Rodent research part 1: FAQs

    Do you know what rodent research entails?

    Our readers expressed a ton of interest in animal research when I asked about it a few weeks ago, with more requests for us to cover it than any topic in recent memory.

    This email will cover the most common questions we got, and in a few weeks I’ll send a part 2 that gets into less common questions and also dives into the findings of some landmark nutrition-related animal trials.

    We happen to have a rodent research expert on staff, Dr. Bill Willis. He’s worked on rodent experiments for many, many years at a large academic research center, and knows a tremendous amount about disease mechanisms. Let’s ask him a few questions!

    Kamal: Why are rodent studies done in the first place?

    Bill: The overall purpose of rodent experiments is to use models to study human diseases in a way that can’t be ethically studied in humans.

    For example, let’s say a large observational study found a strong association between a mutation or variant in a particular gene (let’s call it variant X) and Parkinson’s disease. The correlation may be strong, but this doesn’t prove causation.

    To test the hypothesis that the gene variant X causes Parkinson’s, researchers may turn to a rodent model, where mice or rats are genetically engineered to express the gene variant X.

    The mice would then be monitored over time for development of tremors or signs of Parkinson’s disease compared to ‘wild-type’ mice expressing the normal gene X over several weeks or months. At some point, the mice would be euthanized for brain tissue analysis to allow researchers to look for evidence of pathology in areas of the brain typically affected by Parkinson’s disease.

    Although rodents are imperfect models, the ability of researchers to carry out gene editing and tissue analysis can potentially uncover aspects of disease mechanisms that can’t be directly studied in humans. In the case of Parkinson’s disease, much of the current insight into the nature of brain lesions in humans has come from studies of human brain tissue post-mortem, which is an inherently limited method.

    Having shed light on potentially novel disease mechanisms, the results of the rodent model are used to inform a hypothesis that can be tested in human tissues or samples from human donors for verification. In this way, rodent models and basic research complement human studies, as findings from the research are translated to people with specific health conditions, and vice-versa.

    Kamal: Why exactly are rodents used for research more than other animals?

    Bill: Rodents are often a go-to model for studying human disease due to several characteristics that make them ideal for biomedical research. Many aspects of their anatomy and physiology are similar to humans. Moreover, mice, rats, and humans share 95% of the same genes.

    Rodents also have short gestation times and a large number of offspring, allowing researchers to generate animals for experiments over relatively short periods of time.

    Kamal: Some of our readers prioritize animal welfare above all else when it comes to dietary choices. A handful sent critical replies to our previous email asking about reader interest in animal research.

    Some of them were generally wary of animal experiments because of ethical concerns or questions regarding applicability to human health, but they were still curious to learn more. Other readers, however, were angry that we would provide information on this topic at all. What can you tell us about the process and ethics of animal research?

    Bill: Researchers can’t just start using mice or rats for an experiment on a whim. Animal research is highly regulated and subject to several layers of oversight in the U.S. and throughout much of the world to ensure research animals are treated as ethically and humanely as possible.

    Kamal interjection: If you view all animal experiments as inherently unethical and not worth discussion, this section (and potentially this email as a whole) isn’t for you, so feel free to skip this one! Now, back to Bill …

    In the U.S., all animal research must comply with the Animal Welfare Act (a law enforced by the USDA), and research facilities that receive public health service funding (i.e. NIH/government funding, which includes most universities that perform animal research) must also comply with the Public Health Service Policy on Human Care and Use of Laboratory Animals (PHS policy).

    Compliance is ensured at the research institution level through an Institutional Animal Care and Use Committee (IACUC), which reviews and approves all animal research before it is conducted. IACUC committees have at least five people and include:

    • A doctor of veterinary medicine
    • A scientist with experience in animal research
    • A non-science professional, such as a lawyer, clergy person, or ethicist
    • A member who is not affiliated with the research institution and represents the community

    A rodent study begins with the submission of a detailed experimental protocol to IACUC. The IACUC committee will then review the proposed experiment to ensure that the protocol complies with all regulations, includes justification for using animals, and includes adequate procedures to minimize or eliminate any pain or discomfort that the animals may experience. Often, the IACUC committee will propose changes to the protocol prior to approval in a process that may involve several revisions. Once approved, the researchers are then able to run the experiments as proposed.

    One final note: Since experiments are, well, experiments, it is possible that symptoms or health conditions may develop faster, or in unexpected ways. To prevent unnecessary pain and suffering, all animal protocols include strictly defined early removal criteria (ERC) as a basis for euthanasia to prevent excessive pain or distress that may appear as a result of unexpected side effects or worse than expected symptoms. Depending on the protocol, animals are monitored for ERC over strictly defined weekly, daily, or even hourly intervals during the experiment. ERC may include excessive weight loss, poor body condition, excessive weakness, or, in the case of cancer models, excessive tumor burden.

    Kamal: Could you quickly summarize the main steps of animal experiments?

    Bill: Sure. Animal experiments are set up specifically to comply with PHS policy. They begin with determining the need to include animals in the first place:

    1. Justification. Are animals necessary for this research? Researchers examine whether alternative approaches not involving the use of live animals may be sufficient to answer the scientific question(s) being investigated. If animals are necessary, will the proposed experiment(s) minimize pain and distress to the animals while maximizing the scientific value?
    2. Write the animal protocol.
    3. Obtain regulatory approval.
    4. Get the mice. If available, transgenic mice are often obtained from another investigator or commercial source, and then bred at the vivarium to generate experimental mice. If not, CRISPR or other genetic engineering techniques are used to generate the mouse model. Wild-type mice are sometimes purchased as-needed from a commercial vendor, or generated by the investigator through breeding in the vivarium.
    5. Animal husbandry. The investigator selectively breeds the mice, weans from the mother and collects tissue (tail or ear clips) for DNA isolation and genotyping to generate the model (if transgenic) and maintains or expands the mouse colony as needed for experiments.
    6. Run the experiment. Animals may be housed in the vivarium for long-term experiments, or transported to other locations for treatment or analysis via treadmills, MRI, in-vivo imaging, or other methods.
    7. Processing. Much of the time, mice are euthanized at some point, and tissues are harvested and processed for analysis. Sometimes, mice cells or tissue are maintained in culture or harvested for ex vivo or in vitro studies.
    8. Analyze the results.

    Thanks Bill! This information doesn’t seem to be well-known outside of academic research centers, so hopefully our readers learned something new today. We’ll cover more reader questions as well as some landmark nutrition-related animal studies in a few weeks.


    Kamal Patel
    Co-founder, Examine