1, principle and meaning
In 1981, the British psychologist Morris designed and applied this water maze to study the learning and memory mechanisms of rat brain. In 1984, Morris enriched and improved the original experimental procedure, realized automatic tracking and analysis of the swimming path of rats, changed the training program to detect different aspects of spatial memory, and developed a non-spatial defined learning program. Although the initial experimental subjects were rats, the maze system has since become a classic procedure for assessing spatial learning and memory in rodents, and is widely used in basic and applied research in the fields of neurobiology and pharmacy.
2, advantages
1 Due to the reliable sensitivity to age-related spatial memory impairment, the Morris water maze is a particularly useful tool for judging spatial learning and memory in older mice.
2 Drive animals to escape water stimulation without the need for food and water deprivation. Thus, the metabolic problems associated with deprivation of food and water to experimental animals are avoided, and this problem can be dangerous for certain strains of animals.
3 Animals do not have to receive an electric shock, which is a routine requirement in those appetitive tasks such as radial maze and T-maze.
4 can eliminate odor clues.
5 can provide more experimental parameters, systematically examine the process of spatial cognition processing of experimental animals, and objectively reflect their cognitive level.
6 Separate the learning and memory disorders of experimental animals from sensory and motor deficits, and reduce their interference in the detection of learning and memory processes.
7 can detect both spatial reference memory and spatial working memory. After testing the spatial reference memory of the mice with a fixed platform and then changing the position of the platform to be non-fixed, their working memory ability can be detected. Obviously, the cognitive process of finding an unfixed platform is more complicated, requiring animals to integrate and judge the separated information in time and space.
8 easy to operate, data error is small.
3, insufficient
1 Due to the need for monitoring systems and analysis software, only a few well-equipped laboratories can work.
2 The design of the experimental program needs to consider many factors, and at the same time, the experimenter needs to have certain knowledge of neurophysiology, cognitive physiology and mathematical statistics, which brings difficulties to the development of the experiment and the interpretation of the results, and also limits the maze. In-depth and extensive application.
3 Because the physical exertion is too large, the body temperature is also lost too much, and it is more difficult for the old and the weak rats to complete the task.
4 Not all mouse strains are suitable for the Morris maze test. For example, BALB/c cannot learn the task (the score does not improve with the increase of the number of days), and the academic performance of 129/SvJ is also biased.
5 The results between individuals vary greatly.
6 Some strains, such as the 129/SvJ strain, have difficulty in completing visual-based learning and memory tasks during aging due to age-related visual pathology. In the C57BL/6 strain, due to the presence of severe alopecia, it may cause depression in some mice, and ulcerative dermatitis may eventually affect the swimming ability of the mice and affect the experimental results.
7 The labyrinth procedure may be insensitive to a slight decrease in learning and memory.
8 Immersion of animals in water may cause endocrine or other stress effects. The interaction between the latter and brain damage or pharmacological manipulation is uncertain.
9 The operation of the automatic monitoring system still needs to be done by hand, which may make the experiment a little tedious.
10 of the experimental sites are too large.
4, matters needing attention
1 The way the mouse completed this task was not exactly the same as the rat. Therefore, some of the indicators used to evaluate rats in this task are not suitable for evaluating mice. For example, in a probe trial, the distance traveled in the original target quadrant or the time spent (a typical indicator for determining short-term memory in rats) is often inappropriate for use in mice. The number of parameters instead of passing through the original platform position may be a more sensitive indicator.
2 In comparison, in the Morris water maze, the score of the mouse (C57BL/6 strain) was not as good as that of the rat (Long-Evans strain). This is not because the mice have poor spatial learning and memory ability, but the spatial learning ability of the mice in the swimming pool may be hindered by some non-spatial factors, such as the swimming path is not straight, and the swimming head is more dramatic. To this end, some believe that: a. In water-based tasks, do not match the results of the mouse with the results of the rat, otherwise it will cause confusion. However, if the limitations of the task are well known, the task can still be used for the detection of mice; b. In the dry-land task, especially the task of limiting the locomotion of the animal to the arm, small The results of the rats should match the scores of the rats; c. The behavior exhibited by the mice that can be compared with the rats deserves further study because this difference helps to understand the differences in the species-specific strategies used in spatial behavior. .
3 In terms of mice, the learning and memory scores of mice of different strains in the Morris water maze were very different. For example, C57BL/6J, CD-1, and DBA/2 mice are excellent learners, while BALB/c mice cannot learn this task, as shown in Figure 2. Therefore, it is necessary to evaluate whether the mouse used by the mouse is suitable for the Morris water maze test. However, the performance of each strain in the Morris water maze may be relative, depending on the procedure used. For example, in the C57BL/6J and 129T2/Sv strains of mice, in the standard spatial reference memory program (the position of the platform during the test period is constant), the two strains have the same good results, but in the stepwise learning program. The C57BL/6J strains were worse than the 129T2/Sv strains in each learning stage, but in the massed spatial learning program (the position of the platform changed daily), the C57BL/6J strain scored better than 129T2. /Sv strain.
4 For the size of the pool, Morris originally (1981) used a rat pool of 1.32 meters in diameter and 0.6 meters in height, but later (1984) changed to a diameter of 2.14 meters and a height of 0.4 meters [7a]. For experimental pools in mice, the labyrinth diameters described in the literature vary widely, from as small as 0.6 meters to as large as 2.0 meters [34]. In general, too small a pool increases the chance of a mouse climbing onto a platform and reduces the difficulty of the task.
The water temperature of 5 Morris used in rats was 26 ± 1 °C [7a], but the water temperature used in mice was generally lower (18-22 °C). In recent years, the water temperature mentioned in the literature has gradually increased, and some have reached 25 ° C or 26 ° C or even 28 ° C. However, too high a water temperature tends to cause the mice to float without rushing to swim to find a platform, at least for certain strains, such as Kunming mice and SAM mice. However, too low a water temperature can cause the body temperature of mice to lose too fast and is harmful to health. We observed the effect of water temperature on maze performance in young Kunming mice. The results showed that the mice in the 27~28°C group had the worst performance, while the 17~18°C group and the 21-22°C group had no difference in learning scores. Therefore, our recommended water maze experiment uses 21~22°C water.
6 In the early literature, it was almost unanimously mentioned that the addition of milk to the water, etc., has made the water turbid to cover the platform, but this has rarely been mentioned in recent literature, except for image surveillance purposes. This is because the rat is looking up when swimming, and its field of view is facing up. It can't see the underwater platform whether the water is transparent or not. Furthermore, elderly frail animals may be drowning during swimming, and the addition of water may increase the resistance of the mice during swimming.
7 So far, although there are many complicated evaluation indicators mentioned in the literature, they are not well characterized. For example, swimming speed is obviously an indicator of exercise capacity, and path length is affected by both swimming speed and swimming time (latency). In theory, it should not be a good indicator for judging cognitive ability. Therefore, the nature of the behavior reflected in the indicators needs to be explored, and caution should be exercised when interpreting these indicators. The use of latency alone as an indicator may not provide sufficient information about spatial learning. Because swimming fast does not mean that learning efficiency is high. Therefore, when judging the difference in spatial learning ability between plants, it is possible to mislead only by using the incubation period as an indicator. In addition, 4 mice were used to compare their differences in swimming distance, latency and swimming speed. It was found that C57BL mice had the shortest swimming distance, and the swimming speed and latency of BALB/c mice did not increase with the number of training. Increased, but its swimming distance has a progressive decline, and there is no significant difference between the other groups. However, a recent study showed that BALB/c mice could not learn this task even with swimming distance as an indicator compared to C57BL/6N mice. But in any case, swimming distance is still considered a parameter that may be more reliable than the incubation period.
8 With or without spatial clues, the latency of finding an underwater platform decreased in the previous trainings as the number of experiments increased. The decline in the space-free clue group may be due to the fact that animals learned to swim away from the pool (overcoming the tactility), thereby increasing their chances of random contact with the platform. If the animal does not immediately overcome the tropism, it suggests that it may be too anxious or does have learning and memory impairment.
9 In reverse space missions, animal learning is very fast. According to Morris, simply moving the platform to the opposite quadrant without changing the position of the spatial cues is not exactly called a reverse procedure (as mentioned above). Because the allocentric spatial relationship of the clues in the distant room does not change when the platform moves position. Animals only need to learn the new platform position without having to completely rearrange the clues.
The 10 identification platform task was designed by Morris to determine that brain damage or drug-induced rat navigational damage was not caused by motivation and sensorimotor involvement. After being applied to mice, it is often used to determine the ability of a mouse to determine the visible platform of a change in position (a non-spatial learning memory ability), and in fact, to simultaneously detect the visual acuity and swimming ability of the mouse. In most cases it is scheduled to take place on the day following the end of the positioning navigation test. We believe that it is possible to provide information on the escape platform in the animal water before the positioning navigation test, thereby accelerating the progress of the mouse to learn to locate the navigation task, and also to screen the animals in certain cases where the animal behavior is required to be as uniform as possible. the goal of.
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