Effects of oxytocin ablation on pup rescue, nursing behaviors and response to pup separation in early‐to‐mid postpartum mice

Abstract

Oxytocin, a neuropeptide hormone, is indispensable for milk ejection during nursing and is important for uterine contractions during parturition. The exact functions of oxytocin in postpartum maternal behaviors and motivations require further investigation. To this end, we characterized the role of oxytocin in components of maternal motivations during the mid‐postpartum period, which has not been previously studied. To maintain suckling stimuli, postpartum oxytocin knockout (Oxt−/−) and heterozygous (Oxt+/−) littermates were co‐housed with a wild‐type lactating mother and its litter, and were examined for their ability to retrieve pups under standard or high‐risk conditions, nursing behavior, maternal aggression towards an unfamiliar intruder, and motivation to regain contact with separated pups. One‐third of Oxt−/− mothers exhibited prolonged parturition but were otherwise grossly healthy. Despite their inability to eject milk, Oxt−/− mothers displayed nursing behaviors for similar durations to Oxt+/− mothers during the second postpartum week. In addition, Oxt−/− mothers were essentially intact for pup retrieval under standard conditions and were motivated to stay close to pups, although they showed a mild decrease in maternal care under high‐risk conditions and increased anxiety‐like behaviors in pup‐related contexts. The present findings indicate that oxytocin is dispensable for nursing behavior and maternal motivations, yet suggest that oxytocin may be relevant for stress resilience in the postpartum period.

Maternal physiological calming responses to infant suckling at the breast

“…Oxytocin plays a major role in milk ejection during breastfeeding, and is also well known for its anxiolytic effects partly via the parasympathetic nervous system [ 37 ], although the presence of oxytocin is not essential for the nursing behavior per se [ 24 , 32 ]. The present result indicates that the IBI elevation coincided with the initiation of somatosensory stimulus by touch or latch-on to the breast by the infant mouth, and that IBI rather decreased transiently at the timing of perceived milk ejection (Fig.…”

Parental brain through time: The origin and development of the neural circuit of mammalian parenting

“…Oxytocin is a peptide hormone critical for egg laying and parturition and indispensable for milk ejection in mammals (together with vasopressin homologs 209 ). 2,210,211 However, the genetic ablation of oxytocin leads to surprisingly normal postpartum maternal care in multiple rodent species 27,57,[212][213][214][215][216] (for other vertebrates, see…”

“…In laboratory mice, however, licking/grooming behaviors are less precisely dissociated from self‐grooming or sniffing than in rats, which may cause some variabilities, as discussed below. Please refer to previous literature for references and assessment protocols for each component of parental nurturing behaviors 24–26 and for additional experimental designs of postpartum maternal motivations 27 …”

Parental Brain Through Time: function, anatomy, and molecular mechanisms in contexts

“…In laboratory mice, however, licking / grooming behaviors are less precisely dissociated from self-grooming or sniffing than in rats, which may cause some variabilities as discussed below. Please refer to previous literature [20][21][22] for references and assessment protocols for each component of parental nurturing behaviors and 23 for additional experimental designs of postpartum maternal motivations.…”

“…And numerous publications demonstrate the role of oxytocin in mammalian pro-social behaviors (though also in various non-social functions such as stress responses and energy metabolism) [200][201][202] (see also 203 ). However, the genetic ablation of oxytocin leads to surprisingly normal postpartum maternal care in multiple rodent species 23,45,[204][205][206][207][208] (for other vertebrate species, refer to 209 210 ). The oxytocin's facilitatory effects on paternal and allomaternal care appear even more significant than those on postpartum maternal care (for example, compare 92 and 208 with a similar methodology from the same laboratory) 133 .…”