Research Paves Path for Painkillers Without Addiction
> 8/23/2007 3:37:48 PM

Earlier this week we broke down the possible reasons for rising painkiller use in America, but we glossed over one fundamental reason because it is so obvious and seemingly unchangeable—painkillers both dull pain and trigger addiction. This dual effect makes it easy to slip from medication after an injury to dependence on the drug.

Dr. Zhou-Feng Chen recently presented evidence to the National Academy of Sciences that the connection between painkillers derived from morphine and addiction is not inextricable. The traditional view has been that opiates increase levels of serotonin, which mediates both pain and addiction, but new mouse experiments suggest that one neurotransmitter is not causing both effects.

The special mice required for this research began development four years ago. Chen engineered a mouse breed lacking the Lmx1b gene, rendering them incapable of producing serotonin. It would have been interesting to study the effects of this gene deletion, but the abnormality was too severe for any of the animals to survive for long. Not giving up, Chen tried a more precise ruination of 5-HT neurons, the receptors for serotonin, which allowed mice to live while still depriving them of the use of serotonin.

While these mice were able to live, they did not live well. Altered mice had elevated pain responses and showed lower and sometimes nonexistent responses to opiates. This clearly demonstrated that opiates rely upon serotonin to lessen pain. This additional evidence for a long-held theory is valuable, but not nearly as interesting as the second, theory-undermining observation Chen made: Altered mice received no protection from pain, but they were still vulnerable to addiction. 

Even as they cringed from pain, the altered mice sought out the drug and built up a tolerance just like normal addicts. It follows logically that the addictive properties of painkillers must work through a separate mechanism from the actual pain-dampening. This opens the exciting possibility that a non-addictive painkiller can be developed. If another way of manipulating serotonin is found, the problem of opiate abuse will be greatly diminished. Doctors will not have to deprive suffering patients of painkillers for fear of provoking federal prosecution or feeding an addiction.

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