The hormonal and neural control of maternal aggression

In mice and many other species, aggression levels are low in virgin females but increase dramatically during lactation to protect vulnerable offspring. This aggression, aimed at protecting the young, is known as maternal aggression. It emerges abruptly after parturition, peaks during early lactation, and declines after weaning. Given its stereotyped temporal profile, hormones associated with pregnancy and lactation are believed to play critical roles in its rise and fall. In addition, maternal aggression diminishes within hours of pup separation and rapidly recovers upon pup reunion, indicating a secondary, pup-dependent regulation of its expression. Here, we review current knowledge of the female aggression circuit and the hormonal and neural mechanisms that reshape it during pregnancy and lactation. We propose a two-step model in which pregnancy-associated sex hormone surges refine the aggression circuit, while lactation-associated neuropeptide signals gate circuit output in response to the need to protect offspring.