Effects of early-life stress on fear memory in the developing rat

Early-life stress impairs acquisition and retrieval of fear memories: sex-effects, corticosterone modulation, and partial prevention by targeting glucocorticoid receptors at adolescent age

The early postnatal period is a sensitive time window that is characterized by several neurodevelopmental processes that define neuronal architecture and function later in life. Here, we examined in young adult mice, using an auditory fear conditioning paradigm, whether stress during the early postnatal period 1) impacts fear acquisition and memory consolidation in male and female mice; 2) alters the fear responsiveness to corticosterone and 3) whether effects of early-life stress (ELS) can be prevented by treating mice with a glucocorticoid (GR) antagonist at adolescence. Male and female mice were exposed to a limited nesting and bedding model of ELS from postnatal day (PND) 2-9 and injected i.p with RU38486 (RU486) at adolescent age (PND 28-30). At two months of age, mice were trained in the fear conditioning (FC) paradigm (with and without post training administration of corticosterone - CORT) and freezing behavior during fear acquisition and contextual and auditory memory retrieval was scored. We observed that ELS impaired fear acquisition specifically in male mice and reduced both contextual and auditory memory retrieval in male and female mice. Acute post-training administration of CORT increased freezing levels during auditory memory retrieval in female mice but reduced freezing levels during the tone presentation in particular in control males. Treatment with RU486 prevented ELS-effects in acquisition in male mice and in females during auditory memory retrieval. In conclusion, this study highlights the long-lasting consequences of early-life stress on fear memory processing and further illustrates 1) the potential of a glucocorticoid antagonist intervention during adolescence to mitigate these effects and 2) the partial modulation of the auditory retrieval upon post training administration of CORT, with all these effects being sex-dependent.

The Impact of Chronic Stress on Behavior and Body Mass in New Animal Models

(1) Background: Exposure to different sources of stress can have a significant effect on both psychological and physical processes. (2) Methods: The study took place over a period of 34 days and included a total of 40 animals. Regarding the exposure to chronic stressors, we opted for physiological, non-invasive stressors, e.g., running, swimming, and changes in the intensity of light. An unforeseen stress batch was also created that alternated all these stress factors. The animals were divided into five experimental groups, each consisting of eight individuals. In the context of conducting the open field test for behavioral assessment before and after stress exposure, we aimed to investigate the impact of stress exposure on the affective traits of the animals. We also monitored body mass every two days. (3) Results: The control group exhibited an average increase in weight of approximately 30%. The groups exposed to stress factors showed slower growth rates, the lowest being the running group, recording a rate of 20.55%, and the unpredictable stress group at 24.02%. The anxious behavior intensified in the group with unforeseen stress, in the one with light variations, and in the running group. (4) Conclusions: Our research validates the animal model of intermittent light exposure during the dark phase as a novel method of inducing stress. The modification of some anxiety parameters was observed; they vary according to the type of stress. Body mass was found to increase in all groups, especially in the sedentary groups, likely due to the absence of cognitive, spatial, and social stimuli except for cohabitation.

Early life stress by repeated maternal separation induces long-term neuroinflammatory response in glial cells of male rats

Childhood maltreatment and neglect lead to a wide range of mental disorders highlighted by hormone and immune alterations in neglected children. This social-health challenge has led to the creation of early stress models such as maternal separation (MS) in rodents. We performed a MS model (4 h per day, 21 days; n = 16 MS and n = 16 control), and then measured three parameters in adult male rat brains, in order to look for long-term effects of early life stress. We used immunocytochemistry to mark glial fibrillary acidic protein (GFAP)-positive cells, which indicates changes in astroglia, and ionized calcium binding adaptor molecule 1 (Iba-1)-positive cells, which inform about reactive microglia. In order to study mRNA levels of some immune mediators, interleukin determination (interleukin-6, IL-6; tumor necrosis factor, TNFα) mRNAs were evaluated by real-time polymerase chain reaction (rt-PCR) in discrete brain regions. Measurements of numbers of GFAP-positive cells, and expression of Iba-1, IL-6 and TNFα mRNAs were performed in prefrontal cortex (PFC): cingulate cortex (CG), prelimbic cortex (PL) and infralimbic cortex (IL), striatal areas (dorsal striatum, STD; and nucleus accumbens, ACC), and dorsal hippocampus (HC: CA1, CA3 and dentate gyrus (DG)). We found that MS produces a dramatic and sustained decrease in the astroglial population in all the areas measured (from -25% in CA1 to -85.7% in ACC), whereas increased numbers of microglia were found, in more restricted regions: STD (72.6%), ACC (31%) and CA3 (33.3%) areas. Regarding mRNA measurements, we found increased IL-6 mRNA expression in HC (104.2%), and after MS.

Socioeconomic status and the brain: prospects for neuroscience-informed policy

Socioeconomic status (SES) is associated with health (physical and mental) and cognitive ability. Understanding and ameliorating the problems of low SES have long been goals of economics and sociology; in recent years, these have also become goals of neuroscience. However, opinion varies widely on the relevance of neuroscience to SES-related policy. The present article addresses the question of whether and how neuroscience can contribute to the development of social policy concerning poverty and the social and ethical risks inherent in trying. I argue that the neuroscience approach to SES-related policy has been both prematurely celebrated and peremptorily dismissed and that some of its possible social impacts have been viewed with excessive alarm. Neuroscience has already made modest contributions to SES-related policy, and its potential to have a more effective and beneficial influence can be expected to grow over the coming years.

Beyond Risk and Protective Factors: An Adaptation-Based Approach to Resilience

How does repeated or chronic childhood adversity shape social and cognitive abilities? According to the prevailing deficit model, children from high-stress backgrounds are at risk for impairments in learning and behavior, and the intervention goal is to prevent, reduce, or repair the damage. Missing from this deficit approach is an attempt to leverage the unique strengths and abilities that develop in response to high-stress environments. Evolutionary-developmental models emphasize the coherent, functional changes that occur in response to stress over the life course. Research in birds, rodents, and humans suggests that developmental exposures to stress can improve forms of attention, perception, learning, memory, and problem solving that are ecologically relevant in harsh-unpredictable environments (as per the specialization hypothesis). Many of these skills and abilities, moreover, are primarily manifest in currently stressful contexts where they would provide the greatest fitness-relevant advantages (as per the sensitization hypothesis). This perspective supports an alternative adaptation-based approach to resilience that converges on a central question: “What are the attention, learning, memory, problem-solving, and decision-making strategies that are enhanced through exposures to childhood adversity?” At an applied level, this approach focuses on how we can work with, rather than against, these strengths to promote success in education, employment, and civic life.

The Stress Acceleration Hypothesis of Nightmares

Adverse childhood experiences can deleteriously affect future physical and mental health, increasing risk for many illnesses, including psychiatric problems, sleep disorders, and, according to the present hypothesis, idiopathic nightmares. Much like post-traumatic nightmares, which are triggered by trauma and lead to recurrent emotional dreaming about the trauma, idiopathic nightmares are hypothesized to originate in early adverse experiences that lead in later life to the expression of early memories and emotions in dream content. Accordingly, the objectives of this paper are to (1) review existing literature on sleep, dreaming and nightmares in relation to early adverse experiences, drawing upon both empirical studies of dreaming and nightmares and books and chapters by recognized nightmare experts and (2) propose a new approach to explaining nightmares that is based upon the Stress Acceleration Hypothesis of mental illness. The latter stipulates that susceptibility to mental illness is increased by adversity occurring during a developmentally sensitive window for emotional maturation—the infantile amnesia period—that ends around age 3½. Early adversity accelerates the neural and behavioral maturation of emotional systems governing the expression, learning, and extinction of fear memories and may afford short-term adaptive value. But it also engenders long-term dysfunctional consequences including an increased risk for nightmares. Two mechanisms are proposed: (1) disruption of infantile amnesia allows normally forgotten early childhood memories to influence later emotions, cognitions and behavior, including the common expression of threats in nightmares; (2) alterations of normal emotion regulation processes of both waking and sleep lead to increased fear sensitivity and less effective fear extinction. These changes influence an affect network previously hypothesized to regulate fear extinction during REM sleep, disruption of which leads to nightmares. This network consists of a fear circuit that includes amygdala, hippocampus, and medial prefrontal cortex and whose substantial overlap with the stress acceleration findings allows the latter to be incorporated into a wider, more developmentally coherent framework.