A functional dopamine-beta-hydroxylase gene promoter polymorphism is associated with impulsive personality styles, but not with affective disorders

Individual differences in cognition, affect, and performance: behavioral, neuroimaging, and molecular genetic approaches

We describe the use of behavioral, neuroimaging, and genetic methods to examine individual differences in cognition and affect, guided by three criteria: (1) relevance to human performance in work and everyday settings; (2) interactions between working memory, decision-making, and affective processing; and (3) examination of individual differences. The results of behavioral, functional MRI (fMRI), event-related potential (ERP), and molecular genetic studies show that analyses at the group level often mask important findings associated with sub-groups of individuals. Dopaminergic/noradrenergic genes influencing prefrontal cortex activity contribute to inter-individual variation in working memory and decision behavior, including performance in complex simulations of military decision-making. The interactive influences of individual differences in anxiety, sensation seeking, and boredom susceptibility on evaluative decision-making can be systematically described using ERP and fMRI methods. We conclude that a multi-modal neuroergonomic approach to examining brain function (using both neuroimaging and molecular genetics) can be usefully applied to understanding individual differences in cognition and affect and has implications for human performance at work.

A Potential Role for a Genetic Variation of AKAP5 in Human Aggression and Anger Control

The A-kinase-anchoring protein 5 (AKAP5), a post-synaptic multi-adaptor molecule that binds G-protein-coupled receptors and intracellular signaling molecules has been implicated in emotional processing in rodents, but its role in human emotion and behavior is up to now still not quite clear. Here, we report an association of individual differences in aggressive behavior and anger expression with a functional genetic polymorphism (Pro100Leu) in the human AKAP5 gene. Among a cohort of 527 young, healthy individuals, carriers of the less common Leu allele (15.6% allele frequency) scored significantly lower in the physical aggression domain of the Buss and Perry Aggression Questionnaire and higher in the anger control dimension of the state-trait anger expression inventory. In a functional magnetic resonance imaging experiment we could further demonstrate that AKAP5 Pro100Leu modulates the interaction of negative emotional processing and executive functions. In order to investigate implicit processes of anger control, we used the well-known flanker task to evoke processes of action monitoring and error processing and added task-irrelevant neutral or angry faces in the background of the flanker stimuli. In line with our predictions, Leu carriers showed increased activation of the anterior cingulate cortex (ACC) during emotional interference, which in turn predicted shorter reaction times and might be related to stronger control of emotional interference. Conversely, Pro homozygotes exhibited increased orbitofrontal cortex (OFC) activation during emotional interference, with no behavioral advantage. Immunohistochemistry revealed AKAP5 expression in post mortem human ACC and OFC. Our results suggest that AKAP5 Pro100Leu contributes to individual differences in human aggression and anger control. Further research is warranted to explore the detailed role of AKAP5 and its gene product in human emotion processing.

The involvement of noradrenaline in rapid eye movement sleep mentation

Noradrenaline, one of the main brain monoamines, has powerful central influences on forebrain neurobiological processes which support the mental activities occurring during the sleep-waking cycle. Noradrenergic neurons are activated during waking, decrease their firing rate during slow wave sleep, and become silent during rapid eye movement (REM) sleep. Although a low level of noradrenaline is still maintained during REM sleep because of diffuse extrasynaptic release without rapid withdrawal, the decrease observed during REM sleep contributes to the mentation disturbances that occur during dreaming, which principally resemble symptoms of schizophrenia but seemingly also of attention deficit hyperactivity disorder.

Generational association studies of dopaminergic genes in reward deficiency syndrome (RDS) subjects: selecting appropriate phenotypes for reward dependence behaviors

Abnormal behaviors involving dopaminergic gene polymorphisms often reflect an insufficiency of usual feelings of satisfaction, or Reward Deficiency Syndrome (RDS). RDS results from a dysfunction in the "brain reward cascade," a complex interaction among neurotransmitters (primarily dopaminergic and opioidergic). Individuals with a family history of alcoholism or other addictions may be born with a deficiency in the ability to produce or use these neurotransmitters. Exposure to prolonged periods of stress and alcohol or other substances also can lead to a corruption of the brain reward cascade function. We evaluated the potential association of four variants of dopaminergic candidate genes in RDS (dopamine D1 receptor gene [DRD1]; dopamine D2 receptor gene [DRD2]; dopamine transporter gene [DAT1]; dopamine beta-hydroxylase gene [DBH]).

METHODOLOGY

We genotyped an experimental group of 55 subjects derived from up to five generations of two independent multiple-affected families compared to rigorously screened control subjects (e.g., N = 30 super controls for DRD2 gene polymorphisms). Data related to RDS behaviors were collected on these subjects plus 13 deceased family members.

RESULTS

Among the genotyped family members, the DRD2 Taq1 and the DAT1 10/10 alleles were significantly (at least p < 0.015) more often found in the RDS families vs. controls. The TaqA1 allele occurred in 100% of Family A individuals (N = 32) and 47.8% of Family B subjects (11 of 23). No significant differences were found between the experimental and control positive rates for the other variants.

CONCLUSIONS

Although our sample size was limited, and linkage analysis is necessary, the results support the putative role of dopaminergic polymorphisms in RDS behaviors. This study shows the importance of a nonspecific RDS phenotype and informs an understanding of how evaluating single subset behaviors of RDS may lead to spurious results. Utilization of a nonspecific "reward" phenotype may be a paradigm shift in future association and linkage studies involving dopaminergic polymorphisms and other neurotransmitter gene candidates.

No association of a casein kinase 1ε (CK1ε) gene polymorphism with personality traits in healthy Chinese-Han subjects

The human casein kinase 1 (CK1) family is comprised of seven monomeric serine/threonine kinases (α, β, γ1-γ3, δ, and ε) encoded by seven highly conserved genes. Casein kinases modulate numerous biological and pathological processes by regulating the phosphorylation of the 32 kDa dopamine- and cAMP-regulated phosphoprotein DARPP-32, a major downstream regulator of dopamine signaling. Individual variation in the dopamine signaling system is thought to determine certain dimensions of personality, but there have been no published studies investigating the involvement of CK1 in the biological determination of temperament. We examined the association between the rs135745C/G polymorphism of the CK1ε gene CSNK1E and personality traits as measured by the tridimensional personality questionnaire in healthy Chinese-Han subjects. There were no differences in the total scores for novelty seeking (NS, χ (2) = 4.151, P = 0.125), harm avoidance (χ (2) = 3.299, P = 0.192), or reward dependence (χ (2) = 0.816, P = 0.665) between the rs135745C/G genotypes. In the sub-item analyses, the NS1 scores were significantly different (χ (2) = 7.024, P = 0.030) between rs135745C/G genotypes. However, this difference did not remain statistically significant after Bonferroni correction. Thus, our results did not provide evidence for the association between CK1ε gene and personality traits in healthy Chinese-Han subjects.

Genetic determinants of aggression and impulsivity in humans

Human aggression/impulsivity-related traits have a complex background that is greatly influenced by genetic and non-genetic factors. The relationship between aggression and anxiety is regulated by highly conserved brain regions including amygdala, which controls neural circuits triggering defensive, aggressive, or avoidant behavioral models. The dysfunction of neural circuits responsible for emotional control was shown to represent an etiological factor of violent behavior. In addition to the amygdala, these circuits also involve the anterior cingulated cortex and regions of the prefrontal cortex. Excessive reactivity in the amygdala coupled with inadequate prefrontal regulation serves to increase the likelihood of aggressive behavior. Developmental alterations in prefrontal-subcortical circuitry as well as neuromodulatory and hormonal abnormality appear to play a role. Imbalance in testosterone/serotonin and testosterone/cortisol ratios (e.g., increased testosterone levels and reduced cortisol levels) increases the propensity toward aggression because of reduced activation of the neural circuitry of impulse control and self-regulation. Serotonin facilitates prefrontal inhibition, and thus insufficient serotonergic activity can enhance aggression. Genetic predisposition to aggression appears to be deeply affected by the polymorphic genetic variants of the serotoninergic system that influences serotonin levels in the central and peripheral nervous system, biological effects of this hormone, and rate of serotonin production, synaptic release and degradation. Among these variants, functional polymorphisms in the monoamine oxidase A (MAOA) and serotonin transporter (5-HTT) may be of particular importance due to the relationship between these polymorphic variants and anatomical changes in the limbic system of aggressive people. Furthermore, functional variants of MAOA and 5-HTT are capable of mediating the influence of environmental factors on aggression-related traits. In this review, we consider genetic determinants of human aggression, with special emphasis on genes involved in serotonin and dopamine metabolism and function.

Psychiatric (axis I) and personality (axis II) disorders in patients with burning mouth syndrome or atypical facial pain

Background and aims

Burning mouth syndrome (BMS) and atypical facial pain (AFP) are often persistent idiopathic pain conditions that mainly affect middle-aged and elderly women. They have both been associated with various psychiatric disorders. This study examined current and lifetime prevalence of psychiatric axis I (symptom-based) and II (personality) disorders in patients with chronic idiopathic orofacial pain, and investigated the temporal relationship of psychiatric disorders and the onset of orofacial pain.

Method

Forty patients with BMS and 23 patients with AFP were recruited from Turku university hospital clinics. Mean age of the patients was 62.3 years (range 35–84) and 90% were female. BMS and AFP diagnoses were based on thorough clinical evaluation, and all patients had undergone clinical neurophysiological investigations including blink reflex and thermal quantitative tests. Current and lifetime DSM-IV diagnoses of axis I and II disorders were made on clinical basis with the aid of SCID-I and II-interviews. The detected prevalence rates and their 95% confidence intervals based on binomial distribution were compared to three previous large population-based studies.

Results

Of the 63 patients, 26 (41.3%) had had an axis I disorder that preceded the onset of orofacial pain, and 33 (52.4%) had had a lifetime axis I disorder. Rate of current axis I disorders was 36.5%, indicating that only about 16% of lifetime disorders had remitted, and they tended to run chronic course. The most common lifetime axis I disorders were major depression (30.2%), social phobia (15.9%), specific phobia (11.1%), and panic disorder (7.9%). Twelve patients (19.0%) had at least one cluster C personality disorder already before the emergence of orofacial pain. Patients with cluster C personality disorders are characterized as fearful and neurotic. None of the patients had cluster A (characterized as odd and eccentric) or B (characterized as dramatic, emotional or erratic) personality disorders. The most common personality disorders were obsessive–compulsive personality (14.3%), dependent personality (4.8%), and avoidant personality (3.2%). The majority of the patients (54%) had also one or more chronic pain conditions other than orofacial pain. In almost all patients (94%) they were already present at the onset of orofacial pain.

Conclusions

Our results suggest that major depression, persistent social phobia, and neurotic, fearful, and obsessive–compulsive personality characteristics are common in patients with chronic idiopathic orofacial pain. Most psychiatric disorders precede the onset of orofacial pain and they tend to run a chronic course.

Implications

We propose that the high psychiatric morbidity, and comorbidity to other chronic pain conditions, in chronic idiopathic orofacial pain can be best understood in terms of shared vulnerability to both chronic pain and specific psychiatric disorders, most likely mediated by dysfunctional brain dopamine activity.

Molecular modulation of prefrontal cortex: rational development of treatments for psychiatric disorders

Dysfunction of the prefrontal cortex (PFC) is a central feature of many psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), posttraumatic stress disorder (PTSD), schizophrenia, and bipolar disorder. Thus, understanding molecular influences on PFC function through basic research in animals is essential to rational drug development. In this review, we discuss the molecular signaling events initiated by norepinephrine and dopamine that strengthen working memory function mediated by the dorsolateral PFC under optimal conditions, and weaken working memory function during uncontrollable stress. We also discuss how these intracellular mechanisms can be compromised in psychiatric disorders, and how novel treatments based on these findings may restore a molecular environment conducive to PFC regulation of behavior, thought and emotion. Examples of successful translation from animals to humans include guanfacine for the treatment of ADHD and related PFC disorders, and prazosin for the treatment of PTSD.

Neurobiological and psychopathological variables related to emotional instability: a study of their capability to discriminate patients with bulimia nervosa from healthy controls

OBJECTIVE

To analyze the capability of a set of neurobiological and psychopathological variables to discriminate bulimia nervosa (BN) patients from healthy controls.

METHOD

Seventy-five female patients with purging BN and 30 healthy controls were compared for psychopathology (impulsivity, borderline personality traits, depressive symptoms and self-defeating personality traits) and neurobiological parameters reflecting hypothalamic-pituitary-adrenal axis activity (morning serum cortisol before and after dexamethasone) and monoamine activity (24-hour urinary excretion of norepinephrine, serotonin, dopamine, and their main metabolites: 3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid, and homovanillic acid). Furthermore, the relationships between the 2 sets of variables were compared in the 2 samples.

RESULTS

BN patients displayed higher impulsivity, more severe depressive features, and more borderline and self-defeating personality traits than controls. The 4 psychopathological variables were strongly interrelated in patients, whereas only depressive features correlated with self-defeating personality traits in controls. Patients had lower 24-hour excretion of serotonin and dopamine than controls, as well as lower ability to suppress cortisol. The relations between the biochemical and the psychopathological variables were only significant in the BN patients, but not in the control group. When discriminant analysis methods were applied, patients and controls differed for psychopathology (impulsive behaviors and borderline personality traits) and biological parameters (baseline cortisol and dopamine excretion), but when the variables were analyzed together, the differences in neurobiological parameters appeared as mediated by the psychopathological status.

DISCUSSION

Our results suggest that hypothalamic-pituitary-adrenal axis activity, dopamine activity and other biological parameters are worthy of further study as potential dimensional markers of BN, although they seem to depend on the psychopathological status of the patients, in such a way that the psychopathological items associated with emotional instability (impulsivity and borderline personality traits) seem to be more reliable as clinical markers at the time being.

Catecholamine influences on prefrontal cortical function: relevance to treatment of attention deficit/hyperactivity disorder and related disorders

The primary symptoms of attention deficit/hyperactivity disorder (ADHD) include poor impulse control and impaired regulation of attention. Research has shown that the prefrontal cortex (PFC) is essential for the "top-down" regulation of attention, behavior, and emotion, and that this brain region is underactive in many patients with ADHD. The PFC is known to be especially sensitive to its neurochemical environment; relatively small changes in the levels of norepinephrine and dopamine can produce significant changes in its function. Therefore, alterations in the pathways mediating catecholamine transmission can impair PFC function, while medications that optimize catecholamine actions can improve PFC regulation of attention, behavior, and emotion. This article reviews studies in animals showing that norepinephrine and dopamine enhance PFC function through actions at postsynaptic α(2A)-adrenoceptors and dopamine D1-receptors, respectively. Stimulant medications and atomoxetine appear to enhance PFC function through increasing endogenous adrenergic and dopaminergic stimulation of α(2A)-receptors and D1-receptors. In contrast, guanfacine mimics the enhancing effects of norepinephrine at postsynaptic α(2A)-receptors in the PFC, strengthening network connectivity. Stronger PFC regulation of attention, behavior, and emotion likely contributes to the therapeutic effects of these medications for the treatment of ADHD.

Epigenetics in Developmental Disorder: ADHD and Endophenotypes

Heterogeneity in attention-deficit/hyperactivity disorder (ADHD), with complex interactive operations of genetic and environmental factors, is expressed in a variety of disorder manifestations: severity, co-morbidities of symptoms, and the effects of genes on phenotypes. Neurodevelopmental influences of genomic imprinting have set the stage for the structural-physiological variations that modulate the cognitive, affective, and pathophysiological domains of ADHD. The relative contributions of genetic and environmental factors provide rapidly proliferating insights into the developmental trajectory of the condition, both structurally and functionally. Parent-of-origin effects seem to support the notion that genetic risks for disease process debut often interact with the social environment, i.e., the parental environment in infants and young children. The notion of endophenotypes, markers of an underlying liability to the disorder, may facilitate detection of genetic risks relative to a complex clinical disorder. Simple genetic association has proven insufficient to explain the spectrum of ADHD. At a primary level of analysis, the consideration of epigenetic regulation of brain signalling mechanisms, dopamine, serotonin, and noradrenaline is examined. Neurotrophic factors that participate in the neurogenesis, survival, and functional maintenance of brain systems, are involved in neuroplasticity alterations underlying brain disorders, and are implicated in the genetic predisposition to ADHD, but not obviously, nor in a simple or straightforward fashion. In the context of intervention, genetic linkage studies of ADHD pharmacological intervention have demonstrated that associations have fitted the "drug response phenotype," rather than the disorder diagnosis. Despite conflicting evidence for the existence, or not, of genetic associations between disorder diagnosis and genes regulating the structure and function of neurotransmitters and brain-derived neurotrophic factor (BDNF), associations between symptoms-profiles endophenotypes and single nucleotide polymorphisms appear reassuring.

Differentiating frontostriatal and fronto-cerebellar circuits in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) has long been conceptualized as a neurobiological disorder of the prefrontal cortex and its connections. Circuits with the prefrontal cortex relevant to ADHD include dorsal frontostriatal, orbitofronto-striatal, and fronto-cerebellar circuits. Dorsal frontostriatal circuitry has been linked to cognitive control, whereas orbitofronto-striatal loops have been related to reward processing. Fronto-cerebellar circuits have been implicated in timing. Neurobiological dysfunction in any of these circuits could lead to symptoms of ADHD, as behavioral control could be disturbed by: 1) deficits in the prefrontal cortex itself; or 2) problems in the circuits relaying information to the prefrontal cortex, leading to reduced signaling for control. This article suggests a model for differentiating between interlinked reciprocal circuits with the prefrontal cortex in ADHD. If such a differentiation can be achieved, it might permit a neurobiological subtyping of ADHD, perhaps by defining "dorsal fronto-striatal," "orbitofronto-striatal," or "fronto-cerebellar" subtypes of ADHD. This could be useful as a template for investigating the neurobiology of ADHD and, ultimately, clinically.

The molecular genetics of executive function: role of monoamine system genes

Executive control processes, such as sustained attention, response inhibition, and error monitoring, allow humans to guide behavior in appropriate, flexible, and adaptive ways. The consequences of executive dysfunction for humans can be dramatic, as exemplified by the large range of both neurologic and neuropsychiatric disorders in which such deficits negatively affect outcome and quality of life. Much evidence suggests that many clinical disorders marked by executive deficits are highly heritable and that individual differences in quantitative measures of executive function are strongly driven by genetic differences. Accordingly, intense research effort has recently been directed toward mapping the genetic architecture of executive control processes in both clinical (e.g., attention-deficit/hyperactivity disorder) and nonclinical populations. Here we review the extant literature on the molecular genetic correlates of three exemplar but dissociable executive functions: sustained attention, response inhibition, and error processing. Our review focuses on monoaminergic gene variants given the strong body of evidence from cognitive neuroscience and pharmacology implicating dopamine, noradrenaline, and serotonin as neuromodulators of executive function. Associations between DNA variants of the dopamine beta hydroxylase gene and measures of sustained attention accord well with cognitive-neuroanatomical models of sustained attention. Equally, functional variants of the dopamine D2 receptor gene are reliably associated with performance monitoring, error processing, and reinforcement learning. Emerging evidence suggests that variants of the dopamine transporter gene (DAT1) and dopamine D4 receptor gene (DRD4) show promise for explaining significant variance in individual differences in both behavioral and neural measures of inhibitory control.

Catecholamine influences on dorsolateral prefrontal cortical networks

The symptoms of attention-deficit/hyperactivity disorder (ADHD) involve impairments in prefrontal cortical top-down regulation of attention and behavior. All current pharmacological treatments for ADHD facilitate catecholamine transmission, and basic research suggests that these compounds have prominent actions in the prefrontal cortex (PFC). The dorsolateral PFC is especially sensitive to levels of norepinephrine and dopamine, whereby either too little or too much markedly impairs PFC function. Recent physiological studies have shown that norepinephrine strengthens PFC network connectivity and maintains persistent firing during a working memory task through stimulation of postsynaptic α(2A)-adrenoceptors on PFC neurons. Conversely, dopamine acts at D1 receptors to narrow spatial tuning, sculpting network inputs to decrease noise (i.e., stabilization of the representation). The stimulant medications and atomoxetine appear to enhance PFC function by indirectly increasing these catecholamine actions through blockade of norepinephrine and/or dopamine transporters. In contrast, guanfacine mimics the enhancing effects of norepinephrine at postsynaptic α(2A)-receptors in the PFC, strengthening network connectivity. Stronger PFC regulation of attention, behavior, and emotion likely contributes to the therapeutic effects of these medications for the treatment of ADHD.

Personality traits of aggression-submissiveness and perfectionism associate with ABO blood groups through catecholamine activities

Personality trait research has shown associations with many genes, prominently those of the catecholamine metabolism such as dopamine beta hydroxylase (DBH), catechol-O-methyltransferase (COMT), and monoamine oxidase A (MAOA). Because DBH gene is in linkage disequilibrium with ABO gene, there is reason to think that other catecholamine genes using the same substrate as DBH may also have associations with ABO blood groups, and this paper demonstrates how this may be so. Reasons include similarities in hapmap population frequency distributions, similarities in illness risks between ABO blood groups and DBH activities as well as between ABO blood groups and COMT activities and between ABO blood groups and MAOA activities. If ABO blood groups can be demonstrated to associate with all these catecholamine genes, then the catecholamine personality trait research can be applied to ABO blood groups and tested for confirmation. ABO blood typing is widely available and affords ability to test this hypothesis and thus confirm the possible joint association of personality traits of aggression-submissiveness and perfectionism to catecholamine genes and to ABO blood groups. Clinical applications and implications are discussed.

Personality Measurement and Assessment in Large Panel Surveys*

Personality tests are being added to large panel studies with increasing regularity, such as the Health and Retirement Study (HRS). To facilitate the inclusion and interpretation of these tests, we provide some general background on personality psychology, personality assessment, and the validity of personality tests. In this review, we provide background on definitions of personality, the strengths and weaknesses of the self-report approaches to personality testing typically used in large panel studies, and the validity of personality tests for three outcomes: genetics, income, and health. We conclude with recommendations on how to improve personality assessment in future panel studies.

Role of gene-gene/gene-environment interaction in the etiology of eastern Indian ADHD probands

Associations between attention deficit hyperactivity disorder (ADHD) and genetic polymorphisms in the dopamine receptors, transporter and metabolizing enzymes have been reported in different ethnic groups. Gene variants may affect disease outcome by acting synergistically or antagonistically and thus their combined effect becomes an important aspect to study in the disease etiology. In the present investigation, interaction between ten functional polymorphisms in DRD4, DAT1, MAOA, COMT, and DBH genes were explored in the Indo-Caucasoid population. ADHD cases were recruited based on DSM-IV criteria. Peripheral blood samples were collected from ADHD probands (N=126), their parents (N=233) and controls (N=96) after obtaining informed written consent for participation. Genomic DNA was subjected to PCR based analysis of single nucleotide polymorphisms and variable number of tandem repeats (VNTRs). Data obtained was examined for population as well as family-based association analyses. While case-control analysis revealed higher occurrence of DAT1 intron 8 VNTR 5R allele (P=0.02) in cases, significant preferential transmission of the 7R-T (DRD4 exon3 VNTR-rs1800955) and 3R-T (MAOA-u VNTR-rs6323) haplotypes were noticed from parents to probands (P=0.02 and 0.002 respectively). Gene-gene interaction analysis revealed significant additive effect of DBH rs1108580 and DRD4 rs1800955 with significant main effects of DRD4 exon3 VNTR, DAT1 3'UTR and intron 8 VNTR, MAOA u-VNTR, rs6323, COMT rs4680, rs362204, DBH rs1611115 and rs1108580 thereby pointing towards a strong association of these markers with ADHD. Correlation between gene variants, high ADHD score and low DBH enzymatic activity was also noticed, especially in male probands. From these observations, an impact of the studied sites on the disease etiology could be speculated in this ethnic group.

Epistatic interaction of CREB1 and KCNJ6 on rumination and negative emotionality

G protein-activated K+ channel 2 (GIRK2) and cAMP-response element binding protein (CREB1) are involved in synaptic plasticity and their genes have been implicated depression and memory processing. Excessive rumination is a core cognitive feature of depression which is also present in remission. High scores on the Ruminative Response Scale (RRS) questionnaire are predictive of relapse and recurrence. Since rumination involves memory, we tested the hypothesis that variation in the genes encoding GIRK2 (KCNJ6) and CREB1 mechanisms would influence RRS scores. GIRK2 and CREB1 polymorphisms were studied in two independent samples (n=651 and n=1174) from the general population. Strongly significant interaction between the TT genotype of rs2070995 (located in KCNJ6) and the GG genotype of rs2253206 (located in CREB1) on RRS were found in both samples. These results were validated in an independent third sample (n=565; individuals with personality disorders) showing significant main effect of the variants mentioned as well as significant interaction on a categorical diagnosis of Cluster C personality disorder (obsessional-compulsive, avoidant and dependent) in which rumination is a prominent feature. Our results suggest that genetic epistasis in post-receptor signaling pathways in memory systems may have relevance for depression and its treatment.

The use of &#x03B1;-2A adrenergic agonists for the treatment of attention-deficit/hyperactivity disorder

Neuropsychiatric disorders involve dysfunction of the prefrontal cortex (PFC), a highly evolved brain region that mediates executive functioning. The dorsolateral PFC is specialized for regulating attention and behavior, while the ventromedial PFC is specialized for regulating emotion. These abilities arise from PFC pyramidal cell networks that excite each other to maintain goals and rules 'in mind'. Imaging studies have shown reduced PFC gray matter, weaker PFC connections and altered PFC function in patients with attention-deficit/hyperactivity disorder. Thus, medications that strengthen PFC network connections may be particularly useful for the treatment of attention-deficit/hyperactivity disorder and related disorders. Recent data show that compounds such as guanfacine can enhance PFC function by stimulating postsynaptic α-2A receptors on the dendritic spines of PFC pyramidal cells where networks interconnect. Stimulation of these receptors inhibits cAMP signaling, thus closing potassium channels and strengthening physiological connections. These actions may benefit patients with weak PFC function.

Methylphenidate and atomoxetine enhance prefrontal function through α2-adrenergic and dopamine D1 receptors

OBJECTIVE

This study examined the effects of the attention-deficit/hyperactivity disorder treatments, methylphenidate (MPH) and atomoxetine (ATM), on prefrontal cortex (PFC) function in monkeys and explored the receptor mechanisms underlying enhancement of PFC function at the behavioral and cellular levels.

METHOD

Monkeys performed a working memory task after administration of a wide range of MPH or ATM doses. The optimal doses were challenged with the α(2)-adrenoceptor antagonist, idazoxan, or the D(1) dopamine receptor antagonist, SCH23390 (SCH). In a parallel physiology study, neurons were recorded from the dorsolateral PFC of a monkey performing a working memory task. ATM, SCH, or the α(2) antagonist, yohimbine, were applied to the neurons by iontophoresis.

RESULTS

MPH and ATM generally produced inverted-U dose-response curves, with improvement occurring at moderate doses, but not at higher doses. The beneficial effects of these drugs were blocked by idazoxan or SCH. At the cellular level, ATM produced an inverted-U dose-response effect on memory-related firing, enhancing firing for preferred directions (increasing "signals") and decreasing firing for the nonpreferred directions (decreasing "noise"). The increase in persistent firing for the preferred direction was blocked by yohimbine, whereas the suppression of firing for the nonpreferred directions was blocked by SCH.

CONCLUSIONS

Optimal doses of MPH or ATM improved PFC cognitive function in monkeys. These enhancing effects appeared to involve indirect stimulation of α(2) adrenoceptors and D(1) dopamine receptors in the PFC. These receptor actions likely contribute to their therapeutic effects in the treatment of attention-deficit/hyperactivity disorder.

Lack of association between genetic polymorphisms affecting sympathetic activity and tilt-induced vasovagal syncope

Although the pathophysiology of vasovagal syncope is not completely understood, the involvement of sympathetic nervous system alterations has been suggested. Since predisposition to fainting during orthostatic challenge may be associated with genetic variations, we sought to explore the role of genetic polymorphisms affecting sympathetic nervous system function in the susceptibility to tilt-induced vasovagal syncope. We genotyped 129 subjects with recurrent unexplained syncope who underwent tilt testing, and investigated the recurrence of syncope. The analysed polymorphisms were Arg492Cys (ADRA1A gene), Ser49Gly and Arg389Gly (ADRB1), Arg16Gly and Gln27Glu (ADRB2), 825C/T (GNB3), -1021C/T (DBH) and S/L (SLC6A4). No association of the aforementioned genetic variants with both tilt test outcomes and new syncopal episodes during follow-up was found. None of the considered polymorphisms influencing sympathetic activity is a major risk factor for vasovagal syncope in Italian patients.

Aggressive behavior, related conduct problems, and variation in genes affecting dopamine turnover

A number of dopamine-related genes have been implicated in the etiology of violent behavior and conduct problems. Of these genes, the ones that code for the enzymes that influence the turnover of dopamine (DA) have received the most attention. In this study, we investigated 12 genetic polymorphisms in four genes involved with DA functioning (COMT, MAOA and MAOB, and DbetaH) in 179 incarcerated male Russian adolescents and two groups of matched controls: boys without criminal records referred to by their teachers as (a) "troubled-behavior-free" boys, n=182; and (b) "troubled-behavior" boys, n=60. The participants were classified as (1) being incarcerated or not, (2) having the DSM-IV diagnosis of conduct disorder (CD) or not, and (3) having committed violent or nonviolent crimes (for the incarcerated individuals only). The findings indicate that, although no single genetic variant in any of the four genes differentiated individuals in the investigated groups, various linear combinations (i.e., haplotypes) and nonlinear combinations (i.e., interactions between variants within and across genes) of genetic variants resulted in informative and robust classifications for two of the three groupings. These combinations of genetic variants differentiated individuals in incarceration vs. nonincarcerated and CD vs. no-CD groups; no informative combinations were established consistently for the grouping by crime within the incarcerated individuals. This study underscores the importance of considering multiple rather than single markers within candidate genes and their additive and interactive combinations, both with themselves and with nongenetic indicators, while attempting to understand the genetic background of such complex behaviors as serious conduct problems.

Study on DBH genetic polymorphisms and plasma activity in attention deficit hyperactivity disorder patients from Eastern India

Dysfunctions in the norepinephric pathway have been speculated in the etiology of attention deficit hyperactivity disorder (ADHD), a common problem for children. Synthesis of norepinephrine from dopamine is catalyzed by the enzyme dopamine beta-hydroxylase and numerous polymorphisms in the DBH gene have been found to exert their direct influence on the enzyme activity independently. In the present study association of ADHD with four genetic polymorphisms, DBH-STR, rs1611115, rs1108580, and rs2519152, was examined in subjects belonging to eastern India. ADHD subjects (n = 111) were recruited following DSM-IV criteria. Peripheral blood samples were collected from nuclear families with ADHD probands. A group of ethnically matched healthy volunteers (n = 130) was also recruited. Genomic DNA was analyzed by PCR amplification followed by restriction digestion and genotyping. Data obtained were subjected to both family-based as well as population-based statistical analyses. Plasma DbetaH activity was measured using a photometric assay and its correlation with the genetic polymorphisms was analyzed using analysis of variance. Case-control analysis revealed no significant differences in allelic frequencies; however, significant paternal over-transmission (P = 0.02) of the rs2519152 'G' allele to ADHD probands was noticed. A haplotype, composed of 12R-C-G-G, also showed biased transmission. Strong correlation was observed between enzyme activity and rs1611115, rs1108580, and rs2519152 (P = 1.51E-6, 0.04, and 0.003, respectively). The present study hints toward the fact that DBH gene polymorphisms have some role in the etiology of ADHD in eastern Indian population and their study could be useful for therapeutic intervention.

Behavioral genetics in antisocial spectrum disorders and psychopathy: a review of the recent literature

Behavioral geneticists are increasingly using the tools of molecular genetics to extend upon discoveries from twin, family, and adoption studies concerning the heritability of antisocial spectrum disorders and psychopathy. While there is a substantial body of research concerning antisocial spectrum disorders in the behavioral genetics literature, only a few studies could be located using the phenotype of psychopathy. In this report we summarize some of the recent molecular genetics work concerning antisocial spectrum disorders and psychopathy, with a focus on genes involved in the serotonergic and dopaminergic pathways, while also mentioning some of the novel genetic factors being considered. Monoamine oxidase (MAOA) and the serotonin transporter (5HTT) are reviewed at length, as these genes have received significant scientific attention in recent years and are sites of high biological plausibility in antisocial spectrum disorders and psychopathy.

Molecular genetics of attention-deficit/hyperactivity disorder: an overview

As heritability is high in attention-deficit/hyperactivity disorder (ADHD), genetic factors must play a significant role in the development and course of this disorder. In recent years a large number of studies on different candidate genes for ADHD have been published, most have focused on genes involved in the dopaminergic neurotransmission system, such as DRD4, DRD5, DAT1/SLC6A3, DBH, DDC. Genes associated with the noradrenergic (such as NET1/SLC6A2, ADRA2A, ADRA2C) and serotonergic systems (such as 5-HTT/SLC6A4, HTR1B, HTR2A, TPH2) have also received considerable interest. Additional candidate genes related to neurotransmission and neuronal plasticity that have been studied less intensively include SNAP25, CHRNA4, NMDA, BDNF, NGF, NTF3, NTF4/5, GDNF. This review article provides an overview of these candidate gene studies, and summarizes findings from recently published genome-wide association studies (GWAS). GWAS is a relatively new tool that enables the identification of new ADHD genes in a hypothesis-free manner. Although these latter studies could be improved and need to be replicated they are starting to implicate processes like neuronal migration and cell adhesion and cell division as potentially important in the aetiology of ADHD and have suggested several new directions for future ADHD genetics studies.

The neuropsychopharmacology of fronto-executive function: monoaminergic modulation

We review the modulatory effects of the catecholamine neurotransmitters noradrenaline and dopamine on prefrontal cortical function. The effects of pharmacologic manipulations of these systems, sometimes in comparison with the indoleamine serotonin (5-HT), on performance on a variety of tasks that tap working memory, attentional-set formation and shifting, reversal learning, and response inhibition are compared in rodents, nonhuman primates, and humans using, in a behavioral context, several techniques ranging from microiontophoresis and single-cell electrophysiological recording to pharmacologic functional magnetic resonance imaging. Dissociable effects of drugs and neurotoxins affecting these monoamine systems suggest new ways of conceptualizing state-dependent fronto-executive functions, with implications for understanding the molecular genetic basis of mental illness and its treatment.