Johan Simbade
Mouse Behavior Tests Find Common Causes of Obesity
Mice are commonly used in biomedical research for many reasons. Mice serve as research models for a range of diseases and models of the immune system, including allergies, cancer and asthma. They also provide insights into the mechanisms involved in neurological, cardiovascular, and neurotransmitter disorders. One drawback of using mice in biomedical research is that their behavior can be altered by drug treatments. This issue has led to calls for more studies of the impact of various drugs on laboratory mice.
Mice demonstrate significant activity in two systems: the central nervous system and the retina. Brainstem cells (neuarchal cells) in the periaqueductal grey matter receive strong inputs from both suprachiasmatic (inner ear) and distal cues. During behavioral testing, mice showed a preference for responding to a particular stimulus and showed an avoidance response to others. In Experiment 1, plastic slices of glass were placed into the maze and food (sucrose) was hidden. Mice were tested for hours with no food present and then given an injection of sucrose if they had not returned to the hidden slice. The results showed that, unlike adult animals, Mice spent much time looking at the moving slice and returned to the same spot when it was tested with the sucrose injection, indicating the presence of two systems in the brain.
Experiment 2 replicated this experiment in a Morris maze, but this time, a photopic camera tracked the position of each mouse during the test. Mice chose the same place in each trial and spent considerably less time reaching the end of the maze when their position was visible in the infrared light. When their positions were not visible in the light, however, they reached the end of the maze on average four times as often as controls. This suggests that the infrared camera allows the scientists to test the function of the two systems at the same time.
In order to test whether or not the two systems have different interactions in the brain, researchers repeated Experiment 1. They placed one eye on a piece of plastic that blocked one of the systems while the other eye was on a normal part of the cage. Mice began to explore the new maze more rapidly than controls, but returned to their usual routes each time an eye was removed. This again indicates that the system is performing two separate functions and that changes in the neural circuitry are altering behavior.
This test provides the first evidence that supports the view that the two major systems involved in judgment and action are organized differently in the human brain than in mice. This study has applications far beyond mice, however. It is also relevant to humans, who may differ in a variety of ways from mice, including temperament, intelligence, and mood. For instance, people with Alzheimer’s disease have a problem with both short-term memory and long-term memory. The ability to remember the names of people they have only seen on television is one of the most basic of the cognitive abilities that affects mood.
Although the maze performance test was completed by all members of a study, it did not demonstrate a significant effect in behavior. This suggests that future studies should test single animals, such as rats, or specific types of food, such as spoiled milk, to find differences in behavior. If scientists are able to determine which cells fire in response to the presence of a particular odor, they may be able to use this information to develop an antiobesity drug. Currently, there are no such drugs in development.
