Changes in responsiveness to newborn pups in pregnant, nulliparous golden hamsters

Parental Behavior in Rodents

Members of the order Rodentia are among the best-studied mammals for understanding the patterns, outcomes, and biological determinants of maternal and paternal caregiving. This research has provided a wealth of information but has historically focused on just a few rodents, mostly members of the two Myomorpha families that easily breed and can be studied within a laboratory setting (including laboratory rats, mice, hamsters, voles, gerbils). It is unclear how well this small collection of animals represents the over 2000 species of extant rodents. This chapter provides an overview of the hormonal and neurobiological systems involved in parental care in rodents, with a purposeful eye on providing information known or could be gleaned about parenting in various less-traditional members of Rodentia. We conclude from this analysis that the few commonly studied rodents are not necessarily even representative of the highly diverse members of Myomorpha, let alone other rodent suborders, and that additional laboratory and field studies of members of this order more broadly would surely provide invaluable information toward revealing a more representative picture of the rich diversity in rodent parenting.

Biology and Diseases of Hamsters

The hamster species used as research models include the Syrian (golden), Mesocricetus auratus; the Chinese (striped-back), Cricetulus griseus; the Armenian (gray), C. migratorius; the European, Cricetus cricetus; and the Djungarian, Phodopus campbelli (Russian dwarf) and P. sungorus (Siberian dwarf). Hamsters are classified as members of the order Rodentia, suborder Myomorpha, superfamily Muroidea and in family Cricetidae. Animals in this family are characterized by large cheek pouches, thick bodies, short tails, and an excess of loose skin. They have incisors that erupt continuously and cuspidate molars that do not continue to grow ((I 1/1, C 0/0, PM 0/0, M 3/3) × 2 = 16). In 2010, it was reported that approximately 146,000 hamsters were used in research in the United States (United States Department of Agriculture, 2010).

Disruption to the development of maternal responsiveness? The impact of prenatal depression on mother-infant interactions

Both prenatal and postnatal maternal depression are independently associated with an increased risk of adverse infant development. The impact of postnatal depression on infants may be mediated through the effect of depression in reducing maternal responsiveness. However, the mechanisms underlying the effect of prenatal depression are unclear. Using longitudinal data from over 900 mother-infant pairs in a UK birth cohort (ALSPAC), we found that women with high depressive symptom scores during mid pregnancy, but NOT when their infants were 8 months, had a 30% increased risk of low maternal responsiveness when the infant was 12 months compared to women with consistently low depression. This may provide a mechanism to explain the independent association between prenatal depression and poorer infant development.

Attentional processing of infant emotion during late pregnancy and mother-infant relations after birth

The mother-infant relationship has an important influence on maternal mental health and infant development. Evidence suggests that this relationship is enhanced by a mother's sensitive response towards her infant's distress. We proposed that attentional processing of infant distress may indicate individual differences in this response. Research also suggests that maternal responses develop during pregnancy. We therefore hypothesised that more sensitive attentional processing of distressed infant stimuli during late pregnancy will be associated with more successful mother-infant relationships. Healthy pregnant women were recruited through community midwives. An established computerised paradigm measured women's ability to disengage attention from distressed or non-distressed infant faces. From this paradigm, we derived an index of women's attentional bias towards infant distress. Mother-infant relationships were measured using the postpartum bonding questionnaire (PBQ). A complete case sample of 49 women completed the attentional paradigm during late pregnancy and the PBQ 3-6 months after birth. We found that women who showed greater attentional bias towards infant distress during late pregnancy reported more successful mother-infant relationships. For every 50-ms increase on our measure of attentional bias towards infant distress during late pregnancy, the odds ratio for reporting a higher PBQ score, indicative of a weaker relationship, was 0.43 (95% confidence intervals 0.23-0.81, p = 0.01). The results suggest that women's basic attentional processing of infant emotion during pregnancy influences their relationships with their infant. In the future, women's attentional processing of infant emotion could inform early strategies to promote successful mother-infant relationships in vulnerable mothers to be.

The impact of breastfeeding on mothers' attentional sensitivity towards infant distress

BACKGROUND

Maternal response towards infant distress has an important impact on infant development. In animals it is established that lactation and pup suckling plays an important role in maintaining maternal responses. Previous research suggests that breastfeeding is associated with sensitive maternal responses in human mothers. However, this may be because women who are more sensitive to their infant choose to breastfeed. The current study investigated the attentional sensitivity towards infant distress in women who went on to breast or formula feed during pregnancy as well as after birth. We hypothesised that differences in breast and formula feeding mothers would only emerge after birth once feeding had commenced.

METHOD

Women were recruited during pregnancy through community midwives as part of a longitudinal study. 51 women were seen during late pregnancy and between 3 and 6 months after birth (27 were breast and 24 were formula feeding). Sensitivity to infant distress was measured as the extent of women's attentional bias towards infant distress stimuli.

RESULTS

After birth, we found that our index of attentional bias towards infant distress was 37 ms (0.5 S.D.s) (CI; 6-69, p = 0.021) higher in breastfeeding compared to formula feeding mothers. However, mothers who went on to breastfeed did not show greater attentional bias towards infant distress already during late pregnancy.

CONCLUSIONS

Our results suggest that the act of breastfeeding may influence mothers' attentional sensitivity towards infant distress. Previous research suggests breastfeeding is indicative of sensitive parenting. The current findings may suggest a mechanism by which breastfeeding and/or associated infant interaction could contribute to this sensitivity.

Sex differences in the parental behavior of rodents

The reproductive strategy of many mammalian species that give birth to altricial young involves intense and prolonged care of their offspring. In most cases, the mother provides all nurturance, but in some cases fathers, older siblings, or unrelated conspecifics participate in parental care. The display of these behaviors by animals other than mothers is affected by numerous factors, including their sex. We herein review the literature on similarities and/or differences between male and female laboratory rodents (rats, mice, voles, gerbils, and hamsters) in their parental responsiveness and discuss how the parental behavior of males and females is influenced by hormones, developmental processes, and prior social experiences. Understanding the mechanisms that generate sex differences in the parental responsiveness of rodents may indicate how similar sex differences in parental care are generated in other mammals.

Evidence for the involvement of prolactin in the maternal behavior of the hamster

The hormonal basis of maternal behavior in the hamster has not been clearly established. Treatment of parturient females on the day of delivery with the prolactin release inhibitor, bromocriptine, resulted in a significant disruption of maternal responsiveness at doses as low as 0.5 mg When pregnant females were implanted with ectopic pituitary grafts under the kidney capsule on day 8 or 9 of gestation to elevate circulating prolactin levels, there was no disruption of maternal behavior after bromocriptine injection on the day of delivery. Taken together, these data indicate that prolactin may be an important modulator of the natural onset of maternal behavior at parturition in the hamster.