Several neural diseases, including chronic pain and epilepsy, involve a lack of restraint. That is, damage to nerves in the spine reduces the levels of a signalling chemical called GABA, which silences excitable neurons. The result: too much neural activity.
There are drugs that can restore GABA, but they don’t always work, they are only temporary and they have unwanted side effects like sedation. There is another option: transplant GABA-producing neurons directly into the spine. Scientists have now done this in mice, with successful results.
I covered the story for The Scientist. Check it out.
Photo by Nanny Snowflake
Everyone has felt pain, and many experience it daily. But for such a universal sensation, it is still a mysterious one. We are only starting to understand the molecules that produce a painful sensation. Nature, however, is well ahead of us. Many animals are armed with chemicals that hijack the nervous systems of their targets, producing feelings of intense pain. They are unknowing neuroscientists, and by studying their weapons, we can better understand how pain manifests in our bodies.
Take the Texas coral snake. This brightly coloured serpent, clad in warning hues of red, black and yellow, usually shies away from confrontation. When it’s threatened, it defends itself with venom that can cause excruciating and unremitting pain.
In the past, I have criticised science journalists for not providing enough background in their reports. Both news stories and scientific papers obviously focus on new events and achievements, but they do so in the knowledge that new discoveries stand on giant shoulders. For this reason, when I cover new papers for this blog, I try to describe some of the research that led up to it, a tactic that fits with the growing cries for more context in modern journalism.
And yet, it’s perhaps churlish to expect this to be a routine part of science journalism when many scientists themselves don’t take up the practice. I bring this up in the light of a new paper, published today in Nature Neuroscience, about the controversial topic of acupuncture. I was going to do this as a straight write-up but actually the omissions in the paper are probably just as interesting than the science within it.
The gist is this: Nanna Goldman from the University of Rochester Medical Center claims to have found a biological explanation for the pain-relieving effects of acupuncture. She worked with mice that had inflamed paws, and managed to alleviate their pain by using a needle to pierce a traditional acupuncture point near the knee. This painkilling effect only happened when she rotated the needles after insertion.
This effect depended on a chemical called adenosine, which typically surges in concentration after any stress or injury. Adenosine works by docking at a protein called the adenosine A1 receptor, which has well established roles in suppressing pain and is found on neurons that transmit pain signals. Indeed, other chemicals that stimulated this protein had the same pain-relieving effects as acupuncture. Drugs that prevent the body from breaking down adenosine led to even more potent pain relief. And mice that lacked the A1 receptor altogether experienced no pain relief from the needles.
The placebo effect – the phenomenon where fake medicines sometimes work if a patient believes that they should – is a boon to quacks the world over. Why it happens is still a medical mystery but thanks to a new study, we have confirmation that the spine is involved.
Frank Eippert from the University Medical Center Hamburg-Eppendorf used a technique caled functional magnetic resonance imaging (fMRI) to scan the backbones of volunteers as they experienced the placebo effect. Eippert heated the recruits’ forearms to the point of pain and he gave them cream to soothe the sting. The creams were all shams with no pain-relieving properties, but only half of the recruits were told this. The others were told that they’d been given lidocaine, an anaesthetic.
Sure enough, the volunteers who used the alleged “anaesthetic” felt about a quarter less pain than those who were aware that they were using an ordinary cream – the placebo effect in action. But Eippert also found that the activity of neurons in the spine (specifically an area near the back called the “dorsal horn”) was also strongly allayed.
The dorsal horn is the gateway of pain. It controls the passage of pain impulses from our senses into our central nervous system. Eippert’s results provide direct evidence that our belief in the effectiveness of a fake medicine can close this gate, blocking pain signalling in this all-important area.
Of course, it’s still unclear how this happens, but the answer probably lies with opioids, natural pain-relieving chemicals used by the brain that have been linked to the placebo effect for over 30 years. These chemicals are probably responsible for closing the dorsal horn’s gate.
Eippert’s results build upon, and support, earlier research linking the spine to the placebo effect. Nonetheless, it’s very unlikely that this is the only explanation behind the mysterious placebo effect. For a start, people who suffer from fibromyalgia – a condition characterised by long-term pain all over the body – can still experience in the placebo effect but in a way that doesn’t involve the spine.
Reference: Science 10.1126/science.1180142
It goes without saying that we are capable of noticing changes to our bodies, but it’s perhaps less obvious that the way we perceive our bodies can affect them physically. The two-way nature of this link, between physicality and perception, has been dramatically demonstrated by a new study of people with chronic hand pain. Lorimer Moseley at the University of Oxford found that he could control the severity of pain and swelling in an aching hand by making it seem larger or smaller.
Moseley recruited 10 patients with chronic pain in one of their arms and asked them to perform a series of ten hand movements at a set intensity and to a set pace. The volunteers had to watch their arms as they went through the motions. On some trials, they did so unaided, but on others, they viewed their arms through a pair of binoculars that doubled their size, a pair of clear-glass binoculars that did not magnify at all, or a pair of inverted binoculars that shrunk the image.
On each trial, Moseley asked the recruits to rate their pain on a visual sliding scale. He found that they were in greater pain after they had moved their arms – no surprise there. But the amount of pain they felt depended on how large their arm appeared to them. They experienced the greatest degree of extra pain when they saw magnified views of their arms, and took the longest amount of time to return to normal. Perhaps more surprisingly, the “minified” images actually evoked less pain than normal.