Vasopressin released within the central amygdala promotes maternal aggression.

Vasopressin regulates important aspects of social behaviour. Although vasopressin is more prominent in the expression of male social behaviours, we recently demonstrated its role in the fine-tuned maintenance of maternal care in lactating rats. Here, we investigate the involvement of brain vasopressin in the regulation of maternal aggression in lactating Wistar rats selectively bred for either high (HAB) or low (LAB) anxiety-related behaviour. The genetically determined elevation in vasopressin mRNA expression was confirmed within the hypothalamic paraventricular nucleus of virgin and lactating HAB rats and was additionally found in limbic brain areas. Lactating HAB dams are more maternally aggressive as part of their generally higher level of maternal care compared with LAB rats. Using intracerebral microdialysis, we describe increased vasopressin release within the central amygdala, but not the paraventricular nucleus, during maternal aggression only in HAB dams. Moreover, the release of vasopressin within the central amygdala was positively correlated with the display of offensive behaviour. Blockade of local vasopressin actions by bilateral administration of a selective vasopressin V1a receptor antagonist into the central amygdala reduced maternal aggression in HAB dams, whereas synthetic vasopressin increased the low level of aggression in LAB rats. Vasopressin receptor binding within the central amygdala or the paraventricular nucleus was similar in HAB and LAB females. In conclusion, vasopressin is an important neuropeptide regulating maternal aggressive behaviour, thus further extending its involvement in female social behaviour. Differences in intracerebral vasopressin release within the central amygdala rather than local vasopressin receptor binding contribute to the level of maternal aggression.