Expression of maternal behavior and activation of the bed nucleus of the stria terminalis during predatory threat exposure: modulatory effects of transport stress.

Past work has established that levels of maternal care provided to rat pups during the postpartum period plays an important role in shaping development of the stress response system, such that high levels of pup licking and grooming and active nursing behaviors are associated with more efficient hypothalamic-pituitary-adrenal responses to stressors in adulthood. Furthermore, a prior study from our laboratory has demonstrated facilitation of maternal care for five days following a one-hour predator odor exposure on the day of giving birth. The present study was an investigation of the effects on maternal care during a one-hour predator odor exposure administered on the day of giving birth, with or without the addition of transport stress immediately prior to the odor exposure. Stress-induced activation of the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST), two brain regions involved in regulating maternal behaviors, were also quantified using c-Fos immunohistochemistry. Our results show that predator odor exposure soon after birth does not significantly alter expression of maternal behaviors during the hour-long exposure period, unless the dams are also exposed to transport stress, in which case maternal behaviors are reduced during the first 10min of the exposure but not significantly different during the final 10min. Predator odor exposure (with or without additional transport stress) increased c-Fos immunoreactivity in the BNST, but not the MPOA, relative to control odor exposure, suggesting that the BNST may play an important role in integration of threat cues and transduction of their meaning into long-term effects on expression of maternal care. Future experiments should be designed to test the effects of temporary inactivation of the BNST during postpartum predator odor exposure.