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When studying mice, researchers must assess their behavior. The mice cannot complete a survey or share information verbally, so it falls on the researchers to find other ways to assess changes in their behavior. One way to do so is through the use of a rotarod.

What Is A Rotarod? 

Imagine a treadmill for mice. That’s what many scientists see a rotarod as. This device assesses motor coordination, motor function, motor deficits, balance, motor learning, and performance in mice. In addition, this device can test the gait, coordination, and muscle strength of the mice. The rotarod test is used to assess motor coordination and balance in rodents.

The scientists place the mouse on a rotating horizontal rod. The test begins with the rod operating at a designated speed. As the test progresses, the speed at which the rod rotates accelerates for a predetermined period.

Researchers monitor the mice to see how long they can stay on the rod as it speeds up. The research team looks at both the time the mice stay on the rod and the speed at which the rod accelerates. Scientists can monitor several mice simultaneously when using a rotarod. Vertical barriers separate the mice on the rotating rod.

Researchers frequently use this test when studying rodents. The device does not cause the mice any pain or distress. They know the animals will naturally try to stay on the rod to avoid a fall. However, if they fall, the mice will not be injured.

Many people compare the rotarod test to a hamster or gerbil running on the outside of their exercise wheel. The key difference between the two activities is the rotarod is mechanically driven rather than powered by the mice.

N.W. Dunham and T.S. Miya first created the rotarod technique of testing. Initial rotarods had set speeds, but models today come with contstant or increasing speed. Scientists found set speeds weren’t of benefit, as many mice would fall off the rod initially because of poor coordination. Those that stayed on the rod rotating at a set speed would have their endurance tested rather than their coordination.

The Benefits Of Using Rotarods

Scientists use the rotarod in measuring motor coordination of mice. They can then compare the data of different mouse model. For example, they can initially test mice suffering from a medical condition. They then provide these mice with medication and test them again. The scientists record any differences to determine whether the medication was of benefit.

Using the rotarod allows scientists to have a continuous variable that is discretely measurable. They use the data collected to quantify the results of procedures, conditions, and drugs. Scientists are not required to make subjective judgments regarding the animal behavior like mice. This ensures inter-rater reliability is near perfect.

However, for inter-laboratory reliability, scientists would need to ensure they replicate all parameters. This includes the cylinder size, the constant speed at which it rotates, and how much training or practice the mice receive prior to testing.

Testing Uses For Rotarods

Scientists may use rotarods in a variety of testing scenarios. For instance, researchers often look for impairment in motor tests behavior in mice when testing new prescription medications. They wish to see which medications might lead to subtle impairments in behavior.

These impairments may go undetected in humans for an extended period but are more apparent in mice. They then screen out those drugs that might lead to concerns if used in the human population. Researchers have used this testing method to learn about trauma induced by brain injury. Other studies show alcohol impairs performance in the rotarod test when looking at mice.

When scientists provide mice with different chemical agonists and antagonists, they can determine which neural components bring about the effects of these chemicals. In fact, rotarods have been of great use in learning more about human behavior.

Genetic knockout animals underwent testing on rotarods to figure out which genes control mammalian balance and coordination. Researchers looked at certain brain lesions in different animal models and tested the animals’ performance. When doing so, they could map those structures within the brain that are necessary for mammals to maintain balance.

Omnitech Rotarods

Scientists often turn to Omnitech when they wish to purchase rotarods. The following items are ideal for the testing of rodents today.

The AccuRotor Four Animal Rotarod

The AccuRotor Four Animal Rotarod tests the coordination of rodents. When used with Fusion software, this device allows the user to set up simple or complex trials, depending on the needs of the study. This unit comes equipped with a precision-controlled servo motor. The motor rotates a suspended cylinder designed to facilitate the grip of the rodent. The mouse or rat balances on the rod.

If the rodent falls off, the software immediately records how long they remained on the rod or increments between falls when the scientist is testing for multiple falls in a duration-controlled experiment. Subjects cannot escape or create a false trigger in another lane when they fall thanks to the enclosed chamber design beneath each rod. Each chamber comes with a status indicator, a start button, sensors designed to detect mouse falls, other motor tests, and a tray to collect waste from the subject.

Researchers may use the device with mice and rats, and models come in both standard and tall versions. The scientist may also wish to upgrade to a stand-alone unit that comes with a digital readout display. Users can set up the experiment using the Fusion software quickly and easily. They program the software with the desired number of trials for each subject and the animal batch sizes.

The researcher may also establish individual trial re-run capabilities as needed or create custom acceleration profiles with the help of the acceleration profile editor. This software allows for the testing of large groups and multiple trials for individual animals.

The AccuRotor EzRod

Researchers wishing to test single animals often turn to the AccuRotor EzRod. Used with the Fusion software, this device handles both simple and complex speed and acceleration trials.

As with the AccuRotor Four Animal Rotarod, this device automatically stops the experiment when the subject falls. Sixteen EzRods can connect to a computer simultaneously, as long as the computer can handle this amount. Researchers find they can test animals in rapid succession using these devices. As a result, they often turn to EzRods for high throughput experiments.

Consider rotarods for various experiments. Researchers find them to be of significant benefit when testing rodents under many conditions. However, be sure to check out all Omnitech products to find those best for the experiment being conducted.

Researchers have long been using rodents to test hypotheses related to general mammalian behaviors. In fact, just about all human clinical trials are preceded by animal models like mouse or rat trials, largely because these rodents serve as excellent anatomical, physiological, and genetic analogs. Rodents also make perfect research subjects thanks to their small size, short life cycles, and abundant genetic resources.

Rodent behavioral trials can be used to study everything from anxiety and fear conditioning to locomotor activity and behavior, but only if researchers have access to the right products and systems. While mazes, treadmills, rotarods, and other products may be necessary for some types of rodent behavioral research, anxiety and fear conditioning researchers rely heavily on open field behavior testing.

Open Field Testing?

Open field testing involves the development of simple sensorimotor tests to determine activity levels and exploration habits in rodents. While the particulars of each test vary depending on what is being studied, the general setup is always the same. It features an open arena, typically marked with a grid, with walls to prevent escape. Researchers generally mark the center of the field with a different color to make it easier to differentiate since that is where the rodents generally begin the test.

Until recently, researchers had to make all of their observations in person or with the help of an analog overhead camera. Now, though, open field testing usually involves more modern apparatus equipped with video cameras or infrared beams and associated software programs that can automate assessments.

Rodent Behavioral Patterns Measured In Open Field Tests

Every experimental design is slightly different. However, there are some widely accepted behavioral patterns that can be observed and used to support or disprove hypotheses based on previous research. The most common of them include:

Line Crossings

Line crossings measure the frequency with which a rodent subject crosses the open field’s grid lines with all four paws. This measure of locomotor activity can also be divided into line crossings near the wall vs. in the center of the arena.

Center Square Behaviors

Center square entries refer to the frequency with which subjects enter the colored center square with all four of their paws. Researchers also use the duration of time spent in the center square as a parameter for some behavioral tests.

Rearing Frequency

Rearing behavior, in which a rodent stands on its hind legs and lifts its forepaws without support, is generally accepted by behavioral scientists to be a direct measure of anxiety. Measurements of rearing frequency versus time spent with forepaws at rest against the enclosure’s walls, which has a different set of underlying neural mechanisms, are thus often one of the most important measurements taken during open field testing.

Stretching Postures

Rodents sometimes stretch their bodies out to elongate their heads and shoulders for brief periods before retracting to their original position. If test subjects perform this behavior with high frequency, it’s generally thought to indicate high levels of anxiety.

Defecation And Urination

Some researchers believe that rodent models increase rates of defecation when they are anxious, but this stance remains controversial. There is a general consensus that both urination and defecation rates are indicators of emotionality. However, not all scientists believe that changes in those rates can be assumed to indicate anxiety, in particular.

Applications For Open Field Testing In Rodent Behavioral Research

The applications for open field testing in rodent model research are almost infinite. Anxiety like behavior research receives the majority of the attention from the general scientific community. However, there are also many other behavioral patterns related to general locomotion that can be measured using open field testing. Some researchers study rodent behavior as a simple indicator with limited explanatory power, while others use open field tests to study its functional roles. 

Why Researchers Do Open Field Testing

Anxiety and fear conditioning experiments currently constitute the majority of rodent open field tests. However, some researchers also use this experimental design to assess memory by evaluating subjects’ abilities to recognize objects or stimuli introduced into the arena or to perform novel object recognition tests.

Types Of Equipment Used For Open Field Testing

The primary piece of equipment used for open field testing is an enclosed arena, typically made from plexiglass. A good system will be equipped with an infrared grid for easier recording and analysis of the subjects’ movements and should be easily integrated with other essential research products. The SuperFlex Open Field from Omnitech Electronics, Inc. is a perfect example in that it allows behavioral researchers to study both simple behaviors and their functional roles.

When studying complex behavioral patterns, the housing in which the rodent subjects are reared must also be carefully controlled. Early life conditions, including parental care, single vs social cages, and the presence or absence of environmental enrichment, can all affect behavior later in life. Ordering custom home cage frames and racks is the best way to avoid unnecessary variables and ensure that every subject is reared in the same environment.

Tips For More Effective Open Field Testing

Despite the prevalence of open field testing in behavioral science, there is still a lack of reliability and validity across laboratories. Researchers can help to alleviate these issues by creating more effective and reproducible open field tests. To accomplish this goal, experts recommend:

• Creating more sophisticated testing and result analyses for tests designed to increase understanding of the biological functions of behavior, which should be done in more ethological settings.
• Ensuring that all of the rodents are reared in the same conditions and that those conditions are carefully noted in the experimental design.
• Allow animals to express themselves fully by offering multiple stimuli and possible responses.
• Ensuring that test subjects become familiar with the arena before testing for behaviors of interest.
• Including a sufficient number of subjects in each experimental group.

The Importance Of Good Experimental Design

When designing an open field test, researchers must focus on carefully defined control variables if they want to create reproducible experimental designs. In modern times, they must also be able to gather sufficient data for a complete analysis, often using AI-assisted software programs. The right experimental design always begins with high-quality equipment, so don’t cut corners.