When these receptors sense stimulae such as intense heat, for example, they stimulate neurons that send a pain-transmitting signal to the brain. Well, there are natural enkephalin-producing neurons in the spinal cord which, under certain circumstances, get a signal from the brain to make enkephalin. This enkephalin binds to opiate receptors on pain-transmitting neurons, and blocks or dampens the transmission of pain signals. In our experiments, we've used viruses like the herpes virus as vectors, to carry enkephalins into the pain-transmitting neurons. This blocks the pain transmission.
Enkephalins are as effective as morphine in killing pain.
But unlike morphine, enkephalins are produced naturally by the body and don't alter the brain, Glorioso noted. Also, the body does not develop a tolerance for enkephalins, so there is no risk of addiction, he said. We're currently testing this therapy in primates.