New research in rats suggests that immune system changes in the pregnant body, which protect the fetus, may also extend to the brain. The study found that a decrease in immune cells known as microglia late in gestation could contribute to the onset of maternal behavior. Adult female rats that had never given birth showed an increased care for rat newborns after the depletion of these cells. The loss of microglia and the increase in maternal attentiveness were associated with changes in neuron activity in various regions of the rat brain, indicating a role for immune function in regulating maternal behavior. These findings challenge the notion that maternal care is solely driven by hormones and emphasize the importance of immune changes in maternal behavior.
In a previous study, the researchers observed a decrease in microglia in the brains of rats late in pregnancy. In this study, they aimed to understand why this decrease occurs. The immune system undergoes changes during pregnancy to support a healthy gestation, but little is known about the immune system in the brain during and after pregnancy. To investigate the role of microglia in non-mother rats’ behavior towards foster pups, the researchers depleted microglia in non-mother female rats using a drug. They found that rats with depleted microglia displayed maternal behavior significantly faster than control rats.
The researchers also analyzed the neural activity in the rats’ brains and identified differences in patterns of activation between the control rats and rats with depleted microglia. Certain brain regions showed increased neural activity, such as the prefrontal cortex involved in executive functioning, while other regions displayed decreased neural activity, including regions associated with aversion circuits. These findings suggest a potential connection between microglia and maternal behavior.
The study raises further questions about the mechanism behind the accelerated onset of maternal behavior and the changes in neural activity patterns. It also highlights the need to understand potential differences in microglia functions based on sex, as most previous studies focused on male animals. Investigating the role of microglia in female reproduction provides valuable insights into their functions across the life history of females.
The research was published in the journal Neuropsychopharmacology and was supported by the National Science Foundation, the National Institute of Mental Health, and the National Institute of Neurological Disorders and Stroke.