Year: 1991
Type: article
Abstract: Francis J. Keefe, Ph.D., is associate professor of Medical Psychology and director of the Pain Management Program at Duke University Medical Center. Roger B. Fillingim, Ph.D., is a psychology resident at the Pain Management Center, a division of the Memorial Regional Rehabilitation Center. David Williams, Ph.D., is director of the Pain Management Program at the Georgetown University Medical Center. Francis J. Keefe, Ph.D., is associate professor of Medical Psychology and director of the Pain Management Program at Duke University Medical Center. Roger B. Fillingim, Ph.D., is a psychology resident at the Pain Management Center, a division of the Memorial Regional Rehabilitation Center. David Williams, Ph.D., is director of the Pain Management Program at the Georgetown University Medical Center. Francis J. Keefe, Ph.D., is associate professor of Medical Psychology and director of the Pain Management Program at Duke University Medical Center. Roger B. Fillingim, Ph.D., is a psychology resident at the Pain Management Center, a division of the Memorial Regional Rehabilitation Center. David Williams, Ph.D., is director of the Pain Management Program at the Georgetown University Medical Center. Pain has been defined as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage’ (International Association for the Study of Pain Subcommittee on Taxonomy, 1979). Given that pain is a subjective experience, it is perhaps not surprising that so much effort in human pain assessment is devoted to the measurement and analysis of pain perception. Pain, however, can have very significant effects on the behavior of humans and animals. In clinical settings, patients experiencing pain often display a variety of behaviors that communicate the fact that they are experiencing pain (Fordyce, 1976). These pain behaviors may include complaints of pain, reductions in activity, increased medication intake, or alterations in facial expressions or body posture. Animals who are exposed to painful stimuli are likewise known to exhibit pain behaviors such as withdrawal from the painful stimulus or other self-protective maneuvers. Since pain behaviors are overt, they can be observed and recorded. Systematic assessments of pain behaviors have long been viewed as useful in analyzing pain phenomena in animals and are increasingly viewed as valuable by human pain researchers (Dubner, 1989). In the past 2 decades, standardized methods for carrying out behavioral assessments in humans and animals have been developed and evaluated by a number of researchers. Research carried out by these investigators has demonstrated that objective and reliable measures of behavior can be quite useful in the analysis of pain phenomena. The purpose of this paper is to provide the reader with an overview of behavioral assessment methods commonly used in evaluating pain in animals and humans. The paper reviews behavioral assessment methods utilized in three major settings: (1) the animal laboratory, (2) the human laboratory, and (3) clinical research and practice. For each setting, we describe common pain induction and pain measurement methods, review the strengths and weaknesses of these methods, and highlight important practical and ethical issues. The goal of many nonhuman laboratory pain tests is to measure the presence or absence of analgesia following some experimental manipulation (e.g., surgery, drug administration, or exposure to stress). If the methods of pain induction are equivalent, then any change in pain can be attributed to the experimental manipulation rather than to the pain induction procedure. Pain induction procedures allow experimenters varying degrees of control over the parameters of the pain stimulus (e.g., intensity, duration, location, and temporal patterning). Prominent pain induction methodologies include the tail-flick test, the hot-plate test, the flinch-jump test, the pinch test, and the formalin test. Other pain induction procedures, such as the adjuvant-induced model of arthritis, seek to mimic human forms of clinical pain in hopes of gaining a better understanding of the pathophysiologic basis of disease-related pain phenomena. The tail-flick test was first described by D'Amour and Smith (1941). When radiant heat is directed to the tail of a rat, a stable, spinally mediated nociceptive response occurs in the form of a flicking or jerking of the tail away from the heat source (see Williams and Thorn, 1984 for details on apparatus and procedure). Baseline latencies to remove the tail from the heat are established by adjusting the heat intensity to the point where the average latency to flick the tail is constant for four consecutive trials. Thereafter, the heat source remains constant for the remainder of that testing session. New baselines are established with each new testing session. Differences between the experimental and baseline latencies are interpreted as an index of analgesia. Increases in the latency for the rat to flick its tail are indicative of analgesia, while decreases in tail-flick latency are indicative of hyperalgesia. The expression of the tail-flick reflex has been shown to be modulated by the administration of neurohormonal agents or opioid drugs, or through activation of descending pathways from the brain to the spinal cord (Akil and Mayer, 1972; Akil and Liebeskind, 1975; Yaksh and Wilson, 1979). The sensitivity of this reflex to chemical modulation makes this test particularly attractive for analgesic substance testing. The hot-plate test was first described by Woolfe and MacDonald (1944) as a method for testing the loss of pain perception in rats and mice. A heated platform is constructed that can be maintained at temperatures upwards of 50°C. Rats are dropped onto the platform from an elevation of 5 cm and the latency to emit pain behaviors is recorded. Each trial lasts 30 seconds, and the latency for the pain behaviors to occur decreases as the temperature of the hot-plate increases. Typically a cut off temperature of 70°C is used to prevent tissue damage to the paws of animals. The hot-plate test is commonly used as an assay for the efficacy of analgesic drugs. In these studies, longer latencies to emit pain behaviors are viewed as evidence of drug-induced analgesia. The flinch-jump test was first described by Evans (1961) as a measure of pain sensitivity to electric shock. Rats are placed in a box with an electrical grid floor, Foot shocks are delivered for a duration of 300 msec at 10 second intervals. Initial shock intensities are usually of 0.1 p.A. Some researchers then continue to increase the amperage in .05 ~t A increments until 30 jumps occur (Mayer and Liebeskind, 1974). Other researchers limit the number of shocks (e.g., 10) but use larger increments in amperage on each successive trial (Evans, 1961). After a jump occurs the rat is restarted at 0.1 ∼ A for a series of 10 complete trials (Bodnar et al., 1978). The flinch-jump test offers the researcher an opportunity to measure two separate pain responses while using the same pain stimulus. The flinch is interpreted as the point at which pain perception occurs. In humans this might be analogous to pain threshold. Researchers have interpreted the jump as being a more emotionally driven response (Evans, 1961; Bodnar et al., 1978). The jump might be interpreted as analogous to the concept of pain tolerance. The pinch test was developed as a test for analgesia by Collier (1962). A modified version of the test developed by Mayer and Liebeskind (1974) will be described here. Specially designed needle-nosed pliers are used to randomly pinch the four limbs and the tail of the rat. Folds of tissue about 3 mm deep are chosen. The jaw width of the pliers is 3 mm. As the jaws close, the first aversive response trips a spring that records the force being applied at the first sign of resistance. If no resistance is encountered a maximum force of 12 kg is applied. The test is repeated on the same limb for five trials, thus a total of 20 pinches constitute a full assessment. One advantage of the pinch test is that the same stimulus can be used to assess both and in analgesia using the same pain stimulus. 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Source: ILAR Journal
Authors: F. J. Keefe, R. B. Fillingim, D. A. Williams
Institutions: Georgetown University Medical Center, Duke Medical Center
Language: English
Subfield: Small Animals
Field: Veterinary
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2155355901