Effects of different types of induced neonatal inflammation on development and behavior of C57BL/6 and BTBR mice.

Neuroinflammation in the early postnatal period can disturb trajectories of the completion of normal brain development and can lead to mental illnesses, such as depression, anxiety disorders, and personality disorders later in life. In our study, we focused on evaluating short- and long-term effects of neonatal inflammation induced by lipopolysaccharide, poly(I:C), or their combination in female and male C57BL/6 and BTBR mice. We chose the BTBR strain as potentially more susceptible to neonatal inflammation because these mice have behavioral, neuroanatomical, and physiological features of autism spectrum disorders, an abnormal immune response, and several structural aberrations in the brain. Our results indicated that BTBR mice are more sensitive to the influence of the neonatal immune activation (NIA) on the formation of neonatal reflexes than C57BL/6 mice are. In these experiments, the injection of lipopolysaccharide had an effect on the formation of the cliff aversion reflex in female BTBR mice. Nonetheless, NIA had no delayed effects on either social behavior or anxiety-like behavior in juvenile and adolescent BTBR and C57BL/6 mice. Altogether, our data show that NIA has mimetic-, age-, and strain-dependent effects on the development of neonatal reflexes and on exploratory activity in BTBR and C57BL/6 mice.

A comparison of stress reactivity between BTBR and C57BL/6J mice: an impact of early-life stress.

Early-life stress (ELS) is associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation and can increase the risk of psychiatric disorders later in life. The aim of this study was to investigate the influence of ELS on baseline HPA axis functioning and on the response to additional stress in adolescent male mice of strains C57BL/6J and BTBR. As a model of ELS, prolonged separation of pups from their mothers (for 3 h once a day: maternal separation [MS]) was implemented. To evaluate HPA axis activity, we assessed serum corticosterone levels and mRNA expression of corticotropin-releasing hormone (Crh) in the hypothalamus, of steroidogenesis genes in adrenal glands, and of an immediate early gene (c-Fos) in both tissues at baseline and immediately after 1 h of restraint stress. HPA axis activity at baseline did not depend on the history of ELS in mice of both strains. After the exposure to the acute restraint stress, C57BL/6J-MS mice showed less pronounced upregulation of Crh and of corticosterone concentration as compared to the control, indicating a decrease in stress reactivity. By contrast, BTBR-MS mice showed stronger upregulation of c-Fos in the hypothalamus and adrenal glands as compared to controls, thus pointing to greater activation of these organs in response to the acute restraint stress. In addition, we noted that BTBR mice are more stress reactive (than C57BL/6J mice) because they exhibited greater upregulation of corticosterone, c-Fos, and Cyp11a1 in response to the acute restraint stress. Taken together, these results indicate strain-specific and situation-dependent effects of ELS on HPA axis functioning and on c-Fos expression.

High-resolution MRI data of the brain of C57BL/6J and BTBR mice in three anatomical views.

The research on strain-, sex-, and stress-specific differences in structural and functional connectivity of the brain is important for elucidating various behavioral features and etiologies of psychiatric disorders. Socially impaired BTBR mice are considered a model of autism spectrum disorders. Here we present high-resolution magnetic resonance imaging data from the brain of 89 adolescent mice (C57BL/6J and BTBR) in axial, sagittal, and coronal views. The study [1] includes both females and males differed in early-life experience (normally reared or subjected to prolonged maternal separation: 3 h daily from postnatal day 2 to 15). The MRI data were obtained on a horizontal tomograph Biospec 117/16 instrument with a magnetic field strength of 11.7 T. Thus, multislice Turbo RARE T2-weighted images of the brain were captured in eight groups of mice. Altogether, these data allow to evaluate strain-, sex-, and stress-specific alterations in the volumes of various brain structures and to better understand the relation between brain structural differences and behavioral abnormalities.

Sex-specific behavioral and structural alterations caused by early-life stress in C57BL/6 and BTBR mice.

Lately, the development of various mental illnesses, such as depression, personality disorders, and autism spectrum disorders, is often associated with traumatic events in childhood. Nonetheless, the mechanism giving rise to this predisposition is still unknown. Because the development of a disease often depends on a combination of a genetic background and environment, we decided to evaluate the effect of early-life stress on BTBR mice, which have behavioral, neuroanatomical, and physiological features of autism spectrum disorders. As early-life stress, we used prolonged separation of pups from their mothers in the first 2 weeks of life (3 h once a day). We assessed effects of the early-life stress on juvenile (postnatal day 23) and adolescent (postnatal days 37-38) male and female mice of strains C57BL/6 (B6) and BTBR. We found that in both strains, the early-life stress did not lead to changes in the level of social behavior, which is an important characteristic of autism-related behavior. Nonetheless, the early-life stress resulted in increased locomotor activity in juvenile BTBR mice. In adolescent mice, the stress early in life caused a low level of anxiety in B6 males and BTBR females and increased exploratory activity in adolescent BTBR males and females. In addition, adolescent B6 male and female mice with a history of the early-life stress tended to have a thinner motor cortex as assessed by magnetic resonance imaging. As compared to B6 mice, BTBR mice showed reduced levels of social behavior and exploratory activity but their level of locomotor activity was higher. BTBR mice had smaller whole-brain, cortical, and dorsal hippocampal volumes; decreased motor cortex thickness; and increased ventral-hippocampus volume as compared to B6 mice, and these parameters correlated with the level of exploratory behavior of BTBR mice. Overall, the effects of early postnatal stress are sex- and strain-dependent.

Maternal Separation Early in Life Alters the Expression of Genes Npas4 and Nr1d1 in Adult Female Mice: Correlation with Social Behavior.

Early-life stress affects neuronal plasticity of the brain regions participating in the implementation of social behavior. Our previous studies have shown that brief and prolonged separation of pups from their mothers leads to enhanced social behavior in adult female mice. The goal of the present study was to characterize the expression of genes (which are engaged in synaptic plasticity) Egr1, Npas4, Arc, and Homer1 in the prefrontal cortex and dorsal hippocampus of adult female mice with a history of early-life stress. In addition, we evaluated the expression of stress-related genes: glucocorticoid and mineralocorticoid receptors (Nr3c1 and Nr3c2) and Nr1d1, which encodes a transcription factor (also known as REVERBα) modulating sociability and anxiety-related behavior. C57Bl/6 mice were exposed to either maternal separation (MS, 3 h once a day) or handling (HD, 15 min once a day) on postnatal days 2 through 14. In adulthood, the behavior of female mice was analyzed by some behavioral tests, and on the day after the testing of social behavior, we measured the gene expression. We found increased Npas4 expression only in the prefrontal cortex and higher Nr1d1 expression in both the prefrontal cortex and dorsal hippocampus of adult female mice with a history of MS. The expression of the studied genes did not change in HD female mice. The expression of stress-related genes Nr3c1 and Nr3c2 was unaltered in both groups. We propose that the upregulation of Npas4 and Nr1d1 in females with a history of early-life stress and the corresponding enhancement of social behavior may be regarded as an adaptation mechanism reversing possible aberrations caused by early-life stress.

Stress early in life leads to cognitive impairments, reduced numbers of CA3 neurons and altered maternal behavior in adult female mice.

The hippocampus is a crucial part of the limbic system involved both in cognitive processing and in the regulation of responses to stress. Adverse experiences early in life can disrupt hippocampal development and lead to impairment of the hypothalamic-pituitary-adrenal axis response to subsequent stressors. In our study, two types of early-life stress were used: prolonged separation of pups from their mothers (for 3 hours/day, maternal separation, MS) and brief separation (for 15 minutes/day, handling, HD). In the first part of our study, we found that adult female mice (F0) who had experienced MS showed reduced locomotor activity and impairment of long-term spatial and recognition memory. Analysis of various hippocampal regions showed that MS reduced the number of mature neurons in CA3 of females, which is perhaps a crucial hippocampal region for learning and memory; however, neurogenesis remained unchanged. In the second part, we measured maternal care in female mice with a history of early-life stress (F0) as well as the behavior of their adult offspring (F1). Our results indicated that MS reduced the level of maternal care in adult females (F0) toward their own progeny and caused sex-specific changes in the social behavior of adult offspring (F1). In contrast to MS, HD had no influence on female behavior or hippocampal plasticity. Overall, our results suggest that prolonged MS early in life affects the adult behavior of F0 female mice and hippocampal neuronal plasticity, whereas the mothers' previous experience has effects on the behavior of their F1 offspring through disturbances of mother-infant interactions.

Effects of Early-Life Stress on Social and Anxiety-Like Behaviors in Adult Mice: Sex-Specific Effects.

Stressful events in an early postnatal period have critical implications for the individual's life and can increase later risk for psychiatric disorders. The aim of this study was to investigate the influence of early-life stress on the social behavior of adult male and female mice. C57Bl/6 mice were exposed to maternal separation (MS, 3 h once a day) or handling (HD, 15 min once a day) on postnatal day 2 through 14. Adult male and female mice were tested for social behavior in the social interaction test and for individual behavior in the plus-maze and open-field tests. Female mice exposed to maternal separation had increased social behavior and increased anxiety. MS male mice had no changes in social behavior but had significantly disrupted individual behavior, including locomotor and exploratory activity. Handling had positive effects on social behavior in males and females and decreased anxiety in males. Our results support the hypothesis that brief separation of pups from their mothers (handling), which can be considered as moderate stress, may result in future positive changes in behavior. Maternal separation has deleterious effects on individual behavior and significant sex-specific effects on social behavior.

Consequences of early life stress on genomic landscape of H3K4me3 in prefrontal cortex of adult mice.

BACKGROUND: Maternal separation models in rodents are widely used to establish molecular mechanisms underlying prolonged effects of early life adversity on neurobiological and behavioral outcomes in adulthood. However, global epigenetic signatures following early life stress in these models remain unclear. RESULTS: In this study, we carried out a ChIP-seq analysis of H3K4 trimethylation profile in the prefrontal cortex of adult male mice with a history of early life stress. Two types of stress were used: prolonged separation of pups from their mothers (for 3 h once a day, maternal separation, MS) and brief separation (for 15 min once a day, handling, HD). Adult offspring in the MS group demonstrated reduced locomotor activity in the open field test accompanied by reduced exploratory activity, while the HD group showed decreased anxiety-like behavior only. In a group of maternal separation, we have found a small number (45) of slightly up-regulated peaks, corresponding to promoters of 70 genes, while no changes were observed in a group of handling. Among the genes whose promoters have differential enrichment of H3K4me3, the most relevant ones participate in gene expression regulation, modulation of chromatin structure and mRNA processing. For two genes, Ddias and Pip4k2a, increased H3K4me3 levels were associated with the increased mRNA expression in MS group. CONCLUSION: The distribution of H3K4me3 in prefrontal cortex showed relatively low variability across all individuals, and only some subtle changes were revealed in mice with a history of early life stress. It is possible that the observed long-lasting behavioral alterations induced by maternal separation are mediated by other epigenetic mechanisms, or other brain structures are responsible for these effects.

Molecular Adaptations to Social Defeat Stress and Induced Depression in Mice.

Chronic stress is a risk factor for major depression. Social defeat stress is a well-validated murine model of depression. However, little is known about the gene activity dynamics during the development of a depression-like state. We analyzed the effects of social defeat stress of varying duration (10 and 30 days) on the behavioral patterns and prefrontal-cortex transcriptome of C57BL/6 mice. The 10-day exposure to social defeat stress resulted in a high level of social avoidance with no signs of depression-associated behavior. Most animals exposed to 30 days of social defeat stress demonstrated clear hallmarks of depression, including a higher level of social avoidance, increased immobility in the forced swimming test, and anhedonic behavior. The monitoring of transcriptome changes revealed widespread alterations in gene expression on the 10th day. Surprisingly, the expression of only a few genes were affected by the 30th day of stress, apparently due to a reversal of the majority of the early stress-induced changes to the original basal state. Moreover, we have found that glucocorticoid-sensitive genes are clearly stimulated targets on the 10th day of stress, but these genes stop responding to the elevated corticosterone level by the 30th day of stress. The majority of genes altered by the 30-day stress were downregulated, with the most relevant ones participating in chromatin modifications and neuroplasticity (e.g., guanine nucleotide exchange factors of the Rho-family of GTPases). Very different molecular responses occur during short-term and long-term social stress in mice. The early-stress response is associated with social avoidance and with upregulation and downregulation of many genes, including those related to signal transduction and cell adhesion pathways. Downregulation of a few genes, in particular, genes for histone-modifying methyltransferases, is a signature response to prolonged stress that induces symptoms of depression. Altogether, our data show that the development of depression under social stress conditions is correlated with suppression of the overactive molecular response to induced stress, involving gene regulatory resistance to glucocorticoid molecules, potentially via a chromatin remodeling mechanism.

Brain-derived neurotrophic factor and early-life stress: Multifaceted interplay.

The brain-derived neurotrophic factor (BDNF) is a key regulator of neural development and plasticity. Longterm changes in the BDNF pathway are associated with childhood adversity and adult depression symptoms. Initially, stress-induced decreases in the BDNF pathway were found in some studies, but subsequent reports indicated the relationship between stress and BDNF to be much more complex, and the concept was significantly revised. In the present mini-review, we focus on the structure and regulation of the Bbnf gene as well as on the stress-BDNF interactions under early-life adverse conditions.

Altered Hippocampal Neurogenesis and Amygdalar Neuronal Activity in Adult Mice with Repeated Experience of Aggression.

Repeated experience of winning in a social conflict setting elevates levels of aggression and may lead to violent behavioral patterns. Here, we use a paradigm of repeated aggression and fighting deprivation to examine changes in behavior, neurogenesis, and neuronal activity in mice with positive fighting experience. We show that for males, repeated positive fighting experience induces persistent demonstration of aggression and stereotypic behaviors in daily agonistic interactions, enhances aggressive motivation, and elevates levels of anxiety. When winning males are deprived of opportunities to engage in further fights, they demonstrate increased levels of aggressiveness. Positive fighting experience results in increased levels of progenitor cell proliferation and production of young neurons in the hippocampus. This increase is not diminished after a fighting deprivation period. Furthermore, repeated winning experience decreases the number of activated (c-fos-positive) cells in the basolateral amygdala and increases the number of activated cells in the hippocampus; a subsequent no-fight period restores the number of c-fos-positive cells. Our results indicate that extended positive fighting experience in a social conflict heightens aggression, increases proliferation of neuronal progenitors and production of young neurons in the hippocampus, and decreases neuronal activity in the amygdala; these changes can be modified by depriving the winners of the opportunity for further fights.

Downregulation of serotonergic gene expression in the Raphe nuclei of the midbrain under chronic social defeat stress in male mice.

There is ample experimental evidence supporting the hypothesis that the brain serotonergic system is involved in the control of chronic social defeat stress (CSDS), depression, and anxiety. The study aimed to analyze mRNA levels of the serotonergic genes in the raphe nuclei of midbrain that may be associated with chronic social defeats consistently shown by male mice in special experimental settings. The serotonergic genes were the Tph2, Sert, Maoa, and Htr1a. The Bdnf and Creb genes were also studied. The experimental groups were composed of male mice with experience of defeats in 21 daily encounters and male mice with the same track record of defeats followed by a no-defeat period without agonistic interactions (relative rest for 14 days). It has been shown that mRNA levels of the Tph2, Maoa, Sert, Htr1a, Bdnf, and Creb genes in the raphe nuclei of defeated mice are decreased as compared with the controls. The expression of the serotonergic genes as well as the Creb gene is not restored to the control level after the 2 weeks of relative rest. mRNA levels of Bdnf gene are not recovered to the control levels, although some upregulation was observed in rested losers. CSDS experience inducing the development of mixed anxiety/depression-like state in male mice downregulates the expression of serotonergic genes associated with the synthesis, inactivation, and reception of serotonin. The Bdnf and Creb genes in the midbrain raphe nuclei are also downregulated under CSDS. Period of relative rest is not enough for most serotonergic genes to recover expression to the control levels.