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1.Principle and meaning
In 1981, British psychologist Morris first designed and applied this water maze to study the learning and memory mechanism of rat brain. In 1984, Morris enriched and improved the original experimental program, 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 program for non-spatial definition learning. Although the initial experimental object was a rat, the maze system has since become a classic program for evaluating rodents' spatial learning and memory capabilities, and is widely used in basic and applied research in neurobiology, pharmacy, and other fields.
① Because of its reliable sensitivity to age-related spatial memory impairment, the Morris water maze is a particularly useful tool for judging the spatial learning and memory abilities of elderly mice.
② What drives animals to escape is water stimulation without the need for food and water deprivation. Therefore, the metabolic problems brought to laboratory animals after food and water deprivation are avoided, and this problem may be dangerous for some strains of animals.
③ Animals do not need to receive an electric shock, which is a common requirement in those appetitive tasks such as radial mazes and T mazes.
④ Can eliminate odor clues.
⑤ It can provide more experimental parameters, systematically and comprehensively investigate the process of spatial cognitive processing of experimental animals, and objectively reflect their cognitive level.
⑥ Separate the learning and memory disorders and sensory and motor deficits of experimental animals to reduce their interference with the detection of learning and memory processes.
检测 Can detect both spatial reference memory and spatial working memory. After testing the spatial reference memory of mice with a fixed platform, and then changing the position of the platform to unfixed, their working memory capabilities can be tested. Obviously, the cognitive process of finding an unfixed platform is more complicated, and animals need to integrate and judge the separated information in time and space.
简便 Easy operation and small data error.
① Due to the need for monitoring systems and analysis software, only a few well-equipped laboratories can carry out their work.
② There are many factors to be considered in the design of the experimental program. At the same time, the experimenter needs to have some knowledge in neurophysiology, cognitive physiology and mathematical statistics, which makes it difficult to carry out experiments and interpret the results, and also limits the maze. In-depth and wide application.
③ Due to excessive physical exertion and excessive body temperature loss, it is more difficult for old and 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 grade does not improve with the increase of the number of days), and the academic performance of 129 / SvJ is also biased.
⑤ The results vary greatly among individuals.
⑥ Due to age-related visual pathology in some strains, such as the 129 / SvJ strain, it becomes difficult to complete vision-based learning and memory tasks during aging. In the C57BL / 6 strain, the presence of severe alopecia may cause depression in some mice, and ulcerative dermatitis may eventually affect the swimming ability of the mice and affect the experimental results.
迷宫 The labyrinth procedure may be insensitive to slight impairment of learning and memory abilities.
浸 Immersion of animals in water may cause endocrine or other stress effects. The interaction between the latter and brain damage or pharmacological procedures is uncertain.
⑨ The operation of the automatic monitoring system still needs to be done manually, which may make the experiment tedious.
The experimental area occupied by ⑩ is too large.
4, matters needing attention
① The way that mice accomplish this task is not exactly the same as that of rats. 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 or time spent swimming in the original target quadrant (a typical indicator used to judge short-term memory in rats) is usually inappropriate for mice. The replaced parameter, the number of times to cross the original platform position, may be a more sensitive indicator.
② In comparison, in the Morris water maze, the performance of the mouse (C57BL / 6 strain) is not as good as that of the rat (Long-Evans strain). This is not because the mice have poor spatial learning and memory abilities, but the spatial learning abilities of mice in the swimming pool may be hindered by some non-spatial factors, such as the swimming path is not straight, and the head is more dramatic when swimming. For this reason, some people think: a. In water-based tasks, do not match the results of mice with the results of rats, 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 dry-land tasks, especially in animals where locomotion is restricted by the arm, small Rat performance should match that of rats; c. Behaviors that mice can compare with rats deserve further study because this difference helps to understand the differences in species-specific strategies used in spatial behavior .
③ As far as mice are concerned, the learning and memory scores of different strains of mice in the Morris water maze vary greatly. For example, C57BL / 6J, CD-1, and DBA / 2 mice are excellent learners, while BALB / c mice cannot learn the task, as shown in Figure 2. Therefore, it is necessary to evaluate in advance whether the mouse used 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 program used. For example, between C57BL / 6J and 129T2 / Sv mice, in a standard spatial reference memory program (the position of the platform during the experimental period is constant), the two strains have the same good results, but in the stepwise learning program The C57BL / 6J strains performed worse than the 129T2 / Sv strains in all learning stages, and in the massed spatial learning program (the position of the platform changes daily), the C57BL / 6J strains performed better than 129T2 / Sv strain.
④ Regarding the size of the pool, the pool that Morris originally used for rats was 1.32 meters in diameter and 0.6 meters in height, but later (1984) it was changed to 2.14 meters in diameter and 0.4 meters in height [7a]. For experimental pools of mice, the maze diameters described in the literature vary widely, ranging from as small as 0.6 meters to as large as 2.0 meters . In general, too small pools increase the chance of mice climbing onto the platform, making the task less difficult.
⑤ The water temperature for Morris for rats is 26 ± 1 ° C [7a], but the water temperature for mice is generally lower (18-22 ° C). In recent years, the water temperature mentioned in the literature has a tendency to gradually increase, and some have reached 25 ° C or 26 ° C or even 28 ° C. But too high water temperatures can easily cause mice to float without rushing to swim to find a platform, at least for some strains, such as Kunming mice and SAM mice. However, too low water temperature can cause mice to lose their body temperature too quickly and is harmful to health. We observed the effect of water temperature on the performance of the maze in young Kunming mice, and found that the mice in the 27-28 ° C group had the worst performance, while there was no difference in the learning performance of the mice in the 17-18 ° C group and the 21-22 ° C group. Therefore, we recommend 21 ~ 22 ℃ water for the water maze experiment.
⑥ Early literature almost uniformly mentioned that adding milk etc. to the water has made the water turbid to cover the platform, but the recent literature rarely mentions this unless it is needed for image surveillance purposes. This is because when the rat is swimming, its head is up, its field of view is up, and it cannot see the underwater platform whether the water is transparent or not. Furthermore, elderly frail animals may drown during swimming, and the substance added to water may increase the resistance of mice when swimming.
⑦ So far, although various and complicated evaluation indicators have been mentioned in the literature, these indicators have not been well characterized. For example, swimming speed is obviously an indicator of athletic ability, and the path length is affected by both the swimming speed and the swimming time (latency period). In theory, it should not be a good indicator of cognitive ability. Therefore, the nature of the behaviors reflected in each indicator needs to be discussed, and these indicators must be interpreted with caution. Using latency alone as an indicator may not provide enough information about spatial learning. Because swimming fast doesn't mean high learning efficiency. Therefore, when judging the difference in spatial learning ability between plants, using only the latency as an indicator may be misleading. In addition, 4 mice were used to compare the differences in swimming distance, incubation period, and swimming speed. It was found that C57BL mice had the shortest swimming distance, and the swimming speed and incubation period of BALB / c mice did not increase with the number of training sessions. It increased, but its swimming distance decreased progressively, and there was no significant difference with other groups. However, a recent study showed that compared to C57BL / 6N mice, BALB / c mice were not able to learn the task even with swimming distance as an indicator. In any case, swimming distance is still considered a parameter that may be more reliable than latency.
⑧ Regardless of the presence or absence of spatial clues, it can be found in the previous training sessions that the latency to find an underwater platform decreases with the number of experiments. The decline in the no-space clue group may be due to animals learning to swim away from the pool (overcoming tactile), increasing their chance of randomly touching the platform. If the animal is unable to overcome the tactile traits immediately, it may indicate that it may be too anxious or does have learning and memory disorders.
动物 Animal learning is very fast in reverse space missions. According to Morris, moving the platform to the contralateral quadrant without changing the position of the spatial cues is not exactly a reverse procedure (as mentioned above). Because when the platform moves, the allocentric spatial relationship of the clues in the distant room has not changed. Animals only need to learn new platform positions without completely rearranging clue relationships.
⑩The identification platform task was designed by Morris to determine whether brain damage or drug-induced navigation damage in rats was not caused by motivation and sensory motor involvement. After being applied to mice, it is mostly used to determine the ability of the mouse to determine the visible platform of a change in position (a non-spatial learning and memory ability). In fact, it can also detect the visual acuity and swimming ability of the mouse at the same time. In most cases, it was arranged the day after the end of the positioning test. We believe that the arrangement before the positioning and navigation test can provide information about the escape platform in the animal water, thereby speeding up the progress of the mouse to learn the positioning and navigation task, and in some cases requiring animal behavior to be as consistent as possible, screening animals can be achieved. the goal of.
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