Drug Target Could Explain Opioid Addiction

 
Nearly two million Americans, aged 12 or older, either abused or were dependent on opioids in 2013, according to the Centers for Disease Control (CDC). 
 
Researchers from The Scripps Research Institute (TSRI) may have found a protein that has the potential to be a new drug target for developing less-addictive pain medications. The research was funded by the National Institutes of Health and the Canadian Institutes of Health.
 
Kirill Martemyanov, an associate professor at TSRI, and his team used genetically modified mice to show that those lacking the protein, called RGS7, were likely to be addicted to morphine. According to the study, a specific molecule controls morphine receptor signaling in a small group of brain cells.
 
As Martemyanov explained, “The mu opioid receptor acts as a conductor of the drug’s effects, while RGS7 acts as a brake on the signal. The animals could press a lever to receive an infusion of morphine. We looked at the number of lever press to determine how much they liked it and, judging from this test, mice lacking RGS7 craved the drug much more than their normal siblings.”
 
Responding to the self-administered morphine doses, the animal models that did not have the particular protein demonstrated enhanced reward, increased pain relief, delayed tolerance and heightened withdrawal. Study results were published recently in Biological Psychiatry and reported by Bevin Fletcher in Bioscience Technology. The results provide a hint at genetic predisposition of addiction before the subjects are treated. Results were obtained through a blood test. 
 
Martemyanov explained, “If our findings hold true for human patients, you could look specifically for RGS7 levels for any disabling mutation with a simple blood test. Mutations could indicate a strong reaction to a drug such as morphine – people carrying a deficient copy of the RGS7 gene might need much lower doses of opioids and could be cautioned to be extra careful with these substances.”
 
The researchers concluded that it may not just be the drug-induced high that RGS7 regulates, but reward behavior in general. It appears that animals lacking the protein also worked harder to obtain a food reward.