Suppression of reproductive hormone shown to impact postpartum behavior in rats
Cummings School researchers Bridges, Price publish paper
NORTH GRAFTON—It may be well known that hormones play a major role in motherhood but exactly which hormones trigger maternal behaviors has been the professional focus of Cummings School Biomedical Sciences Professor Robert Bridges, Ph.D.
In his latest study published in Developmental Psychobiology, he and graduate student Anya Price examined what happens when an important hormone, prolactin, is suppressed in the early stages of a female rat’s pregnancy. They found that pregnant dams experiencing a disruption of prolactin production demonstrated deficits in postpartum maternal care in new, unfamiliar situations.
In humans, prolactin is attributed to helping mothers produce milk and possibly alleviating postpartum anxiety. In other species, it is also responsible for stimulating a range of reproductive behaviors. For example, prolactin helps fish swim in a way that increases water flow over their eggs. Based on his earlier published work, Bridges has found that prolactin is also essential for maternal behavior in rats.
To gauge the impact of reduced prolactin levels on postpartum behavior, Bridges and Price designed the study so a group of dams was given a medication called bromocriptine, which inhibits the secretion of prolactin from the pituitary gland, in the early stages of pregnancy. Immediately following birth, these mothers were placed in familiar home cages. After four days, their behavior was assessed in unfamiliar surroundings: an elevated maze and a new cage.
“There was no difference in maternal behavior between the bromocriptine and control group in their home cages,” said Price. “But when the bromocriptine mothers were put into an unfamiliar cage, they spent significantly less time nursing their pups than the control group. Interestingly, we didn’t see behaviors reflecting anxiety in the elevated maze, the gold standard used to assess anxiety in rodents. This prompts a new question: are there separate mechanisms regulating maternal behavior and anxiety?”
Stress has proven to impact prolactin secretions, both by elevating or chronically suppressing levels of the hormone. With as many as one in seven women suffering from postpartum depression, according to a University of Pittsburgh study, understanding endocrine dysfunction is an important step to developing more effective treatments.
But Cummings School researchers caution against making any inferences from their study to explain human maternal behavior.
“The goal here is to develop models that can serve as building blocks for other researchers and advance the science of reproductive health,” said Bridges. “With each new finding, we add a layer of understanding to what might be happening when mothers exhibit signs of depression after giving birth.”
Price AK, Bridges RS. The effects of bromocriptine treatment during early pregnancy on postpartum maternal behaviors in rats. Dev Psychobiol. 2014 Sept;56(6):1431-7. doi: 10.1002/dev.21224. Epub 2014 May 29.