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

Abstract

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 (OxtrFB/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 OxtrFB/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 OxtrFB/FB females appear to have largely normal maternal behaviors. However, with first litters, approximately 40% of the OxtrFB/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, OxtrFB/FB females lost more pups on their first and second litters compared to wildtype females. Possible reasons for higher pup mortality in OxtrFB/FB females are discussed.

(PsycINFO Database Record (c) 2010 APA, all rights reserved).

Figures

Figure 1

Maternal behavior of postpartum Oxtr+/+ and OxtrFB/FB females toward biological offspring. No statistically significant genotypic differences in maternal behavior were observed on (a) Day 1, (b) Day 2, or (c) Day 3.

Figure 2

Maternal behavior of virgin Oxtr+/+ and Oxtr−/− females toward foster pups. No statistically significant genotypic differences in maternal behavior were observed on (a) Day 1, (b) Day 2, or (c) Day 3.

Figure 3

Pup retrievals by virgin Oxtr+/+ and Oxtr−/− females. 100% of Oxtr+/+ females (a) retrieved at least one pup to the nest on Day 1 of testing. In comparison, over 40% of Oxtr−/− females (b) failed to retrieve any pups to the nest on Day 1. However, by Day 3 both genotypes had identical levels of pup retrieval, with 100% retrieving at least one pup and over 80% retrieving 3–4 pups.

Figure 4

Comparison of pup mortality in OxtrFB/FB females across three litters. Both Oxtr+/+ and OxtrFB/FB females lost significantly more pups on their first litter compared with their second litter, regardless of disturbance group. Only OxtrFB/FB females lost significantly more pups on their first litter as compared with their third litter. On both litter 1 (left) and litter 2 (middle), OxtrFB/FB females lost significantly more pups compared with Oxtr+/+ females, regardless of disturbance group. On litter 3, there were no significant differences in pup loss between the two genotypes, and switching the NONE and HIGH groups did not significantly affect pup mortality. Litter 1: Oxtr+/+: NONE = 9; LOW = 9; HIGH = 10; OxtrFB/FB: NONE = 9; LOW = 9; HIGH = 10. Litter 2: Oxtr+/+: NONE = 8, LOW = 10; HIGH = 10; OxtrFB/FB: NONE = 9; LOW = 9; HIGH = 9. Litter 3: Oxtr+/+: NONE = 10; LOW = 9; HIGH = 7; OxtrFB/FB: NONE = 8; LOW = 5; HIGH = 8. *p < .05; **p < .01; ***p < .001.