How do we measure pain in lab rats?

How do we measure pain, anyway? – You can’t exactly ask a rat to point to where it hurts – by Jeremy Delahanty – Neuroscience – UC Davis – July 22, 2019

Where does it hurt? How do you feel? The enormous number of questions a provider can ask reflects the many variables that are important for treating pain. It also makes clear that communication about pain is difficult for both patients and providers.

Pain is subjective and no two experiences are alike.

Everybody can agree on this, yet those who don’t have much pain themselves believe they can know our pain better than we can ourselves. 

And, a fundamental understanding of what pain actually is has evaded science.

nearly 20 percent of the United States is struggling with chronic pain.

Pain’s successful escape from our grasp is due, in part, to the fact that laboratory science does not, and may not be able to, actually study pain psychology, beliefs, and expectations in animals.

I’m glad they are finally admitting what I’ve been pointing out for years: first, they claim that chronic pain is not a physical issue, but rather a biopsychosocial condition to be treated with counseling and more socializing.

But then they use animal models to research “chronic pain”, even though a rat’s biopsychosocial state – if it even has one – cannot possibly model a human’s “real” life, complicated and distorted by constant pain.

There’s also no way to evaluate the psychosocial effects of pain in animals (they can’t fill out the questionnaires and surveys used to determine a human’s mental state) so there’s no way any animal can model our pain.

Additionally, the “chronic pain” researchers create in animals is nothing like what a person with chronic pain lives with for years and decades. I think this makes animal studies irrelevant to choric pain.

Such fabricated measures and results of animal studies should never be assumed to apply to humans.

In fact, we’re very careful to say in animal studies that we don’t study pain at all. We study “pain-like behaviors” after inducing an injury. The ethical limitations of such procedures are constantly evaluated so as to only induce the needed amount of “stimulus” for the purposes of an experiment

But how can we learn if something is truly painful to an animal if we can’t speak with them?

we investigate pain perception in lab animals through reflexes, voluntary movements, and emotional changes 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.

This is only nociceptive pain and says nothing at all about chronic pain.

Finally, a treatment, such as a new drug or exercise therapy, is given and the tests are performed one last time.

But treating pain in animals does not necessarily treat it in humans.

What a surprise! (not)

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.

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

A newer approach to evaluate the subjective nature of pain in animals is the “grimace scale,” which aims to mimic the kinds of facial changes people make when experiencing different magnitudes of pain

Unfortunately, this test is limited not only because nociceptive stimuli and some chronic pain models are not associated with facial changes but also due to the fact that a human observer or human coded computer is the judge of severity.

This kind of technology may be especially difficult to ethically use given that gender and race have been shown to bias practitioner beliefs about, and therefore treatment of, pain.

It wasn’t until 2016 that female mice were required to be included in these studies. All patients could be suffering as a result of failing to be inclusive of all sexes.

There have been calls to study human pain in all its complexity. Perhaps we humans won’t be able to translate mice and rats’ experiences of pain until we discover more ways to understand them without our self-centered biases.

1 thought on “How do we measure pain in lab rats?

  1. Kathy C

    Applying anthropomorphic measures to lab rats and mice is absolutely ridiculous. To check anti depressants, they describe how well the mouse can swim, after taking the drug. When I was a kid I would rescue lab rats and mice, saving them from the horrors of the labs.

    Some of the pain experiments on rats and mice have been horrific, and the data they collected was meaningless, ridiculous, and deliberately deceptive. Misreporting the findings of these experiments has set science back a couple of decades, deliberately mislead the public. The findings are subject to interpretation, so researchers are free to project their own biases. Science does not work this way.

    There are lot of these animal labs, where science is for sale. Pay enough and you get the results you want.

    When Volkswagen wanted fabricated data they turned here, where science is for sale

    https://en.wikipedia.org/wiki/Lovelace_Respiratory_Research_Institute

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