A placebo effect reducing pain can be induced in rats and its brain origin has been identified, Japanese neuroscientists show in the scientific journal Science AdvancesChronic pain in a rat can be relieved by daily injections of an analgesic, but after a few days this effect can be partly reproduced by an inert product administered under the same conditions.
This placebo effect of pain reduction is due to the activation of neurons in the forebrain. The researchers discovered that their intervention was normally blocked by inhibitory neurons called interneurons.
A new means of action at the level of the cerebral cortex
They succeeded in lifting this inhibition by inactivating these interneurons in rats, either through genetic manipulation or by treating them with morphine analogues that also inhibit them. The analgesic properties of opiates and their synthetic derivatives can thus be explained by a novel means of action at the level of the cerebral cortex.
If, on the contrary, these inhibitory neurons are activated by the researchers, the analgesic effect of the placebo disappears in the animals and they become hypersensitive to pain. A similar network appears to exist in humans. It could explain the analgesic effect of a placebo but also, more generally, of morphine and its derivatives in the brain. The study also shows that a placebo effect can occur without the use of speech, which, for the researchers, resembles a conditioned reflex induced by the repetition of the analgesic treatment.
Read alsoPlacebo effect: we finally know how it works
Patients were warned of the inert nature of their treatment
The anticipation of the drug's analgesic effect would be sufficient to replace its action in the brain. The placebo's action on the unconscious is found in patients who are nevertheless warned of the inert nature of their treatment. It could be integrated into pain-relieving treatments based onopiates or opioids synthetic to limit the doses used and their adverse effects, the researchers suggest.
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