Many drugs having effects on central nervous systems (brains) affect locomotion in animals. For examples, anxiolytic benzodiazepines having hypnotic effects show central suppressive effects and decrease locomotion at higher doses. Those at lower doses increase exploratory behaviors in novel environment due to anxiolytic effects and induce increases in locomotion. Centrally stimulative drugs such as psychostimulants having stimulating effects increase locomotion. Because peripheral locomotive disorders, fatigues, infectious fevers and so on decrease locomotion, the decrease is one of basic parameters to speculate systemic condition in rodents. Similarly, a food intake normally reflecting an appetite is also one of parameters to show health conditions. On these backgrounds, measurements of the locomotion and the food intake are necessity for in vivo tests in unanesthetized and freely moving rodents. Circadian variation in nocturnal rodents is observed, in which spontaneous locomotor activities and eating time in freely fed condition are larger in nighttime than those in daytime, and especially the locomotor activities are a good parameter of a circadian rhythm. Further, the food intake in a choice test between two foods and locomotion (exploration) in an open field test become parameters of preference and anxiety, respectively. Thus, measurements of the locomotion and the food intake are basic techniques in behavioral pharmacology.

8-1 Locomotion

Some may guess that amounts of locomotion in human are total amounts of intensive movements like sports such as running and swimming, others total amounts of all movements in daily performance. A pedometer is one device measuring human locomotion but it cannot count movements of an upper body such as hand in a sitting human. Recently, commercially available devices (activity meters) with 3-dimension acceleration sensors can detect movements in whole body as activities which may resemble the latter case.

Because it is also different what locomotion is detected in rodents depend on measurement devices (principles), we should compare locomotion measured by the same device as a general rule. We must refer to the locomotion in literatures taking care of the measurement devices. We below introduce measurement methods and available devices.

8-1-1 Open Field Test

We place a rat or a mouse in a cage with square lines on a floor and count a number of crossing the lines for a predetermined time as locomotion. It needs a wide space although we can conduct it by a manual observation at a low cost. If we confirm behaviors in rodents by video-recorded images, we can count more correctly. If we measure locomotion in central and peripheral areas separately, we can use to evaluate anxiety. We measure movements of places in a novel environment in this test, which is thought to reflect exploratory behaviors in rodents. In the open field test locomotion in rodents is increased in the central area if their anxieties are suppressed. We can also automatically analyze the video-recorded images by software of a personal computer (PC) as described below.

8-1-2 Video Tracking

We conduct video recording a mouse or a rat, detect its position by PC analysis and measure a distance traveled by movements of the positions. If we can conduct correct tracking, it is a very useful method that the distance traveled is correctly measured and many data such as the distance and speed separately in a predetermined area, trajectory, and video images are simultaneously obtained. Because a target animal is generally detected by its differences from backgrounds (a cage bottom) in brightness, the dark (deep color) bottom and less reflection are preferable for a white mouse. If the mouse hides under nesting materials, we cannot conduct the tracking. We also cannot track the target in a dark period with a normal camera (a visible light camera) and we need a special device such as an infrared camera for the tracking in darkness. Generally the target is limited to one animal in one field of view but some software can simultaneously detect multiple colored mice by a color tracking. Because simultaneous tracking multiple targets detected by differences in colors is more difficult than tracking a single target, the correct tracking becomes more difficult.

The video tracking has some limitations described above and is difficult to initial settings. Previously a system of the video tracking is very expensive over 10 million yen but currently less expensive software about a 1/10 price becomes available and it gradually grows popular. We recently apply the video tracking to fishes such as medaka and zebrafish as well as mice and rats.

8-1-3 Devices with Infrared Beam Sensors

There are following two types of devices detecting movements in animals by disruptions of infrared (IR) beam sensors: 1) movements are measured by counting a number of disruptions, 2) movements are calculated based on information of animalfs position detected by the sensors densely equipped. Former is a relatively cheap device having a few IR sensors and measure large movements. The latter can detect small movements and conduct advanced analysis such as separate measurements of locomotion in multiple areas. The both can measure only one animal in one measuring field.

8-1-3-1 Devices Installed around Rearing Cages

High Density Cage Rack Frame
A photo cited from Lafayette Instrument

A device detects locomotion in rodents by a frame with IR sensors placed around a transparent rearing cage, in which numbers and intervals of the sensors are different by their makers. We use this device to measure locomotion for a long time during breeding of rodents and it is suitable for studies on circadian rhythms, spontaneous locomotor activities affecting energy consumption and so on.

8-1-3-2 SCANET

SCANET is a trade name of a devise having IR sensors densely equipped and one of those series, MV-40, has 144 IR sensors (72 in both x and y axes) with an interval of 6 mm. It detects positions of rodents by these sensors and sends information of the positions to PC. SCANET obtained data of distance traveled and time spent in predetermined areas and trajectory. Because SCANET obtains data separately in each area, we can use it with a light/dark cage in a light/dark test measuring anxiety and a conditioned place preference (CPP) test evaluating rewards, and measuring exploratory behaviors in the open field test. Since it can detect small movements in rodents, it is applied to a forced swimming test with a specific cage evaluating depression. SCANET is easy to use, in which we can measure locomotion in darkness by putting a rodent into a cage in it. It is a good device to get various data close to those by the video tracking but we must give attention to following points. Because a measureable area is limited by a size of sensor frame, we cannot measure locomotion in a rodent in a large device such as a maze different from the video tracking. We can only use a cage that penetrates IR beams and cannot place obstacles disrupting the beams in the cage since the sensor detects IR beams from a horizontal direction. If a rodent goes off the beams to a vertical direction by its behaviors such as grasping a lid, it cannot detect the rodent. These cautions are same to the devices installed around rearing cages and we must take care nesting materials, foods, and a water bottle not to disrupt the beams. Further, since SCANET is large (MV-40: ca. 560W x 560D x 330H), a wide space is needed to set it.

8-1-4 Pyroelectric Infrared Sensors

A pyroelectric infrared sensor is equipped to detect a human in a lighting device automatically lights on when someone comes close in it, and it catches infrared rays (heat) emitted by objects and is also used to measure locomotion in rodents. Humans and animals are different in their temperatures from surroundings and can be distinguished by IR. A temperature is changed by movements of such thermal sources, which can be detected by the sensors measuring IR. In a case of the sensor detecting a human, it detects that the thermal source, namely, a human comes close and in a case of a device measuring animal locomotion, it detects and counts thermal changes by moving close and away as a parameter of locomotion. Because a size of detectable area and a blind angle, and a threshold detecting the changes have varieties in devices, locomotion is principally possible to be different depend on the device. We have no data about comparisons in devices between different makers, actually should compare the data of locomotion measured by the same device. Setting places and directions of the pyroelectric sensors may affect the data.

Unlike the IR beam sensors, the pyroelectric sensor can detect grooming and small movements of each limb and a face without horizontal movements. Since it is insensitive in a size of movements and considers a series of movements as 1 count, the locomotion count is generally not correlated to a distance traveled. Because it can detect small movements to every directions, it is suitable to detect immobility and used for a forced swimming test. We can consider that the pyroelectric sensors measure activities in rodents like data obtained in humans by 3D acceleration sensors and use them to study energy consumption set above rearing cages.

Although the sensor is normally set above a cage, we must determine its height taking into account a width of cage because its detectable area concentrically widens. Since obstacles between the sensor and a target (a rodent) disrupt detection, a mesh type is used if the lid is needed. A transparent cage becomes an obstacle unlike in a case of the IR beam sensors. If food pellets are placed on the mesh lid, a blind area may appear below the foods and we must confirm it before locomotion measurement. Spreads of nesting materials do not usually disturb but we give attention to movements of thermal sources outside a cage such as humans and lights which may be detected. If the sensor is set inside a cage face a downward direction, the outside movements are not detected.

8-1-5 Running Wheels

Mouse Single Activity Wheel Chamber
A photo cited from Lafayette Instrument

We use a running wheel can be rotated by rodent's running or walking in it to measure locomotion (a running distance) as a number of rotations. Because the wheel is generally set in a rearing cage and the rodent freely move in and out it, the running wheel measure spontaneous behaviors rotating the wheel. A rotatory number is high in a dark period and low in a light period and shows a typical circadian rhythm. Therefore, it is well used to measure locomotion for studies on the circadian rhythm. Since rodents are limited their movements in a small cage, the running wheel is often set in the cage to promote a long-distance travel. Because rodents can freely determine to move or not in the running wheel, we hardly equalize amounts of locomotion by it. Moreover, we cannot measure total locomotion including the other than behaviors rotating the wheel.

8-1-6 Telemetry

We can measure in freely moving and unanesthetized rodents a body temperature, a blood pressure, a heart rate, an electrocardiogram (ECG), electroencephalogram (EEG), and so on with time by telemetry in which a receiver receives signals from a transmitter with a sensor implanted in rodents. In telemetry with each sensor for each physiological parameter normally measured under a restraint condition, we conduct an implant operation of the transmitter in an appropriate site for a measurement under a free moving condition and can obtain locomotion data with the sensor data. The telemetry system measures locomotion based on a distance from a receiver that is estimated by changes of signal intense from a transmitter. Because we need the expensive transmitter and the labor-consuming operation for the telemetry, it is not used to measure only locomotion. Since the transmitter is relatively large (1.4 g weight and 1.1 cc volume for mice) in small animals, mice, it may affect locomotion.

8-1-7 Other Methods

We historically measured locomotion in rodents with an automatic measurement device called as Animex which detects locomotion by changes of capacitance. It need to adjust sensitivities before the measurement and is difficult to secure reproducible data including sensitivity adjustments, and we hard to understand a definition of locomotion by its measurement. Therefore, we became not to use it with the development of devices measured by IR beam sensors.

A device (a tilting cage) with a bucket-shape cage is named after developers as Gunma University ambulometer in which a contact switch is on and off and counted as locomotion when a rodent moves inside and turns a tilting bucket around. It can measure locomotion in rodents with a low cost but use a tilting and cylindrical cage which is normally not used in breeding. Therefore, it also became not to be used with widely spread of cheap devices measurable in rearing cages with IR beam sensors.

8-2 Food Intake

A food intake is easily measured once a day by manually weighing food containers including food pellets with a balance subtracting a residual weight from a feeding weight. However, we need an automatic monitor of a food intake to obtain data eating time and a time course of the food intake such as a circadian pattern in which rodents eat more in a dark period and less in a light period. A food intake controller, a drinkometer and a device for a two-food choice test as well as a food intake monitor are introduced below.

8-2-1 Food Intake Monitor

There are following two types of devices: 1) a weight of residual foods is monitored and sent to PC with time and a food intake is calculated from decreases in the residual weight, 2) small globular food pellets with the same size are supplied one by one with a pellet feeder and a food intake is calculated from numbers of the pellets supplied. In the latter, a pellet is supplied anew after a rodent took a pellet but a food intake can be not correctly measured since the rodent may not eat the whole pellet and discard a residual fraction. Because a minimum pellet size is determined by technical reasons, the pellet feeder type is not suitable for measurement of a food intake in mice that eat only small amount of foods at once. It is used to analyze food intake patterns including a circadian rhythm since feeding behavior can be monitored in real time. In former weight sensor type, accuracy of a food intake is deeply affected by how the device can collect and weigh residues. Further, since the weight cannot be measured when a rodent is contact to a food container, the weight is recorded slightly later than an actual feeding time when the animal separates from the container.

If residual foods spread in a cage, automatic collection by the device becomes impossible. Therefore, although the food intake monitor is created that the residues are kept within a food container or a residual container, it cannot be protected that rodents put powder of foods on their faces and limbs and bring them into a cage. We can consider it within an error range level because it is enough small compared to a general food intake in mice (several grams a day). However, it is a significant problem when the intake is a small amount such as a kaolin intake in a pica behavior. Although intakes of kaolin and food pellets are separately monitored by two weight sensors to evaluate the pica behavior, this device is specific to rats due to relative amount of kaolin brought into a cage (see "6-2-2 Automatic Measurement Device in Rats" in "6. Emetic Effects"). This device is applicable for a two-food choice test by simultaneous supplying 2 types of foods.

8-2-2 Food Intake Controller

Although we can conduct manual control of food intake in mice and rats by supplying predetermined amounts of foods once a day, detailed control (limitation) is possible by an automatic feeder. The automatic feeder supplies foods set by the predetermined amounts at predetermined times and a novel device that a motorized shutter limits rodents' access to foods and controls their food intakes is also commercially available. The latter called as FDM equips a weight sensor and can control feeding times and feeding amounts together with monitoring the food intake. Moreover, a system of FDM makes possible to conduct a pair feeding method automatically. In this method, multiple animals are paired and the food intake is equalized between pairs by supplying the same amounts eaten by control animals to pair-fed animals on the next day.

8-2-3 Drinkometr

A water intake as well as the food intake can be monitored by weighing residual amounts in a water bottle. It is also manually measured as a volume by a scale of the water bottle and automatically as a count of drops by disruptions of an IR beam sensor. In any case, the water intake is the amount based on assumption that rodents drink all amounts because spillage is not measured.

8-3 Closing

Locomotion and food and water intakes are all measured in one animal with one device. We cannot automatically identify each animal in group-reared rodents and measure their behaviors separately in each animal with devices above described. However, a novel device that identifies each mouse by reading information recorded in a RFID tag (transponder) at a size of 11.5 x 2.2 mm subcutaneously implanted is recently developed (IntelliCage). Gates reading the tag information are set at 4 corners in the cage and the gates open and close after identifying a mouse, which allows a specific mouse enter into inside of the gate. Inside a nose poke evaluating operant responding is detected and water as a reward and air puff (compressed air) as a punishment are supplied and learning and memories can be simultaneously evaluated in multiple mice (1), (2), (3).

IntelliCage is developed to evaluate learning and memories in mice and impossible to measure a food intake but identifying by RFID and the gating system may make us possible to measure automatically the food intake in each animal of group-housing rodents in future.