Nerves Conquer Pain

Several cultures believe that the mind can be harnessed to control aspects of our physiology, such as ramping up the immune system to fight off a cold. Now, this belief has gotten a dose of scientific support from a study that suggests that the central nervous system can regulate pain and even reduce joint damage in arthritic rats.

A team of researchers led by arthritis specialist Gary Firestein of the University of California, San Diego, investigated the influence of the central nervous system in rats with rheumatoid arthritis by blocking a compound made by the spinal cord. The compound, an enzyme called p38 MAP kinase, signals pain and inflammation in rheumatoid arthritis. When the researchers injected a drug into the rats' spines that blocks p38 MAP kinase, swelling in the animals' paws decreased markedly. In addition, rats injected with the drug didn’t respond to ankle pressure, demonstrating reduced pain. Damage to the joints from arthritis was decreased by 60% after spinal injection, compared to untreated animals, the researchers report online 4 September in PLoS Medicine.

Firestein says the findings suggest that the central nervous system senses peripheral tissue inflammation, then activates the p38 pathway. Researchers have previously injected p38 MAP kinase inhibitors into arthritic tissues to control pain and inflammation in animals with some success, but the new work indicates that injecting it into the central nervous system may be more effective, he says. It also hints at a possible biochemical mechanism for the placebo effect, exhibited by about 30% of arthritis sufferers. However, Firestein adds that more work is needed to determine whether placebos prompt the central nervous system to dampen pain via p38 MAP kinase or some other signal.

The study provides pretty convincing evidence that the spinal cord can assuage joint inflammation, at least in rats, says Joan Bathon, director of the Johns Hopkins Arthritis Center in Baltimore, Maryland. But whether p38 MAP kinase inhibitors could be used to treat arthritis in humans is unclear, she says. These compounds have been investigated as arthritis drugs, but none have yet been approved for human use because of harmful side effects. And because the new method requires injection into the spinal column, Bathon says it has a "long way to go" before it becomes clinically useful.