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Morris Water Maze

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Synonyms: (submerged platform) water escape task, Morris water escape task, Morris water navigation task.

The purpose of this test is to evaluate spatial memory. In this test the animal is required to swim in a tank of opaque water until it finds a submerged platform that it can mount to escape the water. Presumably, the animal uses specific visual cues placed around the outside of the tank to learn where the platform is located. An animal that is able to remember the cues will find the platform more quickly each time it completes a trial swim. Animals are initially given a series of “learning trials” in which they are allowed to swim in the tank until they find the platform. Each learning trial lasts a specific amount of time and the time between trials must also be specified. Following this, a “probe trial” is run in which the submerged platform is removed and the time the animal spends swimming in the quadrant of the tank where the platform was previously located is measured. Animals that have learned the position of the platform will spend most of their time in the quadrant where the platform was previously located. Animals that are poor learners will spend time searching other areas of the tank.

See this link for an illustration1 of the Morris water maze.

Species used: Rats and mice. This task was developed for use in rats (generally good swimmers). In mice, performance in this test is highly dependent on genetic background. Special consideration must be given to the use of this test in mouse strains or genotypes with reduced ability to navigate using spatial cues or to swim, e.g., visual or musculoskeletal impairments. In addition, mice with other physiological or behavioral traits such as impaired thermogenesis or high anxiety levels may also perform poorly in this test1.

Important considerations:

Water Tank
  1. Size (diameter) and depth of the tank (varies with species). Water depth of 15-20 cm is adequate for mice. Rats are larger and may dive to the bottom so require deeper water.
  2. Size of platform in relation to the diameter of the tank (task difficulty increases with decreasing size of the platform).
  3. Shape and depth (below the water surface) of the escape platform
    1. Round shape recommended (provides the same tactile cues on all sides)3.
    2. Platform surface should be textured so the animal can maintain a secure grip and close enough to the water surface so the majority of the animal’s body is out of the water when on top of the platform (e.g., mice ≤0.5 cm below water surface).
  4. Water temperature
    1. Mice are more susceptible to hypothermia than rats.
    2. Hypothermia risk can be lessened by increasing the water temperature and/or increasing the inter-trial interval.
    3. Water temperatures < 20⁰C can lead to hypothermia. Temperatures that are too warm may discourage active swimming/searching.
    4. Animals should be allowed to dry in a warm environment after removal from the tank. Absorbent towel(s) may be placed in the holding cage to collect water dripping off the animal and a heating source directed over or underneath the cage may provide warmth. Do not attempt to towel- or blow -dry animals as this is stressful and rough handling can cause injury.
  1. Substance used to make the water opaque
    1. Must be edible and nontoxic because animals will consume the substance when grooming after each trial.
    2. Tempera paint is recommended3. Milk supports bacterial growth, especially in warm water. Lime and chalk may be toxic.
    3. Alternatives that may allow the use of clear water include using a clear Plexiglas platform or using a platform the same color as the tank surface.
  2. Cleaning schedule for the tank (water changes)
    1. Urine and fecal material will accumulate in the water and contribute to bacterial contamination and growth. The tank should be drained and disinfected after each day’s trials. Partial water changes between mice can reduce the accumulation of urine/fecal material. Fecal material may be removed after each animal with a small mesh net3.

Test Procedures
  1. Trials should not exceed 2 minutes.
  2. Inter-trial intervals should be long enough to prevent the development of hypothermia and fatigue over repeated trials. It is recommended that intervals be at least 10-15 minutes, especially in mice5.
  3. Animals must be observed continuously while in the tank and removed from the water if their head sinks below the surface4.
  4. Two to four trials per day are generally adequate for training.

USDA category: E

Alternative tests for spatial learning and memory: Radial arm maze, Barnes circular platform maze

References:
  1. Terry AV Jr. Spatial Navigation (Water Maze) Tasks. In: Buccafusco JJ, editor. Methods of Behavior Analysis in Neuroscience. 2nd edition. Boca Raton (FL): CRC Press; 2009. Chapter 13. Available from: http://www.ncbi.nlm.nih.gov/books/NBK5217/
  2. Crawley JN. What’s Wrong With My Mouse? Behavioral Phenotyping of Transgenic and Knockout Mice, 2nd ed. Hoboken (NJ): Wiley; 2007.
  3. Wahlsten D. Mouse Behavioral Testing: How to use Mice in Behavioral Neuroscience. Amsterdam: Elsevier; 2011.
  4. Guidelines for the Care and Use of Mammals in Neuroscience and Behavioral Research. Washington, DC: The National Academies Press, 2003.
  5. Iivonen H, Nurminen L, Harri M, Tanila H, Puolivali J (2003). Hypothermia in mice tested in Morris Water Maze. Behav Brain Res 141: 207-213.