Neurobiological effects of neonatal maternal separation and post-weaning environmental enrichment

Boosting decision-making in rat models of early-life adversity with environmental enrichment and intranasal oxytocin

Impaired decision-making constitutes a fundamental issue in numerous psychiatric disorders. Extensive research has established that early life adversity (ELA) increases vulnerability to psychiatric disorders later in life. ELA in human neonates is associated with changes in cognitive, emotional, as well as reward-related processing. Maternal separation (MS) is an established animal model of ELA and has been shown to be associated with decision-making deficits. On the other hand, enriched environment (EE) and intranasal oxytocin (OT) administration have been demonstrated to have beneficial effects on decision-making in humans or animals. Given these considerations, our investigation sought to explore the impact of brief exposure to EE and intranasal OT administration on the decision-making abilities of adolescent rats that had experienced MS during infancy. The experimental protocol involved subjecting rat pups to the MS regimen for 180 min per day from postnatal day (PND) 1 to PND 21. Then, from PND 22 to PND 34, the rats were exposed to EE and/or received intranasal OT (2 μg/μl) for seven days. The assessment of decision-making abilities, using a rat gambling task (RGT), commenced during adolescence. Our findings revealed that MS led to impaired decision-making and a decreased percentage of advantageous choices. However, exposure to brief EE or intranasal OT administration mitigated the deficits induced by MS and improved the decision-making skills of maternally-separated rats. Furthermore, combination of these treatments did not yield additional benefits. These results suggest that EE and OT may hold promise as therapeutic interventions to enhance certain aspects of cognitive performance.

Nature and nurture: Comparing mouse behavior in classic versus revised anxiety-like and social behavioral assays in genetically or environmentally defined groups

Widely used rodent anxiety assays like the elevated plus maze (EPM) and the open field test (OFT) are conflated with rodents' natural preference for dark over light environments or protected over open spaces. The EPM and OFT have been used for decades but are often criticized by behavioral scientists. Years ago, two revised anxiety assays were designed to improve upon the "classic" tests by excluding the possibility to avoid or escape aversion. The 3-D radial arm maze (3DR) and the 3-D open field test (3Doft) utilize continual motivational conflict to better model anxiety; each consist of an open space connected to ambiguous paths toward uncertain escape. Despite their utility, the revised assays have not caught on. This could be because no study yet has directly compared classic and revised assays in the same animals. To remedy this, we contrasted behavior from a battery of assays (EPM, OFT, 3DR, 3Doft and a sociability test) in mice defined genetically by isogenic strain, or environmentally by postnatal experience. One major motivation for this work is to inform future studies by offering a transparent look at individual outcomes on these assays, as there is no one-size-fits-all test to assess rodent anxiety-like behavior. Findings suggest that classic assays may sufficiently characterize differences across genetically defined groups, but the revised 3DR may be advantageous for investigating more nuanced behavioral differences such as those stemming from environmental factors. Finally, exposure to multiple assays significantly affected sociability, highlighting concerns for designing and interpreting batteries of rodent behavioral tests.

Adolescent nonpharmacological interventions for early-life stress and their mechanisms

Those with a negative experience of psychosocial stress during the early stage of life not only have a high susceptibility of the psychiatric disorder in all phases of their life span, but they also demonstrate more severe symptoms and poorer response to treatment compared to those without a history of early-life stress. The interventions targeted to early-life stress may improve the effectiveness of treating and preventing psychiatric disorders. Brain regions associated with mood and cognition develop rapidly and own heightened plasticity during adolescence. So, manipulating nonpharmacological interventions in fewer side effects and higher acceptance during adolescence, which is a probable window of opportunity, may ameliorate or even reverse the constantly deteriorating impact of early-life stress. The present article reviews animal and people studies about adolescent nonpharmacological interventions for early-life stress. We aim to discuss whether those adolescent nonpharmacological interventions can promote individuals' psychological health who expose to early-life stress.

The long-term effects of maternal deprivation on the number and size of inhibitory interneurons in the rat amygdala and nucleus accumbens

Introduction

There is an increasing evidence supporting the hypothesis that traumatic experiences during early developmental periods might be associated with psychopathology later in life. Maternal deprivation (MD) in rodents has been proposed as an animal model for certain aspects of neuropsychiatric disorders.

Methods

To determine whether early-life stress leads to changes in GABAergic, inhibitory interneurons in the limbic system structures, specifically the amygdala and nucleus accumbens, 9-day-old Wistar rats were exposed to a 24 h MD. On postnatal day 60 (P60), the rats were sacrificed for morphometric analysis and their brains were compared to the control group.

Results

Results show that MD affect GABAergic interneurons, leading to the decrease in density and size of the calcium-binding proteins parvalbumin-, calbindin-, and calretinin-expressing interneurons in the amygdala and nucleus accumbens.

Discussion

This study indicates that early stress in life leads to changes in the number and morphology of the GABAergic, inhibitory interneurons in the amygdala and nucleus accumbens, most probably due to the loss of neurons during postnatal development and it further contributes to understanding the effects of maternal deprivation on brain development.

Comparison of the effect of postweaning social isolation, enriched environment, and exercise training on learning and memory functions in rats

Background/aim

To assess the effects of postweaning social isolation, an enriched environment, and exercise training on learning and memory functions in rats, as well as their relation with the brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) concentrations in the hippocampus.

Materials and methods

Randomly assigned into 4 groups were 35 female postweaning rats (25 day old), as the control (C), social isolation (SI), enriched environment (EE), and exercise training (E) groups. The SI and the EE groups were housed under their specific conditions and the E and the C groups were housed under standard conditions for 6 weeks. The rats in the E group swam for 60 min/day, 5 days a week, for 6 weeks. After 6 weeks, the rats were evaluated in the Morris water maze (MWM). Following MWM assessment, hippocampal tissue and blood samples were taken to measure the BDNF and NGF.

Results

According to the results of the MWM probe trial session, the thigmotaxis behavior was higher in the SI group compared to the C group (p < 0,05). Furthermore, the time spent in the target quadrant (quadrant with an escape platform) was lower in the SI group compared to the EE group (p < 0.05). The BDNF and NGF levels in the hippocampus and plasma were not different between the groups (p < 0.05).

Conclusion

Postweaning social isolation may increase thigmotaxis behaviors. Postweaning social isolation, enriched environment, and exercise training did not affect the spatial learning, memory function, hippocampal BDNF or NGF levels in female rats.

One day away from mum has lifelong consequences on brain and behaviour

This chapter presents a brief overview of attachment theory and discusses the importance of the neonatal period in shaping an individual's physiological and behavioural responses to stress later in life, with a focus on the role of the parent-infant relationship, particularly in rodents. In rodents, the role of maternal behaviours goes far beyond nutrition, thermoregulation and excretion, acting as hidden regulators of the pup's physiology and development. In this review, we will discuss the inhibitory role of specific maternal behaviours on the ACTH and corticosterone (CORT) stress response. The interest of our group to explore the long-term consequences of maternal deprivation for 24 h (DEP) at different ages (3 days and 11 days) in rats was sparked by its opposite effects on ACTH and CORT levels. In early adulthood, DEP3 animals (males and females alike) show greater negative impact on affective behaviours and stress related parameters than DEP11, indicating that the latter is more resilient in tests of anxiety-like behaviour. These findings create an opportunity to explore the neurobiological underpinnings of vulnerability and resilience to stress-related disorders. The chapter also provides a brief historical overview and highlights the relevance of attachment theory, and how DEP helps to understand the effects of childhood parental loss as a risk factor for depression, schizophrenia, and PTSD in both childhood and adulthood. Furthermore, we present the concept of environmental enrichment (EE), its effects on stress responses and related behavioural changes and its benefits for rats previously subjected to DEP, along with the clinical implications of DEP and EE.

Nature and nurture: comparing mouse behavior in classic versus revised anxiety-like and social behavioral assays in genetically or environmentally defined groups

Widely used rodent anxiety assays like the elevated plus maze (EPM) and the open field test (OFT) are often conflated with rodents' natural preference for dark over light environments or protected over open spaces. The EPM and OFT have been used for many decades, yet have also been criticized by generations of behavioral scientists. Several years ago, two revised anxiety assays were designed to improve upon the "classic" tests by excluding the possibility to avoid or escape aversive areas of each maze. The 3-D radial arm maze (3DR) and the 3-D open field test (3Doft) each consist of an open space connected to ambiguous paths toward uncertain escape. This introduces continual motivational conflict, thereby increasing external validity as an anxiety model. But despite this improvement, the revised assays have not caught on. One issue may be that studies to date have not directly compared classic and revised assays in the same animals. To remedy this, we contrasted behavior in a battery of assays (EPM, OFT, 3DR, 3Doft, and a sociability test) in mice defined either genetically by isogenic strain, or environmentally by postnatal experience. Findings indicate that the optimal assay to assess anxiety-like behavior may depend upon grouping variable (e.g. genetic versus environment). We argue that the 3DR may be the most ecologically valid of the anxiety assays tested, while the OFT and 3Doft provided the least useful information. Finally, exposure to multiple assays significantly affected sociability measures, raising concerns for designing and interpreting batteries of behavioral tests in mice.

Maternal Immune Activation and Enriched Environments Impact B2 SINE Expression in Stress Sensitive Brain Regions of Rodent Offspring

Early life stress (ELS) can have wide-spread neurodevelopmental effects with support accumulating for the idea that genomic mechanisms may induce lasting physiological and behavioral changes following stress exposure. Previous work found that a sub-family of transposable elements, SINEs, are repressed epigenetically after acute stress. This gives support to the concept that the mammalian genome may be regulating retrotransposon RNA expression allowing for adaptation in response to environmental challenges, such as maternal immune activation (MIA). Transposon (TE) RNAs are now thought to work at the epigenetic level and to have an adaptive response to environmental stressors. Abnormal expression of TEs has been linked to neuropsychiatric disorders like schizophrenia, which is also linked to maternal immune activation. Environmental enrichment (EE), a clinically utilized intervention, is understood to protect the brain, enhance cognitive performance, and attenuate responses to stress. This study examines the effects of MIA on offspring B2 SINE expression and further, the impact that EE, experienced throughout gestation and early life, may have in conjunction with MIA during development. Utilizing RT-PCR to quantify the expression of B2 SINE RNA in the juvenile brain of MIA exposed rat offspring, we found dysregulation of B2 SINE expression associated with MIA in the prefrontal cortex. For offspring experiencing EE, the prefrontal cortex exhibited an attenuation of the MIA response observed in standard housed animals. Here, the adaptive nature of B2 is observed and thought to be aiding in the animal's adaptation to stress. The present changes indicate a wide-spread stress-response system adaptation that impacts not only changes at the genomic level but potentially observable behavioral impacts throughout the lifespan, with possible translational relevance to psychotic disorders.

Maternal separation increased memory function and anxiety without effects of environmental enrichment in male rats

Maternal separation is a detrimental postnatal influence, whereas environmental enrichment is a therapeutic and protective agent. It is unclear if long-term environmental enrichment can compensate for the effects of maternal separation stress on memory-related alterations. This study examined how environmental enrichment affected memory functions, anxiety level, Grin2a, Grin2b, BDNF, and cFos expressions in the maternally separated rats. There are seven groups in this study: control (C), maternal separation+standard cage (MS), maternal separation + enriched cage (MSE), enriched cage (E), the maternal separation that decapitated at postnatal 21 (MS21) and standard cage that decapitated at PN21 (C21) for hormone and gene expression analysis. The maternal separation procedure consisted of postnatal 21 days. Learning and memory performance were determined with the Morris water tank test; anxiety and locomotor activity were examined with the open field and elevated plus-maze test. The expression levels of genes were measured by the RT-PCR method. Blood corticosterone level was evaluated by the ELISA method. Results showed that MS increased memory performance, locomotor activity, and anxiety, but it did not change gene expression levels. An enriched environment did not change the memory performance, locomotor activity, and related gene expression levels. MSE group increased their memory performance, but the anxiety, locomotor activity, and gene expression level did not change. Grin2a, Grin2b, and BDNF gene expression and corticosterone levels increased in the MS21 group. Maternal separation increased memory performance, but it also increased anxiety. Environmental enrichment alone was insufficient to cause alterations in the memory performance.

Local CRF and oxytocin receptors correlate with female experience-driven avoidance change and hippocampal neuronal plasticity

Understanding how experiences affect females' behaviors and neuronal plasticity is essential for uncovering the mechanism of neurodevelopmental disorders. The study explored how neonatal maternal deprivation (MD) and post-weaning environmental enrichment (EE) impacted the CA1 and DG's neuronal plasticity in the dorsal hippocampus, and its relationships with passive avoidance, local corticotrophin-releasing factor (CRF) levels, and oxytocin receptor (OTR) levels in female BALB/c mice. The results showed that MD damaged passive avoidance induced by foot shock and hotness, and EE restored it partially. In the CA1, MD raised CRF levels and OTR levels. Parallelly, MD increased synaptic connection levels but reduced the branches' numbers of pyramidal neurons. Meanwhile, in the DG, MD increased OTR levels but lowered CRF levels, DNA levels, and spine densities. EE did not change the CA1 and DG's CRF and OTR levels. However, EE added DG's dendrites of granular cells. The additive of MD and EE raised CA1's synaptophysin and DG's postsynaptic density protein-95 and OTR levels, and meanwhile, shaped avoidance behaviors primarily similar to the control. The results suggest that experience-driven avoidance change and hippocampal neuronal plasticity are associated with local CRF and OTR levels in female mice.

Experiences Shape Hippocampal Neuron Morphology and the Local Levels of CRHR1 and OTR

The dorsal hippocampus is involved in behavioral avoidance regulation. It is unclear how experiences such as the neonatal stress of maternal deprivation (MD) and post-weaning environmental enrichment (EE) affect avoidance behavior and the dorsal hippocampal parameters, including neuronal morphology, corticotrophin-releasing hormone (CRH) signaling, and oxytocin receptor (OTR) level. In male BALB/c mice, we found that MD impaired avoidance behavior in the step-on test compared to non-MD and EE rearing conditions could alleviate that partially. MD increased neuronal branches in the CA1 but decreased synaptic connection levels in the CA2, CA3, and DG. Meanwhile, MD increased the CA1's OTR levels, which negatively correlated with nucleus densities. MD also increased the CA1's and CA2's CRH levels, which positively correlated with CRHR1 levels. However, MD statistically elevated the CA3's CRH receptor 1 (CRHR1) levels, which negatively correlated with nucleus densities and, probably, synaptic connection levels in the CA3. The additive effects of MD and EE maintained similar CRH levels and CRHR1 levels as well as OTR levels in the hippocampal areas as the additive of non-MD and non-EE. However, the presence of MD and EE still decreased the CA1's neuronal branches and the CA2's and DG's synaptic connection levels. The study illustrates how MD and EE affect avoidance behaviors, hippocampal neuron morphology, and CRH and OTR levels. The results indicate that the late-life environmental improvement partially restores the alterations in dorsal hippocampal areas induced by early life stress.

Beneficial effects and neurobiological aspects of environmental enrichment associated to major depressive disorder and autism spectrum disorder

A suitable enriched environment favors development but can also influence behavior and neuronal circuits throughout development. Studies have shown that environmental enrichment (EE) can be used as an essential tool or combined with conventional treatments to improve psychiatric and neurological symptoms, including major depressive disorder (MDD) and autism spectrum disorder (ASD). Both disorders affect a significant percentage of the world's population and have complex pathophysiology. Moreover, the available treatments for MDD and ASD are still inadequate for many affected individuals. Experimental models demonstrate that EE has significant positive effects on behavioral modulation. In addition, EE has effects on neurobiology, including improvement in synaptic connections and neuroplasticity, modulation of neurotransmissions, a decrease in inflammation and oxidative stress, and other neurobiology effects that can be involved in the pathophysiology of MDD and ASD. Thus, this review aims to describe the leading behavioral and neurobiological effects associated with EE in MDD and ASD.

Behavioral effects of environmental enrichment on male and female wistar rats with early life stress experiences

Exposure to adverse childhood experiences or early life stress experiences (ELSs) increase the risk of non-adaptive behaviors and psychopathology in adulthood. Environmental enrichment (EE) has been proposed to minimize these effects. The vast number of methodological variations in animal studies underscores the lack of systematicity in the studies and the need for a detailed understanding of how enrichment interacts with other variables. Here we evaluate the effects of environmental enrichment in male and female Wistar rats exposed to adverse early life experiences (prenatal, postnatal, and combined) on emotional (elevated plus maze), social (social interaction chamber), memory (Morris water maze) and flexibility tasks. Our results—collected from PND 51 to 64—confirmed: 1) the positive effect of environmental enrichment (PND 28–49) on anxiety-like behaviors in animals submitted to ELSs. These effects depended on type of experience and type of enrichment: foraging enrichment reduced anxiety-like behaviors in animals with prenatal and postnatal stress but increased them in animals without ELSs. This effect was sex-dependent: females showed lower anxiety compared to males. Our data also indicated that females exposed to prenatal and postnatal stress had lower anxious responses than males in the same conditions; 2) no differences were found for social interactions; 3) concerning memory, there was a significant interaction between the three factors: A significant interaction for males with prenatal stress was observed for foraging enrichment, while physical enrichment was positive for males with postnatal stress; d) regarding cognitive flexibility, a positive effect of EE was found in animals exposed to adverse ELSs: animals with combined stress and exposed to physical enrichment showed a higher index of cognitive flexibility than those not exposed to enrichment. Yet, within animals with no EE, those exposed to combined stress showed lower flexibility than those exposed to both prenatal stress and no stress. On the other hand, animals with prenatal stress and exposed to foraging-type enrichment showed lower cognitive flexibility than those with no EE. The prenatal stress-inducing conditions used here 5) did not induced fetal or maternal problems and 6) did not induced changes in the volume of the dentate gyrus of the hippocampus.

Enriched environment alleviates adolescent visceral pain, anxiety- and depression-like behaviors induced by neonatal maternal separation

BACKGROUND

Neonatal maternal separation (NMS), a major kind of early life stress, increases the risk of visceral pain, anxiety- and depression-like behaviors in adulthood. An enriched environment (EE) has been shown to successfully rescue the brain from various early life psychological stressors. Therefore, this study aimed to investigate whether NMS induces visceral pain, anxiety- and depression-like behaviors in adolescents and to evaluate the impact of EE in infancy on these symptoms.

METHODS

Male C57BL/6 J mice that had been subjected to NMS were used in this study. The visceral pain threshold test (PTT), open field test (OFT), and sucrose preference test (SPT) were conducted to evaluate visceral pain, anxiety- and depression-like behaviors in mice, respectively. An enzyme linked immunosorbent assay (ELISA) for tumor necrosis factor-α (TNF-α), interleukin-1β, (IL-1β), and interleukin-10 (IL-10) was performed to assess neuroinflammatory responses. Then, the effects of EE (free-turning running wheels, pipes, stairs, and various colored ocean balls, etc.) on NMS-induced behaviors and neuroinflammatory factors were examined.

RESULTS

The impacts of NMS included adolescent visceral pain, anxiety- and depression-like behaviors. The medial prefrontal cortex (mPFC), basolateral amygdala (BLA), and paraventricular nucleus (PVN) were biased towards pro-inflammatory features. Further, EE alleviated adolescent visceral pain, anxiety- and depression-like behaviors. The application of EE up-regulated the expression of IL-10, and down-regulated the expression of IL-1β and TNF-α in mPFC, BLA, and PVN.

CONCLUSIONS

The effects of NMS include adolescent visceral pain, anxiety- and depression-like behaviors, accompanied by an imbalance of neuroinflammation. Intervention with EE in pediatric mice relieved these symptoms by reducing neuroinflammation in the central nervous system.

Early life stress influences basal ganglia dopamine receptors and novel object recognition of adolescent and adult rats

Environmental stimuli in early life are recognized to affect brain development and behavior. Mother-pup interaction constitutes a determinant stimulus during this critical period. It is known that the dopaminergic system undergoes significant reorganization during adolescence and that dopamine receptors are involved in recognition memory. Based on the above, we examined the effects of brief and prolonged maternal separation during the neonatal period (15 or 180 min daily) on basal ganglia dopamine receptors and on the behavior in the novel object recognition task of adolescent and adult male rats. Using the NOR task, we observed that the discrimination index (DI) was decreased in rats with brief maternal separations independent of age. Using receptor autoradiography, we observed that brief maternal separation induced decreases in D1, D2 and D4 receptor binding levels in adult basal ganglia nuclei, while prolonged maternal separation induced increases in D1 receptor binding levels in caudate - putamen (CPu) of adolescent rats. With immunoblotting experiments, we found decreases in D1 and increases in D2 total protein levels in CPu of adult rats with prolonged maternal separations. Α positive correlation was observed between DI and D1 binding levels in CPu, internal globus pallidus and substantia nigra, and D2 binding levels in nucleus accumbens core in adult rats, using the Pearson correlation coefficient. Our results indicate that the long-lasting effects of neonatal mother-offspring separation on dopamine receptors depend on the duration of maternal separation and age and that this early life experience impairs recognition memory in adolescent and adult rats. Furthermore, the present results suggest that modulation of striatal dopamine receptors might underlie the reduced recognition memory of adult rats with brief neonatal maternal separations.

Effects of early life adversities upon memory processes and cognition in rodent models

Exposure to stressors in early postnatal life induces long-lasting modifications in brainfunction.Thisplasticity,an essential characteristic of the brain that enables adaptation to the environment, may also induce impairments in some psychophysiological functions, including learning and memory. Early life stress (ELS) has long-term effects on thehypothalamic-pituitary-adrenal axisresponse to stressors, and has been reported to lead toneuroinflammation,altered levelsof neurotrophic factors, modifications inneurogenesis andsynaptic plasticity,with changes in neurotransmitter systems and network functioning. In this review, we focus on early postnatal stress in animal models and their effects on learning and memory.Many studies have reported ELS-induced impairments in different types of memories, including spatial memory, fear memory, recognition (both for objects and social) memory, working memory and reversal learning. Studies are not always in agreement, however, no effects, or sometimes facilitation, being reported, depending on the nature and intensity of the early intervention, as well as the age when the outcome was evaluated and the sex of the animals. When considering processes occurring after consolidation, related with memory maintenance or modification, there are a very reduced number of reports. Future studies addressing the mechanisms underlying memory changes for ELS should shed some light on the understanding of the different effects induced by stressors of different types and intensities on cognitive functions.

The Relative Benefits of Environmental Enrichment on Learning and Memory are Greater When Stressed: A Meta-analysis of Interactions in Rodents

Environmental enrichment ("EE") is expected to alleviate the negative effects of stress on cognitive performance. However, there are complexities associated with interpreting interactions that obscure determining the benefit EE may play in mitigating the negative effects of stress. To clarify these complexities, we conducted a systematic review with meta-analysis on the main and interactive effects of EE and stress on learning and memory in rodents. We show that EE and stress interact 'synergistically' where EE provides a greater relative benefit to stressed individuals compared to those reared in conventional housing. Importantly, EE can fully-compensate for the negative effects of stress where stressed individuals with EE performed equally to enriched individuals without a stress manipulation. Additionally, we show the importance of other mediating factors, including the order of treatment exposure, duration and type of stress, type of EE, and type of cognitive assays used. This study not only quantifies the interactions between EE and stress, but also provides a clear example for how to conduct and interpret meta-analysis of interactions.

Effects of early life adversity on immediate early gene expression: Systematic review and 3-level meta-analysis of rodent studies

Early-life adversity (ELA) causes long-lasting structural and functional changes to the brain, rendering affected individuals vulnerable to the development of psychopathologies later in life. Immediate-early genes (IEGs) provide a potential marker for the observed alterations, bridging the gap between activity-regulated transcription and long-lasting effects on brain structure and function. Several heterogeneous studies have used IEGs to identify differences in cellular activity after ELA; systematically investigating the literature is therefore crucial for comprehensive conclusions. Here, we performed a systematic review on 39 pre-clinical studies in rodents to study the effects of ELA (alteration of maternal care) on IEG expression. Females and IEGs other than cFos were investigated in only a handful of publications. We meta-analyzed publications investigating specifically cFos expression. ELA increased cFos expression after an acute stressor only if the animals (control and ELA) had experienced additional hits. At rest, ELA increased cFos expression irrespective of other life events, suggesting that ELA creates a phenotype similar to naïve, acutely stressed animals. We present a conceptual theoretical framework to interpret the unexpected results. Overall, ELA likely alters IEG expression across the brain, especially in interaction with other negative life events. The present review highlights current knowledge gaps and provides guidance to aid the design of future studies.

Environmental enrichment and intranasal oxytocin administration reverse maternal separation-induced impairments of prosocial choice behavior

Adverse early life experiences influence behavioral and physiological functions and increase vulnerability to neuropsychiatric disorders. Maternal separation (MS) is an established animal model that reproduces the features of chronic stress or adverse experiences during early life. Previous studies have been shown that MS may lead to impairments of social behaviors. Here, we investigated the effects of MS on mutual reward preferences in a double T-maze prosocial choice task. Since enriched environment (EE) and intranasal oxytocin (OT) administration have beneficial effects on cognition and social behaviors, in the present study we tested whether these treatments, alone or in combination, would affect prosocial behavior of rats which underwent MS during infancy. Rat pups underwent MS paradigm for 180 min/day from postnatal day (PND) 1-21. From PND 22-34, rats were exposed to an EE and/or received intranasal OT (2 μg/μl, 7 days). Hence, the 8 groups consisted of control (CTRL), MS, CTRL+EE, CTRL+OT and the saline groups. Assessment of prosocial choice behavior was started in adolescence. MS impaired prosocial choice behavior and reduced mutual reward preferences. Getting exposed to EE and intranasal OT administration could overcome MS-induced deficits and promoted mutual reward preferences of MS rats. Combination of short-term EE and OT strengthened prosocial behavior. Obtained results showed that EE and OT may be considered as profitable therapeutic approaches for promoting some aspects of social behavior.

Effects of short environmental enrichment on early-life adversity induced cognitive alternations in adolescent rats

Early-life experiences, including parental care, affect cognitive performance later in life. Being exposed to early-life maternal separation (MS) increases susceptibility to stress-related psychopathology. Previous studies suggest that MS could induce learning and memory impairments. Since enriched environment (EE) provides more opportunities for exploration and social interaction, in the present study we evaluated the effects of a short EE paradigm with a duration of 13 days on cognitive abilities of maternally separated rats (MS; 180 min/day, postnatal day (PND) 1-21) during adolescence in four experimental groups: Control, Control+EE, MS, and MS+EE. Plasma corticosterone (CORT) and brain-derived neurotrophic factor (BDNF) levels were also measured in experimental animals. We also studied the induction of long-term potentiation (LTP) in the slices of hippocampal CA1 area. The behavioral and electrophysiological assessments were started at PND 35. MS caused higher basal CORT levels in plasma and impaired spatial learning, memory, and social interaction. LTP induction was also impaired in MS rats and plasma BDNF levels were reduced in these animals. MS also induced more anxiety-like behavior. Short EE reduced plasma CORT levels had the potential to improve locomotor activity and anxiety-like behavior in MS+EE rats and reversed MS-induced impairments of spatial learning, memory, and social behavior. LTP induction and plasma BDNF levels were also enhanced in MS+EE rats. We concluded that short EE might be considered as a therapeutic strategy for promoting cognition.

Poly (I:C)-induced maternal immune activation modifies ventral hippocampal regulation of stress reactivity: prevention by environmental enrichment

Environmental enrichment (EE) has been successfully implemented in human rehabilitation settings. However, the mechanisms underlying its success are not understood. Incorporating components of EE protocols into our animal models allows for the exploration of these mechanisms and their role in mitigation. Using a mouse model of maternal immune activation (MIA), the present study explored disruptions in social behavior and associated hypothalamic pituitary adrenal (HPA) axis functioning, and whether a supportive environment could prevent these effects. We show that prenatal immune activation of toll-like receptor 3, by the viral mimetic polyinosinic-polycytidylic acid (poly(I:C)), led to disrupted maternal care in that dams built poorer quality nests, an effect corrected by EE housing. Standard housed male and female MIA mice engaged in higher rates of repetitive rearing and had lower levels of social interaction, alongside sex-specific expression of several ventral hippocampal neural stress markers. Moreover, MIA males had delayed recovery of plasma corticosterone in response to a novel social encounter. Enrichment housing, likely mediated by improved maternal care, protected against these MIA-induced effects. We also evaluated c-Fos immunoreactivity associated with the novel social experience and found MIA to decrease neural activation in the dentate gyrus. Activation in the hypothalamus was blunted in EE housed animals, suggesting that the putative circuits modulating social behaviors may be different between standard and complex housing environments. These data demonstrate that augmentation of the environment supports parental care and offspring safety/security, which can offset effects of early health adversity by buffering HPA axis dysregulation. Our findings provide further evidence for the viability of EE interventions in maternal and pediatric settings.

Environmental enrichment rescues survival and function of adult-born neurons following early life stress

Adverse experiences early in life are associated with the development of psychiatric illnesses. The hippocampus is likely to play pivotal role in generating these effects: it undergoes significant development during childhood and is extremely reactive to stress. In rodent models, stress in the pre-pubertal period impairs adult hippocampal neurogenesis (AHN) and behaviours which rely on this process. In normal adult animals, environmental enrichment (EE) is a potent promoter of AHN and hippocampal function. Whether exposure to EE during adolescence can restore normal hippocampal function and AHN following pre-pubertal stress (PPS) is unknown. We investigated EE as a treatment for reduced AHN and hippocampal function following PPS in a rodent model. Stress was administered between post-natal days (PND) 25-27, EE from PND 35 to early adulthood, when behavioural testing and assessment of AHN took place. PPS enhanced fear reactions to a conditioned stimulus (CS) following a trace fear protocol and reduced the survival of 4-week-old adult-born neurons throughout the adult hippocampus. Furthermore, we show that fewer adult-born neurons were active during recall of the CS stimulus following PPS. All effects were reversed by EE. Our results demonstrate lasting effects of PPS on the hippocampus and highlight the utility of EE during adolescence for restoring normal hippocampal function. EE during adolescence is a promising method of enhancing impaired hippocampal function resulting from early life stress, and due to multiple benefits (low cost, few side effects, widespread availability) should be more thoroughly explored as a treatment option in human sufferers of childhood adversity.

Exposure to Short Photoperiod Regime Restores Spatial Cognition in Ventral Subicular Lesioned Rats: Potential Role of Hippocampal Plasticity, Glucocorticoid Receptors, and Neurogenesis

Ambient light influences our mood, behavior, and cognition. Phototherapy has been considered as an effective non-pharmacological intervention strategy in the restoration of cognitive functions following central nervous system insults. However, the cellular and molecular underpinnings of phototherapy-mediated functional recovery are yet to be studied. The present study examines the effectiveness of short photoperiod regime (SPR; 6:18-h light:dark cycle) in restoring the cognitive functions in ventral subicular lesioned rats. Bilateral ventral subicular lesion (VSL) resulted in significant impairment of spatial navigational abilities when tested in the Morris water maze (MWM) task. Further, VSL resulted in reduced expression of glucocorticoid receptors (GRs) and activity-regulated cytoskeletal (Arc) protein and suppression of neurogenesis in the hippocampus. VSL also suppressed the magnitude of long-term potentiation (LTP) in the hippocampal Schaffer collateral-CA1 synapses. However, exposure to SPR for 21 days showed significant restoration of spatial performance in the MWM task as the ventral subicular lesioned rats could deploy higher cognitive allocentric navigational strategies to reach the hidden platform. Further, SPR resulted in enhanced expression of hippocampal GR and Arc protein and neurogenesis but not hippocampal LTP suggestive of appropriate need-based SPR intervention. In conclusion, the study demonstrates the effectiveness of SPR in establishing functional recovery as well as the possible molecular and cellular basis of cognitive recovery in a rat model of neurodegeneration. Such studies provide a framework in understanding the efficacy of non-pharmacological strategies in establishing functional recovery in neurodegenerative conditions.

Sex-dependent and ontogenetic effects of low dose ethanol on social behavioral deficits induced by mouse maternal separation

Early life stress can induce lifelong emotional and social behavioral deficits that may in some cases be alleviated by drugs or alcohol. A model for early life stress, rodent maternal separation, recapitulates these behavioral sequelae, which are not limited to potentiated anxiety-like behavior, attenuated social motivation, and altered reward-seeking. Here we employed mouse maternal separation with early weaning (MSEW), consisting of pup-dam separation lasting 4-8 hours on postnatal days (PD) 2-16, with early weaning on PD 17. Prior MSEW studies have limited subjects by age or sex, so we more comprehensively investigated MSEW effects in both sexes, during adolescence and adulthood. We found universal effects of MSEW to include lifelong enhancement of anxiety-like and despair behavior, as well as deficits in social motivation. We also observed some sex-dependent effects of MSEW, namely that female MSEW mice exhibited social habituation to a greater degree than their male counterparts. Low dose ethanol administration had no major effects on the social behavior of non-stressed mice. But interestingly, MSEW-induced social habituation was counteracted by low dose ethanol in adolescent female mice, and potentiated in adolescent male mice. These effects were absent in adult animals, suggesting that ethanol may exert differential effects on the developing brain in such a manner to produce age-, sex-, and stress-dependent effects upon social behavior. Together, results indicate that MSEW reliably produces long-lasting impairments in emotional and social behaviors in both sexes and across the lifespan, but may exert more salient social behavioral effects on female animals.

Intranasal oxytocin administration facilitates the induction of long-term potentiation and promotes cognitive performance of maternally separated rats

Maternal separation (MS) is known to induce permanent changes in the central nervous system and is associated with increased levels of anxiety and cognitive impairments. The neuropeptide oxytocin (OT) has been implicated in a broad spectrum of social and nonsocial and behaviors. Since it plays a significant role in learning and memory and enhances synaptic plasticity, we hypothesized that OT may affect MS-induced changes in synaptic plasticity and cognitive performance. Rat pups underwent MS protocol for 180 min/day from postnatal day (PND) 1-21. OT was administered intranasally (2 μg/μl, 7 days) to control and MS groups from PND 22-34. Plasma corticosterone (CORT) levels, anxiety-like behavior, sociability, learning and memory were measured in adolescent rats. In addition, extracellular evoked field excitatory postsynaptic potentials (fEPSP) were also recorded from hippocampal slices. MS induced higher plasma CORT levels and impaired social interaction, learning and memory. Moreover, MS reduced locomotor activity and increased anxiety-like behavior. Intranasal OT could overcome MS-induced deficits and promoted sociability, learning and memory of MS rats. OT also enhanced locomotor activity in the open field and decreased anxiety-like behavior. Obtained results showed that long term potentiation (LTP) was not induced in MS animals. However, OT injection overcame the MS-induced impairment in LTP generation in CA1 area of the hippocampus.

Early Life Stress Increases Brain Glutamate and Induces Neurobehavioral Manifestations in Rats

Early life stress (ELS) is associated with an increased risk of developing depression and anxiety disorders. Disturbances of the neurobiological glutamatergic system are implicated in depression; however, the long-term effects of ELS on glutamate (Glu) metabolites remain unclear. Our study used 7T proton magnetic resonance spectroscopy (7T ¹H MRS) to detect metabolic Glu in a rat model to investigate maternal deprivation (MD)-induced ELS. MD was established in Sprague-Dawley rats by periodic separation from mothers and peers. Changes in the hippocampal volume and Glu metabolism were detected by 7T ¹H MRS after testing for depression-like behavior via open field, sucrose preference, and Morris water maze tests. Adult MD offspring exhibited depression-like behavior. Compared to the control, the MD group exhibited reduced ratio of central activity time to total time and decreased sucrose consumption (p < 0.05). MD rats spent less time in the fourth quadrant, where the platform was originally placed, in the Morris water maze test. According to 7T ¹H MRS, hippocampus of MD rats had elevated Glu and glutamate + glutamine (Glu+Gln) levels compared with the control group hippocampi, but Gln, γ-aminobutyric acid (GABA), and glutamate + glutamine (Glu+Gln) in the prefrontal cortex of MD rats showed a downward trend. Depression-like behavior and cognition deficits related to ELS may induce region-specific changes in Glu metabolism in the prefrontal cortex and hippocampus. The novel, noninvasive 7T ¹H MRS-identified associations between Glu levels and ELS may guide future clinical studies.

Postweaning Enriched Environment Enhances Cognitive Function and Brain-Derived Neurotrophic Factor Signaling in the Hippocampus in Maternally Separated Rats

Adverse environments during early life may lead to different neurophysiological and behavioral consequences, including depression and learning and memory deficits that persist into adulthood. Previously, we demonstrated that exposure to an enriched environment during adolescence mitigates the cognitive impairment observed after maternal separation in a task-specific manner. However, underlying neural mechanisms are still not fully understood. The current study examines the effects of neonatal maternal separation (MS) and postweaning environmental enrichment (EE) on spatial learning and memory performance in a short version of the Barnes Maze, active and passive behaviors in the forced swim test, and on TrkB/BDNF receptor expression in the hippocampus. Our results revealed that MS impaired acquisition learning and that enriched rats performed better than non-enriched rats in acquisition trials, regardless of early conditions. During the probe, enriched-housed rats demonstrated better performance than those reared in standard conditions. No significant differences between groups were found in the forced swim test. Both MS and EE increase full-length TrkB expression, and the combination of MS and EE treatment caused the highest levels of this protein expression. Similarly, truncated TrkB expression was higher in the MS/EE group. Animal facility rearing (AFR) non-enriched groups present the lowest activation of phosphorylated Erk, a canonical downstream kinase of TrkB signaling. Taken together, our results demonstrate the importance of enriched environment as an intervention to ameliorate the effects of maternal separation on spatial learning and memory. TrkB/BDNF signaling could mediate neuroplastic changes related to learning and memory during exposure to enriched environment.

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.

Environmental enrichment and its influence on rodent offspring and maternal behaviours, a scoping style review of indices of depression and anxiety

Environmental enrichment is a widely used experimental manipulation that consistently shows measurable effects on rodent behaviour across the lifespan. This scoping review assesses and thematically summarizes the literature of the past decade concerning the effects of environmental enrichment applied during sensitive developmental periods in rodent mothers and offspring. Maternal behaviours as well as maternal and offspring anxiety- and depressive-like behaviours are considered. Relevant terms were searched across five databases (Embase, MEDLINE, PsycINFO, PubMed, Web of Science) and articles were screened with inclusion and exclusion criteria. The remaining articles were thematically analysed. Our results suggest that a greater number of articles reviewed the impacts of environmental enrichment on offspring anxiety-like behaviour (n = 23) rather than on depressive-like behaviour (n = 11) or maternal caregiving behaviour (n = 12). Maternal anxiety- (n = 4) or depressive-like (n = 2) behaviours are not often evaluated for in enrichment studies. The main behavioural tests of anxiety that were reviewed include the elevated plus-maze, the open field test, and the light-dark box whereas those for depression included the forced swim test and the sucrose preference test. Our results yielded mixed findings and significant variation in behavioural responses across all tests. In mothers, trends of increased maternal care behaviours and decreased maternal depressive-like behaviours in enriched mothers were appreciated. Enrichment during the gestational period was identified as pivotal to creating behavioural change in mother subjects. In enriched offspring rodents, a trend towards decreased anxiety-like behaviours was observed most often. Potential confounds inherent in enrichment paradigms and relevant theories of enrichment and their relation to rodent behavioural tests are discussed.

Sex-Specific Effects of Early Life Stress on Brain Mitochondrial Function, Monoamine Levels and Neuroinflammation

Sex differences have been reported in the susceptibility to early life stress and its neurobiological correlates in humans and experimental animals. However, most of the current research with animal models of early stress has been performed mainly in males. In the present study, prolonged maternal separation (MS) paradigm was applied as an animal model to resemble the effects of adverse early experiences in male and female rats. Regional brain mitochondrial function, monoaminergic activity, and neuroinflammation were evaluated as adults. Mitochondrial energy metabolism was greatly decreased in MS females as compared with MS males in the prefrontal cortex, dorsal hippocampus, and the nucleus accumbens shell. In addition, MS males had lower serotonin levels and increased serotonin turnover in the prefrontal cortex and the hippocampus. However, MS females showed increased dopamine turnover in the prefrontal cortex and increased norepinephrine turnover in the striatum, but decreased dopamine turnover in the hippocampus. Sex differences were also found for pro-inflammatory cytokine levels, with increased levels of TNF-α and IL-6 in the prefrontal cortex and hippocampus of MS males, and increased IL-6 levels in the striatum of MS females. These results evidence the complex sex- and brain region-specific long-term consequences of early life stress.

Microglial Function in the Effects of Early-Life Stress on Brain and Behavioral Development

The putative effects of early-life stress (ELS) on later behavior and neurobiology have been widely investigated. Recently, microglia have been implicated in mediating some of the effects of ELS on behavior. In this review, findings from preclinical and clinical literature with a specific focus on microglial alterations induced by the exposure to ELS (i.e., exposure to behavioral stressors or environmental agents and infection) are summarized. These studies were utilized to interpret changes in developmental trajectories based on the time at which the stress occurred, as well as the paradigm used. ELS and microglial alterations were found to be associated with a wide array of deficits including cognitive performance, memory, reward processing, and processing of social stimuli. Four general conclusions emerged: (1) ELS interferes with microglial developmental programs, including their proliferation and death and their phagocytic activity; (2) this can affect neuronal and non-neuronal developmental processes, which are dynamic during development and for which microglial activity is instrumental; (3) the effects are extremely dependent on the time point at which the investigation is carried out; and (4) both pre- and postnatal ELS can prime microglial reactivity, indicating a long-lasting alteration, which has been implicated in behavioral abnormalities later in life.

Environmental enrichment effects after early stress on behavior and functional brain networks in adult rats

Early life stress is associated with long-term and pervasive adverse effects on neuroendocrine development, affecting normal cognitive and emotional development. Experimental manipulations like environmental enrichment (EE) may potentially reverse the effects of early life stress induced by maternal separation (MS) paradigm in rodents. However, the functional brain networks involved in the effects of EE after prolonged exposure to MS have not yet been investigated. In order to evaluate possible changes in brain functional connectivity induced by EE after MS, quantitative cytochrome c oxidase (CCO) histochemistry was applied to determine regional brain oxidative metabolism in adult male rats. Unexpectedly, results show that prolonged MS during the entire weaning period did not cause any detrimental effects on spatial learning and memory, including depressive-like behavior evaluated in the forced-swim test, and decreased anxiety-like behavior. However, EE seemed to alter anxiety- and depression-like behaviors in both control and MS groups, but improved spatial memory in the latter groups. Analysis of brain CCO activity showed significantly lower metabolic capacity in most brain regions selected in EE groups probably associated with chronic stress, but no effects of MS on brain metabolic capacity. In addition, principal component analysis of CCO activity revealed increased large-scale functional brain connectivity comprising at least three main networks affected by EE in both MS and control groups. Moreover, EE induced a pattern of functional brain connectivity associated with stress and anxiety-like behavior as compared with non-enriched groups. In conclusion, EE had differential effects on cognition and emotional behavior irrespective of exposure to MS. In view of the remarkable effects of EE on brain function and behavior, implementation of rodent housing conditions should be optimized by evaluating the balance between scientific validity and animal welfare.

Effects of Environmental Enrichment in Maternally Separated Rats: Age and Sex-Specific Outcomes

Maternal separation (MS) early in life is related to an increase in anxiety and depressive-like behaviors and neurobiological alterations mostly related to alterations in hypothalamic pituitary adrenal (HPA) axis reactivity. Environmental enrichment (EE) has been used to ameliorate the effects of MS. However, the outcomes of this intervention at different developmental periods after MS have not been studied. We subjected male and female Sprague–Dawley pups to MS and subsequently compared the effects of EE started either in the pre-pubertal period [postnatal day (PND) 22] or adulthood (PND 78). Anxiety and depressive-like behaviors as well as in hippocampal synaptic density and basal corticosterone, oxytocin, and vasopressin levels were measured. Our results support the beneficial effects of adulthood EE in decreasing anxiety in males as well as promoting synaptic density in ventral hippocampal CA3. Males displayed higher levels of vasopressin while females displayed higher oxytocin, with no changes in basal corticosterone for any group after EE.

Early life maternal sociality predicts juvenile sociality in blue monkeys

Maternal effects are widespread in living organisms though little is known about whether they shape individual affiliative social behavior in primates. Further, it remains a question whether maternal effects on affiliative behavior differ by offspring sex, as they do in other physiological systems, especially in species with high levels of adult sexual dimorphism and divergence in social niches. We explored how direct and indirect experiences of maternal affiliative behavior during infancy predicted affiliative behavior approximately 1-6 years later during the juvenile period, using behavioral data from 41 wild blue monkey juveniles and their 29 mothers, and controlling for individual age, sex, and maternal rank. Female juveniles spent less time grooming with any partner and with peers the more maternal grooming they received during infancy, whereas males groomed more with any partner and with peers. Similarly, the more that mothers groomed with other adult females during subjects' infancy, female subjects played less with peers, and male subjects played more as juveniles. Further, this maternal effect on social behavior appears specific to early life, as the same aspects of mothers' sociality measured throughout subjects' development did not predict juvenile behavior. Overall, our results suggest that both direct and indirect experience of mother's affiliative behavior during infancy influence an individual's affiliation later in life that sexes respond differently to the maternal affiliation, and that the first year of life is a critical window.

Access to a high resource environment protects against accelerated maturation following early life stress: A translational animal model of high, medium and low security settings

Early life exposure to a low security setting, characterized by a scarcity of resources and limited food access, increases the risk for psychiatric illness and metabolic dysfunction. We utilized a translational rat model to mimic a low security environment and determined how this manipulation affected offspring behavior, metabolism, and puberty. Because food insecurity in humans is associated with reduced access to healthy food options the "low security" rat manipulation combined a Western diet with exposure to a limited bedding and nesting manipulation (WD-LB). In this setting, dams were provided with limited nesting materials during the pups' early life (P2-P10). This manipulation was contrasted with standard rodent caging (SD) and environmental enrichment (EE), to model "medium security" and "high security" environments, respectively. To determine if transitioning from a low to high security environment improved outcomes, some juvenile WD-LB offspring were exposed to EE. Maternal care was impacted by these environments such that EE dams engaged in high quality care when on the nest, but spent less time on the nest than SD dams. Although WD-LB dams excessively chased their tails, they were very attentive to their pups, perhaps to compensate for limited resources. Offspring exposed to WD-LB only displayed subtle changes in behavior. However, WD-LB exposure resulted in significant metabolic dysfunction characterized by increased body weight, precocious puberty and alterations in the hypothalamic kisspeptin system. These negative effects of WD-LB on puberty and weight regulation were mitigated by EE exposure. Collectively, these studies suggest that both compensatory maternal care and juvenile enrichment can reduce the impact of a low security environment. Moreover, they highlight how utilizing diverse models of resource (in)stability can reveal mechanisms that confer vulnerability and resilience to early life stress.

Resilience priming: Translational models for understanding resiliency and adaptation to early life adversity

Despite the increasing attention to early life adversity and its long-term consequences on health, behavior, and the etiology of neurodevelopmental disorders, our understanding of the adaptations and interventions that promote resiliency and rescue against such insults are underexplored. Specifically, investigations of the perinatal period often focus on negative events/outcomes. In contrast, positive experiences (i.e. enrichment/parental care//healthy nutrition) favorably influence development of the nervous and endocrine systems. Moreover, some stressors result in adaptations and demonstrations of later-life resiliency. This review explores the underlying mechanisms of neuroplasticity that follow some of these early life experiences and translates them into ideas for interventions in pediatric settings. The emerging role of the gut microbiome in mediating stress susceptibility is also discussed. Since many negative outcomes of early experiences are known, it is time to identify mechanisms and mediators that promote resiliency against them. These range from enrichment, quality parental care, dietary interventions and those that target the gut microbiota.

The Mitochondrion as Potential Interface in Early-Life Stress Brain Programming

Mitochondria play a central role in cellular energy-generating processes and are master regulators of cell life. They provide the energy necessary to reinstate and sustain homeostasis in response to stress, and to launch energy intensive adaptation programs to ensure an organism’s survival and future well-being. By this means, mitochondria are particularly apt to mediate brain programming by early-life stress (ELS) and to serve at the same time as subcellular substrate in the programming process. With a focus on mitochondria’s integrated role in metabolism, steroidogenesis and oxidative stress, we review current findings on altered mitochondrial function in the brain, the placenta and peripheral blood cells following ELS-dependent programming in rodents and recent insights from humans exposed to early life adversity (ELA). Concluding, we propose a role of the mitochondrion as subcellular intersection point connecting ELS, brain programming and mental well-being, and a role as a potential site for therapeutic interventions in individuals exposed to severe ELS.

Effect of enriched environment during adolescence on spatial learning and memory, and voluntary consumption of morphine in maternally separated rats in adulthood

This study was designed to examine the effect of environmental enrichment (EE) during adolescence on spatial learning and memory and voluntary morphine consumption in maternally separated (MS) male and female rats in adulthood. Male Wistar rats were allowed to mate with female virgin Wistar rats. Pups were separated from the dams daily for 180 min during postnatal days 2-14. All pups were weaned on day 21. The pups of both sexes were reared in a standard (SE) or enriched (EE) environment during postnatal days 21-50. Then, adulthood rats were tested for spatial learning and memory (Morris Water Maze), and voluntary consumption of morphine using a two-bottle choice paradigm (TBC). We found that the MS/SE rats showed longer escape latencies to find the platform on the third (the male) and fourth (the female) days of training than No MS/SE rats. Also, exposure to EE shortened the latency to escape in the male and female MS rats as training progressed than MS/SE rats. Moreover, the No MS/EE and MS/EE male rats spent significantly more time in the target zone compared with the SE control groups in the probe test. We also found that voluntary morphine consumption was higher in the male and female MS/SE than No MS/SE rats, while it was lower in the male and female MS/EE rats. The present results have shown that EE treatment may have potential therapeutic application for the prevention of the development of drug addiction and recovery from cognitive deficits following neonatal MS during adulthood.

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 Marlau^TM 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.

Beneficial effects of environmental enrichment on behavior, stress reactivity and synaptophysin/BDNF expression in hippocampus following early life stress

Exposure to environmental enrichment can beneficially influence the behavior and enhance synaptic plasticity. The aim of the present study was to investigate the mediated effects of environmental enrichment on postnatal stress-associated impact with regard to behavior, stress reactivity as well as synaptic plasticity changes in the dorsal hippocampus. Wistar rat pups were submitted to a 3 h maternal separation (MS) protocol during postnatal days 1-21, while another group was left undisturbed. On postnatal day 23, a subgroup from each rearing condition (maternal separation, no-maternal separation) was housed in enriched environmental conditions until postnatal day 65 (6 weeks duration). At approximately three months of age, adult rats underwent behavioral testing to evaluate anxiety (Elevated Plus Maze), locomotion (Open Field Test), spatial learning and memory (Morris Water Maze) as well as non-spatial recognition memory (Novel Object Recognition Test). After completion of behavioral testing, blood samples were taken for evaluation of stress-induced plasma corticosterone using an enzyme-linked immunosorbent assay (ELISA), while immunofluorescence was applied to evaluate hippocampal BDNF and synaptophysin expression in dorsal hippocampus. We found that environmental enrichment protected against the effects of maternal separation as indicated by the lower anxiety levels and the reversal of spatial memory deficits compared to animals housed in standard conditions. These changes were associated with increased BDNF and synaptophysin expression in the hippocampus. Regarding the neuroendocrine response to stress, while exposure to an acute stressor potentiated corticosterone increases in maternally-separated rats, environmental enrichment of these rats prevented this effect. The current study aimed at investigating the compensatory role of enriched environment against the negative outcomes of adverse experiences early in life concurrently on emotional and cognitive behaviors, HPA function and neuroplasticity markers.

Neonatal Stress Has a Long-Lasting Sex-Dependent Effect on Anxiety-Like Behavior and Neuronal Morphology in the Prefrontal Cortex and Hippocampus

The long-lasting effects of early stress on brain development have been well studied. Recent evidence indicates that males and females respond differently to the same stressor. We examined the chronic effects of daily maternal separation (MS) on behavior and cerebral morphology in both male and female rats. Cognitive and anxiety-like behaviors were evaluated, and neuroplastic changes in 2 subregions of the prefrontal cortex (dorsal agranular insular cortex [AID] and cingulate cortex [Cg3]) and hippocampus (CA1 and dentate gyrus) were measured in adult male and female rats. The animals were subjected to MS on postnatal day (P) 3-14 for 3 h per day. Cognitive and emotional behaviors were assessed in the object/context mismatch task, elevated plus maze, and locomotor activity test in early adulthood (P87-P95). Anatomical assessments were performed in the prefrontal cortex (i.e., cortical thickness and spine density) and hippocampus (i.e., spine density). Sex-dependent effects were observed. MS increased anxiety-related behavior only in males, whereas locomotor activity was higher in females, with no effects on cognition. MS decreased spine density in the AID and increased spine density in the CA1 area in males. Females exhibited an increase in spine density in the Cg3. Our findings confirm previous work that found that MS causes long-term behavioral and anatomical effects, and these effects were dependent on sex and the duration of MS stress.

Environmental enrichment and exercise are better than social enrichment to reduce memory deficits in amyloid beta neurotoxicity

Recently, nongenetic animal models to study the onset and development of Alzheimer's disease (AD) have appeared, such as the intrahippocampal infusion of peptides present in Alzheimer amyloid plaques [i.e., amyloid-β (Aβ)]. Nonpharmacological approaches to AD treatment also have been advanced recently, which involve combinations of behavioral interventions whose specific effects are often difficult to determine. Here we isolate the neuroprotective effects of three of these interventions-environmental enrichment (EE), anaerobic physical exercise (AnPE), and social enrichment (SE)-on Aβ-induced oxidative stress and on impairments in learning and memory induced by Aβ. Wistar rats were submitted to 8 wk of EE, AnPE, or SE, followed by Aβ infusion in the dorsal hippocampus. Short-term memory (STM) and long-term memory (LTM) of object recognition (OR) and social recognition (SR) were evaluated. Biochemical assays determined hippocampal oxidative status: reactive oxygen species, lipid peroxidation by thiobarbituric acid reactive substance (TBARS) test, and total antioxidant capacity by ferric reducing/antioxidant power (FRAP), as well as acetylcholinesterase activity. Aβ infusion resulted in memory deficits and hippocampal oxidative damage. EE and AnPE prevented all memory deficits (STM and LTM of OR and SR) and lipid peroxidation (i.e., TBARS). SE prevented only the SR memory deficits and the decrease of total antioxidant capacity decrease (i.e., FRAP). Traditionally, findings obtained with EE protocols do not allow discrimination of the roles of the three individual factors involved. Here we demonstrate that EE and physical exercise have better neuroprotective effects than SE in memory deficits related to Aβ neurotoxicity in the AD model tested.

Reappraising Preclinical Models of Separation Anxiety Disorder, Panic Disorder, and CO2 Sensitivity: Implications for Methodology and Translation into New Treatments

Separation anxiety applies to multiple forms of distress responses seen in mammals during postnatal development, including separation from a caregiver. Childhood separation anxiety disorder is an important risk factor for developing panic disorder in early adulthood, and both conditions display an increased sensitivity to elevated CO₂ concentrations inhaled from the air. By interfacing epidemiological, genetic, and physiological knowledge with preclinical animal research models, it is possible to decipher the mechanisms that are central to separation anxiety and panic disorders while also suggesting possible therapies. Preclinical research models allow for environmentally controlled studies of early interferences with parental care. These models have shown that different forms of early maternal separation in mice and rats induce elevated CO₂ respiratory sensitivity, an important biomarker of separation anxiety and panic disorders. In mice, this is likely due to gene-environment interactions that affect multiple behavioural and physical phenotypes after exposure to this early adversity. Although several questions regarding the causal mechanism of separation anxiety and panic disorder remain unanswered, the identification and improved understanding of biomarkers that link these mental health conditions under the guise of preclinical research models in conjunction with human longitudinal cohort studies can help resolve these issues.

Developmental expression of anxiety and depressive behaviours after prenatal predator exposure and early life homecage enhancement

Stressful events during gestation can have sex-specific effects on brain and behaviour, and may contribute to some of the differences observed in adult stress responding and psychopathology. We investigated the impact of a novel repeated prenatal psychological stress (prenatal predator exposure - PPS) during the last week of gestation in rats on offspring behaviours related to social interaction (play behaviour), open field test (OFT), forced swim test (FST) and sucrose preference test (SP) during the juvenile period and in adulthood. We further examined the role of postnatal environmental, using an enhanced housing condition (EHC), to prevent/rescue any changes. Some effects on anxiety, anhedonia, and stress-related coping behaviours (e.g., OFT, SP and OFT) did not emerge until adulthood. PPS increased OFT anxiety behaviours in adult males, and some OFT and SP behaviours in adult females. Contrary to this, EHC had few independent effects; most were apparent only when combined with PPS. In keeping with age-group differences, juvenile behaviours did not necessarily predict the same adult behaviours although juvenile OFT rearing and freezing, and juvenile FST immobility did predict adult FST immobility and sucrose preference, suggesting that some aspects of depressive behaviours may emerge early and predict adult vulnerability or coping behaviours. Together, these results suggest an important, though complex, role for early life psychological stressors and early life behaviours in creating an adult vulnerability to anxiety or depressive disorders and that environmental factors further modulate the effects of the prenatal stressors.