People suffering from chronic pain wish they were among those whose pain is only temporary like a toothache, a passing headache, or a bang on the shins.
The two types – short- and long-term pain – are very different. A new groundbreaking study at the Hebrew University of Jerusalem (HUJI) seems to have uncovered part of the answer – deep inside the brain stem. The team discovered that when one experiences acute pain, the brain has a built-in way to dial down pain signals – like pressing the brakes – to keep them from going into overdrive.
However, in chronic pain, this braking system fails, and the pain signals just keep firing. This discovery helps explain why some pain goes away while other pain lingers. In fact, our bodies respond to acute (short-term) and chronic (long-lasting) pain in surprisingly different ways at the cellular level.
Hopefully, it creates the possibility of developing new treatments that could stop pain from becoming chronic in the first place, the authors said.
The mouse study has just been published in the prestigious journal Science Advances (the American Association for the Advancement of Science’s open access multidisciplinary journal), under the title “Opposite regulation of medullary pain-related projection neuron excitability in acute and chronic pain.” It was led by doctoral student Ben Title under the guidance of Prof. Alexander Binshtok from the HUJI-Hadassah School of Medicine and HUJI’s Center for Brain Sciences (ELSC).
Binshtok told The Jerusalem Post that the next stage of their research is to understand the mechanism involved in the braking system so they will be able to go on to clinical studies and then – several years later – apply it for patients. Doing the research, which began four years ago, was his idea and pursued by Title and other doctoral students in his lab.
Chronic pain affects over 50 million people in the US alone, often with few effective options for treatment. It is estimated that some 1.5 million Israelis – both those with persistent pain and those experiencing acute pain from injuries and surgery – suffer from chronic pain.
Pain experts at the private Medica Medical Center in Ramat Hahayal believe that over 40% of Israeli adults experience chronic pain of moderate levels or worse, lasting at least six months. The most common causes of chronic pain are those caused by traumatic injuries, migraines, damage to the joints, sinusitis, and carpal tunnel syndrome affecting the wrist.
What causes shift from acute to chronic pain
“WE WANTED to know what causes the shift from acute to chronic pain,” Binshtok continued. “In many people, even pain from physical trauma as after an operation passes, and the body returns to normal, but in others it persists. Women and men are different; females feel more pain than males because of differences in inflammation and they have a lower pain threshold than men.”
He added that physicians believed for a long time, even until just 50 or 60 years ago, that infants did not feel pain. As a result, surgery used to be performed on them without anesthesia! But surgeons began to notice the babies’ reactions – crying and fast heartbeat and breathing, so today all babies who undergo surgery or other potentially painful procedures get the proper protection.
Asked about whether acupuncture can protect against pain, the HUJI expert said it can affect the sympathetic nervous system that prepares the body for intense physical activity by increasing heart rate, breathing, and blood flow to muscles while inhibiting digestion and other non-essential functions.
“But there is apparently a placebo effect in which the patient feels better because he believes it will help him,” he said. “I don’t have any data that proves acupuncture works or not. From what I know, the claims are exaggerated. Serious studies have to be conducted.”
The new Jerusalem study adds an important piece to the puzzle by showing how the nervous system’s built-in pain controls are disrupted in long-term pain conditions, the authors wrote. “By understanding the brain’s own strategies for limiting pain – and why they sometimes fail – we are now one step closer to developing smarter, more precise therapies for those who suffer from chronic pain.”
The team studied a small but crucial region in the brain stem called the medullary dorsal horn, which is home to neurons that act as a relay station for pain signals. These projection neurons help send pain messages from the body to the brain.
They found that during acute inflammatory pain, these neurons actually reduced their own activity. This built-in
“braking system” helps limit the amount of pain-related signals sent to the brain – and when the inflammation and pain subside, the neurons return to their normal state.
However, in chronic pain, this braking system fails. The neurons don’t reduce their activity; in fact, they become more excitable and fire more signals, potentially contributing to the persistence of pain.
Using a combination of electrophysiology and computer modeling, the researchers identified a key mechanism: a specific potassium current known as the A-type potassium current (IA) that helps regulate the excitability of neurons.
In acute pain, IA increases – acting like a natural sedative for the pain pathways – but in chronic pain, this current doesn’t cause them to rise, and the neurons become hyperactive. The absence of this regulation may be one of the biological switches that turns temporary pain into a long-lasting condition, the team suggested.
“This is the first time we’ve seen how the same neurons behave so differently in acute versus chronic pain,” Binshtok noted. “The fact that this natural ‘calming’ mechanism is missing in chronic pain suggests a new target for therapy. If we can find a way to restore or mimic that braking system, we might be able to prevent pain from becoming chronic.”