10 mg/kg, i.p.) significantly mitigated the increase in marble burying and self-grooming, and improved reduced spontaneous alternation in BTBR mice (all p < 0.05). Similarly, reference drugs memantine (MEM, 5 mg/kg, i.p.) and aripiprazole (ARP, 1 mg/kg, i.p.), reversed abnormally high levels of several RRBs in BTBR (p < 0.05). Moreover, ST-2223 palliated the disturbed anxiety levels observed in an open field test (all p < 0.05), but did not restore the hyperactivity parameters, whereas MEM failed to restore mouse anxiety and hyperactivity. In addition, ST-2223 (5 mg/kg, i.p.) mitigated oxidative stress status by decreasing the elevated levels of malondialdehyde (MDA), and increasing the levels of decreased glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) in different brain parts of treated BTBR mice (all p < 0.05). These preliminary in vivo findings demonstrate the ameliorative effects of ST-2223 on RRBs in a mouse model of ASD, suggesting its pharmacological prospective to rescue core ASD-related behaviors. Further confirmatory investigations on its effects on various brain neurotransmitters, e.g., dopamine and histamine, in different brain regions are still warranted to corroborate and expand these initial data.

Influence of cytochrome P450 2D6 polymorphism on hippocampal white matter and treatment response in schizophrenia

Cytochrome P450 2D6 (CYP2D6) is expressed at high levels in the brain and plays a considerable role in the biotransformation and neurotransmission of dopamine. This raises the question of whether CYP2D6 variations and its impact on the brain can confer susceptibility to schizophrenia. We investigated the possible links among the CYP2D6 genotype, white matter (WM) integrity of the hippocampus, and the treatment response to antipsychotic drugs in Korean patients with schizophrenia (n = 106). Brain magnetic resonance imaging and genotyping for CYP2D6 were conducted at baseline. The severity of clinical symptoms and the treatment response were assessed using the Positive and Negative Syndrome Scale (PANSS). After genotyping, 43 participants were classified as intermediate metabolizers (IM), and the remainder (n = 63) were classified as extensive metabolizers (EM). IM participants showed significantly higher fractional anisotropy (FA) values in the right hippocampus compared to EM participants. Radial diffusivity (RD) values were significantly lower in the overlapping region of the right hippocampus in the IM group than in the EM group. After 4 weeks of antipsychotic treatment, the EM group showed more improvements in positive symptoms than the IM group. FAs and RDs in the CYP2D6-associated hippocampal WM region were significantly correlated with a reduction in the positive symptom subscale of the PANSS. Greater improvements in positive symptoms were negatively associated with FAs, and positively associated with RDs in the right hippocampal region. The findings suggest that CYP26D-associated hippocampal WM alterations could be a possible endophenotype for schizophrenia that accounts for individual differences in clinical features and treatment responses.

Tardive Dyskinesia: Spotlight on Current Approaches to Treatment

Tardive dyskinesia (TD) is a debilitating, iatrogenic, and potentially severe movement disorder characterized by involuntary, repetitive, purposeless movements that are present throughout the body. The authors present a review of studies of past, current, and possible future treatment approaches to the management of TD; consider the phenomenology, assessment, and putative pathophysiological mechanisms of TD, early pharmacological trials, a focus on the newer vesicular monoamine transporter 2 inhibitors, and other evidence-based approaches, such as clozapine; and present preliminary evidence for newer approaches, such as deep brain stimulation and repetitive transcranial magnetic stimulation. On the basis of the evidence presented here, the authors highlight the importance of early recognition and assessment of TD, as well as how to best approach management of these often incapacitating symptoms.

PDE10A Inhibitors-Clinical Failure or Window Into Antipsychotic Drug Action?

PDE10A, a phosphodiesterase that inactivates both cAMP and cGMP, is a unique signaling molecule in being highly and nearly exclusively expressed in striatal medium spiny neurons. These neurons dynamically integrate cortical information with dopamine-signaled value to mediate action selection among available behavioral options. Medium spiny neurons are components of either the direct or indirect striatal output pathways. Selective activation of indirect pathway medium spiny neurons by dopamine D2 receptor antagonists is putatively a key element in the mechanism of their antipsychotic efficacy. While PDE10A is expressed in all medium spiny neurons, studies in rodents indicated that PDE10A inhibition has behavioral effects in several key assays that phenocopy dopamine D2 receptor inhibition. This finding gave rise to the hypothesis that PDE10A inhibition also preferentially activates indirect pathway medium spiny neurons, a hypothesis that is consistent with electrophysiological, neurochemical, and molecular effects of PDE10A inhibitors. These data underwrote industry-wide efforts to investigate and develop PDE10A inhibitors as novel antipsychotics. Disappointingly, PDE10A inhibitors from 3 companies failed to evidence antipsychotic activity in patients with schizophrenia to the same extent as standard-of-care D2 antagonists. Given the notable similarities between PDE10A inhibitors and D2 antagonists, gaining an understanding of why only the latter class is antipsychotic affords a unique window into the basis for this therapeutic efficacy. With this in mind, we review the data on PDE10A inhibition as a step toward back-translating the limited antipsychotic efficacy of PDE10A inhibitors, hopefully to inform new efforts to develop better therapeutics to treat psychosis and schizophrenia.

The Influence of Substance Use on Side Effects of Olanzapine, Quetiapine, Risperidone, and Ziprasidone in Psychosis

BACKGROUND

Side effects restrict the optimal use of antipsychotics. Little is known about the influence of substance use on side effects. The aim of this study was to compare antipsychotic side effects in patients with psychosis with and without substance use, while also taking medication history and diagnosis into consideration.

METHODS

All patients (n = 226, mean age 34, females 33%) diagnosed with schizophrenia spectrum disorders (SSD; F20-F29) or other psychosis (F30-F32; F10-F19), were treated with olanzapine, quetiapine, risperidone or ziprasidone, and were assessed at baseline, 4-weeks, 14-weeks, and 27-weeks. The UKU-Side Effects Self-Rating Scale version was used to evaluate the side effect profiles, and the information on substance use was based on the Clinician Drug Use Scale.

RESULTS

At baseline, 30% of the patients used substances, 54% were diagnosed with SSD, and 47% were antipsychotic naïve. The occurrence of side effects in total was not different in patients with substance use compared to without after 4-weeks of treatment, nor in the follow-up period. At 4-weeks there were some group differences in relation to substance use, diagnosis, and medication history for single side effects. Patients with substance use showed more increased dream activity, less reduced salivation, and more gynecomastia. Patients with SSD showed less neurological side effects, orgasm dysfunction, and tension/inner unrest. The medication naïve patients showed increased hypokinesia/akinesia.

CONCLUSION

Substance use alone does not influence the general magnitude of side effects of antipsychotic medication and does not indicate a different prescription practice in patients with psychosis and substance use.

Management of Tardive Syndrome: Medications and Surgical Treatments

Tardive syndrome (TS) is an iatrogenic, often persistent movement disorder caused by drugs that block dopamine receptors. It has a broad phenotype including movement (orobuccolingual stereotypy, dystonia, tics, and others) and nonmotor features (akathisia and pain). TS has garnered increased attention of late because of the Food and Drug Administration approval of the first therapeutic agents developed specifically for this purpose. This paper will begin with a discussion on pathogenesis, clinical features, and epidemiology. However, the main focus will be treatment options currently available for TS including a suggested algorithm based on current evidence. Recently, there have been significant advances in TS therapy, particularly with the development of 2 new vesicular monoamine transporter type 2 inhibitors for TS and with new data on the efficacy of deep brain stimulation. The discussion will start with switching antipsychotics and the use of clozapine monotherapy which, despite the lack of higher-level evidence, should be considered for the treatment of psychosis and TS. Anti-dyskinetic drugs are separated into 3 tiers: 1) vesicular monoamine transporter type 2 inhibitors, which have level A evidence, are approved for use in TS and are recommended first-choice agents; 2) drugs with lower level of evidence for efficacy including clonazepam, Ginkgo biloba, and amantadine; and 3) drugs that have the potential to be beneficial, but currently have insufficient evidence including levetiracetam, piracetam, vitamin B6, melatonin, baclofen, propranolol, zolpidem, and zonisamide. Finally, the roles of botulinum toxin and surgical therapy will be examined. Current therapies, though improved, are symptomatic. Next steps should focus on the prevention and reversal of the pathogenic process.

Arrestin recruitment to dopamine D2 receptor mediates locomotion but not incentive motivation

The dopamine (DA) D2 receptor (D2R) is an important target for the treatment of neuropsychiatric disorders such as schizophrenia and Parkinson's disease. However, the development of improved therapeutic strategies has been hampered by our incomplete understanding of this receptor's downstream signaling processes in vivo and how these relate to the desired and undesired effects of drugs. D2R is a G protein-coupled receptor (GPCR) that activates G protein-dependent as well as non-canonical arrestin-dependent signaling pathways. Whether these effector pathways act alone or in concert to facilitate specific D2R-dependent behaviors is unclear. Here, we report on the development of a D2R mutant that recruits arrestin but is devoid of G protein activity. When expressed virally in "indirect pathway" medium spiny neurons (iMSNs) in the ventral striatum of D2R knockout mice, this mutant restored basal locomotor activity and cocaine-induced locomotor activity in a manner indistinguishable from wild-type D2R, indicating that arrestin recruitment can drive locomotion in the absence of D2R-mediated G protein signaling. In contrast, incentive motivation was enhanced only by wild-type D2R, signifying a dissociation in the mechanisms that underlie distinct D2R-dependent behaviors, and opening the door to more targeted therapeutics.

The Role of Zebrafish and Laboratory Rodents in Schizophrenia Research

Schizophrenia is a severe disorder characterized by positive, negative and cognitive symptoms, which are still not fully understood. The development of efficient antipsychotics requires animal models of a strong validity, therefore the aims of the article were to summarize the construct, face and predictive validity of schizophrenia models based on rodents and zebrafish, to compare the advantages and disadvantages of these models, and to propose future directions in schizophrenia modeling and indicate when it is reasonable to combine these models. The advantages of rodent models stem primarily from the high homology between rodent and human physiology, neurochemistry, brain morphology and circuitry. The advantages of zebrafish models stem in the high fecundity, fast development and transparency of the embryo. Disadvantages of both models originate in behavioral repertoires not allowing specific symptoms to be modeled, even when the models are combined. Especially modeling the verbal component of certain positive, negative and cognitive symptoms is currently impossible.

Retracted: Allosteric Activators of Protein Phosphatase 2A Display Broad Antitumor Activity Mediated by Dephosphorylation of MYBL2

Protein phosphatase 2A (PP2A) enzymes can suppress tumors, but they are often inactivated in human cancers overexpressing inhibitory proteins. Here, we identify a class of small-molecule iHAPs (improved heterocyclic activators of PP2A) that kill leukemia cells by allosterically assembling a specific heterotrimeric PP2A holoenzyme consisting of PPP2R1A (scaffold), PPP2R5E (B56ε, regulatory), and PPP2CA (catalytic) subunits. One compound, iHAP1, activates this complex but does not inhibit dopamine receptor D2, a mediator of neurologic toxicity induced by perphenazine and related neuroleptics. The PP2A complex activated by iHAP1 dephosphorylates the MYBL2 transcription factor on Ser241, causing irreversible arrest of leukemia and other cancer cells in prometaphase. In contrast, SMAPs, a separate class of compounds, activate PP2A holoenzymes containing a different regulatory subunit, do not dephosphorylate MYBL2, and arrest tumor cells in G1 phase. Our findings demonstrate that small molecules can serve as allosteric switches to activate distinct PP2A complexes with unique substrates.

Unprecedented Properties of Phenothiazines Unraveled by a NDH-2 Bioelectrochemical Assay Platform

Type II NADH:quinone oxidoreductase (NDH-2) plays a crucial role in the respiratory chains of many organisms. Its absence in mammalian cells makes NDH-2 an attractive new target for developing antimicrobials and antiprotozoal agents. We established a novel bioelectrochemical platform to characterize the catalytic behavior of NDH-2 from Caldalkalibacillus thermarum and Listeria monocytogenes strain EGD-e while bound to native-like lipid membranes. Catalysis of both NADH oxidation and lipophilic quinone reduction by membrane-bound NDH-2 followed the Michaelis-Menten model; however, the maximum turnover was only achieved when a high concentration of quinone (>3 mM) was present in the membrane, suggesting that quinone availability regulates NADH-coupled respiration activity. The quinone analogue 2-heptyl-4-hydroxyquinoline-N-oxide inhibited C. thermarum NDH-2 activity, and its potency is higher in a membrane environment compared to assays performed with water-soluble quinone analogues, demonstrating the importance of testing compounds under physiologically relevant conditions. Furthermore, when phenothiazines, one of the most commonly identified NDH-2 inhibitors, were tested, they did not inhibit membrane-bound NDH-2. Instead, our assay platform unexpectedly suggests a novel mode of phenothiazine action where chlorpromazine, a promising antitubercular agent and key medicine used to treat psychotic disorders, is able to disrupt pH gradients across bacterial membranes.

A Natural Product with High Affinity to Sigma and 5-HT7 Receptors as Novel Therapeutic Drug for Negative and Cognitive Symptoms of Schizophrenia

Dehydrocorybulbine (DHCB), an alkaloid from Corydalis yanhusuo. W.T, has been identified as a dopamine receptor antagonist. We extended our assessment of its pharmacological profile and found that DHCB exhibits high to moderate binding affinities to sigma 1 and 2 receptors, serotonin 5-HT7 receptor, and histamine H2 receptors. This led us to evaluate DHCB properties in pharmacological (apomorphine and MK-801) animal models of schizophrenia in mice. The pharmacological profile of DHCB was screened through radioligand receptor binding assays. Single dose of DHCB reversed the locomotor hyperactivity, stereotypy, and prepulse inhibition deficits induced by the dopaminergic agonist apomorphine. DHCB also reversed the depressive-like behavior and memory deficit induced by the glutamatergic antagonist MK-801 in the forced swim and the novel object recognition assays, respectively. These results indicate that DHCB effectively improves schizophrenia-like behavioral deficits that are induced by the disruption of dopaminergic and glutamatergic systems. The effectiveness of DHCB in reversing responses that mimic negative and cognitive deficits of schizophrenia might suggest that its anti-schizophrenia effects are mediated through modulating the activities of several receptor particularly sigma 1, sigma 2, 5-HT7 and dopamine receptors. Our study casts DHCB as a promising lead for therapeutic treatment of schizophrenia.

Receptor variants and the development of centrally acting medications

The progressive changes in research paradigms observed in the largest pharmaceutical companies and the burgeoning of biotechnology startups over the last 10 years have generated a need for outsourcing research facilities. In parallel, progress made in the fields of genomics, protein expression in recombinant systems, and electrophysiological recording methods have offered new possibilities for the development of contract research organizations (CROs). Successful partnering between pharmaceutical companies and CROs largely depends upon the competences and scientific quality on offer for the discovery of novel active molecules and targets. Thus, it is critical to review the knowledge in the field of neuroscience research, how genetic approaches are augmenting our knowledge, and how they can be applied in the translation from the identification of potential molecules up to the first clinical trials. Taking these together, it is apparent that CROs have an important role to play in the neuroscience of drug discovery.


Luminescence- and Fluorescence-Based Complementation Assays to Screen for GPCR Oligomerization: Current State of the Art

G protein-coupled receptors (GPCRs) have the propensity to form homo- and heterodimers. Dysfunction of these dimers has been associated with multiple diseases, e.g., pre-eclampsia, schizophrenia, and depression, among others. Over the past two decades, considerable efforts have been made towards the development of screening assays for studying these GPCR dimer complexes in living cells. As a first step, a robust in vitro assay in an overexpression system is essential to identify and characterize specific GPCR–GPCR interactions, followed by methodologies to demonstrate association at endogenous levels and eventually in vivo. This review focuses on protein complementation assays (PCAs) which have been utilized to study GPCR oligomerization. These approaches are typically fluorescence- and luminescence-based, making identification and localization of protein–protein interactions feasible. The GPCRs of interest are fused to complementary fluorescent or luminescent fragments that, upon GPCR di- or oligomerization, may reconstitute to a functional reporter, of which the activity can be measured. Various protein complementation assays have the disadvantage that the interaction between the reconstituted split fragments is irreversible, which can lead to false positive read-outs. Reversible systems offer several advantages, as they do not only allow to follow the kinetics of GPCR–GPCR interactions, but also allow evaluation of receptor complex modulation by ligands (either agonists or antagonists). Protein complementation assays may be used for high throughput screenings as well, which is highly relevant given the growing interest and effort to identify small molecule drugs that could potentially target disease-relevant dimers. In addition to providing an overview on how PCAs have allowed to gain better insights into GPCR–GPCR interactions, this review also aims at providing practical guidance on how to perform PCA-based assays.

Dopamine-dependent, swimming-induced paralysis arises as a consequence of loss of function mutations in the RUNX transcription factor RNT-1

Dopamine (DA) is a neurotransmitter with actions across phylogeny that modulate core behaviors such as motor activity, reward, attention, and cognition. Perturbed DA signaling in humans is associated with multiple disorders, including addiction, ADHD, schizophrenia, and Parkinson's disease. The presynaptic DA transporter exerts powerful control on DA signaling by efficient clearance of the neurotransmitter following release. As in vertebrates, Caenorhabditis elegans DAT (DAT-1) constrains DA signaling and loss of function mutations in the dat-1 gene result in slowed crawling on solid media and swimming-induced paralysis (Swip) in water. Previously, we identified a mutant line, vt34, that exhibits robust DA-dependent Swip. vt34 exhibits biochemical and behavioral phenotypes consistent with reduced DAT-1 function though vt34; dat-1 double mutants exhibit an enhanced Swip phenotype, suggesting contributions of the vt34-associated mutation to additional mechanisms that lead to excess DA signaling. SNP mapping and whole genome sequencing of vt34 identified the site of the molecular lesion in the gene B0412.2 that encodes the Runx transcription factor ortholog RNT-1. Unlike dat-1 animals, but similar to other loss of function rnt-1 mutants, vt34 exhibits altered male tail morphology and reduced body size. Deletion mutations in both rnt-1 and the bro-1 gene, which encodes a RNT-1 binding partner also exhibit Swip. Both vt34 and rnt-1 mutations exhibit reduced levels of dat-1 mRNA as well as the tyrosine hydroxylase ortholog cat-2. Although reporter studies indicate that rnt-1 is expressed in DA neurons, its re-expression in DA neurons of vt34 animals fails to fully rescue Swip. Moreover, as shown for vt34, rnt-1 mutation exhibits additivity with dat-1 in generating Swip, as do rnt-1 and bro-1 mutations, and vt34 exhibits altered capacity for acetylcholine signaling at the neuromuscular junction. Together, these findings identify a novel role for rnt-1 in limiting DA neurotransmission and suggest that loss of RNT-1 may disrupt function of both DA neurons and body wall muscle to drive Swip.

Potential Therapeutic Application for Nicotinic Receptor Drugs in Movement Disorders

Emerging studies indicate that striatal cholinergic interneurons play an important role in synaptic plasticity and motor control under normal physiological conditions, while their disruption may lead to movement disorders. Here we discuss the involvement of the cholinergic system in motor dysfunction, with a focus on the role of the nicotinic cholinergic system in Parkinson's disease and drug-induced dyskinesias. Evidence for a role for the striatal nicotinic cholinergic system stems from studies showing that administration of nicotine or nicotinic receptor drugs protects against nigrostriatal degeneration and decreases L-dopa-induced dyskinesias. In addition, nicotinic receptor drugs may ameliorate tardive dyskinesia, Tourette's syndrome and ataxia, although further study is required to understand their full potential in the treatment of these disorders. A role for the striatal muscarinic cholinergic system in movement disorders stems from studies showing that muscarinic receptor drugs acutely improve Parkinson's disease motor symptoms, and may reduce dyskinesias and dystonia. Selective stimulation or lesioning of striatal cholinergic interneurons suggests they are primary players in this regulation, although multiple central nervous systems appear to be involved.

IMPLICATIONS

Accumulating data from preclinical studies and clinical trials suggest that drugs targeting CNS cholinergic systems may be useful for symptomatic treatment of movement disorders. Nicotinic cholinergic drugs, including nicotine and selective nAChR receptor agonists, reduce L-dopa-induced dyskinesias, as well as antipsychotic-induced tardive dyskinesia, and may be useful in Tourette's syndrome and ataxia. Subtype selective muscarinic cholinergic drugs may also provide effective therapies for Parkinson's disease, dyskinesias and dystonia. Continued studies/trials will help address this important issue.

Treatment of Tardive Dyskinesia: A General Overview with Focus on the Vesicular Monoamine Transporter 2 Inhibitors

Tardive dyskinesia (TD) encompasses the spectrum of iatrogenic hyperkinetic movement disorders following exposure to dopamine receptor-blocking agents (DRBAs). Despite the advent of atypical or second- and third-generation antipsychotics with a presumably lower risk of complications, TD remains a persistent and challenging problem. Prevention is the first step in mitigating the risk of TD, but early recognition, gradual withdrawal of offending medications, and appropriate treatment are also critical. As TD is often a persistent and troublesome disorder, specific antidyskinetic therapies are often needed for symptomatic relief. The vesicular monoamine transporter 2 (VMAT2) inhibitors, which include tetrabenazine, deutetrabenazine, and valbenazine, are considered the treatment of choice for most patients with TD. Deutetrabenazine-a deuterated version of tetrabenazine-and valbenazine, the purified parent product of one of the main tetrabenazine metabolites, are novel VMAT2 inhibitors and the only drugs to receive approval from the US FDA for the treatment of TD. VMAT2 inhibitors deplete presynaptic dopamine and reduce involuntary movements in many hyperkinetic movement disorders, particularly TD, Huntington disease, and Tourette syndrome. The active metabolites of the VMAT2 inhibitors have high affinity for VMAT2 and minimal off-target binding. Compared with tetrabenazine, deutetrabenazine and valbenazine have pharmacokinetic advantages that translate into less frequent dosing and better tolerability. However, no head-to-head studies have compared the various VMAT2 inhibitors. One of the major advantages of VMAT2 inhibitors over DRBAs, which are still being used by some clinicians in the treatment of some hyperkinetic disorders, including TD, is that they are not associated with the development of TD. We also briefly discuss other treatment options for TD, including amantadine, clonazepam, Gingko biloba, zolpidem, botulinum toxin, and deep brain stimulation. Treatment of TD and other drug-induced movement disorders must be individualized and based on the severity, phenomenology, potential side effects, and other factors discussed in this review.

Adenosine Actions on Oligodendroglia and Myelination in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is the most commonly diagnosed neurodevelopmental disorder. Independent of neuronal dysfunction, ASD and its associated comorbidities have been linked to hypomyelination and oligodendroglial dysfunction. Additionally, the neuromodulator adenosine has been shown to affect certain ASD comorbidities and symptoms, such as epilepsy, impairment of cognitive function, and anxiety. Adenosine is both directly and indirectly responsible for regulating the development of oligodendroglia and myelination through its interaction with, and modulation of, several neurotransmitters, including glutamate, dopamine, and serotonin. In this review, we will focus on the recent discoveries in adenosine interaction with physiological and pathophysiological activities of oligodendroglia and myelination, as well as ASD-related aspects of adenosine actions on neuroprotection and neuroinflammation. Moreover, we will discuss the potential therapeutic value and clinical approaches of adenosine manipulation against hypomyelination in ASD.

Dose reduction of high-dose first-generation antipsychotics or switch to ziprasidone in long-stay patients with schizophrenia: A 1-year double-blind randomized clinical trial

Long-stay patients with severe schizophrenia are frequently treated with high doses of first-generation antipsychotics (FGA). Dose reduction or switching to ziprasidone may reduce the severity of negative symptoms and side effects. We investigated in a randomized double-blind trial whether a dose-reduction strategy to achieve an adequate dose of a FGA (5 mg/day haloperidol equivalents, n = 24) or switching to ziprasidone (160 mg/day, n = 24) in treatment resistant patients would decrease negative symptoms after 1 year of treatment. We found that negative symptoms did not change significantly in either condition. Positive symptoms, excited symptoms, and emotional distress worsened over time with ziprasidone, resulting in a significant difference between conditions in favour of FGA dose reduction. Relapse and treatment failure, defined as a prolonged or repeated relapse, occurred more often with ziprasidone than with FGA (45.8% versus 20.8%, and 25.0% versus 16.7%, respectively). Treatment with ziprasidone was superior for extrapyramidal symptoms. Our study establishes that lowering high FGA doses to an equivalent of 5 mg/day haloperidol or switching to ziprasidone is feasible in the vast majority of patients but does not improve negative or other symptoms. Neither FGA dose reduction nor switching to ziprasidone is an adequate alternative to clozapine for long-stay patients with severe treatment resistant schizophrenia.