Effects of early-life stress on serotonin(1A) receptors in juvenile Rhesus monkeys measured by positron emission tomography

Alterations in adolescent brain serotonin (5HT)1A, 5HT2A, and dopamine (D)2 receptor systems in a nonhuman primate model of early life adversity

Stress affects brain serotonin (5HT) and dopamine (DA) function, and the effectiveness of 5HT and DA to regulate stress and emotional responses. However, our understanding of the long-term impact of early life adversity (ELA) on primate brain monoaminergic systems during adolescence is scarce and inconsistent. Filling this gap in the literature is critical, given that the emergence of psychopathology during adolescence has been related to deficits in these systems. Here, we use a translational nonhuman primate (NHP) model of ELA (infant maltreatment by the mother) to examine the long-term impact of ELA on adolescent 5HT1A, 5HT2A and D2 receptor systems. These receptor systems were chosen based on their involvement in stress/emotional control, as well as reward and reinforcement. Rates of maternal abuse, rejection, and infant's vocalizations were obtained during the first three postnatal months, and hair cortisol concentrations obtained at 6 months postnatal were examined as early predictors of binding potential (BP) values obtained during adolescence using positron emission tomography (PET) imaging. Maltreated animals demonstrated significantly lower 5HT1A receptor BP in prefrontal cortical areas as well as the amygdala and hippocampus, and lower 5HT2A receptor BP in striatal and prefrontal cortical areas. Maltreated animals also demonstrated significantly lower D2 BP in the amygdala. None of the behavioral and neuroendocrine measurements obtained early in life predicted any changes in BP data. Our findings suggest that early caregiving experiences regulate the development of brain 5HT and DA systems in primates, resulting in long-term effects evident during adolescence.

In vivo serotonin transporter and 1A receptor binding potential and ecological momentary assessment (EMA) of stress in major depression and suicidal behavior

We examined relationships between the serotonin system and stress in major depression and suicidal behavior. Twenty-five medication-free depressed participants (13 suicide attempters) underwent same-day [11C]DASB and [11C]CUMI-101 positron emission tomography (PET) imaging. Binding potential (BPND) to the serotonin transporter (5-HTT) and serotonin 1A (5-HT1A) receptor, respectively, was quantified using the NRU 5-HT atlas, reflecting distinct spatial distributions of multiple serotonin targets. Ecological momentary assessment (EMA) measured current stress over one week proximal to imaging. EMA stress did not differ between attempters and non-attempters. In all depressed participants, 5-HTT and 5-HT1A BPND were unrelated to EMA stress. There were region-specific effects of 5-HTT (p=0.002) and 5-HT1A BPND (p=0.03) in attempters vs. nonattempters. In attempters, region-specific associations between 5-HTT (p=0.03) and 5-HT1A (p=0.005) BPND and EMA stress emerged. While no post-hoc 5-HTT BPND correlations were significant, 5-HT1A BPND correlated positively with EMA stress in attempters in 9/10 regions (p-values<0.007), including the entire cortex except the largely occipital region 5. Brodmann-based regional analyses found diminished effects for 5-HTT and subcortically localized positive corrrelations between 5-HT1A and EMA stress, in attempters only. Given comparable depression severity and childhood and current stress between attempters and nonattempters, lower 5-HTT binding in attempters vs. nonattempters may suggest a biological risk marker. Localized lower 5-HTT and widespread higher 5-HT1A binding with stress among attempters specifically may suggest that a serotonergic phenotype might be a key determinant of risk or resiliency for suicidal behavior.

In vivo serotonin 1A receptor hippocampal binding potential in depression and reported childhood adversity

BACKGROUND

Reported childhood adversity (CA) is associated with development of depression in adulthood and predicts a more severe course of illness. Although elevated serotonin 1A receptor (5-HT_1AR) binding potential, especially in the raphe nuclei, has been shown to be a trait associated with major depression, we did not replicate this finding in an independent sample using the partial agonist positron emission tomography tracer [¹¹C]CUMI-101. Evidence suggests that CA can induce long-lasting changes in expression of 5-HT_1AR, and thus, a history of CA may explain the disparate findings.

METHODS

Following up on our initial report, 28 unmedicated participants in a current depressive episode (bipolar n = 16, unipolar n = 12) and 19 non-depressed healthy volunteers (HVs) underwent [¹¹C]CUMI-101 imaging to quantify 5-HT_1AR binding potential. Participants in a depressive episode were stratified into mild/moderate and severe CA groups via the Childhood Trauma Questionnaire. We hypothesized higher hippocampal and raphe nuclei 5-HT_1AR with severe CA compared with mild/moderate CA and HVs.

RESULTS

There was a group-by-region effect (p = 0.011) when considering HV, depressive episode mild/moderate CA, and depressive episode severe CA groups, driven by significantly higher hippocampal 5-HT_1AR binding potential in participants in a depressive episode with severe CA relative to HVs (p = 0.019). Contrary to our hypothesis, no significant binding potential differences were detected in the raphe nuclei (p-values > 0.05).

CONCLUSIONS

With replication in larger samples, elevated hippocampal 5-HT_1AR binding potential may serve as a promising biomarker through which to investigate the neurobiological link between CA and depression.

Sex Differences in Depression Caused by Early Life Stress and Related Mechanisms

Depression is a common psychiatric disease caused by various factors, manifesting with continuous low spirits, with its precise mechanism being unclear. Early life stress (ELS) is receiving more attention as a possible cause of depression. Many studies focused on the mechanisms underlying how ELS leads to changes in sex hormones, neurotransmitters, hypothalamic pituitary adrenocortical (HPA) axis function, and epigenetics. The adverse effects of ELS on adulthood are mainly dependent on the time window when stress occurs, sex and the developmental stage when evaluating the impacts. Therefore, with regard to the exact sex differences of adult depression, we found that ELS could lead to sex-differentiated depression through multiple mechanisms, including 5-HT, sex hormone, HPA axis, and epigenetics.

Serotonin 1A Receptor Binding of [11C]CUMI-101 in Bipolar Depression Quantified Using Positron Emission Tomography: Relationship to Psychopathology and Antidepressant Response

BACKGROUND

The pathophysiology of bipolar disorder (BD) remains largely unknown despite it causing significant disability and suicide risk. Serotonin signaling may play a role in the pathophysiology, but direct evidence for this is lacking. Treatment of the depressed phase of the disorder is limited. Previous studies have indicated that positron emission tomography (PET) imaging of the serotonin 1A receptor (5HT1AR) may predict antidepressant response.

METHODS

A total of 20 participants with BD in a current major depressive episode and 16 healthy volunteers had PET imaging with [11C]CUMI-101, employing a metabolite-corrected input function for quantification of binding potential to the 5HT1AR. Bipolar participants then received an open-labeled, 6-week clinical trial with a selective serotonin reuptake inhibitor (SSRI) in addition to their mood stabilizer. Clinical ratings were obtained at baseline and during SSRI treatment.

RESULTS

Pretreatment binding potential (BPF) of [11C]CUMI-101 was associated with a number of pretreatment clinical variables within BD participants. Within the raphe nucleus, it was inversely associated with the baseline Montgomery Åsberg Rating Scale (P = .026), the Beck Depression Inventory score (P = .0023), and the Buss Durkee Hostility Index (P = .0058), a measure of lifetime aggression. A secondary analysis found [11C]CUMI-101 BPF was higher in bipolar participants compared with healthy volunteers (P = .00275). [11C]CUMI-101 BPF did not differ between SSRI responders and non-responders (P = .907) to treatment and did not predict antidepressant response (P = .580). Voxel-wise analyses confirmed the results obtained in regions of interest analyses.

CONCLUSIONS

A disturbance of serotonin system function is associated with both the diagnosis of BD and its severity of depression. Pretreatment 5HT1AR binding did not predict SSRI antidepressant outcome.The study was listed on clinicaltrials.gov with identifier NCT02473250.

Early Rearing Conditions Affect Monoamine Metabolite Levels During Baseline and Periods of Social Separation Stress: A Non-human Primate Model (Macaca mulatta)

A variety of studies show that parental absence early in life leads to deleterious effects on the developing CNS. This is thought to be largely because evolutionary-dependent stimuli are necessary for the appropriate postnatal development of the young brain, an effect sometimes termed the "experience-expectant brain," with parents providing the necessary input for normative synaptic connections to develop and appropriate neuronal survival to occur. Principal among CNS systems affected by parental input are the monoamine systems. In the present study, N = 434 rhesus monkeys (233 males, 201 females) were reared in one of two conditions: as mother-reared controls (MR; n = 269) or without adults with 24-h access to same-aged peers (PR; n = 165). When subjects were six-months-old, they underwent a separation paradigm involving 4, sequential, four-day social separations from their mothers or peers, with each separation followed by three-day reunions with their mothers or their peers. Prior to the separation paradigm, baseline cisternal CSF samples were obtained, as well as at the end of each the four social separations, and after final separation, during a recovery period. CSF was assayed for concentrations of monoamine metabolites and a blood sample was genotyped for the serotonin transporter (5-HTT) genotype. Replicating earlier landmark findings, PR subjects with the s allele exhibited lower baseline concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), when compared to PR subjects homozygous for the L allele. MR subjects were undifferentiated by genotype. PR subjects exhibited lower CSF 5-HIAA concentrations during baseline, but higher CSF 5-HIAA during social separations, when compared to MR subjects. There were rearing effects for the dopamine metabolite homovanillic acid (HVA) and for the norepinephrine metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), with PR subjects showing higher HVA and lower MHPG when compared to MR subjects. These findings indicate that there are long-term deficits in the response of monoamines following early maternal absence. The results of this study confirm and extend earlier findings that early parental absence has deleterious consequences for the development of the monoamine systems, and that these consequences are modulated by the 5-HTT genotype.

Evaluation of the Effects of Developmental Trauma on Neurotransmitter Systems Using Functional Molecular Imaging

Early life stress (ELS) is strongly associated with psychiatric disorders such as anxiety, depression, and schizophrenia in adulthood. To date, biological, behavioral, and structural aspects of ELS have been studied extensively, but their functional effects remain unclear. Here, we examined NeuroPET studies of dopaminergic, glutamatergic, and serotonergic systems in ELS animal models. Maternal separation and restraint stress were used to generate single or complex developmental trauma. Body weights of animals exposed to single trauma were similar to those of control animals; however, animals exposed to complex trauma exhibited loss of body weight when compared to controls. In behavioral tests, the complex developmental trauma group exhibited a decrease in time spent in the open arm of the elevated plus-maze and an increase in immobility time in the forced swim test when compared to control animals. In NeuroPET studies, the complex trauma group displayed a reduction in brain uptake values when compared to single trauma and control groups. Of neurotransmitter systems analyzed, the rate of decrease in brain uptake was the highest in the serotonergic group. Collectively, our results indicate that developmental trauma events induce behavioral deficits, including anxiety- and depressive-like phenotypes and dysfunction in neurotransmitter systems.

Early-life adversity-induced long-term epigenetic programming associated with early onset of chronic physical aggression: Studies in humans and animals

Objectives: To examine whether chronic physical aggression (CPA) in adulthood can be epigenetically programmed early in life due to exposure to early-life adversity. Methods: Literature search of public databases such as PubMed/MEDLINE and Scopus. Results: Children/adolescents susceptible for CPA and exposed to early-life abuse fail to efficiently cope with stress that in turn results in the development of CPA later in life. This phenomenon was observed in humans and animal models of aggression. The susceptibility to aggression is a complex trait that is regulated by the interaction between environmental and genetic factors. Epigenetic mechanisms mediate this interaction. Subjects exposed to stress early in life exhibited long-term epigenetic programming that can influence their behaviour in adulthood. This programming affects expression of many genes not only in the brain but also in other systems such as neuroendocrine and immune. Conclusions: The propensity to adult CPA behaviour in subjects experienced to early-life adversity is mediated by epigenetic programming that involves long-term systemic epigenetic alterations in a whole genome.

Cognitive Control as a 5-HT1A-Based Domain That Is Disrupted in Major Depressive Disorder

Heterogeneity within Major Depressive Disorder (MDD) has hampered identification of biological markers (e.g., intermediate phenotypes, IPs) that might increase risk for the disorder or reflect closer links to the genes underlying the disease process. The newer characterizations of dimensions of MDD within Research Domain Criteria (RDoC) domains may align well with the goal of defining IPs. We compare a sample of 25 individuals with MDD compared to 29 age and education matched controls in multimodal assessment. The multimodal RDoC assessment included the primary IP biomarker, positron emission tomography (PET) with a selective radiotracer for 5-HT1A [(11C)WAY-100635], as well as event-related functional MRI with a Go/No-go task targeting the Cognitive Control network, neuropsychological assessment of affective perception, negative memory bias and Cognitive Control domains. There was also an exploratory genetic analysis with the serotonin transporter (5-HTTLPR) and monamine oxidase A (MAO-A) genes. In regression analyses, lower 5-HT1A binding potential (BP) in the MDD group was related to diminished engagement of the Cognitive Control network, slowed resolution of interfering cognitive stimuli, one element of Cognitive Control. In contrast, higher/normative levels of 5-HT1A BP in MDD (only) was related to a substantial memory bias toward negative information, but intact resolution of interfering cognitive stimuli and greater engagement of Cognitive Control circuitry. The serotonin transporter risk allele was associated with lower 1a BP and the corresponding imaging and cognitive IPs in MDD. Lowered 5HT 1a BP was present in half of the MDD group relative to the control group. Lowered 5HT 1a BP may represent a subtype including decreased engagement of Cognitive Control network and impaired resolution of interfering cognitive stimuli. Future investigations might link lowered 1a BP to neurobiological pathways and markers, as well as probing subtype-specific treatment targets.

Serotonin receptors and suicide, major depression, alcohol use disorder and reported early life adversity

Serotonin neurotransmitter deficits are reported in suicide, major depressive disorder (MDD) and alcohol use disorder (AUD). To compare pathophysiology in these disorders, we mapped brain serotonin transporter (SERT), 5-HT1A, and 5-HT2A receptor binding throughout prefrontal cortex and in anterior cingulate cortex postmortem. Cases and controls died suddenly minimizing agonal effects and had a postmortem interval ≤24 h to avoid compromised brain integrity. Neuropathology and toxicology confirmed absence of neuropathology and psychotropic medications. For most subjects (167 of 232), a DSM-IV Axis I diagnosis was made by psychological autopsy. Autoradiography was performed in right hemisphere coronal sections at a pre-genual level. Linear model analyses included sex and age with group and Brodmann area as interaction terms. SERT binding was lower in suicides (p = 0.004) independent of sex (females < males, p < 0.0001), however, the lower SERT binding was dependent on MDD diagnosis (p = 0.014). Higher SERT binding was associated with diagnosis of alcoholism (p = 0.012). 5-HT1A binding was greater in suicides (p < 0.001), independent of MDD (p = 0.168). Alcoholism was associated with higher 5-HT1A binding (p < 0.001) but only in suicides (p < 0.001). 5-HT2A binding was greater in suicides (p < 0.001) only when including MDD (p = 0.117) and alcoholism (p = 0.148) in the model. Reported childhood adversity was associated with higher SERT and 5-HT1A binding (p = 0.004) in nonsuicides and higher 5-HT2A binding (p < 0.001). Low SERT and more 5-HT1A and 5-HT2A binding in the neocortex in depressed suicides is dependent on Axis I diagnosis and reported childhood adversity. Findings in alcoholism differed from those in depression and suicide indicating a distinct serotonin system pathophysiology.

Early impoverished environment delays the maturation of cerebral cortex

The influence of exposure to impoverished environments on brain development is unexplored since most studies investigated how environmental impoverishment affects adult brain. To shed light on the impact of early impoverishment on developmental trajectories of the nervous system, we developed a protocol of environmental impoverishment in which dams and pups lived from birth in a condition of reduced sensory-motor stimulation. Focusing on visual system, we measured two indexes of functional development, that is visual acuity, assessed by using Visual Evoked Potentials (VEPs), and VEP latency. In addition, we assessed in the visual cortex levels of Insulin-Like Growth Factor 1 (IGF-1) and myelin maturation, together with the expression of the GABA biosynthetic enzyme GAD67. We found that early impoverishment strongly delays visual acuity and VEP latency development. These functional changes were accompanied by a significant reduction of IGF-1 protein and GAD67 expression, as well as by delayed myelination of nerve fibers, in the visual cortex of impoverished pups. Thus, exposure to impoverished living conditions causes a significant alteration of developmental trajectories leading to a prominent delay of brain maturation. These results underscore the significance of adequate levels of environmental stimulation for the maturation of central nervous system.

Social Origins of Developmental Risk for Mental and Physical Illness

Adversity in early childhood exerts an enduring impact on mental and physical health, academic achievement, lifetime productivity, and the probability of interfacing with the criminal justice system. More science is needed to understand how the brain is affected by early life stress (ELS), which produces excessive activation of stress response systems broadly throughout the child's body (toxic stress). Our research examines the importance of sex, timing and type of stress exposure, and critical periods for intervention in various brain systems across species. Neglect (the absence of sensitive and responsive caregiving) or disrupted interaction with offspring induces robust, lasting consequences in mice, monkeys, and humans. Complementary assessment of internalizing disorders and brain imaging in children suggests that early adversity can interfere with white matter development in key brain regions, which may increase risk for emotional difficulties in the long term. Neural circuits that are most plastic during ELS exposure in monkeys sustain the greatest change in gene expression, offering a mechanism whereby stress timing might lead to markedly different long-term behaviors. Rodent models reveal that disrupted maternal-infant interactions yield metabolic and behavioral outcomes often differing by sex. Moreover, ELS may further accelerate or delay critical periods of development, which reflect GABA circuit maturation, BDNF, and circadian Clock genes. Such factors are associated with several mental disorders and may contribute to a premature closure of plastic windows for intervention following ELS. Together, complementary cross-species studies are elucidating principles of adaptation to adversity in early childhood with molecular, cellular, and whole organism resolution.

Early rearing history influences oxytocin receptor epigenetic regulation in rhesus macaques

Epigenetically programmed stress adaptation may be a conduit for informing offspring of environmental challenge. We employed ChIP-sequencing to examine effects of early environment on epigenetic regulation using hippocampal samples from macaques exposed to disruption in maternal care. We found decreased H3K4me3 binding at genes critical to behavioral stress response, the most robust being the oxytocin receptor gene (OXTR), for which we observed a corresponding decrease in RNA expression. Post hoc analysis showed that a gain-of-function OXTR SNP rescued behavioral differences in early stress-exposed subjects. Our data suggest that epigenetic down-modulation of OXTR in brain could contribute to behavioral differences observed in early stress-exposed subjects and that functional genetic variation plays a role. These could have translational implications for human psychiatric disease and personality disorders.

Adaptations to stress can occur through epigenetic processes and may be a conduit for informing offspring of environmental challenge. We employed ChIP-sequencing for H3K4me3 to examine effects of early maternal deprivation (peer-rearing, PR) in archived rhesus macaque hippocampal samples (male, n = 13). Focusing on genes with roles in stress response and behavior, we assessed the effects of rearing on H3K4me3 binding by ANOVA. We found decreased H3K4me3 binding at genes critical to behavioral stress response, the most robust being the oxytocin receptor gene OXTR, for which we observed a corresponding decrease in RNA expression. Based on this finding, we performed behavioral analyses to determine whether a gain-of-function nonsynonymous OXTR SNP interacted with early stress to influence relevant behavioral stress reactivity phenotypes (n = 194), revealing that this SNP partially rescued the PR phenotype. PR infants exhibited higher levels of separation anxiety and arousal in response to social separation, but infants carrying the alternative OXTR allele did not exhibit as great a separation response. These data indicate that the oxytocin system is involved in social-separation response and suggest that epigenetic down-modulation of OXTR could contribute to behavioral differences observed in PR animals. Epigenetic changes at OXTR may represent predictive adaptive responses that could impart readiness to respond to environmental challenge or maintain proximity to a caregiver but also contribute to behavioral pathology. Our data also demonstrate that OXTR polymorphism can permit animals to partially overcome the detrimental effects of early maternal deprivation, which could have translational implications for human psychiatric disorders.

Transgenerational disruption of functional 5-HT1AR-induced connectivity in the adult mouse brain by traumatic stress in early life

Traumatic stress in early life is a strong risk factor for psychiatric disorders that can affect individuals across several generations. Although the underlying mechanisms have been proposed to implicate serotonergic transmission in the brain, the neural circuits involved remain poorly delineated. Using pharmacological functional magnetic resonance imaging in mice, we demonstrate that traumatic stress in postnatal life alters 5-HT_1A receptor-evoked local and global functions in both, the exposed animals and their progeny when adult. Disrupted functional connectivity is consistent across generations and match limbic circuits implicated in mood disorders, but also networks not previously linked to traumatic stress. These findings underscore the neurobiology and functional mapping of transgenerational effects of early life experiences.

Early life stress perturbs the maturation of microglia in the developing hippocampus

Children exposed to abuse or neglect show abnormal hippocampal development and similar findings have been reported in rodent models. Using brief daily separation (BDS), a mouse model of early life stress, we previously showed that exposure to BDS impairs hippocampal function in adulthood and perturbs synaptic maturation, synaptic pruning, axonal growth and myelination in the developing hippocampus. Given that microglia are involved in these developmental processes, we tested whether BDS impairs microglial activity in the hippocampus of 14 (during BDS) and 28-day old mice (one week after BDS). We found that BDS increased the density and altered the morphology of microglia in the hippocampus of 14-day old pups, effects that were no longer present on postnatal day (PND) 28. Despite the normal cell number and morphology seen at PND28, the molecular signature of hippocampal microglia, assessed using the NanoString immune panel, was altered at both ages. We showed that during normal hippocampal development, microglia undergo significant changes between PND14 and PND28, including reduced cell density, decreased ex vivo phagocytic activity, and an increase in the expression of genes involved in inflammation and cell migration. However, microglia harvested from the hippocampus of 28-day old BDS mice showed an increase in phagocytic activity and reduced expression of genes that normally increase across development. Promoter analysis indicated that alteration in the transcriptional activity of PU.1, Creb1, Sp1, and RelA accounted for most of the transcriptional changes seen during normal microglia development and for most of the BDS-induced changes at PND14 and PND28. These findings are the first to demonstrate that early life stress dysregulates microglial function in the developing hippocampus and to identify key transcription factors that are likely to mediate these changes.

The functional serotonin 1a receptor promoter polymorphism, rs6295, is associated with psychiatric illness and differences in transcription

The G/C single-nucleotide polymorphism in the serotonin 1a receptor promoter, rs6295, has previously been linked with depression, suicide and antidepressant responsiveness. In vitro studies suggest that rs6295 may have functional effects on the expression of the serotonin 1a receptor gene (HTR1A) through altered binding of a number of transcription factors. To further explore the relationship between rs6295, mental illness and gene expression, we performed dual epidemiological and biological studies. First, we genotyped a cohort of 1412 individuals, randomly split into discovery and replication cohorts, to examine the relationship between rs6295 and five psychiatric outcomes: history of psychiatric hospitalization, history of suicide attempts, history of substance or alcohol abuse, current posttraumatic stress disorder (PTSD), current depression. We found that the rs6295G allele is associated with increased risk for substance abuse, psychiatric hospitalization and suicide attempts. Overall, exposure to either childhood or non-childhood trauma resulted in increased risk for all psychiatric outcomes, but we did not observe a significant interaction between rs6295 and trauma in modulating psychiatric outcomes. In conjunction, we also investigated the potential impact of rs6295 on HTR1A expression in postmortem human brain tissue using relative allelic expression assays. We found more mRNA produced from the C versus the G-allele of rs6295 in the prefrontal cortex (PFC), but not in the midbrain of nonpsychiatric control subjects. Further, in the fetal cortex, rs6295C allele exhibited increased relative expression as early as gestational week 18 in humans. Finally, we found that the C:G allelic expression ratio was significantly neutralized in the PFC of subjects with major depressive disorder (MDD) who committed suicide as compared with controls, indicating that normal patterns of transcription may be disrupted in MDD/suicide. These data provide a putative biological mechanism underlying the association between rs6295, trauma and mental illness. Moreover, our results suggest that rs6295 may affect transcription during both gestational development and adulthood in a region-specific manner, acting as a risk factor for psychiatric illness. These findings provide a critical framework for conceptualizing the effects of a common functional genetic variant, trauma exposure and their impact on mental health.

Early-life Social Adversity and Developmental Processes in Nonhuman Primates

Most primate species produce offspring that are altricial and highly dependent upon caregivers. As a consequence, a host of developmental trajectories can be dramatically altered by variation in early experiences. We review the impact of early social experiences (in both experimental models and natural contexts) on developmental profiles in three species of nonhuman primates: marmosets, squirrel monkeys, and macaques. Graded exposure to early-life social adversity (ELSA) produces short- to long-term effects on multiple developmental outcomes, including affect, social behavior, cognitive and attentional processes, and in the neural substrates that underlie these sociobehavioral traits.

The developmental origins of chronic physical aggression: biological pathways triggered by early life adversity

Longitudinal epidemiological studies with birth cohorts have shown that physical aggression in humans does not appear suddenly in adolescence as commonly thought. In fact, physically aggressive behaviour is observed as early as 12 months after birth, its frequency peaks around 2-4 years of age and decreases in frequency until early adulthood. However, a minority of children (3-7%) maintain a high frequency of physical aggression from childhood to adolescence and develop serious social adjustment problems during adulthood. Genetic factors and early social experiences, as well as their interaction, have been shown to play an important role in the development of chronic aggressive behaviour. However, the biological mechanisms underlying these associations are just beginning to be uncovered. Recent evidence suggests that epigenetic mechanisms are responsive to adverse environments and could be involved in the development of chronic aggression. Using both gene candidate and genomic approaches, recent studies have identified epigenetic marks, such as DNA methylation alterations in genes involved in the stress response and the serotonin and immune systems to be partly responsible for the long-lasting effects of early adversity. Further longitudinal studies with biological, environmental and behavioural assessments from birth onwards are needed to elucidate the sequence of events that leads to these long-lasting epigenetic marks associated with early adversity and aggression.

Paternal early experiences influence infant development through non-social mechanisms in Rhesus Macaques

BACKGROUND

Early experiences influence the developing organism, with lifelong and potentially adaptive consequences. It has recently become clear that the effects of early experiences are not limited to the exposed generation, but can influence physiological and behavioral traits in the next generation. Mechanisms of transgenerational effects of parental early experiences on offspring development are often attributed to prenatal or postnatal parental influence, but recent data suggest that germ-line plasticity may also play a role in the transgenerational effects of early experiences. These non-genetic transgenerational effects are a potentially important developmental and evolutionary force, but the effects of parental experiences on behavior and physiology are not well understood in socially complex primates. In the non-human primate, the rhesus macaque, nursery rearing (NR) is an early life manipulation used for colony management purposes, and involves separating infants from parents early in life. We examined the effects of maternal and paternal early NR on infant rhesus macaque immunity, physiology, and behavior.

RESULTS

We theorized that differences in behavior or physiology in the absence of parent-offspring social contact would point to biological and perhaps germ-line, rather than social, mechanisms of effect. Thus, all subjects were themselves NR. Male and female infant rhesus macaques (N= 206) were separated from parents and social groups in the first four days of life to undergo NR. These infants differed only in their degree of NR ancestry - whether their dams or sires were themselves NR. At 3-4 months of age, infants underwent a standardized biobehavioral assessment. Factors describing immunity, plasma cortisol, and emotion regulation were generated from these data using factor analysis. Paternal, but not maternal, NR was associated with greater emotionality and higher plasma cortisol, compared with infants born to CONTROL reared fathers.

CONCLUSIONS

These data suggest that macaque biobehavioral makeup is strongly influenced by paternal experiences, and via non-social mechanisms.

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.

The role of maternal obesity in the risk of neuropsychiatric disorders

Recent evidence indicates that perinatal exposure to maternal obesity, metabolic disease, including diabetes and hypertension, and unhealthy maternal diet has a long-term impact on offspring behavior and physiology. During the past three decades, the prevalence of both obesity and neuropsychiatric disorders has rapidly increased. Epidemiologic studies provide evidence that maternal obesity and metabolic complications increase the risk of attention deficit hyperactivity disorder (ADHD), autism spectrum disorders, anxiety, depression, schizophrenia, eating disorders (food addiction, anorexia nervosa, and bulimia nervosa), and impairments in cognition in offspring. Animal models of maternal high-fat diet (HFD) induced obesity also document persistent changes in offspring behavior and impairments in critical neural circuitry. Animals exposed to maternal obesity and HFD consumption display hyperactivity, impairments in social behavior, increased anxiety-like and depressive-like behaviors, substance addiction, food addiction, and diminished cognition. During development, these offspring are exposed to elevated levels of nutrients (fatty acids, glucose), hormones (leptin, insulin), and inflammatory factors (C-reactive protein, interleukin, and tumor necrosis factor). Such factors appear to permanently change neuroendocrine regulation and brain development in offspring. In addition, inflammation of the offspring brain during gestation impairs the development of neural pathways critical in the regulation of behavior, such as serotoninergic, dopaminergic, and melanocortinergic systems. Dysregulation of these circuits increases the risk of mental health disorders. Given the high rates of obesity in most developed nations, it is critical that the mechanisms by which maternal obesity programs offspring behavior are thoroughly characterized. Such knowledge will be critical in the development of preventative strategies and therapeutic interventions.

Positron emission tomography quantification of serotonin(1A) receptor binding in suicide attempters with major depressive disorder

IMPORTANCE

Serotonergic system dysfunction has been associated with increased lethal suicide attempts and suicide. Dysfunction includes higher binding of serotonin(1A) autoreceptor in the brainstem raphe of individuals who die by suicide.

OBJECTIVES

To determine the relationships between brain serotonin(1A) binding and suicidal behavior in vivo in major depressive disorder (MDD) using positron emission tomography and the serotonin(1A) antagonist radiotracer carbon C 11 [11C]-labeled WAY-100635.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional positron emission tomography study at an academic medical center from 1999 through 2009. We compared serotonin(1A) binding between individuals with MDD who did not attempt suicide (nonattempters) (n = 62) and those who attempted suicide (attempters) (n = 29). We subdivided the attempters into those with lower (n = 16) and higher (n = 13) levels of lethality.

MAIN OUTCOMES AND MEASURES

The binding potential (BPF) of [11C]WAY-100635 (calculated as the number of receptors available divided by affinity) in the prefrontal cortex (PFC) and brainstem, estimated by kinetic modeling with an arterial input function; the severity of suicidal behaviors, including lethality and intent of suicide attempts; and suicidal ideation.

RESULTS

Using a linear mixed-effects model, we found no difference between attempters and nonattempters with MDD in serotonin(1A) BPF in the PFC regions (F1,88 = 0.03; P = .87) or in the raphe nuclei (F1,88 = 0.29; P = .59). Raphe nuclei serotonin(1A) BPF was 45.1% greater in higher-lethality attempters compared with lower-lethality attempters (F1,25 = 7.33; P = .01), whereas no difference was observed in the PFC regions (F1,25 = 0.12; P = .73). Serotonin(1A )BPF in the raphe nuclei of suicide attempters was positively correlated with the lethality rating (F1,25 = 10.56; P = .003) and the subjective lethal intent factor (F1,25 = 10.63; P = .003; R2 = 0.32) based on the most recent suicide attempt. Suicide ideation in participants with MDD was positively correlated with serotonin(1A) BPF in the PFC regions (F1,88 = 5.19; P = .03) and in the raphe nuclei (F1,87 = 7.38; P = .008; R2 = 0.12).

CONCLUSIONS AND RELEVANCE

Higher brainstem raphe serotonin(1A)BPF observed in higher-lethality suicide attempters with MDD is in agreement with findings in suicide studies and also with the finding of low cerebrospinal fluid levels of 5-hydroxyindoleacetic acid in higher-lethality suicide attempters. Higher brainstem raphe serotonin(1A) BPF would be consistent with lower levels of serotonin neuron firing and release and supports a model of impaired serotonin signaling in suicide and higher-lethality suicidal behavior. Severity of suicidal ideation in MDD is related to brainstem and prefrontal serotonin(1A) BPF, suggesting a role for both regions in suicidal ideation. Lower levels of serotonin release at key brain projection sites, such as the prefrontal regions, may favor more severe suicidal ideation and higher-lethality suicide attempts.

Early-life experience, epigenetics, and the developing brain

Development is a dynamic process that involves interplay between genes and the environment. In mammals, the quality of the postnatal environment is shaped by parent-offspring interactions that promote growth and survival and can lead to divergent developmental trajectories with implications for later-life neurobiological and behavioral characteristics. Emerging evidence suggests that epigenetic factors (ie, DNA methylation, posttranslational histone modifications, and small non-coding RNAs) may have a critical role in these parental care effects. Although this evidence is drawn primarily from rodent studies, there is increasing support for these effects in humans. Through these molecular mechanisms, variation in risk of psychopathology may emerge, particularly as a consequence of early-life neglect and abuse. Here we will highlight evidence of dynamic epigenetic changes in the developing brain in response to variation in the quality of postnatal parent-offspring interactions. The recruitment of epigenetic pathways for the biological embedding of early-life experience may also have transgenerational consequences and we will describe and contrast two routes through which this transmission can occur: experience dependent vs germline inheritance. Finally, we will speculate regarding the future directions of epigenetic research and how it can help us gain a better understanding of the developmental origins of psychiatric dysfunction.

Genetic and early environmental influences on the serotonin system: consequences for brain development and risk for psychopathology

BACKGROUND

Despite more than 60 years of research in the role of serotonin (5-HT) in psychopathology, many questions still remain. From a developmental perspective, studies have provided more insight into how 5-HT dysfunctions acquired in utero or early in life may modulate brain development. This paper discusses the relevance of the developmental role of 5-HT for the understanding of psychopathology. We review developmental milestones of the 5-HT system, how genetic and environmental 5-HT disturbances could affect brain development and the potential role of DNA methylation in 5-HT genes for brain development.

METHODS

Studies were identified using common databases (e.g., PubMed, Google Scholar) and reference lists.

RESULTS

Despite the widely supported view that the 5-HT system matures in early life, different 5-HT receptors, proteins and enzymes have different developmental patterns, and development is brain region-specific. A disruption in 5-HT homeostasis during development may lead to structural and functional changes in brain circuits that modulate emotional stress responses, including subcortical limbic and (pre)frontal areas. This may result in a predisposition to psychopathology. DNA methylation might be one of the underlying physiologic mechanisms.

LIMITATIONS

There is a need for prospective studies. The impact of stressors during adolescence on the 5-HT system is understudied. Questions regarding efficacy of drugs acting on 5-HT still remain.

CONCLUSION

A multidisciplinary and longitudinal approach in designing studies on the role of 5-HT in psychopathology might help to bring us closer to the understanding of the role of 5-HT in psychopathology.

Corticotropin releasing hormone and imaging, rethinking the stress axis

The stress system provides integration of both neurochemical and somatic physiologic functions within organisms as an adaptive mechanism to changing environmental conditions throughout evolution. In mammals and primates the complexity and sophistication of these systems have surpassed other species in triaging neurochemical and physiologic signaling to maximize chances of survival. Corticotropin releasing hormone (CRH) and its related peptides and receptors have been identified over the last three decades and are fundamental molecular initiators of the stress response. They are crucial in the top down regulatory cascade over a myriad of neurochemical, neuroendocrine and sympathetic nervous system events. From neuroscience, we've seen that stress activation impacts behavior, endocrine and somatic physiology and influences neurochemical events that one can capture in real time with current imaging technologies. To delineate these effects one can demonstrate how the CRH neuronal networks infiltrate critical cognitive, emotive and autonomic regions of the central nervous system (CNS) with somatic effects. Abundant preclinical and clinical studies show inter-regulatory actions of CRH with multiple neurotransmitters/peptides. Stress, both acute and chronic has epigenetic effects which magnify genetic susceptibilities to alter neurochemistry; stress system activation can add critical variables in design and interpretation of basic and clinical neuroscience and related research. This review will attempt to provide an overview of the spectrum of known functions and speculative actions of CRH and stress responses in light of imaging technology and its interpretation. Metabolic and neuroreceptor positron emission/single photon tomography (PET/SPECT), functional magnetic resonance imaging (fMRI), anatomic MRI, diffusion tensor imaging (DTI), and proton magnetic resonance spectroscopy (pMRS) are technologies that can delineate basic mechanisms of neurophysiology and pharmacology. Stress modulates the myriad of neurochemical and networks within and controlled through the central and peripheral nervous system and the effects of stress activation on imaging will be highlighted.

Serotonin transporter-linked polymorphic region (5-HTTLPR) genotype and stressful life events interact to predict preschool-onset depression: a replication and developmental extension

BACKGROUND

Scientific enthusiasm about gene × environment interactions, spurred by the 5-HTTLPR (serotonin transporter-linked polymorphic region) × SLEs (stressful life events) interaction predicting depression, have recently been tempered by sober realizations of small effects and meta-analyses reaching opposing conclusions. These mixed findings highlight the need for further research. Converging evidence suggests that the effects of 5-HTTLPR genotype may be neurodevelopmental in origin, but we are not aware of empirical studies that have investigated whether the 5-HTTLPR genotype × SLE interaction predicts preschool-onset depression (PO-MDD), the earliest validated form of depression.

METHODS

Children (n = 234) aged 3-5 were recruited for a longitudinal study designed to examine PO-MDD. In a comprehensive baseline assessment, the child's primary caregivers completed questionnaires and were interviewed about their child's behaviors, psychiatric symptoms, and exposure to SLEs.

RESULTS

A 5-HTTLPR × SLEs interaction emerged, such that children homozygous for the short allele were more susceptible to depression in the context of elevated SLE than long allele carriers. In contrast, at low SLE exposure, short allele homozygotes had fewer depressive symptoms. The data were best fit by a plasticity model with a substantial reduction in fit by diathesis-stress models.

CONCLUSIONS

Extending studies in adult and adolescent populations, these data suggest that 5-HTTLPR genotype may provide plasticity to environmental influence, for better or worse. Specifically, children homozygous for the short allele were more susceptible to the depressogenic effects of SLEs but benefitted, in the form of reduced depressive symptoms, in the context of relatively benign environmental conditions (i.e. relatively low SLE exposure). These data highlight the importance of examining gene × environment interactions across development, environment, and outcome but should be interpreted cautiously given the small sample size.

Fluoxetine administered to juvenile monkeys: effects on the serotonin transporter and behavior

OBJECTIVE

This study examined the long-term effects of fluoxetine administered to juvenile rhesus monkeys who, as young adults, were imaged with positron emission tomography for two serotonergic markers: serotonin transporter (SERT) and serotonin 1A (5-HT1A) receptor. An equal number of monkeys separated from their mothers at birth-an animal model of human childhood stress-were also studied.

METHOD

At birth, 32 male rhesus monkeys were randomly assigned to either maternal separation or normal rearing conditions. At age 2, half (N=8) of each group was randomly assigned to fluoxetine (3 mg/kg) or placebo for 1 year. To eliminate the confounding effects of residual drug in the brain, monkeys were scanned at least 1.5 years after drug discontinuation. Social interactions were assessed both during and after drug administration.

RESULTS

Fluoxetine persistently upregulated SERT, but not 5-HT1A receptors, in both the neocortex and the hippocampus. Whole-brain voxel-wise analysis revealed that fluoxetine had a significant effect in the lateral temporal and cingulate cortices. In contrast, neither maternal separation by itself nor the rearing-by-drug interaction was significant for either marker. Fluoxetine had no significant effect on the behavioral measures.

CONCLUSIONS

Fluoxetine administered to juvenile monkeys upregulates SERT into young adulthood. Implications regarding the efficacy or potential adverse effects of SSRIs in patients cannot be directly drawn from this study. Its purpose was to investigate effects of SSRIs on brain development in nonhuman primates using an experimental approach that randomly assigned long-term SSRI treatment or placebo.

Stress-protective neural circuits: not all roads lead through the prefrontal cortex

Exposure to an uncontrollable stressor elicits a constellation of physiological and behavioral sequel in laboratory rats that often reflect aspects of anxiety and other emotional disruptions. We review evidence suggesting that plasticity within the serotonergic dorsal raphe nucleus (DRN) is critical to the expression of uncontrollable stressor-induced anxiety. Specifically, after uncontrollable stressor exposure subsequent anxiogenic stimuli evoke greater 5-HT release in DRN terminal regions including the amygdala and striatum; and pharmacological blockade of postsynaptic 5-HT(2C) receptors in these regions prevents expression of stressor-induced anxiety. Importantly, the controllability of stress, the presence of safety signals, and a history of exercise mitigate the expression of stressor-induced anxiety. These stress-protective factors appear to involve distinct neural substrates; with stressor controllability requiring the medial prefrontal cortex, safety signals the insular cortex and exercise affecting the 5-HT system directly. Knowledge of the distinct yet converging mechanisms underlying these stress-protective factors could provide insight into novel strategies for the treatment and prevention of stress-related psychiatric disorders.

Molecular imaging in alcohol dependence

The cellular mechanisms of alcohol's effects in the brain are complex, targeting multiple transmitter systems. Molecular imaging has been used to study the effects of alcohol and alcohol use disorders on these various systems. Studies of dopaminergic indices have provided robust evidence for deficits in D2-mediated transmission in the striatum of chronic recently detoxified alcoholics. Their presence in the at-risk state prior to excessive drinking, and their recovery after long-term sobriety, are unclear and represent an active area of current research. Investigations of the GABAergic system have shown generalized deficits in various brain regions in the chronic abstinence phase. Studies of the opiate system have suggested alterations in some subtypes in discrete brain regions, including the ventral striatum, while studies of serotonin have been negative and those of the cannabinoid system have been inconclusive. Future investigations should target the glutamatergic system, which plays an important role both in the acute intoxicating effects of alcohol as well as in the long-term effects associated with dependence.

Issues in the timing of integrated early interventions: contributions from nutrition, neuroscience, and psychological research

A central issue when designing multidimensional biological and psychosocial interventions for children who are exposed to multiple developmental risks is identification of the age period(s) in which such interventions will have the strongest and longest lasting effects (sensitive periods). In this paper, we review nutritional, neuroscientific, and psychological evidence on this issue. Nutritional evidence is used to identify nutrient-sensitive periods of age-linked dimensions of brain development, with specific reference to iron deficiency. Neuroscience evidence is used to assess the importance of timing of exposures to environmental stressors for maintaining neural, neuroendocrine, and immune systems integrity. Psychological evidence illustrates the sensitivity of cognitive and social-emotional development to contextual risk and protective influences encountered at different ages. Evidence reviewed documents that the early years of life are a sensitive period when biological or psychosocial interventions or exposure to risk or protective contextual influences can produce unique long-term influences upon human brain, neuroendocrine, and cognitive or psychosocial development. However, the evidence does not identify the early years as the sole sensitive time period within which to have a significant influence upon development. Choice of age(s) to initiate interventions should be based on what outcomes are targeted and what interventions are used.

Developmental effects of serotonin 1A autoreceptors on anxiety and social behavior

The serotonin 1A receptor (5-HT1A) has a major role in modulating the effects of serotonin on mood and behavior. Previous studies have shown that knockout of 5-HT1A selectively in the raphe leads to higher levels of anxiety during adulthood. However, it remains unclear whether this phenotype is due to variation in receptor levels specifically during development or throughout life. To test the hypothesis that developmental sensitivity may underlie the effects of 5-HT1A on anxiety, we used an inducible transgenic system to selectively suppress 5-HT1A levels in serotonergic raphe neurons from post-natal days (P) 14 to P30, with a maximal reduction of 40% at P21 and return to regular levels by P30. This developmental decrease in receptor levels has long-lasting consequences, increasing anxiety and decreasing social investigation in adulthood. In addition, post-natal knockdown of autoreceptors leads to long-term increases in the excitability of serotonergic neurons, which may represent a mechanism underlying the effects of post-natal receptor variation on behavior later in life. Finally, we also examined the interplay between receptor variation and juvenile exposure to stress (applied from P14 to P21). Similar to receptor knockdown, juvenile exposure to stress led to increased anxiety phenotypes but did not exacerbate 5-HT1A knockdown-mediated anxiety levels. This work indicates that the effects of 5-HT1A autoreceptors on anxiety and social behaviors are developmentally mediated and suggests that natural variations in the expression of 5-HT1A may act during development to influence individual anxiety levels and contribute to susceptibility to anxiety disorders.

The brain on stress: vulnerability and plasticity of the prefrontal cortex over the life course

The prefrontal cortex (PFC) is involved in working memory and self-regulatory and goal-directed behaviors and displays remarkable structural and functional plasticity over the life course. Neural circuitry, molecular profiles, and neurochemistry can be changed by experiences, which influence behavior as well as neuroendocrine and autonomic function. Such effects have a particular impact during infancy and in adolescence. Behavioral stress affects both the structure and function of PFC, though such effects are not necessarily permanent, as young animals show remarkable neuronal resilience if the stress is discontinued. During aging, neurons within the PFC become less resilient to stress. There are also sex differences in the PFC response to stressors. While such stress and sex hormone-related alterations occur in regions mediating the highest levels of cognitive function and self-regulatory control, the fact that they are not necessarily permanent has implications for future behavior-based therapies that harness neural plasticity for recovery.

5-HT1A sex based differences in Bmax, in vivo KD, and BPND in the nonhuman primate

Serotonin (5-HT) dysfunction has been implicated in neuropsychiatric illnesses and may play a pivotal role in the differential prevalence of depression between the sexes. Previous PET studies have revealed sex-based differences in 5-HT1A binding potential (BPND). The binding potential is a function of the radioligand-receptor affinity (1/KDapp), and receptor density (Bmax). In this work, we use a multiple-injection (MI) PET protocol and the 5-HT1A receptor antagonist, [(18)F]mefway, to compare sex-based differences of in vivo affinity, Bmax, and BPND in rhesus monkeys.

METHODS

PET [(18)F]mefway studies were performed on 17 (6m, 11f) rhesus monkeys using a 3-injection protocol that included partial saturation injections of mefway. Compartmental modeling was performed using a model to account for non-tracer doses of mefway for the estimation of KDapp and Bmax. BPND estimates were also acquired from the first injection (high specific activity [(18)F]mefway, 90-minute duration) for comparison using the cerebellum (CB) as a reference region. Regions of interest were selected in 5-HT1A binding regions of the hippocampus (Hp), dorsal anterior cingulate cortex (dACC), amygdala (Am), and raphe nuclei (RN).

RESULTS

Female subjects displayed significantly (*p<0.05) lower KDapp in the Hp (-32%), Am (-38%), and RN (-37%). Only the Hp displayed significant differences in Bmax with females having a Bmax of -29% compared to males. Male subjects demonstrated significantly lower BPND measurements in the Am (14%) and RN (29%).

CONCLUSION

These results suggest that the higher BPND values found in females are the result of lower [(18)F]mefway KDapp. Although a more experimentally complex measurement, separate assay of KDapp and Bmax provides a more sensitive measure than BPND to identify the underlying differences between females and males in 5-HT1A function.

The serotonin transporter gene is a substrate for age and stress dependent epigenetic regulation in rhesus macaque brain: potential roles in genetic selection and gene × environment interactions

In humans, it has been demonstrated that the serotonin transporter linked polymorphic region (5-HTTLPR) genotype moderates risk in the face of adversity. One mechanism by which stress could interact with genotype is via epigenetic modifications. We wanted to examine whether stress interacted with genotype to predict binding of a histone 3 protein trimethylated at lysine 3 (H3K4me3) that marks active promoters. The brains (N = 61) of male rhesus macaques that had been reared in the presence or absence of stress were archived and the hippocampusi dissected. Chromatin immunoprecipitation was performed with an antibody against H3K4me3 followed by sequencing on a SolexaG2A. The effects of age, genotype (5-HTTLPR long/long vs. short), and stress exposure (peer-reared vs. mother-reared) on levels of H3K4me3 binding were determined. We found effects of age and stress exposure. There was a decline in H3K4me3 from preadolescence to postadolescence and lower levels in peer-reared monkeys and no effects of genotype. When we controlled for age, however, we found that there were effects of 5-HTTLPR genotype and rearing condition on H3K4me3 binding. In a larger sample, we observed that cerebrospinal fluid 5-hydroxyindoleacetic acid levels were subject to interactive effects among age, rearing history, and genotype. Genes containing both genetic selection and epigenetic regulation may be particularly important in stress adaptation and development. We find evidence for selection at the solute carrier family C6 member 4 gene and observe epigenetic reorganization according to genotype, stress, and age. These data suggest that developmental stage may moderate effects of stress and serotonin transporter genotype in the emergence of alternative adaptation strategies and in the vulnerability to developmental or psychiatric disorders.

Recent progress in understanding the pathophysiology of post-traumatic stress disorder: implications for targeted pharmacological treatment

Post-traumatic stress disorder (PTSD) is a common and chronic anxiety disorder that can result after exposure to a traumatic event. Though our understanding of the aetiology of PTSD is incomplete, several neurobiological systems have been implicated in the pathophysiology and vulnerability towards developing PTSD after trauma exposure. We aimed to provide a concise review of benchmark findings in important neurobiological systems related to the aetiology and maintenance of PTSD symptomology. Specifically, we discuss functional aetiologies in the noradrenergic, serotonergic, endogenous cannabinoid and opioid systems as well as the hypothalamic-pituitary adrenal (HPA) axis. This article provides a succinct framework to appreciate the current understanding of neurobiological mechanisms related to the pathophysiology of PTSD and how these findings may impact the development of future, targeted pharmacological treatments for this debilitating disorder.

Genetic approaches for understanding the role of serotonin receptors in mood and behavior

Serotonin (5-hydroxytryptamine; 5-HT) is an ancient signaling molecule that has a conserved role in modulating mood and behavior. Integral to its pleiotropic actions is the existence of multiple receptors, expressed in distinct but often overlapping patterns within the brain and the periphery. The existence of ∼14 mammalian receptor subtypes, many of which possess similar pharmacological profiles, has made assigning functional roles for these receptors challenging. This challenge has been further compounded by the revelation that a single receptor can have several different functions depending upon where and when it is expressed and activated, that is, in brain versus periphery, or at different developmental time points. This review highlights the contribution of genetic techniques to dissect the specific function of distinct serotonin receptor populations across the life course, with an emphasis on the contribution of different serotonin 1A receptor populations to mood and behavior. Similar approaches hold the promise to elucidate the functional roles of other receptors, as well as the interaction of serotonin with other neuroendocrine modulators of mood and behavior.

The epigenetic lorax: gene-environment interactions in human health

Over the last decade, we have witnessed an explosion of information on genetic factors underlying common human diseases and disorders. This 'human genomics' information revolution has occurred as a backdrop to a rapid increase in the rates of many human disorders and diseases. For example, obesity, Type 2 diabetes, asthma, autism spectrum disorder and attention deficit hyperactivity disorder have increased at rates that cannot be due to changes in the genetic structure of the population, and are difficult to ascribe to changes in diagnostic criteria or ascertainment. A likely cause of the increased incidence of these disorders is increased exposure to environmental factors that modify gene function. Many environmental factors that have epidemiological association with common human disorders are likely to exert their effects through epigenetic alterations. This general mechanism of gene-environment interaction poses special challenges for individuals, educators, scientists and public policy makers in defining, monitoring and mitigating exposures.

Mechanism of earthquake simulation as a prenatal stressor retarding rat offspring development and chinese medicine correcting the retardation: hormones and gene-expression alteration

We aimed to investigate the mechanism of shaking as a prenatal stressor impacting the development of the offspring and Chinese medicines correcting the alterations. Pregnant rats were randomized into earthquake simulation group (ESG), herbal group (HG) which received herbal supplements in feed after shaking, and control group (CG). Findings revealed body weight and open field test (OFT) score of ESG offspring were statistically inferior to the CG and HG offspring. The corticosterone levels of ESG were higher than those of CG but not than HG. The dopamine level of ESG was slightly lower than that of the CG and of HG was higher than that of ESG. The 5-HT of ESG was higher than CG and HG. The growth hormone level of the ESG was significantly lower than ESG but not than CG. Gene expression profile showed 81 genes upregulated and 39 genes downregulated in ESG versus CG, and 60 genes upregulated and 28 genes downregulated in ESG versus HG. Eighty-four genes were found differentially expressed in ESG versus CG comparison and were normalized in ESG versus HG. We conclude that maternal shaking negatively affected physical and nervous system development, with specific alterations in neurohormones and gene expression. Chinese herbal medicine reduced these negative outcomes.

The relation of developmental changes in brain serotonin transporter (5HTT) and 5HT1A receptor binding to emotional behavior in female rhesus monkeys: effects of social status and 5HTT genotype

The goal of the present study was to examine how social subordination stress and 5HTT polymorphisms affect the development of brain serotonin (5HT) systems during the pubertal transition in female rhesus monkeys. We also examined associations with developmental changes in emotional reactivity in response to a standardized behavioral test, the Human Intruder (HI). Our findings provide the first longitudinal evidence of developmental increases in 5HT1A receptor and 5HTT binding in the brain of female primates from pre- to peripuberty. The increase in 5HT1A BP(ND) in these socially housed female rhesus monkeys is a robust finding, occurring across all groups, regardless of social status or 5HTT genotype, and occurring in the left and right hemispheres of all prefrontal regions studied, as well as the amygdala, hippocampus, hypothalamus, and raphe nuclei. 5HTT BP(ND) also showed an increase with age in raphe, anterior cingulate cortex, and dorsolateral prefrontal cortex. These changes in brain 5HT systems take place as females establish more adult-like patterns of social behavior, as well as during the HI paradigm. Indeed, the main developmental changes in behavior during the HI (increase in freezing and decrease in submission/appeasement) were related to neurodevelopmental increases in 5HT1A receptors and 5HTT, because the associations between these behaviors and 5HT endpoints emerge at peripuberty. We detected an effect of social status on 5HT1A BP(ND) in the hypothalamus and on 5HTT BP(ND) in the orbitofrontal cortex, with subordinates showing higher BP(ND) than dominants in both cases during the pubertal transition. No main effects of 5HTT genotype were observed for 5HT1A or 5HTT BP(ND). Our findings indicate that adolescence in female rhesus monkeys is a period of central 5HT reorganization, partly influenced by exposure to the social stress of subordination, that likely functions to integrate adrenal and gonadal systems and shape the behavioral response to emotionally challenging social situations.

Measurement of 5-HT(1A) receptor density and in-vivo binding parameters of [(18)F]mefway in the nonhuman primate

The goal of this work was to characterize the in-vivo behavior of [(18)F]mefway as a suitable positron emission tomography (PET) radiotracer for the assay of 5-hydroxytryptamine(1A) (5-HT(1A)) receptor density (B(max)). Six rhesus monkeys were studied using a multiple-injection (M-I) protocol consisting of three sequential bolus injections of [(18)F]mefway. Injection times and amounts of unlabeled mefway were optimized for the precise measurement of B(max) and specific binding parameters k(off) and k(on) for estimation of apparent K(D). The PET time series were acquired for 180 minutes with arterial sampling performed throughout. Compartmental analysis using the arterial input function was performed to obtain estimates for K(1), k(2), k(off), B(max), and K(Dapp) in the cerebral cortex and raphe nuclei (RN) using a model that accounted for nontracer doses of mefway. Averaged over subjects, highest binding was seen in the mesial temporal and dorsal anterior cingulate cortices with B(max) values of 42±8 and 36±8 pmol/mL, respectively, and lower values in the superior temporal cortex, RN, and parietal cortex of 24±4, 19±4, and 13±2 pmol/mL, respectively. The K(Dapp) of mefway for the 5-HT(1A) receptor sites was 4.3±1.3 nmol/L. In conclusion, these results show that M-I [(18)F]mefway PET experiments can be used for the in-vivo measurement of 5-HT(1A) receptor density.

Early pathogenic care and the development of ADHD-like symptoms

Early pathogenic care that is characterised by disregard for the child's basic emotional needs can lead to severe global psychosocial and cognitive dysfunction and deviant developmental trajectories of brain maturation. Reactive attachment disorder (RAD) is a developmental disorder associated with early pathogenic care that is characterised by markedly disturbed ways of relating socially in most contexts. In addition to other severe emotional dysfunctions, children suffering from RAD often display a high number of comorbid attention deficit/hyperactivity disorder (ADHD) symptoms such as inattention, impulsivity and hyperactivity. It is not yet clear whether ADHD-like symptoms in children exposed to pathogenic care represent a true comorbidity of ADHD or similarities in behavioural dysfunction with a different neurodevelopmental pathway in terms of a phenocopy. In this review, we summarise the findings on the neurobiological consequences of early pathogenic care. Pathogenic care is considered a form of care by a primary caretaker involving a lack or a loss of expectable care, e.g., by early separation, frequent change in caregivers, institutionalisation or neglect. The reviewed studies suggest that a primary dysfunction of limbic brain circuits after early pathogenic care might lead to an interference by motivational or emotional cues impinging on prefrontal executive functions resulting in behavioural similarities with ADHD. Thus, the complex phenotype observed after early pathogenic care might be best described by a dimensional approach with behavioural and neurobiological similarities to ADHD coinciding to a certain degree as a function of early experience. Based on this evidence, suggestions for the treatment of ADHD-like symptoms in children after adverse early life experiences are provided.

Effects of extended-release injectable naltrexone on self-injurious behavior in rhesus macaques (Macaca mulatta)

Self-injurious behavior (SIB) is a spontaneous behavior that threatens the health and wellbeing of multiple species. In humans, the opioid antagonist naltrexone hydrochloride has been used successfully to modulate the endogenous opioid system and reduce the occurrence of SIB. This study is the first to assess the efficacy of extended-release naltrexone in the pharmacologic treatment of SIB in rhesus macaques (Macaca mulatta). In an acute pharmacokinetic study of 4 macaques, we determined the mean naltrexone plasma concentration was maintained above the therapeutic level (2 ng/mL) after administration of a single dose (20 mg/kg) of 28-d extended-release naltrexone throughout the release period. For a subsequent treatment study, we selected 8 singly housed macaques known to engage in SIB. The study comprised a 4-wk baseline phase; an 8-wk treatment phase, during which each macaque received 2 doses of extended-release naltrexone 28 d apart; and a 4-wk posttreatment phase. Plasma samples were collected and analyzed weekly for naltrexone concentrations throughout the treatment and posttreatment phases. In addition, total of 6 h of video was analyzed per animal per phase of the study. Compared with baseline phases, both the frequency and the percentage of time spent displaying SIB decreased during the treatment phase, and the percentage of time remained decreased during the posttreatment phase. In contrast, extended-release naltrexone did not alter the expression of other abnormal, anxiety-related, or agonistic behaviors nor were levels of inactivity affected. The present study supports the use of naltrexone in the treatment of SIB in rhesus macaques.

Maternal high-fat diet in mice programs emotional behavior in adulthood

The maternal environment has a significant role in the normal development of the fetus and may have long-term impact on brain development including critical central pathways such as the gamma-aminobutyric acid (GABA), serotonergic and the neurotrophin systems. For example, maternal malnutrition plays an important role in programming many aspects of physiology and behavior including predisposition to mental-health related disorders such as anxiety. Here we investigated the effects of maternal high-fat diet or control diet for nine weeks (prior to gestation, gestation and lactation) on the adult offspring with respect to anxiety related behaviors as well as exploration and conditioned fear response. We found that offspring born to high-fat diet mothers showed increased anxiety-like behaviors, but intact conditioned fear response and exploratory behavior. In addition, brain-derived neurotrophic factor (BDNF) was significantly increased in the dorsal hippocampus, while GABA(A) alpha2 receptor subunit and 5-hydroxytryptamine 1A (5-HT1A) receptor showed increased levels in the ventral hippocampus. In summary, these findings suggest that maternal high-fat diet consumption during critical periods in the development of the fetus, might increase the risk of abnormal behaviors in adulthood related to anxiety.

Pre-gestational stress reduces the ratio of 5-HIAA to 5-HT and the expression of 5-HT1A receptor and serotonin transporter in the brain of foetal rat

Background

Many studies have found that stress before or during pregnancy is linked to an increased incidence of behavioural disorders in offspring. However, few studies have investigated hypothalamic-pituitary-adrenal (HPA) axis activity and the serotonergic system as a consequence of pregestational stress. In the present study, we investigated the effect of pre-gestational stress on HPA axis activity in maternal rats and their foetuses and examined whether changes in HPA axis activity of maternal rats produced functional changes in the serotonergic system in the brain of foetuses.

Results

We used the behavioural tests to assess the model of chronic unpredictable stress (CUS) in maternal rats. We found the activity in the open field and sucrose consumption was lower for rats with CUS than for the controls. Body weight but not brain weight was higher for control foetuses than those from the CUS group. Serum corticosterone and corticotrophin-releasing hormone levels were significantly higher for mothers with CUS before pregnancy and their foetuses than for the controls. Levels of 5-hydroxytryptamine (5-HT) were higher in the hippocampus and hypothalamus of foetuses in the CUS group than in the controls, and 5-hydroxyindoleacetic acid (5-HIAA) levels were lower in the hippocampus in foetuses in the CUS group than in the control group. Levels of 5-HIAA in the hypothalamus did not differ between foetuses in the CUS group and in the control group. The ratio of 5-HIAA to 5-HT was significantly lower for foetuses in the CUS group than in the control group. Levels of 5-HT1A receptor were significantly lower in the foetal hippocampus in the CUS group than in the control group, with no significant difference in the hypothalamus. The levels of serotonin transporter (SERT) were lower in both the foetal hippocampus and foetal hypothalamus in the CUS group than in the control group.

Conclusions

Our data demonstrate that pre-gestational stress alters HPA axis activity in maternal rats and their foetuses, which is associated with functional changes in 5-HT activity (5-HT, 5-HIAA and ratio of 5-HIAA to 5-HT), as well as the levels of the 5-HT1A receptor and SERT in the hippocampus and hypothalamus of foetuses.

Disruptions in serotonergic regulation of cortical glutamate release in primate insular cortex in response to chronic ethanol and nursery rearing

Early-life stress has been shown to increase susceptibility to anxiety and substance abuse. Disrupted activity within the anterior insular cortex (AIC) has been shown to play a role in both of these disorders. Altered serotonergic processing is implicated in controlling the activity levels of the associated cognitive networks. We therefore investigated changes in both serotonin receptor expression and glutamatergic synaptic activity in the AIC of alcohol-drinking rhesus monkeys. We studied tissues from male rhesus monkeys raised under two conditions: Male rhesus monkeys (1) "mother reared" (MR) by adult females (n=9) or (2) "Nursery reared" (NR), that is, separated from their mothers and reared as a separate group under surrogate/peer-reared conditions (n=9). The NR condition represents a long-standing and well-validated nonhuman primate model of early life stress. All monkeys were trained to self-administer ethanol (4% w/v) or an isocaloric maltose-dextrin control solution. Subsets from each rearing condition were then given daily access to ethanol, water, or maltose-dextrin for 12 months. Tissues were collected at necropsy and were further analyzed. Using real time RT-PCR we found that ethanol-naive, NR monkeys had lower AIC levels of 5-HT(1A) and 5-HT(2A) receptor mRNA compared with ethanol-naive, MR animals. Although NR monkeys consumed more ethanol over the 12-month period compared with MR animals, both MR and NR animals expressed greater 5-HT(1A) and 5-HT(2A) receptor mRNA levels following chronic alcohol self-administration. The interaction between nursery-rearing conditions and alcohol consumption resulted in a significant enhancement of both 5-HT(1A) and 5-HT(2A) receptor mRNA levels such that lower expression levels observed in nursery-rearing conditions were not found in the alcohol self-administration group. Using voltage clamp recordings in the whole cell configuration we recorded excitatory postsynaptic currents in both ethanol-naive and chronic self-administration groups of NR and MR monkeys. Both groups that self-administered ethanol showed greater glutamatergic activity within the AIC. This AIC hyperactivity in MR alcohol-consuming monkeys was accompanied by an increased sensitivity to regulation by presynaptic 5-HT(1A) receptors that was not apparent in the ethanol-naive, MR group. Our data indicate that chronic alcohol consumption leads to greater AIC activity and may indicate a compensatory upregulation of presynaptic 5-HT(1A) receptors. Our results also indicate that AIC activity may be less effectively regulated by 5-HT in ethanol-naive NR animals than in NR monkeys in response to chronic ethanol self-administration. These data suggest possible mechanisms for increased alcohol seeking and possible addiction potential among young adults who had previously experienced early-life stress that include disruptions in both AIC activity and serotonin system dynamics.

Serotonin receptor expression in human prefrontal cortex: balancing excitation and inhibition across postnatal development

Serotonin and its receptors (HTRs) play critical roles in brain development and in the regulation of cognition, mood, and anxiety. HTRs are highly expressed in human prefrontal cortex and exert control over prefrontal excitability. The serotonin system is a key treatment target for several psychiatric disorders; however, the effectiveness of these drugs varies according to age. Despite strong evidence for developmental changes in prefrontal Htrs of rodents, the developmental regulation of HTR expression in human prefrontal cortex has not been examined. Using postmortem human prefrontal brain tissue from across postnatal life, we investigated the expression of key serotonin receptors with distinct inhibitory (HTR1A, HTR5A) and excitatory (HTR2A, HTR2C, HTR4, HTR6) effects on cortical neurons, including two receptors which appear to be expressed to a greater degree in inhibitory interneurons of cerebral cortex (HTR2C, HTR6). We found distinct developmental patterns of expression for each of these six HTRs, with profound changes in expression occurring early in postnatal development and also into adulthood. However, a collective look at these HTRs in terms of their likely neurophysiological effects and major cellular localization leads to a model that suggests developmental changes in expression of these individual HTRs may not perturb an overall balance between inhibitory and excitatory effects. Examining and understanding the healthy balance is critical to appreciate how abnormal expression of an individual HTR may create a window of vulnerability for the emergence of psychiatric illness.