Using gene therapy, researchers have successfully blocked the pain response in an animal model of neuropathic pain, a type of chronic pain resulting from damage to nerve fibers due to injuries or diseases such as diabetes or cancer. There are few effective treatments for this condition, and in some patients, may lead to long-term disability and dependence on pain medications.
The [researchers]used a genetically engineered herpes simplex virus (HSV) to deliver the gene for part of the human glycine receptor (GlyR), a receptor found primarily on the surface of nerve cells in the spinal cord and the lower brain but not in the nerves in the limbs, to the paws of rats. A group of control rats received only the HSV vector without the inserted gene. After the delivery of the therapeutic gene or empty vector (for the control group), the researchers injected the same paws of each rat with formalin, an irritant known to simulate the symptoms of a peripheral neuropathic pain at the site of injection. Following formalin injection, the rats were then given an injection of glycine to activate the GlyR receptor.
Both control and GlyR-HSV-infected rats showed a typical pain response to formalin. However, the application of glycine eliminated the pain response in GlyR-HSV infected animals, while it had no effect on animals infected with vector only. This alleviation of the pain response in GlyR-HSV-treated mice was reversed by the subsequent addition of low concentrations of strychnine, a strong GlyR-specific inhibitor, or antagonist.