This Is Why It's Nearly Impossible to Study Pain
Jeremy Delahanty
Well that's all very creepy...
Jeremy Delahanty
Quote:The authors discuss tests that look at reflexive responses to potentially harmful stimuli like too much pressure or excessive heat. The hind paw is the location best understood and most often stimulated for investigating these reflexes in animals. The idea is that there is a certain amount of "painful" stimuli an animal can tolerate and, when that threshold is reached, the animal quickly withdraws its limb. Regardless of what test is used, it's important to find a baseline threshold that causes a reflex behavior.
Once the baseline is found, the researcher then induces an injury and the tests are performed again. In response to the injury, the threshold drops. This new, lower threshold is a condition known as allodynia. The IASP defines it as "pain due to a stimulus that does not normally provoke pain." Think of a pleasant shower becoming painful after getting sunburned. The successful treatment of this condition is one of the foremost foundations upon which all new pain relieving treatments are built upon.
Finally, a treatment, such as a new drug or exercise therapy, is given and the tests are performed one last time. If the threshold rises back to baseline or near baseline levels, the therapy has alleviated the paw's allodynia and therefore successfully treated a key component of pain perception. But treating pain in animals does not necessarily treat it in humans. For example, a couple of decades ago, a class of compounds called NK1 receptor antagonists were found to be effective in rodents and hailed as a potential breakthrough in pain care. When clinical trials were performed, however, Merck Pharmaceutical researchers that helped develop the drug were dismayed to find that "the outcome from clinical trials [was] extremely disappointing with no clear analgesic efficacy." The drugs simply failed in humans.
Well that's all very creepy...