Of Mice Pain and Man Treatment

And that is exactly why I love science. From a statement like that, foundations are shaken. What if the gender of a person running an experiment on pain mattered? What would happen if a single experiment was run by alternating scientists (male and female) on alternating days? Can a pain experiment done by a male be compared to a similar pain experiment done by a female.

This experiment started anecdotally from the something like the reference above. Mice make faces and somebody has been watching them very closely.

Mice grimace less in response to pain when there is a male in the room.

The basic experiment:

The initial experiments were done with Zymosan A injections in the paw. This causes pain. The pain then can be measured by the grimace of the mouse. In this case, when there was a male (human) in the room there was less of a grimace.

Do you need the whole male?

Nope, it turns out you just need the smell of a male. When the experiment was repeated with a male’s t-shirt, the result was similar. Interestingly, the presence of a female t-shirt reversed the effect, and the effect of the male shirt gradually lessened over time. If the

When bedding was used from different male animals, the result was similar, unless the males were castrated. This led the group to believe that the effect was the result of male pheromones.

So how does it work?

To figure this out, the scientists switched to formalin as the pain-causing-agent. The pain generated by formalin falls in to two phases, one following the other. Phase 1 isn’t affected by anti-inflammatories (e.g. Advil) but both phases are affected by opiates.^1,2 Male-stench affected both phases.

Now, using the premise that male-stench was affecting a neurological pathway instead of just reducing inflammation, the group suspected SIA, stress-induced analgesia^[b]. This is a decrease in the transmittance of pain as a result of stress, and of course male-stench-stressed^[c] mice showed a rise in corticosterone.

Is it like drugs?

There are different forms of stress-induced analgesia. Some use the opiate pathways and some do not, and some use a combination.³ It turns out that the male-stench induced SIA is at least partially blocked when the opioid system is blocked.

Fancy wording.

The last paragraph of scientific articles is often what I like to call the grant appeal.^[d] They generally go something like this: “and this may pave the way for a new treatment of (insert disease that has reached epidemiological proportions here).”

The authors made the following statement at the end of their article. “[this] may represent a confound of much existing animal research, extending even to non-behavioral studies in which tissues were obtained from live rodents euthanized by either male or female personnel.” What it means: “well, oh crap, we now have to look at who did any experiment involving pain, opioid systems, and stress.”

This article may pave the way for a new treatment of really, really poor experimental design being conducted by students (mostly mine) everywhere.

Sincerely,

Luke De