New research conducted in an animal model has uncovered an intriguing fact about the uterus, namely that it seems to interact with the brain and affect memory.
The best-known role of the uterus is its function in pregnancy, but does it serve any other purpose beyond that of reproduction?
So far, textbooks of obstetrics and gynecology have stated that, outside of pregnancy, the uterus lies in a dormant state, and does not interact with other organs.
However, new research from Arizona State University in Tempe may soon alter definitions referring to the function of this organ.
In a study on the rat model, senior author Prof. Heather Bimonte-Nelson and colleagues demonstrated that removing the uterus — a surgical procedure known as hysterectomy — has a definite impact on spatial memory.
These findings, which appear in the journal Endocrinology, suggest that this organ communicated with the brain, influencing some cognitive processes.
"There is some research showing that women who underwent hysterectomy but maintained their ovaries had an increased risk for dementia if the surgery occurred before natural menopause," Prof. Bimonte-Nelson notes.
"This finding is striking. We wanted to investigate and understand whether the uterus itself could impact brain function."
Prof. Heather Bimonte-Nelson
The uterus communicates with the brain
While many people may know that the uterus and the ovaries have a connection due to their joint role in reproduction, they may not be aware of the links between the uterus and the brain.
Prof. Bimonte-Nelson explains that the body's autonomic nervous system, which regulates "automated" metabolic processes, such as heart rate, breathing, digestion, and sexual arousal, also has links to the uterus and brain.
Starting from this connection between the uterus and the brain, the researchers wanted to know if the two interact in unobvious ways, and if removing the uterus would impact cognitive function.
To do so, the investigators used female rats, which they divided into four groups. The rats in three of these groups underwent surgeries that mimicked the oophorectomies (surgical removal of the ovaries) and hysterectomies (surgical removal of the uterus) in humans.
In one group, the researchers removed the rats' ovaries, in another their uteruses, and in a third, the researchers removed both the ovaries and the uterus. The rats in the fourth group acted as controls, receiving a fake surgery in which their reproductive organs were left intact.
At 6 weeks after the intervention, the investigators trained all the rats to navigate a complex maze structure. Then, they gradually modified different elements of this maze to see how well the rodents' memories performed under these circumstances.
The researchers found that the female rats that had undergone hysterectomies found it more challenging to navigate the maze than any of the rats in the other groups.
None of the other kinds of surgery appeared to have any impact on the rats' spatial memories or the number of mistakes they made while attempting to navigate the maze.
"The surgical removal of just the uterus had a unique and negative effect on working memory, or how much information the rats were able to manage simultaneously, an effect we saw after the rats learned the rules of the maze," explains first author Stephanie Koebele, who is a psychology graduate student at Arizona State University.
Altered hormonal profiles
Following this experiment, the researchers tried to find an explanation for the potential mechanism that affected cognitive function in the rats that had undergone a hysterectomy.
First, they compared the shape and size of the ovaries in the rats that still retained them. However, this revealed nothing — all of these rodents presented ovaries of similar, normal appearance.
When they tested the levels of various hormones, however, the investigators noticed that the rats in the hysterectomy-only group had a different hormonal profile compared with the ones in the control group.
"Even though the ovaries were structurally similar across all the groups, the hormones that were produced in the group that received hysterectomy alone resulted in a different hormone profile," says Koebele.
"Hormones affect both brain and other body systems, and having an altered hormonal profile could impact the trajectory of cognitive aging and could create different health risks," she explains.
The researchers do not yet understand how the changed hormonal changes impact cognitive function, nor whether this impact is permanent or short-lived, but they aim to find out by conducting further studies.
Below, you can watch Koebele and Prof. Bimonte-Nelson explain how they decided to conduct the current study, and why their findings are meaningful.