Becoming a parent changes your life. Research has shown that it can also change your brain. Although this might not sound surprising to mothers, a new study reveals that fathers need not feel excluded.
Kozorovitskiy and colleagues investigated how fatherhood affects the brains of male marmosets. Marmoset babies are cared for by multiple members of the family, including the father. Marmoset males show parental behaviour: they spend most of the first month of fatherhood carrying their young on their backs, they clean and protect them and, after weaning, also feed them.
Comparing the brains of first-time and experienced marmoset fathers with those of non-fathers, all living with their mating partners, Kozorovitskiy et al. found that fatherhood was associated with changes in the prefrontal cortex (PFC). Interestingly, in humans parts of this area become activated when parents are shown images of their own children. The PFC contains receptors for neuropeptides that are known to mediate parental behaviour, such as vasopressin, oxytocin and prolactin.
Using Golgi staining and the lipophilic neuronal tracer DiI, the researchers showed that marmoset fathers had a higher density of dendritic spines on pyramidal cells in layers II/III of the PFC than non-fathers. The length of the dendrites was unchanged, indicating that an increase in the actual number of dendritic spines probably underlies the observed higher density. In addition, the PFC of marmoset fathers had elevated immunolabelling for the V1a vasopressin receptor and the proportion of dendritic spines that were labelled for this receptor had also increased. Levels of the V1b vasopressin receptor and receptors for oxytocin and prolactin were unaltered.
V1a receptor immunoreactivity in the PFC correlated negatively with offspring age. This suggests that the observed effects might not be permanent, and also that the amount of father–infant contact, which reduces as offspring get older, could drive the changes.
The V1a receptor is activated by vasopression, so the authors next set out to establish where this ligand might be produced. As expected, they found vasopressin immunolabelling in the paraventricular and supraoptic nuclei of the hypothalamus. However, these nuclei do not project to the PFC. Interestingly, vasopressin immunoreactivity was also found in the very cells in the PFC that showed increased dendritic spine density in response to fatherhood. It is therefore possible that locally produced vasopression activates V1a receptors in the PFC, which then stimulate the formation of new dendritic spines.
This study shows that fatherhood modifies the brains of marmosets in regions associated with parental behaviour. The intriguing findings raise some interesting questions about the mechanisms that might underlie such plasticity, and whether the quality of paternal care influences these changes.