First, the experimental principle
Nearly half a century ago, Kivy and Dember et al demonstrated in rats can discriminate the color change T- shaped arms maze (T-maze). They found that male rats were placed in the main arm of the T-shaped labyrinth for 15-30 minutes, allowing them to see but not into the black and white arms. Then, change the color of one of the arms so that both arms are black or white. The rats were allowed to freely select the T-arm. The results show that the rat always chooses the arm that changed the color (new arm). This process relies on the memory of the animal to complete. The resulting T-shaped maze experiment has become one of the most commonly used animal models for evaluating spatial memory. Of course, the current T-shaped maze uses the color of food rather than the arm as the driving force for animal exploration. This model is often used to study the spatial working memory of an animal, i.e., to determine information that is useful only to the animal during current operations. The improved T-shaped maze can also be used to evaluate reference memory, which is information that is useful for any day or any test in this experiment.
The T-maze is a classic behavioral method for detecting spatial working memory in rodents and is associated with prefrontal cortical function. The mice were dieted to 85% of their original body weight.
Second, the experimental equipment
Experimental equipment: The labyrinth consists of two target arms (goal arms) of 46 cm in length, 10 cm in width and 10 cm in height and a 71 cm long, common width and height of the main stem or approach arm (approach alley). . The main arm has a 16 cm x 16 cm starting box built in, and a gate is associated with the other part of the main arm. Drinking water is not limited, but the feeding is controlled at 16-20g per day to keep the body weight at 85% of the weight of non-fed rats. Rats gained no more than 5 g per week throughout the training and testing period. The size of the T labyrinth can be modified according to the reference experimental literature, as shown in Figure 1.1.
Figure 1.1 Shanghai Xinsoft Production
Third, the experimental method
1 2 days before the training, stroke the mouse and put it into the T-maze for 10 min. Put the food in the labyrinth bowl and take it out after the mice have finished feeding.
2 training experiments: each trial consists of two parts, namely forced run and test run. Forced run: Select one arm of the T-maze and close it with a wooden gate. The mouse can only enter one arm to get food. After the feeding is completed, remove it immediately and wash it with alcohol to remove the odor. After 15 s, remove all gates. Test run: Both arms are open, the mouse is placed in the starting arm. If the mouse selects the arm that has not entered, the food is rewarded for correct selection; if it is repeated into the same arm, it is wrong choice, no food is given. Each animal was subjected to 4 trials per day, 15 minutes apart for 4 consecutive days, and the correct rate of each group of mice per day was calculated. When the average correct rate is above 85%, the training phase ends.
3 Test experiment: extend the time interval between forced run and test run to 1 min and 3 min, and calculate the correct rate of each group of mice.
Fourth, matters needing attention
1 Rats and mice have a good spatial discrimination function, which can quickly learn and accurately operate the maze. Therefore, the T-shaped maze and the radial arm maze are widely used to test the spatial memory ability of animals. The T-shaped maze is used to study the effects of different brain regions on spatial memory. It is sensitive to the damage of certain brain structures, especially the hippocampus. In addition, many drugs or toxins can enhance or impair the spatial memory of animals in the T-shaped maze. In addition to rats and mice, the animals used in the experiment include pigs, sheep, turtles and pigeons.
2 The accuracy of animal selection is related to the interval between two choices and the number of selected trainings during each training interval. Normal animals have a very high selection accuracy over short intervals (eg 5 s). And after a very long interval (for example, more than 1 h), its selection is close to random operation. Forced to choose training. If you only select one target arm, the accuracy is usually very high. However, if multiple selections are given, the more the number of selections, the worse the accuracy.
3 rodents have a one-way preference. This one-way preference is related to animal species and strains. For example, C57BL/6J mice, ICR mice, and Purdue-Wistar rats prefer the left side, while Spague-Dawley rats and Wistar rats prefer the right side. Studies have shown that more than two-thirds of male Spague-Dawley rats prefer the right side, preferring less than one-fifth of the left side. This one-way preference can influence the evaluation of animal learning and memory.
4 The gate of the trunk arm is an important feature of the T-shaped maze. It can be used to limit animals to the starting box for a certain period of time between selections, and to prevent animals from exploring the maze between training sessions. Therefore, the animal should be quickly placed back into the starting box in the main arm between the two selection exercises. This is important to ensure that the animal does not explore the contralateral target arm.
5 When the animal's fear of the maze or the experimenter's stress exceeds its desire for inquiry and foraging, the animal's exploration of the maze is reduced, and even staying in the labyrinth does not move to explore the maze. This fear is manifested in the fact that the animal defecates and urinates in the maze; when it is caught, the animal screams. Therefore, adequate stress adaptation is necessary. Otherwise, if the animal does not select the arm within the maze, it is impossible to know whether its memory is normal or weak.
Fifth, the experimental test
(1) The appearance of the T labyrinth is "T" shape, consisting of one trunk and two selection arms, the trunk length is 60 cm, and each arm is 30 cm long, 10 cm wide, and 20 cm high. There is one food cup at the end of the two selection arms for food (the reward food used in this experiment is sunflower seed), and there is a pullable baffle at the proximal end of the selection arm. The labyrinth is completely black, so that the mice have no reference when they get the food reward, and only one end of the correct food placement can be selected according to self-judgment. In order to increase the motivation of mice to find food, the mice's food intake was limited 3 days before the test (fasting for 6 h), and the body weight was reduced to 80%-90% when the food was normally obtained. The training was performed once every 2 days before the test, and the mice were familiar with the environment for a few minutes in the maze so that they could find food.
(2) The experiment was carried out in a quiet room and the environmental conditions remained stable. In the test, the first step is to block one arm of the maze, and only allow the animal to reach the other arm of the T-maze, where the animal gets food; in the second step, both arms of the T-maze are open, but only the original There is food in the blocked arm. The mouse only chooses to enter the arm opposite to the first step to get the food. It is recorded as correct once. For example, the arm that the mouse has gone to the first experiment is recorded as one error. So two steps are a group, and the two-step experiment is separated by 15 s. Each mouse was subjected to 10 or 15 groups of experiments per day, and the correct number of selections was recorded for a total of 3 days.
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