Environmental enrichment protects against the effects of chronic stress on cognitive and morphological measures of hippocampal integrity

Abstract

Chronic stress has detrimental effects on hippocampal integrity, while environmental enrichment (EE) has beneficial effects when initiated early in development. In this study, we investigated whether EE initiated in adulthood would mitigate chronic stress effects on cognitive function and hippocampal neuronal architecture, when EE started one week before chronic stress began, or two weeks after chronic stress onset. Adult male Sprague Dawley rats were chronically restrained (6h/d) or assigned as non-stressed controls and subdivided into EE or non-EE housing. After restraint ended, rats were tested on a radial arm water maze (RAWM) for 2-d to assess spatial learning and memory. The first study showed that when EE began prior to 3-weeks of chronic stress, EE attenuated chronic stress-induced impairments in acquisition, which corresponded with the prevention of chronic stress-induced reductions in CA3 apical dendritic length. A second study showed that when EE began 2-weeks after the onset of a 5-week stress regimen, EE blocked chronic stress-induced impairments in acquisition and retention at 1-h and 24-h delays. RAWM performance corresponded with CA3 apical dendritic complexity. Moreover, rats in EE housing (control or stress) exhibited similar corticosterone profiles across weeks, which differed from the muted corticosterone response to restraint by the chronically stressed pair-housed rats. These data support the interpretation that chronic stress and EE may act on similar mechanisms within the hippocampus, and that manipulation of these factors may yield new directions for optimizing brain integrity and resilience under chronic stress or stress related neuropsychological disorders in the adult.

Potential of Environmental Enrichment to Prevent Transgenerational Effects of Paternal Trauma

“…The reversal might involve adaptive mechanisms resulting from the mismatch between favorable EE conditions and adverse conditions in early life. These mechanisms may also involve epigenetic regulation of GR gene in the hippocampus, consistent with the idea that chronic stress and EE recruit similar pathways within the hippocampus (Hutchinson et al, 2012). Additional molecular pathways may also be involved.…”

“…EE is a non-invasive and natural paradigm that increases the level of sensory, cognitive, and motor stimulation and promotes brain plasticity. It has been used to restore hippocampal integrity after chronic stress (Hutchinson et al, 2012) and may have some potential to counteract symptoms of psychopathologies and neurodegenerative diseases (Hannan, 2014;Nithianantharajah and Hannan, 2006). Our findings demonstrate that EE can reverse the effects of early traumatic stress.…”

“…EE has been reported to reverse some of the behavioral symptoms induced by chronic stress (Hutchinson et al, 2012) or early life adversity (Leshem and Schulkin, 2012). Using EE, we examined if the effects of MSUS on coping behaviors can be reversed (Supplementary Figure S4).…”

Effects of Environmental Conditions on Behavior in an Open Field Test in Rats Born to Females with Chronic Alcoholization

“…Despite the long history of studies of the effects of enriched environmental conditions on neurophysiological characteristics and learning ability [13,[21][22][23]25], this study showed that keeping animals in enriched conditions promotes increases in movement activity, the development of exploratory behavior, and increases in emotional reactivity in situations of moderate stress in the open fi eld. The results provided evidence that mothers with chronic alcoholic liver disease give birth to offspring with nervous system impairments.…”

“…The whole brain and various of its morphological parameters have been shown to change when laboratory animals are placed in specially formulated enriched environments [32]. Enriched environments have positive effects on the state of cognitive functions in animals in health and after exposure to chronic stress [25]. The main inducers of such infl uences are changes in the expression of growth factors in the brains of animals, along with increases in neuro-and synaptogenesis [21,22].…”