The serotonin transporter, encoded by the SLC6A4 gene, influences the synaptic actions of serotonin and is responsive to stress hormones. We hypothesized that 5-HTTLPR, a functional SLC6A4 promoter polymorphism, and two tightly-linked, putatively functional 3' UTR SNPs (rs3813034, rs1042173) might have independent effects on suicidal behavior in the context of childhood trauma (CT).
DNA and Childhood Trauma Questionnaire scores were available for a total of 474 African Americans, including 112 suicide attempters and 362 non-suicide attempters. Genotyping was performed for the triallelic 5-HTTLPR polymorphism, 14 SLC6A4 haplotype-tagging SNPs, and 186 ancestry informative markers.
There were independent G × E interactive effects of 5-HTTLPR (p=0.017) and the rs3813034-rs1042173 diplotype (p=0.011) on suicidal behavior. In individuals exposed to high CT the risk of suicide attempt was 0.52 in carriers of the low activity 5-HTTLPR variant and 0.32 in medium/high activity variant carriers. Likewise, CT exposed carriers of the major rs3813034-rs1042173 ATAT diplotype had an increased risk of suicidal behavior relative to the ATCG/CGCG diplotype carriers (0.40 vs 0.31). Neither the 5' nor the 3' functional variants had an effect in individuals without CT: suicide attempt risk = 0.12 – 0.22. In individuals exposed to high CT the prevalence of suicide attempt was 0.56 in carriers of both 5' and 3' risk variants, 0.39 in carriers of one risk variant and 0.25 in individuals without either risk variant.
Our findings suggest that the 5' and 3' SLC6A4 functional variants have independent effects on the risk for suicidal behavior in CT exposed individuals.
SLC6A4; 5-HTTLPR; substance dependence; rs3813034; rs1042173; suicide attempt
Background. The primary objective of this study was to compare management practices of general emergency physicians (GEMPs) and pediatric emergency medicine physicians (PEMPs) for well-appearing young febrile children.
Methods. We retrospectively reviewed the charts of well-appearing febrile children aged 3–36 months who presented to a large urban children's hospital (PED), staffed by PEMPs, or a large urban general emergency department (GED), staffed by GEMPs. Demographics, immunization status, laboratory tests ordered, antibiotic usage, and final diagnoses were collected. Results. 224 cases from the PED and 237 cases from the GED were reviewed. Children seen by PEMPs had significantly less CXRs (23 (10.3%) versus 51 (21.5%), P = 0.001) and more rapid viral testing done (102 (45%) versus 40 (17%), P < 0.0001). A diagnosis of a viral infection was more common in the PED, while a diagnosis of bacterial infection (including otitis media) was more common in the GED. More GED patients were prescribed antibiotics (41% versus 27%, P = 0.002), while more PED patients were treated with oseltamivir (6.7% versus 0.4%, P < 0.001). Conclusions. Our findings identify important differences in the care of the young, well-appearing febrile child by PEMPs and GEMPs and highlight the need for standardization of care.
Interactions between the central serotonergic and γ-aminobutyric acid (GABA) systems play key roles in the prefrontal cortical regulation of emotion and cognition and in the pathophysiology and pharmacotherapy of highly prevalent psychiatric disorders. The goal of this study was to test the effects of common variants of the tryptophan hydroxylase isoform 2 (TPH2) gene on GABA concentration in the prefrontal cortex (PFC) using magnetic resonance spectroscopy. In this study involving 64 individuals, we examined the associations between prefrontal cortical GABA concentration and 12 single nucleotide polymorphisms (SNPs) spanning the TPH2 gene, including rs4570625 (–703 G/T SNP), a potentially functional TPH2 polymorphism that has been associated with decreased TPH2 mRNA expression and panic disorder. Our results revealed a significant association between increased GABA concentration in the PFC and the T-allele frequencies of 2 TPH2 SNPs, namely, rs4570625 (of –703 G/T) and rs2129575 (p ≤ 0.0004) and the C-allele frequency of 1 TPH2 SNP, namely, rs1386491 (p = 0.0003) in female subjects. We concluded that rs4570625 (–703 G/T), rs2129575, and rs1386491 play a significant role in GABAergic neurotransmission and may contribute to the sex-specific dysfunction of the GABAergic system in the PFC.
GABA; tryptophan hydroxylase 2; magnetic resonance spectroscopy; single nucleotide polymorphisms; genetics
Brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of psychiatric and neurological disorders and in the mechanisms of antidepressant pharmacotherapy. Psychiatric and neurological conditions have also been associated with reduced brain levels of N-acetyl-aspartate (NAA), which has been used as a putative marker of neural integrity. However, few studies have explored the relationship between BDNF polymorphisms and NAA levels directly. Here, we present data from a single-voxel proton magnetic resonance spectroscopy study of 64 individuals and explore the relationship between BDNF polymorphisms and prefrontal NAA level. Our results indicate an association between a single nucleotide polymorphism (SNP) within BDNF, known as rs1519480, and reduced NAA level (p=0.023). NAA levels were further predicted by age and Asian ancestry. There was a significant interaction between rs1519480 and age on NAA level (p=0.031) Specifically, the effect of rs1519480 on NAA level became significant at age ≥ 34.17. NAA level decreased with advancing age for genotype TT (p=0.001) but not for genotype CT (p=0.82) or CC (p=0.34). Additional in silico analysis of 142 postmortem brain samples revealed an association between the same SNP and reduced BDNF mRNA expression in the prefrontal cortex. The rs1519480 SNP influences BDNF mRNA expression and has an impact on prefrontal NAA level over time. This genetic mechanism may contribute to interindividual variation in cognitive performance seen during normal aging, as well as contributing to the risk for developing psychiatric and neurological conditions.
BDNF; N-acetyl-aspartate; proton magnetic resonance spectroscopy; SNP; genetic variation
Impulsivity, defined as the tendency to act without foresight, comprises a multitude of constructs and is associated with a variety of psychiatric disorders. Dissecting different aspects of impulsive behaviour and relating these to specific neurobiological circuits would improve our understanding of the etiology of complex behaviours for which impulsivity is key, and advance genetic studies in this behavioural domain. In this review, we will discuss the heritability of some impulsivity constructs and their possible use as endophenotypes (heritable, disease-associated intermediate phenotypes). Several functional genetic variants associated with impulsive behaviour have been identified by the candidate gene approach and re-sequencing, and whole genome strategies can be implemented for discovery of novel rare and common alleles influencing impulsivity. Via deep sequencing an uncommon HTR2B stop codon, common in one population, was discovered, with implications for understanding impulsive behaviour in both humans and rodents and for future gene discovery.
impulsivity; heritability; genes; sequencing; HTR2B
The A1 allele of the DRD2/ANKK1 Taq1A polymorphism (rs1800497) is associated with reduced striatal D2/3 receptor binding in healthy individuals (Con) as well as depression and addiction. However, the effect of rs1800497 on D2/3 receptor binding in depressed patients as well as the SNP’s effect on D2/3 binding during reward-associated dopamine release is unknown. Twelve unmedicated patients with major depressive disorder (MDD) and 24 Con completed PET scans with [11C]raclopride, once without receiving monetary rewards (baseline) and once while winning money. In Con, the A1 allele was associated with reduced baseline binding potential (BPND) in the middle caudate and ventral striatum. However, in MDD patients the A1 allele was associated with increased baseline BPND in these regions. There were no significant associations between rs1800497 and change in BPND during reward-associated dopamine release. Conceivably, the A1 allele predisposes to depression and addiction via its effect on the post-synaptic D2 receptor.
Depression; dopamine 2 receptor; positron emission tomography; reward; Taq1A
Brain-derived neurotrophic factor (BDNF) promotes survival and synaptic plasticity in the human brain. The Val66Met polymorphism of the BDNF gene interferes with intracellular trafficking, packaging, and regulated secretion of this neurotrophin. The human prefrontal cortex (PFC) shows lifelong neuroplastic adaption implicating the Val66Met BDNF polymorphism in the recovery of higher-order executive functions after traumatic brain injury (TBI). In this study, we examined the effect of this BDNF polymorphism on the preservation of general intelligence following TBI. We genotyped a sample of male Vietnam combat veterans (n = 156) consisting of a frontal lobe lesion group with focal penetrating head injuries for the Val66Met BDNF polymorphism. Val/Met did not differ from Val/Val genotypes in general cognitive ability before TBI. However, we found substantial average differences between these groups in general intelligence (≈ half a standard deviation or 8 IQ points), verbal comprehension (6 IQ points), perceptual organization (6 IQ points), working memory (8 IQ points), and processing speed (8 IQ points) after TBI. These results support the conclusion that Val/Met genotypes preserve general cognitive functioning, whereas Val/Val genotypes are largely susceptible to TBI.
Minimal research links anxiety disorders in adolescents to regional gray matter volume (GMV) abnormalities and their modulation by genetic factors. Prior research suggests that a brain-derived neurotrophic factor (BNDF) Val66Met polymorphism may modulate such brain morphometry profiles.
Using voxel-based morphometry and magnetic resonance imaging, associations of BDNF and clinical anxiety with regional GMVs of anterior cingulate cortex, insula, amygdala, and hippocampus were examined in 39 affected (17 Met allele carriers, 22 Val/Val homozygotes) and 63 nonaffected adolescents (27 Met allele carriers, 36 Val/Val homozygotes).
Amygdala and anterior hippocampal GMVs were significantly smaller in patients than healthy adolescents, with a reverse pattern for the insula. Post-hoc regression analyses indicated a specific contribution of social phobia to the GMV reductions in the amygdala and hippocampus. Additionally, insula and dorsal– anterior cingulate cortex (ACC) GMVs were modulated by BDNF genotype. In both regions, GMVs were larger in the Val/Val homozygote patients than in those carrying the Met allele.
These results implicate reduced GMV in the amygdala and hippocampus in pediatric anxiety, particularly social phobia. In addition, the data suggest that genetic factors may modulate differences in the insula and dorsal ACC.
BDNF; VBM; adolescence; anxiety; insula
Schizophrenia and bipolar disorder are major psychiatric disorders with high heritability and overlapping genetic variance. Here we perform a genome-wide association study in an ethnically homogeneous cohort of 904 schizophrenia cases and 1,640 controls drawn from the Ashkenazi Jewish population. We identify a novel genome-wide significant risk locus at chromosome 4q26, demonstrating the potential advantages of this founder population for gene discovery. The top single-nucleotide polymorphism (SNP; rs11098403) demonstrates consistent effects across 11 replication and extension cohorts, totalling 23, 191 samples across multiple ethnicities, regardless of diagnosis (schizophrenia or bipolar disorder), resulting in Pmeta=9.49 × 10−12 (odds ratio (OR)=1.13, 95% confidence interval (CI): 1.08–1.17) across both disorders and Pmeta=2.67 × 10−8 (OR=1.15, 95% CI: 1.08–1.21) for schizophrenia alone. In addition, this intergenic SNP significantly predicts postmortem cerebellar gene expression of NDST3, which encodes an enzyme critical to heparan sulphate metabolism. Heparan sulphate binding is critical to neurite outgrowth, axon formation and synaptic processes thought to be aberrant in these disorders.
Schizophrenia and bipolar disorder are important psychiatric disorders with overlapping genetic components. Here, the authors identify and replicate a genome-wide significant risk locus for the two disorders, and suggest a role for NDST3 in severe psychiatric disease.
Despite proven heritability, little is known about the genetic architecture of mood disorders. Although a number of family and case–control studies have examined the genetics of mood disorders, none have carried out joint linkage-association studies and sought to validate the results with gene expression analyses in an independent cohort.
We present findings from a large candidate gene study that combines linkage and association analyses using families and singletons, providing a systematic candidate gene investigation of mood disorder. For this study, 876 individuals were recruited, including 83 families with 313 individuals and 563 singletons. This large-scale candidate gene analysis included 130 candidate genes implicated in addictive and other psychiatric disorders. These data showed significant genetic associations for 28 of these candidate genes, although none remained significant after correction for multiple testing. To evaluate the functional significance of these 28 candidate genes in mood disorders, we examined the transcriptional profiles of these genes within the dorsolateral prefrontal cortex and anterior cingulate for 21 cases with mood disorders and 25 nonpsychiatric controls, and carried out a pathway analysis to identify points of high connectivity suggestive of particular molecular pathways that may be dysregulated.
Two primary gene candidates were supported by the linkage-association, gene expression profiling, and network analysis: neurotrophic tyrosine kinase receptor, type 2 (NTRK2), and the opioid receptor, κ1 (OPRK1).
This study supports a role for NTRK2 and OPRK1 signaling in the pathophysiology of mood disorder. The unique approach incorporating evidence from multiple experimental and computational modalities enhances confidence in these findings.
linkage and association; mood disorders; neurotrophic tyrosine kinase receptor; opioid receptor; type 2; κ1
Oxytocin is a neuropeptide that is associated with increases in social affiliative behaviors, particularly toward infants. However, no previous study has investigated healthy adults’ responses to infant faces following oxytocin administration. In addition, given that preliminary evidence suggests that a single nucleotide polymorphism (SNP) of the oxytocin receptor (OXTR) gene, rs53576, may influence behaviors associated with parental sensitivity, we assessed whether such responses vary according to OXTR rs53576 genotype.
The present study assessed the effects of intranasally administered oxytocin and OXTR genotype on human adults’ preferences for infant faces.
A double-blind, between-groups design was used, with 57 genotyped volunteers randomly assigned to receive intranasally administered oxytocin or placebo. Fifty minutes following the administration of oxytocin or placebo, participants viewed infants’ and adults’ faces showing neutral expressions and assessed how appealing they found each face.
Infants’ faces were more strongly preferred following oxytocin inhalation relative to placebo. When participants were separated according to genotype, this effect was only observed for participants homozygous for the rs53576G allele. Parallel effects were not seen for adults’ faces.
The present results are consistent with the hypothesis that acute oxytocin administration increases sensitivity to reward-relevant features of infants and/or reduces sensitivity to their aversive properties. The results also are consistent with suggestions of more efficient oxytocinergic function in rs53576G homozygotes.
Oxytocin; OXTR; parental; faces; affiliation
This study examined the role of orbitofrontal cortex (OFC) and dorsolateral prefrontal cortex (DLPFC) plasticity in controlling implicit and explicit social biases. Normal controls and patients with varied OFC and DLPFC lesion size and single nucleotide polymorphisms (SNPs) in the brain-derived neurotrophic factor (BDNF) gene, which promotes (methionine–valine [Met/Val] SNP) or stifles (valine–valine [Val/Val] SNP) plasticity in damaged PFC regions, completed measures of implicit and explicit social bias. Patients and controls demonstrated comparable levels of implicit bias, but patients with Met/Val SNPs exhibited less implicit bias when they had smaller OFC lesions compared with Val/Val patients with similar size lesions and those with large OFC lesions. Both patients and controls demonstrated patterns of explicit bias consistent with hypotheses. Patients with Met/Val SNPs exhibited less explicit bias when they had smaller DLPFC lesions sizes compared with Val/Val patients with similar size lesions and those with large DLPFC lesions. OFC lesion size and BDNF SNP type did not moderate explicit bias; DLPFC lesion size and BDNF SNP type did not moderate implicit bias (nor did other medial or lateral regions). Findings suggest that plasticity within specific PFC regions modulates the type and degree of social bias that individuals’ exhibit.
BDNF; implicit and explicit bias; PFC plasticity; social neuroscience; TBI
Depression in bipolar disorder is clinically indistinguishable from that observed in major depressive disorder. As in major depression, selective serotonin reuptake inhibitors targeting brain serotonin transporters are first-line treatments for bipolar depression. Associations of serotonin transporter promoter polymorphisms and bipolarity have been reported; however, research on alterations in serotonergic neurotransmission in bipolar depression remains scant.
To assess in vivo brain serotonin transporter binding potential (BP1, proportional to serotonin transporter number) in patients with bipolar depression and controls and to examine the relationship between serotonin transporter binding and genotype.
A sample of 18 medication-free patients with bipolar depression and 41 controls.
Main Outcome Measures
In vivo brain serotonin transporter binding was measured using positron emission tomography and radiolabeled trans-1,2,3,5,6,10-β-hexahydro-6-[4-(methylthio) phenyl]pyrrolo-[2,1-a]-isoquinoline ([11C](+)-McNeil 5652). Participants were genotyped assessing biallelic and triallelic 5-HTTLPR polymorphisms.
Patients with bipolar disorder had 16% to 26% lower serotonin transporter BP1 in the midbrain, amygdala, hippocampus, thalamus, putamen, and anterior cingulate cortex. Triallelic 5-HTTLPR genotypes were unrelated to serotonin transporter BP1.
Lower serotonin transporter BP1 in bipolar depression overlaps with that observed in major depression and suggests that serotonergic dysfunction is common to depressive conditions.
Does cell age matter in virulence? The emergence of persister cells during chronic infections is critical for persistence of infection, but little is known how this occurs. Here, we demonstrate for the first time that the replicative age of the fungal pathogen Cryptococcus neoformans contributes to persistence during chronic meningoencephalitis. Generationally older C. neoformans cells are more resistant to hydrogen peroxide stress, macrophage intracellular killing, and antifungal agents. Older cells accumulate in both experimental rat infection and in human cryptococcosis. Mathematical modeling supports the concept that the presence of older C. neoformans cells emerges from in vivo selection pressures. We propose that advanced replicative aging is a new unanticipated virulence trait that emerges during chronic fungal infection and facilitates persistence. Therapeutic interventions that target old cells could help in the clearance of chronic infections.
Our findings that the generational age of Cryptococcus neoformans cells matters in pathogenesis introduces a novel concept to eukaryotic pathogenesis research. We propose that emerging properties of aging C. neoformans cells and possibly also other fungal pathogens contribute to persistence and virulence. Whereas the replicative life span of strains may not matter for virulence per se, age-related resilience and thus the generational age of individual C. neoformans cells within a pathogen population could greatly affect persistence of the pathogen population and therefore impact outcome.
Oxytocin, classically involved in social and reproductive activities, is increasingly recognized as an antinociceptive and anxiolytic agent, effects which may be mediated via oxytocin’s interactions with the dopamine system. Thus, genetic variation within the oxytocin gene (OXT) is likely to explain variability in dopamine-related stress responses. As such, we examined how OXT variation is associated with stress-induced dopaminergic neurotransmission in a healthy human sample.
Fifty-five young healthy volunteers were scanned using [11C] raclopride positron emission tomography while they underwent a standardized physical and emotional stressor that consisted of moderate levels of experimental sustained deep muscle pain, and a baseline, control state. Four haplotype tagging single nucleotide polymorphisms located in regions near OXT were genotyped. Measures of pain, affect, anxiety, well-being and interpersonal attachment were also assessed.
Female rs4813625 C allele carriers demonstrated greater stress-induced dopamine release, measured as reductions in receptor availability from baseline to the pain-stress condition relative to female GG homozygotes. No significant differences were detected among males. We also observed that female rs4813625 C allele carriers exhibited higher attachment anxiety, higher trait anxiety and lower emotional well-being scores. In addition, greater stress-induced dopamine release was associated with lower emotional well-being scores in female rs4813625 C allele carriers.
Our results suggest that variability within the oxytocin gene appear to explain interindividual differences in dopaminergic responses to stress, which are shown to be associated with anxiety traits, including those linked to attachment style, as well as emotional well-being in women.
oxytocin; genetics; dopamine; positron emission tomography; humans; sex differences
This study examined tribal members’ perspectives on alcohol, risk factors, consequences, and community responses. Focus groups were conducted with five American Indian tribes between 1997 and 2001. Participants were knowledgeable of the cultural lives of their reservation communities. Although there was agreement regarding the pervasiveness of heavy drinking, participants reported different opinions about the meaning of alcohol and appropriate intervention strategies. Three dilemmas were identified, suggesting that community ambivalence may serve as a barrier to reducing problem drinking. Implications, limitations, and future research directions are discussed. The study was funded by the National Institute on Alcohol Abuse and Alcoholism.
American Indian; alcohol; prevention; qualitative research
Although expression patterns of GABAergic genes in rodent brain have largely been elucidated, no comprehensive studies have been performed in human brain. The purpose of this study was to identify global patterns of GABAergic gene expression in healthy adults, including trans and cis effects in the GABAA gene clusters, before determining the effects of chronic alcohol and cocaine exposure on gene expression in the hippocampus. RNA-Seq data from ‘BrainSpan’ was obtained across 16 brain regions from postmortem samples from nine adults. A factor analysis was performed on global expression of 21 GABAergic pathway genes. Factor specificity for response to chronic alcohol/cocaine exposure was subsequently determined from the analysis of RNA-Seq data from postmortem hippocampus of eight alcoholics, eight cocaine addicts and eight controls. Six gene expression factors were identified. Most genes loaded (≥0.5) onto one factor; six genes loaded onto two. The largest factor (0.30 variance) included the chromosome 5 gene cluster that encodes the most common GABAA receptor, α1β2γ2, and genes encoding the α3β3γ2 receptor. Genes within this factor were largely unresponsive to chronic alcohol/cocaine exposure. In contrast, the chromosome 4 gene cluster factor (0.14 variance) encoding the α2β1γ1 receptor was influenced by chronic alcohol/cocaine exposure. Two other factors (0.17 and 0.06 variance) showed expression changes in alcoholics/cocaine addicts; these factors included genes involved in GABA synthesis and synaptic transport. Finally there were two factors that included genes with exceptionally low (0.10 variance) and high (0.09 variance) expression in the cerebellum; the former factor was unaffected by alcohol/cocaine exposure. This study has shown that there appears to be specificity of GABAergic gene groups, defined by covariation in expression, for response to chronic alcohol/cocaine exposure. These findings might have implications for combating stress-related craving and relapse.
Neural systems that identify and respond to salient stimuli are critical for survival in a complex and changing environment. In addition, interindividual differences, including genetic variation, hormonal, and metabolic status likely influence the behavioral strategies and neuronal responses to environmental challenges. Here we examined the relationship between leptin allelic variation and plasma leptin levels with DAD2/3R availability in vivo as measured with [11C]raclopride Positron Emission Tomography (PET) at baseline and during a standardized pain stress challenge. Allelic variation in the leptin gene was associated with varying levels of DA release in response to the pain stressor, but not with baseline D2/3 receptor availability. Circulating leptin was also positively associated with stress-induced dopamine release. These results show that leptin serves as a regulator of neuronal function in humans and provides an etiological mechanism for differences in dopamine neurotransmission in response to salient stimuli as related to metabolic function. The capacity for leptin to influence stress-induced dopaminergic function is of importance for pathological states where dopamine is thought to play an integral role, such as mood, substance use disorders, eating disorders, and obesity.
Neuropeptide Y (NPY) is involved in stress regulation. Genetic variations predict plasma NPY and neural correlates of emotion and stress. We examined whether the functional NPY haplotype modulates stress-induced NPY and anxiety responses, and if plasma NPY stress responses are associated with substance dependence outcomes.
Thirty-seven treatment-engaged, abstinent substance dependent patients (SD) and 28 controls (HC) characterized on NPY diplotypes (HH: high expression; HLLL: intermediate/low expression) were exposed to stress, alcohol/drug cues and neutral relaxing cues, using individualized guided imagery, in a 3-session laboratory experiment. Plasma NPY, heart rate and anxiety were assessed. Patients were prospectively followed for 90-days post-treatment to assess relapse outcomes.
HH individuals showed significantly lower stress-induced NPY with greater heart rate and anxiety ratings, while the HLLL group showed the reverse pattern of NPY, anxiety and heart rate responses. This differential genetic modulation of NPY stress response was suppressed in the SD group, who showed no stress-related increases in NPY and higher heart rate and greater anxiety, regardless of diplotype. Lower NPY predicted subsequent higher number of days and greater amounts of post-treatment drug use.
These preliminary findings are the first to document chronic drug abuse influences on NPY diplotype expression where NPY diplotype modulation of stress-related plasma NPY, heart rate and anxiety responses was absent in the substance abuse sample. The finding that lower stress-related NPY is predictive of greater relapse severity provides support for therapeutic development of neuropeptide Y targets in the treatment of substance use disorders.
Neuropepetide Y; Functional Haplotype; Stress; Substance Use Disorders
Dopamine (DA) neurotransmission through D2 receptors (DRD2) has been implicated in the regulation of reward processing, cognition and the effects of drugs of abuse, and also has significant effects in responses to stressors and salient aversive stimuli. An examination of the influence of genetic variation across multiple psychophysical measures therefore appears critical to understand the neurobiology of DA-modulated complex personality traits and psychiatric illnesses. To examine interindividual variation in the function of DRD2 modulated mechanisms in healthy humans, we used a haplotype-based and single nucleotide polymorphism (SNP) investigation. Their effects were interrogated with functional magnetic resonance imaging (fMRI) during reward and emotional processing. We found that a haplotype block composed by two SNPs, rs4274224 and rs4581480, affected the hemodynamic responses of the dorsolateral prefrontal cortex (DLPFC) during reward expectation and the subgenual anterior cingulate cortices (sgACC) during implicit emotional processing. Exploratory analysis within the significant haplotype block revealed the same functional effects only for the SNP rs4274224. Further analysis on rs4274224 using functional connectivity and positron emission tomography (PET) measures of DA D2/3 receptor mediated neurotransmission confirmed a gene effect on the functional connectivity of the DLPFC during reward anticipation and subcortical stress induced dopamine release. At a phenotypic trait level, significant effects of genotype were obtained for the NEO PI-R “Openness to Experience” and further correlated with neuroimaging data. Overall, these results show significant neurobiological effects of genotype variation in DRD2 on multiple functional domains, such as emotional, stress and reward processing. As such, it contributes to normal variation and potentially to vulnerability to psychopathology associated with those functions, such as risk for mood and substance use disorders.
imaging; dopamine; DLPFC; reward; emotion
Alcoholism is a significant public health problem. A picture of the genetic architecture underlying alcohol-related phenotypes is emerging from genome-wide association studies and work on genetically tractable model organisms.
Addiction; alcohol sensitivity; disease susceptibility; genome-wide association studies; human genetics; model organisms
Abnormalities of motivation and behavior in the context of reward are a fundamental component of addiction and mood disorders. Here we test the effect of a functional missense mutation in the dopamine 3 receptor (DRD3) gene (ser9gly, rs6280) on reward-associated dopamine (DA) release in the striatum. Twenty-six healthy controls (HCs) and 10 unmedicated subjects with major depressive disorder (MDD) completed two positron emission tomography (PET) scans with [11C]raclopride using the bolus plus constant infusion method. On one occasion subjects completed a sensorimotor task (control condition) and on another occasion subjects completed a gambling task (reward condition). A linear regression analysis controlling for age, sex, diagnosis, and self-reported anhedonia indicated that during receipt of unpredictable monetary reward the glycine allele was associated with a greater reduction in D2/3 receptor binding (i.e., increased reward-related DA release) in the middle (anterior) caudate (p<0.01) and the ventral striatum (p<0.05). The possible functional effect of the ser9gly polymorphism on DA release is consistent with previous work demonstrating that the glycine allele yields D3 autoreceptors that have a higher affinity for DA and display more robust intracellular signaling. Preclinical evidence indicates that chronic stress and aversive stimulation induce activation of the DA system, raising the possibility that the glycine allele, by virtue of its facilitatory effect on striatal DA release, increases susceptibility to hyperdopaminergic responses that have previously been associated with stress, addiction, and psychosis.
Mesoaccumbal and nigrostriatal projections are sensitive to stress, and heightened stress sensitivity is thought to confer risk for neuropsychiatric disorders. Serotonin 2C (5-HT2C) receptors mediate the inhibitory effects of serotonin on dopaminergic circuitry in experimental animals, and preclinical findings have implicated 5-HT2C receptors in motivated behaviors and psychotropic drug mechanisms. In humans, a common missense single-nucleotide change (rs6318, Cys23Ser) in the 5-HT2C receptor gene (HTR2C) has been associated with altered activity in vitro and with clinical mood disorders. We hypothesized that dopaminergic circuitry would be more sensitive to stress in humans carrying the Ser23 variant. To test this hypothesis, we studied 54 healthy humans using positron emission tomography and the displaceable D2/D3 receptor radiotracer [11C]raclopride. Binding potential (BPND) was quantified before and after a standardized stress challenge consisting of 20 minutes of moderate deep muscular pain, and reduction in BPND served as an index of dopamine release. The Cys23Ser variant was genotyped on a custom array, and ancestry informative markers were used to control for population stratification. We found greater dopamine release in the nucleus accumbens, caudate nucleus, and putamen among Ser23 carriers, after controlling for sex, age, and ancestry. Genotype accounted for 12% of the variance in dopamine release in the nucleus accumbens. There was no association of Cys23Ser with baseline BPND. These findings indicate that a putatively functional HTR2C variant (Ser23) is associated with greater striatal dopamine release during pain in healthy humans. Mesoaccumbal stress sensitivity may mediate the effects of HTR2C variation on risk of neuropsychiatric disorders.
Previous studies have suggested that polymorphism in the serotonin transporter gene (5-HTTLPR) influences responses to serotonergic manipulation, with opposite effects in patients recovered from depression (rMDD) and controls. Here we sought to clarify the neurocognitive mechanisms underpinning these surprising results. Twenty controls and 23 rMDD subjects completed the study; functional magnetic resonance imaging (fMRI) and genotype data were available for 17 rMDD subjects and 16 controls. Following tryptophan or sham depletion, subjects performed an emotional-processing task during fMRI. Although no genotype effects on mood were identified, significant genotype*diagnosis*depletion interactions were observed in the hippocampus and subgenual cingulate in response to emotionally valenced words. In both regions, tryptophan depletion increased responses to negative words, relative to positive words, in high-expression controls, previously identified as being at low-risk for mood change following this procedure. By contrast, in higher-risk low-expression controls and high-expression rMDD subjects, tryptophan depletion had the opposite effect. Increased neural responses to negative words following tryptophan depletion may reflect an adaptive mechanism promoting resilience to mood change following perturbation of the serotonin system, which is reversed in sub-groups vulnerable to developing depressive symptoms. However, this interpretation is complicated by our failure to replicate previous findings of increased negative mood following tryptophan depletion.
Depression; serotonin transporter polymorphism (5-HTTLPR); acute tryptophan depletion; functional magnetic resonance imaging (fMRI); emotional processing
The Revised Psychopathy Checklist (PCL-R) has shown a moderate association with violence. The efficacy of PCL-R in varying monoamine oxidase A (MAOA) genotypes is, however, unexamined. The aim of this study was to investigate the effect of PCL-R and psychopathy on the risk for violent reconvictions among 167 MAOA genotyped alcoholic offenders. Violent reconvictions and PCL-R scores among violent offenders were assessed after a 7-year non-incarcerated follow-up. Regression analysis was used to evaluate the alcohol exposure and age-adjusted effect of PCL-R score and psychopathy on the risk for reconvictions among differing MAOA genotypes. Results suggest that the PCL-R total score predicts impulsive reconvictions among high-activity MAOA offenders (6.8% risk increase for every one-point increase in PCL-R total score, P=0.015), but not among low-activity MAOA offenders, whereas antisocial behavior and attitudes predicted reconvictions in both genotypes (17% risk increase among high-activity MAOA offenders and 12.8% increase among low-activity MAOA offenders for every one-point increase in factor 2 score). Both narcissistic self-image with related interpersonal style (factor 1 score) and psychopathy (PCL-R≥30) failed to predict future violence. Results suggest that the efficacy of PCL-R is altered by MAOA genotype, alcohol exposure, and age, which seems important to note when PCL-R is used for risk assessments that will have legal or costly preventive work consequences.
Monoamine oxidase; Psychopathology; Antisocial personality disorder; Borderline personality disorder; Personality inventory; Violent crimes; Alcoholism