Washington: Activating nerve cell receptors along two chemical pathways - one that has previously been linked to how the brain senses 'itch' - may improve pain relief when combined with conventional ways to blunt pain using opioid drugs, such as morphine, according to the researchers from Johns Hopkins Medicine.
The study results described experiments in mice that suggest using chemical compounds to jointly activate these receptors may reduce the risk of opioid tolerance and side effects, a problem common to highly addictive painkillers, by reducing the amount of opioids needed overall.
The scientists cautioned that the drug used to activate a human version of a receptor called MrgC11 in their rodent study is not approved for human experimentation or use.
The scientists are working with chemists to develop new drugs that may be able to target both the human Mrg receptor and opioid receptors at the same time.
"Activating two different receptors present in the same sensory neurons seems to have a type of synergy that requires less drug to deliver better pain relief in our animal models, and, if tests in humans pan out, may offer a way to lower the risk for developing tolerance and addiction to pain medications," said researcher Srinivasa Raja.
The new study, Raja noted, builds on decades of observations by several scientists at John Hopkins and other institutions that there are complex biochemical and sensory features that are shared between the senses of itch and pain.
One of the receptors in the current study, MrgC11, which was discovered 20 years ago by scientist Xinzhong Dong belongs to a family of about 50 such receptors found on mice sensory neurons throughout the body.
Dong found that MrgC11 is linked to 'itch' perception in mice, but recent studies indicate that it is linked to pain perception as well.
Receptors are proteins that dot the surface of cells - in this case, neurons - and act as sensors that detect the environment. MrgC11 receptors in mice - and the human equivalent, called MrgX1 - are found on primary sensory neurons, which are the first among neurons to sense the outside world.
The study appears in the journal Science Signaling.
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