freely moving animals, and measurement of hormones in hair, feces, and urine (Cook et al., 2000; Goode and Klein, 2002; Koren et al., 2002).
One of the most important noninvasive methods for assessing distress is observation of animal behavior. At least when measured in situations where animals have behavioral flexibility and choice, behaviors can provide information about what animals prefer or avoid, and hence are indicators of emotional states (Mench, 1998). Behavior is a part of an animal’s adaptive repertoire for responding to stressors, so it is important to distinguish adaptive behaviors from maladaptive behaviors, such as self-mutilation, unresponsiveness to important signals, hyperactivity, and excessive response to stimulation. Useful observation requires knowledge of the natural history and perceptual capacities of the particular species or strain of animal (Bayne, 1996), the usual frequencies and intensities of particular behaviors, and the causes and functions of the behaviors (Mench, 1998; Rushen, 2000). Because of individual variability, a baseline behavioral profile of an animal should be established if changes in behavior are going to be used to monitor the animal for distress. As with the assessment of pain, personnel assessing behavior should be knowledgeable and skilled in the interpretation of behavior, and assessments should not be influenced by the observers’ biases (Bayne, 2000).
Four general approaches are available to minimize pain (Dubner, 1987): the use of general anesthesia, the use of local anesthesia and/or analgesia, the training of animals to avoid situations that produce pain (escape-avoidance behavior), and control of the intensity and/or duration of the stimulus by the neuroscientist.
The selection of a general anesthetic should reflect professional judgment as to which anesthetic best meets the clinical and humane requirements without compromising the scientific aspects of the research protocol (NRC, 1996). That sufficient anesthesia has been provided can be ensured by monitoring reflexive responses to painful stimuli, respiration, pupil size, stability of heart rate and blood pressure or electroencephalographic activity. Occasionally in neuroscience research, surgical lesions are created producing a functional decerebration and thereby eliminating all possibility of pain and the need for general anesthesia.
The use of local anesthesia and/or analgesia is also a widely used technique for alleviating pain and/or distress. Vainio et al. (2002) provide a useful description of the clinical efficacy and adverse effects of opioids and nonsteroidal anti-inflammatory drugs (NSAIDS) for analgesia in laboratory animals, as well as the dose, route, and frequency of administration of the common opioids and NSAIDS.
For a discussion of the training of animals to avoid painful stimulation and of how investigators can control the intensity or duration of painful stimulation, see Chapter 4. In some cases, euthanasia may be the most appropriate means of alleviating pain (see Chapter 2—“Humane Endpoints”).