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Substance Abuse Stimulates Reward Pathways in The Brain: Here’s How

For a long time scientists have known that many chemical compounds are highly addictive, and that they stimulate reward pathways in the brain. This is something that that all neuroscientists today are aware of, and we even had a decent understanding of how that occurs with many drugs.

We know that addictive substances produce a motivational response in the brain by affecting regions associated with reward, and that this reinforces the addictive behavior. Breaking out of an addictive pattern is therefore very difficult, something that any addict or ex-addict can attest to.

New Information on Substance Abuse

Despite the fact that there is a large amount of previous research surrounding addiction and its associated brain regions, there are still a lot of things we don’t know. When one question is answered, ten new ones pop up. Therefore, what is known is not complete, and new advances are always being made in theory to fill in these gaps.

One study, published in the prestigious journal Nature Communications, recently discovered a new pathway and mechanism that underlies some addictive effects (see citation below). Using mice, senior investigator Merisa Morales and her research group identified mechanisms behind the effect of glutamate on reward pathways. This is a great achievement for the furthering of our understanding of complex biological processes that lead to addiction.

The Science Behind Addiction—Including Percocet Addiction

The authors carried out this study in NIDA, or the National Institute on Drug Abuse. They used mice to investigate a particular brain region, known as the dorsal raphe nucleus. This region is of particular interest because it is linked to areas associated with reward and dopamine, the neurotransmitter responsible for changes in the reward system, and in addition is very closely linked to and takes part in the serotonergic system, which is involved in mood and behavior modulation.

They found that a particular subset of glutamatergic neurons in this brain region play a large role in the addiction process. Glutamatergic neurons release glutamate, the primary excitatory neurotransmitter of the brain. In this case, the authors found that the activation of this specific subset of glutamatergic neurons was causing a release of dopamine in the brains of these mice in an area associated with reward and motivation.

This discovery is interesting and relevant because dopamine controls addictive processes, and this brain region does as well. It shows for the first time that glutamate is able to control this process. The fact that they were able to discover what triggered this event is of great importance, because it opens new avenues of research and understanding.

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Jia Qi, Shiliang Zhang, Hui-Ling Wang, Huikun Wang, Jose de Jesus Aceves Buendia, Alexander F. Hoffman, Carl R. Lupica, Rebecca P. Seal, Marisela Morales. A glutamatergic reward input from the dorsal raphe to ventral tegmental area dopamine neuronsNature Communications, 2014; 5: 5390 DOI:10.1038/ncomms6390