Neurobiological traces of grief: Examining the impact of offspring loss after birth on rat mothers' brain and stress-coping behavior in the first week postpartum.

The bond between a mother and her infant is one of the strongest social bonds found in mammals. Consequently, the loss of an infant has immense psychological and physiological effects on the caregiver. Despite the significance of this bereavement, only a few studies have investigated the neurobiological impact of offspring loss in mothers. In an approach to fill this gap, we studied the effects of losing all pups the day after giving birth on rat mothers' brain and stress-coping behavior. Specifically, dams experienced 1-, 3-, or 6-days of total offspring loss. We analyzed the neuronal activity and oxytocin receptor (OXT-R) binding in the brain limbic and maternal network regions, as well as the stress response and stress-coping strategies. Following 1 day of loss, the mothers' neuronal activity increased in the limbic system resulting in a positive correlation between the prelimbic cortex and basolateral amygdala, while OXT-R binding was decreased in the central amygdala following up to 3 days of loss. At all three timepoints, plasma corticosterone concentrations did not differ either under basal conditions or following stressor exposure. Remarkably, following 6 days of offspring loss, the mothers showed a significant increase in passive stress-coping behavior, marking the first evidence of offspring loss affecting rat mothers' stress-coping behavior. Our results emphasize the significant impact of offspring loss on the mothers' neuronal activity and brain oxytocin system thereby providing novel insight into the short-term neurobiological traces of grief and paving new avenues for future research in this field.