Review the role of dopamine D4 receptors in schizophrenia and antipsychotic action

DRD4 VNTR 4/4 homozygosity as a genetic biomarker for treatment selection in patients with schizophrenia

OBJECTIVE

There seems to be an association between the DRD4 48-bp VNTR polymorphisms and antipsychotic treatment response, but there is a rare reference to confirm this finding. Hence, the present study tried to investigate the association between DRD4 48-bp VNTR polymorphisms and the treatment response of antipsychotics in patients with schizophrenia in Taiwan, using a propensity score matching (PSM) method.

METHODS

A total of 882 participants were enrolled in this study and completed informed consent, research questionnaires, including demographic information and the revised Chinese version Beliefs about Voices Questionnaire, and blood sampling. For descreasing of the selection bias and confounding variables, the PSM nearest neighbor matching method was used to select 765 paitents with schizophrenia (ratio of 1:8 between 85 persistent auditory hallucination and 680 controls) with matched and controlled the age and gender.

RESULTS

Schizophrenia patients with DRD4 4 R homozygosity had a lower rate of good antipsychotic treatment response than the other DRD4 genotype carriers (DRD4 non-4/4). Among those 4 R homozygosity carriers, 60 cases of 503 (11.9%) retain persistent auditory hallucinations. Furthermore, this subgroup of patients is accounted for up to 70.6% of cases with poor neuroleptic treatment response.

CONCLUSIONS

A poor treatment outcome for patients with the 4 R homozygosity had presented,that comparing with those DRD non-4/4 genotype carriers. DRD4 VNTR 4 R homozygosity could be a genetic biomarker to predict poor antipsychotic treatment response in schizophrenia. Patients with DRD 4/4 probably receive novel antipsychotic medications preferentially or in combination with alternative therapy, such as psychotherapy or milieu therapy.

Differentiating the third generation of antipsychotics: a focus on lumateperone's similarities and differences

The development of atypical antipsychotics has evolved to include newer pharmacodynamic properties. Lumateperone, aripiprazole, brexpiprazole, and cariprazine are all dopamine-2 receptor partial agonists with varying receptor affinities. This review aims to compare the clinical and pharmacodynamic differences among these four atypical antipsychotics, all of which are unique when compared to first- and second-generation antipsychotics. For consideration is further delineating these agents as being third-generation antipsychotics. PubMed searches were conducted to compile preclinical and clinical studies derived from animal models and human subjects. Information gathered included pharmacological mechanisms, clinical efficacy, future-oriented clinical approaches, and adverse effects. Efficacy for the shared indications of these drugs seems comparable. Differences among these drugs lie more in their adverse effect profiles. For example, lumateperone was found to have the lowest rate of weight gain while brexpiprazole was found to have the highest rate of weight gain associated with increased appetite. Aripiprazole had the lowest rates of extrapyramidal symptoms not including akathisia while cariprazine had the highest. All four agents reviewed have a variety of receptor affinities, which likely generates a variety of different adverse effects. This suggests that in any given patient, clinicians may see differential clinical effects.

Candidate Genes Encoding Dopamine Receptors as Predictors of the Risk of Antipsychotic-Induced Parkinsonism and Tardive Dyskinesia in Schizophrenic Patients

(1) Introduction: Extrapyramidal disorders form the so-called extrapyramidal syndrome (EPS), which is characterized by the occurrence of motor disorders as a result of damage to the basal ganglia and the subcortical-thalamic connections. Often, this syndrome develops while taking medications, in particular antipsychotics (APs). (2) Purpose: To review studies of candidate genes encoding dopamine receptors as genetic predictors of development of AP-induced parkinsonism (AIP) and AP-induced tardive dyskinesia (AITD) in patients with schizophrenia. (3) Materials and Methods: A search was carried out for publications of PubMed, Web of Science, Springer, and e-Library databases by keywords and their combinations over the last 10 years. In addition, the review includes earlier publications of historical interest. Despite extensive searches of these commonly used databases and search terms, it cannot be ruled out that some publications were possibly missed. (4) Results: The review considers candidate genes encoding dopamine receptors involved in pharmacodynamics, including genes DRD1, DRD2, DRD3, and DRD4. We analyzed 18 genome-wide studies examining 37 genetic variations, including single nucleotide variants (SNVs)/polymorphisms of four candidate genes involved in the development of AIP and AITD in patients with schizophrenia. Among such a set of obtained results, only 14 positive associations were revealed: rs1799732 (141CIns/Del), rs1800497 (C/T), rs6275 (C/T), rs6275 (C/T) DRD2; rs167771 (G/A) DRD3 with AIP and rs4532 (A/G) DRD1, rs6277 (C/T), rs6275 (C/T), rs1800497 (C/T), rs1079597 (A/G), rs1799732 (141CIns/Del), rs1045280 (C/G) DRD2, rs6280 (C/T), rs905568 (C/G) DRD3 with AITD. However, at present, it should be recognized that there is no final or unique decision on the leading role of any particular SNVs/polymorphisms in the development of AIP and AITD. (5) Conclusion: Disclosure of genetic predictors of the development of AIP and AITD, as the most common neurological adverse drug reactions (ADRs) in the treatment of patients with psychiatric disorders, may provide a key to the development of a strategy for personalized prevention and treatment of the considered complication of AP therapy for schizophrenia in real clinical practice.

Radiosynthesis and evaluation of 18F-labeled dopamine D4-receptor ligands

INTRODUCTION

The dopamine D4 receptor (D4R) has attracted considerable attention as potential target for the treatment of a broad range of central nervous system disorders. Although many efforts have been made to improve the performance of putative radioligand candidates, there is still a lack of D4R selective tracers suitable for in vivo PET imaging. Thus, the objective of this work was to develop a D4-selective PET ligand for clinical applications.

METHODS

Four compounds based on previous and new lead structures were prepared and characterized with regard to their D4R subtype selectivity and predicted lipophilicity. From these, 3-((4-(2-fluorophenyl)piperazin-1-yl)methyl)-1H-pyrrolo[2,3-b]pyridine I and (S)-4-(3-fluoro-4-methoxybenzyl)-2-(phenoxymethyl)morpholine II were selected for labeling with fluorine-18 and subsequent evaluation by in vitro autoradiography to assess their suitability as D4 radioligand candidates for in vivo imaging.

RESULTS

The radiosynthesis of [18F]I and [18F]II was successfully achieved by copper-mediated radiofluorination with radiochemical yields of 7% and 66%, respectively. The radioligand [18F]II showed specific binding in areas where D4 expression is expected, whereas [18F]I did not show any uptake in distinct brain regions and exhibited an unacceptable degree of non-specific binding.

CONCLUSIONS

The compounds studied exhibited high D4R subtype selectivity and logP values compatible with high brain uptake, but only ligand [18F]II showed low non-specific binding and is therefore a good candidate for further evaluation.

ADVANCES IN KNOWLEDGE

The discovery of new lead structures for high-affinity D4 ligands opens up new possibilities for the development of suitable PET-radioligands.

IMPLICATIONS FOR PATIENT

PET-imaging of dopamine D4-receptors could facilitate understanding, diagnosis and treatment of neuropsychiatric and neurodegenerative diseases.

A standardized social preference protocol for measuring social deficits in mouse models of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social communication deficits and other behavioral abnormalities. The three-chamber social preference test is often used to assess social deficits in mouse models of ASD. However, varying and often contradicting phenotypic descriptions of ASD mouse models can be found in the scientific literature, and the substantial variability in the methods used by researchers to assess social deficits in mice could be a contributing factor. Here we describe a standardized three-chamber social preference protocol, which is sensitive and reliable at detecting social preference deficits in several mouse models of ASD. This protocol comprises three phases that can all be completed within 1 d. The test mouse is first habituated to the apparatus containing two empty cups in the side chambers, followed by the pre-test phase in which the mouse can interact with two identical inanimate objects placed in the cups. During the test phase, the mouse is allowed to interact with a social stimulus (an unfamiliar wild-type (WT) mouse) contained in one cup and a novel non-social stimulus contained in the other cup. The protocol is thus designed to assess preference between social and non-social stimuli under conditions of equal salience. The broad implementation of the three-chamber social preference protocol presented here should improve the accuracy and consistency of assessments for social preference deficits associated with ASD and other psychiatric disorders.

Dopamine receptors in emesis: Molecular mechanisms and potential therapeutic function

Dopamine is a member of the catecholamine family and is associated with multiple physiological functions. Together with its five receptor subtypes, dopamine is closely linked to neurological disorders such as schizophrenia, Parkinson's disease, depression, attention deficit-hyperactivity, and restless leg syndrome. Unfortunately, several dopamine receptor-based agonists used to treat some of these diseases cause nausea and vomiting as impending side-effects. The high degree of cross interactions of dopamine receptor ligands with many other targets including G-protein coupled receptors, transporters, enzymes, and ion-channels, add to the complexity of discovering new targets for the treatment of nausea and vomiting. Using activation status of signaling cascades as mechanism-based biomarkers to foresee drug sensitivity combined with the development of dopamine receptor-based biased agonists may hold great promise and seems as the next step in drug development for the treatment of such multifactorial diseases. In this review, we update the present knowledge on dopamine and dopamine receptors and their potential roles in nausea and vomiting. The pre- and clinical evidence provided in this review supports the implication of both dopamine and dopamine receptor agonists in the incidence of emesis. Besides the conventional dopaminergic antiemetic drugs, potential novel antiemetic targeting emetic protein signaling cascades may offer superior selectivity profile and potency.

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

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

Clozapine use in old age psychiatry

Clozapine is one of the most effective drugs available to psychiatrists for treating psychosis. It is currently licensed for use in treatment-resistant schizophrenia and psychosis in Parkinson's disease, but its use in old age psychiatry is very uncommon. With the ageing population, and the increased incidence of psychosis in older patients, it is important to consider whether this is a drug that is not being used to its full advantage.

LEARNING OBJECTIVES

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DECLARATION OF INTEREST

None.

Neuregulin and Dopamine D4 Receptors Contribute Independently to Depotentiation of Schaffer Collateral LTP by Temperoammonic Path Stimulation

Prior studies have found that dopamine (DA), acting at D4 receptors, and neuregulin (NRG), likely acting at ErbB4 receptors, are involved in a form of depotentiation of long-term potentiation (LTP) at Schaffer collateral (SC) synapses in the hippocampus. Furthermore, DA and NRG actions are intertwined in that NRG induces DA release. We previously found that low-frequency stimulation (LFS) of temperoammonic (TA) inputs to area CA1 also depotentiates previously established SC LTP through a complex signaling pathway involving endocannabinoids, GABA, adenosine, and mitogen-activated protein kinases (MAPKs), but not glutamate. In the present studies, we found that TA-induced SC depotentiation in hippocampal slices from Sprague-Dawley albino rats also involves activation of both D4 receptors and NRG-activated ErbB receptors, but that the roles of these two modulator systems are independent with D4 receptor antagonism failing to alter chemical depotentiation by NRG1β. Furthermore, a selective D4 receptor agonist was unable to depotentiate SC LTP when administered alone, suggesting that D4 receptor activation is necessary but not sufficient for TA-induced SC depotentiation. Chemical depotentiation by NRG1β was inhibited by a Pan-ErbB antagonist and by picrotoxin (PTX), an antagonist of GABA-A receptors (GABA_ARs), indicating that NRG likely promotes SC depotentiation via effects on GABA and interneurons. These findings have implications for understanding the role of DA and NRG in cognitive dysfunction associated with neuropsychiatric illnesses.

Dopamine D4 receptor stimulation contributes to novel object recognition: Relevance to cognitive impairment in schizophrenia

Several atypical antipsychotic drugs (APDs) have high affinity for the dopamine (DA) D₄ receptor, but the relevance to the efficacy for the treatment of cognitive impairment associated with schizophrenia (CIAS) is poorly understood. The aim of this study was to investigate the effects of D₄ receptor stimulation or blockade on novel object recognition (NOR) in normal rats and on the sub-chronic phencyclidine (PCP)-induced novel object recognition deficit. The effect of the D₄ agonist, PD168077, and the D₄ antagonist, L-745,870, were studied alone, and in combination with clozapine and lurasidone. In normal rats, L-745,870 impaired novel object recognition, whereas PD168077 had no effect. PD168077 acutely reversed the sub-chronic phencyclidine-induced novel object recognition deficit. Co-administration of a sub-effective dose (SED) of PD168077 with a sub-effective dose of lurasidone also reversed this deficit, but a sub-effective dose of PD168077 with a sub-effective dose of clozapine, a more potent D₄ antagonist than lurasidone, did not reverse the sub-chronic phencyclidine-induced novel object recognition deficit. At a dose that did not induce a novel object recognition deficit, L-745,870 blocked the ability of clozapine, but not lurasidone, to reverse the novel object recognition deficit. D₄ receptor agonism has a beneficial effect on novel object recognition in sub-chronic PCP-treated rats and augments the cognitive enhancing efficacy of an atypical antipsychotic drug that lacks affinity for the D₄ receptor, lurasidone.

Clozapine-induced dysphagia with secondary substantial weight loss

Dysphagia is listed as a 'rare' side effect following clozapine treatment. In this case report, we describe how significant clozapine-induced dysphagia has led to significant reduction of nutritional intake with subsequent substantial weight loss. An 18-year-old single man with an established diagnosis of treatment-resistant paranoid schizophrenia recovered well on a therapeutic dose of clozapine. However, he was noted to lose weight significantly (up to 20% of his original weight) as the dose was uptitrated. This was brought about by development of dysphagia, likely to be due to clozapine. Addition of nutritional supplementary liquids and initiation of a modified behavioural dietary/swallowing programme, while repeatedly mastering the Mendelsohn manoeuvre technique, alleviated the swallowing difficulties and restored his weight.

Synthesis and characterization of a series of chiral alkoxymethyl morpholine analogs as dopamine receptor 4 (D4R) antagonists

Herein, we report the synthesis and structure-activity relationship of a series of chiral alkoxymethyl morpholine analogs. Our efforts have culminated in the identification of (S)-2-(((6-chloropyridin-2-yl)oxy)methyl)-4-((6-fluoro-1H-indol-3-yl)methyl)morpholine as a novel potent and selective dopamine D4 receptor antagonist with selectivity against the other dopamine receptors tested (<10% inhibition at 1μM against D1, D2L, D2S, D3, and D5).

Discovery and Characterization of ML398, a Potent and Selective Antagonist of the D4 Receptor with in Vivo Activity

Herein, we report the structure-activity relationship of a chiral morpholine-based scaffold, which led to the identification of a potent and selective dopamine 4 (D4) receptor antagonist. The 4-chlorobenzyl moiety was identified, and the compound was designated an MLPCN probe molecule, ML398. ML398 is potent against the D4 receptor with IC50 = 130 nM and K i = 36 nM and shows no activity against the other dopamine receptors tested (>20 μM against D1, D2S, D2L, D3, and D5). Further in vivo studies showed that ML398 reversed cocaine-induced hyperlocomotion at 10 mg/kg.

Effects of the DRD4 genotype on neural networks associated with executive functions in children and adolescents

Genetic variants within the dopamine D4 receptor gene (DRD4) are among the strongest and most consistently replicated molecular genetic findings in attentional functioning as well as attention deficit hyperactivity disorder (ADHD). Functionally, the 7-repeat allele of the DRD4-48 base pair repeat gene leads to a sub-sensitive postsynaptic D4 receptor, which is expressed at a particularly high density in the frontal lobes. We used fMRI to investigate the influence of the 7-repeat allele on BOLD (Blood Oxygen Level Dependency) responses in 26 healthy children and adolescents while they performed a combined stimulus-response Incompatibility Task (IC) and a Time Discrimination Task (TT).

7-repeat non-carriers exhibited increased neural activation of the left middle and inferior frontal gyrus (IFG) in the IC and greater cerebellar activation in the TT. Furthermore, the 7-repeat non-carriers exhibited a stronger coupling in haemodynamic responses between left IFG and the anterior cingulate cortex (ACC) during the IC and between cerebellar activation and brain regions that have high DRD4 density, including the IFG and the ACC during the TT. Our results indicate that the 7-repeat allele influences both regional brain activation patterns as well as connectivity patterns between neural networks of incompatibility and temporal processing.

Factors affecting interindividual differences in clozapine response: a review and case report

OBJECTIVE

Clozapine is the most powerful new‐generation antipsychotic. Although this drug leads to great therapeutic benefits, two types of undesirable conditions frequently occur with its use: side effects and resistance to treatment. Therapeutic drug monitoring of clozapine would be very useful to avoid both these situations. The necessity of monitoring the therapy is the result of a wide interindividual variability in the metabolism of clozapine. In this review, we highlight all the conditions underlying this variability, analyzing them one by one.

METHODS

Relevant literature was identified through a search of MEDLINE and PubMed. In addition, the case of a treatment‐resistant patient with accelerated metabolism of clozapine is reported as representative of utility of therapeutic drug monitoring in terms of clozapine dose adjustment.

RESULTS

Genetic polymorphisms of cytochrome P450 enzymes and of neurotransmitter receptors; drug interactions; interactions of clozapine with other substances such as food and drink; smoking; and nonmodifiable variables such as age, ethnicity, and gender have been examined in relation to the existing scientific literature. The laboratory techniques that clinicians could use to identify these variables and adequate therapies are also reviewed.

Three amino acids in the D2 dopamine receptor regulate selective ligand function and affinity

The D(2) dopamine receptor is an important therapeutic target for the treatment of psychotic, agitated, and abnormal behavioral states. To better understand the specific interactions of subtype-selective ligands with dopamine receptor subtypes, seven ligands with high selectivity (>120-fold) for the D(4) subtype of dopamine receptor were tested on wild-type and mutant D(2) receptors. Five of the selective ligands were observed to have 21-fold to 293-fold increases in D(2) receptor affinity when three non-conserved amino acids in TM2 and TM3 were mutated to the corresponding D(4) amino acids. The two ligands with the greatest improvement in affinity for the D(2) mutant receptor [i.e., 3-{[4-(4-iodophenyl) piperazin-1-yl]methyl}-1H-pyrrolo[2,3-b]pyridine (L-750,667) and 1-[4-iodobenzyl]-4-[N-(3-isopropoxy-2-pyridinyl)-N-methyl]-aminopiperidine (RBI-257)] were investigated in functional assays. Consistent with their higher affinity for the mutant than for the wild-type receptor, concentrations of L-750,667 or RBI-257 that produced large reductions in the potency of quinpirole's functional response in the mutant did not significantly reduce quinpirole's functional response in the wild-type D(2) receptor. In contrast to RBI-257 which is an antagonist at all receptors, L-750,667 is a partial agonist at the wild-type D(2) but an antagonist at both the mutant D(2) and wild-type D(4) receptors. Our study demonstrates for the first time that the TM2/3 microdomain of the D(2) dopamine receptor not only regulates the selective affinity of ligands, but in selected cases can also regulate their function. Utilizing a new docking technique that incorporates receptor backbone flexibility, the three non-conserved amino acids that encompass the TM2/3 microdomain were found to account in large part for the differences in intermolecular steric contacts between the ligands and receptors. Consistent with the experimental data, this model illustrates the interactions between a variety of subtype-selective ligands and the wild-type D(2), mutant D(2), or wild-type D(4) receptors.

Variable number of tandem repeat polymorphisms of DRD4: re-evaluation of selection hypothesis and analysis of association with schizophrenia

Associations have been reported between the variable number of tandem repeat (VNTR) polymorphisms in the exon 3 of dopamine D4 receptor gene gene and multiple psychiatric illnesses/traits. We examined the distribution of VNTR alleles of different length in a Japanese cohort and found that, as reported earlier, the size of allele '7R' was much rarer (0.5%) in Japanese than in Caucasian populations (approximately 20%). This presents a challenge to an earlier proposed hypothesis that positive selection favoring the allele 7R has contributed to its high frequency. To further address the issue of selection, we carried out sequencing of the VNTR region not only from human but also from chimpanzee samples, and made inference on the ancestral repeat motif and haplotype by use of a phylogenetic analysis program. The most common 4R variant was considered to be the ancestral haplotype as earlier proposed. However, in a gene tree of VNTR constructed on the basis of this inferred ancestral haplotype, the allele 7R had five descendent haplotypes in relatively long lineage, where genetic drift can have major influence. We also tested this length polymorphism for association with schizophrenia, studying two Japanese sample sets (one with 570 cases and 570 controls, and the other with 124 pedigrees). No evidence of association between the allele 7R and schizophrenia was found in any of the two data sets. Collectively, this study suggests that the VNTR variation does not have an effect large enough to cause either selection or a detectable association with schizophrenia in a study of samples of moderate size.

Association analysis of exon III and exon I polymorphisms of the dopamine D4 receptor locus in Mexican psychotic patients

In this study, we investigated whether polymorphisms of the dopamine D4 receptor (DRD4) gene were associated with psychotic symptomatology rather than with a unique diagnosis such as schizophrenia. A number of association studies between the DRD4 gene 48 bp-VNTR polymorphism at exon 3 and psychotic disorders have been reported, but the results have been controversial. Both 48 bp-VNTR and the 12 bp-VNTR (at exon 1) polymorphisms of this gene were analyzed in a group of 149 unrelated Mexican subjects with a diagnosis of schizophrenia, schizoaffective disorder, schizophreniform disorder, major depression and bipolar disorder, both with psychotic symptoms, brief psychotic disorder, delusional disorder and non-specific psychotic disorder, and in 169 individuals free of psychiatric illnesses. There were no differences in allele or genotype frequencies between groups for the 12 bp-VNTR polymorphisms. However, a significant excess of "rare" alleles (3-, 5-, 6- and 8-48 bp repeats alleles) was found in the group of psychotics. Moreover, haplotypes 3-A1, 5-A1, 6-A1 and 8-A1 were significantly more frequently associated with cases. This positive association supports a role of this molecule as a genetic risk factor in psychotic disorders.

Relationship between dopamine system genes and extraversion and novelty seeking

Dopamine transmission is known to play an important role in the reinforcement system of the brain. Studies have identified dopamine system genes whose polymorphic variants have been linked with the intensity of psychological traits reflecting the tendency to form behaviors characterized by impulsivity and the need for additional stimulation. The aim of the present work was to seek associations between polymorphisms in the catechol-O-methyltransferase (COMT) and D4 dopamine receptor (DRD4) genes and personality traits in the Russian population. Studies of 130 subjects showed that carriers of the Met/Met genotype of the COMT gene had a greater intensity of the novelty-seeking trait than carriers of the Val/Val and Val/Met genotypes, though this association was seen only in women. In addition, the presence of the C allele of the DRD4 gene in carriers of the Met/Met genotype showed high levels of extraversion and hypomania. These results are consistent with current theoretical concepts of the regulation of dopamine transmission in the brain.

A model for modulation of neuronal synchronization by D4 dopamine receptor-mediated phospholipid methylation

We describe a new molecular mechanism of dopamine-induced membrane protein modulation that can tune neuronal oscillation frequency to attention-related gamma rhythm. This mechanism is based on the unique ability of D4 dopamine receptors (D4R) to carry out phospholipid methylation (PLM) that may affect the kinetics of ion channels. We show that by deceasing the inertia of the delayed rectifier potassium channel, a transition to 40 Hz oscillations can be achieved. Decreased potassium channel inertia shortens spike duration and decreases the interspike interval via its influence on the calcium-dependent potassium current. This mechanism leads to a transition to attention-related gamma oscillations in a pyramidal cell-interneuron network. The higher frequency and better synchronization is observed with PLM affecting pyramidal neurons only, and recurrent excitation between pyramidal neurons is important for synchronization. Thus dopamine-stimulated methylation of membrane phospholipids may be an important mechanism for modulating firing activity, while impaired methylation can contribute to disorders of attention.

D4 Dopamine receptor genes of zebrafish and effects of the antipsychotic clozapine on larval swimming behaviour

Zebrafish, a model developmental genetic organism, is being increasingly used in behavioural studies. We have initiated studies designed to evaluate the response of zebrafish to antipsychotic drugs. This study focuses on characterization of zebrafish D4 dopamine receptors (D4Rs) and the response of larval zebrafish to the atypical antipsychotic clozapine. The D4R is of interest because of its high affinity for clozapine, while interest in clozapine stems from its effectiveness in reducing symptoms in acutely psychotic, treatment-resistant schizophrenic patients. By mining the zebrafish genomic database, we identified three distinct D4R genes, drd4a, drd4b and drd4c, and generated full-length open reading frames encoding each of the three D4Rs by reverse transcription-polymerase chain reaction. Gene mapping studies showed that each D4R gene mapped to a distinct chromosomal location in the zebrafish genome, and each gene exhibited a unique expression profile during embryogenesis. When administered to larval zebrafish, clozapine produced a rapid and profound effect on locomotor activity. The effect of clozapine was dose-dependent, resulted in hypoactivity and was prevented by the D4-selective agonist ABT-724. Our data suggest that the inhibitory effect of clozapine on the locomotor activity of larval zebrafish may be mediated through D4Rs.

Alterations of serotonin transmission in schizophrenia

A role for serotonin alterations in the pathophysiology of schizophrenia has long been suspected because of the psychotogenic effects of serotonergic agonists and the therapeutic effects of 5-HT(2) antagonism. This chapter is a review of the evidence derived from pharmacological studies, postmortem, and imaging studies that have assessed the role of serotonin transmission in schizophrenia. While a clear picture of specific serotonergic alterations in schizophrenia has not emerged despite much research, this review reinforces a modulatory role of serotonergic agents on dopamine transmission in schizophrenia, which may contribute to the therapeutic effects of atypical antipsychotics.

Association and synergistic interaction between promoter variants of the DRD4 gene in Japanese schizophrenics

Recent association studies suggest that polymorphisms in the promoter and exon 1 upstream region of the dopamine D4 receptor (DRD4) gene play a functional role in the development of common psychiatric illnesses, although there are also conflicting results. In this study, we re-sequenced this region to identify all genomic variants, and tested them for association with schizophrenia. A total of 570 Japanese schizophrenic cases with matched controls were studied by genotyping all identified/validated common polymorphisms (−1106T>C, −906T>C, −809G>A, −616G>C, −521T>C, −376C>T, −291C>T and 12-bp repeat) and a known microsatellite (120-bp tandem duplication) in the upstream region. A single nucleotide polymorphism (SNP) −809G>A in the promoter region was found to be significantly associated with disease (P=0.018 and 0.032 for allelic and genotypic comparisons, respectively), although not surviving after Bonferroni correction. Logistic regression analysis showed that a combination of the four polymorphisms, −809G>A, −616G>C, −291C>T and the 12-bp repeat, conferred a susceptibility to schizophrenia. These results suggest that the upstream variants have a primary functional effect in the etiology of schizophrenia in the Japanese population.

Dopamine D4 receptor gene and the −521C>T polymorphism of the upstream region of the dopamine D4 receptor gene in schizophrenia

OBJECTIVE

The dopamine D4 receptor (DRD4) is a candidate gene for increasing genetic susceptibility to schizophrenia. A recent study found that a -521C>T promoter base pair change affects transcriptional regulation of the DRD4 gene. The present study was designed to investigate the role of both the -521C>T single nucleotide polymorphism and the DRD4 variable number tandem repeat (VNTR) polymorphism.

METHODS

A case-control study of 630 Chinese schizophrenic patients and 428 Chinese controls was conducted to test for allelic association with schizophrenia.

RESULTS

The number of DRD4 VNTR fragments was associated with schizophrenia. Long DRD4 VNTR fragments as opposed to short fragments were commoner in schizophrenia. No evidence was found for allelic association between the -521C>T DRD4 polymorphism and schizophrenia.

CONCLUSIONS

This study provides preliminary and unconfirmed evidence for the involvement of the DRD4 repeat VNTR in the pathogenesis of schizophrenia.

Potential clozapine target sites on peripheral hematopoietic cells and stromal cells of the bone marrow

The antipsychotic drug clozapine, acts via interaction with selective neurotransmitter receptor systems. Its use however, is associated with life-threatening agranulocytosis. The mechanism by which this occurs and its possible relationship with the drug's atypicality remain unclear. As a first step in identifying mechanistic pathways involved, profiling of neurotransmitter receptors on human neutrophils, mononuclear and bone marrow stromal cells as putative targets for clozapine-mediated toxicity was undertaken. Expression of mRNA encoding dopaminergic d2, d3, d4; serotonergic 5ht2a, 5ht2c, 5ht3, 5ht6, 5ht7; adrenergic alpha1a, alpha2; histaminergic h1 and muscarinic m1, m2, m3, m4, m5 receptors was analyzed by reverse transcription-polymerase chain reaction methods. While 5ht2c, 5ht6, m1 and m2 mRNA were undetected, the presence of the other receptors indicates sites at which clozapine could bind and induce toxicity of neutrophils and stromal components which regulate granulopoiesis. The functional significance of differential receptor expression while unknown, may argue for neural regulation of hematopoiesis.

Association analysis of polymorphisms in the upstream region of the human dopamine D4 receptor gene in schizophrenia

Several studies have suggested that the transcriptional activity of the DRD4 gene may exert an important role in susceptibility to schizophrenia. To address this issue, we studied the association of schizophrenia and polymorphisms including -616C>G, -603T>del, -602G>del, 600G>C, -521C>T, -376C>T and a 120 bp tandem duplication polymorphism (120 bp repeat) in 1.2 kb upstream from the initiation codon in the promoter region of the DRD4 gene with 210 schizophrenic cases and 206 healthy controls. The results showed a significant excess of allele L of the 120 bp repeat in the schizophrenic patients compared to the controls (X(2)=8.585, df=1, P=0.003, OR=1.546, 95% CI=1.154-2.070). No significant difference was detected in the frequencies of genotype and allele of six other polymorphisms between the two groups. However, haplotypic distribution of 120 bp repeat, -616C>G, -602G>del, -521C>T and -376C>T was significantly different between case and control groups (P=0.005). This might cause the alteration of the transcriptional regulation of the DRD4 gene, as the consensus sequences of binding sites for several known transcription factors are involved in this region.

Asymmetric modulation of a catecholamine-regulated protein in the rat brain, following quinpirole administration

We previously reported a brain-specific 40 kDa catecholamine-regulated protein (CRP40) that binds dopamine (DA) and related catecholamines. CPR40 shares significant sequence homology with human heat shock protein (Hsp70), GRP78/BIP, and human #BQ24193 protein. Recent studies with the DA D(2) receptor antagonist, haloperidol, demonstrated a significant increase in expression of CRP40 in the striatum (STR). The objective of the present study was to investigate CRP40 expression in various brain regions following treatments with the DA D(2)/D(3) receptor agonist quinpirole (QNP) in rats and examine possible relationships between neurochemical parameters and locomotor activity. Rats received injections of either QNP (0.5 mg/kg, for 27 days every third day) or saline (SAL) and their locomotor activities were measured for 90 min after each injection. At injection 9, QNP-treated rats showed locomotor activity that was significantly greater than SAL controls (F(2,28) = 3.88, P < 0.05, Duncan's multiple range test, P < 0.05). Neurochemically, acute QNP-treated rats demonstrated significant differential expression of CRP40 in the left/right prefrontal cortex (PFC) relative to SAL-treated rats (-17.76 +/- 2.10%, -10.35 +/- 1.23%, P < 0.001). Chronic QNP significantly decreased CRP40 expression in the STR, ventral tegmental area (VTA), and left/right PFC (-24.85+/- 2.10%, -18.15 +/- 5.64%, -49.13 +/- 7.05%, -25 +/- 3.63%, P < 0.001). Finally, chronic QNP treatment resulted in a significant increase in CRP40 levels in the nucleus accumbens (NA) (+39.32 +/- 7.00%, P < 0.001). Heat shock protein (i.e., Hsp70 or Hsc70) expression remained unaltered following QNP treatment. Since QNP is a DA D(2)/D(3) agonist, alterations in CRP40 expression following QNP treatment suggest the protein's function in dopaminergic neurotransmission.

Birth insult interacts with stress at adulthood to alter dopaminergic function in animal models: possible implications for schizophrenia and other disorders

Altered subcortical dopaminergic activity is thought to be involved in the pathophysiology of several disorders including schizophrenia, substance abuse and attention deficit hyperactivity disorder. Epidemiological studies have implicated perinatal insults, particularly obstetric complications involving fetal or neonatal hypoxia, as etiological risk factors for schizophrenia. This suggests the possibility that perinatal hypoxia might have lasting effects on dopaminergic function. In animal models, dopaminergic systems appears to be particularly vulnerable to a wide range of perinatal insults, resulting in persistent alterations in function of mesolimbic and mesostriatal pathways. This review summarizes recent work characterizing long-term changes in dopaminergic function and biochemistry in models of Caesarean section (C-section) birth and of C-section birth with added global anoxia in the rat and guinea pig. C-section birth and C-section with anoxia appear to be two distinct hypoxic birth insults, with somewhat differing patterns of lasting effects on dopamine systems. In addition, birth insult alters the manner in which dopaminergic function is regulated by stress at adulthood. The possible relevance of these finding to effects of human birth procedures is discussed.

Quantitative comparison of functional screening by measuring intracellular Ca2+ with radioligand binding at recombinant human dopamine receptors

The purpose of this study was to test whether screening at dopamine receptors performed with a recently described functional assay for G-protein coupled receptors (GPCRs) provides data that correlate significantly with radioligand binding data in the literature, thus possibly allowing researchers to replace radioligand binding with nonradioactive functional screening. Human dopamine receptors hD1 and hD2L (representing Gs [hD1] or Gi [hD2L] coupled GPCRs) were recombinantly expressed in human embryonic kidney (HEK293) cells. Cells were loaded with Oregon Green 488 BAPTA-1/AM and evenly distributed in 384 well plates. Seventeen test compounds were screened for agonistic activity by injection into the cell suspension and monitoringH of intracellular Ca2+ with a fluorescence microplate reader. Then, standard agonists (100nM SKF38393 for hD1, 30nM quinpirole for hD2L) were injected into wells preincubated with test compounds (screening for antagonism). Injection of various agonists resulted in a concentration-dependent increase in fluorescence. Further, preincubation of antagonists with dopamine receptor expressing cells inhibits concentration-dependent the agonist-induced increase in fluorescence. Calculated apparent functional Ki values correlate with radioligand binding data in the literature (r2 = 0.7796 for D1, r2 = 0.7743 for D2). The correlation between apparent functional Ki values and radioligand binding data for the 17 tested compounds suggests that screening of test compounds at dopamine receptors with the functional Ca2+ assay can replace radioligand binding studies. Furthermore, besides apparent Ki values, information about agonistic or antagonistic properties of a test compound can be obtained with the functional Ca2+ assay.

Ethnic heterogeneity in allele variation in the DRD4 gene in schizophrenia

The goal of the present study was to use a meta-analysis on previous studies plus our own unpublished data to confirm and extend findings which indicate that the variation in the dopamine D4 receptor (DRD4) gene is best represented by a mixture of two different ethnic groups. The genotype distribution was divided into either a long or short form using a mixture analysis of normal controls of different ethnic origins under the assumption that there is a single major gene. The meta-analysis was based on the data from 19 independent samples, 18 association studies, and from our own unpublished data, including a total of 1431 schizophrenic patients (sporadic cases 1309, familial cases 122) and 1439 controls. No significant genotype differences were noted between patients and controls for the whole sample. However, reorganization of the studies into different groups by the geographical origin of samples revealed significant ethnic heterogeneity. In addition, there was a significant association between the long form of DRD4 gene and schizophrenia in Caucasians, especially those with familial schizophrenia.

Pharmacogenetics for the individualization of psychiatric treatment

Drug treatment of psychiatric disorders is troubled by severe adverse effects, low compliance and lack of efficacy in about 30% of patients. Pharmacogenetic research in psychiatry aims to elucidate the reasons for treatment failure and adverse reactions. Genetic variations in cytochrome P450 (CYP) enzymes have the potential to directly influence the efficacy and tolerability of commonly used antipsychotic and antidepressant drugs. The activity of psychiatric drugs can also be influenced by genetic alterations affecting the drug target molecule. These include the dopaminergic and serotonergic receptors, neurotransmitter transporters and other receptors and enzymes involved in psychiatric disorders. Association studies investigating the relation between genetic polymorphisms in metabolic enzymes and neurotransmitter receptors on psychiatric treatment outcome provide a step towards the individualization of psychiatric treatment through enabling the selection of the most beneficial drug according to the individual's genetic background.

Astrocytic basic fibroblast growth factor expression in dopaminergic regions after perinatal anoxia

BACKGROUND

Perinatal anoxia leads to persistent behavioral and neurochemical alterations suggestive of sensitized dopaminergic function. Because astrocytic basic fibroblast growth factor (bFGF) activity in the midbrain dopaminergic cell body region is required for the development of enduring changes in dopaminergic function induced by stimulant drugs, we investigated the effects of intrauterine anoxia on astrocytic bFGF expression in dopaminergic regions at 2 weeks of age and after a stress manipulation in adults.

METHODS

We examined bFGF immunoreactivity in dopaminergic regions of young and adult rats born by cesarean section, cesarean section + 15 min of intrauterine anoxia, or vaginally. bFGF immunoreactivity was also assessed before and after tail-pinch stress in adult animals exposed to the same perinatal interventions.

RESULTS

Perinatal anoxia produced persistent decreases in basal bFGF immunoreactivity in the ventral tegmental area (VTA), but enhanced the effect of stress on VTA bFGF immunoreactivity.

CONCLUSIONS

Perinatal anoxia has enduring effects on VTA bFGF immunoreactivity and influences adult neuroadaptations to stress. The mechanisms whereby perinatal anoxia alters dopaminergic function may be similar to those responsible for the development of sensitization to stimulant drugs and may involve bFGF.

Genetic predictors of therapeutic response to clozapine: current status of research

Clozapine is one of the most clinically potent drugs currently available for treating the symptoms of schizophrenia. Compared with conventional antipsychotics it surpasses its predecessors in its ability to treat a wider range of symptoms in otherwise refractory patients, while possessing a low propensity to produce extrapyramidal symptoms. Despite its significant advantages, not all patients benefit from treatment. Some patients react adversely to therapy while others fail to respond adequately. If those most likely to benefit from clozapine could be identified prior to treatment, this would significantly improve the clinical management of these patients. Genetic alterations in drug-metabolising enzymes have previously been demonstrated to influence the efficacy of clinically relevant drugs. It is possible that similar alterations in these and other systems may influence the response variability of patients to clozapine. Pharmacogenetic studies are at present investigating genes encoding drug receptors, drug-metabolising enzymes and neurotransmitter transporters to identify genetic variants that may be important. To date polymorphisms within serotonergic and dopaminergic pathways have been implicated, though the involvement of similar variants in other candidate systems is also likely. This information will ultimately enable the genetic prediction of patients most likely to benefit from the drug, and in the process would alleviate the unnecessary exposure of predisposed individuals to potentially serious adverse effects.

Atypical neuroleptics in child and adolescent psychiatry

Atypical neuroleptics have enriched our treatment programmes, especially in childhood and adolescent schizophrenia. This article reviews the use of atypical neuroleptics in children and adolescents with schizophrenic disorder. It considers the receptor binding profile and pharmacological properties, indications, side effects, clinical applications and trials of atypical neuroleptics in comparison to the classical neuroleptic haloperidol in adolescent schizophrenia. Special emphasis is placed on the most common atypical neuroleptics clozapine, olanzapine and risperidone since most studies are carried out with these compounds, especially with clozapine. More clinically controlled trials have to be conducted since only one was performed so far. The place of the atypical neuroleptics is discussed and further studies are necessary in order to differentiate the indications tested so far and to find out if the spectrum of indications can be broadened.

Progesterone modulation of D5 receptor expression in hypothalamic ANP neurons, the role of estrogen

Aberrant responses to dopamine consequent to a reduction of D1-like receptors in critical regions of the brain have been implicated in schizophrenia. Whereas estrogen may protect against the onset and incidence of psychosis in the illness, the neurobiological effects of the ovarian steroid remain unclear. Recently we have shown that estrogen augments the expression of D5 receptors, a member of the D1-like receptor family, in central neurons and enhances the functions of the host cells. Employing rat hypothalamic neuron cultures, we report here that another important ovarian steroid, progesterone, also augments dopamine D5 receptor expression in hypothalamic atrial natriuretic factor (ANP) neurons. However, unlike the effect of estrogen, progesterone acts indirectly through potentiating estrogen-mediated changes that include enhancement of D5 receptor expression, immunoreactive (ir)-ANP release and pro-ANP mRNA abundance. We conclude that whilst progesterone has little effect by itself, the steroid works in synergism with estrogen to augment the function of ANP neurons. The possibility that progesterone may further enhance the protective effect of estrogen against the incidence of psychosis in schizophrenia now needs to be considered.

Dopamine D4 receptor (DRD4) gene polymorphism in the first psychotic episode

BACKGROUND

Dopamine D4 receptor (DRD4) has shown some interesting properties at genetic and possibly functional levels. It has been suggested that some molecular variants of the DRD4 gene (e.g., four and seven alleles) could be implicated in the pathogenesis of psychotic disorders. Additionally, the VNTR polymorphism could be implicated in part of the response to treatment with neuroleptics. This study tested the possible association between the 48-bp tandem repeats in exon 3 of the DRD4 gene and patients experiencing their first psychotic episode.

METHODS

Patients with a first psychotic episode (FPE, n = 37) were diagnosed and compared with a matched control group (n = 37). The FPE group was subdivided into two categories: those with nonaffective and those with affective psychoses. The variable number of tandem repeats (VNTR) region of the DRD4 gene was amplified by PCR procedures. Chi-square statistics and appropriate corrections and adjustments were used for data analysis.

CONCLUSIONS

A significantly lower frequency of the four repeat (4-R) carriers in the FPE group was observed. This association was sustained mainly by the affective psychotic group (chi2 = 9.99 df = 2, p = 0.0073). Although these results require testing with stringent methods, it is suggested that the DRD4-4R allele may confer some protection against psychosis, mainly of the affective subtype.

SPECT tracer [(123)I]IBZM has similar affinity to dopamine D2 and D3 receptors

Emission tomography investigations of the pathophysiological involvement of the cerebral dopaminergic transmitter system in the living human brain relies heavily on a careful selection of the most suitable radioligand. In recent years, many clinical studies have employed [(123)I]IBZM in SPECT studies. The aim of the present study was to characterize the binding of IBZM to dopaminergic receptor subtypes as a means of elucidating which receptor subtypes are visualized and examined by [(123)I]IBZM. The affinity of IBZM for each of the major human dopamine receptors (D1, D2(short), D3, D4(4. 2), and D5 receptor) was determined by competitive radioligand binding assay using membranes prepared from clonal cell lines expressing the different subtypes. Radioligands with high affinity for the D1(A) and D5 receptors ([(3)H]SCH-23390), dopamine D2(short) and D4(4.2) receptors ([(3)H]Spiroperidol), and dopamine D3 receptor ([(3)H]7-OH-DPAT) were used to measure specific binding. Corresponding unlabeled displacing ligands for determination of nonspecific binding were employed. Assays were performed at 25 degrees C. These experiments show that for IBZM K(i) values were 1.6 nM for dopamine D2(s) receptors and 2.2 nM for dopamine D3 receptors. There was no binding of IBZM to D1(A), D5, or D4(4.2) receptors. In conclusion, when [(123)I]IBZM is used as SPECT tracer, the studies reflect dopaminergic D2 as well as D3 receptor binding.

Dopamine D4 receptors and development of newer antipsychotic drugs

The last ten years have witnessed the generation of a large amount of information on the neurobiology of dopamine receptors. Molecular biology and pharmacology studies have revealed existence of at least five dopamine receptor subtypes, namely D1, D2, D3, D4 and D5. The discovery of D4 receptors and the putative affinity of clozapine for D4 receptors have kindled development of selective D4 receptor antagonists for the treatment of schizophrenia. Studies on expression of D4 receptor proteins have shown selective localisation of D4 receptors in mesolimbic/mesocortical areas which could probably explain the lack of motor side effects with atypical antipsychotics like clozapine and olanzapine. However, neuropathological and genetic studies on the role of D4 receptors in the pathophysiology of schizophrenia and preliminary clinical studies with selective D4 receptor antagonists have been disappointing. There have been, however, complimentary findings between selective D4 receptor antagonism and genetic approaches such as antisense treatment or gene targeting. The therapeutic potential of D4 receptors as a target for developing antipsychotics will be known only when selective D4 receptor-antagonists with varying D2/D4 and D4/5-HT2A ratios are developed and tested in psychiatric patients.

[(3)H]PNU-101958, a D(4) dopamine receptor probe, accumulates in prefrontal cortex and hippocampus of non-human primate brain

The D(4) dopamine receptor has been investigated for its potential role in neuropsychiatric disorders, "novelty-seeking" behaviors, and effects produced by some psychostimulants. An accurate map of D(4) distribution and density in brain is essential to clarify the role of this receptor subtype in normal brain function and in neuropsychiatric disorders. We investigated the autoradiographic distribution of D(4) receptors in non-human primate (Macaca mulatta) brain (N = 3) with the novel D(4) receptor probe [(3)H]PNU-101958. Quantification of [(3)H]PNU-101958 binding sites in 77 brain regions revealed dense levels of D(4) receptors in several cortical areas, especially in prefrontal cortex, uncus, hypothalamic median eminence, hippocampal formation, and distinct thalamic nuclei, but were significantly lower in striatum. The results correspond well with previous reports of brain distribution of D(4) receptors using other radiolabeled probes, and of D(4) mRNA localization (with some exceptions). Overall, this study reveals that [(3)H]PNU-101958 binding sites in non-human primate brain appear to reflect D(4) dopamine receptor distribution. The significance of a dense localization of D(4) receptors in prefrontal cortex and hippocampus, and broad distribution in other brain areas, allows for investigation of the relationship of these receptors to specific neuropsychiatric disorders and effects produced by psychostimulants.

Glucocorticoid modulation of dopamine mediated effects on hypothalamic atrial natriuretic factor neurons

Dopamine (DA) plays an important role in cognition, neuroendocrine functions and psychosis.1,2 Whilst stress adversely affects some of these functions, its neurobiological basis remains unclear.3 In the rat hypothalamus, a concurrent activation of D5and D2 receptors by dopamine produces a biphasic effect on the function of atrial natriuretic factor (ANF) neurons.4 Whereas low doses (10-8 and 10-7 M) of DA suppress the release and pro-ANF mRNA expression, high doses (10-6 and 10-5 M) of the amine produce an opposite effect through the interaction of D5 and D2 receptors. We report here that the augmenting effect of DA on the hypothalamic neurons is inhibited by a synthetic glucocorticoid, dexamethasone (DM), in both time-dependent and dose-related manner with an EC50 of 0.1 nM. Furthermore, the inhibition is blocked by 100 nM of RU38486 (P<0.01), a glucocorticoid receptor antagonist, but not by an equivalent dose of RU28318, a mineralocorticoid receptor antagonist. In contrast, DM failed to modulate low doses (10(-8) to 10(-7) M) of DA-induced suppression of ir-ANF release and pro-ANF mRNA expression that was mediated primarily through D2 receptors. We conclude that glucocorticoids markedly alter DA-induced biphasic effects by down-regulating D5, but not D2, receptor-mediated neurobiological events. Hence, in severe stress, high levels of circulating glucocorticoids may render dopamine to act as a potent suppressor of neurons that possess both D5 and D2 receptors. The possibility that this novel mechanism of stress hormone or glucocorticoids may, in part, undermine DA-mediated neurophysiology in critical regions of the brain, which links to psychosis now needs to be considered.

Neurotransmitter-related genes and antipsychotic response: pharmacogenetics meets psychiatric treatment

Pharmacogenetic research into neurotransmitter-related genes is helping to unravel genetic factors that determine antipsychotic response. Several genetic mutations in neurotransmitter receptors targeted by antipsychotic drugs have been found to be related to clinical response. Modern molecular genetic techniques will facilitate the identification of those mutations that determine treatment response. Future psychiatric prescription will include the genetic characterization of neurotransmitter receptors for the selection of the most beneficial drug according to the individual's pharmacogenetic profile.

Apolipoprotein E4: an allele associated with many diseases

Apolipoprotein E (apoE) was discovered as a plasma protein involved in lipoprotein metabolism. ApoE is synthesized by the liver and is also made locally in the brain. There are three common variants of apoE, resulting from common genetic variation, called E2, E3 and E4. The E3 allele is the most prevalent form, and the proportion of the three alleles differs between populations. Epidemiological studies have found that the E4 allele is associated with decreased longevity, increased plasma cholesterol levels and increased prevalence for cardiovascular disease and particularly for Alzheimer's disease. The apoE polymorphism also affects response to head trauma, cognitive decline upon ageing and several other disorders. Thus, common genetic variation in the apoE gene may be associated with successful ageing.

Pharmacogenetics of antipsychotic treatment: lessons learned from clozapine

The reintroduction of clozapine, the prototype of atypical antipsychotics, in the late 1980s has led to significant advances in the pharmacological management of schizophrenia. Since then, there has been a rapid development of novel "atypical" antipsychotic agents that have been pharmacologically modeled, to a certain extent, after their predecessor clozapine. As with all antipsychotics, there is variability among individuals in their response to these "atypical" drugs. Pharmacogenetics can provide a foundation for understanding this interindividual variability in antipsychotic response. This review first provides a rationale for the pharmacogenetic investigation of this variable trait. Studies of pharmacokinetic and pharmacodynamic factors of antipsychotic therapy are considered in the development of this rationale. Next, the molecular genetic techniques used to study this interindividual variation in response are described. This is followed by a review and discussion of the published studies examining genetic factors involved in clozapine response. From this, several recommendations for future pharmacogenetic investigations of antipsychotic response are proposed. Although still in its early stages, psychiatric pharmacogenetics should provide a basis for individualized pharmacotherapy of schizophrenia, and may also lead to the development of newer, more efficacious antipsychotic agents.