Would you take a painkiller that had been developed from human saliva? A recent study suggests you might in future.
Pain is an essential sensation. Sensory nerves with endings in our skin, tissues and organs, are activated by heat, cold or pressure, or by chemicals that are released from cells after tissue injury. The fibres of these nerves reach the central nervous system, activating neurons in the spinal cord which in turn connect with and activate neurons in a part of the brain known as the cerebral cortex. The cortex gives you the conscious perception of pain – that “ouch!” The system has evolved to produce a quick response. It takes a split second for you to withdraw your hand from a burning flame.
While pain is essential for survival and good health, unless you have masochistic tendencies, too much pain isn’t a good thing. Especially if it persists. Millions of people live with chronic pain. And chronic pain, whether backache, joint pain or neuropathic pain (neuralgia) can make people’s lives unbearable.
Two centuries of morphine
Throughout recorded human history we have searched for substances to dull pain. The most powerful painkillers are the opioids. Morphine, derived from the opium poppy, is an opioid that has been known to alchemists and medics for centuries. Morphine was one of the first ever medicines and has been available in a pure pharmacological form since 1817.
Morphine and synthetic opioids, such as codeine and fentanyl, bind to opioid receptors located on neurons in the spine and inhibit their activity. This prevents them signalling pain sensations to the brain. Some of our nerve cells, positioned in key places on the path along which pain signals travel, release opioid peptides (fragments of proteins) such as enkephalin. These enkephalins attach to opioid receptors and block pain signals reaching the brain. In the 1970s we discovered that opioids like morphine, codeine or fentanyl act as mimics of these naturally-occurring opioid peptides.
Morphine – effective but dangerous. Henk Albert de Klerk/Wikimedia Commons, CC BY-SA