Knowledge Base

Introduction

The Open Field for Rodents

The open field test was first published 1932 by C. S. Hall and E.L. Ballachey to determine the fearfulness of rats. Today, the test is often used with rats and mice to investigate their locomotory behavior and their willingness to explore. Also, the test is one of the most commonly used methods to investigate anxiety in rats and mice. It is based on the natural tendency of rats and mice to spend more time in the corners and the periphery than in the center. Changes in these measures are often used to assess the sedative or stimulant effects of pharmacological agents.

The test arena consists of a circular or rectangular empty open space with walls to prevent the animals from escaping. The arena is divided into a border zone and a center zone. In addition, the arena can be sub-divided into a number of other zones, like north, east, south and west zones, or corner zones.

Common behaviors to be measured are:

• Time spent in the border zone and center.
• Time until the border of the center zone is first crossed.
• Walking distance in each of the zones.
• Percentage of time the animal is mobile/immobile.
• Walking speed in each of the zones.
• Frequency of rearing.

References

• Hall, C., Ballachey, E. L., 1932. A study of the rat's behavior in a field. A contribution to method in comparative psychology. University of California Publications in Psychology, Vol, 1-12.
• Gould, T.D., Dao, D.T., Kovacsics, C.E., 2010. The Open Field Test. Neuromethods, Vol, 1-20.
• De Visser, L., Van Den Bos, R., Kuurman, W.W., Kas, M.J.H., Spruijt, B.M., 2006. Novel approach to the behavioural characterization of inbred mice: automated home cage observations. Genes Brain and Behavior, Vol (6), 458-466.

For the complete list of publications, see the results in Google Scholar. On the downloads section of the Noldus website, my.noldus.com, you can find a number of sample experiments, including the open field.

The Open Field for Zebrafish

Open Field

The open field test is used to evaluate exploratory and affective behaviors. Fish are filmed with a video camera positioned overhead. The bottom of the tank is divided into two virtual zones, center and periphery (a circular zone with inner boundary 5 cm from the testing tank wall), which enables quantification of regional activity.

In addition to standard movement parameters, primary behavioral measures included the distance traveled, number of visits and time spent in central and peripheral zones, and the ratio of time spent in the center zone over total testing time.

Novel Tank Diving Test

The novel tank test is used to assess exploratory and affective domains. The novel tank is a trapezoidal tank maximally filled with treated water and divided into two equal, horizontal regions (top/upper and bottom/lower zones).

Primary behavioral measures include the number of visits and time spent in central and peripheral zones, the ratio of time spent in the top zone over total testing time, latency to enter the top zone, time spent in the top zone, and number of transitions to top zone.

Similar to behavioral tests used in mammalian models, affective phenotypes are inferred from modulation of thigmotaxis (center/periphery in the open field test) and geotaxis (top/bottom in the novel tank diving test).

References

• Kalueff A.V., A.M. Stewart, R. Gerlai (2014). Zebrafish as an emerging model for studying complex brain disorders. Trends in Pharmacological Sciences, Vol (2), 63-75.

Physical Setup

The following suggestions are meant to optimize video tracking:

• Camera position: The camera should have a good view of the entire region the animal can be in. The arena should fill the field of view.
• Lighting evenness: The lighting should be as even as possible throughout the arena. Make sure there are no shadows in the corners. Bright lights are not necessary, but should you need to supplement the light, consider red (or infra-red) light, as the animals will be less sleepy. Regardless of the light level chosen, the investigator should use a light meter to record the lighting level and report this level in any publication.
• Multiple arenas: When working with multiple arenas, make sure that the background light intensity is the same across arenas. This is usually not a problem, as long as the contrast between each animal and its arena background is much bigger than the difference in brightness between arenas.
• Diffuse lighting: The lighting should be diffuse, so as not to cast strong shadows (which might be tracked instead of the animal). Even, diffuse lighting is important to optimize tracking of the nose.
• Background contrast: The background should contrast with the animal. If necessary, use a different setup for light and dark colored animals. Matt, gray walls often give good results.
• Urine pools: Depending on circumstances, pools of urine can cause problems with the tracking because they reflect light. An absorbent base can help.
• Reflective surfaces: Make sure the sides of the box are not reflective (e.g. sanding). Alternatively, exclude the sides from the arena, but make sure that the animal is tracked well in the entire border zone.
• Apparatus position: Always place the apparatus in the same position in the room; cues from overhead might influence the behavior of the animal. For the same reason, the experimenter should not be visible to the animal during the trial (automated tracking makes this possible).
• Audio disturbance: Minimize disturbance from audio sources, especially from ultrasound sources such as ventilation fans, CRT monitors, or strip-lights. You can mask audio disturbance by using the same background sounds, for example of a radio, in the test room as in the room where the animals are normally housed.
• Animal handling: When you handle the animals, be careful to minimize stress.
• Animal isolation: If you use multiple arenas, make sure that the animals in the arena do not influence each other. The animals should, for example, not be able to hear or smell each other.
• EthoVision XT guidance: In EthoVision XT, choose Help > Video Tutorial and watch the video chapter Set Up Your Test Environment. That provides useful tips about the camera position, how to improve lighting and contrast with the background.
• Deep learning tracking: If you intend to use the Deep learning method to track the subject's nose point, note that there are additional requirements and limitations. See the EthoVision XT Help.

Source: EthoVision XT 18 - Application Manual, Noldus Information Technology