Abstract
Oxytocin (Oxt) acting through its single receptor subtype, the Oxtr, is important for the coordination of physiology and behavior associated with parturition and maternal care. Knockout mouse models have been helpful in exploring the contributions of Oxt to maternal behavior, including total body Oxt knockout (Oxt −/−) mice, forebrain conditional Oxtr knockout (Oxtr FB/FB) mice, and total body Oxtr knockout (Oxtr −/−) mice. Since Oxtr −/− mice are unable to lactate, maternal behavior has only been examined in virgin females, or in dams within a few hours of parturition, and there have been no studies that have examined their anxiety-like and depression-like behavior following parturition. To improve our understanding of how the absence of Oxt signaling affects maternal behavior, mood and anxiety, we designed a study using Oxtr −/− mice that separated nursing behavior from other aspects of maternal care, such as licking and grooming by thelectomizing (i.e. removing the nipples) of Oxtr +/+ mice and sham-thelectomizing Oxtr −/− mice, and pairing both genotypes with a wet nurse. We then measured pup abandonment, maternal behavior, and postpartum anxiety-like and depression-like behaviors. We hypothesized that genetic disruption of the Oxtr would impact maternal care, mood and anxiety. Specifically, we predicted that Oxtr −/− dams would have impaired maternal care and increased anxiety-like and depression-like behaviors in the postpartum period. We found that Oxtr −/− dams had significantly higher levels of pup abandonment compared to controls, which is consistent with previous work in Oxtr FB/FB mice. Interestingly, Oxtr −/− dams that initiated maternal care did not differ from wildtype controls in measures of maternal behavior. We also did not find any evidence of altered anxiety-like or depressive-like behavior in the postpartum period of Oxtr −/− dams. Thus, our data suggest that Oxt lowers the threshold for the initiation of maternal behavior.
Highlights
In females, the neuropeptide oxytocin (Oxt) helps to coordinate uterine contractions and milk ejection
There were no significant differences between genotypes in any of the maternal behaviors measured on PND1-3 (See Table 1)
In the current study we used Oxt receptor (Oxtr) 2/2 female mice to assess the importance of Oxt signaling in maternal behavior, anxiety-like, and depression-like behaviors in the postpartum period
Summary
The neuropeptide oxytocin (Oxt) helps to coordinate uterine contractions and milk ejection (for review see[1,2]). One of the changes thought to be necessary for normal maternal behavior is decreased anxiety during the postpartum period [22,23,24,25,26], which allows for a mother to more accept offspring; in turn facilitating social bonding (for review see [27]). In both lactating and virgin rats, chronic intracerebroventricular (icv) infusion of Oxt reduces anxiety-like behavior, as measured by an increase in the amount of time spent in the open arms of an elevated plus maze relative to controls [28,29]. In humans, elevated anxiety during the postpartum period is associated with postpartum depression [31,32,33,34,35,36,37] and lower plasma Oxt concentrations during pregnancy are correlated with increased risk of postpartum depression [38,39]
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