LOCOMOTOR ACTIVITY AND EXPLORATION

Rodents typically display circadian rhythmic variations (defined as a 24-hour rhythm) in behaviors and physiology. Circadian global activity is directly assessed into the animal homecage through long periods (>24h). The activity parameters (locomotion, exploration, stereotypies…) are generally evaluated using automatized procedures (photocell beams, video-tracking system, weight transducers…)

Basal locomotor activity is generally assessed in a specific activity arena (can be an open-field or others) for short-time/intermittent periods (<1h). Locomotion (horizontal activity), exploration (rearing and objects sniffing) and stereotypies (movements without displacement) are then recorded manually or using various automated procedures (photocell beams, video-tracking system, weight transducers…).

The rodent Activity Wheel represents a very simple and clever way to register animal physical activity in its home cage environment. The use of this high throughput tool is particularly relevant for research involving circadian rhythms, phenotyping and drug testing. Typically, the time and distance run on a voluntary running wheel are monitored over several days or weeks to determine whether a particular substance or experimental manipulation has an effect on exercise behaviour.

Locomotor responses to novelty is an animal index of exploration/anxiety that has been shown to represent a predictive factor for the addictive properties of drug or animal vulnerable to drug. Indeed, in an animal model for vulnerability to drug abuse, animals that exhibit greater motor activity in a novel environment (high responders; HR) are found more sensitive to drugs of abuse and are more likely to self-administer these drugs compared to less reactive animals (low responders; LR). In the light of clinical evidence on comorbidity between drug abuse and mood disorders, this model is widely used to investigate whether individual differences in locomotor reactivity to novelty are related to anxiety- and depression-like responsiveness in rodents.

The emergence test is a free exploration paradigm designed to reduce anxiety by providing a safe enclosure within the open field in order to assess approach or exploratory behavior in rodents.
Briefly, the open field contained a white plastic cylinder with an open end located centrally. The subjects are placed into the cylinder and tested for 10-15 min. The parameters commonly evaluated in this task are the latency of emergence from the cylinder, the total time spent inside the cylinder, the time spent exploring the cylinder and general locomotor activity.

The novel object test is a free exploration paradigm that provides animals the opportunity to explore a novel object in a familiar environmental context. Briefly, an object is placed into the center of each open field and the behavior of the animal (time spent exploring the novel object and overall locomotor activity) is registered during a determined period of time.

The holeboard test is a specific test for evaluating exploration in rodents. In this test, the animal is placed on an arena with regularly arranged holes on the floor. Both frequency and duration of spontaneous elicited hole-poking exploratory behavior are then measured manually or using automated procedures (photocell beams, video-tracking system) during a short period of time. Other associated behaviors can also be evaluated, such as grooming, rearing and locomotion.

Treadmill test in rodents is a useful tool with a great value in the study of functional capacity and is a validated standard model for investigations in the field of human metabolism. Basically, a subject is forced to walk/run on a treadmill (adjustable speed and inclination) during specific periods of time. This test allows the study of various physiological and behavioral functions such as long and short-term effort during exercise, locomotion, metabolic exchanges, cardiac function, motor coordination and fatigue.