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Laser Treatment for Cocaine Addiction in Rats
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Drug abuse is one of the prevailing social problems of this age, and has proven difficult for scientists to tackle over the years. From behavioral therapies to lobotomy and substitute substances, the drug-abuse mechanism in the brain has yet to be conquered with significant success. Recent research has pointed to manipulation of neural circuitry as a potentially viable way of affecting and possibly treating the drug abuse tendency of certain individuals.

Lab-animal drug self administration has been a major tool in most drug related research for a few decades now. The experimental setup is intended to show the addictive degree of drugs, and the ability of the animals to resist self administering drugs after certain treatments, or in face of “punishment”. Several such experiments were performed over the years, successfully proving many theories, but it has yet to provide with a successful way of treating severe addictions and preventing drug abuse.

A new research provides helpful insights concerning the cocaine addiction mechanism in rats, scientists report in an article in Nature magazine, April 4th.

These scientists successfully located a region in the brain, an area known as the prelimbic cortex, which serves as the relay point for drug addiction mechanisms, especially in cocaine addiction, and serves as the impulse-control and reward driven behavior center.
The neurons in this area of the brain appear to be sluggish, showing a decrease in activity and impulse firing speed, as a consequence of desensitization caused by ingesting cocaine.

The rats in this experiment were divided into two groups, one control group, and one that had access to a mechanism by which they would activate a lever and receive a dose of cocaine. After roughly two months, the scientists started administering shocks every third time the rats would pull the lever, which caused about 70 percent of the rats to stop using the lever and administering themselves with cocaine, but 30% continued this behavior regardless of the ensuing shock. After being tested with electric current, the brains of these rats showed significantly less responsiveness in their prelimbic cortex region, effectively showing that the neurons were slower and less responsive. They were, in fact, the compulsive cocaine addicts of the group. It has earlier been shown that a decrease in prelimbic cortex neuron sensitivity causes the organisms to lose self control and peruse pleasure-giving action in spite of evident punishment and danger.

Further, the scientists wanted to prove that it is in fact this region and the subsequent loss of sensitivity that caused addiction driven behavior, so they turned to an area called optogenetics. Optogenetics uses light emissions to manipulate the firing and action of neurons in a brain, effectively turning them off or on. The rats were injected with a virus, which infected their brains and inserted a genetically engineered strain which in turn caused the neurons of those rats to exhibit a light sensitive receptor on their surface, allowing for external stimulation by light. Then, they used a laser to stimulate the neurons in the prelimbic cortex, doubling their firing speed. This caused a remarkable drop in addiction-driven behavior; roughly one third of the compulsive cocaine user rats stopped their addiction based behavior. The same experiment performed on the control group had no effect. The scientist then revised the experiment, this time doing the opposite. The non-compulsive group of rats was injected with the same virus, but this time the laser was used to turn the neurons of the prelimbic cortex off, decreasing their firing speed by half. Almost all of these rats exhibited a cocaine addiction after this experiment.

Although remarkable, this study does not show why some rats exhibit a cocaine addiction and some not. The scientists hope to use this findings to come up with an addiction treatment for humans, involving a transcranial magnetic stimulator that would be inserted into the prelimbic cortex of addicts, and hope to move to clinical trials with this.
Although the study was well done, it addresses only one component of addiction, says neuroscientist Peter Kalivas of the Medical University of South Carolina. Other experiments earlier have found that in some cases, silencing the same neurons can have a reducing effect on addiction-driven behavior.


Resources:
B.T. Chen et al. Rescuing cocaine-induced prefrontal cortex hypoactivity prevents compulsive cocaine seeking. Nature. Vol. 496, April 4, 2013. doi: 10.1038/nature12024.
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