Early life stress as a risk factor for mental health: role of neurotrophins from rodents to non-human primates

Adult depression-like behavior, amygdala and olfactory cortex functions are restored by odor previously paired with shock during infant's sensitive period attachment learning

Maltreatment from the caregiver induces vulnerability to later life psychopathologies, yet attraction and comfort is sometimes provided by cues associated with early life maltreatment. We used a rat model of early life maltreatment with odor-0.5 mA shock conditioning to produce depressive-like behaviors and questioned whether stimuli associated with maltreatment would restore emotional neurobehavioral function to control levels. Pups received daily novel odor-0.5 mA shock conditioning from postnatal day 8 to 12. This procedure produces a new maternal odor that controls pups' attachment behaviors. In adulthood, either with or without the infant odor, animals received a Forced Swim Test, Sucrose Preference Test or assessment of amygdala and olfactory system functioning using field potential signal evoked by olfactory bulb paired-pulse electrical stimulation. Following neonatal odor-shock pairings, but not unpaired controls, adults without the odor present showed increased depression-like behavior in the Forced Swim Test and Sucrose Preference Test and a deficit in paired-pulse inhibition in amygdala and piriform (olfactory) cortex. All effects were brought to control levels when the infant conditioned odor was presented during behavioral and neural tests. The ability of cues associated with early life maltreatment to normalize behavior and amygdala activity suggests these cues provide adaptive value in adulthood.

Chronic social instability induces anxiety and defective social interactions across generations

BACKGROUND

Chronic social instability during adolescence and early adulthood is known to produce a variety of long-lasting effects that may contribute to future psychiatric disorders. However, its potential to affect future generations has not been tested.

METHODS

Female and male mice were exposed to chronic social stress involving social instability and disruption of social hierarchy from postnatal day 27 to 76. After treatment, a group of animals was used to evaluate long-term behavioral effects of the stress exposure, and other mice were used to generate F1, F2, and F3 offspring, to test for behavioral effects across generations.

RESULTS

Chronic social instability during adolescence and early adulthood induces persistent behavioral alterations, including enhanced anxiety and social deficits that are transmitted predominantly to females across at least three generations. Both mothers and fathers can transmit all of these altered behaviors to their F1 offspring. However, only F1 fathers transmit all of them to their F2 and F3 daughters. In the F1 generation, enhanced anxiety and social deficits are associated with elevated serum corticosterone levels; however, in the F2 and F3 generations, they are not.

CONCLUSIONS

These findings support the idea that individual risk for psychiatric disorders that involve enhanced anxiety and/or social dysfunction may be dependent not only on the specific alleles of genes that are inherited from one's parents and on one's own experiences, but also on the experiences of one's parents when they were young.

Preclinical studies modeling deep brain stimulation for depression

Deep brain stimulation (DBS) is currently being investigated for the treatment of depression. Results of early clinical trials have been very promising, but the mechanisms responsible for the effects of DBS are still unknown. This article reviews behavioral findings of stimulation applied to different brain targets in rodents, with a particular focus on the ventromedial prefrontal cortex. Mechanisms and substrates involved in the antidepressant-like effects of DBS, including the role of local tissue inactivation, the modulation of fiber pathways in the vicinity of the electrodes, as well as the importance of the serotonergic system and brain derived neurotrophic factor are discussed.

Neurobiological effects of neonatal maternal separation and post-weaning environmental enrichment

Throughout the lifespan, the brain has a considerable degree of plasticity and can be strongly influenced by sensory input from the outside environment. Given the importance of the environment in the regulation of the brain structure, behavior and physiology, the aim of the present work was to analyze the effects of different environmental qualities during two critical ontogenic periods (early life and peripuberty) on behavior and hippocampal physiology. Male Wistar rats were separated from their mothers for 4.5h daily during the first 3 weeks of life. They were weaned on day 21 and housed under either standard or enriched conditions. At 60 d of age, all animals were then housed in same-treatment groups, two per cage, until testing began on day 74. Emotional and cognitive responses were tested using the open field, novel object recognition test and step-down inhibitory avoidance learning. In the dorsal hippocampus, glucocorticoid receptor expression and neuronal activity were examined by immunoreactivity. Grooming behavior in the open field was found to be significantly lower in maternally separated animals, but post-weaning environmental enrichment completely reversed this tendency. Inhibitory avoidance but not object recognition memory was impaired in maternally separated animals, suggesting that early maternal separation alters learning and memory in a task-specific manner. Again, environmental enrichment reversed the effects of maternal separation on the inhibitory avoidance task. Even though maternal separation did not significantly affect Fos and glucocorticoid receptor (GR) expression, environmental enrichment increased both Fos expression in the total hippocampal area and also the overall number of GR positive cells per hippocampal area, mainly due to the changes in CA1. These findings suggest that differential rearing is a useful procedure to study behavioral and physiological plasticity in response to early experience and that, although the effects of adverse experience early in life such as maternal separation can persist until adulthood, some of them can be compensated by early favorable environments, possibly through nervous system plasticity.

How Do Interactions Between Early Caregiving Environment and Genes Influence Health and Behavior?

To promote optimal health and behavioral outcomes in children, nurses have long supported parents in providing the best possible care and nurturance to their offspring. A growing body of neuroscience research argues convincingly for the combined influences of genes and early caregiving on producing an individual's unique health and behavioral phenotype. In this article, we systematically review studies that demonstrate the relationship between qualities of early caregiving and genetic propensity to health and behavioral outcomes. From an initial set of 255 articles, 24 articles met our inclusion criteria. The outcomes fall into four distinct groups: hypothalamic-pituitary-adrenal (HPA) response to stress, externalizing behavior, internalizing behavior, and disorganized attachment. In the articles, authors examined genes that code for the 5-hydroxy tryptamine (serotonin) transporter genes linked polymorphic region [5- HTTLPR] serotonin transporter promoter, D4 dopamine receptor, brain-derived neurotrophic factor, and monoamine oxidase A promoter. The reviewed studies suggest that the effect of the early rearing environment on gene expression relates mainly to HPA response to stress, whereas interactions between genes and caregiving mainly relate to behavior and attachment. Findings have implications for nurses focused on advocacy, prevention, and intervention to support the healthy development of children in families faced with adversity.

Fetal programming by maternal stress: Insights from a conflict perspective

Maternal stress during pregnancy has pervasive effects on the offspring's physiology and behavior, including the development of anxious, reactive temperament and increased stress responsivity. These outcomes can be seen as the result of adaptive developmental plasticity: maternal stress hormones carry useful information about the state of the external world, which can be used by the developing fetus to match its phenotype to the predicted environment. This account, however, neglects the inherent conflict of interest between mother and fetus about the outcomes of fetal programming. The aim of this paper is to extend the adaptive model of prenatal stress by framing mother-fetus interactions in an evolutionary conflict perspective. In the paper, I show how a conflict perspective provides many new insights in the functions and mechanisms of fetal programming, with particular emphasis on human pregnancy. I then take advantage of those insights to make sense of some puzzling features of maternal and fetal physiology and generate novel empirical predictions.

Maternal deprivation effects on brain plasticity and recognition memory in adolescent male and female rats

Data from both human and animal studies suggest that exposure to stressful life events at neonatal stages may increase the risk of psychopathology at adulthood. In particular, early maternal deprivation, 24 h at postnatal day (pnd) 9, has been associated with persistent neurobehavioural changes similar to those present in developmental psychopathologies such as depression and schizophrenic-related disorders. Most neuropsychiatric disorders first appear during adolescence, however, the effects of MD on adolescent animals' brain and behaviour have been scarcely explored. In the present study, we aimed to investigate the emotional and cognitive consequences of MD in adolescent male and female rats, as well as possible underlying neurobiological mechanisms within frontal cortex and hippocampus. Animals were exposed to a battery of behavioural tasks, from pnd 35 to 42, to evaluate cognitive [spontaneous alternation task (SAT) and novel object test (NOT)] and anxiety-related responses [elevated plus maze (EPM)] during adolescence. Changes in neuronal and glial cells, alterations in synaptic plasticity as well as modifications in cannabinoid receptor expression were investigated in a parallel group of control and adolescent (pnd 40) male and female animals. Notably, MD induced a significant impairment in recognition memory exclusively among females. A generalized decrease in NeuN expression was found in MD animals, together with an increase in hippocampal glial fibrillar acidic protein (GFAP) expression exclusively among MD adolescent males. In addition, MD induced in the frontal cortex and hippocampus of male and female adolescent rats a significant reduction in brain derived neurotrophic factor (BDNF) and postsynaptic density (PSD95) levels, together with a decrease in synaptophysin in frontal cortex and neural cell adhesion molecule (NCAM) in hippocampus. MD induced, in animals of both sexes, a significant reduction in CB1R expression, but an increase in CB2R that was statistically significant only for the frontal cortex. Taken together, these results indicate that adolescent females are more vulnerable than males to the cognitive deficits derived from MD despite the changes in neural cells, cannabinoid receptors, as well as the reduction in neural plasticity seem to be similar in both sexes. Further investigation is needed to understand the neurobiological mechanisms underlying the sexual dimorphisms associated to the MD effects, and thus, for a better understanding of the specific sex-dependent vulnerabilities to early life stress. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Early maternal separation has mild effects on cardiac autonomic balance and heart structure in adult male rats

Early life adverse experiences have long-term physiologic and behavioral effects and enhance stress sensitivity. This study examined the effects of maternal separation (MS) on cardiac stress responsivity and structure in adulthood. Male Wistar rats were separated from the dams for 3 h per day from postnatal days 2 through 15. When exposed to 5-day intermittent restraint stress (IRS) as adults, MS, and control rats showed similar acute modifications of cardiac sympathovagal balance, quantified via heart rate variability analysis. In addition, MS had no effect on cardiac pacemaker intrinsic activity (as revealed by autonomic blockade with scopolamine and atenolol) and did not affect the circadian rhythmicity of heart rate, neither before nor after IRS. However, MS differed from control rats in cardiac parasympathetic drive following IRS, which was heightened in the latter but remained unchanged in the former, both during the light and dark phases of the daily rhythm. The evaluation of adult cardiac structure indicated that stress experienced during a crucial developmental period induced only modest changes, involving cardiomyocyte hypertrophy, increased density of vascular structures, and myocardial fibrosis. The mildness of these functional-structural effects questions the validity of MS as a model for early stress-induced cardiac disease in humans.

Social deprivation stress is a triggering factor for the emergence of anxiety- and depression-like behaviours and leads to reduced brain BDNF levels in C57BL/6J mice

Stress is a main risk factor that can trigger psychiatric disorders, including anxiety and major depression. Neurotrophins, such as Brain-Derived Neurotrophic Factor (BDNF), have been identified as neuroendocrine effectors involved in the response to stress and in the neurobehavioural changes associated with depression. Aim of this paper was to study the relationship between neuroendocrine activation (circulating corticosterone and brain BDNF levels) and a wide array of depression- and anxiety-like behaviours (anhedonia, behavioural despair, generalised and social anxiety) resulting from exposure to chronic stress. To this end, 3-month-old C57BL/6J male mice were exposed to either chronic disruption of the social structure (SS), to a stable social structure (SG) or to social deprivation (SD), a condition lacking social stimuli. Results show that, despite not developing anhedonia (decreased preference for a sucrose solution), SD mice were characterised by increased emotionality and hypothalamic-pituitary-adrenal axis reactivity in addition to reduced BDNF levels. By contrast, SG and SS mice showed increased anhedonia accompanied by no alterations in the behavioural and neuroendocrine profile. The results here reported indicate that mice exposed to different social housing conditions use different behavioural strategies to cope with external challenges. In addition they suggest that social deprivation might represent a stressful condition triggering the emergence of both anxiety- and depression-like behaviours and clearly indicate BDNF as a main neurobiological variable mediating these responses.

Effects of early-life abuse differ across development: infant social behavior deficits are followed by adolescent depressive-like behaviors mediated by the amygdala

Abuse during early life, especially from the caregiver, increases vulnerability to develop later-life psychopathologies such as depression. Although signs of depression are typically not expressed until later life, signs of dysfunctional social behavior have been found earlier. How infant abuse alters the trajectory of brain development to produce pathways to pathology is not completely understood. Here we address this question using two different but complementary rat models of early-life abuse from postnatal day 8 (P8) to P12: a naturalistic paradigm, where the mother is provided with insufficient bedding for nest building; and a more controlled paradigm, where infants undergo olfactory classical conditioning. Amygdala neural assessment (c-Fos), as well as social behavior and forced swim tests were performed at preweaning (P20) and adolescence (P45). Our results show that both models of early-life abuse induce deficits in social behavior, even during the preweaning period; however, depressive-like behaviors were observed only during adolescence. Adolescent depressive-like behavior corresponds with an increase in amygdala neural activity in response to forced swim test. A causal relationship between the amygdala and depressive-like behavior was suggested through amygdala temporary deactivation (muscimol infusions), which rescued the depressive-like behavior in the forced swim test. Our results indicate that social behavior deficits in infancy could serve as an early marker for later psychopathology. Moreover, the implication of the amygdala in the ontogeny of depressive-like behaviors in infant abused animals is an important step toward understanding the underlying mechanisms of later-life mental disease associated with early-life abuse.

Dynamics of subcellular proteomes during brain development

Many neurological disorders are caused by perturbations during brain development, but these perturbations cannot be readily identified until there is comprehensive description of the development process. In this study, we performed mass spectrometry analysis of the synaptosomal and mitochondrial fractions from three rat brain regions at four postnatal time points. To quantitate our analysis, we employed (15)N labeled rat brains using a technique called SILAM (stable isotope labeling in mammals). We quantified 167429 peptides and identified over 5000 statistically significant changes during development including known disease-associated proteins. Global analysis revealed distinct trends between the synaptic and nonsynaptic mitochondrial proteomes and common protein networks between regions each consisting of a unique array of expression patterns. Finally, we identified novel regulators of neurodevelopment that possess the identical temporal pattern of known regulators of neurodevelopment. Overall, this study is the most comprehensive quantitative analysis of the developing brain proteome to date, providing an important resource for neurobiologists.

Impartial third-party interventions in captive chimpanzees: a reflection of community concern

Because conflicts among social group members are inevitable, their management is crucial for group stability. The rarest and most interesting form of conflict management is policing, i.e., impartial interventions by bystanders, which is of considerable interest due to its potentially moral nature. Here, we provide descriptive and quantitative data on policing in captive chimpanzees. First, we report on a high rate of policing in one captive group characterized by recently introduced females and a rank reversal between two males. We explored the influence of various factors on the occurrence of policing. The results show that only the alpha and beta males acted as arbitrators using manifold tactics to control conflicts, and that their interventions strongly depended on conflict complexity. Secondly, we compared the policing patterns in three other captive chimpanzee groups. We found that although rare, policing was more prevalent at times of increased social instability, both high-ranking males and females performed policing, and conflicts of all sex-dyad combinations were policed. These results suggest that the primary function of policing is to increase group stability. It may thus reflect prosocial behaviour based upon "community concern." However, policing remains a rare behaviour and more data are needed to test the generality of this hypothesis.

NGF, brain and behavioral plasticity

Nerve Growth Factor (NGF) was initially studied for its role as a key player in the regulation of peripheral innervations. However, the successive finding of its release in the bloodstream of male mice following aggressive encounters and its presence in the central nervous system led to the hypothesis that variations in brain NGF levels, caused by psychosocial stressor, and the related alterations in emotionality, could be functional to the development of proper strategies to cope with the stressor itself and thus to survive. Years later this vision is still relevant, and the body of evidence on the role of NGF has been strengthened and expanded from trophic factor playing a role in brain growth and differentiation to a much more complex messenger, involved in psychoneuroendocrine plasticity.

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.

The Long and the Short of it: Gene and Environment Interactions During Early Cortical Development and Consequences for Long-Term Neurological Disease

Cortical development is a complex amalgamation of proliferation, migration, differentiation, and circuit formation. These processes follow defined timescales and are controlled by a combination of intrinsic and extrinsic factors. It is currently unclear how robust and flexible these processes are and whether the developing brain has the capacity to recover from disruptions. What is clear is that there are a number of cognitive disorders or conditions that are elicited as a result of disrupted cortical development, although it may take a long time for the full pathophysiology of the conditions to be realized clinically. The critical window for the manifestation of a neurodevelopmental disorder is prolonged, and there is the potential for a complex interplay between genes and environment. While there have been extended investigations into the genetic basis of a number of neurological and mental disorders, limited definitive associations have been discovered. Many environmental factors, including inflammation and stress, have been linked to neurodevelopmental disorders, and it may be that a better understanding of the interplay between genes and environment will speed progress in this field. In particular, the development of the brain needs to be considered in the context of the whole materno-fetal unit as the degree of the metabolic, endocrine, or inflammatory responses, for example, will greatly influence the environment in which the brain develops. This review will emphasize the importance of extending neurodevelopmental studies to the contribution of the placenta, vasculature, cerebrospinal fluid, and to maternal and fetal immune response. These combined investigations are more likely to reveal genetic and environmental factors that influence the different stages of neuronal development and potentially lead to the better understanding of the etiology of neurological and mental disorders such as autism, epilepsy, cerebral palsy, and schizophrenia.

Neonatal maternal separation in male rats increases intestinal permeability and affects behavior after chronic social stress

Prolonged maternal separation in rats has several effects on health and behavior. Here we investigated how maternal separation might interact with social stress in adulthood on behavior and gastrointenstinal permeability. The effects of either daily 180 min long term pup-dam separation (LMS) during the stress hyporesponsive period or daily 10 min brief maternal separation (BMS) on behavior, corticosterone and intestinal permeability were investigated, compared to a non-handling (NH) condition in male offspring. The animals from each separation condition were then randomly assigned to adult stress and control conditions, where the stress condition was exposure to 14 days of social instability (CSI). Sucrose preference, elevated plus maze behavior and corticosterone were measured. Colitis was experimentally induced by dextran sulfate sodium for 7 days, followed by measurement of intestinal permeability using the (51)CrEDTA method. Granulocyte marker protein was measured in feces and colons were examined histologically for inflammation. Prior to the social stress, the LMS offspring showed elevated corticosterone levels, lower elevated plus maze activity and less fluid consumption. After social stress, corticosterone levels were suppressed in LMS animals and again they showed less fluid consumption. LMS animals had significantly higher intestinal permeability, but only when also exposed to the social stress in adulthood. The current results support a two-hit model, whereby early life events interact with adult life events in altering animals' vulnerability.

Rearing conditions have long-term consequences for stress responsiveness in free-living great tits

In captivity, the adrenocortical stress response can be permanently altered by events that occur during early life. Free-living animals have rarely been examined in this regard. To examine whether early-life events impact the hypothalamo-pituitary-adrenal (HPA) axis in the natural setting, we evaluated the stress response of free-living interspecifically cross-fostered great tits (Parus major). Cross-fostered birds may show a long-term potentiation of the adrenocortical stress response because species-specific nutritional requirements may not be met in the nest and/or cross-fostered birds may experience psychosocial stress while being raised by heterospecifics. Nevertheless, we hypothesized that in the natural setting, programmed changes in HPA function would be eclipsed by reactive responses to the immediate environment. Thus, we predicted that adult cross-fostered great tits and controls would show no differences in their adrenocortical stress response. Contrary to predictions, we found that stress responsiveness (i.e., the rate of the corticosterone increase associated with capture and handling) was significantly higher in cross-fostered great tits than in controls. Further, stress responsiveness was not significantly different between mature adults and first-year juveniles. Thus, data indicate significant effects of early rearing conditions on adrenocortical reactivity in the natural setting and also suggest that effects of rearing conditions in free-living animals can last into adulthood.

Should neonates sleep alone?

BACKGROUND

Maternal-neonate separation (MNS) in mammals is a model for studying the effects of stress on the development and function of physiological systems. In contrast, for humans, MNS is a Western norm and standard medical practice. However, the physiological impact of this is unknown. The physiological stress-response is orchestrated by the autonomic nervous system and heart rate variability (HRV) is a means of quantifying autonomic nervous system activity. Heart rate variability is influenced by level of arousal, which can be accurately quantified during sleep. Sleep is also essential for optimal early brain development.

METHODS

To investigate the impact of MNS in humans, we measured HRV in 16 2-day-old full-term neonates sleeping in skin-to-skin contact with their mothers and sleeping alone, for 1 hour in each place, before discharge from hospital. Infant behavior was observed continuously and manually recorded according to a validated scale. Cardiac interbeat intervals and continuous electrocardiogram were recorded using two independent devices. Heart rate variability (taken only from sleep states to control for level of arousal) was analyzed in the frequency domain using a wavelet method.

RESULTS

Results show a 176% increase in autonomic activity and an 86% decrease in quiet sleep duration during MNS compared with skin-to-skin contact.

CONCLUSIONS

Maternal-neonate separation is associated with a dramatic increase in HRV power, possibly indicative of central anxious autonomic arousal. Maternal-neonate separation also had a profoundly negative impact on quiet sleep duration. Maternal separation may be a stressor the human neonate is not well-evolved to cope with and may not be benign.

Nerve growth factor (NGF) immunoreactive neurons in the juvenile rat hippocampus: response to acute and long-term high-light open-field (HL-OF) or forced swim (FS) stress stimulation

This study aimed at examining and comparing the influence of two different stress stimuli on the density (number of cells/mm²) of nerve growth factor (NGF) containing neurons in the hippocampal CA1 and CA3 pyramidal cell layers and the dentate gyrus (DG) granule cell layer in juvenile rats (P28; P-postnatal day). The high-light open-field (HL-OF) test and forced swim (FS) test were employed to investigate the effects of a single, 15-min acute exposure and repeated (15 min daily for 21 days) long-term exposure to stress. In order to detect NGF-ir neurons, immunohistochemical (-ir) techniques were used. In comparison with nonstressed animals, acute and long-term HL-OF or FS stimulation resulted in a marked increase (P<0.001) in the density of NGF-ir containing cells in all the hippocampal structures. The frequency of stress application (acute vs. long-term), however, did not have a substantial impact on the studied parameter, with the exception of the CA3 sector, where a decreased density (P<0.001) of NGF-ir neurons was observed after long-term exposure to FS. It may be concluded that a rise in the density of NGF-ir neurons in the juvenile rat hippocampus after exposure to HL-OF or FS stressors could have affected the activity of the hypothalamic-pituitary-adrenocortical (HPA) stress axis. Prolonged HL-OF or FS stress was probably aggravating enough not to trigger the habituation process. The type of stressor applied (HL-OF vs. FS) was not essentially a factor determining the density of NGF-ir cells in the hippocampus.

A meta-analysis of circulating BDNF concentrations in anorexia nervosa

OBJECTIVES

Brain derived neurotrophic factor (BDNF) is involved in neuroplasticity, and in the homeostatic regulation of food intake and energy expenditure. It also has a role in stress responsivity and reward processing. On the basis of its involvement in these various processes, BDNF can be hypothesized to be an important factor in the development and maintenance of anorexia nervosa (AN). This study meta-analytically summarizes investigations of serum BDNF concentrations in people currently ill with AN, in comparison to healthy controls.

METHODS

Seven studies measuring BDNF in serum of individuals with AN (n=155) and healthy controls (n=174) were identified and included in the meta-analysis of the mean differences between case and control groups.

RESULTS

This study confirms that AN is associated with decreased serum BDNF concentrations, in comparison to healthy controls. The combined effect size (standardized mean difference, SMD) was large (SMD=-0.96; 95% CI -1.33 to -0.59; P<0.001). Significant heterogeneity of effect sizes was identified (I(2)=58.3%; P<0.001), which emerged as being primarily attributable to the first published study on the investigated association.

CONCLUSIONS

The present meta-analytical summary of studies measuring circulating BDNF concentrations in women with AN and healthy controls confirms that it is significantly reduced in this patient group. Difficulties associated with the measurement of BDNF have been identified and potential confounding factors have been discussed. Current data do not allow inferences to be made about causal links between levels of circulating BDNF and AN. However, possible explanations for the relationship between BDNF and AN have been presented.

BDNF serum levels, but not BDNF Val66Met genotype, are correlated with personality traits in healthy subjects

Consisting evidence in animal models has suggested that alterations in brain-derived neurotrophic factor (BDNF) brain expression and release are involved in the pathogenesis of mental illnesses, such as, mood, anxiety, and eating disorders. This hypothesis is supported by data emerging from biochemical studies on serum BDNF levels and genetic studies on the functional polymorphism Val66Met in the BDNF gene in patients and control subjects. Anxiety-related personality traits are associated with several mental disorders. However, they are also measurable in non-affected subjects and, so, may represent a useful "endophenotype" to study the biological correlation of the vulnerability factors in the general population. In this study, we analyzed putative correlations in subjects unaffected by mental disorders between personality traits, serum BDNF levels (N = 107), and the BDNF Val66Met genotype (N = 217). Furthermore, we tested the possible interactions between these variables. A significant correlation has been observed between high scores of harm avoidance (HA) measured by the temperament and character inventory (TCI), and low BDNF serum concentration (r = -0.253, P = 0.009). In addition, an association has been evidenced between low BDNF levels in serum and the BDNF Val/Val genotype (P = 0.021). By analyzing putative concomitant effects of different variables on HA scores in a regression model, we observed a significant correlation only with BDNF serum concentrations (P = 0.022). The study results suggest that a decrease in serum BDNF concentrations may represent a biochemical marker associated with anxiety personality traits also retrievable in the general population.

The richness of social stimuli shapes developmental trajectories: Are laboratory mouse pups impoverished?

The early environment is crucial for brain and behavior development. In particular, social experiences involving the mother and the peers are critical in shaping the adult individual. Though animal models of psychiatric disorders have widely investigated the relevance of the mother-offspring interaction, the peer interaction has so far been rarely studied. The communal nest (CN) is an innovative experimental strategy that favors a more comprehensive investigation of the long-term effects of both components. CN is a rearing condition employed by up to 90% of mouse females in naturalistic settings and consists of a single nest where two or more mothers keep their pups together and share care-giving. In a CN, the developing pup is exposed to high levels of both maternal care and interaction with peers. At adulthood, these mice display relevant changes in bran function and behavior, including high levels of neural plasticity markers, such as BDNF, and elaborate adult social competences. Overall, on the one hand, CN is an experimental approach complementary to the ones currently used that allows to investigate how the early environment determines developmental trajectories. On the other, it may represent a strategy to improve the study of animal models of psychiatric disorders characterized by social dysfunction, such as major depression, autism and attention deficit hyperactivity disorder. Indeed, the more elaborate social competences shown by these mice at adulthood may allow to better characterize deficits in the social domain induced by genetic and/or environmental manipulations.

The clinical implications of mouse models of enhanced anxiety

Mice are increasingly overtaking the rat model organism in important aspects of anxiety research, including drug development. However, translating the results obtained in mouse studies into information that can be applied in clinics remains challenging. One reason may be that most of the studies so far have used animals displaying 'normal' anxiety rather than 'psychopathological' animal models with abnormal (elevated) anxiety, which more closely reflect core features and sensitivities to therapeutic interventions of human anxiety disorders, and which would, thus, narrow the translational gap. Here, we discuss manipulations aimed at persistently enhancing anxiety-related behavior in the laboratory mouse using phenotypic selection, genetic techniques and/or environmental manipulations. It is hoped that such models with enhanced construct validity will provide improved ways of studying the neurobiology and treatment of pathological anxiety. Examples of findings from mouse models of enhanced anxiety-related behavior will be discussed, as well as their relation to findings in anxiety disorder patients regarding neuroanatomy, neurobiology, genetic involvement and epigenetic modifications. Finally, we highlight novel targets for potential anxiolytic pharmacotherapeutics that have been established with the help of research involving mice. Since the use of psychopathological mouse models is only just beginning to increase, it is still unclear as to the extent to which such approaches will enhance the success rate of drug development in translating identified therapeutic targets into clinical trials and, thus, helping to introduce the next anxiolytic class of drugs.

Early life stress decreases hippocampal BDNF content and exacerbates recognition memory deficits induced by repeated D-amphetamine exposure

Adverse experiences early in life may have profound influences on brain development, for example, determining alterations in response to psychostimulant drugs, an increased risk of developing a substance abuse disorder, and individual differences in the vulnerability to neuropsychiatric disorders later in life. Here, we investigated the effects of exposure to an early adverse life event, maternal deprivation, combined with repeated d-amphetamine (AMPH) administration in adulthood, on recognition memory and brain-derived neurotrophic factor (BDNF) levels in rats' brain and serum. Rats were exposed to one of the following maternal rearing conditions from postnatal days 1 to 14: non-deprived (ND) or deprived (D). In adulthood, both groups received injections of saline (SAL) or AMPH (2.0mg/kg, i.p.) for 7 days. In Experiment I (performed 24h after the last AMPH injection), AMPH induced long-term memory (LTM) impairments in ND and D groups. The D+AMPH group also presented short-term memory (STM) impairments, indicating that the effects of AMPH on memory were more pronounced when the animals where maternally deprived. The group exposed to D+SAL (SAL) showed only LTM impairments. In Experiment II (performed 8 days after the last injection), AMPH detrimental effects on memory persisted in ND and D groups. BDNF levels were decreased in the hippocampus of D+SAL rats. In conclusion, AMPH produces severe and persistent recognition memory impairments that were more pronounced when the animals were maternally deprived, suggesting that an early adverse life event may increase the vulnerability of cognitive function to exposure to a psychostimulant later in life.

A novel BDNF polymorphism affects plasma protein levels in interaction with early adversity in rhesus macaques

Early stressful events can increase vulnerability for psychopathology, although knowledge on the effectors is still limited. In this report we describe the characterization of a single nucleotide polymorphism (SNP) in rhesus macaques, which results in a Val to Met transition in the pro-BDNF domain, similar to a well described variant in the human gene. Further, we tested the hypothesis that peripheral levels of BDNF, which is involved in the response to stress and in the pathophysiology of anxiety and depression, might be differentially affected in a non-human primate model of early adverse rearing in a genotype-dependent manner. Males and females rhesus macaques reared either with their mothers (MR), in peer-only groups (PR), or in a "surrogate/peer-reared" (SPR) condition with limited peer interactions, were used as experimental subjects. BDNF levels were determined at baseline on postnatal days (PND) 14, 30 and 60 by means of specific ELISA procedure. Data indicate that BDNF levels were increased as a result of peer-rearing and that this increase was moderated by the presence of the SNP. Overall these data indicate that a SNP, which results in a Val to Met transition in the pro-BDNF domain, is present in rhesus macaques and is able to affect BDNF peripheral levels, thus making this primate model a fundamental tool to study gene by environment interactions involving the BDNF gene.

The impact of maternal separation on the number of tyrosine hydroxylase-expressing midbrain neurons during different stages of ontogenesis

Early life stressors have life-long functional and anatomical consequences. Though many neurotransmitters are involved in the functional impact of early life stress, dopamine seems to be important because of its roles in motor control, adaptation to stressful conditions, mood, cognition, attention and reward. Thus, in the present study, we investigated the way that early life stress, in the form of maternal separation (MS), affects the populations of tyrosine hydroxylase-immunoreactive (TH-IR) dopaminergic neurons in rat midbrain structures during ontogenesis. We included in the study the sub-regions of the substantia nigra (SN) and the ventral tegmental area (VTA). In both the control and MS rats, we found that the estimated total number of TH-expressing neurons fluctuated during ontogenesis. Moreover, MS influenced the number of TH-IR cells, especially in the SN pars reticulata (SNr) and VTA. Shortly after the termination of MS, on postnatal day (PND) 15, a decrease in the estimated total number of TH-IR neurons was observed in the SNr and VTA (in both males and females). On PND 35, MS caused a transient increase in the number of TH-IR cells only in the SNr of female rats. On PND 70, MS affected the number of TH-IR neurons in the VTA of females; specifically, an increase in the number of these cells was observed. Additionally, MS did not alter TH-IR cell sizes or the total levels of TH (measured by Western blot analysis) in the SN and VTA for all stages of ontogenesis in both males and females. The results from the study herein indicate that early life stress has enduring effects on the populations of midbrain TH-expressing dopaminergic neurons (especially in female rats), which are critically important for dopamine-regulated brain function throughout ontogenesis.

Glucocorticoids and stress‐related depression: an evaluation of biological mechanisms and the potential for new therapeutics

Purpose

Principles of epigenesis that provide a foundation for research into chronic medical disorders are increasingly being applied in the context of mental health. The purpose of this paper is to consider recent research evidence for epigenetic influences in the pathogenesis of depression, and the putative links with stress biology during exposure to chronic stress, with the aim of placing this into a context of potential new therapeutics.

Design/methodology/approach

Substantive reviews published during the last ten years were identified in a search of the Pubmed database in September 2010 using the terms “epigenetics” or “epigenesis” with “mental health”, “mood disorder”, “depression”, stress', “chronic stress” or “environment”, supplemented by hand‐searching of citations in the reviews.

Findings

Epigenetic mechanisms are both heritable and acquired, and their impact on the underlying genome helps explain individual vulnerability and patterns of occurrence of depression.

Originality/value

The paper shows that this relatively new field of research is in its infancy, and the influence of adverse environments (i.e. stressors) on genetic/epigenetic predisposition has promise for the advent of novel therapeutics based on epigenetic manipulation.

Epigenetic marking of the BDNF gene by early-life adverse experiences

Studies over the past half-century have made it clear that environmental influences in development, particularly stress and traumatic experiences, can remain pervasive across the lifespan. Though it has been hypothesized for some time that the long-term consequences of early-life adversity represent epigenetic influences, it has not been until recently that studies have begun to provide empirical support of experience-driven epigenetic modifications to the genome. Here we focus on this theme, and review current knowledge pertaining to the epigenetics of behavioral development. At the center of our discussion is the brain-derived neurotrophic factor (BDNF) gene, as abnormal BDNF gene activity is a leading etiological hypothesis by which early-life adverse experiences persistently modify brain and behavioral plasticity.

Electrophysiological insights into the enduring effects of early life stress on the brain

Increasing evidence links exposure to stress early in life to long-term alterations in brain function, which in turn have been linked to a range of psychiatric and neurological disorders in humans. Electrophysiological approaches to studying these causal pathways have been relatively underexploited. Effects of early life stress on neuronal electrophysiological properties offer a set of potential mechanisms for these susceptibilities, notably in the case of epilepsy. Thus, we review experimental evidence for altered cellular and circuit electrophysiology resulting from exposure to early life stress. Much of this work focuses on limbic long-term potentiation, but other studies address alterations in electrophysiological properties of ion channels, neurotransmitter systems, and the autonomic nervous system. We discuss mechanisms which may mediate these effects, including influences of early life stress on key components of brain synaptic transmission, particularly glutamate, GABA and 5-HT receptors, and influences on neuroplasticity (primarily neurogenesis and synaptic density) and on neuronal network activity. The existing literature, although small, provides strong evidence that early life stress induces enduring, often robust effects on a range of electrophysiological properties, suggesting further study of enduring effects of early life stress employing electrophysiological methods and concepts will be productive in illuminating disease pathophysiology.

Evolutionary functions of early social modulation of hypothalamic-pituitary-adrenal axis development in humans

The hypothalamic-pituitary-adrenal axis (HPAA) is highly responsive to social challenges. Because stress hormones can have negative developmental and health consequences, this presents an evolutionary paradox: Why would natural selection have favored mechanisms that elevate stress hormone levels in response to psychosocial stimuli? Here we review the hypothesis that large brains, an extended childhood and intensive family care in humans are adaptations resulting from selective forces exerted by the increasingly complex and dynamic social and cultural environment that co-evolved with these traits. Variations in the modulation of stress responses mediated by specific HPAA characteristics (e.g., baseline cortisol levels, and changes in cortisol levels in response to challenges) are viewed as phenotypically plastic, ontogenetic responses to specific environmental signals. From this perspective, we discuss relations between physiological stress responses and life history trajectories, particularly the development of social competencies. We present brief summaries of data on hormones, indicators of morbidity and social environments from our long-term, naturalistic studies in both Guatemala and Dominica. Results indicate that difficult family environments and traumatic social events are associated with temporal elevations of cortisol, suppressed reproductive functioning and elevated morbidity. The long-term effects of traumatic early experiences on cortisol profiles are complex and indicate domain-specific effects, with normal recovery from physical stressors, but some heightened response to negative-affect social challenges. We consider these results to be consistent with the hypothesis that developmental programming of the HPAA and other neuroendocrine systems associated with stress responses may facilitate cognitive targeting of salient social challenges in specific environments.

Early-stress regulates resilience, vulnerability and experimental validity in laboratory rodents through mother-offspring hormonal transfer

The role of early-life stressors in the calibration of individual responses to future challenges has long been investigated in laboratory rodents. Specifically, countless studies show that exposure to early-life stressors - in the form of various periods of maternal separation, administration of exogenous corticosterone and variable feeding conditions - modulate the regulation of defensive responses (e.g. behavioral fearfulness/anxiety and endocrine stress reactivity) in adulthood. Yet, the link between early-life stress and adult defensive responses is not linear. Specifically, while neonatal moderate stress is generally associated with adult subjects characterized by reduced stress reactivity, neonatal elevated stress is often reported to relate to opposite responses. Not only are these findings relevant to the understanding of individual plasticity to contextual features, but also they can have direct implications in the development of rodent models of human disorders. Specifically, these studies demonstrate that the experimental individual responds to early environmental cues with the consequence of adjusting its adaptation to the future environment. If neglected, this aspect may have detrimental consequences in laboratory animal experimentation. For example, neonatal conditions increasing adult responses to moderate stress may result in experimental subjects showing abnormal hypothalamic-pituitary-adrenocortical (HPA) activation to routine husbandry conditions, test environment and general laboratory procedures. The aim of the present review is threefold: (i) propose that neonatal circulating levels of corticosteroids may constitute a potential mediator connecting early and adult defensive systems; (ii) propose that the link between early and adult stress follows a U-shaped curve, with low levels down-regulating individual reactivity to external stressors and high levels exerting opposite effects; (iii) discuss the methodological implications of these considerations in the development of rodent models of human disorders.

Animal models of intellectual disability: towards a translational approach

Intellectual disability is a prevalent form of cognitive impairment, affecting 2-3% of the general population. It is a daunting societal problem characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social and practical adaptive skills. Intellectual disability is a clinically important disorder for which the etiology and pathogenesis are still poorly understood. Moreover, although tremendous progress has been made, pharmacological intervention is still currently non-existent and therapeutic strategies remain limited. Studies in humans have a very limited capacity to explain basic mechanisms of this condition. In this sense, animal models have been invaluable in intellectual disability investigation. Certainly, a great deal of the knowledge that has improved our understanding of several pathologies has derived from appropriate animal models. Moreover, to improve human health, scientific discoveries must be translated into practical applications. Translational research specifically aims at taking basic scientific discoveries and best practices to benefit the lives of people in our communities. In this context, the challenge that basic science research needs to meet is to make use of a comparative approach to benefit the most from what each animal model can tell us. Intellectual disability results from many different genetic and environmental insults. Taken together, the present review will describe several animal models of potential intellectual disability risk factors.

Voluntary exercise and palatable high-fat diet both improve behavioural profile and stress responses in male rats exposed to early life stress: role of hippocampus

Childhood trauma induced by adverse early life experience is associated with increased risk of psychological disorders in adulthood. Disruption of normal development has been shown to affect hippocampal morphology and function, influencing adaptations to stress. Here we investigated whether palatable food and/or exercise would ameliorate the behavioural responses following early life stress in rats. Rats were subjected to 15 (S15) or 180 (S180) minutes separation from dams on postnatal days 2-14. After weaning, rats were assigned to either receive chow (C), high-fat diet (HFD), voluntary exercise (running, R), or combined HFD and R for 11 weeks. In addition to anxiety- and depression-like behaviours, response to restraint stress was measured. Glucocorticoid receptor (GR), brain-derived neurotrophic factor (BDNF) and 5-hydroxytryptamine receptor 1A (5HT1A) receptor mRNA in the hippocampus were measured. S180 rats had similar body weight to S15, however their plasma insulin concentrations were double those of S15 rats when consuming HFD; adding exercise reduced plasma insulin. Anxiety-like behaviour in S180 rats, measured using Light Dark test (LDT) and Elevated Plus Maze (EPM) were ameliorated by the provision of HFD, R or HFD+R. A similar effect was observed on depression-like behaviour assessed by forced swim test (FST), with less time being spent immobile. Exposure to early-life stress during development was associated with significant reductions in hippocampal GR, 5HT1A receptor and BDNF mRNA, and these changes were normalized in S180 rats provided with HFD or exercise. Prolonged maternal separation resulted in exacerbated hyperinsulinemia when consuming HFD suggesting that these rats are metabolically disadvantaged. In summary, voluntary exercise alone or in combination with HFD produced beneficial effects on both behaviour and metabolic outcomes in rats exposed to early life stress.

Brain function and chromatin plasticity

The characteristics of epigenetic control, including the potential for long-lasting, stable effects on gene expression that outlive an initial transient signal, could be of singular importance for post-mitotic neurons, which are subject to changes with short- to long-lasting influence on their activity and connectivity. Persistent changes in chromatin structure are thought to contribute to mechanisms of epigenetic inheritance. Recent advances in chromatin biology offer new avenues to investigate regulatory mechanisms underlying long-lasting changes in neurons, with direct implications for the study of brain function, behaviour and diseases.

Developing a neurobehavioral animal model of infant attachment to an abusive caregiver

BACKGROUND

Both abused and well cared for infants show attachment to their caregivers, although the quality of that attachment differs. Moreover, the infant's attachment to the abusive caregiver is associated with compromised mental health, especially under stress. In an attempt to better understand how abuse by the caregiver can compromise mental health, we explore the neural basis of attachment in both typical and abusive environments using infant rats, which form attachments to the mother through learning her odor. Here, we hypothesize that the neural circuitry for infant attachment differs based on the quality of the attachment, which can be uncovered during stressful situations.

METHODS

We used infant rats to compare infant attachment social behaviors and supporting neurobiology using natural maternal odor, as well as two odor-learning attachment paradigms: odor-stroke (mimics typical attachment) and odor-.5 mA shock conditioning (mimics abusive attachment). Next, to uncover differences in behavior and brain, these pups were injected with systemic corticosterone. Finally, pups were reared with an abusive mother to determine ecological relevance.

RESULTS

Our results suggest that the natural and learned attachment odors indistinguishably control social behavior in infancy (approach to the odor and interactions with the mother). However, with corticosterone injection, pups with an abusive attachment show disrupted infant social behavior with the mother and engagement of the amygdala.

CONCLUSIONS

This animal model of attachment accommodates both abusive and typical attachment and suggests that pups' social behavior and underlying neural circuitry may provide clues to understanding attachment in children with various conditions of care.

Genomic features of the human dopamine transporter gene and its potential epigenetic States: implications for phenotypic diversity

Human dopamine transporter gene (DAT1 or SLC6A3) has been associated with various brain-related diseases and behavioral traits and, as such, has been investigated intensely in experimental- and clinical-settings. However, the abundance of research data has not clarified the biological mechanism of DAT regulation; similarly, studies of DAT genotype-phenotype associations yielded inconsistent results. Hence, our understanding of the control of the DAT protein product is incomplete; having this knowledge is critical, since DAT plays the major role in the brain's dopaminergic circuitry. Accordingly, we reevaluated the genomic attributes of the SLC6A3 gene that might confer sensitivity to regulation, hypothesizing that its unique genomic characteristics might facilitate highly dynamic, region-specific DAT expression, so enabling multiple regulatory modes. Our comprehensive bioinformatic analyzes revealed very distinctive genomic characteristics of the SLC6A3, including high inter-individual variability of its sequence (897 SNPs, about 90 repeats and several CNVs spell out all abbreviations in abstract) and pronounced sensitivity to regulation by epigenetic mechanisms, as evident from the GC-bias composition (0.55) of the SLC6A3, and numerous intragenic CpG islands (27 CGIs). We propose that this unique combination of the genomic features and the regulatory attributes enables the differential expression of the DAT1 gene and fulfills seemingly contradictory demands to its regulation; that is, robustness of region-specific expression and functional dynamics.

Shaping brain development: mouse communal nesting blunts adult neuroendocrine and behavioral response to social stress and modifies chronic antidepressant treatment outcome

Early experiences shape brain function and behavior and, consequently, vulnerability to psychopathology at adulthood. Here we exploited the mouse communal nest (CN) paradigm in order to investigate the effect of the early social environment on the emergence of endophenotypes of depression and on antidepressant efficacy at adulthood. CN, which consists in a single nest where three mothers keep their pups together and share care-giving behavior until weaning, is characterized by high levels of maternal behavior and peer interactions, thus representing an highly stimulating environment. Our results show that, when compared to mice reared in standard laboratory conditions (SN), adult CN mice exhibited greater sucrose preference on the first days of the test, displayed reduced anhedonia during social stress and had lower corticosterone levels after acute and prolonged social stress. Furthermore, in line with previous work, CN displayed longer immobility than SN mice in the forced swim test. Here we show that such behavioral response is differently affected by antidepressants according to early experiences. A 3-week fluoxetine treatment affected only SN mice, leading to an increase of immobility duration up to the levels showed by CN mice, while acute fluoxetine administration decreased immobility duration in both groups. These results show that being reared in a CN profoundly changes developmental trajectories, reducing the adult display of endophenotypes of depression and modifying response to antidepressants. The present findings suggest that early experiences represent one of those factors to be taken into account to identify the appropriate individual pharmacological strategy to treat depression in patients.

Transitions in sensitive period attachment learning in infancy: the role of corticosterone

Survival of altricial infants, including humans and rats, depends on attachment to the caregiver - a process that requires infants to recognize, learn, and remember their attachment figure. The demands of a dynamic environment combined with a maturing organism require frequent neurobehavioral reorganization. This restructuring of behavior and its supporting neural circuitry can be viewed through the unique lens of attachment learning in rats in which preference learning is enhanced and aversion learning is attenuated. Behavioral restructuring is well adapted to securing the crucial infant-caregiver relationship regardless of the quality of care. With maturation and the end of the infant-caregiver attachment learning period, the complex interplay of neural structures, hormones, and social behavior coordinates the developing rat's eventual transition to life outside of the nest. Nevertheless, early-life environmental and physiological stressors can alter the resilient nature of this system, particularly with respect to the amygdala, and these changes may provide important clues to understanding the lasting effects of early stress.

Staging perspectives in neurodevelopmental aspects of neuropsychiatry: agents, phases and ages at expression

Neurodevelopmental risk factors have assumed a critical role in prevailing notions concerning the etiopathogenesis of neuropsychiatric disorders. Staging, diagnostic elements at which phase of disease is determined, provides a means of conceptualizing the degree and extent of factors affecting brain development trajectories, but is concurrently specified through the particular interactions of genes and environment unique to each individual case. For present purposes, staging perspectives in neurodevelopmental aspects of the disease processes are considered from conditions giving rise to neurodevelopmental staging in affective states, adolescence, dopamine disease states, and autism spectrum disorders. Three major aspects influencing the eventual course of individual developmental trajectories appear to possess an essential determinant influence upon outcome: (i) the type of agent that interferes with brain development, whether chemical, immune system activating or absent (anoxia/hypoxia), (ii) the phase of brain development at which the agent exerts disruption, whether prenatal, postnatal, or adolescent, and (iii) the age of expression of structural and functional abnormalities. Clinical staging may be assumed at any or each developmental phase. The present perspective offers both a challenge to bring further order to diagnosis, intervention, and prognosis and a statement regarding the extreme complexities and interwoven intricacies of epigenetic factors, biomarkers, and neurobehavioral entities that aggravate currents notions of the neuropsychiatric disorders.

Early-life stress disrupts attachment learning: the role of amygdala corticosterone, locus ceruleus corticotropin releasing hormone, and olfactory bulb norepinephrine

Infant rats require maternal odor learning to guide pups' proximity-seeking of the mother and nursing. Maternal odor learning occurs using a simple learning circuit including robust olfactory bulb norepinephrine (NE), release from the locus ceruleus (LC), and amygdala suppression by low corticosterone (CORT). Early-life stress increases NE but also CORT, and we questioned whether early-life stress disrupted attachment learning and its neural correlates [2-deoxyglucose (2-DG) autoradiography]. Neonatal rats were normally reared or stressed-reared during the first 6 d of life by providing the mother with insufficient bedding for nest building and were odor-0.5 mA shock conditioned at 7 d old. Normally reared paired pups exhibited typical odor approach learning and associated olfactory bulb enhanced 2-DG uptake. However, stressed-reared pups showed odor avoidance learning and both olfactory bulb and amygdala 2-DG uptake enhancement. Furthermore, stressed-reared pups had elevated CORT levels, and systemic CORT antagonist injection reestablished the age-appropriate odor-preference learning, enhanced olfactory bulb, and attenuated amygdala 2-DG. We also assessed the neural mechanism for stressed-reared pups' abnormal behavior in a more controlled environment by injecting normally reared pups with CORT. This was sufficient to produce odor aversion, as well as dual amygdala and olfactory bulb enhanced 2-DG uptake. Moreover, we assessed a unique cascade of neural events for the aberrant effects of stress rearing: the amygdala-LC-olfactory bulb pathway. Intra-amygdala CORT or intra-LC corticotropin releasing hormone (CRH) infusion supported aversion learning with intra-LC CRH infusion associated with increased olfactory bulb NE (microdialysis). These results suggest that early-life stress disturbs attachment behavior via a unique cascade of events (amygdala-LC-olfactory bulb).

Cognitive and social functions and growth factors in a mouse model of Rett syndrome

Rett syndrome (RTT) is an autism-spectrum disorder caused by mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). Abnormalities in social behavior, stereotyped movements, and restricted interests are common features in both RTT and classic autism. While mouse models of both RTT and autism exist, social behaviors have not been explored extensively in mouse models of RTT. Here, we report cognitive and social abnormalities in Mecp2(1lox) null mice, an animal model of RTT. The null mice show severe deficits in short- and long-term object recognition memories, reminiscent of the severe cognitive deficits seen in RTT girls. Social behavior, however, is abnormal in that the null mice spend more time in contact with stranger mice than do wildtype controls. These findings are consistent with reports of increased reciprocal social interaction in RTT girls relative to classic autism. We also report here that the levels of the neurotrophins brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and nerve growth factor (NGF) are decreased in the hippocampus of the null mice, and discuss how this may provide an underlying mechanism for both the cognitive deficits and the increased motivation for social contact observed in the Mecp2(1lox) null mice. These studies support a differential etiology between RTT and autism, particularly with respect to sociability deficits.

Early life stress as an influence on limbic epilepsy: an hypothesis whose time has come?

The pathogenesis of mesial temporal lobe epilepsy (MTLE), the most prevalent form of refractory focal epilepsy in adults, is thought to begin in early life, even though seizures may not commence until adolescence or adulthood. Amongst the range of early life factors implicated in MTLE causation (febrile seizures, traumatic brain injury, etc.), stress may be one important contributor. Early life stress is an a priori agent deserving study because of the large amount of neuroscientific data showing enduring effects on structure and function in hippocampus and amygdala, the key structures involved in MTLE. An emerging body of evidence directly tests hypotheses concerning early life stress and limbic epilepsy: early life stressors, such as maternal separation, have been shown to aggravate epileptogenesis in both status epilepticus and kindling models of limbic epilepsy. In addition to elucidating its influence on limbic epileptogenesis itself, the study of early life stress has the potential to shed light on the psychiatric disorder that accompanies MTLE. For many years, psychiatric comorbidity was viewed as an effect of epilepsy, mediated psychologically and/or neurobiologically. An alternative – or complementary – perspective is that of shared causation. Early life stress, implicated in the pathogenesis of several psychiatric disorders, may be one such causal factor. This paper aims to critically review the body of experimental evidence linking early life stress and epilepsy; to discuss the direct studies examining early life stress effects in current models of limbic seizures/epilepsy; and to suggest priorities for future research.