NeuroTalk Support Groups - What does dopamine do anyway? from a METH site...

this is a very good analogy found it on a "METH" site -

What does dopamine do anyway?
1) Dopamine is critical to the way the brain controls our movements. Not enough dopamine -- can't move, or control our movements well. Too much dopamine? Uncontrollable/subconscious movements (like picking, tapping, repetitive moments, jerking, twitching). Remember that the heart is a muscle, too, and too much dopamine will result in increased pulse and blood pressure.

2) Dopamine controls the flow of information from other areas of the brain, especially memory, attention and problem-solving tasks. This becomes important when we talk about amphetamine-induced psychosis that is common in meth abusers.

3) When dopamine is released it provides feelings of enjoyment and reinforcement to motivate us to do, or continue doing, certain activities. Dopamine is released by naturally rewarding experiences such as food and sex. This pre-programmed reward system makes sure that people do eat, do desire to procreate, and basically survive. Without enough dopamine, people feel the opposite of enjoyment and motivation -- they feel fatigued and depressed, and experience a lack of drive and motivation.

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How do brain chemicals like Dopamine work?
Brain chemicals, including Dopamine, are stored in cells, which you can think of like barrels full of that chemical. When something occurs like a good meal or great sex the brain pours out some dopamine from the dopamine barrels into an open space in the brain called a synapse. It floats around there. Think of the synapse like a street, and dopamine is like little cars driving around aimlessly on the street.

Across the street (not far) from the barrels of dopamine are Dopamine receptors. These receptors have little parking spaces on them that only fit Dopamine (or a substance VERY similar in chemical shape to Dopamine) into them, like a lock and key. As the Dopamine floats around in the synapse, it finds parking spaces at Dopamine receptors, and "plugs in" to the receptors. THIS is the point where we feel good, when the Dopamine is parked in a receptor's parking space. There are, however, a limited number of receptors with "Dopamine only parking" available, and each receptor has a limited number of parking spaces. So some of the dopamine may not be able to find a place to park.

When all the parking spaces are taken, the remaining dopamine that didn't find a place to park is normally recycled. There are "reuptake molecules" that do this -- think of them like tow trucks. They find the extra dopamine, and tow it back to the barrels of Dopamine so that it can be re-used the next time. After some time has passed, the receptors release the Dopamine that was parked in their parking spaces, and the tow trucks take those Dopamine molecules back to the barrel too.

The brain has a safety-check system that will destroy any excess Dopamine that isn't in a parking space, and didn't get picked up by the tow truck. There are special chemicals in our brains that will break down this extra dopamine. Think of this like the toxic waste crew coming in and sweeping up the street.

As a last resort, after repeated long-term over-stimulation, the brain will shut down Dopamine receptors so that nothing can park there ever again. Think of this like the demolition team coming in and permanently barricading off the driveways.

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This is your brain on Meth!
So now that we have a basic understanding of how things work normally, I'll try to explain how things work when meth is ingested.

When someone eats, snorts, injects, or otherwise gets meth into their system, meth stimulates those barrels of Dopamine to pour out Dopamine. Meth continues to tell the cells to pour out dopamine until the body can break down the meth, which is typically 12 hours or so.

So Dopamine is poured out into the synapse (street) and finds parking spaces at dopamine receptors and makes the user feel high.

But meth is a tricky little chemical. It is shaped closely enough to Dopamine that the tow trucks get confused, and pick up meth thinking that it is dopamine. So the tow trucks are busy driving around hijacked by meth molecules leaving the extra Dopamine molecules floating around in the street (synapse). Well... that means the toxic waste crew comes in and destroys that dopamine that did not get recycled. So for the 12 hours or so it takes for the body to break down the meth, it is also spending that time destroying dopamine.

As long as the user keeps ingesting more meth, this process continues until there is not enough dopamine left to feel high from. When the user finally stops using, and the brain breaks down the meth molecules, the recycle trucks try to salvage what dopamine there is left, while the user crashes.

The end result of a "run" or "binge" on meth is a marked decrease in the amount of dopamine left in the brain. This leaves the user feeling exhausted, hungry, depressed, possibly suicidal and definitely unmotivated. They are literally suffering from a brain chemical imbalance. Self-inflicted mental illness.

How can the brain ever be normal again?

http://www.kci.org/meth_info/lori/Do...es_and_You.htm