Environmental enrichment for adult rats: Effects on trait and state anxiety

Abstract

Experimental evidence indicates that enriched environment (EE) induces neurobiological and behavioural alterations. EE in early life improves learning and memory and reduces trait and state anxiety. However, the effect of EE established in adulthood has rarely been investigated. Thus, the aim of this study was to evaluate the possibility of modifying the levels of trait and/or state anxiety of adult rats exposed to EE. Seventy adult Wistar male rats were first tested in the free-exploratory paradigm (FEP) and were categorized according to their levels of trait anxiety (high, medium and low). Subsequently, half of the animals from each category returned to their home cages (standard condition: SC) and the other half was transferred to an enriched environment (enriched condition: EC). After three weeks, all animals were again tested in FEP. Seven to 10 days later, fifty of the seventy animals were tested on the elevated plus-maze test (EPM). In FEP, EE reduced locomotor activity in the second exposition independently of the anxiety category and, it decreased the levels of trait anxiety of highly anxious rats. No effect of EE was observed on EPM. In conclusion, EE established in adulthood was able to reduce high trait anxiety, a major risk factor for anxiety disorders.

Categories of Wistar Rats Based on Anxiety Traits: A Study Using Factor and Cluster Method

“…A medium level of anxiety, normally observed in rodents, based on the free-exploratory paradigm [23] and EPM test [24], is consistent with the finding of the present study. In the present study, rats displaying medium level of anxiety spent 10-50% of the test time in the open arm of EPM which may be considered as normal anxiety trait in rats according to previous report [20].…”

The impact of early postnatal environmental enrichment on maternal care and offspring behaviour following weaning

“…The sudden loss of maternal care and protection in the laboratory upon weaning generates an aversive situation per se where increased anxiety could possibly have some protective value. Nevertheless further studies should also include behavioural models of trait anxiety which would be based on free exploratory behaviour (Bert et al 2013) because the effects of environmental enrichment can be different in animal that differ in state and trait anxiety (Chapillon et al 1999;Goes et al 2015).…”

A Possible Role of Anhedonia as Common Substrate for Depression and Anxiety

“…For example, in man, opioids can relieve both depression and anxiety [ 60 , 82 ], and alcohol is sought to cope with both conditions [ 83 – 89 ]. In animals, an enriched environment [ 63 , 90 – 93 ] and agreeable foods [ 94 – 96 ] can improve depression and anxiety. This could suggest that anhedonia might contribute to causing, in addition to depression, even anxiety.…”