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

Abstract

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.

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

“…This finding is also in contrast to previous studies which reported that MS did not affect performance of spatial learning and memory in the MWM task (Baudin, et al, ; Dandi et al, ; Levy, et al, ). This difference may be due to the strain of rats which were Long Evans (Baudin, et al, ) or Sprague‐Dawley (Levy, et al, ), while Wistar rats were used in our study.…”

“…Therefore, different strains of rats may respond differently to stress. Furthermore, the number of training trials cannot be ignored in this discrepancy, which was three trials per day for five consecutive days (Baudin, et al, ), or five trials per day for four days (Levy, et al, ) or four trials per day for four days (Dandi, et al, ). In our study, however, rats were trained for five consecutive days using the 2‐trial‐per‐day regimen in the MWM, which shows good discriminative for learning and memory, as described in our previous studies (Miladi‐Gorji et al, ).…”

Social Deprivation of Newborn Rats Modifies Exploratory and Defensive Behavior at Mature Age

“…Thus, the complete absence of social contacts with siblings during of milk nursing period led to an increase in the amount of time spent in open arms [18]. Daily 3-hour separation of the litter from the mother in the first two or three weeks of life, on the contrary, reduced this indicator [19] [20]. In our work, a complete 3-hour social deprivation of pups was performed from the 2 nd to the 8 th day of life.…”

Role of DNA Methylation in Hypobaric Hypoxia-Induced Neurodegeneration and Spatial Memory Impairment

“…Further, studies have been carried out to find the regulation of MeCP2 phosphorylation through neuronal activation, which regulate the expression of BDNF. BDNF is a neurotrophic factor that works as neuroprotective [33], regulate synaptic plasticity [34] and memory formation. There was an increase in the level of different DNMTs (DNMT1 and DNMT3b) at the mRNA as well as protein level in the hippocampus.…”