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

Sex-Dependent Modulation of Acute Stress Reactivity After Early Life Stress in Mice:Relevance of Mineralocorticoid Receptor Expression

Early life stress (ELS) is considered a major risk factor for developing psychopathology. Increasing evidence points towards sex-dependent dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis as a contributing mechanism. Additionally, clinical studies suggest that the mineralocorticoid receptor (MR) may further confer genetic vulnerability/resilience on a background of ELS. The link between ELS, sex and the HPA axis and how this interacts with MR genotype is understudied, yet important to understand vulnerability/resilience to stress. We used the early life-limited nesting and bedding model to test the effect of ELS on HPA properties in adult female and male mice carrying a forebrain-specific heterozygous knockout for MR. Basal HPA axis activity was measured by circadian peak and nadir corticosterone levels, in addition to body weight and weight of stress-sensitive tissues. HPA axis reactivity was assessed by mapping corticosterone levels after 10 min immobilization. Additionally, we measured the effects of ELS on steroid receptor [MR and glucocorticoid receptor (GR)] levels in the dorsal hippocampus and medial prefrontal cortex (mPFC) with western blot. Finally, behavioral reactivity towards a novel environment was measured as a proxy for anxiety-like behavior. Results show that HPA axis activity under rest conditions was not affected by ELS. HPA axis reactivity after immobilization was decreased by ELS in females and increased, at trend-level in males. This effect in females was further exacerbated by low expression of the MR. We also observed a sex*ELS interaction regarding MR and GR expression in the dorsal hippocampus, with a significant upregulation of MR in males only. The sex-dependent interaction with ELS was not reflected in the behavioral response to novel environment and time spent in a sheltered compartment. We did find increased locomotor activity in all groups after a history of ELS, which attenuated after 4 h in males but not females regardless of condition. Our findings support that ELS alters HPA axis functioning sex-dependently. Genetic predisposition to low MR function may render females more susceptible to the harmful effect of ELS whereas in males low MR function promotes resilience. We propose that this model may be a useful tool to investigate the underlying mechanisms of sex-dependent and genetic vulnerability/resilience to stress-related psychopathology

The mouse brain after foot shock in four dimensions:Temporal dynamics at a single-cell resolution

Acute stress leads to sequential activation of functional brain networks. A biologically relevant question is exactly which (single) cells belonging to brain networks are changed in activity over time after acute stress across the entire brain. We developed a preprocessing and analytical pipeline to chart whole-brain immediate early genes’ expression—as proxy for cellular activity—after a single stressful foot shock in four dimensions: that is, from functional networks up to three-dimensional (3D) single-cell resolution and over time. The pipeline is available as an R package. Most brain areas (96%) showed increased numbers of c-fos+ cells after foot shock, yet hypothalamic areas stood out as being most active and prompt in their activation, followed by amygdalar, prefrontal, hippocampal, and finally, thalamic areas. At the cellular level, c-fos+ density clearly shifted over time across subareas, as illustrated for the basolateral amygdala. Moreover, some brain areas showed increased numbers of c-fos+ cells, while others—like the dentate gyrus—dramatically increased c-fos intensity in just a subset of cells, reminiscent of engrams; importantly, this “strategy” changed after foot shock in half of the brain areas. One of the strengths of our approach is that single-cell data were simultaneously examined across all of the 90 brain areas and can be visualized in 3D in our interactive web portal

The behavioral phenotype of early life adversity: a 3-level meta-analysis of rodent studies

Altered cognitive performance has been suggested as an intermediate phenotype mediating the effects of early life adversity (ELA) on later-life development of mental disorders, e.g. depression. Whereas most human studies are limited to correlational conclusions, rodent studies can prospectively investigate how ELA alters cognitive performance in a number of domains. Despite the vast volume of reports, no consensus has yet been reached on the i) behavioral domains being affected by ELA and ii) the extent of these effects. To test how ELA (here: aberrant maternal care) affects specific behavioral domains, we used a 3-level mixed-effect meta-analysis, a flexible model that accounts for the dependency of observations. We thoroughly explored heterogeneity with MetaForest, a machine-learning data-driven analysis never applied before in preclinical literature. We validated the robustness of our findings with substantial sensitivity analyses and bias assessments. Our results, based on over 400 independent experiments, yielded more than 700 comparisons, involving ~8600 animals. Especially in males, ELA promotes memory formation during stressful learning but impairs non-stressful learning. Furthermore, ELA increases anxiety and decreases social behavior. The ELA phenotype was strongest when i) combined with other negative experiences (“hits”); ii) in rats; iii) in ELA models of ~10days duration. Prospective and well-controlled animal studies demonstrate that ELA durably and differentially impacts distinct behavioral domains. All data is now easily accessible with MaBapp, which allows researchers to run tailor-made meta-analyses on the topic, thereby revealing the optimal choice of experimental protocols and study power

Integrating information in stress research

There are few experiences as engulfing as the subjective experience of stress. It affects multiple biological systems, with temporal and spatial specificity. It depends on genetic predisposition, early- and late- life events, and it leads to different responses depending on its type (e.g. psychological vs physiological) and frequency (e.g. acute vs chronic). This complex system has historically been studied by isolating each specific feature in an experiment. While this approach has been extremely successful, understanding stress as a system, rather than a collection of organs and hormones, can bring us closed to comprehend how it works in nature, in health and for the future improvement of disease. In this thesis, we examined stress as a biological system rather than isolating a specific feature in a single experiment. Specifically, we integrated information from multiple sources (i.e., literature, consortia, atlases, and newly generated data) to increase our understanding of the effects of acute stress and chronic stress experienced in early life on brain and behavior. Our approach was fully grounded in Open Science practices of collaboration, data and code sharing, as well as in software development. This thesis is subdivided into three sections. In Part A, we integrate information related to the healthy acute stress response, focusing on the rodent brain and salivary cortisol concentration in humans. While our studies have been conducted in two different species, they both investigate acute stress as a dynamic process that occurs in time. Independently of whether integration of information is applied to animal or human data, it is most efficacious when aimed at investigating the stability and reproducibility of effects. In Part B, we integrated information related to chronic stress experienced early in life by rodents. Adversities early in life can have long lasting consequences on brain development and are one of the main risk factors for several mental health disorders. The effects of early life adversity (ELA) on behavior and neurobiology depend on a complex interaction between early-, late- life events, as well as the acute state of the animal. By using systematic reviews and meta-analyses, we can integrate information of the literature to identify robust conclusions and provide quantitative descriptions. This led to the extraction of 7 principles of ELA, which give insight in what is currently known and can also guide future research. In Part C, we developed methodologies for information integration. Specifically, information of previous control animal groups can be used to improve the statistical power of animal experiments. Open Software was developed to aid scientists to integrate information, and as a knowledge utilization strategy for the smoother communication of scientific results. In conclusion, in this thesis we integrated information related to the acute and chronic (i.e. ELA) stress response. This was achieved 1) by performing new experiments in rodents, 2) by founding and expanding the collaboration within consortia, 3) by extensively and systematically reviewing the literature, and lastly 4) by providing data and scripts freely available online. It is a first step towards a comprehensive, systems-view of stress

Seven principles of early life adversity in rodents

Early life adversity (ELA) alters brain development and function, and it is one of the main risk factors for several psychiatric disorders. Rodent models have been used to better understand the underlying biological mechanisms, but results of single studies are rarely reliable due to various sources of biases. Here, we comprehensively review the literature on the effects of ELA on brain and behavior, with a specific focus on the limbic system. We critically appraise the results of 10 meta-analyses investigating the effects of ELA, based on alteration of maternal care during the first postnatal weeks, on several outcomes. From this we delineated seven principles of ELA in rodents. All data is available for dynamic exploration via our webportal. We propose that a community effort is required to keep integrating the accumulating knowledge on the single outcomes. In all, we are at a turning point towards an integrated understanding of the effects of ELA on rodents’ brain and behavior

Integrating information in stress research

There are few experiences as engulfing as the subjective experience of stress. It affects multiple biological systems, with temporal and spatial specificity. It depends on genetic predisposition, early- and late- life events, and it leads to different responses depending on its type (e.g. psychological vs physiological) and frequency (e.g. acute vs chronic). This complex system has historically been studied by isolating each specific feature in an experiment. While this approach has been extremely successful, understanding stress as a system, rather than a collection of organs and hormones, can bring us closed to comprehend how it works in nature, in health and for the future improvement of disease. In this thesis, we examined stress as a biological system rather than isolating a specific feature in a single experiment. Specifically, we integrated information from multiple sources (i.e., literature, consortia, atlases, and newly generated data) to increase our understanding of the effects of acute stress and chronic stress experienced in early life on brain and behavior. Our approach was fully grounded in Open Science practices of collaboration, data and code sharing, as well as in software development. This thesis is subdivided into three sections. In Part A, we integrate information related to the healthy acute stress response, focusing on the rodent brain and salivary cortisol concentration in humans. While our studies have been conducted in two different species, they both investigate acute stress as a dynamic process that occurs in time. Independently of whether integration of information is applied to animal or human data, it is most efficacious when aimed at investigating the stability and reproducibility of effects. In Part B, we integrated information related to chronic stress experienced early in life by rodents. Adversities early in life can have long lasting consequences on brain development and are one of the main risk factors for several mental health disorders. The effects of early life adversity (ELA) on behavior and neurobiology depend on a complex interaction between early-, late- life events, as well as the acute state of the animal. By using systematic reviews and meta-analyses, we can integrate information of the literature to identify robust conclusions and provide quantitative descriptions. This led to the extraction of 7 principles of ELA, which give insight in what is currently known and can also guide future research. In Part C, we developed methodologies for information integration. Specifically, information of previous control animal groups can be used to improve the statistical power of animal experiments. Open Software was developed to aid scientists to integrate information, and as a knowledge utilization strategy for the smoother communication of scientific results. In conclusion, in this thesis we integrated information related to the acute and chronic (i.e. ELA) stress response. This was achieved 1) by performing new experiments in rodents, 2) by founding and expanding the collaboration within consortia, 3) by extensively and systematically reviewing the literature, and lastly 4) by providing data and scripts freely available online. It is a first step towards a comprehensive, systems-view of stress

Valeria Bonapersona PhD thesis

There are few experiences as engulfing as the subjective experience of stress. It affects multiple biological systems, with temporal and spatial specificity. It depends on genetic predisposition, early- and late- life events, and it leads to different responses depending on its type (e.g. psychological vs physiological) and frequency (e.g. acute vs chronic). This complex system has historically been studied by isolating each specific feature in an experiment. While this approach has been extremely successful, understanding stress as a system, rather than a collection of organs and hormones, can bring us closed to comprehend how it works in nature, in health and for the future improvement of disease. In this thesis, we examined stress as a biological system rather than isolating a specific feature in a single experiment. Specifically, we integrated information from multiple sources (i.e., literature, consortia, atlases, and newly generated data) to increase our understanding of the effects of acute stress and chronic stress experienced in early life on brain and behavior. Our approach was fully grounded in Open Science practices of collaboration, data and code sharing, as well as in software development

Effects of early life adversity on structural plasticity: a systematic review and 3-level meta-analysis of rodent studies

Early life adversity (ELA) is a well-documented risk factor for psychiatric illnesses in humans. This risk may, in part, be conferred by structural changes induced by ELA, lasting into adulthood. We here review the evidence for such lasting structural changes in rodent models for ELA involving altered maternal care during the first two postnatal weeks. In total, we extracted data from 64 studies reporting on 260 comparisons in adult rats or mice which experienced ELA or control treatment. Most of the observations concerned structural changes in the hippocampus of adult male rats earlier exposed to maternal separation. A 3-level meta-analysis revealed that ELA reduced hippocampal volume and the number of dendritic branches as well as dendritic length of principal hippocampal cells. No differences were observed across the hippocampal subfields. In terms of adult neurogenesis in the dentate subgranular zone, both staining for BrdU and the early neuronal marker DCX were significantly reduced, while the general proliferation marker Ki67 remained unchanged. The neuronal growth factor BDNF did not show significant changes, although the unexplained heterogeneity was moderate. Generally, the effect of ELA compared to control on structural markers was not affected by additional stressors experienced in life. Overall, the data available support the notion that ELA, at least in the hippocampus of male rats, lastingly reduces volume, hampers dendritic growth and suppresses adult neurogenesis