ambient temperature requires less adaptation than exposure to such motivating procedures as food or water restriction. Forced swimming is used to create a standardized stress experience (Griebel et al., 2002; Porsolt et al., 1977). Rodents commonly become immobile after several minutes of swimming if there is no possibility of escape from the water. The dependent variable often is the time until the first episode of immobility or the percentage of the test session spent immobile. Animal-welfare issues include maintenance of an appropriate water temperature, and provision of proper care of the wet rodent after it is removed from the water, and the establishment of unambiguous humane endpoints for testing in the animal-use protocol (see “Mood-Disorder Models” in Chapter 9).
Neuroscience studies involving physical conditioning and exercise require appropriate attention to adaptation of the animal to the testing situation, its gradual conditioning to develop stamina, and close animal observation and record keeping during the exercise period. Swim tanks and automated treadmills and running wheels are the most common equipment used to force or promote exercise. Animals should initially be trained on automated devices at low speed, incline, and duration, which should increase gradually as the animals gain stamina. Similarly, the duration of swimming periods should be increased gradually as the animals’ condition improves. Weekly or even daily increases may be possible. However, animals should be closely observed by knowledgeable personnel during training and exercise sessions—particularly during the early phases of a conditioning program, near the end of individual training sessions, and during sessions in which performance requirements are increased—and detailed records of the animal’s performance and general health should be kept and made available to veterinary staff and the IACUC. In some systems, a rodent’s toes or tails may be at risk of becoming entrapped in the treadmill device. The continuous presence of an observer is essential to prevent injury in such situations. The use of remote monitoring systems, such as closed-circuit cameras, is sometimes warranted. As part of its review of the animal-use protocol, the IACUC may consider evaluation of equipment and a preliminary assessment of animal performance in a device.
Many automated treadmill systems apply a mild electric shock to animals whenever they fail to keep up with the programmed pace and drift back on the device. Although the number of shocks experienced by well-trained and conditioned animals is typically low, monitoring and recording shocks that animals experience and the pattern of shock administration during a training session can provide information about the adequacy of the training or exercise in light of the animals’ physical condition. A humane endpoint for removal of animals from the testing situation should be specified in the animal-use protocol and approved by the IACUC.