Effects of variation in postnatal maternal environment on maternal behaviour and fear and stress responses in rats

The Effect of Early Neurological Stimulation on Puppy Welfare in Commercial Breeding Kennels

Throughout their lives, dogs may experience various stressful events. Early neurological stimulation (ENS), which was shown to alter stress responses beneficially in some animals, has not been fully explored in dogs. Seventy-six small-breed puppies from one commercial breeding kennel were divided into three treatment groups: ENS, held, and control. Puppies in the ENS group received 30 s of handling exercises for 21 days after birth; puppies in the held group were simply held for the same amount of time. Puppies in the control group were managed as per normal breeder practices (i.e., routine husbandry and physical health checks). Physical health was assessed weekly, and puppies were generally healthy and clean. Behavioral responses to stranger approach and isolation tests were evaluated pre- and post-ground-transportation to a distributor. Puppies were more affiliative toward a stranger post-isolation than pre-isolation (p < 0.001), and post-transport than pre-transport (p < 0.001). At the distributor, puppies in the isolation test spent less time in exploratory locomotion (p < 0.001) and vocalized more than at the breeder’s kennel (p = 0.011). Treatment did not affect these results. Overall, the results suggest that the type of ENS used in this study may not provide the purported benefits to puppies’ stress responses in commercial breeding populations.

Neural Circuit Mechanisms That Underlie Parental Care

In mammals, parental care is essential for the survival of the young; therefore, it is vitally important to the propagation of the species. These behaviors, differing between the two sexes, are innate, stereotyped, and are also modified by an individual's reproductive experience. These characteristics suggest that neural mechanisms underlying parental behaviors are genetically hardwired, evolutionarily conserved as well as sexually differentiated and malleable to experiential changes. Classical lesion studies on neural control of parental behaviors, mostly done in rats, date back to the 1950s. Recent developments of new methods and tools in neuroscience, which allow precise targeting and activation/inhibition of specific populations of neurons and their projections to different brain structures, have afforded fresh opportunities to dissect and delineate the detailed neural circuit mechanisms that govern distinct components of parental behaviors in the genetically tractably organism, the laboratory mouse (Mus musculus). In this review, we summarize recent discoveries using modern neurobiological tools within the context of traditional lesion studies. In addition, we discuss interesting cross talk between neural circuits that govern parent care with those that regulate other innate behaviors such as feeding and mating.

Uncovering sources of maternal variability: Inherited and environmental contributions to maternal phenotype

Intergenerational patterns of parental behavior, especially maternal behavior, have been observed across mammalian species including humans, non-human primates, and rodents. These patterns are largely experience-dependent as opposed to genetically induced, with experiences in early-life serving an essential role in directing maternal behavior expressed later in life. Environmental conditions can also alter maternal behavior with consequences for offspring neurodevelopment and interactions with the next generation. Here, we describe effects of lineage during developmental environmental disruption using a limited bedding and nesting material manipulation during the first 2 weeks of life. Dams from three lineages were placed in environments containing either abundant nesting material or reduced nesting material. Environmental condition affected eight measures of maternal behavior and dam lineage affected 12 measures of maternal behavior during the first two postnatal weeks. Lineage, condition, and pup sex predicted pup body weight immediately following the manipulation, with lineage accounting for the largest portion of variance in body weight. Although from a limited sample, these data are the first to examine effects of lineage and environment simultaneously and suggest dam lineage may be a better predictor of maternal behavior than current environmental conditions with important implications for pup outcomes.

Bottlenose dolphin calves have multi-year elevations of plasma oxytocin compared to all other age classes

Providing for infants nutritionally via lactation is one of the hallmarks of mammalian reproduction, and infants without motivated mothers providing for them are unlikely to survive. Mothers must maintain regular contact with infants both spatially and temporally while utilising their environment to forage, avoid threats and find shelter. However, mothers can only do this and maximise their reproductive success with some degree of co-operation from infants, despite their developing physical and cognitive capabilities. The neuropeptide hormone oxytocin (OT) triggers proximity-seeking behaviour and acts in a positive feedback loop across mother-infant bonds, stimulating appropriate pro-social behaviour across the pair. However, data on infant OT levels is lacking, and it is unclear how important infants are in maintaining mother-infant associations. The bottlenose dolphin (Tursiops truncatus) is a mammalian species that is fully physically mobile at birth and has multi-year, but individually variable, lactation periods. We investigated OT concentrations in mother-infant pairs of wild individuals compared to other age and reproductive classes. An ELISA to detect OT in dolphin plasma was successfully validated with extracted plasma. We highlight a statistical method for testing for parallelism that could be applied to other ELISA validation studies. OT concentrations were consistently elevated in calves up to at least 4 years of age with lactating mothers (12.1 ± 0.9 pg/ml), while all mothers (4.5 ± 0.4 pg/ml) had OT concentrations comparable to non-lactating individuals (5.9 ± 0.5 pg/ml). Concentrations within infants were individually variable, and may reflect the strength of the bond with their mother. The OT system likely provides a physiological mechanism for motivating infants to perform behaviours that prevent long-term separation from their mothers during this crucial time in their life history. Elevated infant OT has also been linked to energetic and developmental advantages which may lead to greater survival rates. Environmental or anthropogenic disturbances to OT release can occur during bond formation or can disrupt the communication methods used to reinforce these bonds via OT elevation. Variation in OT expression in infants, and its behavioural and physiological consequences, may explain differences in reproductive success despite appropriate maternal behaviour expression.

Childhood Family Instability and Young Adult Health

American children live in a variety of family structures throughout their childhoods. Such instability in family arrangements is common and has important demonstrated implications for short-term child outcomes. However, it is not known whether family instability experienced in childhood has enduring health consequences across the life course. Using demographic, social, and biological data from the National Longitudinal Study of Adolescent to Adult Health, we investigate the family stress model, testing the relationship between parental family instability in childhood and four biological markers of health in young adulthood. This is the first study to examine whether the accumulation of family change in childhood leaves a lasting physiological residue. While family instability is associated with poorer short-term behavioral and socioeconomic outcomes as documented in previous research, we find no evidence of deleterious young adult health consequences. These findings are robust across different measures of physiological health risk and types of family transitions.

Transgenerational transmission of a stress-coping phenotype programmed by early-life stress in the Japanese quail

An interesting aspect of developmental programming is the existence of transgenerational effects that influence offspring characteristics and performance later in life. These transgenerational effects have been hypothesized to allow individuals to cope better with predictable environmental fluctuations and thus facilitate adaptation to changing environments. Here, we test for the first time how early-life stress drives developmental programming and transgenerational effects of maternal exposure to early-life stress on several phenotypic traits in their offspring in a functionally relevant context using a fully factorial design. We manipulated pre- and/or post-natal stress in both Japanese quail mothers and offspring and examined the consequences for several stress-related traits in the offspring generation. We show that pre-natal stress experienced by the mother did not simply affect offspring phenotype but resulted in the inheritance of the same stress-coping traits in the offspring across all phenotypic levels that we investigated, shaping neuroendocrine, physiological and behavioural traits. This may serve mothers to better prepare their offspring to cope with later environments where the same stressors are experienced.

Neonatal corticosterone administration in rodents as a tool to investigate the maternal programming of emotional and immune domains

Neonatal experiences exert persistent influences on individual development. These influences encompass numerous domains including emotion, cognition, reactivity to external stressors and immunity. The comprehensive nature of the neonatal programming of individual phenotype is reverberated in the large amount of experimental data collected by many authors in several scientific fields: biomedicine, evolutionary and molecular biology. These data support the view that variations in precocious environmental conditions may calibrate the individual phenotype at many different levels. Environmental influences have been traditionally addressed through experimental paradigms entailing the modification of the neonatal environment and the multifactorial (e.g. behaviour, endocrinology, cellular and molecular biology) analysis of the developing individual's phenotype. These protocols suggested that the role of the mother in mediating the offspring's phenotype is often associated with the short-term effects of environmental manipulations on dam's physiology. Specifically, environmental manipulations may induce fluctuations in maternal corticosteroids (corticosterone in rodents) which, in turn, are translated to the offspring through lactation. Herein, I propose that this mother-offspring transfer mechanism can be leveraged to devise experimental protocols based on the exogenous administration of corticosterone during lactation. To support this proposition, I refer to a series of studies in which these protocols have been adopted to investigate the neonatal programming of individual phenotype at the level of emotional and immune regulations. While these paradigms cannot replace traditional studies, I suggest that they can be considered a valid complement.

Moderate Childhood Stress Buffers Against Depressive Response to Proximal Stressors: A Multi-Wave Prospective Study of Early Adolescents

Although the majority of research in the field has focused on childhood stressors as a risk factor for psychopathology, a burgeoning body of literature has focused on the possible steeling effect of moderate types of stressful events. The current study investigated the effects of proximal life stressors on prospective changes in depressive symptoms, and whether a history of moderate childhood adversity would moderate this relationship in a multi-wave study of a diverse community sample of early adolescents (N = 163, 52 % female, 51 % Caucasian). Hierarchical linear modeling was run with four waves of data. Adolescents with greater moderately severe early life events evinced a blunted depressive symptom response to changes in proximal stressful events in the previous 9 months, compared to those with fewer early moderately severe experiences of adversity. These results held after controlling for between-subject factors such as race, gender, severe early life stress, and average stress over the four waves of data. Findings indicate that greater exposure to moderate childhood stressors may buffer against the negative effects of subsequent stressors, suggesting the importance of a nuanced developmental approach to studying the effects of early life stress.

Levels of maternal care in dogs affect adult offspring temperament

Dog puppies are born in a state of large neural immaturity; therefore, the nervous system is sensitive to environmental influences early in life. In primates and rodents, early experiences, such as maternal care, have been shown to have profound and lasting effects on the later behaviour and physiology of offspring. We hypothesised that this would also be the case for dogs with important implications for the breeding of working dogs. In the present study, variation in the mother-offspring interactions of German Shepherd dogs within the Swedish breeding program for military working dogs was studied by video recording 22 mothers with their litters during the first three weeks postpartum. The aim was to classify mothers with respect to their level of maternal care and to investigate the effect of this care on pup behaviour in a standardised temperament test carried out at approximately 18 months of age. The results show that females differed consistently in their level of maternal care, which significantly affected the adult behaviour of the offspring, mainly with respect to behaviours classified as Physical and Social Engagement, as well as Aggression. Taking maternal quality into account in breeding programs may therefore improve the process of selecting working dogs.

Peripheral and Central Mechanisms of Stress Resilience

Viable new treatments for depression and anxiety have been slow to emerge, likely owing to the complex and incompletely understood etiology of these disorders. A budding area of research with great therapeutic promise involves the study of resilience, the adaptive maintenance of normal physiology and behavior despite exposure to marked psychological stress. This phenomenon, documented in both humans and animal models, involves coordinated biological mechanisms in numerous bodily systems, both peripheral and central. In this review, we provide an overview of resilience mechanisms throughout the body, discussing current research in animal models investigating the roles of the neuroendocrine, immune, and central nervous systems in behavioral resilience to stress.

Developmental programming: cumulative effects of increased pre-hatching corticosterone levels and post-hatching unpredictable food availability on physiology and behaviour in adulthood

Prolonged exposure to stress during development can have long-term detrimental effects on health and wellbeing. However, the environmental matching hypothesis proposes that developmental stress programs physiology and behaviour in an adaptive way that can enhance fitness if early environments match those experienced later in life. Most research has focused on the harmful effects that stress during a single period in early life may exert in adulthood. In this study, we tested the potential additive and beneficial effects that stress experienced during both pre- and post-hatching development may have on adult physiology and behaviour. Japanese quail experienced different stress-related treatments across two developmental life stages: pre-hatching corticosterone (CORT) injection, post-hatching unpredictable food availability, both pre- and post-hatching treatments, or control. In adulthood, we determined quails' acute stress response, neophobia and novel environment exploration. The pre-hatching CORT treatment resulted in attenuated physiological responses to an acute stressor, increased activity levels and exploration in a novel environment. Post-hatching unpredictable food availability decreased adults' latency to feed. Furthermore, there were cumulative effects of these treatments across the two developmental stages: quail subjected to both pre- and post-hatching treatments were the most explorative and risk-taking of all treatment groups. Such responses to novel environments could enhance survival in unpredictable environments in later life. Our data also suggest that these behavioural responses may have been mediated by long-term physiological programming of the adrenocortical stress response, creating phenotypes that could exhibit fitness-enhancing behaviours in a changing environment.

Neonatal tryptophan depletion and corticosterone supplementation modify emotional responses in adult male mice

The serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis are crucially involved in the regulation of emotions. Specifically, spontaneous and/or environmentally mediated modulations of the functionality of these systems early in development may favour the onset of depressive- and anxiety-related phenotypes. While the independent contribution of each of these systems to the emergence of abnormal phenotypes has been detailed in clinical and experimental studies, only rarely has their interaction been systematically investigated. Here, we addressed the effects of reduced serotonin and environmental stress during the early stages of postnatal life on emotional regulations in mice. To this aim, we administered, to outbred CD1 mouse dams, during their first week of lactation, a tryptophan deficient diet (T) and corticosterone via drinking water (C; 80μg/ml). Four groups of dams (animal facility rearing, AFR; T treated, T; C treated, C; T and C treated, TC) and their male offspring were used in the study. Maternal care was scored throughout treatment and adult offspring were tested for: anhedonia (progressive ratio schedule); anxiety-related behaviour (approach-avoidance conflict paradigm); BDNF, dopamine and serotonin concentrations in selected brain areas. T, C and TC treatments reduced active maternal care compared to AFR. Adult TC offspring showed significantly increased anxiety- and anhedonia-related behaviours, reduced striatal and increased hypothalamic BDNF and reduced dopamine and serotonin in the prefrontal cortex and their turnover in the hippocampus. Thus, present findings support the view that neonatal variations in the functionality of the serotonergic system and of HPA axis may jointly contribute to induce emotional disturbances in adulthood.

Have studies of the developmental regulation of behavioral phenotypes revealed the mechanisms of gene-environment interactions?

This review addresses the recent convergence of our long-standing knowledge of the regulation of behavioral phenotypes by developmental experience with recent advances in our understanding of mechanisms regulating gene expression. This review supports a particular perspective on the developmental regulation of behavioral phenotypes: That the role of common developmental experiences (e.g. maternal interactions, peer interactions, exposure to a complex environment, etc.) is to fit individuals to the circumstances of their lives within bounds determined by long-standing (evolutionary) mechanisms that have shaped responses to critical and fundamental types of experience via those aspects of gene structure that regulate gene expression. The phenotype of a given species is not absolute for a given genotype but rather variable within bounds that is determined by mechanisms regulated by experience (e.g. epigenetic mechanisms). This phenotypic variation is not necessarily random, or evenly distributed along a continuum of description or measurement, but often highly disjointed, producing distinct, even opposing, phenotypes. The potentiality for these varying phenotypes is itself the product of evolution, the potential for alternative phenotypes itself conveying evolutionary advantage. Examples of such phenotypic variation, resulting from environmental or experiential influences, have a long history of study in neurobiology, and a number of these will be discussed in this review: neurodevelopmental experiences that produce phenotypic variation in visual perception, cognitive function, and emotional behavior. Although other examples will be discussed, particular emphasis will be made on the role of social behavior on neurodevelopment and phenotypic determination. It will be argued that an important purpose of some aspects of social behavior is regulation of neurobehavioral phenotypes by experience via genetic regulatory mechanisms.

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

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

Functional specificity in the modulation of novelty exposure effects by reliability of maternal care

Using the within-litter neonatal novelty exposure procedure, we manipulated newborn pups' environmental novelty independently from natural variations in maternal care. To better translate animal models to human development studies, we introduce a measure for maternal care reliability. We examined how this reliability modulates novelty-exposure-induced effects on offspring cognitive, social, and emotional development and show that maternal care reliability acts in a function-specific manner. We discuss our results within the framework of a maternal reliability-based modulation model.

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

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

Abnormal behavioral and neurotrophic development in the younger sibling receiving less maternal care in a communal nursing paradigm in rats

Maternal behavior in rodents has been proposed to vary as a function of the external environment and, in turn, adjust offspring's stress and fear responses. Early handling (brief periods of maternal separation during the first two weeks of life) studies and analyses of spontaneously high-caring rat mothers converge to indicate that increased levels of maternal care may reduce offspring emotionality in adulthood. However, the hypothesis that environment-dependent reduction in maternal care correlates with increased offspring vulnerability to pathology has been scarcely investigated. To test this hypothesis we studied maternal care and offspring development in young, adolescent and young-adult Sprague-Dawley rats reared in a communal nursing situation, characterized by two dams delivering their offspring four days apart and communally caring for them until weaning. We show that dams of the first-born litter show increased aggression towards the pregnant female and that offspring belonging to the second-born litter receive less maternal care compared to older cage-mates. Additionally, second-born rats show increased anxiety-related behavior in a plus-maze test in adolescence and adulthood and abnormal developmental trajectories in terms of social interaction and BDNF levels in the amygdala and hippocampus compared to both the first-born litter and to animal facility reared controls. This is the first indication that adverse environments, not requiring experimenter handling, may reduce maternal care and in turn increase offspring's emotionality and modify social behavior and BDNF developmental trajectories.

Resilience and vulnerability are dose-dependently related to neonatal stressors in mice

Early life experiences have been shown to adjust cognitive abilities, stress reactivity, fear responses and immune activity in adult mammals of many species. However, whereas severe stressors have been generally associated with the emergence of hypothalamic pituitary adreno-cortical (HPA)-mediated pathology, mild neonatal stressful experiences have been traditionally associated with 'positive' effects or resilience. External stressors stimulate the HPA axis to induce a corticosterone secretion in mouse dams, which, in turn is directly transmitted to the progeny through lactation. Such corticosteroid transfer may offer a unitary mechanism whereby early low corticosterone exposure may favor resilience in the offspring and high corticosterone increase vulnerability to pathology. In this study we further investigated this hypothesis by evaluating the long-term effects of a neonatal exposure to low (33 mg/l) and high (100 mg/l) doses of corticosterone during the first 10 days of life in outbred CD-1 mice through supplementation in the maternal drinking water. Offspring attentional set-shifting abilities, central neurotrophic regulation and levels of natural auto-antibodies (na-Abs) directed to serotonin (SERT) and dopamine (DAT) transporters were assessed in adulthood. While low levels of neonatal corticosterone improved adult cognitive abilities and increased na-Abs levels directed to SERT, high doses of neonatal corticosterone reduced hippocampal BDNF levels and na-Abs directed to DAT. These findings confirm and extend our previous findings, supporting the view that both adaptive plasticity and pathological outcomes in adulthood may depend on circulating neonatal corticosterone levels and that these effects follow a U-shaped profile.

Predation threat exerts specific effects on rat maternal behaviour and anxiety-related behaviour of male and female offspring

Differences in the rate of maternal behaviours received by rodent offspring are associated with differential programming of molecular and behavioural components of anxiety and stress-related functions. To determine the degree to which maternal behaviours are sensitive to environmental conditions, Long-Evans rat dams were exposed to the odour of a predator (cat) at two different time points during the first week postpartum. Exposure on the day of birth (DOB), but not the third day following birth, increased levels of maternal care in predator-exposed dams relative to dams exposed to a control condition across the first 5 days post-partum. As adults, female offspring of dams exposed on DOB exhibited a less-anxious phenotype in a novel open-field, spending more time in the center and less time displaying thigmotaxis. In contrast, under the same conditions, male offspring showed the opposite behavioural response, consistent with an increasingly anxious phenotype. Results from a subsequent stressor test (response to a predator odour) were consistent with the notion that the rearing effects were specific to anxiety-related behaviours in offspring. Accordingly, we showed that rearing conditions did not affect GR mRNA or NGFI-A expression in the hippocampus of offspring or cross-fostered offspring. The dissociation between stress and anxiety, as well as the sex-specific alterations in behaviour, may reflect the specificity inherent to neural programming in the face of naturalistic early life conditions.

Effects of foraging demand on maternal behaviour and adult offspring anxiety and stress response in C57BL/6 mice

It has been proposed that developmental plasticity of anxiety and stress responses in rodents is mediated by environment-dependent variations in maternal behaviour, but recent evidence indicates that other factors must be involved. To examine this further, we exposed lactating C57BL/6 mice to environmental conditions that imposed high- (HFD), low- (LFD) or variable-foraging demand (VFD) from postnatal day 1-13, depending on the amount and predictability of food supply. While nest attendance was unaffected by treatment, both HFD and VFD-dams showed increased active maternal care compared to LFD-dams. Anxiety in adult male and female offspring was examined on an elevated-O-maze (EZM) and in the open-field test, while hypothalamo-pituitary-adrenal (HPA) reactivity to 20min novelty/isolation stress was determined based on changes in plasma corticosterone (CORT) levels. There were no persistent treatment effects on the offspring's CORT response to novelty/isolation stress. However VFD-males, but not HFD-males, behaved more anxious than LFD males. Their reduced activities throughout the behavioural tests are indicative of a more passive coping style. Conversely, VFD-females, but not HFD-females, behaved less anxious than LFD-females. Our results demonstrate (1) that maternal behaviour in C57BL/6 mice is sensitive to specific characteristics of the environment, (2) that even subtle environment-dependent variations in maternal behaviour can have persistent effects on the offspring's behavioural phenotype, (3) that other factors besides active maternal care must have contributed to these effects, and (4) that male and female offspring may be differentially sensitive to early maternal and/or environmental cues.

Epigenetic mechanisms and the transgenerational effects of maternal care

The transmission of traits across generations has typically been attributed to the inheritance by offspring of genomic information from parental generations. However, recent evidence suggests that epigenetic mechanisms are capable of mediating this type of transmission. In the case of maternal care, there is evidence for the behavioral transmission of postpartum behavior from mothers to female offspring. The neuroendocrine and molecular mediators of this transmission have been explored in rats and implicate estrogen-oxytocin interactions and the differential methylation of hypothalamic estrogen receptors. These maternal effects can influence multiple aspects of neurobiology and behavior of offspring and this particular mode of inheritance is dynamic in response to environmental variation. In this review, evidence for the generational transmission of maternal care and the mechanisms underlying this transmission will be discussed as will the implications of this inheritance system for offspring development and for the transmission of environmental information from parents to offspring.

Maternal separation and maternal care act independently on the development of HPA responses in male rats

Postnatal manipulations such as brief (early handling, EH) and long, daily mother-offspring separations (maternal separation, MS) in rats are used to study the mechanisms underlying developmental plasticity of stress and fear responses, and to model stress-related disorders in humans and in non-human animals. Current evidence suggests that, compared to non-handled rats, EH reduces hypothalamic-pituitary-adrenal (HPA) reactivity in the adult offspring through stimulating increased levels of active maternal care. In contrast, despite a similar increase in active maternal care, MS does not reduce HPA reactivity, thus suggesting that long mother-offspring separations may counteract the effects of increased active maternal care. We therefore attempted to selectively manipulate levels of active maternal care and durations of mother-offspring separations in neonate rats. Rat pups were exposed to different combinations of EH and MS from postnatal day (PND) 2 to 10 using a split-litter design. Maternal behaviour was recorded from PND 2 to 8 and behavioural and endocrine responses to stress were studied in adult male offspring. Low levels of maternal care combined with long mother-offspring separations increased HPA-reactivity compared to both high maternal care combined with long mother-offspring separations and low maternal care combined with brief separations. These findings further support the hypothesis that active maternal care and long mother-offspring separation act independently, and exert opposing effects, on adult offspring's HPA responses, but that increased maternal care may buffer the adverse consequences of long separations.

Neurobehavioural disorders in the infant reeler mouse model: Interaction of genetic vulnerability and consequences of maternal separation

Studies on heterozygous (HZ) reeler mice suggest a relationship between reelin (a protein of extra cellular matrix) haploinsufficiency and the presence of altered neural networks and behaviour. Neonatal adverse and/or stimulating experiences might interfere with the emergence of this genetic-dependent phenotype. Repeated episodes of maternal separation early in ontogeny result in enduring neuroendocrine, neurochemical and behavioural alterations in the offspring. Therefore, in order to investigate whether developmental indexes of neurobehavioural disorders can be studied in the infant reeler mouse model, and whether ontogenetic adverse experiences may question or improve its suitability, homozygous reeler (RL), heterozygous (HZ) and wild-type (WT) mouse pups underwent maternal separation (SEP, 5h/day) or handling (H, 3min/day) on PND 2-6. As expected, a sex difference appeared, for measure of emotional and communicative behaviour in infant mice. On PND 7, compared to other genotypes, RL mouse pups from the H control group, showed reduced levels of ultrasound (USV) production and of locomotion. Surprisingly, this deficit in RL mice was fully reverted by maternal separation. Maternal separation per se reduced social motivation in the homing test at PND 9 in WT mice, with no effects on HZ and RL ones. Additionally, female pups emitted much lower levels of ultrasound production than males within the H control group. Such a baseline sex difference, however, disappeared in the SEP group. The present results provide evidence that unusual stress and related hormonal stimulation early in development may (i) independently shape individual phenotype and (ii) interact with a genetic make-up to substantially modify its "natural" developmental trajectories.