Do early-life events permanently alter behavioral and hormonal responses to stressors?

Intensification of maternal care by double-mothering boosts cognitive function and hippocampal morphology in the adult offspring

Mice born from high care-giving females show, as adults, low anxiety levels, decreased responsiveness to stress, and substantial improvements in cognitive function and hippocampal plasticity. Given the relevance of this issue for preventing emotional and cognitive abnormalities in high-risk subjects, this study examines the possibility to further enhance the beneficial effects observed in the progeny by augmenting maternal care beyond the highest levels females can display in standard laboratory conditions. This was produced by placing a second female with the dam and its litter in the rearing cage from the partum until pups weaning. Maternal behavior of all females was scored during the first week postpartum, and behavioral indices of emotionality, prestress and poststress corticosterone levels, cognitive performance, and hippocampal morphology were assessed in the adult offspring. We found that pups reared by female dyads received more maternal care than pups reared by dams alone, but as adults, they did not exhibit alterations in emotionality or corticosterone response estimated in basal condition or following restraint stress. Conversely, they showed enhanced performance in hippocampal-dependent tasks including long-term object discrimination, reactivity to spatial change, and fear conditioning together with an increase in dendritic length and spine density in the CA1 region of the hippocampus. In general, the beneficial effects of dyadic maternal care were stronger when both the females were lactating. This study demonstrates that double-mothering exerts a long-term positive control on cognitive function and hippocampal neuronal connectivity. This experimental manipulation, especially if associated with increased feeding, might offer a concrete possibility to limit or reverse the consequences of negative predisposing conditions for normal cognitive development.

Periodic maternal separation decreases hippocampal neurogenesis without affecting basal corticosterone during the stress hyporesponsive period, but alters HPA axis and coping behavior in adulthood

Although not directly evaluated, the early rise of glucocorticoid (GC) levels, as occur after exposure to adverse early life experience, are assumed to affect hippocampal ontogeny by altering the hippocampus negative feedback on adult HPA axis. To test whether hippocampal ontogeny is affected by early exposure to stress we estimated the survival of recently formed hippocampal granule cells in rat pups subjected to periodic maternal separation (180 min/day; MS180) from postnatal days (PND) 1 to 14. Accordingly, MS180 pups injected with bromodeoxyuridine (BrdU, 50 mg/kg, ip) at PND 5 showed decreased density of doublecortin (DCX) positive BrdU-labeled cells at PND 15. MS180 and AFR pups showed similar corticosterone (CORT) basal levels between PND 3 and 12, whereas adult MS180 rats presented with higher CORT levels than AFR adults. Nonetheless, both AFR and MS180 pups and adults showed similar transient increments of CORT levels in response to stress. In addition, MS180 had no effect on the adult anxiety-like behavior evaluated in the elevated plus maze, but evoked a passive coping strategy in the forced swimming test. The data show that the decrease in hippocampal neurogenesis is an early onset phenomenon, and suggests that adverse experiences alter hippocampal ontogeny without chronic elevation of GC levels.

Deprivation of maternal care has long-lasting consequences for the hypothalamic-pituitary-adrenal axis of zebra finches

Early-life stress caused by the deprivation of maternal care has been shown to have long-lasting effects on the hypothalamic-pituitary-adrenal (HPA) axis in offspring of uniparental mammalian species. We asked if deprivation of maternal care in biparental species alters stress responsiveness of offspring, using a biparental avian species--the zebra finch, Taeniopygia guttata. In our experiment, one group of birds was raised by both male and female parents (control), and another was raised by males alone (maternally deprived). During adulthood, offspring of both groups were subjected to two stressors (restraint and isolation), and corticosterone concentrations were measured. Additionally, we measured baseline levels of the two corticosteroid receptors--glucocorticoid receptor (GR) and mineralocorticoid receptor (MR)--in the hippocampus, hypothalamus and cerebellum. Our results suggest that maternally deprived offspring are hyper-responsive to isolation in comparison with controls. Furthermore, mRNA levels of both GR and MR receptors are altered in maternally deprived offspring in comparison with controls. Thus, absence of maternal care has lasting consequences for HPA function in a biparental species where paternal care is available.

Childhood adversity and allostatic overload of the hypothalamic-pituitary-adrenal axis: a vulnerability model for depressive disorders

Childhood adversity is associated with increased risk for onset of depressive episodes. This review will present evidence that allostatic overload of the hypothalamic-pituitary-adrenal axis (HPAA) partially mediates this association. The HPAA is the physiological system that regulates levels of the stress hormone cortisol. First, data from animals and humans has shown that early environmental adversity is associated with long-term dysregulation of the HPAA. This may occur due to permanent epigenetic modification of the glucocorticoid receptor. Second, data from humans has demonstrated that HPAA dysregulation is associated with increased risk of future depression onset in healthy individuals, and pharmacological correction of HPAA dysregulation reduces depressive symptoms. HPAA dysregulation may result in corticoid-mediated abnormalities in neurogenesis in early life and/or neurotoxicity on neural systems that subserve emotion and cognition.

Basal anxiety-like behavior predicts differences in dendritic morphology in the medial prefrontal cortex in two strains of rats

Basal differences in the brain may account for why some individuals are more vulnerable to stress than others. Although trait anxiety behavior varies greatly in human populations, most animal models of anxiety disorders tend to focus on the development of anxiety after a stressful experience. In this study, adult male Sprague-Dawley and Lewis rats were grouped according to baseline anxiety-like behavior in the open field, measured by time spent and distance traveled in the center. Individuals that fell one standard deviation above and below the mean, approximately the top and bottom 15%, were selected for the Low and High Anxiety groups. Pyramidal neurons from layer II/III of the prelimbic region of the medial prefrontal cortex were iontophoretically loaded with Lucifer yellow dye and reconstructed. In both strains, animals in the High Anxiety group had smaller apical dendrites than those in the Low Anxiety group. No difference was found in basal dendrites. Sholl analysis revealed a strain difference in the distribution of dendritic material between anxiety groups. These results illustrate significant variability in dendritic morphology in the prefrontal cortex of healthy adult male rats prior to experimental manipulation that correlates with baseline levels of anxiety-like behavior.

Rodent models of early environment effects on offspring development and susceptibility to neurological diseases in adulthood

Events early in life can program brain for a pattern of neuroendocrine and behavioral responses in later life. This mechanism is named “developmental phenotypic plasticity”. Experimental evidences from rodents show that early experiences influence long-term development of behavioral, neuroendocrine and cognitive functions. While some neonatal conditions lead to positive outcomes, offspring might also display neurological dysfunctions in adulthood in case of adverse conditions during the early development. Different factors have been suggested to mediate the effects of neonatal conditions on offspring development but their exact contribution as well as their interaction still needs to be clarified. Studies based on rodents have been developed to model the long-term effects of early environmental conditions on the developing brain. These studies highlight importance of maternal behavior in mediating the effects of early environmental conditions on the offspring. However, other studies suggest that aside from the level of maternal care, other factors (gender, neonatal glucocorticoid levels) contribute to the adjustment of offspring phenotype to early environmental cues. Altogether, rodents-based evidence suggests that developmental plasticity is a very complex phenomenon mediated by multiple factors that interact one to each other. Ultimately, the goal is to understand how early life events can lead to advantageous phenotype in adult life, or, on the contrary, can predispose individuals to psychopathologies such as depression or anxiety.

Post-weaning to pre-pubertal ('juvenile') stress: a model of induced predisposition to stress-related disorders

Human studies suggest that childhood trauma predisposes individuals to develop stress-related disorders such as depression and post-traumatic stress disorder (PTSD). Recent years have witnessed growing interest in effectively modeling in animals the long-term effects of childhood emotional trauma on stress responses in adulthood. Most studies concerned with the impact of early-life stress on subsequent stress responses in adulthood in rodents have focused on the post-natal pre-weaning period. However, psychiatric studies often refer to human childhood rather than infancy when investigating the patients' traumatic history of stress-related psychopathologies. In accordance with that, we have examined the consequences of stress exposure at a later early-life period, the post-weaning, pre-puberty (juvenile) period, which holds greater resemblance to human childhood. This review summarizes a series of studies examining the impact of exposure of rats to stressors during 'juvenility' ('juvenile stress') on the ability of these animals to cope with stress later in life. Exposure to relatively brief but significant stress experience during juvenility was found to impair the ability of animals to cope with stressful challenges in adulthood. These behavioral manifestations were associated with lasting alterations in limbic system brain regions of neuromodulatory pathways, such as alterations in the expression of cell adhesion molecules, GABAergic system functioning and alterations in levels of circulating corticosterone. Importantly, these studies have also demonstrated considerable individual and sex differences, which call for the development of adequate analysis approaches. The juvenile stress model combined with characterization of individual profiles is presented as a useful model to study in rodents different facets of stress-related disorders and neural mechanisms of vulnerability and resilience to stress.

Gut memories: towards a cognitive neurobiology of irritable bowel syndrome

The brain and the gut are engaged in continual crosstalk along a number of pathways collectively termed the 'brain-gut axis'. Over recent years it has become increasingly clear that dysregulation of the axis at a number of levels can result in disorders such as irritable bowel syndrome (IBS). With recent advances in neuroimaging technologies, insights into the neurobiology of IBS are beginning to emerge. However the cognitive neurobiology of IBS has remained relatively unexplored to date. In this review we summarise the available data on cognitive function in IBS. Moreover, we specifically address three key pathophysiological factors, namely; stress, immune activation and chronic pain, together with other factors involved in the manifestation of IBS, and explore how each of these components may impact centrally, what neurobiological mechanisms might be involved, and consider the implications for cognitive functioning in IBS. We conclude that each factor addressed could significantly impinge on central nervous system function, supporting the view that future research efforts must be directed towards a detailed assessment of cognitive function in IBS.

New frontiers in animal research of psychiatric illness

Alterations in neurodevelopment are thought to modify risk of numerous psychiatric disorders, including schizophrenia, autism, ADHD, mood and anxiety disorders, and substance abuse. However, little is known about the cellular and molecular changes that guide these neurodevelopmental changes and how they contribute to mental illness. In this review, we suggest that elucidating this process in humans requires the use of model organisms. Furthermore, we advocate that such translational work should focus on the role that genes and/or environmental factors play in the development of circuits that regulate specific physiological and behavioral outcomes in adulthood. This emphasis on circuit development, as a fundamental unit for understanding behavior, is distinct from current approaches of modeling psychiatric illnesses in animals in two important ways. First, it proposes to replace the diagnostic and statistical manual of mental disorders (DSM) diagnostic system with measurable endophenotypes as the basis for modeling human psychopathology in animals. We argue that a major difficulty in establishing valid animal models lies in their reliance on the DSM/International Classification of Diseases conceptual framework, and suggest that the Research Domain Criteria project, recently proposed by the NIMH, provides a more suitable system to model human psychopathology in animals. Second, this proposal emphasizes the developmental origin of many (though clearly not all) psychiatric illnesses, an issue that is often glossed over in current animal models of mental illness. We suggest that animal models are essential to elucidate the mechanisms by which neurodevelopmental changes program complex behavior in adulthood. A better understanding of this issue, in animals, is the key for defining human psychopathology, and the development of earlier and more effective interventions for mental illness.

Effects of motherless rearing on basal and stress-induced corticosterone secretion in rat pups

Rearing of rat pups without a mother, artificial rearing (AR), produces substantial changes in the pups' behavior in later life. These changes are similar to those produced by the stress of repeated mother-pup separations. The predominant interpretation is that the long-term effects of disruptions to the mother-pup relationship are mediated by exposure to elevated levels of corticosterone which affect the development of neurobiological systems underlying cognition and behavior. Indeed, repeated separation of pups from the mother sensitizes the pups' corticosterone response to stress. This study examined basal and stress-induced corticosterone release in AR pups. Corticosterone levels were increased immediately following implantation of feeding cannulae. One day after the start of AR, circulating concentrations of corticosterone were not increased unless AR pups were challenged with an additional stressor (injection). Corticosterone levels were lowest when cannulation and AR started on postnatal day (PND) 5 compared with earlier PNDs. On PND 12, there was no evidence of increased corticosterone levels in AR pups at baseline or in response to stress, indicating that AR did not result in persistent sensitization of corticosterone release. The long-term effects of motherless rearing on rat behavior are mediated by mechanisms that are independent of sustained early corticosterone exposure.

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.

Timing is everything: evidence for a role of corticolimbic endocannabinoids in modulating hypothalamic-pituitary-adrenal axis activity across developmental periods

Growing evidence suggests that the endocannabinoid system is vital to ensuring normative maturation of the brain into adulthood. Endocannabinoid signaling contributes to guiding pro-neurogenic processes in early life and the development of neurotransmitter systems. Moreover, there is extensive evidence that recruitment of the endocannabinoid system is crucial in the regulation of neuroendocrine responses to stress via the hypothalamic-pituitary-adrenal (HPA) axis, and contributes to subsequent psychopathological consequences associated with emotionality and anxiety. These stress-induced physiological and behavioural sequelae are regulated by neural structures within the corticolimbic circuit, including the amygdala, hypothalamus, hippocampus, and prefrontal cortex. Based on evidence demonstrating endocannabinoid system involvement in both development and stress-induced changes in HPA axis function, it is reasonable to suggest that endocannabinoid signaling is an important mediator of interactions between stress responsivity and maturational stage. In this review, we discuss the ontogeny of the endocannabinoid system in the central nervous system, clinical and rodent models demonstrating short- and long-term effects of stress exposure, regulation of HPA axis responsivity by endocannabinoid signaling, as well as pharmacological and stress models indicating involvement of the endocannabinoid system in early post-natal and adolescent development on stress reactivity of the HPA, the corticolimbic system, and behaviour.

Living in a dangerous world decreases maternal care: a study in serotonin transporter knockout mice

Adverse early experiences can profoundly influence the adult behavioral profile. When pregnant and lactating mice are confronted with soiled bedding of unfamiliar males (UMB), these stimuli signal the danger of infanticide and thus simulate a "dangerous world". In a previous study, offspring of UMB treated mothers were shown to display increased anxiety-like behavior and reduced exploratory locomotion as adults, compared to mice treated with neutral bedding (NB, "safe environment"). The aim of this study was to elucidate the mechanisms conveying these effects of living in a "dangerous world" to offspring behavior. We hypothesized the mother to be the major link and focused on the influence of UMB on maternal stress hormones and behavior. Thus, we investigated fecal corticosterone metabolites (CM) and maternal care of pregnant and lactating mice either treated with NB or UMB. The offspring were subsequently tested for their anxiety-like and exploratory behavior. Mothers treated with UMB showed a significantly higher increase of fecal CM following the initial treatment, than NB treated mothers, indicating that the odor cues of potentially infanticidal males represented an ethologically relevant stimulus. Whereas the hormonal stress response habituated, living in a "dangerous world" led to a distinct and consistent reduction of maternal care behavior, particularly concerning the duration of licking and grooming the pups. Surprisingly, we could not confirm our former findings of altered phenotypes in the offspring of UMB treated mothers. In summary, we hypothesize that the frequently described effects of early life adversity on the offspring's behavioral profile are mediated primarily by maternal care in altricial rodents.

The impact of stressors on second generation Indian Residential School survivors

From 1863 to 1996, many Aboriginal children in Canada were forced to attend Indian Residential Schools (IRSs), where many experienced neglect, abuse, and the trauma of separation from their families and culture. The present study examined the intergenerational impact of IRS exposure on depressive symptomatology in a convenience sample of 143 First Nations adults. IRS experiences had adverse intergenerational effects in that First Nations adults who had a parent attend IRS (n = 67) reported greater depressive symptoms compared to individuals whose parents did not attend (n = 76). Parental IRS attendance moderated the relations between stressor experiences (adverse childhood experiences, adult traumas, and perceived discrimination) and depressive symptoms, such that second generation Survivors exhibited greater symptomatology. Adverse childhood experiences partially mediated the relation between parental IRS attendance and both adult trauma and perceived discrimination. Moreover, both of these adulthood stressors partially mediated the relation between adverse childhood experiences and depressive symptoms. Finally, all three stressors demonstrated a unique mediating role in the relation between parental IRS attendance and depressive symptoms. Although alternative directional paths could not be ruled out, offspring of IRS Survivors appeared at increased risk for depression, likely owing to greater sensitivity to and experiences of childhood adversity, adult traumas, and perceived discrimination.

The emotional foundations of high moral intelligence

Moral intelligence is grounded in emotion and reason. Neuroscientific and clinical research illustrate how early life co-regulation with caregivers influences emotion, cognition, and moral character. Triune ethics theory (Narvaez, 2008) integrates neuroscientific, evolutionary, and developmental findings to explain differences in moral functioning, identifying security, engagement, and imagination ethics that can be dispositionally fostered by experience during sensitive periods, but also situationally triggered. Mature moral functioning relies on the integration of emotion, intuition, and reasoning, which come together in adaptive ethical expertise. Moral expertise can be cultivated in organizations using the integrative ethical education model.

Mimicking maternal smoking and pharmacotherapy of preterm labor: fetal nicotine exposure enhances the effect of late gestational dexamethasone treatment on noradrenergic circuits

Smoking during pregnancy increases the risk of preterm delivery, which in turn necessitates the common use of glucocorticoids to prevent respiratory distress syndrome. Accordingly, there is a substantial population exposed conjointly to fetal nicotine and glucocorticoids (typically dexamethasone). We administered nicotine to pregnant rats throughout gestation, using a regimen (3 mg/kg/day by osmotic minipump) that maintains plasma nicotine levels within the range seen in smokers; on gestational days 17, 18 and 19, we gave 0.2 mg/kg of dexamethasone. We assessed norepinephrine levels in three brain regions (frontal/parietal cortex, brainstem, cerebellum) throughout adolescence, young adulthood and later adulthood, and contrasted the persistent effects with comparable measures in peripheral tissues (heart, liver). In adolescence, males showed initial deficits in the frontal/parietal cortex with either dexamethasone alone or the combined treatment, with resolution to normal by young adulthood; the group exposed to both nicotine+dexamethasone showed subsequent elevations that emerged in full adulthood and persisted through five months of age, an effect not seen with either agent separately. In females, the combined exposure produced an initial deficit that resolved by young adulthood, without any late-emerging changes. We did not see comparable effects in the other brain regions or peripheral tissues. This indicates that nicotine exposure sensitizes the developing brain to the adverse effects of dexamethasone treatment, producing sex-selective changes in innervation and/or activity of specific noradrenergic circuits. The fact that the combined treatment produced greater effects points to potentially worsened neurobehavioral outcomes after pharmacotherapy of preterm labor in the offspring of smokers.

[The mother-infant encounter at birth must be protected]

The medical decision to separate a newborn baby from his or her mother is frequent. This medical practice must be evaluated. The scientific literature regarding humans and other mammals was reviewed in order to describe the physiology of the interactions between mother and offspring and the consequences of disrupting their interactions around birth. Mother-infant bonding is common to all mammals. Attachment is the result of three mechanisms: behavioral programing, secretion of neuroendocrine substrates, and activation of sensory cues. Breastfeeding is a fourth component that plays a crucial role. Experimental research provides evidence that early-life maternal separation can alter biological responses to stress, disturb learning behaviors, and impair social skills. Recent advances in epigenetic research may partly explain how neonatal maternal deprivation at birth can lead to biological and behavioral disorders in adulthood. Therefore, the decision to separate a newborn infant from his or her mother is not harmless and must be carefully considered. In order to better take into account these data, the organization of perinatal care in France should be revised.

Infantile experience and play motivation

Fully-fledged affective systems in mature animals are in part the result of the impact of infantile experience on brain development. The present experimental series examines whether tactile stimulation in infancy (early handling) influences rough-and-tumble play (R&T) throughout the juvenile period, using a testing regime of 17 days divided into five parts where handled (H) and nonhandled (NH) Wistar rats are assessed daily. In Parts 1 and 2 (age range at the start: 30-33 days) the objective is to study the amount of R&T that the rats are capable of exhibiting under varying lengths of social deprivation. In Part 3 (37-40 days) the objective is to determine whether familiarity with the experimental situation has independent or interactive effects with early handling. In Part 4 (40-43 days) the objective is to obtain evidence of the suppressing effects of an unexpected contextual change. In Part 5 (56-59 days) the objective is to study whether the effects of early handling can still be present at an age when R&T has practically vanished in NH rats. Results show that early handling invigorates R&T affecting pins (i.e., the most rewarding component) at the expense of dorsal contacts by enhancing play motivation in a specific manner, and that it is able to dilate the inverted-U developmental curve of this behavior, thereby providing strong evidence for a direct effect on the neuropsychological systems for play motivation.

Effects of maternal L-tryptophan depletion and corticosterone administration on neurobehavioral adjustments in mouse dams and their adolescent and adult daughters

Major depressive disorder (MDD), a pathology characterized by mood and neurovegetative disturbances, depends on a multi-factorial contribution of individual predisposition (e.g., diminished serotonergic transmission) and environmental factors (e.g., neonatal abuse or neglect). Despite its female-biased prevalence, MDD basic research has mainly focused on male rodents. Most of present models of depression are also devalued due to the fact that they typically address only one of the aforementioned pathogenetic factors. In this paper we first describe the basic principles behind mouse model development and evaluation and then articulate that current models of depression are intrinsically devalued due to poor construct and/or external validity. We then report a first attempt to overcome this limitation through the design of a mouse model in which the genetic and the environmental components of early risk factors for depression are mimicked together. Environmental stress is mimicked through the supplementation of corticosterone in the maternal drinking water while biological predisposition is mimicked through maternal access to an L-tryptophan (the serotonin precursor) deficient diet during the first week of lactation. CD1 dams and their offspring exposed to the L-tryptophan deficient diet (T) and to corticosterone (80mg/l; C) were compared to animal facility reared (AFR) subjects. T and C mice served as intermediate reference groups. Adolescent TC offspring, compared to AFR mice, showed decreased time spent floating in the forced-swim test and increased time spent in the open sectors of an elevated 0-maze. Adult TC offspring showed reduced preference for novelty, decreased breakpoints in the progressive ratio operant procedure and major alterations in central BDNF levels and altered HPA regulation. The route of administration and the possibility to control the independent variables predisposing to depressive-like symptoms disclose novel avenues towards the development of animal models with increased external and construct validity. Furthermore, the observation that, compared to adult subjects, adolescent mice display an opposite profile suggests that peri-pubertal developmental processes may interact with neonatal predispositions to calibrate the adult abnormal phenotype.

Infant maternal separation impairs adult cognitive performance in BALB/cJ mice

RATIONALE

Early life adversity, such as early abuse or parental loss, is thought to increase risk for developing psychiatric disorders in adulthood including mood and anxiety disorders. Human retrospective studies also suggest that early life adversity predicts poor response to antidepressants in adulthood.

OBJECTIVES

We used the infant maternal separation (IMS) paradigm to examine the effects of early adversity on adult emotional behavior, the antidepressant response, and cognitive performance in BALB/cJ mice.

METHODS

Mice were subjected to either standard facility rearing (SFR) or 3 h of daily separation from the dam from postnatal days 2-15. During adulthood, SFR and IMS mice received chronic treatment (∼3 weeks) with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (18 mg/kg/day), and were assessed for anxiety- and depression-related behavior in the light/dark test and forced swim tests (FST), respectively. We then evaluated the effects of IMS on cognition in the fear conditioning, novel object recognition, and T-maze spatial learning and reversal learning tasks.

RESULTS

Chronic fluoxetine treatment produced robust antidepressant effects in both SFR and IMS mice in the FST. IMS did not affect the antidepressant response, or emotional behavior in the light/dark test or FST. However, IMS reduced fear conditioning to the tone and context, disrupted novel object recognition in females, and impaired both spatial and reversal learning in males.

CONCLUSIONS

Our findings suggest that IMS induces deficits in adult emotional, episodic, and spatial memory and reversal learning, but does not alter adult emotional behavior or the response to chronic SSRI treatment in mice.

Animal models of human anxiety disorders: reappraisal from a developmental psychopathology vantage point

We are witnessing a tremendous expansion of strategies and techniques that derive from basic and preclinical science to study the fine genetic, epigenetic, and proteomic regulation of behavior in the laboratory animal. In this endeavor, animal models of psychiatric illness are becoming the almost exclusive domain of basic researchers, with lesser involvement of clinician researchers in their conceptual design, and transfer into practice of new paradigms. From the side of human behavioral research, the growing interest in gene-environment interplay and the fostering of valid endophenotypes are among the few substantial innovations in the effort of linking common mental disorders to cutting-edge clinical research questions. We argue that it is time for cross-fertilization between these camps. In this article, we a) observe that the "translational divide" can-and should-be crossed by having investigators from both the basic and the clinical sides cowork on simpler, valid "endophenotypes" of neurodevelopmental relevance; b) emphasize the importance of unambiguous physiological readouts, more than behavioral equivalents of human symptoms/syndromes, for animal research; c) indicate and discuss how this could be fostered and implemented in a developmental framework of reference for some common anxiety disorders and ultimately lead to better animal models of human mental disorders.

Differences in mouse maternal care behavior - is there a genetic impact of the glucocorticoid receptor?

Depressive episodes are frequently preceded by stressful life events. Evidence from genetic association studies suggests a role for the glucocorticoid receptor (GR), an essential element in the regulation of stress responses, in the pathophysiology of the disorder. Since the stress response system is affected by pregnancy and postpartum-associated changes, it has also been implicated in the pathophysiology of postpartum depression. Using a 2×2 factorial design, we investigated whether a heterozygous deletion of GR would influence maternal care behavior in C57BL/6 and Balb/c mice, two inbred strains known to display qualitative differences in this behavior. Behavioral observation was carried out between postnatal days 1 and 7, followed by a pup retrieval test on postnatal days 7 or 8. While previously noted inter-strain differences were confirmed for different manifestations of caring behavior, self-maintenance and neglecting behaviors as well as the pup retrieval test, no strain-independent effect of the GR mutation was noted. However, an interaction between GR genotype and licking/grooming behavior was observed: it was down-regulated in heterozygous C57BL/6 mice to the level recorded for Balb/c mice. Home cage observation poses minimal disturbance of the dam and her litter as compared to more invasive assessments of dams' emotional behavior. This might be a reason for the absence of any overall effects of the GR mutation, particularly since GR heterozygous animals display a depressive-like phenotype under stressful conditions only. Still, the subtle effect we observed may point towards a role of GR in postpartum affective disorders.

Effects of an early handling-like procedure and individual housing on anxiety-like behavior in adult C57BL/6J and DBA/2J mice

Manipulations of rearing conditions have been used to examine the effects of early experience on adult behavior with varying results. Evidence suggests that postnatal days (PND) 15-21 are a time of particular susceptibility to environmental influences on anxiety-like behavior in mice. To examine this, we subjected C57BL/6J and DBA/2J mice to an early handling-like procedure. Pups were separated from dams from PND 12-20 for 30 minutes daily or received standard care. On PND 21, pups were weaned and either individually- or group-housed. On PND 60, anxiety-like behavior was examined on the elevated zero-maze. Although individually-housed animals took longer to enter an open quadrant of the maze, they spent more time in the open than group-housed animals. Additionally, we observed a trend of reduced anxiety-like behavior in C57BL/6J, but not DBA/2J mice that underwent the handling-like procedure.

Early life experiences affect adult delayed-type hypersensitivity in short and long photoperiods

Environmental experiences during development provide animals with important information about future conditions. Siberian hamsters are photoperiodic rodents that dramatically adjust their physiology and behavior to adapt to seasonal changes. For example, during short winter-like days, hamsters enhance some components of immune function putatively to cope with increasing environmental challenges. Furthermore, early life stress alters the developmental course of the immune system. Overall, immune function is typically suppressed in response to chronic stress, but responses vary depending on the type of stress and components of immune function assessed. This led us to hypothesize that delayed-type hypersensitivity (DTH), an antigen-specific, cell-mediated immune response, would be differentially modulated in hamsters that underwent early life maternal separation (MS) in either short or long photoperiods. At birth, hamsters were assigned to either short (SD; 8 h light/day) or long (LD; 16 h light/day) photoperiods and either daily 3 h MS, daily 15-min brief maternal separation (BMS), or no manipulation from postnatal day 2 through 14. In adulthood DTH was assessed. Hamsters reared in short days enhanced DTH responses. MS and BMS attenuated DTH responses in both short and long days. However, BMS long-day female hamsters did not suppress pinna swelling, suggesting a protective effect of female sex steroids on immune function. As is typical in short days, reproductive tissue was regressed. Reproductive tissue mass was also decreased in long-day MS female hamsters. Furthermore, MS altered photoperiod-induced changes in body mass. Taken together, these findings suggest that manipulations of early life mother-pup interactions in Siberian hamsters result in physiological changes and suppressed cell-mediated immunity.

Fear and exploration in European starlings (Sturnus vulgaris): a comparison of hand-reared and wild-caught birds

The revision of EU legislation will ban the use of wild-caught animals in scientific procedures. This change is partially predicated on the assumption that captive-rearing produces animals with reduced fearfulness. Previously, we have shown that hand-reared starlings (Sturnus vulgaris) indeed exhibit reduced fear of humans compared to wild-caught conspecifics. Here, we asked whether this reduction in fear in hand-reared birds is limited to fear of humans or extends more generally to fear of novel environments and novel objects. Comparing 6-8 month old birds hand-reared in the lab with age-matched birds caught from the wild as fledged juveniles a minimum of 1 month previously, we examined the birds' initial reactions in a novel environment (a small cage) and found that wild-caught starlings were faster to initiate movement compared to the hand-reared birds. We interpret this difference as evidence for greater escape motivation in the wild-caught birds. In contrast, we found no differences between hand-reared and wild-caught birds when tested in novel object tests assumed to measure neophobia and exploratory behaviour. Moreover, we found no correlations between individual bird's responses in the different tests, supporting the idea that these measure different traits (e.g. fear and exploration). In summary, our data show that developmental origin affects one measure of response to novelty in young starlings, indicative of a difference in either fear or coping style in a stressful situation. Our data contribute to a growing literature demonstrating effects of early-life experience on later behaviour in a range of species. However, since we did not find consistent evidence for reduced fearfulness in hand-reared birds, we remain agnostic about the welfare benefits of hand-rearing as a method for sourcing wild birds for behavioural and physiological research.

Resistance to early-life stress in mice: effects of genetic background and stress duration

Early-life stress can induce marked behavioral and physiological impairments in adulthood including cognitive deficits, depression, anxiety, and gastrointestinal dysfunction. Although robust rat models of early-life stress exist there are few established effective paradigms in the mouse. Genetic background and protocol parameters used are two critical variables in such model development. Thus we investigated the impact of two different early-life stress protocols in two commonly used inbred mouse strains. C57BL/6 and innately anxious BALB/c male mice were maternally deprived 3 h daily, either from postnatal day 1 to 14 (protocol 1) or 6 to 10 (protocol 2). Animals were assessed in adulthood for cognitive performance (spontaneous alternation behavior test), anxiety [open-field, light/dark box (L/DB), and elevated plus maze (EPM) tests], and depression-related behaviors (forced swim test) in addition to stress-sensitive physiological changes. Overall, the results showed that early-life stressed mice from both strains displayed good cognitive ability and no elevations in anxiety. However, paradoxical changes occurred in C57BL/6 mice as the longer protocol (protocol 1) decreased anxiety in the L/DB and increased exploration in the EPM. In BALB/c mice there were also limited effects of maternal separation with both separation protocols inducing reductions in stress-induced defecation and protocol 1 reducing the colon length. These data suggest that, independent of stress duration, mice from both strains were on the whole resilient to the maladaptive effects of early-life stress. Thus maternal separation models of brain–gut axis dysfunction should rely on either different stressor protocols or other strains of mice.

Hidden Markov model analysis of maternal behavior patterns in inbred and reciprocal hybrid mice

Individual variation in maternal care in mammals shows a significant heritable component, with the maternal behavior of daughters resembling that of their mothers. In laboratory mice, genetically distinct inbred strains show stable differences in maternal care during the first postnatal week. Moreover, cross fostering and reciprocal breeding studies demonstrate that differences in maternal care between inbred strains persist in the absence of genetic differences, demonstrating a non-genetic or epigenetic contribution to maternal behavior. In this study we applied a mathematical tool, called hidden Markov model (HMM), to analyze the behavior of female mice in the presence of their young. The frequency of several maternal behaviors in mice has been previously described, including nursing/grooming pups and tending to the nest. However, the ordering, clustering, and transitions between these behaviors have not been systematically described and thus a global description of maternal behavior is lacking. Here we used HMM to describe maternal behavior patterns in two genetically distinct mouse strains, C57BL/6 and BALB/c, and their genetically identical reciprocal hybrid female offspring. HMM analysis is a powerful tool to identify patterns of events that cluster in time and to determine transitions between these clusters, or hidden states. For the HMM analysis we defined seven states: arched-backed nursing, blanket nursing, licking/grooming pups, grooming, activity, eating, and sleeping. By quantifying the frequency, duration, composition, and transition probabilities of these states we were able to describe the pattern of maternal behavior in mouse and identify aspects of these patterns that are under genetic and nongenetic inheritance. Differences in these patterns observed in the experimental groups (inbred and hybrid females) were detected only after the application of HMM analysis whereas classical statistical methods and analyses were not able to highlight them.

Role of maternal 5-HT(1A) receptor in programming offspring emotional and physical development

Serotonin(1A) receptor (5-HT(1A)R) deficiency has been associated with anxiety and depression and mice with genetic receptor inactivation exhibit heightened anxiety. We have reported that 5-HT(1A)R is not only a genetic but also a maternal 'environmental' factor in the development of anxiety in Swiss-Webster mice. Here, we tested whether the emergence of maternal genotype-dependent adult anxiety is preceded by early behavioral abnormalities or whether it is manifested following a normal emotional development. Pups born to null or heterozygote mothers had significantly reduced ultrasonic vocalization (USV) between postnatal day (P) 4 and 12, indicating an influence of the maternal genotype. The offspring's own genotype had an effect limited to P4. Furthermore, we observed reduced weight gain in the null offspring of null but not heterozygote mothers, indicating that a complete maternal receptor deficiency compromises physical development of the offspring. Except a short perinatal deficit during the dark period, heterozygote females displayed normal maternal behavior, which, with the early appearance of USV deficit, suggests a role for 5-HT(1A)R during pre-/perinatal development. Consistent with this notion, adult anxiety in the offspring is determined during the pre-/perinatal period. In contrast to heterozygote females, null mothers exhibited impaired pup retrieval and nest building that may explain the reduced weight gain of their offspring. Taken together, our data indicate an important role for the maternal 5-HT(1A)R in regulating emotional and physical development of their offspring. Because reduced receptor binding has been reported in depression, including postpartum depression, reduced 5-HT(1A)R function in mothers may influence the emotional development of their offspring.

Hand-rearing reduces fear of humans in European starlings, Sturnus vulgaris

Pending changes in European legislation ban the use of wild-caught animals in research. This change is partly justified on the assumption that captive-breeding (or hand-rearing) increases welfare of captive animals because these practices result in animals with reduced fear of humans. However, there are few actual data on the long-term behavioural effects of captive-breeding in non-domestic species, and these are urgently needed in order to understand the welfare and scientific consequences of adopting this practice. We compared the response of hand-reared and wild-caught starlings to the presence of a human in the laboratory. During human presence, all birds increased their general locomotor activity but the wild-caught birds moved away from the human and were less active than the hand-reared birds. After the human departed, the wild-caught birds were slower to decrease their activity back towards baseline levels, and showed a dramatic increase in time at the periphery of the cage compared with the hand-reared birds. We interpret these data as showing evidence of a greater fear response in wild-caught birds with initial withdrawal followed by a subsequent rebound of prolonged attempts to escape the cage. We found no effects of environmental enrichment. However, birds in cages on low shelves were less active than birds on upper shelves, and showed a greater increase in the time spent at the periphery of their cages after the human departed, perhaps indicating that the lower cages were more stressful. In demonstrating reduced fear of humans in hand-reared birds, our results support one of the proposed welfare benefits of this practice, but without further data on the possible welfare costs of hand-rearing, it is not yet possible to reach a general conclusion about its net welfare impact. However, our results confirm a clear scientific impact of both hand-rearing and cage position at the behavioural level.

Epidemiology of stress and asthma: from constricting communities and fragile families to epigenetics

Several epidemiologic frameworks, exemplified through extant research examples, provide insight into the role of stress in the expression of asthma and other allergic disorders. Biologic, psychological, and social processes interact throughout the life course to influence disease expression. Studies exploiting a child development framework focus on critical periods of exposure, including the in utero environment, to examine the influence of stress on disease onset. Early stress effects that alter the normal course of morphogenesis and maturation that affect both structure and function of key organ systems (eg, immune, respiratory) may persist into adult life underscoring the importance of a life course perspective. Other evidence suggests that maternal stress influences programming of integrated physiologic systems in their offspring (eg, neuroendocrine, autonomic, immune function) starting in pregnancy; consequently stress effects may be transgenerational. A multilevel approach that includes an ecological perspective may help to explain heterogeneities in asthma expression across socioeconomic and geographic boundaries that to date remain largely unexplained. Evolving studies incorporating psychological, behavioral, and physiologic correlates of stress more specifically inform underlying mechanisms operating in these critical periods of development. The role of genetics, gene by environment interactions, and epigenetic mechanisms of gene expression have been sparsely examined in epidemiologic studies on stress and asthma although overlapping evidence provides proof of concept for such studies in the future.

Development of fearfulness in birds: genetic factors modulate non-genetic maternal influences

The development of fearfulness and the capacity of animals to cope with stressful events are particularly sensitive to early experience with mothers in a wide range of species. However, intrinsic characteristics of young animals can modulate maternal influence. This study evaluated the effect of intrinsic fearfulness on non-genetic maternal influence. Quail chicks, divergently selected for either higher (LTI) or lower fearfulness (STI) and from a control line (C), were cross-fostered by LTI or STI mothers. Behavioural tests estimated the chicks' emotional profiles after separation from the mother. Whatever their genotype, the fearfulness of chicks adopted by LTI mothers was higher than that of chicks adopted by STI mothers. However, genetic background affected the strength of maternal effects: the least emotional chicks (STI) were the least affected by early experience with mothers. We demonstrated that young animal's intrinsic fearfulness affects strongly their sensitivity to non-genetic maternal influences. A young animal's behavioural characteristics play a fundamental role in its own behavioural development processes.

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.

When the serotonin transporter gene meets adversity: the contribution of animal models to understanding epigenetic mechanisms in affective disorders and resilience

Although converging epidemiological evidence links exposure to stressful life events with increased risk for affective spectrum disorders, there is extraordinary interindividual variability in vulnerability to adversity. The environmentally moderated penetrance of genetic variation is thought to play a major role in determining who will either develop disease or remain resilient. Research on genetic factors in the aetiology of disorders of emotion regulation has, nevertheless, been complicated by a mysterious discrepancy between high heritability estimates and a scarcity of replicable gene-disorder associations. One explanation for this incongruity is that at least some specific gene effects are conditional on environmental cues, i.e. gene-by-environment interaction (G × E) is present. For example, a remarkable number of studies reported an association of variation in the human serotonin (5-HT) transporter gene (SLC6A4, 5-HTT, SERT) with emotional and cognitive traits as well as increased risk for depression in interaction with psychosocial adversity. The results from investigations in non-human primate and mouse support the occurrence of G × E interaction by showing that variation of 5-HTT function is associated with a vulnerability to adversity across the lifespan leading to unfavourable outcomes resembling various neuropsychiatric disorders. The neural and molecular mechanisms by which environmental adversity in early life increases disease risk in adulthood are not known but may include epigenetic programming of gene expression during development. Epigenetic mechanisms, such as DNA methylation and chromatin modification, are dynamic and reversible and may also provide targets for intervention strategies (see Bountra et al., Curr Top Behav Neurosci, 2011). Animal models amenable to genetic manipulation are useful in the identification of molecular mechanisms underlying epigenetic programming by adverse environments and individual differences in resilience to stress. Therefore, deeper insight into the role of epigenetic regulation in the process of neurodevelopmental programmes is likely to result in early diagnosis of affective spectrum disorders and will contribute to the design of innovative treatments targeting neural pathways that foster resilience.

Variations in Maternal Behavior in C57BL/6J Mice: Behavioral Comparisons between Adult Offspring of High and Low Pup-Licking Mothers

The amount of maternal licking received by newborn rats affects their adult stress reactivity and maternal behavior. Mouse studies in which litters were cross-fostered between strains that exhibit high vs. low amounts of maternal behavior also suggest that rearing conditions affect adult outcomes. The current study is the first to compare within a single mouse strain (C57BL/6J) behavioral responses between adult animals reared by mothers that exhibited frequencies of pup-licking (PL) at the high end and the low end of the normal distribution within the strain. Maternal behaviors were coded during 10-s intervals every 3 min during five 1-h periods (two light, three dark cycle) on postpartum days 2, 4, 6, and 8 in 36 unrelated C57BL/6J mothers. The distribution of mean frequencies/h for PL, still crouched nursing, hovering over pups, self-grooming, and no contact with pups were determined. Offspring (6-12 weeks of age) from the eight mothers who exhibited the highest mean frequencies of PL and the seven mothers who exhibited the lowest PL frequencies underwent the following tests over three consecutive weeks: (1) elevated plus-maze (EPM) and 1-h open field on three successive days, (2) 3-h open field with an acute stressor (IP saline injection) at the 1-h time point, and (3) acoustic startle and prepulse inhibition. Females reared by low PL mothers exhibited significantly more time in the closed arms of the EPM, less locomotion, center time, and rearing during the first test in the open field, greater reactivity to an acute stressor, and reduced prepulse inhibition, an index of sensorimotor gating. Male offspring from low PL dams had reduced reactivity to an acute stressor, but no other altered performance in the behavioral tests. PL frequencies of C57BL/6J mothers appear to selectively alter behavior outcomes, primarily in female offspring.

Functional genomic and proteomic analysis reveals disruption of myelin-related genes and translation in a mouse model of early life neglect

Early life neglect is an important public health problem which can lead to lasting psychological dysfunction. Good animal models are necessary to understand the mechanisms responsible for the behavioral and anatomical pathology that results. We recently described a novel model of early life neglect, maternal separation with early weaning (MSEW), that produces behavioral changes in the mouse that persist into adulthood. To begin to understand the mechanism by which MSEW leads to these changes we applied cDNA microarray, next-generation RNA-sequencing (RNA-seq), label-free proteomics, multiple reaction monitoring (MRM) proteomics, and methylation analysis to tissue samples obtained from medial prefrontal cortex to determine the molecular changes induced by MSEW that persist into adulthood. The results show that MSEW leads to dysregulation of markers of mature oligodendrocytes and genes involved in protein translation and other categories, an apparent downward biasing of translation, and methylation changes in the promoter regions of selected dysregulated genes. These findings are likely to prove useful in understanding the mechanism by which early life neglect affects brain structure, cognition, and behavior.

Using animal models to disentangle the role of genetic, epigenetic, and environmental influences on behavioral outcomes associated with maternal anxiety and depression

The etiology of complex psychiatric disorders results from both genetics and the environment. No definitive environmental factor has been implicated, but studies suggest that deficits in maternal care and bonding may be an important contributing factor in the development of anxiety and depression. Perinatal mood disorders such as postpartum depression occur in approximately 10% of pregnant women and can result in detriments in infant care and bonding. The consequences of impaired maternal-infant attachment during critical early brain development may lead to adverse effects on socioemotional and neurocognitive development in infants resulting in long-term behavioral and emotional problems, including increased vulnerability for mental illness. The exact mechanisms by which environmental stressors such as poor maternal care increase the risk for psychiatric disorders are not known and studies in humans have proven challenging. Two inbred mouse strains may prove useful for studying the interaction between maternal care and mood disorders. BALB/c (BALB) mice are considered an anxious strain in comparison to C57BL/6 (B6) mice in behavioral models of anxiety. These strain differences are most often attributed to genetics but may also be due to environment and gene by environment interactions. For example, BALB mice are described as poor mothers and B6 mice as good mothers and mothering behavior in rodents has been reported to affect both anxiety and stress behaviors in offspring. Changes in gene methylation patterns in response to maternal care have also been reported, providing evidence for epigenetic mechanisms. Characterization of these two mouse inbred strains over the course of pregnancy and in the postpartum period for behavioral and neuroendocrine changes may provide useful information by which to inform human studies, leading to advances in our understanding of the etiology of anxiety and depression and the role of genetics and the environment.

Development of individual differences in stress responsiveness: an overview of factors mediating the outcome of early life experiences

RATIONALE

Human epidemiology and animal studies have convincingly shown the long-lasting impact of early life experiences on the development of individual differences in stress responsiveness in later life. The interplay between genes and environment underlies this phenomenon.

OBJECTIVES

We provide an overview of studies investigating the impact of early life experiences on the development of individual differences in neuroendocrine stress responsiveness in adulthood and address (1) impact of environment on later stress phenotypes, (2) role of genetic factors in modulating the outcome of environment, and (3) role of nonshared environmental experience in the outcome of gene × environment interplays. We present original findings where we investigated the influence of nonshared experiences in terms of individual differences in maternal care received, on the development of stress phenotype in later life in rats.

RESULTS

Environmental influences in early life exert powerful effects on later stress phenotypes, but they do not always lead to expression of diseases. Heterogeneity in response is explained by the role of particular genetic factors in modulating the influence of environment. Nonshared experiences are important in the outcome of gene × environment interplays in humans. We show that nonshared experiences acquired through within-litter variation in maternal care in rats predict the stress phenotype of the offspring.

CONCLUSION

The outcome of early experience is not deterministic and depends on several environmental and genetic factors interacting in an intricate manner to support stress adaptation. The degree of "match" and "mismatch" between early and later life environments predicts resilience and vulnerability to stress-related diseases, respectively.

Consequences of serotonin transporter genotype and early adversity on behavioral profile - pathology or adaptation?

This review focuses on how behavioral profile is shaped by early adversity in individuals with varying serotonin transporter (5-HTT) genotype. In a recent study on 5-HTT knockout mice Heiming et al. (2009) simulated a 'dangerous environment' by confronting pregnant and lactating females with odor cues of unfamiliar males, indicating the risk of infant killing. Growing up in a dangerous environment induced increased anxiety-related behavior and decreased exploratory locomotion in the offspring, the effects being most pronounced in mice lacking 5-HTT expression. We argue that these alterations in behavioral profile represent adaptive maternal effects that help the individuals to cope with adversity. In principle, such effects of adversity on behavioral profile should not automatically be regarded as pathological. Rather and in accordance with modern evolutionary theory they may represent adaptations, although individuals with 5-HTT genotype induced susceptibility to adversity may be at risk of developing pathologies.

Effects of developmental stress and lead (Pb) on corticosterone after chronic and acute stress, brain monoamines, and blood Pb levels in rats

Despite restrictions, exposure to lead (Pb) continues. Moreover, exposure varies and is often higher in lower socioeconomic status (SES) families and remains a significant risk to cognitive development. Stress is another risk factor. Lower SES may be a proxy for stress in humans. When stress and Pb co-occur, risk may be increased. A few previous experiments have combined Pb with intermittent or acute stress but not with chronic stress. To determine if chronic developmental stress affects outcome in combination with Pb, we tested such effects on growth, organ weight, brain monoamines, and response to an acute stressor. Sprague Dawley rats were gavaged with Pb acetate (1 or 10 mg/kg) or vehicle every other day from postnatal day (P)4-29 and reared in standard or barren cages. Subsets were analyzed at different ages (P11, 19, 29). Chronic stress did not alter blood Pb levels but altered HPA axis response during early development whereas Pb did not. Pb treatment and rearing each altered organ-to-body weight ratios, most notably of thymus weights. Both Pb and rearing resulted in age- and region-dependent changes in serotonin and norepinephrine levels and in dopamine and serotonin turnover. The model introduced here may be useful for investigating the interaction of Pb and chronic developmental stress.

Research review: the neurobiology and genetics of maltreatment and adversity

The neurobiological mechanisms by which childhood maltreatment heightens vulnerability to psychopathology remain poorly understood. It is likely that a complex interaction between environmental experiences (including poor caregiving) and an individual's genetic make-up influence neurobiological development across infancy and childhood, which in turn sets the stage for a child's psychological and emotional development. This review provides a concise synopsis of those studies investigating the neurobiological and genetic factors associated with childhood maltreatment and adversity. We first provide an overview of the neuroendocrine findings, drawing from animal and human studies. These studies indicate an association between early adversity and atypical development of the hypothalamic-pituitary-adrenal (HPA) axis stress response, which can predispose to psychiatric vulnerability in adulthood. We then review the neuroimaging findings of structural and functional brain differences in children and adults who have experienced childhood maltreatment. These studies offer evidence of several structural differences associated with early stress, most notably in the corpus callosum in children and the hippocampus in adults; functional studies have reported atypical activation of several brain regions, including decreased activity of the prefrontal cortex. Next we consider studies that suggest that the effect of environmental adversity may be conditional on an individual's genotype. We also briefly consider the possible role that epigenetic mechanisms might play in mediating the impact of early adversity. Finally we consider several ways in which the neurobiological and genetic research may be relevant to clinical practice and intervention.

Comparative analysis of maternal care in the high-yawning (HY) and low-yawning (LY) sublines from Sprague-Dawley rats

High- and low-yawning rats (HY and LY) were selectively bred as a function of their spontaneous yawning frequency with the LY subline about 2 yawns/hr and the HY 20 yawns/hr. The HY rats have more grooming bouts and travel longer distances in an open field. HY dams spent less time in the nest, retrieved their pups faster, and show a longer latency to licking and mouthing the pups than the LY or outbred Sprague-Dawley (SD) animals. The percentage of HY dams that had atypical retrieving was higher, with a lower nest quality, and produced offspring whose weights were lower than those from the LY subline. We also showed that the pregnant HY dams have fewer pups and the percentage that had lost at least three pups during lactation was higher than the SD and LY dams. In conclusion, HY dams are motivated to take care of their pups, but the "fine tuning" of maternal care is disturbed.

Maternal separation with early weaning: a novel mouse model of early life neglect

Background

Childhood adversity is associated with increased risk for mood, anxiety, impulse control, and substance disorders. Although genetic and environmental factors contribute to the development of such disorders, the neurobiological mechanisms involved are poorly understood. A reliable mouse model of early life adversity leading to lasting behavioral changes would facilitate progress in elucidating the molecular mechanisms underlying these adverse effects. Maternal separation is a commonly used model of early life neglect, but has led to inconsistent results in the mouse.

Results

In an effort to develop a mouse model of early life neglect with long-lasting behavioral effects in C57BL/6 mice, we designed a new maternal separation paradigm that we call Maternal Separation with Early Weaning (MSEW). We tested the effects of MSEW on C57BL/6 mice as well as the genetically distinct DBA/2 strain and found significant MSEW effects on several behavioral tasks (i.e., the open field, elevated plus maze, and forced swim test) when assessed more than two months following the MSEW procedure. Our findings are consistent with MSEW causing effects within multiple behavioral domains in both strains, and suggest increased anxiety, hyperactivity, and behavioral despair in the MSEW offspring. Analysis of pup weights and metabolic parameters showed no evidence for malnutrition in the MSEW pups. Additionally, strain differences in many of the behavioral tests suggest a role for genetic factors in the response to early life neglect.

Conclusions

These results suggest that MSEW may serve as a useful model to examine the complex behavioral abnormalities often apparent in individuals with histories of early life neglect, and may lead to greater understanding of these later life outcomes and offer insight into novel therapeutic strategies.

A prospective population-based study of triggers of symptomatic flares in IBD

OBJECTIVES

We aimed to determine whether any of the nonsteroidal anti-inflammatory drugs (NSAIDs), antibiotics, infections, and stress trigger symptomatic flares of inflammatory bowel diseases (IBDs).

METHODS

Participants drawn from a population-based IBD research registry were surveyed every 3 months for 1 year. They simultaneously tracked the use of NSAIDs, antibiotics, infections, major life events, mood, and perceived stress. Social networks, childhood socioeconomic status, and smoking were assessed at baseline. Disease flare was identified using the Manitoba Inflammatory Bowel Disease Index, a validated disease activity index. Across any two consecutive survey periods, participants were categorized as having a flare (inactive/active), having no flare (inactive/inactive), or remaining active (active/active). Potential triggers were evaluated for the first 3-month period to determine predictive rather than concurrent relationships. Data from only one pair of 3-month periods from an individual were analyzed.

RESULTS

A total of 704 participants completed the baseline survey; 552 (78.3%) returned all 5 surveys. In all, 174 participants who had a flare were compared with 209 who had no flare. Perceived stress, negative affect (mood), and major life events were the only trigger variables significantly associated with flares. There were no differences between those who flared and those who did not, in the use of NSAIDs, antibiotics, or in the presence of infections. Multivariate logistic regression analyses indicated that only high-perceived stress (adjusted odds ratio=2.40 (1.35, 4.26)) was associated with an increased risk of flare.

CONCLUSIONS

This study adds to the growing evidence that psychological factors contribute to IBD symptom flares. There was no support for differential rates of use of NSAIDS, antibiotics, or for the occurrence of (non-enteric) infections related to IBD flares.