Do changes in the immune systems of pregnant women lead to motherly behaviour?

According to the National Institutes of Health, the immune system is one of the most critical systems that not only protects the mother against the environment but also prevents any damage to the foetus. The system also plays a crucial role in the development of both the foetus and the placenta, whilst maintaining a healthy pregnancy.

Despite many previous studies into the subject, aside from identifying various cells and molecules that are key players in these development stages, the specific mechanisms that are needed to achieve these goals in pregnancy have yet to be fully understood.

However, the results of a recent experiment seem to suggest that changes in the immune system could play more of a role in foetal development and establishing motherhood than we think.

It was found that a decrease in immune cells late in gestation may factor into the onset of natural maternal behaviour, meaning that the same level of protection that the immune system provides for the foetus, could very well extend into the mother's brain.

Researchers from the Ohio State University conducted an experiment using adult rats and their new-born rat pups where they assessed the neuron activity and maternal behaviour within the brains of their tiny participants.

In adult female rats that had never given birth, which typically don't like being around babies, the depletion of these immune cells, known as microglia, sped up their care for rat new-borns that were placed in the cage. The loss of the cells and the related spark of motherly attentiveness were associated with changes in neuron activity and shifts in immune function.

Microglia are known for their link to brain injury and disease due to their protective activities under those circumstances, and for helping with brain development. However, this study suggests that they may provide another function to the brain – maternal behaviour.

Kathryn Lenz, co-senior author of the study and associate professor of psychology, said: "Our data shows that microglia are probably also really important for plasticity in the adult brain, its ability to adapt to all kinds of changes, and contribute to normal behavioural function."

Though rats that haven't given birth tend to avoid babies, studies show that they can be gradually coaxed into caring for rat pups through a process of prolonged exposure.

For the study, researchers gave non-mother rats either two doses of a drug that depletes microglia or a placebo that wouldn't affect their cells. Once the microglia had decreased by 75 per cent, the pups were placed with the non-mothers, where the team monitored the adults' behaviour with the pups.

As a result, the rats with depleted microglia proved to be fully sensitised to maternal behaviour significantly faster than the rats which were given placebos.

After screening the rats' brains to assess where neuron activation had increased or decreased over time, the team found that there was increased neural activity in the prefrontal cortex, which is important for being able to meet goals, stay focused and display self-control.

Although a clear link was established between accelerated maternal behaviour and microglia depletion, there is still more to learn about these mechanisms, as well as changes in neural activity.

"Learning about microglia function in the life history of a female adds real complexity to our understanding of what these cells do," Lenz commented. "That's incredibly important."

The study was recently published in the online medical journal, Neuropsychopharmacology.