Reduced brain corticotropin-releasing factor receptor activation is required for adequate maternal care and maternal aggression in lactating rats.

The brain corticotropin-releasing factor (CRF) system triggers a variety of neuroendocrine and behavioural responses to stress. Whether maternal behaviour and emotionality in lactation are modulated by CRF has rarely been investigated. In the present study, we measured CRF mRNA expression within the parvocellular part of the paraventricular nucleus in virgin and lactating Wistar rats bred for high (HAB) and low (LAB) anxiety-related behaviour or non-selected for anxiety (NAB). Further, we intracerebroventricularly infused synthetic CRF or the CRF receptor (CRF-R) antagonist D-Phe to manipulate CRF-R1/2 non-specifically in lactating HAB, LAB, and NAB dams, and monitored maternal care, maternal motivation, maternal aggression, and anxiety. The CRF mRNA expression in the parvocellular part of the paraventricular nucleus was higher in HAB vs. LAB rats independent of reproductive status. The lactation-specific decrease of CRF mRNA was confirmed in LAB and NAB dams but was absent in HAB dams. Intracerebroventricular CRF decreased maternal care under basal conditions in the home cage in all breeding lines and reduced attack behaviour in HAB and LAB dams during maternal defence. In contrast, D-Phe rescued maternal care after exposure to maternal defence in the home cage without influencing maternal aggression. Furthermore, D-Phe decreased and CRF tended to increase anxiety in HAB/NAB and LAB dams, respectively, suggesting an anxiogenic effect of CRF in lactating females. In conclusion, low CRF-R activation during lactation is an essential prerequisite for the adequate occurrence of maternal behaviour.