Scientists have explained the deterioration of memory during pregnancy
Scientists from Baylor College of Medicine and several other research centers have studied the possible mechanism of temporary memory changes during pregnancy. In experiments on mice, they found a link between high levels of estrogen, the activity of hypothalamic neurons and the functioning of the hippocampus region associated with memory. About how hormonal changes can affect memory during pregnancy, see the "Izvestia" article.
"Pregnant forgetfulness": what happens to memory during pregnancy
During pregnancy, some women report that it becomes more difficult for them to concentrate, memorize information, or recall familiar things. ""Mammnesia" is a term used to describe this phenomenon, which can be translated as "pregnant forgetfulness." Until now, the exact biological mechanism of such changes has remained unclear.
Researchers have suggested that one of the reasons may be a prolonged increase in estrogen levels. Unlike the usual cyclical fluctuations of the hormone, during pregnancy its concentration remains high for an extended period. To study the possible effect of this condition on the brain, scientists conducted a series of experiments on mice and separately assessed the memory of women at different stages of pregnancy. The work was published in the journal Science Bulletin.
Zheng Sun, Associate Professor of Medicine, Endocrinology, Diabetes and Metabolism, and Molecular and Cellular Biology at Baylor College of Medicine
We worked with mouse models that mimic consistently high levels of estrogen in the blood during pregnancy. These models showed that elevated estrogen levels cause reversible memory impairments without affecting mood or motivation, indicating a specific cognitive effect rather than a general deterioration in well-being.
How estrogen affects brain function
The researchers focused on the lateral hypothalamus— an area of the brain that is involved in the regulation of various physiological processes. In it, the researchers found a large number of GABAERGIC neurons, that is, nerve cells that use gamma-aminobutyric acid as the main inhibitory mediator.
With prolonged high levels of estrogen, the activity of these cells changed. Analysis of gene expression showed a decrease in signaling through GABAA receptors, at the same time, neurons began to generate spontaneous signals more often.
Estrogen is a group of sex hormones that are involved in the regulation of the reproductive system, menstrual cycle, and pregnancy. They also affect the functioning of the brain, bones, cardiovascular system and metabolism.
The estrogen alpha receptor was also important. It prevailed among the estrogen receptors in the studied area of the hypothalamus. When the scientists removed estrogen receptors from these neurons, memory impairments caused by estrogen or pregnancy were eliminated in mice.
What experiments on mice have shown
The researchers found that GABAERGIC neurons in the lateral hypothalamus direct the processes to the CA3 region of the hippocampus, which is involved in the processes of memory formation and reproduction. This allowed the scientists to check whether the found connection could directly affect the performance of tasks.
Using chemogenetic methods, the researchers suppressed the activity of neurons that send signals to CA3. This effect protected the mice from memory impairments associated with high estrogen levels. By contrast, with artificial activation of these same neurons, cognitive impairments occurred even without an increase in hormone levels.
Zheng Sun
When we genetically removed the estrogen receptors from these hypothalamic neurons, the memory problems caused by estrogen and pregnancy disappeared in the mice.
Thus, the experiments pointed to a specific chain: a high level of estrogen affects the receptors in the neurons of the lateral hypothalamus, changes their activity, after which the transmission of signals to the hippocampus area changes. At the same time, the revealed effect turned out to be reversible.
What the results mean for pregnant women
To test whether a similar relationship is observed in humans, scientists studied the memory of women at different stages of pregnancy. At a later date, they found changes in the performance of individual memory tasks. These indicators were associated with a higher concentration of estrogen in the blood, even after taking into account other factors that could affect the results.
However, the results in women do not mean that there is a general deterioration in cognitive abilities during pregnancy. The changes were specific to individual assignments, and the authors describe them as temporary. In addition, observational data in humans alone do not allow us to prove that it is the neural pathway found in mice that causes memory changes in pregnant women.
Yanlin He, Associate Professor, Pennington Biomedical Research Center
Cyclical exposure to estrogen in small doses appears to support cognitive function, and this is one reason hormone therapy may be beneficial for postmenopausal women. But constant exposure to estrogen in high doses seems to involve a different mechanism, centered in the hypothalamus rather than the hippocampus itself. This distinction can help reconcile a lot of conflicting data in this area.
Переведено сервисом «Яндекс Переводчик»
