Environmental enrichment and its influence on rodent offspring and maternal behaviours, a scoping style review of indices of depression and anxiety.

Environmental enrichment is a widely used experimental manipulation that consistently shows measurable effects on rodent behaviour across the lifespan. This scoping review assesses and thematically summarizes the literature of the past decade concerning the effects of environmental enrichment applied during sensitive developmental periods in rodent mothers and offspring. Maternal behaviours as well as maternal and offspring anxiety- and depressive-like behaviours are considered. Relevant terms were searched across five databases (Embase, MEDLINE, PsycINFO, PubMed, Web of Science) and articles were screened with inclusion and exclusion criteria. The remaining articles were thematically analysed. Our results suggest that a greater number of articles reviewed the impacts of environmental enrichment on offspring anxiety-like behaviour (n = 23) rather than on depressive-like behaviour (n = 11) or maternal caregiving behaviour (n = 12). Maternal anxiety- (n = 4) or depressive-like (n = 2) behaviours are not often evaluated for in enrichment studies. The main behavioural tests of anxiety that were reviewed include the elevated plus-maze, the open field test, and the light-dark box whereas those for depression included the forced swim test and the sucrose preference test. Our results yielded mixed findings and significant variation in behavioural responses across all tests. In mothers, trends of increased maternal care behaviours and decreased maternal depressive-like behaviours in enriched mothers were appreciated. Enrichment during the gestational period was identified as pivotal to creating behavioural change in mother subjects. In enriched offspring rodents, a trend towards decreased anxiety-like behaviours was observed most often. Potential confounds inherent in enrichment paradigms and relevant theories of enrichment and their relation to rodent behavioural tests are discussed.

Effects of combined pre- and post-natal enrichment on anxiety-like, social, and cognitive behaviours in juvenile and adult rat offspring.

The pre- and post-natal periods are characterized by unrivalled growth and are sensitive to environmental changes. A correctly stimulating early environment is essential for developing natural behaviors and maintaining affective wellness. Five litters of rat progeny were co-housed through gestation until juvenile age in housing providing physical and social enrichment. Five control litters were housed separately in standard conditions. Half of the offspring were tested in the elevated plus-maze and the social interaction test as juveniles (five weeks old) with the other half tested in the Morris water maze. As adults (11 weeks old), the testing groups were reversed. Weight was monitored weekly. Enriched offspring had leaner body weights. In the elevated plus-maze, control juvenile progeny spent a higher percentage of time in the open arms, showed greater locomotor activity, less grooming, and more rearing (males only). In the social interaction test, enriched juvenile offspring were found to sniff their conspecific more, display more self-grooming behaviour as well as show less locomotor activity and body contact. In the Morris water maze probe test, enriched rats demonstrated improved memory for the platform position and more effective search strategies with increased platform crossings, middle crossing as well as more time spent in the platform quadrant and less thigmotaxis behaviour. Adult female rat offspring also demonstrated superior memory for the platform position and crossed the maze middle more often. These results suggest that combined pre- and post-natal environmental enrichment influences physiology and behaviour in offspring rats with some of those influences being long-lasting.

The effects of gestational and postpartum environmental enrichment on the mother rat: A preliminary investigation.

Environmental enrichment is known to influence an animal's well-being, provide opportunities for activity, and encourage behaviours appropriate to the species. Female Long-Evans rats were co-housed during their gestational and postpartum times in a colony housing environment comprising numerous cages, with interconnecting tubes, surrounding a multileveled enclosure with many objects scattered throughout. A control group of rats were housed in standard cages. The effects of the physical and social enrichment were determined by evaluating group differences in body weight, litter characteristics, elevated-plus maze performance during the gestational and postpartum periods, and Morris water maze behaviour (postpartum only). Results showed that enriched females were leaner and maintained a constant postpartum weight. Group differences in litter characteristics were observed, with enriched females having heavier but fewer offspring. Behavioural trends were observed in the elevated-plus maze with enriched rats showing greater change in behaviours over time. In the Morris water maze probe test, enriched rats performed less thigmotaxic and more middle maze swimming, as well as an increased tendency to enter the quadrant where the platform was located in non-probe trials. A housing environment, with complex physical and social stimulation, offered more opportunity for environmental interactions producing heartier pups and leaner mothers that displayed differential behavioural responses compared to control mothers. Studying maternal-offspring interactions in a more naturalistic environment allows one to observe a greater repertoire of behaviours that accommodates adequate normal or natural cognitive development than can be observed in the typical standard housing laboratory condition that limits experience and environmental engagement.