Knowledge Base

Getting the Perfect Runs

CatWalk™ XT is a gait analysis system based on the voluntary movement of rats or mice across a corridor, over a glass plate. Generally, animals quickly learn to cross in a consistent manner, especially rats. However, familiarizing them with the system before you start your experiment makes your job a lot easier.

So how do you familiarize and motivate your rats? Kristina Ängeby Möller has a lot of experience with pain research and gait analysis in rats, and shares some tips and tricks.

Five Tips for Getting the Perfect Run

1. Get Rid of Stress

Perhaps the most important factor is to reduce the level of stress as much as possible. Stress will influence the testing but also the results. CatWalk XT helps by providing a relatively dark and safe environment in which the animals can freely move.

Stress relief starts with the care in the animal facility. It is vital to understand where rats come from – they are a prey species that mainly live underground and away from light. They are sensitive to threats from possible predators, including humans. As a researcher, you should always behave in a calm manner, habituate the rats to human handling, and never hold them too tightly. Also, never pick a rat up by the tail – it is one of the most sensitive parts of its body.

Rats have good hearing, so refrain from making any sudden sounds, especially sounds that are similar to squeaks from rats in distress. Having some background sound in the animal facility and in the experimental room, such as music from a radio, is an advantage.

2. Friends Are the Best Motivators

There are different kinds of stimuli one might consider, but a social one – using cage mates as a motivator – seems to work best. Recent versions of CatWalk XT are shipped including a goal box. If you are working with a previous version, try to acquire one.

It really helps a lot to place all rats from a holding cage in the goal box and habituate them; five minutes is enough the first time, which can then be reduced to one to two minutes. Once a rat has crossed the walkway and discovered that there is an exit, it will remember that, and returning to its cage mates is really all the motivation rats need to want to cross.

3. Why Food Does Not Work

Additional attempts to motivate rats with rewards, like food, will not further improve their performance. In the context of a new surrounding, this is not something rats will even willingly try, as it may be threatening to their health. Rats are one of the most successful species that have spread across the globe and are very clever; they usually avoid trying anything new unless they can assess the risk and gain from the consequences.

4. Don't Force Them

Never try to make the rats walk by using sounds to startle them, by pushing them forward, or by any other technique. The more you try that, the more stressed they will get and the less they will want to walk. Instead, once you put them into the walkway, try to stay as silent and unnoticeable as possible.

A recommended limit is 20 minutes of waiting for a rat to cross, but that situation rarely arises – occurring with only about one in two or three hundred rats.

5. Don't Look Down on Them

Do not look down on the rats, or do anything else from above. This will intimidate the rat tremendously, as it will likely interpret your presence as something threatening. The best approach is to keep the walkway covered by a ceiling during the experiment, which is automatically the case in recent CatWalk XT versions. When a rat has become accustomed to crossing the walkway, it can then accept being lifted from it, observed, and exposed to many other distractions.

About the Author

Kristina Ängeby Möller has been setting up and validating in vivo behavioral models in the mouse, rat, and guinea pig for more than 35 years at AstraZeneca R&D Södertälje, R&D CNS Research Orion Corporation Orion Pharma Turku, and Karolinska Institutet. Models include stereotypic behaviors, catalepsy, monoarthritis, and neuropathy. Endpoints include spontaneous behavior, thermal and mechanical sensitivity, and gait analysis.

Department of Physiology and Pharmacology, von Eulers väg 8, Karolinska Institutet, 171 77 Stockholm, Sweden. E-mail: [email protected]

Publications

• Ängeby Möller, K.; Aulin, C.; Baharpoor, A.; Svensson, C. (2020). Pain behaviour assessments by gait and weight bearing in surgically induced osteoarthritis and inflammatory arthritis. Physiology & Behavior, 225, 113079.
• Ängeby Möller, K.; Svärd, H.; Suominen, A.; Immonen, J.; Holappa, J.; Stenfors, C. (2017). Gait analysis and weight bearing in pre-clinical joint pain research. Journal of Neuroscience Methods, 300, 92–102.
• Ängeby Möller, K.; Berge, O.-G.; Finn, A.; Stenfors, C.; Svensson, C.I. (2015). Using gait analysis to assess weight bearing in rats with Freund's complete adjuvant-induced monoarthritis to improve predictivity: Interfering with the cyclooxygenase and nerve growth factor pathways. European Journal of Pharmacology, 756, 75–84.
• Finn, A.; Ängeby Möller, K.; Gustafsson, C.; Abdelmoaty, S.; Nordahl, G.; Ferm, M.; Svensson, C. (2014). Influence of model and matrix on cytokine profile in rat and human. Rheumatology, 53, 2297–2305.
• Ängeby Möller, K.; Kinert, S.; Størkson, R.; Berge, O.-G. (2012). Gait analysis in rats with single joint inflammation: Influence of experimental factors. PLoS ONE, 7, e46129.
• Ängeby Möller, K.; Berge, O.-G.; Hamers, F.P. (2008). Using the CatWalk method to assess weight-bearing and pain behaviour in walking rats with ankle joint monoarthritis induced by carrageenan: Effects of morphine and rofecoxib. Journal of Neuroscience Methods, 174, 1–9.

Source: White paper perfect runs, Noldus Information Technology