Analysis of Learning and Memory Ability in an Alzheimer's Disease Mouse Model using the Morris Water Maze

The Morris Water Maze, or MWM experiment, has become the most widely used and classic behavioral experiment to evaluate the spatial learning and memory ability of animals. Although there are many articles about MWM, in practice, researchers still feel confused. Therefore, this intuitive and rigorous operation process video is particularly important.

We previously performed MWM-based study, suggested that acupuncture can relieve symptoms of AD model mice. Herein, we introduce the operation protocol of MWM used in our recent studies to provide a simple and visible method for researchers to assess the spatial learning and memory of AD model animals. MWM is a powerful technique to assess cognitive function and is widely used in studies.

However, there are no defined or standard parameters to perform the task, such as the size of the pool and platform. So, real demonstration of the method is critical. Begin by setting up for the Morris Water Maze or MWM test according to manuscript directions.

The MWM device and the signal acquisition and processing system should be located in an experiment room designed to maintain sound insulation. A circular white tank surrounded by an opaque cloth should be positioned in the middle of the MWM device. A video camera should be fixed to the ceiling of the device, and connected to a video recorder with an automated tracking system.

Divide the water maze tank into four equal regions using lines labeled north, south, east and west, which will conceptually divide the pool area into four quadrants. Then, place a unique visual cue on the wall of each quadrant within the sight of the mouse. Fill the circular tank with water for a depth of 30 centimeters, And add 150 grams of milk powder to the water to make it opaque.

To perform the Visible Platform trial, place a plastic circular platform one centimeter above the water's surface in any quadrant at random, and put a black flag on it. Release each mouse gently into the water from one of the four start locations facing the tank wall. Activate the computer tracking program as soon as the mouse is released into the water, and give each mouse 60 seconds to reach the platform.

At the end of each trial, place the mouse on the platform, and allow it to stay there for 10 to 30 seconds. Observe the swimming trajectories of the mice on the computer. Record the time the mouse took to find the platform as escape latency, and analyze the mouse's swimming speed.

Then, dry the mouse with towels and warm it with an electric heater. Move the platform and perform four trials per mouse, starting a mouse in different quadrant. Allow the mouse to recover for 15 to 20 minutes between each trial.

To perform the Hidden Platform trial, place the same platform without a flag in the southeast quadrant. Then, place the mouse randomly in one of the four quadrants, and give it 60 seconds to find the hidden platform. If the mouse cannot find the platform in 60 seconds, guide it to the platform and allow it to stay there for 10 to 30 seconds.

Record the escape latency of each trial. Dry the mouse with towels, and keep it warm with an electric heater. Perform four trials per mouse with 15 to 20 minutes between each trial, starting the mouse in a different quadrant each time.

Repeat the trials for five consecutive days with the platform and visual cues at constant positions. To perform the Probe trial, remove the platform and place the mouse in the water facing the tank wall in the northwest quadrant. Record its swimming distance, speed, and platform crossover number.

When finished, dry the mouse and keep it warm. To perform the Reverse trial, position the platform in the northwest quadrant and repeat the Hidden Platform trial. This protocol was used to investigate the effects of Manual Acupuncture or MA on the learning and memory of mice with Alzheimer's disease.

For the MA group, treatment began 15 days prior to MWM testing and continued throughout the 11 days of testing. During the Visible Platform test on the first day of MWM, no statistical differences were observed in the escape latency or swimming speed among the groups. During the Hidden Platform and the Reversal trial, the escape latency of the Alzheimer's disease or AD group remained high, while the latency of the other three groups gradually decreased.

Importantly, the escape latency of the MA group was shorter than that of the AD group. During the Probe trial, the platform crossover number of mice in the MA group was lower than that of the control group, but significantly higher than that of the AD group. Furthermore, the percentage of time that the MA mice spent in the quadrant where the platform was previously located was similar to the drug group, which was less than control, but greater than AD.It is important to remember that if the mouse cannot find the platform in 60 seconds, the researcher should guide it to the platform and allow it to stay there for 10 to 30 seconds.

There are no specific standards for dimensions of the pool and platform size. These parameters must be optimized in preliminary experiments according to the experimental requirements and the condition of the experimental animals. Most studies need to be conducted on basic experiments like MWM.

Presently, the flexibility of MWM as an experimental tool only lies in the ability to choose the basic protocols according to the study proposed is, and therefore this test can be applied to assess cognitive function in greater depth.