Effects of cross-fostering on behaviour and neural development in Octodon degus pups

Abstract

Parental care is essential for social, behavioural, and neural development in offspring. In rodents, parental separation affects the amount of parental care and progression of offspring development. Work to date has focused on maternal and paternal deprivation, but it is unclear how cross-fostering, another form of parental-offspring instability, can affect offspring behaviour and brain development. Stress significantly suppresses neurogenesis and increases inflammation in the dentate gyrus (DG) of the hippocampus, but this can vary between sexes. Octodon degus are highly social rodents with precocial offspring that can receive care from both parents, allowing us to study the effect of early life stress on pup development. This study investigated the effect of cross-fostering on parental care, offspring behaviour and hippocampal development in female and male degus. At postnatal day 8, degus were assigned to either control (pups remained with parents and siblings), partial cross-foster (CF; one pup/litter was cross-fostered), or full CF (the entire litter was cross-fostered). At weaning (5-weeks-old), offspring brains were collected for immunohistochemistry to examine DG volume and expression of immature neurons (using doublecortin, DCX) and microglia (using Iba-1). Partial and full CF did not affect parental care provided by parents compared to controls. In offspring, play fighting behaviour was significantly higher in partial CF females compared to controls. Males initiated play fighting more often than female pups but were not affected by CF. Partial and full CF did not affect the DG volume and optical density of DCX compared to control pups. Full CF pups had fewer ameboid microglia in the dorsal DG compared to controls. In the ventral DG, full CF pups had more intermediate microglia than controls. Our study indicates partial CF affects play fighting behaviour in females, while full CF affects microglia morphology in both sexes suggesting potential changes in hippocampal inflammation and plasticity. This indicates that CF category affects females and males differently depending on the endpoint measured and that these effects do not seem to be associated with changes in parental care. This study contributes to our understanding of how early life environments affect offspring behaviour and brain development in both sexes