New Science Gets to the Root of Opiate Addiction
> 5/15/2008 10:28:38 AM

Research involving genetically modified lab mice has pinpointed a specific protein receptor central to the chemical reality of opiate addiction. The latest related study demonstrated that adenosine a2a receptor, a key player in the brain's reward system that facilitates the transmission of stimuli to neurological pleasure centers, can be eliminated via engineering in order to create a mouse better able to resist opiate addiction. This study reinforces the neurological complexity of addiction and follows previous research in linking the receptor to intoxication, withdrawal and drug-seeking behavior in opiate-addicted lab animals. Were it not for the influence of this crucial link in the pleasure/reward chain, addicts would not experience the intense motivation to use that makes opiate addiction so notoriously hard to shake.

Australian researchers gave a group of lab mice access to self-administered morphine which they could access freely at any time. Rats were divided into a control group and one that had been bred to lack the a2a receptor. The genetically modified mice used less morphine, displayed a less insistent desire for it and did not develop the tolerance to the substance that occurs in chronic users. These mice also failed to develop a conditioned place preference or compulsive attraction to the area in which they used the substance. Associative memory plays a large role in human addiction models, with addicts very closely associating the space in which they usually get high with a certain level comfort and familiarity.

This modification did not, however, eliminate all aspects of the addiction equation. The affected mice who used even small amounts of the substance still went through a withdrawal period characterized by an increased desire to use. It would appear that the receptor, while playing a large role in the physical appeal of the drug, does not control behavioral aspects of its use and dependence. It makes heroin far less appealing but does not eliminate the possibility of dependence or the tendency toward relapse during "cold turkey" abstinence periods.

A large part of addiction truly does exist only in the mind of the user. While the physical reality of opiate dependence is notoriously persistent, the brain (at least in lab mice) can be tricked into a state of indifference regarding the compulsive appeal of heroin use - the major implication being that, if researchers can develop a non-invasive way to tweak the receptor in humans, they may arrive at an extremely effective treatment. Because it would not completely eliminate withdrawal symptoms, it would be most effective for individuals who've yet to enter addiction's most severe stages. The prospect of such a drug is not entirely new, and several pharmaceutical firms have already begun attempting to develop medications designed to block adenosine. The receptor plays a near-identical role in alcohol dependence as well, meaning that any successful drugs could potentially counter both addictions. Medication alone will never be enough to end heroin addiction. Psychiatric intervention, therapy and the support of friends and family play a crucial role in the process. And even though an effective a2a blocker will considerably reduce the likelihood that an individual will be attracted to the continued abuse of heroin, it will not serve as a miracle cure for those with a profound dependence on the drug. But it may prove to be an invaluable link in the recovery chain, and it could be the final key to reverse the fortunes of thousands of addicts worldwide.

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