Rearing in a Shelved Environment Chronically Modifies Offspring Behaviour and Physiology

The study of environmental enrichment in rodents has primarily focused on adolescents and adults, with less information available for nursing dams and their pups. While we have previously observed some differences in behaviour and physiology of pups reared in shelved versus single-level cages, further examination of this relationship is necessary. To understand the impact of rearing in shelved cages, we assessed various parameters in pups including body weight, ultrasonic vocalizations, hair corticosterone concentration, behaviour in the open field and elevated plus maze and spatial working memory in the spontaneous alternation task. In addition, dams were assessed in the open field and elevated plus maze to identify any changes in stress-related behaviour. As adults, rats reared in enriched cages had significantly lower body weights, higher hair corticosterone concentrations and spent less time in the open arms of the elevated plus maze compared to those in standard cages. Additionally, rats reared in enriched cages emitted a lower number of frequency-modulated calls. In agreement with the behaviour observed in their pups, dams housed in enriched cages spent significantly less time in the centre of the open field. The results indicate that there are long-term changes in behaviour and physiology based upon different rearing conditions, reinforcing the importance of considering rearing environment when planning studies of a developmental nature. Furthermore, determining optimal rearing conditions will not only improve laboratory animal welfare but also improve reproducibility in animal research through the standardization of rearing conditions across institutions and laboratories.