Occupancy of dopamine D(1), D (2) and serotonin (2A) receptors in schizophrenic patients treated with flupentixol in comparison with risperidone and haloperidol

Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: Focus on antipsychotics

BACKGROUND

For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialised tools are used. Three tools have been proven useful to personalise drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging.

METHODS

In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 45 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)).

RESULTS

Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings.

CONCLUSION

All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimise treatment effects, minimise side effects and ultimately reduce the global burden of diseases, personalised drug treatment has not yet become the standard of care in psychiatry.

Using in silico methods to determine optimal tapering regimens for decanoate-based long-acting injectable psychosis drugs

Background

Reducing the dose of psychosis drugs in a gradual hyperbolic manner may minimise withdrawal effects and risk of relapse. There is presently limited guidance on tapering decanoate-based long-acting injectable dopamine antagonists (LIDAs).

Objectives

We aimed to apply hyperbolic principles of tapering to the decanoate-based LIDAs flupentixol, zuclopenthixol and haloperidol to develop withdrawal regimens.

Design

We used in silico methodology to predict plasma drug levels and D2 occupancy for different LIDA regimens.

Methods

Existing pharmacokinetic and receptor occupancy data from nuclear neuroimaging studies were used to power modelling. Abrupt discontinuation was examined as a potential strategy, and dose reduction was modelled with pre-defined constraints used in similar work of 10 (fast regimens), 5 (moderate) and 2.5 (slow) percentage points of D2 occupancy change per month.

Results

Abrupt discontinuation of decanoate-based LIDAs leads to excessive change in D2 occupancy which violated our pre-defined constraints, potentially resulting in withdrawal symptoms and increased risk of relapse. Reduction of LIDA dose allowed hyperbolic reduction in plasma level consistent with imposed constraints on receptor occupancy reduction rate. For equivalent per-weekly LIDA dosing, more frequent administration allowed a more gradual reduction of D2 occupancy. However, switching to oral forms is required to continue hyperbolic tapering to full discontinuation; reduction to zero using only LIDA produces too large a reduction in D2 occupancy. Guidance for reduction and cessation of LIDAs according to slow, moderate and fast criteria is provided.

Conclusion

Abrupt cessation of decanoate LIDAs is not consistent with gradual hyperbolic tapering, despite their longer half-lives compared with oral formulations. Reduction to the point of full discontinuation can only be achieved by switching to oral therapy to complete the taper. These results are limited by the in silico and theoretical nature of the study, and there is a need to confirm these findings through real-world observational and interventional studies.

Identification of small molecules that are synthetically lethal upon knockout of the RNA ligase Rlig1 in human cells

Rlig1 is the first RNA ligase identified in humans utilising a classical 5'-3' ligation mechanism. It is a conserved enzyme in all vertebrates and is mutated in various cancers. During our initial research on Rlig1, we observed that Rlig1-knockout (KO) HEK293 cells are more sensitive to the stress induced by menadione than their WT counterpart, representing a type of chemical synthetic lethality. To gain further insight into the biological pathways in which Rlig1 may be involved, we aimed at identifying new synthetically lethal small molecules. To this end, we conducted a high-throughput screening with a compound library comprising over 13 000 bioactive small molecules. This approach led to the identification of compounds that exhibited synthetic lethality in combination with Rlig1-KO. In addition to the aforementioned novel compounds that diverge structurally from menadione, we also tested multiple small molecules containing a naphthoquinone scaffold.

A proposal for reducing maximum target doses of drugs for psychosis: Reviewing dose-response literature

BACKGROUND

Presently, there is limited guidance on the maximal dosing of psychosis drugs that is based on effectiveness rather than safety or toxicity. Current maximum dosing recommendations may far exceed the necessary degree of dopamine D2 receptor blockade required to treat psychosis. This may lead to excess harm through cognitive impairment and side effects.

AIMS

This analysis aimed to establish guidance for prescribers by optimally dosing drugs for psychosis based on efficacy and benefit.

METHODS

We used data from two dose-response meta-analyses and reviewed seven of the most prescribed drugs for psychosis in the UK. Where data were not available, we used appropriate comparison techniques based on D2 receptor occupancy to extrapolate our recommendations.

RESULTS

We found that the likely threshold dose for achieving remission of psychotic symptoms was often significantly below the currently licensed dose for these drugs. We therefore recommend that clinicians are cautious about exceeding our recommended doses. Individual factors, however, should be accounted for. We outline potentially relevant factors including age, ethnicity, sex, smoking status and pharmacogenetics. Additionally, we recommend therapeutic drug monitoring as a tool to determine individual pharmacokinetic variation.

CONCLUSIONS

In summary, we propose a new set of maximum target doses for psychosis drugs based on efficacy. Further research through randomised controlled trials should be undertaken to evaluate the effect of reducing doses from current licensing maximums or from doses that are above our recommendations. However, dose reductions should be implemented in a manner that accounts for and reduces the effects of drug withdrawal.

The impact of fluphenazine withdrawal: a mirror-image study

BACKGROUND

Fluphenazine decanoate licenced as a long-acting injectable (LAI) first-generation antipsychotic (FGA) was withdrawn from sale in 2018. This study evaluates if its withdrawal resulted in increased relapse rates of psychosis in an Irish patient cohort and examines which prescribed alternative antipsychotic medications were associated with more optimal outcomes.

METHODS

Fifteen participants diagnosed with a psychotic disorder were included. A mirror-image study over 24-months' pre-and post-withdrawal of fluphenazine was conducted. Kaplan-Meier survival and proportional hazards analyses were conducted. The impact of alternate antipsychotic agents (LAI flupenthixol compared to other antipsychotic medications) was evaluated. Semi-structured interviews with participants examined subjective opinions regarding the change in their treatment.

RESULTS

Seven participants (46.7%) relapsed in the 24-month period subsequent to fluphenazine discontinuation compared to one individual (6.7%) in the previous identical time-period (p = 0.035). Flupenthixol treatment was associated with reduced relapse rates compared to other antipsychotics (χ2 = 5.402, p = 0.02). Thematic analysis revealed that participants believed that the discontinuation of fluphenazine deleteriously impacted the stability of their mental disorder.

CONCLUSION

The withdrawal of fluphenazine was associated with increased relapse rate in individuals previously demonstrating stability of their psychotic disorder. While acknowledging the limitation of small sample size, preliminary evidence from this study suggests that treatment with the first-generation antipsychotic (FGA) flupenthixol was associated with a lower risk of relapse compared to SGAs. Reasons for this lower risk of relapse are not fully clear but could be related to dopamine hypersensitivity with this treatment change.

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.

Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors

Serotonin (5-hydroxytryptamine, 5-HT) and 5-HT receptors (5-HTRs) have crucial roles in various neuropsychiatric disorders and neurodegenerative diseases, making them attractive diagnostic and therapeutic targets. Positron emission tomography (PET) is a noninvasive nuclear molecular imaging technique and is an essential tool in clinical diagnosis and drug discovery. In this context, numerous PET ligands have been developed for "visualizing" 5-HTRs in the brain and translated into human use to study disease mechanisms and/or support drug development. Herein, we present a comprehensive repertoire of 5-HTR PET ligands by focusing on their chemotypes and performance in PET imaging studies. Furthermore, this Perspective summarizes recent 5-HTR-focused drug discovery, including biased agonists and allosteric modulators, which would stimulate the development of more potent and subtype-selective 5-HTR PET ligands and thus further our understanding of 5-HTR biology.

Current Clinical Psychopharmacology in Borderline Personality Disorder

BACKGROUND

Patients with Borderline Personality Disorder (BPD) manifest affective and behavioral symptoms causing personal distress, relationship difficulties, and reduced quality of life with global functioning impairment, mainly when the disease takes an unfavorable course. A substantial amount of healthcare costs is dedicated to addressing these issues. Many BPD patients receive medications, mostly those who do not respond to psychological interventions.

OBJECTIVE

Our aim was to assess the efficacy of the most used strategies of pharmacological interventions in BPD with a comprehensive overview of the field.

METHODS

We searched the PubMed database for papers focused on the most used psychotropic drugs for BPD. We included randomized controlled trials and open studies in adult patients with BPD, focusing on the efficacy and tolerability of single classes of drugs with respect to specific clinical presentations that may occur during the course of BPD.

RESULTS

Specific second-generation antipsychotics (SGAs) or serotonergic antidepressants can be effective for different core symptoms of BPD, mainly including mood symptoms, anxiety, and impulse dyscontrol. Some atypical antipsychotics can also be effective for psychotic and dissociative symptoms. Specific antiepileptics can be useful in some cases in treating different BPD symptoms, mainly including mood instability, impulsiveness, and anger.

CONCLUSION

No medication is currently approved for BPD, and clinicians should carefully assess the benefits and risks of drug treatment. Further studies are needed to identify specific personalized treatment strategies, also considering the clinical heterogeneity and possible comorbidities of BPD.

In vivo 5-HT6 and 5-HT2A receptor availability in antipsychotic treated schizophrenia patients vs. unmedicated healthy humans measured with [11C]GSK215083 PET

While 5-HT₆ receptor is a potential therapeutic target for cognitive impairment in schizophrenia (SCZ), in vivo 5-HT₆ receptor availability following antipsychotic treatment has not been examined to-date. We examined the availability of 5-HT₆ and 5-HT_2A receptors following treatment with olanzapine, risperidone, aripiprazole and quetiapine in male patients with SCZ vs unmedicated age-matched healthy male controls (HC) using positron emission tomography (PET) imaging with [¹¹C]GSK215083. [¹¹C]GSK215083 has been shown to have selectivity for 5-HT₆ in the striatum and 5-HT_2A in the cortex. Patients with SCZ (n = 9) were scanned with [¹¹C]GSK215083 on HR+ PET scanner at presumed steady-state trough and peak serum levels following 7 days of confirmed inpatient antipsychotic treatment. Time-activity curves in regions-of-interest were fitted with multilinear analysis-1 (MA1). Regional nondisplaceable binding potential (BP_ND) values were calculated using cerebellum as the reference region and corrected for partial volume effects. Compared to HCs (n = 9), olanzapine was associated with significantly lower BP_ND (range: 53%-95%) in ventral striatum, putamen, caudate and frontal cortex at both trough and peak scans. Risperidone was associated with significantly lower BP_ND in frontal cortex at both trough and peak scans. The study provides preliminary evidence that treatment with different second-generation antipsychotics results in differing profiles of 5-HT_2A and 5-HT₆ availability.

Estimating the optimal dose of flupentixol decanoate in the maintenance treatment of schizophrenia-a systematic review of the literature

RATIONALE

The licensed dose range for the long-acting injectable antipsychotic flupentixol decanoate (Depixol®) in the treatment of schizophrenia is very broad. This provides little useful direction to prescribers and may ultimately result in patients receiving unnecessarily high doses.

OBJECTIVES

We aimed to estimate the effect of dose of flupentixol decanoate on relapse rates in schizophrenia and on tolerability by expanding on an earlier review and including non-RCT and German-language studies, as well as using pharmacokinetic and pharmacodynamic data to offer guidance on dosing.

METHODS

A literature review using EMBASE, Medline, PsycINFO and PubMed was conducted. Treatment success rates at 6 months were extracted or extrapolated from the studies and plotted against dose to estimate a dose-response curve.

RESULTS

Data from 16 studies (n = 514) allowed estimation of a dose-response curve which rises steeply between the chosen placebo anchor (25% success rate) and 10 mg every 2 weeks before reaching a maximum between 20 and 40 mg every 2 weeks (80-95% success rates). Extrapyramidal side effects (EPSEs) were frequently seen (12-71% of participants) in that dose range. Two -weekly injections seem to provide the highest trough plasma concentration per dose administered and the lowest peak-to-trough concentration ratio. Plasma concentration varied up to 5-fold among individuals receiving the same dose.

CONCLUSIONS

The optimal dose of flupentixol decanoate is likely to be between 20 mg and 40 mg every 2 weeks although higher doses may be required in some individuals owing to variation in drug handling. Doses of flupentixol should be individually established in the range of 10 to 40 mg every 2 weeks according to response and tolerability.

Disparate effects of first and second generation antipsychotics on cognition in schizophrenia - Findings from the randomized NeSSy trial

Cognitive impairment represents a core feature of schizophrenia. Uncertainty about demonstrable benefits of available antipsychotics on cognition remains an important clinical question relevant to patients' quality of life. The aim of our multi-center, randomized, double-blind "Neuroleptic Strategy Study" (NeSSy) was to compare the effectiveness of selected antipsychotics, conventionally classified as second- (SGAs) (haloperidol, flupentixol) and first generation antipsychotics (FGAs) (aripiprazole, olanzapine, quetiapine), on quality of life in schizophrenia. The effects on cognitive deficits represented a secondary outcome. We used an innovative double randomization for assignment of treatment group, and followed the patients with a neurocognitive test-battery upon six and 24 weeks of treatment. Psychopathology and quality of life were assessed using CGI, PANSS and SF-36. Assessment of cognitive performance was conducted in 114 of the 136 randomized patients. The SGA group (N = 62) showed beneficial effects of small to moderate effect size on cognition during the initial six weeks of treatment (executive functions, verbal fluency) and at 24 weeks (executive functions, working memory). In contrast, the FGA group (N = 52) showed moderately improved executive function, but a decline in verbal fluency at six weeks, with significant declines of moderate to large effect size in executive function, verbal learning and memory, and verbal fluency at 24 weeks. Our study indicates that SGAs present an advantage over FGAs regarding cognitive function during a medium-term treatment for schizophrenia. The results further emphasize a distinction between progression to detrimental effects of FGAs with prolonged treatment in contrast to more persistent cognitive benefits with SGA treatment.

The L-type calcium channel blocker, isradipine, attenuates cue-induced cocaine-seeking by enhancing dopaminergic activity in the ventral tegmental area to nucleus accumbens pathway

Previous preclinical and clinical investigations have focused on the L-type calcium channel (LTCC) as a potential therapeutic target for substance abuse. While some clinical studies have examined the ability of LTCC blockers to alter cocaine's subjective effects, very few LTCC studies have examined cocaine relapse. Here, we examined whether ventral tegmental area (VTA)-specific or systemic administration of the LTCC inhibitor, isradipine, altered cocaine-seeking behavior in a rat model. Male Sprague-Dawley rats first received 10 days of cocaine self-administration training (2 h sessions), where active lever depression resulted in delivery of a ∼0.5 mg/kg cocaine infusion paired with a tone + light cue. Rats then underwent 10 days of forced abstinence, without access to cocaine or cocaine cues. Rats were then returned to the opertant chamber for the cue-induced cocaine-seeking test, where active lever depression in the original training context resulted in tone + light cue presentation. We found VTA specific or systemic isradipine administration robustly attenuated cocaine-seeking, without altering cocaine-taking nor natural reward seeking. Dopamine (DA) signaling in the nucleus accumbens (NAc) core is necessary and sufficient for cue-induced drug-seeking. Surprisingly in our study, isradipine enhanced tonic and phasic DA signaling in cocaine abstinent rats, with no change in sucrose abstinent nor naïve rats. Strikingly, isradipine's behavioral effects were dependent upon NAc core DA receptor activation. Together, our findings reveal a novel mechanism by which the FDA-approved drug, isradipine, could act to decrease cocaine relapse.

PET radioligands for the dopamine D1-receptor: Application in psychiatric disorders

The dopamine (DA) system is considered to be centrally involved in the pathophysiology of several major psychiatric disorders. Using positron emission tomography (PET), aberrations in dopamine D2/D3-receptors (D2-R) levels and uptake of the DA precursor FDOPA have been shown for schizophrenia, substance abuse and depression. Radioligands for the dopamine D1-receptor (D1-R) have been available for more than three decades, however this receptor subtype has received much less attention in psychiatry research. Here, studies investigating D1-R in psychiatric patients in comparison to healthy control subjects are summarized. Although small sample sizes, medication effects and heterogeneous methods of quantification limit the conclusions that can be drawn, the data is suggestive of higher levels of cortical D1-R in drug naïve patients with psychosis, and lower D1-R in patients with affective disorders. Data sharing and reanalysis using harmonized methodology are important next steps towards clarifying the role of D1-R in these disorders.

Extrastriatal dopamine D2/3 receptors and cortical grey matter volumes in antipsychotic-naïve schizophrenia patients before and after initial antipsychotic treatment

OBJECTIVES

Long-term dopamine D_2/3 receptor blockade, common to all antipsychotics, may underlie progressive brain volume changes observed in patients with chronic schizophrenia. In the present study, we examined associations between cortical volume changes and extrastriatal dopamine D_2/3 receptor binding potentials (BP_ND) in first-episode schizophrenia patents at baseline and after antipsychotic treatment.

METHODS

Twenty-two initially antipsychotic-naïve patients underwent magnetic resonance imaging (MRI), [¹²³I]epidepride single-photon emission computerised tomography (SPECT), and psychopathology assessments before and after 3 months of treatment with either risperidone (N = 13) or zuclopenthixol (N = 9). Twenty healthy controls matched on age, gender and parental socioeconomic status underwent baseline MRI and SPECT.

RESULTS

Neither extrastriatal D_2/3 receptor BP_ND at baseline, nor blockade at follow-up, was related to regional cortical volume changes. In post-hoc analyses excluding three patients with cannabis use we found that higher D_2/3 receptor occupancy was significantly associated with an increase in right frontal grey matter volume.

CONCLUSIONS

The present data do not support an association between extrastriatal D_2/3 receptor blockade and extrastriatal grey matter loss in the early phases of schizophrenia. Although inconclusive, our exclusion of patients tested positive for cannabis use speaks to keeping attention to potential confounding factors in imaging studies.

Critical needs in drug discovery for cessation of alcohol and nicotine polysubstance abuse

Polysubstance abuse of alcohol and nicotine has been overlooked in our understanding of the neurobiology of addiction and especially in the development of novel therapeutics for its treatment. Estimates show that as many as 92% of people with alcohol use disorders also smoke tobacco. The health risks associated with both excessive alcohol consumption and tobacco smoking create an urgent biomedical need for the discovery of effective cessation treatments, as opposed to current approaches that attempt to independently treat each abused agent. The lack of treatment approaches for alcohol and nicotine abuse/dependence mirrors a similar lack of research in the neurobiology of polysubstance abuse. This review discusses three critical needs in medications development for alcohol and nicotine co-abuse: (1) the need for a better understanding of the clinical condition (i.e. alcohol and nicotine polysubstance abuse), (2) the need to better understand how these drugs interact in order to identify new targets for therapeutic development and (3) the need for animal models that better mimic this human condition. Current and emerging treatments available for the cessation of each drug and their mechanisms of action are discussed within this context followed by what is known about the pharmacological interactions of alcohol and nicotine. Much has been and will continue to be gained from studying comorbid alcohol and nicotine exposure.

Polymorphisms of serotonin neurotransmission and their effects on antipsychotic drug action

The receptor pharmacology of many antipsychotic drugs includes actions at various serotonin (5-hydroxytryptamine [5-HT]) receptors. The 5-HT neurotransmitter system is thought to be involved in many of the consequences of treatment with antipsychotic drugs, including both symptom response, primarily of negative and depressive symptoms, and adverse effects, notably extrapyramidal side effects and weight gain. There is substantial interindividual variability in these drug effects, to which genetic variability contributes. We review here the influence of functional polymorphisms in genes associated with 5-HT function, including the various processes of neurotransmitter synthesis, receptors, transporters and metabolism, on the clinical response to, and adverse effects of, antipsychotic drugs. The relatively young field of epigenetics also contributes to the variability of 5-HT-related genes in influencing drug response. Several of these findings inform our understanding of the mechanisms of antipsychotic drug action, and also provide the opportunity for the development of genetic testing for personalized medicine.

Haloperidol versus first-generation antipsychotics for the treatment of schizophrenia and other psychotic disorders

BACKGROUND

Haloperidol is worldwide one of the most frequently used antipsychotic drugs with a very high market share. Previous narrative, unsystematic reviews found no differences in terms of efficacy between the various first-generation ("conventional", "typical") antipsychotic agents. This established the unproven psychopharmacological assumption of a comparable efficacy between the first-generation antipsychotic compounds codified in textbooks and treatment guidelines. Because this assumption contrasts with the clinical impression, a high-quality systematic review appeared highly necessary.

OBJECTIVES

To compare the efficacy, acceptability, and tolerability of haloperidol with other first-generation antipsychotics in schizophrenia and schizophrenia-like psychosis.

SEARCH METHODS

In October 2011 and July 2012, we searched the Cochrane Schizophrenia Group's Trials Register, which is based on regular searches of CINAHL, BIOSIS, AMED, EMBASE, PubMed, MEDLINE, PsycINFO, and registries of clinical trials. To identify further relevant publications, we screened the references of all included studies and contacted the manufacturers of haloperidol for further relevant trials and missing information on identified studies. Furthermore, we contacted the corresponding authors of all included trials for missing data.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) that compared oral haloperidol with another oral first-generation antipsychotic drug (with the exception of the low-potency antipsychotics chlorpromazine, chlorprothixene, levopromazine, mesoridazine, perazine, prochlorpromazine, and thioridazine) in schizophrenia and schizophrenia-like psychosis. Clinically important response to treatment was defined as the primary outcome. Secondary outcomes were global state, mental state, behaviour, overall acceptability (measured by the number of participants leaving the study early due to any reason), overall efficacy (attrition due to inefficacy of treatment), overall tolerability (attrition due to adverse events), and specific adverse effects.

DATA COLLECTION AND ANALYSIS

At least two review authors independently extracted data from the included trials. The methodological quality of the included studies was assessed using The Cochrane Collaboration`s 'Risk of bias' tool.We analysed dichotomous outcomes with risk ratios (RR) and continuous outcomes with mean differences (MD), both with the associated 95% confidence intervals (CI). All analyses were based on a random-effects model and we preferably used data on an intention-to-treat basis where possible.

MAIN RESULTS

The systematic review currently includes 63 randomised trials with 3675 participants. Bromperidol (n = 9), loxapine (n = 7), and trifluoperazine (n = 6) were the most frequently administered antipsychotics comparator to haloperidol. The included studies were published between 1962 and 1993, were characterised by small sample sizes (mean: 58 participants, range from 18 to 206) and the predefined outcomes were often incompletely reported. All results for the main outcomes were based on very low or low quality data. In many trials the mechanism of randomisation, allocation, and blinding was frequently not reported. In short-term studies (up to 12 weeks), there was no clear evidence of a difference between haloperidol and the pooled group of the other first-generation antipsychotic agents in terms of the primary outcome "clinically important response to treatment" (40 RCTs, n = 2132, RR 0.93 CI 0.87 to 1.00). In the medium-term trials, haloperidol may be less effective than the other first-generation antipsychotic group but this evidence is based on only one trial (1 RCT, n = 80, RR 0.51 CI 0.37 to 0.69).Based on limited evidence, haloperidol alleviated more positive symptoms of schizophrenia than the other antipsychotic drugs. There were no statistically significant between-group differences in global state, other mental state outcomes, behaviour, leaving the study early due to any reason, due to inefficacy, as well as due to adverse effects. The only statistically significant difference in specific side effects was that haloperidol produced less akathisia in the medium term.

AUTHORS' CONCLUSIONS

The findings of the meta-analytic calculations support the statements of previous narrative, unsystematic reviews suggesting comparable efficacy of first-generation antipsychotics. In efficacy-related outcomes, there was no clear evidence of a difference between the prototypal drug haloperidol and other, mainly high-potency first-generation antipsychotics. Additionally, we demonstrated that haloperidol is characterised by a similar risk profile compared to the other first-generation antipsychotic compounds. The only statistically significant difference in specific side effects was that haloperidol produced less akathisia in the medium term. The results were limited by the low methodological quality in many of the included original studies. Data for the main results were low or very low quality. Therefore, future clinical trials with high methodological quality are required.

Intractable hiccups (singultus) abolished by risperidone, but not by haloperidol

Hiccups or singulata are rhythmic involuntary movements of the diaphragm, caused by a variety of conditions that interfere with the functions of the nerve nuclei in the medulla and supra-spinal hiccup center. Although neurotransmitters and receptors involved in the pathophysiology of hiccups are not defined well, dopamine has been considered to play an important role. In some cases, chlorpromazine or other antipsychotics are used for the treatment of intractable hiccups but their efficacy is often limited. This report involves an 18-year-old patient who experienced two episodes of intractable hiccups triggered by stress, which lasted for weeks or even months. In both episodes, haloperidol was initially used, but there was no significant effect. In contrast, risperidone, the second-generation antipsychotic that possesses a dopamine-serotonin antagonist property, completely abolished the hiccups 6 hours after administration. This is one of few case reports in which two antipsychotics were challenged for a single patient with hiccups, and the effects of the drugs were obviously different. Our finding suggests that, in addition to dopaminergic system, the serotonergic systems may be involved in the pathophysiology of some hiccup cases and that the serotonin-acting antipsychotics such as risperidone should be considered as a choice in the drug treatment of intractable hiccups.

Flupenthixol decanoate (depot) for schizophrenia or other similar psychotic disorders

BACKGROUND

Long-acting depot injections of drugs such as flupenthixol decanoate are extensively used as a means of long-term maintenance treatment for schizophrenia.

OBJECTIVES

To evaluate the effects of flupenthixol decanoate in comparison with placebo, oral antipsychotics and other depot neuroleptic preparations for people with schizophrenia and other severe mental illnesses, in terms of clinical, social and economic outcomes.

SEARCH METHODS

We identified relevant trials by searching the Cochrane Schizophrenia Group Trials Register in March 2009 and then for this update version, a search was run in April 2013. The register is based on regular searches of CINAHL, EMBASE, MEDLINE and PsycINFO. References of all identified studies were inspected for further trials. We contacted relevant pharmaceutical companies, drug approval agencies and authors of trials for additional information.

SELECTION CRITERIA

All randomised controlled trials that focused on people with schizophrenia or other similar psychotic disorders where flupenthixol decanoate had been compared with placebo or other antipsychotic drugs were included. All clinically relevant outcomes were sought.

DATA COLLECTION AND ANALYSIS

Review authors independently selected studies, assessed trial quality and extracted data. For dichotomous data we estimated risk ratios (RR) with 95% confidence intervals (CI) using a fixed-effect model. Analysis was by intention-to-treat. We summated normal continuous data using mean difference (MD), and 95% CIs using a fixed-effect model. We presented scale data only for those tools that had attained prespecified levels of quality. Using Grading of Recommendations Assessment, Development and Evaluation (GRADE) we created 'Summary of findings tables and assessed risk of bias for included studies.

MAIN RESULTS

The review currently includes 15 randomised controlled trials with 626 participants. No trials compared flupenthixol decanoate with placebo.One small study compared flupenthixol decanoate with an oral antipsychotic (penfluridol). Only two outcomes were reported with this single study, and it demonstrated no clear differences between the two preparations as regards leaving the study early (n = 60, 1 RCT, RR 3.00, CI 0.33 to 27.23,very low quality evidence) and requiring anticholinergic medication (1 RCT, n = 60, RR 1.19, CI 0.77 to 1.83, very low quality evidence).Ten studies in total compared flupenthixol decanoate with other depot preparations, though not all studies reported on all outcomes of interest. There were no significant differences between depots for outcomes such as relapse at medium term (n = 221, 5 RCTs, RR 1.30, CI 0.87 to 1.93, low quality evidence), and no clinical improvement at short term (n = 36, 1 RCT, RR 0.67, CI 0.36 to 1.23, low quality evidence). There was no difference in numbers of participants leaving the study early at short/medium term (n = 161, 4 RCTs, RR 1.23, CI 0.76 to 1.99, low quality evidence) nor with numbers of people requiring anticholinergic medication at short/medium term (n = 102, 3 RCTs, RR 1.38, CI 0.75 to 2.25, low quality evidence).Three studies in total compared high doses (100 to 200 mg) of flupenthixol decanoate with the standard doses (˜40mg) per injection. Two trials found relapse at medium term (n = 18, 1 RCT, RR 1.00, CI 0.27 to 3.69, low quality evidence) to be similar between the groups. However people receiving a high dose had slightly more favourable medium term mental state results on the Brief Psychiatric Rating Scale (BPRS) (n = 18, 1 RCT, MD -10.44, CI -18.70 to -2.18, low quality evidence). There was also no significant difference in the use of anticholinergic medications to deal with side effects at short term (2 RCTs n = 47, RR 1.12, CI 0.83 to 1.52 very low quality evidence). One trial comparing a very low dose of flupenthixol decanoate (˜6 mg) with a low dose (˜9 mg) per injection reported no difference in relapse rates (n = 59, 1 RCT, RR 0.34, CI 0.10 to 1.15, low quality evidence).

AUTHORS' CONCLUSIONS

In the current state of evidence, there is nothing to choose between flupenthixol decanoate and other depot antipsychotics. From the data reported in clinical trials, it would be understandable to offer standard dose rather than the high dose depot flupenthixol as there is no difference in relapse. However, data reported are of low or very low quality and this review highlights the need for large, well-designed and reported randomised clinical trials to address the effects of flupenthixol decanoate.

The Role of Dopamine in Motor Flexibility

Humans carry out many daily tasks in a seemingly automatic fashion. However, when unexpected changes in the environment occur, we have the capacity to inhibit prepotent behavior and replace it with an alternative one. Such behavioral flexibility is a hallmark of executive functions. The neurotransmitter dopamine is known to be crucial for fast, efficient, and accurate cognitive flexibility. Despite the perceived similarities between cognitive and motor flexibility, less is known regarding the role of dopamine within the motor domain. Therefore, the aim of this study was to determine the role of dopamine in motor flexibility. In a double-blind, five-session, within-subject pharmacological experiment, human participants performed an RT task within a probabilistic context that was either predictable or unpredictable. The probabilistic nature of the predictable context resulted in prediction errors. This required participants to replace the prepotent or prepared action with an unprepared action (motor flexibility). The task was overlearned, and changes in context were explicitly instructed, thus controlling for contributions from other dopamine-related processes such as probabilistic or reversal learning and interactions with other types of uncertainty. We found that dopamine receptor blockade by high-dose haloperidol (D1/D2 dopamine receptors) impaired participants' ability to react to unexpected events occurring in a predictable context, which elicit large prediction errors and necessitate motor flexibility. This effect was not observed with selective D2 receptor blockade (sulpiride), with a general increase in tonic dopamine levels (levodopa), or during an unpredictable context, which evoked minimal prediction error. We propose that dopamine is vital in responding to low-level prediction errors about stimulus outcome that requires motor flexibility.

Testing the contributions of striatal dopamine loss to the genesis of parkinsonian signs

The diverse and independently-varying signs of Parkinson's disease (PD) are often attributed to one simple mechanism: degeneration of the dopaminergic innervation of the posterolateral striatum. However, growing recognition of the dopamine (DA) loss and other pathology in extra-striatal brain regions has led to uncertainty whether loss of DA in the striatum is sufficient to cause parkinsonian signs. We tested this hypothesis by infusing cis-flupenthixol (cis-flu; a broad-spectrum D1/D2 receptor antagonist) into different regions of the macaque putamen (3 hemispheres of 2 monkeys) while the animal performed a visually-cued choice reaction time task in which visual cues indicated the arm to reach with and the peripheral target to contact to obtain food reward. Following reward delivery, the animal was required to self-initiate release of the peripheral target and return of the chosen hand to its home position (i.e., without the benefit of external sensory cues or immediate rewards). Infusions of cis-flu at 15 of 26 sites induced prolongations of reaction time (9 of 15 cases), movement duration (6 cases), and/or dwell time of the hand at the peripheral target (8 cases). Dwell times were affected more severely (+95%) than visually-triggered reaction times or movement durations (+25% and +15%, respectively). Specifically, the animal's hand often 'froze' at the peripheral target for up to 25-s, similar to the akinetic freezing episodes observed in PD patients. Across injections, slowing of self-initiation did not correlate in severity with prolongations of visually-triggered reaction time or movement duration, although the latter two were correlated with each other. Episodes of slowed self-initiation appeared primarily in the arm contralateral to the injected hemisphere and were not associated with increased muscle co-contraction or global alterations in behavioral state (i.e., inattention or reduced motivation), consistent with the idea that these episodes reflected a fundamental impairment of movement initiation. We found no evidence for an anatomic topography within the putamen for the effects elicited. We conclude that acute focal blockade of DA transmission in the putamen is sufficient to induce marked akinesia-like impairments. Furthermore, different classes of impairments can be induced independently, suggesting that specific parkinsonian signs have unique pathophysiologic substrates.

Antipsychotic medication and prefrontal cortex activation: a review of neuroimaging findings

Decreased prefrontal activation (hypofrontality) in schizophrenia is thought to underlie negative symptoms and cognitive impairments, and may contribute to poor social outcome. Hypofrontality does not always improve during treatment with antipsychotics. We hypothesized that antipsychotics, which share antagonism at dopamine receptors, with a relatively low dopamine receptor affinity and high serotonin receptor affinity may have a sparing effect on prefrontal function compared to strong dopamine receptor antagonists. We systematically investigated the relation between serotonin and dopamine antagonism of antipsychotics and prefrontal functioning by reviewing neuroimaging studies. The weight of the evidence was consistent with our hypothesis that antipsychotics with low dopaminergic receptor affinity and moderate to high serotonergic affinity were associated with higher activation of the prefrontal cortex. However, clozapine, a weak dopamine and strong serotonin antagonist, was associated with decrease in prefrontal activation. Future studies should further elucidate the link between prefrontal activation and negative symptoms using prospective designs and advanced neuroimaging techniques, which may ultimately benefit the development of treatments for disabling negative symptoms.

Dopamine receptor blockade attenuates the general incentive motivational effects of noncontingently delivered rewards and reward-paired cues without affecting their ability to bias action selection

Environmental cues affect our behavior in a variety of ways. Despite playing an invaluable role in guiding our daily activities, such cues also appear to trigger the harmful, compulsive behaviors that characterize addiction and other disorders of behavioral control. In instrumental conditioning, rewards and reward-paired cues bias action selection and invigorate reward-seeking behaviors, and appear to do so through distinct neurobehavioral processes. Although reward-paired cues are known to invigorate performance through a dopamine-dependent incentive motivational process, it is not known if dopamine also mediates the influence of rewards and reward-paired cues over action selection. The current study contrasted the effects of systemic administration of the nonspecific dopamine receptor antagonist flupentixol on response invigoration and action bias in Pavlovian-instrumental transfer, a test of cue-elicited responding, and in instrumental reinstatement, a test of noncontingent reward-elicited responding. Hungry rats were trained on two different stimulus-outcome relationships (eg, tone-grain pellets and noise-sucrose solution) and two different action-outcome relationships (eg, left press-grain and right press-sucrose). At test, we found that flupentixol pretreatment blocked the response invigoration generated by the cues but spared their ability to bias action selection to favor the action whose outcome was signaled by the cue being presented. The response-biasing influence of noncontingent reward deliveries was also unaffected by flupentixol. Interestingly, although flupentixol had a modest effect on the immediate response invigoration produced by those rewards, it was particularly potent in countering the lingering enhancement of responding produced by multiple reward deliveries. These findings indicate that dopamine mediates the general incentive motivational effects of noncontingent rewards and reward-paired cues but does not support their ability to bias action selection.

Structural contributions of antipsychotic drugs to their therapeutic profiles and metabolic side effects

Antipsychotic drugs have various neuropharmacological properties as a result of their structural diversity. Despite their therapeutic benefits, most of the prescribed atypical antipsychotics can induce severe side effects, including weight gain, type II diabetes mellitus, and cardiovascular diseases. Among the developed atypical antipsychotic agents, tetracyclic dibenzodiazepine and thienobenzodiazepine compounds, particularly clozapine and olanzapine, are associated with the greatest weight gain and metabolic disturbances. However, the unique chemical structure of these compounds causes the low risk of side effects reported for typical antipsychotics (e.g. extrapyramidal symptoms and tardive dyskinesia). This report reviews the recent discovery of the potential role of the chemical structure of antipsychotics in their therapeutic properties and metabolic disturbances. By developing structure-activity relationship studies for atypical antipsychotics, we will improve our understanding of the structural modifications of these chemical classes that lead to reduced weight gain, which will be an invaluable step toward the discovery of the next generation of atypical antipsychotics. In this review, we suggest that a novel dibenzodiazepine or thienobenzodiazepine antipsychotic drug with lower affinity for H(1) receptors may significantly advance schizophrenia therapy.

Serotonin 2A receptor antagonists for treatment of schizophrenia

INTRODUCTION

All approved antipsychotic drugs share an affinity for the dopamine 2 (D(2)) receptor; however, these drugs only partially ameliorate the symptoms of schizophrenia. It is, therefore, of paramount importance to identify new treatment strategies for schizophrenia.

AREAS COVERED

Preclinical, clinical and post-mortem studies of the serotonin 5-HT(2A) system in schizophrenia are reviewed. The implications of a combined D(2) and 5-HT(2A) receptor blockade, which is obtained by several current antipsychotic drugs, are discussed, and the rationale for the development of more selective 5-HT(2A) receptor antagonists is evaluated. Moreover, the investigational pipeline of major pharmaceutical companies is examined and an Internet search conducted to identify other pharmaceutical companies investigating 5-HT(2A) receptor antagonists for the treatment of schizophrenia.

EXPERT OPINION

5-HT(2A) receptor antagonists appear to assume an intermediate position by being marginally superior to placebo but inferior to conventional antipsychotic drugs. Three previous 5-HT(2A) receptor antagonists have been discontinued after Phase II or III trials, and available Phase IIa data on the remaining 5-HT(2A) receptor antagonist will need substantial additional validation to be approved as a new treatment strategy against schizophrenia.

SEP-225289 serotonin and dopamine transporter occupancy: a PET study

SEP-225289 is a novel compound that, based on in vitro potencies for transporter function, potentially inhibits reuptake at dopamine, norepinephrine, and serotonin transporters. An open-label PET study was conducted during the development of SEP-225289 to investigate its dopamine and serotonin transporter occupancy.

METHODS

Different single doses of SEP-225289 were administered to healthy volunteers in 3 cohorts: 8 mg (n = 7), 12 mg (n = 5), and 16 mg (n = 7). PET was performed before and approximately 24 h after oral administration of SEP-225289, to assess occupancy at trough levels. Dopamine and serotonin transporter occupancies were estimated from PET using (11)C-N-(3-iodoprop-2E-enyl)-2β-carbomethoxy-3β-(4-methylphenyl)nortropane ((11)C-PE2I) and (11)C-N,N-dimethyl-2-(2-amino-4-cyanophenylthio)benzylamine ((11)C-DASB), respectively. Plasma concentration of SEP-225289 was assessed before ligand injection, and subjects were monitored for adverse events.

RESULTS

Average dopamine and serotonin transporter occupancies increased with increasing doses of SEP-225289. Mean dopamine and serotonin transporter occupancies were 33% ± 11% and 2% ± 13%, respectively, for 8 mg; 44% ± 4% and 9% ± 10%, respectively, for 12 mg; and 49% ± 7% and 14% ± 15%, respectively, for 16 mg. On the basis of the relationship between occupancy and plasma concentration, dopamine transporter IC(50) (the plasma concentration of drug at 50% occupancy) was determined (4.5 ng/mL) and maximum dopamine transporter occupancy was extrapolated (85%); however, low serotonin transporter occupancy prevented similar serotonin transporter calculations. No serious adverse events were reported.

CONCLUSION

At the doses evaluated, occupancy of the dopamine transporter was significantly higher than that of the serotonin transporter, despite similar in vitro potencies, confirming that, in addition to in vitro assays, PET occupancy studies can be instrumental to the drug development process by informing early decisions about indication, dose, and therapeutic potential.

5-HT radioligands for human brain imaging with PET and SPECT

The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5-HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5-HT) receptors, the 5-HT transporter (SERT), and 5-HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include antagonists for the 5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(4) receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging.

Predicting dopamine D₂ receptor occupancy from plasma levels of antipsychotic drugs: a systematic review and pooled analysis

Measuring dopamine D₂ receptor occupancy levels using positron emission tomography (PET) is still widely unavailable. The objective of this study was to evaluate the accuracy of predicting D2 occupancy from the antipsychotic plasma level in patients with schizophrenia. Positron emission tomographic studies that measured plasma levels of antipsychotics and their corresponding D₂ occupancy levels were identified, using MEDLINE and EMBASE (last search: March 2010). Antipsychotics that were investigated in a total of 20 subjects or more were included. All data points for each antipsychotic were fit to a one-site binding model to estimate the total plasma concentration of each antipsychotic associated with a 50% occupancy (ED₅₀) of brain D₂ receptors. The mean prediction error and the root mean squared prediction error were used to measure the predictive performance of individual D₂ receptor occupancies from plasma drug levels derived from a one-site occupancy model using an ED₅₀ value calculated for each data point. A total of 34 treatment arms from 23 studies involving 281 subjects were included. The mean (95% confidence interval) prediction errors and root squared prediction errors were as low as 0.0 (-1.8 to 1.8) and 8.9 (7.6-10.2) for risperidone (n = 98); 0.0 (-3.5 to 3.5) and 15.1 (12.9-17.3) for clozapine (n = 75); -0.1 (-1.2 to 1.2), 0.0 (-1.9 to 1.9), and 4.6 (3.5-5.8) for olanzapine (n = 42); 0.1 (-3.4 to 3.5) and 9.9 (7.3-12.5) for haloperidol (n = 35); and -0.1 (-3.3 to 3.1) and 12.3 (8.8-15.7) for ziprasidone (n = 31), respectively. These findings suggest that D₂ occupancy of antipsychotics could be estimated with a high degree of accuracy using widely available plasma levels.

Emotion processing in schizophrenia: fMRI study of patients treated with risperidone long-acting injections or conventional depot medication

We employed two event-related functional magnetic resonance imaging tasks using the pictures of mild and intense facial emotions of fear or happiness. The sample comprised 16 chronic schizophrenia patients treated with risperidone long-acting injections (RLAI), 16 patients treated with conventional antipsychotic depots (CONV) and 16 healthy controls (HC). The HC and RLAI groups demonstrated greater activation in the left amygdala in response to intensively fearful faces, and in right cerebellum to intensively happy faces compared with CONV patients. The CONV group demonstrated under-activation in the right temporal pole in response to intensively happy faces (compared with HC) and over-activation in ventro-medial prefrontal cortex (VMPFC) in response to both intensively happy and fearful expressions, compared with HC and RLAI groups. Our results suggest that networks implicated in the allocation of attentional resources (VMPFC) and emotion processing (amygdala, cerebellum) are differentially affected in patients on CONV versus RLAI.

Glioblastoma chemotherapy adjunct via potent serotonin receptor-7 inhibition using currently marketed high-affinity antipsychotic medicines

Glioblastoma treatment as now constituted offers increased survival measured in months over untreated patients. Because glioblastomas are active in synthesizing a bewildering variety of growth factors, a systematic approach to inhibiting these is being undertaken as treatment adjunct. The serotonin 7 receptor is commonly overexpressed in glioblastoma. Research documentation showing agonists at serotonin receptor 7 cause increased extracellular regulated kinase 1/2 activation, increased interleukin-6 synthesis, increased signal transducer and activator of transcription-3 activation, increased resistance to apoptosis and other growth enhancing changes in glioblastoma is reviewed in this paper. Because three drugs in wide use to treat thought disorders - paliperidone, pimozide and risperidone - are also potent and well-tolerated inhibitors at serotonin receptor 7, these drugs should be studied for growth factor deprivation in an adjunctive role in glioblastoma treatment.

Postsynaptic nigrostriatal dopamine receptors and their role in movement regulation

The article presents the hypothesis that nigrostriatal dopamine may regulate movement by modulation of tone and contraction in skeletal muscles through a concentration-dependent influence on the postsynaptic D1 and D2 receptors on the follow manner: nigrostriatal axons innervate both receptor types within the striatal locus somatotopically responsible for motor control in agonist/antagonist muscle pair around a given joint. D1 receptors interact with lower and D2 receptors with higher dopamine concentrations. Synaptic dopamine concentration increases immediately before movement starts. We hypothesize that increasing dopamine concentrations stimulate first the D1 receptors and reduce muscle tone in the antagonist muscle and than stimulate D2 receptors and induce contraction in the agonist muscle. The preceded muscle tone reduction in the antagonist muscle eases the efficient contraction of the agonist. Our hypothesis is applicable for an explanation of physiological movement regulation, different forms of movement pathology and therapeutic drug effects. Further, this hypothesis provides a theoretical basis for experimental investigation of dopaminergic motor control and development of new strategies for treatment of movement disorders.

Involvement of Basal Ganglia network in motor disabilities induced by typical antipsychotics

Background

Clinical treatments with typical antipsychotic drugs (APDs) are accompanied by extrapyramidal motor side-effects (EPS) such as hypokinesia and catalepsy. As little is known about electrophysiological substrates of such motor disturbances, we investigated the effects of a typical APD, α-flupentixol, on the motor behavior and the neuronal activity of the whole basal ganglia nuclei in the rat.

Methods and Findings

The motor behavior was examined by the open field actimeter and the neuronal activity of basal ganglia nuclei was investigated using extracellular single unit recordings on urethane anesthetized rats. We show that α-flupentixol induced EPS paralleled by a decrease in the firing rate and a disorganization of the firing pattern in both substantia nigra pars reticulata (SNr) and subthalamic nucleus (STN). Furthermore, α-flupentixol induced an increase in the firing rate of globus pallidus (GP) neurons. In the striatum, we recorded two populations of medium spiny neurons (MSNs) after their antidromic identification. At basal level, both striato-pallidal and striato-nigral MSNs were found to be unaffected by α-flupentixol. However, during electrical cortico-striatal activation only striato-pallidal, but not striato-nigral, MSNs were found to be inhibited by α-flupentixol. Together, our results suggest that the changes in STN and SNr neuronal activity are a consequence of increased neuronal activity of globus pallidus (GP). Indeed, after selective GP lesion, α-flupentixol failed to induce EPS and to alter STN neuronal activity.

Conclusion

Our study reports strong evidence to show that hypokinesia and catalepsy induced by α-flupentixol are triggered by dramatic changes occurring in basal ganglia network. We provide new insight into the key role of GP in the pathophysiology of APD-induced EPS suggesting that the GP can be considered as a potential target for the treatment of EPS.

Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis

Traumatic brain injury (TBI) represents a significant cause of death and disability in industrialized countries. Of particular importance to patients the chronic effect that TBI has on cognitive function. Therapeutic strategies have been difficult to evaluate because of the complexity of injuries and variety of patient presentations within a TBI population. However, pharmacotherapies targeting dopamine (DA) have consistently shown benefits in attention, behavioral outcome, executive function, and memory. Still it remains unclear what aspect of TBI pathology is targeted by DA therapies and what time-course of treatment is most beneficial for patient outcomes. Fortunately, ongoing research in animal models has begun to elucidate the pathophysiology of DA alterations after TBI. The purpose of this review is to discuss clinical and experimental research examining DAergic therapies after TBI, which will in turn elucidate the importance of DA for cognitive function/dysfunction after TBI as well as highlight the areas that require further study.

Haloperidol regulates the phosphorylation level of the MEK-ERK-p90RSK signal pathway via protein phosphatase 2A in the rat frontal cortex

Haloperidol, a classical antipsychotic drug, affects the extracellular signal-regulated kinase (ERK) pathway in the brain. However, findings are inconsistent and the mechanism by which haloperidol regulates ERK is poorly understood. Therefore, we examined the ERK pathway and the related protein phosphatase 2A (PP2A) in detail after haloperidol administration. Haloperidol (0.5 and 1 mg/kg) induced biphasic changes in the phosphorylation level of mitogen-activated protein kinase kinase (MEK), ERK, and p90 ribosomal S6 kinase (p90RSK) without changing Raf-1 phosphorylation. Fifteen minutes after haloperidol administration, MEK-ERK-p90RSK phosphorylation increased, whilst PP2A activity decreased. At 60 min, the reverse was observed and the binding of PP2A to MEK and ERK increased. Higher dosages of haloperidol (2 and 4 mg/kg), affected neither MEK-ERK-p90RSK phosphorylation nor PP2A activity. Accordingly, PP2A regulates acute dose- and time-dependent changes in MEK-ERK-p90RSK phosphorylation after haloperidol treatment. These findings suggest the involvement of a dephosphorylating mechanism in the acute action of haloperidol.