30 Jun How is animal behavior used in research?
Have you ever wondered how animals can be used in research institutions to help scientists investigate diseases? In humans, sometimes diseases lead to changes in behavior. Diseases can change the way people move, sometimes people have trouble remembering things, or sometimes there are changes in behavior that show a person has become depressed. Animals have behaviors too! Studying animal behavior is a valuable tool in research. One of the many advantages of using animals in research is that scientists can study changes in animal behavior to learn about individual diseases. Studying animal behavior can also help determine whether a new research model is useful to study a disease. This article will walk through a few different examples of how scientists study animal behavior to study diseases.
Learning about memory
Each behavioral task has been designed by scientists to study specific disease-associated behavioral changes. Therefore, the behavioral task needs to isolate one specific behavior from others to be successfully used in research. To study learning and memory in mice, scientists may use the Object Recognition Task (OR). This task takes advantage of the fact that a mouse is a curious animal and will spend time sniffing objects trying to identify them, while also acquiring information on their shape, location, size (Figure 1A). The Object Recognition Task works by placing the mouse in a box with two identical objects inside. The mouse will spend time trying to identify each object. Scientists will measure the amount of time the mouse spent exploring each object. After 10 minutes, the mouse is removed from the box and, just like us, it will have formed a memory about the object characteristics.
When the mouse is placed again inside the same box, one of the objects has now been replaced with a new object with a different shape (Figure 1B). A healthy mouse will remember it has already explored the first object (old) and spend more time sniffing and interacting with the new object in the box (Figure 1C). If the animal has troubles with memory, like in Alzheimer’s Disease, it will not remember the old object nor recognize the new object, thus spending an equal amount of time exploring both (Figure 1C).
A change in behavior is also called a behavior phenotype. Scientists can use the information from these tests to identify new potential treatments for behavior phenotypes, like memory loss. For example, scientists could test a new drug for Alzheimer’s disease in the mice, and then have the mouse do the OR task again to see if the mouse’s memory deficits can be reversed by the drug. Sometimes scientists say that a drug or a treatment “rescues the behavior phenotype.” This means that the drug has a positive effect. These days, scientists may manipulate an animal’s genes. Researchers do this in order to identify how genes contribute to the memory deficits that occur due to Alzheimer’s disease.
Learning about motor skills
Given the wide range of disease presentation and symptoms, it is not surprising to learn that many other behavioral tasks exist to investigate specific and varied disease-associated behaviors. Parkinson’s disease for example is associated with motor deficits, thus animal models for Parkinson’s disease use behavioral tasks designed to study motor disabilities. One of these tasks is called Rotarod and is depicted in the illustration below.
In this task, the animal is placed on the Rotarod apparatus for a set amount of time. During this time, the wheel will move (almost like a treadmill for the animal). The animal will try to remain on the spinning apparatus because it will be scared of falling down, while the wheel increases its moving speed.
Scientists measure the time it takes for the animal to fall. Scientists can then compare the time it took to fall for the healthy mouse vs. the mouse with the disease. Mice with motor difficulties will spend significantly less time on top of the Rotarod compared to an animal with healthy motor control.
Learning about anxiety and depression
Animal models can also be used to investigate anxiety or depression-like behaviors. That is possible because the animals present those behaviors innately and the behavior task is just designed to isolate that behavior for investigation purposes. One example of an anxiety-like behavior is the open field task. Now, before getting into the details of the task, let’s imagine you are going to a dance party, but you don’t know many people there. Once you arrive, is your first instinct to go to the middle of the room? Or stay close to a wall? This behavior is innate in humans and mice, and is related to anxiety. Both humans and animals get anxious in the center of an open space and tend to prefer the borders. The open field task is designed to investigate that behavior. So how does the testing work?
The animals are placed inside an open box (Figure 3A). Because mice are curious animals they will start to investigate the place by sniffing around. Now, since the box is an open space the animals will prefer to stick to the walls of the box and avoid the center. That doesn’t mean the mouse will not walk through the center of the box, just that it will spend most of its time closer to the walls than in the center. At the end of the experiment, the mice with higher anxiety-like behavior will have spent a significantly less amount of time at the center of the box (Figure 3B).
All three examples given have one thing in common: a specific task is designed to investigate in animals a symptom of a disease in humans. This article focused on how mice are used to study behavior but other model organisms can be used, too. Researchers study behavior in rats, zebrafish, flies, and worms to name a few!
How is this related to the SLC13A5 patient community?
Behavioral investigations are key to understanding diseases: they can give insight into the brain regions to be investigated, targeted drug approaches, long-term consequences of a disease, among many others. The SLC13A5 patient community has benefited from the use of behavioral investigations in mice.
SLC13A5 Epilepsy is characterized by the presence of seizures very early in life. Within hours or days after birth, kids are already having seizures. As they grow older, kids affected have a developmental delay, tooth issues and intellectual disability. Most kids only say a few words but can understand a lot more than what they can communicate themselves. Thus far, there are no cures. This is where animal models can be useful.
Since the disease is caused by mutations in the SLC13A5 gene, animal models for the disease are obtained by deleting the same gene in mice. The SLC13A5 gene encodes for a sodium-dependent citrate transporter (NaCT), a protein responsible for the movement of citrate into cells. Citrate is important for metabolism, and without a proper functioning NaCT citrate levels build up outside the cell. Indeed, patients have elevated levels of citrate in the blood and the cerebrospinal fluid.
Using behavioral assessments in a model of SLC13A5 Epilepsy
Similarly, mice with a deleted copy of SLC13A5 gene show elevated citrate in the blood and cerebrospinal fluid, and behavioral investigations show the animals have learning disabilities. When we use animal models to study human diseases, we sometimes use behavioral tests to confirm that the animal models are presenting with symptoms that match the human disease-associated symptoms. For example, since cognitive delay and disability is a symptom in the human version of SLC13A5 Epilepsy, memory deficits would also be expected in a mice model during the object recognition test. If the memory deficits appear to be present in a mice model during these tests, then the scientists have shown that the mouse model can be used to study and test treatments.
Mice and humans share a lot of similarities in the genes they express, this is why mice are such great models to investigate human disease. But, even with all similarities, some genes are different between humans and mice, and so is their regulation. Therefore, expressing human genes in mice allows for a more accurate representation of the disease in an animal model. TESS Research Foundation received a grant from the Orphan Disease Center to create a humanized mouse model. This is important because the mouse SLC13A5 gene functions slightly differently than the human SLC13A5 gene. Scientists will be replacing the SLC13A5 gene normally expressed in a mouse with the human copy of SLC13A5. Behavioral tasks can then be used to assess and validate this model.
This article was written by Paula da Silva Frost. Paula is a neuroscience graduate student at the University of California, Riverside. She studies lung allergy and how the brain contributes to respiratory symptoms. She has hosted multiple podcasts, one from Brazil called Neuropod and the other developed in California called Welcome to Grad School. You can follow her on Twitter: @ps_frost.
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