Share thisPain of minor grades is difficult to detect in laboratory mice, because mice hide signs of injury and suffering. Low-grade post-operative pain was detected by continuous measurements of heart beat rate and variability, as well as nesting behaviours. Pain relief regimens with non-steroidal anti inflammatory drugs were shown to be effective.
In 1985, the U.S. Interagency Research Animal Committee (IRAC) advised that “unless the contrary is established, investigators should consider that procedures that cause pain or distress in human beings may cause pain or distress in animals” (www.aclam.org/pub_pain_distress.html). Accordingly, the humane use of research animals requires adequate veterinary medical care during animal experimentations and includes the prevention or the alleviation of pain associated with procedural or surgical protocols (clinical pain). Guidelines on the recognition of pain are accepted by researchers but often not so easy to put into practice, especially with mice, the most frequently used laboratory animals. Why?
Mice live in constant fear of falling prey to their enemies, therefore they are prone to show as few signs of disease, suffering, or weakness as possible (Stasiak et al., 2003; Peterson, 2004, Van Sluyters and Obernier, 2004). Accordingly, during animal experiments, or even when a person is simply present in the room, the mouse will hide almost all signs of light or middle-grade pain. Additionally, endogenous stress-induced analgesic systems that are well developed in mice affect their responses to pain and therefore complicate the recognition of the actual degree of pain (Hohmann et al., 2005).
Decreased food intake or loss of body weight are retrospective indicators of pain or stress and therefore not suitable per se. In consequence, there are no reliable indicators to detect low and middle-grade clinical pain in the mouse. The appearance of clinical signs (e.g. changes in posture, fur, or eyes) often represents severe pain appearing sometimes at a nearly moribund state. Severe pain that is unforeseen, affects the outcome of a study and is terminated by euthanasia. Another consequence of the dilemma is that even a successful analgesic treatment cannot be monitored well and uncertainty remains about the efficacy of many analgesic regimens. Accordingly, more research is necessary to improve the recognition (Flecknell et al., 2005) and justification of pain in laboratory mice.