Morris Water Maze: A Behavioral Approach to Learning and Memory

This experiment was established in 1981 by American scientist Richard GMMorris. Originally used to study the regulation of brain structure on learning and memory, and later gradually developed into the most commonly used model for evaluating animal learning and memory. The basis of this experiment is that rodents have a strong incentive to escape from the water in the water and escape the water environment in the quickest and most direct way. The process of learning to escape the water environment reflects the animal's ability to learn; spatial positioning according to the surrounding environment, purposefully swimming to a safe place (platform) in the water, reflecting the animal's spatial memory ability.  

• (1) Experimental equipment

The experiment was carried out with rats or mice. Rat water maze experimental equipment consists of a gray or black circular pool (200 cm in diameter, 100 cm high; halved in size), a platform (10 cm in diameter), a tracking camera, and a camera-associated computer (Fig. 25- 1). The water in the pool is 50cm deep and the water temperature is 22~24°C. The platform was placed 2 cm below the surface of the water (1 cm for mice). Add water to the water or milk to stir the water to prevent the animal from seeing the underwater platform. The camera is located 200cm above the center of the pool and records the animal's position, swimming distance and time (thus calculating the swimming speed) and swimming path. The pictures on the walls around the room with bright colors and different shapes are used as extra-mazecues.  

• (2) Experimental methods

It is divided into three processes: acquisition training, exploration and alignment training.  
1. The Acquisition phase theoretically divides the pool into four quadrants, with the platform placed in the center of one of the quadrants.  
(1) Put the head of the animal (rat or mouse) into the water in the pool, and place it in one of the four starting positions of East, West, South and North. Record the time (s) at which the animal found the underwater platform. In the previous training sessions, if this time exceeds 60s, the animal is guided to the platform. Let the animal stay on the platform for 10s.  
(2) Remove and dry the animal. Animals (especially rats) were baked under a 150 W incandescent lamp for 5 min, if necessary, and returned to the cage. Each animal was trained 4 times a day, with 15 to 20 minutes between training sessions and 5 days of continuous training.  
2. Probe trial1 On the second day after the last sexual training session, the platform was removed and the 60s exploration training began. The animals were placed in the water from the opposite side of the original platform quadrant. Record the time spent by the animal in the target quadrant (the quadrant where the platform was originally placed) and the number of times it entered the quadrant as a measure of spatial memory.  
3. The working phase is used to determine the working memory of the animal. On the second day after the exploratory training, the four-day match training was started. Place the platform in the opposite quadrant of the quadrant where the original platform is located, in the same way as acquired training. Train 4 times a day. Each time you find the platform's time and swimming distance and swimming speed.  
4. The second day of the last match training of probetrial training (probetrial2). The method is similar to the above exploration training. Record the time spent by the animal in the target quadrant (the second time the platform is located) and the number of times the animal entered the area within 60 seconds.  

• (3) Precautions

1. In contrast to food-driven models (such as the radial arm maze), the biggest advantage of the water maze experiment is that animals have greater motivation to escape the water environment. And no need to fast, especially suitable for testing of older animals. Plus it is particularly sensitive to memory loss caused by aging, so water maze is most commonly used in the study of memory in older animals.  
2. For example, in the case of mice, the diameter of the platform is also small (7.5 cm) except that the size of the swimming pool is about 50% of that of the rat. The experimental method is similar to that of the rat, but the training period is shorter. General acquired training for 16 days in 3 days (4 times on the first day, 6 times a day in the next two days; interval between the two trainings is 5~10min, the fourth day is the exploration training, and the fifth and sixth days are the alignment) Training, training six times a day, the seventh day for the second exploration training.  
3. If observed with the naked eye, the test is always sitting in the same position during all tests, about 60 cm from the nearest edge of the pool.  
4. Test at fixed time every day. The operation is gentle and avoids unnecessary stress irritation.  
5. When compared with other similar experiments, it is necessary to note the effects of various factors such as animal sex, strain, pool size and water temperature on the experimental results. In addition, when swimming speed is used as an observation index, it is necessary to consider the weight, age, and skeletal muscle development of the animal, which may affect the swimming speed.  
6. When conducting experiments with elderly animals, it should be confirmed that the swimming ability and visual acuity of the animals do not affect the behavioral operation due to the increase in age. The method is as follows: the platform is exposed to the water surface to enable the animal to see the platform. After the animals are placed in the pool, they can swim directly to the platform without any difficulty, indicating that the animal's swimming ability and vision are normal, and the experiment can be started.  
7. Swimming is a large stress stimulus for animals that can cause neuroendocrine changes. These changes may interfere with the experimental results. In older animals, cardiovascular disease can be induced in severe cases, leading to stroke or even death. Therefore, if necessary, the animal can be placed in the pool multiple times or the swimming time can be appropriately extended to increase the animal's ability to adapt to swimming.  
8. When using water or milk powder to stir the water in the pool, change the water regularly to prevent the water from spoiling;