Effects of eight-arm maze and dark-avoidance experiments on learning and memory in young rats

Abstract investigate the eight-arm maze, passive avoidance test the impact mechanism of learning and memory in young rats.

【 Methods 】 The SD female model of pregnant SD rats was included in the study (n = 40), all males. Twenty patients were randomly selected from the day of birth to intraperitoneal injection of T42μgP100g to weaning, which was T4 replacement treatment group, and the remaining 20 were The low pups were not treated specially, and another 20 male rats in the normal control group were set up. The 50-day-old A lower group of mice were treated with dark and eight-armed experiments and compared with the normal control and treatment groups at the same age. RESULTS: The 50-day-old group of the hypothyroid mice had the highest number of errors in achieving the learning degree, and the memory latency was shortened after 24 hours. The difference was significant. The reference memory error in the eight-armed experiment of the 50-day-old A. Significant differences, increased working memory errors, significant differences, no significant differences in running time.

【 Conclusion 】 The hypothyroidism caused the decline of learning and memory ability of the pups.

Thyroid hormone plays an important role in mammalian brain development. Perinatal thyroid hormone deficiency will cause irreversible brain damage, causing severe sensation, movement disorder and mental retardation, and the onset time, severity and time to start thyroid hormone therapy. Factors are closely related to the occurrence and recovery of brain damage. On the basis of previous studies on the apoptosis of hippocampal neurons in perinatal hypothyroidism (hypothyroidism), we further used the dark-avoidance and eight-arm maze to detect learning and memory changes in the developmental hypothyroid.

[ Materials and methods ]

Animal model preparation and group replication of hypothyroid model, SD male pups were included in the study, numbering, randomly selected from the day of birth, the thyroxine (T4) was injected intraperitoneally with 2μg P100 g body weight to 21 days of weaning. T4 replacement treatment group (20 rats); Yujia low group rats were not specially treated (20 rats); another normal control group rats (20 rats). 21-day-old pups were weaned, and males were 3-4 per cage until the experiment. Free water, 12 hours of light per day (lighting time: 8: 00 ~ 20: 00). Room temperature 21 ± 2 ° C, relative humidity 40% ~ 60%.

[ Learning Memory Research ]

1. Avoid dark experiment

Test the 50-day-old experimental mice. The SFK2 I type is divided into two types: clear and dark, with small doors communicating with each other; the dark habit avoids the instinct of the pups to enter the darkroom, and the pups entering the dark room are immediately subjected to electric shock (35 mV) and passively escape. Safe room. If you do not enter the darkroom for 5 minutes, you are considered to have completed the study. Record the number of times the pigs mistakenly enter the darkroom before completing the study, which mainly reflects the ability of the young rats to learn recently. After 24 hours, they are returned to the bright room again, and the rats are recorded by the bright room. The time of the dark room, which is the memory latency, mainly reflects the ability of the young mouse to remember in the near future. The dark-avoidance experiment and the eight-arm maze experimental system model are XR-XB102, which is provided by Shanghai Xinsoft Information Technology Co., Ltd.

2, eight arm maze experiment

Test 50 (60) days old experimental mice. The diet of the pups was restricted before the eight-arm maze experiment, and the body weight was maintained at 80% to 85% of the free-fed body weight. Observations were made at 10: 00 to 17: 00. Use a radial eight-arm (four-arm food) maze. The central area of ​​the labyrinth is 30 cm in diameter and extends eight arms (50 cm × 12 cm, surrounded by a wall of 415 cm) at equal angles and equal lengths. The entire labyrinth is 40 cm above the ground. The rats were first adapted to the maze for 2 days before training, once a day. Three to four pups were placed in the maze at the same time, free to move and ingest food for 10 min. After the adaptation, the training was performed once a day for 10 days. In each training, only four of the eight arms were placed with food (Bio2Serv, Frenchtown, NJ, USA), arms 1, 3, 5, and 6, respectively; this sequence was maintained throughout the experiment. The pups are placed in the central area of ​​the maze. At this time, the central area is closed with a door. After 15 s, the door is opened. The pups can choose to enter any arm to ingest food. The pups enter the arm with food and take the food for 1 correct selection, otherwise it is the wrong choice. Record the number of times the parameter was selected incorrectly. Re-entering the food arm is called working memory error (WME), and entering the food arm is called reference memory error (RME).

[ Results ]

1. Compared with the normal control group and the treatment group, the 50-day-old A-low group had more errors in achieving the learning level, and the difference was very significant (P < 01001). There was an increase in the normal control group, but there was no statistical difference (P > 0105). After 24 h, the memory latency of the hypothyroid mice was the shortest, which was significantly different from the normal control and treatment groups (P <01001). The incubation period of the treatment group was shorter than that of the normal control group, but there was no statistical difference (P > 0105). ) , .

2, eight arm maze experiment

According to the website , compared with the normal control and treatment groups, there was no significant change in RME in the hypothyroid group (P < 0105); WME increased significantly (P > 0105); the total number of errors increased significantly (P < 0105) ; There was no significant difference in total running labyrinth time (P > 0105)

[ Discussion ]

Learning and memory are one of the advanced functions of the brain. Learning refers to the acquisition or development of experience (behavioral habits, perceptions, thinking, etc.); memory is the preservation and reproduction of experience. They are two different and closely related neuro-biological processes, on the one hand, the basis of thinking and cognition, and on the other hand, closely related to the sensory and motor functions of the brain; this complex process involves at least acquisition, consolidation and reproduction. Three main stages. Because of the comparability of learning and memory learning in humans, it is often used to study human learning and memory.

At present, there are many experimental models for studying animal learning and memory ability from the overall level. Shuttle box experiment is one of them. Because of its simple and fast operation, it has been widely used in learning and memory experiments. In order to eliminate the influence of the rhythmic law of corticosteroid secretion on learning and memory, the daily experiments were carried out at the same time. This experimental study found that the 50-day-old A. pupae had an increased number of errors in entering the dark room and a shortened memory latency after 24 hours, indicating that perinatal hypothyroidism affects the ability of the mice to learn and remember recently. However, the electrical stimulation used in the experiment may cause the animal to be excited and uneasy, and the non-learning and memory factors such as the animal's own exercise volume and sensitivity to electrical stimulation may also affect the experimental results. The animal spatial memory test is one of the most commonly used methods for studying animal learning and memory. Because the water maze test can effectively separate the spatial recognition and other abilities of animals, the previous study on the effect of A-low on the spatial memory of the offspring is mostly used. However, the main indicator of this experiment is the time it takes for the animal to find a safe platform in the water maze (on-the-shelf latency), which is closely related to the animal's motor function. Any drug that affects the animal's motor function and the state of the animal may affect the state. The results of this experiment. Thyroid hormones not only affect the nervous system, but also the development of skeletal muscles, which may affect the results of the test. In addition, the nature of animals walking around the wall also limits its application.

The eight-arm maze test is an animal that learns and remembers the relative position of itself and the bait (white snack pill placed at the end of the labyrinth arm) by observing some fixed reference objects around it. This method can effectively exclude the animal from being dysfunctional due to its own motor function. Learning and memory observations can also separate and analyze animal WME and RME. To this end, this experiment used the eight-arm maze for the first time to determine the spatial memory reproduction of perinatal A-low rats. The study found that compared with normal controls and treated rats, WME increased in 50-day-old A. pupae, but there was no significant change in RME. This separation of spatial memory can also be seen in the eight-arm maze test in which anticholinergic drugs reduce the acetylcholine content in rat hippocampal neurons. However, significant impairment of hippocampal function causes an increase in both WME and RME. Further research is needed on the spatial memory separation phenomenon and the specific mechanism in the A-low eight-arm test. Learning and memory are closely related to the synaptic structure and functional plasticity of the central nervous system. Thyroid hormone can affect the expression of various brain structural proteins and signal proteins, affect the proliferation, migration, differentiation, synapse development and myelination of nerve cells, affecting the transmission of information between neurons, leading to learning and memory. Such brain function is impaired. This study found that the learning and memory of the T4 replacement treatment in the postnatal rats was significantly improved compared with the A. pupae, but the laboratory test results did not reach the normal level of the same age pups, indicating that the low state of the fetus has caused partial and irreversible brain damage.