Social attachment, brain function, and aggression

The behavioral neuroendocrinology of dopamine systems in differently reared juvenile male rhesus monkeys (Macaca mulatta)

Dopamine (DA) is a critical neuromodulator of behavior. With propensities for addiction, hyper-activity, cognitive impairment, aggression, and social subordinance, monkeys enduring early maternal deprivation evoke human disorders involving dopaminergic dysfunction. To examine whether DA system alterations shape the behavioral correlates of adverse rearing, male monkeys (Macaca mulatta) were either mother-reared (MR: N = 6), or separated from their mothers at birth and nursery-reared (NR: N = 6). Behavior was assessed during 20-minute observations of subjects interacting with same- or differently-reared peers. Cerebrospinal fluid (CSF) biogenic amines, and serum testosterone (T), cortisol (CORT), and prolactin (PRL) were collected before and after pharmacologic challenge with saline or the DA receptor-2 (DRD2) antagonist Raclopride (RAC). Neuropeptide correlations observed in MR were non-existent in NR monkeys. Compared to MR, NR showed reduced DA tone; higher basal serum T; and lower CSF serotonin (5-HT). RAC increased PRL, T and CORT, but the magnitude of responses varied as a function of rearing. Levels of PRL significantly increased following RAC in MR, but not NR. Elevations in T following RAC were only significant among MR. Contrastingly, the net change (RAC CORT - saline CORT) in CORT was greater in NR than MR. Finally, observations conducted during the juvenile phase in a novel play-arena revealed more aggressive, self-injurious, and repetitive behaviors, which negatively correlated with indexes of dopaminergic tone in NR monkeys. In conclusion, early maternal deprivation alters brain DA systems, and thus may be associated with characteristic cognitive, social, and addiction outcomes.

In vitro pharmacological characterization of SPN-810M (molindone)

Background

Impulsive aggression (IA) is considered a maladaptive form of aggression that is reactive and overt and occurs outside of the acceptable social context. Many children and adolescents with attention-deficit/hyperactivity disorder (ADHD) display clinically significant aggression, with the predominant subtype being IA. However, there is currently no Food and Drug Administration-approved medication specifically to treat IA. The pathophysiology of IA is not fully understood, although it has been suggested to include the dopamine, norepinephrine, and serotonin systems.

Methods

SPN-810 (extended-release molindone) is being developed for the novel indication of IA and is currently being studied in patients treated for ADHD. Molindone is an indole derivative and a dopamine D₂ receptor antagonist.

Results

The in vitro pharmacological studies described in the current manuscript demonstrate that the active substance molindone (SPN-810M) is a potent antagonist for the dopamine receptors, D_2S and D_2L, and the serotonin receptor, 5-HT_2B, at therapeutic concentrations. The in vitro studies further demonstrate that the antagonist effect of SPN-810M is due to the parent drug and not the metabolites, and that the antagonism is not affected by the presence of norepinephrine or dopamine neurotransmitters. In addition, studies investigating the potential differential effects of the enantiomers of SPN-810M have demonstrated that the R(−) enantiomer is more potent than S(+), showing greater regulatory effect on D_2S and D_2L receptors.

Conclusion

Overall, the results of the in vitro SPN-810M pharmacological studies provide some insight into how SPN-810M modulates the serotonin and dopamine pathways that play a role in IA.

Using cross-species comparisons and a neurobiological framework to understand early social deprivation effects on behavioral development

Building upon the transactional model of brain development, we explore the impact of early maternal deprivation on neural development and plasticity in three neural systems: hyperactivity/impulsivity, executive function, and hypothalamic-pituitary-adrenal axis functioning across rodent, nonhuman primate, and human studies. Recognizing the complexity of early maternal-infant interactions, we limit our cross-species comparisons to data from rodent models of artificial rearing, nonhuman primate studies of peer rearing, and the relations between these two experimental approaches and human studies of children exposed to the early severe psychosocial deprivation associated with institutional care. In addition to discussing the strengths and limitations of these paradigms, we present the current state of research on the neurobiological impact of early maternal deprivation and the evidence of sensitive periods, noting methodological challenges. Integrating data across preclinical animal models and human studies, we speculate about the underlying biological mechanisms; the differential impact of deprivation due to temporal factors including onset, offset, and duration of the exposure; and the possibility and consequences of reopening of sensitive periods during adolescence.

Nonhuman primate models of depression: effects of early experience and stress

Depression causes significant morbidity in the human population. The Diathesis-Stress/Two-Hit model of depression hypothesizes that stress interacts with underlying (probably genetic) predispositions to produce a central nervous system that is primed to express psychopathology when confronted with stressful experiences later in life. Nonhuman primate (NHP) studies have been extensively utilized to test this model. NHPs are especially useful for studying effects of early experience, because many aspects of NHP infancy are similar to humans, whereas development occurs at an accelerated rate and therefore allows for more rapid assessment of experimental variables. In addition, the ability to manipulate putative risk factors, including introducing experimental stress during development, allows inference of causality not possible with human studies. This manuscript reviews experimental paradigms that have been utilized to model early adverse experience in NHPs, including peer-rearing, maternal separation, and variable foraging. It also provides examples of how this model has been used to investigate the effects of early experience on later neurobiology, physiology, and behavior associated with depression. We conclude that the NHP offers an excellent model to research mechanisms contributing to the Diathesis-Stress/Two-Hit model of depression.

Translating research findings on early experience to prevention: animal and human evidence on early attachment relationships

Recent studies provide a wealth of findings on the mechanisms by which early stress exposure, particularly within the early child-parent attachment relationship, may influence long-term adaptation. Translating these findings to clinical practice and social policy is now underway. In this review, some key considerations in this translational task are examined, specifically, the conceptual bases underlying the research designs, the putative mechanisms involved, and the degree to which currently available findings might shape interventions. Although the primary focus is on depression, a broader range of phenotypes associated with poor early caregiving environments is also considered.

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.

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.

Mothering begets mothering: the transmission of behavior and its neurobiology across generations

Early experiences exert their effects on adult parental behavior in part by altering the development of neurobiological mechanisms that initiate or support the initiation and sustenance of adult parental behavior. The effects of parental behavior on sensory, perceptual and emotional mechanisms in offspring constitute an experientially based mechanism by which neurobiological factors regulating behavior can be transferred from generation to generation somewhat independently of genetic endowment.

Application of the seven-factor model of personality to early childhood

The seven-factor model of personality developed by Cloninger and colleagues describes personality as a function of developmental aspects of character superimposed on heritable dimensions of temperament. The objective of this study was to determine whether this model could be applied to early childhood. We tested a preschool version of the Temperament and Character Inventory (the preschool TCI) in 305 children aged 2-5 years. Exploratory factor analysis provided support for the presence of distinct domains of temperament (comprising four factors) and character (comprising three factors). The preschool TCI demonstrated high internal consistency for each of the seven factors (Cronbach's alpha values: 0.70-0.93). Inter-individual differences in novelty seeking, reward dependence and cooperativeness were highly preserved (Pearson's r values 0.75, 0.64 and 0.80, respectively) in 29 subjects who were studied over a 3-year period from toddlerhood to early school age. Future studies are warranted to test the extent to which early childhood measurements of the seven factors might predict the development of personality disorders.

The ethics of social risk reduction in the era of the biological brain

In keeping with our transdisciplinary orientation, in this article we try to do several things at once. We address research on preventing mental illness and its relation to existing conceptions of public health, a topic to which insufficient attention has been paid in the era of the biological brain, while using this case study to illustrate the limits of conventional approaches in bioethics. After identifying the crucial need for methodological self-consciousness in prevention research and policy, we explore the implications as they relate to (i) the values embedded in the choice of research designs and strategies, and (ii) contrasting intellectual starting points regarding the biological plausibility of preventing mental illness. We then draw attention to the need for more thoughtful analysis of the appropriate role and limits of economics in making choices about prevention of mental illness.

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.

Neurobiology of mother-infant interactions: experience and central nervous system plasticity across development and generations

The optimal coordination between the new mammalian mother and her young involves a sequence of behaviors on the part of each that ensures that the young will be adequately cared for and show healthy physical, emotional, and social development. This coordination is accomplished by each member of the relationship having the appropriate sensitivities and responses to cues that characterize the other. Among many mammalian species, new mothers are attracted to their infants' odors and some recognize them based on their odors; they also respond to their infants' vocalizations, thermal properties, and touch qualities. Together these cues ensure that the mother will nurse and protect the offspring and provide them with the appropriate physical and stimulus environment in which to develop. The young, in turn, orient to the mother and show a suckling pattern that reflects a sensitivity to the mothers odor, touch, and temperature characteristics. This article explores the sensory, endocrine, and neural mechanisms that underlie this early mother-young relationship, from the perspective of, first, the mother and, then, the young, noting the parallels between them. It emphasizes the importance of learning and plasticity in the formation and maintenance of the mother-young relationship and mediation of these experience effects by the brain and its neurochemistry. Finally, it discusses ways in which the infants' early experiences with their mothers (or the absence of these experiences) may come to influence how they respond to their own infants when they grow up, providing a psychobiological mechanism for the inter-generational transmission of parenting styles and responsiveness.

Family psychiatric history, cerebrospinal fluid monoamine metabolites, and temperament in infants

BACKGROUND

Variations in cerebrospinal fluid (CSF) levels of the monoamine metabolites 5-hydroxyindoleacetic acid, 3-methoxy-4-hydroxyphenylglycol, and homovanillic acid have been associated with behavioral abnormalities in nonhuman primates, and with psychopathology in studies of children and adults.

METHODS

We assayed monoamine metabolites in "left-over" spinal fluid from 167 neurologically normal newborn infants (0-3 months of age), and later (at age 18-21 months of age) obtained their family psychiatric histories and assessed their temperament using the Colorado Childhood Temperament Inventory (CCTI).

RESULTS

Family history of antisocial personality disorder predicted significantly lower scores for soothability (p = .003) at 18-21 months. There were no statistically significant associations between newborn monoamine metabolite levels and any aspect of temperament on the CCTI.

CONCLUSIONS

These findings suggest complex relationships between genetic liability for psychiatric disorders and CSF monoamine metabolite levels; those relationships do not seem to be mediated by infant temperament. It appears likely that interindividual differences in monoamine metabolite levels change over the course of development in humans.

Behavioral and neurobiological consequences of social subjugation during puberty in golden hamsters

In golden hamsters, offensive aggression is facilitated by vasopressin and inhibited by serotonin. We tested whether these neurotransmitter systems respond to modifications resulting from the stress of threat and attack (i.e., social subjugation) during puberty. Male golden hamsters were weaned at postnatal day 25 (P25), exposed daily to aggressive adults from P28 to P42, and tested for offensive aggression as young adults (P45). The results showed a context-dependent alteration in aggressive behavior. Subjugated animals were more likely to attack younger and weaker intruders than nonsubjugated controls. Conversely, subjugated animals were less likely to attack animals of similar size and age. After testing, the animals were killed, and their brains were collected to determine whether these behavioral changes are underlined by changes in the vasopressin and serotonin systems. Social subjugation resulted in a 50% decrease in vasopressin levels within the anterior hypothalamus, a site involved in the regulation of aggression. Furthermore, whereas the density of vasopressin-immunoreactive fibers within the area was not significantly altered in subjugated animals, the number of serotonin-immunoreactive varicosities within the anterior hypothalamus and lateral septum was 20% higher in subjugated animals than in their controls. These results establish puberty as a developmental period sensitive to environmental stressors. Furthermore, the results show that changes in the vasopressin and serotonin systems can correlate with behavioral alterations, supporting the role of these two neurotransmitters in the regulation of aggression.

The behavioral neurobiology of self-injurious behavior in rhesus monkeys. Current concepts and relations to impulsive behavior in humans

The objective of this report is to critically review past reports and present new data on the psychobiology of self-injurious behavior (SIB) and/or "risky" or "impulsive" behavior in primates (human and nonhuman). One aim was to reexamine how early social deprivation and neurobiological changes caused by deprivation might contribute to SIB in monkeys, and how the causes of SIB in monkeys might inform us about the psychobiology of suicide in humans. A second aim was to examine the evidence that social deprivation in monkeys produces reductions in brain 5-HT system function that are causal or coincident factors associated with self-injurious or impulsive behavior. Prior studies and new data indicate that the environmental causes of SIB and unusual aggression in rhesus monkeys do not produce reductions in brain 5-HT system activity and that experimental production of low levels of brain 5-HT system activity does not reliably promote either SIB or unusual other-directed aggression in monkeys. A third and final aim was to suggest that in severe cases of environmentally induced SIB and/or aggression in monkeys, having relatively high or low levels of 5-HT system activity may not be related to ongoing behavior because the 5-HT system may not interact with other neurotransmitter systems in the usual way. Overall, the contention is that primates exhibiting SIB and unusual aggression may have altered 5-HT system function, but this may be but one aspect of a more profound disorganization of brain function involving many neurohormonal and transmitter systems. Contemporary theorizing and experimentation tends to be restricted to the idea that altered function in one key system might be the cause of a specific form of psychopathology. In the future, research examining the probable change interactions of neurotransmitter and neuroendocrine systems as underlying causes of behavioral disorders should have a high priority.