Normal maternal behavior, but increased pup mortality, in conditional oxytocin receptor knockout females

Oxytocin (Oxt) and the Oxt receptor (Oxtr) are implicated in the onset of maternal behavior in a variety of species. Recently, we developed two Oxtr knockout lines: a total body knockout (Oxtr^-/-) and a conditional Oxtr knockout (Oxtr^FB/FB) in which the Oxtr is lacking only in regions of the forebrain, allowing knockout females to potentially nurse and care for their biological offspring. In the current study, we assessed maternal behavior of postpartum Oxtr^FB/FB females toward their own pups and maternal behavior of virgin Oxtr^-/- females toward foster pups and compared knockouts of both lines to wildtype (Oxtr^+/+) littermates. We found that both Oxtr^-/- and Oxtr^FB/FB females appear to have largely normal maternal behaviors. However, with first litters, approximately 40% of the Oxtr^FB/FB knockout dams experienced high pup mortality, compared to fewer than 10% of the Oxtr^+/+ dams. We then went on to test whether or not this phenotype occurred in subsequent litters or when the dams were exposed to an environmental disturbance. We found that regardless of the degree of external disturbance, Oxtr^FB/FB females lost more pups on their first and second litters compared to wildtype females. Possible reasons for higher pup mortality in Oxtr^FB/FB females are discussed.