Cognitive Tests in Rodent Models of Stroke
At a glance
Introduction of Cognitive Tests in Rodent Models of Stroke
Cognition is involved in a variety of important neural functions, including memory and emotion. Cognitive impairment is very common after stroke, making it an important area of research in animal models. Numerous behavioral tests have been created to evaluate memory in animals. In primates like humans and monkeys, visual recognition tasks are often used, requiring subjects to identify familiar versus unfamiliar visual stimuli. However, this approach is too complex for rodents due to species differences. Therefore, tests that align with natural rodent behaviors are employed. A range of behavioral tests have been developed to assess memory and cognition in rodents.
Ace Therapeutics offers a wide range of behavioral tests to assess cognition function in animal models of stroke. We can successfully detect changes in cognition, learning, and memory in rodent models of stroke, allowing cognitive testing to measure and quantify the efficacy of novel compounds and pharmacological interventions on cognition.
Related Services
Water Maze Task
Water mazes using a swimming pool are most popular for measuring procedural and working memory in laboratory rodents. It is widely used to evaluate long-term cognitive function after stroke in rodents. In Morris water maze test, animals are placed in a round pool filled with opaque water and and forced to swim. The pool is divided into four quadrants, and a platform is hidden just below the water in one quadrant. The water is colored with paint to prevent visualization of the hidden platform. Animals can escape once they find the hidden platform.
The animal's performance is calculated as the amount of time it takes to reach the platform (evasion latency), the distance it swam (swim distance), and how well it managed to reach the platform on subsequent trials (time spent in each quadrant of the water tank). Increased latency indicates memory deficits and cognitive decline. For more convenient data analysis, a number of commercial automated systems have been developed to visualize and analyze the route of animals, total swimming distance, and average swimming speed to determine memory impairments.
A key advantage of the water maze, compared to other behavioral mazes used for memory testing, is that it lacks olfactory trails, which prevents animals from relying on scent to locate the target. Furthermore, the water maze does not require food deprivation to motivate the animals during the testing process.
Fig.1. Illustration of the water maze task with the hidden platform. (Metz, 2016)
Novel Object Recognition Tests
In rodents, the novel object recognition task is a gold standard for work-memory, attention, anxiety and novelty preference. The normal novel object recognition test has three periods: a habituation, familiarisation and testing stage.
- Habituation period: The animal explores an empty open-field arena to acclimate to the environment.
- Familiarization period: The animal explores the same arena with two identical objects placed equidistant from each other.
- Test period: The arena now contains one familiar object and one novel object to assess recognition memory.
The time spent exploring each object is recorded, with a preference for the novel object indicating effective learning and recognition memory. The novel object recognition/location tests are relatively simple and objective. These tests are also very sensitive and able to assess long-term cognitive function after stroke.
Fig.2. Illustration of the novel object recognition task. (Metz, 2016)
Elevated-plus Maze Test
The elevated-plus maze is able to evaluate anxiety after stroke. the test takes advantage of the natural behavior of rodents, which tend to seek safety in corners or enclosed spaces when they are afraid or stressed. the maze is made up of four mazes arranged in a "cross" shape.
The maze consists of four arms arranged in a "cross" shape, 50 centimeters above the floor. Two of the four arms are open without walls (or with 0.5cm walls to prevent mice from falling), and the other two arms are enclosed with 16cm walls. During the test, the animals were placed in a central area facing one of the closed arms and allowed to explore for 10 minutes. The researchers recorded the number of entries into each arm and the length of stay. Animals with lower levels of anxiety were expected to enter the open arm more frequently and stay there longer.
Y-maze Task
The Y-maze, which utilizes the natural exploratory behavior of rodents to assess cognitive function, has been used to assess short- and long-term cognitive function after ischemic stroke. Rodents generally prefer to explore new environments rather than familiar ones, so animals will explore new branches of the maze before returning to previously visited branches. The Y-maze is a simple test and requires no training. The parameter (spontaneous alternation) is easy to record, and thus this test is less demanding on the observers.
Spontaneous alternation test
In this test, the animal is placed in a Y-shaped maze (which contains three arms at an angle of 120° to each other) and allowed to explore the three arms freely. Exploration time varies from 3 to 15 minutes, depending on the type of study. The order of each entry and the total number of entries are recorded. Spontaneous alternation was indicated by a trend in arm accesses that differed from the previous two visits. This test was used to quantify cognitive deficits in a rodent model of stroke and to assess the cognitive effects of the new compound.
Two-trial memory task in the Y-maze
Because rodents are environmentally adaptive, prolonged exposure to the maze environment may reduce their exploratory activity and affect their tendency to alternate. To minimize these factors, one arm of the Y-maze is blocked and the animal can explore the other two arms. The blocked arm is then opened and treated as a new arm. Animals are allowed to explore all three arms and access to each arm is recorded.
Radial-Arm Test
The radial-arm maze is designed to study working memory in rats, using rewards to motivate decision-making rather than relying on spontaneous alternation like the Y-maze. The maze features eight arms extending from a central platform, with a reward (typically food or water) placed at the end of each arm. A food-deprived rat is placed in the center and allowed to explore until all rewards are collected. Researchers record the total number of arm entrances before all rewards are obtained; fewer entrances suggest stronger working memory as the animal is more likely to visit unfamiliar arms.
The radial-arm maze is a relatively simple and sensitive test. It is able to assess short-term and long-term cognitive function in stroke.
- Metz, G. A. (2016). Behavioral Testing in Rodent Models of Stroke, Part II. Rodent Models of Stroke, 225-241.
