Various mazes are widely used to test the cognitive abilities of animals. In basic research in rodent models of intracerebral hemorrhage, the Morris water maze, Y-maze, and novelty object recognition test are among the most commonly used methods.
1. Morris Water Labyrinth
The Morris Water Maze (MWM) is commonly used to assess spatial Xi and memory after intracerebral hemorrhage (ICH). The required device consisted of a metal pool (120 cm in diameter and 55 cm in height), which was divided into four quadrants, one of which placed a platform (10 cm in diameter and 21 cm in height) for the escape of the animal. The water level in the pool is 2 cm above the platform. The water temperature is kept at 26 1 ° C. Noldus Ethovision tracking software was used to record the delay, frequency, and swimming speed of mice prior to discovery of the plateau. The experiment was divided into two parts: 5 days of training and 6 days of testing. Mice are trained four times at 20-30 min intervals on each training day. When training, the mouse should be gently placed on the instrument, facing the wall. On average, mice find the platform within 90 sec and stay on the platform for 15 sec. If the mouse cannot find the platform within 90 sec, gently guide the mouse to the plateau, stay for 15 sec, and record the latency as 90 sec. After each test, the mouse is towel dried and placed in a heated cage. On the sixth day, the platform was removed and the animals were tested as usual. The results include time spent in the latency and target quadrant of the platform. In training experiments, a shorter latency to the platform may be associated with better spatial Xi and memory ability. Initially, the ICH mice took significantly longer time than the control mice. The escape latency of rats in the sham group is approximately 15 sec). For sham group mice, the escape latency is approximately 45 sec and target traversal takes about 12 sec. However, this incubation period should be significantly shortened over the next few days, indicating that spatial memory has been established.
MWM is one of the most widely used methods for testing memory. In this test, olfactory cues or cues are eliminated. Experimental data can accurately assess the animal's sense of spatial position and orientation, especially in terms of spatial positioning. However, there are some drawbacks to this approach. Swimming is an acute stress stimulus for animals, so neuroendocrine effects may affect the experimental results). In addition, water temperature has a significant impact on animal activity, so it is crucial to keep the water temperature comfortable. Finally, immediately after the end of the experiment, the experimental animals should be dried to prevent illness.
2. Y-maze test
The y-maze is also frequently used to test spatial memory. The apparatus of the Y-maze consists of three arms (rat size 40 cm long, 15 cm wide and 35 cm high, mouse size 30 cm long 10 cm wide and 17 cm high), dispersed 120° from the central point. The entrance to each arm is closed with a barrier. The test was performed 30 days after surgery. When testing, open the obstacle of two random arms. One of them was chosen as the starting arm, and the rest of the arms that still had obstacles were designated as novelty arms. Place the animals into the starting arm and allow them to explore the two open arms freely for 5 min. They are then put back in the cage to rest. After 2 hours, remove all three obstacles and allow the animal to explore freely for 5 minutes. The duration of exploration in the three arms and the length of residence in each arm were recorded. The percentage of novelty arm entry is about 35%. There is another way to calculate it. First, mark the three arms of the maze as A, B, and C. Then start recording. Next, check all the arm entrances and alternate recorded numbers. Finally, the alternating ratio is calculated using the following formula:
Alternation ratio = (number of alternations [total number of arm entries – 2]) 100.
The advantage of the Y-maze test is that it is easy to perform and the device itself is simple and convenient. Sensitivity and reproducibility in the ICH model need to be characterized.
3. Novelty object recognition test
The Novelty Object Recognition Test (NORT) assesses the animal's memory ability. It requires three objects, labeled A, B, and C, and an open field (47 cm 26 cm 20 cm) that can accommodate the object and the mouse. Subject A is identical to Object B (green cube, 4 cm 4 cm 3 cm), and they look different from Object C (a white sphere 5 cm in diameter), which is a novelty. The open field for rats is larger (60 cm, 60 cm, 50 cm). The test consists of three phases: Xi inertia on day 1, training on day 2, and testing 1 hour after training. First, on day 1, mice are placed in an open field and allowed to explore for 10 min. The next day, subjects A and B are placed in an open field, and mice are placed between these two subjects, allowing them to explore freely for 5 min. Then, remove the mice and put them back in their cages to rest. At this point, the site should be cleaned with alcohol to eliminate other odors. After 1 h, replace Subject B with Subject C and return the mouse to the field for exploration for 5 min. Record the duration of exploration for Subject A and Subject C. The movement of the mice is recorded by the camera and analyzed later. Sniffing or touching with the nose and/or forepaws within 2 cm of the subject is defined as an exploratory event. Sitting on or leaning on an object is not considered exploratory behavior. The discrimination index is calculated as the time to explore object c divided by the total time spent exploring the two objects. The baseline of the discrimination index for normal mice or rats is about 70%.
NORT is easy to perform and can be completed in a short time (135). However, because analysis takes a lot of time, the exploratory behavior of animals can sometimes be difficult to classify, so experimental data acquisition is time-consuming. Choosing the right object is difficult because factors such as size, shape, material, and height may influence the animal's preferences.