Maternal Sensitization in Virgin Female Rats: Behavioral Effects of Enriched Environment

In virgin female rats, the continuous presence of pups causes them to express typical maternal behaviors, a process known as maternal sensitization. Previous experience with pups accelerates maternal sensitization. It is also known that in primiparous rats, enriched environment (EE) increases the expression of maternal behaviors. Here, we investigated whether experience, other than pup exposure, affects the process of maternal sensitization and hypothesized that EE increases the expression of maternal behaviors and maternal motivation in virgin rats. Virgin adult females were housed in standard conditions or physical and social EE for 21 days. Then, females were exposed daily to pups until they expressed full maternal behaviors. Thereafter, females performed pup preference, pup motivation in a novel context, and resident-intruder tests. We found that initial pup rejection was higher in EE rats, but eventually, both groups became maternally sensitized simultaneously. The frequency and duration of pup licking were higher in EE rats. In the other tests, EE rats exhibited more entries to the open arms, retrieved more pups toward the closed arms, and were more aggressive towards an intruder. We conclude that housing in a social EE modulates aspects of the pup-induced maternal sensitization, particularly increasing pup licking and motivation in both familiar and novel circumstances.