Scientists find brain cells that make pain hurt

Pain sensation and the emotional experience of pain are not the same, and now, in mice, scientists at Stanford have found the neurons responsible for the latter.


A team of scientists at Stanford University has identified a bundle of brain cells in mice responsible for the latter—that is, the negative emotions of pain.

Supported by animal-brain imaging and molecular testing, the analysts have discovered an ensemble of cells in the amygdala, a region of the brain traditionally connected with feeling and fear, that appears to explicitly work like an on-off switch for pain aversion.

What’s more, in spite of the fact that the finding was made in mice, there’s motivation to figure it would one be able to day fill in as a remedial focus for human pain, since the mouse and human amygdala are same in function.

According to scientists, studying this group of cells could unveil a potential treatment for chronic pain.

Irene Tracey, a pain neuroscientist at Oxford University who wasn’t involved in the study said, “This study is a major advance. It was a tour de force and a welcome addition to understanding this complex and major problem.”

For this study, scientists used a miniature microscope, or miniscope to sift through the tangle of neurons there and identify the ones associated with pain.

Mark Schnitzer, a neuroscientist at Stanford said, “The miniscope allows you to track neurons over time while the mouse is behaving normally.”

Scientists started with introducing a fluorescent protein into the amygdala that releases a tiny burst of light when neurons fire. Then, the team guides this slender scope deep into the brain to see which neurons flash as the mouse reacts to painful stimuli, like needle pricks.

At the point when a mouse is in pain, it reflexively pulls back, similarly as our hand does when we contact a hot stove. Scherrer says that these reflexive behaviors show the sensation of pain, yet aren’t unsavory. Different behaviors such as dodging the painful stimulus or licking the paw that touched it, show that the pain is unpleasant.

Scientists exposed the mice to a variety of painful and benign stimuli and identified a constellation of about 150 neurons in a region called the basolateral amygdala that was active only when the mice appeared to be in pain. Further, it seemed that the more pain the mouse experienced, the brighter this constellation in the BLA glowed.

Grégory Scherrer, who co-led the study said, “At this point, we could only see that these BLA neurons were correlated with pain, but not if they encoded the unpleasantness of pain.”

“To answer the question, we then turned towards creating chemical switches to control the pain neurons. They could then switch these pain neurons off, and see if a mouse behaved differently when pricked.”

Jordan McCall, a neuroscientist at Washington University in St. Louis said, “Getting these switches on pain neurons, and only the pain neurons, required some genetic trickery. This paper really combines a lot of the most advanced techniques in neuroscience.”

“With the switches in place, we turned off the BLA pain neurons, and found that the mice still sensed pain, but they didn’t behave as though it were unpleasant.”

Scherrer said, “They essentially didn’t care about pain anymore.”

The outcomes held up when the researchers looked at mice who had developed chronic pain. Their BLA torment neurons had turned out to be sensitive to the point that they let go at the lightest touch. At the point when Scherrer killed their BLA pain neurons, the mice still encountered the light touch, yet didn’t appear to encounter it as undesirable.

The results suggest that the unpleasantness of both acute and chronic pain stem from these BLA pain neurons, making them a target for treating pain.

Scherrer said, “Opioids can be effective in relieving pain, but they are a blunt tool and affect brain areas associated with behaviors as varied as addiction and breathing, for example. Now that we know what neurons give pain its unpleasantness, we can look for receptors present only in those neurons, and not in other areas of the brain.”

Schnitzer said, “If there are receptors unique to these neurons, researchers could try to design drugs that turn down their activity. If the approach worked, it could lead to a drug that makes the pain more bearable, but doesn’t a dull sensation.”

The study is published in the journal Science.


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