Introduction
Behavioral testing is of great importance in the study of psychiatric disorders, especially in rodents. By observing the behavioral changes in rodents, combined with the symptoms of mental illness in modern clinical practice, it is possible to deepen the understanding of mental illness and facilitate the development of drugs.
Different laboratories choose different behavioral testing methods according to the purpose of the study. Based on the aspect of despair, the behavioral detection methods involved in the included literature are statistically analyzed. The selection of these methods is closely related to disease models and research priorities, and provides rich data and references for the study of psychiatric diseases.
1 Forced Swimming Test (FST):
In 1977, the French scholar Porsolt first invented an experiment and applied it to the depression model of behavioral despair, known as the "forced swim test" (FST). This experiment showed that rodents gave up their struggles when they couldn't get out of the situation, which was considered a sign of "behavioral despair". This behavior is not just a response to a decrease in physical energy or movement, but also an indication of the level of mental activity of the animal. FST has become a good method to simulate the hopelessness of patients with depressive disorders, so it has been widely used in depression research.
First, animals with poor swimming ability need to be excluded before performing FST experiments. Adaptive swimming is usually 10 to 15 minutes. After acclimatization, mice or rats are placed in an experimental environment with a humidity of 45% to 65% and a temperature of 21 to 23 degrees Celsius, followed by formal experiments at intervals of 24 h. In the experiment, water-filled cylinders were selected, which were about 50 cm and 30 cm in height and 30 cm in diameter, respectively. The liquid level height should be adjusted to such a degree that the rat's tail cannot be touched. After acclimatization, the animal is placed in water and recorded, with a recording time of 5 to 10 min for mice or rats. Some teams will place animals in the water for 10 minutes and then record the time spent swimming immobile for 4 to 5 minutes. Once the recording is complete, remove the animals from the water, blow dry and restore body temperature, taking care to change the water while swapping each animal.
The main measure of FST is the behavior of the animal in the water, which includes "rest time". Resting time refers to the amount of time an animal remains afloat, with its body slightly curled up and only its nostrils exposed to maintain breathing, with its front paws stopping to shave and its hindpaws occasionally paddling. Animals that have been at rest for long periods of time are thought to exhibit hopeless behavior, a trait that clearly reflects the depressive phenotype.
When performing FST experiments, it is necessary to pay attention to factors such as the experimental environment and water temperature, as they are important factors that affect the experimental results. First, the strong light of the experiment may shorten the immobility time of rodents, which is not conducive to accurately reflecting their depressive state. Therefore, FST experiments should be performed at no more than 096 watts square meters under ambient light. Secondly, water temperature is also one of the important influencing factors of FST. Studies have shown that water temperature has a U-shaped relationship with the rest state of animals, and that too low or too high water temperature will shorten the immobility time, so it is best to keep the water temperature in the range of 20 to 25 degrees Celsius.
2 Tail Suspension Test (TST):
In 1985, Steru et al. proposed the Tail Suspension Test (TST), which was used to build a model of behavioral despair. Modern research suggests that TST can be used to broadly measure the effects of broad-spectrum antidepressants because it is inexpensive, simple, and easy to automate. In this experiment, the rodent's tail is suspended, and due to the upside-down end of the tail, the animal will struggle violently, and after a period of time, it will not be able to get out of this state, and will appear to be immobile, a state similar to the hopelessness of a depressed person.
According to the literature summary, the experimental teams usually put the mice in an experimental environment with 12 hours of diurnal and night-off lighting, with a humidity control of 45% to 65% and a temperature of 21 to 23 degrees Celsius. In the experiment, use tape to hang the tail end of the mouse from a hanging pole 20 to 25 cm from the floor. When there are many experimental animals, in order to prevent them from observing each other or influencing each other, a partition is used in the middle to ensure that the animals are suspended in the compartment** and that the width and depth are large enough that they do not come into contact with the wall.
In TST experiments, the behavior of mice while suspended is observed, especially the non-struggle state is treated as immobile time. The recording time is usually 5 to 10 minutes, and some experimental teams extend the experiment time to 10 minutes, followed by an immobile time of 4 to 5 minutes after recording. Mice that were immobile for longer periods of time were thought to exhibit hopeless behavior, which is an important indicator to assess the depressive phenotype in TST experiments.
Although the principle of TST is similar to that of FST, it has been reported in the literature that different strains of rodents have a greater impact on the experimental results. For example, rats are larger and may turn up when hanging their tails, so they are not suitable for TST. At the same time, some experimental teams pointed out that C57BL6 mice had a tendency to climb up along the tail, which had a great impact on the TST test results. In order to avoid interference of different strains with the experimental results, it is recommended to measure the percentage of the tail of the experimental animal in the overall length before the experiment to determine the degree of its climbing. For those experimental animals with obvious upward tendency, they can be excluded from data analysis to ensure the accuracy and reliability of experimental results.