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.
Environmental factors interact with biological and genetic factors influencing the development and well‐being of an organism. The interest in better understanding the role of environment on behavior and physiology led to the development of animal models of environmental manipulations. Environmental enrichment (EE), an environmental condition that allows cognitive and sensory stimulation as well as social interaction, improves cognitive function, reduces anxiety and depressive‐like behavior and promotes neuroplasticity. In addition, it exerts protection against neurodegenerative disorders, cognitive aging and deficits aggravated by stressful experiences. Given the beneficial effects of EE on the brain and behavior, preclinical studies have focused on its protective role as an alternative, non‐invasive manipulation, to help an organism to cope better with stress. A valid, reliable and effective animal model of chronic stress that enhances anxiety and depression‐like behavior is the chronic unpredictable mild stress (CUMS). The variety of stressors and the unpredictability in the time and sequence of exposure to prevent habituation, render CUMS an ethologically relevant model. CUMS has been associated with dysregulation of the hypothalamic–pituitary–adrenal axis, elevation in the basal levels of stress hormones, reduction in brain volume, dendritic atrophy and alterations in markers of synaptic plasticity. Although numerous studies have underlined the compensatory role of EE against the negative effects of various chronic stress regimens (e.g. restraint and social isolation), research concerning the interaction between EE and CUMS is sparse. The purpose of the current systematic review is to present up‐to‐date research findings regarding the protective role of EE against the negative effects of CUMS.
This study aims at investigating whether early stress interacts with brain injury due to neonatal hypoxia‐ischemia (HI). To this end, we examined possible changes in synaptophysin (SYN) and brain‐derived neurotrophic factor (BDNF) expression in the medial prefrontal cortex (mPFC) of maternally separated rats that were subsequently exposed to a HI episode. Rat pups (n = 11) were maternally separated during postnatal days 1 to 6 (3hr/day), while another group was left undisturbed (n = 11). On postnatal day 7, a subgroup (n = 12) from each postnatal manipulation was exposed to HI. Synaptophysin and BDNF expression was estimated in mPFC prelimbic and anterior cingulate subregions of the ipsilateral and contralateral to the occluded common carotid artery hemispheres. Maternally separated rats expressed significantly less BDNF and SYN in both hemispheres. Neonatal HI significantly reduced BDNF and SYN expression in the ipsilateral mPFC only and this reduction was not further altered by early stress. Our findings indicate the enduring negative effect of a short period of maternal separation on the expression of mPFC SYN and BDNF. They, also, reveal that the HI‐associated decreases in these markers are limited to the ipsilateral mPFC and are not exacerbated by early stress. These decreases may have important functional implications given the role of prefrontal area in high‐order cognition.
Environmental factors interact with biological and genetic factors
influencing the development and well-being of an organism. The interest
to better understand the role of environment on behavior and physiology
led to the development of animal models of environmental manipulations.
Environmental Enrichment (EE), an environmental condition that allows
cognitive and sensory stimulation as well as social interaction,
improves cognitive function, reduces anxiety and depressive-like
behavior, and promotes neuroplasticity. In addition, it exerts
protection against neurodegenerative disorders, cognitive aging and
deficits aggravated by stressful experiences. Given the beneficial
effects of EE on brain and behavior, preclinical studies focus on its
protective role as an alternative, non-invasive manipulation, to help an
organism to cope better with stress. A valid, reliable and effective
animal model of chronic stress that enhances anxiety and depression-like
behavior is the Chronic Unpredictable Mild Stress (CUMS). The variety of
stressors and the unpredictability in the time and sequence of exposure
to prevent habituation, render CUMS an ethologically relevant model.
CUMS has been associated with dysregulation of the
Hypothalamic-Pituitary-Adrenal axis, elevation in the basal levels of
stress hormones, reduction in brain volume, dendritic atrophy and
alterations in markers of synaptic plasticity. Although numerous studies
have underlined the compensatory role of EE against the negative effects
of various chronic stress regimens (e.g., restraint, social isolation),
research concerning the interaction between EE and CUMS is sparse. The
purpose of the current systematic review is to present up-to-date
research findings regarding the protective role of EE against the
negative effects of CUMS.
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