In biomedical research, “in vivo” refers to studies conducted within a living organism, as opposed to “in vitro” studies performed in a controlled environment like a test tube. This approach is used to understand complex biological systems and disease progression. The intricate interactions between cells, tissues, and organs can be observed, providing insights not possible from in vitro work alone.
Among animal models, mice are the most common, serving as biological surrogates to investigate human health and disease. Researchers use them to explore the safety of new drugs and the mechanisms of genetic disorders in a regulated practice.
Why Researchers Use Mice for In Vivo Studies
The preference for mice in research stems from biological and practical advantages. Genetically, mice share a significant portion of their DNA with humans, meaning many biological processes and diseases like cancer are comparable. This similarity allows scientists to study human conditions in a living system.
Beyond genetics, their small size makes them easy to house, and their short lifespan allows researchers to observe a disease’s entire course in a manageable timeframe. Their rapid reproductive cycle enables the generation of large populations needed for statistically significant results.
The ability to genetically modify mice is another powerful tool. Scientists create “transgenic” mice, which carry a foreign gene, or “knockout” mice, where a specific gene is inactivated. These models are instrumental in understanding a single gene’s function and its role in health and disease. This level of genetic control, combined with their relatively low maintenance costs, makes them a primary model in preclinical research.
Key Areas of In Vivo Mouse Research
In vivo mouse models are used across many biomedical fields. In oncology, researchers implant human tumor cells into immunodeficient mice or use genetically engineered mice that develop tumors. This allows for the evaluation of new anti-cancer drugs in a living system.
Neuroscience relies on mouse models to study neurodegenerative disorders like Alzheimer’s and Parkinson’s disease, as well as psychiatric conditions. By observing behavioral changes and analyzing brain tissue, scientists can identify therapeutic targets.
Mouse models are also used in immunology to study the immune system’s role in autoimmune and infectious diseases and vaccine development. In metabolic research, mice help in understanding conditions like diabetes and obesity, dissecting the genetic and environmental factors involved.
Common Techniques in Mouse-Based Experiments
Standardized procedures are employed in mouse research to ensure data is reliable. The administration of substances like new drug candidates is routine. Common methods include:
- Oral gavage, which uses a small tube to deliver a liquid to the stomach.
- Intraperitoneal injections into the abdominal cavity.
- Intravenous injections into a vein.
- Subcutaneous injections under the skin.
Behavioral testing assesses cognitive function, motor skills, and emotional states. Mazes are used to evaluate learning and memory, while open-field tests can provide insights into anxiety and exploratory behavior. These tests are important in neuroscience for measuring the effects of drugs or genetic modifications.
To monitor disease progression in real-time, researchers use non-invasive imaging. Techniques like bioluminescence and fluorescence imaging allow scientists to visualize processes like tumor growth. More advanced methods like micro-computed tomography (micro-CT) and magnetic resonance imaging (MRI) provide detailed anatomical images. After the experiment, blood and tissue samples are often collected for further analysis.
Ethical Considerations in Animal Research
The use of animals in research is governed by strict ethical principles, primarily the “Three Rs”: Replacement, Reduction, and Refinement. Replacement encourages using non-animal methods like computer modeling when possible. Reduction aims to minimize the number of animals used by employing robust statistical methods.
Refinement focuses on modifying procedures to minimize potential pain or distress. This includes providing appropriate housing, using anesthetics for painful procedures, and establishing humane endpoints to end an experiment early if an animal shows excessive suffering.
Research institutions have oversight bodies, such as the Institutional Animal Care and Use Committee (IACUC) in the United States. These committees review and approve all research protocols before studies begin. The IACUC ensures the research is necessary, the “Three Rs” are addressed, and all personnel are trained in humane animal care.
From Mouse Models to Human Medicine
Findings from mouse studies are a part of preclinical development, where new drugs are tested for safety and efficacy before human clinical trials. Data from these models helps researchers identify risks, determine dosage levels, and predict how a treatment might work in humans. This step is a regulatory requirement, with data often included in submissions to agencies like the U.S. Food and Drug Administration (FDA).
Many drugs on the market for conditions from cancer to autoimmune disorders were first evaluated in mouse models. These studies provided the foundational evidence needed to proceed with testing in people.
However, mouse models have limitations. Physiological and metabolic differences between mice and humans can lead to different responses to a drug or disease. Researchers are continuously working to develop more predictive models, including “humanized” mice that incorporate human cells or genes, to improve the accuracy of preclinical research.