Oxytocin and maternal motivation; Changes in oxytocin-immunoreactive innervation of the ventral striatum and amygdala during motherhood.

Abstract

The neuropeptide oxytocin (OT) has not just an endocrine role in the control of parturition and milk ejection, but also influences social interactions (including maternal behavior) by means of its action as a neurotransmitter in specific circuits of the brain. In the present study in mice, we combine the analysis of motivational aspects of maternal behavior using the motivated pup retrieval test (MPRT), with assessment of the oxytocinergic (OTergic) innervation of the central amygdala (CeA) and the nucleus accumbens (Acb) in dams, godmothers (pup-exposed virgins) and pup-naïve virgin females. This allows us to explore the possible roles of these nuclei and their OTergic innervation in motivational aspects of maternal care. The results can also help to clarify the relative roles of the endocrine regime of motherhood (present only in dams) and pup stimulation (present in both dams and godmothers) in the changes in OTergic innervation and/or maternal motivation associated to motherhood. Our results reveal an increased OTergic innervation in the CeA of dams, as compared to pup-naïve virgin females, likely related to the effect of hormones (estradiol after progesterone withdrawal, lactogenic hormones) during pregnancy, parturition and/or lactation. No increase in OTergic innervation is observed in the Acb. However, motivated behavior is likely to be correlated with the density of the OTergic innervation of the Acb, thus suggesting a role of this innervation in motivational aspects of maternal care. Finally, there is a global, significant correlation between the innervation density of both nuclei (Acb and CeA) suggestive of a common origin of the OT immunoreactive fibers of both nuclei in the same or in closely related (physiologically) brain cells, very likely the paraventricular hypothalamus and the rostral cell group in the anterior commissureanterodorsal preoptic area (AC/ADP).