Summary: A new study reports mother rats who received hormone replacement therapy responded worse to memory and spatial learning tasks than those who had not given birth. Researchers suggest a woman’s reproductive history could impact how the brain responds to hormones later in life.
Source: University of British Columbia.
Researchers have established that the foggy feeling and forgetfulness that many new mothers report during and after pregnancy—known as “mom brain”— is real. But new findings from Dr. Liisa Galea, a professor in UBC’s department of psychology, suggest that the effect of motherhood on the brain appears to last much longer after childbirth than previously believed.
In a study published recently in the journal Neurobiology of Aging, researchers looked at the effect of Premarin, a type of hormone therapy, on the cognitive abilities of female rats. Hormone therapy is often prescribed to relieve menopausal symptoms such as hot flashes and headaches, but there have also been claims that it can protect against cognitive decline.
The researchers found that Premarin did affect the rats’ cognitive abilities— but whether the effect was positive or negative depended on if the animal was a mother or not. Animals that had previously given birth were affected negatively, but those who had never given birth experienced a positive effect.
The findings suggest that a woman’s reproductive history—whether or not she had biological children—may impact the brains ability to respond to hormones later in life.
“Previous research has suggested that our brains do change with pregnancy but it was assumed that it would bounce back a year after giving birth,” said Galea, the study’s lead author who is a member of the Djavad Mowafaghian Centre for Brain Health and director of the graduate program in neuroscience at UBC. “In fact, we are just beginning to understand how motherhood influences the brain—and it appears that these changes may have a lasting effect long after pregnancy.”
Galea and her colleagues chose to look at Premarin for this study because of a 2003 trial that concluded the drug was associated with a higher incidence of dementia in women aged 65-79. Premarin was once the most widely prescribed hormone therapy in the United States but its use declined after the 2003 trial.
For the study, they trained rats in the Morris water maze—a behavioural task widely used in neuroscience to study spatial learning and memory in rodents. One group of rats were given the hormone therapy, while the other served as a control group and were not given any drug.
Before they were given hormone therapy, the researchers found the animals that were previously mothers performed slightly better in the maze and had more neuroplasticity—the ability to form new neural connections—than those that had never given birth.
“But what was interesting was that, after we gave them this hormone therapy, the previous moms and the non-moms responded completely opposite: the previous moms’ performance was impaired, but the non-moms’ performance actually improved,” said Galea.
The researchers also found that, after hormone therapy was administered, immune signalling increased in the previous moms but decreased in the non-moms—suggesting the body’s ability to fight off infectious agents like bacteria or viruses later in life may also depend on reproductive history.
Galea said she plans on looking at the effect of other hormone therapy drugs on cognitive abilities in future research.
But, she said, the findings of this study underscore the necessity of considering reproductive history when treating menopause in aging women.
Funding: The study was funded by CIHR and the Alzheimer Society of Canada.
Source: University of British Columbia
Publisher: Organized by NeuroscienceNews.com.
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Original Research: Abstract for “Premarin has opposing effects on spatial learning, neural activation, and serum cytokine levels in middle-aged female rats depending on reproductive history” by Liisa A. M.Galea, Meighen M. Roes, Christina J. Dimech, Carmen Chow, Rand Mahmoud, Stephanie E. Lieblich, and Paula Duarte-Guterman in Neurobiology of Aging. Published June 30 2018.
Premarin has opposing effects on spatial learning, neural activation, and serum cytokine levels in middle-aged female rats depending on reproductive history
Menopause is associated with cognitive decline, and hormone therapies (HTs) may improve cognition depending on type and timing of HTs. Previous parity may influence cognition in later life. We investigated how primiparity and long-term ovariectomy influence cognition, neurogenesis, hormones, cytokines, and neuronal activation in middle-aged rats in response to Premarin, an HT. Nulliparous and primiparous rats were sham-ovariectomized or ovariectomized, administered vehicle or Premarin 6 months later, and all rats were trained in the Morris water maze. Premarin improved early spatial learning and memory in nulliparous rats but impaired early learning in primiparous rats. With training, primiparity increased hippocampal neurogenesis, and Premarin decreased immature neurons, regardless of parity. Moreover, Premarin increased serum tumor necrosis factor α and the CXC chemokine ligand 1 (CXCL1) in trained nulliparous, but not primiparous, rats. However, Premarin decreased the expression of the immediate early gene zif268 in the dorsal CA3 region in primiparous rats after training. Thus, primiparity alters how Premarin affects spatial learning, neuronal activation, and serum cytokines. These findings have implications for the treatment of age-associated cognitive decline in women.