Paternal and maternal genetic and environmental contributions to cerebrospinal fluid monoamine metabolites in rhesus monkeys (Macaca mulatta)

Serotonergic dysfunction: brain imaging and behavioral correlates

Identification of gene-environment and gene-gene interactions has become increasingly important in understanding psychiatric disorders. Dysfunction of central serotonergic neurotransmission has been implicated in alcoholism, depression, and anxiety. We review the literature on nonhuman primates that assesses the interaction between the genetic constitution of the regulatory region ofthe serotonin transporter (5-HTT) and environmental factors. Prospective studies in nonhuman primates that underwent social stress found a reduction of theserotonin turnover rate among carriers of one or two short alleles in a functional polymorphism of the 5-HTT promoter. In these primates, brain imaging studies showed a relative increase in the availability of raphe serotonin transporters. A low serotonin turnover rate and a high availability of serotonin transporters were associated with reduced response to excessive alcohol intake, anxiety, and impulsive aggression. Animal experiments point to a relationship between serotonergic dysfunction, negative mood states, and excessive alcohol intake, which may in part be mediated by reduced alcohol-induced sedation.

Influence of parenting style on the offspring's behaviour and CSF monoamine metabolite levels in crossfostered and noncrossfostered female rhesus macaques

We investigated the association between variation in parenting style and the offspring's behaviour and CSF monoamine metabolite (5-HIAA, HVA, and MHPG) levels in rhesus monkeys. Study subjects were 25 two-year-old females reared by their biological mothers and 15 same-aged females that were crossfostered at birth and reared by unrelated mothers. Subjects that were rejected more by their mothers in the first 6 months of life engaged in more solitary play and had lower CSF concentrations of 5-HIAA than subjects that were rejected less. The relation between these variables was generally similar in crossfostered and noncrossfostered females. CSF levels of 5-HIAA were negatively correlated with rates of scratching, a behavioural indicator of anxiety. These results suggest that that early exposure to high rates of maternal rejection can result in higher anxiety later in life, and that this effect may be mediated by serotonergic mechanisms. Variation in maternal protectiveness did not affect offspring behaviour and neither protectiveness nor rejection affected CSF levels of HVA and MHPG. CSF levels of MHPG, however, were negatively correlated with solitary play behaviour and avoidance of other individuals, suggesting that individuals with lower CSF MHPG were more fearful and socially phobic than those with higher CSF MHPG. Taken together, these findings suggest that individual differences in anxiety and fearfulness in young rhesus monkeys are accounted for, at least in part, by variation in CSF levels of monoamine metabolites, and that the development of brain monoamine systems, particularly serotonin, can be affected by early exposure to variable maternal behaviour.

A functional polymorphism in the MAOA gene promoter (MAOA-LPR) predicts central dopamine function and body mass index

Variation in brain monoaminergic activity is heritable and modulates risk of alcoholism and other addictions, as well as food intake and energy expenditure. Monoamine oxidase A deaminates the monoamine neurotransmitters serotonin, dopamine (DA), and noradrenaline. The monoamine oxidase A (MAOA) gene (Xp11.5) contains a length polymorphism in its promoter region (MAOA-LPR) that putatively affects transcriptional efficiency. Our goals were to test (1) whether MAOA-LPR contributes to interindividual variation in monoamine activity, assessed using levels of cerebrospinal fluid (CSF) monoamine metabolites; and (2) whether MAOA-LPR genotype influences alcoholism and/or body mass index (BMI). Male, unrelated criminal alcoholics (N=278) and controls (N=227) were collected from a homogeneous Finnish source population. CSF concentration of 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) were available from 208 participants. Single allele, hemizygous genotypes were grouped according to inferred effect of the MAOA alleles on transcriptional activity. MAOA-LPR genotypes had a significant effect on CSF HVA concentration (P=0.01) but explained only 3% of the total variance. There was a detectable but nonsignificant genotype effect on 5-HIAA and no effects on MHPG. Specifically, the genotype conferring high MAOA activity was associated with lower HVA levels in both alcoholics and controls, a finding that persisted after accounting for the potential confounds of alcoholism, BMI, height, and smoking. MAOA-LPR genotype predicted BMI (P<0.005), with the high-activity genotype being associated with lower BMI. MAOA-LPR genotypes were not associated with alcoholism or related psychiatric phenotypes in this data set. Our results suggest that MAOA-LPR allelic variation modulates DA turnover in the CNS, but does so in a manner contrary to our prior expectation that alleles conferring high activity would predict higher HVA levels in CSF. Our results are consistent with an emerging literature that suggests greater complexity in how variation in MAOA expression alters monoaminergic function. Finally, our work suggests that MAOA may be involved in the regulation of BMI. Independent samples are necessary to confirm this preliminary finding.

From risky behavior to health risk: continuity across two generations

The purpose of this study was to determine the impact of childhood aggression and social withdrawal on adolescent health risk behaviors and adult health outcomes, and to examine the transfer of health risk to preschool offspring. This was a prospective, longitudinal, and intergenerational study of 114 mothers from disadvantaged neighborhoods, who were identified in childhood as being highly aggressive and/or withdrawn or with low scores on these 2 behavioral risk dimensions, and their preschool offspring aged 1 to 6 years old. The health histories of mothers (adolescent health risk behavior, health during pregnancy, current symptoms) and target children were taken during structured interviews conducted at home. Regression analyses tested the relationship between maternal childhood risk status and subsequent health outcomes, and these were followed by structural equation modeling of a proposed intergenerational pathway. Maternal childhood aggression predicted current health risk behaviors (e.g., daily cigarette smoking), whereas maternal childhood social withdrawal was not associated with maternal health risk at the time of testing. Mothers who had high scores on both aggression and withdrawal were more likely to engage in adolescent health risk behavior, which was directly related to health problems in preschoolers (even after controlling for covariates, such as neonatal health status and sex). In summary, there are distinct health trajectories for women who are highly aggressive and socially withdrawn in childhood, with implications for women's long-term health. Specifically, aggression in girls is likely to lead to health risk behaviors that may also place the next generation at risk for pediatric illness. Results are interpreted in terms of the health-hostility link, best known in adult men and intergenerational models.

Elevated childhood serotonergic function protects against adolescent aggression in disruptive boys

OBJECTIVE

This longitudinal study examined whether responsiveness of the neurotransmitter serotonin (5-HT) in childhood predicts adolescent aggression.

METHOD

Boys (N = 33) with disruptive behavior disorders who received assessments of central 5-HT function via the prolactin response to fenfluramine between 1990 and 1994 when they were 7 to 11 years old were re-evaluated clinically on average 6.7 years later.

RESULTS

After accounting for baseline aggression, early 5-HT function accounted for a significant proportion of variance in adolescent aggression. This prospective relationship of childhood 5-HT function with adolescent aggression (r = -0.71) and antisocial behavior (r = -0.59) was found primarily in adolescents who were aggressive during childhood. Irrespective of childhood aggression, no child with high 5-HT function was particularly aggressive at follow-up.

CONCLUSIONS

Low childhood 5-HT function appears important, but not sufficient, for the emergence of adolescent aggression. However, early high 5-HT function may protect against adolescent violence and aggression.

Genetic and Other Contributions to Alcohol Intake in Rhesus Macaques (Macaca mulatta)

BACKGROUND

The etiology of alcoholism and alcohol abuse, like many other complex diseases, is heterogeneous and multifactorial. Numerous studies demonstrate a genetic contribution to variation in the expression of alcohol-related disorders in humans. Over the past decade, nonhuman primates have emerged as a valuable model for some aspects of human alcohol abuse because of their phylogenetic proximity to humans. Long-term, longitudinal studies of rhesus macaques (Macaca mulatta) have provided much insight into environmental influences, especially early life experiences, on alcohol consumption and behavior patterns that characterize alcohol intake later in life. It is not known, however, whether there is a genetic component as well to the variation seen in alcohol consumption in rhesus macaques. A significant genetic component to variation in alcohol consumption in rhesus macaques would show for the first time that like humans, for nonhuman primates additive genetic influences are important. Moreover, their use as a model for alcohol-related disorders in humans would have even greater relevance and utility for designing experiments incorporating the expanding molecular genetics field, and allow researchers to investigate the interaction among the known environmental influences and various genotypes.

METHODS

In this study, we investigate factors contributing to variation in alcohol consumption of 156 rhesus macaques collected over 10 years when subjects were adolescent in age, belonging to a single extended pedigree, with each cohort receiving identical early rearing backgrounds and subsequent treatments. To measure alcohol consumption each animal was provided unfettered simultaneous access both to an aspartame-sweetened 8.4% (v/v) alcohol-water solution, the aspartame-sweetened vehicle, and to water for 1 hour each day during the early afternoon between 13:00 and 15:00 in their home cages for a period of 5 to 7 weeks. We use multiple regression to identify factors that significantly affect alcohol consumption among these animals and a maximum likelihood program (ASReml) that, controlling for the significant factors, estimates the genetic contribution to the variance in alcohol consumption.

RESULTS

Multiple regression analysis identified test cohort and rearing environment as contributing to 57 and 2%, respectively, of the total variance in alcohol consumption. Of the remaining 41% of the variance about half (19.8%) was attributable to additive genetic effects using a maximum likelihood program.

CONCLUSION

This study demonstrates that, as in humans, there are additive genetic factors that contribute to variation in alcohol consumption in rhesus macaques, with other nongenetic factors accounting for substantial portions of the variance in alcohol consumption, Our findings show the presence of an additive genetic component and suggest the potential utility of the nonhuman primate as a molecular genetics tool for understanding alcohol abuse and alcoholism.

An initial genetic linkage map of the rhesus macaque (Macaca mulatta) genome using human microsatellite loci

Rhesus macaques (Macaca mulatta) are the most widely used nonhuman primate species in biomedical research. To create new opportunities for genetic and genomic studies using rhesus monkeys, we constructed a genetic linkage map of the rhesus genome. This map consists of 241 microsatellite loci, all previously mapped in the human genome. These polymorphisms were genotyped in five pedigrees of rhesus monkeys totaling 865 animals. The resulting linkage map covers 2048 cM including all 20 rhesus autosomes, with average spacing between markers of 9.3 cM. Average heterozygosity among those markers is 0.73. This linkage map provides new comparative information concerning locus order and interlocus distances in humans and rhesus monkeys. The map will facilitate whole-genome linkage screens to locate quantitative trait loci (QTLs) that influence individual variation in phenotypic traits related to basic primate anatomy, physiology, and behavior, as well as QTLs relevant to risk factors for human disease.

Modeling depression: social dominance-submission gene expression patterns in rat neocortex

Gene expression profiles in the cortex of adult Long-Evans rats as a function of a stressful social loss and victory in inter-male fighting encounters were examined. This social dominance and subordination model has been postulated to simulate early changes in the onset of depression in the losers. Microarrays were fabricated containing 45mer oligonucleotides spotted in quadruplicate and representing 1178 brain-associated genes. Dynamic range, discrimination power, accuracy and reproducibility were determined with standard mRNA "spiking" studies. Gene expression profiles in dominant and subordinate animals were compared using a "universal" reference design [Churchill GA (2002) Fundamentals of experimental design for cDNA microarrays. Nat Genet 32 (Suppl):490-495]. Data were analyzed by significance analysis of microarrays using rank scores [Tusher VG, Tibshirani R, Chu G (2001) Significance analysis of microarrays applied to the ionizing radiation response. Proc Natl Acad Sci USA 98:5116-5121; van de Wiel MA (2004) Significance analysis of microarrays using rank scores. Kwantitatieve Methoden 71:25-37]. Ontological analyses were then performed using the GOMiner algorithm [Zeeberg BR, Feng W, Wang G, Wang MD, Fojo AT, Sunshine M, Narasimhan S, Kane DW, Reinhold WC, Lababidi S, Bussey KJ, Riss J, Barrett JC, Weinstein JN (2003) GoMiner: a resource for biological interpretation of genomic and proteomic data. Genome Biol 4(4):R28]. And finally, genes of special interest were further studied using quantitative reverse transcriptase polymerase chain reaction. Twenty-two transcripts were statistically significantly differentially expressed in the neocortex between dominant and subordinate animals. Ontological analyses revealed that significant gene changes were clustered primarily into functional neurochemical pathways associated with protein biosynthesis and cytoskeletal dynamics. The most robust of these were the increased expression of interleukin-18, heat shock protein 27, beta3-tubulin, ribosome-associated membrane protein 4 in subordinate animals. Interleukin-18 has been found to be over-expressed in human depression and panic disorder as well as other physiological stress paradigms [Takeuchi M, Okura T, Mori T, Akita K, Ohta T, Ikeda M, Ikegami H, Kurimoto M (1999) Intracellular production of interleukin-18 in human epithelial-like cell lines is enhanced by hyperosmotic stress in vitro. Cell Tissue Res 297(3):467-473] and heat shock proteins have been shown to be involved in the pathogenesis of many neurodegenerative and psychiatric disorders [Iwamoto K, Kakiuchi C, Bundo M, Ikeda K, Kato T (2004) Molecular characterization of bipolar disorder by comparing gene expression profiles of postmortem brains of major mental disorders. Mol Psychiatry 9(4):406-416; Pongrac JL, Middleton FA, Peng L, Lewis DA, Levitt P, Mirnics K (2004) Heat shock protein 12A shows reduced expression in the prefrontal cortex of subjects with schizophrenia. Biol Psychiatry 56(12):943-950]. Thus, the gene expression changes that we have observed here are consistent with and extend the observations found in the clinical literature and link them to the animal model used here thereby reinforcing its use to better understand the genesis of depression and identify novel therapeutic targets for its treatment.

Serotonin and aggressive behavior in rodents and nonhuman primates: predispositions and plasticity

This review analyzes psychosocial and genetic determinants of aggressive behavior in rodents and nonhuman primates and the role of the serotonin (5-HT) system on aggressive behaviors in order to trace possible evolutionary common origins between psychopathological and adaptive forms of aggression. Studies in primates suggest that deficit in serotonin activity, as indicated by the levels of the cerebrospinal fluid (CSF) serotonin major metabolite 5-hydroxyindoleacetic acid (5-HIAA) correlates with impulsive and aggressive behavior. It is possible that CSF 5-HIAA reflects the prevailing serotonergic tone and may be related to an aggressive trait. Superimposed on this tone are phasic serotonin changes that may be related to the inhibition of aggressive acts. Genetic factors determine aggressive behaviors as demonstrated by classic selection and strain comparison studies. Manipulations of genes targeting 5-HT receptors, transporters and enzymes can influence aggression. Some of these genes related to the serotonin transporter (5-HTT) and the monoamine oxidase A (MAO-A) show a polymorphism that may predispose, under specific environmental conditions, certain individuals to display pathological forms of aggression.

Parent-child relationships and health problems in adulthood in three UK national birth cohort studies

BACKGROUND

Event-based measures suggest that emotional adversity in childhood has a long-term health impact, but less attention has been paid to chronic emotional stressors such as family conflict, harsh discipline or lack of affection. This study aimed to assess the impact of the latter on health problems and illness in adulthood.

METHODS

Logistic regression and multinomial logistic regression analyses of data collected in three UK national birth cohort studies at ages 43 and 16 years covering subjective report of relationship quality from the 'child', and number of health problems and illnesses reported in adulthood at ages 43, 33 and 26 years adjusted for social class, sex and, in 1946 and 1970 cohorts, for symptoms of mental illness.

RESULTS

Reports of abuse and neglect (1946 cohort), poor quality relationship with mother and father (1958 cohort), and a range of negative relationship descriptors (1970 cohort) predicted reports of three or more illnesses or health problems in adulthood. Results were inconsistent with respect to one or two illnesses or health problems. Adjustment for sex, social class and poor mental health attenuated the odds of poor health, but measures of relationship quality retained a significant independent effect.

CONCLUSIONS

Poor quality parent-child relationships could be a remediable risk factor for poor health in adulthood.

Lack of an association between 5-HT receptor gene polymorphisms and suicide victims

An association between serotonergic dysfunction in the brain and suicidal behavior has previously been suggested. The high affinity of some antipsychotic and antidepressant drugs to serotonin 6 (5-HT6) receptors, and the predominant localization of 5-HT6 receptors in some limbic regions, suggest that 5-HT6 receptors play a role in the pathogenesis of suicide. The objective of the present study was to examine the association between suicide victims and two polymorphisms of the 5-HT6 receptor gene: a biallelic polymorphism (267C/T) in exon 1 and a trinucleotide repeat polymorphism ([GCC](2/3)) in the 5'-upstream region of the gene. The two polymorphisms were genotyped in 163 suicide victims and 166 controls, and the distribution of genotype and allele frequencies between the two groups were compared. Haplotype frequencies of these two polymorphisms were estimated from genotypic data by the maximum-likelihood method. In both polymorphisms, there were no significant differences in genotype or allele frequencies between the suicide victims and the controls. Moreover, there were no significant differences in the haplotype distributions of these polymorphisms between the two groups. These findings suggest that it is unlikely that the 5-HT6 receptor gene is involved in the susceptibility to suicide.

Biological sensitivity to context: II. Empirical explorations of an evolutionary–developmental theory

In two studies comprising 249 children and their families, the authors utilized secondary, exploratory data analyses to examine Boyce and Ellis' (this issue) evolutionary-developmental theory of biological sensitivity to context. The theory proposes that individual differences in stress reactivity constitute variation in susceptibility to environmental influence, both positive and negative, and that early childhood exposures to either highly protective or acutely stressful environments result in heightened reactivity. In Study 1, 127 3- to 5-year old children were concurrently assessed on levels of support/adversity in home and preschool environments and on cardiovascular reactivity to laboratory challenges. In Study 2, 122 children were prospectively assessed on familial stress in both infancy and preschool and on autonomic and adrenocortical reactivity to laboratory challenges at age 7. In both studies, a disproportionate number of children in supportive, low stress environments displayed high autonomic reactivity. Conversely, in Study 2, a relatively high proportion of children in very stressful environments showed evidence of heightened sympathetic and adrenocortical reactivity. Consistent with the evolutionary-developmental theory, the exploratory analyses also generated the testable hypothesis that relations between levels of childhood support/adversity and the magnitude of stress reactivity are curvilinear, with children from moderately stressful environments displaying the lowest reactivity levels in both studies.

Biological sensitivity to context: I. An evolutionary–developmental theory of the origins and functions of stress reactivity

Biological reactivity to psychological stressors comprises a complex, integrated, and highly conserved repertoire of central neural and peripheral neuroendocrine responses designed to prepare the organism for challenge or threat. Developmental experience plays a role, along with heritable, polygenic variation, in calibrating the response dynamics of these systems, with early adversity biasing their combined effects toward a profile of heightened or prolonged reactivity. Conventional views of such high reactivity suggest that it is an atavistic and pathogenic legacy of an evolutionary past in which threats to survival were more prevalent and severe. Recent evidence, however, indicates that (a) stress reactivity is not a unitary process, but rather incorporates counterregulatory circuits serving to modify or temper physiological arousal, and (b) the effects of high reactivity phenotypes on psychiatric and biomedical outcomes are bivalent, rather than univalent, in character, exerting both risk-augmenting and risk-protective effects in a context-dependent manner. These observations suggest that heightened stress reactivity may reflect, not simply exaggerated arousal under challenge, but rather an increased biological sensitivity to context, with potential for negative health effects under conditions of adversity and positive effects under conditions of support and protection. From an evolutionary perspective, the developmental plasticity of the stress response systems, along with their structured, context-dependent effects, suggests that these systems may constitute conditional adaptations: evolved psychobiological mechanisms that monitor specific features of childhood environments as a basis for calibrating the development of stress response systems to adaptively match those environments. Taken together, these theoretical perspectives generate a novel hypothesis: that there is a curvilinear, U-shaped relation between early exposures to adversity and the development of stress-reactive profiles, with high reactivity phenotypes disproportionately emerging within both highly stressful and highly protected early social environments.

Gene-environment interaction in hyperkinetic conduct disorder (HD + CD) as indicated by season of birth variations in dopamine receptor (DRD4) gene polymorphism

Recently, an interaction between season of birth and the expression of candidate genes has been suggested. Season of birth variations in tryptophan hydroxylase (TPH), the serotonin transporter (5-HTTLPR) and the dopamine D4 receptor (DRD4) gene polymorphisms are different for affective disorders and schizophrenia. The DRD4 gene has been postulated as a candidate gene for attention-deficit-hyperactivity disorder (ADHD), equivalent to hyperkinetic disorder (HD). The seven-repeat long variant of this gene (DRD4*7) in comparison to the short repeat variants of the DRD4 gene polymorphism, has been found to be associated with ADHD. A seasonal pattern of birth has also been proposed for different subtypes of ADHD. Therefore, in a subgroup of children with HD and conduct disorder (CD) and in healthy controls, we investigated a possible association between the DRD4*7 allele and HD + CD in association with the season of birth. Supporting this hypothesis, we found an interaction between the seasons of birth and the expression of the DRD4 candidate gene in children with HD + CD as well as in controls, which differ significantly from each other. Depending on the season of birth, children carrying the DRD4*7R allele showed different relative risks for developing HD + CD.

Serotonin 1B (5HT-1B) receptor polymorphism (G861C) in suicide victims: association studies in German and Slavic population

Serotonergic dysfunction is believed to be involved in the susceptibility to suicide due to functional alternations in the serotonin-related genes. Serotonin 1B (5HT-1B) receptor mediates aggressive behavior in mice models and was proposed to be involved in the control of aggression and impulsivity in humans. In this study we have investigated the association of G861C polymorphism of the 5HT-1B receptor gene with suicide commitment. Study was based on two independent samples, one of German (245 suicide victims vs. 248 controls) and the other of Slavic/Croatian (118 suicide victims vs. 192 controls) ethnicity. No significant differences in allele or genotype frequencies between victims and controls were demonstrated either in German or Croatian sample. There were no differences in allele frequencies between German and Croatian population, and the combined sample, having high statistical power, also did not demonstrate significant differences between victims and controls. Results provide evidence that the investigated 5HT-1B receptor gene variants are not implicated in the susceptibility to suicide.

Physiological predictors of reproductive outcome and mother-infant behaviors in captive rhesus macaque females (Macaca mulatta)

Previous research has shown that offspring of females with low cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) concentrations are less likely to survive the first year of life than are offspring of females with high CSF 5-HIAA concentrations. In addition, studies of free-ranging rhesus macaque males have suggested that individuals with low CSF 5-HIAA concentrations suffer reduced reproductive success relative to their high serotonin counterparts. We examined CSF concentrations of the monoamine metabolites 5-HIAA and homovanillic acid (HVA), and plasma cortisol concentrations as predictors of first-time adult reproductive potential, maternal behavior, and overall social interactions in two groups of captive female rhesus macaques and their first offspring. Repeated CSF and blood samples were obtained from adult females in two social groups, and focal observations were performed for both new mothers and infants during the first month following parturition. We found that the reproductively aged nulliparous females who failed to give birth to their first offspring showed significantly lower CSF 5-HIAA concentrations than those females who gave birth. Among those females that gave birth to offspring, females with low CSF 5-HIAA concentrations and females with high plasma cortisol concentrations were overly protective and restrictive with their infants. CSF HVA concentration was not associated with reproductive output, social behavior, aggression, or mother-infant interactions in this sample of rhesus macaque females. We conclude that low CNS serotonin activity and high stress, measured by high plasma cortisol, are correlated with reduced reproductive success and patterns of high maternal restrictiveness in young adult female rhesus macaques.

Genetics of monoamine metabolites in baboons: overlapping sets of genes influence levels of 5-hydroxyindolacetic acid, 3-hydroxy-4-methoxyphenylglycol, and homovanillic acid

BACKGROUND

Monoamine neurotransmitters (serotonin, dopamine, and norepinephrine) are associated with several psychiatric disorders. Limited evidence suggests that monoamine levels are heritable, but no information concerning genetic relationships among monoamines is available. Further genetic analysis can help explain phenotypic correlations among monoamine levels and might eventually help identify genes involved in response to therapy or risk of psychopathology.

METHODS

Levels of the monoamine metabolites homovanillic acid (HVA), 5-hydroxyindolacetic acid (5-HIAA), and 3-hydroxy-4-methoxyphenylglycol (MHPG) were measured in cerebrospinal fluid from 271 baboons (Papio hamadryas). Variance components methods were used to estimate heritabilities, and multivariate analyses were used to estimate genetic correlations (pleiotropy) and environmental correlations between metabolites.

RESULTS

Each metabolite exhibited significant heritability in baboons (5-HIAA: h(2) =.30 +/-.17; MHPG: h(2) =.36 +/-.16; HVA: h(2) =.50 +/-.19). Multivariate analyses revealed genetic correlations between 5-HIAA and HVA and between HVA and MHPG. Environmental correlations were found between 5-HIAA and HVA and between 5-HIAA and MHPG.

CONCLUSIONS

Overlapping, nonidentical sets of genes influence individual variation in 5-HIAA, MHPG, and HVA levels among baboons. The phenotypic correlation between 5-HIAA and HVA observed in nonhuman primates and humans is likely due to both shared genetic and environmental factors. Genetic analyses of monoamine levels in primates can provide novel information concerning the genetics of variation among humans.

Monoamine related functional gene variants and relationships to monoamine metabolite concentrations in CSF of healthy volunteers

BACKGROUND

Concentrations of monoamine metabolites in human cerebrospinal fluid (CSF) have been used extensively as indirect estimates of monoamine turnover in the brain. CSF monoamine metabolite concentrations are partly determined by genetic influences.

METHODS

We investigated possible relationships between DNA polymorphisms in the serotonin 2C receptor (HTR2C), the serotonin 3A receptor (HTR3A), the dopamine D4 receptor (DRD4), and the dopamine beta-hydroxylase (DBH) genes and CSF concentrations of 5-hydroxyindolacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy volunteers (n = 90).

RESULTS

The HTR3A 178 C/T variant was associated with 5-HIAA levels (p = 0.02). The DBH-1021 heterozygote genotype was associated with 5-HIAA (p = 0.0005) and HVA (p = 0.009) concentrations. Neither the HTR2C Cys23Ser variant, nor the DRD4 -521 C/T variant were significantly associated with any of the monoamine metabolites.

CONCLUSIONS

The present results suggest that the HTR3A and DBH genes may participate in the regulation of dopamine and serotonin turnover rates in the central nervous system.

Early life influences on life-long patterns of behavior and health

The stability of a child's early life has profound effects on physical and mental health, and unstable parent-child relationships, as well as abuse, can lead to behavioral disorders and increased mortality and morbidity from a wide variety of common diseases later in life. One common consequence, namely, depressive illness, is associated with chemical imbalances in the brain and hormonal dysregulation, constituting a form of allostatic load that alters interpretations of stimuli and influences, behavioral, and hormonal responses to potentially stressful situations. The brain not only encodes information and controls the behavioral responses but it is also changed structurally by those experiences. Structural changes in the hippocampus and amygdala, which are important brain structures for cognition and emotion, are representative of what may be occurring throughout the brain as a result of allostatic load resulting from the chronic stress of a disorder such as depression. Such structural changes include dendritic debranching and hypertrophy, cell proliferation, and synaptic remodeling; they are produced by the combined overactivity of stress hormones and endogenous neurotransmitters. These mediators are normally involved in adaptation, but can also promote damage when they are dysregulated and over-active. They are very likely to be strongly biased by early life experiences. The findings from animal models thus provide a basis for understanding potential mechanisms of environmental and developmental determinants of individual differences in human stress reactivity, as well as anxiety, depression, and a host of related systemic disorders. There is an increasing amount of translational research that is beginning to tie the basic research to clinical outcomes of individuals exposed to abusive or inconsistent care-giving in early life. A major goal of studies on this important topic is to define times in development and strategies for intervening to prevent or reverse the effects of adverse early life experiences. Although prevention is clearly the preferable route, some degree of reversal of psychopathology and pathophysiology caused by early life adversity appears to be an achievable goal.

Gene-Environment Interactions and the Neurobiology of Social Conflict

Recent research has disclosed marked individual differences in biobehavioral responses to social conflicts exhibited by rhesus monkeys across the life span. For example, approximately 5-10% of rhesus monkeys growing up in the wild consistently exhibit impulsive and/or inappropriately aggressive responses to mildly stressful situations throughout development; those same individuals also show chronic deficits in their central serotonin metabolism. These characteristic patterns of biobehavioral response emerge early in life and remain remarkably stable from infancy to adulthood. Laboratory studies have demonstrated that although these characteristics are highly heritable, they are also subject to major modification by specific early experiences, particularly those involving early social attachment relationships. Moreover, genetic and early experience factors can interact, often in dramatic fashion. For example, a specific polymorphism in the serotonin transporter gene is associated with deficits in early neurobehavioral functioning and serotonin metabolism, extreme aggression, and excessive alcohol consumption among monkeys who experienced insecure early attachment relationships, but not in monkeys who developed secure attachment relationships with their mothers during infancy. Because daughters tend to develop the same type of attachment relationships with their own offspring that they experienced with their mothers early in life, such early experiences provide a possible nongenetic mechanism for transmitting these patterns to subsequent generations.

A magnetic resonance spectroscopic imaging study of adult nonhuman primates exposed to early-life stressors

BACKGROUND

Long-term behavioral, immunologic, and neurochemical alterations have been found in primates exposed to adverse early rearing.

METHODS

Bonnet macaque (Macaca radiata) mother-infant dyads were exposed to uncertain requirements for food procurement (variable foraging demand, VFD) for a few months. Ten years later, these offspring and age- and gender-matched control subjects were studied using proton magnetic resonance spectroscopic imaging (MRSI).

RESULTS

In anterior cingulate, VFD-reared subjects displayed significantly decreased N-acetylaspartate (NAA) resonance and significantly increased glutamate-glutamine-gamma-aminobutyric acid (Glx) resonance relative to the stable neurometabolite creatine (Cr). Across all subjects, NAA/Cr and Glx/Cr ratios in the anterior cingulate were negatively correlated (r = -.638, p =.014). In the medial temporal lobe, the ratio of choline-containing compounds to Cr was significantly increased in VFD subjects.

CONCLUSIONS

These findings indicate that adverse early rearing in primates has an enduring impact on adult MRSI measures considered reflective of neuronal integrity and metabolism, membrane structure and glial function, and cerebral glutamate content, and that these alterations occur in the same brain regions implicated in trauma-related psychiatric disorders.

Effects of acute social stress on alcohol consumption in healthy subjects

BACKGROUND

There has been renewed interest in interactions between stress and use of drugs and alcohol. Although there is evidence that stress increases drug use in human drug users and in laboratory animals, the processes by which stress affects drug-motivated behavior are not understood. Here we examined the effects of an acute social stressor (performing a mental arithmetic task in front of an audience) on consumption of ethanol or placebo beverages in healthy social drinkers.

METHODS

Thirty-seven men and women, ages 21-35, were randomly assigned to a placebo (n = 15) or ethanol group (n = 22). Subjects participated in two sessions, one with stress (Trier Social Stress Test) the other without stress. In each session, immediately after the stress or no-stress period, subjects consumed the first dose (placebo or 0.3 g/kg of ethanol for men or 0.2 g/kg for women). Then, subjects were allowed to choose up to six more beverages (0.1 g/kg each for the ethanol group or placebo beverages for the placebo group). Measures included percentage of beverage consumed, salivary cortisol level, heart rate, blood pressure, and subjective ratings of mood and drug effect.

RESULTS

Subjects in both the placebo and ethanol groups consumed significantly more of their beverages after stress, compared to no stress. Stress increased anxiety, uneasiness, and produced some stimulant-like effects and, in the ethanol group, it dampened some of the acute subjective effects of ethanol. The direct physiologic and mood effects of the stress were fairly short-lived.

CONCLUSIONS

It is concluded that acute stress may produce a modest increase in alcohol consumption in healthy, nonproblem social drinkers but that this increase is not directly related to the pharmacological effects of the drug. Nonpharmacological factors may include expectancies, thirst, or nonspecific facilitation of ongoing behaviors.

The relationship between serotonergic function and the Psychopathy Checklist: Screening Version

Reduced serotonergic (5-HT) neurotransmission has been reported in impulsive and aggressive personality disordered and offender samples. What is not clear is the relationship between 5-HT function and the North American construct of psychopathy assessed using the Psychopathy Checklist and its derivatives, which emphasizes the core interpersonal/affective as well as behavioural components of this syndrome. Fifty-one DSM-III-R personality disordered offenders who had a dynamic assessment of 5-HT function (prolactin response to 30 mg d-fenfluramine challenge) were rated on the Psychopathy Checklist: Screening Version based on interview and file data. The Psychopathy Checklist: Screening Version (PCL: SV) mean score in the sample was similar to other reports in European forensic samples. A three-factor structure best explained the PCL: SV data: arrogant/deceitful, callous-unemotional and impulsive-antisocial behaviour factors. 5-HT function did not correlate with psychopathy as a unidimensional phenomenon. The impulsive-antisocial component correlates negatively with 5-HT function while the arrogant/deceitful component correlates positively with 5-HT. In line with previous research findings, impulsive-antisocial conduct shows an inverse relationship with 5-HT function. Arrogant/deceitful traits correlate positively with 5-HT function and may be an adaptive component of psychopathy.

CSF 5-HIAA concentration as an early screening tool for predicting significant life history outcomes in female specific-pathogen-free (SPF) rhesus macaques (Macaca mulatta) maintained in captive breeding groups

We examined relationships among cerebrospinal fluid (CSF) concentrations of the major serotonin metabolite (5-HIAA, 5-hydroxyindoleacetic acid) and significant medical and behavioral outcomes for female rhesus macaques. Based on earlier findings with males we predicted that low CSF 5-HIAA concentrations would be associated with a range of negative life history outcomes in our captive specific-pathogen-free (SPF) breeding colony. We found that the mean CSF 5-HIAA concentration among animals that died over the course of the study period was significantly lower than among animals that survived. Further examination indicated an inverse relationship between CSF 5-HIAA concentration and number of treatments for illness, further suggesting a link between serotonergic functioning and overall animal health. Examination of behavioral data indicated that individuals with low CSF 5-HIAA concentrations were more often the targets of aggressive bouts than were individuals with high CSF 5-HIAA concentrations. Finally, we found a positive relationship between CSF 5-HIAA concentration and infant survivorship. These results suggest negative life history consequences of impaired serotonergic functioning in captive female rhesus macaques, and indicate that CSF 5-HIAA concentration sampled early in life may provide a useful tool in facilitating colony management decisions concerning utilization of scarce and increasingly valuable non-human primate resources.

Heritability of fearful-anxious endophenotypes in infant rhesus macaques: a preliminary report

BACKGROUND

Research efforts to discover the genetic underpinnings of anxiety and depression is challenging because of the etiologic heterogeneity inherent to these disorders. These efforts might be aided by the study of related behavioral phenotypes in model organisms, such as monkeys.

METHODS

Eighty-five rhesus monkeys (Macaca mulatta) from the Oregon National Primate Research Center were drawn from a standard matriarchal colony and tested for behavioral response in four testing paradigms designed to elicit fearful-anxious reactions. Heritabilities were estimated using variance component-based quantitative genetic analyses with much of the genetic information arising from paternal half-sibs.

RESULTS

Individual behaviors reflecting increased distress responses (e.g., vocalizations and teeth grinding) and behavioral inhibition (e.g., latency to leave mother, latency to inspect novel fruit) showed significant heritability, even though a small number of monkeys were assessed. Exploratory factor analyses identified seven clusters of behaviors across tests, some of which were found to be heritable.

CONCLUSIONS

These results indicate that several specific fearful-anxious behaviors in infant rhesus monkeys are heritable within this colony. Accordingly, these phenotypes, which are believed to represent the genetic liability for anxiety and depression, are good candidates for further genetic investigation in this population.

Experience-dependent asymmetric variation in primate prefrontal morphology

Theories of human development suggest that experiences embedded in social relationships alter prefrontal brain systems that mediate emotional self-regulation. This study tests for experience-dependent effects on prefrontal gray and white matter volumes determined in 39 young adult monkeys (Saimiri sciureus) 4 years after conditions that modified early maternal availability. These conditions were previously shown to alter subsequent measures of emotional behavior, social propensities, and hypothalamic-pituitary-adrenal axis stress physiology. Here we identify significant differences in right but not left adult prefrontal volumes, with experience-dependent asymmetric variation most clearly expressed in ventral medial cortex measured in vivo by magnetic resonance imaging (MRI). Follow-up studies now need to determine whether maternal availability directly affects or interacts with subsequent experiences to alter prefrontal substrates of emotional processing and sensitivity to stress.

Self-rated childhood emotional neglect and CSF monoamine indices in abstinent cocaine-abusing adults: possible implications for suicidal behavior

Non-human primate studies suggest that early environmental influences may have an enduring effect on central serotonin function. Therefore, it was decided to examine in humans whether childhood trauma might be related to cerebrospinal fluid (CSF) concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) as an adult. A total of 29 withdrawn cocaine-dependent patients completed the Childhood Trauma Questionnaire. They also had a lumbar puncture for determination of CSF concentrations of 5-HIAA. CSF concentrations of the dopamine metabolite homovanillic acid (HVA) were also determined. Childhood emotional neglect scores showed significant negative correlations with CSF levels of 5-HIAA and HVA, and patients with emotional neglect scores above the median had significantly lower CSF 5-HIAA and HVA levels than patients with emotional neglect scores at or below the median. These findings suggest the possibility that childhood trauma may have an effect on central monoamine function as an adult.

Serotonergic function and suicidal behavior in schizophrenia

Recent studies suggest that altered serotonergic (5-HT) function, as assessed by lower prolactin (PRL) response to fenfluramine (FEN), a specific 5-HT releaser and uptake inhibitor, is associated with suicidal behavior in either depressed and personality disordered patients. The purpose of this study was to investigate, in schizophrenic patients, the relationship between suicidal behavior and PRL response to D-fenfluramine (D-FEN). A D-FEN test was performed in 18 healthy controls and 33 drug-free DSM-IV schizophrenic patients (12 with a history of suicide attempts, 21 without it). Schizophrenic patients with a history of suicide attempts showed a lower PRL response to D-FEN (Delta PRL) compared to schizophrenic patients without such history (P<0.04) and also compared to healthy controls (P<0.0003). Delta PRL did not differentiate schizophrenic patients without suicide attempts and controls. These findings could not be explained by PRL basal hormonal levels, age, sex, menstrual status, demographic or clinical characteristics. These results suggest that PRL response to D-FEN is a marker of suicidal tendencies also in schizophrenia, supporting the hypothesis that a dysfunction in serotonergic function is associated with suicidal behavior regardless of the psychiatric diagnosis.

Serotonin transporter polymorphisms and measures of impulsivity, aggression, and sensation seeking among African-American cocaine-dependent individuals

Considerable evidence indicates that serotonergic mechanisms, particularly the serotonin transporter (5HTT), may mediate central effects of cocaine and may also be involved in impulsive and aggressive behavior. We investigated whether polymorphisms in the 5HTT gene were related to traits of impulsivity, sensation seeking, and aggression among cocaine abusers. Standardized measures of these personality traits were obtained in a sample of 105 severely affected cocaine-dependent African-American subjects and 44 African-American controls. Two polymorphisms of the 5HTT gene were examined involving the 5' promoter (5HTTLPR) region and a 17 base pair variable-number-tandem-repeat (VNTR) marker among cocaine patients. No significant relationships were observed between polymorphic variants of the 5HTTLPR and VNTR regions and scores on any of the trait measures. Similarly, demographic variables and measures of severity of substance use and depression were unrelated to allele frequencies or genotype distributions of the variants among cocaine patients. As expected, cocaine patients scored significantly higher on total scores of impulsivity, aggression, and sensation seeking compared to controls. The findings do not seem to support an association between these polymorphisms in the 5HTT gene and impulsive-aggressive traits among cocaine-dependent African-American individuals.

Lack of an association between 5-HT1A receptor gene structural polymorphisms and suicide victims

A serotonergic dysfunction in the brain has been reported to be involved in suicidal behavior independently of the presence of a specific psychiatric disorder. Serotonin 1A (5-HT1A) receptors are known to be located on serotonergic nerve terminals and to be involved in the presynaptic regulation of serotonin release. Genetic factors partly explain the risks for suicide, and a suicide completion group is thought to be more uniform than a suicide attempt group. To explore the hypothesis that the 5-HT1A receptor-induced serotonergic dysfunction is implicated genetically in suicide, we focused on the structural polymorphisms, Pro16Leu and Gly272Asp, of the 5-HT1A receptor gene, and examined the association between suicide victims who completed suicide and these two polymorphisms. In both polymorphisms, we found no significant difference in genotype distribution or allele frequencies between suicide victims and controls. These findings suggest that neither of these two polymorphisms is associated with suicide victims and it is unlikely that the 5-HT1A receptor gene is implicated in the susceptibility to suicide.

Early experience and serotonin transporter gene variation interact to influence primate CNS function

Nonhuman primates offer unique opportunities to study the effects of genes, environments, and their interaction, on physiology and complex behavior. We examined genotype and early environment contributions to CNS function in a large sample of rhesus monkeys. In humans, length variation of the serotonin (5-HT) transporter (5-HTT) gene-linked polymorphic region (5-HTTLPR) that results in allelic variation in 5-HTT expression is associated with decreased serotonergic function and 5-HT-mediated psychopathology. We report that an analogous variation of the gene's regulatory region in monkeys interacts with early experience to affect central 5-HT functioning. Monkeys with deleterious early rearing experiences were differentiated by genotype in cerebrospinal fluid concentrations of the 5-HT metabolite, 5-hydroxyindoleacetic acid, while monkeys reared normally were not. These findings demonstrate an environment-dependent effect of the rh5-HTTLPR genotype on CNS 5-HT function and suggest nonhuman primates may provide an important avenue for investigating gene/environment interactions using candidate genes for physiological and behavioral traits.

Socioeconomic differences in children's health: how and why do these relationships change with age?

The effects of socioeconomic status (SES) on health are well documented in adulthood, but far less is known about its effects in childhood. The authors reviewed the literature and found support for a childhood SES effect, whereby each decrease in SES was associated with an increased health risk. The authors explored how this relationship changed as children underwent normal developmental changes and proposed 3 models to describe the temporal patterns. The authors found that a model's capacity to explain SES-health relationships varied across health outcomes. Childhood injury showed stronger relationships with SES at younger ages, whereas smoking showed stronger relationships with SES in adolescence. Finally, the authors proposed a developmental approach to exploring mechanisms that link SES and child health.

Paternal relatedness and age proximity regulate social relationships among adult female rhesus macaques

Kin selection promotes the evolution of social behavior that increases the survival and reproductive success of close relatives. Among primates, maternal kinship frequently coincides with a higher frequency of grooming and agonistic aiding, but the extent to which paternal kinship influences adult female social relationships has not yet been investigated. Here, we examine the effect of both maternal and paternal kinship, as well as age proximity, on affiliative interactions among semifree-ranging adult female rhesus macaques, Macaca mulatta. Kinship was assessed by using both microsatellites and DNA-fingerprinting. Our study confirms that the closest affiliative relationships characterize maternal half-sisters. We provide evidence that adult females are significantly more affiliative with paternal half-sisters than with nonkin. Furthermore, paternal kin discrimination was more pronounced among peers than among nonpeers, indicating that age proximity has an additional regulatory effect on affiliative interactions. We propose that kin discrimination among cercopithecine primates emerges from ontogenetic processes that involve phenotype matching based on shared behavioral traits, such as inherited personality profiles, rather than physiological or physical characteristics.

Autonomic reactivity and psychopathology in middle childhood

BACKGROUND

Better indicators are needed for identifying children with early signs of developmental psychopathology.

AIMS

To identify measures of autonomic nervous system reactivity that discriminate children with internalising and externalising behavioural symptoms.

METHOD

A cross-sectional study of 122 children aged 6--7 years examined sympathetic and parasympathetic reactivity to standardised field-laboratory stressors as predictors of parent- and teacher-reported mental health symptoms.

RESULTS

Measures of autonomic reactivity discriminated between children with internalising behaviour problems, externalising behaviour problems and neither. Internalisers showed high reactivity relative to low-symptom children, principally in the parasympathetic branch, while externalisers showed low reactivity, in both autonomic branches.

CONCLUSIONS

School-age children with mental health symptoms showed a pattern of autonomic dimorphism in their reactivity to standardised challenges. This observation may be of use in early identification of children with presyndromal psychopathology.

No evidence of an association between 5HT1B receptor gene polymorphism and suicide victims in a Japanese population

Serotonergic systems have been reported to mediate the control of aggression and/or impulsivity in humans and to be involved in suicidal behavior. Neurochemical studies showing serotonergic dysfunction in suicide appear to support the functional alteration of serotonergic systems due to gene polymorphisms. Knock-out mice of the 5HT1B receptor gene have been reported to result in increased aggression. We hypothesized that the 5HT1B receptor-mediated serotonergic dysfunction was implicated in suicide through disinhibition of aggression and/or impulsivity. To explore this hypothesis, we examined the association between suicide victims who completed suicide and the 5HT1B receptor gene G861C polymorphism. No significant differences in genotype distribution and allele frequencies were found between suicide victims and controls. Though there is the possibility of failing to detect small effects, these results show no evidence of an association between the 5HT1B receptor gene G861C polymorphism and suicide victims in a Japanese population and indicate that it is unlikely that the 5HT1B receptor is implicated in the susceptibility to suicide.

A regulatory polymorphism of the monoamine oxidase-A gene may be associated with variability in aggression, impulsivity, and central nervous system serotonergic responsivity

This study presents preliminary evidence of an association between polymorphic variation in the gene for monoamine oxidase-A (MAOA) and interindividual variability in aggressiveness, impulsivity and central nervous system (CNS) serotonergic responsivity. An apparently functional 30-bp VNTR in the promoter region of the X-chromosomal MAOA gene (MAOA-uVNTR), as well as a dinucleotide repeat in intron 2 (MAOA-CAn), was genotyped in a community sample of 110 men. All participants had completed standard interview and questionnaire measures of impulsivity, hostility and lifetime aggression history; in a majority of subjects (n=75), central serotonergic activity was also assessed by neuropsychopharmacologic challenge (prolactin response to fenfluramine hydrochloride). The four repeat variants of the MAOA-uVNTR polymorphism were grouped for analysis (alleles '1+ 4' vs. '2+3') based on prior evidence of enhanced transcriptional activity in MAOA promoter constructs with alleles 2 and 3 (repeats of intermediate length). Men in the 1/4 allele group scored significantly lower on a composite measure of dispositional aggressiveness and impulsivity (P<0.015) and showed more pronounced CNS serotonergic responsivity (P<0.02) than men in the 2/3 allele group. These associations were also significant on comparison of the more prevalent one and three alleles alone (encompassing 93% of subjects). Although in linkage disequilibrium with the MAOA-uVNTR polymorphism, MAOA-CAn repeat length variation did not vary significantly with respect to behavior or fenflluramine challenge in this sample. We conclude that the MAOA-uVNTR regulatory polymorphism may contribute, in part, to individual differences in both CNS serotonergic responsivity and personality traits germane to impulse control and antagonistic behavior.

A promoter polymorphism in the monoamine oxidase A gene and its relationships to monoamine metabolite concentrations in CSF of healthy volunteers

Concentrations of monoamine metabolites (MM) in lumbar cerebrospinal fluid (CSF) have been used extensively as indirect estimates of monoamine turnover in the brain. We investigated possible relationships between a putative functional promoter polymorphism in the monoamine oxidase A (MAOA) gene and CSF concentrations of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy volunteers (n=88). Among women (n=37), those carrying at least one copy of the alleles associated with more efficient transcription displayed higher concentrations of HVA (p=0.01) and 5-HIAA (p=0.01). In men (n=51), however, there was a tendency in the opposite direction. The results suggest that MAOA genotypes may participate differentially in the regulation of dopamine and serotonin turnover rates under presumed steady state in the central nervous system. The results should be interpreted with caution until replicated because of the limited sample size.

Prolactin response to D-fenfluramine and suicidal behavior in depressed patients

Previous studies of the prolactin response to D-fenfluramine in depressed patients have yielded inconsistent results. This may be because they did not address the question of suicidality. We carried out this study to test the hypothesis that lower prolactin response to D-fenfluramine is more closely associated with suicidal behavior than with depression itself. A D-fenfluramine test was performed in a sample of 18 healthy control subjects and in 85 drug-free inpatients with a DSM-III-R diagnosis of major depressive episode (49 with a history of suicide attempt, 36 without). Depressed inpatients with a history of suicide attempt showed a significantly lower prolactin response to D-fenfluramine compared to depressed inpatients without such a history and compared to control subjects. Healthy control subjects and depressed inpatients without a history of suicide attempt showed comparable levels of prolactin after D-fenfluramine. Time elapsed since suicide attempt did not influence prolactin level (baseline or post-stimulation). Results show that in our depressed drug-free inpatient sample, prolactin response to D-fenfluramine seems to be a marker of suicidality, but not of depression itself. We suggest that it is a trait marker of suicidality.

Serotonin and aggression in children

Research consistently indicates that in animals and adults, reduced central serotonergic (5-HT) function is associated with increased aggression. This relationship has been elucidated via cerebrospinal fluid monoamine metabolite levels, hormonal responses to pharmacologic challenge using serotonergic probes, platelet receptor binding studies, and, more recently, through molecular genetic approaches. In contrast, studies examining the relationship of 5-HT to aggression in children have been characterized by inconsistent findings. The literature examining the relationship between central 5-HT function and aggression is reviewed. Several hypotheses that might account for the discrepancies in the child literature are examined.

Protective and damaging effects of mediators of stress. Elaborating and testing the concepts of allostasis and allostatic load

Stress is a condition of human existence and a factor in the expression of disease. A broader view of stress is that it is not just the dramatic stressful events that exact their toll but rather the many events of daily life that elevate activities of physiological systems to cause some measure of wear and tear. We call this wear and tear "allostatic load," and it reflects not only the impact of life experiences but also of genetic load; individual habits reflecting items such as diet, exercise, and substance abuse; and developmental experiences that set life-long patterns of behavior and physiological reactivity (see McEwen). Hormones associated with stress and allostatic load protect the body in the short run and promote adaptation, but in the long run allostatic load causes changes in the body that lead to disease. This will be illustrated for the immune system and brain. Among the most potent of stressors are those arising from competitive interactions between animals of the same species, leading to the formation of dominance hierarchies. Psychosocial stress of this type not only impairs cognitive function of lower ranking animals, but it can also promote disease (e.g. atherosclerosis) among those vying for the dominant position. Social ordering in human society is also associated with gradients of disease, with an increasing frequency of mortality and morbidity as one descends the scale of socioeconomic status that reflects both income and education. Although the causes of these gradients of health are very complex, they are likely to reflect, with increasing frequency at the lower end of the scale, the cumulative burden of coping with limited resources and negative life events and the allostatic load that this burden places on the physiological systems involved in coping and adaptation.

Postnatal experiences and genetic effects on squirrel monkey social affinities and emotional distress

Most nonhuman primate research on risk factors underlying vulnerability to stress has focused on early psychosocial experiences in various species of macaques. To test for genetic and experiential effects on emotional vulnerability in randomly bred squirrel monkeys, here we combined a paternal half-sibling analysis with three postnatal rearing protocols that altered aspects of maternal availability. In one condition offspring were periodically removed from natal groups, whereas differences in maternal availability were produced in two other conditions by manipulating the effort required of lactating mothers to successfully locate food. After completion of these protocols at 21 weeks of age, social affinities, maternal separation induced peep-calls, and plasma levels of cortisol were assessed from 29 to 37 weeks of age. Significant postnatal rearing effects and the lowest heritabilities were detected in peak elevations of cortisol measured 1 day after the removal of mothers from otherwise undisturbed groups. Individual differences in cortisol 3-7 days later revealed negligible postnatal rearing effects and the highest heritabilities (h(2) approximately. 70), as offspring sired by certain fathers failed to return to the preseparation level found in undisturbed natal groups. Paternal half-siblings that responded with long lasting increases in cortisol spent more time near their mother in undisturbed groups and exhibited long-lasting increases in separation induced peep-calls. These findings concur with human twin studies that suggest genetic and experiential factors contribute to individual differences in vulnerability to emotional distress.

Behavioral disinhibition induced by tryptophan depletion in nonalcoholic young men with multigenerational family histories of paternal alcoholism

OBJECTIVE

A deficit in serotonergic neurotransmission has been linked to impulsive behavior, as well as to disorders characterized by disinhibition. The present study tested the hypothesis that young men at high risk for alcoholism demonstrate greater behavioral disinhibition after acute dietary depletion of tryptophan, the amino acid precursor of serotonin.

METHOD

A double-blind, placebo-comparison, between-subjects study design was used. Nonalcoholic young men with a multigenerational paternal family history of alcoholism (N = 13) or with no family history of alcoholism (N = 15) in two previous generations were administered mixtures of tryptophan-deficient amino acid to achieve plasma tryptophan depletion. Comparison subjects with a multigenerational paternal family history of alcoholism (N = 1) and comparison subjects with no family history of alcoholism (N = 18) were given a balanced mixture. Five hours after this, all were tested on a modified Taylor task and a go/ no-go task measuring aggressive response and disinhibition, respectively.

RESULTS

Plasma tryptophan levels were reduced by 89% in both groups. Tryptophan depletion had no effect on aggressive response. In contrast, tryptophan-depleted individuals with a family history of alcoholism made more commission errors (responses to stimuli associated with punishment or loss of reward) than did tryptophan-depleted individuals with no family history of alcoholism and those receiving the balanced (comparison) mixture of amino acid in either group.

CONCLUSIONS

Low serotonin levels may be implicated in the high disinhibition or impulsivity observed in some individuals with a genetic vulnerability to alcohol abuse or dependence.

O suicídio e sua relação com o comportamento impulsivo-agressivo

O suicídio é um sério problema de saúde pública, principalmente em países desenvolvidos, onde as altas taxas de suicídio entre jovens adultos do sexo masculino fazem com que este seja uma das principais causas de morte e de anos potenciais de vida perdidos. A etiologia do suicídio é certamente complexa, com diversos fatores contribuindo para a predisposição a este evento. Entre estes se encontram os fatores genéticos. Nos últimos anos, diversos estudos genético-epidemiológicos têm consistentemente sugerido que o componente genético é significativo. Entretanto, o modo exato através do qual os genes aumentam a predisposição de certos indivíduos a cometer o suicídio é ainda desconhecido. Há evidência crescente de que os fatores genéticos devem influenciar a predisposição ao suicídio via uma modulação dos comportamentos impulsivo e impulsivo-agressivo. Este artigo revisa e discute os estudos que investigaram fatores genéticos no comportamento suicida, assim como esta relação com os traços impulsivo-agressivos.