Eight Arm Labyrinth
The radial arm maze experiment is also one of the most commonly used models for evaluating animal learning and memory abilities. It was established by Olton et al. In the mid-1970s. The basic basis is that the animals that control eating are driven by food to explore the arms of the maze; after a certain period of training, the animals can remember the spatial position of the food in the maze. This method can simultaneously determine the working memory and reference memory of the animal. Animals used include rats, mice and pigeons. This model is sensitive to brain damage and multiple drugs. The latter includes ethanol, Dong ### (anticholinergic drugs) and MK-801 (NMDA receptor antagonist).
Most experiments used eight-arm maze, and some used twelve-arm or twenty-four-arm maze. Here is an introduction to the eight-arm maze produced by Shanghai Xinsoft Information Technology Co., Ltd. Each arm is 41.9cm long, 11.4cm wide, and 10.1cm high; it has a transparent cover on it, and two opposite photocells on each side. The diameter of the central octagonal area of ​​the labyrinth is 27.4 cm; there is a transparent top cover. There is a movable door at the entrance of the central zone to each arm, which is used to control the animal's access arm. The maze is connected to the computer. A video tracking system (video tracking system) can also be used to replace the photocell to record the animal's activity in the maze. There are some external cues in the room where the maze is placed. Animals can see these cues in the maze, and use this to locate the space. Experiments were conducted with rats or mice.
(2) Experimental method1. After one week of adaptation to the experimental environment, the animals were weighed and fasted for 24 hours. After the training every day thereafter, the normal foods are restricted (16-20g in rats and 2-3g in mice) to keep the body weight at 80% to 85% of normal rats.
2. The next day, the arms and center of the labyrinth were scattered with food particles (4 to 5 each, about 3 to 4 mm in diameter). Then, place 4 animals in the center of the maze at the same time (the door to each arm opens). Let it eat freely and explore for 10 minutes.
3. On the third day, repeat the training on the second day. This process allows animals to become familiar with the labyrinth environment without strong stress.
4. From the fourth day, the animals are trained individually: put a pellet in each arm near the outer food box to allow the animals to eat freely. Remove the animal after eating or 10 minutes.
5. On the fifth day, put the food in the food box and repeat the training of the previous day, twice a day.
6. After the sixth day, randomly select 4 arms, each arm put a food grain; each arm door is closed, place the animal in the center of the maze; 30s later, the arm door opens, allowing the animal to move freely in the maze and ingest the food grain Until the animal has eaten all four arms. If the pellets are not finished after 10 minutes, the experiment is terminated. Training twice a day, with an interval of more than 1h.
Record the following 4 indicators: 1 working memory errors (working memory errors), that is, the animal enters the arm that has already eaten the food grains in the same training; 2 reference memory errors (reference memory errors), that is, the animal has not missed the food. The arm of the pellet; 3 The total number of arm-entry times; 4 The test time, which is the time it takes the animal to eat all the pellets. In addition, the computer can also record the animal's activity in the radiation arm and the central area, including the movement distance and movement time. If the working memory error is zero for five consecutive training sessions and the reference memory error does not exceed one, you can start a drug test or an experiment to destroy the structure of the inner core of the brain. Generally, the solvent (such as normal saline) is given first, then the memory-impairing drugs (such as Dong ~~~~ MK-801, etc.), and then the memory-enhancing drugs are added, from low to high.
(3) Calculation and data analysisUse two indicators to evaluate animal memory, namely the frequency of working memory errors and the frequency of reference memory errors, which are equal to the working memory errors or reference memory errors and the total number of arm-in ratio. Use these two indicators to evaluate working memory and reference memory respectively. At the same time, the average exploration time (average exploration time), which is the ratio of the test time to the total number of arm-in times, is calculated as an index for evaluating general exercise activity. The frequency of working memory errors and / or reference memory errors is significantly increased depending on the structure of the damaged brain area or the drugs given to weaken memory. Memory enhancement drugs or treatments can reduce this frequency of errors.
Precautions1. The equipment and experimental procedures of the mouse radiation maze are similar to the rats, but the size of the maze should be 1/4 ~ 1/2 smaller than that of the rat maze, so as not to increase the difficulty of behavioral manipulation in mice.
2. This experiment can also be used to determine working memory only. The only difference in the method is that the food particles are placed on all the radiation arms, instead of only four arms.
3. Chronic stress can have an effect on animal maze operation, and there are gender differences. After chronic stress, the memory of male rats weakens, which is manifested by an increase in the frequency of memory errors; instead, the spatial memory of male rats increases, which appears to be a decrease in the frequency of errors.
4. Even under the restricted feeding condition, the weight of rats should be increased by 5g per week to avoid the animals suffering from malnutrition. Remove animals that are in poor physical condition.
5. Any item around the labyrinth can be used by animals as a symbol for space designation. Removal or removal of these marks may make animal manipulation difficult and reduce the accuracy of maze arm selection.
6. The number of arms in different labyrinths can vary according to the purpose of the experiment, including 8, 16, 24, 32, 40, and 48 arm mazes. The fewer the arms of the labyrinth, the smaller the arms that the animal has to remember to explore, and the simpler the animal's behavior. Increasing the number of arms on the one hand increases the requirements for animal spatial memory, on the other hand it also introduces more interference factors that need to be considered (such as the effect of past maze learning on currently measured memory). Therefore, the 8-arm radiation maze is usually used, which can not only reduce unnecessary and excessive arm interference, but also shorten the time spent on training and testing.
7. The food used is usually small pieces with chocolate flavor (one of the animal's favorite flavors) or sweet breakfast rings (10mg each); liquid foods (such as chocolate milk or water) can also be used. The latter is particularly useful for testing certain drugs that affect animals' swallowing of solid foods (such as Dong ###).
8. There are two main factors that affect the operation of animal maze: the fear of the maze or the observer and the habits of animal exploration and the drive of food known to be placed in the arm of the maze. Too strong a fear factor will prevent the operation of the animal's maze, so that the animal stays somewhere in the maze without exploring. Lack of food craving will also produce similar results, increasing the caressing of the animal, and raising the side wall of the labyrinth arm if necessary, will help reduce the animal's fear. If the driving effect of food is insufficient, the amount of food can be reduced, but body weight and general physical condition must be monitored at the same time. Normally, the weight of rats should not be lower than 80% before fasting; for most rats, the body weight can be reduced by 15%.
9. Unlike the water maze, the radial arm maze is suitable for repeated testing or long-term memory testing. It is generally believed that working memory represents short-term memory and reference memory represents long-term memory.
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