Abstract
It is becoming more apparent that exercise is essential for neurogenesis and health. In the laboratory, wheel running is used to stimulate enhanced activity levels. This is despite common objections that it is a sign of neurosis or stereotypy and is not a result of being in captivity. Wild mice should not use a running track in the wild if wheel running is caused by captivity. To our knowledge, this has not been proven. We show here that wild mice will use running wheels even when there is no reward. The wild running wheel behavior is approximately the same as that of captive mice. This finding contradicts one criterion that defines stereotypic behavior and suggests that running wheels is an elective activity. Research into the benefits of physical activity is vital in a world where lifestyle and inactivity are major causes of disease. These findings could help to alleviate the primary concern about running wheels when it comes to exercise research.
Introduction
Exercise can be good for your health. It protects you against heart disease, diabetes, cardiovascular problems, and other diseases. Exercise stimulates neurogenesis, even in older rodents in the hypothalamus or dentate gyrus. As a way to measure and stimulate activity, voluntary wheel running is used in many scientific disciplines. However, it is difficult to understand the biological significance of wheel running . Unnatural wheel running has been claimed. It may even be a form of stereotypy or neurosis, which can only develop in captivity. Kavanaugh cites Konrad Lorenz’s personal communication as a formal experiment. It states that rodents that have escaped from wheels can now enter the running lane and use them.
Running wheels are being used in more laboratory experiments due to their reported positive effects on health and protection against the development of diseases. Running wheel activity in laboratory studies raises questions about whether it is a pathological phenomenon or something that occurs only in captivity. We, therefore, conducted a study to see if running wheel activity can also be expressed in the wild by free-living animals interacting with a wheel in their natural habitat. Two locations were chosen to house feral mice: one in a large, green urban area (data collection October 2009-February 2013) and one in a remote area (data collection June 2011-January 2013. We placed running wheels (24 cm in diameter) with automatic movement detection, passive infrared motion sensors, night vision, and a food tray to attract the mice. The wheel was placed in a cage-like structure that could be easily accessed by any animal up to the size and weight of a rat. The camera used a passive infrared motion detector to record every animal’s visit to the experimental setup. The camera worked at night thanks to active infrared lighting. The infrared light was invisible to mice and did no harm to motion detection. It was possible to identify the animal responsible for the wheel’s movement by using the footage. We have analyzed over 12 000 video fragments that showed wheel movement, which were taken from more than 200 000 recordings of animals visiting the recording site. This was done over a three-year period. To determine the species of an animal found in the wheel, trained observers analyzed video recordings. A small magnet was attached to the wheel, and a stationary magnetometer was used to detect wheel movement. When the sensor was activated, the wheel running was recorded.
Nature observations
Wheel running was observed in both the urban environment (1011 observations in 24 months), of which 734 were of mice, and in the dunes (254 observations over 20 months), of which 232 were of mice. Shrews, rats, and snails caused wheel movement, which was not caused by mice as well as the electronic supplementary material, video clips). Only the snails were able to cause haphazard rather than directional wheel movement and were thus excluded from the analysis. Wheel running was also excluded from cases where animals moved the wheel from the outside.
Feral mice were seen running in the wheels all year. They increased in late spring and reached a peak in summer in the green city area. However, their numbers declined in the dunes in mid-to-late summer, peaking in fall (see supplementary electronic material. While some animals may use the wheel intentionally, frogs, shrews, and rats were able to see how they would leave the wheel to return to it within minutes. This observation suggests that wheel running may be an intentional behavior rather than an accident. Video recordings indicate that wheel-running mice were mostly juveniles. This could explain the high incidence of wheel running in summer. Mice ran more than one minute in 20% of cases. The maximum time they ran was 18 minutes. This is comparable to the running that 200-day-old C57BL6 mice do in the laboratory. Mice ran on our wheels and never moved slowly. The field speed is lower than that of laboratory mice (1.3 km h -1; Mann-Whitney -test _0.0001), but the laboratory speed is greater (5.7 km h -1). The running speed for each bout was calculated by multiplying the number of octets in the bout by the circumference of the wheel and then dividing the result by the bout length. The field is shorter than the laboratory in terms of covered running distance. The laboratory’s wheel running distance is highly variable due to many factors, including the age of the animal, the diameter of the wheel, the friction between the wheel, and the cage size. The laboratory distances reported in nature are similar to those observed in the laboratory.
Next, we analyzed the circadian patterns of wheel running. The absolute number of wheel runs is higher at night than in the urban areas (Mann-Whitney -test, both). We determined the percentage of visits to the recording setup that included wheel running because most of them occurred at night. The dunes have a significantly higher proportion of visitors to the experimental setup that includes wheel running at night (Mann-Whitney -test ). However, in the urban area, wheel running was not found to be a significant part of the visits (Mann-Whitney -test = 0.1602). These data could indicate that animals’ behaviors in urban areas may be affected by light pollution, as low levels of light intensity in the dark phase can disrupt rhythmicity in rats and mice.