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Brain Chemistry and Addiction

Any substance taken into the body results in changes to that body. If the substance is beneficial, such as food or oxygen, the body works better, continues to thrive, lives. If the substance is detrimental, the body's functions are impaired; cell damage and death may ensue. Such is the case with drug use. This entry focuses on the effects of drug use and addiction on the chemistry of the brain.

To understand the effects of drugs on the brain, one must first understand the various structures and neuro-transmitters affected. There are a number of areas in the brain affected by drugs and alcohol; one of the main areas involved is the area often referred to as the "reward center": the limbic system, nucleus accumbens, and the ventral tegmental area. This reward center is important because using drugs and drinking alcohol is often pleasurable. If drug use were not so pleasurable, especially at the onset, people would be less likely to engage in these behaviors. In addition to the reward center, the prefrontal cortex, the locus coeruleus, the amygdala, and the hippocampus are activated when someone uses drugs or drinks alcohol and are particularly important in understanding relapse. There are many structures involved in addiction; there also are a few neurotrans-mitters involved in drug addiction, the main one being dopamine; however, other neurotransmitters, such as serotonin, gamma-aminobutyric acid (GABA), norepi-nephrine, and glutamine, are also be affected.

Structures and Neurotransmitters

The limbic system consists of a set of structures, located in both hemispheres of the brain, under the thalamus. The limbic system is involved in almost everything one does on a given day—good and bad. It takes the stored memories, sensory input, and information regarding body functions to determine one's mood, which can have an effect on behaviors. Your reaction to someone who cuts you off and takes the last parking space may be different if you are stuck in traffic, late for a class, and have not adequately prepared for the day when compared to a day when you arrive early for class completely prepared. The limbic system is also responsible for the behaviors related to the classic "fight or flight" response. You are walking through the woods and see a bear; your heart rate increases, and you must decide on your course of action. The limbic system will have a lot of input into that decision. And more importantly for the current topic, the limbic system regulates feelings of pleasure, particularly those pleasurable behaviors that are required for the survival of the individual (e.g., eating) and the survival of the species (e.g., sex/reproduction).

The nucleus accumbens is located in the fore-brain and consists of a bundle of neurons that are responsible for one's experience of reward and pleasure—making it the perfect target for many drugs to act upon.

The ventral tegmental area (VTA) works closely with the nucleus accumbens especially where the mechanics of drug addiction are involved. The VTA is located in the midbrain at the top of the brain stem. Dopamine is synthesized in the neurons of the VTA. So drugs that affect this part of the brain effect the production of dopamine. The activity in the VTA effects the activity of the neurons in the nucleus accumbens. Thus, the production of dopamine in the VTA results in the stimulation of the neurons in the nucleus accumbens, resulting in the experience of pleasure; that pleasure can be intense if there is an excess of dopamine.

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