Modulation of intracellular cyclic AMP levels by different human dopamine D4 receptor variants

Exploring the genetic contribution in obesity: An overview of dopaminergic system genes

Obesity is a widespread global health concern that affects a significant portion of the population and is associated with reduced quality of life, morbidity, and mortality. It is considered a pandemic, with its prevalence constantly rising in Western countries. As a result, numerous studies have focused on understanding the elements that contribute to obesity. Researchers have focused on neurotransmitters in the brain to develop weight management drugs that regulate food intake. This review explores the literature on genetic influences on dopaminergic processes to determine whether genetic variation has an association with obesity in reward-responsive regions, including mesolimbic efferent and mesocortical areas. Various neurotransmitters play an essential role in regulating food intake, such as dopamine which controls through mesolimbic circuits in the brain that modulate food reward. Appetite stimulation, including primary reinforcers such as food, leads to an increase in dopamine release in the reward centers of the brain. This release is related to motivation and reinforcement, which determines the motivational weighting of the reinforcer. Changes in dopamine expression can lead to hedonic eating behaviors and contribute to the development of obesity. Genetic polymorphisms have been investigated due to their potential role in modulating the risk of obesity and eating behaviors. Therefore, it is crucial to assess the impact of genetic alterations that disrupt this pathway on the obesity phenotype.

Dopamine in Sports: A Narrative Review on the Genetic and Epigenetic Factors Shaping Personality and Athletic Performance

This narrative review examines the relationship between dopamine-related genetic polymorphisms, personality traits, and athletic success. Advances in sports genetics have identified specific single nucleotide polymorphisms (SNPs) in dopamine-related genes linked to personality traits crucial for athletic performance, such as motivation, cognitive function, and emotional resilience. This review clarifies how genetic variations can influence athletic predisposition through dopaminergic pathways and environmental interactions. Key findings reveal associations between specific SNPs and enhanced performance in various sports. For example, polymorphisms such as COMT Val158Met rs4680 and BDNF Val66Met rs6265 are associated with traits that could benefit performance, such as increased focus, stress resilience and conscientiousness, especially in martial arts. DRD3 rs167771 is associated with higher agreeableness, benefiting teamwork in sports like football. This synthesis underscores the multidimensional role of genetics in shaping athletic ability and advocates for integrating genetic profiling into personalized training to optimize performance and well-being. However, research gaps remain, including the need for standardized training protocols and exploring gene-environment interactions in diverse populations. Future studies should focus on how genetic and epigenetic factors can inform tailored interventions to enhance both physical and psychological aspects of athletic performance. By bridging genetics, personality psychology, and exercise science, this review paves the way for innovative training and performance optimization strategies.

Genetics of child aggression, a systematic review

Excessive and persistent aggressiveness is the most common behavioral problem that leads to psychiatric referrals among children. While half of the variance in childhood aggression is attributed to genetic factors, the biological mechanism and the interplay between genes and environment that results in aggression remains elusive. The purpose of this systematic review is to provide an overview of studies examining the genetics of childhood aggression irrespective of psychiatric diagnosis. PubMed, PsycINFO, and MEDLINE databases were searched using predefined search terms for aggression, genes and the specific age group. From the 652 initially yielded studies, eighty-seven studies were systematically extracted for full-text review and for further quality assessment analyses. Findings show that (i) investigation of candidate genes, especially of MAOA (17 studies), DRD4 (13 studies), and COMT (12 studies) continue to dominate the field, although studies using other research designs and methods including genome-wide association and epigenetic studies are increasing, (ii) the published articles tend to be moderate in sizes, with variable methods of assessing aggressive behavior and inconsistent categorizations of tandem repeat variants, resulting in inconclusive findings of genetic main effects, gene-gene, and gene-environment interactions, (iii) the majority of studies are conducted on European, male-only or male-female mixed, participants. To our knowledge, this is the first study to systematically review the effects of genes on youth aggression. To understand the genetic underpinnings of childhood aggression, more research is required with larger, more diverse sample sets, consistent and reliable assessments and standardized definition of the aggression phenotypes. The search for the biological mechanisms underlying child aggression will also benefit from more varied research methods, including epigenetic studies, transcriptomic studies, gene system and genome-wide studies, longitudinal studies that track changes in risk/ameliorating factors and aggression-related outcomes, and studies examining causal mechanisms.

Theory of Mind: A Brief Review of Candidate Genes

Deficits in theory of mind (ToM), known as the ability to understand the other's mind, have been associated with several psychopathological outcomes. The present systematic review aims to summarize the results of genetic studies that investigated gene polymorphisms associated with mentalization performance tasks in children and adults. The systematic review was carried out following PRISMA guidelines, and the literature search was conducted in PubMed and EBSCOhost using the following keywords: 'theory of mind, mentalizing, mindreading' and 'gene, genetic basis'. Nineteen studies met the eligibility criteria for inclusion. Most of the literature focused on the role of DRD4, DAT1, OXTR, OXT, COMT, ZNF804A, AVP, AVPR, SCL6A4, EFHC2, MAO-A, and the family of GTF2I genes in influencing ToM. However, controversial results emerged in sustaining the link between specific genetic polymorphisms and mentalization abilities in children and adults. Available data show heterogeneous outcomes, with studies reporting an association between the same family genes in subjects of the same age and other studies reporting no correlation. This does not allow us to draw any solid conclusions but paves the way for exploring genes involved in ToM tasks.

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.

Candidate gene-environment interactions in substance abuse: A systematic review

BACKGROUND

The abuse of psychogenic drugs can lead to multiple health-related problems. Genetic and environmental vulnerabilities are factors in the emergence of substance use disorders. Empirical evidence regarding the gene-environment interaction in substance use is mixed. Summaries of the latest findings from a candidate gene approach will be useful for revealing the significance of particular gene contributions. Thus, we aim to identify different gene-environment interactions in patterns of substance use and investigate whether any effects trend notably across different genders and races.

METHODS

We reviewed published studies, until March 1, 2022, on substance use for candidate gene-environment interaction. Basic demographics of the included studies, target genes, environmental factors, main findings, patterns of gene-environment interaction, and other relevant information were collected and summarized.

RESULTS

Among a total of 44 studies, 38 demonstrated at least one significant interaction effect. About 61.5% of studies on the 5-HTTLPR gene, 100% on the MAOA gene, 42.9% on the DRD2 gene, 50% on the DRD4 gene, 50% on the DAT gene, 80% on the CRHR1 gene, 100% on the OPRM1 gene, 100% on the GABRA1 gene, and 50% on the CHRNA gene had a significant gene-environment interaction effect. The diathesis-stress model represents a dominant interaction pattern (89.5%) in the studies with a significant interaction effect; the remaining significant effect on substance use is found in the differential susceptibility model. The social push and swing model were not reported in the included studies.

CONCLUSION

The gene-environment interaction research on substance use behavior is methodologically multidimensional, which causes difficulty in conducting pooled analysis, or stated differently-making it hard to identify single sources of significant influence over maladaptive patterns of drug taking. In decreasing the heterogeneity and facilitating future pooled analysis, researchers must (1) replicate the existing studies with consistent study designs and measures, (2) conduct power calculations to report gene-environment correlations, (3) control for covariates, and (4) generate theory-based hypotheses with factorial based experiments when designing future studies.

Dopamine D4 Receptor Agonist Drastically Increases Delta Activity in the Thalamic Nucleus Reuniens: Potential Role in Communication between Prefrontal Cortex and Hippocampus

Network oscillations are essential for all cognitive functions. Oscillatory deficits are well established in psychiatric diseases and are recapitulated in animal models. They are significantly and specifically affected by pharmacological interventions using psychoactive compounds. Dopamine D4 receptor (D4R) activation was shown to enhance gamma rhythm in freely moving rats and to specifically affect slow delta and theta oscillations in the urethane-anesthetized rat model. The goal of this study was to test the effect of D4R activation on slow network oscillations at delta and theta frequencies during wake states, potentially supporting enhanced functional connectivity during dopamine-induced attention and cognitive processing. Network activity was recorded in the prefrontal cortex (PFC), hippocampus (HC) and nucleus reuniens (RE) in control conditions and after injecting the D4R agonist A-412997 (3 and 5 mg/kg; systemic administration). We found that A-412997 elicited a lasting (~40 min) wake state and drastically enhanced narrow-band delta oscillations in the PFC and RE in a dose-dependent manner. It also preferentially enhanced delta synchrony over theta coupling within the PFC-RE-HC circuit, strongly strengthening PFC-RE coupling. Thus, our findings indicate that the D4R may contribute to cognitive processes, at least in part, through acting on wake delta oscillations and that the RE, providing an essential link between the PFC and HC, plays a prominent role in this mechanism.

Art Value Creation and Destruction

I present a theory of creative and destructive value state referring to abstract art. Value is a probabilistic state held as a mixture of its expectation and information forces that coexist in a give-and-take relationship. Expectations are driven by the disclosure of novel information about the value state of various events of desire. Each bit of accumulated information contributes to the improvement of perception up to a threshold level, beyond which begin conscious states. The desire to disclose a value state triggers a triadic system of evaluation which uses concepts, observables and approaches. While the triadic valuation mechanisms can be used to assess various commodities, the scope of this work is limited to the case of artworks, in particular abstract paintings. I assume that art value is basically mediated by the interplay between these value state mechanisms of creation and destruction. Expectations in artwork develop attraction by challenging its contemplator to evaluate (predict) its meaning. Once the relevant information, corresponding to its creative expectations, is acquired (and conditioned), emotional states of indifference, disinterest and desensitization develop.

Multilocus Genetic Profile Reflecting Low Dopaminergic Signaling Is Directly Associated with Obesity and Cardiometabolic Disorders Due to Antipsychotic Treatment

Treatment with second-generation antipsychotics (SGAs) can cause obesity and other cardiometabolic disorders linked to D2 receptor (DRD2) and to genotypes affecting dopaminergic (DA) activity, within reward circuits. We explored the relationship of cardiometabolic alterations with single genetic polymorphisms DRD2 rs1799732 (NG_008841.1:g.4750dup -> C), DRD2 rs6277 (NG_008841.1:g.67543C>T), COMT rs4680 (NG_011526.1:g.27009G>A), and VNTR in both DRD4 NC_000011.10 (637269-640706) and DAT1 NC_000005.10 (1392794-1445440), as well as with a multilocus genetic profile score (MLGP). A total of 285 psychiatric patients treated with SGAs for at least three months were selected. Cardiometabolic parameters were classified according to ATP-III and WHO criteria. Blood samples were taken for routinely biochemical assays and PCR genotyping. Obesity (BMI, waist (W)), high diastolic blood pressure (DBP), and hypertriglyceridemia (HTG) were present in those genetic variants related to low dopaminergic activity: InsIns genotype in rs1799732 (BMI: OR: 2.91 [1.42-5.94]), DRD4-VNTR-L allele (W: OR: 1.73 [1.04-2.87]) and 9R9R variant in DAT1-VNTR (W: OR: 2.73 [1.16-6.40]; high DBP: OR: 3.33 [1.54-7.31]; HTG: OR: 4.38 [1.85-10.36]). A low MLGP score indicated a higher risk of suffering cardiometabolic disorders (BMI: OR: 1.23 [1.05-1.45]; W: OR: 1.18 [1.03-1.34]; high DBP: OR: 1.22 [1.06-1.41]; HTG: OR: 1.20 [1.04-1.39]). The MLGP score was more sensitive for detecting the risk of suffering these alterations. Low dopaminergic system function would contribute to increased obesity, BDP, and HTG following long-term SGA treatment.

Genetic polymorphisms in the serotonin, dopamine and opioid pathways influence social attention in rhesus macaques (Macaca mulatta)

Behaviour has a significant heritable component; however, unpicking the variants of interest in the neural circuits and molecular pathways that underpin these has proven difficult. Here, we present a comprehensive analysis of the relationship between known and new candidate genes from identified pathways and key behaviours for survival in 109 adult rhesus macaques (Macaca mulatta). Eight genes involved in emotion were analysed for variation at a total of nine loci. Genetic data were then correlated with cognitive and observational measures of behaviour associated with wellbeing and survival using MCMC-based Bayesian GLMM in R, to account for relatedness within the macaque population. For four loci the variants genotyped were length polymorphisms (SLC6A4 5-hydroxytryptamine transporter length-polymorphic repeat (5-HTTLPR), SLC6A4 STin polymorphism, Tryptophan 5-hydroxylase 2 (TPH2) and Monoamine oxidase A (MAOA)) whilst for the other five (5-hydroxytryptamine receptor 2A (HTR2A), Dopamine Receptor D4 (DRD4), Oxytocin receptor (OXTR), Arginine vasopressin receptor 1A (AVPR1a), Opioid receptor mu(μ) 1 (OPRM1)) SNPs were analysed. STin genotype, DRD4 haplotype and OXTR haplotype were significantly associated with the cognitive and observational measures of behaviour associated with wellbeing and survival. Genotype for 5-HTTLPR, STin and AVPR1a, and haplotype for HTR2A, DRD4 and OXTR were significantly associated with the duration of behaviours including fear and anxiety. Understanding the biological underpinnings of individual variation in negative emotion (e.g., fear and anxiety), together with their impact on social behaviour (e.g., social attention including vigilance for threat) has application for managing primate populations in the wild and captivity, as well as potential translational application for understanding of the genetic basis of emotions in humans.

Exploring Structural Determinants of Bias among D4 Subtype-Selective Dopamine Receptor Agonists

The high affinity dopamine D₄ receptor ligand APH199 and derivatives thereof exhibit bias toward the G_i signaling pathway over β-arrestin recruitment compared to quinpirole. Based on APH199, two novel groups of D₄ subtype selective ligands were designed and evaluated, in which the original benzyl phenylsemicarbazide substructure was replaced by either a biphenylmethyl urea or a biphenyl urea moiety. Functional assays revealed a range of different bias profiles among the newly synthesized compounds, namely, with regard to efficacy, potency, and GRK2 dependency, in which bias factors range from 1 to over 300 and activation from 15% to over 98% compared to quinpirole. These observations demonstrate that within bias, an even more precise tuning toward a particular profile is possible, which─in a general sense─could become an important aspect in future drug development. Docking studies enabled further insight into the role of the ECL2 and the EPB in the emergence of bias, thereby taking advantage of the diversity of functionally selective D₄ agonists now available.

Dopamine-induced arrestin recruitment and desensitization of the dopamine D4 receptor is regulated by G protein-coupled receptor kinase-2

The dopamine D₄ receptor (D₄R) is expressed in the retina, prefrontal cortex, and autonomic nervous system and has been implicated in attention deficit hyperactivity disorder (ADHD), substance use disorders, and erectile dysfunction. D₄R has also been investigated as a target for antipsychotics due to its high affinity for clozapine. As opposed to the closely related dopamine D₂ receptor (D₂R), dopamine-induced arrestin recruitment and desensitization at the D₄R have not been studied in detail. Indeed, some earlier investigations could not detect arrestin recruitment and desensitization of this receptor upon its activation by agonist. Here, we used a novel nanoluciferase complementation assay to study dopamine-induced recruitment of β-arrestin2 (βarr2; also known as arrestin3) and G protein-coupled receptor kinase-2 (GRK2) to the D₄R in HEK293T cells. We also studied desensitization of D₄R-evoked G protein-coupled inward rectifier potassium (GIRK; also known as Kir3) current responses in Xenopus oocytes. Furthermore, the effect of coexpression of GRK2 on βarr2 recruitment and GIRK response desensitization was examined. The results suggest that coexpression of GRK2 enhanced the potency of dopamine to induce βarr2 recruitment to the D₄R and accelerated the rate of desensitization of D₄R-evoked GIRK responses. The present study reveals new details about the regulation of arrestin recruitment to the D₄R and thus increases our understanding of the signaling and desensitization of this receptor.

The effect of the 7R allele at the DRD4 locus on risk tolerance is independent of background risk in Senegalese fishermen

It has been shown that living in risky environments, as well as having a risky occupation, can moderate risk-tolerance. Despite the involvement of dopamine in the expectation of reward described by neurobiologists, a GWAS study was not able to demonstrate a genetic contribution of genes involved in the dopaminergic pathway in risk attitudes and gene candidate studies gave contrasting results. We test the possibility that a genetic effect of the DRD4-7R allele in risk-taking behavior could be modulated by environmental factors. We show that the increase in risk-tolerance due to the 7R allele is independent of the environmental risk in two populations in Northern Senegal, one of which is exposed to a very high risk due to dangerous fishing.

Prevalence of Common Alleles of Some Stress Resilience Genes among Adolescents Born in Different Periods Relative to the Socioeconomic Crisis of the 1990s in Russia

Social stress is common among people and is considered one of the causes of the declining birth rate. Predisposition to stress and stress-induced disorders is largely determined genetically. We hypothesized that due to differences in stress resistance, carriers of different genetic variants of genes associated with stress resilience and stress-induced diseases may have dissimilar numbers of offspring under conditions of long-term social stress. To test this hypothesis, a comparative analysis of frequencies of seven common polymorphic regions [exon 3 variable number of tandem repeats (VNTR) of the DRD4 gene, rs4680 of COMT, STin2 VNTR and the 5-HTTLPR (rs774676466) insertion/deletion polymorphism of SLC6A4, rs4570625 of TPH2, rs6265 of BDNF, and rs258747 of NR3C1] was performed on standardized groups of randomly selected adolescents born before, during, and after severe socioeconomic deprivation (the crisis of the 1990s in Russia). There were significant differences in frequencies of "long" alleles of the DRD4 gene (p = 0.020, χ² = 5.492) and rs4680 (p = 0.022, χ² = 5.289) in the "crisis" group as compared to the combined "noncrisis" population. It is possible that the dopaminergic system had an impact on the successful adaptation of a person to social stress.

Disordered eating in early childhood: DRD4 and DAT1 gene polymorphisms and quality of mother-child interaction

PURPOSE

Eating disturbances are complex heritable conditions that can be influenced by both genetic and environmental factors but are poorly studied in early development. The aim of this research was to investigate the association of genetic polymorphisms within dopaminergic pathways with early feeding problems.

METHODS

We analyzed the presence of VNTR polymorphisms of DRD4 (rs1805186) and DAT1 (rs28363170) in overeating (N = 45), undereating (N = 48) and control (N = 44) young children. We also assessed presence of externalizing, internalizing and dysregulation symptoms by the Child Behavior Checklist and quality of mother-child interactions during feeding by the Italian adaptation of the Scale for the Assessment of Feeding Interaction, respectively.

RESULTS

Both polymorphisms were associated with children's eating behavior, psychological symptoms and quality of interaction with their mothers, suggesting that: (a) the DRD4 4-repeat allele behaves as a protective factor, the 2-repeats and 7-repeats alleles as risk factors, for undereating behavior, the general quality of mother-child interaction and internalizing, externalizing and dysregulated symptoms; and (b) the DAT1 9-repeats allele behaves as a protective factor, the 10-repeats allele as a risk factor, for overeating behavior, the general quality of mother-child interaction, internalizing, externalizing and dysregulated symptoms. Finally, a gene x gene interaction is suggested between the DAT1 9-repeat or 10-repeat allele and the DRD4 4-repeat allele.

CONCLUSIONS

Our results suggest a role for DRD4 and DAT1 in an early susceptibility to eating disturbances.

LEVEL OF EVIDENCE III

Evidence obtained from well-designed case-control analytic study.

Highly Potent and Selective Dopamine D4 Receptor Antagonists Potentially Useful for the Treatment of Glioblastoma

To better understand the role of dopamine D₄ receptor (D₄R) in glioblastoma (GBM), in the present paper, new ligands endowed with high affinity and selectivity for D₄R were discovered starting from the brain penetrant and D₄R selective lead compound 1-(3-(4-phenylpiperazin-1-yl)propyl)-3,4-dihydroquinolin-2(1H)-one (6). In particular, the D₄R antagonist 24, showing the highest affinity and selectivity over D₂R and D₃R within the series (D₂/D₄ = 8318, D₃/D₄ = 3715), and the biased ligand 29, partially activating D₄R G_i-/G_o-protein and blocking β-arrestin recruitment, emerged as the most interesting compounds. These compounds, evaluated for their GBM antitumor activity, induced a decreased viability of GBM cell lines and primary GBM stem cells (GSC#83), with the maximal efficacy being reached at a concentration of 10 μM. Interestingly, the treatment with both compounds 24 and 29 induced an increased effect in reducing the cell viability with respect to temozolomide, which is the first-choice chemotherapeutic drug in GBM.

[The Genetic Basis of ADHD - An Update]

The Genetic Basis of ADHD - An Update Abstract. Genetic risks play an important role in the etiology of attention-deficit/hyperactivity disorder (ADHD). This review presents the current state of knowledge concerning the genetic basis of the disorder. It discusses the results of twin- and family-based studies, linkage and association studies as well as recent findings resulting from Genome Wide Association Studies (GWAS). Furthermore, it elaborates on the relevance of polygenic risk scores, rare variants, and epigenetic alterations, especially in light of findings on genetic pleiotropy in the context of frequent psychiatric comorbidities in patients with ADHD.

Association Between DRD2 and DRD4 Polymorphisms and Eating Disorders in an Italian Population

Anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED) are the three most common eating disorders (EDs). Their etiopathogenesis is multifactorial where both the environmental and genetic factors contribute to the disease outcome and severity. Several polymorphisms in genes involved in the dopaminergic pathways seem to be relevant in the susceptibility to EDs, but their role has not been fully elucidated yet. In this study, we have analyzed the association between selected common polymorphisms in the DRD2 and DRD4 genes in a large cohort of Italian patients affected by AN (n = 332), BN (n = 122), and BED (n = 132) compared to healthy controls (CTRs) (n = 172). Allelic and genotypic frequencies have been also correlated with the main psychopathological and clinical comorbidities often observed in patients. Our results showed significant associations of the DRD2-rs6277 single nucleotide polymorphism (SNP) with AN and BN, of the DRD4-rs936461 SNP with BN and BED and of DRD4 120-bp tandem repeat (TR) polymorphism (SS plus LS genotypes) with BED susceptibility. Moreover, genotyping of DRD4 48-bp variable number TR (VNTR) identified the presence of ≥7R alleles as risk factors to develop each type of EDs. The study also showed that ED subjects with a history of drugs abuse were characterized by a significantly higher frequency of the DRD4 rs1800955 TT genotype and DRD4 120-bp TR short-allele. Our findings suggest that specific combinations of variants in the DRD2 and DRD4 genes are predisposing factors not only for EDs but also for some psychopathological features often coupled specifically to AN, BN, and BED. Further functional research studies are needed to better clarify the complex role of these proteins and to develop novel therapeutic compounds based on dopamine modulation.

Identification of the Risk Genes Associated With Vulnerability to Addiction: Major Findings From Transgenic Animals

Understanding risk factors for substance use disorders (SUD) can facilitate medication development for SUD treatment. While a rich literature exists discussing environmental factors that influence SUD, fewer articles have focused on genetic factors that convey vulnerability to drug use. Methods to identify SUD risk genes include Genome-Wide Association Studies (GWAS) and transgenic approaches. GWAS have identified hundreds of gene variants or single nucleotide polymorphisms (SNPs). However, few genes identified by GWAS have been verified by clinical or preclinical studies. In contrast, significant progress has been made in transgenic approaches to identify risk genes for SUD. In this article, we review recent progress in identifying candidate genes contributing to drug use and addiction using transgenic approaches. A central hypothesis is if a particular gene variant (e.g., resulting in reduction or deletion of a protein) is associated with increases in drug self-administration or relapse to drug seeking, this gene variant may be considered a risk factor for drug use and addiction. Accordingly, we identified several candidate genes such as those that encode dopamine D₂ and D₃ receptors, mGluR₂, M₄ muscarinic acetylcholine receptors, and α₅ nicotinic acetylcholine receptors, which appear to meet the risk-gene criteria when their expression is decreased. Here, we describe the role of these receptors in drug reward and addiction, and then summarize major findings from the gene-knockout mice or rats in animal models of addiction. Lastly, we briefly discuss future research directions in identifying addiction-related risk genes and in risk gene-based medication development for the treatment of addiction.

ANKK1 and TH gene variants in combination with paternal maltreatment increase susceptibility to both cognitive and attentive impulsivity

Recent scientific findings suggest that dopamine exerts a central role on impulsivity, as well as that aversive life experiences may promote the high levels of impulsivity that often underlie violent behavior. To deepen our understanding of the complex gene by environment interplay on impulsive behavior, we genotyped six dopaminergic allelic variants (ANKK1-rs1800497, TH-rs6356, DRD4-rs1800955, DRD4-exonIII-VNTR, SLC6A3-VNTR and COMT-rs4680) in 655 US White male inmates convicted for violent crimes, whose impulsivity was assessed by BIS-11 (Barratt Impulsiveness Scale). Furthermore, in a subsample of 216 inmates from the whole group, we also explored the potential interplay between the genotyped dopaminergic variants and parental maltreatment measured by MOPS (Measure of Parental Style) in promoting impulsivity. We found a significant interaction among paternal MOPS scores, ANKK1-rs1800497-T allele and TH-rs6356-A allele, which increased the variance of BIS-11 cognitive/attentive scores explained by paternal maltreatment from 1.8 up to 20.5%. No direct association between any of the individual genetic variants and impulsivity was observed. Our data suggest that paternal maltreatment increases the risk of attentive/cognitive impulsivity and that this risk is higher in carriers of specific dopaminergic alleles that potentiate the dopaminergic neurotransmission. These findings add further evidence to the mutual role that genetics and early environmental factors exert in modulating human behavior and highlight the importance of childhood care interventions.

Convergent selective signaling impairment exposes the pathogenicity of latrophilin-3 missense variants linked to inheritable ADHD susceptibility

Latrophilin-3 (Lphn3; also known as ADGRL3) is a member of the adhesion G Protein Coupled Receptor subfamily, which participates in the stabilization and maintenance of neuronal networks by mediating intercellular adhesion through heterophilic interactions with transmembrane ligands. Polymorphisms modifying the Lphn3 gene are associated with attention-deficit/hyperactivity disorder (ADHD) in children and its persistence into adulthood. How these genetic alterations affect receptor function remains unknown. Here, we conducted the functional validation of distinct ADHD-related Lphn3 variants bearing mutations in the receptor's adhesion motif-containing extracellular region. We found that all variants tested disrupted the ability of Lphn3 to stabilize intercellular adhesion in a manner that was distinct between ligands classes, but which did not depend on ligand-receptor interaction parameters, thus pointing to altered intrinsic receptor signaling properties. Using G protein signaling biosensors, we determined that Lphn3 couples to Gαi1, Gαi2, Gαs, Gαq, and Gα13. However, all ADHD-related receptor variants consistently lacked intrinsic as well as ligand-dependent Gα13 coupling efficiency while maintaining unaltered coupling to Gαi, Gαs, and Gαq. Consistent with these alterations, actin remodeling functions as well as actin-relevant RhoA signaling normally displayed by the constitutively active Lphn3 receptor were impeded by select receptor variants, thus supporting additional signaling defects. Taken together, our data point to Gα13 selective signaling impairments as representing a disease-relevant pathogenicity pathway that can be inherited through Lphn3 gene polymorphisms. This study highlights the intricate interplay between Lphn3 GPCR functions and the actin cytoskeleton in modulating neurodevelopmental cues related to ADHD etiology.

Functional and pharmacological role of the dopamine D4 receptor and its polymorphic variants

The functional and pharmacological significance of the dopamine D₄ receptor (D₄R) has remained the least well understood of all the dopamine receptor subtypes. Even more enigmatic has been the role of the very prevalent human DRD4 gene polymorphisms in the region that encodes the third intracellular loop of the receptor. The most common polymorphisms encode a D₄R with 4 or 7 repeats of a proline-rich sequence of 16 amino acids (D_4.4R and D_4.7R). DRD4 polymorphisms have been associated with individual differences linked to impulse control-related neuropsychiatric disorders, with the most consistent associations established between the gene encoding D_4.7R and attention-deficit hyperactivity disorder (ADHD) and substance use disorders. The function of D₄R and its polymorphic variants is being revealed by addressing the role of receptor heteromerization and the relatively avidity of norepinephrine for D₄R. We review the evidence conveying a significant and differential role of D_4.4R and D_4.7R in the dopaminergic and noradrenergic modulation of the frontal cortico-striatal pyramidal neuron, with implications for the moderation of constructs of impulsivity as personality traits. This differential role depends on their ability to confer different properties to adrenergic α_2A receptor (α_2AR)-D₄R heteromers and dopamine D₂ receptor (D₂R)-D₄R heteromers, preferentially localized in the perisomatic region of the frontal cortical pyramidal neuron and its striatal terminals, respectively. We also review the evidence to support the D₄R as a therapeutic target for ADHD and other impulse-control disorders, as well as for restless legs syndrome.

Pharmacogenetics of Addiction Therapy

Drug addiction is a serious relapsing disease that has high costs to society and to the individual addicts. Treatment of these addictions is still in its nascency, with only a few examples of successful therapies. Therapeutic response depends upon genetic, biological, social, and environmental components. A role for genetic makeup in the response to treatment has been shown for several addiction pharmacotherapies with response to treatment based on individual genetic makeup. In this chapter, we will discuss the role of genetics in pharmacotherapies, specifically for cocaine, alcohol, and opioid dependences. The continued elucidation of the role of genetics should aid in the development of new treatments and increase the efficacy of existing treatments.

Genetically-predicted prefrontal DRD4 gene expression modulates differentiated brain responses to food cues in adolescent girls and boys

The dopamine receptor 4 (DRD4) in the prefrontal cortex (PFC) acts to modulate behaviours including cognitive control and motivation, and has been implicated in behavioral inhibition and responsivity to food cues. Adolescence is a sensitive period for the development of habitual eating behaviors and obesity risk, with potential mediation by development of the PFC. We previously found that genetic variations influencing DRD4 function or expression were associated with measures of laboratory and real-world eating behavior in girls and boys. Here we investigated brain responses to high energy–density (ED) and low-ED food cues using an fMRI task conducted in the satiated state. We used the gene-based association method PrediXcan to estimate tissue-specific DRD4 gene expression in prefrontal brain areas from individual genotypes. Among girls, those with lower vs. higher predicted prefrontal DRD4 expression showed lesser activation to high-ED and low-ED vs. non-food cues in a distributed network of regions implicated in attention and sensorimotor processing including middle frontal gyrus, and lesser activation to low-ED vs non-food cues in key regions implicated in valuation including orbitofrontal cortex and ventromedial PFC. In contrast, males with lower vs. higher predicted prefrontal DRD4 expression showed minimal differences in food cue response, namely relatively greater activation to high-ED and low-ED vs. non-food cues in the inferior parietal lobule. Our data suggest sex-specific effects of prefrontal DRD4 on brain food responsiveness in adolescence, with modulation of distributed regions relevant to cognitive control and motivation observable in female adolescents.

DRD4 Exon 3 Gene Polymorphisms in Patients Diagnosed with Polysubstance Use Disorder and Co-Occurrence of a Depressive Episode

Background: There has been a noticeable and systematic growth of the use of psychoactive substances over the past few decades. Dual diagnosis is a clinical term referring to the occurrence of psychoactive substance use disorder comorbid with another psychiatric disorder in the same person. The most common type of dual diagnosis is the co-occurrence of alcohol use disorder and mood disorders in the form of a depressive episode. Co-occurrent substance use disorders are frequently influenced by genetic factors. In selecting our area of research, we focused on dopamine and the DRD4 (Dopamine Receptor D4) gene polymorphism as well as associations with personality features. The aim of the study: The aim of the study was to compare DRD4 exon 3 (DRD4 Ex3) gene polymorphisms in patients diagnosed with polysubstance use disorder and co-occurrence of a depressive episode to DRD4 exon 3 gene polymorphisms in patients diagnosed with polysubstance use disorder and without co-occurrence of a depressive episode and a group of healthy volunteers. The study also aimed at establishing associations between personality features and DRD4 exon 3 gene polymorphisms of male patients diagnosed with polysubstance use disorder with co-occurrence of a depressive episode which may present a specific endophenotype of this group of patients. Methods: The study group comprised 602 male volunteers: patients diagnosed with polysubstance use disorder comorbid with a depressive episode (PUD MDD) (n = 95; mean age = 28.29, standard deviation (SD) = 7.40), patients diagnosed with polysubstance use disorder (PUD) (n = 206; mean age = 28.13, SD = 5.97), and controls (n = 301; mean age = 22.13, SD = 4.57). The patients and control subjects were diagnosed by a psychiatrist using the Mini International Neuropsychiatric Interview (MINI), the NEO Five-Factor Personality Inventory (NEO-FFI), and the State-Trait Anxiety Inventory (STAI) questionnaires. An analysis of the DRD4 exon 3 polymorphism was performed. Results: The patients diagnosed with PUD MDD compared to the control group of healthy volunteers showed significantly higher scores on both the STAI status and features scale and the NEO-FFI Neuroticism and Openness Scale, as well as lower scores on the Extraversion, Agreeableness, and Conscientiousness NEO-FFI scales. In the DRD4 exon 3 gene polymorphism, the s allele was more frequent in the PUD MDD compared to the l allele, which was less frequent. The results of the 2 × 3 factor analysis of variance (ANOVA) in patients and controls and the variant DRD4 exon 3 interaction were found on the Extraversion Scale and the Conscientiousness Scale of the NEO-FFI. Conclusions: The associations show that psychological factors combined with genetic data create a new area of research on addiction, including the problem of dual diagnosis. However, we want to be careful and draw no definite conclusions at this stage of our research.

Genetic differential susceptibility to the parent-child relationship quality and the life span development of compassion

The development of compassion for others might be influenced by the social experiences made during childhood and has a genetic component. No research has yet investigated whether the parent-child relationship quality interacts with genetic variation in the oxytocin and dopamine systems in predicting compassion over the life span. In the prospective Young Finns Study (N = 2099, 43.9% men), we examined the interaction between mother-reported emotional warmth and intolerance toward their child assessed in 1980 (age of participants, 3-18 years) and two established genetic risk scores for oxytocin levels and dopamine signaling activity. Dispositional compassion for others was measured with the Temperament and Character Inventory 1997, 2001, and 2012 (age of participants, 20-50 years). We found a gene-environment interaction (p = .031) that remained marginally significant after adjustment for multiple testing. In line with the differential susceptibility hypothesis, only participants who carry alleles associated with low dopamine signaling activity had higher levels of compassion when growing up with emotionally warm parents, whereas they had lower levels of compassion when their parents were emotionally cold. Children's genetic variability in the dopamine system might result in plasticity to early environmental influences that have a long-lasting effect on the development of compassion. However, our findings need replication.

The Interplay Between Prenatal Adversity, Offspring Dopaminergic Genes, and Early Parenting on Toddler Attentional Function

Background: Few studies have explored the complex gene-by-prenatal environment-by-early postnatal environment interactions that underlie the development of attentional competence. Here, we examined if variation in dopamine-related genes interacts with prenatal adversity to influence toddler attentional competence and whether this influence is buffered by early positive maternal behavior. Methods: From the Maternal Adversity, Vulnerability and Neurodevelopment cohort, 134 participants (197 when imputing missing data) had information on prenatal adversity (prenatal stressful life events, prenatal maternal depressive symptoms, and birth weight), five dopamine-related genes (DAT1, DRD4, DRD2, COMT, BDNF), observed maternal parenting behavior at 6 months and parent-rated toddler attentional competence at 18 and 24 months. The Latent Environmental and Genetic Interaction (LEGIT) approach was used to examine genes-by-prenatal environment-by-postnatal environment interactions while controlling for sociodemographic factors and postnatal depression. Results: Our hypothesis of a three-way interaction between prenatal adversity, dopamine-related genes, and early maternal parenting behavior was not confirmed. However, consistent two-way interactions emerged between prenatal adversity and dopamine-related genes; prenatal adversity and maternal parenting behavior, and dopamine-related genes and maternal parenting behavior in relation to toddler attentional competence. Significant interaction effects were driven by the DAT1, COMT, and BDNF genotypes; prenatal stressful life events; maternal sensitivity, tactile stimulation, vocalization, and infant-related activities. Conclusions: Multiple dopamine-related genes affected toddler attentional competence and they did so in interaction with prenatal adversity and the early rearing environment, separately. Effects were already visible in young children. Several aspects of early maternal parenting have been identified as potential targets for intervention.

Different effects of the DRD4 genotype on intrinsic brain network connectivity strength in drug-naïve children with ADHD and healthy controls

The dopamine D4 receptor gene (DRD4) has been consistently reported to be associated with attention-deficit/hyperactivity disorder (ADHD). Recent studies have linked DRD4 to functional connectivity among specific brain regions. The current study aimed to compare the effects of the DRD4 genotype on functional integrity in drug-naïve ADHD children and healthy children. Resting-state functional MRI images were acquired from 49 children with ADHD and 37 healthy controls (HCs). We investigated the effects of the 2-repeat allele of DRD4 on brain network connectivity in both groups using a parameter called the degree of centrality (DC), which indexes local functional relationships across the entire brain connectome. A voxel-wise two-way ANCOVA was performed to examine the diagnosis-by-genotype interactions on DC maps. Significant diagnosis-by-genotype interactions with DC were found in the temporal lobe, including the left inferior temporal gyrus (ITG) and bilateral middle temporal gyrus (MTG) (GRF corrected at voxel level p < 0.001 and cluster level p < 0.05, two-tailed). With the further subdivision of the DC network according to anatomical distance, additional brain regions with significant interactions were found in the long-range DC network, including the left superior parietal gyrus (SPG) and right middle frontal gyrus (MFG). The post-hoc pairwise analysis found that altered network centrality related to DRD4 differed according to diagnostic status (p < 0.05). This genetic imaging study suggests that the DRD4 genotype regulates the functional integration of brain networks in children with ADHD and HCs differently. This may have important implications for our understanding of the role of DRD4 in altering functional connectivity in ADHD subjects.

Association of DRD4 exon III and 5-HTTLPR VNTR genetic polymorphisms with psychiatric symptoms in hemodialysis patients

Mental illness is prevalent among hemodialysis (HD) patients. Given that the dopaminergic and serotonergic pathways are involved in the etiology of psychiatric disease, this study evaluated the genetic association of dopamine D4 receptor (DRD4) and serotonin transporter (SLC6A4) genes with psychiatric symptom susceptibility among HD patients. Hospital Anxiety and Depression Scale (HADS) was used to assess anxiety and depressive symptoms among patients (n = 265). Genetic polymorphisms of DRD4 (48 bp VNTR) and SLC6A4 (5-HTTLPR VNTR and rs25531) were examined using a conventional polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique, as appropriate. Significant differences were observed in the distribution of 5-HTTLPR genotypes, SLC6A4 tri-allelic-phased genotype, and DRD4-Exon III VNTR genotypes/alleles between patients with anxiety symptoms versus those with normal/borderline conditions (p<0.05). Binary logistic regression analyses showed that the heterozygous 4,5 VNTR genotype of DRD4 was associated with a higher risk of anxiety symptoms after adjusting for other covariates (odds ratio = 4.25, p = 0.028). None of the studied polymorphisms was linked to depression in HD patients. Collectively, the current findings provide genetic clues to psychopathology in HD patients and suggest that the DRD4 exon III VNTR polymorphism is involved in the etiology of anxiety in this patient population.

The neurobiology of human aggressive behavior: Neuroimaging, genetic, and neurochemical aspects

In modern societies, there is a strive to improve the quality of life related to risk of crimes which inevitably requires a better understanding of brain determinants and mediators of aggression. Neurobiology provides powerful tools to achieve this end. Pre-clinical and clinical studies show that changes in regional volumes, metabolism-function and connectivity within specific neural networks are related to aggression. Subregions of prefrontal cortex, insula, amygdala, basal ganglia and hippocampus play a major role within these circuits and have been consistently implicated in biology of aggression. Genetic variations in proteins regulating the synthesis, degradation, and transport of serotonin and dopamine as well as their signal transduction have been found to mediate behavioral variability observed in aggression. Gene-gene and gene-environment interactions represent additional important risk factors for aggressiveness. Considering the social burden of pathological forms of aggression, more basic and translational studies should be conducted to accelerate applications to clinical practice, justice courts, and policy making.

Determination of the Relationship Between Craving and 4-repeat Allele of DRD4 Gene Polymorphism in the Early Withdrawal Period of Alcohol Use Disorders

OBJECTIVE

Alcohol use disorder (AUD) is a disease with chronic relapses. Risk factors of craving, which is thought to be one of the predictors of relapse, have been studied for a long time. The DRD4 gene is located on chromosome 11p and has a 48-base pair variable number of tandem repeat (VNTR) polymorphisms in the 3rd exon. This study aimed to investigate if a relationship existed between craving and DRD4 VNTR polymorphism and to determine the predictors of craving.

METHODS

A total of 125 patients with AUD were included in the study. The sociodemographic data form, the Michigan Alcoholism Screening Test (MAST), the Obsessive Compulsive Drinking Scale (OCDS), and the Penn Alcohol Craving Scale (PACS) were applied to the patients. Polymerase chain reaction (PCR) was used to determine the DRD4 VNTR variant of all participants in the peripheral blood sample.

RESULTS

In the 4R/4R homozygous group, it was found that the age at first alcohol use was higher and the scores of the OCDS on the seventh day were lower, but this relationship could not be demonstrated in further statistical analyses. In the stepwise linear regression model, the age at first alcohol use, MAST score, duration of AUD, and delirium tremens history were found to be the predictors of craving.

CONCLUSION

DRD4 VNTR polymorphism does not play a role as a predictor of craving. A decrease in age at first alcohol use, an increase in the MAST score, and the presence of delirium tremens were found to be the predictors of craving among the participants of this study.

Homobivalent Dopamine D2 Receptor Ligands Modulate the Dynamic Equilibrium of D2 Monomers and Homo- and Heterodimers

Dopamine D₂ receptors (D₂Rs) are major targets in the treatment of psychiatric and neurodegenerative diseases. As with many other G protein-coupled receptors (GPCRs), D₂Rs interact within the cellular membrane, leading to a transient receptor homo- or heterodimerization. These interactions are known to alter ligand binding, signaling, and receptor trafficking. Bivalent ligands are ideally suited to target GPCR dimers and are composed of two pharmacophores connected by a spacer element. If properly designed, bivalent ligands are able to engange the two orthosteric binding sites of a GPCR dimer simultaneously. Taking advantage of previously developed ligands for heterodimers of D₂R and the neurotensin receptor 1 (NTSR1), we synthesized homobivalent ligands targeting D₂R. Employing bioluminescence resonance energy transfer, we found that the bivalent ligands 3b and 4b comprising a 92-atom spacer are able to foster D₂R-homodimerization while simultaneously reducing interactions of D₂R with NTSR1. Both receptors are coexpressed in the central nervous system and involved in important physiological processes. The newly developed bivalent ligands are excellent tools to further understand the pharmacological consequences of D₂R homo- and heterodimerization. Not limited to the dopaminergic system, modifying class A GPCRs' dynamic equilibrium between monomers, homomers, and heteromers with bivalent ligands may represent a novel pharmacological concept paving the way toward innovative drugs.

Dopamine D4 receptor gene polymorphism (DRD4 VNTR) moderates real-world behavioural response to the food retail environment in children

Background

Evidence for the impact of the food retailing environment on food-related and obesity outcomes remains equivocal, but only a few studies have attempted to identify sub-populations for whom this relationship might be stronger than others. Genetic polymorphisms related to dopamine signalling have been associated with differences in responses to rewards such as food and may be candidate markers to identify such sub-populations. This study sought to investigate whether genetic variation of the dopamine D4 receptor gene (DRD4 exon III 48 bp VNTR polymorphism) moderated the association between local exposure to food retailers on BMI and diet in a sample of 4 to12-year-old children.

Methods

Data collected from a birth cohort and a community cross-sectional study conducted in Montreal, Canada, were combined to provide DRD4 VNTR polymorphism data in terms of presence of the 7-repeat allele (DRD4-7R) for 322 children aged between 4 and 12 (M (SD): 6.8(2.8) y). Outcomes were Body Mass Index (BMI) for age and energy density derived from a Food Frequency Questionnaire. Food environment was expressed as the proportion of local food retailers classified as healthful within 3 km of participants’ residence. Linear regression models adjusted for age, sex, income, cohort, and geographic clustering were used to test gene*environment interactions.

Results

A significant gene*food environment interaction was found for energy density with results indicating that DRD4-7R carriers had more energy dense diets than non-carriers, with this effect being more pronounced in children living in areas with proportionally more unhealthy food retailers. No evidence of main or interactive effects of DRD4 VNTR and food environment was found for BMI.

Conclusions

Results of the present study suggest that a genetic marker related to dopamine pathways can identify children with potentially greater responsiveness to unhealthy local food environment. Future studies should investigate additional elements of the food environment and test whether results hold across different populations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-10160-w.

The etiology of maternal postpartum depressive symptoms: Childhood emotional maltreatment, couple relationship satisfaction, and genes

There is a call for integrative studies examining the roles of biological and psychosocial factors and their interrelations in shaping maternal postpartum psychopathology. Using longitudinal data from 198 primiparous mothers, we tested a biopsychosocial model for the etiology of maternal postpartum depressive symptoms that integrated childhood emotional maltreatment, couple relationship satisfaction, and oxytocin and dopamine D4 receptor genes (i.e., OXTR rs53576 and DRD4). Results indicate (a) two indirect effects from childhood emotional maltreatment and DRD4 to depressive symptoms at 1 year postpartum through couple relationship satisfaction at 6 months postpartum; (b) an interactive effect between DRD4 and couple relationship satisfaction at 6 months postpartum in predicting depressive symptoms at 1 year postpartum, which is in concert with the differential susceptibility hypotheses; and (c) no mediating effects or moderating effects (after adjusting for multiple testing with Bonferroni correction) involving OXTR rs53576. Notably, all associations were identified after controlling for several key covariates (e.g., maternal prenatal depressive symptoms). Last, robustness of the currently identified interactive effect involving DRD4 was demonstrated by an extensive set of additional analyses considering the effects of rGE, G × Covariates, and/or E × Covariates. Taken altogether, this study represents one of the initial efforts for a more sophisticated portrayal of how nature and nurture forces may work in conjunction with each other to shape new mothers' psychopathology. Yet given the current modest sample size and candidate gene approach, our findings are preliminary, should be cautiously interpreted, and need to be replicated with more rigorous designs. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Dopamine in Health and Disease: Much More Than a Neurotransmitter

Dopamine is derived from an amino acid, phenylalanine, which must be obtained through the diet. Dopamine, known primarily to be a neurotransmitter involved in almost any higher executive action, acts through five types of G-protein-coupled receptors. Dopamine has been studied extensively for its neuronal handling, synaptic actions, and in relation to Parkinson's disease. However, dopamine receptors can be found extra-synaptically and, in addition, they are not only expressed in neurons, but in many types of mammalian cells, inside and outside the central nervous system (CNS). Recent studies show a dopamine link between the gut and the CNS; the mechanisms are unknown, but they probably require cells to act as mediators and the involvement of the immune system. In fact, dopamine receptors are expressed in almost any cell of the immune system where dopamine regulates various processes, such as antigen presentation, T-cell activation, and inflammation. This likely immune cell-mediated linkage opens up a new perspective for the use of dopamine-related drugs, i.e., agonist-antagonist-allosteric modulators of dopamine receptors, in a variety of diseases.

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.

Presynaptic vesicular accumulation is required for antipsychotic efficacy in psychotic-like rats

BACKGROUND

The therapeutic effects of antipsychotic drugs (APDs) are mainly attributed to their postsynaptic inhibitory functions on the dopamine D2 receptor, which, however, cannot explain the delayed onset of full therapeutic efficacy. It was previously shown that APDs accumulate in presynaptic vesicles during chronic treatment and are released like neurotransmitters in an activity-dependent manner triggering an auto-inhibitory feedback mechanism. Although closely mirroring therapeutic action onset, the functional consequence of the APD accumulation process remained unclear.

AIMS

Here we tested whether the accumulation of the APD haloperidol (HAL) is required for full therapeutic action in psychotic-like rats.

METHODS

We designed a HAL analog compound (HAL-F), which lacks the accumulation property of HAL, but retains its postsynaptic inhibitory action on dopamine D2 receptors.

RESULTS/OUTCOMES

By perfusing LysoTracker fluorophore-stained cultured hippocampal neurons, we confirmed the accumulation of HAL and the non-accumulation of HAL-F. In an amphetamine hypersensitization psychosis-like model in rats, we found that subchronic intracerebroventricularly delivered HAL (0.1 mg/kg/day), but not HAL-F (0.3-1.5 mg/kg/day), attenuates psychotic-like behavior in rats.

CONCLUSIONS/INTERPRETATION

These findings suggest the presynaptic accumulation of HAL may serve as an essential prerequisite for its full antipsychotic action and may explain the time course of APD action. Targeting accumulation properties of APDs may, thus, become a new strategy to improve APD action.

Recent findings leading to the discovery of selective dopamine D4 receptor ligands for the treatment of widespread diseases

Since its discovery, the dopamine D₄ receptor (D₄R) has been suggested to be an attractive target for the treatment of neuropsychiatric diseases. Novel findings have renewed the interest in such a receptor as an emerging target for the management of different diseases, including cancer, Parkinson's disease, alcohol or substance use disorders, eating disorders, erectile dysfunction and cognitive deficits. The recently resolved crystal structures of D₄R in complexes with the potent ligands nemonapride and L-745870 strongly improved the knowledge on the molecular mechanisms involving the D₄R functions and may help medicinal chemists in drug design. This review is focused on the recent development of the subtype selective D₄R ligands belonging to classical or new chemotypes. Moreover, ligands showing functional selectivity toward G protein activation or β-arrestin recruitment and the effects of selective D₄R ligands on the above-mentioned diseases are discussed.

The Dopamine D4 Receptor (DRD4) Exon 3 VNTR Contributes to Adaptive Personality Differences in an Italian Small Island Population

The search for evolutionary forces shaping the diversity of human personality traits encouraged studies that have found that islanders are relatively closed and introverted, with little interest in the external world. The ‘personality gene flow’ hypothesis was proposed to explain the mechanism underlying this difference, suggesting that the frequency of alleles that influence islander personality traits might progressively increase in the gene pools on islands because of selective emigration of individuals not displaying these alleles. We genotyped 96 individuals from the Italian mainland and 117 from Giglio Island, whose residents were previously assessed regarding their personality traits. We genotyped three polymorphisms: the dopamine D4 receptor (DRD4) exon 3 repeat region, the serotonin–transporter SLC6A4 5–HTTLPR indel and the dopamine transporter SLC6A3 DAT1 3′UTR repeat region. Only the DRD4 exon 3 repeat was hypothesised to show varying allele frequencies because this polymorphism could be associated with human migration and personality traits such as extraversion, openness and novelty seeking. As predicted, no differences in allele frequencies were found for the SLC6A4 and SLC6A3 polymorphisms, whereas significant differences were observed in the frequency of the DRD4 exon 3 alleles. The DRD4.2 repeat was more common in mainlanders, as expected, whereas the DRD4.7 allele was over–represented among islanders who never emigrated. This last result contradicts the suggested association of this allele with long–distance migrations. We suggest that emigration might have caused gene flow out the island that resulted in somewhat unpredictable changes in the frequencies of specific alleles, thus influencing islander personality traits. Copyright © 2013 European Association of Personality Psychology

DRD4, DRD2, DAT1, and ANKK1 Genes Polymorphisms in Patients with Dual Diagnosis of Polysubstance Addictions

Background: Approximately 25–50% of people diagnosed with substance use disorder experience psychiatric disorders, and this percentage is even higher if subclinical psychopathological symptomatology is taken into consideration. ”Dual diagnosis” implies the comorbidity of two disorders (mental disorder and addiction), but in a clinical setting, numerous dual diagnoses involve multiple addictions (polysubstance use means the concurrent use of more than one psychoactive substance). Clinical observations and epidemiological studies showed that the use of stimulants in combination with other substances results in additional risks. Apart from the clinical significance of the specificity of stimulants used in combination with other substances, only non-exhaustive research on the specificity of this comorbidity has been performed to date. The aim of the study was to analyze polymorphisms of the genes (DRD4 VNTR in exon III Ex3, DRD2 rs1076560, rs1800498, rs1079597, rs6276, as well as in the PROM promoter region (rs1799732, ANKK1 Tag1A rs1800497, DAT) in a group of patients diagnosed with polysubstance use disorder, including addiction to stimulants, and the co-occurrence of specific mental disorders in a group of patients diagnosed with polysubstance use disorder, including addiction to stimulants, compared to the group of patients diagnosed with polysubstance use disorder. Methods: The study group consisted of 601 male volunteers with psychoactive substance dependence (n = 300) and non-dependent controls (n = 301). The genomic DNA was extracted from venous blood using standard procedures. Genotyping was conducted with the real-time PCR method. All computations were performed using STATISTICA 13. Results: Psychotic disorders were significantly more common in the group of males with polysubstance addiction, including addiction to stimulants, compared to the group of males with polysubstance addiction without addiction to stimulants. In our own research, different statistical significances were found in the frequency of the DRD4 Ex3 gene polymorphism: s/s was more common in the study group. Psychotic disorders were more common in people addicted to stimulants compared to people addicted to other substances. Conclusions: In our study, psychotic disorders occurred more frequently in the study group of patients with polysubstance addiction, including addiction to stimulants, compared to the control group of patients with polysubstance addiction, but with no addiction to stimulants. Different statistical significances were found in the frequency of the DRD4 Ex3 gene polymorphism: s/s was more common in the study group, while the l/l genotype was less frequent in the study group. In DRD2 PROM rs 1799732, the del allele occurred more often than the ins allele in the study group. In the DRD4 Ex3 gene polymorphism, the s allele was more common in the study group, and the l allele was less frequent. In the DRD4 Ex3 gene polymorphism for the s/s genotype, psychotic disorders and generalized anxiety were more common, while for the s/l and l/l genotype, they were less frequent. The DRD4 Ex3 polymorphism s alleles were more common for depressive episode, dysthymia, and psychotic disorders as well as generalized anxiety disorder. We see a clear genetic aspect here. However, we want to be careful and draw no definite conclusions.

Psychotic disorders, dopaminergic agents and EEG/MEG resting-state functional connectivity: A systematic review

Both dysconnectivity and dopamine hypotheses are two well researched pathophysiological models of psychosis. However, little is known about the association of dopamine dysregulation with brain functional connectivity in psychotic disorders, specifically through the administration of antipsychotic medication. In this systematic review, we summarize the existing evidence on the association of dopaminergic effects with electro- and magnetoencephalographic (EEG/MEG) resting-state brain functional connectivity assessed by sensor- as well as source-level measures. A wide heterogeneity of results was found amongst the 20 included studies with increased and decreased functional connectivity in medicated psychosis patients vs. healthy controls in widespread brain areas across all frequency bands. No systematic difference in results was seen between studies with medicated and those with unmedicated psychosis patients and very few studies directly investigated the effect of dopamine agents with a pre-post design. The reported evidence clearly calls for longitudinal EEG and MEG studies with large participant samples to directly explore the association of antipsychotic medication effects with neural network changes over time during illness progression and to ultimately support the development of new treatment strategies.

Dopamine Related Genes Differentially Affect Declarative Long-Term Memory in Healthy Humans

In humans, monetary reward can promote behavioral performance including response times, accuracy, and subsequent recognition memory. Recent studies have shown that the dopaminergic system plays an essential role here, but the link to interindividual differences remains unclear. To further investigate this issue, we focused on previously described polymorphisms of genes affecting dopaminergic neurotransmission: DAT1 40 base pair (bp), DAT1 30 bp, DRD4 48 bp, and cannabinoid receptor type 1 (CNR1). Specifically, 669 healthy humans participated in a delayed recognition memory paradigm on two consecutive days. On the first day, male vs. female faces served as cues predicting an immediate monetary reward upon correct button presses. Subsequently, participants performed a remember/know recognition memory task on the same day and 1 day later. As predicted, reward increased accuracy and accelerated response times, which were modulated by DAT 30 bp. However, reward did not promote subsequent recognition memory performance and there was no interaction with any genotype tested here. Importantly, there were differential effects of genotype on declarative long-term memory independent of reward: (a) DAT1 40 bp was linked to the quality of memory with a more pronounced difference between recollection and familiarity in the heterozygous and homozygous 10-R as compared to homozygous 9-R; (b) DAT1 30 bp was linked to memory decay, which was most pronounced in homozygous 4-R; (c) DRD4 48 bp was linked to overall recognition memory with higher performance in the short allele group; and (d) CNR1 was linked to overall memory with reduced performance in the homozygous short group. These findings give new insights into how polymorphisms, which are related to dopaminergic neuromodulation, differentially affect long-term recognition memory performance.

Is contrast sensitivity a physiological marker in attention-deficit hyperactivity disorder?

Attention-deficit hyperactivity disorder (ADHD) is one of the most common childhood-onset psychiatric disorders. Although the etiology is complex and has not yet been clarified, dopamine is thought to play a role in the etiology. Methylphenidate (MPH) is a psychostimulant drug used as first-line treatment for ADHD and it inhibits dopamine and norepinephrine reuptake transporters. Dopamine also has an effect on retina and contrast sensitivity. Despite evidence indicating the effects of dopamine on contrast sensitivity, the results of studies examining contrast sensitivity in ADHD patients are inconsistent. Also, no studies have been encountered examining the possible effect of MPH on contrast sensitivity. The hypotheses of this study are that children with ADHD who have not used MPH will have lower contrast sensitivity levels than the members of the control group, that contrast sensitivity levels increase after the use of MPH, and that contrast sensitivity is a potential physiological marker for ADHD. The study was conducted with 30 children with ADHD and 30 children without ADHD. Psychiatric evaluations of the participants were conducted with the Schedule for Affective Disorders and Schizophrenia for School Age Children-Present and Lifetime-Turkish version, Conner's Parent Rating Scale-Revised Short form and the Turgay DSM-IV-based Child and Adolescent Behavioral Disorders Screening and Rating Scale. Photopic contrast sensitivity was measured using the Functional Acuity Contrast Test (FACT). Results showed that FACT mean values of the control group were significantly higher than those of the ADHD group (pre-treatment) in all spatial frequencies. In four spatial frequencies (CPD 1.5, 3, 12 and 18), the FACT mean values of the control group were significantly higher than the ADHD group (during the OROS-MPH treatment). At all spatial frequencies, the mean values of the ADHD group during the OROS-MPH treatment were significantly higher than before the OROS-MPH treatment. In conclusion, the present study showed that contrast sensitivity is low in children with ADHD and increases significantly after OROS-MPH medication, but still did not reach the levels of the children without ADHD. Our findings suggest that contrast sensitivity may be a potential physiological marker in ADHD.

A Behavioral Genetic Model of the Mechanisms Underlying the Link Between Obesity and Symptoms of ADHD

Objective: The ADHD-obesity link has been suggested to result from a shared underlying basis of suboptimal dopamine (DA); however, this theory conflicts evidence that an amplified DA signal increases the risk for overeating and weight gain. A model was tested in which ADHD symptoms, predicted by hypodopaminergic functioning in the prefrontal cortex, in combination with an enhanced appetitive drive, predict hedonic eating and, in turn, higher body mass index (BMI). Method: DRD2 and DRD4 markers were genotyped. The model was tested using structural equation modeling in a nonclinical sample (N = 421 adults). Results: The model was a good fit to the data. Controlling for education, all parameter estimates were significant, except for the DRD4-ADHD symptom pathway. The significant indirect effect indicates that overeating mediated the ADHD symptoms-BMI association. Conclusion: Results support the hypothesis that overeating and elevated DA in the ventral striatum-representative of a greater reward response-contribute to the ADHD symptom-obesity relationship.

Underlying Susceptibility to Eating Disorders and Drug Abuse: Genetic and Pharmacological Aspects of Dopamine D4 Receptors

The dopamine D4 receptor (DRD4) has a predominant expression in the prefrontal cortex (PFC), brain area strictly involved in the modulation of reward processes related to both food and drug consumption. Additionally, the human DRD4 gene is characterized by a variable number of tandem repeats (VNTR) in the exon 3 and, among the polymorphic variants, the 7-repeat (7R) allele appears as a contributing factor in the neurobiological mechanisms underlying drug abuse, aberrant eating behaviors and related comorbidities. The 7R variant encodes for a receptor with a blunted intracellular response to dopamine, and carriers of this polymorphism might be more tempted to enhance dopamine levels in the brain, through the overconsumption of drugs of abuse or palatable food, considering their reinforcing properties. Moreover, the presence of this polymorphism seems to increase the susceptibility of individuals to engage maladaptive eating patterns in response to negative environmental stimuli. This review is focused on the role of DRD4 and DRD4 genetic polymorphism in these neuropsychiatric disorders in both clinical and preclinical studies. However, further research is needed to better clarify the complex DRD4 role, by using validated preclinical models and novel compounds more selective for DRD4.

Predicted DRD4 prefrontal gene expression moderates snack intake and stress perception in response to the environment in adolescents

Body weight is substantially determined by eating behaviors, which are themselves driven by biological factors interacting with the environment. Previous studies in young children suggest that genetic influences on dopamine function may confer differential susceptibility to the environment in such a way that increases behavioral obesity risk in a lower socioeconomic status (SES) environment but decreases it in a higher SES environment. We aimed to test if this pattern of effect could also be observed in adolescence, another critical period for development in brain and behavior, using a novel measure of predicted expression of the dopamine receptor 4 (DRD4) gene in prefrontal cortex. In a sample of 76 adolescents (37 boys and 39 girls from Baltimore, Maryland/US, aged 14-18y), we estimated individual levels of DRD4 gene expression (PredDRD4) in prefrontal cortex from individual genomic data using PrediXcan, and tested interactions with a composite SES score derived from their annual household income, maternal education, food insecurity, perceived resource availability, and receipt of public assistance. Primary outcomes were snack intake during a multi-item ad libitum meal test, and food-related impulsivity assessed using a food-adapted go/no-go task. A linear regression model adjusted for sex, BMI z-score, and genetic ethnicity demonstrated a PredDRD4 by composite SES score interaction for snack intake (p = 0.009), such that adolescents who had lower PredDRD4 levels exhibited greater snack intake in the lower SES group, but lesser snack intake in the higher SES group. Exploratory analysis revealed a similar pattern for scores on the Perceived Stress Scale (p = 0.001) such that the low PredDRD4 group reported higher stress in the lower SES group, but less stress in the higher SES group, suggesting that PredDRD4 may act in part by affecting perceptions of the environment. These results are consistent with a differential susceptibility model in which genes influencing environmental responsiveness interact with environments varying in obesogenicity to confer behavioral obesity risk in a less favorable environment, but behavioral obesity protection in a favorable one.

After the Honeymoon: Neural and Genetic Correlates of Romantic Love in Newlywed Marriages

In Western culture, romantic love is commonly a basis for marriage. Although it is associated with relationship satisfaction, stability, and individual well-being, many couples experience declines in romantic love. In newlyweds, specifically, changes in love predict marital outcomes. However, the biological mechanisms underlying the critical transition to marriage are unknown. Thus, for the first time, we explored the neural and genetic correlates of romantic love in newlyweds. Nineteen first-time newlyweds were scanned (with functional MRI) while viewing face images of the partner versus a familiar acquaintance, around the time of the wedding (T1) and 1 year after (T2). They also provided saliva samples for genetic analysis (AVPR1a rs3, OXTR rs53576, COMT rs4680, and DRD4-7R), and completed self-report measures of relationship quality including the Eros (romantic love) scale. We hypothesized that romantic love is a developed form of the mammalian drive to find, and keep, preferred mates; and that its maintenance is orchestrated by the brain's reward system. Results showed that, at both time points, romantic love maintenance (Eros difference score: T2-T1) was associated with activation of the dopamine-rich substantia nigra in response to face images of the partner. Interactions with vasopressin, oxytocin, and dopamine genes implicated in pair-bonding (AVPR1a rs3, OXTR rs53576, COMT rs4680, and DRD4-7R) also conferred strong activation in the dopamine-rich ventral tegmental area at both time points. Consistent with work highlighting the role of sexual intimacy in relationships, romantic love maintenance showed correlations in the paracentral lobule (genital region) and cortical areas involved in sensory and cognitive processing (occipital, angular gyrus, insular cortex). These findings suggest that romantic love, and its maintenance, are orchestrated by dopamine-, vasopressin- and oxytocin-rich brain regions, as seen in humans and other monogamous animals. We also provide genetic evidence of polymorphisms associated with oxytocin, vasopressin and dopamine function that affect the propensity to sustain romantic love in early stage marriages. We conclude that romantic love maintenance is part of a broad mammalian strategy for reproduction and long-term attachment that is influenced by basic reward circuitry, complex cognitive processes, and genetic factors.

Parsing out the role of dopamine D4 receptor gene (DRD4) on alcohol-related phenotypes: A meta-analysis and systematic review

Genetics account for moderate variation of individual differences in developing alcohol use disorder (AUD), but it is unclear which genetic variations contribute to AUD risk. One candidate gene investigated due to its association with AUD is the dopamine D4 receptor gene (DRD4), which contains a 48-base pair variable number tandem repeat (VNTR) in exon 3 of its coding region. To date, no quantitative synthesis of the published literature on the effects of DRD4 VNTR variation on alcohol-related phenotypes has been conducted. MEDLINE, Embase, Web of Science, and PsycInfo were searched for studies that reported on alcohol craving, alcohol consumption, severity of AUD, and case-control (AUD versus no diagnosis of AUD) studies in DRD4L (seven repeats or more) carriers compared with DRD4S (six repeats or less) homozygotes. Random-effects meta-analysis was used for all analyses. A pooled sample size of 655 to 13,360 of 28 studies were included. Compared with DRD4S homozygotes, DRD4L carriers had increased number of drinking days (SMD: 0.205; 95% CI: 0.008 to 0.402), binge drinking days (SMD: 0.217; 95% CI: 0.0532 to 0.380), and severity of AUD (SMD: 0.143; 95% CI: 0.028 to 0.259). There was no difference between DRD4 VNTR genotypes on drinks per drinking day, largest number of drinks per day/occasion, and case-control analysis. It was not possible to conduct a meta-analysis of the craving data, but a systematic review of this literature found mixed results on DRD4 VNTR genotype effect. The present meta-analysis suggests DRD4 VNTR variation may be a risk factor for problematic alcohol use. Our findings are limited, however, by the absence of ancestry data from studies included in our analysis, precluding our ability to adjust for population stratification. Due to the likelihood of type I error in candidate gene approaches, our work highlights the critical need for studies with larger and more inclusive samples that account for sex and genetic ancestry to fully understand this relationship.