Study confirms why neuroscience research needs female mice – Harvard Gazette

Mice have long been at the center of neuroscience research, providing a flexible model that scientists can control and study to learn more about the complex inner workings of the brain. Historically, researchers preferred male mice to female mice in their experiments. This is due to concerns that female hormonal cycles can cause behavioral changes that can ruin the results.

But new research from Harvard Medical School challenges this notion, suggesting that many experiments may not justify that concern.

research result, Published March 7 in Current Biologyfound that despite ongoing hormonal fluctuations, female mice exhibited more stable exploratory behavior than male mice.

Using strains of mice commonly studied in the laboratory, the researchers analyzed how the animals behaved as they freely explored open spaces. They found that the hormonal cycle had a negligible effect on behavior and that differences in behavior between individual female mice were much greater. And it was larger in men than in women.

The results underscore the importance of including both sexes in mouse research, the research team said.

“I think this is very strong evidence that if you are studying naturalistic, spontaneous exploratory behavior, you should include both genders in your experiment. Which leads to the argument that if you can only pick one, you should really be working on women.” Sundeep Robert DuttaProfessor of Neurobiology at the Bravatnik Institute at HMS, who co-led the study Rebecca Shansky of Northeastern University.

From rodents to humans: a history of prejudice

When neuroscientists try to better understand the human brain, they routinely turn to mice. Dutta sees the mouse as “the go-to vertebrate model for understanding how the brain works.”

This is because mouse and human brains share a considerable amount of structural organization and genetic information. As such, scientists can easily manipulate the mouse genome to address specific problems and build models of human disease.

“Much of what we understand about the relationship between genes and neural circuits, and the relationship between neural activity and behavior, has come from basic research in mice, and mouse models are useful for a variety of neurological diseases. It has the potential to become a truly central tool in the fight against and psychological illness,” said Datta.

For more than 50 years, researchers have preferentially used male mice in their experiments, but nowhere has this practice been more prominent than in neuroscience. in fact, 2011 analysis Male mice were found to have five times more gender-specific neuroscience studies than female mice. Over time, this practice has resulted in a better understanding of the female brain, which may contribute to misdiagnosis of women’s mental and neurological conditions and the development of drugs with more side effects in women. Outlook for 2021 Nature Neuroscience.

Disparities in gender expression common in animal research have historically been reflected in human studies as well.

“This bias starts in basic science, but its effects extend into drug development, leading to biases in the drugs that are manufactured and how they are matched by gender,” said the first author. Dana Levy, Neurobiology Research Fellow at HMS. For example, Levi said states such as anxiety, depression and pain are known to manifest differently in female mice and females than in male mice, which are more often used in early-stage drug testing. pointed out.

To address the issue of gender bias in scientific research, the National Institutes of Health announced a policy in 2016 requiring researchers to include male and female subjects and samples in their experiments. However, in a follow-up study overlooking the scientific field and Looking specifically at neuroscience Indicates slow progress.

The reasons for this longstanding bias in neuroscience are complex, Datta said. I want to change. “

But perhaps the biggest reason for excluding female mice is the rodent version of the menstrual cycle, known as the estrous cycle, whose behavior is broadly influenced by cyclic fluctuations in hormones such as estrogen and progesterone. It comes from assumptions, Datta said. According to Datta and Levy, the estrous state is known to strongly influence certain social and sexual behaviors in mice. However, data on the effects of estrous state in other behavioral situations are mixed, leading to what Datta calls “genuine inconsistency in the literature.”

“We wanted to measure how much the estrus cycle appeared to influence basic patterns of exploration,” said Datta. “Our question was whether these ongoing changes in the hormonal status of the mice affect other neural circuits in ways that would confuse researchers.”

“Like everyone else, I thought adding women would only complicate the experiment,” Levy added.

Assumption test

The researchers studied genetically identical males and females from common strains of laboratory mice in a circular open field, a standard laboratory setting for behavioral neuroscience experiments. In practice, the test involved placing a mouse in a 5-gallon Home Depot bucket for his 20-minute period and using a camera to record in 3D the mouse’s movements and behavior as it freely explored space. The researchers swabbed each female mouse to determine the estrous state and repeated the bucket test multiple times on the same individual.

The team used MoSeq, an artificial intelligence technology previously developed by the lab, to analyze the videos. This technology uses machine learning algorithms to break down mouse movements into about 50 different “syllables” or body language components. Using MoSeq, researchers collected detailed, high-resolution data on the structure and patterns of mouse behavior during each session.

The researchers found that estrous state had little effect on the exploratory behavior of female mice. Instead, patterns of behavior tended to differ much more between female mice than throughout the estrus cycle.

“Give us any video from our pile and we’ll tell you which mouse it is. That’s the personalization of behavioral patterns,” said Datta, noting that behavioral research “has a lot of variability in the data.” The dominant aspect is the fact that individuals have subtly different life histories.”

When the researchers compared female and male mice, they found something surprising: males also exhibited behavioral idiosyncrasies, but more behaviors within a single mouse and between mice than females. There was a change in

“People have made this assumption that male mice can be used to reliably compare within and between experiments, but our data are limited to the fact that female mice have an estrous cycle. Nonetheless, it suggests that they are more stable in terms of behavior,” Datta said.

Change case

Scientists generally agree that the inclusion of female mice is important from a fairness standpoint, but some are concerned that it could complicate research. The findings provide a strong scientific rationale for using female mice in experiments.

“The fact that women’s behavior is more reliable suggests that including women may actually reduce the overall variability of the data under many circumstances,” says Datta. says Mr.

Based on their findings, Datta Lab researchers switched from male mice to mixed groups or female mice in other experiments, including a circular open field test.

Datta cautioned that because the study only examined one mouse strain in one lab setting, the results cannot be generalized to other strains and settings without further testing. However, he notes that tension and set-up are commonly used in neuroscience research, including early-stage drug development to test how potential drugs affect locomotion in mice.

Dutta said the findings “should encourage those interested in drug development in this context to include both sexes in their analyses.”

Datta and Levy are now interested in examining how internal states beyond hormonal states, such as hunger, thirst, pain, and disease, affect exploratory behavior in mice.

“The question is who wins in this tug-of-war between your current internal state and your personal identity,” Levy explained.

They also want to delve deeper into the neural underpinnings of the behavioral personalities in mice seen in the study.

“We were struck by the steady variability between individuals that we observed, as if these mice were really individuals,” says Datta. “We tend to think of lab mice as swappable widgets, but they’re not at all. So what controls these individualized behavioral patterns?”

“We want to understand the mechanisms of individuality: how diversity between individuals arises, how it influences behavior, what can change it, which brain We want to understand if the domain supports it,” Levy added.

To this end, the Datta Lab will examine mouse behavior from birth to death to see how individualized behavioral patterns emerge and crystallize during development and how they change throughout life. I understand.

The researchers also open the door to more rigorous and quantitative studies of whether and how the estrus cycle affects mouse behavior in other contexts, such as the completion of complex tasks. hope to open

“This is a very interesting example of how hypotheses that influence the way we do and design science are sometimes just hypotheses. It’s important to test them directly because they are true.” It may not be,” Levy said.

Other authors include Nigel Hunter, Sherry Lynn, Emma Robinson, Winthrop Gillis, Eli Conlin, and Rockwell Anoha of HMS.

Datta serves on the scientific advisory boards of Neumora, Inc., which licensed the MoSeq technology, and Gilgamesh Pharmaceuticals.

This work was supported by the NIH (U19NS113201; RF1AG073625; R01NS114020), the Brain Research Foundation, the Simons Collaboration on Global Brains, the Simons Collaboration on Plasticity in the Aging Brain, the Human Frontier Science Program, and the Zuckerman STEM Leadership Program. .