Variation in the mu-opioid receptor gene (OPRM1) moderates the influence of maternal sensitivity on child attachment

The endogenous opioid system is thought to play an important role in mother-infant attachment. In infant rhesus macaques, variation in the μ-opioid receptor gene (OPRM1) is related to differences in attachment behavior that emerges following repeated separation from the mother; specifically, infants carrying at least one copy of the minor G allele of the OPRM1 C77G polymorphism show heightened and more persistent separation distress, as well as a pattern of increased contact-seeking behavior directed towards the mother during reunions (at the expense of affiliation with other group members). Research in adult humans has also linked the minor G allele of the analogous OPRM1 A118G polymorphism with greater interpersonal sensitivity. Adopting an interactionist approach, we examined whether OPRM1 A118G genotype and maternal (in)sensitivity are associated with child attachment style, predicting that children carrying the G allele may be more likely to develop an ambivalent attachment pattern in response to less sensitive maternal care. The sample consisted of 191 mothers participating with their children (n = 223) in the Maternal Adversity, Vulnerability and Neurodevelopment (MAVAN) project, a community-based, birth cohort study of Canadian mothers and their children assessed longitudinally across the child's development. Maternal sensitivity was coded from at-home mother-child interactions videotaped when the child was 18 months of age. Child attachment was assessed at 36 months using the Strange Situation paradigm. As predicted, G allele carriers, but not AA homozygotes, showed increasing odds of being classified as ambivalently attached with decreasing levels of maternal sensitivity. Paralleling earlier non-human animal research, this work provides support for the theory that endogenous opioids contribute to the expression of attachment behaviors in humans.

Brain charts for the human lifespan

Over the past few decades, neuroimaging has become a ubiquitous tool in basic research and clinical studies of the human brain. However, no reference standards currently exist to quantify individual differences in neuroimaging metrics over time, in contrast to growth charts for anthropometric traits such as height and weight1. Here we assemble an interactive open resource to benchmark brain morphology derived from any current or future sample of MRI data ( http://www.brainchart.io/ ). With the goal of basing these reference charts on the largest and most inclusive dataset available, acknowledging limitations due to known biases of MRI studies relative to the diversity of the global population, we aggregated 123,984 MRI scans, across more than 100 primary studies, from 101,457 human participants between 115 days post-conception to 100 years of age. MRI metrics were quantified by centile scores, relative to non-linear trajectories2 of brain structural changes, and rates of change, over the lifespan. Brain charts identified previously unreported neurodevelopmental milestones3, showed high stability of individuals across longitudinal assessments, and demonstrated robustness to technical and methodological differences between primary studies. Centile scores showed increased heritability compared with non-centiled MRI phenotypes, and provided a standardized measure of atypical brain structure that revealed patterns of neuroanatomical variation across neurological and psychiatric disorders. In summary, brain charts are an essential step towards robust quantification of individual variation benchmarked to normative trajectories in multiple, commonly used neuroimaging phenotypes.

SUN-722 Liver Leptin Receptor Gene Network Moderates the Effects of Early Life Adversity on Anxiety and Depression Problems in Children and Adolescents

Leptin is a hormone involved in the regulation of food intake, with receptors largely expressed centrally and peripherally, in structures like the hypothalamus and the liver. Beyond its well-known actions as an energy-balance regulator, leptin is linked to psychiatric disorders. Considering that the association between genetic and early environmental factors contributes to psychopathology, disruptions of leptin signaling could be a key mechanism in this interaction. To investigate this possibility, we created an expression-based polygenic risk score (ePRS) reflecting variations in the function of the LepR gene network in the liver and hypothalamus, and investigated its interaction with postnatal adversity on Child Behavior Checklist in 4 years old children (main cohort: MAVAN, N=137) and 17 years old teenagers (Replication Cohort: ALSPAC, N=2630). There is an interaction effect between adversity exposure and liver-based LepR-ePRS, increasing depressive and anxiety problems on the MAVAN cohort (β=78.16, p=0.02, β=83.77, p=0.01). In ALSPAC, the results were replicated, showing an interaction between adversity exposure and liver-based LepR-ePRS, increasing the depression score and somatic symptoms (β=24.65, p=0.005; β=33.51, p=0.009). No significant interactions were found using the hypothalamus-based LepR-ePRS (p>0.05), suggesting specificity for the liver LepR gene network to predict these behavioral outcomes. A parallel-independent component analysis showed relationships between the SNPs from the liver ePRS-LepR and gray matter density in cortical areas involved in emotion regulation (middle frontal gyrus, inferior parietal lobule and anterior cingulate). Finally, the relationship between gene and MRI components in this analysis is moderated by the history of early life adversity exposure. Enrichment analysis of the liver LepR co-expression network shows that these genes are related to biological processes including regulation of glucose transport, cholesterol metabolism and cellular glucose homeostasis, which indicates possible underlying mechanisms linking peripheral metabolism-related gene expression and the development of emotional symptoms. Our data supports the hypothesis that exposure to early adversity affects emotional behavior, and the liver LepR gene network is an important moderator of these effects. Further studies on development of emotional symptoms should consider metabolic markers to understand these complex phenotypes.

MON-722 Cross-Species Glucocorticoid-Sensitive Posterior Dentate Gyrus Gene Network: Developing a Polygenic Score Associated to Susceptibility to Depression After Early Life Adversity Exposure in Humans

Exposure to stress during the life-course has consistently been associated with neuropsychological disorders, but the precise role of stress released glucocorticoids remains unclear in this context. We aimed at using hippocampal gene expression data from macaques to identify clusters of genes sensible to glucocorticoid exposure and create a biologically relevant polygenic score to investigate emotional disorders in a child and adult humans exposed to early adversity. RNA-sequencing data from the posterior dentate gyrus (pDG) of adult Macaca fascicularis females treated with Betamethasone (glucocorticoid) or saline injections for 8 consecutive days were analyzed from two cohorts: Singapore (reference) and Vietnam (replication) with N=12/each. Weighted gene co-expression network analysis (WGCNA) was used to identify clusters (modules) of co-expressed genes associated with betamethasone. In Singaporean animals, genes were clustered in 52 modules, in which 5 were associated with betamethasone. Two modules were preserved in a replication dataset (Vietnam) and in data from female rats treated with corticosterone for 6 weeks, being the black module (557 genes, P=0.01, r=0.7) the one having the highest correlation with glucocorticoid exposure. Gene ontology analysis (FDR<0.05, Metacore®) revealed that this module is associated with transcription processes. The SNPs derived from genes within the module were used to calculate an expression-based polygenic risk score (ePRS) in the human samples, weighing each SNP by the slope of the association between genotype and gene expression (GTex). Linear regression analysis showed a significant interaction between ePRS and early adversity on the Dominique - major depressive disorder domain (β=1304; P=0.003; N=65) in girls aged 6 years (MAVAN), in which a higher ePRS was associated with more symptoms as the adversity scores increases (simple slope analysis,P=0.004). A comparable interaction between the ePRS and postnatal adversity was also observed in adult women (UK Biobank), in which there was an increased risk for early depression onset (β= -424.3, P=0.04; N=13899). In the adult cohort, whole brain gray matter volume was also associated with differences in the expression of the genes that composed the ePRS-black network (main ePRS effect, β=1865776, P=0.03, N=10902). Glucocorticoid exposure affects a specific group of genes in pDG of adult female macaques and rats, influencing transcriptional processes. Variations in the expression of this gene network sensible to glucocorticoids were associated with susceptibility for the development of depression in girls and adult women exposed to early life adversity. These show the importance of glucocorticoids on the development of depressive symptoms. The gene network affected by glucocorticoids can guide future pharmacological or mechanistic studies in other samples or species.

Moderating effect of PLIN4 genetic variant on impulsivity traits in 5-year-old-children born small for gestational age

Poor fetal growth is associated with long-term behavioral, metabolic and psychiatric alterations, including impulsivity, insulin resistance, and mood disorders. However, the consumption of omega-3 polyunsaturated fatty acid (n-3 PUFA) seems to be protective for this population, improving inhibitory control and behavioral reactivity. We investigated whether the presence of the A allele of rs8887 SNP (PLIN4 gene), known to be associated with increased sensitivity to the consumption of n-3 PUFAs, interacts with fetal growth influencing inhibitory control. 152 five-year-old children were genotyped and performed the Stop Signal Task (SSRT). There was a significant interaction between birth weight and the presence of the A allele on SSRT performance, in which lower birth weight associated with poorer inhibitory control only in non-carriers. These results suggest that a higher responsiveness to n-3 PUFAS protects small for gestational age children from developing poor response inhibition, highlighting that optimizing n-3 PUFA intake may benefit this population.

Does the maternal vaginal microbiota play a role in seeding the microbiota of neonatal gut and nose?

The acquisition and early maturation of infant microbiota is not well understood despite its likely influence on later health. We investigated the contribution of the maternal microbiota to the microbiota of infant gut and nose in the context of mode of delivery and feeding. Using 16S rRNA sequencing and specific qPCR, we profiled microbiota of 42 mother-infant pairs from the GUSTO birth cohort, at body sites including maternal vagina, rectum and skin; and infant stool and nose. In our study, overlap between maternal vaginal microbiota and infant faecal microbiota was minimal, while the similarity between maternal rectal microbiota and infant microbiota was more pronounced. However, an infant's nasal and gut microbiota were no more similar to that of its own mother, than to that of unrelated mothers. These findings were independent of delivery mode. We conclude that the transfer of maternal vaginal microbes play a minor role in seeding infant stool microbiota. Transfer of maternal rectal microbiota could play a larger role in seeding infant stool microbiota, but approaches other than the generally used analyses of community similarity measures are likely to be needed to quantify bacterial transmission. We confirmed the clear difference between microbiota of infants born by Caesarean section compared to vaginally delivered infants and the impact of feeding mode on infant gut microbiota. Only vaginally delivered, fully breastfed infants had gut microbiota dominated by Bifidobacteria. Our data suggest that reduced transfer of maternal vaginal microbial is not the main mechanism underlying the differential infant microbiota composition associated with Caesarean delivery. The sources of a large proportion of infant microbiota could not be identified in maternal microbiota, and the sources of seeding of infant gut and nasal microbiota remain to be elucidated.

Influences of prenatal and postnatal maternal depression on amygdala volume and microstructure in young children

Maternal depressive symptoms influence neurodevelopment in the offspring. Such effects may appear to be gender-dependent. The present study examined contributions of prenatal and postnatal maternal depressive symptoms to the volume and microstructure of the amygdala in 4.5-year-old boys and girls. Prenatal maternal depressive symptoms were measured using the Edinburgh Postnatal Depression Scale (EPDS) at 26 weeks of gestation. Postnatal maternal depression was assessed at 3 months using the EPDS and at 1, 2, 3 and 4.5 years using the Beck's Depression Inventory-II. Structural magnetic resonance imaging and diffusion tensor imaging were performed with 4.5-year-old children to extract the volume and fractional anisotropy (FA) values of the amygdala. Our results showed that greater prenatal maternal depressive symptoms were associated with larger right amygdala volume in girls, but not in boys. Increased postnatal maternal depressive symptoms were associated with higher right amygdala FA in the overall sample and girls, but not in boys. These results support the role of variation in right amygdala structure in transmission of maternal depression to the offspring, particularly to girls. The differential effects of prenatal and postnatal maternal depressive symptoms on the volume and FA of the right amygdala suggest the importance of the timing of exposure to maternal depressive symptoms in brain development of girls. This further underscores the need for intervention targeting both prenatal and postnatal maternal depression to girls in preventing adverse child outcomes.

Infant frontal EEG asymmetry in relation with postnatal maternal depression and parenting behavior

Right frontal electroencephalogram (EEG) asymmetry associates with negative affect and depressed mood, which, among children, are predicted by maternal depression and poor parenting. This study examined associations of maternal depression and maternal sensitivity with infant frontal EEG asymmetry based on 111 mother-6-month-infant dyads. There were no significant effects of postnatal maternal depression or maternal sensitivity, or their interaction, on infant EEG frontal asymmetry. However, in a subsample for which the infant spent at least 50% of his/her day time hours with his/her mother, both lower maternal sensitivity and higher maternal depression predicted greater relative right frontal EEG asymmetry. Our study further showed that greater relative right frontal EEG asymmetry of 6-month-old infants predicted their greater negative emotionality at 12 months of age. Our study suggested that among infants with sufficient postnatal maternal exposure, both maternal sensitivity and mental health are important influences on early brain development.

Maternal sensitivity, infant limbic structure volume and functional connectivity: a preliminary study

Mechanisms underlying the profound parental effects on cognitive, emotional and social development in humans remain poorly understood. Studies with nonhuman models suggest variations in parental care affect the limbic system, influential to learning, autobiography and emotional regulation. In some research, nonoptimal care relates to decreases in neurogenesis, although other work suggests early-postnatal social adversity accelerates the maturation of limbic structures associated with emotional learning. We explored whether maternal sensitivity predicts human limbic system development and functional connectivity patterns in a small sample of human infants. When infants were 6 months of age, 20 mother-infant dyads attended a laboratory-based observational session and the infants underwent neuroimaging at the same age. After considering age at imaging, household income and postnatal maternal anxiety, regression analyses demonstrated significant indirect associations between maternal sensitivity and bilateral hippocampal volume at six months, with the majority of associations between sensitivity and the amygdala demonstrating similar indirect, but not significant results. Moreover, functional analyses revealed direct associations between maternal sensitivity and connectivity between the hippocampus and areas important for emotional regulation and socio-emotional functioning. Sensitivity additionally predicted indirect associations between limbic structures and regions related to autobiographical memory. Our volumetric results are consistent with research indicating accelerated limbic development in response to early social adversity, and in combination with our functional results, if replicated in a larger sample, may suggest that subtle, but important, variations in maternal care influence neuroanatomical trajectories important to future cognitive and emotional functioning.

The psychometric properties of the Quantitative-Checklist for Autism in Toddlers (Q-CHAT) as a measure of autistic traits in a community sample of Singaporean infants and toddlers

Background

There is growing research evidence that subclinical autistic traits are elevated in relatives of individuals with autism spectrum disorder (ASD), continuously distributed in the general population and likely to share common etiology with ASD. A number of measures have been developed to assess autistic traits quantitatively in unselected samples. So far, the Quantitative-Checklist for Autism in Toddlers (Q-CHAT) is one of very few measures developed for use with toddlers as young as 18 months, but little is known about its measurement properties and factor structure.

Methods

The present study examined internal consistency, factor structure, test-retest stability, and convergent validity of the Q-CHAT in a sample of toddlers in Singapore whose caregivers completed the Q-CHAT at 18 (n = 368) and 24 months (n = 396).

Results

Three factors were derived accounting for 38.1 % of the variance: social/communication traits, non-social/behavioral traits, and a speech/language factor. Internal consistency was suboptimal for the total and speech/language scores, but acceptable for the social/communication and non-social/behavioral factor scores. Scores were generally stable between 18 and 24 months. Convergent validity was found with the Pervasive Developmental Disorders subscale of the Child Behavior Checklist (CBCL) completed by caregivers when their children were 24 months. Q-CHAT total scores in this sample were higher than those reported in other unselected samples from the UK.

Conclusions

The Q-CHAT was found to have a three-factor structure, acceptable internal consistency for its two main factor scores (social/communication and non-social/behavioral), normally distributed scores in an unselected sample, and similar structure and measurement properties as those reported in other published studies. Findings are discussed in relation to existing literature and future directions for the validation of the Q-CHAT.

Maternal childhood adversity and child temperament: an association moderated by child 5-HTTLPR genotype

We examined transgenerational effects of maternal childhood adversity on child temperament and a functional promoter polymorphism, 5-HTTLPR, in the serotonin-transporter gene (SLC6A4) as potential moderators of such maternal influences in 154 mother-child dyads, recruited into a longitudinal birth cohort study. We examined the interactive effects of maternal childhood experience using an integrated measure derived from Childhood Trauma Questionnaire (CTQ) and Parental Bonding Index (PBI). Triallelic genotyping of 5-HTTLPR was performed. A measure of 'negative emotionality/behavioural dysregulation' was derived from the Early Childhood Behaviour Questionnaire at 18 and 36 months. Negative emotionality/behavioural dysregulation was highly stable between 18 and 36 months and predicted psychosocial problems at 60 months. After controlling multiple demographics as well as both previous and concurrent maternal depression there was a significant interaction effect of maternal childhood adversity and offspring 5-HTTLPR genotype on child negative emotionality/behavioural dysregulation (β = 1.03, t(11,115) = 2.71, P < .01). The results suggest a transgenerational effect of maternal developmental history on emotional function in the offspring, describing a pathway that likely contributes to the familial transmission of vulnerability for psychopathology.

Prenatal maternal depression alters amygdala functional connectivity in 6-month-old infants

Prenatal maternal depression is associated with alterations in the neonatal amygdala microstructure, shedding light on the timing for the influence of prenatal maternal depression on the brain structure of the offspring. This study aimed to examine the association between prenatal maternal depressive symptomatology and infant amygdala functional connectivity and to thus establish the neural functional basis for the transgenerational transmission of vulnerability for affective disorders during prenatal development. Twenty-four infants were included in this study with both structural magnetic resonance imaging (MRI) and resting-state functional MRI (fMRI) at 6 months of age. Maternal depression was assessed at 26 weeks of gestation and 3 months after delivery using the Edinburgh Postnatal Depression Scale. Linear regression was used to identify the amygdala functional networks and to examine the associations between prenatal maternal depressive symptoms and amygdala functional connectivity. Our results showed that at 6 months of age, the amygdala is functionally connected to widespread brain regions, forming the emotional regulation, sensory and perceptual, and emotional memory networks. After controlling for postnatal maternal depressive symptoms, infants born to mothers with higher prenatal maternal depressive symptoms showed greater functional connectivity of the amygdala with the left temporal cortex and insula, as well as the bilateral anterior cingulate, medial orbitofrontal and ventromedial prefrontal cortices, which are largely consistent with patterns of connectivity observed in adolescents and adults with major depressive disorder. Our study provides novel evidence that prenatal maternal depressive symptomatology alters the amygdala's functional connectivity in early postnatal life, which reveals that the neuroimaging correlates of the familial transmission of phenotypes associated with maternal mood are apparent in infants at 6 months of age.

Maternal anxiety and infants' hippocampal development: timing matters

Exposure to maternal anxiety predicts offspring brain development. However, because children's brains are commonly assessed years after birth, the timing of such maternal influences in humans is unclear. This study aimed to examine the consequences of antenatal and postnatal exposure to maternal anxiety upon early infant development of the hippocampus, a key structure for stress regulation. A total of 175 neonates underwent magnetic resonance imaging (MRI) at birth and among them 35 had repeated scans at 6 months of age. Maternal anxiety was assessed using the State-Trait Anxiety Inventory (STAI) at week 26 of pregnancy and 3 months after delivery. Regression analyses showed that antenatal maternal anxiety did not influence bilateral hippocampal volume at birth. However, children of mothers reporting increased anxiety during pregnancy showed slower growth of both the left and right hippocampus over the first 6 months of life. This effect of antenatal maternal anxiety upon right hippocampal growth became statistically stronger when controlling for postnatal maternal anxiety. Furthermore, a strong positive association between postnatal maternal anxiety and right hippocampal growth was detected, whereas a strong negative association between postnatal maternal anxiety and the left hippocampal volume at 6 months of life was found. Hence, the postnatal growth of bilateral hippocampi shows distinct responses to postnatal maternal anxiety. The size of the left hippocampus during early development is likely to reflect the influence of the exposure to perinatal maternal anxiety, whereas right hippocampal growth is constrained by antenatal maternal anxiety, but enhanced in response to increased postnatal maternal anxiety.

Genetic variation in oxytocin rs2740210 and early adversity associated with postpartum depression and breastfeeding duration

Mothers vary in duration of breastfeeding. These individual differences are related to a variety of demographic and individual maternal factors including maternal hormones, mood and early experiences. However, little is known about the role of genetic factors. We studied single-nucleotide polymorphisms (SNPs) in the OXT peptide gene (rs2740210; rs4813627) and the OXT receptor gene (OXTR rs237885) in two samples of mothers from the Maternal adversity, Vulnerability and Neurodevelopment study (MAVAN), a multicenter (Hamilton and Montreal, Canada) study following mothers and their children from pregnancy until 7 years of age. Data from the Hamilton site was the primary sample (n = 201) and data from Montreal was the replication sample (n = 151). Breastfeeding duration, maternal mood (measured by the CES-D scale) and early life adversity (measured by the CTQ scale) were established during 12 months postpartum. In our primary sample, polymorphisms in OXT rs2740210, but not the other SNPs, interacted with early life adversity to predict variation in breastfeeding duration (overall F8,125  = 2.361, P = 0.021; interaction effect b = -8.12, t = -2.3, P = 0.023) and depression (overall F8,118  = 5.751, P ≤ 0.001; interaction effect b = 6.06, t = 3.13, P = 0.002). A moderated mediation model showed that higher levels of depression mediated the inverse relation of high levels of early life adversity to breastfeeding duration, but only in women possessing the CC genotype [effect a' = -3.3401, 95% confidence interval (CI) = -7.9466 to -0.0015] of the OXT SNP and not in women with the AA/AC genotype (a' = -1.2942, ns). The latter findings (moderated mediation model) were replicated in our Montreal sample (a' = -0.277, 95% CI = -0.7987 to -0.0348 for CC; a' = -0.1820, ns for AA/AC).

Dopamine receptors D1 and D2 are related to observed maternal behavior

The dopamine pathway and especially the dopamine receptors 1 and 2 (DRD1 and DRD2) are implicated in the regulation of mothering in rats. Evidence for this in humans is lacking. Here, we show that genetic variation in both DRD1 and DRD2 genes in a sample of 187 Caucasian mothers predicts variation in distinct maternal behaviors during a 30-min mother-infant interaction at 6 months postpartum. Two DRD1 single-nucleotide polymorphisms (SNPs rs265981 and rs686) significantly associated with maternal orienting away from the infant (P = 0.002 and P = 0.003, respectively), as did DRD1 haplotypes (P = 0.03). Two DRD2 SNPs (rs1799732 and rs6277) significantly associated with maternal infant-directed vocalizing (P = 0.001 and P = 0.04, respectively), as did DRD2 haplotypes (P = 0.01). We present evidence for heterosis in DRD1 where heterozygote mothers orient away from their infants significantly less than either homozygote group. Our findings provide important evidence that genetic variation in receptors critical for mothering in non-human species also affect human maternal behaviors. The findings also highlight the importance of exploring multiple dimensions of the complex human mothering phenotype.

Nature, nurture or nutrition? Impact of maternal nutrition on maternal care, offspring development and reproductive function

We have previously reported that offspring of mothers fed a high fat (HF) diet during pregnancy and lactation enter puberty early and are hyperleptinaemic, hyperinsulinaemic and obese as adults. Poor maternal care and bonding can also impact offspring development and disease risk.We therefore hypothesized that prenatal nutrition would affect maternal care and that an interaction may exist between a maternal HF diet and maternal care, subsequently impacting on offspring phenotype.Wistar rats were mated and randomized to control dams fed a control diet (CON) or dams fed a HF diet from conception until the end of lactation (HF). Maternal care was assessed by observing maternal licking and grooming of pups between postnatal day (P)3 and P8. Postweaning (P22), offspring were fed a control (–con) or HF (–hf) diet. From P27, pubertal onset was assessed. At ∼P105 oestrous cyclicity was investigated. Maternal HF diet reduced maternal care; HF-fed mothers licked and groomed pups less than CON dams.Maternal fat:lean ratio was higher in HF dams at weaning and was associated with higher maternal plasma leptin and insulin concentrations, but there was no effect of maternal care on fat:lean ratio or maternal hormone levels. Both female and male offspring of HF dams were lighter from birth to P11 than offspring of CON dams, but by P19, HF offspring were heavier than controls. Prepubertal retroperitoneal fat mass was greater in pups from HF-fed dams compared to CON and was associated with elevated circulating leptin concentrations in females only, but there was neither an effect of maternal care, nor an interaction between maternal diet and care on prepubertal fat mass. Pups from HF-fed dams went into puberty early and this effect was exacerbated by a postweaning HF diet.Maternal and postweaning HF diets independently altered oestrous cyclicity in females: female offspring of HF-fed mothers were more likely to have prolonged or persistent oestrus, whilst female offspring fed a HF diet postweaning were more likely to have irregular oestrous cycles and were more likely to have prolonged or persistent oestrus. These data indicate that maternal HF nutrition during pregnancy and lactation results in a maternal obese phenotype and has significant impact on maternal care during lactation. Maternal and postweaning nutritional signals, independent of maternal care, alter offspring body fat pre-puberty and female reproductive function in adulthood, which may be associated with advanced ovarian ageing and altered fertility.

Variation in maternal care influences ventromedial hypothalamus activation in the rat

Natural variation in maternal care in the rat is an important source of individual differences in the female neuroendocrine system and sexual behaviours. Thus, females reared by low licking and grooming (LG) mothers are sexually more receptive to males, showing higher lordosis ratings, and are more motivated to mate compared to female offspring of high LG mothers. In the present study, we investigated the effect of natural variations in maternal care on the ventrolateral part of the ventromedial hypothalamus (VMHvl) cell population and on the reproductive success of the female rat. Immunohistochemistry for phosphorylated oestrogen-receptor (pER) α and progesterone receptor (PR) were used to study the VMHvl of female offspring of high and low LG mothers at pro-oestrus and dioestrus. A second experiment investigated sexual behaviour and the effect of mating on c-Fos expression in the VMHvl of pro-oestrus and ovariectomised high and how female offspring. Lastly, we investigated the maternal effect on the establishment of the progestational state. A greater number of VMHvl pERα immunoreactive cells was found in the pro-oestrous female offspring of low LG mothers and PR was most abundant at pro-oestrus compared to dioestrus in both high and low LG females. Interestingly it is the less receptive high females that show the greater c-Fos expression in the VMH after mating in the pro-oestrous group. The difference in c-Fos expression after mating disappeared when the two groups were ovariectomised and received steroid replacement. Finally, low LG female offspring reached pseudopregnancy more often when receiving only seven intromissions at a 5-min interval compared to high LG females. Lower levels of maternal care may favour the reproductive success of low LG offspring by increasing pERα and oestrogen-dependent lordosis behaviour and lowering c-Fos after mating, resulting in inhibition of termination of oestrus.

Serotonin transporter allelic variation in mothers predicts maternal sensitivity, behavior and attitudes toward 6-month-old infants

Maternal behavior in the new mother is a multidimensional set of responses to infant cues that are influenced by the mother's early life experiences. In this study, we wanted to test if mothers' early life experiences and mothers' genotype have interactive effects on maternal behaviors and attitudes, something which has not been previously explored. In a sample of 204 mothers, we assessed maternal genotype at the serotonin transporter-linked polymorphic region (5-HTTLPR) and an adjacent upstream polymorphism (rs25531), together giving rise to three alleles: short (S), L(G) and L(A). Controlling for maternal age and parity, we showed that this genotype can predict differences in maternal sensitivity at 6 months postpartum: mothers with an S (or the functionally similar L(G)) allele were more sensitive than mothers who lacked the allele during a 30-min recorded mother-infant interaction (F (4,140) = 3.43; P = 0.01). Furthermore, we found highly significant gene-environment interactions in association with maternal behavior, such that mothers with no S or L(G) alleles oriented away more frequently from their babies if they also reported more negative early care quality (F (5,138) = 3.28; P = 0.008). Finally, we found significant gene-environment associations with maternal attitudes; mothers with the S allele and with greater early care quality scored higher on ratings of their perceived attachment to their baby (F (5,125) = 3.27; P = 0.008). The regression results show significant interactions between the reported quality of care mothers received from their own parents and genotype on both their frequency of orienting away from the infant during the interaction (F(5, 138) = 3.28; P = 0.008, Fig. 1a) and their perceived attachment feelings to the infant (F(5, 125) = 3.27; P = 0.008, Fig. 1b); however the direction of the effects for these two outcome measures were different from one another. With increasing care quality, mothers with the L(A)L(A) genotype (no S or L(G) allele) oriented away less frequently, while S or L(G) allele carriers showed no significant change. In contrast, with increasing early care quality. L(A)L(A) (no S or L(G) allele) mothers scored lower on perceived attachment to their infants, whereas S or L(G) allele carrying mothers scored higher. [corrected].

Epigenetic programming of phenotypic variations in reproductive strategies in the rat through maternal care

Studies across multiple organisms reveal considerable phenotypic variation in reproductive tactics. In some species, this variation is associated with maternal effects in which variation in maternal investment results in stable individual differences in reproductive function. Recent studies with the rat suggest that maternal effects can alter the function of neuroendocrine systems associated with female sexual behaviour as well as maternal behaviour. These maternal effects appear to be mediated by epigenetic modifications at the promoter for oestrogen receptor alpha (ERalpha) and subsequent effects on gene expression. The tissue-specific nature of such effects may underlie the co-ordinated variation in multiple forms of reproductive function, resulting in distinct reproductive strategies.

Central and feedback regulation of hypothalamic corticotropin-releasing factor secretion

Physical, emotional and metabolic stressors activate the hypothalamo-pituitary-adrenal (HPA) axis via multiple neural pathways. Final hypothalamic coding of stressor-induced adrenocorticotropic hormone (ACTH) secretion is mediated by differential release of ACTH secretagogues. These include, but may not be limited to, corticotropin-releasing factor (CRF), arginine vasopressin, oxytocin and, possibly, adrenaline. Among these substances, CRF serves as the predominant regulatory factor of this axis because its presence is obligatory for the action of intrinsically weaker secretagogues. Because neural input-encoding qualities of individual stressors utilize, in part, stimulus-specific pathways, the effectiveness of glucocorticoid negative feedback in modulating ongoing and subsequent activity of the HPA axis is dependent upon the type of stressor and the nature of the neural pathways mediating the initial activity. Studies suggest that responses to physical stressors (for example, haemorrhage) are resistant to classical intermediate feedback, whereas those to emotional/cognitive stressors (such as a novel environment) are strongly susceptible to feedback. Overall functional characteristics of the HPA axis in adult organisms are at least partially a result of neonatal experience. In the adult differences in hypothalamic CRF mRNA levels, median eminence peptide content and pituitary responsiveness to stressors can be correlated with aspects of neonatal experience.

Neurotensin receptor levels as a function of brain aging and cognitive performance in the Morris water maze task in the rat

The present study evaluated whether neurotensin (NT) binding sites were altered in the aged rat brain and if these alterations were related to the cognitive status of the animal. Aged (24-25 months old) Long-Evans rats were behaviorally screened using the Morris water maze task and were classified as either aged, cognitively impaired (AI) or cognitively unimpaired (AU) based on their relative performances in the task compared to young control (Y) animals. Decreases in specific [125I]NT binding were observed in the hippocampal formation, namely the dentate gyrus (DG), as well as in the septum and hypothalamus. Both aged groups also showed significant reductions in specific [125I]NT binding levels compared to the Y animals in the hippocampal CA3 sub-field, with the AI animals exhibiting the lowest levels. In the Substantia Nigra Zona Compacta (SNc) and the ventral tegmental area (VTA), specific [125I]NT binding was decreased as a function of age while binding in the paraventricular nucleus of the hypothalamus (PVNh) was decreased as a function of age and cognitive status. These alterations in the level of specific [125I] NT binding in the aged animals suggest decreases in NT receptor signaling as a function of age and potential involvement of NT-ergic systems in the etiology of age-related cognitive deficits.

Influence of naturally occurring variations in maternal care on prepulse inhibition of acoustic startle and the medial prefrontal cortical dopamine response to stress in adult rats

In rats, naturally occurring variations in maternal care contribute to the development of individual differences in the behavioral and neuroendocrine responses to stress during adulthood. The dopamine (DA) projection to the medial prefrontal cortex (mPFC) plays an important role in mediating stress responsivity and is thought to be involved also in regulating sensorimotor gating. In the present study, we compared prepulse inhibition (PPI) of acoustic startle as well as the left and right mPFC DA stress responses in the adult offspring of high- and low-licking/grooming (LG) dams. Our data indicate that the offspring of low-LG animals are impaired on measures of PPI compared with high-LG animals. We also observed in low-LG animals a significant blunting of the mPFC DA stress responses that was lateralized to the right hemisphere, whereas in high-LG animals, the left and right mPFC DA stress responses were equally attenuated. Although mPFC levels of DA transporter did not differ between the two groups of animals, mPFC levels of catechol-O-methyl transferase immunoreactivity of low-LG animals were significantly lower than those of high-LG animals. These data provide evidence that variations in maternal care can lead to lasting changes in mPFC DA responsivity to stress and suggest the possibility that such changes in mesocorticolimbic DA function can also lead to deficits in sensorimotor gating.

Alpha1 adrenoreceptors mediate the stimulatory effects of oestrogen on stress-related hypothalamic-pituitary-adrenal activity in the female rat

Variation in challenge-induced adrenocorticotropin hormone (ACTH) release over the oestrous cycle occurs in response to fluctuations in circulating concentrations of oestrogen and progesterone. However, how these ovarian steroids interact to regulate the principal ACTH cosecretagogues, corticotropin-releasing hormone (CRH) and arginine vasopressin is not understood. Here, we measured median eminence CRH and vasopressin content in intact cycling female rats, and in ovariectomized (OVX) females steroid-replaced in a manner that approximates the relative release patterns of oestrogen and progesterone seen over the oestrous cycle. Intact cycling females showed significantly higher median eminence CRH and vasopressin concentrations during proestrous and oestrous compared to the diestrous phase. In OVX rats, a single 10 micro g injection of oestrogen failed to mimic this increase in median eminence CRH and vasopressin. However, this dose significantly elevated CRH and vasopressin content in OVX rats previously exposed to diestrous concentrations of oestrogen and progesterone. Moreover, oestrogen priming enhanced restraint-induced depletion of CRH and vasopressin from the median eminence, but only against a background of low oestrogen and progesterone replacement. Oestrogen-induced elevations in median eminence vasopressin (but not CRH) content were reduced by peripheral administration of the alpha1 adrenoreceptor antagonist prazosin. Finally, plasma ACTH concentrations following central injection of the alpha1 receptor agonist, phenylephrine, were significantly higher in rats during proestrous compared to diestrous. These results indicate that the stimulatory effect of oestrogen on both the expression and stress-induced release of ACTH cosecretagogues is exerted only against a background of low oestrogen and progesterone levels, and is mediated, in part, via the alpha1 adrenoreceptor.

Long-term effects of BIBN-99, a selective muscarinic M2 receptor antagonist, on improving spatial memory performance in aged cognitively impaired rats

Aged Long-Evans rats were screened for spatial memory deficits using the Morris water maze task. Rats found to have impaired performance on the task (aged-impaired, AI) were then treated with a selective muscarinic M2 receptor antagonist, 5,11-dihydro-8-chloro-11-[[4-[3-[(2,2-dimethyl-1-oxopentyl)ethylamino]propyl]-1-piperidinyl]acetyl]-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one (BIBN-99; 0.5 mg/kg, s.c.), for 3 successive days while receiving additional water maze training. BIBN-99 significantly improved performance in the task during the 3 days of drug treatment. Treatment was then ceased for the remainder of the study and rats were tested again in the water maze on days 10, 17, and 24. Compared to vehicle-treated rats, enhanced performance was observed in the AI rats that had previously been treated with BIBN-99. These results indicate that BIBN-99 enhances spatial learning in AI animals and that enhanced (or long-term) memory persists in the absence of the drug. In a second experiment, a 2-month delay was imposed in between the original water maze screening and the drug treatment regime. Again, BIBN-99 significantly improved performance in AI rats. This latter study suggests that reference memory does not decay, even in an AI animal that had displayed poor learning following original water maze screening. Together, these studies help provide further insight into possible mechanism(s) of reference memory and its potential clinical usefulness.

Partial reversal of the effect of maternal care on cognitive function through environmental enrichment

Maternal care influences hippocampal development in the rat. The offspring of mothers that exhibit increased levels of pup licking/grooming and arched-back nursing (High LG-ABN mothers) show increased hippocampal N-methyl-D-aspartate (NMDA) receptor binding and enhanced hippocampal-dependent spatial learning. In these studies we examined whether environmental enrichment from days 22-70 of life might reverse the effects of low maternal care. Environmental enrichment eliminated the differences between the offspring of High and Low LG-ABN mothers in both Morris water maze learning and object recognition. However, enrichment did not reverse the effect of maternal care on long-term potentiation in the dentate gyrus or on hippocampal NMDA receptor binding. In contrast, peripubertal enrichment did reverse the effects of maternal care on hippocampal alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor binding. These findings provide evidence for the reversal of the effects of reduced maternal investment in early life on cognitive function in adulthood. Such effects might involve compensatory changes associated with peripubertal enrichment.

Acute modulation of aged human memory by pharmacological manipulation of glucocorticoids

In a previous longitudinal study of basal cortisol levels and cognitive function in humans, we showed that elderly humans with 4- to 7-yr cumulative exposure to high levels of cortisol present memory impairments, compared with elderly humans with moderate cortisol levels over years. Here, we measured whether memory performance in two groups of elderly humans separated on the basis of their cortisol history over a 5-yr period could be modulated by a hormone-replacement protocol in which we inhibited cortisol secretion by the administration of metyrapone and then restored baseline cortisol levels by infusion of hydrocortisone. We showed that in elderly subjects with a 5-yr history of moderate cortisol levels (n = 8), metyrapone treatment significantly impaired memory performance, a deficit that was reversed following hydrocortisone replacement. In the elderly subjects with a 5-yr history of high cortisol levels and current memory deficits (n = 9), metyrapone treatment did not have any significant effect on memory performance, but hydrocortisone treatment significantly decreased delayed memory. These results suggest that memory function in elderly humans can be intensely modulated by pharmacological manipulation of glucocorticoids, although the direction of these effects depends on the cortisol history of each individual.

Naturally occurring differences in maternal care are associated with the expression of oxytocin and vasopressin (V1a) receptors: gender differences

Variations in maternal care have been associated with long-term changes in neurochemistry and behaviour in adult rats. Rats receiving high levels of licking and grooming as pups are less fearful and more maternal than rats receiving low levels of maternal licking and grooming. Central pathways for oxytocin and vasopressin have been implicated in the neurobiology of anxiety and social behaviours. We assessed whether variations in maternal care were associated with differences in oxytocin receptors (OTR) or vasopressin (V1a) receptors in the brains of adult offspring. In the central nucleus of the amygdala and bed nucleus of the stria terminalis, OTR binding was increased in adult females, but not adult males, that had received high levels of maternal licking and grooming as pups. Conversely, amygdala V1a receptor binding was increased in males, but not females, that had received high levels of maternal licking and grooming. These findings suggest that variations in maternal care may influence the expression of oxytocin and vasopressin receptors in a gender-specific manner.

Can poverty get under your skin? basal cortisol levels and cognitive function in children from low and high socioeconomic status

It is well known that individuals from more advantaged social classes enjoy better mental and physical health than do individuals within lower classes. Various mechanisms have been evoked to explain the association between socioeconomic status (SES) and health. One mechanism that has received particular attention in recent years is stress. It has been shown that individuals lower in SES report greater exposure to stressful life events and a greater impact of these events on their life than individuals higher in SES. In order to measure whether the development of the relationship between SES and mental health is sustained by exposure to high levels of glucocorticoids, we measured morning salivary cortisol levels as well as cognitive function (memory, attention, and language) in 307 children (from 6 to 16 years of age) from low versus high SES in the Montreal area in Canada. The results revealed that low SES children from 6 to 10 years old present significantly higher salivary cortisol levels when compared to children from high SES. This difference disappears at the time of school transition, and no SES differences are observed in salivary cortisol levels during high school. However, children from low and high SES do not differ with regard to memory or to attentional and linguistic functions. Also, mothers of low SES children reported higher feelings of depression and more unhealthy behaviors, while mothers of high SES children reported higher stress related to work or family transitions. Altogether, these results show that low SES in young children is related to increased cortisol secretion, although the impact of SES on cortisol secretion is absent after transition to high school. These data are interpreted within the context of the equalization process of class patterning. Four social explanatory factors are suggested to explain the disappearance of SES differences in basal cortisol levels after school transition, taking into account the influence of family environment on the child's secretion of stress hormones.

Early environmental regulation of hippocampal glucocorticoid receptor gene expression: characterization of intracellular mediators and potential genomic target sites

Environmental conditions in early life permanently alter the development of glucocorticoid receptor gene expression in the hippocampus and hypothalamic-pituitary-adrenal responses to acute or chronic stress. In part, these effects can involve an activation of ascending serotonergic pathways and subsequent changes in the expression of transcription factors that might drive glucocorticoid receptor expression in the hippocampus. This paper summarizes the evidence in favor of these pathways as well as recent studies describing regulatory targets on the promoter region of the rat hippocampal glucocorticoid receptor gene.

Development of adult ethanol preference and anxiety as a consequence of neonatal maternal separation in Long Evans rats and reversal with antidepressant treatment

RATIONALE

This study was based on the findings of a high comorbidity among anxiety and depression as well as with alcohol abuse.

OBJECTIVE

To evaluate first exposure alcohol preference in a rodent model of moderate neonatal maternal separation.

METHODS

Rat pups were exposed to either normal animal facility rearing (AFR) or 15 min (HMS15) or 180 min (HMS180) of maternal separation from postnatal days 2-14. The adult (>60 days) male Long Evans progeny was tested for pituitary-adrenal axis responsiveness to airpuff startle, anxiety-like behavior in the elevated plus maze, and alcohol preference using a two-bottle, free-choice test.

RESULTS

In response to home cage airpuff startle, HMS180 rats displayed an elevation in the integrated adrenocorticotropic hormone and corticosterone responses. In addition, HMS180 rats spent less time in the open arms and more time in the closed arms in the elevated plus maze. HMS180 rats drank significantly less of a water-sucrose solution and significantly more of an ethanol-sucrose solution than AFR or HMS15 rats. No rearing group differences were observed in total fluid intake. The integrated corticosterone response to airpuff startle was highly correlated with ethanol consumption and there was a negative correlation between percentage of time spent in the open arms of the elevated plus maze and ethanol consumption. Treatment with the selective serotonin reuptake inhibitor paroxetine for 21 days eliminated differences in the elevated plus maze and HPA axis responsiveness, and significantly reduced the amount of ethanol consumed by the HMS180 rats, without affecting these parameters in the HMS15 rats.

CONCLUSIONS

These observations suggest that this maternal separation paradigm is a good model to study the effects of early adverse experience on the development of alcohol preference and anxiety.

Like mother, like daughter: evidence for non-genomic transmission of parental behavior and stress responsivity

Considerable evidence demonstrates that the quality of the early environment influences patterns of development that, in turn, determine the health and productivity of the individual throughout their life span. However, the processes through which early life influences health are not clearly understood. Through the activation of the hypothalamo-pituitary-adrenal (HPA) axis and corticotropin-releasing hormone (CRH) pathways, prolonged or exaggerated responses to stress have profound effects on physiological and cognitive functions. Early maternal separation or handling of neonatal rats can program widespread and lifelong changes in various transmitter systems that regulate the HPA and CRH systems. Our studies show that a high level of maternal licking/grooming, and arched-back nursing correlates with reduced CRH mRNA expression and enhanced glucocorticoid negative feedback, and lower stress responses in the adult. This behavior is stably transmitted between generations and cross-fostering studies show that the offspring inherit the behavior from the nursing mother and not the biological mother. Such intergenerational transmission of maternal behavior is seen in rodents, primates and humans, and may underlie adaptive changes in the HPA axis. The neural basis of this inheritance pattern appears to reside in the central oxytocin system which determines features of maternal behavior. Through these various adaptive neural mechanisms the environmental demand on the mother is reflected in the quality of maternal care to her offspring. This, in turn, programs stress reactivity and maternal behavior patterns of the offspring. This not only determines certain health outcomes but also establishes the relationships between mother and offspring in the next generation. These findings suggest that for neurobiologists, the function of the family is an important level of analysis and the critical question is that of how environmental events regulate neural systems that mediate the expression of parental care.

Naturally occurring variations in maternal behavior in the rat are associated with differences in estrogen-inducible central oxytocin receptors

Naturally occurring variations in maternal licking/grooming influence neural development and are transmitted from mother to female offspring. We found that the induction of maternal behavior in virgin females through constant exposure to pups (pup sensitization) was significantly shorter in the offspring of High compared with Low licking/grooming mothers, suggesting differences in maternal responsivity. In randomly selected females screened for individual differences in maternal responsivity and subsequently mated, there was a significant and negative correlation (r = -0.73) between the latency to exhibit maternal behavior in the pup sensitization paradigm and the frequency of pup licking/grooming during lactation. Females that were more maternally responsive to pups and that showed increased levels of pup licking/grooming also showed significantly higher oxytocin receptor levels in the medial preoptic area, the lateral septum, the central nucleus (n.) of the amygdala, the paraventricular n. of the hypothalamus, and the bed n. of the stria terminalis. Intracerebroventricular administration of an oxytocin receptor antagonist to mothers on postpartum day 3 completely eliminated the differences in pup licking/grooming, suggesting that differences in oxytocin receptor levels are functionally related to maternal behavior. Finally, estrogen treatment of virgin females significantly increased oxytocin receptor binding in the medial preoptic area and lateral septum of female offspring of High, but not Low, licking/grooming mothers. These findings suggest that maternal licking/grooming influences the development of estrogen sensitivity in brain regions that regulate maternal behavior, providing a potential mechanism for the intergenerational transmission of individual differences in maternal behavior.

Summary of a National Institute of Mental Health workshop: developing animal models of anxiety disorders

RATIONALE

There exists a wide range of animal models and measures designed to assess anxiety or fearfulness. However, the relationship between these models and clinical anxiety symptoms and syndromes is unclear. The National Institute of Mental Health convened a workshop to discuss the relationship between existing behavioral models of anxiety and the clinical profile of anxiety disorders. A second goal of this workshop was to outline various approaches towards modeling components of anxiety disorders.

OBJECTIVES

To briefly describe epidemiological and behavioral manifestations of clinical anxiety syndromes and how they relate to commonly employed animal models of anxiety. To describe approaches and considerations for developing, improving, and adapting anxiety models to better understand the neurobiology of anxiety.

METHODS

Clinicians, psychiatrists and clinical and basic neuroscientists presented data exemplifying different approaches towards understanding anxiety and the role of animal models. Panel members outlined what they considered to be critical issues in developing and employing animal models of anxiety.

RESULTS

This review summarizes the discussions and conclusions of the workshop including recommendations for improving upon existing models and strategies for developing novel models.

CONCLUSIONS

The probability of developing comprehensive animal models that accurately reflect the relative influences of factors contributing to anxiety disorder syndromes is quite low. However, ample opportunity remains to better define and extend existing models and behavioral measures related to specific processes that may be disrupted in anxiety disorders and to develop new models that consider the impact of combined factors in determining anxious behaviors.

Maternal care, gene expression, and the transmission of individual differences in stress reactivity across generations

Naturally occurring variations in maternal care alter the expression of genes that regulate behavioral and endocrine responses to stress, as well as hippocampal synaptic development. These effects form the basis for the development of stable, individual differences in stress reactivity and certain forms of cognition. Maternal care also influences the maternal behavior of female offspring, an effect that appears to be related to oxytocin receptor gene expression, and which forms the basis for the intergenerational transmission of individual differences in stress reactivity. Patterns of maternal care that increase stress reactivity in offspring are enhanced by stressors imposed on the mother. These findings provide evidence for the importance of parental care as a mediator of the effects of environmental adversity on neural development.

Maternal care, gene expression, and the transmission of individual differences in stress reactivity across generations

Naturally occurring variations in maternal care alter the expression of genes that regulate behavioral and endocrine responses to stress, as well as hippocampal synaptic development. These effects form the basis for the development of stable, individual differences in stress reactivity and certain forms of cognition. Maternal care also influences the maternal behavior of female offspring, an effect that appears to be related to oxytocin receptor gene expression, and which forms the basis for the intergenerational transmission of individual differences in stress reactivity. Patterns of maternal care that increase stress reactivity in offspring are enhanced by stressors imposed on the mother. These findings provide evidence for the importance of parental care as a mediator of the effects of environmental adversity on neural development.

Nature, nurture, and the disunity of knowledge

The Human Genome Project and the tools of modern molecular biology bring enormous promise for the understanding of human biology. Juxtaposed, however, is a conceptual stagnation reflected in the continued nature/nurture debate. More sophisticated models reflecting the inevitable interdependence of gene and environment are essential if we are to realize the potential offered by today's technological advances.

Variations in maternal care in infancy regulate the development of stress reactivity

Naturally occurring variations in maternal care in early postnatal life are associated with the development of individual differences in behavioral and hypothalamic-pituitary-adrenal responses to stress in the rat. These effects appear to be mediated by the influence of maternal licking/grooming on the development of central systems that serve to activate (corticotropin-releasing factor) or inhibit (gamma-aminobutyric acid) the expression of behavioral and endocrine responses to stress through effects on forebrain noradrenergic systems. Importantly, individual differences in maternal care are transmitted from mother to daughter, providing a mechanism for the behavioral transmission of individual differences in stress reactivity across generations.

Variations in maternal behaviour are associated with differences in oxytocin receptor levels in the rat

Female Long-Evans rats exhibit stable individual differences in maternal behaviours such as pup licking/grooming and arched-back nursing posture (LG-ABN). These variations in maternal behaviour are accompanied by differences in lactation-induced increases in oxytocin receptor levels in brain regions known to mediate the expression of maternal care in this species (i.e. the bed nucleus of the stria terminalis, the medial preoptic area and the lateral septum). Oxytocin receptor levels in the central nucleus of the amygdala were significantly higher in high compared to low LG-ABN females regardless of reproductive status. These findings suggest that individual differences in maternal behaviour may be directly related to variations in oxytocin receptor expression.

Child's stress hormone levels correlate with mother's socioeconomic status and depressive state

BACKGROUND

Individuals with lower socioeconomic status report greater exposure to stressful life events and a greater impact of these events on their lives than individuals with higher socioeconomic status, and this relationship between socioeconomic status and health begins at the earliest stages of life. To extend on these results, we performed a psychoneuroendocrine study of 217 children and 139 mothers.

METHODS

Salivary cortisol levels and cognitive function were assessed in children, and a semistructured phone interview measuring symptoms of stress and depression was conducted with their mothers.

RESULTS

Children with low socioeconomic status present significantly higher salivary cortisol levels than children with high socioeconomic status, and this socioeconomic status effect emerges as early as age 6. We also report that a child's cortisol level is significantly correlated with his or her mother's extent of depressive symptomatology.

CONCLUSIONS

These results offer a neurobiological determinant to the well-known association between socioeconomic status and health that begins early in life.

Maternal care, hippocampal synaptogenesis and cognitive development in rats

We report that variations in maternal care in the rat promote hippocampal synaptogenesis and spatial learning and memory through systems known to mediate experience-dependent neural development. Thus, the offspring of mothers that show high levels of pup licking and grooming and arched-back nursing showed increased expression of NMDA receptor subunit and brain-derived neurotrophic factor (BDNF) mRNA, increased cholinergic innervation of the hippocampus and enhanced spatial learning and memory. A cross-fostering study provided evidence for a direct relationship between maternal behavior and hippocampal development, although not all neonates were equally sensitive to variations in maternal care.

Enhanced nucleus accumbens dopamine and plasma corticosterone stress responses in adult rats with neonatal excitotoxic lesions to the medial prefrontal cortex

The medial prefrontal cortex modulates the nucleus accumbens dopamine response to stress and has been implicated in feedback regulation of hypothalamic-pituitary-adrenal axis activation by stress. Here we report on the effects of bilateral neonatal (postnatal day 7) ibotenate-induced lesions to the medial prefrontal cortex on nucleus accumbens dopamine and neuroendocrine function in adult rats. Voltammetry was used to monitor the dopamine response to each of five, once-daily exposures to tail-pinch stress whereas alterations in neuroendocrine function were determined from the plasma corticosterone response to a single 20-min episode of restraint stress. Potential lesion-induced deficits in sensory-motor gating were assessed by measuring prepulse inhibition of the acoustic startle response before and after repeated stress. Our data show that each daily stress episode elicited larger and longer-lasting dopamine increases in prefrontal cortex-lesioned animals than in sham-lesioned controls. Furthermore, greater stress-induced elevations in plasma corticosterone were seen in lesioned animals than in their sham-lesioned counterparts. However, while repeated stress potentiated startle responses in animals of both groups, there was no effect of lesion on the amplitude or on prepulse inhibition of the startle response.Together, these findings indicate that neonatal prefrontal cortex damage can lead to changes in mesolimbic dopamine and neuroendocrine function during adulthood. They also add to a growing body of experimental and clinical evidence implicating abnormal prefrontal cortex neuronal development in the pathophysiology of schizophrenia and other disorders linked to central dopamine dysfunction.

Postnatal handling increases the expression of cAMP-inducible transcription factors in the rat hippocampus: the effects of thyroid hormones and serotonin

Postnatal handling increases glucocorticoid receptor expression in the rat hippocampus, thus altering the regulation of hypothalamic synthesis of corticotropin-releasing hormone and the hypothalamic-pituitary-adrenal response to stress. The effect on glucocorticoid receptor gene expression represents one mechanism by which the early environment can exert a long-term effect on neural development. The handling effect on hippocampal glucocorticoid receptor expression is dependent on peripheral thyroid hormone release and the activation of ascending serotonergic pathways. In primary hippocampal cell cultures, serotonin (5-HT) increases glucocorticoid receptor expression, and this effect appears to be mediated by increased cAMP levels. In the current studies we examined the in vivo effects of handling on hippocampal cAMP-protein kinase A (PKA) activity. In 7-d-old rat pups, we found that (1) postnatal handling increased adenylyl cyclase activity and hippocampal cAMP levels, (2) the effect of handling on cAMP levels was completely blocked by treatment with either propylthiouracil (PTU), a thyroid hormone synthesis inhibitor, or the 5-HT receptor antagonist, ketanserin, and (3) handling also increased hippocampal PKA activity. We then examined the effects of handling on cAMP-inducible transcription factors. Handling rapidly increased levels of the mRNAs for nerve growth factor-inducible factor A (NGFI-A) (zif268, krox24) and activator protein-2 (AP-2) as well as for NGFI-A and AP-2 immunoreactivity throughout the hippocampus. Finally, we found that the effects of handling on NGFI-A and AP-2 expression were significantly reduced by concurrent treatment with either PTU or ketanserin, effects that paralleled those on cAMP formation. NGFI-A and AP-2 have been implicated in the regulation of glucocorticoid receptor expression during development. Thus, these findings suggest that postnatal handling might alter glucocorticoid receptor gene expression via cAMP-PKA pathways involving the activation of NGFI-A and AP-2.

5'-heterogeneity of glucocorticoid receptor messenger RNA is tissue specific: differential regulation of variant transcripts by early-life events

Glucocorticoid receptor (GR) gene expression is regulated in a complex tissue-specific manner, notably by early-life environmental events that program tissue GR levels. We have identified and characterized several new rat GR mRNAs. All encode a common protein, but differ in their 5'-leader sequences as a consequence of alternate splicing of, potentially, 11 different exon 1 sequences. Most are located in a 3-kb CpG island, upstream of exon 2, that exhibits substantial promoter activity in transfected cells. Ribonuclease (RNase) protection analysis demonstrated significant levels of six alternate exons 1 in vivo in rat, with differences between liver, hippocampus, and thymus reflecting tissue-specific differences in promoter activity. Two of the alternate exons 1 (exons 1(6) and 1(10)) were expressed in all tissues examined, together present in 77-87% of total GR mRNA. The remaining GR transcripts contained tissue-specific alternate first exons. Importantly, tissue-specific first exon usage was altered by perinatal environmental manipulations. Postnatal handling, which permanently increases GR in the hippocampus, causing attenuation of stress responses, selectively elevated GR mRNA containing the hippocampus-specific exon 1(7). Prenatal glucocorticoid exposure, which increases hepatic GR expression and produces adult hyperglycemia, decreased the proportion of hepatic GR mRNA containing the predominant exon 1(10), suggesting an increase in a minor exon 1 variant. Such tissue specificity of promoter usage allows differential GR regulation and programming.

Increased cortisol levels and impaired cognition in human aging: implication for depression and dementia in later life

Perhaps the most prominent feature of human aging is the variability in decline of intellectual processes. Although many research avenues have been used to study the origin of such an increased variability with aging, new studies show that some biological factors may be associated with normal and pathological cognitive aging. One biological parameter that came under scrutiny in the past few years is the hypothalamic-pituitary-adrenal (HPA) axis, an endocrine closed-loop system controlling the secretion of stress hormones (glucocorticoids). In this review, we summarize data obtained in both animals and humans suggesting that cumulative exposure to high levels of glucocorticoids can be particularly detrimental for the aged hippocampus, a brain structure involved in learning and memory in both animals and humans. We then analyze the implication of these data for the study of dementia and depression in later life, two disorders characterized by increased glucocorticoid secretion in a significant proportion of patients. Finally, we suggest various factors that could explain the development of glucocorticoid hypersecretion in later life.

Neonatal handling permanently alters hypothalamic-pituitary- adrenal axis function, behaviour, and body weight in boars

Neonatal handling permanently alters hypothalamic- pituitary-adrenal axis (HPA) function in rats. In the rat, this treatment increases hippocampal glucocorticoid receptors (GR) and dampens plasma ACTH and corticosterone responses to stressors. The objectives of this study were to determine whether neonatal handling of pigs would effect permanent changes in plasma corticosteroid binding capacity (CBG), basal or stressor-induced plasma cortisol and ACTH concentrations, brain or pituitary GR levels, dexamethasone suppression of plasma cortisol and ACTH concentrations, behaviour in an open field-test pen, and body weights. Twelve litters of pigs were randomly assigned to either neonatal handling or no disturbance. Handled litters were removed from the farrowing crate for 10 min per day for the first 14 days of life. Male pigs were kept for the study and the boars were weighed monthly. At 7 months of age, boars were tested for locomotory behaviour in an open field-test pen. The boars were implanted with indwelling ear-vein catheters and blood samples were obtained basally, during and after application of a nose snare, and after 0.04 mg/kg dexamethasone. Boars were killed and blood samples were obtained and the brain and pituitary glands collected. Handled boars had greater (P<0.05) plasma CBG binding and lower basal total (P<0.05) and calculated free (P<0.03) plasma cortisol concentrations. No significant differences between treatments were found in plasma ACTH or cortisol responses to a nose-snare stressor; however, when killed, handled boars had greater (P<0.02) plasma ACTH concentrations. Handled and non-handled boars did not differ in plasma ACTH or cortisol responses to dexamethasone. There was no treatment effect on GR expression in the pituitary gland, frontal cortex, hippocampus, or hypothalamus. Behaviourally, the handled boars had higher (P<0.03) locomotor scores over inner squares and a lower (P<0.05) ratio of outer:inner squares entered in open field-tests. During the first 7 months of life, body weights were lower (P<0.004) for handled boars. In conclusion, neonatal handling permanently altered HPA function in pigs, but in a manner dissimilar to that found in the rat. These changes induced in the pig were not beneficial for commercial production with respect to body weight.

The effects of early rearing environment on the development of GABAA and central benzodiazepine receptor levels and novelty-induced fearfulness in the rat

We compared the effects of handling or maternal separation from the day following birth until postnatal day 14 on behavioral responses to novelty and on GABAA and central benzodiazepine (CBZ) receptor levels in the rat. As adults, handled animals showed reduced startle responsivity, increased exploration in a novel open field, and decreased novelty-induced suppression of feeding relative to the handled (H) and/or maternal separation (MS) groups. As compared with handled animals, both nonhandled (NH) and MS animals displayed: (1) reduced GABAA receptor levels in the locus coeruleus (LC) and the n. tractus solitarius (NTS); (2) reduced CBZ receptor sites in the central and lateral n. of the amygdala, the frontal cortex, and in the LC and NTS; and (3) reduced levels of the mRNA for the gamma 2 subunit of the GABAA receptor complex, which confers high affinity BZ binding, in the amygdaloid nuclei as well as in the LC and NTS. Both the amygdala and the ascending noradrenergic systems have been considered as critical sites for the anxiolytic effects of benzodiazepines. These data suggest that early life events influence the development of the GABAA receptor system, thus altering the expression of fearfulness in adulthood.

Influence of neonatal rearing conditions on stress-induced adrenocorticotropin responses and norepinepherine release in the hypothalamic paraventricular nucleus

Postnatal rearing conditions influence the development of hypothalamic-pituitary-adrenal (HPA) responses to stress in the rat. Thus, postnatal handling dampens HPA responsivity to stress, while prolonged periods of maternal separation have the opposite effect. HPA responses to stress are initiated by the release of corticotropin-releasing factor and/or arginine vasopressin from the neurones of the paraventricular nucleus of the hypothalamus (PVNh). A major source of input to the PVNh arises from brainstem noradrenergic neurones with signalling occurring via alpha1 adrenoreceptors. We examined the noradrenergic response to stress in the PVNh in adult animals exposed to daily periods of handling or maternal separation over the first 2 weeks of life using microdialysis in conscious animals. Maternal separation increased, while handling greatly decreased and norepinepherine responses to restraint stress in the PVNh as compared to non-handled controls; the same pattern was observed for plasma adrenocorticotropic hormone (ACTH) responses to stress. Rearing condition did not affect either alpha1 or alpha2 receptor levels in the PVNh. However, alpha2 receptor binding levels in the noradrenergic cell body regions of the locus coeruleus and the n. tractus solitarius were significantly increased in handled animals. These alpha2 receptors are principally located on noradrenergic neurones (i.e. autoreceptors) and inhibit noradrenaline release at terminal sites. The effects on alpha2 receptor levels could serve as a mechanism for the differences in stress-induced noradrenaline levels in the PVNh and in HPA activity among handled vs non-handled and maternal separation animals. Thus, early life events may serve to influence the differentiation of noradrenergic neurones and thus alter HPA responses stress in adulthood.

Nongenomic transmission across generations of maternal behavior and stress responses in the rat

In the rat, variations in maternal care appear to influence the development of behavioral and endocrine responses to stress in the offspring. The results of cross-fostering studies reported here provide evidence for (i) a causal relationship between maternal behavior and stress reactivity in the offspring and (ii) the transmission of such individual differences in maternal behavior from one generation of females to the next. Moreover, an environmental manipulation imposed during early development that alters maternal behavior can then affect the pattern of transmission in subsequent generations. Taken together, these findings indicate that variations in maternal care can serve as the basis for a nongenomic behavioral transmission of individual differences in stress reactivity across generations.