Aims: 

Oxytocin is known to play a pivotal role in rat parturition as it acts within the brain to facilitate its own release. In rodents oxytocin has profound influences on social behaviour including the onset of maternal behaviour in the peripartum period. Here we examined the oxytocin system in the brain during pregnancy, parturition and the post partum period. Methods:

We quantified in the rat brain (1) oxytocin receptor (OTR) mRNA (using a ³⁵S-riboprobe) throughout the peripartum period (2) OTR activation at parturition using double immunocytochemical labeling for the expression of the immediate early gene Fos and OTR and (3) oxytocin and OTR cell activation (Oxytocin or OTR and Fos double immunocytochemistry) during exhibition of one component of maternal behaviour, aggressive protection of the offspring from an intruder.

Results: 

Our data show that not only does OTR mRNA increase dynamically in brain regions such as the supraoptic nucleus, olfactory bulbs, preoptic area, brain stem and limbic regions perinatally, but that OTR positive-cells in specific brain regions express Fos at birth. Moreover our results demonstrate Fos activation in the oxytocin system during maternal aggression.

Conclusion: 

These findings provide evidence for dynamic changes in oxytocin sensitivity within oxytocin-producing and brainstem regions that mediate feedback from the uterus at parturition. The alteration in oxytocin sensitivity and the activation of oxytocin neurones in specific brain regions during maternal aggression presents further evidence for the crucial role this hormone plays in orchestrating maternal behaviour.

Supported by the BBSRC and Wellcome Trust