The association of DRD4 and novelty seeking is found in a nonhuman primate model

The dopaminergic system and Alzheimer's disease

Alzheimer's disease is a common neurodegenerative disorder in older adults. Despite its prevalence, its pathogenesis remains unclear. In addition to the most widely accepted causes, which include excessive amyloid-beta aggregation, tau hyperphosphorylation, and deficiency of the neurotransmitter acetylcholine, numerous studies have shown that the dopaminergic system is also closely associated with the occurrence and development of this condition. Dopamine is a crucial catecholaminergic neurotransmitter in the human body. Dopamine-associated treatments, such as drugs that target dopamine receptor D and dopamine analogs, can improve cognitive function and alleviate psychiatric symptoms as well as ameliorate other clinical manifestations. However, therapeutics targeting the dopaminergic system are associated with various adverse reactions, such as addiction and exacerbation of cognitive impairment. This review summarizes the role of the dopaminergic system in the pathology of Alzheimer's disease, focusing on currently available dopamine-based therapies for this disorder and the common side effects associated with dopamine-related drugs. The aim of this review is to provide insights into the potential connections between the dopaminergic system and Alzheimer's disease, thus helping to clarify the mechanisms underlying the condition and exploring more effective therapeutic options.

DRD4 allele frequencies in greylag geese vary between urban and rural sites

With the increasing urbanization of the last decades, more and more bird species occur in urban habitats. Birds which thrive in urban habitats often have a higher tolerance toward human disturbance and show behaviors which differ from their rural counterparts. There is increasing evidence that many behaviors have a genetic basis. One candidate gene is the dopamine receptor D4 (DRD4), which has been associated with fear and thus, flight initiation distance (FID). In this study, we analyzed a segment of DRD4 in greylag geese Anser anser, describing the variability of this gene across several geographically distant populations, and comparing its variability between an urban and a rural site in south-west Germany. We additionally measured FIDs of urban and rural geese to test for a possible correlation with DRD4 genotypes. We found a high variation within DRD4, with 10 variable sites leading to 11 alleles and 35 genotypes. Two genotypes occurred in 60% of all geese and were thus defined as common genotypes versus 33 rare genotypes. Population differentiation was very low between the urban and rural sites in Germany but common genotypes occurred more often in the urban area and rare genotypes more often in the rural area. FID was significantly higher at the rural site, but no significant correlation between FID and DRD4 genotypes could be detected. Nevertheless, our results suggest that local site selection may be related to DRD4 genotypes.

Research Relevant Conditions and Pathology in Nonhuman Primates

Biomedical research involving animal models continues to provide important insights into disease pathogenesis and treatment of diseases that impact human health. In particular, nonhuman primates (NHPs) have been used extensively in translational research due to their phylogenetic proximity to humans and similarities to disease pathogenesis and treatment responses as assessed in clinical trials. Microscopic changes in tissues remain a significant endpoint in studies involving these models. Spontaneous, expected (ie, incidental or background) histopathologic changes are commonly encountered and influenced by species, genetic variations, age, and geographical origin of animals, including exposure to infectious or parasitic agents. Often, the background findings confound study-related changes, because numbers of NHPs used in research are limited by animal welfare and other considerations. Moreover, background findings in NHPs can be exacerbated by experimental conditions such as treatment with xenobiotics (eg, infectious morphological changes related to immunosuppressive therapy). This review and summary of research-relevant conditions and pathology in rhesus and cynomolgus macaques, baboons, African green monkeys, common marmosets, tamarins, and squirrel and owl monkeys aims to improve the interpretation and validity of NHP studies.

Experimental evidence for a role of dopamine in avian personality traits

There is increasing interest in the genetic and physiological bases of behavioural differences among individuals, namely animal personality. One particular dopamine (DA) receptor gene (the dopamine receptor D4 gene) has been used as candidate gene to explain personality differences, but with mixed results. Here, we used an alternative approach, exogenously manipulating the dopaminergic system and testing for effects on personality assays in a social bird species, the common waxbill (Estrilda astrild). We treated birds with agonists and antagonists for DA receptors of both D1 and D2 receptor pathways (the latter includes the D4 receptor) and found that short-term manipulation of DA signalling had an immediate effect on personality-related behaviours. In an assay of social responses (mirror test), manipulation of D2 receptor pathways reduced time spent looking at the social stimulus (mirror image). Blocking D2 receptors reduced motor activity in this social assay, while treatment with a D2 receptor agonist augmented activity in this social assay but reduced activity in a non-social behavioural assay. Also, in the non-social assay, treatment with the D1 receptor antagonist markedly increased time spent at the feeder. These results show distinct and context-specific effects of the dopaminergic pathways on waxbill personality traits. Our results also suggest that experimental manipulation of DA signalling can disrupt a behavioural correlation (more active individuals being less attentive to mirror image) that is habitually observed as part of a behavioural syndrome in waxbills. We discuss our results in the context of animal personality, and the role of the DA system in reward and social behaviour.

Genetic Polymorphisms on OPRM1, DRD2, DRD4, and COMT in Young Adults: Lack of Association With Alcohol Consumption

Background: Risk behaviors for young adults such as alcohol use are associated with increased risk of morbidity and mortality. Patterns of risk behavior may be genetically determined and vary between genders. Previous studies in both young adults and heavy drinking adult samples have demonstrated that some genotypes, such as OPRM1 A118G, COMT Val158Met and DRD2 Taq1A and DRD4 C52IT, may predict addictive behaviors including alcohol consumption and impulsivity, although results have been mixed. Methods: This study aimed to investigate the predictive relationship of these four single nucleotide polymorphisms (SNPs) prospectively on student patterns of drinking using a micro-longitudinal daily diary design in a sample of 628 young adults ages 18-25 of predominantly of European ethnicity. Linear mixed models were used to examine the effect of SNPs on the number of drinks per drinking session with gender as a moderating variable. Results: There were no main effects for genotype on alcohol consumption, nor for gender × genotype for any of the SNPs. There was a trend for an effect of the DRD2 Taq1A on the number of drinks per drinking day and for the interaction of gender and DRD2 Taq1A on the number of drinks per drinking day. Conclusion: These findings suggest that the DRD2 Taq1A, OPRM1 A118G, DRD4 C521T, or COMT Val158Met polymorphisms, are not associated with alcohol consumption in young adults, although there may be a relationship between DRD2 Taq1A and alcohol consumption in young adult males.

Primates got personality, too: Toward an integrative primatology of consistent individual differences in behavior

In recent years, research on animal personality has exploded within the field of behavioral ecology. Consistent individual differences in behavior exist in a wide range of species, and these differences can have fitness consequences and influence several aspects of a species' ecology. In comparison to studies of other animals, however, there has been relatively little research on the behavioral ecology of primate personality. This is surprising given the large body of research within psychology and biomedicine showing that primate personality traits are heritable and linked to health and life history outcomes. In this article, I bring together theoretical perspectives on the ecology and evolution of animal personality with an integrative review of what we know about primate personality from studies conducted on captive, free-ranging, and wild primates. Incorporating frameworks that emphasize consistency in behavior into primate behavioral ecology research holds promise for improving our understanding of primate behavioral evolution.

Dopamine D4 Receptor-Selective Compounds Reveal Structure-Activity Relationships that Engender Agonist Efficacy

The dopamine D4 receptor (D4R) plays important roles in cognition, attention, and decision making. Novel D4R-selective ligands have promise in medication development for neuropsychiatric conditions, including Alzheimer's disease and substance use disorders. To identify new D4R-selective ligands, and to understand the molecular determinants of agonist efficacy at D4R, we report a series of eighteen novel ligands based on the classical D4R agonist A-412997 (1, 2-(4-(pyridin-2-yl)piperidin-1-yl)- N-( m-tolyl)acetamide). Compounds were profiled using radioligand binding displacement assays, β-arrestin recruitment assays, cyclic AMP inhibition assays, and molecular dynamics computational modeling. We identified several novel D4R-selective ( Ki ≤ 4.3 nM and >100-fold vs other D2-like receptors) compounds with diverse partial agonist and antagonist profiles, falling into three structural groups. These compounds highlight receptor-ligand interactions that control efficacy at D2-like receptors and may provide insights into targeted drug discovery, leading to a better understanding of the role of D4Rs in neuropsychiatric disorders.

Gene polymorphisms associated with temperament

When individuals are exposed to stressful environmental challenges, the response varies widely in one or more of three components: psychology, behavior and physiology. This variability among individuals can be defined as temperament. In recent years, an increasing large body of evidence suggests that the dimensions of temperament, as well as personality, psychological disorders and behavioral traits, are influenced by genetic factors, and much of the variation appears to involve variation in genes or gene polymorphisms in the hypothalamic-pituitary-adrenocortical (HPA) axis and the behavior-controlling neurotransmitter networks. Here, we review our current understanding of the probabilistic impact of a number of candidate gene polymorphisms that control temperament, psychological disorders and behavioral traits in animals and human, including the gene polymorphisms related to corticotrophin-releasing hormone (CRH) production and adrenal cortisol production involved in the HPA axis, and a large number of gene polymorphisms in the dopaminergic and serotonergic neurotransmitter networks. It will very likely to assist in diagnosis and treatment of human relevant disorders, and provide useful contributions to our understanding of evolution, welfare and conservation, for animals in the wild and in production systems. Additionally, investigations of gene-gene and gene-environment complex interactions in humans and animals need further clear illustration.

Interhemispheric gene expression differences in the cerebral cortex of humans and macaque monkeys

Handedness and language are two well-studied examples of asymmetrical brain function in humans. Approximately 90% of humans exhibit a right-hand preference, and the vast majority shows left-hemisphere dominance for language function. Although genetic models of human handedness and language have been proposed, the actual gene expression differences between cerebral hemispheres in humans remain to be fully defined. In the present study, gene expression profiles were examined in both hemispheres of three cortical regions involved in handedness and language in humans and their homologues in rhesus macaques: ventrolateral prefrontal cortex, posterior superior temporal cortex (STC), and primary motor cortex. Although the overall pattern of gene expression was very similar between hemispheres in both humans and macaques, weighted gene correlation network analysis revealed gene co-expression modules associated with hemisphere, which are different among the three cortical regions examined. Notably, a receptor-enriched gene module in STC was particularly associated with hemisphere and showed different expression levels between hemispheres only in humans.

Genes, social transmission, but not maternal effects influence responses of wild Japanese macaques (Macaca fuscata) to novel-object and novel-food tests

Using long-term maternal pedigree data, microsatellite analysis, and behavioral tests, we examined whether personality differences in wild Japanese macaques (Macaca fuscata) are associated with additive genetic effects, maternal influences, or belonging to a particular social group. Behaviors elicited by novel-object tests were defined by a component related to caution around novel-objects (Ob-PC1) and behaviors elicited by novel food-tests were defined by correlated components related to consummatory responses (Fo-PC1) and caution around novel foods (Fo-PC2). The repeatability of Ob-PC1 was modest and not significant; the repeatabilities of Fo-PC1 and Fo-PC2 were moderate and significant. Linear mixed effects models found that sex, age, sex × age, provisioning, trial number, date, time of day, season, and distance to the closest monkey were not related to personality. Linear mixed effects models of females older than 2 years found that high rank was associated with greater caution around novel objects. Linear models were used to determine whether sex, age, group membership, maternal kinship, or relatedness had independent effects on the personality similarity of dyads. These analyses found that pairs of macaques that lived in the same group were less similar in their caution around novel objects, more closely related pairs of macaques were more similar in their tendency to eat novel food, and that pairs of macaques in the same group were more similar in how cautious they were around novel foods. Together, these findings suggest that personality in this population of wild monkeys was driven by rank, genetic effects, and group effects, the latter possibly including the need to exploit different niches in the environment.

Threats from the past: Barbados green monkeys (Chlorocebus sabaeus) fear leopards after centuries of isolation

Ability to recognize and differentiate between predators and non-predators is a crucial component of successful anti-predator behavior. While there is evidence that both genetic and experiential mechanisms mediate anti-predator behaviors in various animal species, it is unknown to what extent each of these two mechanisms are utilized by the green monkey (Chlorocebus sabaeus). Green monkeys on the West Indies island of Barbados offer a unique opportunity to investigate the underpinnings of anti-predator behaviors in a species that has been isolated from ancestral predators for over 350 years. In the first experiment, monkeys in two free-ranging troops were presented with photographs of an ancestral predator (leopard, Panthera pardus) and a non-predator (African Buffalo, Syncerus caffer). Relative to non-predator stimuli, images of a leopard elicited less approach, more alarm calls, and more escape responses. Subsequent experiments were conducted to determine whether the monkeys were responding to a leopard-specific feature (spotted fur) or a general predator feature (forward facing eyes). The monkeys showed similar approach to images of an unfamiliar non-predator regardless of whether the image had forward facing predator eyes or side facing non-predator eyes. However, once near the images, the monkeys were less likely to reach for peanuts near the predator eyes than the non-predator eyes. The monkeys avoided an image of spotted leopard fur but approached the same image of fur when the dark spots had been removed. Taken together, the results suggest that green monkey anti-predator behavior is at least partially mediated by genetic factors.

Associations between temperament and gene polymorphisms in the brain dopaminergic system and the adrenal gland of sheep

Sheep of calm or nervous temperament differ in their physiological (cortisol secretion) and behavioural (motor activity) responses to stressors, perhaps due to variation in genes that regulate glucocorticoid synthesis or brain dopamine activity. Using ewes that had been selected over 20 generations for nervous (n=58) or calm (n=59) temperament, we confirmed the presence of a polymorphism in a gene specifically involved in cortisol production (CYP17), and identified polymorphisms in three genes specifically associated with personality and behavioural traits: dopamine receptors 2 and 4 (DRD2, DRD4), and monoamine oxidase A (MAOA). The calm and nervous lines differed in their frequencies of CYP17 SNP628 (single nucleotide A-G mutation at position 628) and DRD2 SNP939 (single nucleotide T-C mutation at position 939), but not for other SNPs detected in DRD2 or MAOA. In a second experiment, we then genotyped a large, non-selected flock of ewes for DRD2 SNP939 and CYP17 SNP628. Responses to the 'arena' and 'isolation box' challenges were associated with the DRD2 SNP939 genotype and the response to ACTH challenge was associated with the CYP17 SNP628 genotype. We conclude that, for sheep, a combination of the DRD2 SNP939 C allele and the CYP17 SNP628 A/A genotype could be used as a genetic marker for nervous temperament, and that a combination of DRD2 SNP939 T/T and CYP17 SNP628 G/G could be used as a genetic marker for calm temperament.

Chimpanzee sociability is associated with vasopressin (Avpr1a) but not oxytocin receptor gene (OXTR) variation

The importance of genes in regulating phenotypic variation of personality traits in humans and animals is becoming increasingly apparent in recent studies. Here we focus on variation in the vasopressin receptor gene 1a (Avpr1a) and oxytocin receptor gene (OXTR) and their effects on social personality traits in chimpanzees. We combine newly available genetic data on Avpr1a and OXTR allelic variation of 62 captive chimpanzees with individual variation in personality, based on behavioral assessments. Our study provides support for the positive association of the Avpr1a promoter region, in particular the presence of DupB, and sociability in chimpanzees. This complements findings of previous studies on adolescent chimpanzees and studies that assessed personality using questionnaire data. In contrast, no significant associations were found for the single nucleotide polymorphism (SNP) ss1388116472 of the OXTR and any of the personality components. Most importantly, our study provides additional evidence for the regulatory function of the 5' promoter region of Avpr1a on social behavior and its evolutionary stable effect across species, including rodents, chimpanzees and humans. Although it is generally accepted that complex social behavior is regulated by a combination of genes, the environment and their interaction, our findings highlight the importance of candidate genes with large effects on behavioral variation.

Studying longitudinal trajectories in animal models of psychiatric illness and their translation to the human condition

Many forms of psychopathology and/or psychiatric illness can occur through the pathways of altered environmental sensitivity, impulsivity, social functioning, and anxious responding. While these traits are also heritable, environmental conditions are known to play a critical role. The genetic factors that contribute to these traits may be adaptive in certain contexts, but can - under the environmental conditions commonly faced among modern humans - also be key moderators of risk for psychopathological outcomes. This article will discuss how animal studies inform us of the various environmental mechanisms through which prenatal or early postnatal environmental challenge can produce long-term effects on behavior and will briefly address how pre-copulatory, pre-natal and early postnatal epigenetic effects can contribute to persistent alterations in offspring behavior. Its main focus will be how nonhuman primate studies have helped us to understand how genetic vulnerability factors can moderate responses to early environmental factors, suggesting pathways through which early stress might produce long-term effects, thus pointing to systems that might moderate risk for psychiatric illnesses in humans.

Dopamine D4 receptor genotype variation in free-ranging rhesus macaques and its association with juvenile behavior

A polymorphism in the dopamine receptor D4 (DRD4) gene has been associated with significant variation in behavioral impulsivity, novelty-seeking, and risk-taking in humans and other animals. Rhesus macaques are an excellent animal model for research on the genetic basis of behavior using the candidate gene approach. Little is known, however, about allelic variation in DRD4 in large free-ranging populations of rhesus macaques and how this allelic variation relates to emotion regulation and behavior. In this study, we genotyped for the DRD4 polymorphism 178 individuals of different age and sex categories in the free-ranging rhesus macaque population on the island of Cayo Santiago, PR. Moreover, we examined the possible association between DRD4 allelic variation and three measures of juvenile behavior (time spent in proximity to the mother, avoidance of other individuals, and behavioral restlessness). Five different DRD4 alleles (5R, 5.5R, 6R, 6.5R, and 7R) were identified in the subject population. The most common allele was the 5R allele (78.5%), followed by the 7R allele (16.1%). Juveniles carrying the long form of the DRD4 allele (7R) spent less time in proximity to their mothers, avoided other individuals more often, and scored higher on behavioral restlessness than juveniles carrying the shorter alleles. Behavioral restlessness was also influenced by maternal DRD4 genotype. These results highlight both similarities and differences in the relative occurrence of DRD4 alleles and their association with behavior in this rhesus macaque population, other nonhuman primate species or populations, and humans.

Combined epigenetic and intraspecific variation of the DRD4 and SERT genes influence novelty seeking behavior in great tit Parus major

DNA methylation is one of the main epigenetic mechanisms that can regulate gene expression and is an important means for creating phenotypic variation. In the present study, we performed methylation profiling of 2 candidate genes for personality traits, namely DRD4 and SERT, in the great tit Parus major to ascertain whether personality traits and behavior within different habitats have evolved with the aid of epigenetic variation. We applied bisulphite PCR and strand-specific sequencing to determine the methylation profile of the CpG dinucleotides in the DRD4 and SERT promoters and also in the CpG island overlapping DRD4 exon 3. Furthermore, we performed pyrosequencing to quantify the total methylation levels at each CpG location. Our results indicated that methylation was ∼1-4% higher in urban than in forest birds, for all loci and tissues analyzed, suggesting that this epigenetic modification is influenced by environmental conditions. Screening of genomic DNA sequence revealed that the SERT promoter is CpG poor region. The methylation at a single CpG dinucleotide located 288 bp from the transcription start site was related to exploration score in urban birds. In addition, the genotypes of the SERT polymorphism SNP234 located within the minimal promoter were significantly correlated with novelty seeking behavior in captivity, with the allele increasing this behavior being more frequent in urban birds. As a conclusion, it seems that both genetic and methylation variability of the SERT gene have an important role in shaping personality traits in great tits, whereas genetic and methylation variation at the DRD4 gene is not strongly involved in behavior and personality traits.

Genetics of cattle temperament and its impact on livestock production and breeding – a review

Abstract. Cattle temperament, which describes individual behaviour differences with regard to a stressor or environmental challenge, is known for its impact on working safety, adaptability to new housing conditions, animal productivity and for evaluation of animal welfare. However, successful use of temperament in animal breeding and husbandry to improve keeping conditions in general or animal welfare in particular, requires the availability of informative and reproducible phenotypes and knowledge about the genetic modulation of these traits. However, the knowledge about genetic influences on cattle temperament is still limited. In this review, an outline is given for the interdependence between production systems and temperament as well as for the phenotyping of cattle temperament based on both behaviour tests and observations of behaviour under production conditions. In addition, the use of temperament as a selection criterion is discussed.

Social behavioral changes in MPTP-treated monkey model of Parkinson's disease

Parkinsonian patients experience not only the physical discomfort of motor disorders but also the considerable psychological distress caused by cognitive deficits and behavioral disorders. These two factors can result in a disruption of social relationships during the symptomatic and even the presymptomatic motor states of the disease. However, it remains difficult, if not impossible, to evaluate social relationships in presymptomatic patients. The present study focused on the evaluation of social relationships within a group of female long-tailed macaques during presymptomatic and symptomatic motor states induced by Chronic Low-Dose (CLD) and then Chronic High-Dose (CHD) systemic administration of 1-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP). Dopaminergic denervation within basal ganglia and cortical areas was evaluated using Positron Emission Tomography (PET) scans with (18)F-DOPA (6-[18F]-fluoro-L-3,4-dihydroxyphenylalanine) radiotracer. Interestingly, social behavioral changes could be identified in the presymptomatic motor state before any motor and/or cognitive impairment occurred. Stronger effects were observed in subordinate animals compared to dominant animals. From baseline state to CLD-presymptomatic motor state, the frequency of emitted affiliative and aggressive behaviors increased. From CLD-presymptomatic to CHD-presymptomatic motor states, the frequency of the three categories of social behaviors (aggressive, submissive and affiliative) decreased. At this time, quantitative data analysis in PET scans highlighted a dopaminergic denervation in the insula and the posterior caudate nucleus. Finally, the frequency of the three categories of social behaviors decreased during the stable-symptomatic motor state compared to baseline and presymptomatic motor states; this was also associated with motor and cognitive disorders and a dopaminergic denervation in all the evaluated cortical and subcortical structures.

Functional interactions of dopamine cell groups reflect personality, sex, and social context in highly social finches

Dopamine (DA) is well known for its involvement in novelty-seeking, learning, and goal-oriented behaviors such as social behavior. However, little is known about how DA modulates social processes differentially in relation to sex and behavioral phenotype (e.g., personality). Importantly, the major DA cell groups (A8-A15) are conserved across all amniote vertebrates, and thus broadly relevant insights may be obtained through investigations of avian species such as zebra finches (Taeniopygia guttata), which express a human-like social organization based on biparental nuclear families that are embedded within larger social groups. We here build upon a previous study that quantified multidimensional personality structures in male and female zebra finches using principal components analysis (PCA) of extensive behavioral measures in social and nonsocial contexts. These complex dimensions of behavioral phenotype can be characterized as Social competence/dominance, Gregariousness, and Anxiety. Here we analyze Fos protein expression in DA neuronal populations in response to social novelty and demonstrate that the Fos content of multiple dopamine cell groups is significantly predicted by sex, personality, social context, and their interactions. In order to further investigate coordinated neuromodulation of behavior across multiple DA cell groups, we also conducted a PCA of neural variables (DA cell numbers and their phasic Fos responses) and show that behavioral PCs are associated with unique suites of neural PCs. These findings demonstrate that personality and sex are reflected in DA neuron activity and coordinated patterns of neuromodulation arising from multiple DA cell groups.

Systems biology of the vervet monkey

Nonhuman primates (NHP) provide crucial biomedical model systems intermediate between rodents and humans. The vervet monkey (also called the African green monkey) is a widely used NHP model that has unique value for genetic and genomic investigations of traits relevant to human diseases. This article describes the phylogeny and population history of the vervet monkey and summarizes the use of both captive and wild vervet monkeys in biomedical research. It also discusses the effort of an international collaboration to develop the vervet monkey as the most comprehensively phenotypically and genomically characterized NHP, a process that will enable the scientific community to employ this model for systems biology investigations.

Interactive association of dopamine receptor (DRD4) genotype and ADHD on alcohol expectancies in children

Positive and negative alcohol expectancies (AEs) are beliefs about the consequences of alcohol use (e.g., happy, sad, lazy) and they predict patterns of adolescent and adult alcohol engagement in clinical and nonclinical samples. However, significantly less is known about predictors of AE in children, despite significant variability in AE early in and across development. To identify temporally ordered risk factors that precede AE, we evaluated the independent and interactive association of the functional 7-repeat polymorphism of the dopamine D4 receptor (DRD4) genotype and attention-deficit/hyperactivity disorder (ADHD) with respect to individual differences in positive-social, negative-arousal, sedated/impaired, and wild/crazy AE in school-age children (N = 149) prospectively followed from 6-9 to 8-13 years of age. Controlling for age, sex, and wave, DRD4 7+ carriers reported more wild/crazy AE, but DRD4 was unrelated to the remaining AE domains. ADHD symptoms independently predicted higher negative-arousal, sedated/impaired, and wild/crazy AE, but not positive-social. We also observed a significant interaction in which ADHD symptoms positively predicted wild/crazy AE only in youth with the 7-repeat DRD4 genotype; the same interaction marginally predicted sedated/impaired AE. No interactive effects were observed for the remaining AE domains. These preliminary results suggest that, among DRD4 youth, early ADHD symptoms predict that children will expect alcohol to have wild/crazy effects. We consider these results within a developmental framework to better understand pathways to and from youth alcohol problems.

The relationship between DRD4 polymorphisms and phenotypic correlations of behaviors in the collared flycatcher

There is increasing evidence that the genetic architecture of exploration behavior includes the dopamine receptor D4 gene (DRD4). Such a link implies that the within-individual consistency in the same behavior has a genetic basis. Behavioral consistency is also prevalent in the form of between-individual correlation of functionally different behaviors; thus, the relationship between DRD4 polymorphism and exploration may also be manifested for other behaviors. Here, in a Hungarian population of the collared flycatcher, Ficedula albicollis, we investigate how males with distinct DRD4 genotypes differ in the consistent elements of their behavioral displays during the courtship period. In completely natural conditions, we assayed novelty avoidance, aggression and risk-taking, traits that were previously shown repeatable over time and correlate with each other, suggesting that they could have a common mechanistic basis. We identified two single-nucleotide polymorphisms (SNP554 and SNP764) in the exon 3 of the DRD4 gene by sequencing a subsample, then we screened 202 individuals of both sexes for these SNPs. Focusing on the genotypic variation in courting males, we found that “AC” heterozygote individuals at the SNP764 take lower risk than the most common “AA” homozygotes (the “CC” homozygotes were not represented in our subsample of males). We also found a considerable effect size for the relationship between SNP554 polymorphism and novelty avoidance. Therefore, in addition to exploration, DRD4 polymorphisms may also be associated with the regulation of behaviors that may incur fear or stress. Moreover, polymorphisms at the two SNPs were not independent indicating a potential role for genetic constraints or another functional link, which may partially explain behavioral correlations.

Dissecting impulsivity and its relationships to drug addictions

Addictions are often characterized as forms of impulsive behavior. That said, it is often noted that impulsivity is a multidimensional construct, spanning several psychological domains. This review describes the relationship between varieties of impulsivity and addiction-related behaviors, the nature of the causal relationship between the two, and the underlying neurobiological mechanisms that promote impulsive behaviors. We conclude that the available data strongly support the notion that impulsivity is both a risk factor for, and a consequence of, drug and alcohol consumption. While the evidence indicating that subtypes of impulsive behavior are uniquely informative--either biologically or with respect to their relationships to addictions--is convincing, multiple lines of study link distinct subtypes of impulsivity to low dopamine D2 receptor function and perturbed serotonergic transmission, revealing shared mechanisms between the subtypes. Therefore, a common biological framework involving monoaminergic transmitters in key frontostriatal circuits may link multiple forms of impulsivity to drug self-administration and addiction-related behaviors. Further dissection of these relationships is needed before the next phase of genetic and genomic discovery will be able to reveal the biological sources of the vulnerability for addiction indexed by impulsivity.

Quantitative Genetics of Response to Novelty and Other Stimuli by Infant Rhesus Macaques (Macaca mulatta) Across Three Behavioral Assessments

Primate behavior is influenced by both heritable factors and environmental experience during development. Previous studies of rhesus macaques (Macaca mulatta) examined the effects of genetic variation on expressed behavior and related neurobiological traits (heritability and/or genetic association) using a variety of study designs. Most of these prior studies examined genetic effects on the behavior of adults or adolescent rhesus macaques, not in young macaques early in development. To assess environmental and additive genetic variation in behavioral reactivity and response to novelty among infants, we investigated a range of behavioral traits in a large number (N = 428) of pedigreed infants born and housed in large outdoor corrals at the Oregon National Primate Research Center (ONPRC). We recorded the behavior of each subject during a series of brief tests, involving exposure of each infant to a novel environment, to a social threat without the mother present, and to a novel environment with its mother present but sedated. We found significant heritability (h² ) for willingness to move away from the mother and explore a novel environment (h² = 0.25 ± 0.13; P = 0.003). The infants also exhibited a range of heritable behavioral reactions to separation stress or to threat when the mother was not present (h² = 0.23 ± 0.13-0.24 ± 0.15, P < 0.01). We observed no evidence of maternal environmental effects on these traits. Our results extend knowledge of genetic influences on temperament and reactivity in nonhuman primates by demonstrating that several measures of behavioral reactivity among infant rhesus macaques are heritable.

Neurogenetics of aggressive behavior: studies in primates

Aggressive behavior can have adaptive value in certain environmental contexts, but when extreme or executed inappropriately, can also lead to maladaptive outcomes. Neurogenetic studies performed in nonhuman primates have shown that genetic variation that impacts reward sensitivity, impulsivity, and anxiety can contribute to individual differences in aggressive behavior. Genetic polymorphisms in the coding or promoter regions of the Mu-Opioid Receptor (OPRM1), Corticotropin Releasing Hormone (CRH), Monoamine Oxidase A (MAOA), Dopamine D4 Receptor (DRD4), and Serotonin Transporter (SLC6A4) genes have been shown to be functionally similar in humans and rhesus macaques and have been demonstrated to contribute to individual differences in aggression. This body of literature suggests mechanisms by which genetic variation that promotes aggressivity could simultaneously increase evolutionary success while making modern humans more vulnerable to psychopathology.

DRD4 and TH gene polymorphisms are associated with activity, impulsivity and inattention in Siberian Husky dogs

Both dopamine receptor D4 (DRD4) exon 3 and tyrosine hydroxylase (TH) intron 4 repeat polymorphisms have been linked to activity and impulsivity in German Shepherd dogs (GSDs). However, the results in GSDs may not be generalisable to other breeds, as allelic frequencies vary markedly among breeds. We selected the Siberian Husky for further study, because it is highly divergent from most dog breeds, including the GSD. The study sample consisted of 145 racing Siberian Huskies from Europe and North America. We found that this breed possesses seven DRD4 length variants, two to five more variants than found in other breeds. Among them was the longest known allele, previously described only in wolves. Short alleles of the DRD4 and TH repeat polymorphisms were associated with higher levels of activity, impulsivity and inattention. Siberian Huskies possessing at least one short allele of the DRD4 polymorphism displayed greater activity in a behavioural test battery than did those with two long alleles. However, the behavioural test was brief and may not have registered variation in behaviour across time and situations. Owners also completed the Dog-Attention Deficit Hyperactivity Disorder Rating Scale (Dog-ADHD RS), a more general measure of activity and attention. Siberian Huskies from Europe with two short alleles of the TH polymorphism received higher ratings of inattention on the Dog-ADHD RS than did those with the long allele. Investigation of the joint effect of DRD4 and TH showed that dogs possessing long alleles at both sites were scored as less active-impulsive than were others. Our results are aligned with previous studies showing that DRD4 and TH polymorphisms are associated with activity-impulsivity related traits in dogs. However, the prevalence of variants of these genes differs across breeds, and the functional role of specific variants is unclear.

Personality assessment and its association with genetic factors in captive Asian and African elephants

Elephants live in a complex society based on matrilineal groups. Management of captive elephants is difficult, partly because each elephant has a unique personality. For a better understanding of elephant well being in captivity, it would be helpful to systematically evaluate elephants' personalities and their underlying biological basis. We sent elephant' personality questionnaires to keepers of 75 elephants. We also used 196 elephant DNA samples to search for genetic polymorphisms in genes expressed in the brain that have been suggested to be related to personality traits. Three genes, androgen receptor (AR), fragile X related mental retardation protein interacting protein (NUFIP2), and acheate-scute homologs 1 (ASH1) contained polymorphic regions. We examined the association of personality with intraspecific genetic variation in 17 Asian and 28 African elephants. The results suggest that the ASH1 genotype was associated with neuroticism in Asian elephants. Subjects with short alleles had lower scores of neuroticism than those with long alleles. This is the first report of an association between a genetic polymorphism and personality in elephants.

Maternal and offspring dopamine D4 receptor genotypes interact to influence juvenile impulsivity in vervet monkeys

The merging of psychological and genetic methodologies has led to an increasing appreciation of environmental moderators of the relationships between genotype and phenotype. Here we used a nonhuman-primate model to study the moderating effect of the mother's genotype on the association of a dopamine D4 receptor (DRD4) gene polymorphism with juvenile impulsivity, assessed in a standardized social-challenge test. The results showed that juvenile carriers of the rare 5-repeat variant of the exon III 48-base-pair repeat polymorphism scored significantly higher in social impulsivity than juveniles homozygous for the common 6-repeat allele. In addition, juvenile genotype interacted with maternal genotype to influence impulsivity, with the highest rates of impulsivity found in variant offspring with variant mothers. These results highlight the importance of considering the genotype of the parents in studies of early experience and vulnerability genes for impulsivity-related traits.

Aging does not reduce heat shock protein 70 in the absence of chronic insulin resistance

Heat shock protein (HSP)70 decreases with age. Often aging is associated with coincident insulin resistance and higher blood glucose levels, which also associate with lower HSP70. We aimed to understand how these factors interrelate through a series of experiments using vervet monkeys (Chlorocebus aethiops sabaeous). Monkeys (n = 284, 4-25 years) fed low-fat diets showed no association of muscle HSP70 with age (r = .04, p = .53), but levels were highly heritable. Insulin resistance was induced in vervet monkeys with high-fat diets, and muscle biopsies were taken after 0.3 or 6 years. HSP70 levels were significantly greater after 0.3 years (+72%, p < .05) but were significantly lower following 6 years of high-fat diet (-77%, p < .05). Associations with glucose also switched from being positive (r = .44, p = .03) to strikingly negative (r = -.84, p < .001) with increasing insulin resistance. In conclusion, a low-fat diet may preserve tissue HSP70 and health with aging, whereas high-fat diets, insulin resistance, and genetic factors may be more important than age for determining HSP70 levels.

Polymorphism in the tyrosine hydroxylase (TH) gene is associated with activity-impulsivity in German Shepherd Dogs

We investigated the association between repeat polymorphism in intron 4 of the tyrosine hydroxylase (TH) gene and two personality traits, activity-impulsivity and inattention, in German Shepherd Dogs. The behaviour of 104 dogs was characterized by two instruments: (1) the previously validated Dog-Attention Deficit Hyperactivity Disorder Rating Scale (Dog-ADHD RS) filled in by the dog owners and (2) the newly developed Activity-impulsivity Behavioural Scale (AIBS) containing four subtests, scored by the experimenters. Internal consistency, inter-observer reliability, test-retest reliability and convergent validity were demonstrated for AIBS.

Dogs possessing at least one short allele were proved to be more active-impulsive by both instruments, compared to dogs carrying two copies of the long allele (activity-impulsivity scale of Dog-ADHD RS: p = 0.007; AIBS: p = 0.023). The results have some potential to support human studies; however, further research should reveal the molecular function of the TH gene variants, and look for the effect in more breeds.

A novelty seeking phenotype is related to chronic hypothalamic-pituitary-adrenal activity reflected by hair cortisol

Reduced hypothalamic pituitary adrenal (HPA) activity is associated with greater novelty seeking in humans. Hair cortisol represents an integrated proxy measure of total cortisol production/release over an extended period of time and may be a valuable tool for tracking the HPA system. Sampling approaches (collection of blood, saliva, urine, or feces) for socially housed nonhuman primates present a number of technical challenges for collection particularly when repeated sampling is necessary. Herein we describe a relationship between cortisol levels measured in hair collected from 230 socially housed female vervet (Chlorocebus aethiops sabaeus) monkeys and a free-choice novelty seeking phenotype. A predator-like object was placed at the periphery of the outdoor enclosures for 30 min and speed of approach (latency to approach within 1m) and persistence of interest (number of 1 min intervals within 1m) were scored. A composite Novelty Seeking score, combining these two measures, was calculated. The intra-class correlation coefficient (ICC=.68) for two different objects across years indicated that this score reflects a stable aspect of temperament. Hair samples were collected from each subject approximately 3-6 months following the second assessment; cortisol levels were determined from the hair. A significant inverse relationship of Novelty Seeking score with hair cortisol level (p<.01) was noted. The high hair cortisol groups had significantly lower Novelty Seeking scores than the low cortisol groups both years (p's<.05). These results suggest that low average cortisol levels promote novelty seeking, while high average levels inhibit novelty seeking behavior.

Single-nucleotide polymorphisms in the TNF gene are associated with obesity-related phenotypes in vervet monkeys

Tumor necrosis factor (TNF) promoter single-nucleotide polymorphisms (SNPs) have been extensively characterized in humans, with numerous reports of associations with obesity-related phenotypes as well an array of infectious, immune-mediated, and inflammatory disease phenotypes. Controlling for the multitude of environmental risk factors in human studies has been a major confounder of efforts to elucidate the role and relative contribution of TNF promoter SNPs. As part of an ongoing initiative to further genetically and phenotypically characterize the St Kitts-origin vervet monkey (Chlorocebus aethiops ssp.) as an animal model of human obesity, we have conducted association analyses between TNF SNPs and previously defined obesity-related phenotypes in 265 pedigreed vervets. We report eight SNPs (-809G, -756A, -352C, -322A, +1285T, +2133T, +2362A, +2405), all contained within the same haplotype block and comprising a single haplotype, to be significantly associated with BMI, waist circumference, total plasma cholesterol (P < 0.05), and high-density lipoprotein-cholesterol (HDL-C) (P < 0.01). This study provides additional validation of the St Kitts-origin vervet model of obesity by demonstrating genetic associations analogous to that shown in humans.

Environmental stress alters genetic regulation of novelty seeking in vervet monkeys

Considerable attention has been paid to identifying genetic influences and gene–environment interactions that increase vulnerability to environmental stressors, with promising but inconsistent results. A nonhuman primate model is presented here that allows assessment of genetic influences in response to a stressful life event for a behavioural trait with relevance for psychopathology. Genetic and environmental influences on free-choice novelty seeking behaviour were assessed in a pedigreed colony of vervet monkeys before and after relocation from a low stress to a higher stress environment. Heritability of novelty seeking scores, and genetic correlations within and between environments were conducted using variance components analysis. The results showed that novelty seeking was markedly inhibited in the higher stress environment, with effects persisting across a 2-year period for adults but not for juveniles. There were significant genetic contributions to novelty seeking scores in each year (h² = 0.35–0.43), with high genetic correlations within each environment (rhoG > 0.80) and a lower genetic correlation (rhoG = 0.35, non-significant) between environments. There were also significant genetic contributions to individual change scores from before to after the move (h² = 0.48). These results indicate that genetic regulation of novelty seeking was modified by the level of environmental stress, and they support a role for gene–environment interactions in a behavioural trait with relevance for mental health.

A web-based brain atlas of the vervet monkey, Chlorocebus aethiops

Vervet monkeys are a frequently studied animal model in neuroscience research. Although equally distantly related to humans, the ancestors of vervets diverged from those of macaques and baboons more than 11 million years ago, antedating the divergence of the ancestors of humans, chimpanzees and gorillas. To facilitate anatomic localization in the vervet brain, two linked on-line electronic atlases are described, one based on registered MRI scans from hundreds of vervets (http://www.loni.ucla.edu/Research/Atlases/Data/vervet/vervetmratlas/vervetmratlas.html) and the other based on a high-resolution cryomacrotome study of a single vervet (http://www.loni.ucla.edu/Research/Atlases/Data/vervet/vervetatlas/vervetatlas.html). The averaged MRI atlas is also available as a volume in Neuroimaging Informatics Technology Initiative format. In the cryomacrotome atlas, various sulcal and subcortical structures have been anatomically labeled and surface rendered views are provided along the primary planes of section. Both atlases simultaneously provide views in all three primary planes of section, rapid navigation by clicking on the displayed images, and stereotaxic coordinates in the averaged MRI atlas space. Despite the extended time period since their divergence, the major sulcal and subcortical landmarks in vervets are highly conserved relative to those described in macaques.

Fetal and maternal factors associated with infant mortality in vervet monkeys

BACKGROUND

Causes of infant death remain unknown in significant proportions of human and non-human primate pregnancies.

METHODS

A closed breeding colony with high rates of infant mortality had pregnancies assessed (n=153) by fetal measurements and maternal characteristics. Infant outcome was classified as neonatal death (stillborn or died <48 hours from birth), postnatal death (died 2-30 days) or surviving (alive after 30 days).

RESULTS

Fetal size did not predict outcome. Poor maternal glycemic control and low social ranking increased odds for adverse outcome (OR=3.72, P=0.01 and 2.27, P=0.04, respectively). Male sex was over-represented in stillbirths (P=0.04), and many were macrosomic, but size did not associate with maternal glycemic control measured as glycated hemoglobin A1c. Postnatally dead infants were smaller (P<0.01), which associated with behavioral factors and glycemic control.

CONCLUSIONS

Fetal growth estimates predicted gestational age but not fetal outcome. Maternal social status and metabolic health, particularly glycemic control, increased risks of adverse pregnancy outcome.

Insight into the relationship between impulsivity and substance abuse from studies using animal models

Drug use disorders are often accompanied by deficits in the capacity to efficiently process reward-related information and to monitor, suppress, or override reward-controlled behavior when goals are in conflict with aversive or immediate outcomes. This emerging deficit in behavioral flexibility and impulse control may be a central component of the progression to addiction, as behavior becomes increasingly driven by drugs and drug-associated cues at the expense of more advantageous activities. Understanding how neural mechanisms implicated in impulse control are affected by addictive drugs may therefore prove a useful strategy in the search for new treatment options. Animal models of impulsivity and addiction could make a significant contribution to this endeavor. Here, some of the more common behavioral paradigms used to measure different aspects of impulsivity across species are outlined, and the importance of the response to reward-paired cues in such paradigms is discussed. Naturally occurring differences in forms of impulsivity have been found to be predictive of future drug self-administration, but drug exposure can also increase impulsive responding. Such data are in keeping with the suggestion that impulsivity may contribute to multiple stages within the spiral of addiction. From a neurobiological perspective, converging evidence from rat, monkey, and human studies suggest that compromised functioning within the orbitofrontal cortex may critically contribute to the cognitive sequelae of drug abuse. Changes in gene transcription and protein expression within this region may provide insight into the mechanism underlying drug-induced cortical hypofunction, reflecting new molecular targets for the treatment of uncontrolled drug-seeking and drug-taking behavior.

Dopamine receptors in a songbird brain

Dopamine is a key neuromodulatory transmitter in the brain. It acts through dopamine receptors to affect changes in neural activity, gene expression, and behavior. In songbirds, dopamine is released into the striatal song nucleus Area X, and the levels depend on social contexts of undirected and directed singing. This differential release is associated with differential expression of activity-dependent genes, such as egr1 (avian zenk), which in mammalian brain are modulated by dopamine receptors. Here we cloned from zebra finch brain cDNAs of all avian dopamine receptors: the D1 (D1A, D1B, D1D) and D2 (D2, D3, D4) families. Comparative sequence analyses of predicted proteins revealed expected phylogenetic relationships, in which the D1 family exists as single exon and the D2 family exists as spliced exon genes. In both zebra finch and chicken, the D1A, D1B, and D2 receptors were highly expressed in the striatum, the D1D and D3 throughout the pallium and within the mesopallium, respectively, and the D4 mainly in the cerebellum. Furthermore, within the zebra finch, all receptors, except for D4, showed differential expression in song nuclei relative to the surrounding regions and developmentally regulated expression that decreased for most receptors during the sensory acquisition and sensorimotor phases of song learning. Within Area X, half of the cells expressed both D1A and D2 receptors, and a higher proportion of the D1A-only-containing neurons expressed egr1 during undirected but not during directed singing. Our findings are consistent with hypotheses that dopamine receptors may be involved in song development and social context-dependent behaviors. J. Comp. Neurol. 518:741–769, 2010. © 2009 Wiley-Liss, Inc.