The programming of individual differences in defensive responses and reproductive strategies in the rat through variations in maternal care

Family environments, adrenarche, and sexual maturation: a longitudinal test of a life history model

Life history theorists have proposed that humans have evolved to be sensitive to specific features of early childhood environments and that exposure to different environments biases children toward development of different reproductive strategies, including differential pubertal timing. The current research provides a longitudinal test of this theory. Assessments of family environments, based on interviews with mothers and fathers, were conducted in preschool, and children were then followed prospectively through middle childhood. Adrenal hormones were assayed in a selected subsample of 120 children (73 girls) at age 7, and parent and child reports of secondary sexual characteristics were collected in the full female sample of 180 girls at age 11. Higher quality parental investment (from both mothers and fathers) and less father-reported Marital Conflict/Depression forecast later adrenarche. Older age at menarche in mothers, higher socioeconomic status, greater mother-based Parental Supportiveness, and lower third-grade body mass index each uniquely and significantly predicted later sexual development in daughters. Consistent with a life history perspective, quality of parental investment emerged as a central feature of the proximal family environment in relation to pubertal timing.

Motherhood induces and maintains behavioral and neural plasticity across the lifespan in the rat

Maternal behavior is multidimensional, encompassing many facets beyond the direct care of the young. Formerly unfamiliar activities are required of the mother. These include behaviors such as retrieving, grouping, crouching-over, and licking young, and protecting them against predators, together with enhancements in other behaviors, such as nest building, foraging, and aggression (inter/intra-species, predatory, etc.). When caring for young, the mother must strike a seemingly lose-lose bargain: leave the relative safety of the nest and her helpless offspring to forage for food and resources where predators await both mother and her vulnerable young, or remain entrenched and safe, thereby ensuring a slow and inexorable fate. Two predictions thus arise from this maternal cost-benefit ratio: first, there may be enhancements in behaviors on which the female relies, for example, predation and spatial ability, used for acquiring food and resources and for navigating her environment. Second, there may be reductions in the fear and anxiety inherent to the decision to leave the nest and to forage in an unforgiving environment where encounters with predators or reluctant/resistant prey await. There is overwhelming support for both hypotheses, with improvements in learning and memory accompanied by a diminution in stress responses and anxiety. The current review will examine the background for the phenomenon that is the maternal brain, and recent relevant data. In sum, the data indicate a remarkable set of changes that take place in the maternal (and, to a lesser extent, the paternal), brain, arguably, for the natural, simple but singular experience of reproduction.

Gene-environment interaction affects substance P and neurokinin A in the entorhinal cortex and periaqueductal grey in a genetic animal model of depression: implications for the pathophysiology of depression

Evidence implies a role for corticotropin-releasing hormone (CRH) and tachykinins, e.g. substance P (SP) and neurokinin A (NKA) in the pathophysiology of depression. We have previously shown that SP- and NKA-like immunoreactivity (-LI) concentrations were altered in the frontal cortex and striatum of the congenitally 'depressed' Flinders Sensitive Line (FSL) compared to the Flinders Resistant Line (FRL) control rats. It is also known that environmental stress may affect brain levels of tachykinins. In view of these results we decided to superimpose maternal deprivation, an early life environmental stressor, onto the genetically predisposed 'depressed' FSL rats and the FRL control rats and use this paradigm as a model of gene-environment interaction. The adult animals were sacrificed, adrenal glands and brains dissected out and SP-, NKA- and CRH-LI levels were determined in ten discrete brain regions. Maternal deprivation led to a marked increase in SP-LI and NKA-LI levels in the periaqueductal grey (PAG) and entorhinal cortex of the 'depressed' FSL strain while it had no significant effect in the FRL controls. Furthermore, specific strain differences in peptide-LI content were confirmed. No difference was found in relative adrenal gland weight, which is consistent with the finding that CRH-LI levels in the hypothalamus were similar across strains, and insensitive to stress in either strain. Taken together, these data are in line with behavioural experiments showing ameliorating effects of NK1 and NK2 receptor antagonists against anxiety and depression-like symptoms in rodents, and therefore further implicate the tachykinin systems in the pathophysiology of depression and adult life psychopathology.

Sex Differences in Heritability of Ischemic Stroke

Background and Purpose— Using data from Oxfordshire, UK, we recently showed that women are more likely than men to have a family history of stroke in female versus male first degree relatives. To test the generalizability of this finding, we did a comprehensive systematic review of all available published and unpublished data.

Methods— Studies were included in the present review if they reported the frequency of family history of stroke in relation to sex of parent or proband. Where necessary, we contacted authors of studies to obtain unpublished data. Data from the Oxford Vascular Study (OXVASC) and 3 other Oxford cohorts (1925 patients) were secondarily pooled with the data from other studies.

Results— We obtained data from 18 studies (7941 patients), including unpublished data from 7 studies. Female probands were slightly more likely to have a parental history of stroke than male probands (pooled OR=1.15; 95% CI: 1.03 to 1.29; P (sig) =0.028; P (het) =0.45). Maternal history of stroke was more common than paternal history (pooled OR=1.25; 1.15 to 1.37; P (sig) <0.00001; P (het) =0.12). However, the maternal excess was only present in female probands (pooled OR=1.47; 1.27 to 1.70; P (sig) <0.00001; P (het) =0.11). In contrast, male probands were no more likely to have maternal than paternal history of stroke (pooled OR=1.02; 0.88 to 1.17, P (sig) =0.43; P (het) =0.09).

Conclusions— Women with stroke are more likely than men to have a parental history of stroke, which is accounted for by an excess maternal history of stroke. This finding could be explained by sex-specific genetic, epigenetic, or nongenetic mechanisms.

Family rearing antecedents of pubertal timing

Two general evolutionary hypotheses were tested on 756 White children (397 girls) studied longitudinally: (1) rearing experiences would predict pubertal timing; and (2) children would prove differentially susceptible to rearing. Analysis of pubertal measurements, including some based on repeated physical assessments, showed that mothering and fathering, earlier and later in childhood, predicted pubertal development, but only for girls, with negative parenting appearing most influential; maternal harsh control predicted earlier menarche. Rearing effects varied by infant negative emotionality, proving stronger (and opposite) for girls who in infancy were lower rather than higher in negativity. Maternal menarche, controlled in all analyses, was a stronger predictor than rearing. Findings are discussed in terms of theory development, genetic and nutritional influences, and sample restrictions.

Exploring interactive effects of genes and environments in etiology of individual differences in reading comprehension

It is established that reading and reading-related processes are heritable; genes thus play an important role in the foundation of individual differences in reading. In this article, we focus on one facet of reading–comprehension. Comprehension is a higher order cognitive skill that requires many other cognitive processes for it to unfold completely and successfully. One such process is executive functioning, which has been associated with genetic variation in the catechol-O-methyltransferase (COMT) gene. Genotypes and haplotypes of four single nucleotide polymorphisms in COMT were investigated in 179 incarcerated adolescent delinquents. Four hierarchical logistic regression models predicting the presence/absence of comprehension difficulties were fitted to the data; genetic variation in COMT and the presence/absence of maternal rejection were investigated as main effects and as effects acting interactively. Three out of four interaction terms were found to be important predictors of individual differences in comprehension. These findings were supported by the results of the haplotype analyses, in which the four investigated polymorphisms were considered simultaneously.

Moderate neonatal stress decreases within-group variation in behavioral, immune and HPA responses in adult mice

BACKGROUND

The significance of behavioral neuroscience and the validity of its animal models of human pathology largely depend on the possibility to replicate a given finding across different laboratories. Under the present test and housing conditions, this axiom fails to resist the challenge of experimental validation. When several mouse strains are tested on highly standardized behavioral test batteries in different laboratories, significant strain x lab interactions are often detected. This limitation, predominantly due to elevated within-group variability observed in control subjects, increases the number of animals needed to address fine experimental questions. Laboratory rodents display abnormal stress and fear reactions to experimental testing, which might depend on the discrepancy between the stability of the neonatal environment and the challenging nature of the adult test and housing conditions.

METHODOLOGY/PRINCIPAL FINDINGS

Stimulating neonatal environments (e.g. brief maternal separations, increased foraging demands or maternal corticosterone supplementation) reduce stress and fear responses in adulthood. Here we tested whether reduced fearfulness associated with experimental testing would also reduce inter-individual variation. In line with our predictions, we show that a moderate elevation in neonatal corticosterone through maternal milk significantly reduces fear responses and inter-individual variability (average 44%) in adult mouse offspring.

CONCLUSIONS/SIGNIFICANCE

We observed reduced variation in pain perception, novelty preference, hormonal stress response and resistance to pathogen infection. This suggests that the results of this study may apply to a relatively broad spectrum of neuro-behavioral domains. Present findings encourage a reconsideration of the basic principles of neonatal housing systems to improve the validity of experimental models and reduce the number of animals used.

Effects of maternal care on the development, emotionality, and reproductive functions in male and female rats

Variations in maternal behavior induce long-lasting effects on behavioral and neuroendocrine responses to stress. The aim of this study was to analyze developmental parameters, reproductive function, and anxiety-related behaviors of male and female rats raised by mothers that naturally display high and low levels of maternal licking behavior. Results showed that an increase in licking behavior received by the pups accelerated their eye opening and reduced fear behavior assessed in the open field test. Additionally, female offspring of high licking (HL) mothers showed decreased ovulation and lordosis intensity. In contrast, males from HL and low licking (LL) mothers did not differ in their reproductive function, suggesting a gender difference in maternal effects. Present results showed that individual differences in maternal behavior appear not only to be predictive of later emotionality and stress-responsivity in the offspring, but can also modulate the reproductive function of females. Maternal genetic factors, differences in the prenatal intrauterine milieu, or a combination of these cannot be excluded to explain the effects observed.

Regulation of anxiety during the postpartum period

Healthy mother-infant interactions are critical for the physical, cognitive, and psychological development of offspring. Such interactions rely on numerous factors, including a positive maternal emotional state. However, many postpartum women experience emotional dysregulation, often involving elevated anxiety. Neuroendocrine factors contributing to the onset of postpartum anxiety symptoms are mostly unknown, but irregularities in hypothalamic-pituitary-adrenal axis function, reduced prolactin and oxytocin signaling, or parturitional withdrawal of ovarian, placental and neural steroids could contribute to anxiety in susceptible women. Although the causes of initial onset are unclear, postpartum anxiety can be mitigated by recent contact with infants. Numerous neurochemical systems, including oxytocin, prolactin, GABA, and norepinephrine mediate this anxiolytic effect of infant contact. Insight into the etiology of postpartum anxiety disorders, and how contact with infants helps counter existing anxiety dysregulation, will surely facilitate the diagnosis and treatment of postpartum women at risk for, or experiencing, an anxiety disorder.

Plastic changes induced by neonatal handling in the hypothalamus of female rats

Early-life events can exert profound long-lasting effects on several behaviors such as fear/anxiety, sexual activity, stress responses and reproductive functions. Present study aimed to examine the effects of neonatal handling on the volume and number of cells in the hypothalamic paraventricular nucleus (pPVN, parvocellular and mPVN, magnocellular regions) and the supraoptic nucleus (SON) in female rats at 11 and 90 days of age. Moreover, in the same areas, immunohistochemistry for oxytocin (OT) and glial fibrillary acidic protein (GFAP) were analyzed in the adult animals. Daily handling during the first 10 postnatal days reduced the number of cells in the pPVN and SON at both the 11 and 90 days. Handling decreased the number of OT-positive parvocellular cells in the PVN in adult females. No significant differences were detected on the optical density (OD) of GFAP-positive cells between the handled and nonhandled adult females. The effect of handling on cell loss was observed 24 h after the 10-day handling period and persisted into adulthood, indicating a stable morphological trace. Results suggest that neonatal handling can induce plastic changes in the central nervous system.

Mechanisms of Disease: glucocorticoids, their placental metabolism and fetal 'programming' of adult pathophysiology

Epidemiological evidence suggests that an adverse prenatal environment permanently 'programs' physiology and increases the risk of cardiovascular, metabolic, neuroendocrine and psychiatric disorders in adulthood. Prenatal stress or exposure to excess glucocorticoids might provide the link between fetal maturation and adult pathophysiology. In a variety of animal models, prenatal stress, glucocorticoid exposure and inhibition (or knockout of) 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2)--the fetoplacental barrier to maternal glucocorticoids--reduce birth weight and cause increases in adult blood pressure, glucose levels, hypothalamic-pituitary-adrenal (HPA) axis activity and anxiety-related behaviors. In humans, mutations in the gene that encodes 11beta- hydroxysteroid dehydrogenase type 2 are associated with low birth weight. Babies with low birth weight have higher plasma cortisol levels throughout life, which indicates HPA-axis programming. In human pregnancy, severe maternal stress affects the offspring's HPA axis and is associated with neuropsychiatric disorders; moreover, maternal glucocorticoid therapy alters offspring brain function. The molecular mechanisms that underlie prenatal programming might reflect permanent changes in the expression of specific transcription factors, including the glucocorticoid receptor; tissue specific effects reflect modification of one or more of the multiple alternative first exons or promoters of the glucocorticoid receptor gene. Intriguingly, some of these effects seem to be inherited by subsequent generations that are unexposed to exogenous glucocorticoids at any point in their lifespan from fertilization, which implies that these epigenetic effects persist.

Brain plasticity and recovery from early cortical injury

There is a general view that early brain damage leads to a far better outcome than damage later in life. Although there is a grain of truth to this idea, the reality is far more complex. We have identified a set of nine principles that underlie behavioral and anatomical changes after neonatal cortical injury as well as describing a variety of pre- and postnatal factors that modulate brain and behavioral plasticity after neonatal cortical lesions.

Intergenerational transmission of maternal behavior in rhesus macaques and its underlying mechanisms

Thirteen group-living rhesus macaque females that were crossfostered shortly after birth were followed longitudinally until they gave birth for the first time. Their maternal behavior was compared to the behavior of both their foster and their biological mothers, and analyzed in relation to the cerebrospinal fluid (CSF) concentrations of serotonin, dopamine, and norepinephrine metabolites (5-HIAA, HVA, and MHPG) measured in their second year of life. Crossfostered females were similar to their foster mothers in their rates of maternal rejection and grooming, whereas their contact-making behavior was more similar to that of their biological mothers. Crossfostered females with lower CSF concentrations of 5-HIAA exhibited higher rates of maternal rejection than females with higher CSF 5-HIAA. In a related article (Maestripieri et al., 2006), we reported that rhesus infants reared by highly rejecting mothers had lower CSF 5-HIAA in their first 3 years of life. Taken together, these findings suggest that early social experience and experience-related long-term changes in serotonergic function may play a role in the intergenerational transmission of maternal rejection from mothers to daughters.

Importance of early lighting conditions in maternal care by dam as well as anxiety and memory later in life of offspring

Rodent studies have revealed that the early rearing environment plays an important role in the development of stress vulnerability, memory and cognition. Although early lighting conditions (ELC) are involved in these neuronal developments through both maternal and offspring behavior, their influence has not been fully elucidated. Thus, by using Sprague-Dawley rats, we examined whether ELC affected maternal care by the dam and the subsequent neurodevelopment of the offspring. Prolonged dark phase conditions (PDC) (light/dark, 6/18 h) and prolonged light phase conditions (light/dark, 18/6 h) were administered from postnatal day 2 to postnatal day 14. Throughout this period, maternal care and the circadian rhythmicity of dams were investigated. In adolescence and adulthood of the offspring, we measured anxiety-like behavior, social interaction, object recognition memory, activity rhythm and corticosterone response to stress with hippocampal expression of N-methyl-D-aspartate and glucocorticoid receptor mRNAs. PDC altered maternal care and circadian rhythmicity in the dam compared with normal lighting conditions and prolonged light phase conditions. PDC markedly increased anxiety-like behavior, decreased social interaction and object recognition memory, and inhibited corticosterone feedback in offspring later in life. Furthermore, hippocampal levels of glucocorticoid receptor mRNA and N-methyl-D-aspartate receptor 2B mRNA in rats subjected to PDC were significantly lower than in animals subjected to normal lighting conditions. In the adult offspring, the circadian rhythm of locomotor activity was not affected. These findings suggested that ELC affect mother-infant interactions and subsequently at least partially alter the neurobehavioral development of offspring.

Neurodevelopmental sequelae of postnatal maternal care in rodents: clinical and research implications of molecular insights

Parental care plays an important role in the emotional and cognitive development of the offspring. Children who have been exposed to abuse or neglect are more likely to develop numerous psychopathologies, while good parent-infant bonding is associated with improved resiliency to stress. Similar observations have also been reported in non-human primates and rodents, suggesting that at least some neurodevelopmental aspects of parent-offspring interactions are conserved among mammals and could therefore be studied in animals. We present data to suggest that frequency of licking and grooming provided by the dam during a critical period in development plays an important role in modifying neurodevelopment. These findings are examined in the broader context in which exposure to other sensory modalities such as vision or hearing during a specific period in development shapes brain development with functional consequences that persist into adulthood. We also discuss recent rodent work showing that increased frequency of licking and grooming provided by the dam during the first week of life is associated with changes in DNA methylation of promoter elements that control expression of these genes and behavior. The stability of DNA methylation in postmitotic cells provides a possible molecular scaffold by which changes in gene expression and behavioral traits induced by postnatal maternal care are maintained throughout life. Finally, the relevance of findings reported in rodents to those noted in non-human primates and humans are assessed and the research and clinical implications of these observations for future work are explored.

PTSD and stress sensitisation: a tale of brain and body Part 2: animal models

Animal models that are characterised by long-lasting conditioned fear responses as well as generalised behavioural sensitisation to novel stimuli following short-lasting but intense stress have a phenomenology that resembles that of PTSD in humans. These models include brief sessions of shocks, social confrontations, and a short sequence of different stressors. Subgroups of animals with different behavioural traits or coping styles during stress exposure show a different degree or pattern of long-term sensitisation. Weeks to months after the trauma, treated animals on average also show a sensitisation to novel stressful stimuli of neuroendocrine, cardiovascular and gastrointestinal motility responses as well as altered pain sensitivity and immune function. Functional neuroanatomical and pharmacological studies in these animal models have provided evidence for involvement of amygdala and medial prefrontal cortex, and of brain stem areas regulating neuroendocrine and autonomic function and pain processing. They have also generated a number of neurotransmitter and neuropeptide targets that could provide novel avenues for treatment in PTSD.

Maternal deprivation and early handling affect density of calcium binding protein-containing neurons in selected brain regions and emotional behavior in periadolescent rats

Adverse early life experiences can induce neurochemical changes that may underlie modifications in hypothalamic-pituitary-adrenal axis responsiveness, emotionality and cognition. Here, we investigated the expression of the calcium binding proteins (CBPs) calretinin, calbindin and parvalbumin, which identify subpopulations of GABAergic neurons and serve important functional roles by buffering intracellular calcium levels, following brief (early handling) and long (maternal deprivation) periods of maternal separation, as compared with non-handled controls. CBP-expressing neurons were analyzed in brain regions related to stress and anxiety. Emotionality was assessed in parallel using the social interaction test. Analyses were carried out at periadolescence, an important phase for the development of brain areas involved in stress responses. Our results indicate that density of CBP-immunoreactive neurons decreases in the paraventricular region of deprived rats but increases in the hippocampus and lateral amygdala of both early-handled and deprived rats when compared with controls. Emotionality is reduced in both early-handled and deprived animals. In conclusion, early handling and deprivation led to neurochemical and behavioral changes linked to stress-sensitive brain regions. These data suggest that the effects of early experiences on CBP containing neurons might contribute to the functional changes of neuronal circuits involved in emotional response.

Heritability of ischaemic stroke in women compared with men: a genetic epidemiological study

BACKGROUND

Ischaemic stroke is partly heritable. However, although the genetic and non-genetic factors responsible could be sex-specific, interactions between the sex of the parent affected and the sex of the proband or affected siblings are unknown. We sought to assess the relation between the sex and phenotype of affected probands and the sex of affected first-degree relatives.

METHODS

We determined the prevalence of history of stroke in the mother, father, and other first-degree relatives in female and male probands with ischaemic stroke or transient ischaemic attack in the population-based Oxford Vascular Study (OXVASC). We validated our findings using unpublished individual patient data from two independent Oxford studies.

FINDINGS

In OXVASC, detailed family history was available in 806 (93%) probands. Female probands were more likely than males to have at least one affected first-degree relative (146/423 vs 104/383; OR 1.4, 95% CI 1.1-2.0, p=0.02) due entirely to an excess of affected female relatives in female probands (female relative vs male relative OR=1.7, 1.3-2.4, p=0.0004; female only vs male only OR=2.1, 1.4-3.1, p=0.0001). Maternal stroke was more common than paternal stroke in female probands (OR=1.8, 1.2-2.7, p=0.001) but not in males (OR=1.1, 0.7-1.7, p=0.38), and female probands were more likely than males to have an affected sister (OR=3.1, 1.5-6.7, p=0.004) but not an affected brother (OR=1.1, 0.6-2.1, p=0.80). Ages at first stroke were also correlated within families among affected females (r=0.36, p=0.004) but not among affected males, such that the excess of affected female relatives of female probands was greatest when the difference in age at first stroke was less than 5 years (OR=3.7, 1.6-8.6, p=0.0007) and fell as the age difference increased (p for trend=0.004). These findings were independent of traditional risk factors and stroke subtype. Data from the other Oxford studies confirmed the excess maternal history of stroke in female probands (OR=2.3, 1.5-3.8, p<0.00001) and the lack in males (OR=1.0, 0.7-1.4, p=0.58).

INTERPRETATION

Heritability of ischaemic stroke is greater in women than in men, with an excess of affected mothers and affected sisters in female probands independent of traditional vascular risk factors, which could be explained by sex-specific genetic, epigenetic, or non-genetic mechanisms.

Prenatal stress and early adoption effects on benzodiazepine receptors and anxiogenic behavior in the adult rat brain

Chronic maternal stress during pregnancy has been associated with behavioral alterations that persist into adulthood. Moreover, adoption procedures performed immediately after birth can reverse these alterations. In this study, we examined the effects of prenatal restraint stress and adoption at birth (cross-fostering) on the behavioral response to an anxiety-provoking situation and on the adult male offspring expression of benzodiazepine (BDZ) receptors in selected brain areas. Adult offspring of rats stressed during the last week of pregnancy exhibited higher levels of anxiety than control rats. The anxiogenic behavior found at the elevated plus maze (EPM) has been related to the reduced levels of BDZ receptor levels in specific brain areas. Adult offspring of rats stressed during pregnancy exhibited a decrease in the number of BDZ receptors binding sites in the central amygdaloid nucleus (Ce), CA1, CA3, and the dentate gyrus regions of the hippocampus when compared to controls. Regarding the adoption procedure, control pups raised by a foster gestationally stressed mother showed similar levels of anxiety as stressed groups. Stressed offspring raised by a foster control mother showed reduced anxiety levels compared to that of the control groups. Adoption per se showed no difference in time spent, neither in the open arms of the plus maze nor in BDZ receptor levels, when compared to the corresponding control and stressed groups. Stressed offspring raised by a foster control mother reverted BDZ receptor levels to control values. However, control pups raised by a gestationally stressed foster mother showed similar values compared to the control offspring in hippocampus, in spite of showing an anxiogenic behavior in the EPM. We found a significant increase of Ce BDZ receptor levels in control offspring raised by a foster stressed mother that could be explained as a compensatory effect to a GABA receptor desensitization. In summary, the behavioral outcome of the adult offspring is vulnerable both to the stress experience during the late prenatal period as well as to possible variations in care during lactation by mothers subjected to chronic stress during gestation. There seems to be a direct correlation between anxiety state and BDZ receptor levels in the adult offspring raised by their biological mothers. However, the mechanism of BDZ regulation leading to an anxious behavior might be different if the insult is received only postnatally as opposed to both pre and postnatally.

Environmental Programming of Phenotypic Diversity in Female Reproductive Strategies

Among invertebrates, certain hermaphroditic species reproduce sexually, but with no process of sexual differentiation. In such cases the brain is bisexual: Each member of the species develops male and female sexual organs and retains the capacity to express both male and female patterns of reproductive behavior. Members of such species can reproduce socially or alone. Mammals and many other species reproduce both sexually and socially, which requires an active process of sexual differentiation of reproductive organs and brain. The primary theme of this chapter is simply that this process admits to variation and thus individual differences in gender-specific patterns of reproductive function. The focus on this chapter is the often neglected variation in the development of reproductive function in the female mammal. The basic premise is that evolution has not defined any single, optimal reproductive phenotype, but rather encourages plasticity in specific reproductive traits among same sex members of the species that are derived from variations in the quality of the prevailing environment during development that are mediated by alterations in parent-offspring interactions. Thus, the variations in parental care that define the reproductive phenotype of the offspring are influenced by the quality of the environment (i.e., nutrient availability, predation, infection, population density, and so on).

Effect of resource availability on biparental care, and offspring neural and behavioral development in the California mouse (Peromyscus californicus)

Maternal care influences cognitive function in humans, primates and rodents; however, little is known about the effect of biparental care. Environmental factors such as resource availability play an important role in modulating parental investment strategies with subsequent effects on the offspring. Thus, we examined the interaction between foraging demand and biparental care on hippocampal development and novel object recognition in the monogamous, biparental California mouse. We characterized biparental behavior for 15 days in families exposed to either control (ad libitum feeding) or a high-foraging demand across the weaning period. Adult male offspring were then tested in the open field, and for novel object and place recognition, as well as for hippocampal synaptic density and the expression of genes encoding for subunits of the N-methyl-D-aspartate (NMDA) receptor complex, and the postsynaptic density (PSD)-95 scaffolding protein. Under high-foraging demand, the mothers' body weight was decreased at weaning and fathers spent significantly less time in contact with pups. Offspring reared under high-foraging demand weighed less at weaning and, as adults, were more fearful in the open field and showed profound deficits in both novel object and place recognition. While synaptic density and NR1 mRNA expression were unaffected, offspring reared under high-foraging demand showed increased NR2A and decreased NR2B mRNA expression. Further, PSD-95 protein expression was decreased in mice reared under high-foraging demand. Together, the results suggest that resource availability affects biparental investment strategies, with subsequent effects on hippocampal development and novel object recognition in the offspring.

Maximizing resilience through diverse levels of inquiry: Prevailing paradigms, possibilities, and priorities for the future

The study of resilience has two core characteristics: it is fundamentally applied in nature, seeking to use scientific knowledge to maximize well-being among those at risk, and it draws on expertise from diverse scientific disciplines. Recent advances in biological processes have confirmed the profound deleterious effects of harsh caregiving environments, thereby underscoring the importance of early interventions. What remains to be established at this time is the degree to which insights on particular biological processes (e.g., involving specific brain regions, genes, or hormones) will be applied in the near future to achieve substantial reductions in mental health disparities. Aside from biology, resilience developmental researchers would do well to draw upon relevant evidence from other behavioral sciences as well, notably anthropology as well as family, counseling, and social psychology. Scientists working with adults and with children must remain vigilant to the advances and missteps in each others' work, always ensuring caution in conveying messages about the "innateness" of resilience or its prevalence across different subgroups. Our future research agenda must prioritize reducing abuse and neglect in close relationships; deriving the "critical ingredients" in effective interventions and going to scale with these; working collaboratively to refine theory on the construct; and responsibly, proactively disseminating what we have learned about the nature, limits, and antecedents of resilient adaptation across diverse at-risk groups.

Gene-environment interdependence

Behavioural genetics was initially concerned with partitioning population variance into that due to genetics and that due to environmental influences. The implication was that the two were separate and it was assumed that gene-environment interactions were usually of so little importance that they could safely be ignored. Theoretical considerations suggested that that was unlikely to be true and empirical findings are now accumulating on the demonstrated and replicated biological interactions between identified common single genetic variants and the operation of environmentally mediated risks. The paper outlines the evidence and considers why it is changing concepts in ways that matter.

Effects of neonatal novelty exposure on sexual behavior, fear, and stress-response in adult rats

Environmental stimuli in early life may result in permanent behavioral and physiological changes. Present study evaluated the effects of exposing pups to a novel environment on behaviors (open-field test and sexual behavior) and prolactin stress-responses in adult male rats. Half of a litter was daily removed outside (OUT) from the nest and stimulated by handling for 3 min, while the other half remained inside (IN) the nest and was also handled for the same period during the first 10 days postpartum. Maternal behavior after all the pups were returned to the nest was not different between IN and OUT littermates. In adulthood, OUT males showed increased general and central locomotion activity in the open-field test, reduced sexual behavior, and attenuated prolactin secretion in response to restraint stress compared with the IN littermates. The repeated exposition of rat pups to a novel environment is a causal factor for the long-lasting behavioral and endocrine changes. The premature exposition of the pup to unfamiliar environments decreases fear and stress-response, and also reduces sexual behavior. We suggest that the absence of the odor of the mother may be crucial to explain the effects detected in adulthood.

Developmental plasticity of HPA and fear responses in rats: a critical review of the maternal mediation hypothesis

Developmental plasticity of HPA and fear responses in rats has been proposed to be mediated by environment-dependent variation in active maternal care. Here, we review this maternal mediation hypothesis based on the postnatal manipulation literature and on our own recent research in rats. We show that developmental plasticity of HPA and fear responses in rats cannot be explained by a linear single-factor model based on environment-dependent variation in active maternal care. However, by adding environmental stress as a second factor to the model, we were able to explain the variation in HPA and fear responses induced by postnatal manipulations. In this two-factor model, active maternal care and environmental stress (as induced, e.g., by long maternal separations or maternal food restriction) exert independent, yet opposing, effects on HPA reactivity and fearfulness in the offspring. This accounts well for the finding that completely safe and stable, as well as, highly stressful maternal environments result in high HPA reactivity and fearfulness compared to moderately challenging maternal environments. Furthermore, it suggests that the downregulation of the HPA system in response to stressful maternal environments could reflect adaptive developmental plasticity based on the increasing costs of high stress reactivity with increasingly stressful conditions. By contrast, high levels of environmental stress induced by environmental adversity might constrain such adaptive plasticity, resulting in non-adaptive or even pathological outcomes. Alternatively, however, developmental plasticity of HPA and fear responses in rats might be a function of maternal HPA activation (e.g., levels of circulating maternal glucocorticoid hormones). Thus, implying a U-shaped relationship between maternal HPA activation and HPA reactivity and fearfulness in the offspring, increasing maternal HPA activation with increasing environmental adversity would explain the effects of postnatal manipulations equally well. This raises the possibility that variation in active maternal care is an epiphenomenon, rather than a causal factor in developmental plasticity of HPA and fear responses in rats. Developmental plasticity of HPA and fear responses in rats and other animals has important implications for the design of animal experiments and for the well-being of experimental animals, both of which depend on the exact underlying mechanism(s). Importantly, however, more naturalistic approaches are needed to elucidate the adaptive significance of environment-dependent variation of HPA reactivity and fearfulness in view of discriminating between effects reflecting adaptive plasticity, phenotypic mismatch and pathological outcomes, respectively.

Evolutionary Basis of Adaptation in Resilience and Vulnerability: Response to Cicchetti and Blender

This masterful and wide-ranging paper gives us a clear picture of the need for interdisciplinary studies of resilience and vulnerability. We need to go beyond the interacting events at the different levels to see clearly that multiple levels of analysis and concept do not themselves interact, but instead give us different aspects of a biological, psychological, or behavioral event. Thus, no levels are reducible to any of the others. In the rest of my discussion, I raise the likelihood that the multiple level responses of "resilience" are no more adaptive in their evolutionary history than the very different responses we call "vulnerability." Keeping in mind the evolved functions of these responses, and the circumstances of their selection during evolution, will provide us with new ideas and approaches for understanding and intervention.

Social ecology of children's vulnerability to environmental pollutants

BACKGROUND

The outcomes of exposure to neurotoxic chemicals early in life depend on the properties of both the chemical and the host's environment. When our questions focus on the toxicant, the environmental properties tend to be regarded as marginal and designated as covariates or confounders. Such approaches blur the reality of how the early environment establishes enduring biologic substrates.

OBJECTIVES

In this commentary, we describe another perspective, based on decades of biopsychological research on animals, that shows how the early, even prenatal, environment creates permanent changes in brain structure and chemistry and behavior. Aspects of the early environment-encompassing enrichment, deprivation, and maternal and neonatal stress-all help determine the functional responses later in life that derive from the biologic substrate imparted by that environment. Their effects then become biologically embedded. Human data, particularly those connected to economically disadvantaged populations, yield equivalent conclusions.

DISCUSSION

In this commentary, we argue that treating such environmental conditions as confounders is equivalent to defining genetic differences as confounders, a tactic that laboratory research, such as that based on transgenic manipulations, clearly rejects. The implications extend from laboratory experiments that, implicitly, assume that the early environment can be standardized to risk assessments based on epidemiologic investigations.

CONCLUSIONS

The biologic properties implanted by the early social environment should be regarded as crucial elements of the translation from laboratory research to human health and, in fact, should be incorporated into human health research. The methods for doing so are not clearly defined and present many challenges to investigators.

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

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

Gene-environment interplay and psychopathology: multiple varieties but real effects

Gene-environment interplay is a general term that covers several divergent concepts with different meanings and different implications. In this review, we evaluate research evidence on four varieties of gene-environment interplay. First, we consider epigenetic mechanisms by which environmental influences alter the effects of genes. Second, we focus on variations in heritability according to environmental circumstances. Third, we discuss what is known about gene-environment correlations. Finally, we assess concepts and findings on the interaction between specific identified genes and specific measured environmental risks. In order to provide an understanding of what may be involved in gene-environment interplay, we begin our presentation with a brief historical review of prevailing views about the role of genetic and environmental factors in the causation of mental disorders, and we provide a simplified account of some of the key features of how genes 'work'.

Environmental programming of stress responses through DNA methylation: life at the interface between a dynamic environment and a fixed genome

Early experience permanently alters behavior and physiology. These effects are, in part, mediated by sustained alterations in gene expression in selected brain regions. The critical question concerns the mechanism of these environmental “programming” effects. We examine this issue with an animal model that studies the consequences of variations in mother-infant interactions on the development of individual differences in behavioral and endocrine responses to stress in adulthood. Increased levels of pup licking/grooming by rat mothers in the first week of life alter DNA structure at a glucocorticoid receptor gene promoter in the hippocampus of the offspring. Differences in the DNA methylation pattern between the offspring of high- and low-lickinglgrooming mothers emerge over the first week of life; they are reversed with cross-fostering; they persist into adulthood; and they are associated with altered histone acetylation and transcription factor (nerve growth factor-induced clone A [NGFIA]) binding to the glucocorticoid receptor promoter. DNA methylation alters glucocorticoid receptor expression through modifications of chromatin structure. Pharmacological reversal of the effects on chromatin structure completely eliminates the effects of maternal care on glucocorticoid receptor expression and hypothalamic-pituitary-adrenal (HPA) responses to stress, thus suggesting a causal relation between the maternally induced, epigenetic modification of the glucocorticoid receptor gene and the effects on stress responses in the offspring. These findings demonstrate that the structural modifications of the DNA can be established through environmental programming and that, in spite of the inherent stability of this epigenomic marker, it is dynamic and potentially reversible.

Maternal programming of steroid receptor expression and phenotype through DNA methylation in the rat

Increased levels of pup licking/grooming and arched-back nursing by rat mothers over the first week of life alter the epigenome at a glucocorticoid receptor gene promoter in the hippocampus of the offspring. Differences in the DNA methylation pattern between the offspring of High and Low licking/grooming--arched-back mothers emerge over the first week of life, are reversed with cross-fostering, persist into adulthood and are associated with altered histone acetylation and transcription factor (NGFI-A) binding to the glucocorticoid receptor promoter. Central infusion of the adult offspring with the histone deacetylase inhibitor trichostatin A removes the previously defined epigenomic group differences in histone acetylation, DNA methylation, NGFI-A binding, glucocorticoid receptor expression, and hypothalamic-pituitary-adrenal responses to stress, thus suggesting a causal relation between the epigenomic state, glucocorticoid receptor expression and the effects of maternal care on stress responses in the offspring. These findings demonstrate that an epigenomic state of a gene can be established through a behavioral mode of programming and that in spite of the inherent stability of this epigenomic mark, it is dynamic and potentially reversible.

Genetic and Environmental Influences on Antisocial Behaviors: Evidence from Behavioral–Genetic Research

This article reviews behavioral-genetic research into human antisocial behavior. The focus is on studies of antisocial behavior that have been leading the way in investigating environmental and genetic influences on human behavior. The first generation of studies, which provided quantitative estimates attesting that genes and environments each influence about half of the population's variation in antisocial behaviors is interpreted. Then how behavioral-genetic methods are being applied to test developmental theory and to detect environmental causes of antisocial behavior is illustrated. Evidence for interactions between genes and the environment in the etiology of antisocial behavior is also examined. The article ends by envisioning future work on gene-environment interplay in the etiology of antisocial behavior.