The Open Field Test Is A Behavioral
The open field test is a behavioral test developed by Calvin Springer Hall to study the physical and physiological behavior of rodents when put into an environment which could be manipulated. The open field test is composed of a box that could be opaque or clear and made of square compartments high enough so that the rodent may not escape. Along with this box is the attachment of a video camera with a special software which is used to observe and track the movement of the rodents. Experimenters tested to see elevated levels of anxiety in the mice once placed in the box. They observed whether the mice would stay near the inner edges of the square, have higher distance traveled in the box, and if they would leave more amounts of fecal pellets. It was believed that when placed in a new environment, rodents will display higher levels of anxiety. The test was also found useful to observe the results of anxiolytic and anxiogenic drugs. This task could also be used alongside other behavioral tasks such as the elevated maze task and the elevated zero maze task to test for more thorough results or to confirm what has already been observed. It was concluded that mice have the tendency to stay near the inner edges, their distance of travel increases, and they will defecate more. The results may vary however differ between different strains of mice and can also depend on each individual rodent.
The open field test was developed in 1934 by Calvin S Hall. It was designed to observe anxiety, locomotor activity, and willingness to explore and is now one of the most widely used experiments to test anxiety today(Seibenhener & Wooten, 2015). In an attempt to gain a better understanding of physiological and psychological responses in humans as a result of anxiety, the open field maze was developed to observe these responses on a smaller, slightly different scale. The basis of this research is that mice that have higher levels of anxiety will not be as willing to explore than mice that have lower levels of anxiety. When placed in a new environment with new stimuli mice will tend to be reserved and display levels of anxiety (Seibenhener & Wooten, 2015). This experiment proved to be extremely popular because of its simplicity. The rats do not have to be trained in any particular manner, and the experimenters are not required to undergo specialized training as well. The experiment can also be conducted quickly and can provide almost instantons results (Seibenhener & Wooten, 2015). The experimenters can test the psychological and physiological response which are simple to detect. The open field test studies different strains of mice such as wild type and laboratory mice. However, the study can also be conducted across several species such as lobster, pigs, rabbits, primates, and honeybees. This causes for variation in results however, the results should remain fairly similar (Seibenhener & Wooten, 2015).
The open field test is made up of a box that contains square compartments. The walls of the box are high enough so that the rodents are not able to escape. The compartments that the rodents are in has to be big enough to the ratio of the rodent so that the rodent will sense a feeling of openness. This causes the rodent to feel exposed and in danger because it is unable to protect itself in this type of environment. However, a rodent’s natural inclination to explore its surroundings counteracts with its feeling of vulnerability and causes anxiety (Seibenhener & Wooten, 2015). In a study conducted by Michael L. Seibenhener and Michael C. Wooten, a dense plastic box with four square chambers was obtained, and each chamber measured 50 centimeters in length, 50 centimeters in width, and 38 centimeters in height. To conduct this particular experiment only the use of one chamber was necessary. The walls of the chamber were smooth while the floor was rough to facilitate movement of the mice. Before beginning the experiment, the chamber was doused in 95% ethanol so that any subsequent scents from mice that were tested before this experiment could be erased. Any commercial video tracking camera and software can be used for this experiment so that the experimenter can concisely track the movement of the mice. After the camera and software are set up, the mice can now be brought in their home cage from their housing room into the testing room. Allow the mice to get accustomed to the testing room environment for approximately 30 minutes. Lightly grab a mouse by the tail and take it out of its home cage and place into the middle of one of the compartments of the square. At the same time, turn on the software that will help detect and record the movement of the mouse. Allow the mouse to roam freely in the compartment for 10 minutes. Make sure there are no interruptions and that there are no obstructions in the box. After the 10 minutes are complete, pick up the mouse by the tail and place back into its home cage. Observe the fecal pellets left by the mouse and count and record the number present. The fecal matter is then removed, and the box must be wiped down again with 95% ethanol(Seibenhener & Wooten, 2015).
There are a few behaviors that the mice display that can be observed and measured to determine if the mouse is experiencing high levels of anxiety. This can be measured in many ways such as total distance moved, time spent in the center, time spent near the edges, rest time, and a number of fecal pellets (Seibenhener & Wooten, 2015).
Since its development, the open field test has been one of the most widely used tests in animal psychology. This is due to its simplicity in design and straightforward results. As stated earlier, the test was able to help experimenters determine basic responses in rodents that are thought to be effects of anxiety. Not only is it possible to test natural responses to a new environment, with the use of anxiogenics and anxiolytics experimenters are also able to test how the results might change with the use of drugs that affect anxiety. Anxiogenics are drugs that cause anxiety whereas anxiolytics reduce it(Bystritsky, Khalsa, Cameron, & Schiffman, 2013). As a result, mice given anxiogenics may be more inclined to stay towards the corners and may never venture to the middle while mice given anxiolytics will go towards the middle of the box(Bystritsky et al., 2013). The use and effects of these drugs on rodents can provide great insight into what the effects and complications of these drugs on humans might be. For example, a study in 2017 was conducted to observe the effects of methamphetamine and buprenorphine on anxiety like behavior in male rodents. Methamphetamine abuse is a global problem and several studies have shown that it is an anxiogenic drug. It has effects on both laboratory animals and humans which include symptoms such as depression, anxiety, insomnia, and psychosis(Etaee et al., 2017). Buprenorphine is a semisynthetic drug with anxiolytic like properties. It was believed that treating mice dependent on meth with buprenorphine could reduce the anxiety like symptoms of the mice(Etaee et al., 2017). Over a period of 7 days 40 mice were administered either Meth, Bup, Meth and Bup, or no drug. It was observed that when put in an open field test, the mice that the administration of Meth and Bup alone was anxiolytic whereas the administration of both drugs was anxiogenic. This showed that the treatment of people with meth dependency with the drug buprenorphine may not be beneficial (Etaee et al., 2017).
Although the open field maze task was a huge breakthrough in the study of anxiety symptoms and behavior, it is too general of an experiment and experimenters cannot base their findings solely on the results of it. Instead many have used the open field test in convergence with other studies such as light-dark box test and the elevated maze test. The elevated maze tests look at the inherent nature of mice and their need to explore their surroundings. In this experiment, there are four arms in the maze, two are enclosed and the other two are open. The mouse is given the option to stay in the unprotected and open part of the maze or the enclosed part of it. The number of times the subject comes in and out of each section and the time spent in each section is recorded (Bystritsky et al., 2013). In this experiment, it is shown that the mice avoid the open areas and tend to stay in the closed ones. Administering drugs such as benzodiazepines which are anxiolytic reduces anxiety in the mice and causes them to explore the open areas (Bystritsky et al., 2013). Similar to this test is the light-dark exploration test. In this test, however, the mouse has an option to explore the lighted exposed areas or the darker compartments of the box. Mice tend to stay in darker areas. What is being measured in this experiment is how likely the mouse is to explore the lighted areas which in turns measures its level of anxiety. Giving the mice anxiolytic drugs in this experiment did not change their preferences for the darker areas, but instead made them more willing to explore their lighted surroundings as well (Bystritsky et al., 2013).
Although rodents are often used as models for humans because of their closely related pathologies, it is unclear exactly how much one can compare a human’s experience with that of a rodent. Anxiety in rodents produces fear, increased heartrate and vigilance, freezing, and suppressed food consumption (Lezak, Missig, & Carlezon, 2017). These responses resemble human responses of “anxiety-like” behavior however in rodents these symptoms may resemble something else. Thorough examination of brain areas suggest that the amygdala mediates fear-like behaviors to short, discrete, and proximal aversive cues, whereas the bed nucleus of the stria terminalis (BNST)mediates anxiety-like or worry-like behaviors. These two brain areas are responsible in regulating one another to coordinate activation of brain regions that mediate similar outputs (Lezak et al., 2017). Conclusion
The open field test is one of the most popular tests in anxiety research. However, there are many things one must take into consideration when conducting this experiment to realize that there may be some experimental flaws because variables can be changed around. Handling history of the mice may have an impact on how the mice performed in the experiment. Some mice are handled by their experimenters daily and are stroked for several minutes whereas some mice are handles very minimally before the experiment. This may cause different behavioral results. It has been observed that larger open field size is correlated with more distance moved in mice than a smaller sizer. The lighting in the open field area must also be consistently controlled. This is because mice have a natural aversion to light and as a result prefer darker areas. It has also been shown that mice exposed to a dull red light drop less fecal boli than when they are exposed to white light. Most open field tests do not have ceilings. However, some tests have been undergone with ceilings present at different heights. The result was that the mice were more active in the open fields with low ceilings than in the open fields with higher ceilings (Tatem et al., 2014).
Three main things were being tested in the open field test. They were total distance covered during the ten minutes the test was conducted, thigmotaxic which is the amount of time the mouse stayed near the edges of the field, and the number of fecal pellets left in the field. When comparing the two different strains of mice, wild-type (WT) and genetic knockout mice (KO), there was no difference in total distance traveled between the two. However, when it came to thigmotaxic or staying closer to the walls, the KO mice remained closer to the walls during the ten-minute session than the WT mice which crossed of the field occasionally. Increased defecation is a sign of anxiety in animals over a short-term period. In this study, KO mice had higher levels of boli than WT mice. (Seibenhener & Wooten, 2015)
In conclusion, anxiety cannot be pinpointed through just one experiment or symptom. A combination of different tests and measuring different variables can help determine if someone is experiencing anxiety.