Environmental Enrichment Duration Differentially Affects Behavior and Neuroplasticity in Adult Mice

Abstract

Environmental enrichment is a powerful way to stimulate brain and behavioral plasticity. However the required exposure duration to reach such changes has not been substantially analyzed. We aimed to assess the time-course of appearance of the beneficial effects of enriched environment. Thus, different behavioral tests and neurobiological parameters (such as neurogenesis, brain monoamines levels, and stress-related hormones) were concomitantly realized after different durations of enriched environment (24 h, 1, 3, or 5 weeks). While short enrichment exposure (24 h) was sufficient to improve object recognition memory performances, a 3-week exposure was required to improve aversive stimulus-based memory performances and to reduce anxiety-like behavior; effects that were not observed with longer duration. The onset of behavioral changes after a 3-week exposure might be supported by higher serotonin levels in the frontal cortex, but seems independent of neurogenesis phenomenon. Additionally, the benefit of 3-week exposure on memory was not observed 3 weeks after cessation of enrichment. Thus, the 3-week exposure appears as an optimal duration in order to induce the most significant behavioral effects and to assess the underlying mechanisms. Altogether, these results suggest that the duration of exposure is a keystone of the beneficial behavioral and neurobiological effects of environmental enrichment.

Late enrichment maintains accurate recent and remote spatial memory only in aged rats that were unimpaired when middle aged

“…Only a few studies have assessed whether enrichment has an impact on remote memory. Enrichment was shown to enhance long-term memory for object recognition (i.e., 48 h after exposure) in both young (Bruel-Jungerman et al 2005;Leger et al 2015) and aged rats (Leal-Galicia et al 2008), and our team has previously shown that long-life environmental enrichment protects young and middle-aged rats against spontaneous forgetting (Harati et al 2013). The results of the present study extend these findings by showing that late enrichment also enables aged rats to form memory traces that are less sensitive to degradation.…”

Simple shelter-style environmental enrichment alters behavior in mice

“…This was somewhat unexpected -we had predicted the most salient effects of shelters to be emotional and social behaviors. [21,[42][43][44][45][46], but it should be noted that enrichment procedures, genetic background and social housing all vary across these studies. We conclude that there are highly complex effects of the shelters on the expression of anxiety that appear to be assay specific and in some cases suggest enrichment-induced increases in anxiety, which has also been reported by at least two other groups [47,48].…”

“…Thus, it is also vital to consider the effects on the biomedical research at hand [13,14]. For example, within neuroscience, environmental enrichment has been shown to affect a wide variety of responses, including exploratory behavior [6,11,15], cognition [6,[16][17][18], emotionality [12,19,20], brain neurochemistry [21,22], gene expression patterns [9], stress resiliency [23], and even responses to addictive drugs such as cocaine [9,24,25]. These data lead to understandable resistance by researchers to adopt even the most rudimentary forms of enrichment, such as nesting materials and shelters.…”

Paternal environmental enrichment transgenerationally alters affective behavioral and neuroendocrine phenotypes

“…In contrast, the antidepressive effects of enrichment remain controversial. While there are reports that even a short 7-day period of environmental enrichment reduces forced-swim test (FST) immobility time in rats (Zanca et al, 2015), other evidence in rats and mice suggest that EE does not alter latency to immobility and total immobility time in the FST (Leger et al, 2015;Possamai et al, 2014).…”

“…EE also has the capacity to influence peripheral stress-response as demonstrated by its correction of adrenal hyper-responsivity pathology in a mouse model of Huntington's disease (Du et al, 2012). In normal rodents, EE has consistently been shown to reduce anxiety-like behavior in the elevated-plus maze and the open-field test (Sztainberg et al, 2010), with recent evidence suggesting the requirement of a minimum 3-week enrichment period (Leger et al, 2015). In contrast, the antidepressive effects of enrichment remain controversial.…”