Aripiprazole differentially affects mesolimbic and nigrostriatal dopaminergic transmission: implications for long-term drug efficacy and low extrapyramidal side-effects

Functional neuroimaging biomarkers of anhedonia response to escitalopram plus adjunct aripiprazole treatment for major depressive disorder

BACKGROUND

Identifying neuroimaging biomarkers of antidepressant response may help guide treatment decisions and advance precision medicine.

AIMS

To examine the relationship between anhedonia and functional neurocircuitry in key reward processing brain regions in people with major depressive disorder receiving aripiprazole adjunct therapy with escitalopram.

METHOD

Data were collected as part of the CAN-BIND-1 study. Participants experiencing a current major depressive episode received escitalopram for 8 weeks; escitalopram non-responders received adjunct aripiprazole for an additional 8 weeks. Functional magnetic resonance imaging (on weeks 0 and 8) and clinical assessment of anhedonia (on weeks 0, 8 and 16) were completed. Seed-based correlational analysis was employed to examine the relationship between baseline resting-state functional connectivity (rsFC), using the nucleus accumbens (NAc) and anterior cingulate cortex (ACC) as key regions of interest, and change in anhedonia severity after adjunct aripiprazole.

RESULTS

Anhedonia severity significantly improved after treatment with adjunct aripiprazole.There was a positive correlation between anhedonia improvement and rsFC between the ACC and posterior cingulate cortex, ACC and posterior praecuneus, and NAc and posterior praecuneus. There was a negative correlation between anhedonia improvement and rsFC between the ACC and anterior praecuneus and NAc and anterior praecuneus.

CONCLUSIONS

Eight weeks of aripiprazole, adjunct to escitalopram, was associated with improved anhedonia symptoms. Changes in functional connectivity between key reward regions were associated with anhedonia improvement, suggesting aripiprazole may be an effective treatment for individuals experiencing reward-related deficits. Future studies are required to replicate our findings and explore their generalisability, using other agents with partial dopamine (D2) agonism and/or serotonin (5-HT2A) antagonism.

Antipsychotic drug-aripiprazole against schizophrenia, its therapeutic and metabolic effects associated with gene polymorphisms

Second-generation antipsychotics are widely used for the treatment of schizophrenia. Aripiprazole (ARI) is classified as a third-generation antipsychotic drug with a high affinity for dopamine and serotonin receptors. It is considered a dopamine-system stabilizer without severe side effects. In some patients the response to ARI treatment is inadequate and they require an effective augmentation strategy. It has been found that the response to the drug and the risk of adverse metabolic effects can be related to gene polymorphisms. A reduced dose is recommended for CYP2D6 poor metabolizers; moreover, it is postulated that other polymorphisms including CYP3A4, CYP3A5, ABCB1, DRD2, and 5-HTRs genes influence the therapeutic effect of ARI. ARI can increase the levels of prolactin, C-peptide, insulin, and/or cholesterol possibly due to specific genetic variants. It seems that a pharmacogenetic approach can help predict drug response and improve the clinical management of patients with schizophrenia.

Diagnosis and Drug Prediction of Parkinson's Disease Based on Immune-Related Genes

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Immune mechanisms play an important role in the development of PD. The purpose of this study was to identify potential differentially expressed immune-related genes (IRGs), signaling pathways, and drugs in PD, which may provide new diagnostic markers and therapeutic targets for PD. Differentially expressed genes (DEGs) and IRGs were respectively obtained from the Gene Expression Omnibus (GEO) dataset and the ImmPort database. Weighted gene co-expression network analysis (WGCNA) was utilized to further identify hub IRGs. Core IRGs were obtained by intersection of DEGs and hub genes in the module of WGCNA, followed by construction of diagnostic models and regulation network establishment of long non-coding RNAs (lncRNAs)-miRNAs-diagnostic IRGs. Analysis of functional enrichment and protein-protein interaction (PPI) network and identification of related drugs of DEGs was performed. LILRB3 and CSF3R were identified as potential diagnostic markers for PD. Two regulatory pairs were identified based on LILRB3 and CSF3R, including XIST-hsa-miR-214-3p/hsa-miR-761-LILRB3 and XIST-hsa-miR-485-5p/hsa-miR-654-5p-CSF3R. LEP and IL1A were drug targets of Olanzapine. MMP9 and HSP90AB1 were drug targets of Bevacizumab. In addition, LEP and MMP9 were respectively drug targets of Lovastatin and Celecoxib. Herpes simplex infection (involved TNFRSF1A) and cytokine-cytokine receptor interaction (involved CSF3R, LEP, and IL1A) were the most remarkably enriched signaling pathways of DEGs. Identified IRGs and related signaling pathways may play critical roles in the development of PD. Additionally, LILRB3 and CSF3R can be considered as potential immune-related diagnostic markers for PD. LEP, IL1A, MMP9, and HSP90AB1 may be regarded as immune-related therapeutic targets for PD.

Risperidone Induced DNA Methylation Changes in Dopamine Receptor and Stathmin Genes in Mice Exposed to Social Defeat Stress

Objective

Methods

Results

Conclusion

Antipsychotic Drug Development: From Historical Evidence to Fresh Perspectives

Schizophrenia is a complex disorder of varied etiology, manifesting symptoms that can differ between patients and change throughout an individual's lifespan. Antipsychotic drugs have evolved through first (e.g., haloperidol), second (olanzapine and clozapine) and a possible third (aripiprazole) generation of drugs in an attempt to improve efficacy and tolerability, with minimal side-effects. Despite robust scientific efforts over the past 70 years, there remains a need to develop drugs with greater efficacy, particularly in relation to the negative and cognitive symptoms of schizophrenia, addressing treatment resistance, with a lower side-effects profile compared to existing antipsychotic drugs. Identifying and investigating novel therapeutic targets remains an important component of future antipsychotic drug discovery; however, mounting evidence demonstrates neurobiological, neuroanatomical and functional heterogeneity in cohorts of individuals with schizophrenia. This presents an opportunity to refresh the approach to drug trials to a more targeted strategy. By increasing understanding of the basic science and pharmacological mechanisms underlying the potential antipsychotic efficacy of novel therapeutics prior to clinical trials, new drugs may be appropriately directed to a target population of schizophrenia subjects based on the drug mechanisms and correlating biological sub-groupings of patient characteristics. Improving the lives of sub-populations of people with schizophrenia that share common biological characteristics and are likely to be responsive to a particular compound may be more achievable than aiming to treat the complexities of schizophrenia as a homogenous disorder. This approach to clinical trials in antipsychotic research is discussed in the present review.

A unifying theory for the pathoetiologic mechanism of tardive dyskinesia

INTRODUCTION

Chronic treatment with dopamine D2 receptor antagonists has been proposed to lead to dopamine receptor supersensitivity. Frequently, this is conceptualized as upregulation or changes in the structure or function of the post-synaptic D2 receptor. However, the measured 1.4-fold increase in D2 receptor density and the lack of actual receptor supersensitivity are probably inadequate to explain outcomes such as tardive dyskinesia (TD) and dopamine supersensitivity psychosis.

HYPOTHESIS

Recent data suggest that TD may result from a combination of presynaptic, synaptic, and postsynaptic changes.

DISCUSSION

Presynaptic increase in dopamine release occurs when super-therapeutic blockade of postsynaptic D2 receptors results in excess synaptic unbound dopamine which ultimately ends up being reuptaken by the presynaptic neuron through the dopamine transporter. The increased availability of recycled dopamine results in higher vesicular dopamine concentrations. Since the quantity of neurotransmitter released (known as quanta) is determined by the number of presynaptic neurotransmitter vesicles, the increase in the number (concentration) of dopamine molecules in the vesicles results in a higher concentration of synaptic dopamine with successive depolarization events. Synaptic changes such as the appearance of perforated synapses which is an early step in new synapse formation have been shown in animal models of TD. Finally, postsynaptic increases in D2 receptor expression without demonstration of increased sensitivity or potency has been demonstrated.

CONCLUSION

TD likely develops due to changes across the synapse and terminology such as 'dopamine receptor supersensitivity' can be misleading. 'Synaptic upregulation' may be a more correct term.

Modulation by chronic antipsychotic administration of PKA- and GSK3β-mediated pathways and the NMDA receptor in rat ventral midbrain

RATIONALE

Antipsychotics exert therapeutic effects by modulating various cellular signalling pathways and several types of receptors, including PKA- and GSK3β-mediated signalling pathways, and NMDA receptors. The ventral midbrain, mainly containing the ventral tegmental area (VTA) and substantia nigra (SN), are the nuclei with dopamine origins in the brain, which are also involved in the actions of antipsychotics. Whether antipsychotics can modulate these cellular pathways in the ventral midbrain is unknown.

OBJECTIVE

This study aims to investigate the effects of antipsychotics, including aripiprazole (a dopamine D₂ receptor (D₂R) partial agonist), bifeprunox (a D₂R partial agonist), and haloperidol (a D₂R antagonist) on the PKA- and GSK3β-mediated pathways and NMDA receptors in the ventral midbrain.

METHODS

Male rats were orally administered aripiprazole (0.75 mg/kg, t.i.d. (ter in die)), bifeprunox (0.8 mg/kg, t.i.d.), haloperidol (0.1 mg/kg, t.i.d.) or vehicle for either 1 week or 10 weeks. The levels of PKA, p-PKA, Akt, p-Akt, GSK3β, p-GSK3β, Dvl-3, β-catenin, and NMDA receptor subunits in the ventral midbrain were assessed by Western Blots.

RESULTS

The results showed that chronic antipsychotic treatment with aripiprazole selectively increased PKA activity in the VTA. Additionally, all three drugs elevated the activity of the Akt-GSK3β signalling pathway in a time-dependent manner, while only aripiprazole stimulated the Dvl-3-GSK3β-β-catenin signalling pathway in the SN. Furthermore, chronic administration with both aripiprazole and haloperidol decreased the expression of NMDA receptors.

CONCLUSION

This study suggests that activating PKA- and GSK3β-mediated pathways and downregulating NMDA receptor expression in the ventral midbrain might contribute to the clinical effects of antipsychotics.

Early antipsychotic exposure affects NMDA and GABAA receptor binding in the brains of juvenile rats

Antipsychotics were developed to treat schizophrenia in adults; however they have been increasingly prescribed in children and adolescents. The NMDA and GABA_A receptors are involved in neurodevelopment and the pathophysiology of various mental disorders in children and adolescents. Male and female juvenile rats were treated orally with risperidone (0.3 mg/kg, 3 times/day), aripiprazole (1 mg/kg), olanzapine (1 mg/kg) or vehicle (control), starting from postnatal day (PD) 23 (±1 day) for 3 weeks (corresponding to the childhood-adolescent period in humans). Quantitative autoradiography was used to detect the binding density of [³H]MK-801 (an NMDA receptor antagonist) and [³H]muscimol (a selective GABA_A receptor agonist). Aripiprazole elevated the [³H]MK801 binding levels in the NAcC of male rats, and the NAcS and CPu of female rats. Risperidone increased [³H]MK801 levels in the CPu of female rats, and the NAcS of male rats. Aripiprazole upregulated [³H]muscimol binding levels in the CPu and NAcC of male rats, while it elevated the [³H]muscimol levels in the PFC of female rats, compared to controls. These results suggest that early treatment with these antipsychotics modulates NMDA and GABA_A neurotransmission in juveniles, which may play a role in their clinical efficacy in the control of mental disorders in children and adolescents.

Pharmacological insights into impulsive-compulsive spectrum disorders associated with dopaminergic therapy

Impulsive-compulsive spectrum disorders are associated with dopamine agonist therapy in some patients. These untoward outcomes occur with direct-acting, full and partial agonists at D2 dopamine family receptors. The disorders typically emerge during chronic treatment, and exhibit common features that are independent of the neurological or psychiatric pathology for which the initial therapy was indicated. It is well-documented that the brain is 'plastic', changing in response to alterations to internal factors (e.g., disease processes), as well as external factors (e.g., therapies). The complexities of these clinical scenarios have eluded a clear depiction of the neurobiology for impulsive-compulsive spectrum disorders and engendered considerable debate regarding the mechanistic underpinnings of the disorders. In this opinion, we use pharmacological concepts related to homeostatic compensation subsequent to chronic receptor activation to provide a unifying construct. This construct helps explain the occurrence of impulsive-compulsive spectrum disorders across disease states, and during therapy with full and partial agonists.

Effects of short- and long-term aripiprazole treatment on Group I mGluRs in the nucleus accumbens: Comparison with haloperidol

The D2 receptor partial agonist, aripiprazole, has shown increased therapeutic efficacy for schizophrenia, autism and Tourette's syndrome compared to traditional antipsychotics such as the D2 receptor antagonist, haloperidol. Recent evidence suggests this superior profile may be associated with downstream effects on glutamatergic synapses. Group 1 metabotropic glutamate receptors (mGluRs) and their endogenous modulators, Norbin and Homer1, are regulated by D2 receptor activity, particularly within the nucleus accumbens (NAc), a target region of aripiprazole and haloperidol. This study sought to evaluate the effects of aripiprazole on Group 1 mGluRs, Norbin and Homer1 in the NAc, in comparison to haloperidol. Sprague-Dawley rats were orally administered daily doses of aripiprazole (2.25mg/kg), haloperidol (0.3mg/kg) or vehicle for 1 or 10-weeks. Immunoblot analyses revealed Group 1 mGluR protein levels were not altered following 1-week and 10-week aripiprazole or haloperidol treatment, compared to vehicle treated rodents. However, 1-week aripiprazole and haloperidol treatment significantly elevated Homer1a and Norbin protein expression, respectively. After 10 weeks of treatment, aripiprazole, but not haloperidol, significantly increased Norbin expression. These findings indicate the antipsychotics, aripiprazole and haloperidol, exert differential temporal effects on Norbin and Homer1 expression that may have consequences on synaptic glutamatergic transmission underlying their therapeutic profile.

Unbiased screen identifies aripiprazole as a modulator of abundance of the polyglutamine disease protein, ataxin-3

No disease-modifying treatment exists for the fatal neurodegenerative polyglutamine disease known both as Machado-Joseph disease and spinocerebellar ataxia type 3. As a potential route to therapy, we identified small molecules that reduce levels of the mutant disease protein, ATXN3. Screens of a small molecule collection, including 1250 Food and Drug Administration-approved drugs, in a novel cell-based assay, followed by secondary screens in brain slice cultures from transgenic mice expressing the human disease gene, identified the atypical antipsychotic aripiprazole as one of the hits. Aripiprazole increased longevity in a Drosophila model of Machado-Joseph disease and effectively reduced aggregated ATXN3 species in flies and in brains of transgenic mice treated for 10 days. The aripiprazole-mediated decrease in ATXN3 abundance may reflect a complex response culminating in the modulation of specific components of cellular protein homeostasis. Aripiprazole represents a potentially promising therapeutic drug for Machado-Joseph disease and possibly other neurological proteinopathies.

3-Aminomethyl Derivatives of 2-Phenylimidazo[1,2-a]-pyridine as Positive Allosteric Modulators of GABAA Receptor with Potential Antipsychotic Activity

Schizophrenia is a mental illness characterized by behavioral changes as well as anatomical and neurochemical abnormalities. There has been remarkable progress in the drug discovery for schizophrenia; however, antipsychotics that act through molecular targets, other than monoaminergic receptors, have not been developed. One of the hypotheses of schizophrenia states that GABAergic dysfunction might be implemented in the pathophysiology of this disease. Our recent findings and previous clinical observations have suggested that modulation of GABAergic system through α₁-GABA_A receptors would represent an original approach for the treatment of schizophrenia. This study presents the synthesis and biological evaluation of a series of fluorinated 3-aminomethyl derivatives of 2-phenylimidazo[1,2-a]-pyridine as potential antipsychotic agents. Compound 7 has a high affinity for GABA_A receptor (K_i = 27.2 nM), high in vitro metabolic stability, and antipsychotic-like activity in amphetamine-induced hyperlocomotion test in rats (MED = 10 mg/kg). Compound 7 represents a promising point of entry in the course of development of antipsychotic agents with a nondopaminergic mechanism of action.

Partial regimen replacement with aripiprazole reduces serum prolactin in patients with a long history of schizophrenia: A case series

AIM

Aripiprazole (ARP) is a popular antipsychotic drug that has demonstrated ameliorative effects on hyperprolactinemia. However, no study to date has studied the utility of ARP in patients with a long history of schizophrenia and antipsychotic treatment. We therefore examined the effect of partial antipsychotic regimen replacement with ARP on hyperprolactinemia induced by chronic antipsychotic use in patients with schizophrenia.

METHODS

Sixteen patients with a schizophrenia diagnosis (F2) based on the International Classification of Diseases (version 10) were recruited. At months 0, 1, 3, and 6 of the study, serum prolactin, body weight, and blood glucose were measured, and QOL and psychotic symptoms were assessed using Global Assessment of Functioning scores and Clinical Global Impressions of Improvement (CGI-I) scores.

RESULTS

Nine patients with an average age of 46.7±9.6 years and mean disease duration of 15.9±10.4 years were included in the final analysis. Serum prolactin levels significantly decreased and GAF and CGI-I scores improved significantly over the 6-month period after partial replacement with ARP. Additionally, no changes were observed in body weight or blood glucose over the 6-month period.

CONCLUSION

Partial antipsychotic regimen replacement with ARP improves hyperprolactinemia, and may improve the QOL of patients with a long history of schizophrenia.

CLINICAL TRIAL REGISTRATION NUMBER

Japan Medical Association, Center for clinical trials D: JMA-IIA00245.

Early Antipsychotic Treatment in Juvenile Rats Elicits Long-Term Alterations to the Dopamine Neurotransmitter System

Prescription of antipsychotic drugs (APDs) to children has substantially increased in recent years. Whilst current investigations into potential long-term effects have uncovered some alterations to adult behaviours, further investigations into potential changes to neurotransmitter systems are required. The current study investigated potential long-term changes to the adult dopamine (DA) system following aripiprazole, olanzapine and risperidone treatment in female and male juvenile rats. Levels of tyrosine hydroxylase (TH), phosphorylated-TH (p-TH), dopamine active transporter (DAT), and D₁ and D₂ receptors were measured via Western blot and/or receptor autoradiography. Aripiprazole decreased TH and D₁ receptor levels in the ventral tegmental area (VTA) and p-TH levels in the prefrontal cortex (PFC) of females, whilst TH levels decreased in the PFC of males. Olanzapine decreased PFC p-TH levels and increased D₂ receptor expression in the PFC and nucleus accumbens (NAc) in females only. Additionally, risperidone treatment increased D₁ receptor levels in the hippocampus of females, whilst, in males, p-TH levels increased in the PFC and hippocampus, D₁ receptor expression decreased in the NAc, and DAT levels decreased in the caudate putamen (CPu), and elevated in the VTA. These results suggest that early treatment with various APDs can cause different long-term alterations in the adult brain, across both treatment groups and genders.

Chronic administration of aripiprazole activates GSK3β-dependent signalling pathways, and up-regulates GABAA receptor expression and CREB1 activity in rats

Aripiprazole is a D2-like receptor (D2R) partial agonist with a favourable clinical profile. Previous investigations indicated that acute and short-term administration of aripiprazole had effects on PKA activity, GSK3β-dependent pathways, GABAA receptors, NMDA receptor and CREB1 in the brain. Since antipsychotics are used chronically in clinics, the present study investigated the long-term effects of chronic oral aripiprazole treatment on these cellular signalling pathways, in comparison with haloperidol (a D2R antagonist) and bifeprunox (a potent D2R partial agonist). We found that the Akt-GSK3β pathway was activated by aripiprazole and bifeprunox in the prefrontal cortex; NMDA NR2A levels were reduced by aripiprazole and haloperidol. In the nucleus accumbens, all three drugs increased Akt-GSK3β signalling; in addition, both aripiprazole and haloperidol, but not bifeprunox, increased the expression of Dvl-3, β-catenin and GABAA receptors, NMDA receptor subunits, as well as CREB1 phosphorylation levels. The results suggest that chronic oral administration of aripiprazole affects schizophrenia-related cellular signalling pathways and markers (including Akt-GSK3β signalling, Dvl-GSK3β-β-catenin signalling, GABAA receptor, NMDA receptor and CREB1) in a brain-region-dependent manner; the selective effects of aripiprazole on these signalling pathways might be associated with its unique clinical effects.

Early antipsychotic exposure affects serotonin and dopamine receptor binding density differently in selected brain loci of male and female juvenile rats

BACKGROUND

Antipsychotic drugs (APDs) were developed to treat schizophrenia in adults; however they have been increasingly prescribed (mostly "off-label") for children and adolescents. This study aimed to investigate the effects of aripiprazole, olanzapine and risperidone on the binding of serotonin (5-HT) and dopamine receptors in juvenile rat brain regions that are involved in antipsychotic efficacy.

METHODS

Male and female rats were treated orally with aripiprazole (1mg/kg), olanzapine (1mg/kg), risperidone (0.3mg/kg) or vehicle 3 times/day starting from postnatal day 23 (±1day) for 20 days. Quantitative autoradiography was performed to examine the receptor binding densities.

RESULTS

Olanzapine significantly decreased 5-HT2A (5-HT2AR) and 5-HT2C receptor (5-HT2CR) binding in the prefrontal cortex (PFC), cingulate cortex (Cg) and nucleus accumbens (NAc) of both male and female rats. In the caudate putamen (CPu), olanzapine attenuated 5-HT2AR binding in both genders, and reduced 5-HT2CR binding in male rats. Olanzapine increased D2 receptor (D2R) binding in the NAcS of male rats, but decreased it in females. Olanzapine increased D1 receptor (D1R) binding in the Cg, while aripiprazole decreased D1R binding in the PFC of males. Aripiprazole significantly reduced 5-HT2AR binding in the male PFC. Risperidone decreased 5-HT2AR binding in the PFC of female rats, while attenuating D1R binding in the PFC and Cg of males. However, APDs have no effects on the binding of serotonin and dopamine transporters.

CONCLUSION

This study revealed that aripiprazole, olanzapine and risperidone affected 5-HT2AR, 5-HT2CR, 5-HTT, D1R and D2R bindings differently in the brains of juvenile male and female rats.

Acute Dystonia Following a Switch in Treatment from Atomoxetine to Low-dose Aripiprazole

The present report describes the cases of a 17-year-old male patient and a 13-year-old female patient who developed acute dystonia following the administration of low-dose aripiprazole (5 mg/day) after the cessation of atomoxetine treatment. Although aripiprazole-induced dystonia has been previously reported in the literature, it is rare, and most of these cases were associated with doses higher than 5 mg/day. Furthermore, both of the patients in the present study discontinued atomoxetine prior to the initiation of aripiprazole treatment; thus, this report also discussed the possible mechanisms underlying the manifestation of dystonia from the perspective of neurotransmitter activity.

Aripiprazole Increases the PKA Signalling and Expression of the GABAA Receptor and CREB1 in the Nucleus Accumbens of Rats

The GABAA receptor is implicated in the pathophysiology of schizophrenia and regulated by PKA signalling. Current antipsychotics bind with D2-like receptors, but not the GABAA receptor. The cAMP-responsive element-binding protein 1 (CREB1) is also associated with PKA signalling and may be related to the positive symptoms of schizophrenia. This study investigated the effects of antipsychotics in modulating D2-mediated PKA signalling and its downstream GABAA receptors and CREB1. Rats were treated orally with aripiprazole (0.75 mg/kg, ter in die (t.i.d.)), bifeprunox (0.8 mg/kg, t.i.d.), haloperidol (0.1 mg/kg, t.i.d.) or vehicle for 1 week. The levels of PKA-Cα and p-PKA in the prefrontal cortex (PFC), nucleus accumbens (NAc) and caudate putamen (CPu) were detected by Western blots. The mRNA levels of Gabrb1, Gabrb2, Gabrb3 and Creb1, and their protein expression were measured by qRT-PCR and Western blots, respectively. Aripiprazole elevated the levels of p-PKA and the ratio of p-PKA/PKA in the NAc, but not the PFC and CPu. Correlated with this elevated PKA signalling, aripiprazole elevated the mRNA and protein expression of the GABAA (β-1) receptor and CREB1 in the NAc. While haloperidol elevated the levels of p-PKA and the ratio of p-PKA/PKA in both NAc and CPu, it only tended to increase the expression of the GABAA (β-1) receptor and CREB1 in the NAc, but not the CPu. Bifeprunox had no effects on PKA signalling in these brain regions. These results suggest that aripiprazole has selective effects on upregulating the GABAA (β-1) receptor and CREB1 in the NAc, probably via activating PKA signalling.

The Treatment of Adult Bipolar Disorder with Aripiprazole: A Systematic Review

Bipolar disorder is characterized by exacerbations of opposite mood polarity, ranging from manic to major depressive episodes. In the current nosological system of the Diagnostic and Statistical Manual – 5^th edition (DSM-5), it is conceptualized as a spectrum disorder consisting of bipolar disorder type I, bipolar disorder type II, cyclothymic disorder, and bipolar disorder not otherwise specified. Treatment of all phases of this disorder is primarily with mood stabilizers, but many patients either show resistance to the conventional mood stabilizing medications or are intolerant to their side-effects. In this setting, second-generation antipsychotics have gained prominence as many bipolar subjects who are otherwise treatment refractory show response to these agents. Aripiprazole is a novel antipsychotic initially approved for the treatment of schizophrenia but soon found to be effective in bipolar disorder. This drug is well studied, as randomized controlled trials have been conducted in various phases of bipolar disorders. Aripiprazole exhibits the pharmacodynamic properties of partial agonism, functional selectivity, and serotonin-dopamine activity modulation – the new exemplars in the treatment of major psychiatric disorders. It is the first among a new series of psychotropic medications, which now also include brexpiprazole and cariprazine. The current review summarizes the data from controlled trials regarding the efficacy and safety of aripiprazole in adult bipolar patients. On the basis of this evidence, aripiprazole is found to be efficacious in the treatment and prophylaxis of manic and mixed episodes but has no effectiveness in acute and recurrent bipolar depression.

Aripiprazole and Haloperidol Activate GSK3β-Dependent Signalling Pathway Differentially in Various Brain Regions of Rats

Aripiprazole, a dopamine D₂ receptor (D₂R) partial agonist, possesses a unique clinical profile. Glycogen synthase kinase 3β (GSK3β)-dependent signalling pathways have been implicated in the pathophysiology of schizophrenia and antipsychotic drug actions. The present study examined whether aripiprazole differentially affects the GSK3β-dependent signalling pathways in the prefrontal cortex (PFC), nucleus accumbens (NAc), and caudate putamen (CPu), in comparison with haloperidol (a D₂R antagonist) and bifeprunox (a D₂R partial agonist). Rats were orally administrated aripiprazole (0.75 mg/kg), bifeprunox (0.8 mg/kg), haloperidol (0.1 mg/kg) or vehicle three times per day for one week. The levels of protein kinase B (Akt), p-Akt, GSK3β, p-GSK3β, dishevelled (Dvl)-3, and β-catenin were measured by Western Blots. Aripiprazole increased GSK3β phosphorylation in the PFC and NAc, respectively, while haloperidol elevated it in the NAc only. However, Akt activity was not changed by any of these drugs. Additionally, both aripiprazole and haloperidol, but not bifeprunox, increased the expression of Dvl-3 and β-catenin in the NAc. The present study suggests that activation of GSK3β phosphorylation in the PFC and NAc may be involved in the clinical profile of aripiprazole; additionally, aripiprazole can increase GSK3β phosphorylation via the Dvl-GSK3β-β-catenin signalling pathway in the NAc, probably due to its relatively low intrinsic activity at D₂Rs.

Early antipsychotic treatment in childhood/adolescent period has long-term effects on depressive-like, anxiety-like and locomotor behaviours in adult rats

Childhood/adolescent antipsychotic drug (APD) use is exponentially increasing worldwide, despite limited knowledge of the long-term effects of early APD treatment. Whilst investigations have found that early treatment has resulted in some alterations to dopamine and serotonin neurotransmission systems (essential to APD efficacy), there have only been limited studies into potential long-term behavioural changes. This study, using an animal model for childhood/adolescent APD treatment, investigated the long-term effects of aripiprazole, olanzapine and risperidone on adult behaviours of male and female rats. Open-field/holeboard, elevated plus maze (EPM), social interaction and forced swim (FS) tests were then conducted in adult rats. Our results indicated that in the male cohort, early risperidone and olanzapine treatment elicited long-term hyper-locomotor effects (open-field/holeboard and FS tests), whilst a decrease in depressive-like behaviour (in FS test) was observed in response to olanzapine treatment. Furthermore, anxiolytic-like behaviours were found following testing in the open-field/holeboard and EPM in response to all three drug treatments. Effects in the female cohort, however, were to a far lesser extent, with behavioural attributes indicative of an increased depressive-like behaviour and hypo-locomotor activity exhibited in the FS test following early risperidone and olanzapine treatment. These results suggest that various APDs have different long-term effects on the behaviours of adult rats.

Glutamatergic agents for schizophrenia: current evidence and perspectives

Suboptimal outcomes in schizophrenia are a consequence of lacking insight into the etiology, biomarkers and treatment-relevant subgroups, the therapeutic restriction to dopaminergic-modulating antipsychotics that fail to significantly improve negative and cognitive symptoms, non-adherence, and, in the case of treatment-resistance, the underutilization of clozapine. Evidence suggests additional, extra-dopaminergic abnormalities in amino acid neurotransmission, particularly the glutamatergic system. Antidopaminergic antipsychotics modulate this system on several levels, as do mood stabilizers, including lamotrigine, topiramate and pregabaline. Recently, agonists at metabotropic glutamate receptors and glycine uptake inhibitors failed in large placebo-controlled trials for schizophrenia. Problems to overcome for successfully leveraging glutamatergic agents for schizophrenia are patient selection, focus on positive symptoms and late disease stages, and dose-response relationships. Because glutamate guides processes of brain development and maturation, clinical research should focus on the at-risk mental state or first-episode psychosis, address cognition and negative symptoms and use monotherapy designs in parallel to augmentation strategies.

Pretreatment or Posttreatment with Aripiprazole Attenuates Methamphetamine-induced Stereotyped Behavior in Mice

Aripiprazole is a third-generation atypical antipsychotic and a dopamine D₂ receptor partial agonist. In the present study, we investigated whether a single administration of aripiprazole to mice, either as a pretreatment or as a posttreatment, would affect stereotypy induced by methamphetamine (METH). Pretreatment of male ICR mice with aripiprazole (1 or 10 mg/kg, i.p.) attenuated the incidence of METH-induced stereotypical behavior in a dose-dependent manner. Pretreatment of mice with 1 mg/kg aripiprazole produced an increase in the locomotor activity in mice treated with METH compared with mice treated with vehicle plus METH and with 10 mg/kg aripiprazole plus METH. This increase in locomotion is indicative of a rightward shift in the dose–response curve for METH, consistent with a shift in the type of stereotypical behavior observed from biting to sniffing. Aripiprazole posttreatment, after METH-induced stereotypical behavior, was fully expressed and also significantly attenuated overall stereotypy in an aripiprazole dose-dependent manner. These data suggest that the antagonism of METH effects by aripiprazole should be investigated as a potential treatment for acute METH overdose.

The safety, efficacy and tolerability of Abilify Maintena for the treatment of schizophrenia

Relapse in schizophrenia has been associated with poor adherence to oral medication. A possible method to optimize medication adherence could be to switch patients from oral to depot medication. In this respect, aripiprazole long acting injectable (ALAI) significantly delayed time to impending relapse when compared with placebo (p < 0.0001), while ALAI was generally well tolerated during both short-term and long-term studies. A literature search, using PubMed was conducted to identify relevant publications. Available evidence suggests that ALAI may be a viable treatment option for patients with schizophrenia, but before it can be concluded whether or not all schizophrenia patients could benefit from a switch to depot formulations, several questions remain to be answered. Thus, there is a great need for randomized controlled trials comparing depot medications with their oral equivalents.

Unique Effects of Acute Aripiprazole Treatment on the Dopamine D2 Receptor Downstream cAMP-PKA and Akt-GSK3β Signalling Pathways in Rats

Aripiprazole is a wide-used antipsychotic drug with therapeutic effects on both positive and negative symptoms of schizophrenia, and reduced side-effects. Although aripiprazole was developed as a dopamine D₂ receptor (D₂R) partial agonist, all other D₂R partial agonists that aimed to mimic aripiprazole failed to exert therapeutic effects in clinic. The present in vivo study aimed to investigate the effects of aripiprazole on the D₂R downstream cAMP-PKA and Akt-GSK3β signalling pathways in comparison with a D₂R antagonist – haloperidol and a D₂R partial agonist – bifeprunox. Rats were injected once with aripiprazole (0.75mg/kg, i.p.), bifeprunox (0.8mg/kg, i.p.), haloperidol (0.1mg/kg, i.p.) or vehicle. Five brain regions – the prefrontal cortex (PFC), nucleus accumbens (NAc), caudate putamen (CPu), ventral tegmental area (VTA) and substantia nigra (SN) were collected. The protein levels of PKA, Akt and GSK3β were measured by Western Blotting; the cAMP levels were examined by ELISA tests. The results showed that aripiprazole presented similar acute effects on PKA expression to haloperidol, but not bifeprunox, in the CPU and VTA. Additionally, aripiprazole was able to increase the phosphorylation of GSK3β in the PFC, NAc, CPu and SN, respectively, which cannot be achieved by bifeprunox and haloperidol. These results suggested that acute treatment of aripiprazole had differential effects on the cAMP-PKA and Akt-GSK3β signalling pathways from haloperidol and bifeprunox in these brain areas. This study further indicated that, by comparison with bifeprunox, the unique pharmacological profile of aripiprazole may be attributed to the relatively lower intrinsic activity at D₂R.

Differential effects of short- and long-term antipsychotic treatment on the expression of neuregulin-1 and ErbB4 receptors in the rat brain

Neuregulin-1 (NRG1) and ErbB4 genes have been identified as candidate genes for schizophrenia. Post-mortem studies indicated that NRG1-ErbB4 signalling is impaired in schizophrenia subjects. This study investigated whether short- or long-term antipsychotic treatment has different effects on the expression of NRG1 and ErbB4 receptors. Female Sprague-Dawley rats were treated orally with either aripiprazole (0.75 mg/kg), haloperidol (0.1 mg/kg), olanzapine (0.5 mg/kg), or vehicle, 3 times/day for 1 or 12 weeks. Western blotting was performed to examine the expression of NRG1 isoforms (135 kDa, 70 kDa and 40 kDa) and ErbB4 receptors. Both 1-week haloperidol and olanzapine treatment increased NRG1-70kDa expression in the hippocampus; haloperidol also up-regulated ErbB4 levels in the prefrontal cortex (PFC). In the 12-week group, aripiprazole decreased the expression of all three NRG1 isoforms and ErbB4 receptors in the PFC, NRG1-70 kDa and -40 kDa in the cingulate cortex (Cg), and NRG1-135 kDa, -70 kDa and ErbB4 receptors in the hippocampus; haloperidol reduced NRG1-135 kDa in the PFC, NRG1-40 kDa in all three brain regions, and ErbB4 receptor levels in the PFC and hippocampus; NRG1-40 kDa in the PFC and Cg was also down-regulated by olanzapine. These results suggest that the time-dependent and region-specific effects of antipsychotics on NRG1-ErbB4 signalling may contribute to the efficacy of antipsychotics to treat schizophrenia.

Update on the Mechanism of Action of Aripiprazole: Translational Insights into Antipsychotic Strategies Beyond Dopamine Receptor Antagonism

Dopamine partial agonism and functional selectivity have been innovative strategies in the pharmacological treatment of schizophrenia and mood disorders and have shifted the concept of dopamine modulation beyond the established approach of dopamine D2 receptor (D2R) antagonism. Despite the fact that aripiprazole was introduced in therapy more than 12 years ago, many questions are still unresolved regarding the complexity of the effects of this agent on signal transduction and intracellular pathways, in part linked to its pleiotropic receptor profile. The complexity of the mechanism of action has progressively shifted the conceptualization of this agent from partial agonism to functional selectivity. From the induction of early genes to modulation of scaffolding proteins and activation of transcription factors, aripiprazole has been shown to affect multiple cellular pathways and several cortical and subcortical neurotransmitter circuitries. Growing evidence shows that, beyond the consequences of D2R occupancy, aripiprazole has a unique neurobiology among available antipsychotics. The effect of chronic administration of aripiprazole on D2R affinity state and number has been especially highlighted, with relevant translational implications for long-term treatment of psychosis. The hypothesized effects of aripiprazole on cell-protective mechanisms and neurite growth, as well as the differential effects on intracellular pathways [i.e. extracellular signal-regulated kinase (ERK)] compared with full D2R antagonists, suggest further exploration of these targets by novel and future biased ligand compounds. This review aims to recapitulate the main neurobiological effects of aripiprazole and discuss the potential implications for upcoming improvements in schizophrenia therapy based on dopamine modulation beyond D2R antagonism.

Antipsychotic treatment modulates glutamate transport and NMDA receptor expression

Schizophrenia patients often suffer from treatment-resistant cognitive and negative symptoms, both of which are influenced by glutamate neurotransmission. Innovative therapeutic strategies such as agonists at metabotropic glutamate receptors or glycin reuptake inhibitors try to modulate the brain's glutamate network. Interactions of amino acids with monoamines have been described on several levels, and first- and second-generation antipsychotic agents (FGAs, SGAs) are known to exert modulatory effects on the glutamatergic system. This review summarizes the current knowledge on effects of FGAs and SGAs on glutamate transport and receptor expression derived from pharmacological studies. Such studies serve as a control for molecular findings in schizophrenia brain tissue and are clinically relevant. Moreover, they may validate animal models for psychosis, foster basic research on antipsychotic substances and finally lead to a better understanding of how monoaminergic and amino acid neurotransmissions are intertwined. In the light of these results, important differences dependent on antipsychotic substances, dosage and duration of treatment became obvious. While some post-mortem findings might be confounded with multifold drug effects, others are unlikely to be influenced by antipsychotic treatment and could represent important markers of schizophrenia pathophysiology. In similarity to the convergence of toxic and psychotomimetic effects of dopaminergic, serotonergic and anti-glutamatergic substances, the therapeutic mechanisms of SGAs might merge on a yet to be defined molecular level. In particular, serotonergic effects of SGAs, such as an agonism at 5HT1A receptors, represent important targets for further clinical research.

The effectiveness of aripiprazole in the management of problem behaviour in people with intellectual disabilities, developmental disabilities and/or autistic spectrum disorder--a systematic review

The management of problem behaviours (PB) in individuals with intellectual disabilities (ID), developmental disabilities (DD) and/or autistic spectrum disorders (ASD) can be challenging. Antipsychotic medications are commonly prescribed where other strategies have failed. A systematic review (SR) was conducted to establish the research evidence for the efficacy of aripiprazole in the management of PB in adults and children with ID, DD and/or ASD. Although included studies supported the efficacy of aripiprazole for this indication, the overall quality of studies was poor. Of the 20 studies included in this systematic review there were only two randomised controlled trials (RCTs) on children with ASD and/or ID/DD, both of which were conducted by the pharmaceutical company that manufactures aripiprazole, and it is not clear whether a number of same participants were included in both RCTs. One of the RCTs was extended into an open label long term follow up, which showed that aripiprazole's efficacy lasted over 52 weeks and the adverse effects were tolerable. Four studies were open label prospective studies, 11 were retrospective case reports which included four single case reports, and two were prospective case series. Most studies reported adverse effects from aripiprazole in the form of weight gain, increased appetite, sedation, tiredness, drooling and tremor. However, aripiprazole improved serum prolactin level in some participants and overall did not show any adverse effect on QTc interval. There is a need for more carefully designed RCTs into the use of aripiprazole in the management of PB in people with ID/DD and/or ASD, which should be carried out independent of pharmaceutical companies.

Mismatch negativity: translating the potential

The mismatch negativity (MMN) component of the auditory event-related potential has become a valuable tool in cognitive neuroscience. Its reduced size in persons with schizophrenia is of unknown origin but theories proposed include links to problems in experience-dependent plasticity reliant on N-methyl-d-aspartate glutamate receptors. In this review we address the utility of this tool in revealing the nature and time course of problems in perceptual inference in this illness together with its potential for use in translational research testing animal models of schizophrenia-related phenotypes. Specifically, we review the reasons for interest in MMN in schizophrenia, issues pertaining to the measurement of MMN, its use as a vulnerability index for the development of schizophrenia, the pharmacological sensitivity of MMN and the progress in developing animal models of MMN. Within this process we highlight the challenges posed by knowledge gaps pertaining to the tool and the pharmacology of the underlying system.

Effects of olanzapine and betahistine co-treatment on serotonin transporter, 5-HT2A and dopamine D2 receptor binding density

Olanzapine is widely used in treating multiple domains of schizophrenia symptoms but induces serious metabolic side-effects. Recent evidence has showed that co-treatment of betahistine (a histaminergic H1 receptor agonist and H3 receptor antagonist) is effective for preventing olanzapine-induced weight gain/obesity, however it is not clear whether this co-treatment affects on the primary therapeutic receptor binding sites of olanzapine such as serotonergic 5-HT2A receptors (5-HT2AR) and dopaminergic D2 receptors (D2R). Therefore, this study investigated the effects of this co-treatment on 5-HT2AR, 5-HT transporter (5-HTT) and D2R bindings in various brain regions involved in antipsychotic efficacy. Female Sprague Dawley rats were administered orally (t.i.d.) with either olanzapine (1mg/kg), betahistine (2.7 mg/kg), olanzapine plus betahistine (O+B), or vehicle (control) for 2 weeks. Quantitative autoradiography was used to detect the density of [(3)H]ketanserin, [(3)H]paroxetine and [(3)H]raclopride binding site to 5-HT2AR, 5-HTT and D2R. Compared to the controls, olanzapine significantly decreased [(3)H]ketanserin bindings to 5-HT2AR in the prefrontal cortex, cingulate cortex, and nucleus accumbens. Similar changes in 5-HT2AR bindings in these nuclei were also observed in the O+B co-treatment group. Olanzapine also significantly decreased [(3)H]paroxetine binding to 5-HTT in the ventral tegmental area and substantia nigra, however, both olanzapine only and O+B co-treatment did not affect [(3)H]raclopride binding to D2R. The results confirmed the important role of 5-HT2AR in the efficacy of olanzapine, which is not influenced by the O+B co-treatment. Therefore, betahistine co-treatment would be an effective combination therapy to reduce olanzapine-induced weight gain side-effects without affecting olanzapine's actions on 5-HT2AR transmissions.

Psychotropic drug effects on gene transcriptomics relevant to Parkinson's disease

OBJECTIVES

Psychotropic drugs are widely prescribed in Parkinson's disease (PD) without regard to their pathobiological effects, and these drugs affect the transcription of a large number of genes. Effects of these drugs on PD risk gene transcription were therefore surveyed.

METHODS

Results summarize a comprehensive survey of psychotropic effects on messenger ribonucleic acid (mRNA) expression evident in published data for 70 genes linked to PD risk.

RESULTS

Psychotropic drugs can meaningfully affect PD risk gene mRNA transcription, including antipsychotics (upregulate dopamine receptors D2 and D3 (DRD2, DRD3); downregulate low-density lipoprotein receptor-related protein 8 (LRP8), ubiquitin carboxyl-terminal esterase L1 (UCHL1, also known as PARK5)), haloperidol (upregulates DRD3, parkin (PRKN, also known as PARK2), DRD2; downregulates brain-derived neurotrophic factor (BDNF)), risperidone (upregulates monoamine oxidase B (MAOB), DRD2), olanzapine (upregulates transmembrane protein 163 (TMEM163), BDNF, glutathione S-transferase mu 1 (GSTM1), MAOB, DRD2, solute carrier organic anion transporter family, member 3A1 (SLCO3A1)), aripiprazole (upregulates DRD2), quetiapine, paliperidone, lurasidone, carbamazepine, and many antidepressants (upregulate BDNF), lithium and bupropion (downregulate BDNF), amitriptyline (upregulates DRD3, DRD2), imipramine (upregulates BDNF, DRD3, DRD2), desipramine (upregulates BDNF, DRD3), and fluoxetine (upregulates acid beta-glucosidase (GBA), coiled-coil domain containing 62 (CCDC62), BDNF, DRD3, UCHL1, unc-13 homolog B (UNC13B), and perhaps huntingtin interacting protein 1 related (HIP1R); downregulates microtubule-associated protein tau (MAPT), methylcrotonoyl-coenzyme A carboxylase I (MCCC1), GSTM1, 28kDa calbindin 1 (CALB1)). Fluoxetine effects on BDNF and UCHL1 in GEO Profiles were statistically robust.

CONCLUSIONS

This report provides an initial summary and framework to understand the potential impact of psychotropic drugs on PD-relevant genes. Antipsychotics and serotoninergic antidepressants may potentially attenuate PD risk, and lithium and bupropion may augment risk, through MAPT, GBA, CCDC62, HIP1R, BDNF, and DRD2 transcription, with MAPT, GBA, and CCDC62 being strongly associated with PD risk in recent meta-analyses. Limitations of these findings and a research agenda to better relate them to the nigrostriatum and PD are discussed.

The neuroprotective disease-modifying potential of psychotropics in Parkinson's disease

Neuroprotective treatments in Parkinson's disease (PD) have remained elusive. Psychotropics are commonly prescribed in PD without regard to their pathobiological effects. The authors investigated the effects of psychotropics on pathobiological proteins, proteasomal activity, mitochondrial functions, apoptosis, neuroinflammation, trophic factors, stem cells, and neurogenesis. Only findings replicated in at least 2 studies were considered for these actions. Additionally, PD-related gene transcription, animal model, and human neuroprotective clinical trial data were reviewed. Results indicate that, from a PD pathobiology perspective, the safest drugs (i.e., drugs least likely to promote cellular neurodegenerative mechanisms balanced against their likelihood of promoting neuroprotective mechanisms) include pramipexole, valproate, lithium, desipramine, escitalopram, and dextromethorphan. Fluoxetine favorably affects transcription of multiple genes (e.g., MAPT, GBA, CCDC62, HIP1R), although it and desipramine reduced MPTP mouse survival. Haloperidol is best avoided. The most promising neuroprotective investigative priorities will involve disease-modifying trials of the safest agents alone or in combination to capture salutary effects on H3 histone deacetylase, gene transcription, glycogen synthase kinase-3, α-synuclein, reactive oxygen species (ROS), reactive nitrogen species (RNS), apoptosis, inflammation, and trophic factors including GDNF and BDNF.

Pharmacological blockade of dopamine D2 receptors by aripiprazole is not associated with striatal sensitization

The partial agonist profile of novel antipsychotics such as aripiprazole has hardly been demonstrated in biochemical assays on animal tissues. As it is established that responses induced by dopamine D₂ receptor agonists are increased in models of dopaminergic sensitization, this paradigm was used in order to facilitate the detection of the partial agonist properties of aripiprazole. At variance with all other partial and full agonists tested, the partial agonist properties of aripiprazole were not revealed in guanosine 5′-O-(γ-[³⁵S]thiotriphosphate ([³⁵S]GTPγS) binding assays on striatal membranes from haloperidol-treated rats. Hence,aripiprazole behaved as an antagonist, efficiently inhibiting the functional response to dopamine. Similarly, in behavioural assays, aripiprazole dose-dependently inhibited the stereotypies elicited by apomorphine. However, at variance with haloperidol, repeated administrations of aripiprazole(3 weeks) at the doses of 10 and 30 mg/kg did not induce any up-regulation or hyperfunctionality of the dopamine D₂ receptors in the striatum. These data highlight the putative involvement of other pharmacological targets for aripiprazole that would support in the prevention of secondary effects commonly associated with the blockade of striatal dopamine D₂ receptors. Hence, in additional experiments, aripiprazole was found to efficiently promote [³⁵S]GTPγS binding in hippocampal membranes through the activation of 5-HT(₁A) receptors. Further experiments investigating the second messenger cascades should be performed so as to establish the functional properties of aripiprazole and understand the mechanism underlying the prevention of dopamine receptor regulation in spite of the observed antagonism.

Blocking dopamine D2 receptors by haloperidol curtails the beneficial impact of calorie restriction on the metabolic phenotype of high-fat diet induced obese mice

Calorie restriction is the most effective way of expanding life-span and decreasing morbidity. It improves insulin sensitivity and delays the age-related loss of dopamine receptor D(2) (DRD2) expression in the brain. Conversely, high-fat feeding is associated with obesity, insulin resistance and a reduced number of DRD2 binding sites. We hypothesised that the metabolic benefit of calorie restriction involves the preservation of appropriate DRD2 transmission. The food intake of wild-type C57Bl6 male mice was restricted to 60% of ad lib. intake while they were treated with the DRD2 antagonist haloperidol or vehicle using s.c. implanted pellets. Mice with ad lib. access to food receiving vehicle treatment served as controls. All mice received high-fat food throughout the experiment. After 10 weeks, an i.p. glucose tolerance test was performed and, after 12 weeks, a hyperinsulinaemic euglycaemic clamp. Hypothalamic DRD2 binding was also determined after 12 weeks of treatment. Calorie-restricted (CR) vehicle mice were glucose tolerant and insulin sensitive compared to ad lib. (AL) fed vehicle mice. CR mice treated with haloperidol were slightly heavier than vehicle treated CR mice. Haloperidol completely abolished the beneficial impact of calorie restriction on glucose tolerance and partly reduced the insulin sensitivity observed in CR vehicle mice. The metabolic differences between AL and CR vehicle mice were not accompanied by alterations in hypothalamic DRD2 binding. In conclusion, blocking DRD2 curtails the metabolic effects of calorie restriction. Although this suggests that the dopaminergic system could be involved in the metabolic benefits of calorie restriction, restricting access to high-fat food does not increase (hypothalamic) DRD2 binding capacity, which argues against this inference.

The effects of antipsychotic drugs administration on 5-HT1A receptor expression in the limbic system of the rat brain

Increasing evidence suggests that 5-HT1A receptors are involved in the pathophysiology and treatment of schizophrenia. This paper investigated 5-HT1A receptor mRNA expression and binding density in female rats treated with aripiprazole (2.25 mg/kg/day), olanzapine (1.5 mg/kg/day), haloperidol (0.3 mg/kg/day) or vehicle (control) orally three times/day for 1 or 12 weeks. Animals were sacrificed 48 h after the last administration. Aripiprazole significantly increased 5-HT1A receptor binding density by 33% in the CA1 region of the hippocampus and by 21% in the medial posterodorsal nuclei of posterior amygdala (MeP) compared to the control group after 1 week of treatment. Olanzapine significantly decreased 5-HT1A receptor binding density by 17-22% in Layers I-IV of the cingulate cortex after 1 week of treatment. Neither of these antipsychotic drugs affected 5-HT1A receptor binding density after 12 weeks drug treatment. As expected, haloperidol treatment did not have any significant effect on 5-HT1A binding density after 1 or 12 weeks of treatment. 5-HT1A receptor mRNA expression was not altered by antipsychotic treatment in any brain region. The results indicate that aripiprazole and olanzapine have differential effects on 5-HT1A receptor expression, which may contribute to their distinct profiles in improving negative symptoms and cognitive deficits in schizophrenia. Aripiprazole and olanzapine may produce adaptation and desensitization of 5-HT1A receptor expression after long term treatment.