Maternal contact differentially modulates central and peripheral oxytocin in rat pups during a brief regime of mother-pup interaction that induces a filial huddling preference

Abstract

Central oxytocin mediates the acquisition of a filial preference for maternal odour in rat pups, manifested by their huddling preferences. The present study was designed to examine whether maternal care modulates oxytocin concentrations in rat pups and, if so, how different types of maternal contact are associated with the pups' oxytocin concentrations. Pairs of 14-day-old littermates were removed from their home cage for 1 h and then placed with a lactating foster mother for 2 h, or they remained isolated at room temperature. Enzyme immunoassays revealed that maternal care and maternal separation can differentially modulate pups' oxytocin concentrations. Both hypothalamic and serum oxytocin increased during the 1-h separation. Pups placed with a foster mother after the separation maintained the same concentrations in the hypothalamus and serum through the fostering period. By contrast, pups placed with no mother showed a further increase in hypothalamic oxytocin but serum oxytocin decreased. Behavioural analyses revealed that skin-to-skin contact with the mother, but not simple physical contact or maternal licking/grooming, was positively correlated with the pups' hypothalamic oxytocin concentrations. These neuroendocrine data match previous findings showing that skin-to-skin contact with mother facilitates the acquisition of the pups' huddling preference for a maternally-associated odour. Taken together, the present study suggests that maternal skin-to-skin contact stimulates pups' central oxytocin, at the same time as creating the conditions for inducing a preference for maternal odour and establishing a social affiliation in rat pups; the natural schedule of maternal separation and reunion may modulate pups' oxytocin concentrations, providing scaffolding for the acquisition of their filial huddling preference.

Fig. 1

Hypothalamic (HYP: A) and serum (B) oxytocin (OT) concentrations (mean ± SEM) at the beginning of 1-h separation (0 h), at the end of 1-h separation (1 h), and at the end of treatment (3 h) with either a foster mother (closed circle) or no mother (open circle). Significant differences from basal concentration and from the concentration at the end of 1-h separation are indicated by an asterisk (*) and dagger (†), respectively. A significant difference between the two treatments is indicated by a hash symbol (#).

Fig. 2

Correlation of oxytocin (OT) concentrations in the hypothalamus (HYP) with total duration (A) and bout duration (B) of skin-to-skin contact between mother and pup.

Fig. 3

Correlation between central and peripheral oxytocin (OT) concentrations at baseline (A), after the 1-h separation (B), in pups being with mother for 2 h after the separation (C), and in pups being with no mother for 2 h after the separation (D). Significant correlation is indicated by a line. HYP, hypothalamus; NS, not significant.