Researchers have developed a new technique to switch off pain directly at the source, potentially eliminating the need for highly addictive painkillers.
The breakthrough from the Flinders Medical Centre in South Australia means chronic pain sufferers may not need drugs, such as morphine, that have so many side effects.
The research team, led by Associate Professor Nick Spencer, is closing in on a way to suppress pain arising from conditions such as neuropathic pain, inoperable tumours or terminal cancers that trigger pain receptors at specific sites in the body.
The innovation follows three years of work to map the exact locations of all the nerve endings that detect pain from different internal organs and how these pain receptors are activated in the body.
"Current therapies for pain relief are very poor because they are incredibly non-specific," Spencer said.
"If we don't know where the nerve endings are that detect pain and we don't know how they're activated, it is very difficult to develop selective therapies to prevent their activation," he said. "Today if someone has severe pain they will probably be given an opioid like morphine that is very good at relieving pain but has a whole range of side effects.
"You can get sedated, addicted, build tolerance, suffer from withdrawal and constipation, you can't drive a vehicle or think straight - your whole body is affected by the pain medication - that's the big problem."
Spencer conducted the mapping on animal models by injecting a small volume of liquid dye into a specific part of the nervous system that contains all the nerve cells that detect painful stimuli.
The dye is then drawn up by the nerve axons and transported to their endings within internal organs such as the bladder, lungs or uterus. This allows the team to directly visualise where all the nerve endings that detect painful stimuli are located without also labelling all the other classes of nerves in the body.
Spencer and his team then devised a technique to inject a harmless virus - containing a specific molecule - into the organ or site from which the pain originates. The virus is then transported back up into the spinal cord where the molecule selectively shuts down the development of a particular sodium channel that is essential for pain perception.
"It was based on the idea that pain information is detected by specific classes of sensory neurons that lie just near the spinal cord and by targeting only these neurons, we could shut down only those neurons that detect the painful stimuli," he said.
"This is the latest technology, very much like gene therapy, where you can deliver a gene or silence a gene to enhance the behaviour or suppress the behaviour of particular cells or organs."
Laboratory tests targeting the gastrointestinal tract have registered a 75 per cent reduction in pain without affecting other organs in the body.
"Turning pain off is not instant, it can take days to weeks, but the big advantage is that the pain can be suppressed for long periods without the classic side effects of current pain therapies," he said. "We can suppress pain for months to years, so it's very exciting."
Spencer said that that with severe neuropathic pain, for example, there is often damage that is life long.
"If you fall off a ladder you can damage spinal nerve routes that lead to lifelong neuropathic pain, which is basically incurable," he said. "There is no point in that pain in a patient for their entire life. We know there is damage, so in that case there is huge demand to suppress pain from the target site without opioids."
The first phase of experiments involved suppressing incurable pain linked to the stomach, small intestine and large intestine. However, Spencer said it was a technique that could be applied to all internal organs.
"We are very excited by our new technique and what it tells the community," he said. "I would envisage myself spending the next decade on this, because there's so little known and the ramifications could be so substantial."
In 2013 Associate Professor Spencer was awarded more than $900,000 in funding by Australia's National Health and Medical Research Council to conduct the research.