Complex Housing, but Not Maternal Deprivation Affects Motivation to Liberate a Trapped Cage-Mate in an Operant Rat Task.

Early life environment influences the development of various aspects of social behavior, particularly during sensitive developmental periods. We studied how challenges in the early postnatal period or (early) adolescence affect pro-social behavior. To this end, we designed a lever-operated liberation task, to be able to measure motivation to liberate a trapped conspecific (by progressively increasing required lever pressing for door-opening). Liberation of the trapped rat resulted either in social contact or in liberation into a separate compartment. Additionally, a condition was tested in which both rats could freely move in two separate compartments and lever pressing resulted in social contact. When partners were not trapped, rats were more motivated to press the lever for opening the door than in either of the trapped configurations. Contrary to our expectations, the trapped configuration resulted in a reduced motivation to act. Early postnatal stress (24 h maternal deprivation on postnatal day 3) did not affect behavior in the liberation task. However, rearing rats from early adolescence onwards in complex housing conditions (Marlau cages) reduced the motivation to door opening, both in the trapped and freely moving conditions, while the motivation for a sucrose reward was not affected.

The relevance of a rodent cohort in the Consortium on Individual Development.

One of the features of the Consortium on Individual Development is the existence of a rodent cohort, in parallel with the human cohorts. Here we give an overview of the current status. We first elaborate on the choice of rat and mouse models mimicking early life adverse or beneficial conditions during development. We performed a systematic literature search on early life adversity and adult social behavior to address the status quo. Next, we describe the behavioral tasks we used and designed to examine behavioral control and social competence in rodents. The results so far indicate that manipulation of the environment in the first postnatal week only subtly affects social behavior. Stronger effects were seen in the model that targeted early adolescence; once adult, these rats are characterized by increased attention, a higher degree of impulsiveness and reduced social interest in peers. Many experiments in our rodent models with tightly controlled conditions were inspired by findings in human cohorts, and now allow in-depth mechanistic investigations. Vice versa, some of the findings in rodents are currently followed up by dedicated investigations in the human cohorts. This exemplifies the added value of animal investigations in a consortium encompassing primarily human developmental cohorts.

Pro-social preference in an automated operant two-choice reward task under different housing conditions: Exploratory studies on pro-social decision making.

In this study, we aimed to develop a behavioral task that measures pro-social decision making in rats. A fully automated, operant pro-social two-choice task is introduced that quantifies pro-social preferences for a mutual food reward in a set-up with tightly controlled task contingencies. Pairs of same-sex adult Wistar rats were placed in an operant chamber divided into two compartments (one rat per compartment), separated by a transparent barrier with holes that allowed the rats to see, hear, smell, but not touch each other. Test rats could earn a sucrose pellet either for themselves (own reward) or for themselves and the partner (both reward) by means of lever pressing. On average, male rats showed a 60 % preference for the lever that yielded a food reward for both themselves and their partner. In contrast, females did not show lever preference, regardless of the estrous cycle phase. Next, the impact of juvenile environmental factors on male rat social decision making was studied. Males were group-housed from postnatal day 26 onwards in complex housing Marlau™ cages that provided social and physical enrichment and stimulation in the form of novelty. Complex housed males did not show a preference for the pro-social lever.

Maternal care of heterozygous dopamine receptor D4 knockout mice: Differential susceptibility to early-life rearing conditions.

The differential susceptibility hypothesis proposes that individuals who are more susceptible to the negative effects of adverse rearing conditions may also benefit more from enriched environments. Evidence derived from human experiments suggests the lower efficacy dopamine receptor D4 (DRD4) 7-repeat as a main factor in exhibiting these for better and for worse characteristics. However, human studies lack the genetic and environmental control offered by animal experiments, complicating assessment of causal relations. To study differential susceptibility in an animal model, we exposed Drd4+/- mice and control litter mates to a limited nesting/bedding (LN), standard nesting (SN) or communal nesting (CN) rearing environment from postnatal day (P) 2-14. Puberty onset was examined from P24 to P36 and adult females were assessed on maternal care towards their own offspring. In both males and females, LN reared mice showed a delay in puberty onset that was partly mediated by a reduction in body weight at weaning, irrespective of Drd4 genotype. During adulthood, LN reared females exhibited characteristics of poor maternal care, whereas dams reared in CN environments showed lower rates of unpredictability towards their own offspring. Differential susceptibility was observed only for licking/grooming levels of female offspring towards their litter; LN reared Drd4+/- mice exhibited the lowest and CN reared Drd4+/- mice the highest levels of licking/grooming. These results indicate that both genetic and early-environmental factors play an important role in shaping maternal care of the offspring for better and for worse.

The effects of different rearing conditions on sexual maturation and maternal care in heterozygous mineralocorticoid receptor knockout mice.

Sexual and social development is affected by a complex interplay between genetic makeup and the early-life rearing environment. While many rodent studies focused primarily on the detrimental effects of early-life stress, human literature suggests that genetic susceptibility may not be restricted to negative environments; it may also enhance the beneficial effects of positive rearing conditions. To examine this interaction in a controlled setting, heterozygous mineralocorticoid receptor knockout (MR+/-) mice and control litter mates were exposed to a limited nesting/bedding (LN, impoverished), standard nesting (SN, control) or communal nesting (CN, enriched) paradigm from postnatal day 2-9 (P2-P9). Offspring was monitored for puberty onset between P24-P36 and, in females, maternal care-giving (i.e. as F1) during adulthood, after which basal corticosterone was measured. Different home-cage environments resulted in profound differences in received maternal care and offspring body weight. In male offspring, LN resulted in delayed puberty onset that was mediated by body weight and unpredictability of maternal care received during early development. In female offspring, rearing condition did not significantly alter sexual maturation and had little effect on their own maternal care-giving behavior. Genotype did affect maternal care: female MR+/- offspring exhibited a less active nursing style and upregulated fragmentation during adulthood, irrespective of early life conditions. Basal corticosterone levels were highest in MR+/- mice with a background of LN. Overall, we found a gene-by-environment interaction with respect to basal corticosterone levels, but not for sexual maturation or maternal behavior.

Effects of Maternal Deprivation and Complex Housing on Rat Social Behavior in Adolescence and Adulthood.

Early life context and stressful experiences are known to increase the risk of developing psychiatric disorders later in life, including disorders with deficits in the social domain. Our study aimed to investigate the influence of early life environment on social behavior in a well-controlled animal model. To this end we tested the effects of maternal deprivation (MD) on rat social play behavior in adolescence and social interaction in adulthood. Additionally, we provided a stimulating environment during adolescence (complex housing) as a potential intervention to diminish the effects of early life stress. Male and female Wistar rats were deprived from their mother for 24 h on postnatal day 3 (PND 3) or were left undisturbed. Complex housing started 5 days after weaning and consisted of housing 10 same-sex conspecifics in large, two-floor MarlauTM cages until the end of the study. Social play behavior in adolescence was tested under different conditions (3 h vs. 24 h social isolation prior to testing). Maternally deprived males - but not females - showed a longer latency to play and a decreased total amount of social play behavior, after a 24 h isolation period. In adulthood, social discrimination was impaired in deprived male and female rats in the three-chamber social approach task. Complex housing did not moderate the effects of MD, but in itself induced a strong behavioral phenotype. Both complex housed males and females hardly displayed any play behavior after a 3 h isolation period. However, after 24 h of isolation, these animals showed shorter latencies to engage in social play behavior. Only complex housed males truly showed more social play behavior here, while showing less social interest in adulthood. We conclude that MD has mild negative effects on social behavior in adolescence and adulthood, which are not counteracted by complex housing. Complex housing induces a specific phenotype associated with rapid habituation; a lack of social play after short isolation periods, while increasing play behavior after a prolonged period of isolation in adolescence, and less social interest, paired with intact social discrimination in adulthood. In both early life settings, males seem to be more influenced by the early life environment compared to females.

The added value of rodent models in studying parental influence on offspring development: opportunities, limitations and future perspectives.

Over the past decades, the influence of parental care on offspring development has been a topic of extensive research in both human and animal models. Rodent models offer several unique advantages over human studies, allowing for higher levels of environmental control, exploration of interventions, genetic control and examination of underlying neurobiological mechanisms in greater spatiotemporal detail. Although exploitation of these opportunities has led to increased understanding of the neurobiological mechanisms underlying susceptibility to the early-life environment, translation of results to human parenting and child development appears to be challenging. Attuning animal models to the human situation and application of novel structural and functional techniques is therefore of crucial importance to reduce the gap between rodent and human research.

Mifepristone Treatment during Early Adolescence Fails to Restore Maternal Deprivation-Induced Deficits in Behavioral Inhibition of Adult Male Rats.

Early life adversity has a profound impact on brain development and later life health. Animal models have provided insight how early life stress programs stress responsiveness and might contribute to the development of psychiatric disorders. In the present study, the long-term effects of maternal deprivation (MD) on behavioral inhibition and attention were examined in adult male Wistar rats. To this end animals were tested in the 5-choice serial reaction time task (5-choice SRTT). We also explored the potential of a 3-day treatment with the glucocorticoid receptor (GR) antagonist mifepristone during early adolescence to normalize putative behavioral effects of early life stress. Deprivation of the mother for 24 h on postnatal day (PND) 3 led to a modest but significant increase in premature responses in the 5-choice SRTT, but did not affect measures of attention. Body weight was lower in deprived animals from weaning until the start of testing. Early adolescent mifepristone treatment (PND 26-28) did not influence performance on the 5-choice SRTT and did not mitigate the deprivation-related impairment in behavioral inhibition. Our results indicate that MD leads to impaired behavioral inhibition, and that mifepristone treatment during early adolescence does not normalize the behavioral changes caused by early life stress.

Complex Living Conditions Impair Behavioral Inhibition but Improve Attention in Rats.

Rapid adaptation to changes, while maintaining a certain level of behavioral inhibition is an important feature in every day functioning. How environmental context and challenges in life can impact on the development of this quality is still unknown. In the present study, we examined the effect of a complex rearing environment during adolescence on attention and behavioral inhibition in adult male rats. We also tested whether these effects were affected by an adverse early life challenge, maternal deprivation (MD). We found that animals that were raised in large, two floor Marlau(TM) cages, together with 10 conspecifics, showed improved attention, but impaired behavioral inhibition in the 5-choice serial reaction time task. The early life challenge of 24 h MD on postnatal day 3 led to a decline in bodyweight during adolescence, but did not by itself influence responses in the 5-choice task in adulthood, nor did it moderate the effects of complex housing. Our data suggest that a complex rearing environment leads to a faster adaptation to changes in the environment, but at the cost of lower behavioral inhibition.

Effects of intranasal oxytocin administration on memory for infant cues: moderation by childhood emotional maltreatment.

Oxytocin has been implicated in parent-infant attachment and social recognition. With respect to emotion recognition memory, both memory-enhancing and impairing effects have been observed, suggesting an influence of individual factors. We assessed the effects of oxytocin on memory for infant cues, and whether these effects are moderated by self-reported childhood emotional maltreatment. Nulliparous females (N = 102) participated in a randomized, double-blind, between-subjects study with intranasal oxytocin or placebo administration. Participants' memory was tested using the Baby Social Reward Task, where participants were asked to select the happier infant from a pair of two infants based on the information that they received about the infants' mood in the previous phase. Participants reporting more childhood emotional maltreatment were less accurate in this task after inhaling oxytocin. Our findings add to a growing body of literature showing that the effects of intranasal oxytocin on memory and social behavior are moderated by adverse early life experiences.

Salivary oxytocin mediates the association between emotional maltreatment and responses to emotional infant faces.

Childhood emotional maltreatment has been associated with a higher risk for maltreating one's own offspring. In the current study, we explored a possible role of oxytocin in mediating the association between childhood emotional maltreatment and participants' interpretation of infant facial expressions. Oxytocin levels were measured in 102 female participants using saliva samples. They rated the mood of thirteen infants with happy, sad and neutral facial expressions. Emotional maltreatment indirectly influenced responses to happy infant faces by modulating oxytocin levels: higher self-reported emotional maltreatment was related to higher levels of salivary oxytocin which were in turn related to a more positive evaluation of happy infant expressions, but not to the evaluation of sad infant expressions. Oxytocin receptor polymorphism rs53576 did not moderate the relation between maltreatment experiences and salivary oxytocin levels. Early emotional maltreatment might indirectly affect emotional information processing by altering the oxytonergic system.

Deletion of the forebrain mineralocorticoid receptor impairs social discrimination and decision-making in male, but not in female mice.

Social interaction with unknown individuals requires fast processing of information to decide whether it is friend or foe. This process of discrimination and decision-making is stressful and triggers secretion of corticosterone activating mineralocorticoid receptor (MR) and glucocorticoid receptor (GR). The MR is involved in appraisal of novel experiences and risk assessment. Recently, we have demonstrated in a dual-solution memory task that MR plays a role in the early stage of information processing and decision-making. Here we examined social approach and social discrimination in male and female mice lacking MR from hippocampal-amygdala-prefrontal circuitry and controls. The social approach task allows the assessment of time spent with an unfamiliar mouse and the ability to discriminate between familiar and unfamiliar conspecifics. The male and female test mice were both more interested in the social than the non-social experience and deletion of their limbic MR increased the time spent with an unfamiliar mouse. Unlike controls, the male MR(CaMKCre) mice were not able to discriminate between an unfamiliar and the familiar mouse. However, the female MR mutant had retained the discriminative ability between unfamiliar and familiar mice. Administration of the MR antagonist RU28318 to male mice supported the role of the MR in the discrimination between an unfamiliar mouse and a non-social stimulus. No effect was found with a GR antagonist. Our findings suggest that MR is involved in sociability and social discrimination in a sex-specific manner through inhibitory control exerted putatively via limbic-hippocampal efferents. The ability to discriminate between familiar and unfamiliar conspecifics is of uttermost importance for territorial defense and depends on a role of MR in decision-making.

One doll fits all: validation of the Leiden Infant Simulator Sensitivity Assessment (LISSA).

Children vary hugely in how demanding of their caregivers they are. This creates differences in demands on parents during observation, making the comparison of sensitivity between parents difficult. It would therefore be of interest to create standard situations in which all caregivers are faced with the same level of demand. This study developed an ecologically valid but standardized setting using an infant simulator with interactive features, the Leiden Infant Simulator Sensitivity Assessment (LISSA). The infant simulator resembles a real infant in appearance and it produces crying sounds that are life-like. The simulator begins with fussing and progresses to more intense crying in case of no care or inappropriate care. It responds by being calm again if appropriate care is given. One hundred and eighty-one female participants took care of the infant simulator for two evenings and in a 30 min lab session with increasing competing demands. Sensitive parenting behavior during the lab session was coded with the Ainsworth Sensitivity Scale. Sensitivity ratings covered the whole range of the scale (1-9), and were stable across settings (free play, competing demands). Sensitivity was related to an increase of positive affect during caretaking, and insensitivity was related to intended harsh caregiving response during a computerized cry paradigm. Sensitivity was unrelated to social desirability and self-reported quality of care given to the infant simulator. We discuss the potentials of the infant simulator for research on sensitive parenting, for preventive interventions, and for clinical practices.

Mifepristone treatment affects the response to repeated amphetamine injections, but does not attenuate the expression of sensitization.

UNLABELLED: Rationale Glucocorticoid hormones facilitate sensitization to repeated administration of psychostimulants, an effect that is mediated by glucocorticoid receptors (GRs). It is still unclear, however, at which stage of psychomotor sensitization are stress and GR-mediated effects involved. OBJECTIVES: In the present study, we have tested the hypothesis that GR-mediated effects during the phase of repeated amphetamine injections play a crucial role in the long-term expression of sensitization. For this purpose, we used DBA/2 mice, an inbred strain commonly used for the study of stress effects on psychostimulant sensitization. METHODS: Animals were treated with the GR antagonist mifepristone (200 mg/kg) at 2.5 h before each daily injection of amphetamine (2.5 mg/kg) or saline in a 5-day protocol. The amphetamine or saline injections were given in the home or a novel context. This was followed by a 2.5-week withdrawal period, without any drug delivery. Following the withdrawal period, two low-dose amphetamine challenges (1.25 mg/kg) were given subsequently, without additional mifepristone. RESULTS: The animals receiving amphetamine in the novel context showed a higher expression of sensitization at challenge as compared to those in the home condition. Mifepristone treatment influenced locomotor response to repeated amphetamine injections, but this effect during the initial phase did not affect the expression of sensitization after a withdrawal period. CONCLUSION: Our results indicate that GR-related processes during the initial phase of sensitization are involved in, but not crucial for, the development of long-term sensitization.

Elevated Salivary Levels of Oxytocin Persist More than 7 h after Intranasal Administration.

We addressed the question how long salivary oxytocin levels remain elevated after intranasal administration, and whether it makes a difference when 16 or 24 IU of oxytocin administration is used. Oxytocin levels were measured in saliva samples collected from 46 female participants right before intranasal administration (at 9:30 a.m.) of 16 IU (n = 18) or 24 IU (n = 10) of oxytocin, or a placebo (n = 18), and each hour after administration, for 7 h in total. Oxytocin levels did not differ among conditions before use of the nasal spray. Salivary oxytocin levels in the placebo group showed high stability across the day. After oxytocin administration oxytocin levels markedly increased, they peaked around 1 h after administration, and were still significantly elevated 7 h after administration. The amount of oxytocin (16 or 24 IU) did not make a difference for oxytocin levels. The increase of oxytocin levels for at least 7 h shows how effective intranasal administration of oxytocin is. Our findings may raise ethical questions about potentially persisting behavioral effects after participants have left the lab setting. More research into the long-term neurological and behavioral effects of sniffs of oxytocin is urgently needed.

Interplay of maternal care and genetic influences in programming adult hippocampal neurogenesis.

BACKGROUND: Adult hippocampal neurogenesis, which is involved in the physiopathology of hippocampal functions, is genetically determined and influenced by early life events. However, studies on the interaction of these determining forces are lacking. This prompted us to investigate whether adult hippocampal neurogenesis can be modulated by maternal care and whether this influence depends upon the genetic background of the individual. METHODS: We used a model of fostering that allows singling out the influence of the genetic make-up of the pups on the outcome of maternal behavior. Mice from two different inbred strains (C57BL/6J and DBA/2J) known to differ in their baseline neurogenesis as well as in their sensitivity to the influence of environmental experiences were raised by nonrelated mothers from the AKR/Ola (AKR) and C3H/He (C3H) strains exhibiting low- and high-pup-oriented behavior, respectively. Neurogenesis was then assessed in the dentate gyrus of the adult adopted C57BL/6J and DBA/2J mice. RESULTS: We show that both the number and the morphological features of newborn granule cells in the dentate gyrus are determined by the maternal environment to which mice were exposed as pups and that this sensitivity to maternal environment is observed only in genetically vulnerable subjects. CONCLUSIONS: Altogether, our data indicate interplay between early environment and the genetic envelop of an individual in determining adult hippocampal neurogenesis. Our experimental approach could thus contribute to the identification of factors determining the neurogenic potential of the adult hippocampus.

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

RATIONALE: Human epidemiology and animal studies have convincingly shown the long-lasting impact of early life experiences on the development of individual differences in stress responsiveness in later life. The interplay between genes and environment underlies this phenomenon. OBJECTIVES: We provide an overview of studies investigating the impact of early life experiences on the development of individual differences in neuroendocrine stress responsiveness in adulthood and address (1) impact of environment on later stress phenotypes, (2) role of genetic factors in modulating the outcome of environment, and (3) role of nonshared environmental experience in the outcome of gene × environment interplays. We present original findings where we investigated the influence of nonshared experiences in terms of individual differences in maternal care received, on the development of stress phenotype in later life in rats. RESULTS: Environmental influences in early life exert powerful effects on later stress phenotypes, but they do not always lead to expression of diseases. Heterogeneity in response is explained by the role of particular genetic factors in modulating the influence of environment. Nonshared experiences are important in the outcome of gene × environment interplays in humans. We show that nonshared experiences acquired through within-litter variation in maternal care in rats predict the stress phenotype of the offspring. CONCLUSION: The outcome of early experience is not deterministic and depends on several environmental and genetic factors interacting in an intricate manner to support stress adaptation. The degree of "match" and "mismatch" between early and later life environments predicts resilience and vulnerability to stress-related diseases, respectively.

Brain development under stress: hypotheses of glucocorticoid actions revisited.

One of the conundrums in today's stress research is why some individuals flourish and others perish under similar stressful conditions. It is recognized that this individual variability in adaptation to stress depends on the outcome of the interaction of genetic and cognitive/emotional inputs in which glucocorticoid hormones and receptors play a crucial role. Hence one approach towards understanding individual variation in stress coping is how glucocorticoid actions can change from protective to harmful. To address this question we focus on four hypotheses that are connected and not mutual exclusive. First, the classical Glucocorticoid Cascade Hypothesis, in which the inability to cope with chronic stress causes a vicious cycle of excess glucocorticoid and downregulation of glucocorticoid receptors (GR) in the hippocampus triggering a feed-forward cascade of degeneration and disease. Second, the Balance Hypothesis, which takes also the limbic mineralocorticoid receptors (MR) into account and proposes that an integral limbic MR:GR imbalance is causal to altered processing of information in circuits underlying fear, reward, social behaviour and resilience, dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and impairment of behavioural adaptation. The MR:GR balance is altered by gene variants of these receptor complexes and experience-related factors, which can induce lasting epigenetic changes in the expression of these receptors. A particular potent epigenetic stimulus is the maternal environment which is fundamental for the Maternal Mediation Hypothesis. The outcome of perinatal gene x environment interaction, and thus of MR:GR-mediated functions depends however, on the degree of 'matching' with environmental demands in later life. The Predictive Adaptation Hypothesis therefore presents a conceptual framework to examine the role of glucocorticoids in understanding individual phenotypic differences in stress-related behaviours over the lifespan.

Stress and addiction: glucocorticoid receptor in dopaminoceptive neurons facilitates cocaine seeking.

The glucocorticoid receptor is a ubiquitous transcription factor mediating adaptation to environmental challenges and stress. Selective Nr3c1 (the glucocorticoid receptor gene) ablation in mouse dopaminoceptive neurons expressing dopamine receptor 1a, but not in dopamine-releasing neurons, markedly decreased the motivation of mice to self-administer cocaine, dopamine cell firing and the control exerted by dopaminoceptive neurons on dopamine cell firing activity. In contrast, anxiety was unaffected, indicating that glucocorticoid receptors modify a number of behavioral disorders through different neuronal populations.

Maternal environment influences cocaine intake in adulthood in a genotype-dependent manner.

BACKGROUND: Accumulating epidemiological evidence points to the role of genetic background as a modulator of the capacity of adverse early experiences to give rise to mental illness. However, direct evidence of such gene-environment interaction in the context of substance abuse is scarce. In the present study we investigated whether the impact of early life experiences on cocaine intake in adulthood depends on genetic background. In addition, we studied other behavioral dimensions associated with drug abuse, i.e. anxiety- and depression-related behaviors. METHODOLOGY/PRINCIPAL FINDINGS: For this purpose, we manipulated the maternal environment of two inbred mouse strains, the C57BL/6J and DBA/2J by fostering them with non-related mothers, i.e. the C3H/HeN and AKR strains. These mother strains show respectively high and low pup-oriented behavior. As adults, C57BL/6J and DBA/2J were tested either for cocaine intravenous self-administration or in the elevated plus-maze and forced swim test (FST). We found that the impact of maternal environment on cocaine use and a depression-related behavior depends upon genotype, as cocaine self-administration and behavior in the FST were influenced by maternal environment in DBA/2J, but not in C57BL/6J mice. Anxiety was not influenced by maternal environment in either strain. CONCLUSIONS/SIGNIFICANCE: Our experimental approach could contribute to the identification of the psychobiological factors determining the susceptibility or the resilience of certain individuals to develop psychopathologies.